Currents and Transport across the eastern Sabrina Basin, East Antarctica

Abstract:

Freshwater budgets of some Antarctic continental shelf sectors are key to the global Meridional Overturning Circulation. Poorly understood interactions of marginal currents with glaciers and ice-shelves are reported to have a sea level rise potential of about 50 m. The Moscow University Ice Shelf (MUIS) and Totten Glacier (TG) system alone accounts for one-eighth of East Antarctic Ice Sheet discharge, roughly the same as estimated for total Western Antarctic Ice Sheet drainage. Observational studies of the circulation, stratification, and exchange of oceanic, shelf and melt waters in the adjacent Sabrina Basin began in in the austral summer of 2014, with a unique set of shipboard measurements aboard the RVI Nathaniel B. Palmer.

Among them are, for the first time over Antarctic margins, simultaneous underway profiling of ocean currents, temperature and salinity. Optimally averaged and quality controlled data from the Shipboard Acoustic Dopper Current Profiler (SADCP) and Underway Conductivity/Temperature/Depth (uCTD) system are analyzed to map flow patterns from the surface to the bottom. Unprecedented spatial (~1 km) and temporal (~30 min) profiling allowed the completion of multiple synoptic sections that effectively resolved the main characteristics of the slope (ASC) and Antarctic Coastal Current (ACoC). Adjusted geostrophic currents and volume transport across these sections were calculated for density layers spanning surface and thermocline waters with oceanic and shelf origin.

After following the western flank of the Dalton Ice Tongue (DIT) to the south, the ACoC turns westward and continues alonog the MUIS front toward TG. Injection of meltwater to the ACoC at varying levels is revealed along this path. Highly contrasting bottom topography is also observed to differentially steer bottom waters. A smooth sedimentary dome found below the Dalton Polynya appears to drive an interior recirculation; whereas a relaitvely rough and narrow escarpment flank in front of MUIS accelerates westward flow, channels inflow to sub-ice cavities and likely intensifies vertical mixing.