The death mask of the antarctic ice sheet: Comparison of glacial geomorphic features across the continental shelf

Abstract

Multibeam swath bathymetry data, seismic lines, and shallow cores were collected seaward of all of the major drainage outlets of the Antarctic Ice Sheet from the Pennell Coast of North Victoria Land to the northwestern Weddell Sea. The results show that during the last glacial maximum, the ice sheet extended onto the outer shelf in all areas, to the shelf break in many. Swath bathymetry and deep-tow sidescan sonar data from the continental shelf also record the geomorphology left by the retreating ice sheet. Glacial troughs occur offshore of all major glacial outlets. In each drainage area except for parts of the Ross Sea, the inner shelf is characterized by acoustic basement interpreted as crystalline substrate. The geomorphology of these inner shelf areas consists of erosional features such as grooves that show that ice flow tended to follow the structural grain of the bedrock. Outer shelf areas are floored by sedimentary substrate where the direction of ice flow was more directly offshore and depositional features characterize the seafloor. In these areas the signature of the grounded ice consists of till deposits and large-scale geomorphic features, mega-scale glacial lineations. Drumlins occur within the region of contact between crystalline and sedimentary substrates. Meltwater channels also have been imaged in both inner and outer shelf settings. While the presence of meltwater across the shelf has long been suspected, we present here the first multibeam image of a meltwater channel on the outer continental shelf of Antarctica. At the shelf break gullies are in all areas where we know ice reached the shelf break. We note the remarkable similarity in form of mega-scale glacial lineations observed on the outer shelf over sedimentary substrate across all areas surveyed, typically measuring 200–600 m crest to crest. This suggests that the shape of these landforms is governed by the same process in each drainage area and that process was occurring under a large area of the ice sheet. The erosional and transitional features show much variability in form and distribution.