EVIDENCE FOR RAPID ICE SHEET RETREAT SINCE THE LAST GLACIAL MAXIMUM IN THE EASTERN ROSS SEA, ANTARCTICA

Marine geophysical and sedimentological data from the continental shelf of the eastern Ross Sea, Antarctica give evidence for rapid retreat of the West Antarctic Ice Sheet (WAIS) since the last glacial maximum. The eastern Ross Sea is characterized by large troughs extending from the inner shelf to the continental shelf edge. These troughs are believed to have been occupied by ice streams during the last glacial maximum. Cores, seismic data and multibeam bathymetric images were taken along the axes of these troughs in order to study the history of the ice sheet in this region.

Multibeam data shows mega-scale lineations trending the entire length of the troughs, indicating the presence of streaming ice flowing over a deforming bed. Sedimentary wedges are imaged seismically only in shelf edge and inner shelf positions and record pauses in ice sheet retreat. Boundaries of the troughs are comprised of sedimentary strata and show evidence of significant lateral migration. Sediment cores taken in a transect down the axes of the troughs sample thin deposits of diatomaceous mud and silty clay overlying muddy diamicton. These deposits, which reflect deposition under open marine conditions are very thin, less than 0.7 m thick. This is below the resolution of our deep tow chirp-sonar. This finding contrasts sharply with the western Ross Sea where the draping unit of diatomaceous mud is typically a few meters thick. Diamictons, interpreted as tills, were penetrated in all of the core sites. Their presence, combined with mega-scale lineations imaged in the axes of the troughs indicate sediment deformation beneath rapidly flowing ice streams.

The combined geomorphic, stratigraphic and sedimentologic evidence leaves open the possibility of ice sheet collapse in the eastern Ross Sea.