期刊
JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE
卷 126, 期 3, 页码 -出版社
AMER GEOPHYSICAL UNION
DOI: 10.1029/2020JF005689
关键词
basal roughness; bed conditions; Greenland Ice Sheet; ice stream; Northeast Greenland Ice Stream; radio‐ echo sounding
资金
- Denmark (A. P. MOller Foundation)
- Denmark (University of Copenhagen)
- USA (US National Science Foundation, Office of Polar Programs)
- Germany (Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research)
- Japan (National Institute of Polar Research)
- Norway (Bergen Research Foundation)
- Switzerland (Swiss National Science Foundation)
- France (French Polar Institute Paul-Emile Victor)
- France (Institute for Geosciences and Environmental research)
- China (Chinese Academy of Sciences)
- China (Beijing Normal University)
- University of Kansas
- NASA Operation IceBridge grant [NNX16AH54G]
- NSF [ACI-1443054, OPP-1739003, IIS-1838230]
- Projekt DEAL
- Japan (Arctic Challenge for Sustainability)
- Norway (University of Bergen)
- NASA [NNX16AH54G, 901711] Funding Source: Federal RePORTER
The study evaluates the basal conditions of the onset region of the Northeast Greenland Ice Stream (NEGIS) using airborne ultra-wideband radar data, revealing changes in basal roughness and anisotropy in subglacial structures. In the upstream area, excess ice mass flux is evacuated through ice flow acceleration, while the downstream part shows rougher bed topography and decreased flow acceleration. This suggests two distinct zones in the NEGIS: one collecting water with reduced basal traction, and one where the ice stream slows down and widens on a rougher bed with basal water distributed towards shear margins.
The ice stream geometry and large ice surface velocities at the onset region of the Northeast Greenland Ice Stream (NEGIS) are not yet well reproduced by ice sheet models. The quantification of basal sliding and a parametrization of basal conditions remains a major gap. In this study, we assess the basal conditions of the onset region of the NEGIS in a systematic analysis of airborne ultra-wideband radar data. We evaluate basal roughness and basal return echoes in the context of the current ice stream geometry and ice surface velocity. We observe a change from a smooth to a rougher bed where the ice stream widens, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. In the upstream region, the excess ice mass flux through the shear margins is evacuated by ice flow acceleration and along-flow stretching of the ice. At the downstream part, the generally rougher bed topography correlates with a decrease in flow acceleration and lateral variations in ice surface velocity. Together with basal water routing pathways, this hints to two different zones in this part of the NEGIS: the upstream region collecting water, with a reduced basal traction, and downstream, where the ice stream is slowing down and is widening on a rougher bed, with a distribution of basal water toward 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.
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