The Upper 1000-m Slope Currents North of the South Shetland Islands and Elephant Island Based on Ship Cruise Observations

Abstract

While the Antarctic Slope Current (ASC) has been intensively studied for the East Antarctica slope area and the Weddell Sea, its fate in the western Antarctic Peninsula (WAP) region remains much less known. Data from two cruises conducted near the South Shetland Islands (SSIs) and the Elephant Island (EI), one in austral summer of 2004 and one in austral winter of 2006, were analyzed to provide a broad picture of the circulation pattern over the continental slope of the surveyed area, and an insight into the dynamical balance of the circulation. The results indicate that southwestward currents are present over the upper slope in the study area, indicating the ASC in the WAP region. Near the Shackleton Gap (SG) north of the EI, the southwestward slope currents near the shelf break are characterized by a water mass colder and fresher than the ambient water, which produces cross-slope density gradients and then vertical shear of the along-slope (or along-isobath) velocity. The vertical shear is associated with a reversal of the along-slope current from northeastward at surface to southwestward in deeper layers, or a depth-intensification of the southwestward slope currents. The water mass with temperature and salinity characteristics similar to the observed cold and fresh water is also revealed on the southern slope of the Scotia Sea, suggesting that this cold and fresh water is originated from the Scotia Sea slope and flows southwestward through the SG. Over the shelf north of the SSIs, the cold and fresh water mass is also observed and originates mainly from the Bransfield Strait. In this area, vertical structure of the southwestward slope currents is associated with the onshore intrusion of the upper Circumpolar Deep Water that creates cross-slope density gradients.