Under Ice-Shelf Eddy at the Stancomb-Wills Ice Tongue

Abstract

Eddies are considered important for the dynamics within the Antarctic Slope Current but are difficult to observe due to the often year-round ice cover in the southern Weddell Sea. Here we present novel findings from acoustically tracked profiling floats, which observed the spin-down of an eddy under an ice shelf. Two profiling floats were deployed at 8°W in the Antarctic Slope Current and drifted westward along the slope at 800 m depth. One of the floats was captured by an anticyclonic eddy in the wake of the Riiser-Larsen Ice shelf. We postulate the eddy was generated by baroclinic instability due to the interaction of the Antarctic Slope Current with floating ice shelves. Float trajectories show the eddy propagated westward along the slope and ultimately became trapped under the Stancomb-Wills Ice Tongue, where the eddy spun down because of ocean-ice shelf stresses. Simple bulk mixing calculations were fitted to observations to explore the role of eddies under the ice shelf, in relation to an “Eddy-Ice-Pumping” mechanism, and revealed that significant basal melting occurred. Subsequent vertical mixing of the eddy's cold and fresh core, due to the Eddy-Ice-Pumping mechanism, resulted in a cold and fresh subsurface signal which was still evident downstream at the Filchner Trough 3 months later. Estimates of eddy contributions to basal melt and freshwater transport show eddies could have a significant impact on the stratification and thermocline depth downstream, potentially affecting the inflow of modified Warm Deep Water into the Filchner Trough.