ALBERT

Description: Brief communication "Snow profile associated measurements (SPAM) – a new instrument for quick snow profile measurements" The Cryosphere Discussions, 5, 1737-1748, 2011 Author(s): P. Lahtinen A new instrument concept (SPAM) for snow profile associated measurements is presented. The potential of the concept is demonstrated by presenting preliminary results obtained with the prototype instrument. With this concept it is possible to retrieve rapid snow profiles of e.g. light extinction, reflectance, temperature and snow layer structure with high vertical resolution. As a side-product, also snow depth is retrieved.

Description: Modeling the impact of wintertime rain events on the thermal regime of permafrost The Cryosphere Discussions, 5, 1697-1736, 2011 Author(s): S. Westermann, J. Boike, M. Langer, T. V. Schuler, and B. Etzelmüller In this study, we present field measurements and numerical process modeling from Western Svalbard showing that the ground surface temperature below the snow is impacted by strong wintertime rain events. During such events, rain water percolates to the bottom of the snow pack, where it freezes and releases latent heat. In the winter season 2005/2006, on the order of 20 to 50 % of the wintertime precipitation fell as rain, thus confining the surface temperature to close to 0 °C for several weeks. The measured average ground surface temperature during the snow-covered period is −0.6 °C, despite of a snow surface temperature of on average −8.5 °C. For the considered period, the temperature threshold below which permafrost is sustainable on long timescales is exceeded. We present a simplified model of rain water infiltration in the snow coupled to a transient permafrost model. While small amounts of rain have only minor impact on the ground surface temperature, strong rain events have a long-lasting impact. We show that consecutively applying the conditions encountered in the winter season 2005/2006 results in the formation of an unfrozen zone in the soil after three to five years, depending on the prescribed soil properties. If water infiltration in the snow is disabled in the model, more time is required for the permafrost to reach a similar state of degradation.

Description: Investigating changes in basal conditions of Variegated Glacier prior and during its 1982–1983 surge The Cryosphere Discussions, 5, 1461-1494, 2011 Author(s): M. Jay-Allemand, F. Gillet-Chaulet, O. Gagliardini, and M. Nodet The Variegated Glacier (Alaska) is known to surge periodically after a sufficient amount of cumulative mass balance is reached, but this observation is difficult to link with changes in the basal conditions. Here, using a 10-year dataset, consisting in surface topography and surface velocity observations along a flow line for 25 dates, we have reconstructed the evolution of the basal conditions prior and during the 1982–1983 surge. The model solves the full-Stokes problem along the central flow line using the finite element method. For the 25 dates of the dataset, the basal friction parameter distribution is inferred using the inverse method proposed by Arthern and Gudmundson (2010). This method is here slightly modified by incorporating a regularisation term in the cost function to avoid short wave length changes in the friction parameter. Our results indicate that dramatic changes in the basal conditions occurred between 1973 to 1983. Prior to the surge, periodical changes can be observed between winter and summer, with a regular increase of the sliding from 1973 to 1982. During the surge, the basal friction decreased dramatically and an area of very low friction moved from the upper part of the glacier to its terminus. Using a more complex friction law, these changes in basal sliding are then interpreted in terms of basal water pressure. It confirms that dramatic changes took place in the subglacial drainage system of Variegated Glacier, moving from a relatively efficient drainage system prior to the surge to an inefficient one during the surge. By reconstructing the water pressure evolution at the base of the glacier it is possible to infer realistic scenarios for the hydrological history leading to the occurrence of a surge.

Description: Warming of waters in an East Greenland fjord prior to glacier retreat: mechanisms and connection to large-scale atmospheric conditions The Cryosphere Discussions, 5, 1335-1364, 2011 Author(s): P. Christoffersen, R. I. Mugford, K. J. Heywood, I. Joughin, J. A. Dowdeswell, J. P. M. Syvitski, A. Luckman, and T. J. Benham Hydrographic data acquired in Kangerlugssuaq Fjord and adjacent seas in 1993 and 2004 are used together with ocean reanalysis to elucidate water mass change and ice-ocean-atmosphere interactions in East Greenland. The hydrographic data show substantial warming of fjord waters between 1993 and 2004 and warm subsurface conditions coincide with the rapid retreat of Kangerlugssuaq Glacier in 2004–2005. The ocean reanalysis shows that the warm properties of fjord waters in 2004 are related to a major peak in oceanic shoreward heat flux into a cross-shelf trough on the outer continental shelf. The heat flux into this trough varies according to seasonal exchanges with the atmosphere as well as from deep seasonal intrusions of subtropical waters. Both mechanisms contribute to high (low) shoreward heat flux when winds from the northeast are weak (strong). The combined effect of surface heating and inflow of subtropical waters is seen in the hydrographic data, which were collected after periods when along-shore coastal winds from the north were strong (1993) and weak (2004). We show that coastal winds vary according to the pressure gradient defined by a semi-permanent atmospheric pressure system over Greenland and a persistent atmospheric low situated near Iceland. The magnitude of this pressure gradient is controlled by longitudinal variability in the position of the Icelandic Low.

Description: Recent wind driven high sea ice export in the Fram Strait contributes to Arctic sea ice decline The Cryosphere Discussions, 5, 1311-1334, 2011 Author(s): L. H. Smedsrud, A. Sirevaag, K. Kloster, A. Sorteberg, and S. Sandven Arctic sea ice area decrease has been visible for two decades, and continues at a steady rate. Apart from melting, the southward drift through Fram Strait is the main loss. We present high resolution sea ice drift across 79° N from 2004 to 2010. The ice drift is based on radar satellite data and correspond well with variability in local geostrophic wind. The underlying current contributes with a constant southward speed close to 5 cm s −1 , and drives about 33 % of the ice export. We use geostrophic winds derived from reanalysis data to calculate the Fram Strait ice area export back to 1957, finding that the sea ice area export recently is about 25 % larger than during the 1960's. The increase in ice export occurred mostly during winter and is directly connected to higher southward ice drift velocities, due to stronger geostrophic winds. The increase in ice drift is large enough to counteract a decrease in ice concentration of the exported sea ice. Using storm tracking we link changes in geostrophic winds to more intense Nordic Sea low pressure systems. Annual sea ice export likely has a significant influence on the summer sea ice variability and we find low values in the 60's, the late 80's and 90's, and particularly high values during 2005–2008. The study highlight the possible role of variability in ice export as an explanatory factor for understanding the dramatic loss of Arctic sea ice the last decades.

Description: Spatio-temporal measurements and analysis of snow depth in a rock face The Cryosphere Discussions, 5, 1383-1418, 2011 Author(s): V. Wirz, M. Schirmer, S. Gruber, and M. Lehning Snow in rock faces plays a key role in the alpine environment for permafrost distribution, snow water storage or run off in spring. However, a detailed assessment of snow depths in steep rock walls has never been attempted. To understand snow distribution in rock walls a high-resolution terrestrial laser scanner (TLS), including a digital camera, was used to obtain snow depth (HS) data with a resolution of one metre. The mean HS, the snow covered area and their evolution in the rock face were compared to a neighbouring smoother catchment and a flat field station at similar elevation. Further we analyzed the patterns of HS distribution in the rock face after different periods and investigated the main factors contributing to them. In a first step we could show that with TLS reliable information on surface data of a steep rocky surface can be obtained. In comparison to the flatter sites in the vicinity, mean HS in the rock face was lower during the entire winter, but trends of snow depth changes were similar. We observed repeating accumulation and ablation patterns in the rock face, while maximum snow depth loss always occurred at those places with maximum snow depth gain. Further analysis of the main factors contributing to the snow depth distribution in the rock face revealed terrain-wind-interaction processes to be dominant. Processes related to slope angle seem to play a role, but no linear function of slope angle and snow depth was found. Further analyses should involve measurements in rock faces with other characteristics and higher temporal resolutions to be able to distinguish individual processes better. Additionally the relation of spatial and temporal distribution of snow depth to terrain-wind interactions should be tested.

Description: Utility of late summer transient snowline migration rate on Taku Glacier, Alaska The Cryosphere Discussions, 5, 1365-1382, 2011 Author(s): M. Pelto On Taku Glacier, Alaska a combination of field observations of snow water equivalent (SWE) from snowpits and probing in the vicinity of the transient snowline (TSL) are used to quantify the mass balance gradient. The balance gradient is determined from the difference in elevation and SWE from the TSL to snowpits at 1000 m from 1998–2010 and ranges from 2.6–3.8 mm m −1 . Probing transects from 950 m–1100 m directly measure SWE and yield a slightly higher balance gradient of 3.3–3.8 mm m −1 . TSL is identified in MODIS and Landsat 4 and 7 Thematic Mapper imagery for 31 dates during the 2004–2010 period on Taku Glacier to assess the consistency of its rate of rise and usefulness in assessing mass balance. In 2010, the TSL rose from 750 m on 28 July, 800 m on 5 August, 875 m on 14 August, 925 m on 30 August, and to 975 m on 20 September. The mean observed probing balance gradient was 3.3 mm m −1 and TSL rise was 3.7 m day −1 , yielding an ablation rate of 12.2 mm day −1 on Taku Glacier from mid-July to mid-September. A comparison of the TSL rise in the region from 750–1100 m on Taku Glacier during eleven different periods of more than 14 days during the ablation season with repeat imagery indicates a mean TSL rise of 3.7 m day −1 on Taku Glacier, the rate of rise is relatively consistent ranging from 3.0 to 4.8 m day −1 . This is useful for ascertaining the final ELA if imagery or observations are not available within a week or two of the end of the ablation season. From mid-July-mid-September the mean ablation from 750–1100 m determined from the TSL rise and the observed balance gradient varied from 11 to 18 mm day −1 on Taku Glacier during the 2004–2010 period.

Description: Spatial and temporal variability of snow accumulation in Dronning Maud Land, East Antarctica, including two deep ice coring sites at Dome Fuji and EPICA DML The Cryosphere Discussions, 5, 2061-2114, 2011 Author(s): S. Fujita, P. Holmlund, I. Andersson, I. Brown, H. Enomoto, Y. Fujii, K. Fujita, K. Fukui, T. Furukawa, M. Hansson, K. Hara, Y. Hoshina, M. Igarashi, Y. Iizuka, S. Imura, S. Ingvander, T. Karlin, H. Motoyama, F. Nakazawa, H. Oerter, L. E. Sjöberg, S. Sugiyama, S. Surdyk, J. Ström, R. Uemura, and F. Wilhelms To better understand the spatio-temporal variability of the glaciological environment in Dronning Maud Land (DML), East Antarctica, investigations were carried out along the 2800-km-long Japanese-Swedish IPY 2007/2008 traverse. The route covers ice sheet ridges and two deep ice coring sites at Dome Fuji and EPICA DML. The surface mass balance (SMB) distribution was derived based on analysis of isochrones within snow pits, firn cores and subsurface radar signals. The SMB averaged over various time scales in the Holocene was determined. This was then compared with various glaciological data. We find that the large-scale distribution of the SMB depends on the surface elevation, continentality and interactions between ice sheet ridges and the prevailing counterclockwise windfield in DML. A different SMB is found for the windward and leeward sides of the ridges. Local-scale variability in the SMB is essentially governed by bedrock topography which determines the local surface topography. In the eastern part of DML, the accumulation rate in the second half of the 20th century is found to be higher by 15 % compared to averages over longer periods of 722 a or 7.9 ka before AD 2008. A similar trend has been reported for many inland plateau sites in East Antarctica.

Description: Relative effect of slope and equilibrium line altitude on the retreat of Himalayan glaciers The Cryosphere Discussions, 5, 2571-2604, 2011 Author(s): T. N. Venkatesh, A. V. Kulkarni, and J. Srinivasan A majority of glaciers in the Himalayas have been retreating. In this paper, we show that there are two major factors which control the advance/retreat of the Himalayan glaciers. They are the slope of the glacier and changes in the equilibrium line altitude. While it is well known, that these factors are important, we propose a new way of combining them and use it to predict retreat. Our model has been applied to the movement of eight Himalayan glaciers during the past 25 years. The model explains why the Gangotri glacier is retreating while Zemu of nearly the same length is stationary, even though they are subject to similar environmental changes. The model has also been applied to a larger set of glaciers in the Parbati basin, for which retreat based on satellite data is available, though over a shorter time period.

Description: Brief Communication: Can recent ice discharges following the Larsen-B ice-shelf collapse be used to infer the driving mechanisms of millennial-scale variations of the Laurentide ice sheet? The Cryosphere Discussions, 5, 3113-3127, 2011 Author(s): J. Alvarez-Solas, A. Robinson, and C. Ritz The effects of an ice-shelf collapse on inland glacier dynamics have recently been widely studied, especially since the breakup of Antarctic Peninsula's Larsen-B ice shelf in 2002. Several studies have documented acceleration of the ice streams that were flowing into the former ice shelf. The mechanism responsible for such a speed-up lies with the removal of the ice-shelf backforce. Independently, it is also well documented that during the last glacial period, the Northern Hemisphere ice sheets experienced large discharges into the ocean, likely reflecting ice flow acceleration episodes on the millennial time scale. The classic interpretation of the latter is based on the existence of an internal thermo-mechanical feedback with the potential to generate oscillatory behavior in the ice sheets. Here we would like to widen the debate by considering that Larsen-B-like glacial analog episodes could have contributed significantly to the registered millennial-scale variablity.

Description: Optimisation of quasi-3D electrical resistivity imaging – application and inversion for investigating heterogeneous mountain permafrost The Cryosphere Discussions, 5, 3383-3421, 2011 Author(s): D. Schwindt and C. Kneisel This study aimed to optimise the application, efficiency and interpretability of quasi-3D resistivity imaging for investigating the heterogeneous permafrost distribution at mountain sites by a systematic forward modelling approach. A three dimensional geocryologic model, representative for most mountain permafrost settings, was developed. Based on this geocryologic model quasi-3D models were generated by collating synthetic orthogonal 2D arrays, demonstrating the effects of array types and electrode spacing on resolution and interpretability of the inversion results. The effects of minimising the number of 2D arrays per quasi-3D grid were tested by enlarging the spacing between adjacent lines and by reducing the number of perpendicular tie lines with regard to model resolution and loss of information value. Synthetic and measured quasi-3D models were investigated with regard to the lateral and vertical resolution, reliability of inverted resistivity values, the possibility of a quantitative interpretation of resistivities and the response of the inversion process on the validity of quasi-3D models. Results show that setups using orthogonal 2D arrays with electrode spacings of 2 m and 3 m are capable of delineating lateral heterogeneity with high accuracy and also deliver reliable data on active layer thickness. Detection of permafrost thickness, especially if the permafrost base is close to the penetration depth of the setups, and the reliability of absolute resistivity values emerged to be a weakness of the method. Quasi-3D imaging has proven to be a promising tool for investigating permafrost in mountain environments especially for delineating the often small-scale permafrost heterogeneity, and therefore provides an enhanced possibility for aligning permafrost distribution with site specific surface properties and morphological settings.

Description: Seasonal variations of glacier dynamics at Kronebreen, Svalbard revealed by calving related seismicity The Cryosphere Discussions, 5, 3291-3321, 2011 Author(s): A. Köhler, A. Chapuis, C. Nuth, J. Kohler, and C. Weidle We detect and cluster waveforms of seismic signals recorded close to the calving front of Kronebreen, Svalbard, to identify glacier-induced seismic events and to investigate their relation to calving processes. Single-channel geophone data recorded over several months in 2009 and 2010 are combined with eleven days of direct visual observations of the glacier front. We apply a processing scheme which combines conventional seismic event detection using a sensitive trigger algorithm and unsupervised clustering of all detected signals based on their waveform characteristics by means of Self-Organizing Maps (SOMs). We are able to distinguish between false detections, instrumental artifacts, and three classes of signals which are, with different degrees of uncertainty, emitted by calving activity. About 10 % of the directly observed calving events close to the geophone (

Description: Recent acceleration of ice loss in the Northern Patagonia Icefield based on an updated decennial evolution The Cryosphere Discussions, 5, 3323-3381, 2011 Author(s): P. López and G. Casassa Ice elevation changes of the Northern Patagonia Icefield (NPI) were analyzed by comparing three Digital Elevation Models (DEM) corresponding to 1975 (constructed based on topographic maps), the SRTM DEM of 2000 yr and a SPOT 5 DEM of 2005. In addition, the glacier length fluctuations and the surface area evolution between 2001 and 2011 of 25 glaciers of the NPI were studied: the information extracted from the Landsat ETM+ satellite image of 11 March 2001 was compared to the measurements performed based on the Landsat ETM+ satellite image of 19 February 2011. From a global point of view, the majority of the studied glaciers thinned, retreated and lost surface between 2001 and 2011, only few glaciers (Leones, Nef, Pared Sur and Soler) located on the eastern side of the NPI have been stable. Glaciers located on the western side of the NPI suffered a stronger wasting compared to the glaciers located on the eastern side. Overall, over the ablation areas of the NPI (below 1150 m a.s.l.) a more rapid thinning of 2.6 m yr −1 occurred between 2000 and 2005 yr compared to the period 1975–2000, in which a mean thinning of 1.7 m yr −1 was measured for the same zones of the NPI. For the whole period (1975–2005) the most important thinning of the ablation areas has been estimated for HPN-1 Glacier (4.4 m yr −1 ) followed by Benito (3.4 m yr −1 ), Fraenkel (2.4 m yr −1 ), Gualas (2.1 m yr −1 ) and Acodado glaciers, all of them located on the western side of the NPI. Between 2001 and 2011, a noteworthy retreat of 1.9 km was experienced by Gualas Glacier and by Reichert Glacier with 1.6 km, both located on the north-western side of the NPI. On the south-western side of the NPI, during the same decennia, Steffen Glacier experienced a remarkable retreat of 1.6 km as well. During the 2001–2011 period, Steffen Glacier more than doubled its rate of retreat (compared to the 1979–2001 period) and experienced the disintegration of its main front as well as a lateral tongue that retreated 3.1 km. The most significant retreat observed on the eastern side was experienced by Colonia Glacier (1 km). Area loss was also relevant during the period 2001–2011. Overall, the icefield experienced a reduction of 50.6 km 2 which represents a 1.3 % relative to the surface area calculated for 2001 yr. The most remarkable surface reduction was observed for HPN-1 Glacier that lost 3.2 % of its surface estimated in 2001, followed by Steffen Glacier (2.8 %). We suggest that the glacier shrinking observed in the NPI is controlled firstly by atmospheric warming, as it has been reported in this area. Nevertheless, updated climatic studies are needed in order to confirm this suggestion. If the detected past climate trends persist, in the future, glaciers of the NPI will continuous or even increase their rate of shrinking generating important consequences for this region like the production of Glacier Lake Outburst Flood events or the decrease of the melt-water runoff in the long-term future.

Description: Brief Communication: Greenland's shrinking ice cover: ″fast times″ but not that fast The Cryosphere Discussions, 5, 3207-3219, 2011 Author(s): J. S. Kargel, A. P. Ahlstrøm, R. B. Alley, J. L. Bamber, T. J. Benham, J. E. Box, C. Chen, P. Christoffersen, M. Citterio, J. G. Cogley, H. Jiskoot, G. J. Leonard, P. Morin, T. Scambos, T. Sheldon, and I. Willis A map of Greenland in the 13th edition (2011) of the Times Comprehensive Atlas of the World made headlines because the publisher's media release mistakenly stated that the permanent ice cover had shrunk 15 % since the previous 10th edition (1999) revision. The claimed shrinkage was immediately challenged by glaciologists, then retracted by the publisher. Here we show: (1) accurate maps of ice extent based on 1978/1987 aerial surveys and recent MODIS imaging; and (2) shrinkage at 0.019 % a −1 in ∼ 50 000 km 2 of ice in a part of east Greenland that is shown as ice-free in the Times Atlas .

Description: Sensitivity of a distributed temperature-radiation index melt model based on a four melt season AWS record from Hurd Peninsula glaciers, Livingston Island, Antarctica The Cryosphere Discussions, 5, 3221-3258, 2011 Author(s): U. Y. Jonsell, F. J. Navarro, M. Bañón, J. J. Lapazaran, and J. Otero We use an automatic weather station and mass balance dataset spanning four melt seasons collected on Hurd Peninsula Glaciers, South Shetland Islands, to investigate the point surface energy balance, to determine the absolute and relative contribution of the various energy fluxes acting on the glacier surface and to estimate the sensitivity of melt to ambient temperature changes. Long-wave incoming radiation is the main energy source for melt, while short-wave radiation is the most important flux controlling the variation of both seasonal and daily mean surface energy balance. Short-wave and long-wave radiation fluxes do in general balance each other, resulting in a high correspondence between daily mean net radiation flux and available melt energy flux. We calibrate a distributed melt model driven by air temperature and an expression for the incoming short-wave radiation. The model is calibrated with the data from one of the melt seasons and validated with the data of the three remaining seasons. The model results deviate at most 0.14 m w.e. from the corresponding observations using the glaciological method. The model is very sensitive to changes in ambient temperature: a 0.5 °C increase results in 56 % higher melt rates.

Description: Albedo of the ice-covered Weddell and Bellingshausen Sea The Cryosphere Discussions, 5, 3259-3289, 2011 Author(s): A. I. Weiss, J. C. King, T. A. Lachlan-Cope, and R. S. Ladkin This study investigates the surface albedo of the sea ice areas adjacent to the Antarctic Peninsula during the austral summer. Aircraft measurements of the surface albedo which were conducted in the sea ice areas of the Weddell and Bellingshausen Sea show significant differences between these two regions. The averaged surface albedo varied between 0.13 and 0.81. The ice cover of the Bellingshausen Sea consisted mainly of first year ice and the sea surface showed an averaged sea ice albedo of α i = 0.64 ± 0.2 (± standard deviation). The mean sea ice albedo of the pack ice area in the Western Weddell Sea was α i = 0.75 ± 0.05. In the Southern Weddell Sea, where new, young sea ice prevailed, a mean albedo value of α i = 0.38 ± 0.08 was observed. Relatively warm open water and thin, newly formed ice had the lowest albedo values, whereas relatively cold and snow-covered pack ice had the highest albedo values. All sea ice areas consist of a mixture of a large variability of different sea ice types. An investigation of commonly used parameterizations of albedo as a function of surface temperature in the Weddell and Bellingshausen Sea ice areas showed that the albedo parameterizations don't work well in particular for areas with new, young ice. We determined typical linear temperature-albedo functions for three sea ice areas adjacent to the Antarctic Peninsula, which are reflecting the differences in the mixture of ice age, thickness and sea ice surface cover.

Description: Preliminary assessment of model parametric uncertainty in projections of Greenland Ice Sheet behavior The Cryosphere Discussions, 5, 3175-3205, 2011 Author(s): P. J. Applegate, N. Kirchner, E. J. Stone, K. Keller, and R. Greve Lack of knowledge about the values of ice sheet model input parameters introduces substantial uncertainty into projections of Greenland Ice Sheet contributions to future sea level rise. Computer models of ice sheet behavior provide one of several means of estimating future sea level rise due to mass loss from ice sheets. Such models have many input parameters whose values are not well known. Recent studies have investigated the effects of these parameters on model output, but the range of potential future sea level increases due to model parametric uncertainty has not been characterized. Here, we demonstrate that this range is large, using a 100-member perturbed-physics ensemble with the SICOPOLIS ice sheet model. Each model run is spun up over 125 000 yr using geological forcings, and subsequently driven into the future using an asymptotically increasing air temperature anomaly curve. All modeled ice sheets lose mass after 2005 AD. After culling the ensemble to include only members that give reasonable ice volumes in 2005 AD, the range of projected sea level rise values in 2100 AD is 30 % or more of the median. Data on past ice sheet behavior can help reduce this uncertainty, but none of our ensemble members produces a reasonable ice volume change during the mid-Holocene, relative to the present. This problem suggests that the model's exponential relation between temperature and precipitation does not hold during the Holocene, or that the central-Greenland temperature forcing curve used to drive the model is not representative of conditions around the ice margin at this time (among other possibilities). Our simulations also lack certain observed physical processes that may tend to enhance the real ice sheet's response. Regardless, this work has implications for other studies that use ice sheet models to project or hindcast the behavior of the Greenland ice sheet.

Description: Estimating ice phenology on large northern lakes from AMSR-E: algorithm development and application to Great Bear Lake and Great Slave Lake, Canada The Cryosphere Discussions, 5, 3129-3173, 2011 Author(s): K.-K. Kang, C. R. Duguay, and S. E. L. Howell Time series of brightness temperatures ( T B ) from the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) are examined to determine ice phenological parameters on the two largest lakes of northern Canada: Great Bear Lake (GBL) and Great Slave Lake (GSL). T B measurements from the 18.7, 23.8, 36.5, and 89.0 GHz channels (H- and V- polarization) are compared to assess their potential for detecting freeze-onset/melt-onset and ice-on/ice-off dates on both lakes. The 18.7 GHz (H-pol) channel is found to be the most suitable for estimating these ice dates as well as the duration of the ice cover and ice-free seasons. A new algorithm is proposed using this channel and applied to map all ice phenological parameters on GBL and GSL over seven ice seasons (2002–2009). Analysis of the spatio-temporal patterns of each parameter at the pixel level reveals that: (1) both freeze-onset and ice-on dates occur on average about one week earlier on GBL than on GSL (Day of Year (DY) 318 and 333 for GBL; DY 328 and 343 for GSL); (2) the freeze-up process or freeze duration (freeze-onset to ice-on) takes a slightly longer amount of time on GBL than on GSL (about 1 week on average); (3) melt-onset and ice-off dates occur on average one week and approximately four weeks later, respectively, on GBL (DY 143 and 183 for GBL; DY 135 and 157 for GSL); (4) the break-up process or melt duration (melt-onset to ice-off) lasts on average about three weeks longer on GBL; and (5) ice cover duration estimated from each individual pixel is on average about three weeks longer on GBL compared to its more southern counterpart, GSL. A cross-comparison of dates for several ice phenological parameters derived from other satellite remote sensing products (e.g. NOAA Interactive Multisensor Snow and Ice Mapping System (IMS), QuikSCAT, and Canadian Ice Service Database) show that, despite its relatively coarse spatial resolution, AMSR-E 18.7 GHz provides a viable means for monitoring of ice phenology on large northern lakes.

Description: Influence of leads widths distribution on turbulent heat transfer between the ocean and the atmosphere The Cryosphere Discussions, 5, 2765-2797, 2011 Author(s): S. Marcq and J. Weiss Leads are linear-like structures of open water within the sea ice cover that develop as the result of fracturing due to divergence or shear. Through leads, air and water come into contact and directly exchange latent and sensible heat through convective processes driven by the large temperature and moisture differences between them. In the central Arctic, leads only cover 1 to 2% of the ocean during winter, but account for more than 80% of the heat fluxes. Furthermore, narrow leads (several meters) are more than twice as efficient at transmitting turbulent heat than larger ones (several hundreds of meters). We show that lead widths are power law distributed, P(X) ~ X −a with a 〉1, down to very small spatial scales (20 m or below). This implies that the open water fraction is by far dominated by very small leads. Using two classical formulations, which provide first order turbulence closure for the fetch-dependence of heat fluxes, we find that the mean heat fluxes (sensible and latent) over open water are up to 55 % larger when considering the lead width distribution obtained from a SPOT satellite image of the ice cover, compared to the situation where the open water fraction constitutes one unique large lead and the rest of the area is covered by ice, as it is usually considered in climate models at the grid scale. This difference may be even larger if we assume that the power law scaling of lead widths extents down to smaller (~1 m) scales. Such estimations may be a first step towards a subgrid scale parameterization of the spatial distribution of open water for heat fluxes calculations in ocean/sea ice coupled models.

Description: Ice shelf flexures modeled with a 2-D elastic flow line model The Cryosphere Discussions, 5, 2841-2863, 2011 Author(s): Y. V. Konovalov Ice shelf flexures modeling was performed using a 2-D finite-difference elastic model, which takes into account sub-ice-shelf sea water flow. The sub-ice water flow was described by the wave equation for the sub-ice-shelf pressure perturbations (Holdsworth and Glynn, 1978). In the model ice shelf flexures result from variations in ocean pressure due to changes in prescribed sea levels. The numerical experiments were performed for a flow line down one of the fast flowing ice streams of the Academy of Sciences Ice Cap. The profile includes a part of the adjacent ice shelf. The numerical experiments were carried out for harmonic incoming pressure perturbations P ' and the ice shelf flexures were obtained for a wide spectrum of the pressure perturbations frequencies, ranging from tidal periods down to periods of a few seconds (0.004..0.02 Hz). The amplitudes of the ice shelf deflections obtained by the model achieve a maxima at about T ≈ 165 s in concordance with previous investigations of the impact of waves on Antarctic ice shelves (Bromirski et al., 2010). The explanation of the effect is found in the solution of the corresponding eigenvalue problem revealing the existence of a resonance at these high frequencies.

Description: A minimal model for reconstructing interannual mass balance variability of glaciers in the European Alps The Cryosphere Discussions, 5, 2799-2839, 2011 Author(s): B. Marzeion, M. Hofer, A. H. Jarosch, G. Kaser, and T. Mölg We present a minimal model of the glacier surface mass balance. The model relies solely on monthly precipitation and air temperatures as forcing. We first train the model individually for 15 glaciers with existing mass balance measurements. Based on a cross validation, we present a thorough assessment of the model's performance outside of the training period. The cross validation indicates that our model is robust, and our model's performance compares favorably to that from a less parsimonious model based on seasonal sensitivity characteristics. Then, the model is extended for application on glaciers without existing mass balance measurements, and cross validated using the 15 glaciers above, in order to measure its performance on glaciers not included in the model training. This cross validation indicates that the model retains considerable skill even when applied on glaciers without mass balance measurements. As an exemplary application, the model is then used to reconstruct time series of interannual mass balance variability, covering the past two hundred years, for all glaciers in the European Alps contained in extended format of the world glacier inventory. Based on this reconstruction, we present a spatially detailed attribution of the glaciers' mass balance variability to temperature and precipitation variability.

Description: Thermal remote sensing of ice-debris landforms using ASTER The Cryosphere Discussions, 5, 2895-2933, 2011 Author(s): A. Brenning, M. A. Peña, S. Long, and A. Soliman Remote sensors face challenges in characterizing mountain permafrost and ground thermal conditions or mapping rock glaciers and debris-covered glaciers. We explore the potentials of thermal imaging and in particular thermal inertia mapping in mountain cryospheric research, focusing on the relationships between ground surface temperatures and the presence of ice-debris landforms on one side and land surface temperature (LST) and apparent thermal inertia (ATI) on the other. In our case study we utilize ASTER daytime and nighttime imagery and in-situ measurements of near-surface ground temperature (NSGT) in the Mediterranean Andes during a snow-free and dry observation period in late summer. Spatial patterns of LST and NSGT were mostly consistent with each other both at daytime and at nighttime. Daytime LST over ice-debris landforms was decreased and ATI consequently increased compared to other debris surfaces under otherwise equal conditions, but NSGT showed contradictory results, which underlines the complexity and possible scale dependence of ATI in heterogeneous substrates with the presence of a thermal mismatch and a heat sink at depth. While our results demonstrate the utility of thermal imaging and ATI mapping in a mountain cryospheric context, further research is needed for a better interpretation of ATI patterns in complex thermophysical conditions

Description: Melt ponds on Arctic sea ice determined from MODIS satellite data using an artificial neural network The Cryosphere Discussions, 5, 2991-3024, 2011 Author(s): A. Rösel, L. Kaleschke, and G. Birnbaum Melt ponds on sea ice strongly reduce the surface albedo and accelerate the decay of Arctic sea ice. Due to different spectral properties of snow, ice, and water, the fractional coverage of these distinct surface types can be derived from multispectral sensors like MODIS using a spectral unmixing algorithm. The unmixing was implemented using a multilayer perceptron (MLP) to reduce computational costs. Arctic-wide melt pond fractions and sea ice concentrations are derived from the level 3 MODIS surface reflectance product. The validation of the MODIS melt pond data set was conducted with aerial photos from the MELTEX campaign 2008 in the Beaufort Sea, data sets from the National Snow and Ice Data Center (NSIDC) for 2000 and 2001 from four sites spread over the entire Arctic, and with ship observations from the trans-Arctic HOTRAX cruise in 2005. The root-mean-square errors (RMSE) range from 3.8 % for the comparison with HOTRAX data, over 10.7 % for the comparison with NSIDC data, to 10.3 % and 11.4 % for the comparison with MELTEX data, with correlations coefficients ranging from R 2 = 0.28 to R 2 = 0.45. The mean annual cycle of the melt pond fraction for the entire Arctic shows a strong increase in June, reaching a maximum of 15 % by the end of June. The zonal mean of melt pond fractions indicates a dependence of the temporal development of melt ponds from the geographical latitude, and has its maximum in mid-July in latitudes between 80° and 88° N. Furthermore, the MODIS results are used to estimate the influence of melt ponds on retrievals of sea ice concentrations from passive microwave data. Results from a case study comparing sea ice concentrations from ASI-, NASA Team 2-, and Bootstrap-algorithms with MODIS sea ice concentrations indicate an underestimation of around 40 % for sea ice concentrations retrieved with microwave algorithms.

Description: Relation between surface topography and sea-salt snow chemistry from Princess Elizabeth Land, East Antarctica The Cryosphere Discussions, 5, 2967-2989, 2011 Author(s): K. Mahalinganathan, M. Thamban, C. M. Laluraj, and B. L. Redkar Previous studies on variability of sea-salt records in Antarctic snow have established an unambiguous relationship with the proximity to the sea and have been directly correlated with the site specific features like elevation and distance from the coast. On the other hand, variations in Cl − /Na + ratio in have been attributed with the reaction mechanisms involving atmospheric acids. In the present study, annual records of Na + , Cl − and SO 4 2− records were investigated using snow cores along a 180 km coast to inland transect in Princess Elizabeth Land, East Antarctica. Exceptionally high Na + concentrations varying between 1000 and 2000 μg l −1 were observed within 50 km of the transect. Large variations in Cl − /Na + ratio were observed within 50 km from the coast. A rapid increase in the elevation (0–1115 m) was noticed up to 50 km from the coast, whereas a steady elevation change (1115–2200 m) occurred between 50 and 180 km. The largest slope of the entire transect was observed (33.7 m km −1 ) between 20 and 30 km and records from this area correspondingly revealed extensive modifications in snow sea-salt chemistry, with Cl − /Na + ratios as low as 0.2. Statistical analysis showed a strong association between the slope of the ice sheet and variation of the sea-salt ions along the transect. While distance from coast accounted for some variability, the altitude by itself seem to have no significant control on the distribution of sea-salt ions. We suggest that the degree of slope of the ice sheet on the coastal regions of Antarctica could have a major influence the sea-salt chemistry.

Description: Surface mass budget and meltwater discharge from the Kangerlussuaq sector of the Greenland ice sheet during record-warm year 2010 The Cryosphere Discussions, 5, 2319-2347, 2011 Author(s): D. van As, A. Hubbard, B. Hasholt, A. B. Mikkelsen, M. van den Broeke, and R. S. Fausto The year 2010 has been anomalously warm in most of Greenland, most notably in the south and along the western coast. Our study targets the Kangerlussuaq region around 67° N in Southwest Greenland, where the temperature anomalies were record setting. In 2010, the average temperature was 5 °C (2.7 standard deviations) above the 1974–2010 average in the town of Kangerlussuaq. High temperatures were also observed over the ice sheet, with the positive anomaly increasing with altitude. Also surface albedo, from calibrated MODIS measurements, was anomalously low in 2010, chiefly in the upper ablation zone. The low albedo was caused by the high ablation in 2010, which profited in turn from high temperatures, low albedo, and of low wintertime accumulation. The largest melt excess (166%) was found in the upper ablation zone, where higher temperatures and lower albedo contributed equally to the melt anomaly. In total, we estimate that 6.6 km 3 of surface meltwater ran off the ice sheet in the Kangerlussuaq catchment area in 2010, exceeding "normal" year 2009 by 145%. When compared to discharge estimated from discharge measurements in the proglacial river we find good agreement. The time lag between the records is caused by storage within and underneath the ice sheet, and suggests adaption of the subglacial drainage system to meltwater availability, with more efficient drainage occurring after the peak of the melt season.

Description: How reversible is sea ice loss? The Cryosphere Discussions, 5, 2349-2363, 2011 Author(s): J. K. Ridley, J. A. Lowe, and H. T. Hewitt It is well accepted that increasing atmospheric CO 2 results in global warming, leading to a decline in polar sea ice area. Here, the specific question of whether there is a tipping point in the sea ice cover is investigated. The global climate model HadCM3, is used to map the trajectory of sea ice area under idealised scenarios. The atmospheric CO 2 is first ramped up to four times pre-industrial levels (4 × CO 2 ) then ramped down back to pre-industrial levels. We also examine the impact of stabilising climate at 4 × CO 2 prior to ramping CO 2 down to pre-industrial levels. Against global mean temperature Arctic sea ice area has little hysteresis while the Antarctic sea ice shows significant hysteresis – its rate of change slower, with falling temperatures, than its rate of change with rising temperatures. However, we show that the driver of the hysteresis is the hemispherical differences in temperature change between transient and stabilisation periods. We find no irreversible behaviour in the sea ice cover.

Description: Hydrologic controls on coastal suspended sediment plumes around the Greenland ice sheet The Cryosphere Discussions, 5, 2365-2407, 2011 Author(s): V. W. Chu, L. C. Smith, A. K. Rennermalm, R. R. Forster, and J. E. Box Rising sea levels and increased surface melting of the Greenland ice sheet have heightened the need for direct observations of meltwater release from the ice edge to ocean. Buoyant sediment plumes that develop in fjords downstream of outlet glaciers are controlled by numerous factors, including meltwater runoff. Here, Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery is used to average surface suspended sediment concentration (SSC) in fjords around ~80% of Greenland from 2000–2009. Spatial and temporal patterns in SSC are compared with positive-degree-days (PDD), a proxy for surface melting, from the Polar MM5 regional climate model. Over this decade significant geographic covariance occurred between ice sheet PDD and fjord SSC, with outlet type (land- vs. marine-terminating glaciers) also important. In general, high SSC is associated with high PDD and/or a high proportion of land-terminating glaciers. Unlike previous site-specific studies of the Watson River plume at Kangerlussuaq, temporal covariance is low, suggesting that plume dimensions best capture interannual runoff dynamics whereas SSC allows assessment of long-term conditions across much broader fjord environments around the ice sheet. Remote sensing of both plume charactersitics thus offers a viable approach for observing spatial and temporal patterns of meltwater release exiting the Greenland ice sheet to the global ocean.

Description: Inter-annual variations of snow days over Switzerland from 2000–2010 derived from MODIS satellite data The Cryosphere Discussions, 5, 2409-2435, 2011 Author(s): N. Foppa and G. Seiz Snow cover plays a vital role in the Swiss Alps and therefore it is of major interest to determine and understand its variability on different spatiotemporal scales. Within the activities of the National Climate Observing System (GCOS Switzerland) inter-annual variations of snow days over Switzerland were derived from 2000 to 2010 based on data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Terra satellite. To minimize the impact of cloud cover on the MODIS snow product MOD10C1, we implemented a post-processing technique based on a forward and backward gap-filling approach. Using the proposed methodology it was possible to determine the total number of annual snow days over Switzerland from 2000 to 2010 (SCD MODIS ). The accuracy of the calculated snow days per year were quantitatively evaluated against three in situ snow observation sites representing different climatological regimes (SCD in_situ ). The correlation ( c ) between annual SCD MODIS and SCD in_situ is highest for the lowland regions by ( c = 0.90) with a slightly lower correlation for the Central Alps of 0.82 and a mean absolute difference of −6 to −7 days (SCD in_situ − SCD MODIS ). Differences were further analysed on a monthly and daily resolution over the entire period. The overall agreement between SCD MODIS and SCD in_situ on a daily basis over 10 yr is 88 % to 94 %, depending on the regional characteristics of each validation site. Differences between SCD MODIS and SCD in_situ vary with higher mean absolute differences during the snow accumulation period in autumn and smaller differences after spring, in particularly for the Central Alps. These findings are in agreement with other studies.

Description: Laboratory study of frazil ice accumulation under wave conditions The Cryosphere Discussions, 5, 1835-1886, 2011 Author(s): S. De la Rosa and S. Maus Ice growth in turbulent seawater is often accompanied by the accumulation of frazil ice crystals at its surface. The thickness and volume fraction of this ice layer play an important role in shaping the gradual transition from a loose to a solid ice cover, however, observations are very sparse. Here we analyse an extensive set of observations of frazil ice, grown in two parallel tanks with controlled wave conditions and thermal forcing, focusing on the first one to two days of grease ice accumulation. The following unresolved issues are addressed: (i) at which volume fraction the frazil crystal rising process starts and how densely they accumulate at the surface, (ii) how the grease ice solid fraction evolves with time until solid ice starts to form and (iii) how do these conditions affect, and are affected by, waves and heat loss from the ice. We obtained estimates of the initial frazil ice solid fraction (0.04–0.05), the maximum solid fraction to which it accumulates (0.24–0.28), as well as the time-scale of packing, at which 95 % of the frazil reaches the maximum solid fraction (12–18 h). Comparison of ice thickness and wave observations also indicates that grease ice first begins to affect the wave field significantly when its thickness exceeds the initial wave amplitude. These results are relevant for modelling frazil ice accumulation and freeze-up of leads, polynyas and the seasonal ice zone.

Description: Changes in the marine-terminating glaciers of central east Greenland and potential connections to ocean circulation, 2000–2010 The Cryosphere Discussions, 5, 2865-2894, 2011 Author(s): K. M. Walsh, I. M. Howat, Y. Ahn, and E. M. Enderlin Outlet glaciers on the periphery of the Greenland Ice Sheet have undergone substantial changes in the past decade. Limited geophysical observations of the marine-terminating glaciers of eastern Greenland's Geikie Plateau and Blosseville Coast suggest rapid rates of mass loss and short-term variability in ice dynamics since 2002. Glaciers in this region terminate into the Denmark Strait, which is a thermodynamic transition zone between the Arctic and North Atlantic oceans spanning from 66° N to 69° N. We examine time series of thinning, retreat and flow speed of 38 marine-terminating glaciers along the central east Greenland coast from 2000 to 2010 and compare this record with coastal sea surface temperatures to investigate a potential relationship between warming of the sea surface and increased melt at the glacier termini. We find that glacial retreat, thinning and acceleration have been more pronounced throughout the Denmark Strait, supporting our hypothesis that ocean warming associated with shifts in the Irminger and East Greenland currents are causing increased melt at the ice-ocean interface.

Description: Longitudinal surface structures (flowstripes) on Antarctic glaciers The Cryosphere Discussions, 5, 3085-3112, 2011 Author(s): N. F. Glasser and G. H. Gudmundsson Longitudinal surface structures (''flowstripes'') are common on many glaciers but their origin and significance are poorly understood. In this paper we present observations of the development of these longitudinal structures from four different Antarctic glacier systems (the Lambert Glacier/Amery Ice Shelf area, outlet glaciers in the Ross Sea sector, ice-shelf tributary glaciers on the Antarctic Peninsula, and the onset zone of a tributary to the Recovery Glacier Ice Stream in the Filchner Ice Shelf area). Mapping from optical satellite images demonstrates that longitudinal surface structures develop in two main situations: (1) as relatively wide flow stripes within glacier flow units and (2) as relatively narrow flow stripes where there is convergent flow around nunataks or at glacier confluence zones. Our observations indicate that the confluence features are narrower, sharper, and more clearly defined features. They are characterised by linear troughs or depressions on the ice surface and are much more common than the former type. Longitudinal surface structures within glacier flow units have previously been explained as the surface expression of localised bed perturbations but a universal explanation for those forming at glacier confluences is lacking. Here we propose that these features are formed at zones of ice acceleration and extensional flow at glacier confluences. We provide a schematic model for the development of longitudinal surface structures based on extensional flow that can explain their ridge and trough morphology as well as their down-ice persistence.

Description: Refreezing on the Greenland ice sheet: a comparison of parameterizations The Cryosphere Discussions, 5, 2723-2764, 2011 Author(s): C. H. Reijmer, M. R. van den Broeke, J. Ettema, and L. B. Stap Retention and refreezing of meltwater are acknowledged to be important processes for the mass budget of polar glaciers and ice sheets. Several parameterizations of these processes exist for use in energy and mass balance models. Due to a lack of direct observations, validation of these parameterizations is difficult. In this study we compare a set of 6 refreezing parameterizations against output of the Regional Atmospheric Climate Model (RACMO2), applied to the Greenland ice sheet. In RACMO2, refreezing is explicitly calculated in a snow model that calculates vertical profiles of temperature, density and liquid water content. For consistency, the parameterizations are forced with output (surface temperature, precipitation and melt) of RACMO2. For the ice sheet-integrated amount of refreezing and its inter-annual variations, all parameterizations give similar results, especially after some tuning. However, the spatial distributions differ significantly. Results are especially sensitive to the choice of the depth of the thermally active layer, which determines the cold content of the snow in most parameterizations.

Description: Transfer function models to quantify the delay between air and ground temperatures in thawed active layers The Cryosphere Discussions, 5, 2935-2966, 2011 Author(s): E. Zenklusen Mutter, J. Blanchet, and M. Phillips Air temperatures influence ground temperatures with a certain delay, which increases with depth. Borehole temperatures measured at 0.5 m depth in Alpine permafrost and air temperatures measured at or near the boreholes have been used to model this dependency. Statistical transfer function models have been fitted to the daily difference series of air and ground temperatures measured at seven different permafrost sites in the Swiss Alps. The relation between air and ground temperature is influenced by various factors such as ground surface cover, snow depth, water or ground ice content. To avoid complications induced by the insulating properties of the snow cover and by phase changes in the ground, only the mostly snow-free summer period when the ground at 0.5 m depth is thawed has been considered here. All summers from 2006 to 2009 have been analysed, with the main focus on summer 2006. The results reveal that in summer 2006 daily air temperature changes influence ground temperatures at 0.5 m depth with a delay ranging from one to six days, depending on the site. The fastest response times are found for a very coarse grained, blocky rock glacier site whereas slower response times are found for blocky scree slopes with smaller grain sizes.

Description: Worldwide widespread decadal-scale decrease of glacier speed revealed using repeat optical satellite images The Cryosphere Discussions, 5, 3025-3051, 2011 Author(s): T. Heid and A. Kääb Matching of repeat optical satellite images to derive glacier velocities is an approach that is much used within glaciology. Lately, focus has been put into developing, improving, automating and comparing different image matching methods. This makes it now possible to investigate glacier dynamics within large regions of the world and also between regions to improve knowledge about glacier dynamics in space and time. In this study we investigate whether the negative glacier mass balance seen over large parts of the world has caused the glaciers to change their speeds. The studied regions are Pamir, Caucasus, Penny Ice Cap, Alaska Range and Patagonia. In addition we derive speed changes for Karakoram, a region assumed to have positive mass balance and that contains many surge-type glaciers. We find that the mapped glaciers in the five regions with negative mass balance have decreased their speeds over the last decades, Pamir by 43 % in average per decade, Caucasus by 8 % in average per decade, Penny Ice Cap by 25 % in average per decade, Alaska Range by 11 % in average per decade and Patagonia by 20 % in average per decade. Glaciers in Karakoram have generally increased their speeds, but surging glaciers and glaciers with flow instabilities are most prominent in this area.

Description: Borehole temperatures reveal details of 20th century warming at Bruce Plateau, Antarctic Peninsula The Cryosphere Discussions, 5, 3053-3084, 2011 Author(s): V. Zagorodnov, O. Nagornov, T. A. Scambos, A. Muto, E. Mosley-Thompson, E. C. Pettit, and S. Tyuflin Two ice core boreholes of 143.74 m and 447.65 m (bedrock) were drilled during the 2009–2010 austral summer on the Bruce Plateau at a location named LARISSA Site Beta (66°02' S, 64°04' W, 1975.5 m a.s.l.). Both boreholes were logged with thermistors shortly after drilling. The shallow borehole was instrumented for 4 months with a series of resistance thermometers with satellite uplink. Surface temperature proxy data derived from an inversion of the borehole temperature profiles are compared to available multi-decadal records from weather stations and ice cores located along a latitudinal transect of the Antarctic Peninsula to West Antarctica. The LARISSA Site Beta profiles show temperatures decreasing from the surface downward through the upper third of the ice, and warming thereafter to the bed. The average temperature for the most recent year is −14.78 °C (measured at 15 m depth, abbreviated T 15 . A minimum temperature of −15.8 °C is measured at 173 m depth and basal temperature is estimated to be −10.2 °C. Current mean annual temperature and the gradient in the lower part of the measured temperature profile have a best fit with an accumulation rate of 1.9 × 10 3 kg m −2 a −1 and basal heat flux ( q ) of 88 mW m −2 , if steady-state conditions are assumed. However, the mid-level temperature variations show that recent temperature has varied significantly. Reconstructed surface temperatures ( T s = T 15 over the last 200 yr are derived by an inversion technique. From this, we find that cold temperatures (minimum T s =−16.2 °C) prevailed from ~1920 to ~1940, followed by a gradual rise of temperature to −14.2 °C around 1995, then cooling over the following decade and warming in the last few years. The coldest period was preceded by a relatively warm 19th century at T 15 ≥ −15 °C. To facilitate regional comparisons of the surface temperature history, we use our T 15 data and nearby weather station records to refine estimates of lapse rates (altitudinal, adjusted for latitude: Γ a(l)) . Good temporal and spatial consistency of Γ a(l)) over the last 35 yr are observed, implying that the climate trends observed here are regional and consistent over a broad altitude range.

Description: Temperature variability and thermal offset in steep alpine rock and ice faces The Cryosphere Discussions, 5, 721-753, 2011 Author(s): A. Hasler, S. Gruber, and W. Haeberli The thermal condition of high-alpine mountain flanks can be an important determinant of climate change impact on slope stability and correspondingly down-slope hazard regimes. In this study we analyze new time-series from 17 shallow temperature-depth profiles at two field sites in steep bedrock and ice. Extending earlier studies that revealed the topographic variations in temperatures, we demonstrate considerable differences of annual mean temperatures for variable surface characteristics and depths within the measured profiles. This implies that measurements and models related to compact and near-vertical bedrock temperatures may deviate considerably from conditions in the majority of bedrock slopes in mountain ranges that are usually non-vertical and fractured. For radiation-exposed faces, for instance, mean annual temperatures at depth are up to 3 °C lower and permafrost is likely to exist at lower elevations than reflected by current estimates based on the near-vertical case. Retention of thin snow cover and ventilation effects in open clefts are most likely responsible for this cooling. The presented or similar data could be used in the future to support the development and testing of models related to the thermal influence of snow-cover and fractures in steep bedrock. This would allow generalizing the here-presented findings.

Description: Changes in seasonal snow cover in Hindu Kush-Himalayan region The Cryosphere Discussions, 5, 755-777, 2011 Author(s): D. R. Gurung, A. V. Kulkarni, A. Giriraj, K. S. Aung, B. Shrestha, and J. Srinivasan The changes in seasonal snow covered area in the Hindu Kush-Himalayan (HKH) region have been examined using Moderate – resolution Imaging Spectroradiometer (MODIS) 8-day standard snow products. The average snow covered area of the HKH region based on satellite data from 2000 to 2010 is 0.76 million km 2 which is 18.23% of the total geographical area of the region. The linear trend in annual snow cover from 2000 to 2010 is −1.25±1.13%. This is in consistent with earlier reported decline of the decade from 1990 to 2001. A similar trend for western, central and eastern HKH region is 8.55±1.70%, +1.66% ± 2.26% and 0.82±2.50%, respectively. The snow covered area in spring for HKH region indicates a declining trend (−1.04±0.97%). The amount of annual snowfall is correlated with annual seasonal snow cover for the western Himalaya, indicating that changes in snow cover are primarily due to interannual variations in circulation patterns. Snow cover trends over a decade were also found to vary across seasonally and the region. Snow cover trends for western HKH are positive for all seasons. In central HKH the trend is positive (+15.53±5.69%) in autumn and negative (−03.68±3.01) in winter. In eastern HKH the trend is positive in summer (+3.35±1.62%) and autumn (+7.74±5.84%). The eastern and western region of HKH has an increasing trend of 10% to 12%, while the central region has a declining trend of 12% to 14% in the decade between 2000 and 2010. Snow cover depletion curve plotted for the hydrological year 2000–2001 reveal peaks in the month of February with subsidiary peaks observed in November and December in all three regions of the HKH.

Description: The seasonal cycle and interannual variability of surface energy balance and melt in the ablation zone of the west Greenland ice sheet The Cryosphere Discussions, 5, 779-809, 2011 Author(s): M. van den Broeke, R. van de Wal, and P. Smeets We present the seasonal cycle and interannual variability of the surface energy balance (SEB) in the ablation zone of the west Greenland ice sheet, using seven years (September 2003–August 2010) of hourly observations from three automatic weather stations (AWS). The AWS are situated along the 67° N latitude circle at elevations of 490 m a.s.l. (S5), 1020 m a.s.l. (S6) and 1520 m a.s.l. (S9) at distances of 6, 38 and 88 km from the ice sheet margin. The hourly AWS data are fed into a model that calculates all SEB components and melt rate; the model allows for shortwave radiation penetration in ice and time-varying surface momentum roughness. Snow depth is prescribed from albedo and sonic height ranger observations. Modelled and observed surface temperatures for non-melting conditions agree very well, with RMSE's of 0.97–1.26 K. Modelled and observed ice melt rates at the two lowest sites also show very good agreement, both for total cumulative and 10-day cumulated amounts. Melt frequencies and melt rates at the AWS sites are discussed. Although absorbed shortwave radiation is the most important energy source for melt at all three sites, interannual melt variability at the lowest site is driven mainly by variability in the turbulent flux of sensible heat. This is explained by the quasi-constant summer albedo in the lower ablation zone, limiting the influence of the melt-albedo feedback, and the proximity of the snow free tundra, which heats up considerably in summer.

Description: Modelling the temperature evolution of permafrost and seasonal frost in southern Norway during the 20th and 21st century The Cryosphere Discussions, 5, 811-854, 2011 Author(s): T. Hipp, B. Etzelmüller, H. Farbrot, and T. V. Schuler A heat flow model was used to simulate both past and future ground temperatures of mountain permafrost in Southern Norway. A reconstructed air temperature series back to 1860 was used to evaluate the permafrost evolution since the end of the Little Ice Age in the region. The impact of a changing climate on discontinuous mountain permafrost until 2100 is predicted by using downscaled temperatures from an ensemble of downscaled climate models for the A1B scenario. From 13 borehole locations two consecutive years of ground temperature, air temperature and snow cover data are available for model calibration and validation. The boreholes are located at different elevations and in substrates having different thermal properties. With an increase of air temperature of ~+1.5 °C over 1860–2010 and an additional warming of +2.8 °C towards 2100 in air temperature, we simulate the evolution of ground temperatures for the borehole locations. According to model results, the active-layer thickness has increased since 1860 by about 0.5–5 m and 〉10 m for the sites Juvvass and Tron, respectively. The simulations also suggest that at an elevation of about 1900 m a.s.l. permafrost will degrade until the end of this century with a likelihood of 55–75% given the chosen A1B scenario.

Description: A spatial framework for assessing current conditions and monitoring future change in the chemistry of the Antarctic atmosphere The Cryosphere Discussions, 5, 885-950, 2011 Author(s): D. A. Dixon, P. A. Mayewski, E. Korotkikh, S. B. Sneed, M. J. Handley, D. S. Introne, and T. A. Scambos This is the first study to measure more than 25 chemical constituents in the surface snow and firn across extensive regions of Antarctica. It is also the first to report total-Cs concentrations. We present major ion, trace element, heavy metal, rare earth element and oxygen isotope data from a series of surface snow samples and shallow firn sections collected along four US ITASE traverses across East and West Antarctica. In each sample we measure dissolved concentrations of Na + , K + , Mg 2+ , Ca 2+ , Cl − , NO 3 − , SO 4 2− , and MS − using ion chromatography and total concentrations of Sr, Cd, Cs, Ba, La, Ce, Pr, Pb, Bi, U, As, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co, Na, Mg, Li, and K using inductively coupled plasma sector field mass spectrometry. We also measure δ 18 O by isotope ratio mass spectrometry. The 2002/2003 traverse began at Byrd Surface Camp, West Antarctica, and ended close to South Pole, East Antarctica. The 2003/2004 traverse began at South Pole, passed through AGO4 in central East Antarctica before turning north and finishing at Taylor Dome. The combined 2006/2007 and 2007/2008 traverses started out at Taylor Dome and headed south, passing through the Byrd Glacier drainage basin and ending at South Pole. In this study, we utilize satellite remote sensing measurements of microwave backscatter and grain size to assist in the identification of glaze/dune areas across Antarctica and show how chemical concentrations are higher in these areas, precluding them from containing useful high-resolution chemical climate records. The majority of the non-glaze/dune samples in this study exhibit similar, or lower, concentrations to those from previous studies. Consequently, the results presented here comprise a conservative baseline for Antarctic surface snow chemical concentrations. The elements Cd, Pb, Bi, As, and Li are enriched across Antarctica relative to both ocean and upper crust elemental ratios. Global volcanic outgassing accounts for the majority of the Bi measured in East and West Antarctica and for a significant fraction of the Cd in East Antarctica. Nonetheless, global volcanic outgassing cannot account for the enriched values of Pb or As. Local volcanic outgassing from Mount Erebus may account for a significant fraction of the As and Cd in West Antarctica and for a significant fraction in East Antarctic glaze/dune areas. However, despite potential contributions from local and global volcanic sources, significant concentrations of Pb, Cd, and As remain across much of Antarctica. Most importantly, this study provides a baseline from which changes in the chemistry of the atmosphere over Antarctica can be monitored under expected warming scenarios and continued intensification of industrial activities in the Southern Hemisphere.

Description: The "tipping" temperature within Subglacial Lake Ellsworth, West Antarctica and its implications for lake access The Cryosphere Discussions, 5, 1003-1020, 2011 Author(s): M. Thoma, K. Grosfeld, C. Mayer, A. M. Smith, J. Woodward, and N. Ross We present results from new geophysical data allowing 3-D modelling of the water flow within Subglacial Lake Ellsworth (SLE), West Antarctica. Our simulations indicate that this lake has a novel temperature distribution due to significantly thinner ice than other surveyed subglacial lakes. The critical pressure boundary (tipping depth), established from the semi-empirical Equation of State, defines whether the lake's flow regime is convective or stratified. It passes through SLE and separates different temperature (and flow) regimes on either side of the lake. Our results have implications for the location of proposed access holes into SLE, the choice of which will depend on scientific or operational priorities. If an understanding of subglacial lake water properties and dynamics is the priority, holes are required in a basal freezing area at the North end of the lake. This would be the preferred priority suggested by this paper, requiring temperature and salinity profiles in the water column. A location near the Southern end, where bottom currents are lowest, is optimum for detecting the record of life in the bed sediments; to minimise operational risk and maximise the time span of a bed sediment core, a location close to the middle of the lake, where the basal interface is melting and the lake bed is at its deepest, remains the best choice. Considering potential lake-water salinity and ice-density variations, we estimate the critical tipping depth , separating different temperature regimes within subglacial lakes, to be in about 2900 to 3045 m depth.

Description: Glacier changes on Sierra Velluda massif, Chile (37° S): mountain glaciers of an intensively-used mid-latitude landscape The Cryosphere Discussions, 5, 685-720, 2011 Author(s): A. Fernández, A. Santana, E. Jaque, C. Martínez, and R. Sáez The central-southern section of Chile is defined as one of the Latin American hot spots in the last IPCC Report due to the impact of glacier retreat on water resources, the transitional character of the climate, and its importance in terms of agricultural and forestry activities. In order to provide a better understanding of glacier behavior in this zone, this paper analyzes the volumetric changes of glaciers in the Sierra Velluda, located in the upper Bío Bío River Basin. Bibliographic sources, satellite images, and DEMs were used to estimate frontal, areal, and volumetric changes. An analysis of significance was performed in order to provide accurate estimations of the fluctuations. The results indicate that Sierra Velluda glaciers have suffered a significant reduction since the 1960s, despite some short periods of positive fluctuations. A maximum position of a glacier for the year 1828 was identified, which is in concordance with other proxies registered elsewhere in Chile. These changes agree with measurements of glacier fluctuation elsewhere in Chile. While short-term fluctuations are consistent with the inter-annual precipitation variability, lake levels records, and a warm phase of the El Niño Southern Oscillation (ENSO), the general shrinkage agrees with the shift of the ENSO (PDO) in 1976. Therefore, it is proposed that Sierra Velluda's glaciers are highly sensitive to high frequency climatic fluctuations and even to inter-annual variability. Considering that models project a reduction in Andean precipitation and an altitudinal increase in the 0 °C isotherm, these ice bodies are expected to continue to shrink.

Description: Characterization of glacier debris cover via in situ and optical remote sensing methods: a case study in the Khumbu Himalaya, Nepal The Cryosphere Discussions, 5, 499-564, 2011 Author(s): K. A. Casey, A. Kääb, and D. I. Benn Field spectrometry and physical samples of debris, snow and ice were collected from the ablation zones of Ngozumpa and Khumbu glaciers of the Khumbu Himalaya, Nepal in November and December 2009. Field acquired spectral reflectances and mineral and chemical composition of samples were used as ground truth for comparison with satellite optical remote sensing data. Supraglacial debris was characterized by several optical remote sensing methods, including hyperspectral reflectance analysis, multispectral band composites and indices, spectral angle relationships, thermal band temperature and emissivity analysis, as well as repeat image derived glacier velocity and theoretical supraglacial particle transport. Supraglacial mineral components were identified and mineral abundances were estimated on Khumbu Himalayan glaciers. Mass flux was estimated by false color composites and glacier velocity displacement fields. Supraglacial temperatures were compared with mineral abundances, implying potential parameters to estimate differential melt. Overall, glaciologic implications of debris cover characterizations are applicable to (1) glacier energy balance, (2) glacial kinematics and (3) mapping glacial extent. The methods presented can be used in synergy to improve supraglacial debris quantification and reduce errors associated with debris covered ice extent mapping, surface radiative properties, as well as debris covered ice mass flux and loss estimations.

Description: Retrieval of snow grain size and albedo of Western Himalayan snow cover using satellite data The Cryosphere Discussions, 5, 605-653, 2011 Author(s): H. S. Negi and A. Kokhanovsky In the present study we describe the retrievals of snow grain size and spectral albedo (plane and spherical albedo) for Western Himalayan snow cover using Hyperion sensor data. The asymptotic radiative transfer (ART) theory was explored for the snow retrievals. To make the methodology operational only five spectral bands (440, 500, 1050, 1240 and 1650 nm) of Hyperion were used for snow parameters retrieval. The bi-spectral method (440 nm in the visible and 1050/1240 nm in the NIR region) was used to retrieve snow grain size. Spectral albedos were retrieved using satellite reflectances and estimated grain size. A good agreement was observed between retrieved snow parameters and ground observed snow-meteorological conditions. The satellite retrieved grain sizes were compared with field spectroradiometer retrieved grain sizes and close results were found for Lower Himalayan snow. The wavelength 1240 nm was found to be more suitable compared to 1050 nm for grain size retrieval along the steep slopes. The methodology was able to retrieve the spatial variations in snow parameters in different parts of Western Himalaya which are due to snow climatic and terrain conditions of Himalaya. This methodology is of importance for operational snow cover and glacier monitoring in Himalayan region using space-borne and air-borne sensors.

Description: Scale-dependent measurement and analysis of ground surface temperature variability in alpine terrain The Cryosphere Discussions, 5, 307-338, 2011 Author(s): S. Gubler, J. Fiddes, S. Gruber, and M. Keller Measurements of environmental variables are often used to validate and calibrate physically-based models. Depending on their application, models are used at different scales, ranging from few meters to tens of kilometers. Environmental variables can vary strongly within the grid cells of these models. Validating a model with a single measurement is therefore delicate and susceptible to induce bias in further model applications. To address the question of uncertainty associated with scale in permafrost models, we present data of 390 spatially-distributed ground surface temperature measurements recorded in terrain of high topographic variability in the Swiss Alps. We illustrate a way to program, deploy and refind a large number of measurement devices efficiently, and present a strategy to reduce data loss reported in earlier studies. Data after the first year of deployment is presented. The measurements represent the variability of ground surface temperatures at two different scales ranging from few meters to some kilometers. On the larger scale, the dependence of mean annual ground surface temperature on elevation, slope, aspect and ground cover type is modelled with a linear regression model. Sampled mean annual ground surface temperatures vary from −4 °C to 5 °C within an area of 16 km 2 subject to elevational differences of approximately 1000 m. The measurements also indicate that mean annual ground surface temperatures vary up to 6 °C (i.e., from −2 °C to 4 °C) even within an elevational band of 300 m. Furthermore, variations can be high (up to 2.5 °C) at distances of less than 14 m in homogeneous terrain. The effect of this high variability of an environmental variable on model validation and applications in alpine regions is discussed.

Description: Record mass loss from Greenland's best-observed local glacier The Cryosphere Discussions, 5, 461-477, 2011 Author(s): S. H. Mernild, N. T. Knudsen, W. H. Lipscomb, J. C. Yde, J. K. Malmros, B. H. Jakobsen, and B. Hasholt Warming in the Arctic during the past several decades has caused glaciers to thin and retreat, resulting in increased freshwater runoff to the ocean. Local glaciers peripheral to the ice sheet are also retreating, but few mass-balance observations are available to quantify that retreat and determine the extent to which these glaciers are out of equilibrium with present-day climate. Here, we document record mass loss in 2009/2010 for the Mittivakkat Glacier (henceforth MG), the only local glacier in Greenland for which there exist long-term observations of both the surface mass balance and glacier front fluctuations. We attribute this mass loss to record high mean summer (June–August) and higher-than-average winter (September–May) temperatures and to lower-than-average winter precipitation. Also, we use the 15-year mass-balance record to estimate present-day and equilibrium accumulation-area ratios for the MG. We show that the glacier is significantly out of balance and will likely lose approximately 70% of its current area and 80% of its volume even in the absence of further climate changes. Temperature records from coastal stations in Southeast Greenland suggest that recent MG mass losses are not merely a local phenomenon, but are indicative of glacier changes in the broader region. Mass-balance observations for the MG therefore provide unique documentation of the general retreat of Southeast Greenland's local glaciers under ongoing climate warming.

Description: Refined broad-scale sub-glacial morphology of Aurora Subglacial Basin, East Antarctica derived by an ice-dynamics-based interpolation scheme The Cryosphere Discussions, 5, 655-684, 2011 Author(s): J. L. Roberts, R. C. Warner, D. Young, A. Wright, T. D. van Ommen, D. D. Blankenship, M. Siegert, N. W. Young, I. E. Tabacco, A. Forieri, A. Passerini, A. Zirizzotti, and M. Frezzotti Ice thickness data over much of East Antarctica are sparse and irregularly distributed. This poses difficulties for reconstructing the homogeneous coverage needed to properly assess underlying sub-glacial morphology and fundamental geometric constraints on sea level rise. Here we introduce a new physically-based ice thickness interpolation scheme and apply this to existing ice thickness data in the Aurora Subglacial Basin region. The skill and robustness of the new reconstruction is demonstrated by comparison with new data from the ICECAP project. The interpolated morphology shows an extensive marine-based ice sheet, with considerably more area below sea-level than shown by prior studies. It also shows deep features connecting the coastal grounding zone with the deepest regions in the interior. This has implications for ice sheet response to a warming ocean and underscores the importance of obtaining additional high resolution data in these marginal zones for modelling ice sheet evolution.

Description: Geophysical evidence for soft bed sliding at Jakobshavn Isbrae, West Greenland The Cryosphere Discussions, 5, 339-366, 2011 Author(s): A. E. Block and R. E. Bell Jakobshavn Isbrae is Greenland's fastest moving outlet glacier and a major contributor to sea level rise. We analyze new gravity and magnetic profiles across the glacier, extending from the mouth of the outlet fjord to 64 km inland of the 2008 grounding line. Our results provide new insights into Jakobshavn Isbrae's geologic underpinnings and controls on the basal velocities. Earlier studies of basal processes minimized basal slip as a fast flow mechanism. Currently, velocities are up to double those considered in these studies, necessitating a reanalysis of the basal conditions. The gravity field along the glacier's main trunk cannot be attributed to the gravitational effect of bed topography and the overlying ice sheet. We interpret the remaining gravity signal as evidence of up to 2400 m of low density sediment beneath the main trunk. Examining recent velocities, we find basal slip is a major contributor to ice flow along most of the sediment filled trough. Within 54 km of the grounding line, only isolated 1–3 km wide regions have velocities that possibly result solely from internal deformation of the ice. We conclude soft bed sliding over the thick sediment wedge beneath Jakobshavn Isbrae is the dominant mechanism of fast flow.

Description: Modelling the spatial pattern of ground thaw in a small basin in the arctic tundra The Cryosphere Discussions, 5, 367-400, 2011 Author(s): S. Endrizzi, W. L. Quinton, and P. Marsh In the arctic tundra the ground is normally composed by a relatively thin organic soil layer, overlying mineral sediment. Subsurface water drainage generally occurs in the organic layer for its high hydraulic conductivity. However, the organic layer shows significant decrease of hydraulic conductivity with depth. The position and the topography of the frost table, which here acts as a relatively impermeable surface, are therefore crucial in determining the hillslope drainage rate. This work aims at understanding how the topography of the ground surface affects the spatial variability of the depth of thaw in a 1 km 2 low-elevation arctic tundra basin with a fine resolution model that fully couples energy and water flow processes. The simulations indicate that the spatial patterns of ground thaw are not dominated by slope and aspect, but are instead entirely controlled by the spatial distribution of soil moisture, which is determined by subsurface flow patterns. Measured thaw depths have a similar range of variability to the simulated values for each stage of active layer development, although the model slightly overestimated the depth of thaw.

Description: Glacial debris cover and melt water production for glaciers in the Altay, Russia The Cryosphere Discussions, 5, 401-430, 2011 Author(s): C. Mayer, A. Lambrecht, W. Hagg, and Y. Narozhny Glaciers are important water storages on a seasonal and long-term time scale. Where high mountains are surrounded by arid lowlands, glacier runoff is an important source of water during the growing season. This situation can be found in the Altay mountains in Southern Siberia, where the recent glacierization of 〉700 km 2 is subject to continuous mass loss, even though the shrinking is comparably slow. The glacier retreat is accompanied by an extension of supra-glacial moraine, which itself strongly influences ablation rates. To quantify these effects, the spatial evolution of debris cover since 1952 was analysed for three glaciers in the North Chuya Ridge using satellite and airborne imagery. In summer 2007, an ablation experiment was carried out on debris covered parts of Maliy Aktru glacier. Thermistors in different depths within the moraine provided data to calculate thermal resistance of the debris. A set of ablation stakes was installed at locations with differing debris thickness and observed regularly throughout the entire melt season. Air temperature from an AWS was used to calculate degree day factors in dependence of the debris thickness. To take into account the shading effect of surrounding walls and peaks, the potential solar radiation and its evolution throughout the summer was determined from a digital elevation model. This allows us to extrapolate our measurements from Maliy Aktru to the other two glaciers of the Aktru basin and to estimate basin melt rates. In addition accumulated ice melt was derived for 12 glaciers in the North Chuya Range. Changes in summer runoff from the 1960s are compared to the results from our melt model and the evolution of debris cover is analysed in respect to the melt activity.

Description: A comparison of glacier melt on debris-covered glaciers in the northern and southern Caucasus The Cryosphere Discussions, 5, 431-459, 2011 Author(s): A. Lambrecht, C. Mayer, W. Hagg, V. Popovnin, A. Rezepkin, N. Lomidze, and D. Svanadze The glacier coverage in the Caucasus Mountains underwent considerable changes during the last decades. Besides a reduction in glacier area which in some areas is comparable to area changes in the European Alps, also the concentration of supra-glacial debris increased on many glaciers. Only a few glaciers in the Caucasus are monitored on a regular basis, while for most areas no field measurements are available on a continuous basis. In this study the regional differences between the well studied Adyl-su basin on the northern slope of the Caucasus is compared with a similar basin in the South (Zopkhito basin). Special focus is laid on the effect of supra-glacial debris cover on the melt conditions during the ablation season. Systematic differences can be shown for the distribution and temporal increase of the debris cover on the glaciers. While in the Adyl-su basin an extensive debris cover on the glacier tongues is common, only some low lying glacier tongues in the Zopkhito basin show considerable supra-glacial debris. Also the temporal increase in debris cover is decidedly stronger in the North. Field experiments show that the thermal resistance of the debris cover is somewhat higher than in other glacerised regions in the world. A simple ablation model which includes the effect of the debris cover on ice melt indicates considerably stronger melt rates in the northern basin, despite the much more widespread debris distribution. This is due to the different meteorological conditions with more frequent cloud cover and precipitation in the South. Still ablation is strongly influenced in both basins by the occurrence of supra-glacial debris cover, reducing the total amount of melt on the glacier by about 20%. Especially in the lower tongue areas this effect mitigates the area loss of the glaciers considerably.

Description: In-situ multispectral and bathymetric measurements over a supraglacial lake in western Greenland using a remotely controlled watercraft The Cryosphere Discussions, 5, 479-498, 2011 Author(s): M. Tedesco and N. Steiner We report concurrent in-situ multi-spectral and depth measurements over a supraglacial lake in West Greenland, collected by means of a remotely controlled boat equipped with a GPS, a sonar and a spectrometer. We focus our attention on the analysis of some of the key parameters widely used for multispectral spaceborne bathymetry, namely the lake bottom albedo and the water attenuation coefficient. The analysis of in-situ data highlights the exponential trend of the water-leaving reflectance with lake depth. The values of the attenuation factor are obtained from in-situ data and compared with those computed using approaches proposed in the literature. Also, the values of the lake bottom albedo from in-situ measurements are compared with those obtained from the analysis of reflectance of shallow-waters. Finally, we quantify the error between in-situ measured and satellite-estimated lake depth values for the lake under study.

Description: Comparison of direct and geodetic mass balances on an annual time scale The Cryosphere Discussions, 5, 565-604, 2011 Author(s): A. Fischer, H. Schneider, G. Merkel, and R. Sailer Very accurate airborne laserscanning (ALS) elevation data was used to calculate the annual volume changes for Hintereisferner and Kesselwandferner in the Ötztal Alps, Austria for 2001/2002–2008/2009. The comparison of the altitude of 51 recently GPS surveyed ground control points showed that the accuracy of the ALS DEMs is better than 0.3 m. The geodetic mass balance was calculated from the volume change using detailed maps of the firn cover and applying corrections for the seasonal snow cover. The maximum snow height at the time of the elevation data flight was 0.5 m averaged over the glacier surface. The volume change data was compared to in situ mass balance data for the total area and at the stakes. For the total period of 8 yr, the difference between the geodetic and the direct mass balance is 2.398 m w.e. on Hintereisferner and 1.380 m w.e. on Kesselwandferner, corresponding to about two times the mean annual mass balance. The vertical ice flow velocity was measured and found to be on the same order of magnitude as the mass balance at KWF. This is an indicator that volume change data does not allow the calculation of ablation or accumulation rates without detailed measurements or models of the vertical ice flow velocity. Therefore, only direct mass balance data allow process studies or investigation of the climatic controls of the resulting mass changes.

Description: Monitoring spatial and temporal variations of surface albedo on Saint Sorlin Glacier (French Alps) using terrestrial photography The Cryosphere Discussions, 5, 271-305, 2011 Author(s): M. Dumont, P. Sirguey, Y. Arnaud, and D. Six Accurate knowledge of temperate glacier mass balance is essential to understand the relationship between glacier and climate. Defined as the reflected fraction of incident radiation over the whole solar spectrum, the surface broadband albedo is one of the leading variable of their mass balance. This study presents a new method to retrieve the albedo of frozen surfaces from terrestrial photography at visible and near infrared wavelengths. This method accounts for the anisotropic reflectance of snow and ice surfaces and uses a radiative transfer model for narrow-to-broadband conversion. The accuracy of the method was assessed using concomitant measurements of albedo during the summers 2008 and 2009 on Saint Sorlin Glacier (Grandes Rousses, France). These albedo measurements are performed at two locations on the glacier, one in the ablation area and the other in the accumulation zone, with a net radiometer Kipp and Zonen CNR1. Main sources of uncertainty are associated with the presence of high clouds and the georeferencing of the photographs.

Description: The multiphase physics of sea ice: a review The Cryosphere Discussions, 5, 1949-1993, 2011 Author(s): E. C. Hunke, D. Notz, A. K. Turner, and M. Vancoppenolle Rather than being solid throughout, sea ice contains liquid brine inclusions, solid salts, microalgae, trace elements, gases, and other impurities which all exist in the interstices of a porous, solid ice matrix. This multiphase structure of sea ice arises from the fact that the salt that exists in seawater cannot be embedded into the water-ice crystal lattice upon formation of sea ice, but remains in liquid solution. Depending on the ice porosity (determined by temperature and salinity), this brine can drain from the ice, taking other sea ice constituents with it. Thus, sea ice salinity and microstructure are tightly interconnected and play a significant role in polar ecosystems and climate. As large-scale climate modeling efforts move toward "earth system" simulations that include biological and chemical cycles, renewed interest in the multiphase physics of sea ice has strengthened research initiatives to observe, understand and model this complex system. This review article provides an overview of these efforts, highlighting known difficulties and requisite observations for further progress in the field. We focus on mushy-layer theory, which describes general multiphase materials, and on numerical approaches now being explored to model the multiphase evolution of sea ice and its interaction with chemical, biological and climate systems.

Description: Basal crevasses in Larsen C Ice Shelf and implications for their global abundance The Cryosphere Discussions, 5, 2035-2060, 2011 Author(s): A. Luckman, D. Jansen, B. Kulessa, E. C. King, P. Sammonds, and D. I. Benn Basal crevasses extend upwards from the base of ice bodies and can penetrate more than halfway through the ice column under conditions found commonly on ice shelves. As a result, they may locally modify the exchange of mass and energy between ice shelf and ocean, and by altering the shelf's mechanical properties could play a fundamental role in ice shelf stability. Although early studies revealed that such features may be abundant on Antarctic ice shelves, their geometrical properties and spatial distribution has gained little attention. We investigate basal crevasses in Larsen C Ice Shelf using field radar survey, remote sensing and numerical modelling. We demonstrate that a group of features visible in MODIS imagery are the surface expressions of basal crevasses in the form of surface troughs, and find that basal crevasses can be generated as a result of stresses well downstream of the grounding line. We show that linear elastic fracture mechanics modelling is a good predictor of basal crevasse penetration height where stresses are predominantly tensile, and that measured surface trough depth does not always reflect this height, probably because of snow accumulation in the trough, marine ice accretion in the crevasse, or stress bridging from the surrounding ice. We conclude that all features visible in MODIS imagery of ice shelves and previously labelled simply as "crevasses", where they are not full thickness rifts, must be basal crevasse troughs, highlighting a fundamental structural property of many ice shelves that may have been previously overlooked.

Description: An improved semi-empirical model for the densification of Antarctic firn The Cryosphere Discussions, 5, 1921-1948, 2011 Author(s): S. R. M. Ligtenberg, M. M. Helsen, and M. R. van den Broeke A firn densification model is presented that simulates steady-state Antarctic firn density profiles, as well as the temporal evolution of firn density and surface height. The model uses an improved firn densification expression that is tuned to fit depth-density observations. Liquid water processes (meltwater percolation, retention and refreezing) are also included. Two applications are presented. The steady-state model version is used to simulate the strong spatial variability in firn layer thickness across the Antarctic ice sheet. The time-dependent model is run for 3 Antarctic locations. It reveals a gentle upward motion of the surface during autumn, winter and spring, while during summer there is a more rapid lowering of the surface. Accumulation and (if present) melt introduce large inter-annual variability in surface height trends, possibly hiding ice dynamical thickening and thinning.

Description: A three-dimensional full Stokes model of the grounding line dynamics: effect of a pinning point beneath the ice shelf The Cryosphere Discussions, 5, 1995-2033, 2011 Author(s): L. Favier, O. Gagliardini, G. Durand, and T. Zwinger The West Antarctic ice sheet is confined by a large area of ice shelves, fed by inland ice through fast flowing ice streams. The dynamics of the grounding line, i.e. the line-boundary between grounded ice and the downstream ice shelf, has a major influence on the dynamics of the whole ice sheet. However, most of the ice sheet models use simplifications of the flow equations, i.e., they do not include all the stress components, and are known to fail in their mathematical representation of the grounding line dynamics. Here, we present a 3-D full Stokes model of a marine ice sheet, in which the flow problem is coupled with the evolution of the upper and lower free surfaces, and the position of the grounding line determined by solving a contact problem between the shelf/sheet lower surface and the bedrock. Simulations are performed using the open-source finite-element code Elmer/Ice within a parallel environment. The effect of a pinning point, inserted beneath the ice shelf, on the ice dynamics is studied to demonstrate the model's ability to cope with curved and multiple grounding lines. Starting from a steady state, the sea level is slightly decreased to create a contact point between a seamount and the ice shelf. The model predicts a dramatic decrease of the shelf velocities, leading to an advance of the grounding line until both grounded zones merge together, during which an ice rumple forms above the contact area at the pinning point. Finally, we show that once the contact is created, increasing the sea level to its initial value does not cease the interaction with the pinning point and has no effect on the ice dynamics, indicating a stabilizing effect of pinning points.

Description: The impact of a seasonally ice free Arctic Ocean on the climate and surface mass balance of Svalbard The Cryosphere Discussions, 5, 1887-1920, 2011 Author(s): J. J. Day, J. L. Bamber, P. J. Valdes, and J. Kohler General circulation models (GCMs) predict a rapid decrease in Arctic sea ice extent in the 21st century. The decline of September sea ice is expected to continue until the Arctic Ocean is seasonally ice free, leading to a much perturbed Arctic climate with large changes in surface energy flux. Svalbard, located on the present day sea ice edge, contains many low lying ice caps and glaciers which are extremely sensitive to changes in climate. Records of past accumulation indicate that the surface mass balance (SMB) of Svalbard is also sensitive to changes in the position of the sea ice edge. To investigate the impact of 21st Century sea ice decline on the climate and surface mass balance of Svalbard a high resolution (25 km) regional climate model (RCM) was forced with a repeating cycle of sea surface temperatures (SSTs) and sea ice conditions for the periods 1961–1990 and 2061–2090. By prescribing 20th Century SSTs and 21st Century sea ice for one simulation, the impact of sea ice decline is isolated. This study shows that the coupled impact of sea ice decline and SST increase results in a decrease in SMB, whereas the impact of sea ice decline alone causes an increase in SMB of similar magnitude.

Description: Spatial analyses of thermokarst lakes and basins in Yedoma landscapes of the Lena Delta The Cryosphere Discussions, 5, 1495-1545, 2011 Author(s): A. Morgenstern, G. Grosse, F. Günther, I. Fedorova, and L. Schirrmeister Distinctive periglacial landscapes have formed in late-Pleistocene ice-rich permafrost deposits (Ice Complex) of Northern Yakutia, Siberia. Thermokarst lakes and thermokarst basins alternate with ice-rich Yedoma uplands. We investigate different thermokarst stages in Ice Complex deposits of the Lena River Delta using remote sensing and geoinformation techniques. The morphometry and spatial distribution of thermokarst lakes on Yedoma uplands, thermokarst lakes in basins, and thermokarst basins are analyzed, and possible dependence upon relief position and cryolithological context is considered. Of these thermokarst stages, developing thermokarst lakes on Yedoma uplands alter ice-rich permafrost the most, but occupy only 2.2 % of the study area compared to 20.0 % occupied by thermokarst basins. The future potential for developing large areas of thermokarst on Yedoma uplands is limited due to shrinking distances to degradational features and delta channels that foster lake drainage. Further thermokarst development in existing basins is restricted to underlying deposits that have already undergone thaw, compaction, and old carbon mobilization, and to deposits formed after initial lake drainage. Therefore, a distinction between developmental stages of thermokarst and landscape units is necessary to assess the potential for future permafrost degradation and carbon release due to thermokarst in Siberian Yedoma landscapes.

Description: A statistical permafrost distribution model for the European Alps The Cryosphere Discussions, 5, 1419-1459, 2011 Author(s): L. Boeckli, A. Brenning, S. Gruber, and J. Noetzli Permafrost distribution modeling in densely populated mountain regions is an important task to support the construction of infrastructure and for the assessment of climate change effects on permafrost and related natural systems. In order to analyze permafrost distribution and evolution on an Alpine-wide scale, one consistent model for the entire domain is needed. We present a statistical permafrost model for the entire Alps based on rock glacier inventories and rock surface temperatures. Starting from an integrated model framework, two different sub-models were developed, one for debris covered areas (debris model) and one for steep rock faces (rock model). For the debris model a generalized linear mixed-effect model (GLMM) was used to predict the probability of a rock glacier being intact as opposed to relict. The model is based on the explanatory variables mean annual air temperature (MAAT), potential incoming solar radiation (PISR) and the mean annual sum of precipitation (PRECIP), and achieves an excellent discrimination (area under the receiver-operating characteristic, AUROC = 0.91). Surprisingly, the probability of a rock glacier being intact is positively associated with increasing PRECIP for given MAAT and PISR conditions. The rock model was calibrated with mean annual rock surface temperatures (MARST) and is based on MAAT and PISR. The linear regression achieves a root mean square error (RMSE) of 1.6 °C. The final model combines the two sub-models and accounts for the different scales used for model calibration. Further steps to transfer this model into a map-based product are outlined.

Description: Derivation and analysis of a high-resolution estimate of global permafrost zonation The Cryosphere Discussions, 5, 1547-1582, 2011 Author(s): S. Gruber Permafrost underlies much of Earths' surface and interacts with climate, eco-systems and human systems. It is a complex phenomenon controlled by climate and (sub-) surface properties and reacts to change with variable delay. Heterogeneity and sparse data challenge the modeling of its spatial distribution. Currently, there is no data set to adequately inform global studies of permafrost. The available data set for the Northern Hemisphere is frequently used for model evaluation, but its quality and consistency are difficult to assess. A global model of permafrost extent and dataset of permafrost zonation are presented and discussed, extending earlier studies by including the Southern Hemisphere, by consistent data and methods, and most importantly, by attention to uncertainty and scaling. Established relationships between air temperature and the occurrence of permafrost are re-formulated into a model that is parametrized using published estimates. It is run with a high-resolution (

Description: Permafrost degradation risk zone assessment using simulation models The Cryosphere Discussions, 5, 1021-1053, 2011 Author(s): R. P. Daanen, T. Ingeman-Nielsen, S. S. Marchenko, V. E. Romanovsky, N. Foged, M. Stendel, J. H. Christensen, and K. Hornbech Svensen Climate change is detrimental to permafrost and related processes, from hydrological and ecological to societal. We present the current and future state of permafrost in Greenland as modeled numerically with the GIPL model driven by HIRHAM climate projections till 2075. In this paper we developed the Permafrost Thaw Potential (PTP). This is the potential active layer increase due to climate warming and surface alterations. PTP was used in a simple risk assessment procedure usefull for engineerings. Climate warming will result in wide-spread permafrost warming and degradation. Construction on sedimentary deposits with permafrost should be avoided south of latitude 67.

Description: An assessment of uncertainties in using volume-area modelling for computing the twenty-first century glacier contribution to sea-level change The Cryosphere Discussions, 5, 1655-1695, 2011 Author(s): A. B. A. Slangen and R. S. W. van de Wal A large part of present-day sea-level change is formed by the melt of glaciers and ice caps (GIC). This study focuses on the uncertainties in the calculation of the GIC contribution on a century timescale. The model used is based on volume-area scaling, combined with the mass balance sensitivity of the GIC. We assess different aspects that contribute to the uncertainty in the prediction of the contribution of GIC to future sea-level rise, such as (1) the volume-area scaling method (scaling constant), (2) the choice of glacier inventory, (3) the imbalance of glaciers with climate, (4) the mass balance sensitivity, and (5) the climate models. Additionally, a comparison of the model results to the 20th century GIC contribution is presented. We find that small variations in the scaling constant cause significant variations in the initial volume of the glaciers, but only limited variations in the glacier volume change. If two existing glacier inventories are tuned such that the initial volume is the same, the GIC sea-level contribution over 100 yr differs by 0.027 m. It appears that the mass balance sensitivity is also important: variations of 20 % in the mass balance sensitivity have an impact of 17 % on the resulting sea-level projections. Another important factor is the choice of the climate model, as the GIC contribution to sea-level change largely depends on the temperature and precipitation taken from climate models. Combining all the uncertainties examined in this study leads to a total uncertainty of 4.5 cm or 30 % in the GIC contribution to global mean sea level. Reducing the variance in the climate models and improving the glacier inventories will significantly reduce the uncertainty in calculating the GIC contributions, and are therefore crucial actions to improve future sea-level projections.

Description: Snow accumulation and compaction derived from GPR data near Ross Island, Antarctica The Cryosphere Discussions, 5, 1-39, 2011 Author(s): N. C. Kruetzmann, W. Rack, A. J. McDonald, and S. E. George We present a new method of using ground penetrating radar (GPR) for estimating snow accumulation and compaction rates in Antarctica. We process 500 MHz data to produce radargrams with unambiguous reflection horizons that can be observed and tracked in repeat GPR measurements made one year apart. Our processing methodology is a deterministic deconvolution via the Fourier domain using an estimate of the emitted waveform from direct measurement. At two measurement sites near Scott Base, Antarctica, point measurements of average accumulation from snow pits and firn cores are extrapolated to a larger area by identifying a dateable dust layer in the radargrams. Over an 800 m×800 m area on the McMurdo Ice Shelf (77°45´ S, 167°17´ E) the average accumulation is found to be 269 ± 9 kg m −2 a −1 . The accumulation over an area of 400 m×400 m in the dry snow zone on Ross Island (77°40´ S, 167°11´ E, 350 m a.s.l.) is found to be higher (404 ± 22 kg m −2 a −1 ) and shows increased variability related to undulating terrain. Compaction of snow between 2 m and 13 m depth is estimated at both sites by tracking several internal reflection horizons along the radar profiles and calculating the average change in separation of horizon pairs from one year to the next. The derived compaction rates range from 7 cm m −1 at a depth of two metres, down to no measurable compaction at 13 m depth, and are similar to published values from point measurements.

Description: A model study of the energy and mass balance of Chhota Shigri glacier in the Western Himalaya, India The Cryosphere Discussions, 5, 95-129, 2011 Author(s): F. Pithan The impact of climate change on Himalaya mountain glaciers is increasingly subject of public and scientific debate. However, observational data are sparse and important knowledge gaps remain in the understanding of what drives changes in these glaciers' mass balances. The present study investigates the glacier regime on Chhota Shigri, a benchmark glacier for the observation of climate change in the monsoon-arid transition zone of Western Himalaya. Results of an energy-balance model driven by reanalysis data and the observed mass balances from three years on 50 m altitude intervals across the glacier display a correlation coefficient of 0.974. Contrary to prior assumptions, monsoon precipitation accounts for a quarter to a third of total accumulation. It has an additional importance because it lowers the surface albedo during the ablation season. Results confirm radiation as the main energy source for melt on Himalaya glaciers. Latent heat flux acts as an important energy sink in the pre-monsoon season. Mass balance is most sensitive to changes in atmospheric humidity, changing by 900 mm w.e. per 10% change in humidity. Temperature sensitivity is 220 mm w.e.K −1 . Model results using 21st century anomalies from a regional climate model based on the SRES A2 scenario suggest that a monsoon increase might offset the effect of warming.

Description: Velocity structure, front position changes and calving of the tidewater glacier Kronebreen, Svalbard The Cryosphere Discussions, 5, 41-73, 2011 Author(s): M. Sund, T. Eiken, and C. Rolstad Denby Glacier calving and retreat constitute a substantial portion of the ablation of tidewater glaciers and is therefore of interest in climate models in order to get more accurate predictions of future development of glaciers and their contribution to sea level rise. We use photogrammetry, global navigation satellite system, surface elevation and bathymetric data from Kronebreen to test a crevasse-depth calving model, investigate meteorological controls on near terminus velocity fluctuations and finally short-term and longer term (multi annual to decadal) controls of the front positions and calving. The relationship between velocity structure, crevasse formation, and calving events at Kronebreen is found to be more complex than outlined in the crevasse-depth calving model. Surface meltwater is found to be closely connected to velocities, but no direct relationship between velocity variation and calving could be seen along the investigated transect. On a long term basis the front positions of Kronebreen are results of a combination of several factors, particularly the interplay with the confluent glacier Kongsvegen, and change in discharge fluxes as a result of surge dynamics. Yet the bed topography is found to be an important control on the retreat of this glacier, similar to several other tidewater glaciers.

Description: Snow characteristics, distribution and disappearance in a subtropical volcano (Teide, Canary Islands) The Cryosphere Discussions, 5, 75-93, 2011 Author(s): R. Martín Moreno An analysis is carried out of the snow characteristics, distribution and disappearance on a subtropical volcano. Teide (28° 16′ N–16° 38′ W), is a stratovolcano with the highest altitude in Spanish territory at 3718 m a.s.l. It is characterized by an arid climate, with only 12.7 days of snow per year and very clear skies during most of the year. The snow cover is rarely continuous even during the cold season. In addition, the particular geothermal conditions of its ground, the layout of the lava flows from the crater, and not only its subtropical latitudinal position, are responsible for its special snow distribution and ablation processes, such as the banded and radial snow pattern, the hollows in the base layer of the snowpack and snow penitents. These features create a unique snow cover within the high mountain environments.

Description: Variability and changes of Arctic sea ice thickness distribution under different AO/DA states The Cryosphere Discussions, 5, 131-167, 2011 Author(s): A. Oikkonen and J. Haapala Changes of the mean sea ice thickness and concentration in the Arctic are well known. However, comparable little is known about the ice thickness distribution and the composition of ice pack in quantity. In this paper we determine the ice thickness distributions, mean and modal thicknesses, and their regional and seasonal variability in the Arctic under different large scale atmospheric circulation modes. We compare characteristics of the Arctic ice pack during the periods 1975–1987 and 1988–2000, which have a different distribution in the AO/DA space. The study is based on submarine measurements of sea ice draft. The prevalent feature is that the peak of sea ice thickness distributions has generally taken a narrower form and shifted toward thinner ice. Also, both mean and modal ice thickness have generally decreased. These noticeable changes result from a loss of thick, mostly deformed, ice. In the spring the loss of the volume of ice thicker than 5 m exceeds 35% in all regions except the Nansen Basin, and the reduction is as much as over 45% at the North Pole and in the Eastern Arctic. In the autumn the volume of thick, mostly deformed ice has decreased by more than 40% in the Canada Basin only, but the reduction is more than 30% also in the Beaufort Sea and in the Chukchi Sea. In the Beaufort Sea region the decrease of the modal draft has been so strong that the peak has shifted from multiyear ice to first-year type ice. Also, the regional and seasonal variability of the sea ice thickness has decreased, since the thinning has been the most pronounced in the regions with the thickest pack ice (the Western Arctic), and during the spring (0.6–0.8 m per decade).

Description: Getting around Antarctica: new high-resolution mappings of the grounded and freely-floating boundaries of the Antarctic ice sheet created for the International Polar Year The Cryosphere Discussions, 5, 183-227, 2011 Author(s): R. Bindschadler, H. Choi, A. Wichlacz, R. Bingham, J. Bohlander, K. Brunt, H. Corr, R. Drews, H. Fricker, M. Hall, R. Hindmarsh, J. Kohler, L. Padman, W. Rack, G. Rotschky, S. Urbini, P. Vornberger, and N. Young The boundary of grounded ice and the location of ice transitioning to a freely floating state are mapped at 15-m resolution around the entire continent of Antarctica. These data products are produced by participants of the International Polar Year project ASAID using customized software combining Landsat-7 imagery and ICESat laser altimetry. The grounded ice boundary is 53 610 km long; 74% of it abuts to floating ice shelves or outlet glaciers, 19% is adjacent to open or sea-ice covered ocean, and 7% of the boundary are land terminations with bare rock. Elevations along each line are selected from 6 candidate digital elevation models: two created from the input ICESat laser altimetry and Landsat data, two from stereo satellite imagery, and two from compilations of primarily radar altimetry. Elevation selection and an assignment of confidence in the elevation value are based on agreement with ICESat elevation values and shape of the surface inferred from the Landsat imagery. Elevations along the freely-floating boundary (called the hydrostatic line) are converted to ice thicknesses by applying a firn-correction factor and a flotation criterion. The relationship between the seaward offset of the hydrostatic line from the grounding line only weakly matches a prediction based on beam theory. Airborne data are used to validate the technique of grounding line mapping, elevation selection and ice thickness derivation. The mapped products along with the customized software to generate them and a variety of intermediate products are available from the National Snow and Ice Data Center.

Description: Petermann Glacier, North Greenland: massive calving in 2010 and the past half century The Cryosphere Discussions, 5, 169-181, 2011 Author(s): O. M. Johannessen, M. Babiker, and M. W. Miles Greenland's marine-terminating glaciers drain large amounts of solid ice through calving of icebergs, as well as melting of floating glacial ice. Petermann Glacier, North Greenland, has the Northern Hemisphere's long floating ice shelf. A massive (~270 km 2 ) calving event was observed from satellite sensors in August 2010. In order to understand this in perspective, here we perform a comprehensive retrospective data analysis of Petermann Glacier calving-front variability spanning half a century. Here we establish that there have been at least four massive (100 + km 2 ) calving events over the past 50 years: (1) 1959–1961 (~153 km 2 ), (2) 1991 (~168 km 2 ), (3) 2001 (~71 km 2 ) and (4) 2010 (~270 km 2 ), as well as ~31 km 2 calved in 2008. The terminus position in 2010 has retreated ~15 km beyond the envelope of previous observations. Whether the massive calving in 2010 represents natural episodic variability or a response to global and/or ocean warming in the fjord remains speculative, although this event supports the contention that the ice shelf recently has become vulnerable due to extensive fracturing and channelized basal melting.

Description: Modeling the thermal dynamics of the active layer at two contrasting permafrost sites The Cryosphere Discussions, 5, 229-270, 2011 Author(s): J. Weismüller, U. Wollschläger, J. Boike, and K. Roth The thermal and hydraulic dynamics of unsaturated active layers are described in a one-dimensional numerical forward model. Hydraulic and thermal transport processes are coupled in a set of partial differential equations based on Richards' equation, conductive and convective heat flow and a phenomenological description of soil freezing. The model is applied to the detailed data sets of two rather different field sites, one in the Arctic on Svalbard and one on the Tibetan Plateau. Soil temperatures and water contents as well as important quantities like the thaw depth and the duration of the isothermal plateau can be reproduced. To examine the influence of different heat transport processes, three scenarios of different complexity are studied. We show that heat conduction is the dominant process at both sites. While representing this process is sufficient for rough thaw depth estimates, a more detailed representation is necessary for an accurate representation of the active layer thermal dynamics. With our detailed model, characteristic deviations between measurements and simulations can still be observed. As possible explanations we discuss downward vapor migration in the upper soil layer and mechanical deformations.

Description: Modelling the 20th and 21st century evolution of Hoffellsjökull glacier, SE-Vatnajökull, Iceland The Cryosphere Discussions, 5, 1055-1088, 2011 Author(s): G. Aðalgeirsdóttir, S. Guðmundsson, H. Björnsson, F. Pálsson, T. Jóhannesson, H. Hannesdóttir, S. Þ. Sigurðsson, and E. Berthier The Little Ice Age maximum extent of glaciers in Iceland was reached about 1890 AD and most glaciers in the country have retreated during the 20th century. A model for the surface mass balance and the flow of glaciers is used to reconstruct the 20th century retreat history of Hoffellsjökull, a south-flowing outlet glacier of Vatnajökull, which is located close to the southeast coast of Iceland. The bedrock topography was surveyed with radio-echo soundings in 2001. A wealth of data are available to force and constrain the model, e.g. surface elevation maps from ~1890, 1936, 1946, 1986, 2001, 2008 and 2010, mass balance observations conducted in 1936–1938 and after 2001, energy balance measurements after 2001, and glacier surface velocity derived by DGPS and correlation of SPOT5 images. The 21% volume loss of this glacier in the period 1895–2010 is realistically simulated with the model. After calibration of the model with past observations, it is used to simulate the future response of the glacier during the 21st century. The mass balance model was forced with an ensemble of temperature and precipitation scenarios from a study of the effect of climate change on energy production in the Nordic countries (the CES project). If the average climate of 2000–2009 is maintained into the future, the volume of the glacier is projected to be reduced by 30% with respect to the present at the end of this century, and the glacier will almost disappear if the climate warms as suggested by most of the climate change scenarios. Runoff from the glacier is predicted to increase for the next 30–40 years and decrease after that as a consequence of the diminishing ice-covered area.

Description: The evolution of the western rift area of the Fimbul Ice Shelf, Antarctica The Cryosphere Discussions, 5, 1089-1122, 2011 Author(s): A. Humbert and D. Steinhage This paper studies the evolution of a zone in the Fimbul Ice Shelf that is characterised by large crevasses and rifts west of Jutulstraumen, an outlet glacier flowing into Fimulisen. High-resolution radar imagery and radio echo sounding data were used to study the surface and internal structure of this rift area and to define zones of similar characteristics. The western rift area is dominated by two factors: a small ice rumple that leads to basal crevasses and disturbs the homogeneity of the ice, and a zone with fibre-like blocks. Downstream of the rumple we found down-welling of internal layers and local thinning, which we explain as a result of basal crevasses due to the basal drag at the ice rumple. North of Ahlmannryggen the ice looses its lateral constraint and forms individual blocks, which are deformed like fibres under shear, where the ice stream merges with slower moving ice masses of the western side. There, the ice looses its integrity, which initiates the western rift system. The velocity difference between the slow moving western part and the fast moving extension of Jutulstraumen produces shear stress that causes the rifts to form tails and expand them to the major rifts of up to 30 km length.

Description: Brief Communication : "An inventory of permafrost evidence for the European Alps" The Cryosphere Discussions, 5, 1201-1218, 2011 Author(s): E. Cremonese, S. Gruber, M. Phillips, P. Pogliotti, L. Boeckli, J. Noetzli, C. Suter, X. Bodin, A. Crepaz, A. Kellerer-Pirklbauer, K. Lang, S. Letey, V. Mair, U. Morra di Cella, L. Ravanel, C. Scapozza, R. Seppi, and A. Zischg The investigation and modelling of permafrost distribution, particularly in areas of discontinuous permafrost, is challenging due to spatial heterogeneity, remoteness of measurement sites and data scarcity. We have designed a strategy for standardizing different local data sets containing evidence of the presence or absence of permafrost into an inventory for the entire European Alps. With this brief communication, we present the structure and contents of this inventory. This collection of permafrost evidence not only highlights existing data and allows new analyses based on larger data sets, but also provides complementary information for an improved interpretation of monitoring results.

Description: Simulation of permafrost and seasonal thaw depth in the JULES land surface scheme The Cryosphere Discussions, 5, 1263-1309, 2011 Author(s): R. Dankers, E. J. Burke, and J. Price Land surface models (LSMs) need to be able to simulate realistically the dynamics of permafrost and frozen ground. In this paper we evaluate the performance of the LSM JULES (Joint UK Land Environment Simulator), the stand-alone version of the land surface scheme used in Hadley Centre climate models, in simulating the large-scale distribution of surface permafrost. In particular we look at how well the model is able to simulate the seasonal thaw depth or active layer thickness (ALT). We performed a number of experiments driven by observation-based climate datasets. Visually there is a very good agreement between areas with permafrost in JULES and known permafrost distribution in the Northern Hemisphere, and the model captures 97% of the area where the permafrost coverage is at least 50% of the grid cell. However, the model overestimates the total extent as it also simulates permafrost where it occurs sporadically or only in isolated patches. Consistent with this we find a cold bias in the simulated soil temperatures, especially in winter. However, when compared with observations on end-of-season thaw depth from around the Arctic, the ALT in JULES is generally too deep. Additional runs at three sites in Alaska demonstrate how uncertainties in the precipitation input affect the simulation of soil temperatures by affecting the thickness of the snowpack and therefore the thermal insulation in winter. In addition, changes in soil moisture content influence the thermodynamics of soil layers close to freezing. We also present results from three experiments in which the standard model setup was modified to improve physical realism of the simulations in permafrost regions. Extending the soil column to a depth of 60 m and adjusting the soil parameters for organic content had relatively little effect on the simulation of permafrost and ALT. A higher vertical resolution improves the simulation of ALT, although a considerable bias still remains. Future model development in JULES should focus on a dynamic coupling of soil organic carbon content and soil thermal and hydraulic properties, as well as allowing for sub-grid variability in soil types.

Description: Deriving mass balance and calving variations from reanalysis data and sparse observations, Glaciar San Rafael, northern Patagonia, 1950–2005 The Cryosphere Discussions, 5, 1123-1166, 2011 Author(s): M. Koppes, H. Conway, L. A. Rasmussen, and M. Chernos Mass balance variations of Glaciar San Rafael, the most equatorial tidewater glacier in the North Patagonian Icefield, are reconstructed over the period 1950–2005 using NCEP-NCAR reanalysis climate data together with sparse, local historical observations of air temperature, precipitation, accumulation, ablation, thinning, calving, and glacier retreat. The combined observations over the past 50 yr indicate that Glaciar San Rafael has thinned and retreated since 1959, with a total mass loss of ~22 km 3 of ice equivalent. Over that period, except for a short period of cooling from 1998–2003, the climate has become progressively warmer and drier, which has resulted primarily in pervasive thinning of the glacier surface and a decrease in calving rates, with only minor acceleration in retreat of the terminus. A comparison of calving fluxes derived from the mass balance variations and from theoretical calving and sliding laws suggest that calving rates are inversely correlated with retreat rates, and that terminus geometry is more important than changes in balance fluxes to the terminus in driving calving dynamics. For Glaciar San Rafael, regional climate warming has not yet resulted in the significant changes in glacier length seen in other calving glaciers in the region, emphasizing the complex dynamics between climate inputs, topographic constraints and glacier response in calving glacier systems.

Description: On the influence of model physics on simulations of Arctic and Antarctic sea ice The Cryosphere Discussions, 5, 1167-1200, 2011 Author(s): F. Massonnet, T. Fichefet, H. Goosse, M. Vancoppenolle, P. Mathiot, and C. König Beatty Two hindcast (1983–2007) simulations are performed with the global, ocean-sea ice models NEMO-LIM2 and NEMO-LIM3 driven by atmospheric reanalyses and climatologies. The two simulations differ only in their sea ice component, while all other elements of experimental design (resolution, initial conditions, atmospheric forcing) are kept identical. The main differences in the sea ice models lie in the formulation of the subgrid-scale ice thickness distribution, of the thermodynamic processes, of the sea ice salinity and of the sea ice rheology. To assess the differences in model skill over the period of investigation, we develop a set of metrics for both hemispheres, comparing the main sea ice variables (concentration, thickness and drift) to available observations and focusing on both mean state and seasonal to interannual variability. Based upon these metrics, we discuss the physical processes potentially responsible for the differences in model skill. In particular, we suggest that (i) a detailed representation of the ice thickness distribution increases the seasonal to interannual variability of ice extent, with spectacular improvement for the simulation of the recent observed summer Arctic sea ice retreats, (ii) the elastic-viscous-plastic rheology enhances the response of ice to wind stress, compared to the classical viscous-plastic approach, (iii) the grid formulation and the air-sea ice drag coefficient affect the simulated ice export through Fram Strait and the ice accumulation along the Canadian Archipelago, and (iv) both models show less skill in the Southern Ocean, probably due to the low quality of the reanalyses in this region and to the absence of important small-scale oceanic processes at the models' resolution (~1°).

Description: Ice stream or not? Radio-echo sounding of Carlson Inlet, West Antarctica The Cryosphere Discussions, 5, 1219-1238, 2011 Author(s): E. C. King The Antarctic Ice Sheet loses mass to the surrounding ocean mainly by drainage through a network of ice streams: fast-flowing glaciers bounded on either side by ice flowing one or two orders of magnitude more slowly. Ice streams flow despite low driving stress because of low basal resistance but are known to cease flowing if the basal conditions change, which can take place when subglacial sediment becomes dewatered by freezing or by a change in hydraulic pathways. Carlson Inlet, Antarctica has been interpreted as a stagnated ice stream, based on surface and basal morphology and shallow radar reflection profiling. To resolve the question of whether the flow history of Carlson Inlet has changed in the past, I conducted a ground-based radar survey of Carlson Inlet, the adjacent part of Rutford Ice Stream, and Talutis Inlet, West Antarctica. This survey provides details of the internal ice stratigraphy and allows the flow history to be interpreted. Tight folding of isochrones in Rutford Ice Stream and Talutis Inlet is interpreted to be the result of lateral compression during convergent flow from a wide catchment into a narrow, fast-flowing trunk. In contrast, the central part of Carlson Inlet has gently-folded isochrones that drape over the bed topography, suggestive of local accumulation and slow flow. A 1-D thermo-mechanical model was used to estimate the age of the ice. I conclude that the ice in the centre of Carlson Inlet has been near-stagnant for between 3500 and 6800 years and that fast flow has not occurred there during that time period.

Description: Application of asymptotic radiative transfer theory for the retrievals of snow parameters using reflection and transmission observations The Cryosphere Discussions, 5, 1239-1262, 2011 Author(s): H. S. Negi, A. Kokhanovsky, and D. K. Perovich An asymptotic analytical radiative transfer (AART) theory was used to retrieve snow optical parameters such as extinction coefficient, diffuse exponent, asymptotic flux extinction coefficient (AFEC), snow optical thickness and probability of photon absorption (PPA). This theory was applied to the reflection and transmission data for a temperate snow cover from 400–1000 nm wavelength region, to retrieve AFEC for different types of snow cover (thick, thin, dry, wet, new and old snow). The AFEC values were found at 450 nm wavelength region in the range from 0.06 to 0.22 cm −1 , where high values were observed for increased wetness and impurity in snow. A good agreement between AART retrieved and other radiative transfer model retrieved parameter shows that AART theory can work well for different types of snow. The extinction coefficients for temperate snow ranged from 0.5 to 1.0 mm −1 and the e-folding depths ranged from 5 to 25 cm. The snow physical characteristics such as grain size and density were also retrieved using derived optical parameters and found in agreement with ground measurements. The main advantages of the proposed AART method are the simple analytical equations that provide a valuable alternative from complex numerical radiative transfer solutions.

Description: Ideal climatic variables for the present-day geometry of the Gregoriev Glacier, Inner Tien Shan, Kyrgyzstan, derived from GPS data and energy-mass balance measurements The Cryosphere Discussions, 5, 855-883, 2011 Author(s): K. Fujita, N. Takeuchi, S. A. Nikitin, A. B. Surazakov, S. Okamoto, V. B. Aizen, and J. Kubota We conducted 2 yr (2005–2007) of in situ meteorological and glaciological observations on the Gregoriev Glacier, a flat-top glacier within the Inner Tien Shan, Kyrgyzstan. Differential GPS surveys reveal a vertical surface deletion at the summit of the glacier. Based on snow density data and an energy-mass balance model, we estimate that the annual precipitation and summer mean temperature required to maintain the glacier in the modern state are 289 mm and −3.85 °C at the glacier summit (4600 m above sea level, a.s.l.), respectively. The good agreement between the long-term estimated and observed precipitation at a nearby station in the Tien Shan (292 mm at 3614 m a.s.l. for the period 1930–2002) suggests that the glacier dynamics have been regulated by the long-term average accumulation. The glacier mass-balance, reconstructed based on meteorological data from the Tien Shan station for the past 80 yr, explains the observed fluctuations in glacier extent, particularly the negative mass balance in the 1990s.

Description: Stable water isotopes of precipitation and firn cores from the northern Antarctic Peninsula region as a proxy for climate reconstruction The Cryosphere Discussions, 5, 951-1001, 2011 Author(s): F. Fernandoy, H. Meyer, and M. Tonelli In order to investigate the climate variability in the north Antarctic Peninsula region, this paper focuses on the relationship between stable isotope content of precipitation and firn, and main meteorological variables (air temperature, relative humidity, sea surface temperature, and sea ice extent). Between 2008 and 2010, we collected precipitation samples and retrieved firn cores from several key sites in this region. We conclude that the deuterium excess oscillation represents a robust indicator of the meteorological variability on a seasonal to sub-seasonal scale. Low absolute deuterium excess values and the synchronous variation of both deuterium excess and air temperature imply that the evaporation of moisture occurs in the adjacent Southern Ocean. The δ 18 O–air temperature relationship is complicated and significant only at a (multi) seasonal scale. Backward trajectory calculations show that air-parcels arriving at the region during precipitation events predominantly originate at the South Pacific Ocean and Bellingshausen Sea. These investigations will be used as a calibration for on-going and future research in the area, suggesting that appropriate locations are located above 600 m a.s.l. We selected the Plateau Laclavere, Antarctic Peninsula as the most promising site for a deeper drilling campaign.

Description: Reformulating the full-Stokes ice sheet model for a more efficient computational solution The Cryosphere Discussions, 5, 1749-1774, 2011 Author(s): J. K. Dukowicz The first-order or Blatter-Pattyn ice sheet model is an attractive alternative to the full Stokes model in many applications because of its reduced computational demands, in spite of an approximate stress tensor and a limitation to small basal boundary slopes. In contrast, the full unapproximated Stokes ice sheet model is more difficult to solve and computationally more expensive. This is due to the fact that while both models arise from a variational principle, the Blatter-Pattyn variational functional is positive-definite and involves just the horizontal velocity components, while the Stokes functional is indefinite and involves all three velocity components, as well as the pressure. These unfavorable properties arise because Stokes flow is treated as a constrained minimization problem where the pressure acts as a Lagrange multiplier that enforces incompressibility or zero velocity divergence. To alleviate these problems we reformulate the full-Stokes problem as an unconstrained, positive-definite minimization problem, quite analogous to the Blatter-Pattyn model but without the associated approximations, by introducing a velocity field that is already divergence-free and satisfies appropriate boundary conditions, thus dispensing with the need for a pressure. Such a velocity field is obtained by vertically integrating the continuity equation to obtain the vertical velocity as a function of the horizontal velocity components, as is done in the Blatter-Pattyn model. This leads to a reduced system for just the horizontal velocity components, again just as in the Blatter-Pattyn model. We thus obtain not only a reformulated action principle, which itself is sufficient for obtaining an efficient discrete model, but also a novel set of Euler-Lagrange partial differential equations and boundary conditions that specify the Stokes problem in terms of just the horizontal velocities. The derivations are performed not only for the common case of an ice sheet in contact with and sliding along the bed, which again is analogous to the Blatter-Pattyn model, but also for more general situations, such as for a floating ice shelf.

Description: Variability of snow depth at the plot scale: implications for mean depth estimation and sampling strategies The Cryosphere Discussions, 5, 1627-1653, 2011 Author(s): J. I. López-Moreno, S. R. Fassnacht, S. Beguería, and J. B. P. Latron Snow depth variability over small distances can affect the representativeness of depth samples taken at the local scale, which are often used to assess the spatial distribution of snow at regional and basin scales. To assess spatial variability at the plot scale, intensive snow depth sampling was conducted during January and April 2009 in 15 plots in the Rio Ésera Valley, central Spanish Pyrenees Mountains. Each plot (10 × 10 m; 100 m 2 ) was subdivided into a grid of 1 m 2 squares; sampling at the corners of each square yielded a set of 121 data points that provided an accurate measure of snow depth in the plot (considered as ground truth). The spatial variability of snow depth was then assessed using sampling locations randomly selected within each plot. The plots were highly variable, with coefficients of variation up to 0.25. This indicates that to improve the representativeness of snow depth sampling in a given plot the snow depth measurements should be increased in number and averaged when spatial heterogeneity is substantial. The spatial autocorrelation of snowpack distribution can affect the local representativeness of snowpack. Snow depth distributions were simulated at the same plot scale under varying levels of standard deviation and spatial autocorrelation, to enable the effect of each factor on snowpack representativeness to be established. The results showed that the snow depth estimation error increased markedly as the standard deviation increased. The results indicated that in general at least 5 snow depth measurements should be taken in each plot to ensure that the estimation error is

Description: Comparison of MODIS-derived land surface temperatures with near-surface soil and air temperature measurements in continuous permafrost terrain The Cryosphere Discussions, 5, 1583-1625, 2011 Author(s): S. Hachem, C. R. Duguay, and M. Allard In Arctic and sub-Arctic regions, meteorological stations are scattered and poorly distributed geographically; they are mostly located along coastal areas and are often unreachable by road. Given that high-latitude regions are the ones most significantly affected by recent climate warming, there is a need to supplement existing meteorological station networks with spatially continuous measurements such as those obtained by spaceborne platforms. In particular, land surface (skin) temperature (LST) retrieved from satellite sensors offer the opportunity to utilize remote sensing technology to obtain a consistent coverage of a key parameter for climate, permafrost, and hydrological research. The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor aboard the Terra and Aqua satellite platforms offers the potential to provide spatial estimates of near-surface temperature values. In this study, LST values from MODIS were compared to ground-based near-surface air and soil temperature measurements obtained at herbaceous and shrub tundra sites located in the continuous permafrost zone of northern Québec, Canada, and the North Slope of Alaska, USA. LST values were found to be better correlated with near-surface air temperature (1–2 m above the ground) than with soil temperature (3–5 cm below the ground) measurements. A comparison between mean daily air temperature from ground-based station measurements and mean daily MODIS LST, calculated from daytime and nighttime temperature values of both Terra and Aqua acquisitions, for all sites and all seasons pooled together reveals a high correlation between the two sets of measurements ( R 〉0.93 and mean difference of −1.86 °C). Mean differences ranged between −0.51 °C and −5.13 °C due to the influence of surface heterogeneity within the MODIS 1 km 2 grid cells at some sites. Overall, it is concluded that MODIS offers a great potential for monitoring surface temperature changes in high-latitude tundra regions and provides a promising source of input data for integration into spatially-distributed permafrost models.

Description: The fate of lake ice in the North American Arctic The Cryosphere Discussions, 5, 1775-1834, 2011 Author(s): L. C. Brown and C. R. Duguay Lakes comprise a large portion of the surface cover in northern North America forming an important part of the cryosphere. The timing of lake ice phenological events (e.g. break-up/freeze-up) are useful indicators of climate variability and change, which is of particular relevance in environmentally sensitive areas such as the North American Arctic. Further alterations to the present day ice regime could result in major ecosystem changes, such as species shifts and the disappearance of perennial ice cover. Lake ice models are a valuable tool for examining the response of lake ice cover to changing climate conditions. The use of future climate scenario data in these models can provide information on the potential changes in ice phenology, ice thickness and composition. The Canadian Lake Ice Model (CLIMo) was used to simulate lake ice phenology across the North American Arctic from 1961–2100 using climate scenarios produced by the Canadian Regional Climate Model (CRCM). Results from the 1961–1990 time period were validated using 15 locations across the Canadian Arctic, with both in situ ice cover observations from the Canadian Ice Database as well as additional ice cover simulations using nearby weather station data. Projected changes to the ice cover using the 30 yr mean data between 1961–1990 and 2041–2070 suggest a shift towards shorter ice cover durations by an average of just over 3 weeks, with a 25 cm average reduction of the total ice thickness – varying based on location, lake depth and snow cover amounts.

Description: An Antarctic monitoring initiative for fast ice and comparison with the Arctic The Cryosphere Discussions, 5, 2437-2463, 2011 Author(s): P. Heil, S. Gerland, and M. A. Granskog While Arctic and Antarctic fast-ice observations are required by a number of interest groups for planning and logistical activities, or to support scientific research, obtaining those data is not trivial. Sea-ice extent is reasonably well observed using camera-based or satellite-borne instruments, however, in situ and satellite-based ice-thicknesss measurements remain a challenge. As the seasonal fast-ice thickness is directly linked to regional atmospheric and oceanographic conditions, monitoring of fast-ice thickness across a station network around Antarctica and in the Arctic is crucial to assess how climate change affects the polar system. The Antarctic Fast-Ice Network (AFIN) was recently established to provide the scientific community with fast-ice observations from sites operated by international contributors. Based on AFIN data a recent increase in interannual variability in annual maximum ice and snow thicknesses has been identified. Maximum Arctic fast-ice thickness generally exhibits a similar interannual variability, however, both positive and negative trends in ice thickness have been observed in the Arctic. Comparing the two hemispheres, we find that in the Arctic the fast ice establishes itself at a faster rate than in the Antarctic, where repeated cyclone action tends to intermittently remove the fast ice during autumn. Also, Arctic sites investigated here exhibit less snow cover than those from East Antarctic coastal sites.

Description: Thermal state of the active layer and permafrost along the Qinghai-Xizang (Tibet) railway from 2006 to 2010 The Cryosphere Discussions, 5, 2465-2481, 2011 Author(s): Q. Wu, T. Zhang, and Y. Liu In this study, we investigated changes in active layer thickness (ALT) and permafrost temperatures at different depths using data from permafrost monitoring network along the Qinghai-Xizang (Tibet) Railway since 2005. Among sites, average ALT is about 3.1 m with a range from about 1.1 m to 4.9 m. From 2006 through 2010, ALT has increased at a rate of about 6.3 cm a −1 . The mean rising rate of permafrost temperature at the depth of 6.0 m is about 0.02 °C a −1 estimated by linear regression using five years of data, and the mean rising rate of mean annual ground temperature (MAGT) at depth of zero amplitude is about 0.012 °C a −1 . Changes for colder permafrost (MAGT 〈 −1.0 °C) is greater than that for relatively warmer permafrost (MAGT 〉 −1.0 °C). This is consistent with results observed in the Arctic and Subarctic.

Description: Brief communication "Modeled rain on snow in CLM3 warms soil under thick snow cover and cools it under thin" The Cryosphere Discussions, 5, 2557-2570, 2011 Author(s): J. Putkonen, H. P. Jacobson, and K. Rennert Rain-on-snow has decimated ungulate herds in the North and warmed permafrost significantly in Spitsbergen. As the permafrost temperatures are used as an integrated signal of the climate change, there is an urgent need to characterize the relationship between rain-on-snow and permafrost temperatures. By incorporating reanalysis based (ERA40) climate forcing into the land model (CLM3) and introducing an artificial rain on snow event on all model pixels the areas with thick snow cover (〉0.5 m) experienced season average permafrost warming, sites with intermediate snow depths (0.15–0.5 m) experienced cooling, while sites with thin snow cover were more sensitive to other factors.

Description: A multi-parameter hydrochemical characterization of proglacial runoff, Cordillera Blanca, Peru The Cryosphere Discussions, 5, 2483-2521, 2011 Author(s): P. Burns, B. Mark, and J. McKenzie The Cordillera Blanca, located in the central Peruvian Andes, is the most glacierized mountain range in the tropics. The study objective is to determine the spatial and topographic controls on geochemical and isotopic parameters in the Quilcayhuanca drainage basin. During the dry season of July 2009, surface water and groundwater samples were collected from the proglacial zone of the 90 km 2 Quilcayhuanca basin which is 20% glacierized. The basin water samples ( n = 25) were analyzed for pH, conductivity, major cations (Ca, Mg, Na, K, Fe(II)), major anions (F, Cl, SO 4 ), nutrients (total N, total P, and Si), and stable isotopes of water (δ 18 O, δ 2 H). The valley's surface water is acidic (pH 3–4) and is dominated by Ca 2+ , Mg 2+ , and SO 4 2− , the last of which is likely due to pyrite oxidation. Total P and total N show no trend with elevation down valley, while Si generally increases with decreasing elevation. Groundwater samples are differentiated from surface water samples by lower pH, specific conductance, and total P and higher Na + , K + , HCO 3 − , Si, and δ 18 O. A two-component mixing model indicates that discharge from the watershed is approximately two-thirds surface water (mostly glacier melt) and one-third groundwater. The results were compared to data from the Rio Santa and indicate that this trend may persist at the regional scale.

Description: Use of a thermal imager for snow pit temperatures The Cryosphere Discussions, 5, 2523-2556, 2011 Author(s): C. Shea, B. Jamieson, and K. W. Birkeland Weak snow of interest to avalanche forecasting often forms and changes as thin layers. Thermometers, the current field technology for measuring the temperature gradients across such layers – and for thus estimating the expected vapour flux and future type of crystal metamorphism – are difficult to use at distances shorter than 1 cm. In contrast, a thermal imager can provide thousands of simultaneous temperature measurements across small distances with better accuracy. However, a thermal imager only senses the exposed surface, complicating its methods for access and accuracy with respect to buried temperatures. This paper presents methods for exposing buried layers on pit walls and using a thermal imager to measure temperatures on these walls, correct for lens effects, adjust temperature gradients adjust time exposed, and calculate temperature gradients over millimetre distances. We find lens error on temperature gradients to be on the order of 0.03 °C between image centre and corners. We find temperature gradient change over time to usually decrease – as expected with atmospheric equalization as a strong effect. Case studies including thermal images and visual macro photographs of crystals, collected during the 2010–2011 winter, demonstrate large temperature differences over millimetre-scale distances that are consistent with observed kinetic metamorphism.

Description: Present-day mass changes for the Greenland ice sheet and their interaction with bedrock adjustment The Cryosphere Discussions, 5, 3455-3477, 2011 Author(s): M. Olaizola, R. S. W. van de Wal, M. M. Helsen, and B. de Boer Since the launch in 2002 of the Gravity Recovery and Climate Experiment (GRACE) satellites, several estimates of the mass balance of the Greenland Ice Sheet (GrIS) have been produced. To obtain ice mass changes estimates, data need to be corrected for the effect of deformation changes of the Earth's crust. This is usually done by independently modeling the Glaciological Isostatic Adjustment (GIA) trend and then by removing it from the data. Recently, Wu et al. (2010) proposed a new method to simultaneously estimate GIA and the present-day ice mass change, reporting an ice mass loss of around half of the previously published estimates and a general bedrock subsidence concentrated in the central parts of Greenland. This subsidence appears to be counterintuitive since the ice sheet is loosing mass at present. It was suggested by the authors that this could be a new evidence for additional net past ice accumulation. In this study, a 3-D ice-sheet model with a surface mass balance forcing based on a mass balance gradient approach has been used to: (a) analyze the bedrock response to changes in the ice load in order to evaluate whether bedrock subsidence and ice thinning can exist simultaneously; (b) study the magnitude and the pattern of the bedrock movement; and (c) evaluate if present-day bedrock subsidence could be the result of a net past mass accumulation. Under a sine forcing of the annual temperature, that mimics the temperature variations in the Holocene, mass changes yield a delay of the bedrock response of 200 years. Thinning of the ice as well as bedrock subsidence coexist during this period with an order of magnitude equal to the observations by Wu et al. (2010). Although, the resulting pattern of bedrock changes differs considerable: instead of the general bedrock subsidence reported before, we found areas of bedrock uplift as well as areas of bedrock subsidence. A simulation since the last glacial maximum (with the temperature represented as a linear increase from −10 K to present-day) yields a time lag of 1990 years for the bedrock response relative to the temperature forcing and an average uplift of 0.3 mm yr −1 for present-day. The spatial pattern of bedrock-change shows subsidence in the south and northwest as well as uplift in the center and northeast. We obtained these results assuming that the solid earth is a flat elastic lithosphere resting over a viscous relaxed asthenosphere (ELRA model). Using a more sophisticated Self Gravitational Viscoelastic (SGVE) model, we obtain qualitatively similar results: a 2200 years lag and an average uplift for present-day of 0.2 mm yr −1 . The spatial pattern of bedrock movement is similar as well. Finally, results are shown for a temperature reconstruction based on ice core data confirming the deglaciation experiment. According to this study, a bedrock subsidence with a maximum in the central parts of Greenland cannot be that recent explained by a net past ice accumulation. This undermines results suggesting that recent loss is only half of the regular ice mass loss changes.

Description: Glacier changes from 1966–2009 in the Gongga Mountains, on the south-eastern margin of the Qinghai-Tibetan Plateau and their climatic forcing The Cryosphere Discussions, 5, 3479-3516, 2011 Author(s): B. Pan, G. Zhang, J. Wang, B. Cao, J. Wang, C. Zhang, H. Geng, and Y. Ji In order to monitor the changes of the glaciers in the Gongga Mountain region on the south-eastern margin of the Qinghai-Tibetan Plateau, 74 monsoonal temperate glaciers were investigated by comparing the Chinese Glacier Inventory (CGI), recorded in the 1960s, with Landsat MSS in 1974, Landsat TM in 1989, 1994, 2005, and ASTER data in 2009. The remote sensing data have been applied to map the glacier outline by threshold ratio images (TM4/TM5). Moreover, the glacier outlines were verified by GPS survey on four large glaciers (Hailuogou, Mozigou, Yanzigou, and Dagongba) in 2009. The results show that the area dominated by the 74 glaciers has shrunk by 11.3 % (29.2 km 2 ) from 1966 to 2009. Glacier area on the eastern and western slope of the Gongga Mountains decreased by 14.1 km 2 (5.5 % in 1966) and 15.1 km 2 (5.9 % in 1966), respectively. The loss in glacier area and length is respectively 0.8 km 2 and 1146.4 m (26.7 m yr −1 ) for the Hailuogou glacier, 2.1 km 2 and 501.8 m (11.7 m yr −1 ) for the Mozigou Glacier, 0.8 km 2 and 724.8 m (16.9 m yr −1 ) for the Yanzigou Glacier, and 2.4 km 2 and 1002.3 m (23.3 m yr −1 ) for the Dagongba Glacier. Decades of climate records obtained from three meteorological stations in the Gongga Mountains were analyzed to evaluate the impact of the temperature and precipitation on glacier retreat. During 1966–2009, the mean annual temperature over the eastern and western slope of the Gongga Mountains has been increasing by 0.21 °C/10 yr and 0.13 °C/10 yr, respectively. Moreover, it was stable in the mean annual precipitation. This evidence indicates that the warming of the climate is probably responsible for the glacier retreat in the study region.

Description: A new glacier inventory for 2009 reveals spatial and temporal variability in glacier response to atmospheric warming in the Northern Antarctic Peninsula, 1988–2009 The Cryosphere Discussions, 5, 3541-3595, 2011 Author(s): B. J. Davies, J. L. Carrivick, N. F. Glasser, M. J. Hambrey, and J. L. Smellie The Northern Antarctic Peninsula has recently exhibited ice-shelf disintegration, glacier recession and acceleration. However, the dynamic response of land-terminating, ice-shelf tributary and tidewater glaciers has not yet been quantified or assessed for variability, and there are sparse published data for glacier classification, morphology, area, length or altitude. This paper firstly uses ASTER images from 2009 and a SPIRIT DEM from 2006 to classify the area, length, altitude, slope, aspect, geomorphology, type and hypsometry of 194 glaciers on Trinity Peninsula, Vega Island and James Ross Island. Secondly, this paper uses LANDSAT-4 and ASTER images from 1988 and 2001 and data from the Antarctic Digital Database (ADD) from 1997 to document glacier change 1988–2009. From 1988–2001, 90 % of glaciers receded, and from 2001–2009, 79 % receded. Glaciers on the western side of Trinity Peninsula retreated relatively little. On the eastern side of Trinity Peninsula, the rate of recession of ice-shelf tributary glaciers has slowed from 12.9 km 2 a −1 (1988–2001) to 2.4 km 2 a −1 (2001–2009). Tidewater glaciers on the drier, cooler Eastern Trinity Peninsula experienced fastest recession from 1988–2001, with limited frontal retreat after 2001. Land-terminating glaciers on James Ross Island also retreated fastest in the period 1988–2001. Large tidewater glaciers on James Ross Island are now declining in areal extent at rates of up to 0.04 km 2 a −1 . This east-west difference is largely a result of orographic temperature and precipitation gradients across the Antarctic Peninsula. Strong variability in tidewater glacier recession rates may result from the influence of glacier length, altitude, slope and hypsometry on glacier mass balance. High snowfall means that the glaciers on the Western Peninsula are not currently rapidly receding. Recession rates on the eastern side of Trinity Peninsula are slowing as the floating ice tongues retreat into the fjords and the glaciers reach a new dynamic equilibrium. The rapid glacier recession of tidewater glaciers on James Ross Island is likely to continue because of their low elevations and flat profiles. In contrast, the higher and steeper tidewater glaciers on the Eastern Antarctic Peninsula will attain more stable frontal positions after low-lying ablation areas are removed.

Description: Stable isotope and gas properties of two ice wedges from Cape Mamontov Klyk, Laptev Sea, Northern Siberia The Cryosphere Discussions, 5, 3627-3660, 2011 Author(s): T. Boereboom, D. Samyn, H. Meyer, and J.-L. Tison This paper presents and discusses the texture, fabric and gas properties (contents of total gas, O 2 , N 2 , CO 2 , and CH 4 ) of two ice wedges from Cape Mamontov Klyk, Laptev Sea, Northern Siberia. The two ice wedges display contrasting structures: one being of relatively "clean" ice and the other showing clean ice at its centre as well as debris-rich ice on its sides (referred to as ice-sand wedge). A comparison of gas properties, crystal size, fabrics and stable isotope data (δ 18 O and δD) allows discriminating between three different facies of ice with specific paleoenvironmental signatures, suggesting different climatic conditions and rates of biological activity. More specifically, total gas content and composition reveal variable intensities of meltwater infiltration and show the impact of biological processes with contrasting contributions from anaerobic and aerobic conditions. Stable isotope data are shown to be valid for discussing changes in paleoenvironmental conditions and/or decipher different sources for the snow feeding into the ice wedges with time. Our data also give support to the previous assumption that the composite ice wedge was formed in Pleistocene and the ice wedge in Holocene times. This study sheds more light on the conditions of ice wedge growth under changing environmental conditions.

Description: Melting of Northern Greenland during the last interglacial The Cryosphere Discussions, 5, 3517-3539, 2011 Author(s): A. Born and K. H. Nisancioglu The Greenland ice sheet (GrIS) is losing mass at an increasing rate, making it the primary contributor to global eustatic sea level rise. Large melting areas and rapid thinning at its margins has raised concerns about its stability. However, it is conceivable that these observations represent the transient adjustment of the fastest reacting parts of the ice sheet, masking slower processes that dominate the long term fate of the GrIS and its contribution to sea level rise. Studies of the geological past provide valuable information on the long term response of the GrIS to warm periods. We simulate the GrIS during the Eemian interglacial, a period 126 000 yr before present (126 ka) with Arctic temperatures comparable to projections for the end of this century. The northeastern part of the GrIS is unstable and retreats significantly, despite moderate melt rates. Unlike the south and west, strong melting in the northeast is not compensated by high accumulation, or fast ice flow. The analogy with the present warming suggests that in coming decades, positive feedbacks could increase the rate of mass loss of the northeastern GrIS, exceeding the currently observed melting in the south.

Description: Glacier ice in rock glaciers: a case study in the Vanoise Massif, Northern French Alps The Cryosphere Discussions, 5, 3597-3626, 2011 Author(s): S. Monnier, C. Camerlynck, F. Rejiba, C. Kinnard, and P.-Y. Galibert We investigated the Sachette rock glacier, Vanoise Massif, Northern French Alps, using former equilibrium line altitude reconstruction from glacial deposits, aerial photograph analysis, and ground-penetrating radar (GPR). The rock glacier is a young (probably 0.15–0.16 m ns −1 ) and reflectors having a dipping-syncline structure, typical of true glaciers. Consequently, the rock glacier structure is described as being constituted of a glacial massive ice core embedded into diamictons. Our study of the Sachette rock glacier highlights possible significance of rock glaciers and interactions between glacier and permafrost in alpine environments.

Description: A numerical model for meltwater channel evolution in glaciers The Cryosphere Discussions, 5, 2605-2628, 2011 Author(s): A. H. Jarosch and M. T. Gudmundsson Meltwater channels form an integral part of the hydrological system of a glacier. Better understanding of how meltwater channels develop and evolve is required to fully comprehend supraglacial and englacial meltwater drainage. Incision of supraglacial stream channels and subsequent roof closure by ice deformation has been proposed in recent literature as a possible englacial conduit formation process. Field evidence for supraglacial stream incision has been found in Svalbard and Nepal. In Iceland, where volcanic activity provides meltwater with temperatures above 0 °C, rapid enlargement of supraglacial channels has been observed. By coupling, for the first time, a numerical ice dynamic model to a hydraulic model which includes heat transfer, we investigate the evolution of meltwater channels and their incision behaviour. We present results for different, constant meltwater fluxes, different channel slopes, different meltwater temperatures as well as temporal variations in meltwater flux. The key parameters governing incision rate and depth are the channel slope and the meltwater temperature loss to the ice. Meltwater flux controls channel width and to a lesser degree incision behaviour. Calculated Nusselt numbers suggest that turbulent forced convection is the main heat transfer mechanism in the studied meltwater channels.

Description: Influence of surface heterogeneity on observed borehole temperatures at a mountain permafrost site in the Upper Engadine, Swiss Alps The Cryosphere Discussions, 5, 2629-2663, 2011 Author(s): S. Schneider, M. Hoelzle, and C. Hauck Compared to lowland (polar) regions, permafrost in high mountain areas occurs in a large variety of surface and subsurface material and texture. This work presents an eight-year (2002–2010) data set of borehole temperatures for five different (sub-) surface materials from a high alpine permafrost area, Murtel-Corvatsch, Switzerland. The influence of the material on the thermal regime was investigated by borehole temperature data, the TTOP-concept and the apparent thermal diffusivity (ATD). The results show that during the last eight years material specific temperature changes were more significant than for all boreholes consistent, climate-induced temperature trends. At coarse blocky, ice-rich sites no changes in active layer depth were observed, whereas the bedrock and the fine-grained sites appear to be highly sensitive to changes in the microclimate. The results confirm that the presence and growth of ice as well as a thermally driven air-circulation within the subsurface are the key factors for the occurence and preservation of alpine permafrost.

Description: Kinematic first-order calving law implies potential for abrupt ice-shelf retreat The Cryosphere Discussions, 5, 2699-2722, 2011 Author(s): A. Levermann, T. Albrecht, R. Winkelmann, M. A. Martin, M. Haseloff, and I. Joughin Recently observed large-scale disintegration of Antarctic ice shelves has moved their fronts closer towards grounded ice. In response, ice-sheet discharge into the ocean has accelerated, contributing to global sea-level rise and emphasizing the importance of calving-front dynamics. The position of the ice front strongly influences the stress field within the entire sheet-shelf-system and thereby the mass flow across the grounding line. While theories for an advance of the ice-front are readily available, no general rule exists for its retreat, making it difficult to incorporate the retreat in predictive models. Here we extract the first-order large-scale kinematic contribution to calving which is consistent with large-scale observation. We emphasize that the proposed equation does not constitute a comprehensive calving law but represents the first order kinematic contribution which can and should be complemented by higher order contributions as well as the influence of potentially heterogeneous material properties of the ice. When applied as a calving law, the equation naturally incorporates the stabilizing effect of pinning points and inhibits ice shelf growth outside of embayments. It depends only on local ice properties which are, however, determined by the full topography of the ice shelf. In numerical simulations the parameterization reproduces multiple stable fronts as observed for the Larsen A and B Ice Shelves including abrupt transitions between them which may be caused by localized ice weaknesses. We also find multiple stable states of the Ross Ice Shelf at the gateway of the West Antarctic Ice Sheet with back stresses onto the sheet reduced by up to 90% compared to the present state.