Deep Circulation in the South Atlantic Induced by Bottom-Intensified Mixing over the Midocean Ridge

Abstract

The deep circulation in the South Atlantic is studied through numerical experiments, using an oceanic general circulation model based on z coordinates. The new feature of these numerical experiments is that diapycnal mixing is idealized as strong bottom-intensified mixing on both sides of the midocean ridge; elsewhere diapycnal mixing is set at a low background value. The bottom-intensified diapycnal mixing induces strong equatorward (poleward) flow along the western (eastern) slope of the midocean ridge. In addition, the strong vertical gradient of diapycnal mixing rate induces downwelling in the basin interior and intensifies the upwelling near the axis of the midocean ridge. The strong ridge-following currents induce anticlockwise circulation in both the eastern and western deep basins, and such circulation is opposite to the classical Stommel?Arons circulation. This study indicates that bottom topography, strong mixing over the midocean ridge, and strong localized mixing associated with overflows can have major impact on the strength of the deep meridional overturning cell and deep water properties in the whole deep basin.