The Circulation And Dynamics Of The Antarctic Slope Current West Of The Antarctic Peninsula

Although the Antarctic slope just accounts for a relatively small portion of the Antarctic Ocean,it is a crucial area for the formation of Antarctic Bottom Water,biogeochemical cycling and ecosystem functioning.Therefore it is of great importantce for us to understand the circulation and dynamics of the Antarctic Slope Current(ASC).While ASC has been intensively studied for East Antarctica 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 of the circulation.The results indicate that on the deep part of the the EI and SSIs slope,the ASC is mainly affected by the Antarctic Circumpolar Current(ACC)and flows northeastward.Howerve,over the shallow part of the EI and SSIs slope,southwestward currents exist below the surface layer,indicating the ASC west of the Antarctic Peninsula.Near the EI,the southwestward slope currents are characterized by a cold and fresh water mass on the shallow part of the slope,which produces cross-slope(along-transect)density gradients and then vertical shear of the cross-transect(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.North of the SSIs,occurrence of the southwestward slope currents is also associated with the intrusion of the upper Circumpolar Deep Water.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.The horizontal circulation field confirms the southwestward ASC over the shallow part of the WAP and the cyclonic circulation in Bransfield Strait,including a strong flow to the east-northeast along the southern slope of the SSIs and a less intense southwestward flow in the near-Peninsula part of the Strait.The transport is consistent with the circulation in the region of the WAP.