The flow field of the subtropical gyre of the South Indian Ocean


  • L. Stramma,

  • J. R. E. Lutjeharms


The mean state of the transport field of the subtropical gyre of the South 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 recirculates in the western and central parts of the basin. In the upper 1000 m the eastward transport of the South Indian Ocean Current starts with 60 Sv in the region southeast of South Africa. Between the longitudes of 40° and 50°E about 20 Sv of the 60 Sv recirculates in a southwest Indian subgyre. Another major diversion northward occurs between 60° and 70°E. At 90°E the remaining 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 to move northward near Australia. Near Australia, there is indication of the poleward flowing Leeuwin Current with a transport of 5 Sv. In the central tropical Indian Ocean between 10°S and 20°S, about 15 Sv flows to the west. The western boundary current of this subtropical gyre consists of the Agulhas Current along the east coast of southern Africa. Its mean flow is composed of 25 Sv from east of Madagascar and 35 Sv from recirculation in the southwest Indian subgyre south of Madagascar, with only 5 Sv being contributed from the Mozambique Channel. A net southward transport of 10 Sv results for the upper 1000 m of the South Indian Ocean. In contrast to the triangular shape of the subtropical gyre in the South Atlantic, probably caused by the cross-equatorial flow into the North Atlantic, the area influenced by the subtropical gyre in the South Indian Ocean is more rectangular.