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

Eddies are under sampled in the Weddell Sea, due to an extensive ice cover for large parts of the year. There are even fewer observations of eddies under ice, with none detailing the dynamic and thermodynamic interactions between them. Here we present novel observations of an eddy spinning down under an ice shelf. Two acoustically tracked profiling floats were deployed at 8^oW in the Antarctic Slope Current and drifted westward along the slope at 800m depth. One of the floats was captured by an anticyclonic eddy in the wake of 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. Trajectory data 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 are 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 mixing of the eddy’s cold and fresh core vertically in the upper water column, due to the Eddy-Ice-Pumping mechanism, resulted in a cold and fresh subsurface signal which was still evident downstream at the Filchner Trough three 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-Ronnie Ice Shelf. Since the Filchner-Ronnie Ice Shelf is where much of the source water for Antarctic Bottom Water is produced, eddy modified water column properties could affect the properties of this source water, and thus Antarctic Bottom Water.