Cross-equatorial pathways of salt and tracers from the northern Indian Ocean: Modelling results

The pathways of cross-equatorial flows originating in the Arabian Sea and the Bay of Bengal are modelled using a 4.5-layer model of the Indian Ocean. Passive tracers and drifters are used to diagnose the transports. The model results show that relatively fresh Bay of Bengal water is transported southward across the equator throughout the year east of 90°E, but during the southwest monsoon as far west as 60°E. In the western part of the ocean, northward transport of low-salinity water across the equator takes place in a narrow region of positive relative vorticity flows in the Somali Current. Substantial southward cross-equatorial exchange of Arabian Sea water occurs as far east as 95°E, primarily from May to September. During the northeast monsoon the net transport is small, but large variability in the exchange of Arabian Sea water is associated with planetary equatorial waves. The cross-equatorial circulation emerge as a clockwise gyre, with southward flow in the mixed layer of the interior of the ocean, and a northward flow in the western boundary current region, including the mixed layer as well as subsurface layers. The path of the low-salinity or freshwater transport is associated with this circulation.