Hazard assessment of glacial lake outburst floods from Kyagar Glacier, Karakoram Mountains, P.R. China
Christoph HAEMMIG, Hansrudolf KEUSEN, Matthias HUSS, Josef HESS, Urs WEGMÜLLER, Zhigang AO, Wubuli KULUBAYI
Corresponding author: Christoph Haemmig
Corresponding author e-mail: email@example.com
Kyagar Glacier is located in the Karakoram Mountains in the southwest of Xinjiang Uygur Autonomous Region, P.R. China. The glacier tongue entirely blocks the riverbed in the upper Shaksgam valley and impounds a glacial lake at 4750 m a.s.l., which was the source of several violent and disastrous glacial lake outburst floods (GLOFs). The spontaneous floods are a threat for over one million inhabitants in the floodplains of Yarkant River. A GLOF early warning system, combining satellite remote sensing and two automatic terrestrial observation and warning stations, was implemented in 2012. The stations are also equipped with weather sensors to monitor local climate. A further goal of the ongoing project is to elaborate scenario-based forecasts of the future glacial lake developments, considering ice-flow dynamics of Kyagar Glacier as well as surface mass-balance response to climate change. Comparison of two high-resolution digital elevation models (DEMs) for the ice dam show surface lowering rates of up to 4 m a–1 between 2002 and 2011, leading to a significant reduction in lake volume and hence a decreasing GLOF hazard potential. Glacier melt modelling based on climate scenarios indicates a rapid retreat of the glacier tongue over the next decades. However, two DEMs covering the entire glacier for the period 2000–2008 show small elevation changes in the accumulation area and even a slight mass gain in the central part. This is supported by the observation of a moderate ice-flow speed-up in this region. This pattern is typical for surge-type glaciers and is consistent with the numerous documented glacier surges in the Karakoram. The displacement rate of the glacier surface and the ice dam between 2011 and 2012 is analysed based on feature tracking of very high resolution synthetic aperture radar (SAR) images. We present an integrative analysis of recent changes in mass balance and ice-flow dynamics of Kyagar Glacier. These assessments are crucial for estimating the future GLOF hazard potential of Kyagar Glacier Lake and risk management in the floodplain. The project is supported by a cooperation between the Swiss Agency for Development and Cooperation (SDC) and the Federal Office for the Environment (FOEN). On the Chinese side, local authorities, such as the Xinjiang Department of Water Resources and the Xinjiang Kashgar Hydrographic & Water Resources Survey Bureau, support the project.
Sensitivity of Pine Island Glacier, West Antarctica, to ocean melting
G. Hilmar GUDMUNDSSON
Corresponding author: G. Hilmar Gudmundsson
Corresponding author e-mail: firstname.lastname@example.org
The sensitivity of Pine Island Glacier (PIG) to different ocean melting scenarios is investigated through numerical modelling. Melt rates are derived using an ocean circulation model (MIT/GCM), and an ice-flow model is used to calculate rates of grounding-line migration and ice drawdown over the next two centuries. The ice-flow model uses unstructured grids and allows for robust and accurate calculation of grounding-line positions and ice-shelf buttressing effects. It is found that changing a baseline reference ice-shelf melt-rate distribution by a factor of two can either lead to a stable grounding line at approximately the currently observed location, or to an irrevocable retreat of PIG. Calculated near-future ice loss is, hence, strongly dependent on applied basal melt rates. This high sensitivity illustrates the importance of using realistic ocean forcing when assessing the future contribution of PIG to global sea levels.
Predicting mass movement processes induced in periglacial areas
Daniel TOBLER, Peter MANI, Nils HÄHLEN
Corresponding author: Daniel Tobler
Corresponding author e-mail: email@example.com
Based on glacier retreat and degrading permafrost in high alpine regions across the Bernese Oberland (central Switzerland), several new hazardous source areas for mass movement processes became evident within the last years. The evaluation of susceptible periglacial areas and the assignment of resulting processes by modelling will be one of the major tasks to be solved in near future. The prediction of those processes and their consequences is an interdisciplinary question. Meteorological scenarios for the next 30–50 years derived from climate change scenarios stand at the beginning of the decision chain. Based on those, susceptible periglacial areas that act as starting zones for mass movements (rockfall, landslides, debris flows) or new sediment sources can be calculated through sophisticated permafrost and glacier retreat models. The bed-load characterization is based on extensive field investigation and laboratory testing subsequent to the October 2011 events in Switzerland. There many debris flows originated in periglacial areas; deep gully erosion phenomena in permafrost induced debris fans at the foot of steep rock faces have been evident. A vast basic monitoring of the permafrost by BTS measurements helps in understanding the ongoing processes and is fundamental for the bed-load calculation in the periglacial area. This is measured by monitoring systems at representative and characteristic locations within the study area (e.g. Spreitgraben near Guttannen, Switzerland). Dealing with large investigation areas of several 100 km2 it is important to use adequate models. Well established simulation tools like ROFMOD 3D (rockfall), SLIDISP and SLIDEPOT (landslides) and RAMMS (debris flows) have been used within the project. The result is a so-called periglacial hazard indication map visualizing endangered areas for mass movement processes as well as other natural hazards like floods, glacial ice avalanche or subglacial lake outburst.
Greenland ice sheet contribution to future global sea-level rise based on CMIP5 models
Qing YAN, Huijun WANG, Ola M. JOHANNESSEN, Zhongshi ZHANG
Corresponding author: Qing Yan
Corresponding author e-mail: firstname.lastname@example.org
Sea-level rise (SLR) is one of the major societal-economic risks associated with global warming. Mass losses from the Greenland ice sheet (GrIS) will be partially responsible for future SLR, although there are large uncertainties in modeled climate and ice-sheet behavior. Here, we use ice-sheet modeling applied to climate projections from 20 CMIP5 models to constrain the Greenland ice sheet contribution to global SLR. It is estimated that the GrIS contributes 0–17 (0–27) cm to global SLR by 2100 under Representative Concentration Pathways (RCP) 4.5 (RCP 8.5). With model evaluation and hence model selection, the GrIS contribution is constrained to 3–5 (7–10) cm based on the top three models in simulating the present summer temperature over Greenland. These results underscore the need for objective evaluation and selective use of model output to reduce uncertainty in future sea-level projections.
Instability of glaciations to local variations: the role of radiation factor
Irina KORNEVA, Sergey SEMENOV
Corresponding author: Irina Korneva
Corresponding author e-mail: email@example.com
One of the reasons for concern connected with the recent global warming is the instability of the main objects of the cryosphere, such as the Greenland and Antarctic ice sheets and Arctic sea ice. Essential decreasing of the volume of the ice can have serious geophysical, ecological and economic consequences. Therefore, considerable attention of researchers is now paid to the problem of stability of the aforementioned objects of the cryosphere. Some aspects of this problem were studied in this work. In particular the role of surface absorbed radiation flux was studied using the distribution of radiation equilibrium temperature on the surface. The data about radiation fluxes and temperature were obtained from the SRB project (Surface Radiation Budget, NASA) and MERRA reanalysis data for the period 1984–2007. The comparison between the equilibrium and normal temperature of the surface showed that besides the radiation flux the latent heat flux plays an important role. On the ice-covered surfaces it is the flux connecting with the accumulation and melting of the ice. The calculations also showed that increases in absorbed radiation flux and approaching albedo to 0 cause the local instability of mountain glaciers and permafrost. On the opposite side, the Greenland and Antarctic ice sheets and Arctic sea ice on an annual scale remain in the local stable state.
Atmospheric dust deposition retrieved from a Mount Geladaindong ice core, central Tibetan Plateau
Yulan ZHANG, Shichang KANG, Bjorn GRIGHOLM, Susan KASPARI, Qinglong YOU, Dahe QIN, Paul MAYEWSKI, Qianggong ZHANG, Jie HUANG
Corresponding author: Shichang Kang
Corresponding author e-mail: firstname.lastname@example.org
A 147 m ice core was drilled from Guoqu Glacier (33°34.60' N, 91°10.76' E, 5750 m a.s.l.) during the Sino–US cooperation expedition of Mount Geladaindong in the central Tibetan Plateau (TP). Here we investigate the high resolution of atmospheric dust records by using the insoluble particles and crustal ions (Ca2+ and Mg2+) from the upper segments of 109.93 m, covering the period AD 1477–1982. There is a positive correlation between dust records of ice core and dust days of the nearby meteorological stations in recent decades, indicating the insoluble particles and crustal ions in the Geladaindong ice core be the index to reconstruct the past atmospheric dust variability. The temporal variations of the insoluble particles and crustal ions show high concentrations in the 18th and 19th centuries and low concentrations in the 20th century, which are identified by the reconstructed precipitation in the western TP and snow-cover variability over the central TP and its surroundings. The ice-core dust records are also positively correlated with zonal wind, winter NAO and PDO index, suggesting that NAO and PDO may be teleconnected to dust entrainment over the inner TP. Thus, this long-term ice core provides an approach to understanding the atmospheric dust variability over the past 500 years in the central TP.
Creep deformation of damaged ice shelves
Christopher P. BORSTAD, Eric RIGNOT
Corresponding author: Christopher P. Borstad
Corresponding author e-mail: email@example.com
Ice shelves are important buttresses through which the majority of the Antarctic ice sheet drains to the ocean. Ice shelves are also good targets for theoretical study because they have well defined boundary conditions and lack any vertical gradient in velocity. Weertman developed the first analytical theory for the creep of an ice shelf in 1957, and this theory has been the foundation for many key insights into the nature of glacier ice deformation. Here, we present the first major revision to this theory in nearly 30 years by introducing a scalar damage variable to account for the softening influence of fractures on the deformation of floating ice. A new governing equation for the strain rate of an ice shelf is derived by applying a damage-dependent linear mapping to the existing theory. The strain rate of damaged ice is enhanced compared with pure ice, and damage can be calculated explicitly from observations of ice thickness, temperature and surface velocity. By combining the new theory with an inversion for the ice rigidity, the buttressing back-stress provided by the ice shelf can also be determined. The combined maps of damage and back-stress paint a picture of the mechanical integrity of an ice shelf and its susceptibility to further weakening and collapse. Using the Ice Sheet System Model (ISSM), we demonstrate the validity of this new theory by calculating damage for several Antarctic ice shelves, finding good spatial agreement between areas of inferred damage and observations of rifts and crevasses in satellite imagery. The Larsen C ice shelf appears to be stable at present, whereas the floating ice shelf of Pine Island Glacier experienced a 20% reduction in back-stress during the period 1996–2007.
Spatial and temporal variations of moraines in the Qilian Mountains based on simulation in the artificial neural networks model
Yuehua LIANG, Chaolu YI
Corresponding author: Chaolu Yi
Corresponding author e-mail: firstname.lastname@example.org
Moraine morphology is a basic material for the reconstruction of paleao-glaciation, understanding of geomorphological processes and assessment of mountain erosion. Some methods have been used to simulate moraine; however, the results are limited in methodology and by data resources. By using artificial neural networks (ANN) in MatLab and differential GPS (DGPS) data we simulate moraines in four glacial valleys in the Qilian Mountains. The results show very good agreement between the simulation surface of moraine and the data measured in the field. They indicate that the ANN model is a reliable and efficient method for moraine simulation. ANN is a mathematical model that outputs its simulation results through changing its structure during a self-learning phase based on inputs. Through choosing parameters and comparing virtual topography, ANN is a semi-auto method that can be used in glacial geomorphology. The topography of moraines is set to be the target, which will be calculated from the survey line equipped with DGPS data. Under the same inputs, the performance of the ANN model is strongly affected by mean squared error goal and spread of radial basis functions. Simulation results are examined in four glacial valleys from the northwest to the southeast. The results show that the mean error is no more than 1 m between the simulated result and measured data, the mean relative error is between 0.1 and 0.2% and the standard deviation is no more than 3 m. They suggest that the precision and accuracy of the ANN model are high enough for the recovery of moraine morphology. The results show that the volume of moraines varies from 0.01 to 0.02 km3 in the Little Ice Age, from 0.05 to 0.07 km3 in the Neoglacial and from 0.4 to 0.8 km3 in the Last Glacial. According to the analysis of fitting curves of moraines, the slope of the moraine is coherently dependent on topography in the same glacial valley. We suggest that the moraine morphology is locally dictated to some extent by glacial valley curvature in the valley.
Glacier mass balance and runoff modeling for the contribution of snow and glacier melt to the discharge in highly glacierized catchments in Norway
Markus ENGELHARDT, Thomas Vikhamar SCHULER, Liss Marie ANDREASSEN
Corresponding author: Markus Engelhardt
Corresponding author e-mail: email@example.com
Daily discharge rates are available for the catchments of Ålfotbreen (8.3 km2, since 1984), Nigardsbreen (64 km2, since 1962) and for Storbreen (8.0 km2, since 2010). The catchments are situated on a west–east profile from a highly maritime to a more continental climate. The discharge measurements are compared with simulated discharge rates calculated from a melt model for both the glacierized and non-glacierized parts of the catchment. The model uses runs gridded temperature and precipitation from seNorge (http://senorge.no) as input and runs on a daily time-step from 1957 to present. It accounts for accumulation and melt of snow, firn and ice as well as evaporation, retention of surface water, refreezing processes and discharge routing. The simulated discharge data can be split up into their water sources rain, ice and firn melt, snowmelt on and outside the glacier area in the catchment. For validation of the melt model, both measured seasonal and annual mass-balance measurements of the glacier are used. In addition, daily melt rates are available from sonic rangers located in the ablation zones of Storbreen (1580 m a.s.l.) and Nigardsbreen (600 and 1000 m a.s.l.). Results show that the on average 20% increase in discharge in the 2000s compared with the 1990s is mainly caused by increased ice melt and to a lesser extent by increased precipitation. The increase in discharge is accompanied by increased interannual variations.
Instrumentation and methodology for small manned airplane observation using an integrated lidar system over complex glacier surfaces – applications to the surge of the Bering–Bagley glacier system
Brian McDONALD, Ute HERZFELD, Maciej STACHURA, Griffin HALE
Corresponding author: Brian McDonald
Corresponding author e-mail: firstname.lastname@example.org
This paper aims to describe the instrumentation and methodology of the integrated lidar system used in the Bering–Bagley surge observation campaigns (2011–2012). The integrated lidar system combines a ULS laser profilometer with several other components, including GPS and cameras, to produce high-resolution data of surface elevation and microtopography. The study area is the Bering–Bagley glacier system, Alaska, which is currently surging (2010–2012–?). During a surge, a glacier accelerates by two orders of magnitude, causing heavy crevassing and changes in the glacial hydrology. The surge manifests itself in distinctive types of complex forms of crevassing. Extensive presence of water on the surface of the glacier indicates a switch to an inefficient englacial drainage system. Hence the surface of a surging glacier presents challenges in observation methods and at the same time is ideal for instrument testing since it covers large ranges of surface roughness and surface properties. This paper will cover the data collection process, primary data analysis (ground and noise detection) and its application to glaciology.
The 2012 phase of the surge of the Bering–Bagley glacier system: airborne and satellite observations and analysis
Ute HERZFELD, Brian McDONALD, Thomas TRANTOW, Robert GRIFFIN HALE, Alex WELTMAN, Owen LAMB, Almut HERZFELD MAYER
Corresponding author: Ute Herzfeld
Corresponding author e-mail: email@example.com
The Bering–Bagley glacier system, Alaska, the largest glacier system in North America, surged in 2011. Velocities decreased towards the end of 2011, while the surge kinematics continued to expand. In this paper, we report results from new airborne observations collected in June/July and September/October 2012. Fresh crevassing and surface lowering document a new surge phase, which started in early summer 2011. Crevassing indicates accelerations in several widespread locations. Airborne observations include simultaneously collected laser altimeter data, videographic data, GPS data and photographic data. The observations as well as the analysis are complemented by satellite imagery from WorldView1 and WorldView2 (DigitalGlobe).
Evolution of surface elevation in the Bering–Bagley glacier system before and during the 2011–2012 surge based on CryoSat-2 data and airborne observations
Ute HERZFELD, Brian McDONALD
Corresponding author: Ute Herzfeld
Corresponding author e-mail: firstname.lastname@example.org
The Bering–Bagley glacier system, which includes America’s largest and longest glacier, is currently surging (2011–2012–?). It is known that a surge-type glacier builds up a bulge in elevation (reservoir area) during its quiescent phase. When the reservoir build-up reaches a threshold, the glacier surges and ice is redistributed from the reservoir down-glacier and also up-glacier. In this paper, we analyze CryoSat-2 observations (April 2010–December 2012) to create a time series of digital elevation models (DEMs) to document the evolution of surface elevation in the Bering–Bagley glacier system. Elevation data from CryoSat are compared with laser altimeter data that we collected during three airborne campaigns in 2011 and 2012. The elevation DEM time series provides observational constraints that allow us to study the physical processes leading up to the surge and mass redistribution during the surge.
Snow-cover dynamics and hydrological regime of the Aksu River basin, northwestern China
Jing LI, Shiyin LIU, Wanqin GUO, Donghui SHANGGUAN, Qiao LIU, Junli XU, Junfeng WEI, Weijia BAO, Xiujuan ZHANG
Corresponding author: Jing Li
Corresponding author e-mail: email@example.com
A major proportion of flow in the Tarim River is contributed by its snow- and glacier-fed river catchments situated in the Tien Shan ranges. It is therefore essential to understand the cryosphere dynamics in this area for water resource management. The MODIS MOD10A2 remote-sensing database of snow-cover products from March 2000 to December 2012 was selected to analyse the snow-cover changes in the Aksu River basin (the snow- and glacier-fed subcatchment of the Tarim River). A database of monthly flows for the Akesu River at Xida Bridge over a period of 40 years and climate data (precipitation and temperature) from meteorological stations within the catchment was made available to investigate the hydrological regime in the area. Analysis of remotely sensed cryosphere suggest a shrinkage of glacier in the area. The increase in snow cover may be the result of an increase in winter precipitation caused by westerly circulation. The increase in runoff is mostly caused by the rising temperature causing more meltwater. But the impact of global warming is not very great because a large part of the basin area lies under high altitudes where the temperature remains negative throughout most of the year.
Climate variation and the response of representative glaciers in western China since 1960
Yinge LIU, Ninglian WANG, Lingang WANG, Xiaobo WU
Corresponding author: Ninglian Wang
Corresponding author e-mail: firstname.lastname@example.org
Mountain glaciers are the most sensitive to changes in climate response and are primarily located in western China. The following areas in western China were selected for study: the Altay Mountains, Tien Shan, Tanglha ang Anima Qing Mountain range of the Tibetan Plateau, eastern and central Himalayan Mountains and Qilian Mountains. Based on surface observation climate data during 1960–2009 and the statistics of glaciers by the remote-sensing image-processing and analyzing method, the climate trend and response of glaciers to climate change were analyzed systematically. The results indicate that, in the above five regions, the maximum temperature, minimum temperature, average temperature, precipitation and amount of snow on the whole have increased in the past 50 years, especially since the 1990s when the increase has been more obvious. The average change rate is 0.36°C (10 a)–1, 0.51°C (10 a)–1, 0.32°C (10 a)–1, 11.9 mm (10 a)–1 and 1.1 m (10 a)–1, respectively. However, the wind speed, sunshine hours and snow days are decreasing and the change rate is –1.0 m (10 a)–1, –78.3 h (10 a)–1, –5.6 days (10 a)–1, respectively. However, precipitation is decreasing and sunshine hours are increasing in the middle Himalayan Mountains. Statistics of glaciers showed that, for five regional glaciers average, the annual percentage of area change of glaciers is about –0.43%, the percentage of average area change of glaciers is about –14.66% and the average area change of glaciers is about –1.28 km2 a–1, moreover the glacier and climate variations exhibited obvious temporal and spatial differences. After carrying out a comparative study on glacier shrinkage in western China, it was found that glacial shrinkage in the Altay and Qilian Mountains is bigger than in other regions. Furthermore, the relations among equilibrium-line altitude, glacier mass balance and climate factors were established, and the response of glaciers to climate change were also discussed. It is believed that the strong warming and decrease in snow days may be the principal factors driving most of the glacier retreat, although precipitation has increased and the reduction in sunshine hours and wind speed may slow the melting of glaciers. Finally, in the climate background assumed, glacier change is predicted.
Preliminary result of mass-balance observation of Rikha Samba Glacier, Hidden Valley, Mustang, Nepal
Bikas Chandra BHATTARAI, Rijan Bhakta KAYASTHA, Dorothea STUMM, Sharad P. JOSHI, Niraj Shankar PRADHANANGA, Abhishek MANANDHAR, Lea HARTL, Urs H. FISCHER, Pradeep K. MOOL
Corresponding author: Bikas Chandra Bhattarai
Corresponding author e-mail: email@example.com
This paper provides preliminary observations of the glacier mass-balance measurements of Rikha Samba Glacier in Hidden Valley, Mustang district in Nepal. Climate change is a major concern in the Himalaya because of potential impacts on water resources, economy, ecology and its environment. Many studies have been conducted on glacier mass balance worldwide, but only few short-term studies have been carried out in the Hindu Kush Himalayan region. Hence, this study is carried out to investigate the annual mass balance and terminus change of Rikha Samba Glacier. The glaciological method is applied to calculate the annual mass balance and Landsat satellite images, ASTER DEM and terminus survey data are used to detect glacier terminus changes. In September 2011 five stakes (stake no. 1, 2, 3, 4 and 5) were installed at altitudes from 5482 to 5740 m a.s.l. Measurements of stakes show net mass balance of stake no. 1–5 are –4.3, –3.1, –1.8, –1.1 and –1.1 m w.e., respectively. The satellite data analysis from 1989 to 2011 shows that the area of the glacier is decreasing at a rate of 0.017 km2 a–1 (R2 = 0.89) meanwhile the terminus altitude shifted up with a rate of 3.9 m a–1 (R2 = 0.94). These results will be useful for glacio-hydrological studies in this glacierized basin.
Estimation of discharge from Langtang Khola basin, Rasuwa, Nepal, using a glacio-hydrological model
Niraj Shankar PRADHANANGA, Rijan B. KAYASTHA, Joseph M. SHEA, Tirtha R. ADHIKARI, Suresh C. PRADHAN, Bikas C. BHATTARAI, Lochan P. DEVKOTA, Arun B. SHRESTHA, Pradeep K. MOOL
Corresponding author: Niraj Shankar Pradhananga
Corresponding author e-mail: firstname.lastname@example.org
This paper provides the result of glacio-hydrological modeling of a glacierized river basin in Nepal where climate change plays an important role in future water scenarios. To assess and analyze the hydrological regime of glacier-fed rivers is thus essential. The main objective of this study is to estimate the present and future discharge from the glacierized Langtang Khola basin in Langtang Valley, Rasuwa district in Nepal, using a positive degree-day model (PDDM). The total area of the Langtang Khola basin is 359.3 km2 of which 28.15% is glacierized. The PDDM is a simple model which requires monthly temperature and precipitation and some glaciological data as input parameters. Discharge is estimated by calculating ablation from glacierized portions of the basin using separate degree-day factors for snow, debris-covered ice and debris-free ice. Infiltration and base flow are assumed to be constant, evapotranspiration is estimated using the Blaney–Criddle equation, and precipitation and temperature are distributed in the basin as a function of elevation. In this model, the basin has been divided into 18 elevation bands ranging from an altitude 3700 to 7200 m a.s.l. The PDDM was calibrated for the period 1995–2005 using observed discharge data of Kyangjing hydrological station obtained from the Department of Hydrology and Meteorology, Government of Nepal. The model is able to reproduce the discharge quite well with a coefficient of determination of 0.96 for the calibration period. Furthermore, projected temperature and precipitation data are generated using the Weather Research and Forecasting (WRF) model of Langtang Khola basin from 2010 to 2059, which are bias corrected using 1988–2007 observed data at Kyangjing meteorological station. Projected temperature and precipitation data show the increasing trend of 0.02°C a–1 and 14.33 mm a–1, respectively. The monthly minimum and maximum calculated discharge are 1.14 and 56.30 m3 s–1, respectively. As temperature and precipitation are driving parameters of PDDM, increasing trend in these parameters showed the increasing trend in river discharge as well.
Projecting 21st century glacier runoff of all Alaskan glaciers
Regine HOCK, Andy BLISS, Andrew Cody BEEDLOW, Valentina RADIC, Eran HOOD
Corresponding author: Regine Hock
Corresponding author e-mail: email@example.com
Glaciers significantly modify streamflow both in quantity and timing, even with low percentages of catchment ice cover. Glaciers cover roughly 90 000 km2 in Alaska and have been thinning and retreating dramatically during the last decades, recently at an accelerating rate. These changes will have profound effects on river runoff quantity, seasonality and peak flows in Alaskan drainage basins. Annual runoff from a glacierized basin is a function of glacier mass balance, with years of negative balance producing more runoff than years of positive balance. As climate changes and causes glacier mass balances to become progressively more negative, total glacier runoff will initially increase followed by a reduction in runoff totals as the glaciers retreat. With high percentage of ice cover the initial increase in runoff can be substantial, considerably exceeding the runoff changes to be expected from any other component of the water budget. However in the long term the loss of ice will lead to lower watershed yields of water. Using a new complete glacier inventory and an elevation-dependent temperature-index model we compute the glacier mass changes and resulting glacier runoff (defined as melt – refreezing + rain) of all Alaskan glaciers (including adjacent Canadian glaciers) until 2100. We force the model with monthly temperature and precipitation output of several global climate models. We find that generally the glaciers lose mass over the 21st century; however, the glacier runoff response of individual glaciers varies widely. Some glaciers show an increase in runoff, while others show a decrease or an increase followed by a decrease in runoff. We analyze the runoff response for different glacier sizes and elevation ranges and also for different regions in Alaska. We find that while all regions show substantial mass loss, some of the regions show an increase in glacier runoff, while others show a decrease. Results indicate the importance of modeling accurately glacier retreat and thinning in addition to glacier mass balance.
An energy-budget-based glacier melting model for the Tibetan Plateau
Baohong DING, Kun YANG, Yingying CHEN, Lei WANG
Corresponding author: Kun Yang
Corresponding author e-mail: firstname.lastname@example.org
There have been rapid glacier retreats during the past few decades on the Tibetan Plateau, which not only have far-reaching impacts on the water resources in this region, but also potentially pose a threat downstream through glacial lake outburst floods. It is therefore important to model the physical link between glacier melting and climate changes and its implication in water resources. There have been a few studies on glacier melting models, of which the applicability is limited to some areas and the simulation capability also needs to be improved. This paper presents a new energy-budget-based model for the melting of mountain glaciers. Enthalpy, rather than temperature, is used in the energy-balance equations to simplify the computation for the energy transfer through water phase transition and within-snow liquid water movement. Heat transfer is computed in both snow and ice layers, and the inhomogeneous layering method is employed to describe the temperature profiles better, especially at the interface between snow and atmosphere as well as that between snow and ice. A new parameterization scheme is introduced into the model to calculate turbulent heat transfer over glacier surfaces. This model was validated based on the data collected from a field experiment that was implemented in the melting zone of Parlung No. 4 Glacier in the southeastern Tibetan Plateau from May to August in 2009. The results show that the RMSE of the simulated hourly surface temperature is about 0.97°C and R2 is 0.81. The RMSE of the simulated hourly latent heat flux and hourly sensible heat flux is 14.5 W m–2 and 23.5 W m–2, respectively, and R2 is 0.92 and 0.93. In general, this energy-budget-based model could reasonably simulate the glacier melting process. The model is still under development for a better simulation of glacier melting and its contribution to the water resources.
A distributed energy–mass-balance model for Dongkemadi and Muztagh Glaciers
Corresponding author: Liqiao Liang
Corresponding author e-mail: email@example.com
The Tibetan Plateau (TP) contains the largest number of glaciers outside the polar regions, the mass balance of which will affect water discharge of large rivers originating from the plateau. In order to better model hydrological processes of a glacierized basin and study the impacts of glacier ablation/accumulation resulting from climate change on water resources, a watershed hydrological model must also describe glacier ablation/accumulation. A distributed energy–mass-balance model for glacier is set up to simulate multi-year energy and mass balance in two regions: Dongkemadi Glacier situated in the interior of the TP and Muztagh Glacier situated on Pamir Plateau-Karakoram Mountain. The difference in simulation of glacier ablation/accumulation in the two regions is analyzed by comparing the estimated and observed energy components, i.e. net shortwave radiation, net longwave radiation, sensible heat flux, latent heat flux, ground heat flux, precipitation heat flux and mass balance. The applicability of the glacier model in different regions in the TP is then evaluated. Also, the contributions of each energy component to glacier ablation/accumulation are compared.
Sensitivities and feedbacks affecting the global mass balance of glaciers
Ben MARZEION, Alex H. JAROSCH, Jonathan M. GREGORY
Corresponding author: Ben Marzeion
Corresponding author e-mail: firstname.lastname@example.org
We use a minimal model of the specific mass balance of mountain glaciers, which is driven by temperature and precipitation data and based on the identification of time periods when glaciers with existing mass-balance measurements would have been in equilibrium with local climate if they had had present-day geometries. These periods are extrapolated to unsampled glaciers in order to determine the necessary model parameters. Length and area changes of the glaciers are accounted for by employing a parameterization based on linear relaxation to modeled volume changes. The model has been used to reconstruct the past global mass balance of mountain glaciers based on observations of temperature and precipitation, and to project the future changes based on CMIP5 scenarios. Here, we present equilibrium sensitivities of the model, and quantify the role of feedbacks (e.g. changes in terminus elevation and surface area) affecting the response of the global glacier mass balance to climate change.
Glaciological and hydrological regime of Astore catchment, Upper Indus River Basin (UIB), north Pakistan
Yinsheng ZHANG, Suhaib BIN FARHAN
Corresponding author: Yinsheng Zhang
Corresponding author e-mail: email@example.com
The Indus River is one of the world’s largest rivers, which separates the central Karakoram from the Greater Himalaya. It emerges from the Tibetan Plateau and flows towards northern Pakistan, where it changes its direction towards south and flows into the Arabian Sea. The Astore basin is a part of the UIB having a drainage area of 3995 km2 and is situated in the high-altitude extreme western Himalayan region, with a mean catchment elevation of 3980 m a.s.l and an elevation range from 1202 to 8061 m a.s.l. Average annual precipitation in the Astore basin is 672 mm, at valley floor station (2394 m a.s.l.) reaches 500 mm and at the high-elevation Burzil station (4030 m a.s.l.) increases to 870 mm a–1, with a precipitation lapse rate of 2.18 mm (100 m)–1 altitude. Two-thirds of the annual precipitation in the Astore basin falls in winter and spring as a result of the influence of the westerlies and one-third is from the monsoon component. Data from the period 1980–2010 indicate a decreasing tendency in the catchment temperatures in summer (August–September), while an increasing trend is found during the remaining months. Mean monthly precipitation trends based on a 30 year time series observed at Astore station from 1980 to 2010 evidences the increase in precipitation trend in January and February (winter) and also in the monsoon season (June–July). The Astore River has a mean annual flow of 137 m3 s–1. More than 75% of its runoff depends upon glaciers and seasonal snowmelt. The area of seasonal snow is an order of magnitude greater than the area of perennial snow and ice, although depleted through the melt season. The snow accumulation period in the Astore basin starts from September at higher altitudes, mean annual snow-cover area (SCA) reaches 80% in March–April, the melt period starts in early April and almost all the snow has melted by June–July, after which time most of the Astore River flow depends upon glacier melt. All the glaciers in the Astore basin have been evaluated with the help of various types of datasets and most of the glaciers were found to be in a stable state, neither growing nor retreating, during the past 40 years. For just two valley glaciers there was evidence of some retreat, but the terminus did not show any significant depletion, whereas the cirque/mountain-type glaciers do not show any retreat. The summer temperature reductions and positive trends in winter precipitation imply reduced ablation and increased accumulation of Astore glaciers, which may lead to positive or balance glacier ice mass. In addition, most of the Astore valley-type glaciers are heavily debris covered – this supraglacial debris cover influences the terminus dynamics by modifying a glacier’s interaction with the atmosphere, which may elaborate one of the reasons. The overall analysis suggests that the glaciers in the Astore basin have not been much affected by the warming due to climate change during the past few decades.
The firn layer over the ice sheets of Antarctica and Greenland
Peter KUIPERS MUNNEKE, Stefan R.M. LIGTENBERG, Jan H. VAN ANGELEN, Michiel R. VAN DEN BROEKE, David G. VAUGHAN, Ward GORTER, Richard R. FORSTER
Corresponding author: Peter Kuipers Munneke
Corresponding author e-mail: firstname.lastname@example.org
Both laser and radar altimetry studies indicate that the Greenland ice sheet volume is diminishing. Also, many of the floating ice shelves in Antarctica are thinning. To convert this volume reduction into a mass reduction, we need to consider potential changes in the firn density. For the ice shelves, it is relevant to know whether the observed thinning is due to basal melt, or merely by compaction of the firn layer overlying the ice shelf. To that extent, we use firn models that compute both the dry compaction rate and a basic firn hydrology that includes meltwater production, percolation, and refreezing. The applications of these firn models are very diverse. First of all, altimetric observations of surface height change can be corrected for firn processes, revealing the true ice-dynamic component of the observed thinning. Second, the firn model enables us to quantitatively assess the conditions necessary to form perennial bodies of liquid water within the firn, which have recently been discovered on the Greenland ice sheet. Third, we hypothesise that the firn layer on Antarctic ice shelves has played an important role in the recent break-up of ice shelves in the Antarctic Peninsula. In this contribution, we present a kaleidoscopic view over our firn model and its applications in various fields of glaciology.
Variation in climate change projections for the Greater Himalaya region and the response of glaciers to climate drivers
Louise PARRY, Jonathan BAMBER, Paul VALDES, Jim FREER
Corresponding author: Louise Parry
Corresponding author e-mail: email@example.com
Since the IPCC AR4 (2007) there has been an increase in the number of studies on glacial and hydrological processes within the Himalaya in an attempt to bridge the knowledge gap in understanding of Himalayan glacier extent and response to climate, and the linkage with downstream hydrology. However, a recurring major limitation to all reported trends is the significantly limited data availability and quality across the region for use in analyses, and the variation in climate projections. The results presented here are from the first stages of a longer-term project underway to analyse the hydrological response of Himalayan catchments with glaciated headwaters to variations in climate over the recent past and future. The sensitivity of the systems to different climate drivers are to be analysed with quantification of the uncertainties inherent in the cascaded modelling approach. The results from the climate modelling and initial glacier modelling are presented here. To analyse fluctuations in meltwater production in response to climate forcings, a temperature-index modelling approach coupled with a simple snowpack model is employed in consideration of the limited observed data availability for calibration and to allow multiple simulations for assessment of climate and parameter uncertainty. Surface mass balance (SMB) is modelled as a function of temperature, incoming shortwave radiation and albedo, which along with precipitation can be derived from downscaling the output from the regional climate model (RCM). Seven RCM hindcast simulations for the period 1960–2010 were run using HadRM3at a 0.44° (~50 km) grid resolution, driven by simulations of HadCM3 at the lateral boundaries, observed GHG concentrations and prescribed SST from HadISST. The sensitivity of the model results to the lateral boundary and initial conditions was tested to assess the sources of variation in model output. Particular focus is given to simulation of precipitation in terms of totals, type, seasonal and interannual patterns associated with the monsoon. To assess potential future variations in climate across the region, several RCM simulations, driven by GCM output from the CMIP5 project, were run for different climate change scenarios for the period 1960–2100. The hindcast results are indicative of model predictive skill, particularly for surface temperature, at yearly to decadal timescales, but indicate that the skill varies across the region and that the model simulations are linked to the lateral boundary conditions from the driving GCM.
Results of the Glacier_CCI round robin experiment on the estimation of surface elevation changes
Francesca TICCONI, Andrew SHEPHERD, Alan MUIR, Geir MOHOLD, Eero RINNE
Corresponding author: Francesca Ticconi
Corresponding author e-mail: firstname.lastname@example.org
Recently the European Space Agency (ESA) has launched the Climate Change Initiative (CCI), which focuses on those essential climate variables where the biggest impact on advancing understanding of the climate system is expected, maximizing the use of data from the ESA and other European archives. The glaciers and ice caps have been identified as one of these variables because of their sensitive reaction to even small climatic changes. Within the project three parameters have been selected as key parameters for describing the state and changes of the glaciers and ice caps: glacier area outlines, surface elevation changes, surface velocities. This work presents the results of the round robin experiment, a research activity performed within the framework of the project, aimed at comparing estimates of ice-cap surface elevation changes using different repeat altimetry techniques and different sensors. The goal of this comparison was the identification of the best performing algorithm, in terms of accuracy, coverage and processing effort, for the generation of surface elevation change maps. The results presented here have been derived using laser and radar acquisitions over Devon Ice Cap and Austfonna. The approaches investigated are the dual cycle crossover method and the repeat-track method. With regards to the latter, two different algorithms based on two different modes for considering the local slope have been compared. The absolute differences between the elevation change products have been evaluated. The results show the limitation of the crossover method in terms of spatial coverage and the almost equivalence of the repeat-track algorithms, which show an RMSE comparable with the estimated measurement accuracy.
Topographic and glaciological controls on glacier changes since the Little Ice Age in central Tien Shan
Yingkui LI, Yanan LI
Corresponding author: Yingkui Li
Corresponding author e-mail: email@example.com
The magnitude of glacial changes is not only affected by climate change, but also controlled by local topographic and glaciological factors. Here we examined the topographic and glaciological controls on glacial changes since the Little Ice Age (LIA) in central Tien Shan, where the timing of the LIA glacial advances has been constrained by cosmogenic nuclides, lichenometry and radiocarbon dating. We delineated the extents of the maximum LIA glacial advances and their corresponding modern termini of >700 glaciers using Google Earth high-resolution imagery and extracted their topographic and glaciological factors, including the slope, area, aspect and shape of the glaciers, from 30 m ASTER global digital elevation models (GDEM). Assuming that the climate impacts on glacial changes in this relatively small region are similar, we used this dataset to examine the relationship between the magnitude of glacial changes (changes in area, distance and ELA) and local topographic and glaciological factors (slope, area, aspect and shape) using multivariate regression analysis. Our results indicated that: (1) glaciers with steeper slopes have relatively larger ELA depressions but shorter retreating distances since the LIA; (2) small glaciers are retreating relatively faster than larger glaciers in terms of area-changing percentage; (3) south-facing glaciers are retreating faster than glaciers facing other directions; and (4) elongated glaciers mainly distributed within glacial valleys are relatively more stable than rounded glaciers/ice caps with less shaded surface areas. This study provides significant insights into the local topographic and glaciological controls on glacial changes in the past several hundred years, knowledge that is of critical importance to understand glacial changes in the relative long term and assess future impacts of climate and glacial changes on water supply in this arid and semiarid region.
Improved atmosphere–ice-sheet coupling for the UK Meteorological Office Unified Model
Robin S. SMITH, Jonathan GREGORY
Corresponding author: Robin S. Smith
Corresponding author e-mail: firstname.lastname@example.org
The UK Meteorological Office Unified Model is one of the most successful and widely used global climate models. Coupling with ice-sheet models has so far been limited to calculating surface mass-balance terms with very simple positive-degree-day (PDD) schemes which conserve neither energy nor water in the coupled system. Simulations with this system have also been shown to be very sensitive to the exact values used in the PDD scheme. Here we present the first results of a new coupled climate–ice-sheet model, where the SMB forcing is calculated explicitly in the climate model through the implementation of a multi-layer snowpack model, which includes refreezing and the dependence of albedo on snow grain size and density. For non-regional modelling cases, where the resolution of the global climate model grid is low, a subgridscale surface scheme simulates the snowpack over a range of elevations and surface types in each climate model gridbox. The explicit SMB terms from the climate model are then interpolated in three dimensions to provide forcing for the Glimmer-CISM ice-sheet model, which in turn updates the topography and surface characteristics in the climate model. The coupling conserves the energy and water in the system as the ice sheet and climate evolve and interact. Coupled simulations of modern-day Greenland conducted with both a regional climate model (PRECIS) and a low-resolution global configuration of the UM capable of simulating millennial timescales (FAMOUS) are presented and evaluated as a case study of how the new coupled system behaves.
Distribution and recent changes of supraglacial ponds and lakes in the Khan Tengri-Tomur Tien Shan, central Asia
Qiao LIU, Christoph MAYER, Shiyin LIU
Corresponding author: Qiao Liu
Corresponding author e-mail: email@example.com
Supraglacial lakes are widely distributed on the Tumor-type glaciers in the Tomur-Khan Tengri Tien Shan. The total amount of water storage and release of these supraglacial lakes probably plays an important role in glacial runoff events. Here a bulk of Landsat imageries were used to extract glacial lake boundaries for the whole Khan Tengri-Tomur region and two Google Earth images with high resolution were used to produce a more detailed map of supraglacial lakes in the Tomur glacial basin. The Inylchek Glacier basin and Tomur Glacier basin accounted for most supraglacial distribution in the Khan Tengri-Tomur Tien Shan. Most supraglacial lakes were identified located on the glacier with surface gradient <10°. Our primary results also show that their total area in summer, both for the whole Tomur-Khan Tengri region and the Tomur Glacier basin, experienced an increasing trend in recent years (1999–2010).
A new method for measuring mountain glaicer thickness change
Jianmin ZHOU, Zhen LI
Corresponding author: Jianmin Zhou
Corresponding author e-mail: firstname.lastname@example.org
It is important to monitor thickness changes of mountain glaciers for their contributions to calculations of ice volume loss and mass balance. Although traditional ground-based techniques exist for measuring glacier thickness changes directly and interannually, they tend to be labor-intensive and expensive and provide very limited spatial coverage. Differencing multitemporal digital elevation models (DEMs) generated from spaceborne or airborne observations becomes one of the effective methods to monitor the spatial patterns of glacier elevation and volume changes. These methods include generation of DEMs from radar interferometry, for example the Shuttle Radar Topography Mission (SRTM) DEM acquired in February 2000, or from spaceborne or airborne photogrammtery, or laser altimetry. However, these methods may introduce more errors caused by the DEMs. This paper presents, for the first time, a novel method to monitor the thickness changes of mountain glaciers based on the deformation extracted by D-InSAR of the glacier surface. To estimate changes in surface elevation through time, we make use of differential phase and get the deformation of the glacier surface in the line of sight (LOS). Then we separate the vertical components from the deformation of the glacier surface in the LOS and use these components to calculate thickness changes within glacier polygons. Using this method, we can monitor the thickness changes in a level of accuracy of centimeters. In order to demonstrate this method a practical example, the monitoring of thickness changes of Dongkemadi Glacier on the northern slope of Tanggula Mountain, China, is given.
Integrated risk evaluation of glacier lake outburst flood (GLOF) disasters in the central Chinese Himalaya
Shijin WANG, Tao ZHANG, Jiawen REN
Corresponding author: Shijin Wang
Corresponding author e-mail: email@example.com
Along with regional warming, the glaciers on the central Chinese Himalaya have retreated and thinned rapidly in recent decades, resulting in the formation of new glacial lakes, the expansion of existing glacial lakes and the concomitant increase in the threat of glacier lake outburst flood (GLOF) disasters. However, previous studies have focused mainly on the characteristics and mechanism of glacial lake outburst in the disaster-starting area, while neglecting the risks to the economic and social systems in the hazard-bearing area. For better understanding of the integrated risk of GLOF disasters in the disaster-starting and -bearing areas, this study took into consideration the dangerous risk of glacial lake outburst and the exposure, vulnerability and adaptability risk of hazard-affected bodies, built up a quantitative integrated risk evaluation system, and obtained the objective weight of all evaluation factors by using the analytical hierarchy process (AHP). Finally, the study evaluated synthetically the integrated risks of GLOF disasters in Dinggyê, Tingri, Nyalam and Gangba counties, central Chinese Himalaya, by using the multi-objective linear weighting function. The research results showed that the number of glacial lakes with areas in excess of 0.02 km2 has increased by 19.51% and the total area of glacial lakes has increased by 28.74% in 2010 compared with 1990 data. Specifically, there are 55 moraine-dammed lakes of ?0.2 km2 in 2010, of which 23 potentially dangerous glacial lakes (PDGLs) are indentified; their area increased by 77.46% (0.37 km2 a–1) between 1990 and 2010 and the increase rate is obviously higher than the 39% of non-PDGLs in the same period. Among the four counties, Dinggyê has the higher exposure degree in hazard-bearing area and lower adaptive abilities to deal with GLOF disasters, resulting in its higher integrated risk index. Nyalam has a higher dangerous index of glacial lake outburst, but it has relatively strong abilities to adapt to GLOF disasters, thereby slowing down the integrated risk of GLOF disasters. Gamba has a lower economic base and the ability to adapt to GLOF disasters, but it has a lower dangerous risk index of glacial lake outburst and less vulnerable risk index of economic and social systems in hazard-bearing areas. Therefore, Gamba has the smallest integrated risk index of GLOF disasters. Overall, Dinggyê has the highest integrated risk index of GLOF disasters, followed by Tingri and Nyalam, while Gangba has the lowest risk.
Meteorological characteristics and their climatic implications in the high altitude region of Mount Yulong, southwest China
Huijuan XIN, Yuanqing HE, Hewen NIU, Jiankuo DU
Corresponding author: Huijuan Xin
Corresponding author e-mail: firstname.lastname@example.org
Four automatic weather stations are installed, located at Lijiang (2400 m a.s.l.), Ganhaizi (3046 m) and the terminus of the ice tongue (4300 m) and accumulation zone (4800 m) of Baishui Glacier No. 1, on the eastern slope of Mount Yulong, China. The main features of the vertical profiles of meteorological elements on the subtropical mountain were investigated by the dataset collected from the four stations from October 2008 to September 2012. Monthly and annual temperature present an approximate linear decreasing trend with height, although linear tendency in the dry winter season is weaker than during the wet monsoon season. Correspondingly, the duration of the warm season is shortened with altitude and there are 6 months above freezing at the equilibrium-line altitude of the glacier. Lapse rates present a considerably temporal and spatial variation and are greatly related to the precipitation amount. The annual temperature range is bi-modal with elevation. The rainfall profile is a two-peak type in the monsoon season: the first peak is between 2800 and 3200 m and may supply plenty of moisture to the forest area; the second largest zone is in the glacier-covered area between 4600 and 5000 m, providing mass accumulation for glacier formation. Heavy precipitation is mainly concentrated in JJA. The vertical profile of annual RH also displays a two-peak type, but the second peak is obviously larger than the first one. Adequate monitoring reveals that high frequent occurrence of daily temperatures above freezing, positive net radiation, vast latent heat of condensation from liquid state rainfall in the monsoon season and strong wind speeds during the dry winter accelerate mass losses on Baishui Glacier No. 1.
Surface area and elevation changes of glaciers in the Qinghai-Tibetan Plateau interior area since the 1970s based on historical topographical maps and remote-sensing data
Junfeng WEI, Shiyin LIU, Wanqin GUO, Junli XU
Corresponding author: Junfeng Wei
Corresponding author e-mail: email@example.com
The Qinghai–Tibetan Plateau interior area (QTPIA), often termed the Qangtang Plateau, is located between the central-west part of the Kunlun Mountains to the north and the Gandise Range to the south. In the region, various closed drainage basins are developed with the distribution of many dome-like mountains higher than 6000 m a.s.l. These mountains provide a prevalent condition for the development of ice caps of various sizes, such as Purog Kangri and Zangser Kangri. Glaciers in the study area are of the extreme continental type with ice frozen to the bedrock. Water generated from these glaciers flows into different lake basins in the region, acting as an important regulator to water-level changes and valuable water resource to wildlife and livestock, as well as human activities. Based on historical topographical maps in ~1970, 5947 glaciers with an area of 8036.39 km2 have been inventoried. Landsat images acquired in ~2009 show that these glaciers have been retreating, with their total area decreased to 7269.74 km2, 9.5% of that in the early 1970s. The Bangong Co Basin is the most glacierized basin with the total number and area accounting for about 40% of the relevant totals in the whole QTPIA. Glaciers in the basin inventoried with good quality maps and satellite images have been shrinking by 0.27% annually in the area since the 1970s. Glaciers in the Zhari Namco Basin have experienced the greatest shrinkage, with the area decreasing by 23.75%. There exists a regional gradient of glacier area reduction whereby the larger decrease in area occurred in the south and the smaller decrease in the north of the plateau. Most of glaciers have been thinning at the same time as detected for glaciers in some of the mountains by the difference in digital elevation models from maps and SRTM (Shuttle Radar Topography Mission). The mean annual thinning rate ranged from –0.65 ± 0.23 m a–1 to –0.06 ± 0.23 m a–1. Compared with changes in glaciers in other regions of the Qinghai–Tibetan Plateau, glaciers in the QTPIA were less sensitive to regional climate warming.
Annual and daily meteorological cycles at high altitude on a temperate glacier area
Huijuan XIN, Yuanqing HE, Hewen NIU
Corresponding author: Huijuan Xin
Corresponding author e-mail: firstname.lastname@example.org
An automated weather station was installed on 20 September 2011 at the summit of Mount Yulong (4500 m, 27°100–27°400 N, 100°90–100°200 E), which is the southernmost region in mainland Eurasia where glaciers exist. Meteorological conditions on the mountain are being observed to facilitate development of a comprehensive insight into climatic conditions at high altitude in this remote region of subtropical temperature glaciers. Based on the first year’s records, the annual and daily near-surface meteorological cycles of Baishui Glacier No. 1 are analyzed and discussed here. Variables analyzed include air temperature, relative humidity, wind, pressure (at 2 m and 5 m tower column) and radiation (2.5 m). A large diurnal fluctuation was recorded in most variables, which is distinguished from other types of glacier and not unexpected given the location at 27°N; the data also reveal seasonal differences between the wet monsoon season and the dry season. The diurnal changes of temperature show single-peak type distribution, with the minimum appearing at 07:00 and the maximum at 15:00 (local standard time), and influenced by radiation, temperature at 5 m is greater than that at 2 m. Relative humidity peaks appear at 12:00 and 19:00, the minimum in the early morning. Owing to the effect of glacier wind in the valley, the prevalent wind is a downslope wind (southeast wind) and wind speed in the dry season is greater than that in the wet season. Solar radiation and longwave radiation peaks appear at 12:00 and 13:00, respectively, but due to rainy-cloud, incoming solar radiation and longwave radiation in the wet season is greater than that in the dry season.
Modeling impacts of climate change on glacial runoff of the debris-covered Koxkar Glacier
Haidong HAN, Jian WANG
Corresponding author: Haidong Han
Corresponding author e-mail: email@example.com
This paper aims to improve the understandings of glacial runoff variability of a debris-covered glacier against the changing climate. A distributed conceptual hydrological model was developed to address the meltwater generation and concentration through the glacier. Compared with other hydrological models for glacierized areas, the role of debris cover in glacial runoff generation was presented because of the extensive development of a supraglacial debris mantle on the glacier. Owing to thermal isolation, a debris layer with thickness greater than ~20 cm may inhibit the melting of ice underneath, the massive debris entrainments on a glacier greatly suppress melting and prevent rapid glacier wastage. The hydrology of the debris-covered area is, however, complicated by the existence of many ice cliffs. Backwasting of ice cliffs can be significant during the ablation period due to more intense melting over the bare-ice slopes than under the debris mantle. Melting of ice cliffs may therefore be an important meltwater source in the debris-covered area. Daily meteorological data from 2007 to 2011 was used to run the model or to provide mathematical relations of climatic variables across the glacier. Twelve climatic scenarios were assumed to test the meltwater variability against the changing temperatures and precipitations, out of which six scenarios set the annual temperatures rising and declining by 0.5°C, 1°C and 2°C, respectively, relative to temperature of the reference station, and others assume the yearly precipitation increasing and decreasing by 10%, 30% and 50%, respectively, compared with that of the reference station. Preliminary results show that temperature variations yield great influences on glacial runoff – amplitude of 1°C will lead to a 22.5% increase in meltwater and when temperatures rise by 2°C nearly 45% of an increasse in runoff could be expected. Comparatively, changes in precipitation have less influence on glacial runoff variations, partly because a large portion of precipitation on glaciers appears to be snow, which cannot contribute to runoff immediately. Note that the increase in precipitation will potentially increase the duration of rainfall, which may bring down the air temperatures.
Recent glacial lake expansion and its impact on water resources in Tien Shan
Xin WANG, Lianghong JIANG, Shiyin LIU
Corresponding author: Wang Xin
Corresponding author e-mail: firstname.lastname@example.org
The variability and impacts on water resource of glacial lakes were assessed in the Tien Shan from 1990 to 2010 on the basis of Landsat TM/ETM images. In the past 20 years, glacial lakes in the Tien Shan have expanded with an average rate of 0.680 km2 a–1 or 0.8% a–1. The eastern Tien Shan contributes over half of the area expansion value by a rate of 0.359 km2 a–1 and northern Tien Shan follows at a rate of 0.165 km2 a–1. The relatively lower rates of 0.065 and 0.090 km2 a–1 occur in western and central Tien Shan, respectively. The lake area increases in most 100-elevation bands except at altitudes of <2900 m and >4100 m. The fastest growth 100-elevation bands are in the range from 3400 to 4100 m with a rate of 1.5% a–1. Both regional warming and widely glacier wastage lead to glacial lake expansion, while small- and medium-sized (<0.6 km2) lakes respond most sensitively to glacier retreat. The glacial lake expansion can slow down regional glacier meltwater losses due to climate warming to some degree and on average ~0.006 Gt a–1 glacier meltwater was held temporarily in the glacial lakes over the past two decades. However, it may also increase simultaneously the frequency and damage of glacial lake outburst floods (GLOFs) or debris flow in this region.
Results from 30 years of international ship-based observations of Antarctic icebergs
Olav ORHEIM, Barry GILES, Harvey GOODWIN, T.H. JACKA, Jan-Gunnar WINTHER, Neal YOUNG
Corresponding author: Olav Orheim
Corresponding author e-mail: email@example.com
In 1981 the Norwegian Polar Institute (NPI) initiated a programme for the 6 hourly shipborne collection of data on Antarctic icebergs, following an endorsement by SCAR’s Working Group on Glaciology. Since then, more than 300 ship cruises from 15 different nations have produced data on 320 000 icebergs classified into five size classes. In parallel the Australian Antarctic Division (AAD) conducted a more detailed collection of iceberg data from ships they operated, using seven size classes. Typically the visual or radar extent of the observer is 12 nautical miles. The 6 hour interval between observations means that a ship travelling at 4 knots or higher speed has little duplication in observation. The observations can thus be seen as a series of 1550 km2 area snap-shots of the Southern Ocean. The value of an individual observation is small, but the total dataset shows significant patterns. A joint programme between NPI and AAD has now started full analyses of all these data, and this paper presents some early results. The observations cover all of the Southern Ocean, with the lowest densities in the Amundsen and Bellingshausen Seas. On average, each observation counted 11 icebergs. Bergs with length <200 m account for 70%, while those >1000 m represent only 2% of the total numbers. The latter nevertheless account for >80% of the total mass of the observed icebergs. The icebergs are not evenly distributed around the continent, in part obviously caused by regional differences in calving rates. The drift patterns of large and small bergs show differences, but both generally follow the westerly directed coastal current to certain ‘exit zones’ where the icebergs drift northward into the clockwise circum-Antarctic circulation. The main exit zones of the bergs from the continent are around 150° W–165° E, 70–110° E and 15–60° W. Icebergs >1000 m are relatively more common far from the continent, with many observed north of 50° S. That there would be a large number of zero iceberg observations in near-coastal waters, especially in the Ross Sea, was more unexpected. As already shown by Jacka and Giles for parts of the Australian data, the size distribution of icebergs moving in a latitude corridor clockwise around the continent allows calculation of dissolution rates. Similarily the total dataset can be used to estimate iceberg calving rates for the whole circumference of Antarctica.
A direct measured glacier thinning in the southern Tibetan Plateau (Xixiabangma, Yangbajing and Naimona’nyi Glaciers)
Lide TIAN, Jibiao ZONG, Tandong YAO, Linglong MA, Jianchen PU
Corresponding author: Lide Tian
Corresponding author e-mail: firstname.lastname@example.org
Various work has confirmed the fast retreat of the Tibetan Plateau glaciers in recent decades due to global warming, especially the area shrinkage as detected by the remote-sensing method. In recent years, more concern has been focused on the effect of glacier melting on available water resources surrounding the glacier region. Consequently, the change in glacier ice volume is of more importance in this sense. In this work, we present results from directly measured glacier surface altitude change by differential GPS. By comparing the preciously measured altitude change from 2007 to 2011 at three glaciers in the southern Tibetan Plateau, we can give a reliable glacier thinning ratio in the past few years. The measured results from Gurenhekou Glacier, Yangbajing, show the ice depth loss is 3.96 m in the 4 years from 2007 to 2011. In Kangwure Glacier, Xixiabangma, the average depth loss is 2.70 m in 3 years, and thus the annual glacier depth loss is 0.90 m based on the observations from September 2007 to August 2010. The glacier depth loss is 1.4 m on Naimona’nyi Glacier, one of the largest glaciers in the western Himalaya, with an average annual loss of 0.7 m. Although the monitoring period is still limited, the similar ice loss ratio (0.7–1.0 m a–1) in the southern Himalaya indicates quite homogenous ice loss in different regions and with different glacier sizes and orientations. This work also shows that both the ablation zone and the accumulation zone are losing ice, indicating the glacier flow is also involved in glacier thinning rather than surface melting. This result emphasizes the importance of GPS measurements compared with stake-based mass-balance observations. We are still working on a longer period of monitoring and a greater number of glaciers to obtain more representative data to evaluate the glacier melting trends in the Tibetan Plateau.
Assessing glacier area and length changes using the inventory of Norwegian glaciers and topographic maps
Solveig H. WINSVOLD, Liss M. ANDREASSEN
Corresponding author: Solveig H. Winsvold
Corresponding author e-mail: email@example.com
The Inventory of Norwegian glaciers has, together with topographic maps, been used to assess glacier area and length changes. In some regions, up to four epochs are used in the change analysis: (1) old analogue maps covering five of the northernmost ice caps in Norway (1895–1907); (2) the first edition N50/M711 topographic maps from the Norwegian Mapping Authorities (1952–1985); (3) glacier area outline product from the project CryoClim (1988–1997); and (4) the inventory of Norwegian glaciers from NVE (1999–2006). Epochs 2 and 4 cover all glacier regions in mainland Norway, but some glacier regions in the dataset from epoch 3 are lacking due to absence of preferable satellite scenes. For epochs 1 and 2, the glacier area is derived from three older analogue map sheets and 168 first edition 1:50 000 topographic map sheets based on aerial photographs. These maps have been scanned, georeferenced and the glacier outlines digitized. Epochs 3 and 4 are based on satellite imagery from the complete time series of Landsat TM 4, 5 and 7 ETM+, using 8 and 12 satellite scenes, respectively. Calculation of glacier changes was done using GIS analysis and the same hydrological basins were used for the new glacier inventory, with some adjustments. In many cases, change assessments were challenging and uncertain, as different sources were compared and due to adverse snow conditions in the map datasets. Preliminary results reveal regional area changes from close to 0% change down to –28% in the Svartisen region (1968–1999) and the northernmost glaciated region in Norway (1966–2006), respectively. At a national level, preliminary results reveal nearly no change (–0.31%) in glacier area between epochs 3 and 4, but –12% area change between epochs 2 and 4 (378 km2). Although it is challenging to compare each epoch due to the variation of years and different analysis conditions, results clearly point to regional differences in glacier area change.
Climate change and glacier retreat in the Qilian Mountains, China, from 1956 to 2010
Hongzhen TIAN, Taibao YANG, Qinping LIU
Corresponding author: Hongzhen Tian
Corresponding author e-mail: firstname.lastname@example.org
Glaciers in the Qilian Mountains, located in the northeastern part of the Tibetan Plateau, China, constitute an important freshwater resource for downstream populations and natural systems. To enhance our understanding of the variability of the glaciers, temporally and spatially comprehensive information about them is essential. The glacier outlines of 1990, 2000 and 2010 in the whole area were delineated in a semi-automated manner using band TM3/TM5 ratio images of Landsat ETM+ or TM scenes with the help of a merged ASTER GDEM/SRTM v4.1 digital elevation model. Combined with the results of previous studies, we found that the area of the glacier shrank by 30.36% from 1956 to 2010 and the shrinkage was accelerated in the last decade. Climate trend analysis showed a pronounced temperature increase from 1961 to 2010. There was a small increase in precipitation on average, but it was not significant. Glaciers shrank mainly due to the increasing temperature. A positive mass balance in the Qilian Mountains was very unlikely over the past decade. Moreover, given the trend toward higher temperatures, the glaciers in this region will continue to retreat. In the short term, as glaciers retreat and lose mass, they will add to an increase in runoff. In the long term, as glacier coverage decreases, runoff may decline. As the population dependent on these waters is foreseen to increase over the coming decades, a severe water crisis is expected to occur, which will only exacerbate conflict in this area.
Simulating glacier mass balance and impacts on hydrological regimes
Simon ROGERSON, Nigel ARNELL
Corresponding author: Simon Rogerson
Corresponding author e-mail: email@example.com
Glacier retreat is often cited as the most visible representation of a warming climate and further retreat is expected to have impacts on freshwater availability in many regions across the globe. However, due to the remoteness and lack of observation data for the vast majority of the world’s glaciers, there has been a shortage of studies combining glacier mass-balance modelling, estimates of glacier runoff and impacts on hydrological regimes. This project aims to develop a generalized mass-balance model to run with sparse input data, which can be used to assess glacier sensitivities to climate change, the impact of different climate scenarios on global glacier mass balance, the contribution of glacier runoff to hydrological regimes of different scales and the impact on these hydrological regimes of different climate scenarios. A distributed temperature-index-based glacier mass-balance model has been developed, which uses temperature and precipitation data from observations, reanalysis or climate model data in conjunction with glacier location, elevation and size data from the World Glacier Inventory. This model has successfully simulated glacier mass balance of individual glaciers at various locations representing different latitudes, elevations and climates, as well as successfully simulating regional mass balances across the globe. The mass-balance model has also been used to test glacier sensitivity to changes in climates and suggests that glaciers with long melt seasons, such as those in tropical or maritime climates, are most sensitive to changes in temperature. The mass-balance model also suggests that glaciers in areas where there is low mean air temperature in the ablation zone during the melt season, such as those in tropical or continental climates, will have a low contribution of sensible heat and longwave radiation to the energy available for melt; therefore, there will be a high contribution of incoming shortwave radiation and subsequently the albedo effect will be large in these areas and there will be high separation between degree-day factors of snow and ice, respectively. Mass-balance modelling also suggests that glaciers with high values of positive degree sum (length of melt season multiplied by mean air temperature during melt season), such as those in maritime climates, will be most sensitive to choice of degree-day factors of ice and snow.
Studies on the characteristics of surface movement on the glaciers Austre Lovénbreen and Pedersenbreen, Svalbard, Arctic
Peng LI, Ming YAN, Songtao AI, Yuetong XU, Leibao LIU, Weijun SUN
Corresponding author: Ming Yan
Corresponding author e-mail: firstname.lastname@example.org
The glaciers Austre Lovénbreen and Pedersenbreen are located near Ny-Ålesund, Svalbard, Arctic. The characteristics of surface movement are analyzed based on filed data from 2005 to 2011 on both glaciers. The results are as follows: (1) The average horizontal velocities of Austre Lovénbreen and Pedersenbreen are 2.14 and 6.28 m a–1, respectively, and their corresponding variation coefficients are 0.24 and 0.14, respectively. The average horizontal velocity in summer of the two glaciers is slightly higher than that in winter. There is a multinomial relationship between the glacial horizontal velocity and its elevation. The horizontal velocity is larger along the glacial mainstream line than that on both sides and its distribution is not symmetrical on both sides of Austre Lovénbreen glacier. Based on the glacial movement features, Austre Lovénbreen can be divided into three regions from its origin to terminus, and they are compressional region, stretching region and compressional region in order. (2)The average vertical velocities of Austre Lovénbreen and Pedersenbreen are 0.76 and 0.90 m a–1, respectively, and their corresponding variation coefficients are 0.81 and 0.59, respectively. The vertical velocities are bigger in summer with a smaller variation coefficient than that in winter .There is a linear relationship between the glacial vertical velocity and its elevation. According to their contribution to the composition of vertical velocity on Austre Lovénbreen, height changes caused by surface mass balance make the greatest contribution of 64%, followed by compensation flow (19%) and horizontal velocity components (16%). On Pedersenbreen, in contrast, height change caused by surface mass balance makes the greatest contribution at 40%, followed by horizontal velocity components (35%) and compensation flow (25%). (3) The surface strain rate first decreases and then increases along the mainstream line direction on Austre Lovénbreen and Pedersenbreen, and their corresponding average variation coefficients are 0.19 and 0.15, respectively.
Supraglacial lakes on ice sheets and ice shelves: a comparison
Alison BANWELL, Marta CABALLERO, Mac CATHLES, Neil ARNOLD, Neil GLASSER, Douglas MacAYEAL
Corresponding author: Alison Banwell
Corresponding author e-mail: email@example.com
The development of supraglacial lakes in the surface ablation zones of Greenland and Antarctica (mostly on ice shelves) constitute a major impact of environmental warming in the polar regions. However, it remains to be fully explained how the increasing lake coverage will drive changes to the ice sheets. Current thinking suggests that lakes on grounded ice sheets are fundamentally different from lakes on ice shelves, because in the former case, lake location (and therefore maximum water depth and volume) is constrained by bedrock topography, and in the latter case, lakes respond to the flexure made possible by floating ice. Large surface melt rates in Greenland are necessary to produce large lake volumes, but persistent multi-year lakes on ice shelves in the Antarctic may develop equivalent water volumes despite lower surface melt rates. Through the analysis of satellite imagery, this study seeks to establish a quantitative comparison among the spatial patterns, shapes, sizes and volumes between surface lakes on the Larsen B Ice Shelf (before its break-up in 2002) and on the grounded ice of Paakitsoq, a land-terminating region of the Greenland ice sheet. We suggest that the generic differences between lakes in the two regions help explain why the rapid drainage of lakes on the Greenland ice sheet can contribute to summer speed-up and why Antarctic ice-shelf lakes can be devastating to ice-shelf stability. This intercomparison across the full spectrum of supraglacial lake phenomena also highlights the range of behaviors that these lakes display in response to differing rates of surface ablation.
Future Mer de Glace (France) fluctuations assessed from a parameterized model and past data relative to thickness changes
Christian VINCENT, HARTER, GILBERT, BERTHIER, SIX
Corresponding author: Christian Vincent
Corresponding author e-mail: firstname.lastname@example.org
Mer de Glace is the largest glacier located in the French Alps (Mont Blanc area). Length variations and thickness changes of the tongue have been measured since the beginning of the 20th century. Annual mass balance and ice-flow velocity measurements have been carried out continuously since 1979. The topography of the bedrock was also measured in the lower part of the glacier. Future thickness changes and glacier retreat are then simulated using a simple parameterization calibrated from numerous thickness changes and glacier-wide mass balance observed over the last century. The method, proposed initially by Huss and others (2008), describes the spatial distribution of the glacier surface elevation change in response to a change in mass balance. This method is suitable for glaciers for which bedrock topography remains unknown in the accumulation zone and for which 3-D ice-snflalized function of thickness change is determined from a digital elevation model derived either from topographic maps or from aerial photographs between 1905 and 2008. Given that the method assumes that the redistribution of the annual surface accumulation by ice flow is instantaneous, it does not enable reconstruction of the annual fluctuations of the glaciers. However, the method, which is mass conserving, allows us to simulate long-term simulations of glacier fluctuations. We analyze the uncertainties and limitations of the method, particularly during positive mass-balance periods. Our study reveals that Mer de Glace, under present climatic conditions, will continue to decrease dramatically in the next decades.
Improved Antarctic surface mass-balance remote sensing using ASCAT
Alexander D. FRASER, Simon WOTHERSPOON, Hiroyuki ENOMOTO, Neal W. YOUNG
Corresponding author: Alexander D. Fraser
Corresponding author e-mail: email@example.com
Large-scale distribution of Antarctic surface mass balance (SMB) is currently poorly understood. High-quality in situ measurements of SMB are sparse, particularly in the interior of the continent. Remote sensing can be used to guide interpolation between in situ measurements. Previously, passive microwave polarization ratio, which is sensitive to the density of horizons of different dielectric properties in the upper snowpack (a proxy for SMB), has been used to guide interpolation of SMB points in Antarctica. We present evidence that maps of alternative parameters may be more suitable maps upon which to base interpolated fields. These maps come from the EUMETSAT Advanced Scatterometer (ASCAT) C-band scatterometer, which was launched in 2007. In particular, we use the ‘A’ (isotropic component of backscatter, sensitive to grain size within the C-band penetration depth of ~20 m) and ‘B’ (linear component of backscatter dependence on incidence angle, sensitive to grain-size profile). Importantly, these maps are sensitive to recently mapped extensive areas of surface wind glaze, which are areas of near-zero net accumulation and thus are less prone to overestimation of SMB compared with earlier large-scale SMB maps. A further focus of this work is a comparison of several statistical interpolation methods, including a careful consideration of the statistical treatment of negative SMB values. A primary output of this work is a new SMB map of the Antarctic continent based on these improved fields.
Synoptic-timescale observations of Antarctic snowfall/wind redistribution events from scatterometer data
Alexander D. FRASER, Melissa A. NIGRO, John CASSANO, Neal W. YOUNG, Benoit LEGRESY, Hiroyuki ENOMOTO
Corresponding author: Alexander D. Fraser
Corresponding author e-mail: firstname.lastname@example.org
The orbit and swath configuration of the EUMETSAT Advanced Scatterometer (ASCAT) instrument gives C-band backscatter measurements from a wide range of azimuth and incidence angles over most of the Antarctic continent. A 5 day orbital subcycle combined with this excellent observation angle diversity means that complete maps of accumulation-sensitive parameters can be produced on a 5 day basis. Analysis of time series of these parameters reveals several abrupt changes in localized regions, particularly in the ‘A’ parameter (isotropic component of backscatter, which is sensitive to snow grain size) and the ‘M2’ parameter (the magnitude of the second-order Fourier term describing the near-bi-sinusoidal azimuthal response, which is an indicator of the presence/magnitude of sastrugi/other surface microrelief). Using 15 km grid spacing Antarctic Mesoscale Prediction System (AMPS) numerical weather prediction model data, we show these abrupt changes in the ‘A’ and ‘M2’ parameters are associated with snowfall events arising from incursions of air from lower latitudes. Both the ‘A’ and ‘M2’ parameters show a complex response to precipitation events, with both the sign and magnitude of the response depending on wind reworking/redistribution. This observation of changes in near-surface snowpack conditions complements recent results from other authors using GRACE-derived gravity and CloudSat-derived snowfall observations to detect similar snowfall events in East Antarctica.
GRACE RL05-based ice-mass change in the typical regions of Antarctica from 2004 to 2012
Xiaoleij JU, Yunzhong SHEN, Zizhan ZHANG
Corresponding author: Yunzhong Shen
Corresponding author e-mail: email@example.com
As the biggest ice sheet in the world, the mass change of Antarctica plays an important role in global climate change. Gravity Recovery and Climate Experiment (GRACE) provides a good way to monitor mass variation of the Antarctic ice sheet. In April 2012, the new RL05 data with better spatial resolution, better accuracy and periodical characteristics were officially released by CSR, JPL and GFZ. By using the newly released data we analyzed the mass change from 2004 to 2012 in the typical areas, e.g. Antarctic Peninsula (AP, West Antarctica) and Lambert–Amery System (LAS, East Antarctica). Based on the RL05 data of CSR, JPL and GFZ, the AP mass change rates are –16.41 ± 2.92 Gt a–1 (2004–2012), –15.99 ± 2.79 Gt a–1 (2004–2012) and –16.44 ± 2.12 Gt a–1 (2005–2012) and the LAS mass change rates are –1.81 ± 5.04 Gt a–1 (2004–2012), –5.92 ± 7.76 Gt a–1 (2004–2012) and 6.95 ± 8.90 Gt a–1 (2005–2012), respectively. The results show that the mass changes derived from CSR, JPL and GFZ data are of great differences, with larger uncertainties for the LAS. However, the mass changes in the AP derived from the three agencies are much closer to each other and the uncertainties are significantly smaller than the mass change rates.
Understanding the climatological water balance for the Langtang Kyanging areas of the Nepal Himalaya
Tirtha Raj ADHIKARI
Corresponding author: Tirtha Raj Adhikari
Corresponding author e-mail: firstname.lastname@example.org
For the protection of the environment, climate and water studies play a key role. This study attempts to assess the potential water availability in the Langtang region of the Nepal Himalaya. Potential evapotranspitration is calculated by the Penman Monttith equation (PET) with the help of maximum and minimum temperature, relative humidity, wind speed and sunshine hours. The climatic water balance of water bodies is calculated on the basis of the Thornthwait procedure. These calculations help to examine annual water surplus (WS) and water deficit (WD) periods. Potential water surplus at Langtang station is calculated by the above techniques for the time period 1988–2008 on an annual basis. The main aim of this study is to compare the seasonal trends in AE, WS and WD for understanding the snow accumulation of the Nepal Himalaya. Seasonal variations in AE of 22.5 mm, in WD of 38.5 mm and in WS of 0.0 mm in DJF have been found. The distribution of AE, WD and WS in Langtang Kyanging gradually differed as AE 46% ,WD 38% and WS 16%. Climatic water balance of Langtang region WD is found to be higher than WS snow and glacier field. Little mass of snow has accumulated and large amounts of snow and glacier have melted in this area. As a result, limited fresh water is being reserved in this area. This result may be useful for planners of water resources and for local people for sustainable management of the glacierized environment in the Langtang Kyanging area.
How accurately can radar altimetry contribute to estimate the Antarctic ice sheet volume and mass balance?
B. LEGRÉSY, M. HORWATH, S.R.M. LIGTENBERG, M.R. VAN DEN BROEKE, F. BLAREL
Corresponding author: B. Legresy
Corresponding author e-mail: email@example.com
Knowing the interannual variations of the Antarctic ice sheet net snow accumulation, or surface mass balance (SMB), is essential for analyzing and interpreting present-day observations. For example, accumulation events like the one in East Antarctica in 2009 challenge our ability to interpret observed decadal-scale trends in terms of long-term changes versus natural fluctuations. We developed a higher accuracy time series of radar altimetry with ERS2 and Envisat data from 1995 to 2010. We will present the surface topography variations, the internal error levels for both altimeters and the radar echo and ground miss-repeat corrections made. We show that a different echo correction has to be applied to ERS2 and Envisat as the firn changed in between the two periods of observation. Therefore the possibility to correct the radar altimetry data for echo shape changes from the echo shape is limited, limiting the attainable accuracy of volume change estimates. We illustrate the great potential and limitations of radar altimetry by internal assessment and by comparing with other changes estimates as temporal gravity variations and atmospheric modeling of firn densification. We evaluate the limits of techniques depending on the temporal and spatial scales of interest. SMB variations cause changes in the firn density structure, which need to be accounted for when converting volume trends from satellite altimetry into mass trends. Recent assessments of SMB and firn volume variations mainly rely on atmospheric modeling and firn densification modeling. The modeling results need observational validation, which has been limited until now. Geodetic observations by satellite altimetry and satellite gravimetry reflect interannual firn volume and mass changes, among other signals like changes in ice-flow dynamics. Therefore, these observations provide a means of validating modeling results over the observational period. We present comprehensive comparisons between seasonal and interannual volume variations from radar altimetry and firn densification modeling, and between interannual mass variations from SMB.
Dynamics of Mertz Glacier and its ice tongue, East Antarctica: implications of its calving and changes at various timescales
B. LEGRÉSY, B.K. GALTON-FENZI, L.G. LESCARMONTIER, E. COUGNON, C. MAYET, L. TESTUT, N. YOUNG, R. MASSOM, R. WARNER, R. COLEMAN
Corresponding author: B. Legresy
Corresponding author e-mail: firstname.lastname@example.org
In February 2010, the tongue of Mertz Glacier calved, releasing an 80 km × 30 km iceberg. We had anticipated this calving event and started observing its development as well as gathering data to monitor the dynamics of the glacier. Here, we present the main characteristics of Mertz Glacier in the context of this calving event. In addition to regular collection of satellite images, a number of observations have been made within the Cooperative Research into Antarctic Calving (CRACICE) project. For investigations of the glacier dynamics and rift development we have used the following data types: ERS SAR interferometry, RADARSAT and Envisat SAR images, Landsat and SPOT images, SPOT stereo imagery, airborne ice thickness radar profiles and in situ GPS measurements. We improved the ocean bathymetry using airborne gravimetry, iceberg movements and grounding points, and new bathymetric soundings. We used numerical model studies to integrate and compare the various derived information. We compare the basal melt/freeze rates derived from an ice/ocean model (ROMS) with that from mass balance of the glacier tongue. We use the ocean circulation in the Mertz region derived from a barotropic model (TUGO), together with continuous GPS measurements of the movement and flexure of the ice tongue, to assess the response of the glacier tongue to ocean forcing. They are found to be a main driver of the rifting and calving. We describe the sequence of events in the calving process. We evaluate the various forces acting on the ice tongue. We evaluate the dynamics changes with regard to climate variability as well as pre-/post-calving situations both toward the glacier and toward its glacial and oceanic environment.
Glacial change in the Koshi River, Himalaya, using RS during 1976–2009
Corresponding author: Donghui SHANGGUAN
Corresponding author e-mail: email@example.com
Retreat and thinning of Himalayan glaciers are reported against the background of global warming. Owing to the remote location and wide distribution of these glaciers, monitoring has been sparse in the Himalaya, especially with respect to direct monitoring of mass balance and ice thickness. Insufficient numbers of in situ measurements have led to recent controversy about future Himalayan glacier change in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report – differences in mass balance in the Himalaya derived from in situ observation and Gravity Recovery and Climate Experiment (GRACE) were inconsistent or even conflicting. In this work, we will use remote-sensing technology and GIS technology to monitoring glacier changes in the Koshi River, which is located in the central region of the Himalaya between 26°50′01″–29 °06′37&Prime N and 85°23′14&Prime–88°57′50&Prime E, with the average altitude above 4500 m and with a basin area of 61 000 km2. The Koshi River is an international river of China and Nepal. There are 2436 glaciers in the Koshi River, with a total area of 4041.74 km2: 1365 glaciers with a total area of 2412.17 km2 in China and 1071 glaciers with a total area of 1629.56 km2 in Nepal. By using remote-sensing images to monitor glacier change in the Koshi River, the results show that the glaciers have been retreating in the past 40 years. About 209 glaciers have disappeared, accounting for 8.6% with respect to all glaciers in the Koshi river. Furthermore, glacier area has decreased by about 866.76 km2, accounting for 21.4% of the total glacier area. The glacier shrinkage in Nepal (25.5%) is larger than that in China (18.7%). Based on records from the Dingri weather station, the temperature increase (precipitation stable) is the main reason for glacier retreat.
Past century trend of refractory black carbon preserved in ice-core archive from the Caucasus
Saehee LIM, Patrick GINOT, X. FAÏN, Vladimir MIKHALENKO, Stanislav KUTUZOV, Suzanne PREUNKERT, Michel LEGRAND, Paolo LAJ
Corresponding author: Saehee Lim
Corresponding author e-mail: firstname.lastname@example.org
Black carbon (BC), which enters the atmosphere exclusively as a primary emission originating mainly from incomplete combustion of biomass and fossil fuel, has received attention for its role as the second most important component of global warming after CO2. Documenting and understanding the variability of its atmospheric concentrations is therefore relevant both for climate and air quality studies. However, multi-year observations of ambient BC concentrations are scarce, in particular over Europe, which limit analysis of long-term BC trend in Europe. The atmospheric composition record derived from ice cores from European high altitudes and cold regions can therefore be extremely useful to assess past trends of atmospheric species and identify changes in emission sources over Europe. In this study, we present the preliminary results of refractory BC (rBC) measurements in a 182 m long core extracted from Mount Elbrus (43°20′53,9″ N, 42°25′36,0″ E, 5115 m a.s.l.) in September 2009. Firn and ice were melted on a heated melter head and continuously analyzed using a coupling of nebulizer (APEX-Q, EPOND, Switzerland) and single particle soot photometer (SP2, Droplet Measurement Technologies, USA). Only firn samples from the surface to a depth of 7.2 m were analyzed discretely with a resolution of ~10 cm. The Elbrus firn archive analyzed as discrete samples (surface to 7.2 m) showed elevated rBC concentrations during the summer season identified with chemistry data. During this period, rBC background (20th percentile) and mean levels were 4.5 μg L–1 and 13.8 ± 12.8 μg L–1, respectively. This mean level is three times higher than that observed in Alpine surface snow samples collected in the French Alps (Col du Dôme, Mont Blanc, 4250 m a.s.l.) summertime samples. rBC levels found in the firn at depths of 27–41 m melted continuously remained similar or slightly higher than in the surface firn, with background and mean levels of 4.4 μg L–1 and 14.6 ± 13.8 μg L–1, respectively. In contrast, the deeper ice (e.g. 83–97 m depth) revealed significantly reduced rBC, with background and mean level of 2.8 μg L–1 and 8.8 ± 8.1 μg L–1, respectively. Although further measurements are required to conclude, the elevated rBC concentrations in the more recent sections of the Elbrus core are probably related to increased emission from anthropogenic combustion sources in Russia, western and eastern Europe and in the Middle East.
Quantifying feedbacks between Greenland surface mass balance and ice dynamics under future climate warming
Johannes J. FÜRST, Heiko GOELZER, Philippe HUYBRECHTS, Xavier FETTWEIS
Corresponding author: Johannes J. Fürst
Corresponding author e-mail: email@example.com
Model projections of the contribution of the Greenland ice sheet to future sea-level rise have mostly focussed on changes of the surface mass balance (SMB). Separate model studies have dealt with ice discharge across calving fronts. Yet little attention so far has been paid to the feedbacks between the SMB and the ice-dynamic response in a unified framework for large-scale ice volume projections. Results from parameterized treatments indicate that the surface-elevation–SMB feedback may account for ~10% of the total mass loss on a centennial timescale. Such simple parameterizations, however, become increasingly inappropriate towards the end of the 21st century when intense margin thinning alters many aspects of the local SMB. To deal with this issue, we interactively couple the regional climate model MAR to the 3-D higher-order ice-flow model GISM. This allows us to take into account both the ice-dynamic response of marine-terminated outlet glaciers and the dynamic adjustment of the ice geometry to the SMB forcing. Moreover, this allows us to fully account for the feedbacks between ice surface elevation and SMB. Such an interactive model coupling is of crucial importance for reducing uncertainties in the future ice volume evolution. GISM is initialized to the currently observed ice geometry and includes parameterizations for basal lubrication and margin acceleration of outlet glaciers driven by ocean temperature. For these projections, the coupled model is driven with climatic forcing from the global model MIROC5 for a high impact scenario (RCP8.5). Within this experimental setup, feedbacks between the geometric adjustments, the ice-dynamic response and the SMB changes are quantified in terms of sea-level relevant volume changes and the importance of individual feedbacks is assessed.
Carbon dioxide flux in the ablation area of Koxkar Glacier, western Tien Shan, China
Jian WANG, Haidong HAN, Shiqiang ZHANG
Corresponding author: Jian Wang
Corresponding author e-mail: firstname.lastname@example.org
The drawdown of CO2 from the atmosphere during mineral weathering plays a major role in the global budget of this greenhouse gas. Glacial ice, one of the most important freshwater resources, covers 11% of global terrestrial area and its ablation variation could influence the CO2 cycle. Most research about calculations of atmospheric CO2 consumption is confined to the chemical ionic mass-balance method or the analog modeling method. In our study, gradient method was carried out on the surface of Koxkar Glacier, located in the western Tien Shan, in 2012. The amplitudes of dominant fluctuation in net glacier system CO2 exchange rate (NGE) were about –2.26 and –3.22 μg m–2 s–1 of bare ice and superglacial moraine observation points, respectively. This means that atmospheric CO2 might drawdown during ice melting due to consumption of H+ of the CO2 hydrolysis reaction in the course of dissolvable substance chemical reactions. The CO2 storage term (?) mean values of two monitoring points were +2.59 and –1.42 mg m–2 d–1 and were only about 1.36% and 0.51% of NGE, respectively. These show that CO2 storage (?) rates had little effect on NGE rates in glacierized areas. Affected by glacier surface temperature rapidly increasing in daylight, the value might appear positive, and this illustrated atmospheric CO2 below the CO2 infrared sensors could release. The CO2 release of bare observation points from the glacial ice was only about 1.16% of the NGE rate from 10 August to 24 September 2012. As a result, this could be ignored while net glacier-system CO2 exchange rate was analyzed in the glacial region. The dominant factors influencing the NGE rates might be soluble material source, rainfall or soluble ionic concentrations, etc. but ice melting because that there was not a noteworthy relationship between ice-melting intensity and the NGE rates, whether bare ice or superglacial moraine observation points.
Changes of snow/glacier cover in an arid mountain watershed using multisource remote-sensing data
Corresponding author: Xingong Li
Corresponding author e-mail: email@example.com
Snow and glaciers in the mountain watersheds of the Tarim River basin in western China provide the only water resources to cover the needs of downstream oases. Remote sensing provides a practical approach for monitoring changes in snow and glacier cover in those mountain watersheds. This study investigated the change of snow/glacier cover in one such mountain watershed using multisource remote-sensing data, including Moderate Resolution Imaging Spectroradiometer (MODIS), Landsat (MSS, TM and ETM+) and Corona imagery. Based on the analyses of 10 years of daily MODIS snow-cover data, Landsat images spanning more than 30 years and high-resolution images from Corona and Google Earth, our study found no evidence of significant changes in snow/glacier cover in the watershed, which is contrast to a wide glacier recession reported in the region.
Validation of surface energy-balance modeling in the central Alaska range on sub-daily timescales
Dominic WINSKI, Karl KREUTZ, Erich OSTERBERG, Seth CAMPBELL, Peter KOONS, Cameron WAKE
Corresponding author: Dominic Winski
Corresponding author e-mail: firstname.lastname@example.org
To test the performance of a surface energy-balance model for Kahiltna Glacier, we used meteorological data from an automatic weather station positioned at an elevation of 2200 m a.s.l. and representative of accumulation zones that experience summer melt in the central Alaska Range. During the period of study (26 May–11 June 2010), temperatures were typically above freezing and there were four snow events that deposited between 10 and 50 mm w.e. of snow per storm. We assessed the reliability of the energy-balance model to predict ablation on hourly timescales by comparing model output to a network of five ablation stakes spaced ~30 m from one another. Overall during the study period the ablation stakes recorded 289 mm of ablation compared with 265 mm as predicted by the energy-balance model. However, by comparing the energy-balance model results with ablation stake data on sub-daily timescales we found that the model’s ability to predict ablation, as measured by the stake network, varied substantially over time. To quantify this, we performed regression analyses between the degree of model overestimation and a suite and atmospheric and snowpack properties that were measured twice daily. Three sets of circumstances were identified in which model results failed to match measured ablation rates: (1) the model overestimates ablation under conditions of high sensible heat flux (r = 0.72); (2) the model overestimates ablation when surface grain size is large (r = 0.58); and (3) the model underestimates melt directly following snow events. These results emphasize the impact of sensible heat flux and snow condition assumptions on model-based ablation estimates in central Alaska and highlight the need for a better understanding of these processes for accurate mass-balance calculation.
Moraine size response to precipitation in the Little Ice Age and Last Glacial Maximum in Qilian Shan
Chaolu YI, Guocheng DONG, Yao JIN, Marc CAFFEE
Corresponding author: Chaolu Yi
Corresponding author e-mail: email@example.com
Reconstruction of precipitation in glacial stadials provides insight into Earth’s climatic system. Here we use moraine, which is widely present and contains precipitation information. Using differential GPS, we measured seven terminal moraines produced in the Little Ice Age (LIA) along the Qilian Shan, northwestern Tibet, simulated their surface in ArcGIS and obtained their volume. In contrast to the expectation that large glaciers produce large moraines, we find that moraine size moraine production rate (MPR), with the unit of m2 m–3, is closely correlated with precipitation rather than glacier area, rock type and valley slope. We ascribe this close relationship to precipitation-induced glacial erosion. The spatial change of the MPR suggests that the Asian monsoon still influenced the eastern part of the Qilian Shan in the LIA. We also find that the MPR of the Last Glacial Maximum (LGM) was uniform and did not display spatial change through the Qilian Shan. We suggest that the westerlier controlled the Qilian Shan and it was dry throughout the Qilian Shan in the LGM.
Spatial and temporal variability of surface mass balance (1999–2011) from Zhongshan station to Dome A, East Antarctica
Minghu DING, Cunde XIAO, Jiawen REN
Corresponding author: Minghu Ding
Corresponding author e-mail: firstname.lastname@example.org
Stake measurements have been carried out along a 1248 km traverse from Zhongshan station to Dome A, East Antarctica. Spatial analysis suggests that the post-depositional process might be the most important factor influencing surface micro-morphology, and precipitation is another. Thus the representiveness of firn/ice core in different areas differs largely with each other and it should be discussed with local climate features. An overall estimation showed that the Lambert Glacier basin might be experiencing a slight loss trend, with a –0.5% annual average accumulation rate from 1999. This loss mainly happens in the coastal and Dome areas, yet the surface mass balance of the middle part from 202 to 800 km is still increasing.
Mass changes on Guliya Ice Cap in the western Kunlun Mountains during 2001–2011 derived from multi-source remote-sensing data
Weijia BAO, Shiyin LIU
Corresponding author: Shiyin Liu
Corresponding author e-mail: email@example.com
Recent studies show that glaciers in the western Kunlun Mountains to the northwest of the Tibetan Plateau may be in a stable or slightly retreating state based on length changes of some glaciers in the region. In this study, we aim to derive mass changes on Guliya Ice Cap to understand the processes controlling the response of glaciers in the region. In our study, daily daytime MODIS land-surface temperature (LST) product onboard the Terra spacecraft (MOD11A1) was applied to monitor melting events on the glacier surface of Guliya Ice Cap from 2000 to 2012. We introduce a novel algorithm that can reconstruct incomplete LST image owing to clouds and other atmospheric disturbances based on regression analysis of LST with elevation in each sliding window of the original image. The reconstructed daily MODIS LST was verified with the LST retrieved from the TIR band of Landsat TM/ETM+ images (one TM scene and ten ETM+ scenes in the whole of 2011). The melt duration and mean ablation area were extracted using this reconstructed MODIS LST dataset. A series of ENVISAT ASAR winter images were used to monitor the temporal and spatial development of the firn line (FL) position from 2004 to 2012. Interannual mass-balance fluctuations were observed by comparing the altitude of the firn lines in winter for each year. Finally, we used 15 GLAS/ICESat L1B Global Elevation Data profiles (2003–08) to calculate annual mass balance for 2004–08 using an elevation band method based on the SRTM V4 digital elevation model. The correlation between all the parameters (melt duration, mean ablation area and the altitude of the firn line) and the annual mass balance derived from GLAS data was calculated. Results show a statistically significant trend at the 95% confidence level. The annual mean ablation area is strongly correlated with annual mass balance (2004–08), allowing reconstruction of annual mass balance for the period 2001–11.
Reconstruction of Qugaqie Palaeoglacier in the Nyainqêntanglha range in the Last Glacial Maximum
Yao JIN, Chaolu YI, Baojin QIAO, Xiangke XU, Jinhua LIU
Corresponding author: Chaolu Yi
Corresponding author e-mail: firstname.lastname@example.org
During the Quaternary, there are a lot of glaciers in the Tibetan Plateau, leaving behind a wealth of Quaternary glacial relics. Quaternary glacial landforms, which are products of palaeoglacial activities, are the basic materials for study both in palaeoglaciation and palaeo-environmental reconstruction, and have very important climatic significance. Combining glacier flow equations and palaeo-landform information, researchers can reconstruct the surface of a palaeoglacier, accurately calculate the ancient palaeo-volume and palaeo-equilibrium-line altitude (ELA), then extrapolate the palaeo-climate and palaeo-environment. During the Quaternary, there have been massive palaeoglacial activities in the Nyainqêntanglha range and much palaeoglacial geomorphology has been preserved. In this paper, firstly, we produced a palaeoglacier geomorphologic map by investigating in the field and extracting palaeogeomorphology information with 3S (GIS, RS and GPS) technology. Secondly, based on the palaeoglacier geomorphologic map and the longitude section palaeoglacier model, we reconstructed the surface of a palaeoglacier in the Last Glacial Maximum (LGM). Thirdly, we calculated the ice volume and ELA in the LGM based on the surface of the palaeoglacier and palaeogeomorphology information. Finally, we discussed the palaeo-climate and palaeo-environment in the LGM. Primary results and conclusions are as follows. In the Tibetan Plateau, traditional fieldwork investigation, 3S technology to identify geomorphologic information and the longitude section palaeoglacier model are able to reconstruct palaeoglaciers. Especially in areas with well preserved palaeoglacial geomorphology, this approach is easy to operate and is able to accurately recover the palaeoglacial surface morphology. In the LGM, the scale parameters of the palaeoglacier in Qugaqie are as follows: the length of glacier is 18.5 km, the average thickness is 102.1 m, the area is 59.1 km2 and the volume is 6.0 km3, which is 8.34 times the glacier area and 18.33 times the ice volume than that of the recent glacier. 75.3% of Qugaqie valley is covered by glaciers. In the LGM, the ELA of Qugaqie had a minimum of 5405 m, a maximum of 5496 m and an average of about 5446 m, which are 300–400 m lower than modern values. This confirms the point of Shi Yafeng that an even global ELA lowering value of about 1000 m did not virtually exist.
Mapping blue-ice areas in Antarctica using ETM+ and MODIS data
Fengming HUI, Tianyu CI, Xiao CHENG, Yanmei ZHANG, Yan LIU
Corresponding author: Xiao Cheng
Corresponding author e-mail: email@example.com
We have mapped Antarctic blue-ice areas using the Landsat-7 and MODIS Antarctica cloud-free image mosaic established by Beijing Normal University. The mosaic consists of 1073 scenes of ETM+ images acquired from 1999 to 2003 and MODIS data acquired from 2003 to 2004. The blue-ice feature is classified using threshold algorithm from band ratio. The underlying principle is that blue ice can be separated from snow/firn or rock according to spectral discrepancies caused by different grain sizes. The algorithm is proved to be effective and accuarate. The total area of blue ice in Antarctica during 1993–2004 is estimated to be 225 207 km2, accounting for 1.65% of the whole area of Antarctica. The majority of the blue-ice areas are located in coastal or mountain regions. Comparing our results with previously published results, the differences in terms of acquisition dates of satellite images, spatial resolution, algorithm and land cover change in Antarctica were revealed. This high-resolution blue-ice area map would benefit multi-disciplinary research or multi-purpose applications, for example glaciology, meteorology, climatology, paleoclimatology, meteorite collection and airport site selection.
Integrated measurements of snow depth and air temperature variability from ground GPS receivers in northern Canada
Nasser NAJIBI, Shuanggen JIN
Corresponding author: Nasser Najibi
Corresponding author e-mail: firstname.lastname@example.org
Air temperature is well known as a primal factor affecting the permafrost, especially the snow-covered surface in middle high latitude regions such as northern Canada where vast snowy lands, icy lakes and frozen flora exist perpetually. The variations in the surface air temperature basically lead to the fluctuations in the Earth’s surface with the fresh glaciers and/or newly accumulated snow, which will influence GPS reflected signals. In this study, we investigate the integrated functions of snow depth and air temperature variability from ground GPS reflected signals in northern Canada during winter and spring seasons. The methodology is based on the non-parametric analysis of those independent components that can affect, or be affected by, each other in the direct and inverse solutions of non-parametric modeling. The results demonstrate correlations in the thermal regime, snow depth fluctuations and GPS reflected signals from the geometric free linear combination (L4) of the dual frequency GPS receiver’s carrier phases. Moreover, variability of snow depth and air temperature is presented from the integrated methods with ground GPS reflected signals.
Numerical simulation of Urumch Glacier No. 1 in the eastern Tien Shan, central Asia, from 2005 to 2050
Corresponding author: Keqin Duan
Corresponding author e-mail: email@example.com
Owing to climatic change, most of the alpine glaciers have retreated dramatically during the past decades. Thus it is significent to evaluate alpine glacier variability in the future for a better understanding of the impact of climate change on water resources. In this paper, we perform a numerical simulation on Urumch Glacier No. 1 in the eastern Tien Shan, central Asia (hereafter referred to as Glacier No. 1), by considering both the mass balance and ice flow. Given the shape of Glacier No. 1, the velocity of the glacier obtained by solving a two-dimensional nonlinear Stokes equation is agreement with the observation. In order to predict the variability of Glacier No. 1 until 2070, a climatic scenario is constructed with a temperature rise rate of 0.17°C (10 a)–1 and precipitation remaining constant during the period 2005–2050. The simulation result shows the glacier terminus will retreat slowly while the glacier thickness in the ablation area will decrease dramatically before 2040. Subsequently the glacier terminus will accelerate to retreat. This numerical simulation proves that the retreat rate of alpine glaciers will increase under the condition of global warming.
Glacier area change in the Xiying River basin, eastern Qilian Mountains, China
Yushuo LIU, Xiang QIN, Wentao DU, Weijun SUN, Xueyan ZHANG, Mingjie ZHANG, Jizu CHEN, Xiaolong XIE
Corresponding author: Xiang Qin
Corresponding author e-mail: firstname.lastname@example.org
The Xiying River is one of the Shiyang River’s tributaries, is located at Lenglongling, east of the Qilian Mountains, and is formed by the confluence of Luotuo River, Qingyang River, Ningchan River and Shuiguan River. There are 42 glaciers in the Xiying basin, the majority of which are towards NE. In this study three Landsat images (acquired in 1987, 1995 and 2008) and two topographic maps have been used; every image and map is registered into UTM. Glacier area information has been obtained by vector quantization artificial. Changes in glaciers in the Xiying basin have been analyzed and the results show that glacier area increased slightly in 1987 and since then glacier shrinkage has increased; in the past 50 years, nine glaciers have disappeared. The rate of glacier retreat in the Luotuo River was the fastest. We split the study area into 100 m intervals and in each elevation zone glacier retreat showed a different rate: at 4000–4100 m, already there is no ice; at 4100–4200 m, glacier area has retreated by about 62%. With an increase in altitude, the rate of glacier retreat was a weakening trend and at the top of the glacier there was a certain amount of shrinkage. The retreat rate of glaciers towards NE was the fastest, the glaciers toward SW showed a retreat rate faster than the others. Compared with other research on glacier change in the Qilian Mountains, this shows that in the Xiying River basin the rate of glacier change is greater and the response is more sensitive to climate change.
Modelling Haizishan Ice Cap on the southeastern Tibetan Plateau
Ping FU, Julien SEGUINOT, Arjen P. STROEVEN
Corresponding author: Ping Fu
Corresponding author e-mail: email@example.com
The Haizishan Plateau, a low-relief plateau at 4000–5000 m a.s.l. on the southeastern Tibetan Plateau, is surrounded by deeply cut glacial and fluvial valleys and flanked by high mountain peaks. Previous studies using geomorphological mapping and cosmogenic nuclide exposure dating have provided a detailed reconstruction of the Haizishan Plateau glacial history. An ice cap measuring almost 4000 km2 formed at or before marine isotope stage 6 (with minimum ages at 102.3 ± 10.0–183.6 ± 17.0 ka) and during the Last Glacial Maximum (21.6 ± 2.0 ka). At its largest extent, the ice cap covered the entire plateau and formed outlet glaciers in valleys emanating from its flanks. Here we use the Parallel Ice Sheet Model (PISM) to simulate the growth and decay of Haizishan Ice Cap and contrast its modelled history to the mapped distribution of landforms. Mountain-centred ice centres first initiate on the highest peaks on the plateau and then expand and merge to form an ice cap which ultimately covers the entire plateau. Fast-flowing outlet glaciers develop in the deep valleys emanating from the plateau, causing occasional migrations of the ice-cap divide. Modelled flow directions differ significantly during the inception phase and the retreat phase and explain some of the variability observed in the mapped record.
An analysis of the glacial geomorphological characteristics of the Tianger Peak area, Xinjiang, in the Last Glacial Period and their paleo-environmental implications
Zhenyu NIE, Renyi PAN, Chuanchuan LI, Mei ZHANG, Gengnian LIU
Corresponding author: Gengnian Liu
Corresponding author e-mail: firstname.lastname@example.org
The application of digital elevation model (DEM) and GIS techniques has been an important trend in glacial geomorphological and Quaternary environmental studies. Combining a paleoglacier distribution map with DEM data, this study analyzes the glacial geomorphological characteristics of the Tianger Peak area, Xinjiang, in the Last Glacial Period. The correlation between slope, aspect, drainage area and the characteristics of ELAs (including accumulation–area ratio (AAR), toe–headwall altitude ratio (THAR), toe–summit altitude method (TSAM) and Höfer) are discussed. Glaciers with a smaller slope and larger area have relatively lower AARs, and the AARs of these glaciers are relatively better correlated with their THARs, TSAMs and Höfers. The AARs of glaciers reflect the climate and environment, i.e. glaciers with higher AARs are more continental in the climatic glacial gradient of alpine glaciers. The comparison between glaciers of the Urumqi River source area in the early to middle stage of the Last Glacial and LGM shows that glaciers in the earlier period have higher AARs and larger accumulation areas and so are more continental. Another comparison between glaciers of the Tianger Peak area in the early to middle stage of the Last Glacial and those of the Tibetan Plateau and the Himalaya in the LGM shows that glaciers of the former area are more continental.
A new calving law based on continuous damage and fracture mechanics
J. KRUG, J. WEISS, G. DURAND, O. GAGLIARDINI
Corresponding author: J. Krug
Corresponding author e-mail: email@example.com
A number of studies have shown that mechanical ice loss through calving is responsible for most of the ice discharge from glaciers and ice sheets. However calving processes are complex and still poorly understood. Representation of calving in ice-sheet models is still limited and the estimation of future ice loss from the Greenland and Antarctic ice sheets is therefore inaccurate. This is the reason why the last IPPC report asked for a better understanding and representation of calving processes. Several approaches are necessary to represent at the same time the slow deformation of the ice, the initiation of crevasses and their rapid propagation preceding the calving event. First, the effect of damage and small-scale fracturing on this slow viscous deformation can be represented by continuous damage mechanics (CDM). CDM describes the evolution of damage in the ice from a state in which the ice has no defect to the appearance of a macro-crack. This evolution depends on the stress field and is advected with the flow of ice. Second, the fast propagation of pre-existing crevasses into the media can be satisfyingly described using linear elastic fracture mechanics (LEFM) for which ice is considered as an elastic medium. This approach allows us to deal with the stress concentration at the tip of the crack and so differs from the traditionally used Nye’s criterion. Together, they may propose a complete and versatile calving law that covers first-order processes (related to longitudinal stretching and surface velocity gradients) as well as second-order processes occurring at the glacier front (subaqueous melting, force imbalance, etc.). These two approaches are combined and implemented into the Elmer/Ice full-Stokes ice-flow model. An initial grounded terminated glacier is perturbed by an increase in frontal subaqueous melting. This process, called undercutting, results in a block of ice overhanging the sea, followed by the calving of the aerial part. Strength of the model to various physical parameters is tested, such as the ratio between water depth and ice thickness, the inlet velocity and the temperature of the ice. The shape of the bedrock is also investigated.
A full-Stokes anisotropic ice-flow model for Dome A, Antarctica
Thomas ZWINGER, Liyun ZHAO, John MOORE, Dong ZHANG, Xueyuan TANG, Carlos MARTIN, Bo SUN
Corresponding author: Liyun Zhao
Corresponding author e-mail: firstname.lastname@example.org
Chinese scientists will start to drill a deep ice core at Kunlun station near Dome A in the near future. It is important to know the basal temperature of ice and estimate the age of the ice core. We apply a three-dimensional thermomechanically coupled full-Stokes model to a 70 km2 × 70 km2 domain around Kunlun station, using the package Elmer/Ice. We make simulations using isotropic and different prescribed anisotropic fabrics which strongly affect the vertical advection which as a consequence controls both the basal temperature and age profile. Parts of the bed in the domain reach pressure-melting point, which seems to be consistent with radar observations in the Gamburtsev Mountains. We determine melt rates in those areas and also assess basal age by using steady-state velocity results.
Dynamics of meltwater plumes under ice shelves: frictional geostrophy and melt-channelling instability
Felix NG, Adrian JENKINS
Corresponding author: Felix Ng
Corresponding author e-mail: email@example.com
The flow of buoyant meltwater plumes under several ice shelves has been reproduced in numerical simulations that represent such plumes as a well-mixed layer, and researchers have begun using these simulations to explore how ocean warming could cause irreversible melting and retreat of ice shelves. Here we present a new mathematical theory for the coupled ice-shelf–meltwater-plume system to illuminate two aspects of this problem. The first aspect concerns the two-dimensional flow field of the plume and how it determines the spatial distribution of the rate of sub-ice-shelf basal melt. By starting with the equations used in the simulations, we derive a simplified model of plume physics that explains how sub-shelf friction and Coriolis force conspire to govern the plume water flux and deflection angle. This leads us to explain why the plumes always transition from friction-dominated flow near the grounding line towards geostrophic flow farther out under the shelf. This theory identifies plume buoyancy, the Coriolis parameter and shelf-base slope as key factors of the transition and elucidates how they impact the sub-shelf melt rate. The second aspect of the problem concerns the origin of basal melt channels that have been observed under many ice shelves, including the floating tongue of Petermann Glacier in Greenland and the ice shelf fed by Pine Island Glacier in Antarctica. By conducting a linear stability analysis of our model, we find that with typical parameters the coupled shelf–plume system is unstable to perturbations so that incipient channels with spacing of the order of kilometres form across the ice-shelf base. This analysis establishes how model parameters control the incipient-channel spacing and orientation and pinpoints the mechanisms behind the instability. These results inform future studies that seek to understand how fully developed basal channels affect how an ice shelf evolves.
Long-term seasonal mass balance on four Alpine French glaciers: what does this dataset tell us new about climate sensitivity?
Delphine SIX, Christian VINCENT
Corresponding author: Delphine Six
Corresponding author e-mail: firstname.lastname@example.org
Annual glacier mass balances are highly sensitive to climate change. Some long-term series of annual mass balance are now available around the world to determine the climatic evolution in remote places located at high altitude. Nevertheless, inferring the long-term climatic signal from annual mass-balance series is not easy as accumulation and ablation are related to different processes at the surface of the glacier (solid precipitation, energy exchanges). In the French Alps, 18 years of summer and winter mass-balance observations are now available on four glaciers. This dataset covers a large range of altitude, various aspects and slopes. From this dataset, the relationships between climatic parameters and surface mass balance have been thoroughly studied. First, the sensitivity of winter mass balance to valley precipitation was analysed and the gradient with altitude was assessed. Secondly, we investigated the summer ablation series to determine the sensitivity of ablation to summer temperature. It allows us to determine the evolution of the ablation season duration and the evolution of the sensitivity of ablation to temperature during the summer. This analysis was possible thanks to numerous ablation measurements performed four to five times during each summer, allowing for sensitivity tests to be carried out when the surface is covered by snow or in ice. In a restricted part of our dataset, energy fluxes were calculated using data from meteorological stations located in the vicinity of the glaciers. It allowed us to detail the observed sensitivity. Finally, the sensitivity of equilibrium-line altitude to temperature has been assessed. The results reveal that this sensitivity is much lower than those generally used in the literature.
Adaptation to dramatic temperature changes and versatile utilization of carbon substrates: two survival strategies documented by culturable bacteria from a Mount Everest ice core
Yongqin LIU, Tandong YAO, Baiqing XU, Liang SHEN
Corresponding author: Yongqin Liu
Corresponding author e-mail: email@example.com
Meltwater from a complete section of a 22 m long ice core drilled in East Rongbuk Glacier, Mount Everest, was incubated using two methods: spreading ice meltwater directly onto the surface of agar-solidified media and preliminary incubation of ice meltwater in liquid media at 4°C prior to plating on agar media. The latter approach enabled us to obtain a greater number of colonies than did the former method. Concentrations of culturable bacteria varied at different depths with various trends in the two methods of incubation. They correlated significantly with the concentration of NO3– and Ca2+ in directly spreading and spreading after enrichment plates, respectively. Thus, liquid medium incubation was of huge benefit to the recovery of soil-associated bacteria. High NO3– concentration indicates good nutrient conditions where microorganisms were of relatively better metabolic state and able to be recovered directly. Strains recovered from the two kinds of incubation were diverse and affiliated to four groups: Firmicutes, Actinobacteria, Alpha-Proteobacteria and Gamma-Proteobacteria, with Firmicutes being the most abundant elements. Bacillus cereus and Micrococcus sp. were dominant in the direct spreading method, but Bacillus cereus and Bacillus pumilus were dominant in spreading after enrichment. Most isolates could grow at a wide temperature range and were capable of carbon utilization. Accordingly, both adaptation to a wide temperature range and versatile utilization of carbon substrate were likely the survival strategy for bacteria in a high-altitude ice core.
Numerical simulation on the outburst flood due to overtopping of the moraine-dammed Lake Zhangzangbo
Xiujuan ZHANG, Shiyin LIU
Corresponding author: Xiujuan Zhang
Corresponding author e-mail: firstname.lastname@example.org
The failure of moraine-dammed lakes by overtopping is commonly found in high mountain glacierized regions, which can form floods with abnormal peak discharge. The hazard caused by such a glacial lake outburst flood (GLOF) depends on the physical characteristic of the dam, the volume of lake water, its breaching discharge and settings down the valley. The mitigation of GLOF hazards has become a focal point, but requires understanding of the breaching processes of the dam. This paper analyzes the catastrophic outburst flood in July 1981 of Lake Zhangzangbo, a moraine-dammed lake at the head of a tributary of Poiqu River in the central-western Himalaya. The flood and then mudflow damaged the Friendship Bridge along the China–Nepal Highway and Sun Kosi Hydroelectric Station. In the study, BASEMENT, a dam breach model, is applied to reconstruct the breaching process and the flood wave propagation of the outburst flood. Our results indicate that the failure of the moraine dam was probably caused by overtopping due to an ice avalanche event, resulting in increased lateral and vertical erosion to the dam and the final dam failure. The length and area changed, respectively, from 1.7 to 1.1 km and 0.643 to 0.265 km2 during the outburst event. The outburst released a volume of water of ~19 × 107 m3 with addition of debris of ~4 × 107 m3 during its flow down to the valley. At the breach, the peak discharge and average longitudinal slope are ~16 000 m3 s–1 and 0.25, respectively. At the Friendship Bridge, the peak discharge and average longitudinal slope are ~6500 m3 s–1 and 0.12. Because of the narrow river channel, the mudflow was blocked resulting in a high water level of 20 m, scour erosion, landslide and finally damage to the bridge and all villages nearby. At Bharabise, the peak discharge and average longitudinal slope are ~2300 m3 s–1 and 0.008. At Sun Kosi Hydroelectric Station, the peak discharge and average longitudinal slope are ~2000 m3 s–1 and 0.006. Owing to a large number of mudflow deposits, the riverbed near the station rose significantly. The dynamic dam breaching model provides a valuable attempt to simulate the complex dam break process and flood propagation and the basis for hazard mitigation in the future.
Characteristics and source of aerosols at Shiyi Glacier, Qilian Mountains, China
Xiaoyu ZHANG, Zhongqin LI, Feiteng WANG, Shengjie WANG
Corresponding author: Xiaoyu Zhang
Corresponding author e-mail: email@example.com
Aerosol samples were collected at Shiyi Glacier, Qilian Mountains, from 24 July to 19 August 2012 and analyzed for eight water-soluble ionic species (Na+, NH4+, K+, Mg2+, Ca2+, Cl–, NO3– and SO42–) by ion chromatography. The three most abundant ions were NH4+, SO42– and NO3–, with average concentrations of 70.8, 54.77 and 23.8 neq m–3, respectively, accounting for 36.9%, 28.6% and 12.4% of the total water-soluble ions analyzed. Size, morphology and elemental compositions of more than 20 000 particles were determined by scanning electron microscopy equipped with an energy dispersive spectrometer (SEM-EDX). Based on the morphology and elemental compositions, particles were classed into five groups: Si-rich particles, Ca-rich particles, Fe-rich particles, K-rich particles and P-rich particles. The particles primarily ranged from 0.57 to 142.7 μm with average diameter of 0.78 μm. Particles <2.5 μm (PM2.5) accounted for about 93.44% of the total number of particles. The relationships between aerosol optical depth (AOD) and dusty weather were analyzed based on the AOD from MODIS data. Results indicated that the atmospheric AOD has close correlation with the dusty weather of 5 and 14 August. Backward air mass trajectory analysis also suggests that the arid and semi-arid regions of central Asia are the primary source of particles to Shiyi Glacier.
Spatial–temporal characteristics of lake area variations in the Hoh Xil region during 1970–2011
Xiaojun YAO, Shiyin LIU, Meiping SUN, Long LI
Corresponding author: Shiyin Liu
Corresponding author e-mail: firstname.lastname@example.org
As one of the concentrated areas of lakes on the Tibetan Plateau, the Hoh Xil region has numerous lakes which have an extremely important role in the fragile plateau ecology and environment. Based on topographic maps from the 1970s and Landsat TM/ETM+ images from the 1990s and 2000–2011, the areas of 83 lakes of >10 km2 were obtained by the digitization method and artificial visual interpretation technology, and the causes of lake variations were also analyzed. Some conclusions can be drawn as follows. (1) From the 1970s to 2011, the lakes in the Hoh Xil region first shrank and then expanded. In particular, the area of lakes generally decreased during the 1970s to the 1990s. Then the lakes started expanding during the 1990s to 2000 so their areas were slightly more than those in the 1970s. Lake areas increased dramatically after 2000. (2) During 2000–2011, lakes with areas of different scales in the Hoh Xil region as a whole showed a trend of expansion. However, the characteristics of some regional differences were also discovered. Most of the lakes that were expanding were distributed widely in the northern, middle and western areas of the Hoh Xil region. Some lakes merged together or happened to water overflowing due to their rapid expansion. There were only small numbers of lakes showing a trend of decreasing area or strongly fluctuating area. These were scattered in the central and southern parts of the study area and their variations were related to the supply conditions or hydraulic connection with downstream lakes or rivers. (3) The increase in precipitation was the dominant factor resulting in the expansion of lakes in the Hoh Xil region. The secondary cause was the increase of meltwater from glaciers and frozen soil due to climate warming.
Modelling the grain-size profile in polar ice cores: the origin of steady-state grain sizes
Felix NG, T.H. JACKA
Corresponding author: Felix Ng
Corresponding author e-mail: email@example.com
In several deep ice cores, the depth profiles of mean crystal size D (linear dimension) show a region of steady D at intermediate depth, below the region of normal grain growth near the surface and above the onset of rapid grain growth caused by migration recrystallization. The steady-state grain sizes have been interpreted to result from a balance between the rates of normal grain growth and polygonization. Separately, laboratory experiments that deform polycrystalline ice in uniaxial compression to the tertiary creep stage show that D reaches steady-state values that vary with the applied stress in a power law. Here we suggest a universal explanation of both observations, by presenting a mathematical model that describes how grain size evolves as normal grain growth and polygonization compete dynamically, modulated by geometrical change of the grains as they deform. The model relates the polygonization rate to the bulk strain rate through the dislocation density in the grains, and uses differential equations to track multiple directional properties of the mean grain (width, height, horizontal area) rather than a single grain-size variable. At equilibrium, the model reproduces the steady-state grain sizes observed in the ice cores and laboratory experiments, including the stress dependence of D found in the latter. When applied to six ice-core sites in Antarctica and Greenland (Byrd, Siple Dome, DSS on Law Dome, GRIP, NGRIP, GISP2), the model also successfully simulates their grain-size profiles down to the depth where migration recrystallization begins. Two other findings are that geometric flattening can strongly influence how grain size evolves in the vertical compression regimes of ice divides and in the experiments, and that the steady grain size behaves more like a palaeo strain-rate meter than piezometer or wattmeter. Our continuum descriptions of the grain evolution processes complement microscopic study of these processes and may aid studies trying to integrate texture evolution into models of ice rheology.
The glacial area changes since the Last Glacial Maximum in Basum Lake catchment, southeastern Tibet
Jinhua LIU, Gang HU, Chaolu YI
Corresponding author: Chaolu Yi
Corresponding author e-mail: firstname.lastname@example.org
Study of Quaternary glaciations in monsoon-influenced southeastern Tibet helps us understand palaeoclimatic change in the Third Pole. Extensive glaciations left behind abundant glacial relics. We identified glacial moraines and other glacial relics in the Basum Lake catchment in the eastern Nyainqentanglha Mountains based on field investigation and with the help of remote sensing, GPS survey and GIS mapping, and have reconstructed the glacial areas and the equilibrium-line altitudes (ELA) in the Little Ice Age (LIA) and the Last Glacial Maximum (LGM). The total glacial area of Basum Lake catchment was about 1–103 km2 in the LGM, seven times the modern glacier area. Glaciers occupied the main valley and northern and eastern branches of the river in the LGM, while it was very limited in the upper reach of the Zara River. We interpret it to the lower altitude of the western mountain in the LGM. The ELAs were higher and glacial area was smaller in the Zara valley, the western branch of the Basum River valley than the other branches in the LGM. The ELAs rose nearly 900 m in the Zara valley, while 600–800 m in the other branches since the LGM. We ascribe it to the rise in global temperature after the LGM.
Microbial diversity and potential methanogenic activity in Antarctic subglacial sediment
Wenkai YAN, Yu ZHANG, Xiang XIAO, Bo SUN, Yinke DOU, Hongmei MA
Corresponding author: Hongmei Ma
Corresponding author e-mail: email@example.com
The subglacial ecosystem has been recognized as an environment with considerable methanogenic activity and therefore has a significant impact on the global methane budget and is sensitive to climate change (Tung, Bramall and others, 2005). Although the presence and diversity of methanogens have been reported in a few subglacial environments (Stibal, Wadham and others, 2012), the in situ microbial activity is as yet insufficiently envisaged. Moreover, the responses of the main microbial players to changes in geochemical environments, e.g. as glaciers recede or advance, have not been well studied due to technical difficulties in sampling and cultivation. In this study, we attempted to answer the above questions by applying an integrated approach, including molecular analysis and in vitro simulation, to sediment samples from Antarctic glaciers. 16S rRNA-based diversity analysis revealed that Euryarchaeota is the only phylum detected while most of the Archaea found are of the Methanomicrobia class. Furthermore, a phylogenetic tree based on the functional gene (mcrA gene, the terminal enzyme complex in the methane generation pathway, which is a specific marker for methanogen) was constructed. Results showed that the methanogens from Antarctic subglacial environments are more similar to methanogens reported in freshwater sediment than to those from polar environments. These results provide us with evidence on the potential substrate utilization of subglacial methanogens. With this in mind, we can further incubate the sediment samples in the simulated conditions to estimate the in situ and potential microbial activities. Therefore, we will obtain a better understanding of the effect of glacier recession on the subgalcial ecosystem. This study will also help us to explore the evolutional process and cold-adaptation mechanisms of methanogenic microorganisms.
Mass changes of the Greenland ice sheet influenced by the Arctic Oscillation based on satellite gravity measurements
Chuangdong ZHU, Yang LU, Hongling SHI, Zizhan ZHANG, Zongliang DU, Yi TU, Chunchun GAO
Corresponding author: Chuangdong ZHU
Corresponding author e-mail: firstname.lastname@example.org
With the change of global climate, the Greenland ice sheet (GrIS) is also undergoing rapid changes. In this paper, updated Gravity Recovery and Climate Experiment (GRACE) RL05 data are used to estimate the mass changes and investigate signals of anomalous winter precipitation caused by the Arctic Oscillation (AO) in the GrIS during the period January 2004 to April 2012. For the GrIS, the mass loss rate is –255 ± 16 km3 a–1 and significantly accelerating at –15.2 ± 1.1 km3 a–2, which indicates accelerated mass loss in the GrIS. GRACE measurements reveal significant mass losses in the southeastern, western and northern GrIS, and these mass loss rates are accelerating. The mass loss rates in the eastern GrIS have slowed down since 2004. Signals of anomalous winter precipitation inferred from GRACE also show highly positive and negative correlations with the Arctic Oscillation indices (AOI) in northern and southern (boundary ~75° N) parts of the GrIS, respectively, which indicate that the AO has a remarkable influence on winter precipitation in the GrIS.
Description of the flow form of snow avalanches by a sliding-block model
Wei ZHANG, Yuanqing HE
Corresponding author: Wei Zhang
Corresponding author e-mail: email@example.com
A reasonable description of the flow form and traveling distance of snow avalanches is important to the assessment and development of mitigating measures for the hazard and risk of snow avalanches. Based on the present understanding of the forming mechanism and a thorough analysis of the dynamic mechanism of snow avalanches, a sliding-block model is developed for predicting the flow form and traveling distance of snow avalanches, adopting the limit equilibrium analysis approach. In this model, snow deformation is considered in the calculation of snow movements, the critical state is considered as the initial stress state, and the inter-slice forces are obtained considering the equivalence of deformation energy. Therefore, the whole travel process of the snow mass from the onset of a snow avalanche to final stable form can be simulated by applying this model. To show the applicability of the model, a snow avalanche reported was modeled using the model. The calculated results are comparable with the reported results and it is concluded from the calculation that the fundamental causes of the snow avalanche are the decline of the resultant friction force during sliding and a notable fall of the gravity centre of the back part of the snow mass.
Lake changes and their climate indicative significance of the three holy lakes from 1990 to 2012
Long LI, Jing LI, Xiaojun YAO, Jing LUO, Yongsheng HUANG, Yaya FENG
Corresponding author: Long LI
Corresponding author e-mail: firstname.lastname@example.org
Against a background of global warming, significant changes have taken place in the lakes of the Qinghai–Tibetan Plateau. Namtso,Yamzho-yumco and Mapam-yamco are the three holy lakes of Tibet. Based on topographic maps from the 1970s, Landsat TM/ETM+ images from the 1990s and satellite altimeter data and meteorological station observation data for 1998–2012, RS and GIS technology was used to obtain the area, water level and water storage of the three holy lakes and subsequently a comparative analysis was made of the status and causes of such changes. The conclusions are as follows: (1) From 1970 to 2012, the three holy lakes in Tibet have shown obvious changes and these changes differ from each other. Namco showed a trend of rapid expansion – its lake area increased from 1943.35 km2 to 2025.05 km2 with a rate of 1.9 km2 a–1 and water storage increased 11.371 km3 during the period 1976–2009; Yamzho-yumco shrank rapidly – its area decreased from 643.25 km2 to 557.42 km2 with a rate of 2.0 km2 a–1 and water storage decreased 0.871 km3 during the period 2005–2008; Mapam-yamco has shown a slight reducing trend but the overall change is small – its area decreased from 417.00 km2 to 412.56 km2 with a rate of 0.1 km2 a–1 and water storage decreased 0.044 km3 during the period 2003–2009. (2) Namco’s rapid expansion occured mainly during the period 1970–2007; its area increase slowed down after 2008. The area of Yamzho-yumco decreased dramatically between 1970 and 1990. The lake appeared to show slow expansion from 1990 to 2004 and a smooth reduction during 2004–2012. The area of Mapam-yamco decreased between 1970 and 1999. After 2000 its area has increased, but the area is still smaller compared with that in the 1970s. (3) The changes in the three holy lakes are closely related to the glacier meltwater, precipitation and evaporation of the valley, but these factors are different in impact. The increase of glacial meltwater, the increase of river basin precipitation caused by the rise in temperature and the reducion of lake evaporation are the reasons for Namco’s expansion and its increase of water storage. The decrease of valley glacier area, rainfall and the increase of evaporation account for the reduction of Yamzho-yumco. In addition, the pumped storage hydropower station also contributes to the decrease of Yamzho-yumco. River basin precipitation reduction is the major cause of Mapam-yamco’s atrophy and the other reason is the increasing evaporation caused by the higher temperature.
Estimation of the impact of debris cover on the future behaviour of East Rongbuk Glacier, Qomolangma
Tong ZHANG, Cunde XIAO
Corresponding author: Tong Zhang
Corresponding author e-mail: email@example.com
We run prognostic experiments of East Rongbuk Glacier (ERG) into the future (2010–2100) under three different climate scenarios (RCP2.6, RCP4.5 and RCP8.5) and study the impact of debris-covered region on the future change of ERG. The results show that: (1) the terminus position of ERG is likely to remain stable before 2055 while ERG itself is expected to lose much ice mass due to strong surface ablation; (2) in 2100, the length and volume of ERG will be ~16–48% and ~3–22% of the values in 2009, respectively; and (3) if we neglect the impact of debris cover on ice surface mass balance, we will probably overestimate ~11% of the meltwater runoff before 2030 and underestimate ~4% during 2030–2070.
Glacial recession and evolution of landforms in the Schirmacher Range and adjoining area, cDML, East Antarctica
M. Javed BEG, Prakash K. SHRIVASTAVA, Amit DHARWADKAR, Ashit K. SWAIN, S.A.I. MUJTABA, Rajesh ASTHANA, Sandip K. ROY
Corresponding author: M. Javed Beg
Corresponding author e-mail: firstname.lastname@example.org
The polar ice sheets showed glacial build-up and deglaciation during the early Quaternary period. Schirmacher Range, Baalshrudfjellet and Veteheia nunatak play a major role in controlling the ice flow in this region. Abundantly observed erosional as well as depositional landforms reveal vital information about the exhumation and Quaternary evolution of this region. Features such as roches moutonnées, glacially polished and abraded rocky outcrops having glacial striations preserved on exposed highlands and some low-lying areas indicate paleo-movements of the overriding glaciers. Such features depict a general north-northeast forward sense of glacial movement. The majority of boulders show their longer axis trending in NNE-WSW to NE-SW directions, particularly observed in two different valleys between Indian and Russian stations in the Schirmacher Range. Different generations of glacial valleys with overlapping timescales are widely observed. The highest point (212 m a.s.l.) of the Schirmacher Range also exhibits glacial striations signifying its submergence beneath the polar ice. In order to understand glaciation/deglaciation during the Quaternary thermo-luminescence (TL) dating of moraines is used with substantiating field observations. TL dates of glacial sediments and lake sediments show age variation between 171 and 63 ka deciphering different climatic fluctuations. The sequence of events during different episodes of glacial evolution of this area has been discussed.
Study of atmosphere–land interaction over the Tibetan Plateau and surrounding areas
Corresponding author: Yaoming Ma
Corresponding author e-mail: email@example.com
Centered on the Tibetan Plateau, the Third Pole area stretches from the Pamir and Hindu Kush in the west to the Hengduan Mountains in the east, from the Kunlun and Qilian Mountains in the north to the Himalaya in the south, covering over 5000 km2 with an elevation >4000 m. As a unique geological and geographical unit, the Third Pole area dramatically impacts the world’s environment and especially controls climatic and environmental changes in China, Asia and even in the Northern Hemisphere. Supported by the Chinese Academy of Sciences and some international organizations, the Third Pole Environment (TPE) Programme is now being implemented. TPE is focusing on the land surface processes and environment over the plateau and surrounding areas, with an emphasis on atmosphere–land interaction. Firstly the background of the establishment of the TPE, the establishing and monitoring plan of long-term scale of the TPE and six comprehensive observation and study stations will be introduced. Then the preliminary observational analysis results, such as the characteristics of surface fluxes partitioning and the structure of the atmospheric boundary layer (ABL) will also been shown. The study on the regional distribution of land surface heat fluxes are of paramount importance over the heterogeneous landscape of the Third Pole area. A parameterization methodology based on Moderate Resolution Imaging Spectroradiometer (MODIS) data, Advanced Very High Resolution Radiometer (AVHRR) data and in situ data is described and tested for deriving the regional surface heat fluxes (net radiation flux, soil heat flux, sensible heat flux and latent heat flux) over the heterogeneous landscape. As a case study, the methodology was applied to the whole Tibetan Plateau area. Eight images of MODIS data and four images of AVHRR data were used in this study for comparison among winter, spring, summer and autumn and the annual variation analysis. The derived results were also validated by using the ‘ground truth’ measured in the stations of the Tibetan Observation and Research Platform (TORP). The results show that the derived surface heat fluxes in four different seasons over the Tibetan Plateau area are in good accordance with the land surface status. They show a wide range due to the strong contrast of surface features over the Tibetan Plateau. Also, the estimated surface heat fluxes are in good agreement with the ground measurements, and their absolute percent difference (APD) is <10% in the validation sites. The results from AVHRR were also in agreement with MODIS, with the latter usually displaying a higher level of accuracy. It is therefore concluded that the proposed methodology is successful for the retrieval of surface heat fluxes using MODIS data, AVHRR data and in situ data over the Tibetan Plateau area, and that the MODIS data are the best and should be used widely for the determination of regional land surface heat fluxes over this area.
Climate-controlled difference of Quaternary glaciations along the middle and western Himalaya
Baojin QIAO, Chaolu YI, Yao JIN
Corresponding author e-mail: Chaolu Yi
Corresponding author e-mail: firstname.lastname@example.org
In order to know the impact of the Indian monsoon on mountain glaciers in the Himalaya, we studied the changes of glacier areas in the Last Glacial Maximum (LGM) and the Little Ice Age (LIA) along the middle and western Himalaya. Two study mountains are located in the middle and another in the west of the Himalaya. Using Google Earth images and with the help of field investigation, we determine the glacier boundaries in the LGM, LIA and present, and calculate their areas in ArcGIS software. We use the extension index, which is the same as the ratio of palaeoglacier area to contemporary glacier area, to describe the glacier changes. The value of extension is higher in Mount Everest than Gurla Mandhata (Naimon’anyi), indicating that the moisture decreased from east to west along the Himalaya. However, the extension index is much higher in Shishibangma, which is located between Mount Everest and Gurla Mandhata, than Mount Everest. We ascribe this abnormality to a water vapor channel from Nepal to Himalaya. More moisture could be brought to Shishibangma through the channel and lead to advance extensively in ice ages.
Changes in ice thickness of Qiyi Glacier, Qilian Mountains, northwest China, over the period of 1984–2007 by repeated measurements using GPR
Ninglian WANG, Xi JIANG, Zhen LI, Jianqiao HE, Jianchen PU
Corresponding author: Ninglian Wang
Corresponding author e-mail: email@example.com
With global warming, much attention has been paid to worldwide glacier shrinkage which can result in water resource shortages and sea-level rise. In the high mountains in central Asia and the Tibetan Plateau, there has been much research on the variations of glaciers, but most work has focused on the variations in glacier areas and/or termini and little on the changes in glacier ice thicknesses and/or volumes. Qiyi Glacier, 3.66 km long and with an area of 2.698 km2, is located in the Qilian Mountains and its meltwater flows into the Heihe River basin, the second largest inland river basin in China. The ice thicknesses of the glacier were measured by using ground-penetrating radar (GPR) in 1984 and 2007. It was found that the glacier was thinning by about 19 m on average over the study period and the largest thinning occurred around the terminus. A further investigation of ice thickness data showed that the distribution of ice thinning matched very well with the distribution of ice melting rate calculated by the mass energy-balance model in the lower part of the glacier, and that there existed a dynamic thinning in the upper part the glacier. This result is very important for understanding the behavior of a mountain glacier under climate change.
EOF reconstruction of sea level from tide gauges using satellite altimetry waveform retracking data
Lizhen LIAN, Weian WANG
Corresponding author: Lizhen Lian
Corresponding author e-mail: firstname.lastname@example.org
Because of the respective shortcomings of tide gauge and satellite altimetry measurements, combining the shorter but essentially complete global coverage offered by satellite altimetry with the longer but sparsely distributed tide gauge dataset is an active research area. Using a technique known as empirical orthogonal function (EOF) reconstruction, several attempts at combining tide gauge data and satellite altimetry have been published. While altimeter waveforms are contaminated by the terrain and some inadequate corrections in coastal oceans so that the accuracy of altimeter data is obviously lower than that over open oceans. By using waveform retracking it is possible to improve the quality of altimeter data over coastal oceans. Here, based on the tide gauge RLR data provided by Permanent Service for Mean Sea Level (PSMSL) and the post-processing gridded sea-level anomaly, we build on the recently developed method for reconstructing sea level involving EOF and, in particular, examine how the reconstruction varies as a result of the domain used to compute the EOF basis functions. Our focus is a timescale going back ~60 years, allowing reasonable regional availability of tide gauge data. This allows for better sensitivity analysis with respect to spatial distribution, and tide gauge data are available around the East China Sea and South China Sea, which may be important for the middle-latitude reconstruction.
Estimation of the influence of black carbon and snow grain size on snow/ice albedo
Zhongming GUO, Ninglian WANG, Ruijuan MAO, Xiaobo WU, Hongbo WU, Yuwei WU
Corresponding author: Ninglian Wang
Corresponding author e-mail: email@example.com
The snow/ice albedo plays an important role in the energy balance between the Earth and the atmosphere, and black carbon and snow grain size are major influencing factors on snow/ice albedo. In this paper, we collected snow samples for determation of black carbon content and measured snow grain size using a handheld lens in a fixed site over Qiyi Glacier, Qilian Mountains, during 6–15 September in 2011. Simultaneously, the snow/ice spectrums were observed using ASD Spectroradiometers FieldSpec Pro. Then we quantitatively estimated the influence of black carbon and snow grain size on the snow/ice albedo. Moreover, we compared the measurements of spectral reflectance with the results from the SNICAR model. Additionally, the HYSPLIT air mass backward trajectory model was used to track the source of black carbon.
Temporal variations of Nam Co Lake water level and glacier mass-balance changes on the western Nyainqentanglha Range, Tibetan Plateau, using ICESat altimetry data over 2003–2009
Hongbo WU, Ninglian WANG, Zhongming GUO, Yuwei WU
Corresponding author: Ninglian Wang
Corresponding author e-mail: firstname.lastname@example.org
Water-level fluctuations of continental lakes are related to regional-scale climate changes. Water-level fluctuations reflect variations in evaporation, precipitation and glacier melted water over the lake area and its catchment area. In this study, ICESat altimetry data are used to estimate the Nam Co Lake water elevation changes of the south of the Tibetan Plateau (TP) over 2003–2009. The Nam Co Lake is the second largest Tibetan lake covering an area of about 1000 km2 and situated at an elevation of 4718 m a.s.l. Over such inland water bodies, ICESat satellite altimetry data offers both a worldwide coverage and a satisfactory spatial and temporal accuracy. We combine remote sensing and GIS to map and measure changes in glaciers using a 7 year series of Landsat TM images (from 2003 to 2009) and digital elevation models (DEMs) from SRTM3 DEM data. They indicate significant changes in the hydrological system triggered by the glacier mass balance. However, the most spectacular feature is the water-level rise occurring from 2003 to 2009 and the precipitation is decreasing all the same. The Nam Co Lake water level increased at a rate of 0.49 m a–1 from 23 February 2003 to 9 October 2009 and the mean glacier mass balance is –478 mm water equivalent (w.e.) in the same period. The latter appropriates to the observation value using ICESat data much more. In these years, the Nam Co Lake area is from 1974.78 km2 to 2098 km2 and the whole mountain range glaciers covered an area from 1032.25 km2 to 980 km2, while the drainage basin of Nam Co Lake covered 238.1 km2. The temporal lake level fluctuation correlates with the dominant precipitation over the same time span. Nevertheless, similar rainfall anomaly, but with lesser intensity, occurred after 2006 without any noticeable effect on lake level. The precipitation appears to be related to the glacier mass balance during 2003–2009.
Glacier changes in the drainage basin of Issyk-Kul Lake, Kyrgyzstan, during the 1960s to the 2010s
Wanqin GUO, Shiyin LIU, Jiewen FU, Juanxiao GONG, Saadat TASHBAEVA, Bakytbek ERMENBAEV
Corresponding author: Wanqin Guo
Corresponding author e-mail: email@example.com
Issyk-Kul is the second largest mountain lake in the world and covers an area of 6236 km2. Kungei Alatau Mountain on the north side of the Issyk-Kul and Teskei Alatau on the south side have high altitudes with peak elevations of 4711 m and 5216 m, respectively, leading to the development of large numbers of glaciers over these two mountains. The glacier meltwater has a very important hydrological role for Issyk-Kul Lake basin. Previous observations have illustrated that a cirque glacier named Karbatkak, which is situated on the north slope of central Teskei Alatau, has lost about 18 m of its surface mass during the last 40 years (1957–1997), delineating that glaciers in the Issyk-Kul basin must have changed dramatically during the past few decades. However, currently the glacier changes in the lake basin are still poorly understood. Based on different sources of remote-sensing data, we studied the glacier changes over the entire Issyk-Kul basin during the 1960s to the 2010s. Declassified Corona and Landsat TM/ETM+ imageries were used to delineate the glacier outlines around 1965, 1990, 2000 and 2010. The glacier outlines from Corona images were digitized via manual works, while the glacier outlines from Landsat images were extracted by the widely used band ratio method plus some manual modification. Our results identified more than 950 glaciers in the Issyk-Kul basin in the 1960s, with a total area of about 710 km2, where 85% of them are located on the north slope of Teskei Alatau. The results also show that the glaciers in the Issyk-Kul basin have changed significantly during the last 50 years, as suggested by the results of field observations of representative glaciers. The total area of glaciers over the whole basin has decreased more than 22% during the 1960s to the 2010s. Meanwhile, there are some differences between the southern and northern mountain glaciers. The glaciers on the south slope of Kungei Alatau have shrunk about 25% of their total area, while the glaciers on the north slope of Teskei Alatau have smaller shrinkage (about 21%). The multi-decadal analysis also retrieved some temporal variations of glacier changes in different time stages between the 1960s and the 2010s. Our results show that the glacier change during 2000s–2010s in Issyk-Kul Lake basin are smaller than changes during 1990s–2000s and 1960s–1990s. By contrast, the period 1990s–2000s has the largest glacier change between the 1960s and 2010s. This result is consistent with the field observations. However, the shrinkage of glaciers on Kungei Alatau Mountain, which are smaller in size than glaciers on Teskei Alatau (0.57 vs 0.65 km2 average area), were continuously accelerated during the last 50 years, implying that the glaciers on the north side of Issyk-Kul Lake are more sensitive to climate change.
Surface energy budget and ablation modeling in the ablation zone of Laohugou Glacier No. 12, western Qilian Mountains, China
Weijun SUN, Xiang QIN, Qiudong ZHAO, Wentao DU, Tong ZHANG, Yuetong XU, Jinkui WU, Jiawen REN
Corresponding author: Weijun Sun
Corresponding author e-mail: firstname.lastname@example.org
The physical melting process at the glacial surface can be described by the energy-balance melt model. To quantify the component proportion of glacial surface energy fluxes and indicate dominating factors affecting glacial melting during the ablation period in an arid and high-latitude area of northwest China, an experiment of glacial surface energy budget was carried out at 4550 m a.s.l. on the ablation zone of Laohugou Glacier No. 12 in the Qilian Mountains. Based on meteorological data (1 June–30 September 2011) from an automatic weather station, glacial surface energy budget was analyzed and turbulence fluxes calculated by the bulk aerodynamic approach were corrected by measurements from the eddy covariance system. The simulated mass balances were validated by measurements from stakes. Net shortwave radiation was the primary source of the surface energy balance (126 W m–2, 95%), followed by sensible heat flux. Melting energy was the main output of surface energy (74.7 W m–2, 52%) and latent heat flux was the least one (11%). Although sensible and latent heat fluxes were underestimated by 3.4 and 1.2 W m–2, respectively, the calculated and measured values were very close. The simulated mass balance was –1703 mm w.e., larger than the measured value by 90 mm w.e., and mass balance simulated by the glacial surface energy-balance model was good. Besides daily positive accumulated temperature, low albedo is one of the most important factors accelerating glacier melting, and the minimum daily mean of albedo was 0.13 due to the influence of glacial surface dust. The climate change sensitivity test also showed that mass balance was very sensitive to albedo, and mass balance varied by 36% when albedo changed by 0.1.
The analytical asymptotic solution for reduction of snow albedo by dust and soot versus in situ measurements
Xuelei ZHANG, Guangjian WU, Tianli XU, Daniel TONG
Corresponding author: Guangjian Wu
Corresponding author e-mail: email@example.com
Many studies have paid attention to the significant reduction of snow albedo by black carbon (BC) particles for Himalayan glaciers around the Third Pole area, but this was by comparing clean snow to clean snow with BC added. Forcing due to BC in snow in the Himalaya and Tibetan Plateau is significant in the limited model studies available to date, but there are indications that these estimates are biased high due to overestimates in modeled snow BC concentrations and snow cover or by not accounting for the role of dust and soil in snow reducing snow albedo. Future studies must account for the effects of dust particles in mountain snow and glaciers when determining the effects of BC on snowmelt. As the SNICAR model based on the spectrally detailed radiative transfer solution and the PBSAM model based on the ‘double-adding’ methods are sophisticated and time-consuming, we present a computationally simple, theoretically based parameterization for the spectral albedo of snow with dust and BC that can accurately reproduce the theoretical spectral albedo under a wide range of snow and atmospheric conditions. This simple model only requires three input parameters, snow grain size, snow particle morphology and solar zenith angle, to reproduce the snow albedo for a wide spectral range starting from the UV until ~1.4 μm. We compared our simple model results with the SNICAR model and Yasunari’s snow albedo parameterized scheme to evaluate its accuracy. Validation tests against in situ observed data were performed in Hulun Buir, China. This simple model can be used for the retrieval of snow grain size and impurity concentrations using both ground and satellite measurements of snow reflectance in future. The findings also illustrate the importance of parameterizing the influence of dust particles together with BC on the snow surface albedo for proper simulation of the related climate forcing.
Comparisons of hydrological process in glacierized and non-glacierized catchments at Urumqi River, eastern Tien Shan, China
Meiping SUN, Xiaojun YAO
Corresponding author: Meiping Sun
Corresponding author e-mail: firstname.lastname@example.org
Based on meteorological and hydrological data every 10 min from Ürümqi Glacier No. 1 gauging station and Empty Cirque gauging station in the Urumqi River resource region, located on the northern side of the eastern Tien Shan, the hydrological processes were compared to analyze the difference in the melt season (May–September) between the glacierized and the non-glacierized catchment. The results showed that discharge increased from May onwards, reached its highest value in July and then decreased in two catchments. The distribution of daily runoff was obviously different in the glacierized catchment (Glacier No. 1) and non-glacierized catchment (Empty Cirque). In particular, in the Glacier No. 1 catchment, the maximum discharge of daily runoff appeared in 14–18 h and the minimum was in 8–10 h, whereas in the Empty Cirque catchment, the maximum appeared in the evening (23–1 h of the next day) and the minimum was in the afternoon (13–15 h). The storage characteristics of glacier and snow meltwater were also reflected by a comparable magnitude of runoff during the daytime (9–20 h) and the nighttime (21–8 h). The day runoff was more than that at night in the Glacier No. 1 catchment, which was the opposite to that in the Empty Cirque catchment. This indicated that the water storage capability of Glacier No. 1 was weak, possibly due to its small size (only 3.34 km2). In addition, the methods proposed by Singh and Jobard, respectively, were used to analyze the time lag between the daily discharge peak and the maximum temperature in two cases of inclusion and exclusion of precipitation influence. The time lag of Glacier No. 1 ranged from 1 to 3 hours on clear weather days. However, in conditions of the influence of precipitation, the time lag was 1 hour. The time of the maximum runoff of Empty Cirque appeared lagged 10–16 hours than that of the highest temperature, regardless of precipitation influence. If it was taken into account, the time lag was 13 hours. This demonstrated that the precipitation process could make the ice and snow meltwater confluence more rapidly.
Preliminary results of mass-balance observations of Yala Glacier and analysis of temperature and precipitation gradients in Langtang valley, Rasuwa, Nepal
Prashant BARAL, Rijan Bhakta KAYASTHA, Dorothea STUMM, Walter W. IMMERZEEL, Stephan GALOS, Sonika SHAHI, Claudia SPRINGER, Sharad P. JOSHI, Pradeep MOOL
Corresponding author: Prashant Baral
Corresponding author e-mail: email@example.com
This paper provides preliminary results of mass-balance observations of Yala Glacier and analysis of temperature and precipitation data from Langtang valley in the Rasuwa district, Nepal, carried out under the Cryosphere Monitoring Project (CMP) funded by the Ministry of Foreign Affairs, Government of Norway. Yala Glacier (5110–5700 m a.s.l.) in the Langtang valley is a debris-free glacier where glaciological and meteorological field observations have been carried out intermittently since 1981. Mass-balance observations using the glaciological method and climatic measurements have been carried out along a specified transect of the glacier by the CMP since November 2011. Six stakes were installed at an altitude of 5100–5300 m a.s.l. and five snow pits were dug at an altitude of 5300–5500 m a.s.l. in November 2011. Measurements of stakes show specific mass balance of –2.62, –3.55, –2.75, –2.85, –3.22 and –2.01 m w.e. at an altitude of 5161, 5176, 5194, 5201, 5229 and 5244 m a.s.l., respectively, for the period from November 2011 to November 2012. It confirms that the mass balance in 2012 was very negative. Rain gauges and temperature loggers have been installed at Syafrubesi (1406 m), Lama Hotel (2370 m), Langtang (3539 m), Kyangjing (3857 m), Jathang (3875 m) and Numthang (3981 m) and a pluviometer with temperature and snow depth sensor near Yala Glacier (4831 m) in May 2012 for the study of precipitation and temperature gradients in the valley. The observation of cumulative precipitation data shows that Lama Hotel received 1244 mm, the maximum amount of monsoon rainfall, and Numthang received 520 mm, the minimum amount of monsoon rainfall. This confirms the general trend of decreasing precipitation with altitude, yet the relation between altitude and precipitation as a result of mesoscale valley circulation remains a topic of further study.
Glacier zones and snow/firn lines detection using SAR imagery on glaciers in Qinghai-Tibetan Plateau
Lei HUANG, Zhen LI
Corresponding author: Lei Huang
Corresponding author e-mail: firstname.lastname@example.org
Glaciers on the Qinghai–Tibetan plateau are a sensitive indicator of local and global indicators. In this paper, Dongkemadi Glacier, which lies inland in the Qinghai–Tibetan plateau, is monitored with 18 SAR images over 15 years. This study shows that in late summer the wet-snow–ice boundary, which is termed the late summer firn line (LSFL), is distinct on SAR images. By comparison of the LSFL and equilibrium line in three different years, it is found that the LSFL advances in positive years and retreats in negative years. In winter SAR images, the firn that is thicker than 40 cm is distinct because its backscatter is strong. The firn that is thicker than 40 cm is called névé basin and the lower boundary of the névé basin is stable over the observed 8 years in winter. By combination of the C-band SAR imagery, fieldwork and the history record, the spatiotemporal backscatter signature specific to the typical continental glacier is identified.
Mass balance of a maritime glacier on the southeast Tibetan Plateau and its climatic sensitivity
Wei YANG, Tandong YAO, Xiaofeng GUO, Meilin ZHU, Shenhai LI
Corresponding author: Wei Yang
Corresponding author e-mail: email@example.com
Based on glacio-meteorological measurements and mass-balance stake records during the 5 year period 2005–2010 on the southeast Tibetan Plateau, an energy mass-balance model was applied to study the glacier surface mass balance of Parlung No. 94 Glacier and its response to regional climate conditions. Primary physical parameters in the modeling were locally calibrated by using the present glacio-meteorological datasets. The good agreement between the snowpack height/mass-balance simulations and the in situ measurements available at a total of 12 monitoring stakes over this glacier confirmed the satisfactory performance of the energy mass-balance model. Results showed that the recent state of Parlung No. 94 Glacier was far removed from the ‘ideal’ climatic region for zero mass balance, with its annual mass balance being approximately –0.9 m w.e. during 2005–2010. Climatic sensitivity experiments were also carried out to interpret the observed mass-balance changes and the experiments demonstrated that the maritime glaciers concerned herein were theoretically more vulnerable to the ongoing climatic warming on the Tibetan Plateau than potential changes in the amount of precipitation. An important causal explanation for the recent glacier shrinkage in this region should be the increasing air temperature. Moreover, both the mass-balance simulations and the field measurements indicated that the mass accumulation over this maritime glacier occurred primarily in the boreal spring. Such ‘spring-accumulation-type’ glaciers are mainly distributed in a limited wedge-shaped region along the Brahmaputra River. Furthermore, climatic sensitivity of glacier mass balance is also found to be closely linked to the precipitation seasonality that is simultaneously modulated by a multitude of atmospheric circulations, such as the southern westerlies and the Bay of Bengal vortex in the spring season and the Indian monsoon in the summer season.
Influence of glacial meltwater on water-balance processes of two lakes on the southern Tibetan Plateau indicated by water δ18O
Jing GAO, Tandong YAO, Daniel JOSWIAK
Corresponding author: Jing Gao
Corresponding author e-mail: firstname.lastname@example.org
δ18O measurements based on systematic sampling and isotopic modeling have been adopted to study the effects of glacial meltwater in two lake basins (Lakes Yamdrok-tso and Puma Yum-tso) at two different elevations on the southern Tibetan Plateau. Temporally, δ18O values in precipitation and lake water display a seasonal fluctuation in both lakes. Spatially, δ18O values in the two lake basins increase by 10‰ from the termini of glaciers to the lake shores, by about 1‰ from the lakeshores to the lake center, by 0.4‰ from the water surface to depth in these lakes. The obvious annual δ18O variations indicate that lake water mixes sufficiently in a short time. Model results show that glacial meltwater is an important factor in lake water-balance processes. Equilibrium δ18O values decrease 0.8‰ for Yamdrok-tso Lake and 0.6‰ for Puma Yum-tso Lake when contributions of glacial meltwater to these lakes shrink by 60%. δ18O ratios increase rapidly during the initial stages and take a relatively longer time to approach the equilibrium value. The modeled results also show that the surface lake water temperature has a minimal impact on this process.
Hypsometric analysis reveals river system evolution controlled by tectonics and climate at the Qing–Tibetan Plateau northern margin: a case study of Golmud River
Chuanchuan LI, Mei ZHANG, Jingchun ZHANG, Zhijiu CUI, Gengnian LIU
Corresponding author: Chuanchuan Li
Corresponding author e-mail: email@example.com
The interaction between tectonics and climate on landform has sparked much interest over the years. The hypsometric integral (HI) value could reflect both tectonic activity and climate change, and might be a promising tool that links those two aspects. Based on SRTM-DEM data, this paper withdraws the measuring indicators of the landform and hypsometric integral from the third-order basins and some of the second-order basins in the Golmud River drainage basin using GIS spatial analysis, discusses the area and space dependence for the hypsometric integral, and presents its significance in indicating tectonics, lithology and the degree of glacial erosion. The results show that: the HI value depends on area and space; the southern fault of east Kunlun (F4)–Xidatan (F3) fault can be divided into two parts, the east and the west, by the Kunlun Pass; both of them show a similar scenario that the activity decreases from the center to the sides; there is no apparent change in the activity of the central fault of east Kunlun (F1); intrusive rock shows greatest erosion-resistance while schist shows the least and carbonate rocks shows modest, respectively; glacial processes could rework the landform and change the degree of erosion; drainage basins with modern glaciers and/or with extensively distributed paleoglaciers have higher HI values and develop U-shaped valleys, compared with those without or with limited paleoglaciers.
Research on glacier lake change and its latent disaster in the southeast Tibetan Plateau
Lihong WANG, Anxin LU, Ninglian WANG
Corresponding author: Anxin Lu
Corresponding author e-mail: firstname.lastname@example.org
Accelerating glacier retreat and glacial lake expansion as a result of global warming result in an increase in the frequency and the aggravating effect of great glacial disasters caused by glacial lake outburst floods. Southeastern Tibet has one of the highest incidences of glacial disasters. In this paper, variations of typical glacial lakes in the Palong River drainage area and Niyang River basin in the southeast Tibetan Plateau were investigated for the period 1970–2008 by analyzing the datasets from satellite images, Landsat TM from 2008 and topographical maps from the 1970s. The results show that the lake area had increased by 3.69%. In addition, the authors made a systematic analysis on potential outburst lakes in the southeastern Tibetan Plateau based on the discussion of stability evaluation.
Seasonal and annual mass balances of Mera and Pokalde Glaciers (Nepal Himalaya) since 2007
P. WAGNON, C. VINCENT, Y. ARNAUD, E. BERTHIER, E. VUILLERMOZ
Corresponding author: P. Wagnon
Corresponding author e-mail: email@example.com
In 2007, a long-term ground-based monitoring program was started on the debris-free Mera Glacier (27.7° N, 86.9° E; 5.1 km2, 6420–4940 m a.s.l.) located in Hinku valley, Everest region, Nepal. This glacier lies in the southern flank of the eastern Himalaya under the direct influence of the Indian monsoon, which brings precipitation mainly in summer. Here, we present 5 years of mass-balance and surface velocity measurements as well as glacier thickness derived from ground-penetrating radar survey. Over this period, the glacier-wide mass balance was just slightly negative at –0.10 ± 0.40 m w.e. a–1. The interannual variability was high, with two positive years (maximum value of +0.46 m w.e. in 2010–11; equilibrium-line altitude (ELA) at 5340 m a.s.l.), two negative years (minimum value of –0.77 m w.e. in 2011–12; ELA at 6055 m a.s.l.) and a balanced year in 2008–09. Seasonal mass-balance measurements confirm that ablation and accumulation are concomitant in summer but, unexpectedly, show that ablation occurs at any elevation in winter due to wind erosion and sublimation. Known as ‘summer-accumulation-type glaciers’, Nepalese glaciers can also be referred to as ‘winter-ablation-type glaciers’. This specific feature is confirmed by additional seasonal mass balances measured since 2009 on the small Pokalde Glacier (27.9° N, 86.8° E; 0.1 km2, 5690–5430 m a.s.l.) located 25 km north of Mera Glacier, in a much inner and drier position inside the mountain range. The mean vertical gradient of mass balance in the ablation zone of Mera Glacier strongly depends on the orientation, going from 0.50 m w.e. (100 m)–1 in north to west orientations to 0.85 m w.e. (100 m)–1 for northeast slopes. Surface velocities are low, always below 15 m a–1, in agreement with the reduced net accumulation measured at 6330 m a.s.l., which never exceeded 1 m w.e. over the measurement period.
Basal topographic controls on the rapid retreat of Humboldt Glacier, northern Greenland
J. Rachel CARR, Andreas VIELI, Chris Stokes
Corresponding author: J. Rachel Carr
Corresponding author e-mail: firstname.lastname@example.org
The Greenland ice sheet has rapidly lost mass in the past decade, through a combination of negative surface mass balance and accelerated discharge from marine-terminating outlet glaciers. However, the factors driving changes in ice dynamics are poorly understood. Here, we assess the impact of climatic/oceanic and basal topographic controls on the behaviour of Humboldt Glacier, one of the largest marine-terminating outlet glaciers in Greenland. We use a combination of ESA SAR image Mode data and Landsat imagery to demonstrate that Humboldt Glacier retreated rapidly between 1999 and 2012 (162 m a–1), following decades of gradual retreat between 1975 and 1999 (37 m a–1). Comparison of frontal positions with climatic/oceanic forcing data suggests that the primary driver of retreat was increased summer air temperatures, which warmed by almost 3°C between 1999 and 2012, with a secondary contribution from reduced summer sea-ice concentrations. Retreat rates at Humboldt Glacier were an order of magnitude greater on the northern portion of the terminus, which we attribute to the presence of a large basal trough beneath this section. We suggest that this overdeepening brought the northern section close to floatation and increased its sensitivity to climatic/oceanic forcing, thus promoting rapid retreat. The basal trough continues up to 40 km inland and may facilitate sustained and substantial mass loss from Humboldt Glacier throughout the 21st century. Our results imply that basal topography is likely to be a critical control on the magnitude and rate of mass loss from Humboldt Glacier in the near future and highlights the potential for overdeepenings to influence contemporary Arctic outlet glacier behaviour.
Glacial lake change in the central Himalaya, 1990–2010
Yong NIE, Qiao LIU, Shiying LIU
Corresponding author: Yong Nie
Corresponding author e-mail: email@example.com
Against the background of global warming, most Himalayan glaciers have experienced remarkable downwasting and, as a consequence, glacial lakes were widely formed and expanded. Glacial lakes are of ever-increasing concern because of their destructive disasters (glacial lake outburst floods, GLOFs) for local people and infrastructure. Most of the reported GLOFs have happened in the central Himalaya. However, a poor understanding of the distribution and temporal and spatial changes in glacial lakes within the whole central Himalaya makes it difficult for the relative adaptation and disaster alleviation. In this study, the extents of glacial lakes in the central Himalaya were extracted using the object-based image-processing method providing four periods of TM or ETM images between 1990 and 2010. The same spatial resolution (30 m) of the images from these four periods reduces the uncertainty in the estimation of glacial lake changes. A time series inspecting method has been applied to keep the reliability of glacial lake changes for 1990, 2000, 2005 and 2010 data. Our results show that the glacial lakes have been expanding rapidly. The glacial lake area in 2010 was 189.74 km2. From 1990 to 2010, glacial lakes expanded by 28.84 km2 (an increase of 17.92%). The number of glacial lakes with an area >0.1 km2 shows a distinct increase from 327 in 1990, 351 in 2000, 363 in 2005 to 367 in 2010. Many large glacial lakes appeared in recent years, including 31 glacial lakes with an area larger than 1 km2 in 2010. The increased warming and glacier shrinkage in the whole central Himalaya are the main contributors to glacial lake expansion. The rapid expansion of glacial lakes aggravates the risk of GLOFs. An effective monitoring system and adaptive strategy for rapid expansion of glacial lakes are still required urgently.
Spatial and climatic observations in Batura Glacier over the last 40 years
Khurrum Waqas HAIDER, Ghulam RASUL, Qin DAHE
Corresponding author: Khurrum Waqas Haider
Corresponding author e-mail: firstname.lastname@example.org
In this study we attempt to analyze the relationship between climatic data and observed spatial changes in Batura Glacier during last 40 years. For this purpose, climate data and remote-sensing techniques were used along with field observations from 1975 and 2012 expeditions. Meteorological data from nearby observatories, AWS and gridded datasets (CRU, NCEP) were analyzed. Landsat (MSS, TM, ETM+) and ASTER images were used to delimit the glacier snout and bare ice flow. Imagery from 1972 to 2012 along with field observations were utilized in the analysis. Results showed initial retreat of the glacier snout from 1975 to 1998, after which the snout showed advancement of about 500 m. Analysis also focused on the ice line over the glacier, which was observed to be under continuous retreat since 1972 by over 2.5 km in length, showing the direct influence of temperature. Climatic analysis also depicted an increase in temperature trend over the study area, although precipitation does not show any significant change over the study period.
Measurement of ice-flow velocity at the Amery Ice Shelf from optical and interferometric SAR satellite imagery
Yi LIU, Shuang LIU, Huan XIE, Weian WANG, Fei YAN, Marco SCAIONI, Xiaohua TONG, Rongxing LI
Corresponding author: Yi Liu
Corresponding author e-mail: email@example.com
Antarctica plays an important role for explotion of the relationship between global climate change and sea-level rise. Ice-flow velocity is one of the most fundamental measurements for studying the dynamics of ice sheets and for calculating the mass balance of ice sheets. The Amery Ice Shelf (AIS), which is one of the largest ice shelves in Antarctica, has been studied over the past 50 years. A number of research papers have reported velocity measurements in this area. Among them, most results are based on two methods: field survey and remote sensing. The field survey is less cost-effective and sometimes depends on opportunities, while the remote-sensing method mostly uses optical and interferometric SAR satellite imagery. Accordingly, there are two approaches: feature-based and interferometry-based techniques. The former is usually based on the method of normalized cross correlation, which can cover large areas with lower costs, but may be subject to errors caused by mismatches. The latter is often concerned with the lack of imagery data because of the strict requirements of building interferometric pairs. In this paper, we propose a combined optical/SAR imagery approach to calculate glacier ice-flow velocity based on Landsat ETM+ and SAR imagery. First, we compared the advantages of several interest point operators and presented an integrated method by combing these operators together for feature extraction. Second, we developed a coarse-to-fine match method to match these extracted point features from optical imagery. Third, we proposed a new loopy-belief-propagation (LBP) method to densify the matched points. Finally, in some local areas, we used the interferometry method to obtain a more accurate result of ice-flow velocities based on interferometric SAR by using ERS-1/2 tandem data. We tested our proposed method in the Amery Ice Shelf region. The results showed that our proposed method combines the complementary advantages of the two individual techniques and obtains the measurement of ice-flow velocities more accurately and effectively.
Effects of black carbon and dust on the albedo in Zhadang Glacier, southern Tibetan Plateau
Shichang KANG, Bin QU, Jing MING, Guoshuai ZHANG
Corresponding author: Shichang Kang
Corresponding author e-mail: firstname.lastname@example.org
Warming over the Tibetan Plateau (TP) in recent decades has resulted in significant reductions of glaciers and ice caps. Observations on Zhadang Glacier, southern Tibetan Plateau, show a large deficit of mass balance with an average of –1286 mm a–1 during 2005–2012 and the equalibrium-line altitude has moved up beyond the upper glacier, indicating dramatic glacier melting in recent years. The glacier mass balance is closely correlated with the surface albedo of Zhadang Glacier: low annual surface albedo corresponds with more negative mass balance. Black carbon (BC, or element carbon) and dust deposited on glaciers reduces the surface albedo resulting in more solar radiation absorption, thus accelerating the melting of glaciers. To investigate the effects of BC and dust on glacier albedo, we sampled surface firn/ice during the strong melting days in July and surface fresh snow which covered the whole glacier in August 2012, and measured surface albedo on Zhadang Glacier. Average concentrations of BC (257.7 ppbm) and dust (624.0 ppmm) in firn/ice are one (and two) magnitudes higher than values in fresh snow (BC with 52.0 ppbm; dust with 6.4 ppmm), indicating that BC and dust can accumulate when snow experiences melt. The snow, ice and aerosol radiative (SNICAR) model is used to quantify the contribution rate of BC and dust to the reduction in snow albedo. When the glacier was covered by fresh snow, BC and dust contributed 47.7% and 13.6% of the surface albedo reduction, respectively, suggesting BC was a major factor for snowmelting on Zhadang Glacier. However, when the glacier was experiencing strong ablation, BC contributed 9.5% and 35% of the surface albedo reduction from the lower to the upper part of the glacier, while the dust contribution reached 70.7% (lower) and 50% (upper), indicating dust was a key factor for the whole glacier melting.
Regional estimates of glacier runoff for the 21st century
Andrew BLISS, Regine HOCK, Valentina RADIC
Corresponding author: Andrew Bliss
Corresponding author e-mail: email@example.com
The hydrology of many important river systems in the world is influenced by the presence of glaciers in their upper reaches. While recent work has considered the future behavior of glaciers and river systems independently, few studies have attempted to combine the two. Mass-balance projections for all the glaciers in the world (outside the ice sheets) indicate that global glacier volume will decrease by 30–40% by 2100. These mass-balance figures are often directly translated into an equivalent sea-level rise (15–20 cm), neglecting the hard-to-model terrestrial hydrology. We explore the fate of glacier runoff in greater detail. Using an elevation-dependent glacier mass-balance model, we project glacier runoff for all glaciers in the world until the year 2100. The model is forced with temperature and precipitation scenarios from 14 global climate models. We define runoff as rain falling on the glacier, plus melt of seasonal snow from the glacier, plus melt of glacier ice, minus any water that refreezes on the glacier. Aggregating over all the glaciers in each of 19 regions, we consider the relative importance of these components, as well as their changes over time. Furthermore, we compare trends in runoff from large versus small glaciers and high-elevation versus low-elevation glaciers, finding a variety of responses in neighboring glaciers. Our eventual goal is to couple the glacier runoff to a global hydrology model to trace the water as it moves from the glacier to the sea.
Environmental change records of delta and sand wedge of the lakeshore at LingGo Co of the Qiangtang Plateau
Baolin PAN, Chaolu YI, Zhongping LAI, Guocheng DONG
Corresponding author: Baolin Pan
Corresponding author e-mail: firstname.lastname@example.org
Environmental information from the river delta is very complex. Whereas, according to the sedimentary structure of the river delta, sediments can be judged to belong to lacustrine deposition or river deposition, the sedimentary environment can be conformed, a stream sedimentary environment or lake sedimentary environment. One section has been found that lies in the biggest delta in the inlet of the biggest river of the northeast of Linggo Co (Co means lake). The height of the section is 4.56 m and it recorded the different environment. Optically stimulated luminescence (OSL) can be used to gain an insight into when the lake level rises and falls. Seven samples were collected, the ages of which are 5.90 ± 0.50 to 7.30 ± 1.00, 3.30 ± 0.30 to 3.30 ± 0.30, 5.90 ± 0.80 to 4.80 ± 0.40 and 10.70 ± 1.00 ka BP, from up to down the section, respectively. These data can be divided into four groups. The results indicate that: (1) the first two data (G1) are from river sedimentary environment which is made up of coarse gravel, suggesting that signal retreated incompletely; (2) the behind three groups of data (G2) show that the positions of these data were lacustrine deposition, most likely corresponding to a higher lake level than the modern lakeshore. The climate may be warmer and wetter. Sand wedge can indicate the ancient temperature on the whole and represents the period of dry and cold. In the east coast of the lake, one sand wedge was found about 1.7 m high. Four samples were obtained from this sand-wedge section. OSL measurements also were made use of for the ages and showed 0.43 ± 0.037, 1.50 ± 0.20, 1.40 ± 0.10 and 6.5 ± 0.50, respectively. These data illustrate the annual average land temperature is about –5°C–8°C, formed about 1500 and 6500 years ago and the lake level is lower than the sand-wedge section, belonging to the cool period.
Asian–Pacific Oscillation signal from a Qomolangma (Mount Everest) ice-core chemical record
Hao XU, Shugui HOU, Hongxi PANG
Corresponding author: Shugui Hou
Corresponding author e-mail: email@example.com
Ice cores retrieved from the accumulation zone of glaciers over the Tibetan Plateau preserve a wealth of fine-resolution paleoclimatic and environmental information. In 2002, a 108.83 m ice core was drilled from East Rongbuk (ER) Glacier (27°59' N, 86°55' E, 6518 m) on the northeast slope of Qomolangma (Mount Everest) in the central Himalaya. Empirical orthogonal function (EOF) analysis conducted on the time series of the major ions of the ER ice core reveals the common structure and inter-species relations of the major ions. The crustal ions (Mg2+, Ca2+, SO42– and NO3–) are highly loaded on EOF1, which represents activities of the continental air mass, and the marine ions (Cl– and Na+) are highly loaded on EOF2, which indicates the intensity of the south Asia monsoon. Investigations on 54 year EOF time series and upper tropospheric temperature (UTT; 200–500 hpa) indicated that higher (lower) EOF1 associated with negative (positive) anomalies of UTT over the Mongolian Plateau, and higher (lower) EOF2 associated with positive (negative) anomalies of summer UTT over the Mongolian Plateau. These situations resemble the Asia–Pacific Oscillation (APO), which is a climate pattern indicating the thermal difference between Asia land and northeast Pacific. Further investigations on 982 year EOF time series and a reconstructed APO index showed that summer EOF1 were negatively correlated with summer APO index (p < 0.01) and summer EOF2 were positively related to summer APO index (p < 0.01). This suggests that summer larger (lower) ocean–land thermal difference (associated with higher APO index) drives the marine air mass shift northward more (less), the northward-moving marine air mass forced the continental air mass over the southern Tibetan Plateau, and weakened (strengthened) it. The larger (lower) winter ocean–land thermal difference (associated with lower APO index) strengthened (weakened) the westerly over the southern Tibetan Plateau.
A study of ablation, velocity and meteorological conditions on Batura Glacier, Karakoram, Pakistan
Khurrum WAQAS, Shangguan DONGHUI, Qin DAHE, Ghulam RASUL
Corresponding author: Khurrum Waqas
Corresponding author e-mail: firstname.lastname@example.org
This research presents initial results from a recent expedition (July–August 2012) to Batura Glacier in the Hunza valley of Pakistan. To measure the ablation, 6 m long stakes were installed at different elevations with different debris depths on the glacier surface. Ablation data along with velocity profiles were combined with meteorological data from the AWS installed by the team during September 2010. The team also measured the local lapse rate and the degree-day factor by comparing air temperature data from Batura and Passu automatic weather stations. Results from 8 stake profiles suggest average ablation of ~4.3 cm d–1 during the study period. Velocity from stakes was calculated as 10 m month–1 averaged from different measurement points. Results were also compared with similar data obtained during a 1970s expedition to Batura Glacier by Chinese scientists combined with climatological data to understand the changes that have occurred during this duration because of the changed climatology of the study area.
Influence of a debris layer on the melting of ice on a Himalayan glacier: a case study on Lirung Glacier, Langtang valley, Rasuwa, Nepal
Sonika SHAHI, Rijan Bhakta KAYASTHA, Francesca PELLICCIOTTI, Lene PETERSEN, Silvan RAGETTLI, Prashant BARAL, Arun Bhakta SHRESTHA, Pradeep MOOL
Corresponding author: Sonika Shahi
Corresponding author e-mail: email@example.com
Total runoff from glacierized river basins has been commonly modelled using two approaches: physically based energy-balance models and more empirical temperature-index models. This study uses an energy-balance model (EBM) at the point scale to calculate melt under a debris-covered glacier. Because of the high heterogeneity of the surface layer, the ablation rate varies throughout the glacier. Accurate melt modelling at different locations of the debris-covered glacier is important to understand the effect of a highly variable debris layer on melt and thus improve the distributed modelling, which in turn gives estimates of the amount of discharge from the glacier, an important component of the local water resources. This work provides information about the influence of a debris cover on the melting of Lirung Glacier in Langtang valley, Rasuwa district, Nepal. From May to October 2012 an extensive field campaign was carried out. The setup consisted of: one automatic weather station (AWS) measuring incoming and reflected shortwave radiation, air temperature, relative humidity, wind speed, wind direction, surface temperature and snow height; nine ablation stakes along the glacier in correspondence to different debris thicknesses ranging from 6 to 40 cm; a thermistor chain to measure the temperature profile of the debris layer; three tiny-tags to measure temperature on the top and bottom of the debris layer for different debris thicknesses; and 14 temperature sensors to measure air temperature at 2 m above the debris layer, seven of which had an additional sensor on the surface. As all the meteorological variables are measured directly, all the fluxes governing the melt can be determined and hence the point melt rate can be estimated. Direct measurements of surface lowering at the ablation stakes were conducted during May (installation period), late June, early September and late October 2012. The results of the EBM at each of these locations are examined and melt rate and energy fluxes are compared. The differences among the locations and possible reasons for their variability are discussed.
Elevation change analysis of the Antarctic in the last two decades
Tiantian FENG, Zhenxiong GU, Marco SCAIONI, Hangbin WU, Jun LIU, Xiaohua TONG, Rongxing LI
Corresponding author: Tiantian Feng
Corresponding author e-mail: firstname.lastname@example.org
The research on global climate change has been attracting the attention of more and more researchers in the last decades. The surface elevation change of the polar ice sheets (mainly Antarctica and Greenland) is a sensitive indicator of climate change because the mass balance of the ice sheets directly affects the sea level. The objective of this paper is to investigate the elevation change on the Antarctic ice sheet in the period from the 1990s to the 2010s. In order to obtain the surface elevation change, three DEMs produced at different periods and from data of different satellite altimetry missions were used. The earliest DEM product we used here is generated by J.L. Bamber by using ~20 × 106 data points, which are derived from ERS-1 radar altimetry during the geodetic phase from March 1994 to May 1995. This DEM provides the surface elevation information for the Antarctic up to 81.5° S latitude at a resolution of 5 km. In our investigation, this DEM required a filtering process for some regions (e.g. the Antarctica Peninsula and other areas with steep slopes) where ERS altimeter data are not reliable, as also indicated by other publications. The second DEM is generated in our study by using the recently reprocessed and released data of the first seven operational periods (from February 2003 through June 2005) of the Geoscience Laser Altimeter System (GLAS) instrument onboard ICESat. It is provided on polar stereographic grids at 500 m grid spacing. The grid covers the Antarctic up to 86° S latitude. The third DEM is produced based on the inverse-distance-weighted interpolation algorithm using CryoSat-2 radar altimetry data collected from February 2011 to September 2012. The initial surface elevation changes are obtained through the difference analysis between the three DEM products, after resampling at a common spatial resolution (5 km × 5 km). One of the most important tasks in this work is to analyze the errors that appeared in the computed elevation changes. Blunders or large errors mainly associated with slopes and early missions are detected and removed. For example, in the comparison of ERS-1 (radar altimetry) and GLAS (laser altimetry) data, the mean elevation changes are computed for every 0.02° in the slope range of [0°, 2°]. A linear correlation between the errors in elevation differences and the slope was found in the slope range of [0°, 0.4°]. This trend is interpreted as slope-induced systematic error. A linear correction model is established by a regression analysis and applied to the computed elevation changes. Finally, the surface elevation changes are compared with the result derived from gravity data in the same period.
The status and decadal change of glaciers in Bhutan from 1980 to 2010 based on satellite data
Samjwal Ratna BAJRACHARYA, Sudan B. MAHARJAN, Finu SHRESTHA
Corresponding author: Samjwal Ratna Bajracharya
Corresponding author e-mail: email@example.com
In order to monitor the changes in the glaciers in the Bhutan Himalaya, a repeat decadal glacier inventory was carried out from Landsat images of 1980, 1990, 2000 and 2010. The base map of glacier polygons was obtained from the object-based image classification (OBIC) method using the multispectral Landsat images of 2010. This method is used separately to delineate clean-ice and debris-covered glaciers. Later these two layers were merged to a single layer to obtain the glacier parameters of 2010. The glacier polygons of 2010 are modified manually by overlaying separately the Landsat images of 2000, 1990 and 1980 to obtain the glacier polygons of the respective years. The inventory of 2010 shows 885 glaciers with total area of about 642 km2. The glacier area is 1.6% of total land cover in Bhutan. The result of repeat inventory shows 23.4 ± 0.9% glacial area loss between 1980 and 2010, with the highest loss of 11.6 ± 1.2% between 1980 and 1990 and the lowest of 6.7 ± 0.1% between 2000 and 2010. The trend of glacier area changes from the 1980s to 2010 is found as –6.4 ± 1.6%. Loss of glacier area was mostly observed below an elevation of 5600 m a.s.l. and was greater for clean-ice glaciers. The upward shifting of equilibrium-line altitudes (ELA) has been noticed from 5170 ± 110 m a.s.l. to 5350 ± 150 m a.s.l. in the years 1980–2010.
Statistical analysis of the relationship between ice-core δ18O and temperature on the Tibetan Plateau
Huabiao ZHAO, Baiqing XU, Tandong YAO, Ninglian WANG
Corresponding author: Huabiao Zhao
Corresponding author e-mail: firstname.lastname@example.org
The variation of ice-core δ18O on the northern Tibetan Plateau (TP) is highly related to air temperature, while it is still controversial at present on the southern TP. The annually resolved δ18O records from 12 ice cores equally located in the northern and southern TP are carefully selected to evaluate the potential to capture the air temperature changes. The δ18O records from the respective regions are spatially integrated by a normalization method and compared with the respective regional averaged air temperature. The results show that the standardized δ18O records over the northern, southern and whole TP are all significantly correlated with the annual air temperature time series, with the coefficients of 0.69, 0.43 and 0.66, respectively. The correlations are much improved on the basis of multi-year running means of the records. This analysis implies that the ice-core δ18O record in the TP is potentially the proxy of air temperature and that the spatially integrated δ18O record is much better than the individual in exploring the past variations of regional air temperature.
Crevasse changes over the Antarctic Mertz Ice Shelf before disintegration
Xianwei WANG, Xiao CHENG
Corresponding author: Xianwei Wang
Corresponding author e-mail: email@example.com
Crevasse depth and central large rifts on the Mertz Ice Shelf were investigated from laser altimetry data (ICESat/GLAS) and remotely sensed images (Landsat and ENVISAT-ASAR). The smaller footprint of ICESat/GLAS enables its application in large crevasse depth detection. The method to calculate crevasse depth based on track observation of GLA12 data was proposed. The histogram of crevasse depth on the Mertz Ice Shelf from 2003 to 2009 showed nearly the same annual distribution, indicating the almost stable situation. The crevasse depth range from 2 to 10 m takes more than 70% every year, with the remaining 30% greater than 10 m and smaller than 56 m. The area of large rift in the right side along the ice shelf advancing showed an increasing trend (4.05 to 19.4 km2) from 1989 to 2003 and a decreasing trend (19.05 to 17.6 km2) from 2003 to 2009. However, a large rift in the left side along the ice shelf advancing occurred at about 2002 and the area increased to 11.38 km2 at the end of 2009. Deep crevasses on the surface and expansion of the central large rift made the Mertz Ice Shelf fragile and disintegrated after collision by an iceberg.
Ground-penetrating radar surveys and ice volume estimates of Wedel Jarlsberg Land glaciers, Svalbard
Francisco J. NAVARRO, Alba MARTÍN-ESPAÑOL, Jaime OTERO, Javier J. LAPAZARAN, Evgeny V. VASILENKO, Mariusz GRABIEC
Corresponding author: Francisco J. Navarro
Corresponding author e-mail: firstname.lastname@example.org
We present volume calculations, with detailed error estimates, for eight glaciers on Wedel Jarlsberg Land, southern Spitsbergen, Svalbard, and compare them to those obtained from area–volume scaling relationships. The volume estimates are based upon a dense net of GPR-retrieved ice thickness data collected over several field campaigns spanning the period 2004–2011. The total area and volume of the ensemble are 502.9 ± 18.6 km2 and 80.72 ± 2.85 km3, respectively. Excluding Ariebreen (a tiny glacier <0.4 km2 in area), the individual areas, volumes and average ice thicknesses lie within 4.7–141.0 km2, 0.30–25.85 km3 and 64–183 m, respectively, with a maximum recorded ice thickness of 619 ± 13 m in Austre Torellbreen. To estimate the ice volume of small non-echo-sounded tributary glaciers, we used a function providing the best fit to the ice thickness along the centre line of a collection of such tributaries where echo soundings were available and assuming parabolic cross sections. We did some tests on the effect on the measured ice volumes of the distinct radiowave velocity (RWV) of firn as compared with ice and cold versus temperate ice, concluding that the changes in volume implied by such corrections were within the error bounds of our volume estimate using a constant RWV for the entire glacier inferred from common midpoint measurements on the upper ablation area.
Modelling Nordaustlandet’s ice-caps
Martina SCHÄFER, Rupert GLADSTONE, Thomas ZWINGER, Dorothée VALLOT, Yongmei GONG, Veijo POHJOLA, Rickard PETTERSSON, Thorben DUNSE, Tazio STROZZI, Marco MÖLLER
Corresponding author: Rupert Gladstone
Corresponding author e-mail: email@example.com
Nordaustlandet is the second largest island in Svalbard and has two ice caps: Austfonna and Vestfonna. For present-day and near-future simulations Vestfonna and Austfonna can be modelled separately since they are currently not connected. Both feature fast-flowing outlet glaciers, many of which are known to exhibit surge behaviour. The outlet glaciers Franklinbreen of Vestfonna and Basin 3 of Austfonna ice cap have increased in velocity dramatically since 1995. The ability to simulate surging behaviour is essential in order to carry out accurate quantitative future projections. We use the Elmer/Ice full-Stokes model for ice dynamics to infer spatial distributions of basal drag for pre-melt time periods in 1995, 2008 and 2011 with a Robin inverse method which is based on minimizing discrepancy between modelled and observed surface velocities, using satellite-based velocity fields. We generate steady-state temperature distributions for the three time periods. Frictional heating caused by basal sliding contributes significantly to basal temperatures of the outlet glaciers, a key feature of surge behaviour. Firn heating is important in the upper part of the ice at the thicker central parts. We present sensitivity experiments that are of importance for future prognostic simulations. The observed large differences in basal drag for our three datasets highlight the potential weakness of future projections initialized with basal drag fields and kept constant through the simulation. Sensitivity experiments consisting of transient simulations under present-day forcing demonstrate that using a temporally fixed basal drag field obtained through inversion can lead to significant errors in the thickness change. Hence it is essential to incorporate in a model for future projection the evolution of basal processes governing outlet glacier speed. Informed by a combination of our inverse method results and previous studies, we hypothesize a system of processes and feedbacks involving till deformation and basal hydrology to explain both the summer speed-up and the ongoing pre-melt speed-up. Century-length prognostic simulations addressing the sensitivity to the used basal drag distribution and the coupling to a surface mass-balance model will also be presented.
Proxies in Antarctic ice cores of climate change over the southern Indian Ocean: a review
Corresponding author: Cunde Xiao
Corresponding author e-mail: firstname.lastname@example.org
Several shallow ice cores were retrieved from the Chinese Antarctic traverse route (Zhongshan to Dome A) of the International Trans-Antarctic Scientific Expedition (ITASE) program. These ice cores cover time periods from decades to thousands of years. Ice cores from the coastal and medium-altitudinal terrains of the ice sheet contain promising climatic proxies. For example, water stable isotopes from the DT001 ice core indicate changes of sea surface temperature (SST) over the north ocean of Prydz Bay, southern Indian Ocean (SIO). Sea salts from the ice core are a reliable proxy of sea-level pressure (SLP) of high SIO. Methylsulfonate (MS–) and sodium (Na+) in the LGB69 ice core are indicators of sea-ice extent (SIE) over the SIO sector. Quantitatively, SIE is a function of MS– (Na+) and meridional wind strength. Three modes of Antarctic climate, i.e. Southern Annular Mode (SAM), Trans-Polar Index (TPI) and Antarctic Circumpolar Wave (ACW), are identified using proxies in ice cores from the coastal regions. Records in other ice cores from the SIO sector of the ice sheet (such as Law Dome) also support some aspects of the above results.
Past and future glacier change in the Southern Alps, New Zealand
Brian ANDERSON, Andrew MACKINTOSH, Christian ZAMMIT, Johannes OERLEMANS
Corresponding author: Andrew Mackintosh
Corresponding author e-mail: email@example.com
Glaciers in the Southern Alps last reached a maximum stand in the late 1800s. Since that time, many of the larger glaciers have lost kilometers of length and hundreds of metres of ice thickness. This ice loss has been the result of warming estimated between 0.7 and 1 K. To assess the overall ice volume loss since the late 1800s, and estimate future glacier volume loss given various climate change scenarios, we use a coupled mass-balance/ice-flow model. To start, an equilibrium state at the late 1800s position is generated by imposing a cooling of 0.8 K from the 1980–2010 mean temperature. Historic maps and geomorphic evidence are used to tune the uncertain precipitation distribution to achieve a good match between observed and modelled extent. Owing to the present-day glacier imbalance, a ‘dynamic calibration’ is carried out where the temperature forcing is progressively warmed from late-1800s to present-day values. During the 100 years between the ‘1990s’ (1980–2000) and the ‘2090s’ (2080–2100) the warming in the central Southern Alps, based on the A1B, A2 and A1FI emissions scenarios and a downscaled 12-model GCM ensemble average, is estimated to be between 2.0 and 2.8 K, with a concurrent increase in precipitation of 10–15%. These future warming scenarios are then imposed upon the model glaciers. Preliminary results show that, in the central part of the Southern Alps, ice volume decreased from 53 km3 in the late 1800s to 40 km3 by 1980. Projected warming and precipitation increases result in a modelled ice volume of between 16 km3 (A1FI) and 20 km3 (A1B) by 2100.
Evaluation of parameter transferability using an enhanced temperature-index model for glacier melt in the tropical Andes
Pablo FUCHS, Yoshihiro ASAOKA, So KAZAMA
Corresponding author: Pablo Fuchs
Corresponding author e-mail: firstname.lastname@example.org
This paper discusses the applicability of an enhanced temperature-index melt model in glaciers with different physiographic and/or climatic characteristics (e.g. orientation, size, precipitation regimes) using a set of parameters determined at a location to estimate the hydrological response at a different location, in an exploration to find general insights into the functioning of glaciated basins. In this model, melt is computed based on precipitation, temperature, global radiation and albedo (broadly defined as the ratio of reflected to incoming shortwave radiation) as input variables and two parameters, namely the temperature factor and the shortwave radiation factor. Water originating from the glacier-free area is reduced by a runoff coefficient. A preselected critical temperature is used to decide the phase of precipitation as solid precipitation or rainfall. Glacier melt and rain water are routed to the outlet of the hydrological basin using a single non-linear store controlled by a recession coefficient. The basin is subdivided into hydrologic response units (HRU) based on elevation (i.e. elevation bands delineated at intervals of about 250 m) for which the input variables are extrapolated. Firstly, we derived model parameters using meteorological forcing and discharge data from the well-studied Zongo Glacier. Secondly, we tested a parameterization to estimate the temporal and spatial variations of albedo in the ablation zone. Thirdly, we incorporated the albedo parameterization into the model scheme and, finally, we applied the model to a nearby glacier using the predetermined set of parameters to evaluate model transferability in the region.
Estimated ICESat inter-campaign bias and its impact on the determination of ice-sheet mass balance
Donghui YI, H. Jay ZWALLY, John W. ROBBINS, Jun LI, Jack L. SABA, Jinlun ZHANG
Corresponding author: Donghui Yi
Corresponding author e-mail: email@example.com
ICESat operated for 18 campaign periods from March 2003 to October 2009. Most of the operational periods were between 34 and 38 days long. Because of laser failure and orbit transition from 8 day to 91 day orbit, there were four periods lasting 57, 16, 23 and 12 days. Owing to laser characteristic changes (three different lasers, laser energy decreasing with time, the changes in laser pulse shape and beam pattern, etc.), there are range biases (D) between ICESat campaign periods. The long-term trend of the inter-campaign biases (dD/dt) directly affects the derived ice-sheet mass-balance results. In this study, we used the ICESat measured mean sea level over the sea-ice-covered Arctic Ocean to estimate ICESat inter-campaign biases and evaluate the impact of the inter-campaign biases on ice-sheet mass balance. The mean sea level was calculated by averaging the elevation of the leads (open water and thin ice) within the Arctic Ocean sea-ice pack, with waveform saturation correction, inverse barometer correction, dry and wet troposphere corrections, and tidal corrections applied. The ocean dynamic topography effect was also evaluated. We adjusted the derived D by a trend of 0.31 ± 0.07 cm a–1 to account for the current rate of sea-level rise. The resulting mean inter-campaign bias trend (dDsl/dt) from September 2003 to November 2008 (the four full year period of ICESat’s 91 day orbit operation) is –1.60 ± 0.77 cm a–1. Converting this to a volume change rate (dV/dt), we get about 28 km3 a–1 for Greenland and about 198 km3 a–1 for Antarctica. Comparing ICESat elevation profiles over Lake Vostok, Antarctica, with ERS elevation profile over the same region, the bias-corrected ICESat profiles show more consistency than the profiles with no bias correction. The ICESat data used in this study are release version 633 with transmitted pulse Gaussian/Centroid peak location correction (G-C) applied.
Mountain glaciers of the south of eastern Siberia: current state and changes since the Little Ice Age
Eduard OSIPOV, Olga OSIPOVA
Corresponding author: Eduard Osipov
Corresponding author e-mail: firstname.lastname@example.org
Modern glaciers of the south of eastern Siberia are located on the three high-mountain ridges of the Baikal rift zone (East Sayan, Baikalsky and Kodar). The last detailed investigations of the glaciers based on aerial pictures are dated to the mid-1950s. In this study we present the regional glacier inventory based on GIS mapping derived from high- to moderate-resolution satellite imagery (Landsat 7 ETM+, Cartosat-1, QuickBird-2, WorldView-1) of 2001–2009 and field investigations of 2006–2012. The inventory includes about 50 glaciers with sizes ranging from 0.1 to 1.3 km2. These are mainly cold base cirque and cirque-valley glaciers with a large proportion of snow redistribution (avalanches, wind scores) in annual accumulation during spring seasons. The most recent maximal ice extent has been delineated from terminal moraine complexes. Likhen thalli diameter measurements allowed us to attribute the moraines to the final phase of the Little Ice Age (LIA). Total shrinkage of glacier areas from the end of the LIA is estimated to be 49–58% in different areas. Comparison with previous inventory data suggests irregular wastage over the 20th century. The maximal rate of glacier reduction occurred during 1960–1990s. Analysis of meteorological data suggests good correlation between glacier wastage and increasing summer air temperature for that interval. Mass-balance modeling performed for separate glaciers demonstrates a prominent negative trend of cumulative balance since the 1960s, with short-term intervals of stabilization. However during the last decade we observe a slight decrease of summer temperature with reduced deglaciation rate. This study was supported by the Russian Foundation for Basic Research (project No. 11-05-00713) and the Department of Earth Sciences of the Russian Academy of Sciences (project No. 12.11).
Remote-sensing approaches to construct calibration and validation datasets for glacio-hydrological modeling in a data-sparse debris-covered basin, Langtang Khola, Nepal
Evan MILES, Ian WILLIS, Neil ARNOLD, Francesca PELLICCIOTTI
Corresponding author: Ian Willis
Corresponding author e-mail: email@example.com
Glacier retreat in response to climate warming changes the pattern and timing of meltwater production, routing and storage, resulting in substantial changes to the hydrographs of glaciated basins. Glacio-hydrological modeling has been successfully applied to assess these changes, particularly for study sites with a good record of high-quality input data including climate, hydrologic and glacier extent records. However, the communities most vulnerable to changes in glacier discharge are often situated downstream of glaciers with unreliable or broken environmental records. This is evident in High Mountain Asia, which supplies water to over one-quarter of the world’s population, but combines several glaciological challenges: high climate variability, lack of historic data, uncertainties in climate change and glacier response, and numerous debris-covered glaciers. This research applies remote-sensing analyses of readily available datasets to generate additional calibration and validation datasets for glacio-hydrological modeling in the ~100 km2 Langtang Khola basin of Nepal. Particular data needs addressed presently are twofold: snow-cover records for melt model calibration and glacial lake area and volume for hydrologic model validation. All Landsat scenes (all sensors) covering the basin are accessed and a subset of these are selected for further analysis based on cloud cover. These images are then orthorectified using the CGIAR-CSI SRTM4.1 digital elevation model and converted to surface reflectance using the LandCor MATLAB implementation of the 6S atmospheric correction model, creating a long-term record of imagery with similar radiometric parameters. ETM+ data are pan-sharpened using a principal component approach to improve feature resolution. This record is then used to calculate NDSI, NDWI and band ratios. The combination of these indices and the surface reflectance data is classified using an unsupervized migrating-means algorithm for each sensor type (across the many records for each sensor) to distinguish between vegetation, rock/debris, snow/ice, water over debris and water over ice/frozen water. A maximum likelihood supervized classification is also run for a subset of images for each sensor to assess the misclassification of the images seasonally. The resulting historical snow and glacial lake datasets are limited to the temporal resolution of Landsat sensors (16 and 18 days) at the very best. Still, these data products allow a glacio-hydrological model to be run with fewer simplifying assumptions and to improved accuracy, and will enable a more rigorous analysis of the glacio-hydrological system for debris-covered glaciers.
Reconstruction of the annual mass balance of Chhota Shigri Glacier, Lahaul and Spiti valley, western Himalaya, India, since 1969
Mohd Farooq AZAM, Patrick WAGNON, Christian VINCENT, Alagappon RAMANATHAN, Anurag LINDA, Virendra Bhadur SINGH
Corresponding author: Mohd Farooq Azam
Corresponding author e-mail: firstname.lastname@example.org
A recent study showed the balanced conditions or slight mass gain of glaciers in the Lahaul and Spiti region (northern India, Himalaya) during the 1990s preceded recent mass loss. The present study is an attempt to reconstruct the mass balance of a regional benchmark glacier, Chhota Shigri Glacier, and to understand the regional climatic forcing responsible for the evolution of this glacier over the last four decades. The annual mass balance of Chhota Shigri Glacier is simulated by a classical degree-day approach since 1969 using daily air temperature and precipitation records from the nearest meteorological station at Bhuntar airport, Kullu (1092 m a.s.l., 50 km SW of Chhota Shigri Glacier) as input data. Temperature lapse rates and precipitation gradients between Bhuntar airport and the glacier were derived using direct measurements performed at the elevations of the glacier (an automatic weather station has been operated since August 2009 at 4863 m a.s.l. on lateral moraine, whereas accumulation measurements were performed at 5550 m a.s.l.). Degree-day factors for ice, snow and debris-covered glacier have been computed by comparing measured ablation at different altitudes at the glacier surface with cumulative positive temperatures (more than 500 measurements between 2009 and 2012). The model is calibrated against 10 years of annual point mass-balance measurements made at ~28 sites on the glacier between 2002 and 2012 and decadal cumulative mass balance between 1988 and 2010. Based on the observed simulated results, the mass-balance trend over Chhota Shigri Glacier can be divided into two deficit periods (1969–1985 and 2000–2012) with considerable mass loss and one near-steady-state period (1986–1999) when the glacier mass balance remains close to zero. The climatic causes that explain the near steady state over the period 1986–1999 are also analyzed.
Large-scale teleconnections as recorded in climate records of low- to mid-latitude mountain glaciers
Lonnie G. THOMPSON, Tandong YAO, Ellen MOSLEY-THOMPSON, Ping-nan LIN
Corresponding author: Lonnie G. Thompson
Corresponding author e-mail: email@example.com
Glaciers serve as recorders and early indicators of climate change. For 35 years our research team has recovered ice-core records of climatic and environmental variations from both polar regions and from low- to mid-latitude high-elevation ice fields. Tropical records covering the last 25 000 years allow comparison of glacial stage conditions in the tropics with those of the polar regions. High-resolution records of δ18O (in part a temperature proxy) demonstrate that the current warming at high elevations in the mid- to lower latitudes is unprecedented for at least the last two millennia, although the early Holocene appears much warmer at many sites. The warming observed across the Third Pole since 1920 and in Eastern and Western Hemisphere isotopic records from 1500 CE to the present argue that δ18O is not heavily influenced by local precipitation and that hydrologic influences retained from the lowland regions upwind may be very important. The remarkable similarity between changes in the highland and coastal cultures of Peru and climate variability, especially with regard to precipitation, implies a strong connection between prehistoric human activities and climate in this region. Ice cores retrieved from shrinking glaciers around the world confirm their continuous existence for hundreds to thousands of years, suggesting that the climatological conditions dominating those regions today are different from those under which these ice fields originally grew and have been sustained. The current warming is therefore unusual when viewed from both the millennial-scale perspective provided by multiple lines of proxy evidence and the 160-year perspective from direct temperature measurements. The ongoing widespread melting of high-elevation glaciers and ice caps, particularly in low to middle latitudes, provides strong evidence that a large-scale pervasive and, in some cases, rapid change in Earth’s climate system is underway. Recent isotopic enrichment and accelerating glacier retreat are consistent with IPCC projections for enhanced warming at high elevations in the low latitudes. The history and fate of these ice caps, many on some of the world’s most remote mountain tops, provide a global perspective of climate change by highlighting observations of 20th and 21st century glacier shrinkage in the Andes, the Himalaya, on Kilimanjaro in Africa and on glaciers near Puncak Jaya in Indonesia (New Guinea). Carbon-14 dating of wetland plants collected between 2002 and 2011 along the retreating margins of Quelccaya ice cap indicate that it has not been smaller than today in ~6000 years.
Feedbacks of Greenland ice sheet in a warmer climate as simulated by EC-EARTH coupled with an ice-sheet model
Shuting YANG, Marianne S. MADSEN, Synne H. SVENDSEN, Guðinna AÐALGEIRSDÓTTIR, Chistian RODEHACKE
Corresponding author: Shuting Yang
Corresponding author e-mail: firstname.lastname@example.org
A newly developed global climate model incorporated with an ice-sheet model is used to investigate the feedbacks of the Greenland ice sheet to the climate system. The model system consists of the atmosphere, ocean and sea-ice model system EC-EARTH coupled with the Parallel Ice Sheet Model (PISM). The coupling of the PISM includes a modified surface physical parameterization adapted to the land ice surface over glaciated regions in Greenland. To ensure the conservation of mass and energy, the surface mass balance (SMB) accounting for the precipitation, the surface evaporation and the melting of snow and ice over land ice are computed inside the EC-EARTH atmospheric module. The PISM, forced with the above EC-EARTH-simulated surface mass balance and surface temperature, provides, in turn, basal melt, ice discharge and ice cover (extent and thickness) as boundary conditions to EC-EARTH. The Greenland ice sheet is initialized using PISM with the standard paleo-climatological spin-up followed by forcing of the EC-EARTH preindustrial climate to reach an equilibrium state with the model preindustrial climate. The EC-EARTH/PISM system is integrated under the preindustrial condition until it has reached the quasi-stationary state for a considerably long period (control experiment). To study the interaction of the Greenland ice sheet, simulations for warm climate scenarios are performed and analyzed. In particular, an experiment with an idealized 1% CO2 per year increase from the atmospheric CO2 at preindustrial level to four-times CO2 is performed for 300 years (i.e. stabilized at 4×CO2 for 160 years). The evolution of the Greenland ice sheet under the warm climate and its impacts on the climate system are investigated and compared with that in the control run. Freshwater flux from the Greenland ice sheet melt and discharge to the North Atlantic basin and its role in the change of the strength of the North Atlantic Meridional Overturning Circulation are analyzed. The regional climate changes associated with the dynamic and thermodynamic effect of the Greenland ice sheet change are also quantified.
Subaqueous melting of Store Glacier, West Greenland, from three-dimensional high-resolution numerical modeling
Yun XU, Eric RIGNOT, Dimitris MENEMENLIS, Ian FENTY
Corresponding author: Yun Xu
Corresponding author e-mail: email@example.com
Greenland tidewater glaciers dominate the total ice discharge from Greenland to the ocean and many of them have accelerated as warm subsurface water intruded the glacial fjords. Subaqueous melting at the calving front is a potential trigger for glacier acceleration. Here, we present three-dimensional high-resolution (1 m grid spacing) simulations of ice melting at the calving face of Store Glacier, a major tidewater glacier in central West Greenland, using the Massachusetts Institute of Technology general circulation model (MITgcm). We compare the model results with an estimate of ice melt derived from oceanographic data. The model simulations replicate the turbulent upwelling and spreading of the freshwater-laden plume along the ice face and the vigorous melting of ice at rates of several meters per day. The simulated summer melt rate is close to the melt rate calculated from the oceanographic data. Melting is most pronounced at depth, in the region above the subglacial channel. Melt rates increase below linear with the subglacial water flux and above linear with ocean thermal forcing, but the sensitivity to these forcings decreases for high subglacial flow regimes. This subglacial water is the direct result of surface runoff in the glacier drainage basin. Our simulations therefore indicate that an increase in surface runoff will increase the melting of the glacier ice faces by the ocean. This will occur even in the absence of changes in ocean temperature.
Recent dust activity under global warming on the Tibetan Plateau: evidence from the Tanggula ice core
Guangjian WU, Tandong YAO, Baiqing XU, Chenglong ZHANG, Ninglian WANG
Corresponding author: Guangjian Wu
Corresponding author e-mail: firstname.lastname@example.org
The dustiness on the remote Tibetan Plateau and its trend within the ongoing global warming perspective are not well understood. In this study, we present the detailed dust history from AD 1850 to 2004 on an annual timescale from a shallow ice core from Tanggula, central Tibetan Plateau. Two periods of strong dustiness, one at the end of the Little Ice Age (1860–1874) and the other during the period 1930–1954, occurred during low oxygen isotope stage, which is correlated with temperature on multi-year and decadal timescales. The extremely high level of dust flux between 1860 and 1874 was unique – this level has not occurred again during the past century and the dustiness of the 1930s was characterized more by strong wind and dust storms rather than drought, as shown by the great grain size but low dust flux. We have used the composite analysis of modern meteorological data to study the possible dustiness mechanism and found that strengthened high-level westerlies over the Tibetan Plateau and intensified low-pressure activities in the upward potential source regions, such as the Tarim basin, are the possible causes for high dust flux in Tanggula. Those results have revealed that although the dustiness on the Tibetan Plateau normally occurs in cold conditions, pronounced warming since the 1960s can change the dust pattern and strengthen the dustiness in this remote and high-altitude region and can thus induce associated environmental issues by creating dustier conditions.
contrast analysis of glacial retreat between Ürümqi Glacier No. 1 and central Tuyuksu Glacier, Tien Shan, central Asia
Guofei ZHANG, Zhongqin LI, Wenbin WANG, Huilin LI
Corresponding author: Guofei Zhang
Corresponding author e-mail: email@example.com
Under the impact of climate warming, the majority of glaciers in central Asia have been experiencing a negative glacial mass balance and have been retreating rapidly in the past five decades. As the available ‘reference’ glaciers, Ürümqi Glacier No. 1 and Central Tuyuksu Glacier provide the longest glaciological monitoring record. Based on continuous long-term observation data, we analyse the variations and differences of the two glaciers. Results show that mass balance decreased rapidly, ELA ascended endlessly, AAR decreased continually and area reduced significantly. Mean annual mass balances are –0.286 m w.e. for Ürümqi Glacier No. 1 and –0.385 m w.e. for Central Tuyuksu Glacier. The cumulative mass balances are –14.9 m w.e. in 1959–2010 for Ürümqi Glacier No. 1 and –20.8 m w.e. in the period 1957–2010 for Central Tuyuksu Glacier. The average ELA and AAR for the two glaciers are 4067 m a.s.l. and 46% (Ürümqi Glacier No. 1) and 3823 m a.s.l. and 41% (Central Tuyuksu Glacier). Statistical analysis showed that the steady-state ELA0 and equilibrium-state AAR0 are 4018 m a.s.l. and 56% (Ürümqi Glacier No. 1) and 3740 m a.s.l. and 54% (gentral Tuyuksu Glacier). Comparisons demonstrate that Central Tuyuksu Glacier has a high fluctuation range and its melting is greater than Ürümqi Glacier No. 1, but its continental characteristics are weaker than Ürümqi Glacier No. 1, which implies that the sensitivity of Central Tuyuksu Glacier to climate change is more intense than Ürümqi Glacier No. 1. We attribute these discrepancies to the distance from moisture source and the variability of the micro-climate – these may be related to the predominant orientation of the mountain range, as well as the altitude and surface morphology of the glacier itself.
Accelerated mass loss of Ürümqi Glacier No. 1 in eastern Tien Shan, China
Guofei ZHANG, Zhongqin LI, Huilin LI, Wenbin WANG
Corresponding author: Guofei Zhang
Corresponding author e-mail: firstname.lastname@example.org
As the best monitored glacier in China, Ürümqi Glacier No. 1 (43°08' N, 86°82' E) has experienced an accelerated mass loss in the period 1997–2010. According to the observed record, the mean annual mass balance declined from –0.14 m w.e. a–1 in 1959–1996 to –0.69 m w.e. a–1 in 1997–2010, which has increased by almost five times, and the extreme values are 63 mm (2009) and –1327 mm (2010). Averaged winter balance is from 0.45 m w.e. a–1 to 0.10 m w.e. a–1 and summer balance is from –0.60 m w.e. a–1 to –0.73 m w.e. a–1. The cumulative mass balance is from 5.2 m w.e. during the period 1959–1996 to 9.7 m w.e. in 1997–2010 (this is rather unfavorable for glaciers), the 14 year mass loss accounting for 65% of the total mass losses during the past 52 years. On average the glacier ELA is 4046 m a.s.l. in 1959–1996, 4125 m a.s.l. in 1997–2010 and the highest ELA observed in 2010, overstepping the glacier summit. Glacial area reduced by 5.6% during 1959–1996 and 10% in 1997–2010. Between those two periods, there was a 1°C increase in air temperature and a 19% increase in precipitation observed at a vicinal meteorological station. We analyse the current trends in glacial mass balance and how their evolution is affected by the climate changes. We attribute the accelerated mass losses to a combination of decreased winter balance and strongly increased melt. The increasing melt is associated with higher summer temperature, and the decreased winter balance is attributed to the rising temperatures in winter, despite the increase in annual precipitation during the last 14 years.
Variations in the equilibrium-line altitude of Ürümqi Glacier No. 1, Tien Shan, over the past 50 years
Corresponding author: Zhiwen Dong
Corresponding author e-mail: email@example.com
Glacier equilibrium-line altitude (ELA) is one of the important parameters reflecting climate change. Based on observations of the ELA of Ürümqi Glacier No. 1 in the Tien Shan, we established a statistical model between ELA and its major influencing factors, warm season air temperature (air temperature averages for May, June, July and August) and annual precipitation. Results showed that warm season air temperature was the leading climatic factor influencing ELA variations. The glacier ELA ascends (descends) 61.7 m when warm season air temperature increases (decreases) by 1°C, and ascends (descends) 13.1 m when cold season precipitation decreases (increases) by 10%. In the period 1959–2008, the glacier ELA showed a general increasing trend, ascending108 m and reaching its highest altitude in 2008 at 4168 m a.s.l., close to the glacier summit. If future climate is similar to that in the past 50 years, the ELA of Ürümqi Glacier No. 1 will still ascend with a speed of 2.16 m a–1. However, if future climate is similar to that in the period 2000–2008, the ELA will still ascend with a speed of 6.5 m a–1 before it is stable. As a result of ELA variation, the accumulation area ratio (AAR) of the glacier showed a decreasing trend during the past 50 years.
Application of GIS and RS in the area of China’s mountain glaciers
Baojuan HUAI, Zhongqin LI
Corresponding author: Zhongqin Li
Corresponding author e-mail: firstname.lastname@example.org
The use of remote-sensing data for glacier monitoring is an effective way for the dynamic change of China’s glaciers to provide timely, accurate and inexpensive data. The content of this thesis is divided into two parts: the comparison of traditional methods of remote-sensing image extraction of glacier information with object-oriented information extraction methods; application of topographic map DEMs and SRTM4 to calculate the relative thickness of the glacier change. This study looked at two typical continental glacier areas: the Kanas headwater region and the Qilian Heihe Hulugou watershed. In the Kanas headwater region, integrated visual interpretation and computer automatic interpretation, glacier interpretation of traditional methods and object-oriented image feature extraction methods are applied to glacier boundary extraction. Ice volume is the most direct parameter of glacier water resource change and the core problem of estimating ice volume is the measurement of the thickness, so calculating the thickness of the Heihe Hulugou watershed in the past 50 years enables estimation of glacier change in the Heihe river basin. In this paper, the main results are as follows. (1) We used the traditional interpretation of remote-sensing methods and object-oriented interpretation to extract glacier boundary information for the Kanas headwater region. We found that visual interpretation of high precision, although time-consuming and labor-intensive, was applicable to any type of glacier. Automatic interpretation of traditional computer methods has advantages and disadvantages: the threshold method is simple, but the effect is not obvious distinction; the NDSI method is more accurate than the threshold method, but the results are also unsatisfactory; the unsupervised classification method has low accuracy; the supervised classification method is accurate and significantly has higher accuracy than the unsupervised classification, but some snow and rock are likely to be misclassified; and the band ratio method is relatively simple and has high precision. An automatically generated decision tree can avoid subjectivity compared with an artificially generated decision tree, the method cannot identify errors in the sample data, has apparent misclassification; the object-oriented method is able to extract a variety of surface features which have a characteristic type, and this method has higher accuracy. (2) The emergence of multi-source DEM data makes it possible to obtain glacier thickness. Using topographic map DEM and SRTM-DEM data to study changes in glacier thickness leads to more precise study of glacier change with the shift from two-dimensional to three-dimensional.
Glacier changes in the Kuitun River basin, Tien Shan, and its effect on water resources during the last 40 years
Lin WANG, Zhongqin LI, Huilin LI
Corresponding author: Lin Wang
Corresponding author e-mail: email@example.com
Fluctuations in the size of glaciers are widely recognized as an important indicator of climate change. In arid and semi-arid regions, especially in northwest China, glacier runoff is the main contributor to water resources that are used to support the sustainable development of the environment, industry and agriculture. Kuitun River basin is located on the north slope of the western Tien Shan and southwest of the Junggar basin. It is surrounded by mountains to the north, west and south. There is a typical temperate arid continental climate, with the mountain–oasis–desert system having the typical characteristics of temperate arid ecology. The glacier melt runoff of this region has played a significant role in the economic development of Xinjiang. During the past 40 years, the ecology and environment of the Kuitun River basin have seriously degenerated due to the impacts of natural causes and human activities. The aim of this study is to evaluate glacier fluctuations and analyze the causes of the glacier changes in the Kuitun River basin. Fluctuations of the glaciers for the past four decades were reconstructed from historical documents, aerial photographs and remote-sensing data. The results show the total area of the studied glaciers in the Kuitun River basin decreased by 15.4% of the 1964 value, from 87.06 to 73.69 km2, over 40 years (0.4% a–1). The maximum area loss occurred in the 0.1–0.5 km2 size class, which decreased in total area from 17.1 to 11.4 km2, or 33.5%. According to the statistics of glacier area reduction at the 18 elevation gradients, glacier area decrease percentage reduces with increasing altitude. Ablation occurs mainly below 4200 m, with a combined area reduction of 12.29 km2, or 91.9% of the total. The other seven gradients, above 4200 m a.s.l., have a total area reduction of only 1.08 km2, or 8.1% of the total. Glacial ablation in the Kuitun River basin tends to be strong, and water resources in this region are deteriorating. Glacier melt runoff in this region played a significant role in the economic development of Xinjiang.
Major river basin glacier systems of the Hindu Kush–Himalaya and Aral Sea region: climate change sensitivity and likely changes towards the end of the 21st century
Oxana S. SAVOSKUL, Vladimir U. SMAKHTIN
Corresponding author: Oxana S. Savoskul
Corresponding author e-mail: firstname.lastname@example.org
The study presented here is based on the comprehensive assessment of climate change impact on glacier systems in the Indus, Ganges, Brahmaputra, Amu Darya, Syr Darya and Mekong river basins in the past 50 years. Climate change between baseline (1961–1990) and current (2000–2010) periods is assessed using gridded monthly climatologies for air temperature and precipitation with a resolution of 0.5–0.5°. The changes between baseline and current states of glacier systems are evaluated using all existing glacier inventories, data of the World Glacier Monitoring Service and a wide range of published studies based on remote sensing. It is illustrated that glacier-covered area in the study basins has reduced by 14–29% in the past 50 years. Glacier system sensitivity to climate change is defined here as the critical warming signal required for the complete disappearance of glaciers in a basin. It is illustrated that at the scale of major river basins, it depends mainly on the structural diversity of a glacier system, which is analyzed using size-class frequency distributions of glacier numbers, ice-covered area, ice volume and, where available, the data on variability of ELA and maximum and minimum glacier elevations. It is shown that glacier system in the Indus River basin is likely to disappear only under an air temperature rise of 13–15°C compared with its baseline value. In the Ganges, Brahmaputra and Amu Darya basins, a warming of 10–12°C will be required to melt down all the glaciers; in the Amu Darya basin, it is 6–8°C. Under a warming signal of 4–5°C, i.e. by the end of the 21st century, only Syr Darya and Mekong basins are likely to become glacier-free. In the Indus, Ganges, Brahmaputra and Amu Darya river basins, only glaciers belonging now to the large and medium size classes (i.e. larger than 10 km2) can be expected to survive the warming of 4–5°C, with total basin glacier area reduced by 70–90% and total basin ice reserves reduced by 50–80% relative to 1961–1990.
210Pb dating of the Miaoergou ice core from the eastern Tien Shan, China
Chaomin WANG, Shugui HOU, Hongxi PANG, Yaping LIU, Heinz Walter GAEGGELER, Leonhard TOBLER, Sonke SZIDAT, Edith VOGEL
Corresponding author: Shugui Hou
Corresponding author e-mail: email@example.com
Ice-core dating is the first step in ice-core research and is also the fundamental standpoint of ice-core research results. Most mountain glaciers are located in densely populated low-latitude regions, for which ice-core studies can reveal climatic and environmental changes of these regions. Therefore, accurate determination of the age of the ice core should be the premise and foundation of the study. In this paper, we attempt for the first time to use 210Pb to date the Miaoergou ice core drilled from the eastern Tien Shan, China. On the basis of 210Pb dating method, the age of the Miaoergou ice core at 35 m w.e. depth is 154 ± 6 years BP. The surface activity concentration of 210Pbex is about 400 mBq kg–1, which is higher than those observed at nearby continental sites. This means that the concentration of 222Rn in air and 238U in soil around Miaoergou must be high, as this is the source of 210Pb. The average annual net accumulation rate is 210 mm w.e. a–1. The glacial meltwater in this area is the major water supply for the oasis city of Kumul, which is the extremely dry region in China. This is the first time the 210Pb method has been used to date the Miaoergou flat-topped glacier in the eastern Tien Shan. This method can also be applied to dating other ice cores drilled from the mountains of western China.
Impact of ice cover on phytoplankton biomass, aerosol optical depth and North Atlantic Oscillation in the Greenland Sea
Bo QU, Gabric J. ALBERT, Hehe LI, Hailang LU
Corresponding author: Bo Qu
Corresponding author e-mail: firstname.lastname@example.org
Arctic sea ice will decline through the 21st century. This will have great impact on the Arctic ecosystems, hence the region and global climate. We used satellite data to study the temporal and spatial coherence between ice cover (ICE), chlorophyll _a (CHL) (a proxy for algal biomass), aerosol optical depth (AOD) (related to the atmospheric burden of aerosol) and North Atlantic Oscillation (NAO) in the Greenland Sea (20° W–10° E, 70°N–80° N) during 2003–2012. The influences of ice cover to CHL, AOD and NAO were determined. In general, the peak of ICE was in March. ICE began to melt until September. The polar front was located in the region 70° N–75° N where ICE was almost totally melted. The region 75° N–80° N was our focus area for the correlation study. ICE, CHL, AOD and NAO were correlated with a time lag. In general, ICE reached a peak 3 months ahead of CHL. When ice started melting, CHL started to increase. The melting ice contributed ice algae for the growth of phytoplankton biomass. ICE had an influence on AOD with a 1 month time lag ahead of AOD. EViews statistical software was used to conduct lag regression analysis and then cointegration analysis was carried out. There was cointegration between CHL and ICE and AOD and ICE, which means that they both had a long-term equilibrium relationship. NAO and melting ice had a positive correlation, melting ice lagged 3 months behind NAO, which explained why NAO had an influence on ICE. CHL and NAO had negative correlations. This research provides a valuable reference for the polar ecosystem and global climate predictions.
Development of an ice thickness model over the southern extremity of the Amery Ice Shelf and re-assessment of the mass budget of Lambert Glacier basin
Jiahong WEN, Long HUANG, Fan YANG, Weili WANG, V. Damm
Corresponding author: Jiahong Wen
Corresponding author e-mail: email@example.com
The previous results of mass budgets of the Lambert Glacier basin differ greatly due mainly to the ice thickness data from different sources and approaches (e.g. Wen and others, 2007; Yu and others, 2010). In this paper we use a geographic information system environment to combine the ice thickness data from the BEDMAP project and the PCMEGA expedition (the Prince Charles Mountains expedition of Germany and Australia during the Antarctic season 2002/03) to generate a digital ice thickness model (DITM) over the southern extremity of the Amery Ice Shelf and re-estimate the mass budget of Lambert Glacier gasin including Lambert, Mellor and Fisher Glaciers. The DITM shows that the thickest ice up to 2789 m is located at the transition zone from grounded ice to floating ice shelf of the Mellor flowband. The overall ice thickness along the grounding line is slightly larger than that presented by Yu and others (2010) interpolating data from the BEDMAP project, but much smaller than that derived assuming hydrostatic equilibrium (Wen and others, 2007). The ice flux through the southern grounding of the Amery Ice Shelf is 36.6 ± 2 Gt a–1, which is similar to the result of 38.9 ± 2.8 Gt a–1 provided by Yu and others (2010), but much smaller than that of 54.0 ± 5.4 Gt a–1 (Wen and others, 2007). The Lambert Glacier basin is in a positive mass balance.
Vulnerability assessment of areas affected by Chinese cryospheric changes from 1981 to 2000
Yong HE, Yongfeng WU, Qiufeng LIU
Corresponding author: Yong He
Corresponding author e-mail: firstname.lastname@example.org
Using the definition of vulnerability provided by the Intergovernmental Panel on Climate Change, this paper assesses the vulnerability of areas affected by Chinese cryospheric changes from 1981 to 2000. Seven indices are used in the vulnerability assessment: glacial area fraction, interannual variability of permafrost depth, interannual variability of surface snow area fraction, interannual variability of surface runoff, interannual variability of surface temperature, interannual variability of vegetation growth, and interannual variability of the human development index. Assessment results show that the vulnerability index varies from 0.1752 to 0.4731, averaging 0.2644. The areas in the middle and eastern parts of China are less vulnerable compared with western parts and parts of the Tibetan Plateau. Five vulnerable clusters are formed from the four thresholds using the cluster analysis, including the slight-vulnerable area (lower than 0.22), light-vulnerable area (from 0.22 to 0.36), medium-vulnerable area (from 0.36 to 0.56), strong-vulnerable area (from 0.56 to 0.77) and very-strong-vulnerable area (0.77 and above). The slight-vulnerable area distributes in northeastern China and the eastern part of northern China. The areas of medium-vulnerable, strong-vulnerable and very-strong-vulnerable in Tibet are the biggest among the five regions in the studied area. The variation of vulnerability is attributed to the variation of exposure, sensitivity and adaptation to Chinese cryospheric changes.
Recently measured black carbon in the global snow and ice and the trends and implications for the climate
Corresponding author: Ming Jing
Corresponding author e-mail: email@example.com
Black carbon (BC) is thought to be a very important climate-warming agent during these years. Suspended as an aerosol in the atmosphere, it can shield the land surface and cool it, and in the meantime it will heat and warm the high and ambient air over land. Deposited in snow and ice surfaces, it can absorb incoming solar radiation and lower their albedos causing additional warming. In case of the reason for the complex role of BC in the climate, it has always been a highlight in the climate forcings since IPCC TAR. In the voice of request for reducing BC emission, the potential impacts of BC on the survival of ice bodies are still uncertain, including the current melting impact and potential trends. In this work, we will review the global distribution status of BC deposited in snow and ice, assess the impact of BC on the absorption of solar radiation in them, and presume the future trends of the impact of BC on them.
Glacier variations in response to recent climate changes in the Tibetan Plateau and surrounding region
Corresponding author: Tandong Yao
Corresponding author e-mail: firstname.lastname@example.org
The glacier status over the past 30 years was studied by investigating the glacial length change of 82 glaciers, area variation of 7090 glaciers and mass-balance fluctuation of 15 glaciers in the Tibetan Plateau and surrounding region. Results showed that systematic differences in glacier status are apparent from region to region. The most intensive shrinkage occurs in the Himalaya (excluding the Karakorum), which are characterized by the greatest reduction in glacial length and area and the most negative mass balance. The shrinkage generally decreases from the Himalaya to the continental interior and is the least in the eastern Pamir, characterized by the least glacial retreat, area reduction and recent positive mass balance. Recent mass-balance data revealed the fact that except for the possible slight positive mass balance in the eastern Parmir/Karakorum, most glaciers are losing mass and showing an accelerating trend of more negative since the early 1990s. Moreover, the large-scale patterns of precipitation from GPCP and ground measurements were analyzed to explain the mechanism of glacier status pattern. Our results indicates that, in addition to rising temperature, decreased precipitation in the Himalaya and increasing precipitation in the eastern Pamir accompanied by different atmospheric circulation patterns (the weakening Indian monsoon and strengthening westerlies) are probably driving these systematic differences in the Tibetan Plateau and surrounding region.
Synoptic patterns of ablation seasons of Kodar glaciers, East Siberia
Olga OSIPOVA, Eduard OSIPOV
Corresponding author: Olga Osipova
Corresponding author e-mail: email@example.com
Kodar Ridge is located in continental Asia far from the oceans. There are about 35 contemporary glaciers with a total area of about 9 km2 at altitudes of 1800–2700 m a.s.l. This area is characterized by a sparse weather station network; therefore, for meteorological analysis we used data from the nearest Chara WS (located 40 km to the east) and field ablation and temperature measurements in the glaciarized zone during 2009–2012. Analysis of atmospheric circulation patterns over the ridge was performed with using daily synoptic maps and multi-level pressure data of the NCEP/NCAR reanalysis for the summers of 2009–2012. For each day we analyzed peculiarities of the baric field over the study area and revealed the predominant type of baric formation and the parameters of the air mass advection. The relationships between ice/snow ablation and circulation processes in the lower troposphere have been defined. It has been found that ablation periods are characterized by high cyclonic activity, significant air mass variability with frequent presence of frontal weathers. Cyclones are mainly displaced from the south and southeast. Anticyclones tend to move from the west and the south (particularly in August). It has been established that more intensive ablation occurs for circulation type I, defined by the presence of Arctic anticyclone and low-pressure field over eastern Siberia at the 700 hPa level (with heat advection). Minimal ablation is observed for the type II circulation, defined by intense cyclone over northeastern Siberia (up to the 500 hPa level) and entrance of south cyclone (with cold advection at the 850 hPa level). Occurrence of the presented types of atmospheric circulation implies the changes in weather regime and changes in glacier ablation which define further evolution of Kodar glaciers. This study was supported by the Russian Foundation for Basic Research (project No. 11-05-00713).
A glacier velocity measurement method based on hierarchical image matching
Fei YAN, Yi LIU
Corresponding author: Fei Yan
Corresponding author e-mail: firstname.lastname@example.org
Global warming is a pressing problem and glacier velocity can be an indicator of climate change providing the monitoring of glacier changes is scientifically sound. In the current scenarios of climate change, the ongoing trend of worldwide and rapid, if not accelerating, glacier shrinkage on the century timescale is most likely of a non-periodic nature. Such rapid environmental changes require that the international glacier monitoring efforts make use of the swiftly developing new technologies, such as remote sensing and geoinformatics, and relate them to the more traditional field observations. Because satellite images are more readily available than fieldwork, many methods based on image matching to measurements of glacier velocity are researched, but most are error prone. This paper presents a triangulation-based hierarchical image-matching algorithm for satellite imagery, which is used to calculate feature displacement then glacier velocity. It uses a coarse-to-fine hierarchical strategy and combines feature points and gridpoints to provide dense, precise and reliable results. First, coefficients of geometric transformation between images are extracted using the SIFT algorithm with the RANSAC approach to remove mismatches and enhance robustness, and the searching image is transformed and resampled using these coefficients. Then, an area-based matching is carried out between the reference and the transformed searching images and the final matching results are obtained via inverse transformation into the original image plane. In the process of hierarchical image matching, the parallaxes from upper levels are transferred to levels beneath with the triangle constraint. At last, outliers are detected and removed based on local smooth constraint of parallax. Also, a bidirectional image-matching method is adopted to verify the matching results and increase the number of matched points. Experiments using Landsat-7 ETM+ and MODIS images show that the proposed method has the capacity to generate reliable and dense matching results for calculation of glacier velocity in the Antarctic.
Observation and parameterization of glacier-air flux exchange on the southeast Tibetan Plateau
Kun YANG, Xiaofeng GUO, Long ZHAO, Wei YANG
Corresponding author: Kun Yang
Corresponding author e-mail: email@example.com
We present a field investigation of turbulent fluxes over a valley glacier (Parlung No. 4) on the southeast Tibetan Plateau. In the ablation zone, aerodynamic roughness lengths (z0M) vary on the order of 1–10 mm, the evolution of which corresponds to three melt phases with distinct surface cover and moisture exchange: snow (sublimation/evaporation), bare ice (deposition/condensation) and ice hummocks (sublimation/evaporation). We evaluate three parameterizations of the scalar roughness lengths (z0T for temperature and z0q for humidity), viz. key factors for the accurate estimation of sensible heat and latent heat fluxes using the bulk aerodynamic method. The first approach is based on surface-renewal models and has been widely applied in glaciated areas; the second has never received application over an ice/snow surface, despite its validity in (semi-)arid regions; the third, a derivative of the first, is proposed for use specifically over rough ice defined as z0M > 1 mm or so. This empirical z0M threshold value is deemed of general relevance to glaciated areas (e.g. ice sheet/cap and valley/outlet glaciers), above which the first approach gives notably underestimated z0T,q. The first and third approaches tend to underestimate and overestimate turbulent heat/moisture exchange, respectively, frequently leading to relative errors higher than 30%. Comparatively, the second approach produces fairly low errors in energy flux estimates both in individual melt phases and over the whole ablation season; it thus emerges as a practically useful choice to parameterize z0T,q in glaciated areas. This approach has been applied to an energy-balance-based glacier melt model and reasonable results are obtained.
Seasonal mass-balance determination in the Indian Himalaya: Chhota Shigri Glacier, Himachal Pradesh, 2009–2012
Anurag LINDA, A.L. RAMANATHAN, Parmanand SHARMA, Thupstan ANGCHUK, Virendra Bahadur SINGH, Jose George POTTAKKAL, Arindan MANDAL, Naveen KUMAR, Mohd Farooq AZAM, Patrick WAGNON, Christian VINCENT
Corresponding author: A.L. Ramanathan
Corresponding author e-mail: firstname.lastname@example.org
The annual and seasonal mass balance of Chhota Shigri Glacier (India, 32°20′ N, 77°30′ E) between 2009 and 2012 has been measured by the glaciological method. Annual mass balances during this period are 0.13, 0.33, 0.11 and –0.45 (± 0.40 m w.e. a–1), respectively. Annual mean winter temperatures for the balance years 2009/10, 2010/11 and 2011/12 are –10.98, –11.95 and –12.19, respectively, and winter mass balances for the same period are 1.96, 1.53 and 1.48 m w.e (± 0.20 m w.e. a–1), respectively. This glacier has the longest reported dataset for annual mass balance by the in situ method in the Indian Himalaya. However, no seasonal mass balance data have been reported to date. This paper is an attempt to understand the seasonal mass balance characteristics of this benchmark glacier. The reported meteorological data during this period show that temperature does not play a significant role in mass balance behavior, but attempts are not yet made for other meteorological components to understand their influence on the mass balance. In this study it was observed that the winter precipitation plays an important role in governing the annual mass balance of Chhota Shigri Glacier and it is inferred that this glacier responds slowly to temperature variation. The positive relation between mean winter temperature and precipitation was observed. This paper also highlights the role of debris-cover thickness on annual mass balance of the glacier, with a debris thickness of less than ~5 cm resulting in an increased rate of surface melting.
Climate change: the physical science basis – some progresses of WG1 AR5 IPCC
Corresponding author: Qin Dahe
Corresponding author e-mail: email@example.com
The Intergovernmental Panel on Climate Change (IPCC) has been established by WMO and UNEP to assess scientific, technical and socio-economic information relevant for the understanding of climate change, its potential impacts and options for adaptation and mitigation. It is open to all members of the UN and of WMO. The IPCC Working Group I (WGI) assesses the physical scientific aspects of the climate system and climate change. At present, the IPCC has begun the government and expert review of the Working Group contributions, and preparations for the Fifth Assessment Report (AR5) are entering the final stage. Compared with previous reports, the AR5 will put greater emphasis on assessing the socio-economic aspects of climate change and the implications for sustainable development, risk management and the framing of a response through both adaptation and mitigation. Since the release of IPCC AR4, a number of questions on climate change sciences were left unresolved. For example, has climate change accelerated, is the Greenland ice sheet stable, will the Himalayan glacier have disappeared in 2035, what is the role of clouds and aerosols, is the carbon cycle feedback positive, will there be more disasters such as droughts, etc? AR5 will provide an update of knowledge on them. Ice sheets and sea-level rise is one of the key cross-cutting themes in AR5. In the WGI report, there are two chapters stating the progress in cryosphere and sea-level studies, i.e. the fourth chapter (Observations: Cryosphere) and the thirteenth chapter (Sea Level Change). Both the extensive thinning of margins and mass loss of ice sheets in Greenland and Antarctica are remarkable. Details will be introduced in the presentation.
Internal layers along a traverse line from Zhongshan station to Dome A, East Antarctica, by ground-based radio-echo sounding
Xueyuan TANG, Bo SUN, Tiantian WANG
Corresponding author: Xueyuan Tang
Corresponding author e-mail: firstname.lastname@example.org
A profile of grounded radio-echo sounding between Zhangshan station and Kunlun station by the Chinese National Research Expedition (CHINARE) in the austral summers (2004/05) was obtained for the East Antarctic ice sheet. The internal isochronous layers and subglacial geometry were traced by the radar datasets. The geometry of internal layers allows significant information on the subglacical water, ice dynamics and crystal orientation fabrics (COF) to be established. The traverse profile passes through Princess Elizabeth Land, Lambert Glacier and the eastern Gamburtsev Mountains to the summit of Dome A, and reveals that there is a thick (>500 m) echo-free zone (EFZ) of basal ice from ~90 km to ~200 km. The continuous layers appear at the upper EFZ. The shallower layers in a ~200 m width band below the ice surface are continuous and approximately parallel to the surface topography. The layers of the transition between the shallower stratigraphy and the EFZ are recorded by what are shown to be the feature of overriding or draping the basal bedrock perturbations. The pattern of the layers shows that there exists some relatively steady flow areas in the inland region of the ice sheet. Some layer disruption was also identified in the profile, which was likely caused by changes in basal shear stresses and enhanced ice flow.
Increasing depositional flux of black soot on the Tibetan Plateau over the last 150 years
Baiqing XU, Mo WANG, Ninglian WANG, Guangjian WU
Corresponding author: Baiqing Xu
Corresponding author e-mail: email@example.com
We integrate black soot records of five ice cores and find that annual depositional flux of black carbon (BCf) and organic carbon (OCf) has greatly increased since AD 1852 on the Tibetan plateau. It was eightfold of BCf in the 2000s relative to the 1850s and was nearly fivefold for OCf, indicating that black soot deposition on glaciers might be an important reason for the accelerated glacial retreat on the Tibetan Plateau due to its strong light absorption. Tibetan BCf showed good correlated to Asian BC emission inventory data, but the highest correlation coefficient was found to be with the total BC emissions from Asia, Europe and Africa, except the emission inventory of the 1950s–1960s. Beyond all doubt, the transport and impact of anthropogenic BC emissions were global and BC emissions during the 1950s–1960s, likely from Europe, were underestimated in Bond’s inventory.
Effect of Drygalski Ice Tongue calving events on the extent changes of the Terra Nova Bay polynya
Chen ZHAO, Xiao CHENG, Fengming HUI, Jing KANG, Yan LIU, Xianwei WANG, Fang WANG
Corresponding author: Chen Zhao
Corresponding author e-mail: firstname.lastname@example.org
The Terra Nova Bay polynya (TNBP) is a large, stable, annually recurring feature in the western Ross Sea which markedly influences sea-ice dynamics and physical oceanography in that region. The persistence of the TNBP is due to the strong persistent katabatic winds that advect the newly formed ice offshore and the blockage of northward drifting sea ice to the northeast by the Drygalski Ice Tongue. The maximum eastward extent of the polynya is limited by the length of the Drygalski Ice Tongue, while the katabatic winds affected the polynya width. In March 2005 a giant 120 km long iceberg collided with the end of the ice tongue breaking off two large (70 km2) pieces. A year later in March 2006 another giant iceberg broke another piece off of around 100 km2 in size. Here, we used MODIS data in 2000 and ENVISAT ASAR data in 2010 to monitor the annul changes of the polynya extent. By analyzing the polynya extent changes before and after the two calving events of the Drygalski Ice Tongue, we found that the minimum size of the polynya in 2000 is larger than that in 2010. Combining the katabatic wind data from the Eneide and Rita automatic meteorological station, we analyzed the relationship among the polynya, the katabatic winds and the Dragalski Ice Tongue, which illustrates quantificationally that the calving events of the Drygalski Ice Tongue play a significant role in the extent changes of the polynya.
Movement and variation of several typical glaciers in the Qilian Mountains
Zhefan JING, Kun WANG, Li LIU
Corresponding author: Zhefan Jing
Corresponding author e-mail: email@example.com
In this work, several typical glaciers in the Qilian Mountains are selected, then their movement and variation were investigated using advanced technologies, such as remote sensing, photography measurement, GPS, etc. The velocity of glacier movement in the Qilian Mountains is relatively low and there is no significant variation during the past 50 years. Its motion maintains a normal style. The movement velocity of Laohugou No. 12 Glacier presented a decreasing trend (decreased by 48%) during 1960–2012. The movement velocity of ‘Qiyi’ Glacier also presented a decreasing trend (decreased by 48.1%) over 1958–2012, decreasing by 29.4% during 1958–1977 and 26.5% over 1977–2012, which indicates that the movement velocity varied greatly over the former 20 years (1958–1977), but the movement velocity variation presents a small decreasing trend during the later 30 years. However, the variation extent of both glaciers with different size is consistent.
Distributed temperature logging on the Amery Ice Shelf – challenges and scientific opportunities
Roland WARNER, Stefan W. VOGEL, Mike CRAVEN, Alan ELCHEIKH, Adam CHRISTENSEN, Adam TREVERROW, Shavawn DONOGHUE, Kelly BRUNT, Jeremy RIDGEN, Steve CANN, David TULLOH, Scott TYLER, Ian ALLISON, Ben GALTON FENZI
Corresponding author: Stefan W. Vogel
Corresponding author e-mail: firstname.lastname@example.org
Antarctic ice shelves are coupled to the climate of the Southern Ocean by the sub-ice ocean circulation, with interactions ranging from substantial basal melting to the accretion of thick layers of marine ice. They are vulnerable to increased melting from a warming ocean and from changes in ocean currents. Hidden beneath kilometre thick ice, sub-ice-shelf processes are difficult to study. During the 2009/2010 field season the AMSIOR team installed two fibre-optic cables through the Amery Ice Shelf as part of a sub-ice ocean observation network. Optical fibre light-scattering properties can be used for distributed temperature sensing (DTS). DTS measurements provide continuous temperature profiles at a resolution of ~1 m. Here we discuss the opportunities DTS systems provide for sub-ice and englacial temperature monitoring as well as the challenges that come with installing and operating a DTS system in Antarctica, including system set-up and calibration challenges.
Monitoring glacier vertical changes in 1976–2006 from space and in situ in the Mount Naimona’Nyi region in the Himalaya
Jibiao ZONG, Qinghua YE, Lide TIAN
Corresponding author: Qinghua Ye
Corresponding author e-mail: email@example.com
Glaciers, especially those in mountain regions, are considered as one of the sensitive indicators of climate change. Furthermore, glacier changes on the Tibetan Plateau and surrounding regions significantly affect water resources and ecosystems. As glaciers are always located in remote regions, in situ measurements are limited, while remote-sensing technology has the advantage of monitoring glacier areal changes widely and consistently. In this paper, glacier volume changes were studied by multitemporal DEMs and in situ measurements. A DEM for the Naimona’Nyi region was generated by stereo pairs acquired by ALOS/PRISM in 2006, which was evaluated and corrected by in situ differential GPS points, 1:50 000 topographic maps and the base 1:50 000 DEM in 1976. The vertical change on glacier surfaces was calculated by the difference between the PRISM DEM and the base DEM. The results suggest that the elevation was decreased in most of the glaciers, with an average downcasting rate of ~0.5 m a–1.
Surface velocity and altitude variation of Austre Lovénbreen in Svalbard using GPS method (2005–2010)
Songtao AI, Zhiyue LU, Zemin WANG, Dongchen E, Ming YAN
Corresponding author: Songtao Ai
Corresponding author e-mail: firstname.lastname@example.org
The Chinese National Arctic Research Expedition (CHINARE) started field research in 2005 on the typical valley glacier Austre Lovénbreen in Svalbard, Arctic. This paper describes the GPS tracking station and the field high-precision GPS surveys measured <10 km from the Chinese Arctic river station each summer from 2005 to 2010. Annual velocities of the glacier surface motion were calculated in both horizontal and vertical directions. Data analysis shows that the range of surface horizontal motion velocity was from 0.360 m a–1 to 3.986 m a–1 on Austre Lovénbreen and the rate of surface altitude variation changed from +9.6 cm a–1 to –115.8 cm a–1. The results indicate that the mass balance of this particular glacier is negative and the surface is melting for the 5 years measured.
A test of DHSVM coupled with a glacier melt model in a glacier basin in the central Tibetan Plateau
Guoshuai ZHANG, Shichang KANG, Lan CUO, Koji FUJITA
Corresponding author: Shichang Kang
Corresponding author e-mail: email@example.com
Modeling snow and ice melt from glaciers is pivotal to assessing hydrology in the cryosphere. To better understand the hydrological process in cold areas, the Distributed Hydrology Soil Vegetation Model (DHSVM) coupled with a glacier accumulation and melt progress model was set up and tested in the central Tibetan Plateau. The study area, with a 1.7 km2 glacier area, is the Zhadang watershed (7.6 km2) located on the southern slopes of Mount Nyainqentanglha. The observed hourly meteorology data from three AWS stations in the basin are used to drive the model during the period 2010–2012. The model outputs were both validated by the melt stakes distributed on the glacier and the river discharge monitoring.
A method of automatically tracking ice flowlines
Yan LIU, Xiao CHENG, Fengming HUI
Corresponding author: Yan Liu
Corresponding author e-mail: firstname.lastname@example.org
The discharge from the Antarctic ice shelves is drained through widespread complex flow in the interior of the Antarctic ice sheet. The detailed features of the Antarctic complex flow are still unclear. Here, we propose a method that automatically assesses the beginning positions and the whole route of an ice flowline on surface based on the horizontal flow direction map calculated from the surface velocity map. This method has been used to track the full range of high-density ice flowlines of Antarctica, which provides the most direct view of the Antarctic complex flow system and shows the detailed path of the interior ice flowing into the sea. Based on this map, the precise boundaries of drainage basins and main flow units of the Antarctic ice shelves can be delineated. This work has important consequences for reducing uncertainty in the estimation of the Antarctic mass balance.
The progress of Chinese radio-echo sounding around Kunlun station in the EAIS
Corresponding author: Xiangbin Cui
Corresponding author e-mail: email@example.com
During CHINARE21 (2004/05), the radio-echo sounding technique was introduced firstly to detect the ice thickness and subglacial topography. Since then, we have conducted four inland expeditions between Zhongshan and Kunlun stations and different radar systems were used to survey the ice and subglacial features, especially around Kunlun station. We finished a detailed grid survey of the subglacial topography and give out a typical mountain glacial landform of the Gamburtsev subglacial mountains, which helps us to uncover the early evolution of the Antarctic ice sheet and the GSM. In addtion, two radar systems are being developed according to our requirements for study of subglacial conditions and shallow internal layers.
Climate sensitivity of glaciers in the Dudh Kosi basin, Nepal
Joseph SHEA, Patrick WAGNON, Walter IMMERZEEL, Christian VINCENT
Corresponding author: Joseph Shea
Corresponding author e-mail: firstname.lastname@example.org
The Dudh Koshi basin in central Nepal contains a glacierized area of ~340 km2, which represents 9.1% of the total basin area (3716 km2). The region contains some of the world’s highest mountain peaks, including Sagarmatha (Mount Everest), Cho Oyu, Makalu, Lhotse and Nuptse, and the Dudh Kosi River is a major contributor to the Kosi River, which contains nearly one-quarter of Nepal’s exploitable hydroelectric potential. In this study, we examine the climate sensitivity of glaciers in the basin using a distributed glacier model. Surface mass-balance inputs for the model are derived from temperature and precipitation fields extracted from the APHRODITE project. These fields are bias-corrected using a set of high-altitude meteorological station data. A modified degree-day factor which takes variations of slope and aspect and debris cover into account is used to estimate daily melt totals. Glacier mass change is modelled on daily time steps, and mass accumulated in the upstream portions of the basin is moved downstream following the procedure of Immerzeel and others (2012). We evaluate the model skill by comparing: (1) modelled glacier extents with a glacier satellite inventory; (2) modelled glacier thicknesses with ground-penetrating radar observations at Mera Glacier; and (3) modelled mass-balance gradients with mass-balance gradients observed at Mera Glacier. The climate sensitivity of glaciers in the region is assessed with a simple delta approach based on hypothetical climate change scenarios. We show that future change in precipitation will be an important factor for the fate of the glaciers in the Dudh Kosi basin. In particular, we examine changes in modelled glacier extents and volumes, which will affect future hydrology in the basin.
Ice dolines in East Antarctica: ice–ocean interactions from surface meltwater drainage events
Stefan W. VOGEL, Alex D. FRASER, Petra HEIL, Ben GALTON-FENZI, David ALEXANDER
Corresponding author: Stefan W. Vogel
Corresponding author e-mail: email@example.com
Surface melting and meltwater streams are common features on outlet glaciers along the East Antarctic coast during summer. One of the big questions about surface melting in Antarctica is what happens to the meltwater? With Antarctic winters being long and cold, most meltwater likely refreezes in the snowpack with little to no impact on the overall mass balance of the ice sheet. One mechanism for surface meltwater to reach the ocean and mass being lost from the ice sheet is drainage through ice shelves. Ice dolines are longitudinal surface depressions, which are believed to be the remains of meltwater lakes that have drained through the ice. Dolines have been reported from various parts of Antarctica and pose a plausible mechanism through which significant amounts of fresh water may reach the ocean beneath ice shelves with potential impact on the sea-ice environment, Antarctic bottom water formation and ocean circulation in general. Here we revisit the topic of surface meltwater drainage and report on the evolution of Amery Ice Shelf dolines and on a very recent doline drainage event on the Mawson coast. Satellite observations indicate that dolines may be a standing feature, which reforms as the original feature moves with the flow of ice downstream. In addition to the water draining during the lake drainage events both features (Amery and Mawson coast) are at the receiving end of larger meltwater catchment areas and bear the potential that significant amounts of surface meltwater drains year after year through hidden openings at the bottom of the partially snow-covered dolines.
Surface melting and melt features on the Amery Ice Shelf – implications for ice-shelf, ice-sheet stability
Stefan W. VOGEL, Alex D. FRASER, Petra HEIL
Corresponding author: Stefan W. Vogel
Corresponding author e-mail: firstname.lastname@example.org
A general notion about Antarctica is that it is dry and cold. Yet along its coastline significant melting is observed each summer. In various places meltwater has been responsible for changes in the dynamic of glaciers, ice sheet and ice shelves. One spectacular event was the collapse of the Larsen B Ice Shelf. Here meltwater ponding had a destabilizing effect on the ice shelf. Meltwater draining through an ice sheet can enhance lubrication of the glacier bed, leading to flow acceleration and enhanced ice discharge. Freshwater input to the sub-ice-shelf environment may enhance thermohaline circulation with the potential of enhancing the draw of warmer water masses into the sub-ice-shelf cavity. Here we present initial results investigating surface melting and surface melt distribution on the Lambert Graben–Amery Ice Shelf. Clearly visible from space, each year a network of lakes and rivers forms on the surface of the Amery Ice Shelf south of Jetty Peninsula (~70.5° S). Surface melt features are absent in the front half of the Amery Ice Shelf likely due to high snow accumulation. Microwave imagery as well as snow temperature data indicate melting with meltwater percolation into and refreezing inside the snow cover. Closer examination of satellite imagery shows an extensive surface hydrological network covering the back of the Amery Ice Shelf transporting meltwater over large distances. During high melt years supraglacial lakes can reach tens of kilometres in length and >1 km in width. The most southern surface lake is found adjacent to Cumpston Massif on Mellor Glacier (73.5° S). This is a significant distance upstream from the ice-shelf grounding zone and raises the possibility that surface melting under 21st century climate warming scenarios could enhance lubrication of East Antarctic outlet glaciers.
East Antarctic surface melting – biggest 21st century sea-level change threat?
Stefan W. VOGEL, Alex D. FRASER, Petra HEIL, Rob MASSOM, Neal YOUNG, Mike CRAVEN
Corresponding author: Stefan W. Vogel
Corresponding author e-mail: email@example.com
Antarctica: driest and coldest place on Earth. The East Antarctic coastline in summer, however, provides a contrasting picture. Along the coast surface melting and an extensive network of meltwater streams are the dominant features in summer. While Greenland melting is at the forefront of science and extensive attention is given to its interannual variability as well its impact on ice dynamics, Antarctic melting has received comparably little attention, with most of the attention coming from broad-scale remote-sensing applications. Direct measurements validating remote-sensing applications are however scarce as are estimates of surface accumulation/ablation and the fate of meltwater during winter. With surface melting already being widespread at present, surface melting in Antarctica will only increase under 21st century warming scenarios, raising the question as to when the East Antarctic margin will catch up with the Antarctic Peninsula and/or Greenland. This presentation provides a visual overview of melting along the East Antarctic margin and discusses the potential impact of surface melting on ice dynamics, ice-shelf stability and the Southern Ocean environment. In general surface meltwater can have a destabilizing effect on ice shelves, while freshwater flux into the ocean impacts thermohaline circulation, sea-ice production and the Southern Ocean ecosystem in general. Potential loss of East Antarctic ice shelves and their buttressing effect, as seen along the Antarctic Peninsula, could easily double the discharge of ice from major East Antarctic outlet glaciers, which would be enough ice to double the rate at which sea-level currently rises.
From precipitation to runoff: stable isotopic fractionation effect of glacier melting on a catchment scale
Shiqiao ZHOU, Zheng WANG, Daniel R. JOSWIAK
Corresponding author: Shiqiao Zhou
Corresponding author e-mail: firstname.lastname@example.org
Stable isotope variability and fractionation associated with transformation of precipitation/accumulation to firn to glacial river water is critical in a variety of climatic, hydrological and paleoenvironmental studies. This paper documents the modification of stable isotopes in water from precipitation to glacier runoff in an alpine catchment located in the central Tibetan Plateau. Isotopic changes are observed by sampling firn-pack profiles, glacier surface snow/ice, meltwater on the glacier surface and catchment river water at different times during a melt season. Results show the isotopic fractionation effects associated with glacier melt processes. The slope of the δD–δ18O regression line and the deuterium excess values decreased from the initial precipitation to the melt-impacted firn pack (slope from 9.3 to 8.5 and average d-excess from 13.4‰ to 7.4‰). The slope of the δD–δ18O line further decreased to 7.6 for the glacier runoff water. The glacier surface snow/ice from different locations, which produces the main runoff, had the same δD–δ18O line slope but lower deuterium excess (by 3.9‰) compared with values observed in the firn-pack profile during the melt season. The δD–δ18O regression line for the river water exhibited a lower slope compared with the surface snow/ice samples, although they were closely located on the δD–δ18O plot. Isotope values for the river and glacier surface meltwater showed little scatter around the δD–δ18O regression line although the samples were from different glaciers and were collected on different days. Results indicate a high consistency of isotopic fractionation in the δD–δ18O relationships, as well as a general consistency and temporal covariation of meltwater isotope values at the catchment scale.
Platelet ice and marine ice layer formation processes beneath the Amery Ice Shelf
Stefan W. VOGEL, Mike CRAVEN, Roland WARNER, Laura HERRAIZ BORREGUERO, Ben GALTON FENZI
Corresponding author: Stefan W. Vogel
Corresponding author e-mail: email@example.com
Frazil/platelet ice formation processes are an elusive process hidden beneath a dark ice-covered ocean. Frazil and platelet ice are important for sea-ice formation as well as the formation of marine ice at the base of ice shelves. Craven and others (in preparation) report frazil/platelet-ice-induced mooring uplifts in the order of 10–20 dbar. Detailed analysis of the oceanographic data (temperature, salinity and pressure) surrounding these serendipitous events provides new insight into ice-shelf boundary layer processes, the formation of frazil/platelet ice through the year and marine ice accretion processes. In general the observed mooring uplift events follow periods of cooling and are associated with periods of supercooling in the ice-shelf boundary layer. While conditions favourable for frazil ice formation and platelet ice growth develop slowly, these events end abruptly with changes in thermal conditions. While the formation of frazil ice and the actual growth of platelet ice require a significant amount of thermal heat deficit, coagulation and attachment of ice suspended in the water column requires only small changes in the thermal budget to cause disaggregation. The frontal part of the Amery Ice Shelf (AM01 and AM04) appears to be dominated by seasonal cyclicity. Here periods of accumulation (5–10 cm d–1) at a long-term net accumulation of 1–3 m a–1 are followed by periods of erosion. In the centre of the ice shelf (AM05) on the other hand ice formation and associated mooring uplifts are observed year round.
Surface ablation and energy budget in the ablation zone of Xiao Dongkemadi Glacier on the central Tibetan Plateau
Xiaobo HE, Jian ZHANG, Baisheng YE, Yongjian DING
Corresponding author: Xiaobo He
Corresponding author e-mail: firstname.lastname@example.org
Winter snow accumulation and summer snow and ice ablation were measured at Xiao Dongkemadi Glacier (XDG) in the central Tibetan Plateau to estimate glacier mass-balance quantities for the balance years from 2008 to 2011. A 5 year record of data from an automatic weather station (AWS) operating at 5610 m a.s.l. on XDG has been used to calculate the annual cycle of the local surface heat budget. The four components of the radiation budget and surface height are measured, and the turbulent fluxes were calculated using the bulk aerodynamic method. On average, the observed melting rate is 3.7 mm w.e. d–1 and surface net radiation is 40 W m–2. Both of them are among the lowest values compared with those reported in previous studies worldwide.
Observation and analysis of ice-flow velocity on Lambert Glacier–Amery Ice Shelf using interferometric and GPS data
Chunxia ZHOU, Fanghui DENG, Zemin WANG, Dongchen E, Shengkai ZHANG
Corresponding author: Chunxia Zhou
Corresponding author e-mail: email@example.com
Ice-flow velocity is a fundamental parameter of the ice dynamic model which indicates how the ice is transported from the interior regions to the ocean and how ice mass evolves with time. The Lambert Glacier–Amery Ice Shelf system (LAS) is the largest ice stream system in East Antarctica. The ice streams of LAS flow towards to the sea through a narrow drainage area, the length of which is only 1/60 of the Antarctic coastline. So study of the ice velocity of LAS is of great importance for the ice dynamic changes and mass balance in Antarctica. During the Chinese National Antarctic Research Expedition (CHINARE), multi-term GPS observations were carried out on the Amery Ice Shelf with the support of helicopters. Meanwhile, the SAR interferometry technique is significant to estimate ice sheet and glacier surface motion. This paper discusses ice-flow velocity estimation with InSAR pairs and validation with GPS data of LAS. ERS-1/2 tandem SAR data and Envisat ASAR data were adopted for ice-flow velocity estimation in this study. The D-InSAR and speckle tracking methods were utilized for ice velocity derivation. In order to generate a 2-D ice velocity map with high accuracy, the combination of the displacement in the range direction estimated by D-InSAR with the displacement in the azimuth direction calculated by speckle tracking was applied for most image pairs. It can be seen from the ice velocity map that several tributary ice streams coming separately from Fisher Glacier, Mellor Glacier and Lambert Glacier flowed towards to the Amery Ice Shelf and converged into the mainstream. The ice velocity at the meeting point reached as high as 800 m a–1, while the ice velocity along the mainstream decreased to about 350 m a–1 and then increased quickly near the front edge of the Amery Ice Shelf. The ice velocity near the edge was about 1500 m a–1. Taking static nunataks and rocks as checking points, the average velocity error in LAS was about 8 m a–1. Our results also showed close agreement with the in situ measurements near the meeting point and the front of the Amery Ice shelf.
Fully coupled ice-sheet-MPI-ESM simulations of the Greenland ice sheet and the interacting climate system under rising CO2 concentration
Christian RODEHACKE, Miren VIZCAINO, Florian ZIEMEN, Uwe MIKOLAJEWICZ
Corresponding author: Christian Rodehacke
Corresponding author e-mail: firstname.lastname@example.org
The warming in the Arctic and the northward-flowing tropical water masses seem to trigger enhanced melting of the Greenland ice sheet. A continuation of the observed accelerated melting and freshwater release could stabilize the water column in the adjacent deep water formation sides. With our fully coupled ice-sheet–earth system we approach the question if this weakens the formation of deep water masses and reduces the oceanic thermohaline driven meridional overturning circulation (MOC). With our two-way fully coupled ice-sheet–earth system model we investigate the response of the system under rising atmospheric carbon dioxide (CO2) concentration. We will present the building blocks of our fully coupled system, which includes a physically based calculation of the ice-sheet surface mass balance and ice-sheet–ocean interaction; the ESM instead is subject to orographic changes and freshwater fluxes, for example. Since the behaviour of an ice sheet in the near future is controlled by both the external forcing and by its initial conditions, we have performed Latin Hyper Cube (LHC) simulations of the ice-sheet model PISM over more than one glacial–interglacial cycle utilizing standard techniques to obtain a reasonable initial state. According to several quantities the best performing LHC member is exposed afterwards to boundary conditions determined from energy-balance calculations again obtained from simulated forcing fields. Finally the fully coupled system is brought near a quasi equilibrium under pre-industrial conditions before idealized scenarios have been started. In contrast to commonly used strategies, our coupled ice sheet inherits the memory of a glacial cycle simulation obtained exclusively from ESM fields. Under different CO2 forcing scenarios – for example raising CO2 by 1% a–1 until four times the pre-industrial concentration (4×CO2) has reached, abrupt raise to 4×CO2 – the response of the coupled system is analysed. For instance, an abrupt CO2 forcing leads to an immediate response of the Greenland ice sheet. The surface mass balance turns strongly negative with a couple of years, causing skyrocketing melting rates and sea-level rise. The contribution of the ocean–ice-sheet interaction decreases instead, because the ice sheet retreats from the coast and is therefore less susceptible to an eroding ocean. The additionally released fresh water and the heat both have the potential to stifle the MOC. However, sensitivity experiments indicate that the warming drives the MOC reduction but the additional fresh water prevents the MOC recovering after two centuries. For the study we use the current CMIP5 Earth system model MPI-ESM that comprises the atmosphere model ECHAM6 (T63L47), vegetation model JSBACH and the ocean biogeochemical model MPIOM/HAMOCC (nominal horizontal resolution of 1.5° with one pole over Greenland). The ESM is coupled to the Parallel Ice Sheet Model (PISM) covering Greenland with a horizontal resolution of 10 km.
Mass-balance variability of Xiaodongkemadi Glacier in the central Tibetan Plateau
Corresponding author: Jianchen Pu
Corresponding author e-mail: email@example.com
Mass balance and equilibrium-line altitude (ELA) of alpine glaciers respond to climate change directly. Xiaodongkemadi Glacier in the cental Tibetan Plateau has been monitored since 1989. The mass balance showed a fluctuating declining trend from 1989 to 2007 and the accumulated mass balance reached –3982 mm during that period. From 1989 to 1993, the glacier saw a positive mass balance and the accumulation had reached 970 mm. However, the mass balance changed from distinct positive to strong negative since 1994, and the accumulated mass balance was –4953 mm from 1994 to 2007. The most negative mass balance appeared in 2006 and reached –917 mm. The glacier ELA had ascended about 200 m from 1989 to 2007 with a rate of 10 m a–1. The negative mass balance and ascending ELA of the glacier have shown that glaciers have melted strongly in the central Tibetan Plateau in recent years.
Uncertainties in retrieved ice thickness from freeboard measurements due to surface melting
Peng LU, Zhijun LI
Corresponding author: Peng Lu
Corresponding author e-mail: firstname.lastname@example.org
As one of the most important parameters in evaluating the response of polar sea ice to global climate changes, ice thickness is always difficult to access on large spatial and temporal scales. Remote sensing of ice freeboard from airborne and spaceborne platforms offers a good method to retrieve total ice thickness in the polar oceans; however, the accuracy of the retrieved data is highly limited by the factors altering the isostatic balance of ice floes such as snow cover and surface melting. Contrary to the abundant studies on the influence from snow loads, little attentions has been paid to the role of melt ponds, partly because of the absence of freeboard measurements in melt seasons at present (for example ICESat and CryoSat) . However, a theoretical model is still developed to investigate the uncertainties in retrieved ice thickness from freeboard due to surface melt ponds. The first goal of this study is to meet the deficit in the present study and the second is to provide a theoretical basis for future instruments that are able to access sea-ice freeboard in the melting season. The total ice thickness was firstly quantitatively related to the freeboard, melt pond fraction and pond depth, and then an error analysis was carried out to study the influence of melt-pond morphology on the retrieved ice thickness. The results reveal that exclusion of the melt ponds from the isostatic balance of ice floes will lead to an overestimation of total ice thickness, especially for the first-year ice having high pond fraction but shallow pond water. Meanwhile, errors in pond fraction and pond depth will also pose considerable influence on the retrieved ice thickness as does freeboard.
Multiple climate shifts in the Southern Hemisphere over the past three centuries based on glaciological and geochemical investigations in central Antarctic snow pits and ice cores
Alexey EKAYKIN, Anna KOZACHEK
Corresponding author: Alexey Ekaykin
Corresponding author e-mail: email@example.com
Based on data from geochemical and glaciological investigations in snow pits and on shallow cores, regional stack series of the air temperature and the snow accumulation rate in central Antarctica (Vostok station area) have been obtained for the last 350 years. It has been shown that these parameters varied quasi-periodically with the wavelength of 30–60 years superimposed on the slight positive trend. The correlation of the newly obtained records with the circulation indices of the Southern Hemisphere (SH) shows that the central Antarctic climate is mainly governed by the type of the circulation in the SH: under conditions of zonal circulation the negative anomalies of temperature and precipitation rate are observed, whereas the sign of the anomalies is opposite during the meridional circulation. It has been found that in the 1970s the sign of the relationship between many climatic parameters has changed, which is likely related to the rearrangement of the climatic system of the SH. The data suggest that during the past 350 years such events have happened at least five times. We have also analyzed the recent warming observed in the region of Vostok station in the 2010s. The data on the snow isotope content from the snow pits indeed confirm that this period was warmer than average, although the temperature increase in the decade 2000–2010 was not the highest in the whole 350 year record. Finally, our data suggest that the isotope content of the central Antarctic snow is governed by the summer temperature rather than by mean annual temperature, which is interpreted as the influence of the ‘post-depositional’ effects.
Remote-sensing study of glacier changes in the Mount Everest region (Himalaya) from the 1970s to 2010
Xiaoyin GUO, Cunde XIAO
Corresponding author: Cunde Xiao
Corresponding author e-mail: firstname.lastname@example.org
Geographic variability of the recent changes of glaciers on Mount Everest, Himalaya, is assessed using Landsat TM, Landsat ETM, HJ-1 and ASTER satellite images from 1976 to 2010. The study results showed that glacier area shrank by 3.68% from 1976 to 1990 on the north slope. Between the years 1990–2000, 2000–2005 and 2005–2010 glacier area shrank by 2.25%, 1.94% and 0.79% on the north slope and by 2.36%, 1.32% and 1.93% on the south slope. Regional climate changes showed that the increasing temperature is the key factor influencing glacier shrinkage.
Topographic control of snow distribution and seasonal variation in the Koshi basin, Himalaya, from improved MODIS snow products
Yang GAO, Tandong YAO, Yang XIANG
Corresponding author: Yang Gao
Corresponding author e-mail: email@example.com
Snow in the Himalaya plays a vital role in sustaining seasonal water availability and supplies large amounts of water for more than 0.75 billion people. Monitoring the distribution and seasonal variation of snow cover in the Koshi basin, Himalaya, having the typical vertical zonation of the Himalaya, is significant to understanding of the local and regional response of ongoing climate change. Moderate Resolution Imaging Spectroradimeter (MODIS) snow-cover products are appealing for regional snow-cover mapping because of their good accuracy under clear skies, 500 m spatial and daily temporal resolution. Their main limitation, however, is cloud obscuration. In this study, we apply and improve five snow retrieval methods, termed temporal, spatial and regional snow-cover characteristics, to remove cloud obscuration and obtain cloudless daily snow-cover products. These successive methods include combing MODIS data form Terra and Aqua satellites, deducing using adjacent temporal information, estimating based on regional snow/land transition zone, spatial filtering using the majority of non-cloud pixels in the eight closest neighboring pixels, and removing based on pixel snow cycle. Since no snow observations are available from this region, the performance of the proposed methodology was evaluated using the cloud generated MODIS snow-cover data as possible ‘ground truth’ information. Based on snow-cover fraction, spring snow-cover duration and snowmelt date from improved MODIS snow-cover products from 2000–2012, the spatial-temporal distribution and variation of snow cover over the Koshi basin are statistical analyzed. It is found that snow persistence over the Koshi basin varies in different elevation ranges and generally become longer with increase in the terrain elevation. Moreover, the spatial distribution of snow cover is controlled by regional topography besides elevation. Since warm and moist air comes from the southern India Ocean and there is huge shielding from the Himalaya, there is more and longer snow cover on the south slope of the Himalaya with aspect to the north slope, although the mean elevation of the north slope is higher than that of the south slope. The 13 years of observation data show high seasonal and interannual variability of snow-cover fraction and duration. There is a slight decreasing trend in SCF from 2000 to 2012.
Thermal diffusivity of thermokarst lake ice in Beiluhe basin of the Qinghai–Tibetan Plateau
Liqiong SHI, Zhijun LI, Wenfeng HUANG, Peng LU, Enmin FENG, Hongwei HAN
Corresponding author: Liqiong Shi
Corresponding author e-mail: firstname.lastname@example.org
The ice cover in the Qinghai–Tibetan Plateau plays an important role in environmental and ecological systems. This paper analyzed the in situ observations of ice growth and decay, especially ice temperature, and examined the thermal diffusivity of a thermokarst lake in the Beiluhe basin, Qinghai–Tibetan Plateau. According to previous research on thermal properties, such as the thermal conductivity of ice, specific heat capacity and density, the change of the thermal diffusivity of thermokarst lake ice with ice temperature is illustrated mathematically by establishing an optimal control model. In addition, the effects of air bubbles and the density on the thermal diffusivity were investigated on the basis of ice samples from the thermokarst lake. Finally, the thermal diffusivity variation with ice temperature was compared between obtained in the study and calculated with the effective thermal conductivity measured by QTD-3 Thermal Properties Analyzer, the formula of the specific heat capacity and the observed ice density, and also the difference between them was discussed briefly.
20 years of elevation change in the Dome A region of the Antarctic from multimission satellite radar altimetry
Qiang QIANG, Chunxia ZHOU, Zemin WANG, Dongchen E
Corresponding author: Chunxia Zhou
Corresponding author e-mail: email@example.com
Glaciers and ice sheets are important components that control sea-level change. In response to a warming climate, the Greenland and Antarctic ice sheets have lost mass significantly. During the past century, the sea level has risen by 10–20 cm. This sea-level rise has already seriously affected the daily lives of people in coastal areas. Therefore, in particular, the mass balance of the Antarctic and Greenland is required to assess their contribution to sea-level rise as well as to evaluate their sensitivities to variable future forcings. In the past few decades, many scholars have proved that the ice sheets in the Antarctic are losing mass and that loss may be increasing. However, the regions investigated are concentrated mainly in the north of 80° S while investigation in the region south of 80° S is lacking. As the summit of the Antarctic ice cap, Dome A is a proper experimental place for mass-balance study over the ice-sheet interiors. To improve our understanding of the dynamics of cryospheric change, interactions with the climate and the impact on the living environment of Dome A, in this paper we used data acquired between 1992 and 2013 by four satellite radar altimeter missions (ERS-1, ERS-2, Envisat and CryoSat-2) to assess the current state of Dome A and determine multidecadal elevation change rates (dh/dt). Field GPS measurements carried out several times during the CHINARE expedition were used as validation data.
Hasty retreat of glaciers in the Palena province of Chile
Frank PAUL, Nico MÖLG, Tobias BOLCH
Corresponding author: Frank Paul
Corresponding author e-mail: firstname.lastname@example.org
Mapping glacier extent from optical satellite data has become a most efficient tool to create or update glacier inventories and determine glacier changes over time. A most valuable archive in this regard is the nearly 30 year time series of Landsat thematic mapper (TM) data that is freely available (already orthorectified) for most regions in the world from the USGS. One region with a most dramatic glacier shrinkage and a missing systematic assessment of changes is the Palena province in Chile, south of Puerto Montt. A major bottleneck for accurate determination of glacier changes in this region is related to the huge amounts of snow falling in this very maritime region, hiding the perimeter of glaciers throughout the year. Consequently, we found only 3 years with Landsat scenes that can be used to map glacier extent through time. Here we present the results of a glacier change analysis from six Landsat scenes (path-rows 232-89/90) acquired in 1985, 2000 and 2011 covering the Palena district in Chile. Clean glacier ice was mapped automatically with a standard technique (TM3/TM band ratio) and manual editing was applied to remove wrongly classified lakes and to add debris-covered glacier parts. The digital elevation model (DEM) from SRTM was used to derive drainage divides, determine glacier-specific topographic parameters and analyse the area changes in regard to topography. The scene from 2000 has the best snow conditions and was used to eliminate seasonal snow in the other two scenes by digital combination of the binary glacier masks. The observed changes show a huge spatial variability with a strong dependence on elevation and glacier hypsometry. While small mountain glaciers at high elevations and steep slopes show virtually no change over the 26 year period, ice at low elevations from large valley glaciers shows a dramatic decline (area and thickness loss). Some glaciers retreated more than 3 km over this time period or even disappeared completely. Typically, these glaciers lost contact to the accumulation areas of tributaries and now consist of an ablation area only. Furthermore, numerous proglacial lakes formed or expanded rapidly, increasing the local hazard potential. On the other hand, some glaciers located on or near to (still active) volcanoes have also advanced in the same time period. Observed trends in temperature (decreasing) are in contrast to the observed strong glacier shrinkage.
Melt energy comparison of a degree-day model and an enhanced temperature index at Robertson Glacier, Alberta, Canada
Corresponding author: Ryan Scanlon
Corresponding author e-mail: email@example.com
An enhanced temperature index (ETI), which incorporates incoming shortwave radiation and albedo, is compared with a degree-day model to calculate available melt energy for the 2012 ablation season at Robertson Glacier, Alberta, Canada. These models will be run with both measured and modeled data in order to determine if the physically based ETI better represents the melt energy available than the empirically based degree-day model. One automatic weather station and 14 temperature and RH sensors were deployed from July to September 2012 on Robertson Glacier. Ablation rates were measured throughout the season and will be used to compare with the modeled outputs. The performance of the ETI will be tested at each of the 14 sensor locations and at the automatic weather station. The ETI is expected to show a significant improvement over the degree-day method when modeling available melt energy. This improvement is expected to be less significant when albedo and incoming shortwave radiation are parameterized, thus offering a better alternative to an empirical model that only requires temperature data to be inputted.
Characterization of surface, englacial and basal ice-sheet condition in the region of Dome A, East Antarctica: an optical site for deep ice core drilling
Bo SUN, Xiangbin CUI, Jingxue GUO, Xueyuan TANG, Leibao LIU
Corresponding author: Bo Sun
Corresponding author e-mail: firstname.lastname@example.org
The CHINARE science plan is for deep ice coring to be drilled in the Dome A region of East Antarctica. We present glaciological characteristics of Dome Argus, East Antarctica, and systematically discuss the merits and possible ventures of its potential as a deep ice-core site. According to recent observations by high-precision GPS in the Dome A region, the horizontal velocity of the ice surface is close to zero. A shallow ice core from Dome A indicates the mean accumulation rate of 23.2 mm w.e. a–1 over the last 3000 years. Ground-based ice-penetrating radar surveys generated a subglacial topography digital elevation model (DEM), covering the central 30 km × 30 km region at Dome A, with a 150 m × 150 m grid resolution. Radar stratigraphy shows that internal ice layers are stable and the isochronous layers are not anomalous. Using a two-parameter roughness index of the bedrock elevation, calculated results of the roughness index from the base of Dome A indicate that the features of the subglacial topography of Dome A correspond to lower rates of deposition from erosion, indicating that the bottom has a colder and slower ice flow. A full-Stokes ice-flow model using the finite-element code Elmer for the vicinity of Dome A suggests that the basal temperature is below the pressure-melting point, constraining through the radar isochronous layers with both geothermal heat flux and the ice fabric.
A 132 year biomass burning history record in a Muztagh Ata ice core, west Tibetan Plateau
Ping YAO, Valérie F. SCHWAB, Baiqing XU, Tandong YAO, Gerd GLEIXNER
Corresponding author: Ping Yao
Corresponding author e-mail: email@example.com
As an unambiguious molecular marker for biomass burning, levoglucosan has been extracted from snow and ice-core samples from Greenland, south polar and northeast Asia. Forest fire acitivity of the original districts from mordern times to historical periods reconcentructed on this basis will improve our knowledge of the past atmospheric circulation and variation. Here we report a 132 year biomass burning history from a Muztagh Ata ice core in the western Tibetan Plateau (38°17' N 75°04' E, 6350 m a.s.l.). Annual levoglucosan showed two lower peaks in the 1860s–1870s and 1930s–1940s and a strong peak from the 1960s to the 1990s. Located in the western Tibetan Plateau, Muztagh Ata Glacier is mainly influenced by the westerly winds that bring air masses from central Asia. The variation of levoglucosan concentration was in accordance with the previous estimation of the distribution of burned areas in this area. The present study demonstrates that levoglucosan preserved in ice cores could provide historical records of biomass burning in the Tibetan Plateau.
Variation characteristics of nitrate in the superficial snow on the transit from Zhongshan base to Dome Argus, East Antarctica
Corresponding author: Guitao Shi
Corresponding author e-mail: firstname.lastname@example.org
In the Antarctic inlands, the main sources of nitrate in the snow are still controversial, and the nitrate air-to-snow transfer mechanism remains under discussion, although there is a large amount of data from surface snow and ice core sampled over Antarctica. Therefore, characterizing the spatial variation of nitrate in the superficial snow remains significant for further understanding of the sources and post-depositional processes of nitrate in the Antarctic inlands. In this study, 120 superficial snow samples were collected during the 2011/12 Antarctic summer season and the variation characteristics of nitrate in the surface snow in the profile of Zhongshan base to Dome Argus were investigated. The results showed that nitrate concentrations varied from 38.47 μg L–1 to 316.17 μg L–1, with an average of 146.6 μg L–1. Nitrate in the superficial snow along the transit showed a moderate-intensity variation, with a variation coefficient of 0.478, indicating the different main sources or post-depositional processes in varied geographical zones along the transit. The results of the correlation analysis indicated that altitude, distance to coastline, accumulation rate and coexistence impurities as well as the isotopic compositions of water were important factors controlling nitrate concentrations in the superficial snow. Nitrate concentrations increased with an increase in altitude by and large, with a level constant with the altitude below 2000 m. Nitrate levels rose with increasing distance to the coastline and decreased with the reduction in accumulation rate. In the superficial snow samples, nitrate correlated well with calcium and sulfate, with the confidence level >99.9%, probably indicating their common sources. The good correlation between nitrate concentrations and δ18O suggested that temperature was also an important factor influencing nitrate levels, the lower temperature probably relating to the higher nitrate concentrations in the Antarctic inland superficial snow.
Evaluation of energy exchange of an Andean tropical glacier with a multi-layer snow model
Yoshihiro ASAOKA, Takeshi YAMAZAKI, Pablo FUCHS, Gonzalo LEONARDINI, Edson RAMIREZ, So KAZAMA
Corresponding author: Yoshihiro Asaoka
Corresponding author e-mail: email@example.com
We applied a multi-layer snow model to Huayna Potosi Glacier, Bolivia, to evaluate energy exchange on the snow/ice surface. This model calculates energy exchange on the surface and heat conductivity, infiltration and compaction for each layer with meteorological input. Three types of numerical simulation were conducted: (1) under current conditions, (2) precipitation sensitivity and (3) temperature sensitivity. All simulations start under the common initial condition that snow does not cover the glacier surface and the vertical profile of ice temperature is constant. Model simulation under current conditions successfully accounted for variations in surface temperature on the surface in the dry season. However, results of surface temperature have some problems in wet seasons because thermal conductivity varies largely with a repeat of snow cover and disappear on the glacier. As a result, solar radiation is the main component of melt flux in both dry and wet seasons. However, melt rate is low in the dry season due to low longwave radiation. Melt flux in the mid-wet season was lower than in the early-wet season because of continuous snow cover and its high albedo. The sensitivity experiment of precipitation also showed that surface glacier without snow cover has a higher melt rate than with snow cover and snow accumulation on the glacier decreases the melt rate in the wet season because of the high albedo for snow. The sensitivity experiment of temperature showed that a large part of snowfall changes rainfall in the dry season with temperature rise because the frequency of precipitation for temperature is the highest at around 0°C in the wet season and the highest at around –3°C in the dry season. Moreover, low albedo on the glacier surface leads to higher melt rate. These results suggest that mass balance for tropical glaciers is affected by precipitation seasonality and precipitation form.
Observational study on glaciers in the Hulugou watershed, Heihe River basin, northwestern China
Corresponding author: Zhongqin Li
Corresponding author e-mail: firstname.lastname@example.org
Heihe River basin is located in the vast arid region in northwestern China, being the vital source of water for several cities and more than ten million people in lower reaches. Because of the dry climatic regime, glaciers play an important role in both the human living environment and the ecosystem of this region. To investigate the characteristics of glaciers and their responses to climate change, a small and representative watershed named Hulugou (~24.5 km2) was selected on which to carry out in situ glacial observations and measurements (i.e. topography survey, mass balance, surface velocity and ice temperature, etc.) since 2010. According to observed and remote-sensing data, all five glaciers in the watershed are small in size (0.24 km2 on average in 2011), declined by 17.9% from 1956 and have been in accelerated shrinkage in recent years. Ice volume is recovered as 2320 × 104 m3 in total. Four of the glaciers are hanging glaciers with steep surface and limited thickness (~20 m in maximum). The glacier with the largest area, Shiyi Glacier, is a valley glacier with two branches. Its annual mass balance is lower than –0.5 m w.e. and the ablation at its snout is around 3.2 m w.e. in 2011, which caused a ~5.0 m a–1 retreat. The ELA in this watershed is found between 4750 and 4800 m a.s.l. in the observed years. The heads of all the glaciers are in or lower than this range, which means 95% of the glacier surface is in the ablation area. Although there might be bias because of the short-term measurements, we can conclude that glaciers in the Hulugou watershed (even in Heihe River basin) are greatly vulnerable to current climate conditions. With increasing temperature, there is a high possibility that the glaciers will vanish in a few decades in future.
Future response of glaciers in Hulugou, Heihe River basin, northwestern China, to climate change
Huilin LI, Zhongqin LI
Corresponding author: Huilin Li
Corresponding author e-mail: email@example.com
Heihe River basin is located in the vast arid region in northwestern China. Because of the dry climatic regime, glaciers play an important role in both the human living environment and the ecosystem of this region. However, their future responses to climate change are seldom studied. In this paper, a small and representative watershed named Hulugou (~24.5 km2) with only five glaciers in it was selected as the study area. Because all glaciers in it are small in size (<0.6 km2) with relatively high aspect ratio, a 2-D higher-order flow model coupled with a simple energy-balance model is applied to do the analysis. Results show that >85% of the glacier area will vanish in the following 30 years under current climate conditions. About 10% developed in the troughs of hillsides are protected from sunshine and will survive to the end of this century. With climate forcing specified by IPCC emission scenarios, all glaciers will strongly recede and four of them will vanish within the next 30 years. One cirque glacier at higher altitude will have an area of 0.04 km2 remaining in 2040 and will ultimately disappear around 2080. The above results indicate that glaciers in the Hulugou watershed (even in Heihe River basin) are greatly vulnerable to current climate conditions and far out of steady state. With increasing temperature, most of them will vanish in a few decades and further studies are needed to investigate the influence of deglaciation on local hydrology and water resources.
Tidal pacing, skipped slips and the influence of stick–slip motion on the slowdown of the Whillans Ice Stream, Antarctica
J. Paul WINBERRY, Sridhar ANANDAKRISHNAN, Doug WIENS, Richard B. ALLEY
Corresponding author: J. Paul Winberry
Corresponding author e-mail: firstname.lastname@example.org
Whillans Ice Stream (WIS) is a major route for ice transiting from the interior of the West Antarctic ice sheet (WAIS) into the Ross Sea. It has been observed that WIS has been slowing, contributing to a positive mass balance in the Ross Sea sector of the WAIS. Examination of velocity time series for WIS reveal that the deceleration is not occurring at a steady rate, but varies at the sub-decadal timescale. Superimposed on this decadal-scale trend of deceleration is motion driven by a tidally modulated stick–slip cycle at the daily timescale. These sub-daily oscillations are characterized by extended periods (6–24 hours) of minimal motion followed by brief periods (30 min) of rapid motion when the ice stream lurches forward by ~0.5 m. Comparison of new results collected during 2010–2011 with earlier measurements show that the deceleration has continued and the timing of slip events has become less regular. The reduced regularity of slip events has resulted in a less efficient release of stored elastic strain during slip events, pointing toward non-linear feedbacks at the daily scale that influence the decadal timescale behavior of the ice stream.
Variable glacier mass changes in High Mountain Asia 1975–2010
Tobias BOLCH, Geir MOHOLDT, Alex S. GARDNER, Niklas NECKEL, Tino PIEZCONKA, Nicolai HOLZER, Jan KROPACEK, Etienne BERTHIER, Andreas KÄÄB
Corresponding author: Tobias Bolch
Corresponding author e-mail: email@example.com
Glaciers are characteristic elements in High Mountain Asia (HMA) and have an important regulating role in regard of the water resources and freshwater supply of the region. Detailed knowledge of past changes is essential to understand the heterogeneity of the glacier response to climate. Acquiring such knowledge can be difficult as glaciers in HMA are numerous and cover an area of >100 000 km2 in mostly inaccessible terrain. We investigated glacier volume changes for the entire region in the recent decade based on ICESat laser altimetry data and compared them with other geodetic assessments using the 2000 SRTM DEM and recent DEMs from various sources for selected regions. Declassified reconnaissance imagery from the Corona and Hexagon missions flown in the 1960s and 1970s allow the time series of glacier change to be extended back, putting the recent glacier behavior into a long-term perspective. An important prerequisite to doing such analysis is a precise glacier inventory for the entire region. We used the Randolph Glacier Inventory and glacier outlines from GLIMS as baseline data and improved them where necessary. Results reveal that the majority of the glaciers lost mass during the last decade. The highest mass loss occurred in the Tien Shan (–0.49 ± 0.22 m w.e. a–1) and west (–0.53 ± 0.17 m w.e. a–1) and east Himalaya (–0.52 ± 0.18 m w.e. a–1). Glaciers in southeast Tibet showed mass budgets of –0.39 ± 0.26 m w.e. a–1 and in northeast Tibet of –0.42 ± 0.32 m w.e. a–1. However, glaciers in the Karakoram (–0.02 ± 0.17 m w.e. a–1), Pamir (+0.01 ± 0.17 m w.e. a–1), western Kunlun (+0.16 ± 0.18 m w.e. a–1) and the central Tibetan Plateau (+0.06 ± 0.11 m w.e. a–1) experienced near-balanced budgets. The results of the different methods and studies are, in general, in good agreement with the highest disagreements occurring in east Himalaya. For the northern and central Tien Shan and also the central Himalaya, mass loss rates are similar during 1975–2000 and for the last decade. In the Pamirs we found on average slight mass loss of the investigated glaciers in the last decades of the 20th century, whereas mostly balanced mass budgets are measured for the 21st century.
Glaciers in the Aksu catchment (central Tien Shan) 1975–2010: changes and hydrological importance
Tobias BOLCH, Tino PIECZONKA, Shiyin LIU
Corresponding author: Tobias Bolch
Corresponding author e-mail: firstname.lastname@example.org
The Tarim River is nourished to a high degree by glacier meltwater from the central Tien Shan located both in Kyrgyzstan and China and is the main artery for the oases at the northern margin of the Taklamakan desert located in Xinjiang/China. The precise knowledge about the reaction of the glaciers to climate change and the past and future meltwater release is therefore of uttermost importance for the development of this arid region. Glacier area and its changes are comparatively easy to measure using multitemporal satellite images. Glaciers cover an area of about 3500 km2, which is about 8% of the entire Aksu catchment. The glaciers shrank less than 0.2% a–1 for the period ~1975–2010 on average. However, only the mass budget of the glaciers shows an almost direct signal to climate but long-term measurements of glacier mass budgets are currently rare across the high mountains of Asia and do not exist in the study region. Therefore time series of digital terrain models (DTMs) for different parts of the Aksu-Tarim catchment were generated based on KH9-Hexagon imagery from the 1970s, the SRTM3 DTM and recent high-resolution stereo data such as SPOT5 and Cartosat-1. Quality assessments of the generated DTMs showed promising results but careful co-registration and relative adjustments were necessary. Preliminary results show significant mass loss in the order of about –0.4 m w.e. a–1 for the investigated glaciers despite partly thick debris cover. Few glacier surges were also detected. The mass changes in the recent decade were in the same order or even slightly lower. Run-off measurements reveal an average of 9 km3 a–1 since the mid-1970s and our results reveal an average glacier mass loss of ~1.4 Gt a–1. Based on this result the contribution of the glacier meltwater to the overall run-off of the Aksu River would be in the order of 15–20%. This is significant but lower than previous estimates. Further work is underway to evaluate this number based on hydrological and mass-balance models.
Climate impacts on local glaciers and ice caps on Greenland based on RACMO2 (ERA-Interim) output
Philipp RASTNER, Horst MACHGUTH, Tobias BOLCH, Frank PAUL
Corresponding author: Philipp Rastner
Corresponding author e-mail: email@example.com
The recently finalized complete glacier inventory of Greenland’s local glaciers and ice caps (GIC) allowed for the first time determination of their mass changes independent from the ice sheet. Using spaceborne laser altimetry data from ICESat, Greenland’s GIC showed a mean lowering of 0.45 m a–1 for the period October 2003–March 2008. The mass loss differs substantially among the regions, with the highest specific mass loss occurring in the southeastern sector (–1.37 m a–1) whereas the lowest was measured in the north-central (–0.18 m a–1) part of Greenland. In this study we investigate the meteorological forcing that might have triggered the mass changes separately for ten different zones on Greenland. We address this question by (1) investigating the influence of their respective sensitivities to a changing climate and (2) by bringing observed regional mass loss into the context of regional changes in climate. For that purpose we use output from a regional climate model (RACMO2, 1980–2011 forced from ERA-interim) and investigate precipitation and temperature trends from 1980 to 2010 in the ten zones on Greenland. Uncertainties and potential biases of RACMO2 temperature and precipitation data are evaluated by comparison to in situ weather station data. Moreover RACMO2 temperature is corrected for elevation differences between the coarse RACMO2 topography (11 km grid) and a higher-resolution DEM. The precipitation in RACMO2 is evaluated by approximating the precipitation at the equilibrium line of the GICs based on empirical relations. Finally, the mass changes derived from ICESat are compared with the modified mean temperature and precipitation from RACMO2 by linear and multiple regression analysis. After cross validation of RACMO2 with in situ weather stations, trends are reproduced well. Over the last 30 years, temperatures in all regions are strongly increasing; however, precipitation amounts show no clear trend is visible. Mean summer temperatures are fairly constant between the regions, but in the winter a clear trend of decreasing temperatures from south to north is visible. A clear precipitation difference between winter and summer is only visible for three regions (south-east, south-west and east-southern), which is more than twice as much as in summer. Finally, we found clear negative correlation trends for the mass changes with temperature and precipitation.
Response of the Amery Ice Shelf basal melting to ocean temperature change
Fan YANG, Jiahong WEN, Weili WANG, T.H. Jacka
Corresponding author: Jiahong Wen
Corresponding author e-mail: firstname.lastname@example.org
The relationship between ice-shelf basal melting beneath the Amery Ice Shelf, East Antarctica, and ocean temperature is studied using a numerical model. The basal melting and freezing rates under the ice shelf, a column-averaged ice density model, sea-water temperature and salinity measurements and projected Southern Ocean temperate rise over the 21st century are employed in the analysis. The difference between the ocean temperature and the sea-water freezing point under the ice shelf is numerically modeled. Our results show that the basal melting rate increases quadratically as the ocean offshore from the ice-shelf front warms. Near the grounding zone where the strongest thermal forcing exists, we find the basal melting rate increases by 12.5 m a–1, associated with a 1° rise in ocean temperature, in good agreement with previous studies. However, we find no correlation between changes in basal freezing/melting rate and ocean temperature in the marine ice zone. The different response patterns of the basal melting/freezing to variations in ocean temperature between the melting area and the refreezing marine ice area may suggest an important role for frazil dynamics. Considering the sensitivity of melting rate and thermal forcing, the net basal melting of the Amery Ice Shelf within the next three decades may be greater than 81 km3 a–1.
Ice elevation and surface changes over the Puruogangri ice field in the central Tibetan Plateau from geodetic observations
Liming JIANG, Liu LIN, Yafei SUN, Hansheng WANG
Corresponding author: Liming Jiang
Corresponding author e-mail: email@example.com
The Puruogangri is located in the central Tibetan Plateau (TiP), being the largest modern ice field in the TiP covered by an area of 400 km2 in total. The study area is of special interest for glacier dynamics research as it is under the complex influence of both the prevailing westerlies and the Indian Monsoon system and information on the glacier dynamics is scarce due to the difficulty of reaching the area. In this paper, we aim to utilize ICEsat elevation data and GPS observations to calibrate the TanDEM-X (TDX) raw DEM derived by SAR interferometry and to evaluate its potential to measure the surface elevation and changes in glacial areas in the TiP. First, a pair of co-registered TanDEM-X bistatic InSAR data, acquired on 26 January 2012 over all of the study area, was processed to generate a raw DEM that was affected by both systematic and noise-like height errors. Then, 367 ICEsat data located at non-glacial and flat areas were used as GCPs to correct the point-point relative height errors and calibrate the constant absolute height shifts in the raw DEM. Finally, the absolute accuracy of the resultant DEMs was assessed by comparing with our tens of GPS observations measured in October 2012 with GPS-RTK techniques. For the raw DEM, the mean difference with GPS observations is 4.79 m and the RMSE is 2.57 m, which are consistent with the TDX DEM specifications published by DLR. The corrected DEM accuracy was significantly improved with the mean difference of 1.91 m and the RMSE of 0.76 m. Furthermore we found a remarkable thinning of around 1.6 m in average ice thickness by comparing the calibrated TDX DEM in 2012 with the SRTM-X DEM in 2000. The preliminary results demonstrate that the geodetic data have a significant potential to detect the mountain glacier surface elevation and its changes.
Multi-decadal ice velocity fields over the Amery Ice Shelf system derived from joint analysis of optical and SAR satellite images
Liming JIANG, Liu LIN, Qiang SHEN, Yongling SUN, Hansheng WANG
Corresponding author: Liming Jiang
Corresponding author e-mail: firstname.lastname@example.org
The Amery Ice Shelf (AIS) system, located in East Antarctica, is one of the largest glacial basins in the world. Its glacier dynamics is crucial in determining the mass balance of East Antarctica as well as global sea-level contribution from the Antarctic ice sheet. In this paper, multi-decadal ice velocity fields over the AIS and its three major tributary glaciers have been derived by analysis of complementary satellite optical and radar data acquired from the 1980s to 2011s. The analysis technique used the feature-tracking algorithm in pairs of Landsat TM/ETM+ images and the speckle-tracking technique was applied to analysis of ERS-1/2 and Envisat SAR images. Spatially complete and temporally continuous velocity fields have been generated benefiting from complementary ice velocity products from optical and radar satellite images. This high-resolution velocity field can serve as a key input for modelling glacier dynamics processes. The velocities generated were compared with those of recent compilations of satellite-derived velocities and the limited GPS sites. Our velocities generally show good agreement with the measures for large portions of the study region; however, our results show a faster ice flow over the grounding line. Finally we analyzed long-term change characteristics in glacier velocity. The preliminary results show that the three major upstream glaciers of the AIS, Fisher, Lambert and Mellor Glaciers, are close to steady state, while the flow over the grounding line shows accelerations of about 1–3%. The velocity along the AIS has not changed significantly, but the ice flow velocity of its front edge may occur slightly increased
Sensitivity of the Greenland ice sheet to basal sliding change
Weili WANG, H. Jay ZWALLY, Jun LI
Corresponding author: Weili Wang
Corresponding author e-mail: email@example.com
This paper presents the modeling experiments of the Greenland ice sheet from the Sea-level Response to Ice Sheet Evolution (SeaRISE) project, a community ice-sheet modeling effort to provide quantitative estimates of ice-sheet contributions to sea-level rise in the 21st century for 5th IPCC report. In order to study the sensitivity of ice sheet to changes of sliding at the subglacial interface, the SeaRISE experiments are set to enhance the basal sliding velocity by an amplification factor of 2×, 2.5× and 3×, respectively. We perform the experiments by applying two versions of anisotropic ice-flow (AIF) model to the Greenland ice sheet. Two models (AIFa and AIFb) use the different basal sliding laws, i.e. the basal sliding velocities are estimated based on the cubic (AIFa) and linear (AIFb) power relation of the basal share stress, respectively. The changes of the ice-sheet volume show that the models predict larger ice losses when the basal sliding is an exponential function of the basal stress as compared with the linear function. Large mass losses in the margin areas correspond to strong basal sliding perturbations. Strong perturbations enhance upstream propagation and result in dynamic thinning of interior ice sheet. We will compare the results from the two models to show the impact of basal sliding on the dynamic change of the Greenland ice sheet.
Estimation of ice thickness under consideration of debris cover – case example in the central Tien Shan
Tino PIECZONKA, Tobias BOLCH, Shiyin LIU
Corresponding author: Tino Pieczonka
Corresponding author e-mail: firstname.lastname@example.org
Glacier meltwater contributes to river discharge especially in the arid regions along the northern margin of the Taklamakan desert. Glacier area is easy to measure, whereas for the projection of water availability into the future, knowledge of total ice volume is needed. However, glacier volume estimations are still rare in the Tien Shan. Our study area, comprising the Aksu Tarim catchment in Kyrgyzstan and China, is characterized by large debris-covered glaciers and highly dynamic glaciers the activity of which is characterized by surging activities. The determination of glacier ice thickness based on the shallow-ice approximation is a common approach successfully applied in several mountain areas. However, this method is accompanied by uncertainties of about 30% and the effect of debris cover is not taken into account. Debris cover influences the shear stress on the glacier ice–bedrock interface; therefore, the shallow-ice approximation might not be applicable in its common form to debris-covered glaciers. Different geological conditions, glacier downwasting rates, glacier topography, topography of the area adjacent to the glacier, erosion on the glacier ice–bedrock interface, thermal conditions of glaciers, and glacier velocity are driving factors for both debris thickness and ice thickness as well as debris distribution. In areas of thick debris cover erosive processes on the glacier bedrock interface are negligible and glacier downwasting is the prevailing process changing the glacier thickness. We extend the existing approaches to estimate ice thickness based on the shallow-ice approximation by debris thickness. In a first step we include velocity measurements derived from multitemporal optical imagery (e.g. Landsat-ETM+ and ALOS) with a time span of about 1 year in order to distinguish active and stagnant glacier parts. The results can then be transferred in order to adapt the expected basal shear stresses. Results of the model will be evaluated using existing GPR-based ice thickness measurements available for a sample of glaciers in the Akshirak Mountain massif (Kyrgyzstan) and the Tomur region (China).
The role of ice dynamics in projections of the centennial mass evolution of the Greenland ice sheet
Philippe HUYBRECHTS, Heiko GOELZER, Johannes J. FÜRST
Corresponding author: Philippe Huybrechts
Corresponding author e-mail: email@example.com
Continuing global warming will have a strong impact on the mass balance of the Greenland ice sheet in the coming centuries. The resulting contribution to sea-level change will depend on changes in snow accumulation and ice melting, and on ice dynamics, which operates on a wide range of timescales. The ice-dynamic response includes adjustment to changes in ice-sheet geometry, meltwater-induced basal lubrication and ocean-induced changes of ice discharge at marine-terminated outlet glaciers. Here, we use a higher-order three-dimensional thermomechanical ice-flow model to project future ice mass changes. The model is initialized to the present-day state from a palaeo spin-up over several glacial–interglacial cycles. First the sensitivity of the projections is investigated to different formulations of the surface mass balance, to a generalization of prescribed outlet glacier dynamics from flowline models and to a parametric treatment of basal lubrication. This is done for a fixed climate scenario using output from a high-resolution regional climate model. The simulations are subsequently forced by a suite of ten CMIP5 AOGCMs using four RCP scenarios up to AD 2300 to take into account climate model uncertainty. In these projections, increased ice discharge of outlet glaciers is linked to the regional pattern of ocean warming at mid-depth. We find Greenland contributions to global sea-level rise between 1.4 and 16.6 cm by AD 2100 and to up to 32 cm by AD 2300 for RCP4.5. The mass loss is predominantly caused by changes in surface mass balance. Interaction between surface mass balance and ice discharge limits the importance of outlet glacier dynamics as both processes are mutually competitive in removing mass from the ice sheet. Increasing runoff reduces the ice volume that reaches the marine margin and thereby decreases ice discharge rates. Discharge is also limited by a gradual loss of the ocean contact and a retreat of the ice-sheet margin on land. The direct effect of subglacial meltwater drainage that lubricates the base is negligibly small. The results suggest that observed rates of change over the last decade cannot simply be extrapolated over the 21st century on account of a different balance of processes causing mass loss over time. They also indicate that the largest source of uncertainty arises from the surface mass balance and the underlying climate change projections, and not from ice dynamics.
Travelling the last mile: communicating cryospheric knowledge
Corresponding author: Robert Bindschadler
Corresponding author e-mail: firstname.lastname@example.org
There is no doubt within the cryospheric community that ‘our’ world, dominated by ice and low temperatures, is reacting strongly to increased warming of our planet. I address the challenges these physical changes pose for our scientific community. In a sense, we were caught with our pants down, equally astonished, as was the global audience, by the surprises of disintegrating ice shelves, accelerating outlet glaciers and shrinking land ice. We have responded by focusing on new areas of research and have been treated to impressively precise datasets that inform us about ongoing change. The excitement and, I’d like to think, the importance of what is happening to land ice across the globe has attracted new colleagues to share in our investigations, forming new collaborations and interdisciplinary teams. But are these changes enough? Are we simply recasting the science we do rather than transforming the landscape of what it means to be a ‘cryosopher’? Being thrust to the front and center of the climate change stage not only provides new attention and frequent headlines, but new responsibilities as well. What are these new responsibilities and how do we meet them?
Margin lakes and ice-stream grounding-line migration
Mason J. FRIED, Christina HULBE, Mark FAHNESTOCK
Corresponding author: Christina Hulbe
Corresponding author e-mail: email@example.com
The lateral ‘corners’ where Kamb and Whillans Ice Streams (KIS and WIS) discharge into the Ross Ice Shelf share common geometries and ice mechanical settings. At both corners of the now-stagnant KIS outlet, shear margins of apparently different ages confine regions with a relatively flat, smooth surface expression. These features are called ‘the Duckfoot’ on the northern right-lateral side and ‘the Goosefoot’ on the other. The right-lateral outlet of the currently active WIS looks much the same, though with a less-developed inboard margin. It has been suggested, on evidence found in ice internal layers, that the flat ice terrains on KIS were afloat in the recent past, at a time when the ice-stream grounding line was upstream of its present location. The overdeepening in the bed just upstream of the KIS grounding line supports this view of the past geometry. Here, we consider the history of these features and their role in ice-stream variability by comparison of the relict and modern features and via numerical modeling of ice-shelf grounding and ungrounding in response to variations in ice flow. We propose two scenarios for lake (flat ice terrain) development at the outlets of ice streams. In the first, development of a lake in the hydraulic potential low along a shear margin forces a margin jump as shearing develops along the inboard shore of the margin lake. In the second, a remnant lake is formed by grounding-line advance around a relative low in the bed, creating adjacent margins along the lake shores. Discerning which of these scenarios is appropriate at the KIS outlet has implications for understanding the history of the ice-stream grounding line. While the second process is consistent with a paleo-grounding line upstream of the present location, if the margin lake model is instead appropriate, then the accepted interpretation of grounding-line history is incorrect.
Wind glaze, wind scour and megadunes in East Antarctica
Ted A. SCAMBOS
Corresponding author: Ted A. Scambos
Corresponding author e-mail: firstname.lastname@example.org
The East Antarctic Plateau is host to unique interactions between surface snow and near-surface winds, producing widespread regions of very low net accumulation termed wind glaze (near-zero accumulation), wind scour (slighly negative accumulation) and snow megadunes (alternating bands of high accumulation and wind glaze). These regions have been mapped by both their remote-sensing characteristics and by prediction based on surface slope, regional accumulation and regional wind direction. Profound changes occur in the firn below wind glaze regions due to the prolonged period of exposure to annual temperature oscillations. The alternating dune and glaze surfaces have potential impacts on ice-core interpretation through post-deposition effects on snow chemistry and isotopes. These features represent a kind of new facies in the ice sheet, in effect a variation of the dry-snow zone that is nearly unrepresented in Greenland.
Glacier mass-balance and runoff modelling in Xiying River basin, eastern Qilian Mountains, China
Bo CAO, Baotian PAN, Jie WANG
Corresponding author: Baotian Pan
Corresponding author e-mail: email@example.com
Global warming is causing widespread glacier retreat, with small glaciers disappearing. As there are few studies on the Lenglongling Mountains, located in the northeastern margin of the Tibetan Plateau, 33 stakes were drilled on the NC01 and SG04 glaciers, which are part of Xiying River basin, in Sepember 2010 to observe the mass balance of these two glaciers. The results suggest that the two glaciers are retreating and have a negative mass balance. The equilibrium-line altitude (ELA) exceeds the maximum altitude of the NC01 glacier, that is the whole glacier is in the ablation zone. The mean annual mass balance is –1260 mm for the NC01 glacier. The ELA rose 180 m for the SG04 glacier from 1972 to now, with a mean rate of 3.75 m a–1. The mean annual mass balances of the whole SG04 glacier and ablation zone are –294 mm and –808 mm, respectively. Based on analysis of meteorological data, which is set up on the lateral moraine of the NC01 glacier, the simple degree-day model was used to model the mechanism of response of glaciers to climate change. The area of the 30 glaciers in the Xiying River basin only accounts for 0.8% of the total area of Xiying River basin; however, the glacier meltwater accounts for 5.8% of the total runoff. Furthermore if the temperature rose by 1 K, the summer glacier melt of the NC01 glacier will increase by 208 mm.
Monitoring spatio-temporal variations of snow cover using a new MODIS daily cloud-free snow-cover product
Xianwei WANG, Hailing ZHENG
Corresponding author: Xianwei Wang
Corresponding author e-mail: firstname.lastname@example.org
Cloud is one of the main factors affecting the optical remote-sensing Earth observation. The mean cloud of standard MODIS daily snow cover amounts to 50% and can even reach 95% for some days in northern Xinjiang. The standard MODIS snow-cover products are seriously affected by the enormous cloud and there is large uncertainty in the spatio-temporal features derived from MODIS standard snow-cover products due to cloud blockage. Thus, a variety of cloud-free methods are developed to mitigate the cloud interference problems of MODIS standard snow-cover products. This study develops an algorithm to combine the Terra and Aqua MODIS daily snow-cover products (MOD10A1 and MYD10A1) to generate a cloud-free snow-cover product. A daily cloudless snow-cover product (MODMYD_DC) is first generated by a maximum snow-cover combination from Terra and Aqua MODIS standard daily snow-cover products (MOD10A1 and MYD10A1), then the cloud-covered pixels on the current day MODMYD_DC are replaced with the cloud-free pixels on the previous day MODMYD_DC until all cloud-covered pixels are cleared up. Finally a new daily cloud-free snow-cover product (MODMYD_MC) is generated and used to study the spatio-temporal variations of snow cover. MODIS tile h26v04 that primarily covers Heilongjiang Province is used to test the algorithm, and in situ snow depth measurements during 2000–2011 at 53 stations are used to validate the accuracy of snow-cover products. The results show that the mean snow-cover accuracies of MOD10A1, MYD10A1, MODMYD_DC and MODMYD _MC are 42%, 40%, 51% and 91%, respectively. The snow-covered days (SCD) that are derived from MODMYD_MC are in agreement (95.3%) with those obtained from in situ measurement, with a mean absolute difference of 4.3 days. Meanwhile, among all MODMYD_MC images over 11 hydrologic years, the mean percentage of pixels that were cloud-free on each day is 59%, and it is 90% after 3-day image combination. All these indicate that MODMYD_MC can be used to efficiently monitor the spatio-temporal variations of snow cover world around. Taking the Xiao Xing An Ling basin as an example by using SCD and snow-cover index (SCI) developed from MODMYD_MC, this study illustrates detailed variation maps of SCD and finds that the snow cover in this area has an increasing trend since 2000, with minimum value in 2001–2002 hydrologic year and maximum in 2009–2010; mountainous regions with higher elevation have a smaller interannual snow-cover variation than the plains with lower elevation.
Snowpack chemistry and seasonal variability at an alpine temperate glacier on Mount Yulong, southeastern part of the Tibetan Plateau
Tao PU, Yuanqing HE
Corresponding author: Tao Pu
Corresponding author e-mail: email@example.com
Seven snowpacks were sampled in 2008/2009 on Baishui Glacier No. 1 on Yulong Mountain to define snowpack chemistry and environmental significance. Soluble ions of winter snowpack showed low values in the middle part and high values in the lower and upper part, influenced by the atmospheric deposition of snow accumulation. The larger variations of ionic concentrations in spring snowpack were associated with the variable atmospheric income, with high dust content in spring leading to higher ionic concentrations in the upper snowpack. Strong meltwater percolation resulted in quick migration and redistribution of ions for the profile during monsoon. The ions elution sequence was Ca2+ > SO42– > NH4+· NO3+·> Mg2+·> K+·> Na+·> Cl– and the potential sources were identified as wet deposition, marine and local terrestrial source. δ18O of late autumn and winter snowpack experienced high–low–high variation from the bottom to the surface snow, whereas the value in spring witnessed complex curve, reflecting the temperature of snow accumulation. The higher values of δ18O in the upper part of the spring snowpack were a reflection of local water vapor enriched 18O. Homogenization was apparent influenced by a large amount of meltwater in the ablation season.
The impact of surface lakes on the stress regime of the Larsen B Ice Shelf
Douglas MacAYEAL, Alison BANWELL, Olga SERGIENKO, Martamaria CABALLERO, Neil GLASSER
Corresponding author: Douglas MacAyeal
Corresponding author e-mail: firstname.lastname@example.org
The most conspicuous change to the Larsen B Ice Shelf in the years prior to its explosive break-up in February/March 2002 was the build-up of thousands of supraglacial lakes in response to environmental warming. In the present contribution, we present a numerical model study of the stress regime these lakes were likely to have introduced as a result of ice-shelf flexure in response to water load. Our goal is to illustrate how lake-induced stress regime is capable of fragmenting the ice shelf to the extent necessary to produce the multitude of small ice-shelf fragments characteristic of the explosive break-up.
A particle-based simulation model for glacier dynamics
J.C. MOORE, J.A. ÅSTRÖM, T. RIIKILÄ, T. TALLINEN, T. ZWINGER, D. BENN, J. TIMONEN
Corresponding author: J.C. MOORE
Corresponding author e-mail:
A particle-based computer simulation model has been developed with the objective of investigating the dynamics of glaciers. To describe ice dynamics in a realistic fashion, a model must include elastic deformation, granular flow and fracture of large ice bodies. In spite of several simplifications, which include restriction to two dimenions only and simplified rheology for ice and water, the present model is able to reproduce iceberg and small debris size distributions observed in calving. The observed size distributions are well approximated by universal scaling laws. On a moderate slope a large ice-block (here 50 m high and 200 m long) is stable as long there is enough friction with the substrate. This is a quiescent state. At a critical extent of frictional contact there is an onset of global sliding and the model glacier begin to surge. During the surge, the glacier is fragmented into small pieces. In this case the fragment size distribution has the shape that is typically observed for grinding processes.
Cryochemical processes and mass balance of the Hans Glacier
Corresponding author: Piotr Glowacki
Corresponding author e-mail: email@example.com
The problem of precise determination of glacier mass balance as an indicator of climate changes has always been a field of considerable interest. Mass balance of the ablation part of a glacier is relatively easy to determine. There are still many questions concerning the accumulation zone, especially in areas with percolating meltwater. An attempt was made to analyse the influence of melting and related physicochemical processes on the total mass balance of the glacier systems. Long-term observations (1988–1997) of the ions from natural sources (e.g. sea aerosols) and anthropogenic pollutions deposited in snow on the Hans Glacier surface and their migration with meltwater were carried out. The mean total dissolved solid concentration (TDS) in water flowing on the glacier surface (14.8 mg/dcm3) is different from the TDS in water in englacial channels in water-bearing layers (114 mg/dcm3). Such a difference may be result of cryochemical processes, which occur in the ablation part of the glacier within firn layers. Part of the water that percolates inside the glacier freezes in its interior as a result of winter cooling, constituting its internal feeding. The mean annual internal accumulation for the Hans Glacier, determined by cryochemical method, is 0.26 m w.e., while the average balance, determined by classical methods, is negative (-0.31 m w.e.). The corrected mean net balance of this glacier, without accounting for calving, is only slightly negative and amounts to -0.05 m w.e. Proposed new method, which assesses cryochemical processes, seems to be relatively simple and easy tool to correct results of mass balance calculations of Spitsbergen glaciers by internal feeding.
Mass balance of Antarctic ice sheet 1992–2008 from ERS and ICESat: gains exceed losses
H. Jay ZWALLY, Jun LI, John ROBBINS, Jack L. SABA, Donghui YI, Anita BRENNER
Corresponding author: H. Jay ZWALLY
Corresponding author e-mail: firstname.lastname@example.org
During 2003–2008, the mass gain of the Antarctic ice sheet from snow accumulation exceeded the loss from ice discharge by 73±23 Gt a–1 (3.7% of input), as derived from ICESat laser altimetry. The 131 Gt a–1 gain in East Antarctica (EA) and the 70 Gt a–1 gain in four drainage systems (DS) of West Antarctic (WA2) exceeded combined losses of 98 Gt a–1 from three coastal DS of West Antarctic (WA1) and 28 Gt a–1 from the Antarctic Peninsula (AP). Re-analysis of ERS radar-altimeter data, including a new post-glacial-rebound correction, indicates an even larger overall gain of 120 ± 51 Gt a–1 during 1992–2001. In WA2 and EA, persistent dynamic thickening (deficiency of ice flow relative to long-term accumulation) contributed more than 200 Gt a–1 to the net positive balance in both periods. Consistent with observed outlet-glacier accelerations, loss increases of 38 Gt a–1 in WA1 and 21 Gt a–1 in AP from increased dynamic thinning dominated a gain increase of 9 Gt a–1 from positive accumulation anomalies in WA1 and AP. These decadal-scale changes are small relative to the long-term dynamic thickening in EA and WA2, which may buffer additional dynamic thinning for several decades.
Modeling dynamic thickening in East Antarctica as observed from ICESat
Weili WANG, H. Jay ZWALLY, Jun LI
Corresponding author: Weili WANG
Corresponding author e-mail: email@example.com
Mass changes of the Antarctic ice sheet derived from ICESat laser altimetry show that during 2003–08 mass gains from snow accumulation exceeded losses from ice discharge by 73 Gt a–1 (0.20 mm a–1 sea level depletion). Results from ERS radar altimetry give a similar net gain of 120 Gt a–1 for 1992–2001. In East Antarctica and four West Antarctic drainage systems, most of the net mass gain is caused by persistent dynamic thickening (excess of long-term accumulation relative to ice flow) at a rate of 207 Gt a–1, and not by contemporaneous increases in snowfall. To investigate the dynamic thickening rate, we apply a 3-D ice-sheet model to the Antarctic ice sheet for the sensitivity experiments with climate change. The model results indicate that the East Antarctic ice sheet has been growing due to increased snowfall after the last ice age. The modeled thickening rate near Vostok is 2.5 cm a–1 for the present time, which is consistent with the observations from ICESat and ERS data. Overall, the model and observations indicate a long-term mass gain for East Antarctica and the interior of West Antarctic, which has been offsetting dynamic losses that have increased in the Antarctic Peninsula and West Antarctica during the last two decades.