Vulnerability of Eastern Thwaites Ice Shelf, West Antarctica to Warm Ocean Water: Insights from First AUV Exploration of Sub-Ice-Shelf Environment

Erin C Pettit, Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, United States, Anna Wahlin, University of Gothenburg, Department of Marine Sciences, Gothenburg, Sweden, Karen J. Heywood, University of East Anglia, Norwich, United Kingdom, Bastien Yves Queste, University of East Anglia, Centre for Ocean and Atmospheric Sciences, Norwich, United Kingdom, Rob Hall, University of East Anglia, Norwich, NR4, United Kingdom, Lars Boehme, Scottish Oceans Institute, Sea Mammal Research Unit, St. Andrews, United Kingdom, Ted A Scambos, University of Colorado Boulder, Boulder, CO, United States, Jan Lenaerts, University of Colorado Boulder, Department of Atmospheric and Oceanic Sciences, Boulder, United States, Martin Truffer, University of Alaska Fairbanks, Geophysical Institute, Fairbanks, AK, United States, Atsuhiro Muto, The Pennsylvania State University, University Park, PA, United States and Christian Thomas Wild, Oregon State University, CEOAS, Corvallis, United States
Thwaites and neighboring glaciers and ice shelves in West Antarctica are rapidly losing mass and perceived as vulnerable to warm ocean water entering the sub-ice-shelf cavity. Predictions of future ice-shelf and glacier dynamic behavior still lack understanding of the dominant processes and feedbacks, particularly the spatial and temporal variability of ice melt and its atmospheric and oceanic drivers. Here we present the first direct observations of ocean temperature and salinity underneath Thwaites ice shelf collected by an autonomous underwater vehicle as part of the TARSAN (Thwaites-Amundsen Regional Survey and Network) Project. We provide an initial interpretation in the context of nearby ship-based temperature and salinity profiles, recently improved bathymetric maps, radar-derived ice geometry, and related data. Our analyses suggests that deep water (> 1000 m) underneath the central part of the Thwaites ice shelf originates in Pine Island Bay, which suggests more complex deep water circulation than previously understood. Further, mid-depth water (700 - 1000 m) enters the cavity from both sides of a buttressing point for the Eastern Thwaites Ice Shelf. We observe large spatial gradients of density and temperature and infer that this is a region of strong current shear and active mixing processes. The findings highlight a vulnerability of the main buttressing point to warm water inflow from all sides and challenge conceptual models of ice-ocean interactions at glacier grounding zones. Finally, we provide an initial assessment of the possible local short-term dynamic response of the ice shelf to loss of this buttressing point. The Thwaites and other West Antarctic glaciers and ice shelves are rapidly changing; the potential for complex flow patterns that generate localized melting and loss of buttressing to feed back onto and alter those flow patterns remains a large uncertainty in predicting sea-level rise through the next decades.