Variability of the Antarctic Coastal Current in the Amundsen Sea

Abstract

The nature of the Antarctic Coastal Current (AACC) and its seasonal and non-seasonal (several-day) variability were investigated using long-term mooring data obtained near the Dotson Ice Shelf (DIS) in the Amundsen Sea. The moored instruments operated from February 2012 to January 2014 in the Dotson Trough (DT), which is one of the deep troughs on the Amundsen Sea shelf. This hydrographic structure of sigma density distribution found that of the ice shelf (27.25 kg m^-3 at the surface) was higher than the continental shelf (27.00 kg m^-3), whereas in the middle layer, 27.45 kg m-3 isopycnal extended 300 m depth near the ice shelf but below 200 m depth in the offshore. The surface mixed layer thickened from the shelf break toward the ice shelf. This thickening was caused partially by coastal downwelling resulting from onshore Ekman transport and by Ekman pumping in the coastal area. The baroclinic component of the AACC near the DIS increased from July to October and decreased from January to June in 2013. In comparison with other potential driving forces, the seasonality and non-seasonal (short-term) variation of the AACC correlated well with density variability, determined principally by salinity variation. Therefore, it is suggested that the variability of the isopycnocline by Ekman pumping in the coastal area is one of the important factors controlling the seasonality and non-seasonal variability of the AACC.