THE FLOW-FIELD OF THE SUBTROPICAL GYRE OF THE SOUTH INDIAN-OCEAN

The mean state of the transport field of the subtropical gyre of the S outh Indian Ocean has been derived for the upper 1000 m from selected historical hydrographic data. The subtropical gyre in the southwestern Indian Ocean is stronger than the flow in the other two oceans of the southern hemisphere. Most of the water in the South Indian gyre recir culates in the western and central parts of the basin. In the upper 10 00 m the eastward transport of the South Indian Ocean Current starts w ith 60 Sv in the region southeast of South Africa. Between the longitu des of 40 degrees and 50 degrees E about 20 Sv of the 60 Sv recirculat es in a southwest Indian subgyre. Another major diversion northward oc curs between 60 degrees and 70 degrees E. At 90 degrees E the remainin g 20 Sv of the eastward flow splits up, 10 Sv going north to join the westward flow and only 10 Sv continuing in a northeastward direction t o move northward near Australia. Near Australia, there is indication o f the poleward flowing Leeuwin Current with a transport of 5 Sv. In th e central tropical Indian Ocean between 10 degrees S and 20 degrees S, about 15 Sv flows to the west. The western boundary current of this s ubtropical gyre consists of the Agulhas Current along the east coast o f southern Africa. Its mean flow is composed of 25 Sv from east of Mad agascar and 35 Sv from recirculation in the southwest Indian subgyre s outh of Madagascar, with only 5 Sv being contributed from the Mozambiq ue Channel. A net southward transport of 10 Sv results for the upper 1 000 m of the South Indian Ocean. In contrast to the triangular shape o f the subtropical gyre in the South Atlantic, probably caused by the c ross-equatorial flow into the North Atlantic, the area influenced by t he subtropical gyre in the South Indian Ocean is more rectangular.