The Pathways and Heat Transport of Circumpolar Deep Water into the Thwaites and the Pine Island Glaciers, West Antarctica

Abstract:

It is known that upwelling Circumpolar Deep Water (CDW) is destabilizing Western Antarctic ice shelves — Thwaites and Pine Island — and accelerating basal melt rates by delivering warm water underneath the ice, which can significantly contribute to future sea-level rise. Its detailed pathways, however, into the two ice shelves and modification of its property remain unclear primarily due to lack of in-situ observations in a necessary resolution. Here, we present initial results by analyzing hydrographic data collected using the Korea Polar Research Institute Icebreaker ARAON-based CTD/LADCP castings off the ice shelves and University of Tasmania Autonomous Underwater Vehicle (AUV; nupiri muka)-based CTD/ADCP measurements under the sea ice during 2019-2020 cruise. In this study, we confirmed poleward pathways of warm and saline CDW into the ice shelves that are mostly following deep (> 660 m or neutral density of 28.03 kg/m³) troughs with cooling and freshening, which is broadly good agreement with a regional ocean circulation model. Furthermore, consistent rates of declining water temperature and salinity (0.0008±0.0006 ^oC/km and 0.0001±0.0009 /km) are estimated along the key isopycnal (neutral density of 28.09 kg/m³) at the main CDW path toward the ice shelf that connects the ice shelves — Thwaites and Pine Island — through the cavity below the Thwaites ice shelf. Total amounts of heat transport into the ground zone of the Thwaites and Pine Island Glaciers are 2.1±1.1 and 2.9±1.9 TW, respectively, which may help to constrain basal melt rates in this region. Our study provides detailed information on the pathways and heat transport (temperature gradient) of CDW — how much heat is delivered all the way to the grounding zone — that allows us to better predict a tipping point or timing of collapse of the glaciers.