FORAMINIFERAL ASSEMBLAGES REVEAL MULTIPLE SUPER-INTERGLACIALS DURING THE MID-PLEISTOCENE TRANSITION, ROSS SEA, ANTARCTICA

The Mid-Pleistocene Transition (MPT) represents a critical phase in Earth's climatic history during which the dominant periodicity of orbital forcing shifted from a 40,000-year cycle to a 100,000-year cycle. This transition remains a topic of significant scientific interest and has prompted numerous studies to determine the underlying mechanisms. Within the MPT timeframe, Marine Isotope Stage 31 (MIS-31) emerged as a prominent super-interglacial period, exhibiting distinctive climatic and environmental characteristics. We are examining planktic and benthic foraminifera from IODP Site U1523 located at the shelf break of the Ross Sea to provide a comprehensive and high-resolution snapshot of the MPT, including the MIS 31 interval from Antarctica. These microfossil assemblages reveal evidence for multiple super-interglacials in the Ross Sea region between MIS 39 and MIS 25 (~1.29-0.96 Ma) based on high abundances of planktic foraminifera through this interval. Notably, previous studies conducted in the Cape Roberts and ANDRILL projects have reported similar patterns to MIS 31, highlighting the importance of integrating these findings across the Ross Sea. The selected foraminiferal assemblages are dominated by planktic Neogloboquadrina pachyderma and benthics Trifarina earlandi and Globocassidulina subglobosa. These species have proven valuable in paleoclimatic reconstructions due to their sensitivity to environmental changes, including variations in sea surface temperature, productivity, and bottom current activity, such as the Antarctic Slope Current (ASC). For example, increased abundances of the planktic N. incompta correspond to interglacials MIS-39, -37, -31, -25, and 15. In general, benthics Rosalina globularis and Nonionella iridea are also more closely associated with interglacials during the MPT, while T. earlandi is more closely associated with glacials. A decrease in abundance and diversity of benthics after MIS-25 may signal increased sedimentation, dilution, and/or dissolution associated with increased production of High Salinity Shelf Water (HSSW). High resolution stable isotopic analyses will be employed to augment the microfossil records, providing further insights into past climate dynamics and the presence of multiple super-interglacials during the MPT.