Open marine sedimentation in the southwestern Ross Sea during the Last Glacial Maximum

Abstract

Growing evidence suggests that the Antarctic ice sheet may not have been in its maximum extent during the Last Glacial Maximum (LGM). Recent radiocarbon results imply that the West Antarctic Ice Sheet (WAIS) retreated from the eastern Ross Sea prior to LGM. In the western Ross Sea, however, it was generally considered that a thick ice sheet was grounded to the sea floor during the LGM and the retreat of that ice sheet did not begin until ~13 ky BP. Here we show evidence that the ice sheet retreated not only from the eastern Ross Sea but also from the western Ross Sea during the LGM, and then the latest ice sheet advanced into the western Ross Sea, followed by the final retreat. Diatomaceous mud layers underlie stratified diamicton in the southern Drygalski Trough, indicating a seasonally open marine sedimentation prior to the last glacial event in the western Ross Sea. Ramped PyrOx radiocarbon dating of this diatomaceous mud shows that ice sheet on the western Ross Sea retreated at ~24 ky BP, and advanced at ~21 ky BP. In order to preserve the diatomaceous mud, we infer that the most recent advance featured a thinner ice sheet than the previous advance. Multibeam swath bathymetry and sub-bottom profile data show that the latest ice sheet in the southern Drygalski Trough retreated to the northwest. The flow direction suggests that (1) the latest ice sheet in the SW Ross Sea was the East Antarctic Ice Sheet (EAIS) advanced through the Transantarctic Mountains and (2) the WAIS that can deflect the flow direction to the north did not advance into the study area during the final retreat. The WAIS either retreated much earlier than the EAIS or did not advance into the SW Ross Sea during the last glacial event