Miocene to Pliocene/Pleistocene shift in West Antarctic Ice Sheet dynamics in the Bellingshausen Sea and Amundsen Sea sectors

The attention on the current enormous ice mass loss of the West Antarctic Ice Sheet (WAIS) leads to questions about its behavior in the geological past, in particular during past extended warm periods such as those in the Miocene and Pliocene. The compilation of the network of seismic lines linked to relevant ocean drilling sites of ODP Leg 178 at the western Antarctic Peninsula and IODP Expedition 379 on the Amundsen Sea continental rise enables analyses of the temporal and spatial evolution of the WAIS in the southeastern Pacific sector from early expansions to the continental shelves in the Oligocene-Miocene to variations in its dynamic behavior up to the Pliocene/Pleistocene. This includes significant warm periods with major grounded ice retreat events in the middle to late Pliocene. Our analyses indicate that long-period expansion and retreat phases of the main ice-stream outflow systems in the Bellingshausen Sea sector and the Amundsen Sea sector occurred less synchronously than previously assumed. In the Bellingshausen Sea sector, the earliest high-intensity advances of grounded ice occurred in the Miocene with mid- to low-intensity advances in the Pliocene. Extended ice sheet retreat periods during the Pliocene warm times are not as clearly observed as in the Amundsen Sea sector. On the other hand, the Amundsen Sea sector experienced its earliest low-intensity ice advances in the Miocene and high-intensity advances in the Pliocene with extended ice-sheet retreat periods embedded during the so-called Pliocene Amundsen Sea Warm Period from 4.2 to 3.2 Ma. Different paleotopographic conditions of the respective hinterlands likely caused different ice-stream/ice-sheet dynamics. In addition, regional ocean circulation patterns, that were prevalent at particular times, seem to have had a major control on expansion and retreat phases. We show newest seismic data analyses and try to synthesize our observations into a consistent model for past WAIS dynamics from the Miocene to the Pleistocene.