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  • INT GLACIOL SOC  (3)
  • Copernicus GmbH  (1)
  • MDPI  (1)
  • 1
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    Viscous and viscoelastic stress states at the calving front of Antarctic ice shelves (2016)
    INT GLACIOL SOC
    In:  EPIC3Annals of Glaciology, INT GLACIOL SOC, 57(73), pp. 10-18, ISSN: 0260-3055
    Details
    Publication Date: 2017-01-02
    Description: Calving mechanisms are still poorly understood and stress states in the vicinity of ice-shelf fronts are insufficiently known for the development of physically motivated calving laws that match observations. A calving model requires the knowledge of maximum tensile stresses. These stresses depend on different simulation approaches and material models. Therefore, this study compares results of a two-dimensional (2-D) continuum approach using finite elements with results of a one- dimensional (1-D) beam model elaborated in Reeh (1968). A purely viscous model, as well as a viscoelas- tic Maxwell model, is applied for the 2-D case. The maximum tensile stress usually appears at the top surface of an ice shelf. Its location and magnitude are predominantly influenced by the thickness of the ice shelf and the height of the freeboard, the traction-free part at the ice front. More precisely, doub- ling the thickness leads to twice the stress maximum, while doubling the freeboard, based on changes of the ice density, results in an increase of the stress maximum by 61%. Poisson’s ratio controls the evolu- tion of the maximum stress with time. The viscosity and Young’s modulus define the characteristic time of the Maxwell model and thus the time to reach the maximum principal stress.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
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    On the link between surface and basal structures of the Jelbart Ice Shelf, Antarctica (2015)
    INT GLACIOL SOC
    In:  EPIC3Journal of Glaciology, INT GLACIOL SOC, 61(229), pp. 975-986, ISSN: 0022-1430
    Details
    Publication Date: 2017-10-17
    Description: To understand the dynamics of ice shelves, a knowledge of their internal and basal structure is very important. As the capacity to perform local surveys is limited, remote sensing provides an opportunity to obtain the relevant information. We must prove, however, that the relevant information can be obtained from remote sensing of the surface. That is the aim of this study. The Jelbart Ice Shelf, Antarctica, exhibits a variety of surface structures appearing as stripe-like features in radar imagery. We performed an airborne geophysical survey across these features and compared the results to TerraSAR-X imagery. We find that the stripe-like structures indicate surface troughs coinciding with the location of basal channels and crevasse-like features, revealed by radio-echo sounding. HH and VV polarizations do not show different magnitude. In surface troughs, the local accumulation rate is larger than at the flat surface. Viscoelastic modelling is used to gain an understanding of the surface undulations and their origin. The surface displacement, computed with a Maxwell model, matches the observed surface reasonably well. Our simulations show that the surface troughs develop over decadal to centennial timescales.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Numerical simulations of major ice streams in western Dronning Maud Land, Antarctica, under wet and dry basal conditions (2014)
    INT GLACIOL SOC
    In:  EPIC3Journal of Glaciology, INT GLACIOL SOC, 60(220), pp. 215-232, ISSN: 0022-1430
    Details
    Publication Date: 2014-06-23
    Description: We study the presence and effect of subglacial water on the motion of the inland ice in western Dronning Maud Land. A full-Stokes model including three routing schemes for a thin film of subglacial water and a modification of a Weertman-type sliding relation to account for higher sliding velocities under wet basal conditions were used to perform 200 ka spin-up simulations on a 2.5 km grid. Subsequent 30 ka simulations with wet and dry basal conditions were analysed for the effects of sliding on the thermal regime and velocities. The occurrence of the major ice streams in this area is mainly controlled by the ice and bedrock geometry. Smaller glaciers only appear as pronounced individual glaciers, when subglacial water is taken into account. The thermal regime is affected by creep instabilities produced by an ice rheology including a microscopic water content, leading to a cyclic behaviour on millennial time scales of the ice flow and occurrence of temperate ice at the base.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Dark Glacier Surface of Greenland’s Largest Floating Tongue Governed by High Local Deposition of Dust (2020)
    MDPI
    In:  EPIC3Remote Sensing, MDPI, 12(22), pp. 3793-3793, ISSN: 2072-4292
    Details
    Publication Date: 2023-10-24
    Description: Surface melt, driven by atmospheric temperatures and albedo, is a strong contribution of mass loss of the Greenland Ice Sheet. In the past, black carbon, algae and other light-absorbing impurities were suggested to govern albedo in Greenland’s ablation zone. Here we combine optical (MODIS/Sentinel-2) and radar (Sentinel-1) remote sensing data with airborne radar and laser scanner data, and engage firn modelling to identify the governing factors leading to dark glacier surfaces in Northeast Greenland. After the drainage of supraglacial lakes, the former lake ground is a clean surface represented by a high reflectance in Sentinel-2 data and aerial photography. These bright spots move with the ice flow and darken by more than 20% over only two years. In contrast, sites further inland do not exhibit this effect. This finding suggests that local deposition of dust, rather than black carbon or cryoconite formation, is the governing factor of albedo of fast-moving outlet glaciers. This is in agreement with a previous field study in the area which finds the mineralogical composition and grain size of the dust comparable with that of the surrounding soils.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 5
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    A parallel implementation of the confined–unconfined aquifer system model for subglacial hydrology: design, verification, and performance analysis (CUAS-MPI v0.1.0) (2023)
    Copernicus GmbH
    In:  EPIC3Geoscientific Model Development, Copernicus GmbH, 16(18), pp. 5305-5322, ISSN: 1991-9603
    Details
    Publication Date: 2023-10-24
    Description: 〈jats:p〉Abstract. The subglacial hydrological system affects (i) the motion of ice sheets through sliding, (ii) the location of lakes at the ice margin, and (iii) the ocean circulation by freshwater discharge directly at the grounding line or (iv) via rivers flowing over land. For modeling this hydrology system, a previously developed porous-media concept called the confined–unconfined aquifer system (CUAS) is used. To allow for realistic simulations at the ice sheet scale, we developed CUAS-MPI, an MPI-parallel C/C++ implementation of CUAS (MPI: Message Passing Interface), which employs the Portable, Extensible Toolkit for Scientific Computation (PETSc) infrastructure for handling grids and equation systems. We validate the accuracy of the numerical results by comparing them with a set of analytical solutions to the model equations, which involve two types of boundary conditions. We then investigate the scaling behavior of CUAS-MPI and show that CUAS-MPI scales up to 3840 MPI processes running a realistic Greenland setup on the Lichtenberg HPC system. Our measurements also show that CUAS-MPI reaches a throughput comparable to that of ice sheet simulations, e.g., the Ice-sheet and Sea-level System Model (ISSM). Lastly, we discuss opportunities for ice sheet modeling, explore future coupling possibilities of CUAS-MPI with other simulations, and consider throughput bottlenecks and limits of further scaling. 〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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