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  • 1
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    Ice flow and the conditions of the ice-bed interface at the onset of the Northeast Greenland Ice Stream (2020)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2020 - Online Everywhere, Online, 2020-12-01-2020-12-17American Geophysical Union
    Details
    Publication Date: 2020-12-15
    Description: The Northeast Greenland Ice Stream (NEGIS) is an important dynamic component contributing to the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The ice stream geometry and surface velocities in the onset region of the NEGIS are not yet sufficiently well reproduced by ice sheet models. We present an assessment of the basal conditions of the onset region in a systematic analysis of airborne ultra-wideband radar data. Our data yield a new detailed model of ice-thickness distribution and basal topography in the upstream part of the ice stream. We observe a change from a smooth to a rougher bed where the ice stream widens from 10 to 60 km, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. The observation of off-nadir reflections that are symmetrical to the bed reflection in the radargrams suggests that these structures are elongated subglacial landforms, which in turn indicate potential streamlining of the bed. Together with basal water routing pathways, our observations hint to two different zones in this part of the NEGIS: an accelerating and smooth upstream region, which is collecting water, with reduced basal traction, and in the further downstream part, where the ice stream is slowing down and is widening, with a distribution of basal water towards the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 2
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    Detailed Seismic Bathymetry Beneath Ekström Ice Shelf, Antarctica: Implications for Glacial History and Ice‐Ocean Interaction (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47, pp. e2019G, ISSN: 0094-8276
    Details
    Publication Date: 2020-08-03
    Description: The shape of ice shelf cavities are a major source of uncertainty in understanding ice‐ocean interactions. This limits assessments of the response of the Antarctic ice sheets to climate change. Here we use vibroseis seismic reflection surveys to map the bathymetry beneath the Ekström Ice Shelf, Dronning Maud Land. The new bathymetry reveals an inland‐sloping trough, reaching depths of 1,100 m below sea level, near the current grounding line, which we attribute to erosion by palaeo‐ice streams. The trough does not cross‐cut the outer parts of the continental shelf. Conductivity‐temperature‐depth profiles within the ice shelf cavity reveal the presence of cold water at shallower depths and tidal mixing at the ice shelf margins. It is unknown if warm water can access the trough. The new bathymetry is thought to be representative of many ice shelves in Dronning Maud Land, which together regulate the ice loss from a substantial area of East Antarctica.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Physical Conditions of Fast Glacier Flow: 2. Variable Extent of Anisotropic Ice and Soft Basal Sediment From Seismic Reflection Data Acquired on Store Glacier, West Greenland (2018)
    Wiley
    In:  EPIC3Journal of Geophysical Research: Earth Surface, Wiley, 123, pp. 349-362
    Details
    Publication Date: 2018-04-03
    Description: Outlet glaciers of the Greenland Ice Sheet transport ice from the interior to the ocean and contribute directly to sea level rise because because discharge and ablation often exceed the accumulation. To develop a better understanding of these fast flowing glaciers, we investigate the basal conditions of Store Glacier, a large outlet glacier flowing into Uummannaq Fjord in West Greenland. We use two crossing seismic profiles acquired near the centreline, 30 km upstream of the calving front, to interpret the physical nature of the ice and bed. We identify one notably englacial and two notably subglacial seismic reflections on both profiles. The englacial reflection represents a change in crystal orientation fabric, interpreted to be the Holocene–Wisconsin transition. From Amplitude Versus Angle (AVA) analysis we infer that the deepest ∼80 m of ice of the parallel-flow profile below this reflection is anisotropic with an enhancement of simple shear of ∼2. The ice is underlain by ∼45 m of unconsolidated sediments, below which there is a strong reflection caused by the transition to consolidated sediments. In the across-flow profile subglacial properties vary over small scale and the polarity of the ice–bed reflection switches from positive to negative. We interpret these as patches of different basal slipperiness associated with variable amounts of water. Our results illustrate variability in basal properties, and hence ice-bed coupling, at a spatial scale of ∼100 m, highlighting the need for direct observations of the bed to improve the basal boundary conditions in ice-dynamic models.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Liquid water in snow (2014)
    American Geophysical Union
    In:  EPIC3Workshop at the Institute for Snow and Avalanche Research, EOS, Davos, Switzerland, American Geophysical Union
    Details
    Publication Date: 2019-07-17
    Description: From 2-4 April 2014 about 50 researchers attended the workshop „Liquid water in snow – measurements techniques and modeling approaches“ that took place at the Institute for Snow and Avalanche Research (SLF) in Davos, Switzerland – the first one since 1982 in Innsbruck, Austria. This is the report thereof.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Miscellaneous , notRev
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  • 5
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    Reassembling Gondwana: A new high quality constraint from vibroseis exploration of the sub-ice shelf geology of the East Antarctic continental margin (2014)
    Wiley
    In:  EPIC3Journal of Geophysical Research: Solid Earth, Wiley, 119(12), pp. 9171-9182, ISSN: 2169-9356
    Details
    Publication Date: 2019-07-17
    Description: The breakup of Gondwana is manifested by coeval early Jurassic Karoo magmatism in South Africa and East Antarctica. In South Africa, the large volumes of volcanic rocks of the adjoining Lebombo and Mwenetzi-Save monoclines represent a volcanic rift margin, and in East Antarctica, a corresponding feature, the Explora Wedge is buried below sediments and floating ice shelves on the continental margin of Dronning Maud Land. We use the seismic vibrator source to explore the sub-ice geology in Antarctica, and the new seismic reflection and available regional aeromagnetic data enable us to outline a dogleg landward extent of the Explora Wedge in Dronning Maud Land. The congruent inboard wedge geometries on the two continents define a high quality constraint, which facilitate for the first time, a geologically consistent and tight reconstruction of Africa relative to East Antarctica within Gondwana. The uncertainties in correlations of major geological features (mobile belts) from one continent to the other may now be of the order of ten’s of kilometers rather than hundreds of kilometers.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    A novel sensor combination (upGPR-GPS) to continuously and nondestructively derive snow cover properties (2015)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 42(9), pp. 3397-3405, ISSN: 0094-8276
    Details
    Publication Date: 2016-12-20
    Description: Monitoring seasonal snow cover properties is critical for properly managing natural hazards such as snow avalanches or snowmelt floods. However, measurements often cannot be conducted in difficult terrain or lack the high temporal resolution needed to account for rapid changes in the snowpack, e.g., liquid water content (LWC). To monitor essential snowpack properties, we installed an upward looking ground-penetrating radar (upGPR) and a low-cost GPS system below the snow cover and observed in parallel its evolution during two winter seasons. Applying external snow height (HS) information, both systems provided consistent LWC estimates in snow, based on independent approaches, namely measurements of travel time and attenuation of electromagnetic waves. By combining upGPR and GPS, we now obtain a self-contained approach instead of having to rely on external information such as HS. This allows for the first time determining LWC, HS, and snow water equivalent (SWE) nondestructively and continuously potentially also in avalanche-prone slopes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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