On the structure and the transport of the eastern Weddell Gyre

The circulation pattern and volume transports in the eastern Weddell Gyre a re estimated on the basis of hydrographic data collected by R.V. Polarstern between 1989 and 1996. In the northeastern edge of the Weddell Gyre, eastw ard-flowing water masses from the Antarctic Circumpolar Current and the Wed dell Sea converge. Due to the strong effect of topographic constraints on o cean currents in the weakly stratified waters of high latitudes, the wedge- like structure of the Southwest Indian Ridge can cause the convergence. The increased shear leads to instabilities of the current at the eastern end o f the ridge, which produce an intense mesoscale eddy field between 15 degre es and 30 degrees E. In the eddies, water from the Weddell cold regime and the Antarctic Circumpolar Current waters mix and form the water masses of t he Weddell warm regime. These waters are advected southward and flow toward s the westward southern rim current, which is driven by the Antarctic eastw ind band. Hence, there is not a continous flow from the northern to the sou thern rim, but a decay of the mean flow in the northeast and a reformation in the south. Volume transports across the Greenwich Meridian, estimated on the basis of a combined CTD/ADCP data set, result in an eastward flow of 6 1 Sv in the northern rim current and a westward return flow of 66 Sv in the southern part of the gyre. The transport is about twice as high as previou s estimates between Kapp Norvegia and the northern tip of the Antarctic Pen sinsula, indicating a significant gyre circulation north of 70 degrees S. ( C) 1999 Elsevier Science Ltd. All rights reserved.