EARLY PLIOCENE DRAWDOWN AND EXPANSION OF THE ANTARCTIC PENINSULA ICE SHEET IN MARGUERITE BAY

Sandra Passchier , Ridley Joseph, Monika Ghimire, Xiaona Li

The Antarctic Peninsula Ice Sheet (APIS) is situated in a rapidly and persistently warming region of Antarctica and its behavior under warmer conditions projected for Earth’s future remains poorly constrained. Interpretations of stratigraphic records of ice-sheet change from periods of warmth in Earth’s past are essential in providing boundary conditions for estimates of future ice loss and its climate feedbacks. The early Pliocene exhibited surface temperatures that were 3-4 °C higher than present under similar greenhouse forcing. Here we present new sedimentological and geochemical data from the early Pliocene section recovered in Ocean Drilling Program Site 1097 to assess the effects of atmospheric and ocean warming on ice extent and glacial regime. The reconstruction of Pliocene glacial processes and sediment provenance within an updated chronology of Site 1097, indicates that ice was absent from the Marguerite Bay with supply from local glaciers only at ~5.2 to 4.8 Ma. A subsequent shift in sediment provenance suggests that the APIS began to dominate ice drainage into Marguerite Bay ~4.5 Ma with the sedimentology of the deposits pointing to a subpolar, meltwater-intensive glacial system before ~4.3 Ma. In contrast, a massive and stratified diamictite-dominated section younger than ~4.3 Ma, shows characteristics similar to Pleistocene deposits from the Marguerite Ice Stream Trough. These changes in sedimentary systems reflect enhanced accumulation and retreat phases of the terrestrial Antarctic Peninsula Ice Sheet under Pliocene peak warming and stable marine ice-sheet growth upon cooling, providing critical insights into the dynamics of this ice sheet in response to sustained warmth.