Weakening of meltwater plume reduces basal melting in summer at Ekström Ice Shelf, Antarctica

Basal melting of ice shelves significantly contributes to the mass loss of the Antarctic Ice Sheet. However, little is known about the ocean-driven melting of the numerous ice shelves of Dronning Maud Land in East Antarctica. We present a multi-year record of basal melt rates at the Ekström Ice Shelf, obtained using an autonomous phase-sensitive radar system. Our data reveal a low mean annual melt rate of 0.45 m a-1, with seasonal patterns showing reduced melt in summer and peaks in winter and spring. Sea-ice growth just in front of Ekström Ice Shelf correlates with the melt rate time series. A simple ice shelf water plume simulation suggests that melting is reduced in summer in the presence of Antarctic Surface Water, which reduces the velocity of the ice shelf water plume due to the lower density contrast. In winter, when dense water from the sea ice formation erodes the stratification below the ice shelf, more vigorous plumes cause an increase in melt rates. Thus, meltwater plume velocity primarily drives the basal melt rate at the Ekström Ice Shelf, with ambient water temperature being a secondary factor. Upscaling these observations to other ice shelves in this Antarctic sector will improve the overall assessment of the ice-shelf mass balance and improve future projections.