Variability of the Antarctic Coastal Current (AACC) and its causes in the Amundsen Sea

Abstract

The Antarctic Coastal Current (AACC) or east wind drift flows westward around Antarctica. Coastal current is mainly barotropic component by the wind driven Ekman transport (Sverdrup 1953) and baroclinic component is generated by a density gradient between Antarctic Surface Water and Shelf Water (Fahrbach et al., 1992). Ismael and Fahrbach (2009) show the contribution of the mechanisms driving the coastal and its seasonality in the Weddell Sea. Therefore, the present study attempts to quantify the contribution of the mechanisms driving the AACC and its seasonality and decadal variation of coastal current in the Amundsen Sea. We evaluated variability of coastal current and its driving forcing in the Amundsen Sea using observed and calculated ocean current. The observation data was collected here was obtained from KOPRI mooring stations in the Dotson Trough (DT), which is one of the deep troughs in the Amundsen shelf. The westward current shows in front of the Dotson ice shelf (DIS) and it strong seasonal variation. The seasonality of the AACC was well matched with the seasonality of the pressure gradient in the DT. We calculated the surface ocean currents to understand decadal time scale variation of the AACC, which was the difficult to observe below sea-ice using the satellite data. We used a simplified linear formula to understand the relationship between the sea ice motion and sea surface wind as Kimura (2004). This previous study was evaluated relationship using sea ice properties about speed reduction factor and turning angle in the Southern Ocean. Although the estimated coastal current speed was smaller than observation, decadal time scale of the westward flow of the coastal current was increased.