Millennial-timescale East Antarctic Ice Sheet variability and recurrent seafloor oxidation pulses during the Miocene Climatic Optimum at Prydz Bay

The Amery Ice Shelf, the third largest ice shelf at the head of Prydz Bay, and one of the four regions where Antarctic Deep Waters form, is reported as one of the most stable portions of the East Antarctic Ice Sheet (EAIS). Yet, its response to future warming remains uncertain. The Miocene Climatic Optimum (MCO, ~17–15 million years ago) is the warmest period of the past 23 million years, with global temperatures 3–8°C above modern and pCO₂ of 400–600 ppm, similar to end-century projections. It therefore provides a valuable opportunity to investigate EAIS stability under warm conditions. Here, we present a combined lipid biomarker, palynology and XRF record from ODP Site 1165, offshore Prydz Bay, spanning ~16.3-16 Ma at an unprecedented millennial-scale resolution, crucial for understanding the near-future EAIS conditions in a warmer world. Interestingly, the record shows recurrent pulse-like intense organic matter oxidation events associated with elevated proportions of reworked and oxidation-resistant in situ dinoflagellate cysts as well as ice-rafted debris (IRD). IRD presence in this record was previously interpreted as evidence for deglaciation. However, deglaciation, meltwater and subsequent stratification are somewhat in contrast with seafloor oxidation. 

Oxidation events at the seafloor may rather be linked to oxygen-rich deepwater associated with EAIS and sea ice dynamics at location, or other processes we are investigating. Excluding the interval where organic matter oxidation is recorded, the remaining record indicates relatively stable seawater conditions. Specifically regarding sea water temperature (SST) based on glycerol dialkyl glycerol tetraethers (GDGTs)-based SST proxy (TEX₈₆) and alkenone-based SST proxy both suggest SSTs around 9-16°C, although hydroxylated-GDGTs suggest much lower SSTs around 4-9°C. Furthermore, the occurrence of plant-derived fatty acids and pollen-spore assemblages indicate a sustained woody-tundra vegetation and an intensified hydrological cycle on the hinterland than modern throughout the record.