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  • 1
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    Elastic deformation plays a non-negligible role in Greenland’s outlet glacier flow (2021)
    Christmann, Julia ; Helm, Veit ; Khan, Shfaqat Abbas ; [et al.]
    Nature Publishing Group UK
    Details
    Publication Date: 2023-11-13
    Description: Future projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland’s outlet glaciers. Here we study Nioghalvfjerdsbræ, an outlet glacier of the Northeast Greenland Ice Stream that holds 1.1 m sea-level equivalent of ice. We use GPS observations and numerical modelling to investigate the role of tides as well as the elastic contribution to glacier flow. We find that ocean tides alter the basal lubrication of the glacier up to 10 km inland of the grounding line, and that their influence is best described by a viscoelastic rather than a viscous model. Further inland, sliding is the dominant mechanism of fast glacier motion, and the ice flow induces persistent elastic strain. We conclude that elastic deformation plays a role in glacier flow, particularly in areas of steep topographic changes and fast ice velocities.
    Description: Ice flow dynamics in Greenland’s outlet glaciers are influenced by elastic deformation, both in the area of tidal influence up to 14 km inland from the grounding line and further upstream, suggest analyses of GPS observations and numerical simulations.
    Description: Bundesministerium für Bildung und Forschung (Federal Ministry of Education and Research) https://doi.org/10.13039/501100002347
    Description: European Union’s Horizon 2020 Research and Innovation Programme
    Description: https://doi.org/10.1594/PANGAEA.928940
    Description: https://nsidc.org/data/IDBMG4
    Description: https://gitlab.awi.de/jchristm/viscoelastic-79ng-greenland
    Description: https://doi.org/10.5281/zenodo.5507115
    Description: https://doi.org/10.5281/zenodo.5506953
    Keywords: ddc:551.31 ; Climate change ; Cryospheric science ; Hydrology
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    Depth-averaged pure ice attenuation rates (two-way) from PISM model ensemble for Antarctica - link to NetCDF file (2018)
    PANGAEA
    Details
    Publication Date: 2023-03-16
    Keywords: Antarctica; AWI_Glac; Glaciology @ AWI
    Type: Dataset
    Format: application/x-netcdf, 12.8 MBytes
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    DATA PANGAEA
  • 3
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    Ice thickness for Recovery Glacier, Antarctica (2018)
    PANGAEA
    Details
    Publication Date: 2023-03-16
    Keywords: Antarctica; AWI_Glac; DATE/TIME; Glaciology @ AWI; Ice thickness, glacier; LATITUDE; LONGITUDE
    Type: Dataset
    Format: text/tab-separated-values, 104080 data points
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    DATA PANGAEA
  • 4
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    Ice thickness from radio-echo sounding (RES) and radar attenuation from numerical modelling for Recovery Glacier, Antarctica (2018)
    PANGAEA
    In:  Supplement to: Humbert, Angelika; Steinhage, Daniel; Helm, Veit; Beyer, Sebastian; Kleiner, Thomas (2018): Missing Evidence of Widespread Subglacial Lakes at Recovery Glacier, Antarctica. Journal of Geophysical Research-Earth Surface, 123(11), 2802-2826, https://doi.org/10.1029/2017JF004591
    Details
    Publication Date: 2023-03-16
    Description: Recovery Glacier reaches far into the East Antarctic Ice Sheet. Recent projections point out that its dynamic behaviour has a considerable impact on future Antarctic ice loss (Golledge et al. 2017). Subglacial lakes are thought to play a major role in the initiation of the rapid ice flow (Bell et al. 2007). Satellite altimetry observations have even suggested several actively filling and draining subglacial lakes beneath the main trunk (Smith et al. 2009). We present new data of the geometry of this glacier and investigate its basal properties employing radio-echo sounding. Using ice-sheet modelling, we were able to constrain estimates of radar absorption in the ice, but uncertainties remain large. The magnitude of the basal reflection coefficient is thus still poorly known. However, its spatial variability, in conjunction with additional indicators, can be used to infer the presence of subglacial water. We find no clear evidence of water at most of the previously proposed lake sites. Especially locations where altimetry detected active lakes, do not exhibit lake characteristics in RES. We argue that lakes far upstream the main trunk are not triggering enhanced ice flow, which is also supported by modeled subglacial hydrology.
    Keywords: Antarctica; AWI_Glac; Glaciology @ AWI
    Type: Dataset
    Format: application/zip, 2 datasets
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    DATA PANGAEA
  • 5
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    Modelling calving front dynamics using a level-set method: application to Jakobshavn Isbræ, West Greenland, links model results in MATLAB format (2016)
    PANGAEA
    In:  Supplement to: Bondzio, Johannes H; Seroussi, Hélène; Morlighem, Mathieu; Kleiner, Thomas; Rückamp, Martin; Humbert, Angelika; Larour, Eric Y (2016): Modelling calving front dynamics using a level-set method: application to Jakobshavn Isbræ, West Greenland. The Cryosphere, 10(2), 497-510, https://doi.org/10.5194/tc-10-497-2016
    Details
    Publication Date: 2023-01-13
    Description: Calving is a major mechanism of ice discharge of the Antarctic and Greenland ice sheets, and a change in calving front position affects the entire stress regime of marine terminating glaciers. The representation of calving front dynamics in a 2-D or 3-D ice sheet model remains non-trivial. Here, we present the theoretical and technical framework for a level-set method, an implicit boundary tracking scheme, which we implement into the Ice Sheet System Model (ISSM). This scheme allows us to study the dynamic response of a drainage basin to user-defined calving rates. We apply the method to Jakobshavn Isbræ, a major marine terminating outlet glacier of the West Greenland Ice Sheet. The model robustly reproduces the high sensitivity of the glacier to calving, and we find that enhanced calving triggers significant acceleration of the ice stream. Upstream acceleration is sustained through a combination of mechanisms. However, both lateral stress and ice influx stabilize the ice stream. This study provides new insights into the ongoing changes occurring at Jakobshavn Isbræ and emphasizes that the incorporation of moving boundaries and dynamic lateral effects, not captured in flow-line models, is key for realistic model projections of sea level rise on centennial timescales.
    Keywords: Jakobshavn_Isbræ_drainage_basin; West Greenland
    Type: Dataset
    Format: application/zip, 469.2 MBytes
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    DATA PANGAEA
  • 6
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    Band-pass-filtered ice-sheet surface elevation, thickness, velocity and derived data maps for the northern Greenland Ice Sheet (2018)
    PANGAEA
    In:  Supplement to: Bons, Paul D; Kleiner, Thomas; Llorens, Maria-Gema; Prior, David J; Sachau, Till; Weikusat, Ilka; Jansen, Daniela (2018): Greenland Ice Sheet: Higher Nonlinearity of Ice Flow Significantly Reduces Estimated Basal Motion. Geophysical Research Letters, 45(13), 6542-6548, https://doi.org/10.1029/2018GL078356
    Details
    Publication Date: 2023-02-06
    Description: In times of warming in polar regions, the prediction of ice sheet discharge is of utmost importance to society, because of its impact on sea level rise. In simulations the flow rate of ice is usually implemented as proportional to the differential stress to the power of the exponent n=3. This exponent influences the softness of the modeled ice, as higher values would produce faster flow under equal stress. We show that the stress exponent, which best fits the observed state of the Greenland Ice Sheet, equals n=4, Our results, which are not dependent on a possible basal sliding component of flow, indicate that most of the interior northern ice sheet is currently frozen to bedrock, except for the large ice streams and marginal ice.
    Keywords: File content; File format; File name; File size; MULT; Multiple investigations; Northern_Greenland_Ice_Sheet; Uniform resource locator/link to file
    Type: Dataset
    Format: text/tab-separated-values, 75 data points
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    DATA PANGAEA
  • 7
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    Basal roughness in East Antarctica (2021)
    PANGAEA
    Details
    Publication Date: 2024-04-20
    Description: We provide a data set to investigate the subglacial properties of the East Antarctic Ice Sheet by statistically analysing the roughness of the bed topography, inferred from radio-echo sounding measurements. We analyse two sets of roughness parameters, one derived in the spatial and the other in the spectral domain, with two roughness parameters each. This enables us to compare the suitability of the four roughness parameters to classify the subglacial landscapes below the ice sheet.
    Keywords: Antarctica; bedrock; Binary Object; Binary Object (File Size); East_Antarctica; MULT; Multiple investigations; Radar Data; radio-echo sounding
    Type: Dataset
    Format: text/tab-separated-values, 14 data points
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    DATA PANGAEA
  • 8
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    Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice (2018)
    Details
    Publication Date: 2021-03-29
    Description: Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450 m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450–1700 m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000 m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700–2030 m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030–2385 m depth) is an indicator of shear dominance. Region 5 (below approx. 2385 m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural observations are compared with results from a numerical ice sheet model (PISM, isotropic) for comparison of strain rate trends predicted from the large-scale geometry of the ice sheet and borehole logging data. This comparison confirms the segmentation into these depth regions and in turn provides a wider view of the ice sheet.
    Keywords: polar ice core; microstructure; borehole deformation; fabric; texture; ice flow modelling ; 551
    Language: English
    Type: article , publishedVersion
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