East Antarctic ocean-ice sheet interactions during Miocene warmth

Regions of Antarctica were most recently ice-free during the Miocene Climatic Optimum (MCO, ~17-14 Ma). During this warm interval, the East Antarctic Ice Sheet (EAIS) exhibited highly dynamic behavior and episodic wide-scale retreat associated with global sea level rise. During the subsequent Middle Miocene Climate Transition (MMCT), the EAIS expanded and stabilized with contemporaneous global cooling. However, little is directly known about drivers of EAIS behavior during the Miocene due to a lack of continuous, high-resolution climate records near Antarctica. Here, we present multi-proxy (U^k’₃₇ and TEX₈₆) biomarker records of sea surface temperatures (SSTs) from Ocean Drilling Program (ODP) Site 1165 in the polar Southern Ocean to constrain ocean-ice sheet interactions in the Prydz Bay region of East Antarctica throughout the Miocene. Our records span 5 to 19 Ma, with orbital-resolution data (5 kyr) during the MMCT from 13.2 to 15.1 Ma. We find peak SSTs during the MCO up to 18°C warmer than modern as well as polar-amplified cooling synchronous with the establishment of permanent Antarctic glaciation and broader global cooling during the MMCT (13.8 Ma) and Late Miocene (6-8 Ma). Comparison of our high-resolution SST record and ice rafted debris at the same site shows that ice rafting disappeared when SSTs warmed above 12°C, demonstrating the vulnerability of the marine ice margin to ocean warming. However, comparison with global benthic oxygen isotope records indicates that terrestrial-based ice volume exhibited threshold behavior as transient cooling during the MMCT crossed a tipping point for terrestrial ice sheet growth and stabilization, which subsequent warming was not sufficient to reverse. These results constrain the EAIS response to elevated greenhouse gas concentrations during the past global warmth of the Miocene, with implications for potential future long-term behavior of Earth’s largest ice sheet.