A model study of exchanges of salt and tracers in the northern and equatorial Indian Ocean

Net evaporation in the western part and net precipitation in the eastern part of the northern Indian Ocean region give rise to a relative high salinity in the Arabian Sea and a relatively low salinity in the Bay of Bengal. To maintain long-term average salinities, a net freshwater flux must occur into the Arabian Sea and out of the Bay of Bengal. A 4.5 layer model of the Indian Ocean with passive tracers as an additional tool, is used to map the transport of water masses in the region north of the equator. Our model results show that southward transport of low salinity water out of the Bay of Bengal primarily occurs along the coast of the eastern Indian Ocean. A smaller fraction is leaving the Bay of Bengal south of Sri Lanka and crossing the equator in the central Indian Ocean. This equatorial crossing is strongly correlated with the annual monsoon. Intrusion of high salinity water from the Arabian Sea into the Bay of Bengal takes place by the end of the southwest monsoon season. The inflow of low salinity wator into the Arabian Sea occurs in the Somali Current during the southwest monsoon. This northward advection of of equatorial water along the coast includes a substantial fraction of water with origin south of the equator. Only a small fraction of low salinity water is advected into the eastern Arabian Sea from the Bay of Bengal.