Subglacial processes on an Antarctic ice stream bed 1: sediment transport and bedform genesis inferred from marine geophysical data

The spatial pattern and morphometry of bedforms and their relationship to sediment thickness have been analysed in the Marguerite Bay Palaeo-Ice Stream Trough, western Antarctic Peninsula. Over 17,000 glacial landforms were measured from geophysical datasets, and sediment thickness maps were generated from acoustic sub-bottom profiler data. These analyses reveal a complex bedform pattern characterised by considerable spatial diversity, influenced heavily by the underlying substrate. The variability in length and density of mega-scale lineations indicates an evolving bedform signature, whereby landforms are preserved at different stages of maturity. Lineation generation and attenuation is associated with regions of thick, soft till where deformation was likely to be greatest. The distribution of soft till and the localised extent of grounding-zone wedges (GZWs) indicate a dynamic sedimentary system characterised by considerable spatio-temporal variability in sediment erosion, transport and deposition. Formation of GZWs on the outer shelf of Marguerite Trough, within the error range of the radiocarbon dates, requires large sediment fluxes (upwards of 1000 m3 yr-1 per meter width of grounding line), and a >1 m thick mobile till layer, or rapid basal sliding velocities (upwards of 6 km yr-1).