East Antarctic Ice Sheet response to ocean forcing during the Middle Miocene Climate Transition: Insights from Prydz Bay

Abstract

Understanding ocean-ice sheet interactions in the geological past is critical for evaluating the ice sheet sensitivity to ocean forcing in future climate warming. Geological evidence suggests major oceanographic changes across the Southern Ocean during the Middle Miocene Climate Transition (MMCT) (~15-12 Million years ago (Ma)). However, the response of the East Antarctic Ice Sheet to these changes remains poorly constrained. Here we explore ocean-ice interactions during the MMCT by presenting data from two marine sedimentary cores along a latitudinal transect offshore Prydz Bay (East Antarctica). Ocean Drilling Program (ODP) Site 1165 is located on the continental rise off Prydz Bay (64◦27.27o S, 67◦13.08o E, 3537.5 water depth) and ODP Site 744 is located on the Southern Kerguelen Plateau (61o 34.66´S, 80o 35.43´E, 2307 m water depth). Neodymium and strontium isotopic compositions of fine-grained (< 63μm) detrital sediments from ODP Site 1165 were generated to constrain potential changes in sediment provenance, revealing potential changes in ice sheet dynamics (expansion/retreat). Neodymium isotope ratios (εNd) from fossil fish teeth from ODP Site 744 were used to trace regional water masses and Southern Ocean circulation changes for the same period. Additionally, marine productivity records generated from both ODP sites were used to track changes on the position of the Southern Ocean frontal system. We report an equatorward migration of the Southern Ocean frontal system around 13 Ma, associated with global climate cooling, sea ice expansion and CO2 decline during the MMCT. Despite this major ocean-climate reorganization, our data suggest the presence of a rather stable and large ice sheet in the Prydz Bay throughout the MMCT, implying that the ice sheet was less sensitive to ocean forcing during the MMCT.