Bedform topography and basal conditions beneath a fast-flowing West Antarctic ice stream |
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| Authors: | Andy M Smith Tavi Murray |
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| Institution: | 1. British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK;2. CASP, 181A Huntingdon Road, Cambridge CB3 0DH, UK;3. Swedish Museum of Natural History, Box 50007 SE-104 05, Stockholm, Sweden;1. Utrecht University, Department of Physical Geography, PO Box 80115, Utrecht, The Netherlands;2. International Centre for Integrated Mountain Development, GPO Box 3226, Kathmandu, Nepal;3. ETH Zurich, Institute of Environmental Engineering, Hydrology and Water Resources Management, Wolfgang-Pauli-Str. 15, 8093 Zurich, Switzerland;1. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA;2. Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA 90095, USA;3. Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Box 355640, Seattle, WA 98105, USA;4. U.S. National/Naval Ice Center, NOAA Satellite Operations Facility, 4251 Suitland Road, Washington, DC 20395, USA |
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| Abstract: | A grid of seismic reflection lines has been used to image basal topography and infer basal conditions and flow processes beneath ～140 km2 of Rutford Ice Stream, West Antarctica. The subglacial topography in this region consists of two troughs flanking a central high and the bed is composed of water-saturated sediments. The two troughs are filled with deforming sediment, whereas the bed in the central region appears to undergo a transition from largely deforming conditions upstream to basal sliding downstream. The deforming bed is very flat along flow, but undulates across flow. Sliding areas show rougher bed topography. Cross-stream bed topography is characterised by streamlined mounds of deforming sediment aligned in the ice flow direction. These bedforms occur superimposed on the bed in regions of both basal sliding and sediment deformation. In places, they form finger-like mounds of material, which extend into the sliding region further downstream. Mean bedform height is 22 m, mean width is 267 m, and many of them extend for at least 1–2 km along flow. We interpret most of these bedforms as drumlins and one as a mega-scale glacial lineation. The juxtaposition of different basal conditions is consistent with models proposed from terrestrial studies in which the glacier bed is a mosaic of stable and deforming bed areas, variable both spatially and temporally. Any theory of subglacial sediment rheology must also be able to account for our conclusion that, at any given time, pervasive deformation extends at least a few metres into the bed and can persist over a considerable area (many km2). Bedform geometry and basal conditions concur with interpretations of former ice streams, with evidence for increasing elongation ratio with distance downstream. However, those studies also identified bedrock cropping out at the ice-bed interface, for which there is no evidence on Rutford Ice Stream. |
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