A diatom-based reconstruction of the MPT and MIS-31 from the Southern Ocean's Iceberg Alley

The mid-Pleistocene transition (MPT) represents a significant reorganization of Earths climate system, from obliquity-paced, lower magnitude glacial cycles to eccentricity-paced, higher magnitude glacial cycles. Understanding how this transition affected Antarctica and the Southern Ocean is vital for understanding modern climate change. Diatoms recovered from sediments recovered at International Ocean Discovery Project Site U1537, Expedition 382, Iceberg Alley and Subantarctic Ice and Ocean Dynamics, are used to understand the MPT in this region. Diatom species relative abundances and diatom absolute abundance reveal progressive cooling and expansion of sea ice during this time. Furthermore, movements of the polar front can be detected. Marine Isotope Stage 31 (MIS-31) represents a significant warming event which occurred during the MPT. MIS-31 is specifically evaluated in greater resolution during this timeframe. Comparison of the diatom record of MIS-31 at U1537 to other Southern Ocean sites reveals a more complex pacing of warming, with peak warm conditions moving south throughout MIS-31. While precession is seen to be the driver of warmth in the northern portion of the Southern Ocean, obliquity pacing is identified in the southern portion of the Southern Ocean.