The fingerprint of Indian Ocean rain and river water in salinity and circulation.

The tropical Indian Ocean receives the world's most significant tropical ocean rain and river runoff per unit area. The 3-dimensional spreading of Rain and River Water (RRW) entering the tropical Indian Ocean and associated salinity and circulation anomalies are explored for 60 years using ocean reanalysis data tailored to a tracer transport model. Over 60 years, the cumulative impact of RRW entering the tropical Indian Ocean is to freshen the Indian Ocean basin as large as 2.0–0.1 p.s.u from the surface to 500 m via subduction and transport. The RRW propagates to a vast extent of the Indian Ocean and a limited extent of the Atlantic and Pacific Oceans via general circulation pathways. A quasi-equilibrium model of accumulation of RRW over the tropical Indian Ocean suggests that it induces clockwise geostrophic currents from the Bay of Bengal to the Arabian Sea over 0–500 m depths with a net transport tendency of 0.80 ± 0.14 Sv year−1. The study implies that coupled climate models with precipitation biases may miscalculate such salinity and circulation anomalies due to RRW and aggravating biases in simulated climate dynamics. • The spreading of rain and river water entering the tropical Indian Ocean for 60 yr is identified from ocean reanalysis data. • RRW mixes in the surface, subducts and spreads, offering a dilution in salinity and expansion in dynamic heights. • RRW offers a net transport tendency of water from the Bay of Bengal to the Arabian Sea at a rate of 0.80 ± 0.14 Sv year−1. [ABSTRACT FROM AUTHOR]