ALBERT

Description: Numerical simulations of the Cordilleran ice sheet through the last glacial cycle The Cryosphere Discussions, 9, 4147-4203, 2015 Author(s): J. Seguinot, I. Rogozhina, A. P. Stroeven, M. Margold, and J. Kleman Despite more than a century of geological observations, the Cordilleran ice sheet of North America remains poorly understood in terms of its former extent, volume and dynamics. Although geomorphological evidence is abundant, its complexity is such that whole ice-sheet reconstructions of advance and retreat patterns are lacking. Here we use a numerical ice sheet model calibrated against field-based evidence to attempt a quantitative reconstruction of the Cordilleran ice sheet history through the last glacial cycle. A series of simulations is driven by time-dependent temperature offsets from six proxy records located around the globe. Although this approach reveals large variations in model response to evolving climate forcing, all simulations produce two major glaciations during marine oxygen isotope stages 4 (61.9–56.5 ka) and 2 (23.2–16.8 ka). The timing of glaciation is better reproduced using temperature reconstructions from Greenland and Antarctic ice cores than from regional oceanic sediment cores. During most of the last glacial cycle, the modelled ice cover is discontinuous and restricted to high mountain areas. However, widespread precipitation over the Skeena Mountains favours the persistence of a central ice dome throughout the glacial cycle. It acts as a nucleation centre before the Last Glacial Maximum and hosts the last remains of Cordilleran ice until the middle Holocene (6.6–6.2 ka).

Description: Utilisation of CryoSat-2 SAR altimeter in operational ice charting The Cryosphere Discussions, 9, 4117-4145, 2015 Author(s): E. Rinne and M. Similä We present methods to utilise Cryosat-2 (CS-2) Synthetic Aperture (SAR) mode data in operational ice charting. We compare CS-2 data qualitatively to Synthetic Aperture Radar (SAR) mosaics over Barents and Kara seas. Furthermore, we compare the CS-2 to archived operational ice charts. We present distributions of four CS-2 waveform parameters for different ice types as presented in the ice charts. We go on to present an automatic classification method for CS-2 data which, after training with operational ice charts, is capable of determining open water from ice with a hit rate of 〉 90 %. The training data is dynamically updated every five days using the most recent 15 days CS-2 data and operative ice charts. This helps the adaption of the classifier to the evolving ice/snow conditions throughout winter. The classifier is also capable of detecting three different ice classes (thin and thick first year ice as well as old ice) with success rates good enough for the output to be usable to support operational ice charting. Finally, we present a near real time CS-2 product just plotting the waveform characteristics and conclude that even such a simple product is usable for some of the needs of ice charting.

Description: Long-term coastal-polynya dynamics in the Southern Weddell Sea from MODIS thermal-infrared imagery The Cryosphere Discussions, 9, 3959-3993, 2015 Author(s): S. Paul, S. Willmes, and G. Heinemann Based upon high-resolution thermal-infrared Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite imagery in combination with ERA-Interim atmospheric reanalysis data, we derived long-term polynya parameters such as polynya area, thin-ice thickness distribution and ice-production rates from daily cloud-cover corrected thin-ice thickness composites. Our study is based on a thirteen year investigation period (2002–2014) for the austral winter (1 April to 30 September) in the Antarctic Southern Weddell Sea. The focus lies on coastal polynyas which are important hot spots for new-ice formation, bottom-water formation and heat/moisture release into the atmosphere. MODIS has the capability to resolve even very narrow coastal polynyas. Its major disadvantage is the sensor limitation due to cloud cover. We make use of a newly developed and adapted spatial feature reconstruction scheme to account for cloud-covered areas. We find the sea-ice areas in front of Ronne and Brunt Ice Shelf to be the most active with an annual average polynya area of 3018 ± 1298 and 3516 ± 1420 km 2 as well as an accumulated volume ice production of 31 ± 13 and 31 ± 12 km 3 , respectively. For the remaining four regions, estimates amount to 421 ± 294 km 2 and 4 ± 3 km 3 (Antarctic Peninsula), 1148 ± 432 km 2 and 12 ± 5 km 3 (Iceberg A23A), 901 ± 703 km 2 and 10 ± 8 km 3 (Filchner Ice Shelf) as well as 499 ± 277 km 2 and 5 ± 2 km 3 (Coats Land). Our findings are discussed in comparison to recent studies based on coupled sea-ice/ocean models and passive-microwave satellite imagery, each investigating different parts of the Southern Weddell Sea.

Description: Climatic controls and climate proxy potential of Lewis Glacier, Mt Kenya The Cryosphere Discussions, 9, 3887-3924, 2015 Author(s): R. Prinz, L. I. Nicholson, T. Mölg, W. Gurgiser, and G. Kaser The Lewis Glacier on Mt Kenya is one of the best studied tropical glaciers and has experienced considerable retreat since a maximum extent in the late 19th century (L19). From distributed mass and energy balance modelling, this study evaluates the current sensitivity of the surface mass and energy balance to climatic drivers, explores climate conditions under which the L19 maximum extent might have sustained, and discusses the potential for using the glacier retreat to quantify climate change. Multiyear meteorological measurements at 4828 m provide data for input, optimization and evaluation of a spatially distributed glacier mass balance model to quantify the exchanges of energy and mass at the glacier–atmosphere interface. Currently the glacier loses mass due to the imbalance between insufficient accumulation and enhanced melt, because radiative energy gains cannot be compensated by turbulent energy sinks. Exchanging model input data with synthetic climate scenarios, which were sampled from the meteorological measurements and account for coupled climatic variable perturbations, reveal that the current mass balance is most sensitive to changes in atmospheric moisture (via its impact on solid precipitation, cloudiness and surface albedo). Positive mass balances result from scenarios with an increase of annual (seasonal) accumulation of 30 % (100 %), compared to values observed today, without significant changes in air temperature required. Scenarios with lower air temperatures are drier and associated with lower accumulation and increased net radiation due to reduced cloudiness and albedo. If the scenarios currently producing positive mass balances are applied to the L19 extent, negative mass balances are the result, meaning that the conditions required to sustain the glacier in its L19 extent are not reflected in today's observations. Alternatively, a balanced mass budget for the L19 extent can be explained by changing model parameters that imply a distinctly different coupling between the glacier's local surface-air layer and its surrounding boundary-layer. This result underlines the difficulty of deriving paleoclimates for larger glacier extents on the basis of modern measurements of small glaciers.

Description: The electrical self-potential method is a non-intrusive snow-hydrological sensor The Cryosphere Discussions, 9, 4437-4457, 2015 Author(s): S. S. Thompson, B. Kulessa, R. L. H. Essery, and M. P. Lüthi Our ability to measure, quantify and assimilate hydrological properties and processes of snow in operational models is disproportionally poor compared to the significance of seasonal snowmelt as a global water resource and major risk factor in flood and avalanche forecasting. Encouraged by recent theoretical, modelling and laboratory work, we show here that the diurnal evolution of aerially-distributed self-potential magnitudes closely track those of bulk meltwater fluxes in melting in-situ snowpacks at Rhone and Jungfraujoch glaciers, Switzerland. Numerical modelling infers temporally-evolving liquid water contents in the snowpacks on successive days in close agreement with snow-pit measurements. Muting previous concerns, the governing physical and chemical properties of snow and meltwater became temporally invariant for modelling purposes. Because measurement procedure is straightforward and readily automated for continuous monitoring over significant spatial scales, we conclude that the self-potential geophysical method is a highly-promising non-intrusive snow-hydrological sensor for measurement practice, modelling and operational snow forecasting.

Description: Tilt error in cryospheric surface radiation measurements at high latitudes: a model study The Cryosphere Discussions, 9, 4355-4376, 2015 Author(s): W. S. Bogren, J. F. Burkhart, and A. Kylling We have evaluated the magnitude and makeup of error in cryospheric radiation observations due to small sensor misalignment in in-situ measurements of solar irradiance. This error is examined through simulation of diffuse and direct irradiance arriving at a detector with a cosine-response foreoptic. Emphasis is placed on assessing total error over the solar shortwave spectrum from 250 to 4500 nm, as well as supporting investigation over other relevant shortwave spectral ranges. The total measurement error introduced by sensor tilt is dominated by the direct component. For a typical high latitude albedo measurement with a solar zenith angle of 60°, a sensor tilted by 1, 3, and 5° can respectively introduce up to 2.6, 7.7, and 12.8 % error into the measured irradiance and similar errors in the derived albedo. Depending on the daily range of solar azimuth and zenith angles, significant measurement error can persist also in integrated daily irradiance and albedo.

Description: Halogen-based reconstruction of Russian Arctic sea ice area from the Akademii Nauk ice core (Severnaya Zemlya) The Cryosphere Discussions, 9, 4407-4436, 2015 Author(s): A. Spolaor, T. Opel, J. R. McConnell, O. J. Maselli, G. Spreen, C. Varin, T. Kirchgeorg, D. Fritzsche, and P. Vallelonga The role of sea ice in the Earth climate system is still under debate, although it is known to influence albedo, ocean circulation, and atmosphere-ocean heat and gas exchange. Here we present a reconstruction of AD 1950 to 1998 sea ice in the Laptev Sea based on the Akademii Nauk ice core (Severnaya Zemlya, Russian Arctic). The halogens bromine (Br) and iodine (I) are strongly influenced by sea ice processes. Bromine reacts with the sea ice surface in auto-catalyzing "Bromine explosion" events causing an enrichment of the Br / Na ratio and the bromine excess (Br exc ) in snow compared to that in seawater. Iodine is emitted from algal communities growing under sea ice. The results suggest a connection between Br exc and spring sea ice area, as well as a connection between iodine concentration and summer sea ice area. These two halogens are therefore good candidates for extended reconstructions of past sea ice changes in the Arctic.

Description: A moving point approach to model shallow ice sheets: a study case with radially-symmetrical ice sheets The Cryosphere Discussions, 9, 4237-4270, 2015 Author(s): B. Bonan, M. J. Baines, N. K. Nichols, and D. Partridge Predicting the evolution of ice sheets requires numerical models able to accurately track the migration of ice sheet continental margins or grounding lines. We introduce a physically-based moving point approach for the flow of ice sheets based on the conservation of local masses. This allows the ice sheet margins to be tracked explicitly and the waiting time behaviours to be modelled efficiently. A finite difference moving point scheme is derived and applied in a simplified context (continental radially-symmetrical shallow ice approximation). The scheme, which is inexpensive, is validated by comparing the results with moving-margin exact solutions and steady states. In both cases the scheme is able to track the position of the ice sheet margin with high precision.

Description: Fram Strait spring ice export and September Arctic sea ice The Cryosphere Discussions, 9, 4205-4235, 2015 Author(s): M. H. Halvorsen, L. H. Smedsrud, R. Zhang, and K. Kloster The Arctic Basin exports ~ 10 % of the sea ice area southwards annually through Fram Strait. A larger than normal export decreases the remaining mean thickness and ice area. A new updated timeseries from 1979–2013 of Fram Strait sea ice area export shows an overall increase until today, and that more than 1 million km 2 has been exported annually in recent years. The new timeseries has been constructed from high resolution radar satellite imagery of sea ice drift across 79° N from 2004–2013, regressed on the observed cross-strait surface pressure difference, and shows an increasing trend of 7 % per decade. The trend is caused by higher southward ice drift speeds due to stronger southward geostrophic winds, largely explained by increasing surface pressure on Greenland. Spring and summer area export increases more (~ 14 % per decade) than in autumn and winter, and these export anomalies have a large influence on the following September mean ice extent.

Description: Tomography-based observation of sublimation and snow metamorphism under temperature gradient and advective flow The Cryosphere Discussions, 9, 4845-4864, 2015 Author(s): P. P. Ebner, M. Schneebeli, and A. Steinfeld Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. Time-lapse X-ray micro-tomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. The sublimation of water vapor for saturated air flowing across the snow sample was experimentally determined via variations of the porous ice structure. The results showed that the exothermic gas-to-solid phase change is favorable vis-a-vis the endothermic solid-to-gas phase change, thus leading to more ice deposition than ice sublimation. Sublimation has a marked effect on the structural change of the ice matrix but diffusion of water vapor in the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible leading to a constant porosity profile. However, the strong reposition process of water molecules on the ice grains is relevant for atmospheric chemistry.

Description: Glacier dynamics over the last quarter of a century at Jakobshavn Isbræ The Cryosphere Discussions, 9, 4865-4892, 2015 Author(s): I. S. Muresan, S. A. Khan, A. Aschwanden, C. Khroulev, T. Van Dam, J. Bamber, M. R. van den Broeke, B. Wouters, P. Kuipers Munneke, and K. H. Kjær Observations over the past two decades show substantial ice loss associated with the speedup of marine terminating glaciers in Greenland. Here we use a regional 3-D outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in west Greenland. Using atmospheric and oceanic forcing we tune our model to reproduce the observed frontal changes of JI during 1990–2014. We identify two major accelerations. The first occurs in 1998, and is triggered by moderate thinning prior to 1998. The second acceleration, which starts in 2003 and peaks in summer 2004, is triggered by the final breakup of the floating tongue, which generates a reduction in buttressing at the JI terminus. This results in further thinning, and as the slope steepens inland, sustained high velocities have been observed at JI over the last decade. As opposed to other regions on the Greenland Ice Sheet (GrIS), where dynamically induced mass loss has slowed down over recent years, both modelled and observed results for JI suggest a continuation of the acceleration in mass loss. Further, we find that our model is not able to capture the 2012 peak in the observed velocities. Our analysis suggests that the 2012 acceleration of JI is likely the result of an exceptionally long melt season dominated by extreme melt events. Considering that such extreme surface melt events are expected to intensify in the future, our findings suggest that the 21st century projections of the GrIS mass loss and the future sea level rise may be larger than predicted by existing modelling results.

Description: About the consistency between Envisat and CryoSat-2 radar freeboard retrieval over Antarctic sea ice The Cryosphere Discussions, 9, 4893-4923, 2015 Author(s): S. Schwegmann, E. Rinne, R. Ricker, S. Hendricks, and V. Helm Knowledge about Antarctic sea-ice volume and its changes over the past decades has been sparse due to the lack of systematic sea-ice thickness measurements in this remote area. Recently, first attempts have been made to develop a sea-ice thickness product over the Southern Ocean from space-borne radar altimetry and results look promising. Today, more than 20 years of radar altimeter data are potentially available for such products. However, data come from different sources, and the characteristics of individual sensors differ. Hence, it is important to study the consistency between single sensors in order to develop long and consistent time series over the potentially available measurement period. Here, the consistency between freeboard measurements of the Radar Altimeter 2 on-board Envisat and freeboard measurements from the Synthetic-Aperture Interferometric Radar Altimeter on-board CryoSat-2 is tested for their overlap period in 2011. Results indicate that mean and modal values are comparable over the sea-ice growth season (May–October) and partly also beyond. In general, Envisat data shows higher freeboards in the seasonal ice zone while CryoSat-2 freeboards are higher in the perennial ice zone and near the coasts. This has consequences for the agreement in individual sectors of the Southern Ocean, where one or the other ice class may dominate. Nevertheless, over the growth season, mean freeboard for the entire (regional separated) Southern Ocean differs generally by not more than 2 cm (5 cm, except for the Amundsen/Bellingshausen Sea) between Envisat and CryoSat-2, and the differences between modal freeboard lie generally within ±10 cm and often even below.

Description: Brief Communication: Upper air relaxation in RACMO2 significantly improves modelled interannual SMB variability in Antarctica The Cryosphere Discussions, 9, 4981-4995, 2015 Author(s): W. J. van de Berg and B. Medley The regional climate model RACMO2 has been a powerful tool for improving SMB estimates from GCMs or reanalyses. However, new yearly SMB observations for West Antarctica show that the modelled interannual variability in SMB is poorly simulated by RACMO2, in contrast to ERA-Interim, which resolves this variability well. In an attempt to remedy RACMO2 performance, we included additional upper air relaxation (UAR) in RACMO2. With UAR, the correlation to observations is similar for RACMO2 and ERA-Interim. The spatial SMB patterns and ice sheet integrated SMB modelled using UAR remain very similar to the estimates of RACMO2 without UAR. We only observe an upstream smoothing of precipitation in regions with very steep topography like the Antarctic Peninsula. We conclude that UAR is a useful improvement for RCM simulations, although results in regions with steep topography should be treated with care.

Description: Modeling Antarctic subglacial lake filling and drainage cycles The Cryosphere Discussions, 9, 6545-6579, 2015 Author(s): C. F. Dow, M. A. Werder, S. Nowicki, and R. T. Walker The growth and drainage of active subglacial lakes in Antarctica has previously been inferred from analysis of ice surface altimetry data. We use a subglacial hydrology model applied to a synthetic Antarctic ice stream to determine internal controls on the filling and drainage of subglacial lakes and their impact on ice stream dynamics. Our model outputs suggest that the highly constricted subglacial environment of the ice stream, combined with relatively high rates of water flow funneled from large catchments, can combine to create a system exhibiting slow-moving pressure waves. Over a period of years, the accumulation of water in the ice stream onset region results in a buildup of pressure creating temporary channels, which then evacuate the excess water. This increased flux of water through the ice stream drives lake growth. As the water body builds up, it too steepens the hydraulic gradient and allows greater flux out of the overdeepened lake basin. Eventually this flux is large enough to create channels that cause the lake to drain. Due to the presence of the channels, the drainage of the lake causes high water pressures around 50 km downstream of the lake rather than immediately in the vicinity of the overdeepening. Following lake drainage, channels again shut down. Lake drainage depends on the internal hydrological development in the wider system and therefore does not directly correspond to a particular water volume or depth. This creates a highly temporally and spatially variable system, which is of interest for assessing the importance of subglacial lakes in ice stream hydrology and dynamics.

Description: Assessment of error in satellite derived lead fraction in Arctic The Cryosphere Discussions, 9, 6315-6344, 2015 Author(s): N. Ivanova, P. Rampal, and S. Bouillon Leads within consolidated sea ice control heat exchange between the ocean and the atmosphere during winter thus constituting an important climate parameter. These narrow elongated features occur when sea ice is fracturing under the action of wind and currents, reducing the local mechanical strength of the ice cover, which in turn impact the sea ice drift patterns. This makes a high quality lead fraction (LF) dataset to be in demand for sea ice model evaluation, initialization and for assimilation of such data in regional models. In this context, the available LF dataset retrieved from satellite passive microwave observations (Advanced Microwave Scanning Radiometer – Earth Observing System, AMSR-E) is of great value, providing pan-Arctic light- and cloud-independent daily coverage since 2002. Here we quantify errors in this dataset using accurate LF estimates retrieved from Synthetic Aperture Radar (SAR) images employing a threshold technique, also introduced in this work. We find a consistent overestimation by a factor of 2–4 of the LF estimates in the AMSR-E LF product. We show for a data sample from the AMSR-E LF dataset that a simple adjustment of the tie points used in the method to estimate the LF can reduce the pixel-wise error by a factor of 2 on average. Applying such adjustment to the full dataset may thus significantly increase the quality and value of the original dataset.

Description: Acquisition of isotopic composition for surface snow in East Antarctica and the links to climatic parameters The Cryosphere Discussions, 9, 6275-6313, 2015 Author(s): A. Touzeau, A. Landais, B. Stenni, R. Uemura, K. Fukui, S. Fujita, S. Guilbaud, A. Ekaykin, M. Casado, E. Barkan, B. Luz, O. Magand, G. Teste, E. Le Meur, M. Baroni, J. Savarino, I. Bourgeois, and C. Risi The isotopic composition of oxygen and hydrogen in ice cores are invaluable tools for the reconstruction of past climate variations. Used alone, they give insights into the variations of the local temperature, whereas taken together they can provide information on the climatic conditions at the point of origin of the moisture. However, recent analyses of snow from shallow pits indicate that the climatic signal can become erased in very low accumulation regions, due to local processes of snow reworking. The signal to noise ratio decreases and the climatic signal can then only be retrieved using stacks of several snow pits. Obviously, the signal is not completely lost at this stage, otherwise it would be impossible to extract valuable climate information from ice cores as has been done, for instance, for the last glaciation. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. First, we look at the relationship between isotopes and temperature from a geographical point of view, using results from three traverses across Antarctica, to see how the relationship is built up through the distillation process. We also take advantage of these measures to see how second order parameters (d-excess and 17 O-excess) are related to δ 18 O and how they are controlled. d-excess increases in the interior of the continent (i.e. when δ 18 O decreases), due to the distillation process, whereas 17 O-excess decreases in remote areas, due to kinetic fractionation at low temperature. In both cases, these changes are associated with the loss of original information regarding the source. Then, we look at the same relationships in precipitation samples collected over one year at Dome C and Vostok, as well as in surface snow at Dome C. We note that the slope of the δ 18 O / T relationship decreases in these samples compared to those from the traverses, and thus advocate caution when using spatial slopes for past climate reconstruction. The second-order parameters behave in the same way in the precipitation as in the surface snow from traverses, indicating that similar processes are active. Finally we check if the same relationships between δ 18 O and second-order parameters are also found in the snow from four snow pits. While the d-excess remains opposed to δ 18 O in most snow pits, the 17 O-excess is no longer positively correlated to δ 18 O and even shows anti-correlation to δ 18 O at Vostok. This may be due to a stratospheric influence at this site and/or to post-deposition processes.

Description: Characterizing Arctic sea ice topography using high-resolution IceBridge data The Cryosphere Discussions, 9, 6495-6543, 2015 Author(s): A. A. Petty, M. C. Tsamados, N. T. Kurtz, S. L. Farrell, T. Newman, J. P. Harbeck, D. L. Feltham, and J. A. Richter-Menge We present an analysis of Arctic sea ice topography using high resolution, three-dimensional, surface elevation data from the Airborne Topographic Mapper, flown as part of NASA's Operation IceBridge mission. Surface features in the sea ice cover are detected using a newly developed surface feature picking algorithm. We derive information regarding the height, volume and geometry of surface features from 2009–2014 within the Beaufort/Chukchi and Central Arctic regions. The results are delineated by ice type to estimate the topographic variability across first-year and multi-year ice regimes. The results demonstrate that Arctic sea ice topography exhibits significant spatial variability, mainly driven by the increased surface feature height and volume (per unit area) of the multi-year ice that dominates the Central Arctic region. The multi-year ice topography exhibits greater interannual variability compared to the first-year ice regimes, which dominates the total ice topography variability across both regions. The ice topography also shows a clear coastal dependency, with the feature height and volume increasing as a function of proximity to the nearest coastline, especially north of Greenland and the Canadian Archipelago. A strong correlation between ice topography and ice thickness (from the IceBridge sea ice product) is found, using a square-root relationship. The results allude to the importance of ice deformation variability in the total sea ice mass balance, and provide crucial information regarding the tail of the ice thickness distribution across the western Arctic. Future research priorities associated with this new dataset are presented and discussed, especially in relation to calculations of atmospheric form drag.

Description: Committed near-future retreat of Smith, Pope, and Kohler Glaciers inferred by transient model calibration The Cryosphere Discussions, 9, 4459-4498, 2015 Author(s): D. Goldberg, P. Heimbach, I. Joughin, and B. Smith A glacial flow model of Smith, Pope and Kohler Glaciers has been calibrated by means of inverse methods against time-varying, annualy resolved observations of ice height and velocities, covering the period 2002 to 2011. The inversion – termed "transient calibration" – produces an optimal set of time-mean, spatially varying parameters together with a time-evolving state that accounts for the transient nature of observations and the model dynamics. Serving as an optimal initial condition, the estimated state for 2011 is used, with no additional forcing, for predicting grounded ice volume loss and grounding line retreat over the ensuing 30 years. The transiently calibrated model predicts a near-steady loss of grounded ice volume of approximately 21 km 3 a −1 over this period, as well as loss of 33 km 2 a −1 grounded area. We contrast this prediction with one obtained following a commonly used "snapshot" or steady-state inversion, which does not consider time dependence and assumes all observations to be contemporaneous. Transient calibration is shown to achieve a better fit with observations of thinning and grounding line retreat histories, and yields a quantitatively different projection with respect to ice volume loss and ungrounding. Sensitivity studies suggest large near-future levels of unforced, i.e. committed sea level contribution from these ice streams under reasonable assumptions regarding uncertainties of the unknown parameters.

Description: Photopolarimetric retrievals of snow properties The Cryosphere Discussions, 9, 3055-3074, 2015 Author(s): M. Ottaviani, B. van Diedenhoven, and B. Cairns Polarimetric observations of snow surfaces, obtained in the 410–2264 nm range with the Research Scanning Polarimeter onboard the NASA ER-2 high-altitude aircraft, are analyzed and presented. These novel measurements are of interest to the remote sensing community because the overwhelming brightness of snow plagues aerosol and cloud retrievals based on air- and space-borne total reflection measurements. The spectral signatures of the polarized reflectance of snow are therefore worthwhile investigating in order to provide guidance for the adaptation of algorithms currently employed for the retrieval of aerosol properties over soil and vegetated surfaces. At the same time, the increased information content of polarimetric measurements allows for a meaningful characterization of the snow medium. In our case, the grains are modeled as hexagonal prisms of variable aspect ratios and microscale roughness, yielding retrievals of the grains' scattering asymmetry parameter, shape and size. The results agree with our previous findings based on a more limited dataset, with the majority of retrievals leading to moderately rough crystals of extreme aspect ratios, for each scene corresponding to a single value of the asymmetry parameter.

Description: A prognostic model of the sea ice floe size and thickness distribution The Cryosphere Discussions, 9, 2955-2997, 2015 Author(s): C. Horvat and E. Tziperman Sea ice exhibits considerable seasonal and longer-term variations in extent, concentration, thickness and age, and is characterized by a complex and continuously changing distribution of floe sizes and thicknesses. Models of sea ice used in current climate models keep track of its concentration and of the distribution of ice thicknesses, but do not account for the floe size distribution and its potential effects on air–sea exchange and sea-ice evolution. Accurately capturing sea-ice variability in climate models may require a better understanding and representation of the distribution of floe sizes and thicknesses. We develop and demonstrate a model for the evolution of the joint sea-ice floe size and thickness distribution that depends on atmospheric and oceanic forcing fields. The model accounts for effects due to multiple processes that are active in the marginal and seasonal ice zones: freezing and melting along the lateral side and base of floes, mechanical interactions due to floe collisions (ridging and rafting) and sea-ice fracture due to swell propagation into the ice pack. The model is then examined and demonstrated in a series of idealized test cases.

Description: ENSO influence on surface energy and mass balance at Shallap Glacier, Cordillera Blanca, Peru The Cryosphere Discussions, 9, 2999-3053, 2015 Author(s): F. Maussion, W. Gurgiser, M. Großhauser, G. Kaser, and B. Marzeion The El Niño/Southern Oscillation (ENSO) is a major driver of climate variability in the tropical Andes, where recent Niño and Niña events left an observable footprint on glacier mass balance. The nature and strength of the relationship between ENSO and glacier mass balance, however, varies between regions and time periods, leaving several unanswered questions about its exact mechanisms. The starting point of this study is a four-year long time series of distributed surface energy and mass balance (SEB/SMB) calculated using a process-based model driven by observations at Shallap Glacier (Cordillera Blanca, Peru). These data are used to calibrate a regression-based downscaling model that links the local SEB/SMB fluxes to atmospheric reanalysis variables on a monthly basis, allowing an unprecedented quantification of the ENSO influence on the SEB/SMB at climatological time scales (1980–2013, ERA-Interim period). We find a stronger and steadier anti-correlation between pacific sea surface temperature (SST) and glacier mass balance than previously reported. This relationship is most pronounced during the wet season (December–May) and at low altitudes where Niño (Niña) events are accompanied with a snowfall deficit (excess) and a higher (lower) radiation energy input. We detect a weaker but significant ENSO anti-correlation with total precipitation (Niño dry signal) and positive correlation with the sensible heat flux, but find no ENSO influence on sublimation. Sensitivity analyses comparing several downscaling methods and reanalysis datasets resulted in stable mass balance correlations with pacific SST but also revealed large uncertainties in computing the mass balance trend of the last decades. The newly introduced open-source downscaling tool can be applied easily to other glaciers in the tropics, opening new research possibilities on even longer time scales.

Description: Changing surface–atmosphere energy exchange and refreezing capacity of the lower accumulation area, west Greenland The Cryosphere Discussions, 9, 2867-2913, 2015 Author(s): C. Charalampidis, D. van As, J. E. Box, M. R. van den Broeke, W. T. Colgan, M. MacFerrin, H. Machguth, and P. P. Smeets We present five years (2009–2013) of automatic weather station measurements from the lower accumulation area (1840 m a.s.l.) of the ice sheet in the Kangerlussuaq region, western Greenland. Here, the summers of 2010 and 2012 were both exceptionally warm, but only 2012 resulted in a strongly negative surface mass budget (SMB) and surface meltwater runoff. The observed runoff was due to a large ice fraction in the upper 10 m of firn that prevented meltwater from percolating to available pore volume below. Analysis reveals a relatively low 2012 summer albedo of ~0.7 as meltwater was present at the surface. Consequently, during the 2012 melt season the surface absorbed 29% (213 MJ m -2 ) more solar radiation than the average of all other years. A surface energy balance model is used to evaluate the seasonal and interannual variability of all surface energy fluxes. The model reproduces the observed melt rates as well as the SMB for each season. A sensitivity test reveals that 71% of the additional solar radiation in 2012 was used for melt, corresponding to 36% (0.64 m) of the 2012 surface lowering. The remaining 1.14 m was primarily due to the high atmospheric temperatures up to +2.6 °C daily average, indicating that 2012 would have been a negative SMB year at this site even without the melt-albedo feedback. Longer time series of SMB, regional temperature and remotely sensed albedo (MODIS) show that 2012 was the first strongly negative SMB year with the lowest albedo at this elevation on record. The warm conditions of the last years resulted in enhanced melt and reduction of the refreezing capacity at the lower accumulation area. If high temperatures continue the current lower accumulation area will turn into a region with superimposed ice in coming years.

Description: The relative contributions of calving and surface ablation to ice loss at a lake-terminating glacier The Cryosphere Discussions, 9, 2915-2953, 2015 Author(s): M. Chernos, M. Koppes, and R. D. Moore Bridge Glacier is a lake-terminating glacier in the Coast Mountains of British Columbia and has retreated over 3.55 km since 1972, with the majority of the retreat having occurred since 1991. This retreat is out of proportion to surface melt inferred from regional climate indices, suggesting that it has been driven primarily by calving as the glacier retreated across an over-deepened basin. In order to better understand the primary drivers of mass balance, the relative importance of surface melt and calving is investigated during the 2013 melt season using a distributed energy balance model and time-lapse imagery. Calving is responsible for 23% of the mass loss during the 2013 melt season, and is limited by modest flow speeds and a small terminus cross-section. Calving and summer balance estimates over the last 30 years suggest that calving is consistently a smaller contributor of mass loss relative to surface melt. Although calving is estimated to be responsible for up to 49% of ice loss for individual seasons, averaged over multiple summers it typically accounts for 10 to 25%. Calving has been driven primarily by buoyancy and water depths, and fluxes were greatest between 2005 and 2010 as the glacier retreated over the deepest part of Bridge Lake. These losses are part of a transient stage in the glacier's retreat, and are expected to diminish as the terminus recedes into shallower water. Surface melt is the primary driver of ice loss at Bridge Glacier, and future mass loss and retreat is dependent on governing climatic conditions.

Description: Coastal dynamics and submarine permafrost in shallow water of the central Laptev Sea, East Siberia Pier Paul Overduin, Sebastian Wetterich, Frank Günther, Mikhail N. Grigoriev, Guido Grosse, Lutz Schirrmeister, Hans-Wolfgang Hubberten, and Aleksandr Makarov The Cryosphere, 10, 1449-1462, doi:10.5194/tc-10-1449-2016, 2016 How fast does permafrost warm up and thaw after it is covered by the sea? Ice-rich permafrost in the Laptev Sea, Siberia, is rapidly eroded by warm air and waves. We used a floating electrical technique to measure the depth of permafrost thaw below the sea, and compared it to 60 years of coastline retreat and permafrost depths from drilling 30 years ago. Thaw is rapid right after flooding of the land and slows over time. The depth of permafrost is related to how fast the coast retreats.

Description: Age of the Mt. Ortles ice cores, the Tyrolean Iceman and glaciation of the highest summit of South Tyrol since the Northern Hemisphere Climatic Optimum Paolo Gabrielli, Carlo Barbante, Giuliano Bertagna, Michele Bertó, Daniel Binder, Alberto Carton, Luca Carturan, Federico Cazorzi, Giulio Cozzi, Giancarlo Dalla Fontana, Mary Davis, Fabrizio De Blasi, Roberto Dinale, Gianfranco Dragà, Giuliano Dreossi, Daniela Festi, Massimo Frezzotti, Jacopo Gabrieli, Stephan Galos, Patrick Ginot, Petra Heidenwolf, Theo M. Jenk, Natalie Kehrwald, Donald Kenny, Olivier Magand, Volkmar Mair, Vladimir Mikhalenko, Ping Nan Lin, Klaus Oeggl, Gianni Piffer, Mirko Rinaldi, Ulrich Schotterer, Margit Schwikowski, Roberto Seppi, Andrea Spolaor, Barbara Stenni, Davdi Tonidandel, CChiara Uglietti, Victor Zagorodnov, Thomas Zanoner, and Piero Zennaro The Cryosphere Discuss., doi:10.5194/tc-2016-159,2016 Manuscript under review for TC (discussion: open, 0 comments) New ice cores were extracted from Alto dell'Ortles, the highest glacier of South Tyrol in the Italian Alps, to check whether prehistoric ice, that is coeval to the famous 5200 years old Tyrolean Iceman, is still preserved in this region. Dating of the ice cores confirms the hypothesis and indicates that the drilling site was glaciated since the end of the Northern Hemisphere Climatic Optimum (7000 BP). We also infer that an unprecedented acceleration of the glacier flow has just recently begun.

Description: Combined diurnal variations of discharge and hydrochemistry of the Isunnguata Sermia outlet of the Greenland Ice Sheet give in sight on sub glacial conditions Joseph Graly, Joel Harrington, and Neil Humphrey The Cryosphere Discuss., doi:10.5194/tc-2016-137,2016 Manuscript under review for TC (discussion: open, 0 comments) At a major outlet of the Greenland Ice Sheet in West Greenland, we find that the chemical solutes is the emerging subglacial waters are out of phase with water discharge and can spike in concentration during waning flow. This suggests that the subglacial waters are spreading out across a large area of the glacial bed throughout the day, stimulating chemical weathering beyond the major water distribution channels.

Description: Inversion of geothermal heat flux in a thermomechanically coupled nonlinear Stokes ice sheet model Hongyu Zhu, Noemi Petra, Georg Stadler, Tobin Isaac, Thomas J. R. Hughes, and Omar Ghattas The Cryosphere, 10, 1477-1494, doi:10.5194/tc-10-1477-2016, 2016 We study how well the basal geothermal heat flux can be inferred from surface velocity observations using a thermomechanically coupled nonlinear Stokes ice sheet model. The prospects and limitations of this inversion is studied in two and three dimensional model problems. We also argue that a one-way coupled approach for the adjoint equations motivated by staggered solvers for forward multiphysics problems can lead to an incorrect gradient and premature termination of the optimization iteration.

Description: Increased nitrate and decreased δ 15 N–NO 3 − in the Greenland Arctic after 1940 attributed to North American oil burning Nathan J. Chellman, Meredith G. Hastings, and Joseph R. McConnell The Cryosphere Discuss., doi:10.5194/tc-2016-163,2016 Manuscript under review for TC (discussion: open, 0 comments) This manuscript analyzes the changing sources of nitrate deposition to Greenland since 1760 CE using a dataset consisting of sub-seasonally resolved nitrogen isotopes of nitrate and source tracers. Correlations amongst ion concentration, source tracers, and the δ 15 N–NO 3 − provide evidence of the impact of biomass burning and fossil fuel combustion emissions of nitrogen oxides and suggest that oil combustion is the likely driver of increased nitrate concentration in Greenland ice since 1940 CE.

Description: Slight glacier reduction over the northwestern Tibetan Plateau despite significant recent warming Yetang Wang, Shugui Hou, Wenling An, Hongxi Pang, and Yaping Liu The Cryosphere Discuss., doi:10.5194/tc-2016-165,2016 Manuscript under review for TC (discussion: open, 0 comments) This study further confirms "Pamir–Karakoram–Western-Kunlun-Mountain (northwestern Tibetan Plateau) Glacier Anomaly". Slight glacier reduction over the northwestern Tibetan Plateau may result from more accumulation from increased precipitation in winter which to great extent protects it from mass reductions under climate warming during 1961–2000. Warming slowdown since 2000 happening at this region may further mitigate glacier mass reduction.

Description: Response of seasonal soil freeze depth to climate change across China Xiaoqing Peng, Oliver W. Frauenfeld, Tingjun Zhang, Kang Wang, Bin Cao, Xinyue Zhong, Hang Su, and Cuicui Mu The Cryosphere Discuss., doi:10.5194/tc-2016-129,2016 Manuscript under review for TC (discussion: open, 0 comments) Previous researches paid more attention on the permafrost, e.g. active layer thickness, soil temperature, permafrost area extent, and associated with permafrost degradation leading other changes. However, seasonally frozen ground, vast area extent, did not focus by so much attention. Here, we combined more than 800 observation station data and gridded data to investigate soil freeze depth across China. The results indicate that soil freeze depth increase with climate warming.

Description: Characteristics of an avalanche-feeding and partially debris-covered glacier and its response to atmospheric warming in Mt. Tomor, Tian Shan, China Puyu Wang, Zhongqin Li, and Huilin Li The Cryosphere Discuss., doi:10.5194/tc-2016-138,2016 Manuscript under review for TC (discussion: open, 0 comments) A cirque-valley glacier with complex topography and partially debris-covered area was investigated in the Mt. Tomor, Tian Shan. The glacier is analogous to temperate one on movement and temperature regimes. The strongest ablation and most significant terminus retreat and area reduction occurred at the end of last century and the beginning of this century. Since inhibition of debris cover to melting, it is expected to keep shrinkage in the coming decades, but the terminus retreat is to be slower.

Description: An ice-sheet-wide framework for englacial attenuation from ice-penetrating radar data T. M. Jordan, J. L. Bamber, C. N. Williams, J. D. Paden, M. J. Siegert, P. Huybrechts, O. Gagliardini, and F. Gillet-Chaulet The Cryosphere, 10, 1547-1570, doi:10.5194/tc-10-1547-2016, 2016 Ice penetrating radar enables determination of the basal properties of ice sheets. Existing algorithms assume stationarity in the attenuation rate, which is not justifiable at an ice sheet scale. We introduce the first ice-sheet-wide algorithm for radar attenuation that incorporates spatial variability, using the temperature field from a numerical model as an initial guess. The study is a step toward ice-sheet-wide data products for basal properties and evaluation of model temperature fields.

Description: Circumpolar polynya regions and ice production in the Arctic: Results from MODIS thermal infrared imagery for 2002/2003 to 2014/2015 with a regional focus on the Laptev Sea Andreas Preußer, Günther Heinemann, Sascha Willmes, and Stephan Paul The Cryosphere Discuss., doi:10.5194/tc-2016-133,2016 Manuscript under review for TC (discussion: open, 0 comments) Our study presents spatial and temporal characteristics of 16 prominent polynya regions over the entire Arctic basin. By using an energy balance model, we are able to derive daily thin-ice thickness distributions from satellite and atmospheric reanalysis data. All polynyas combined yield an average ice production of about 1444 km 3 per winter. Interestingly, we find distinct regional differences in calculated trends over the last 13 years. Finally, we set a special focus on the Laptev Sea region.

Description: Statistical indicators of Arctic sea-ice stability – prospects and limitations Sebastian Bathiany, Bregje van der Bolt, Mark S. Williamson, Timothy M. Lenton, Marten Scheffer, Egbert H. van Nes, and Dirk Notz The Cryosphere, 10, 1631-1645, doi:10.5194/tc-10-1631-2016, 2016 We examine if a potential "tipping point" in Arctic sea ice, causing abrupt and irreversible sea-ice loss, could be foreseen with statistical early warning signals. We assess this idea by using several models of different complexity. We find robust and consistent trends in variability that are not specific to the existence of a tipping point. While this makes an early warning impossible, it allows to estimate sea-ice variability from only short observational records or reconstructions.

Description: Signature of Arctic first-year ice melt pond fraction in X-band SAR imagery Ane S. Fors, Dmitry V. Divine, Anthony P. Doulgeris, Angelika H. H. Renner, and Sebastian Gerland The Cryosphere Discuss., doi:10.5194/tc-2016-125,2016 Manuscript under review for TC (discussion: open, 0 comments) This paper investigates the signature of melt ponds in satellite borne synthetic aperture radar (SAR) imagery. The study shows that polarimetric X-band SAR can be used to extract melt pond fraction from drifting first-year sea ice, and discusses the influence of factors like wind speed, SAR incidence angle and instrument noise floor. Melt ponds strongly influence the Arctic sea ice energy budget, and the results imply prospective opportunities for expanded monitoring of melt ponds from space.

Description: Greenland annual accumulation along the EGIG line, 1959–2004, from ASIRAS airborne radar and neutron-probe density measurements Thomas B. Overly, Robert L. Hawley, Veit Helm, Elizabeth M. Morris, and Rohan N. Chaudhary The Cryosphere, 10, 1679-1694, doi:10.5194/tc-10-1679-2016, 2016 We demonstrate that snow accumulation rates across the Greenland Ice Sheet, determined from RADAR layers and modeled snow density profiles, are identical to ground-based measurements of snow accumulation. Three regional climate models underestimate snow accumulation compared to RADAR layer estimates. Using RADAR increases spatial coverage and improves accuracy of snow accumulation estimates. Incorporating our results into climate models may reduce uncertainty of sea-level rise estimates.

Description: Thermal impacts of engineering activities and vegetation layer on permafrost in different alpine ecosystems of the Qinghai–Tibet Plateau, China Qingbai Wu, Zhongqiong Zhang, Siru Gao, and Wei Ma The Cryosphere, 10, 1695-1706, doi:10.5194/tc-10-1695-2016, 2016 Climate warming and engineering activities have various impacts on the thermal regime of permafrost in alpine ecosystems of the Qinghai–Tibet Plateau. Using recent observations of permafrost thermal regimes along the Qinghai–Tibet highway and railway, the changes of such regimes beneath embankments constructed in alpine meadows and steppes are studied. The results show that alpine meadows on the Qinghai–Tibet Plateau can have a controlling role among engineering construction effects on permafrost beneath embankments. As before railway construction, the artificial permafrost table (APT) beneath embankments is not only affected by climate change and engineering activities but is also controlled by alpine ecosystems. However, the change rate of APT is not dependent on ecosystem type, which is predominantly affected by climate change and engineering activities. Instead, the rate is mainly related to cooling effects of railway ballast and heat absorption effects of asphalt pavement. No large difference between alpine and steppe can be identified regarding the variation of soil temperature beneath embankments, but this difference is readily identified in the variation of mean annual soil temperature with depth. The vegetation layer in alpine meadows has an insulation role among engineering activity effects on permafrost beneath embankments, but this insulation gradually disappears because the layer decays and compresses over time. On the whole, this layer is advantageous for alleviating permafrost temperature rise in the short term, but its effect gradually weakens in the long term.

Description: Impact of Icebergs on Net Primary Productivity in the Southern Ocean Shuang-Ye Wu and Shugui Hou The Cryosphere Discuss., doi:10.5194/tc-2016-166,2016 Manuscript under review for TC (discussion: open, 0 comments) The primary productivity in the Southern Ocean (SO) is limited by the amount of iron available for biological activities. Recent studies show that icebergs could be a main source of iron to the SO. Based on remote sensing data, our study shows that iceberg presence has a small, yet statistically significant, positive impact on productivity. As iceberg quantity increases, their positive influence on productivity also increases. This impact could serve as a negative feedback to the climate system.

Description: Possible groundwater dominance in the subglacial hydrology of ice sheet interiors: example at Dome C, East Antarctica Brad T. Gooch, Sasha P. Carter, Omar Ghattas, Duncan A. Young, and Donald D. Blankenship The Cryosphere Discuss., doi:10.5194/tc-2016-141,2016 Manuscript under review for TC (discussion: open, 0 comments) Our work investigates the potential significance of groundwater flow underneath the interior of East Antarctica where the ice doesn't rapidly melt. We attempt to describe the relationship between two hydrologic systems (water under the ice and in the ground) and how they might interact along a flow path between lakes under the ice. We find that groundwater is significant in regional water transport for melt water under the ice in areas of low melting in East Antarctica.

Description: Design of a scanning laser meter for monitoring the spatio-temporal evolution of snow depth and its application in the Alps and in Antarctica Ghislain Picard, Laurent Arnaud, Jean-Michel Panel, and Samuel Morin The Cryosphere, 10, 1495-1511, doi:10.5194/tc-10-1495-2016, 2016 A cost-effective automatic laser scan has been built to measure snow depth spatio-temporal variations. Deployed in the Alps and in Dome C (Antarctica), two devices acquired daily scans covering a surface area of 100–150 m 2 . The precision and long-term stability of the measurements are about 1 cm and the accuracy is better than 5 cm. These high performances are particularly suited at Dome C, where it was possible to reveal that most of the accumulation in the year 2015 stems from a single event.

Description: Arctic sea-ice diffusion from observed and simulated Lagrangian trajectories Pierre Rampal, Sylvain Bouillon, Jon Bergh, and Einar Ólason The Cryosphere, 10, 1513-1527, doi:10.5194/tc-10-1513-2016, 2016 Due to the increasing activity in Arctic, sea-ice–ocean models are now frequently used to produce operational forecasts, for oil spill trajectory modelling and to assist in offshore operations planning. In this study we evaluate the performance of two models with respect to their capability to reproduce observed sea ice diffusion properties by using metrics based on Lagrangian statistics. This paper presents a new and useful evaluation metric for current coupled sea ice–ocean models.

Description: Retrieval of the thickness of undeformed sea ice from simulated C-band compact polarimetric SAR images Xi Zhang, Wolfgang Dierking, Jie Zhang, Junmin Meng, and Haitao Lang The Cryosphere, 10, 1529-1545, doi:10.5194/tc-10-1529-2016, 2016 In this work, we introduced a parameter ("CP ratio") for the retrieval of the thickness of undeformed first-year sea ice that is specifically adapted to compact polarimetric SAR images. Based on a validation using other compact polarimetric SAR images from the Labrador Sea, we found a root mean square error of 8 cm and a maximum correlation coefficient of 0.94 for the retrieval procedure when applying it to level ice between 0.1 m and 0.8 m thick.

Description: High resolution boundary conditions of an old ice target near Dome C, Antarctica Duncan A. Young, Jason L. Roberts, Catherine Ritz, Massimo Frezzotti, Enrica Quartini, Marie G. P. Cavitte, Carly R. Tozer, Daniel Steinhage, Stefano Urbini, Hugh F. J. Corr, Tas Van Ommen, and Donald D. Blankenship The Cryosphere Discuss., doi:10.5194/tc-2016-169,2016 Manuscript under review for TC (discussion: open, 0 comments) Glacial ice can preserve records of Earth's ancient atmosphere (including greenhouse gases) that can be compared to ocean sediment records of ice sheet size to better understand climate feedbacks. To find records of the greenhouse gases found in key periods of climate transition, we need to find sites of unmelted old ice near the base of the ice sheet. We performed a high resolution survey of such a site near Europe's Concordia station in East Antarctica, using a multi instrument aircraft.

Description: Snowpack modelling in the Pyrenees driven by kilometric-resolution meteorological forecasts Louis Quéno, Vincent Vionnet, Ingrid Dombrowski-Etchevers, Matthieu Lafaysse, Marie Dumont, and Fatima Karbou The Cryosphere, 10, 1571-1589, doi:10.5194/tc-10-1571-2016, 2016 Simulations are carried out in the Pyrenees with the snowpack model Crocus, driven by meteorological forecasts from the model AROME at kilometer resolution. The evaluation is done with ground-based measurements, satellite data and reference simulations. Studying daily snow depth variations allows to separate different physical processes affecting the snowpack. We show the benefits of AROME kilometric resolution and dynamical behavior in terms of snowpack spatial variability in a mountain range.

Description: Radiocarbon dating of glacier ice Chiara Uglietti, Alexander Zapf, Theo M. Jenk, Sönke Szidat, Gary Salazar, and Margit Schwikowski The Cryosphere Discuss., doi:10.5194/tc-2016-160,2016 Manuscript under review for TC (discussion: open, 0 comments) A meaningful interpretation of the climatic history contained in ice cores requires a precise chronology. For dating the older and deeper part of the glaciers, radiocarbon analysis can be used, when organic matter such as plant or insect fragments is found in the ice. Since this happens rarely, a complementary dating tool is based on radiocarbon dating of the insoluble fraction of carbonaceous aerosols entrapped in the ice, allowing dating ice with ages between 200 and more than 10 000 years.

Description: Effects of stratified active layers on high-altitude permafrost warming: a case study on the Qinghai–Tibet Plateau Xicai Pan, Yanping Li, Qihao Yu, Xiaogang Shi, Daqing Yang, and Kurt Roth The Cryosphere, 10, 1591-1603, doi:10.5194/tc-10-1591-2016, 2016 Using a 9-year dataset in conjunction with a process-based model, we verify that the common assumption of a considerably smaller thermal conductivity in the thawed season than the frozen season is not valid at a site with a stratified active layer on the Qinghai–Tibet Plateau (QTP). The unique hydraulic and thermal mechanism in the active layer challenges the concept of thermal offset used in conceptual permafrost models and hints at the reason for rapid permafrost warming on the QTP.

Description: Brief communication: Organochlorine pesticides in an archived firn core from Law Dome, East Antarctica Marie Bigot, Mark A. J. Curran, Andrew D. Moy, Derek C. G. Muir, Darryl W. Hawker, Roger Cropp, Camilla F. Teixeira, and Susan Bengtson Nash The Cryosphere Discuss., doi:10.5194/tc-2016-178,2016 Manuscript under review for TC (discussion: open, 0 comments) Organochlorine pesticides (OCPs) were, for the first time, quantified in archived firn cores from the East Antarctic ice sheet representative of 1945–1957 C.E. and 1958–1967 C.E. The core sections were melted under high purity nitrogen atmosphere and the melt water analysed. Methods allowed quantification of hexachlorocyclohexanes, heptachlor, trans-chlordane, dieldrin and endrin. While the core presented evidence of nominal modern-use chemical contamination, indicating handling and/or storage contamination, legacy OCP concentrations and deposition rates reported are orders of magnitude lower than those from Arctic regions, lending support for their validity. The study further provides a description of equipment used and suggests adapted methods to overcome logistical challenges associated with trace organic contaminant detection in Polar Regions.

Description: Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica Benjamin E. Smith, Noel Gourmelen, Alexander Huth, and Ian Joughin The Cryosphere Discuss., doi:10.5194/tc-2016-180,2016 Manuscript under review for TC (discussion: open, 0 comments) In this paper we investigate elevation changes of Thwaites Glacier, West Antarctica, one of the main sources of excess ice discharge into the ocean. We find that in early 2013, four subglacial lakes separated by 100 km drained suddenly, discharging more than three cubic kilometers of water under the fastest part of the glacier in less than six months. Concurrent ice-speed measurements show only minor changes, suggesting that ice dynamics are not strongly sensitive to changes in water flow.

Description: Isotopic exchange on the diurnal scale between near-surface snow and lower atmospheric water vapor at Kohnen station, East Antarctica François Ritter, Hans Christian Steen-Larsen, Martin Werner, Valérie Masson-Delmotte, Anais Orsi, Melanie Behrens, Gerit Birnbaum, Johannes Freitag, Camille Risi, and Sepp Kipfstuhl The Cryosphere, 10, 1647-1663, doi:10.5194/tc-10-1647-2016, 2016 We present the first successful continuous measurements of water vapor isotopes performed in Antarctica in January 2013. The interest is to understand the impact of the water vapor isotopic composition on the near-surface snow isotopes. Our study reveals a diurnal cycle in the snow isotopic composition in phase with the vapor. This finding suggests fractionation during the sublimation of the ice, which has an important consequence on the interpretation of water isotope variations in ice cores.

Description: Evaposublimation from the snow in the Mediterranean mountains of Sierra Nevada (Spain) Javier Herrero and María José Polo The Cryosphere Discuss., doi:10.5194/tc-2016-161,2016 Manuscript under review for TC (discussion: open, 0 comments) This manuscript presents 7 years of field work and modelling to assess the importance of the loss of water from the snow by means of sublimation in the Mediterranean mountains of Sierra Nevada. The actual sublimation rates were detected through detailed measurement of the mass fluxes from the snow. These data have led to some improvements in the modelling of the snow in this kind of mountainous semiarid regions. The sublimation is estimated to range between 24–33 % of total annual snowfall.

Description: An automated methodology for differentiating rock from snow, clouds and sea in Antarctica from Landsat 8 imagery: a new rock outcrop map and area estimation for the entire Antarctic continent Alex Burton-Johnson, Martin Black, Peter T. Fretwell, and Joseph Kaluza-Gilbert The Cryosphere, 10, 1665-1677, doi:10.5194/tc-10-1665-2016, 2016 We present a new rock outcrop map for the entire Antarctic continent, a principal base dataset for research and mapping in Antarctica with broad applications. To derive the map, a new methodology was developed and applied to allow automated identification of rock outcrops from Landsat 8 satellite images whilst excluding sunlit and shaded snow, clouds and liquid water – the first such automated methodology. The new dataset reveals that exposed rock forms only 0.18 % of the entire continent.

Description: Diagnosing the decline in climatic mass balance of glaciers in Svalbard over 1957–2014 Torbjørn Ims Østby, Thomas Vikhamar Schuler, Jon Ove Hagen, Regine Hock, Jack Kohler, and Carleen H. Reijmer The Cryosphere Discuss., doi:10.5194/tc-2016-172,2016 Manuscript under review for TC (discussion: open, 0 comments) We present modeled climatic mass balance for all glaciers in Svalbard for the period 1957–2014 at 1 km resolution using a coupled surface energy balance and snowpack model, thereby closing temporal and spatial gaps in direct and geodetic mass balance estimates. Supporting previous studies, our results indicate increased mass loss over the period. A detailed analysis of the involved energy fluxes reveals that increased mass loss is caused by atmospheric warming further amplified by feedbacks.

Description: Simulating ice layer formation under the presence of preferential flow in layered snowpacks Nander Wever, Sebastian Würzer, Charles Fierz, and Michael Lehning The Cryosphere Discuss., doi:10.5194/tc-2016-185,2016 Manuscript under review for TC (discussion: open, 0 comments) The study presents a dual domain approach to simulate liquid water flow in snow using the 1-dimensional physics based snow cover model SNOWPACK. In this approach, the pore space is separated into a part for matrix flow and a part that represents preferential flow. Using this approach, water can percolate sub-freezing snow and form dense (ice) layers. A comparison with snow pits shows that some of the observed ice layers were reproduced by the model while others remain challenging to simulate.

Description: Marine ice sheet model performance depends on basal sliding physics and sub-shelf melting Rupert Michael Gladstone, Roland Charles Warner, Benjamin Keith Galton-Fenzi, Olivier Gagliardini, Thomas Zwinger, and Ralf Greve The Cryosphere Discuss., doi:10.5194/tc-2016-149,2016 Manuscript under review for TC (discussion: open, 0 comments) Computer models are used to simulate the behaviour of glaciers and ice sheets. It has been found that such models are required to be run at very high resolution (which means high computational expense) in order to accurately represent the evolution of marine ice sheets (ice sheets resting on bedrock below sea level), in certain situations.

Description: Effects of Seasonal Snow Cover on Hydrothermal Conditions of the Active Layer in the Northeastern Qinghai-Tibet Plateau Ji Chen, Yu Sheng, Qingbai Wu, Lin Zhao, Jing Li, and Jingyi Zhao The Cryosphere Discuss., doi:10.5194/tc-2016-134,2016 Manuscript under review for TC (discussion: open, 0 comments) The extreme thin and short-time snow cover in the northeastern Qinghai-Tibet plateau is predominantly during spring and autumn. Removal of seasonal snow cover is beneficial for cooling the active layer in the first few years. Seasonal snow cover maintains the high water content of the active layer because of the inhibitory action of snow cover on the evaporation capacity in the natural site during the daytime and in summer. Snow removal can therefore lead to a rapid decrease of soil moisture.

Description: Surface mass balance and water stable isotopes derived from firn cores on three ice rises, Fimbul Ice Shelf, Antarctica Carmen P. Vega, Elisabeth Schlosser, Dmitry V. Divine, Jack Kohler, Tõnu Martma, Anja Eichler, Margit Schwikowski, and Elisabeth Isaksson The Cryosphere Discuss., doi:10.5194/tc-2016-164,2016 Manuscript under review for TC (discussion: open, 0 comments) Surface mass balance and water stable isotopes from firn cores on three ice rises at Fimbul Ice Shelf, are reported. The results suggest that the ice rises are suitable sites for the retrieval of longer firn and ice cores. The first deuterium excess data for the area suggests a possible role of seasonal moisture transport changes on the annual isotopic signal. Large-scale atmospheric circulation patterns most likely provide the dominant influence on water stable isotope ratios at the sites.

Description: Reflective properties of white and snow-covered sea ice Aleksey Malinka, Eleonora Zege, Georg Heygster, and Larysa Istomina The Cryosphere Discuss., doi:10.5194/tc-2016-153,2016 Manuscript under review for TC (discussion: open, 0 comments) The amount of melt ponds on Arctic summer sea ice and its reflectance are required for better climate modelling and weather prediction. In order to derive these quantities from optical satellite observations, simple analytical formulas for the bidirectional reflectance factor and albedo at direct and diffuse incidence are derived from basic assumptions and verified with in situ measurements made during the expedition ARK-XXVII/3 of research vessel Polarstern in 2012.

Description: Application and validation of long-range terrestrial laser scanning to monitor the mass balance of very small glaciers in the Swiss Alps Mauro Fischer, Matthias Huss, Mario Kummert, and Martin Hoelzle The Cryosphere, 10, 1279-1295, doi:10.5194/tc-10-1279-2016, 2016 This study provides the first thorough validation of geodetic glacier mass changes derived from close-range high-resolution remote sensing techniques, and highlights the potential of terrestrial laser scanning for repeated mass balance monitoring of very small alpine glaciers. The presented methodology is promising, as laborious and potentially dangerous in situ measurements as well as the spatial inter- and extrapolation of point measurements over the entire glacier can be circumvented.

Description: Development and calibration of an automatic spectral albedometer to estimate near-surface snow SSA time series Ghislain Picard, Quentin Libois, Laurent Arnaud, Gauthier Verin, and Marie Dumont The Cryosphere, 10, 1297-1316, doi:10.5194/tc-10-1297-2016, 2016 Albedo of snow surfaces depends on snow grain size. By measuring albedo during 3 years at Dome C in Antarctica with an automatic spectroradiometer, we were able to monitor the snow specific surface area and show an overall growth of the grains in spring and summer followed by an accumulation of small-grained snow from mid-summer. This study focuses on the uncertainties due to the spectroradiometer and concludes that the observed variations are significant with respect to the precision.

Description: Operational algorithm for ice/water classification on dual-polarized RADARSAT-2 images Natalia Zakhvatkina, Anton Korosov, Stefan Muckenhuber, Stein Sandven, and Mohamed Babiker The Cryosphere Discuss., doi:10.5194/tc-2016-131,2016 Manuscript under review for TC (discussion: open, 0 comments) The presented fully automated algorithm distinguishes open water (rough/calm) and sea ice based on dual-polarized RS2 SAR images. Texture features are used for Support Vector Machines supervised image classification. The algorithm includes pre-processing and validation procedures. More than 2700 scenes were processed and the results show the good discrimination between open water and sea ice areas with accuracy 91 % compared with ice charts produced by MET Norway service.

Description: Three-year monitoring of stable isotopes of precipitation at Concordia Station, East Antarctica Barbara Stenni, Claudio Scarchilli, Valerie Masson-Delmotte, Elisabeth Schlosser, Virginia Ciardini, Giuliano Dreossi, Paolo Grigioni, Mattia Bonazza, Anselmo Cagnati, Daniele Karlicek, Camille Risi, Roberto Udisti, and Mauro Valt The Cryosphere Discuss., doi:10.5194/tc-2016-142,2016 Manuscript under review for TC (discussion: open, 0 comments) Here, we focus on the Concordia Station, central East Antarctic plateau, providing a multi-year record (2008–2010) of daily precipitation types identified from crystal morphologies, precipitation amounts, and isotopic composition. Relationships between local meteorological data and precipitation oxygen isotope composition are investigated. Our dataset is available for in depth model evaluation at the synoptic scale.

Description: Greenland Ice Sheet seasonal and spatial mass variability from model simulations and GRACE (2003–2012) Patrick M. Alexander, Marco Tedesco, Nicole-Jeanne Schlegel, Scott B. Luthcke, Xavier Fettweis, and Eric Larour The Cryosphere, 10, 1259-1277, doi:10.5194/tc-10-1259-2016, 2016 We compared satellite-derived estimates of spatial and seasonal variations in Greenland Ice Sheet mass with a set of model simulations, revealing an agreement between models and satellite estimates for the ice-sheet-wide seasonal fluctuations in mass, but disagreement at finer spatial scales. The model simulations underestimate low-elevation mass loss. Improving the ability of models to capture variations and trends in Greenland Ice Sheet mass is important for estimating future sea level rise.

Description: Development and analysis of a continuous record of global near-surface soil freeze/thaw patterns from AMSR-E and AMSR2 data Tongxi Hu, Tianjie Zhao, Jiancheng Shi, Tianxing Wang, Dabin Ji, Ahmad Al Bitar, Bin Peng, and Yurong Cui The Cryosphere Discuss., doi:10.5194/tc-2016-115,2016 Manuscript under review for TC (discussion: open, 0 comments) We present an approach of satellite remote sensing to derive a continuous long term and stable data record of the near-surface freeze/thaw cycle over the permafrost and seasonally frozen ground. We find that the distribution of the frost days and its trend variations are consistent with the minimum temperature anomalies. Analysis over the Qinghai-Tibetan Plateau demonstrates that the frost period is shortening slightly over the past decade, and the last frost date is advanced in most regions.

Description: Which are the highest peaks in the US Arctic? Fodar settles the debate Matt Nolan and Kit DesLauriers The Cryosphere, 10, 1245-1257, doi:10.5194/tc-10-1245-2016, 2016 We measured the heights of the five tallest peaks in the US Arctic using fodar, a new airborne photogrammetric technique using structure-from-motion software. The highest peaks are Mt Isto (2735.6 m), Mt. Hubley (2717.6 m), Mt. Chamberlin (2712.3 m), Mt. Michelson (2698.1 m), and an unnamed peak (2694.9 m). We found fodar suitable for topographic change detection on the centimeter scale in steep mountain terrain, such as for measuring snow depths.

Description: Assessment of Arctic and Antarctic Sea Ice Predictability in CMIP5 Decadal Hindcasts Chao-Yuan Yang, Jiping Liu, Yongyun Hu, Radley M. Horton, Liqi Chen, and Xiao Cheng The Cryosphere Discuss., doi:10.5194/tc-2016-97,2016 Manuscript under review for TC (discussion: open, 0 comments) This paper examines the ability of coupled global climate models to predict decadal variability of Arctic and Antarctic sea ice. We analyze decadal hindcasts/predictions of 11 CMIP5 models. Decadal hindcasts exhibit a large multi-model spread in the simulated sea ice extent, with some models deviating significantly from the observations. For the models having large biases and using full-field initialization, the predicted sea ice extent quickly drifts away from the initial constraint, deteriorating the decadal predictive skill. The anomaly correlation analysis between the decadal hindcast and observed sea ice suggests that in the Arctic, for most models, the areas showing significant predictive skill become broader associated with increasing lead times. This area expansion is largely because nearly all the models are capable of predicting the observed decreasing Arctic sea ice cover. Sea ice extent in the north Pacific has better predictive skill than that in the north Atlantic (particularly at a lead-time of 3–7 years), but there is a re-emerging predictive skill in the north Atlantic at a lead-time of 6–8 years. In contrast to the Arctic, Antarctic sea ice decadal hindcasts do not show broad predictive skill at any time scales, and there is no obvious improvement linking the areal extent of significant predictive skill to lead-time increase. This might be because nearly all the models predict a retreating Antarctic sea ice cover, opposite to the observations. For the Arctic, the predictive skill of the MMEE outperforms most models and the persistence prediction at longer time scales, which is not the case for the Antarctic.

Description: Relationships between Snowfall Densities and the Main Types of Solid Hydrometeors Deduced from Measured Size and Fall Speed, for snowpack modeling applications Masaaki Ishizaka, Hiroki Motoyoshi, Satoru Yamaguchi, Sento Nakai, Toru Shina, and Ken-ichiro Muramoto The Cryosphere Discuss., doi:10.5194/tc-2016-68,2016 Manuscript under review for TC (discussion: open, 0 comments) We measured the snowfall densities, simultaneously observing the predominant snowfall types determined by the measured size and the fall speed with CCD camera. We obtain the quantitative relationships between snowfall densities and presumed density derived from the size and mass components with CCD camera. This suggests the possibility of estimating snowfall densities from the measured size and the fall speed data, and using them as the initial densities for a snow pack in a numerical model.

Description: On the recent contribution of the Greenland ice sheet to sea level change Michiel van den Broeke, Ellyn Enderlin, Ian Howat, Peter Kuipers Munneke, Brice Noël, Willem Jan van de Berg, Erik van Meijgaard, and Bert Wouters The Cryosphere Discuss., doi:10.5194/tc-2016-123,2016 Manuscript under review for TC (discussion: open, 0 comments) We present recent (1958–2015) mass balance time series for the Greenland ice sheet. We show that recent mass loss is caused by a combination of increased surface meltwater runoff and solid ice discharge. Most meltwater above 2000 m a.s.l. refreezes in the cold firn and does not leave the ice sheet, but this goes at the expense of firn heating and densifying. In spite of a temporary rebound in 2013, it appears that the ice sheet remains in a state of persistent mass loss

Description: Improving satellite-retrieved surface radiative fluxes in polar regions using a smart sampling approach Kristof Van Tricht, Stef Lhermitte, Irina V. Gorodetskaya, and Nicole P. M. van Lipzig The Cryosphere Discuss., doi:10.5194/tc-2016-103,2016 Manuscript under review for TC (discussion: open, 0 comments) Despite the crucial role of polar regions in the global climate system, the limited availability of observations on the ground hampers a detailed understanding of their energy budget. Here we develop a method to use satellites to fill these observational gaps. We show that by sampling satellite observations in a smart way, coverage is greatly enhanced. We conclude that this method might help improving our understanding of the polar energy budget, and ultimately its effects in the global climate.

Description: Reconstructing the mass balance of Brewster Glacier, New Zealand, using MODIS-derived glacier-wide albedo Pascal Sirguey, Holly Still, Nicolas J. Cullen, Marie Dumont, Yves Arnaud, and Jonathan P. Conway The Cryosphere Discuss., doi:10.5194/tc-2016-98,2016 Manuscript under review for TC (discussion: open, 0 comments) 14 years of satellite observations are used to monitor the albedo of Brewster Glacier, New Zealand and estimate annual and seasonal balances. This confirms the governing role of the summer balance in the annual balance and allows the reconstruction of the annual balance back to 1977 using a photographic record of the snowline. The longest mass balance record for a New Zealand glacier shows that negative balances after 2008 yielded a loss of 35 % of the gain accumulated over the previous 30 years.

Description: Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics Steven J. Phipps, Christopher J. Fogwill, and Christian S. M. Turney The Cryosphere Discuss., doi:10.5194/tc-2016-111,2016 Manuscript under review for TC (discussion: open, 0 comments) We explore the effects of melting of the East Antarctic Ice Sheet on the Southern Ocean. Using a climate model, we find that melting changes the ocean circulation and causes warming of more than 1 ºC at depth. We also discover the potential existence of a "domino effect", whereby the initial warming spreads westwards around the Antarctic continent. Melting of just one sector could therefore destabilise the wider Antarctic Ice Sheet, leading to substantial increases in global sea level.

Description: Modeling debris-covered glaciers: response to steady debris deposition Leif S. Anderson and Robert S. Anderson The Cryosphere, 10, 1105-1124, doi:10.5194/tc-10-1105-2016, 2016 Mountains erode and shed rocks down slope. When these rocks (debris) fall on glacier ice they can suppress ice melt. By protecting glaciers from melt, debris can make glaciers extend to lower elevations. Using mathematical models of glaciers and debris deposition, we find that debris can more than double the length of glaciers. The amount of debris deposited on the glacier, which scales with mountain height and steepness, is the most important control on debris-covered glacier length and volume.

Description: Estimating the extent of Antarctic summer sea ice during the Heroic Age of Exploration Tom Edinburgh and Jonathan J. Day The Cryosphere Discuss., doi:10.5194/tc-2016-90,2016 Manuscript under review for TC (discussion: open, 0 comments) A lack of sea ice data in the pre-satellite period limits our ability to quantify the sensitivity of sea ice to climate change and validate climate models. This paper analyses direct observations of the nature of sea ice as recorded in ship logbooks during the Heroic Age of Antarctic exploration for the first time and shows that the summer ice edge was up to 1.7° further north in the Weddell Sea during this period but that ice conditions were comparable to the present day in other sectors.

Description: Glacier melting and precipitation trends detected by surface area changes in Himalayan ponds Franco Salerno, Sudeep Thakuri, Nicolas Guyennon, Gaetano Viviano, and Gianni Tartari The Cryosphere Discuss., doi:10.5194/tc-2016-39,2016 Manuscript under review for TC (discussion: open, 0 comments) This contribution shows that the surface area variations of unconnected glacial ponds, i.e., ponds not directly connected to glaciers, can be considered suitable proxies for detecting changes in the main hydrological components of the water balance on the south side of Mt. Everest.

Description: Brief Communication: Twelve-year cyclic surging episodes at Donjek Glacier in Yukon, Canada Takahiro Abe, Masato Furuya, and Daiki Sakakibara The Cryosphere, 10, 1427-1432, doi:10.5194/tc-10-1427-2016, 2016 We identified 12-year cyclic surging episodes at Donjek Glacier in Yukon, Canada. The surging area is limited within the ~20km section from the terminus, originating in an area where the flow width significantly narrows downstream. Our results suggest strong control of the valley constriction on the surge dynamics.

Description: Strain localisation and dynamic recrystallisation in the ice-air aggregate: A numerical study Florian Steinbach, Paul D. Bons, Albert Griera, Daniela Jansen, Maria-Gema Llorens, Jens Roessiger, and Ilka Weikusat The Cryosphere Discuss., doi:10.5194/tc-2016-167,2016 Manuscript under review for TC (discussion: open, 0 comments) How glaciers or ice sheets flow is a result of microscopic processes controlled by the properties of individual ice crystals. We performed computer simulations on these processes and the effect of air bubbles between crystals. The simulations show that small scale ice deformation is locally stronger than in other regions, which is enhanced by bubbles. This causes the ice crystals to recrystallise and change their properties in a way that potentially also affects the large scale flow properties.

Description: Glacier melting and precipitation trends detected by surface area changes in Himalayan ponds Franco Salerno, Sudeep Thakuri, Nicolas Guyennon, Gaetano Viviano, and Gianni Tartari The Cryosphere, 10, 1433-1448, doi:10.5194/tc-10-1433-2016, 2016 This contribution shows that the surface area variations of unconnected glacial ponds, i.e. ponds not directly connected to glacier ice, can be considered as suitable proxies for detecting past changes in the main hydrological components of the water balance (glacier melt, precipitation, evaporation) on the south side of Mt Everest.

Description: Landfast ice thickness in the Canadian Arctic Archipelago from observations and models Stephen E. L. Howell, Frédéric Laliberté, Ron Kwok, Chris Derksen, and Joshua King The Cryosphere, 10, 1463-1475, doi:10.5194/tc-10-1463-2016, 2016 The Canadian Ice Service record of observed landfast ice and snow thickness represents one of the longest in the Arctic that spans over 5 decades. We analyze this record to report on long-term trends and variability of ice and snow thickness within the Canadian Arctic Archipelago (CAA). Results indicate a thinning of ice at several sites in the CAA. State-of-the-art climate models still have difficultly capturing observed ice thickness values in the CAA and should be used with caution.

Description: Microstructure representation of snow in coupled snowpack and microwave emission models Melody Sandells, Richard Essery, Nick Rutter, Leanne Wake, Leena Leppänen, and Juha Lemmetyinen The Cryosphere Discuss., doi:10.5194/tc-2016-181,2016 Manuscript under review for TC (discussion: open, 0 comments) This study looks at a wide range of options for simulating sensor signals for satellite monitoring of water stored as snow, though an ensemble of 1323 coupled snow evolution and microwave scattering models. The greatest improvements will be made with better computer simulations of how the snow microstructure changes, followed by how the microstructure scatters radiation at microwave frequencies. Snow compaction should also be considered in systems to monitor snow mass from space.

Description: Wave climate in the Arctic 1992–2014: seasonality and trends Justin E. Stopa, Fabrice Ardhuin, and Fanny Girard-Ardhuin The Cryosphere, 10, 1605-1629, doi:10.5194/tc-10-1605-2016, 2016 Satellite observations show the Arctic sea ice has decreased the last 30 years. From our wave model hindcast and satellite altimeter datasets we observe profound increasing wave heights, which are caused by the loss of sea ice and not the driving winds. If ice-free conditions persist later into fall, then regions like the Beaufort–Chukchi Sea will be prone to developing larger waves since the driving winds are strong this time of year.

Description: Correction of albedo measurements due to unknown geometry The Cryosphere Discussions, 9, 2709-2744, 2015 Author(s): U. Weiser, M. Olefs, W. Schöner, G. Weyss, and B. Hynek The diurnal albedo variation of glaciers on clear sky days can be relatively high due to geometric effects induced by tilt errors. In the present paper, these tilt errors of albedo measurements are corrected in cases where tilts of both, the sensors and the slopes are not accurately measured. For this method of correction, a nearby reference measurement with a horizontally levelled sensor is needed to determine atmospheric parameters. Based on that a model is developed that is fitted to the measured data to determine tilts and directions of sensors and slopes, which vary daily due to changing atmospheric conditions and snow cover. Once these parameters are determined, the albedo, the radiative balance and the energy balance can be corrected. The differences between measured and corrected values show an obvious under- or overestimation of albedo, depending on the direction of the slope. It is also demonstrated that the difference between measured and corrected albedo is highest for high solar zenith angles.

Description: Verification of the multi-layer SNOWPACK model with different water transport schemes The Cryosphere Discussions, 9, 2655-2707, 2015 Author(s): N. Wever, L. Schmid, A. Heilig, O. Eisen, C. Fierz, and M. Lehning The widely-used detailed SNOWPACK model has undergone constant development over the years. A notable recent extension is the introduction of a Richards Equation (RE) solver as an alternative for the bucket-type approach for describing water transport in the snow and soil layers. In addition, continuous updates of snow settling and new snow density parametrisations have changed model behaviour. This study presents a detailed evaluation of model performance against a comprehensive multi-year data set from Weissfluhjoch near Davos, Switzerland. The data set is collected by automatic meteorological and snowpack measurements and manual snow profiles. During the main winter season, snow height (RMSE:

Description: Satellite observations of changes in snow-covered land surface albedo during spring in the Northern Hemisphere The Cryosphere Discussions, 9, 2745-2782, 2015 Author(s): K. Atlaskina, F. Berninger, and G. de Leeuw Thirteen years of MODIS surface albedo data for the Northern Hemisphere during the spring months (March–May) were analysed to determine temporal and spatial changes over snow-covered land surfaces. Tendencies in land surface albedo change north of 50° N were analysed using data on snow cover fraction, air temperature, vegetation index and precipitation. To this end, the study domain was divided into six smaller areas, based on their geographical position and climate similarity. Strong differences were observed between these areas. As expected, snow cover fraction (SCF) has a strong influence on the albedo in the study area and can explain 56% of variation of albedo in March, 76% in April and 92% in May. Therefore the effects of other parameters were investigated only for areas with 100% SCF. The second largest driver for snow-covered land surface albedo changes is the air temperature when it exceeds −15 °C. At monthly mean air temperatures below this value no albedo changes are observed. Enhanced vegetation index (EVI) and precipitation amount and frequency were independently examined as possible candidates to explain observed changes in albedo for areas with 100% SCF. Amount and frequency of precipitation were identified to influence the albedo over some areas in Eurasia and North America, but no clear effects were observed in other areas. EVI is positively correlated with albedo in Chukotka Peninsula and negatively in Eastern Siberia. For other regions the spatial variability of the correlation fields is too high to reach any conclusions.

Description: Interaction of katabatic wind and local surface mass balance at Scharffenbergbotnen Blue Ice Area, Antarctica The Cryosphere Discussions, 9, 2231-2257, 2015 Author(s): T. Zwinger, T. Malm, M. Schäfer, R. Stenberg, and J. C. Moore We model the wind causing the formation of a blue ice area in Scharffenbergbotnen valley, Antarctica, using the finite element code Elmer. The high resolution numerical simulations of the local wind flow from katabatic wind fronts show highly spatially variable wind impact patterns and good congruence between places of enhanced wind-impact and the blue ice area. The results were fortuitously confirmed by the destruction of a field camp located in a high wind speed area and its subsequent redistribution to low velocity areas. In addition we perform wind simulations on an altered glacier geometry that resembles the thicker ice cover at the Late Glacial Maximum (LGM). These simulations indicate that the pronounced spatial wind-impact patterns depend on present day geometry and did not occur during the LGM. This leads to the conclusion that the formation of the blue ice area that is situated more inside the valley of Scharffenbergbotnen started only after the lowering of the ice surface, later than the LGM. Experiments with smoothed surface topography suggest that detailed positions of the high wind regions and hence individual blue ice fields, may have varied as the ice sheet lowered. The experiments and the field observations are consistent with localized violent katabatic events, rather than synoptic scale storms, playing the dominant role in the formation and maintenance of this, and perhaps many blue ice areas.

Description: Impact of model developments on present and future simulations of permafrost in a global land-surface model The Cryosphere Discussions, 9, 1965-2012, 2015 Author(s): S. E. Chadburn, E. J. Burke, R. L. H. Essery, J. Boike, M. Langer, M. Heikenfeld, P. M. Cox, and P. Friedlingstein There is a large amount of organic carbon stored in permafrost in the northern high latitudes, which may become vulnerable to microbial decomposition under future climate warming. In order to estimate this potential carbon-climate feedback it is necessary to correctly simulate the physical dynamics of permafrost within global Earth System Models (ESMs) and to determine the rate at which it will thaw. Additional new processes within JULES, the land surface scheme of the UK ESM (UKESM), include a representation of organic soils, moss and bedrock, and a modification to the snow scheme. The impact of a higher vertical soil resolution and deeper soil column is also considered. Evaluation against a large group of sites shows the annual cycle of soil temperatures is approximately 25 % too large in the standard JULES version, but this error is corrected by the model improvements, in particular by deeper soil, organic soils, moss and the modified snow scheme. Comparing with active layer monitoring sites shows that the active layer is on average just over 1 m too deep in the standard model version, and this bias is reduced by 70 cm in the improved version. Increasing the soil vertical resolution allows the full range of active layer depths to be simulated, where by contrast with a poorly resolved soil, at least 50% of the permafrost area has a maximum thaw depth at the centre of the bottom soil layer. Thus all the model modifications are seen to improve the permafrost simulations. Historical permafrost area corresponds fairly well to observations in all simulations, covering an area between 14–19 million km 2 . Simulations under two future climate scenarios show a reduced sensitivity of permafrost degradation to temperature, with the near-surface permafrost lost per degree of warming reduced from 1.5 million km 2 °C −1 in the standard version of JULES to between 1.1 and 1.2 million km 2 °C −1 in the new model version. However, the near-surface permafrost area is still projected to approximately half by the end of the 21st century under the RCP8.5 scenario.

Description: Revealing glacier flow and surge dynamics from animated satellite image sequences: examples from the Karakoram The Cryosphere Discussions, 9, 2597-2623, 2015 Author(s): F. Paul Although animated images are very popular on the Internet, they have so far found only limited use for glaciological applications. With long time-series of satellite images becoming increasingly available and glaciers being well recognized for their rapid changes and variable flow dynamics, animated sequences of multiple satellite images reveal glacier dynamics in a time-lapse mode, making the otherwise slow changes of glacier movement visible and understandable for a wide public. For this study animated image sequences were created from freely available image quick-looks of orthorectified Landsat scenes for four regions in the central Karakoram mountain range. The animations play automatically in a web-browser and might help to demonstrate glacier flow dynamics for educational purposes. The animations revealed highly complex patterns of glacier flow and surge dynamics over a 15-year time period (1998–2013). In contrast to other regions, surging glaciers in the Karakoram are often small (around 10 km 2 ), steep, debris free, and advance for several years at comparably low annual rates (a few hundred m a −1 ). The advance periods of individual glaciers are generally out of phase, indicating a limited climatic control on their dynamics. On the other hand, nearly all other glaciers in the region are either stable or slightly advancing, indicating balanced or even positive mass budgets over the past few years to decades.

Description: Simulated high-latitude soil thermal dynamics during the past four decades The Cryosphere Discussions, 9, 2301-2337, 2015 Author(s): S. Peng, P. Ciais, G. Krinner, T. Wang, I. Gouttevin, A. D. McGuire, D. Lawrence, E. Burke, X. Chen, C. Delire, C. Koven, A. MacDougall, A. Rinke, K. Saito, W. Zhang, R. Alkama, T. J. Bohn, B. Decharme, T. Hajima, D. Ji, D. P. Lettenmaier, P. A. Miller, J. C. Moore, B. Smith, and T. Sueyoshi Soil temperature ( T s ) change is a key indicator of the dynamics of permafrost. On seasonal and inter-annual time scales, the variability of T s determines the active layer depth, which regulates hydrological soil properties and biogeochemical processes. On the multi-decadal scale, increasing T s not only drives permafrost thaw/retreat, but can also trigger and accelerate the decomposition of soil organic carbon. The magnitude of permafrost carbon feedbacks is thus closely linked to the rate of change of soil thermal regimes. In this study, we used nine process-based ecosystem models with permafrost processes, all forced by different observation-based climate forcing during the period 1960–2000, to characterize the warming rate of T s in permafrost regions. There is a large spread of T s trends at 20 cm depth across the models, with trend values ranging from 0.010 ± 0.003 to 0.031 ± 0.005 °C yr −1 . Most models show smaller increase in T s with increasing depth. Air temperature ( T a ) and longwave downward radiation (LWDR) are the main drivers of T s trends, but their relative contributions differ amongst the models. Different trends of LWDR used in the forcing of models can explain 61% of their differences in T s trends, while trends of T a only explain 5% of the differences in T s trends. Uncertain climate forcing contributes a larger uncertainty in T s trends (0.021 ± 0.008 °C yr −1 , mean ± SD) than the uncertainty of model structure (0.012 ± 0.001 °C yr −1 ), diagnosed from the range of response between different models, normalized to the same forcing. In addition, the loss rate of near-surface permafrost area, defined as total area where the maximum seasonal active layer thickness (ALT) is less than 3 m loss rate is found to be significantly correlated with the magnitude of the trends of T s at 1 m depth across the models ( R = −0.85, P = 0.003), but not with the initial total near-surface permafrost area ( R = −0.30, P = 0.438). The sensitivity of the total boreal near-surface permafrost area to T s at 1 m, is estimated to be of −2.80 ± 0.67 million km 2 °C −1 . Finally, by using two long-term LWDR datasets and relationships between trends of LWDR and T s across models, we infer an observation-constrained total boreal near-surface permafrost area decrease comprised between 39 ± 14 × 10 3 and 75 ± 14 × 10 3 km 2 yr −1 from 1960 to 2000. This corresponds to 9–18% degradation of the current permafrost area.

Description: Effects of pan-Arctic snow cover and air temperature changes on soil heat content Xiaogang Shi, Tara J. Troy, and Dennis P. Lettenmaier The Cryosphere Discuss., doi:10.5194/tc-2016-70,2016 Manuscript under review for TC (discussion: open, 0 comments) Soil heat content (SHC) provides an estimate of the integrated effect of changes in the land surface energy balance. It considers the specific heat capacity, soil temperature, and phase changes of soil moisture as a function of depth. In contrast, soil temperature provides a much more limited view of land surface energy flux changes. This is particularly important at high latitudes, which have and are undergoing surface energy flux changes as a result of changes in seasonal variations of snow cover extent (SCE) and hence surface albedo changes, among other factors. Using the Variable Infiltration Capacity (VIC) land surface model forced with gridded climate observations, we simulate spatial and temporal variations of SCE and SHC over the pan-Arctic land region for the last half-century. On the basis of the SCE trends derived from NOAA satellite observations in 5° latitude bands from April through June for the period 1972–2006, we define a snow covered sensitivity zone (SCSZ), a snow covered non-sensitivity zone (SCNZ), and a non-snow covered zone (NSCZ) for North America and Eurasia. We then explore long-term trends in SHC, SCE, and surface air temperature (SAT) and their corresponding correlations in NSCZ, SCSZ and SCNZ for both North America and Eurasia. We find that snow cover downtrends have a significant impact on SHC changes in SCSZ for North America and Eurasia from April through June. SHC changes in the SCSZ over North America are dominated by downtrends in SCE rather than increasing SAT. Over Eurasia, increasing SAT more strongly affects SHC than in North America. Overall, increasing SAT during late spring and early summer is the dominant factor that has resulted in SHC changes over the pan-Arctic domain, whereas reduced SCE plays a secondary role that is only important in the SCSZ.

Description: Multi-level spatiotemporal validation of snow/ice mass balance and runoff modeling in glacierized catchments Florian Hanzer, Kay Helfricht, Thomas Marke, and Ulrich Strasser The Cryosphere Discuss., doi:10.5194/tc-2016-58,2016 Manuscript under review for TC (discussion: open, 0 comments) The hydroclimatological model AMUNDSEN is set up to simulate snow and ice accumulation, ablation, and runoff for a study region in the Ötztal Alps (Austria) in the period 1997–2013. A new validation concept is introduced and demonstrated by evaluating the model performance using several independent data sets, e.g. snow depth measurements, satellite-derived snow maps, lidar data, glacier mass balances, and runoff measurements.

Description: Brief communication: The challenge and benefit of using sea ice concentration satellite data products with uncertainty estimates in summer sea ice data assimilation Qinghua Yang, Martin Losch, Svetlana N. Losa, Thomas Jung, Lars Nerger, and Thomas Lavergne The Cryosphere, 10, 761-774, doi:10.5194/tc-10-761-2016, 2016 We assimilate the summer SICCI sea ice concentration data with an ensemble-based Kalman Filter. Comparing with the approach using a constant data uncertainty, the sea ice concentration estimates are further improved when the SICCI-provided uncertainty are taken into account, but the sea ice thickness cannot be improved. We find the data assimilation system cannot give a reasonable ensemble spread of sea ice concentration and thickness if the provided uncertainty are directly used.

Description: Metamorphism during temperature gradient with undersaturated advective airflow in a snow sample Pirmin Philipp Ebner, Martin Schneebeli, and Aldo Steinfeld The Cryosphere, 10, 791-797, doi:10.5194/tc-10-791-2016, 2016 Changes of the porous ice structure were observed in a snow sample. Sublimation occurred due to the slight undersaturation of the incoming air into the warmer ice matrix. Diffusion of water vapor opposite to the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible, leading to a constant porosity profile. However, the strong recrystallization of water molecules in snow may impact its isotopic or chemical content.

Description: Quantifying ice loss in the eastern Himalayas since 1974 using declassified spy satellite imagery Joshua M. Maurer, Summer B. Rupper, and Joerg M. Schaefer The Cryosphere Discuss., doi:10.5194/tc-2016-48,2016 Manuscript under review for TC (discussion: open, 0 comments) Here we utilize declassified spy satellite imagery to quantify ice volume loss of glaciers in the eastern Himalayas over approximately the last three decades. Clean-ice and debris-covered glaciers show similar magnitudes of ice loss, while calving glaciers are contributing a disproportionately large amount to total ice loss. Results highlight important physical processes affecting the ice mass budget and associated water resources in the Himalayas.

Description: Brief Communication: Evidence of a developing Polynya off Commonwealth Bay, East Antarctica, triggered by grounding of iceberg Christopher J. Fogwill, Erik van Sebille, Eva A. Cougnon, Chris S. M. Turney, Steve R. Rintoul, Graeme F. Clark, E. M. Marzinelli, Eleanor B. Rainsley, and Lionel Carter The Cryosphere Discuss., doi:10.5194/tc-2016-19,2016 Manuscript under review for TC (discussion: open, 0 comments) Here we report new data from in situ oceanographic surveys and high-resolution ocean modelling experiments in the Commonwealth Bay region of East Antarctica, where in 2010 there was a major reconfiguration of the regional ice-scape due to the collision of the 97 km long iceberg B09B with the Mertz Glacier Tongue. Here we compare post-calving observations with high-resolution ocean modelling which suggest that this reconfiguration has led to the development of a new polynya off Commonwealth Bay.

Description: A fully automated methodology for differentiating rock from snow, clouds and sea in Antarctica from Landsat imagery: A new rock outcrop map and area estimation for the entire Antarctic continent Alex Burton-Johnson, Martin Black, Peter T. Fretwell, and Joseph Kaluza-Gilbert The Cryosphere Discuss., doi:10.5194/tc-2016-56,2016 Manuscript under review for TC (discussion: open, 0 comments) Differentiating exposed rock from snow and ice is a particular problem in Antarctica where extensive cloud cover and widespread shaded regions lead to classification errors. The existing rock outcrop dataset has significant georeferencing issues including overestimation and generalisation of rock exposure areas. The most commonly used method for automated rock and snow differentiation, the Normalised Difference Snow Index (NDSI), has difficulty differentiating rock and snow in Antarctica due to misclassification of shaded pixels and cannot differentiate illuminated rock from clouds. This study presents a new method for identifying rock exposures using Landsat 8 data. This is the first fully automated methodology for snow and rock differentiation that excludes areas of snow (both illuminated and shaded), clouds and liquid water whilst identifying both sunlit and shaded rock, achieving higher and more consistent accuracies than alternative data and methods such as the NDSI. The new methodology has been applied to the whole Antarctic continent (north of 82°40' S) using Landsat 8 data to produce a new rock outcrop dataset for Antarctica. The new data (merged with existing data south of 82°40' S) reveals that exposed rock forms 0.18 % of the total land area of Antarctica; half of previous estimates.

Description: Thinning of the Quelccaya Ice Cap over the last thirty years C. D. Chadwell, D. R. Hardy, C. Braun, H. H. Brecher, and L. G. Thompson The Cryosphere Discuss., doi:10.5194/tc-2016-40,2016 Manuscript under review for TC (discussion: open, 0 comments) The Quelccaya Ice Cap in southern Peru is the largest tropical glacier on earth. Aerial photographs and satellite images have documented retreat of its margins since 1963. While thinning of the glacier has been observed at its margins, here we document for the first time that the glacier has thinned all over during the past 30 years, including the elevation lowering 4.4 m within the highest regions of the glacier above ~ 5400 m a.s.l., where snow accumulation feeds the glacier.

Description: A Retrospective, Iterative, Geometry-Based (RIGB) tilt-correction method for radiation observed by automatic weather stations on snow-covered surfaces: application to Greenland Wenshan Wang, Charles S. Zender, Dirk van As, Paul C. J. P. Smeets, and Michiel R. van den Broeke The Cryosphere, 10, 727-741, doi:10.5194/tc-10-727-2016, 2016 We identify and correct station-tilt-induced biases in insolation observed by automatic weather stations on the Greenland Ice Sheet. Without tilt correction, only 40 % of clear days have the correct solar noon time (±0.5 h). The largest hourly bias exceeds 20 %. We estimate the tilt angles based on solar geometric relationship between insolation observed on horizontal surfaces and that on tilted surfaces, and produce shortwave radiation and albedo that agree better with independent data sets.

Description: Landfast ice thickness in the Canadian Arctic Archipelago from Observations and Models Stephen E. L. Howell, Frédéric Laliberté, Ron Kwok, Chris Derksen, and Joshua King The Cryosphere Discuss., doi:10.5194/tc-2016-71,2016 Manuscript under review for TC (discussion: open, 0 comments) The Canadian Ice Service record of observed landfast ice and snow thickness represents one of the longest in the Arctic that spans over five decades. We analyze this record to report on long term trends and variability of ice and snow thickness within the Canadian Arctic Archipelago (CAA). Results indicate a thinning of ice at several sites in the CAA. State-of-the-art climate models still have difficultly capturing observed ice thickness values in the CAA and should be used with caution.

Description: Spatio-temporal evolution of snow depth observed by time-lapse laser scanning in the Alps and in Antarctica Ghislain Picard, Laurent Arnaud, Jean-Michel Panel, and Samuel Morin The Cryosphere Discuss., doi:10.5194/tc-2016-67,2016 Manuscript under review for TC (discussion: open, 0 comments) A cost-effective automatic laserscan has been built to measure snow depth spatio-temporal variations. Deployed in the Alps and in Dome C (Antarctica) two devices acquired daily scans covering a surface area of 100–150 m 2 . The precision and long term stability of the measurements are about 1 cm and the accuracy is better than 5 cm. These high performances are particularly suited at Dome C where it was possible to reveal that most of the accumulation in year 2015 stems from a single event.

Description: The influence of a model subglacial lake on ice dynamics and internal layering Eythor Gudlaugsson, Angelika Humbert, Thomas Kleiner, Jack Kohler, and Karin Andreassen The Cryosphere, 10, 751-760, doi:10.5194/tc-10-751-2016, 2016 This paper explores the influence of a subglacial lake on ice dynamics and internal layers by means of numerical modelling as well as simulating the effect of a subglacial drainage event on isochrones. We provide an explanation for characteristic dip and ridge features found at the edges of many subglacial lakes and conclude that draining lakes can result in travelling waves at depth within isochrones, thus indicating the possibility of detecting past drainage events with ice penetrating radar.

Description: On retrieving sea ice freeboard from ICESat laser altimeter Kirill Khvorostovsky and Pierre Rampal The Cryosphere Discuss., doi:10.5194/tc-2016-50,2016 Manuscript under review for TC (discussion: open, 0 comments) We analyse two methods of freeboard retrieval from ICESat satellite data that were used to derived the two widely used Arctic sea ice thickness products. We show that although different factors results in significant local differences between freeboards, they are roughly compensating each other with respect to overall freeboard estimation. Thus the difference found between the sea ice thickness datasets should be attributed to different parameters used in the freeboard-to-thickness conversion.

Description: Estimating supraglacial lake depth in western Greenland using Landsat 8 and comparison with other multispectral methods The Cryosphere Discussions, 9, 3257-3292, 2015 Author(s): A. Pope, T. A. Scambos, M. Moussavi, M. Tedesco, M. Willis, D. Shean, and S. Grigsby Liquid water stored on the surface of ice sheets and glaciers impacts surface mass balance, ice dynamics, and heat transport. Supraglacial lakes, therefore, play a significant role in ice sheet behavior as a surface expression of the glacial hydrological system. Multispectral remote sensing can be used to detect supraglacial lakes and estimate their depth and area. In this study, we use in situ spectral and bathymetric data to assess lake depth retrieval using the recently launched Landsat 8 Operational Land Imager (OLI). We also extend our analysis to other multispectral sensors to evaluate their performance with similar methods. Digital elevation models derived from WorldView stereo imagery (pre-lake filling and post-drainage) are used to validate spectrally derived depths, combined with a lake edge determination from imagery. The optimal supraglacial lake depth retrieval is a physically based single-band model applied to two OLI bands independently (red and panchromatic) that are then averaged together. When OLI- and WorldView-derived depths are differenced, they yield a mean and standard deviation of 0.0 ± 1.6 m. This method is then applied to OLI data for the Sermeq Kujalleq (Jakobshavn Isbrae) region of Greenland to study the spatial and intra-seasonal variability of supraglacial lakes during summer 2014. We also give coefficients for estimating supraglacial lake depth using a similar method as OLI with other multispectral sensors.