Oral

IAPSO

JCP05 - Ice sheet-ocean interactions and impacts

Drivers of Pine Island and Thwaites Ice Shelf Melting, Antarctica

The Amundsen Sea in West Antarctica is undergoing rapid ice shelf melting, affecting ice-sheet stability and contributing to global sea level rise. A key factor controlling basal melt rates is thermocline depth (TD) variability, which separates cold Winter Water (WW) from warm modified Circumpolar Deep Water (mCDW) at the ice shelf front. Despite its importance, the mechanisms driving interannual TD variability remain not well understood. Using a high-resolution ocean model optimized for the Amundsen-Bellingshausen Seas, we identify on-shelf circulation variability in the eastern Amundsen Sea as the primary driver of TD fluctuations, influencing the melt rates of Pine Island and Thwaites Ice Shelves (PIIS/TIS), which is often referred to as the Doomsday Glacier due to its potential to contribute significantly to global sea level rise if it collapses. This variability arises from meandering on-shelf currents along submarine glacial troughs, which generate vertical velocity at the bottom through interactions with the seafloor. These interactions modulate mCDW upwelling, leading to fluctuations in TD and, consequently, ice shelf basal melt. Our results further reveal that interannual variations in off-shelf zonal winds play only a minor role in transporting ocean heat into PIIS/TIS cavities. This revises the widely accepted concept that atmospheric forcing dominates and instead highlights the critical role of on-shelf circulation in modulating ice shelf melt. Given the ongoing changes in Antarctic coastal currents, understanding these processes can improve predictions of future ice loss and its global impact. In this talk, we will review recent studies suggesting multiple processes driving cross-shelf transport of mCDW and aim to discuss the relative contributions of these oceanic processes to West Antarctic ice shelf melting. Additionally, we will introduce research efforts utilizing the icebreaker Araon in the Amundsen Sea, Ross Sea, and Antarctic Circumpolar Current regions. These investigations, combined with high-resolution model simulations, aim to better understand the processes controlling heat and meltwater transport in Antarctic shelf seas and the Southern Ocean, which play a role in global ocean circulation and climate dynamics.