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  • 1
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    PANGAEA
    In:  Supplement to: Paul, Stephan; Willmes, Sascha; Hoppmann, Mario; Hunkeler, Priska A; Wesche, Christine; Nicolaus, Marcel; Heinemann, Günther; Timmermann, Ralph (2015): The impact of early-summer snow properties on Antarctic landfast sea-ice X-band backscatter. Annals of Glaciology, 56(69), 263-273, https://doi.org/10.3189/2015AoG69A715
    Publication Date: 2020-01-17
    Description: Up to now, snow cover on Antarctic sea ice and its impact on radar backscatter, particularly after the onset of freeze/thaw processes, are not well understood. Here we present a combined analysis of in situ observations of snow properties from the landfast sea ice in Atka Bay, Antarctica, and high-resolution TerraSAR-X backscatter data, for the transition from austral spring (November 2012) to summer (January 2013). The physical changes in the seasonal snow cover during that time are reflected in the evolution of TerraSAR-X backscatter. We are able to explain 76-93% of the spatio-temporal variability of the TerraSAR-X backscatter signal with up to four snowpack parameters with a root-mean-squared error of 0.87-1.62 dB, using a simple multiple linear model. Over the complete study, and especially after the onset of early-melt processes and freeze/thaw cycles, the majority of variability in the backscatter is influenced by changes in snow/ice interface temperature, snow depth and top-layer grain size. This suggests it may be possible to retrieve snow physical properties over Antarctic sea ice from X-band SAR backscatter.
    Type: Dataset
    Format: application/zip, 3 datasets
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  • 2
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    PANGAEA
    In:  Supplement to: Rackow, Thomas; Wesche, Christine; Timmermann, Ralph; Hellmer, Hartmut H; Juricke, Stephan; Jung, Thomas (2017): A simulation of small to giant Antarctic iceberg evolution: Differential impact on climatology estimates. Journal of Geophysical Research: Oceans, 21 pp, https://doi.org/10.1002/2016JC012513
    Publication Date: 2020-01-17
    Description: We present four melt climatology estimates based on a simulation of Antarctic iceberg drift and melting that includes small, medium-sized, and giant tabular icebergs with a realistic size distribution. For the first time, an iceberg model is initialized with a set of nearly 7000 observed iceberg positions and sizes around Antarctica. We simulate drift and lateral melt using iceberg-draft averaged ocean currents, temperature, and salinity. A new basal melting scheme, originally applied in ice shelf melting studies, uses in situ temperature, salinity, and relative velocities at an iceberg's bottom. The climatology estimates based on simulations of small (SMA), 'small-to-medium'-sized (MED12 & MED123), and small-to-giant icebergs (ALL) exhibit differential characteristics: successive inclusion of larger icebergs leads to a reduced seasonality of the iceberg meltwater flux and a shift of the mass input to the area north of 58°S, while less meltwater is released into the coastal areas. This highlights the necessity to account for larger and giant icebergs in order to obtain accurate melt climatologies. The four monthly melt climatologies [mm/day] are available as netCDF files with 1°x1° spatial resolution and can be used, e.g., for sensitivity studies with uncoupled sea ice-ocean models, or as spatio-temporal templates for the redistribution of land ice from the Antarctic ice sheet over the Southern Ocean in climate models.
    Type: Dataset
    Format: text/tab-separated-values, 20 data points
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  • 3
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    PANGAEA
    In:  Supplement to: Hoppmann, Mario; Nicolaus, Marcel; Paul, Stephan; Hunkeler, Priska A; Heinemann, Günther; Willmes, Sascha; Timmermann, Ralph; Boebel, Olaf; Schmidt, Thomas; Kühnel, Meike; König-Langlo, Gert; Gerdes, Rüdiger (2014): Ice platelets below Weddell Sea landfast sea ice. Annals of Glaciology, 56(69), https://doi.org/10.3189/2014AoG69A678
    Publication Date: 2020-01-17
    Description: Basal melt of ice shelves may lead to an accumulation of disc-shaped ice platelets underneath nearby sea ice, to form a sub-ice platelet layer. Here we present the seasonal cycle of sea ice attached to the Ekström Ice Shelf, Antarctica, and the underlying platelet layer in 2012. Ice platelets emerged from the cavity and interacted with the fast-ice cover of Atka Bay as early as June. Episodic accumulations throughout winter and spring led to an average platelet-layer thickness of 4 m by December 2012, with local maxima of up to 10 m. The additional buoyancy partly prevented surface flooding and snow-ice formation, despite a thick snow cover. Subsequent thinning of the platelet layer from December onwards was associated with an inflow of warm surface water. The combination of model studies with observed fast-ice thickness revealed an average ice-volume fraction in the platelet layer of 0.25 +/- 0.1. We found that nearly half of the combined solid sea-ice and ice-platelet volume in this area is generated by heat transfer to the ocean rather than to the atmosphere. The total ice-platelet volume underlying Atka Bay fast ice was equivalent to more than one-fifth of the annual basal melt volume under the Ekström Ice Shelf.
    Type: Dataset
    Format: application/zip, 5 datasets
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  • 4
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 828 data points
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  • 5
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    PANGAEA
    In:  Supplement to: Schaffer, Janin; Timmermann, Ralph; Arndt, Jan Erik; Kristensen, Steen Savstrup; Mayer, Christoph; Morlighem, Mathieu; Steinhage, Daniel (2016): A global, high-resolution data set of ice sheet topography, cavity geometry, and ocean bathymetry. Earth System Science Data, 8(2), 543-557, https://doi.org/10.5194/essd-8-543-2016
    Publication Date: 2020-01-17
    Description: The ocean plays an important role in modulating the mass balance of the polar ice sheets by interacting with the ice shelves in Antarctica and with the marine-terminating outlet glaciers in Greenland. Given that the flux of warm water onto the continental shelf and into the sub-ice cavities is steered by complex bathymetry, a detailed topography data set is an essential ingredient for models that address ice–ocean interaction. We followed the spirit of the global RTopo-1 data set and compiled consistent maps of global ocean bathymetry, upper and lower ice surface topographies, and global surface height on a spherical grid with now 30 arcsec grid spacing. For this new data set, called RTopo-2, we used the General Bathymetric Chart of the Oceans (GEBCO, 2014) as the backbone and added the International Bathymetric Chart of the Arctic Ocean version 3 (IBCAOv3) and the International Bathymetric Chart of the Southern Ocean (IBCSO) version 1. While RTopo-1 primarily aimed at a good and consistent representation of the Antarctic ice sheet, ice shelves, and sub-ice cavities, RTopo-2 now also contains ice topographies of the Greenland ice sheet and outlet glaciers. In particular, we aimed at a good representation of the fjord and shelf bathymetry surrounding the Greenland continent. We modified data from earlier gridded products in the areas of Petermann Glacier, Hagen Bræ, and Sermilik Fjord, assuming that sub-ice and fjord bathymetries roughly follow plausible Last Glacial Maximum ice flow patterns. For the continental shelf off Northeast Greenland and the floating ice tongue of Nioghalvfjerdsfjorden Glacier at about 79° N, we incorporated a high-resolution digital bathymetry model considering original multibeam survey data for the region. Radar data for surface topographies of the floating ice tongues of Nioghalvfjerdsfjorden Glacier and Zachariæ Isstrøm have been obtained from the data centres of Technical University of Denmark (DTU), Operation Icebridge (NASA/NSF), and Alfred Wegener Institute (AWI). For the Antarctic ice sheet/ice shelves, RTopo-2 largely relies on the Bedmap-2 product but applies corrections for the geometry of Getz, Abbot, and Fimbul ice shelf cavities.
    Type: Dataset
    Format: text/tab-separated-values, 76 data points
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  • 6
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 240 data points
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  • 7
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    PANGAEA
    In:  Supplement to: Schaffer, Janin; Kanzow, Torsten; von Appen, Wilken-Jon; von Albedyll, Luisa; Arndt, Jan Erik; Roberts, David H (in review): Bathymetry constrains ocean heat supply to Greenland's largest glacier tongue. Nature Geoscience
    Publication Date: 2020-01-17
    Description: As an update to the RTopo-2.0.1 data set (https://doi.org/10.1594/PANGAEA.856844), RTopo-2.0.4 contains new original bathymetry data for the Northeast Greenland continental shelf. In the Southern Ocean, we added the Rosier et al. (JGR Oceans, 2018) bathymetry grid below Filchner Ice Shelf. This work was supported in part through the Deutsche Forschungsgemeinschaft (DFG) within the Special Priority Program (SPP) 1889 "Regional Sea Level Change and Society" (grant OGreen79), the German Federal Ministry for Education and Research (BMBF) within the GROCE project (Grant 03F0778A), the Natural Environment Research Council (NERC) large grant "Ice shelves in a warming world: Filchner Ice Shelf System" (NE/L013770/1), the NERC project "Greenland in a warmer climate: What controls the advance & retreat of the NE Greenland Ice Stream" (Grant NE/N011228/1), and the Helmholtz Climate Initiative "Regional Climate Change" (REKLIM).
    Type: Dataset
    Format: text/tab-separated-values, 56 data points
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  • 8
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 760 data points
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  • 9
    Publication Date: 2019-07-16
    Description: We apply a global finite element sea ice/ice shelf/ocean model (FESOM) to the Antarctic marginal seas to analyze projections of ice shelf basal melting in a warmer climate. The model is forced with the atmospheric output from two climate models: (1) the Hadley Centre Climate Model (HadCM3) and (2) Max Planck Institute’s ECHAM5/MPI-OM. Results from their 20th-century simulations are used to evaluate the modeled present-day ocean state. Sea-ice coverage is largely realistic in both simulations. Modeled ice shelf basal melt rates compare well with observations in both cases, but are consistently smaller for ECHAM5/MPI-OM. Projections for future ice shelf basal melting are computed using atmospheric output for IPCC scenarios E1 and A1B. While trends in sea ice coverage, ocean heat content, and ice shelf basal melting are small in simulations forced with ECHAM5 data, a substantial shift towards a warmer regime is found in experiments forced with HadCM3 output. A strong sensitivity of basal melting to increased ocean temperatures is found for the ice shelves in the Amundsen Sea. For the cold-water ice shelves in the Ross and Weddell Seas,decreasing convection on the continental shelf in the HadCM3 scenarios leads to an erosion of the continental slope front and to warm water of open ocean origin entering the continental shelf. As this water reaches deep into the Filchner-Ronne Ice Shelf (FRIS) cavity, basal melting increases by a factor of three to six compared to the present value of about 100 Gt/yr. Highest melt rates at the deep FRIS grounding line causes a retreat of 〉 200km, equivalent to an land ice loss of 110 Gt/yr.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
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  • 10
    Publication Date: 2019-07-17
    Description: Sea ice fastened to coasts, icebergs and ice shelves is of crucial importance for climateand ecosystems. At the same time, it is not represented in climate models and many processes affecting its energy- and mass balance are currently only poorly understood. Near Antarctic ice shelves, which fringe about 44 % of the coastline, this landfast sea ice exhibits unique characteristics that distinguish it from most other sea ice: 1. Ice platelets form and grow in supercooled water masses, which originate from cavities below the ice shelves. These crystals rise to the surface, where they accumulate beneath the solid sea-ice cover. Through freezing of interstitial water they are incorporated into the sea-ice fabric as platelet ice. 2. A thick and highly stratified snow cover accumulates on the fast ice, altering the response of the surface to remote sensing and affecting sea-ice energy- and mass balance. Combining a variety of methods from different disciplines, we aim to improve our understanding of Antarctic sea-ice, its interaction with ice shelves and its role in the climate system. Here we present our major research questions, introduce our methods and present some exemplary results.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
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