Warm. Circumpolar Deep Water at the Western Getz Ice Shelf Front, Antarctica

The Getz Ice Shelf is one of the largest sources of fresh water from ice shelf basal melt in Antarctica. We present new observations from three moorings west of Siple Island 2016-2018. All moorings show a persistent flow of modified Circumpolar Deep Water toward the western Getz Ice Shelf. Unmodified Circumpolar Deep Water with temperatures up to 1.5 degrees C reaches the ice shelf front in frequent episodes. These represent the warmest water observed at any ice shelf front in the Amundsen Sea. Mean currents within the warm bottom layer of 18-20 cm/s imply an advection time scale of 7 days from shelf break to ice shelf front. Zonal wind stress at the shelf break affects heat content at the ice shelf front on weekly to monthly time scales. Our 2-year mooring records also evince that upwelling over the shelf break controls thermocline depth on subannual to annual time scales. Plain Language Summary The recent retreat of the West Antarctic Ice Sheet has been linked to changes in the transport of warm ocean water up to 1.5 degrees C to the floating ice shelves in the Amundsen Sea. One of these is the Getz Ice Shelf that produces one of the largest amounts of ice shelf melt water in Antarctica. To measure how much ocean heat is transported toward this ice shelf, we deployed a series of temperature, salinity, and current sensors at its western end from 2016 to 2018. We find a constant flow of warm water toward the ice shelf cavity. Comparing our ocean observations with wind data from the area, we found that stronger easterly winds in the area make it harder for the warm water to reach the ice shelf front by depressing the warm bottom layer over the shelf break. Climate projections indicate that these easterlies will weaken in future, making it easier for the warm water to reach the ice shelf base. Gradients in the wind field over the shelf break control the thickness of the warm layer on longer time scales. This provides the missing ocean evidence for previous studies that have linked this wind mechanism to ice sheet changes.