Extent and dynamics of the West Antarctic Ice Sheet on the outer continental shelf of Pine Island Bay during the last glaciation

Abstract

Swath bathymetry and TOPAS sub-bottom profiler acoustic data reveal the presence of a major cross-shelf bathymetric trough containing streamlined subglacial bedforms formed in soft till that extends to the continental shelf edge of outer Pine Island Bay, Amundsen Sea, West Antarctica. The new data indicate that the West Antarctic Ice Sheet (WAIS) extended to the shelf edge of Pine Island Bay during the last glaciation, and was drained by a grounded, fast-flowing palaeo-ice stream through this outer-shelf trough. Topography and subglacial geology are likely to have exerted a strong control on the development and location of palaeo-ice streams in Pine Island Bay. TOPAS records show that mega-scale glacial lineations are formed in an acoustically transparent sediment layer interpreted to be soft till and are inferred to be the product of subglacial sediment deformation beneath the palaeo-ice stream. The flat to irregular nature of the basal reflector of the acoustically transparent layer of soft till implies that a combination of groove-ploughing of the substrate and subglacial sediment deformation were important processes beneath the palaeo-ice stream in the outer trough of Pine Island Bay, as well as palaeo-ice streams elsewhere in Antarctica. Therefore, the formation of the soft till layer, and possibly associated subglacial bedforms, are likely to be a function of these palaeo-ice stream processes. In a regional context, the WAIS extended to the continental shelf edge of the Bellingshausen, Amundsen and Ross Seas, and was drained by a number of palaeo-ice streams during the last glaciation.