ALBERT

Beschreibung: Impact of icebergs on net primary productivity in the Southern Ocean Shuang-Ye Wu and Shugui Hou The Cryosphere, 11, 707-722, doi:10.5194/tc-11-707-2017, 2017 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 is associated with elevated levels of ocean productivity, particularly in iron-deficient regions. This impact could serve as a negative feedback to the climate system.

Beschreibung: Bromine, iodine and sodium in surface snow along the 2013 Talos Dome–GV7 traverse (northern Victoria Land, East Antarctica) Niccolò Maffezzoli, Andrea Spolaor, Carlo Barbante, Michele Bertò, Massimo Frezzotti, and Paul Vallelonga The Cryosphere, 11, 693-705, doi:10.5194/tc-11-693-2017, 2017 Sea ice is a crucial parameter within Earth's climate system. Understanding its dynamics and its response to other climatic variables is therefore of primary importance in view of a warming climate and sea ice decline. In this work we investigate some features of a chemical parameter in ice cores, bromine enrichment, which is linked to sea ice and can therefore be used to reconstruct sea ice in the past.

Beschreibung: Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard Johannes Jakob Fürst, Fabien Gillet-Chaulet, Toby J. Benham, Julian A. Dowdeswell, Mariusz Grabiec, Francisco Navarro, Rickard Pettersson, Geir Moholdt, Christopher Nuth, Björn Sass, Kjetil Aas, Xavier Fettweis, Charlotte Lang, Thorsten Seehaus, and Matthias Braun The Cryosphere Discuss., doi:10.5194/tc-2017-30,2017 Manuscript under review for TC (discussion: open, 0 comments) For the large majority of glaciers and ice caps, there is no information on the thickness of the ice cover. Any attempt to predict glacier demise under climatic warming and to estimate the future contribution to sea-level rise is limited as long as the glacier thickness is not well constrained. Here, we present a two-step mass-conservation approach for mapping ice thickness. Measurements are naturally reproduced. The reliability is readily assessible from a complementary map of error estimates.

Beschreibung: Ice-shelf damming in the glacial Arctic Ocean: dynamical regimes of a basin-covering kilometre thick ice shelf Johan Nilsson, Martin Jakobsson, Chris Borstad, Nina Kirchner, Göran Björk, Raymond T. Pierrehumbert, and Christian Stranne The Cryosphere Discuss., doi:10.5194/tc-2017-37,2017 Manuscript under review for TC (discussion: open, 0 comments) Recent data suggest that a one-kilometre thick ice shelf extended over the glacial Arctic Ocean during MIS 6, about 140 000 years ago. Here, we theoretically analyse the development and equilibrium features of such an ice shelf. The ice shelf was effectively dammed by the Fram Strait and the mean ice-shelf thickness was controlled primarily by the horizontally-integrated mass balance. Our results can aid to resolve some outstanding questions of the state of the glacial Arctic Ocean.

Beschreibung: Reanalysis of a 10-year record (2004–2013) of seasonal mass balances at Langenferner/Vedretta Lunga, Ortler Alps, Italy Stephan Peter Galos, Christoph Klug, Fabien Maussion, Federico Covi, Lindsey Nicholson, Lorenzo Rieg, Wolfgang Gurgiser, Thomas Mölg, and Georg Kaser The Cryosphere, 11, 1417-1439, https://doi.org/10.5194/tc-11-1417-2017, 2017 Records of glacier mass balance represent important data in climate science and their uncertainties affect calculations of sea level rise and other societally relevant environmental projections. In order to reduce and quantify uncertainties in mass balance series obtained by direct glaciological measurements, we present a detailed reanalysis workflow which was applied to the 10-year record (2004 to 2013) of seasonal mass balance of Langenferner, a small glacier in the European Eastern Alps. The approach involves a methodological homogenization of available point values and the creation of pseudo-observations of point mass balance for years and locations without measurements by the application of a process-based model constrained by snow line observations. We examine the uncertainties related to the extrapolation of point data using a variety of methods and consequently present a more rigorous uncertainty assessment than is usually reported in the literature. Results reveal that the reanalyzed balance record considerably differs from the original one mainly for the first half of the observation period. For annual balances these misfits reach the order of  〉 300 kg m −2 and could primarily be attributed to a lack of measurements in the upper glacier part and to the use of outdated glacier outlines. For winter balances respective differences are smaller (up to 233 kg m −2 ) and they originate primarily from methodological inhomogeneities in the original series. Remaining random uncertainties in the reanalyzed series are mainly determined by the extrapolation of point data to the glacier scale and are on the order of ±79 kg m −2 for annual and ±52 kg m −2 for winter balances with values for single years/seasons reaching ±136 kg m −2 . A comparison of the glaciological results to those obtained by the geodetic method for the period 2005 to 2013 based on airborne laser-scanning data reveals that no significant bias of the reanalyzed record is detectable.

Beschreibung: Models for polythermal ice sheets and glaciers Ian J. Hewitt and Christian Schoof The Cryosphere, 11, 541-551, doi:10.5194/tc-11-541-2017, 2017 Many glaciers contain ice both below and at the melting temperature. Predicting the evolution of temperature and water content in such ice masses is important because they exert a strong control on the flow of the ice. We present two new models to calculate these quantities, demonstrate a number of example numerical calculations, and compare the results with existing methods. The novelty of the new methods is the inclusion of gravity-driven water transport within the ice.

Beschreibung: Experimental observation of transient δ 18 O interaction between snow and advective airflow under various temperature gradient conditions Pirmin P. Ebner, Hans Christian Steen-Larsen, Barbara Stenni, Martin Schneebeli, and Aldo Steinfeld The Cryosphere Discuss., doi:10.5194/tc-2017-16,2017 Manuscript under review for TC (discussion: open, 0 comments) Stable water isotopes (δ 18 O) obtained from snow and ice samples from polar regions are used to reconstruct past climate variability. We present an experimental study on the effect on the snow isotopic composition by airflow through a snowpack in controlled laboratory conditions. The disequilibrium between snow and vapor isotopes changed the isotopic content of the snow. These measurements suggest that the history of metamorphism affects the snow isotopic composition.

Beschreibung: Distinguishing between old and modern permafrost sources 1 with compound-specific δ 2 H analysis Jorien E. Vonk, Tommaso Tesi, Lisa Bröder, Henry Holmstrand, Gustaf Hugelius, August Andersson, Oleg Dudarev, Igor Semiletov, and Örjan Gustafsson The Cryosphere Discuss., doi:10.5194/tc-2017-17,2017 Manuscript under review for TC (discussion: open, 0 comments) Pleistocene ice complex permafrost deposits contain roughly a quarter of the organic carbon (OC) stored in permafrost terrain. When permafrost thaws, its OC is remobilized into the (aquatic) environment where it is available for degradation, transport or burial. Aquatic or coastal environments contain sedimentary reservoirs that can serve as archives of past climatic change. As permafrost thaw is increasing throughout the Arctic, these reservoirs are important locations to assess the fate of remobilized permafrost OC. We here present compound-specific deuterium (δ 2 H) analysis on leaf waxes as a tool to distinguish between OC released from thawing Pleistocene permafrost (Ice Complex Deposits; ICD) and from thawing Holocene permafrost (from near-surface soils). Bulk geochemistry (%OC, δ 13 C, %total nitrogen; TN) was analyzed as well as the concentrations and δ 2 H signatures of long-chain n -alkanes (C 21 to C 33 ) and mid/long-chain n -alkanoic acids (C 16 to C 30 ) extracted from both ICD-PF samples ( n  = 9) and modern vegetation/O-horizon (Topsoil-PF) samples ( n  = 9) from across the northeast Siberian Arctic. Results show that these Topsoil-PF samples have higher %OC, higher OC/TN values, and more depleted δ 13 C-OC values than ICD-PF samples, suggesting that these former samples trace a fresher soil and/or vegetation source. Median concentrations of high-molecular weight n -alkanes (sum of C 25 -C 27 -C 29 -C 31 ) were 210 ± 350 µg/gOC (median ± IQR) for Topsoil-PF and 250 ± 81 µg/gOC for ICD-PF samples. Long-chain n -alkanoic acids (sum of C 22 -C 24 -C 26 -C 28 ) were more abundant than long-chain n -alkanes, both in Topsoil-PF samples (4700 ± 3400 µg/gOC) and in ICD samples (6630 ± 3500 µg/gOC). Whereas the two investigated sources differ on the bulk geochemical level, they are, however, virtually indistinguishable when using leaf wax concentrations and ratios. However, on the molecular-isotope level, leaf wax biomarker δ 2 H values are statistically different between Topsoil-PF and ICD-PF. The mean δ 2 H value of C 29 n -alkane was −246 ± 13 ‰ (mean ± stdev) for Topsoil-PF and −280 ± 12 ‰ for ICD-PF, whereas the C31 n -alkane was −247 ± 23 ‰ for Topsoil-PF and −297 ± 15 ‰ for ICD-PF. The C 28 n -alkanoic acid δ 2 H value was −220 ± 15 ‰ for Topsoil-PF and −267 ± 16 ‰ for ICD-PF. With a dynamic isotopic range (difference between two sources) of 34 to 50 ‰, the isotopic fingerprints of individual, abundant, biomarker molecules from leaf waxes can thus serve as end-members to distinguish between these two sources. We tested this molecular δ 2 H tracer along with another source-distinguishing approach, dual-carbon (δ 13 C-δ 14 C) isotope composition of bulk OC, for a surface sediment transect in the Laptev Sea. Results show that general offshore patterns along the shelf-slope transect are similar, but the source apportionment between the approaches vary, which may highlight the advantages of either. The δ 2 H molecular approach has the advantage that it circumvents uncertainties related to a marine end-member, yet the δ 13 C-δ 14 C approach has the advantage that it represents the bulk OC fraction thereby avoiding issues related to the molecular-bulk upscaling challenge. This study indicates that the application of δ 2 H leaf wax values has potential to serve as a complementary quantitative measure of the source and differential fate of OC thawed out from different permafrost compartments.

Beschreibung: Snowfall in the Alps: Evaluation and projections based on the EURO-CORDEX regional climate models Prisco Frei, Sven Kotlarski, Mark A. Liniger, and Christoph Schär The Cryosphere Discuss., doi:10.5194/tc-2017-7,2017 Manuscript under review for TC (discussion: open, 0 comments) Snowfall is central to Alpine environments, and its future changes will be associated with pronounced impacts. We here assess future snowfall changes in the European Alps based on an ensemble of state-of-the-art regional climate model experiments and on two different greenhouse gas emission scenarios. The results reveal pronounced changes in the Alpine snowfall climate with considerable snowfall reductions at low and mid elevations, but also snowfall increases at high elevations in mid-winter.

Beschreibung: Wave-ice interactions in the neXtSIM sea-ice model Timothy D. Williams, Pierre Rampal, and Sylvain Bouillon The Cryosphere Discuss., doi:10.5194/tc-2017-24,2017 Manuscript under review for TC (discussion: open, 0 comments) As the Arctic sea ice extent drops, there is more ship traffic seeking to take advantage of this, and with it a need for better wave and sea ice forecasts. One aspect of this is the location of the sea ice edge. The waves here can be quite large, but they die away as they travel into the ice. This causes momentum to be transferred from the waves to the ice, causing ice drift. However, our study found that the effect of the wind drag had more impact on the ice edge position than the waves.

Beschreibung: Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland Graham L. Gilbert, Stefanie Cable, Christine Thiel, Hanne H. Christiansen, and Bo Elberling The Cryosphere, 11, 1265-1282, doi:10.5194/tc-11-1265-2017, 2017 We reconstruct the Holocene development of the Zackenberg River delta (northeast Greenland) using a combination of sedimentology, cryostratigraphy, and geochronology. We distinguish four major depositional environments and identify three cryofacies. We apply the principles of cryostratigraphy to infer the aggradational history of permafrost. This paper contains an archive of ground ice in epigenetic permafrost in northeast Greenland.

Beschreibung: Recent dynamic changes on Fleming Glacier after the disintegration of Wordie Ice Shelf, Antarctic Peninsula Peter Friedl, Thorsten C. Seehaus, Anja Wendt, Matthias H. Braun, and Kathrin Höppner The Cryosphere Discuss., doi:10.5194/tc-2017-91,2017 Manuscript under review for TC (discussion: open, 0 comments) Fleming Glacier is the biggest tributary glacier of the former Wordie Ice Shelf (south-western Antarctic Peninsula). Radar satellite data and airborne ice elevation measurements show that the glacier accelerated by ~ 30 % from 2007–2011 and that tinning of the glacier increased by ~ 60–70 %. This was a response to an ungrounding of the glacier tongue from the glacier bed between 2008 and 2011, which was likely crucially triggered by increased basal melt at the grounding line due to ocean warming.

Beschreibung: Evaluation of different methods to model near-surface turbulent fluxes for an alpine glacier in the Cariboo Mountains, BC, Canada Valentina Radić, Brian Menounos, Joseph Shea, Noel Fitzpatrick, Mekdes A. Tessema, and Stephen J. Déry The Cryosphere Discuss., doi:10.5194/tc-2017-80,2017 Manuscript under review for TC (discussion: open, 0 comments) Our overall goal is to improve the numerical modelling of glacier melt in order to better predict the future of glaciers in Western Canada and worldwide. Most commonly used models rely on simplifications of processes that dictate melting at a glacier surface, in particular turbulent processes of heat exchange. We compared modelled against directly measured turbulent heat fluxes at a valley glacier in British Columbia, Canada, and found that more improvements are needed in all the tested models.

Beschreibung: Calibrated cryo-cell UV-LA-ICPMS elemental concentrations from the NGRIP ice core reveal abrupt, sub-annual variability in dust across the GI-21.2 interstadial period Damiano Della Lunga, Wolfgang Müller, Sune Olander Rasmussen, Anders Svensson, and Paul Vallelonga The Cryosphere, 11, 1297-1309, https://doi.org/10.5194/tc-11-1297-2017, 2017 In our study we combined the wealth of information provided by Greenland ice cores with an ultra-high-resolution technique well known in geoscience (laser ablation). Our set-up was developed and applied to investigate the variability in concentration of ions across a rapid climatic change from the oldest part of the last glaciation, showing that concentrations drop abruptly from cold to warm periods, representing a shift in atmospheric transport that happens even faster than previously thought.

Beschreibung: Evaluation of different methods to model near-surface turbulent fluxes for an alpine glacier in the Cariboo Mountains, BC, Canada Valentina Radić, Brian Menounos, Joseph Shea, Noel Fitzpatrick, Mekdes A. Tessema, and Stephen J. Déry The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-80,2017 Manuscript under review for TC (discussion: open, 0 comments) Our overall goal is to improve the numerical modelling of glacier melt in order to better predict the future of glaciers in Western Canada and worldwide. Most commonly used models rely on simplifications of processes that dictate melting at a glacier surface, in particular turbulent processes of heat exchange. We compared modelled against directly measured turbulent heat fluxes at a valley glacier in British Columbia, Canada, and found that more improvements are needed in all the tested models.

Beschreibung: Recent dynamic changes on Fleming Glacier after the disintegration of Wordie Ice Shelf, Antarctic Peninsula Peter Friedl, Thorsten C. Seehaus, Anja Wendt, Matthias H. Braun, and Kathrin Höppner The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-91,2017 Manuscript under review for TC (discussion: open, 0 comments) Fleming Glacier is the biggest tributary glacier of the former Wordie Ice Shelf (south-western Antarctic Peninsula). Radar satellite data and airborne ice elevation measurements show that the glacier accelerated by ~ 30 % from 2007–2011 and that tinning of the glacier increased by ~ 60–70 %. This was a response to an ungrounding of the glacier tongue from the glacier bed between 2008 and 2011, which was likely crucially triggered by increased basal melt at the grounding line due to ocean warming.

Beschreibung: Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland Graham L. Gilbert, Stefanie Cable, Christine Thiel, Hanne H. Christiansen, and Bo Elberling The Cryosphere, 11, 1265-1282, https://doi.org/10.5194/tc-11-1265-2017, 2017 We reconstruct the Holocene development of the Zackenberg River delta (northeast Greenland) using a combination of sedimentology, cryostratigraphy, and geochronology. We distinguish four major depositional environments and identify three cryofacies. We apply the principles of cryostratigraphy to infer the aggradational history of permafrost. This paper contains an archive of ground ice in epigenetic permafrost in northeast Greenland.

Beschreibung: Iceberg calving of Thwaites Glacier, West Antarctica: full-Stokes modeling combined with linear elastic fracture mechanics Hongju Yu, Eric Rignot, Mathieu Morlighem, and Helene Seroussi The Cryosphere, 11, 1283-1296, https://doi.org/10.5194/tc-11-1283-2017, 2017 We combine 2-D ice flow model with linear elastic fracture mechanics (LEFM) to model the calving behavior of Thwaites Glacier, West Antarctica. We find the combination of full-Stokes (FS) model and LEFM produces crevasses that are consistent with observations. We also find that calving is enhanced with pre-existing surface crevasses, shorter ice shelves or undercut at the ice shelf front. We conclude that the FS/LEFM combination is capable of constraining crevasse formation and iceberg calving.

Beschreibung: Characterizing permafrost soil active layer dynamics and sensitivity to landscape spatial heterogeneity in Alaska Yonghong Yi, John S. Kimball, Richard Chen, Mahta Moghaddam, Rolf H. Reichle, Umakant Mishra, Donatella Zona, and Walter C. Oechel The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-87,2017 Manuscript under review for TC (discussion: open, 0 comments) An important feature of the Arctic is large spatial heterogeneity in active layer conditions, which is generally poorly represented by global models. In this study, we developed a spatially integrated modelling and analysis framework combining field observations, local scale (~ 50 m) active layer thickness (ALT) and soil moisture maps derived from airborne low frequency (L + P-band) radar measurements, and global satellite environmental observations to investigate the ALT sensitivity to recent climate trends and landscape heterogeneity in Alaska. Model simulated ALT results show good correspondence with in-situ measurements in higher permafrost probability (PP ≥ 70 %) areas (n = 33, R = 0.60, mean bias = 1.58 cm, RMSE = 20.32 cm). The model results also reveal widespread ALT deepening since 2001, with smaller ALT increases in northern Alaska (mean trend = 0.32 ± 1.18 cm yr -1 ) and much larger increases (〉 3 cm yr -1 ) across interior and southern Alaska. The positive ALT trend coincides with regional warming and a longer snow-free season (R = 0.60 ± 0.32). Uncertainty in the spatial and vertical distribution of soil organic carbon (SOC) was found to be the most important factor affecting model ALT accuracy. Potential improvements in characterizing SOC heterogeneity, including better spatial sampling of soil conditions and advances in remote sensing of SOC and soil moisture, will enable more accurate predictions of permafrost active layer conditions.

Beschreibung: Centuries of intense surface melt on Larsen C Ice Shelf Suzanne Bevan, Adrian Luckman, Bryn Hubbard, Bernd Kulessa, David Ashmore, Peter Kuipers Munneke, Martin O'Leary, Adam Booth, Heidi Sevestre, and Daniel McGrath The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-81,2017 Manuscript under review for TC (discussion: open, 0 comments) Five 90 m boreholes drilled into an Antarctic Peninsula ice shelf show units of ice that are denser than expected and must have formed from refrozen surface melt which has been buried and transported downstream. We used surface flow speeds and snow accumulation rates to work out where and when these units formed. Results show that as well as recent surface melt, a period of strong melt occurred during the 18th century. Surface melt is thought to be a factor in causing recent ice shelf break up.

Beschreibung: Modelling debris transport within glaciers by advection in a full-Stokes ice flow model Anna Wirbel, Alexander Helmut Jarosch, and Lindsey Nicholson The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-92,2017 Manuscript under review for TC (discussion: open, 0 comments) As debris cover affects the melt water production and behaviour of glaciers it is important to understand how, and over what timescales, it forms. Here we develop an advanced 3D numerical model that describes transport of sediment through a glacier to the point where it emerges at the surface. The numerical performance of the model is satisfactory and it reproduces debris structures observed within real-world glaciers, thereby offering a useful tool for future studies of debris-covered glaciers.

Beschreibung: Wave-induced stress and breaking of sea ice in a coupled hydrodynamic–discrete-element wave–ice model Agnieszka Herman The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-95,2017 Manuscript under review for TC (discussion: open, 0 comments) It is often assumed that ocean waves break sea ice into floes with sizes depending on wavelength. The results of this modeling study (in agreement with some earlier observations and models) suggest that this is not the case and instead the sizes of ice floes produced by waves depend only on ice thickness and mechanical properties. This may have important consequences for predicting sea ice response to oceanic and atmospheric forcing in regions where sea ice is influenced by waves.

Beschreibung: The modelled liquid water balance of the Greenland Ice Sheet Christian R. Steger, Carleen H. Reijmer, and Michiel R. van den Broeke The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-88,2017 Manuscript under review for TC (discussion: open, 0 comments) Mass loss from the Greenland Ice Sheet, which contributes to sea level rise, is currently dominated by surface melt and runoff. The relation between these two variables is rather uncertain due to the firn layer’s potential to buffer melt in solid (refreezing) or liquid (firn aquifer) form. To address this uncertainty, we analyse output of a numerical firn model run over 1960–2014. Results show a spatially variable response of the ice sheet to increasing melt and an upward migration of aquifers.

Beschreibung: Stable accumulation patterns around Dome C, East Antarctica, over the last glacial cycle Marie G.~P. Cavitte, Frédéric Parrenin, Catherine Ritz, Duncan A. Young, Donald D. Blankenship, Massimo Frezzotti, and Jason L. Roberts The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-71,2017 Manuscript under review for TC (discussion: open, 0 comments) We reconstruct the pattern of surface accumulation in the region around Dome C, East Antarctica, through the last glacial cycle. We use internal isochrones interpreted from ice-penetrating radar surveys and a 1D pseudo-steady ice flow model to invert for both time-averaged accumulation rates and paleoaccumulation rates. We observer that surface accumulation patterns are stable through the last 128 kyrs, this suggests a stable position of the dome throughout the last glacial cycle.

Beschreibung: Glaciological settings and recent mass balance of the Blåskimen Island in Dronning Maud Land, Antarctica Vikram Goel, Joel Brown, and Kenichi Matsuoka The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-61,2017 Manuscript under review for TC (discussion: open, 0 comments) Ice rises are locally-grounded features surrounded by ice shelves. They help stabilize the Antarctic Ice Sheet and in turn are affected by ice-sheet evolution. However, details of these influences depend on the glaciological settings of the ice rises. We report first detailed ground-based investigations from Blåskimen Island ice rise in East Antarctica. We found that the ice rise is at least ~ 600 year old and has been thickening by ~ 0.2 m per year over the past decade.

Beschreibung: Self-affine subglacial roughness: consequences for radar scattering and basal water discrimination in northern Greenland Thomas M. Jordan, Michael A. Cooper, Dustin M. Schroeder, Christopher N. Williams, John D. Paden, Martin J. Siegert, and Jonathan L. Bamber The Cryosphere, 11, 1247-1264, https://doi.org/10.5194/tc-11-1247-2017, 2017 Using radio-echo sounding data from northern Greenland, we demonstrate that subglacial roughness exhibits self-affine (fractal) scaling behaviour. This enables us to assess topographic control upon the bed-echo waveform, and explain the spatial distribution of the degree of scattering (specular and diffuse reflections). Via comparison with a prediction for the basal thermal state (thawed and frozen regions of the bed) we discuss the consequences of our study for basal water discrimination.

Beschreibung: Spatial and temporal variability of water-filled crevasse hydrologic states along the shear margins of Jakobshavn Isbrae, Greenland Casey A. Joseph and Derrick J. Lampkin The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-86,2017 Manuscript under review for TC (discussion: open, 0 comments) This work characterizes the spatial and temporal variability in the hydrologic state (filled or drained) of seven crevasse groups on Jakobshavn Isbræ from 2000–2015 using several optical satellite platforms. Meltwater from these crevasse groups can be transported to the bedrock and accelerate mass loss. The frequency of multi-drainage events were observed to increase over the study period. Multi-drain events may be related to temperature, terminus front location, and strain rate.

Beschreibung: A new approach to estimate ice dynamic rates using satellite observations in East Antarctica Bianca Kallenberg, Paul Tregoning, Janosch Fabian Hoffmann, Rhys Hawkins, Anthony Purcell, and Sébastien Allgeyer The Cryosphere, 11, 1235-1245, https://doi.org/10.5194/tc-11-1235-2017, 2017 Mass balance changes of the Antarctic ice sheet are of significant interest due to its sensitivity to climatic changes and its contribution to changes in global sea level. While regional climate models successfully estimate mass input due to snowfall, it remains difficult to estimate the amount of mass loss due to ice dynamic processes. It has often been assumed that changes in ice dynamic rates only need to be considered when assessing long-term ice sheet mass balance; however, 2 decades of satellite altimetry observations reveal that the Antarctic ice sheet changes unexpectedly and much more dynamically than previously expected. Despite available estimates on ice dynamic rates obtained from radar altimetry, information about ice sheet changes due to changes in the ice dynamics are still limited, especially in East Antarctica. Without understanding ice dynamic rates, it is not possible to properly assess changes in ice sheet mass balance and surface elevation or to develop ice sheet models. In this study we investigate the possibility of estimating ice sheet changes due to ice dynamic rates by removing modelled rates of surface mass balance, firn compaction, and bedrock uplift from satellite altimetry and gravity observations. With similar rates of ice discharge acquired from two different satellite missions we show that it is possible to obtain an approximation of the rate of change due to ice dynamics by combining altimetry and gravity observations. Thus, surface elevation changes due to surface mass balance, firn compaction, and ice dynamic rates can be modelled and correlated with observed elevation changes from satellite altimetry.

Beschreibung: Dark ice dynamics of the south-west Greenland Ice Sheet Andrew J. Tedstone, Jonathan L. Bamber, Joseph M. Cook, Christopher J. Williamson, Xavier Fettweis, Andrew J. Hodson, and Martyn Tranter The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-79,2017 Manuscript under review for TC (discussion: open, 0 comments) The bare-ice albedo of the south-west Greenland ice sheet varies dramatically between melt seasons. Darkening by inorganic particulates, cryoconite hole processes and ice algae can occur, but the reasons for inter-annual albedo variability are unclear. We use satellite imagery to examine dark ice dynamics, and climate model outputs to find likely climatological controls. Melt-out particulates best explain the spatial extent of dark ice, but the darkening itself is likely due to ice algae growth.

Beschreibung: Methanesulfonic acid (MSA) migration in polar ice: Data synthesis and theory Matthew Osman, Sarah B. Das, Olivier Marchal, and Matthew J. Evans The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-84,2017 Manuscript under review for TC (discussion: open, 0 comments) We combine a synthesis of 22 ice core records and a model of soluble impurity transport to investigate the enigmatic, post-depositional migration of methanesulfonic acid (MSA) in polar ice. Our findings suggest that migration may be universal across coastal regions of Greenland and Antarctica, though is mitigated at sites with higher accumulation and (or) lower impurity content. Records exhibiting severe migration may still be useful for inferring decadal and lower-frequency climate variability.

Beschreibung: Optical properties of laboratory grown sea ice doped with light absorbing impurities (black carbon) Amelia A. Marks, Maxim L. Lamare, and Martin D. King The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-76,2017 Manuscript under review for TC (discussion: open, 0 comments) Arctic sea ice extent is declining rapidly. Prediction of sea ice trends rely on sea ice models that need to be evaluated with real data. A realistic sea ice environment is created in a laboratory by the Royal Holloway sea ice simulator and is used to show a sea ice model can replicate measured properties of sea ice e.g. reflectance. Black carbon, a component of soot found in atmospheric pollution, is also experimentally shown to reduce the reflectance of sea ice, which could exacerbate melting.

Beschreibung: Exceptional retreat of Novaya Zemlya's marine-terminating outlet glaciers between 2000 and 2013 J. Rachel Carr, Heather Bell, Rebecca Killick, and Tom Holt The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-32,2017 Manuscript under review for TC (discussion: open, 0 comments) Glaciers on Novaya Zemlya (NVZ) retreated rapidly between 2000 and 2013. This was far faster than the previous 25 years, but retreat then slowed from 2013 onward. This may result from changes in broad-scale climatic patterns. Glaciers ending in lakes retreated at a similar rate to those ending in the ocean and retreat rates were very consistent between glaciers, which contrasts with previous studies.

Beschreibung: Properties of black carbon and other insoluble light-absorbing particles in seasonal snow of northwestern China Wei Pu, Xin Wang, Hailun Wei, Yue Zhou, Jinsen Shi, Zhiyuan Hu, Hongchun Jin, and Quanliang Chen The Cryosphere, 11, 1213-1233, https://doi.org/10.5194/tc-11-1213-2017, 2017 We conducted a large field campaign to collect snow samples in Xinjiang. We measured insoluble light-absorbing particles with estimated black carbon concentrations of 10–150 ng g-1 . We found a probable shift in emission sources with the progression of winter and dominated contributions of BC and OC to light absorption. A PMF model indicated an optimal three-factor/source solution that included industrial pollution, biomass burning, and soil dust.

Beschreibung: Improving gridded snow water equivalent products in British Columbia, Canada: multi-source data fusion by neural network models Andrew Snauffer, William Hsieh, Alex Cannon, and Markus Schnorbus The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-56,2017 Manuscript under review for TC (discussion: open, 0 comments) Estimating winter snowpack throughout British Columbia is challenging due to the complex terrain, thick forests and high snow accumulations present. This paper describes a way to make better snow estimates by combining publicly available data using machine learning, a branch of artificial intelligence research. These improved estimates will help water resources managers better plan for changes in rivers and lakes fed by springtime snowmelt and will aid other research that supports such planning.

Beschreibung: Hypsometric amplification and routing moderation of Greenland ice sheet meltwater release Dirk van As, Andreas Bech Mikkelsen, Morten Holtegaard Nielsen, Jason E. Box, Lillemor Claesson Liljedahl, Katrin Lindbäck, Lincoln Pitcher, and Bent Hasholt The Cryosphere, 11, 1371-1386, https://doi.org/10.5194/tc-11-1371-2017, 2017 The Greenland ice sheet melts faster in a warmer climate. The ice sheet is flatter at high elevation, therefore atmospheric warming increases the melt area exponentially. For current climate conditions, we find that the ice sheet shape amplifies the total meltwater generation by roughly 60 %. Meltwater is not stored underneath the ice sheet, as previously found, but it does take multiple days for it to pass through the seasonally developing subglacial drainage channels, moderating discharge.

Beschreibung: Water flow in the active layer along an arctic slope – An investigation based on a field campaign and model simulations Sebastian F. Zastruzny, Bo Elberling, Lars Nielsen, and Karsten H. Jensen The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-97,2017 Manuscript under review for TC (discussion: open, 0 comments) The hydrological regime in the arctic will change as the climate conditions change and the release and associated transport of nutrients will also be affected. In this study we analyze water flow and tracer transport along a sloping transect in Disko Island in Greenland. The results suggest that the movement of dissolved nitrogen compounds such as nitrate, being released along the slope in consequence of permafrost thawing, can quickly influence nitrogen cycling at the end of the slope.

Beschreibung: Inter-comparison of snow depth retrievals over Arctic sea ice from radar data acquired by Operation IceBridge Ron Kwok, Nathan T. Kurtz, Ludovic Brucker, Alvaro Ivanoff, Thomas Newman, Sinead L. Farrell, Joshua King, Stephen Howell, Melinda A. Webster, John Paden, Carl Leuschen, Joseph A. Macgregor, Jacqueline Richter-Menge, Jeremy Harbeck, and Mark Tschudi The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-103,2017 Manuscript under review for TC (discussion: open, 0 comments) Since 2009, the ultra-wideband snow-radar on Operation IceBridge has acquired data in annual campaigns conducted during the Arctic and Antarctic springs. Existing snow depth retrieval algorithms differ in the way the air-snow and snow-ice interfaces are detected and localized in the radar returns, and in how the system limitations are addressed. Here, we assess five retrieval algorithms by comparisons with field measurements, ground-based campaigns, and analysed fields of snow depth.

Beschreibung: Brief communication: The global signature of post-1900 land ice wastage on vertical land motion Riccardo E. M. Riva, Thomas Frederikse, Matt A. King, Ben Marzeion, and Michiel R. van den Broeke The Cryosphere, 11, 1327-1332, https://doi.org/10.5194/tc-11-1327-2017, 2017 The reduction of ice masses stored on land has made an important contribution to sea-level rise over the last century, as well as changed the Earth's shape. We model the solid-earth response to ice mass changes and find significant vertical deformation signals over large continental areas. We show how deformation rates have varied strongly throughout the last century, which affects the interpretation and extrapolation of recent observations of vertical land motion and sea-level change.

Beschreibung: Snow farming: Conserving snow over the summer season Thomas Grünewald, Michael Lehning, and Fabian Wolfsperger The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-93,2017 Manuscript under review for TC (discussion: open, 0 comments) Snowfarming is the conservation of snow during summer. Large snow piles are covered with a saw-dust insulation layer, reducing melt and guaranteeing a specific amount of snow available in autumn independent of the weather conditions. Snow volumes changes of two heaps were monitored showing that about 1/3 of the snow was lost. Model simulations confirmed the large effect of the insulation on energy balance and melt. The model can now be used as a tool to examine future snowfarming projects.

Beschreibung: Sonar gas flux estimation by bubble insonification: application to methane bubble flux from seep areas in the outer Laptev Sea Ira Leifer, Denis Chernykh, Natalia Shakhova, and Igor Semiletov The Cryosphere, 11, 1333-1350, https://doi.org/10.5194/tc-11-1333-2017, 2017 Vast Arctic methane deposits may alter global climate and require remote sensing (RS) to map. Sonar has great promise, but quantitative inversion based on theory is challenged by multiple bubble acoustical scattering in plumes. We demonstrate use of a real-world in situ bubble plume calibration using a bubble model to correct for differences in the calibration and seep plumes. Spatial seep sonar maps were then used to improve understanding of subsurface geologic controls.

Beschreibung: Wind-driven snow conditions control the occurrence of contemporary marginal mountain permafrost in the Chic-Choc Mountains, south-eastern Canada: a case study from Mont Jacques-Cartier Gautier Davesne, Daniel Fortier, Florent Domine, and James T. Gray The Cryosphere, 11, 1351-1370, https://doi.org/10.5194/tc-11-1351-2017, 2017 This study presents data from Mont Jacques-Cartier, the highest summit in the Appalachians of south-eastern Canada, to demonstrate that the occurrence of contemporary permafrost body is associated with a very thin and wind-packed winter snow cover which brings local azonal topo-climatic conditions on the dome-shaped summit. This study is an important preliminary step in modelling the regional spatial distribution of permafrost on the highest summits in eastern North America.

Beschreibung: Measuring snow water equivalent from common offset GPR records through migration velocity analysis James St. Clair and W. Steven Holbrook The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-90,2017 Manuscript under review for TC (discussion: open, 0 comments) We investigate the performance of a semi-automated algorithm for measuring snow water equivalent (SWE) from common-offset ground-penetrating-radar (GPR) data. The algorithm automatically estimates SWE from a selected portion of the data and the user is only required for quality control. GPR derived SWE estimates are similar to manual measurements indicating that the method is reliable. Our results will hopefully make GPR a more attractive tool for monitoring SWE in mountain watersheds.

Beschreibung: Impacts of freshwater changes on Antarctic sea ice in an eddy-permitting sea-ice–ocean model Verena Haid, Doroteaciro Iovino, and Simona Masina The Cryosphere, 11, 1387-1402, https://doi.org/10.5194/tc-11-1387-2017, 2017 Since the Antarctic sea ice extent shows a recent increase, we investigate the sea ice response to changed amount and distribution of surface freshwater addition in the Southern Ocean with the ocean–sea ice model NEMO/LIM2. We find that freshwater addition within the range of current estimates increases the ice extent, but higher amounts could have an opposing effect. The freshwater distribution is of great influence on the ice dynamics and the ice thickness is strongly influenced by it.

Beschreibung: Brief communication: Estimation of hydraulic properties of active layers using ground-penetrating radar (GPR) and 2D inverse hydrological modeling Xicai Pan, Stefan Jaumann, Jiabao Zhang, and Kurt Roth The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-77,2017 Manuscript under review for TC (discussion: open, 0 comments) This study proposes a new method for estimating hydraulic properties of active layers using ground-penetrating radar (GPR) and 2D inverse hydrological modeling. This method creatively turns over the adverse features of undulating frost table for 1D inverse estimation of hydraulic parameters to assets for 2D inverse estimation. Its advantages include non-destructive observations, a bigger scale of the soil hydraulic properties and efficiency for permafrost studies.

Beschreibung: Numerical modelling of convective heat transport by air flow in permafrost talus slopes Jonas Wicky and Christian Hauck The Cryosphere, 11, 1311-1325, https://doi.org/10.5194/tc-11-1311-2017, 2017 Talus slopes are a widespread geomorphic feature, which may show permafrost conditions even at low elevation due to cold microclimates induced by a gravity-driven internal air circulation. We show for the first time a numerical simulation of this internal air circulation of a field-scale talus slope. Results indicate that convective heat transfer leads to a pronounced ground cooling in the lower part of the talus slope favoring the persistence of permafrost.

Beschreibung: A multi-layer physically-based snowpack model simulating direct and indirect radiative impacts of light-absorbing impurities in snow Francois Tuzet, Marie Dumont, Matthieu Lafaysse, Ghislain Picard, Laurent Arnaud, Didier Voisin, Yves Lejeune, Luc Charrois, Pierre Nabat, and Morin Samuel The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-94,2017 Manuscript under review for TC (discussion: open, 0 comments) Light absorbing impurities deposited on snow, such as soot or dust, strongly modify its evolution. We implemented impurities deposition and evolution in a detailed snowpack model, thereby expanding the reach of such models into addressing the subtle interplays between snow physics and impurities optical properties. Model results were evaluated based on innovative field observations at an alpine site. This allows future investigations in the fields of climate, hydrology and avalanche prediction.

Beschreibung: A statistical fracture model for Antarctic glaciers Veronika Emetc, Paul Tregoning, and Malcolm Sambridge The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-98,2017 Manuscript under review for TC (discussion: open, 0 comments) We developed a statistics-based method to identify zones of Antarctic ice shelves that are likely to fracture, with an average accuracy of 77 % when compared to observed fractures identified in optical imagery. We find that we can identify 4 main groups of ice shelf regions having similar characteristics. Our method of identifying fracture regions provides the initial step in the modelling of the propagation of crevasses and can form the basis for modelling ice shelf calving processes.

Beschreibung: Blowing snow detection from ground-based ceilometers: application to East Antarctica Alexandra Gossart, Niels Souverijns, Irina Valerievna Gorodetskaya, Stef Lhermitte, Jan Thérèse Maria Lenaerts, Jan Herbert Schween, Alexander Mangold, Quentin Laffineur, and Nicole Petra Marie van Lipzig The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-89,2017 Manuscript under review for TC (discussion: open, 0 comments) Blowing snow plays an important role on local surface mass balance of Antarctica. We present here the blowing snow detection algorithm, to retreive blowing snow occurence from the attenuated backscatter signal of ceilometers set up at two station. There is a good correspondance in detection of heavy blowing snow by the algorithm, and the visual observations performed at Neumayer station. Moreover, most of the blowing snow occurs duringevents bringing precipitation from the coast inland.

Beschreibung: Seafloor geomorphology of western Antarctic Peninsula bays: a signature of ice flow behaviour Yuribia P. Munoz and Julia S. Wellner The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-108,2017 Manuscript under review for TC (discussion: open, 0 comments) We mapped submarine landforms in western Antarctic Peninsula bays. These landforms were formed by flowing ice and can provide insight into the local controls on glacial ice advance and retreat. We used a sonar to collect bathymetric data and then created seafloor maps. We conclude that the length and width of bays exert a control on the number and type of landforms found in the bays, narrower bays tend to stabilize ice flow, and shallower water depths may accelerate ice retreat.

Beschreibung: Antarctic sub-shelf melt rates via PICO Ronja Reese, Torsten Albrecht, Matthias Mengel, Xylar Asay-Davis, and Ricarda Winkelmann The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-70,2017 Manuscript under review for TC (discussion: open, 0 comments) Floating ice shelves surround most of Antarctica and melting at their bases in contact with the ocean is a major reason for its current sea-level contribution. We developed a simple model that captures the vertical ocean circulation generally present in ice-shelf cavities and allows simulating melt rates in accordance with physical processes beneath the ice. We test the model for all Antarctic ice shelves and find that melt rates and melt patterns from our model agree well with observations.

Beschreibung: Submarine melt rates and mass balance for Greenland's remaining ice tongues Nat Wilson, Fiammetta Straneo, and Patrick Heimbach The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-99,2017 Manuscript under review for TC (discussion: open, 0 comments) We estimate submarine melt rates from ice tongues in northern Greenland using WorldView satellite imagery. At Ryder Glacier, melt is strongly concentrated around regions where subglacier channels likely enter the fjord. At 79 North Glacier, we find a large volume imbalance in which melting removes a greater quantity of ice than is replaced by inflow over the grounding line. This leads us to predict a reduction in the spatial extent of the ice tongue over the coming decade.

Beschreibung: Numerical homogenization of the viscoplastic behavior of snow based on X-ray tomography images Antoine Wautier, Christian Geindreau, and Frédéric Flin The Cryosphere, 11, 1465-1485, https://doi.org/10.5194/tc-11-1465-2017, 2017 The results shown in the present paper consist in predicting the overall viscous behavior of snow from the sole knowledge of the microstructure and the ice viscous behavior. This is done thanks to multi-scale modeling techniques and an original approach is used to handle the nonlinearity of the ice behavior. An application of the developed formulation can be found in the simulation of the densification of the snowpack in order to enhance avalanche risk forecasting.

Beschreibung: Transient modeling of the ground thermal conditions using satellite data in the Lena River delta, Siberia Sebastian Westermann, Maria Peter, Moritz Langer, Georg Schwamborn, Lutz Schirrmeister, Bernd Etzelmüller, and Julia Boike The Cryosphere, 11, 1441-1463, https://doi.org/10.5194/tc-11-1441-2017, 2017 We demonstrate a remote-sensing-based scheme estimating the evolution of ground temperature and active layer thickness by means of a ground thermal model. A comparison to in situ observations from the Lena River delta in Siberia indicates that the model is generally capable of reproducing the annual temperature regime and seasonal thawing of the ground. The approach could hence be a first step towards remote detection of ground thermal conditions in permafrost areas.

Beschreibung: A weekly Arctic sea-ice thickness data record from merged CryoSat-2 and SMOS satellite data Robert Ricker, Stefan Hendricks, Lars Kaleschke, Xiangshan Tian-Kunze, Jennifer King, and Christian Haas The Cryosphere, 11, 1607-1623, https://doi.org/10.5194/tc-11-1607-2017, 2017 We developed the first merging of CryoSat-2 and SMOS sea-ice thickness retrievals. ESA’s Earth Explorer SMOS satellite can detect thin sea ice, whereas its companion CryoSat-2, designed to observe thicker perennial sea ice, lacks sensitivity. Using these satellite missions together completes the picture of the changing Arctic sea ice and provides a more accurate and comprehensive view on the actual state of Arctic sea-ice thickness.

Beschreibung: Climate warming has led to the degradation of permafrost stability in the past half century over the Qinghai-Tibet Plateau Youhua Ran, Xin Li, and Guodong Cheng The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-120,2017 Manuscript under review for TC (discussion: open, 0 comments) Approximately 87.98 % of the permafrost area in the 1960s has been degraded to lower levels of stability in the past half century over the Tibetan Plateau. The mean elevations of the extremely stable, stable, sub-stable, transitional, unstable, and extremely unstable permafrost areas increased by 88 m, 97 m, 155 m, 185 m, 161 m and 250 m, respectively. This degradation has led to increases in risks to infrastructure, water resources, and positive climate feedback.

Beschreibung: Snow water equivalent in the Alps as seen by gridded data sets, CMIP5 and CORDEX climate models Silvia Terzago, Jost von Hardenberg, Elisa Palazzi, and Antonello Provenzale The Cryosphere, 11, 1625-1645, https://doi.org/10.5194/tc-11-1625-2017, 2017 The estimate of the current and future conditions of snow resources in mountain areas depends on the availability of reliable fine-resolution data sets and of climate models capable of properly representing snow processes and snow–climate interactions. This work considers the snow water equivalent data sets from remote sensing, reanalyses, regional and global climate models available for the Alps and explores their ability to provide a coherent view of the snowpack features and its changes.

Beschreibung: The significance of vertical moisture diffusion on drifting Snow sublimation near snow surface Ning Huang and Guanglei Shi The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-116,2017 Manuscript under review for TC (discussion: open, 0 comments) Snow is an important part of the cryosphere, and blowing snow sublimation is an important method to change the snow distribution. However, in the previous studies blowing snow sublimation near surface was ignored. Herein, we built a blowing snow sublimation model to study the sublimation in near-surface region. The results showed that the mass of snow sublimation near surface accounted for even more than half of the total. Therefore, blowing snow sublimation near surface can’t be neglected.

Beschreibung: Design and results of the ice sheet model initialisation experiments initMIP-Greenland: an ISMIP6 intercomparison Heiko Goelzer, Sophie Nowicki, Tamsin Edwards, Matthew Beckley, Ayako Abe-Ouchi, Andy Aschwanden, Reinhard Calov, Olivier Gagliardini, Fabien Gillet-Chaulet, Nicholas R. Golledge, Jonathan Gregory, Ralf Greve, Angelika Humbert, Philippe Huybrechts, Joseph H. Kennedy, Eric Larour, William H. Lipscomb, Sébastien Le clec´h, Victoria Lee, Mathieu Morlighem, Frank Pattyn, Antony J. Payne, Christian Rodehacke, Martin Rückamp, Fuyuki Saito, Nicole Schlegel, Helene Seroussi, Andrew Shepherd, Sainan Sun, Roderik van de Wal, and Florian A. Ziemen The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-129,2017 Manuscript under review for TC (discussion: open, 0 comments) We have compared a wide spectrum of different initialisation techniques used in the ice sheet modelling community to define the modelled present-day Greenland ice sheet state as starting point for physically-based future sea-level change projections. Compared to earlier community-wide comparisons we find better agreement across different models, which implies overall improvement of our understanding of what is needed to produce such initial states.

Beschreibung: Black carbon and mineral dust in snow cover on the Third Pole Yulan Zhang, Shichang Kang, Michael Sprenger, Zhiyuan Cong, Tanguang Gao, Chaoliu Li, Shu Tao, Xiaofei Li, Xinyue Zhong, Min Xu, Wenjun Meng, and Mika Sillanpää The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-111,2017 Manuscript under review for TC (discussion: open, 0 comments) Light-absorbing impurities deposited on snow can reduce surface albedo and contribute to the near-worldwide melting of snowpack and ice. This study focused on the black carbon and mineral dust in snow cover on the Third Pole region. We discussed their concentrations, distributions, possible sources, and albedo reduction and radiative forcing. Findings indicated that the impacts of black carbon and mineral dust needed to be properly accounted for in future regional climate projections.

Beschreibung: Mechanisms influencing seasonal-to-interannual prediction skill of sea ice extent in the Arctic Ocean in MIROC Jun Ono, Hiroaki Tatebe, Yoshiki Komuro, Masato I. Nodzu, and Masayoshi Ishii The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-122,2017 Manuscript under review for TC (discussion: open, 0 comments) Sea ice in the Arctic Ocean has experienced rapid decline since the satellite era. To assess the predictability of sea ice extent in the Arctic Ocean and to clarify the underlying physical processes, we conducted prediction experiments using an initialized climate model (MIROC5). The present study reveals that subsurface ocean heat content originating from the North Atlantic contributes to the predictability of winter sea ice extent up to 1 year ahead, through the advection and vertical mixing.

Beschreibung: Simulating ice thickness and velocity evolution of Upernavik Isstrøm 1849–2012 by forcing prescribed terminus positions in ISSM Konstanze Haubner, Jason E. Box, Nicole J. Schlegel, Eric Y. Larour, Mathieu Morlighem, Anne M. Solgaard, Kristian K. Kjellerup, Signe H. Larsen, and Kurt H. Kjær The Cryosphere Discuss., https//doi.org/10.5194/tc-2017-121,2017 Manuscript under review for TC (discussion: open, 0 comments) We investigate the effect of neglecting calving on Upernavik Isstrøm, West Greenland, between 1849 and 2012. Our simulation is forced with observed terminus positions in discrete time steps and is responsive to the prescribed ice front changes. Simulated frontal retreat is needed to obtain a realistic ice surface elevation and velocity evolution of Upernavik. Using the prescribed terminus position change we get insight to mass loss partitioning during different time periods.

Beschreibung: Could promontories have restricted sea-glacier penetration into marine embayments during Snowball Earth events? Adam J. Campbell, Betzalel Massarano, Edwin D. Waddington, and Stephen G. Warren The Cryosphere, 11, 1141-1148, doi:10.5194/tc-11-1141-2017, 2017 How could plant life, that needs light to survive, live on a planet covered with ice? Such a situation is thought to have existed during what are called the Snowball Earth events over 600 million years ago. Here we find that ice shadows , regions where ice has difficulty flowing into, may have a played a role in that survival of early plant life.

Beschreibung: How unusual was 2015 in the 1984–2015 period of North Cascade Glacier Annual Mass Balance? Mauri S. Pelto The Cryosphere Discuss., doi:10.5194/tc-2017-62,2017 Manuscript under review for TC (discussion: open, 0 comments) In 1983 the North Cascade Glacier Climate Project (NCGCP) began annual monitoring 10 glaciers throughout the range, to identify their response to climate change. The annual observations include mass balance, terminus behavior, and accumulation area ratio (AAR). In 2015 the region experienced the warmest conditions in at least the last 50 years. This paper places 2015 in context of the thirty-two-year mass balance record and local climate records.

Beschreibung: Rapidly-changing subglacial hydrology pathways at a tidewater glacier revealed through simultaneous observations of water pressure, supraglacial lakes, meltwater plumes and surface velocities Penelope How, Douglas I. Benn, Nicholas R. J. Hulton, Bryn Hubbard, Adrian Luckman, Heïdi Sevestre, Ward J. J. van Pelt, Katrin Lïndback, Jack Kohler, and Wim Boot The Cryosphere Discuss., doi:10.5194/tc-2017-74,2017 Manuscript under review for TC (discussion: open, 0 comments) This study provides valuable insight into subglacial hydrology and dynamics at tidewater glaciers, which remains a poorly understood area in glaciology. It is a unique study because of the wealth of information provided by simultaneous observations of glacier hydrology at Kronebreen, a tidewater glacier in Svalbard. All these elements build a strong conceptual picture of the glacier's hydrological regime over the 2014 melt season.

Beschreibung: A multiphysical ensemble system of numerical snow modelling Matthieu Lafaysse, Bertrand Cluzet, Marie Dumont, Yves Lejeune, Vincent Vionnet, and Samuel Morin The Cryosphere, 11, 1173-1198, doi:10.5194/tc-11-1173-2017, 2017 Physically based multilayer snowpack models suffer from various modelling errors. To represent these errors, we built the new multiphysical ensemble system ESCROC by implementing new representations of different physical processes in a coupled multilayer ground/snowpack model. This system is a promising tool to integrate snow modelling errors in ensemble forecasting and ensemble assimilation systems in support of avalanche hazard forecasting and other snowpack modelling applications.

Beschreibung: Optical properties of laboratory grown sea ice doped with light absorbing impurities (black carbon) Amelia A. Marks, Maxim L. Lamare, and Martin D. King The Cryosphere Discuss., doi:10.5194/tc-2017-76,2017 Manuscript under review for TC (discussion: open, 0 comments) Arctic sea ice extent is declining rapidly. Prediction of sea ice trends rely on sea ice models that need to be evaluated with real data. A realistic sea ice environment is created in a laboratory by the Royal Holloway sea ice simulator and is used to show a sea ice model can replicate measured properties of sea ice e.g. reflectance. Black carbon, a component of soot found in atmospheric pollution, is also experimentally shown to reduce the reflectance of sea ice, which could exacerbate melting.

Beschreibung: The modelled liquid water balance of the Greenland Ice Sheet Christian R. Steger, Carleen H. Reijmer, and Michiel R. van den Broeke The Cryosphere Discuss., doi:10.5194/tc-2017-88,2017 Manuscript under review for TC (discussion: open, 0 comments) Mass loss from the Greenland Ice Sheet, which contributes to sea level rise, is currently dominated by surface melt and runoff. The relation between these two variables is rather uncertain due to the firn layer’s potential to buffer melt in solid (refreezing) or liquid (firn aquifer) form. To address this uncertainty, we analyse output of a numerical firn model run over 1960–2014. Results show a spatially variable response of the ice sheet to increasing melt and an upward migration of aquifers.

Beschreibung: Dynamic changes on the Wilkins Ice Shelf during the 2006–2009 retreat derived from satellite observations Melanie Rankl, Johannes Jakob Fürst, Angelika Humbert, and Matthias Holger Braun The Cryosphere, 11, 1199-1211, doi:10.5194/tc-11-1199-2017, 2017 The vast ice shelves around Antarctica provide significant restraint to the outflow from adjacent tributary glaciers. This important buttressing effect became apparent in the last decades, when outlet glaciers accelerated considerably after several ice shelves were lost around the Antarctic Peninsula (AP). The present study aims to assess dynamic changes on the Wilkins Ice Shelf (WIS) during different stages of ice-front retreat and partial collapse between early 2008 and 2009. The total ice-shelf area lost in these events was 2135 ± 75 km 2 ( ∼  15 % of the ice-shelf area relative to 2007). Here, we use time series of synthetic aperture radar (SAR) satellite observations (1994–1996, 2006–2010) in order to derive variations in surface-flow speed from intensity-offset tracking. Spatial patterns of horizontal strain-rate, stress and stress-flow angle distributions are determined during different ice-front retreat stages. Prior to the final break up of an ice bridge in 2008, a strong speed up is observed, which is also discernible from other derived quantities. We identify areas that are important for buttressing and areas prone to fracturing using in-flow and first principal strain rates as well as principal stress components. Further propagation of fractures can be explained as the first principal components of strain rates and stresses exceed documented threshold values. Positive second principal stresses are another scale-free indicator for ice-shelf areas, where fractures preferentially open. Second principal strain rates are found to be insensitive to ice-front retreat or fracturing. Changes in stress-flow angles highlight similar areas as the in-flow strain rates but are difficult to interpret. Our study reveals the large potential of modern SAR satellite time series to better understand dynamic and structural changes during ice-shelf retreat but also points to uncertainties introduced by the methods applied.

Beschreibung: Properties of black carbon and other insoluble light-absorbing particles in seasonal snow of northwestern China Wei Pu, Xin Wang, Hailun Wei, Yue Zhou, Jinsen Shi, Zhiyuan Hu, Hongchun Jin, and Quanliang Chen The Cryosphere, 11, 1213-1233, doi:10.5194/tc-11-1213-2017, 2017 We conducted a large field campaign to collect snow samples in Xinjiang. We measured insoluble light-absorbing particles with estimated black carbon concentrations of 10–150 ng g-1 . We found a probable shift in emission sources with the progression of winter and dominated contributions of BC and OC to light absorption. A PMF model indicated an optimal three-factor/source solution that included industrial pollution, biomass burning, and soil dust.

Beschreibung: A new approach to estimate ice dynamic rates using satellite observations in East Antarctica Bianca Kallenberg, Paul Tregoning, Janosch Fabian Hoffmann, Rhys Hawkins, Anthony Purcell, and Sébastien Allgeyer The Cryosphere, 11, 1235-1245, doi:10.5194/tc-11-1235-2017, 2017 Mass balance changes of the Antarctic ice sheet are of significant interest due to its sensitivity to climatic changes and its contribution to changes in global sea level. While regional climate models successfully estimate mass input due to snowfall, it remains difficult to estimate the amount of mass loss due to ice dynamic processes. It has often been assumed that changes in ice dynamic rates only need to be considered when assessing long-term ice sheet mass balance; however, 2 decades of satellite altimetry observations reveal that the Antarctic ice sheet changes unexpectedly and much more dynamically than previously expected. Despite available estimates on ice dynamic rates obtained from radar altimetry, information about ice sheet changes due to changes in the ice dynamics are still limited, especially in East Antarctica. Without understanding ice dynamic rates, it is not possible to properly assess changes in ice sheet mass balance and surface elevation or to develop ice sheet models. In this study we investigate the possibility of estimating ice sheet changes due to ice dynamic rates by removing modelled rates of surface mass balance, firn compaction, and bedrock uplift from satellite altimetry and gravity observations. With similar rates of ice discharge acquired from two different satellite missions we show that it is possible to obtain an approximation of the rate of change due to ice dynamics by combining altimetry and gravity observations. Thus, surface elevation changes due to surface mass balance, firn compaction, and ice dynamic rates can be modelled and correlated with observed elevation changes from satellite altimetry.

Beschreibung: Dark ice dynamics of the south-west Greenland Ice Sheet Andrew J. Tedstone, Jonathan L. Bamber, Joseph M. Cook, Christopher J. Williamson, Xavier Fettweis, Andrew J. Hodson, and Martyn Tranter The Cryosphere Discuss., doi:10.5194/tc-2017-79,2017 Manuscript under review for TC (discussion: open, 0 comments) The bare-ice albedo of the south-west Greenland ice sheet varies dramatically between melt seasons. Darkening by inorganic particulates, cryoconite hole processes and ice algae can occur, but the reasons for inter-annual albedo variability are unclear. We use satellite imagery to examine dark ice dynamics, and climate model outputs to find likely climatological controls. Melt-out particulates best explain the spatial extent of dark ice, but the darkening itself is likely due to ice algae growth.

Beschreibung: Methanesulfonic acid (MSA) migration in polar ice: Data synthesis and theory Matthew Osman, Sarah B. Das, Olivier Marchal, and Matthew J. Evans The Cryosphere Discuss., doi:10.5194/tc-2017-84,2017 Manuscript under review for TC (discussion: open, 0 comments) We combine a synthesis of 22 ice core records and a model of soluble impurity transport to investigate the enigmatic, post-depositional migration of methanesulfonic acid (MSA) in polar ice. Our findings suggest that migration may be universal across coastal regions of Greenland and Antarctica, though is mitigated at sites with higher accumulation and (or) lower impurity content. Records exhibiting severe migration may still be useful for inferring decadal and lower-frequency climate variability.

Beschreibung: A simple model for the evolution of melt pond coverage on permeable Arctic sea ice Predrag Popović and Dorian Abbot The Cryosphere, 11, 1149-1172, doi:10.5194/tc-11-1149-2017, 2017 During summer, a large portion of sea ice in the Arctic is typically covered with meltwater. We present a simple model for the evolution of melt ponds on permeable sea ice that both fits observations and allows us to understand the behavior of melt ponds in a way that is often not possible with more complex models. We use this model to show that pond coverage will increase under global warming. This work is important as melt ponds affect the overall reflectance of sea ice.

Beschreibung: The first luminescence dating of Tibetan glacier basal sediment Zhu Zhang, Shugui Hou, and Shuangwen Yi The Cryosphere Discuss., doi:10.5194/tc-2017-68,2017 Manuscript under review for TC (discussion: open, 0 comments) We provide the first luminescence dating of the basal sediment of the Chongce ice cap in the west Kunlun Mountains on the northwest Tibetan Plateau (TP), which gives an upper limit age of 42 ± 4 ka. The age is more than one magnitude younger than the previously suggested age of bottom ice in the west Kunlun Mts. This work provides an important step towards better understanding the TP ice cores and more accurate interpretation of their records.

Beschreibung: Changes in Andes Mountains snow cover from MODIS data 2000–2014 Freddy A. Saavedra, Stephanie K. Kampt, Steven R. Fassnacht, and Jason S. Sibold The Cryosphere Discuss., doi:10.5194/tc-2017-72,2017 Manuscript under review for TC (discussion: open, 0 comments) This manuscript presents a large latitude and elevation range analysis for snow trends in the Andes Mountains using satellite images (MODIS) snow cover product. The research approach is also significant because it presents a novel strategy for defining trends in snow persistence from remote sensing data, and this allows us to improve understanding of climate change effects on snow in areas with sparse and unevenly ground climate data.

Beschreibung: Exceptional retreat of Novaya Zemlya's marine-terminating outlet glaciers between 2000 and 2013 J. Rachel Carr, Heather Bell, Rebecca Killick, and Tom Holt The Cryosphere Discuss., doi:10.5194/tc-2017-32,2017 Manuscript under review for TC (discussion: open, 0 comments) Glaciers on Novaya Zemlya (NVZ) retreated rapidly between 2000 and 2013. This was far faster than the previous 25 years, but retreat then slowed from 2013 onward. This may result from changes in broad-scale climatic patterns. Glaciers ending in lakes retreated at a similar rate to those ending in the ocean and retreat rates were very consistent between glaciers, which contrasts with previous studies.

Beschreibung: Process-level model evaluation: a snow and heat transfer metric Andrew G. Slater, David M. Lawrence, and Charles D. Koven The Cryosphere, 11, 989-996, doi:10.5194/tc-11-989-2017, 2017 This work defines a metric for evaluation of a specific model snow process, namely, heat transfer through snow into soil. Heat transfer through snow regulates the difference in air temperature versus soil temperature. Accurate representation of the snow heat transfer process is critically important for accurate representation of the current and future state of permafrost. Utilizing this metric, we can clearly identify models that can and cannot reasonably represent snow heat transfer.

Beschreibung: Arctic sea ice drift-strength feedback modelled by NEMO-LIM3.6 David Docquier, François Massonnet, Neil F. Tandon, Olivier Lecomte, and Thierry Fichefet The Cryosphere Discuss., doi:10.5194/tc-2017-60,2017 Manuscript under review for TC (discussion: open, 0 comments) Sea ice cover and thickness have substantially decreased in the Arctic Ocean since the beginning of the satellite era. As a result, sea ice strength has been reduced, allowing more deformation and fracturing and leading to increased sea ice drift speed. The resulting increased sea ice export is thought to further lower sea ice concentration and thickness. We use the global ocean-sea ice NEMO-LIM3.6 model (Nucleus for European Modelling of the Ocean coupled to the Louvain-la-Neuve sea Ice Model), satellite and buoy observations, as well as reanalysis data over the period from 1979 to 2013 to study this positive feedback for the first time in such detail. Overall, the model agrees well with observations in terms of sea ice extent, concentration and thickness. Although the seasonal cycle of sea ice drift speed is reasonably well reproduced by the model, the recent positive trend in drift speed is weaker than observations in summer. NEMO-LIM3.6 is able to capture the relationships between sea ice drift speed, concentration and thickness in terms of seasonal cycle, with higher drift speed for both lower concentration and lower thickness, in agreement with observations. Sensitivity experiments are carried out by varying the initial ice strength and show that higher values of ice strength lead to lower sea ice thickness. We demonstrate that higher ice strength results in a more uniform sea ice thickness distribution, leading to lower heat conduction fluxes, which provide lower ice production, and thus lower ice thickness. This shows that the positive feedback between sea ice drift speed and strength is more than just dynamic, more complex than originally thought and that other processes are at play. The methodology proposed in this analysis provides a benchmark for a further model intercomparison related to the interactions between sea ice drift speed and strength.

Beschreibung: Quantifying bioalbedo: A new physically-based model and critique of empirical methods for characterizing biological influence on ice and snow albedo Joseph M Cook, Andrew J Hodson, Alex S Gardner, Mark Flanner, Andrew J Tedstone, Christopher Williamson, Tristram DL Irvine-Fynn, Johan Nilsson, Robert Bryant, and Martyn Tranter The Cryosphere Discuss., doi:10.5194/tc-2017-73,2017 Manuscript under review for TC (discussion: open, 0 comments) Biological growth darkens snow and ice, causing it to melt faster. This process is often referred to as "bioalbedo". Quantifying bioalbedo has not been achieved because of difficulties isolating the biological contribution from the optical properties of ice and snow, and from inorganic impurities in field studies. In this paper, we provide a physical model that enables bioalbedo to be quantified from first principles and we use it to guide future field studies.

Beschreibung: Validation of satellite altimetry by kinematic GNSS in central East Antarctica Ludwig Schröder, Andreas Richter, Denis V. Fedorov, Lutz Eberlein, Evgeny V. Brovkov, Sergey V. Popov, Christoph Knöfel, Martin Horwath, Reinhard Dietrich, Alexey Y. Matveev, Mirko Scheinert, and Valery V. Lukin The Cryosphere, 11, 1111-1130, doi:10.5194/tc-11-1111-2017, 2017 The paper describes the processing of kinematic GNSS data observed over nine seasons in East Antarctica. The obtained surface elevation profiles are used to validate several data sets of satellite altimetry. Thus, we find a clear recommendation that processing versions provide the highest accuracy and precision. The profiles are used to derive a new set of ICESat laser campaign biases and finally, to evaluate several DEMs.

Beschreibung: Investigating the Local Scale Influence of Sea Ice on Greenland Surface Melt Julienne C. Stroeve, John R. Mioduszewski, Asa Rennermalm, Linette N. Boisvert, Marco Tedesco, and David Robinson The Cryosphere Discuss., doi:10.5194/tc-2017-65,2017 Manuscript under review for TC (discussion: open, 0 comments) As the sea ice has declined strongly in recent years there has been a corresponding increase in Greenland melting. While both are likely a result of changes in atmospheric circulation patterns that favor summer melt, this study evaluates whether or not sea ice reductions around the Greenland ice sheet are having an influence on Greenland summer melt through enhanced sensible and latent heat transport from open water areas onto the ice sheet.

Beschreibung: Location and distribution of micro-inclusions in the EDML and NEEM ice cores using optical microscopy and in situ Raman spectroscopy Jan Eichler, Ina Kleitz, Maddalena Bayer-Giraldi, Daniela Jansen, Sepp Kipfstuhl, Wataru Shigeyama, Christian Weikusat, and Ilka Weikusat The Cryosphere, 11, 1075-1090, doi:10.5194/tc-11-1075-2017, 2017 This study contributes to investigations of the effect of impurities on ice microstructure and flow properties. For the first time we mapped over 5000 micro-inclusions in four samples from the EDML and NEEM polar ice cores. The particle distributions show no correlation with grain boundaries and thus we conclude that particle pinning plays only a secondary role for the microstructure evolution. Alternative mechanisms are discussed.

Beschreibung: Mapping and inventorying active rock glaciers in the northern Tien Shan of China using satellite SAR interferometry Xiaowen Wang, Lin Liu, Lin Zhao, Tonghua Wu, Zhongqin Li, and Guoxiang Liu The Cryosphere, 11, 997-1014, doi:10.5194/tc-11-997-2017, 2017 Rock glaciers are abundant in high mountains in western China but have been ignored for 20 years. We used a new remote-sensing-based method to map active rock glaciers in the Chinese part of the Tien Shan and compiled an inventory of 261 active rock glaciers and included quantitative information about their locations, geomorphic parameters, and downslope velocities. Our dataset suggests that the lower limit of permafrost there is 2500–2800 m.

Beschreibung: Brief communication: Changing mid-twentieth century Antarctic sea ice variability linked to tropical forcing Chris S.~M. Turney, Andrew Klekociuk, Christopher J. Fogwill, Violette Zunz, Hugues Goosse, Claire L. Parkinson, Gilbert Compo, Matthew Lazzara, Linda Keller, Rob Allan, Jonathan G. Palmer, Graeme Clark, and Ezequiel Marzinelli The Cryosphere Discuss., doi:10.5194/tc-2017-51,2017 Manuscript under review for TC (discussion: open, 0 comments) We demonstrate that a mid-twentieth century decrease in geopotential height in the southwest Pacific marks a Rossby wave response to equatorial Pacific warming, leading to enhanced easterly airflow off George V Land. Our results suggest that in contrast to ozone hole-driven changes in the Amundsen Sea, the 1979–2015 increase in sea ice extent off George V Land may be in response to reduced northward Ekman drift and enhanced (near-coast) production as a consequence of low latitude forcing.

Beschreibung: Brief communication: Impacts of ocean-wave-induced breakup of Antarctic sea ice via thermodynamics in a stand-alone version of the CICE sea-ice model Luke G. Bennetts, Siobhan O'Farrell, and Petteri Uotila The Cryosphere, 11, 1035-1040, doi:10.5194/tc-11-1035-2017, 2017 A numerical model is used to investigate how Antarctic sea ice concentration and volume are affected by increased melting caused by ocean-wave breakup of the ice. When temperatures are high enough to melt the ice, concentration and volume are reduced for ~ 100 km into the ice-covered ocean. When temperatures are low enough for ice growth, the concentration recovers, but the reduced volume persists.

Beschreibung: Is there 1.5 million-year old ice near Dome C, Antarctica? Frédéric Parrenin, Marie G. P. Cavitte, Donald D. Blankenship, Jérome Chappellaz, Hubertus Fischer, Olivier Gagliardini, Valérie Masson-Delmotte, Olivier Passalacqua, Catherine Ritz, Jason Roberts, Martin J. Siegert, and Duncan A. Young The Cryosphere Discuss., doi:10.5194/tc-2017-69,2017 Manuscript under review for TC (discussion: open, 0 comments) The oldest dated deep ice core drilled in Antarctica has been retrieved at EPICA Dome C (EDC), reaching ~ 800,000 years. Obtaining an older paleoclimatic record from Antarctica is one of the greatest challenges of the ice core community. Here, we estimate the age of basal ice in the Dome C area. We find that old ice (〉 1 Myr, 1 million years) likely exists in two regions a few tens of kilometres away from EDC: "Little Dome C" and "North Patch".

Beschreibung: Spatio-temporal Patterns of High Mountain Asia's Snowmelt Season Identified with an Automated Snowmelt Detection Algorithm, 1987–2016 Taylor Smith, Bodo Bookhagen, and Aljoscha Rheinwalt The Cryosphere Discuss., doi:10.5194/tc-2017-67,2017 Manuscript under review for TC (discussion: open, 0 comments) High Mountain Asia’s rivers, which serve more than a billion people, receive a significant portion of their water budget in the form of snow. We develop an algorithm to track the onset, end, and length of the snowmelt season using passive microwave data from 1987–2016. We find that most of High Mountain Asia has experienced shorter melt seasons, earlier snow clearance, and earlier snowmelt onset, but that these changes are highly spatially and temporally heterogeneous.

Beschreibung: Response of seasonal soil freeze depth to climate change across China Xiaoqing Peng, Tingjun Zhang, Oliver W. Frauenfeld, Kang Wang, Bin Cao, Xinyue Zhong, Hang Su, and Cuicui Mu The Cryosphere, 11, 1059-1073, doi:10.5194/tc-11-1059-2017, 2017 Previous research has paid significant attention to permafrost, e.g. active layer thickness, soil temperature, area extent, and associated degradation leading to other changes. However, less focus has been given to seasonally frozen ground and vast area extent. We combined data from more than 800 observation stations, as well as gridded data, to investigate soil freeze depth across China. The results indicate that soil freeze depth decreases with climate warming.

Beschreibung: Implementing an empirical scalar tertiary anisotropic rheology (ESTAR) into large-scale ice sheet models Felicity S. Graham, Mathieu Morlighem, Roland C. Warner, and Adam Treverrow The Cryosphere Discuss., doi:10.5194/tc-2017-54,2017 Manuscript under review for TC (discussion: open, 0 comments) Ice sheet flow is anisotropic, depending on the nature of the stress applied. However, most large-scale ice sheet models rely on the Glen flow relation, which ignores anisotropic effects. We implement an anisotropic flow relation (ESTAR) in a large-scale ice sheet model. In simulations of an ice shelf, the Glen flow relation overestimates velocities by up to 17 % compared with ESTAR. Our results have implications for ice sheet model simulations of paleo-ice extent and sea level rise predictions.

Beschreibung: Discovery and characterization of submarine groundwater discharge in the Siberian Arctic seas: A case study in Buor-Khaya Gulf, Laptev Sea Alexander N. Charkin, Michiel Rutgers van der Loeff, Natalia E. Shakhova, Örjan Gustafsson, Oleg V. Dudarev, Maxim S. Cherepnev, Anatoly N. Salyuk, Andrey V. Koshurnikov, Eduard A. Spivak, Alexey Y. Gunar, and Igor P. Semiletov The Cryosphere Discuss., doi:10.5194/tc-2017-33,2017 Manuscript under review for TC (discussion: open, 0 comments) It has been suggested that increasing freshwater discharge to the Arctic Ocean may also occur as submarine groundwater discharge (SGD), yet there are no direct observations of this phenomenon in the Arctic shelf seas. This study tests the hypothesis that SGD does exist in the Siberian-Arctic shelf seas but its dynamics may be largely controlled by complicated geocryological conditions such as permafrost. The field-observational approach in the southeast Laptev Sea used a combination of hydrological (temperature, salinity), geological (bottom sediment drilling, geoelectric surveys) and geochemical ( 224 Ra, 223 Ra and 222 Rn) techniques. Active SGD was documented in the vicinity of the Lena River delta with two different operational modes. In the first system, groundwater discharges through tectonogenic permafrost talik zones was registered in both wintertime and summertime seasons. The second SGD mechanism was cryogenic squeezing out of brine and water-soluble salts detected on the periphery of ice hummocks in the wintertime season. The proposed mechanisms of groundwater transport and discharge in the arctic land-shelf system is elaborated. Through salinity versus 224 Ra and 224 Ra/ 223 Ra diagrams, the three main SGD-influenced water masses were identified and their end-member composition was constrained. Further studies should apply these techniques to a broader scale with the objective to reach an estimate of the relative importance of the SGD transport vector relative to surface freshwater discharge for both the water balance and aquatic components such as dissolved organic carbon, carbon dioxide, methane, and nutrients.

Beschreibung: Winter sea ice export from the Laptev Sea preconditions the local summer sea ice cover Thomas Krumpen and Polona Itkin The Cryosphere Discuss., doi:10.5194/tc-2017-28,2017 Manuscript under review for TC (discussion: open, 0 comments) By means of airborne sea ice thickness surveys, remote sensing data and results from a numerical model, we show that winter ice dynamic in the Laptev Sea has a preconditioning effect on local summer ice extent in addition to atmospheric processes acting on the ice cover between May and September. We conclude that the observed tendency towards an increased ice export further accelerates pack ice retreat in summer and fast ice decay.

Beschreibung: Assessment of NASA airborne laser altimetry data using ground-based GPS data near Summit Station, Greenland Kelly M. Brunt, Robert L. Hawley, Eric R. Lutz, Michael Studinger, John G. Sonntag, Michelle A. Hofton, Lauren C. Andrews, and Thomas A. Neumann The Cryosphere, 11, 681-692, doi:10.5194/tc-11-681-2017, 2017 This manuscript presents an analysis of NASA airborne lidar data based on in situ GPS measurements from the interior of the Greenland Ice Sheet. Results show that for two airborne altimeters, surface elevation biases are less than 0.12 m and measurement precisions are 0.09 m or better. The study concludes that two NASA airborne lidars are sufficiently characterized to form part of a satellite data validation strategy, specifically for ICESat-2, scheduled to launch in 2018.

Beschreibung: Arctic Ocean geostrophic circulation 2003-2014 Thomas W. K. Armitage, Sheldon Bacon, Andy L. Ridout, Alek A. Petty, Steven Wolbach, and Michel Tsamados The Cryosphere Discuss., doi:10.5194/tc-2017-22,2017 Manuscript under review for TC (discussion: open, 0 comments) We present a new 12-year record of geostrophic currents at monthly resolution in the ice-covered and ice-free Arctic Ocean and characterise their seasonal to decadal variability. We also present seasonal climatologies of eddy kinetic energy, and examine the changing location of the Beaufort Gyre. Geostrophic current variability highlights the complex interplay between seasonally varying forcing and sea ice conditions, changing ice-ocean coupling and increasing ocean surface stress in the '00s.

Beschreibung: Modelling radiative transfer through ponded first-year Arctic sea ice with a plane parallel model Torbjørn Taskjelle, Stephen R. Hudson, Mats A. Granskog, and Børge Hamre The Cryosphere Discuss., doi:10.5194/tc-2017-36,2017 Manuscript under review for TC (discussion: open, 0 comments) Under-ice irradiance measurements were done on ponded first-year pack ice along three transects during the ICE12 expedition north of Svalbard. Bulk transmittances (400–900 nm) were found to be on average 0.15–0.20 under bare ice, and 0.39–0.46 under ponded ice. Radiative transfer modelling was done with a plane parallel model. While simulated transmittances deviate significantly from measured transmittances close to the edge of ponds, spatially averaged bulk transmittances agree well. That is, transect-average bulk transmittances, calculated using typical simulated transmittances for ponded and bare ice weighted by the fractional coverage of the two surface types, is in good agreement with the measured values. Radiative heating rates calculated from model output indicates that about 20 % of the incident solar energy is absorbed in bare ice, and 50 % in ponded ice (35 % in pond itself, 15 % in the underlying ice). This large difference is due to the highly scattering surface scattering layer (SSL) increasing the albedo of the bare ice.

Beschreibung: Geothermal heat flux and basal melt rate in the DomeC region inferred from radar reflectivity and thermal modelling Olivier Passalacqua, Catherine Ritz, Frédéric Parrenin, Stefano Urbini, and Massimo Frezzotti The Cryosphere Discuss., doi:10.5194/tc-2017-23,2017 Manuscript under review for TC (discussion: open, 0 comments) As the Dome C region is a key area for oldest-ice research, we need to better constrain the geothermal heat flux (GHF) so that past basal melt rates are known well enough. Our inverse heat model significantely reduces the confidence intervals of the GHF regional field. Radar echoes need to be interpreted knowing the time lag of the climate signal to reach the bed. Several old-ice targets are confirmed, and a new one is suggested, where the GHF is very low.

Beschreibung: Dynamic response of an Arctic epishelf lake to seasonal and long-term forcing: implications for ice shelf thickness Andrew K. Hamilton, Bernard E. Laval, Derek R. Mueller, Warwick F. Vincent, and Luke Copland The Cryosphere Discuss., doi:10.5194/tc-2017-19,2017 Manuscript under review for TC (discussion: open, 0 comments) Meltwater runoff trapped by an ice shelf can create a freshwater lake floating directly on seawater. We show that the depth of the freshwater-seawater interface varies substantially due to changes in meltwater inflow and drainage under the ice shelf. By accounting for seasonality the interface depth can be used to monitor long-term changes in the thickness of ice shelves. We show that the Milne Ice Shelf, Ellesmere Island, was stable before 2004, after which time the ice shelf thinned rapidly.

Beschreibung: Influence of temperature fluctuations on equilibrium ice sheet volume Troels Bøgeholm Mikkelsen, Aslak Grinsted, and Peter Ditlevsen The Cryosphere Discuss., doi:10.5194/tc-2017-47,2017 Manuscript under review for TC (discussion: open, 0 comments) The atmospheric temperature increase poses a real risk of ice sheets collapsing. We show that this risk might have been underestimated since variations in temperature will move the ice sheets to the tipping point of destability. We show this by using a simple computer model of a large ice sheet and investigate what happens if the temperature varies from year to year. The total volume of the ice sheet becomes lower because a cold year followed by an equally warm year does not cancel out.

Beschreibung: Measured and Modeled Snow Cover Properties across the Greenland Ice Sheet Sascha Bellaire, Martin Proksch, Martin Schneebeli, Masashi Niwano, and Konrad Steffen The Cryosphere Discuss., doi:10.5194/tc-2017-55,2017 Manuscript under review for TC (discussion: open, 0 comments) The Greenland ice sheet (GrIS) is known to be contributing to sea level rise in a warming climate. The snow cover on the ice sheet is the direct link between a potentially warmer atmosphere and the ice itself. However, little is known about the microstructure and especially about the spatial and temporal variability of the snow cover, except from indirect evidence from remote sensing. The detailed snowpack stratigraphy is relevant for processes such as the albedo feedback, water infiltration and firn densification. During a field campaign in 2015, spatially distributed snow observations of the GrIS were gathered at stations belonging to the Greenland Climate Network (GC-Net). High-resolution snow profiles of density, specific surface area and hardness were measured. Hardness was measured with the SnowMicroPen, which was also used to assess the spatial variability of the snow density with depth. The snow cover model SNOWPACK was forced with reanalysis data from the model NHM-SMAP. The measured mean density of the upper snow cover was in good agreement with the simulations using constant densities for snow accumulation, i.e. new snow, depending on the geographical location on the GrIS. However, the observed stratigraphy in terms of density and SSA could not be reproduced. We found that for a one-dimensional snowpack model it is difficult to parameterize for snowpacks undergoing multiple erosion and redeposition events, as is typical for the GrIS and other perennial polar snowpacks. This limitation may be a drawback to understanding past and future changes of the snow, and the associated processes.

Beschreibung: Impact of impurities and cryoconite on the optical properties of the Morteratsch glacier (Swiss Alps) Biagio Di Mauro, Giovanni Baccolo, Roberto Garzonio, Claudia Giardino, Dario Massabò, Andrea Piazzalunga, Micol Rossini, and Roberto Colombo The Cryosphere Discuss., doi:10.5194/tc-2017-66,2017 Manuscript under review for TC (discussion: open, 0 comments) In the paper, we demonstrate the potential of field and satellite hyperspectral reflectance data in characterizing the spatial distribution of impurities on the Morteratsch glacier. In situ reflectance spectra showed that impurities reduce of 80–90 % the reflectance of ice in visible wavelengths. Satellite data also showed the outcropping of dust during the melting season in the upper parts of the glacier. Laboratory measurements of cryoconite showed the presence of elemental and organic carbon.

Beschreibung: Combined diurnal variations of discharge and hydrochemistry of the Isunnguata Sermia outlet, Greenland Ice Sheet Joseph Graly, Joel Harrington, and Neil Humphrey The Cryosphere, 11, 1131-1140, doi:10.5194/tc-11-1131-2017, 2017 At a major outlet of the Greenland Ice Sheet in West Greenland, we find that the chemical solutes in 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.