Ocean‐Forced Instability of the West Antarctic Ice Sheet Since the Mid‐Pleistocene

Evidence on West Antarctic Ice Sheet (WAIS) instability through Pleistocene glacial/interglacial cycles can provide fundamental constraints on interactions between the climate system and cryosphere. To explore such ice sheet‐ocean‐climate processes on orbital timescales over the last ∼770 ka, we provide continuous records of iceberg‐rafted debris (IRD) content and clay mineralogy, supported by detrital Sr‐Nd isotopes from the pronounced IRD peaks, in gravity core ANT34/A2‐10 from the Amundsen abyssal plain. The IRD record reveals interglacial WAIS instability since ∼770 ka, while comparison to the clay mineralogy record and published records of regional oceanic and atmospheric forcing suggests a temporal link with a strengthened Antarctic Circumpolar Current, enhanced deepwater ventilation, and poleward‐shifted southern westerly winds. In addition, the Sr‐Nd isotope signature of the detrital sediments indicates a shift in provenance around Marine Isotope Stage (MIS) 16, potentially linked to regional oceanic circulation changes. We suggest that an expanded Ross Gyre was important for controlling iceberg trajectories and sediment transport to the site before MIS 16, whereas modern‐like iceberg trajectories were established after MIS 16, probably related to a poleward shift of the Amundsen Sea Low after the end of the Mid‐Pleistocene Transition. This reorganization of the ocean and atmospheric circulation was followed by an interval of enhanced WAIS variability during MIS 15 to 13, which was linked to strong orbital and ocean forcing. These insights into the role of ocean‐atmosphere forcing on the past behavior of the WAIS may improve our framework for understanding future changes in this region. Plain Language Summary Understanding the vulnerability of the West Antarctic Ice Sheet (WAIS) to a warming climate is critical for constraining its future contributions to global sea‐level rise. Previous studies on marine sediment cores have provided evidence for WAIS instability in response to warming ocean waters during recent glacial/interglacial cycles. Here, we extend such work over a longer timescale by generating iceberg‐rafted debris (IRD) content and clay mineralogy records from the Amundsen Sea offshore of West Antarctica back to ∼770 ka. Enhanced IRD content during warm interglacial periods provides evidence for the instability of the WAIS and was accompanied by a shift in clay mineralogy. These changes also coincided with a strengthened Antarctic Circump