Influence of local and remote climate processes on driving the salinification followed by freshening phases in the eastern Arabian Sea

Abstract

Sea surface salinity (SSS) modulates upper-ocean stratification, air–sea coupling, and freshwater redistribution in the North Indian Ocean, yet its interannual variability in the eastern Arabian Sea (EAS) remains insufficiently quantified. This study evaluates satellite-derived SSS from the Soil Moisture and Ocean Salinity, Soil Moisture Active Passive, and European Space Agency-Climate Change Initiative (CCI) products using high-precision shipborne measurements across the EAS. Validation results show that CCI SSS exhibits strong agreement with in situ observations and best reproduces the spatiotemporal variability of the in situ gridded dataset (Willmott skill score 0.81). CCI also exhibit relatively lower spatial root-mean-square error (0.93 PSU) compared to other Satellite derived datasets. The analysis of interannual SSS variability using the CCI dataset during 2010–2023 reveals two contrasting regimes: a salinification phase during 2015–2019 (+0.5 PSU) followed by a pronounced freshening phase during 2020–2023 (−0.5 PSU). Analysis of precipitation, ocean circulation, and climate indices indicates that reduced rainfall and weak horizontal advection dominated the salinification phase. In contrast, the freshening phase was driven by enhanced precipitation and intensified freshwater transport from the Bay of Bengal. This period coincides with the rare triple-dip La Niña (2020–2022), which strengthened coastal Kelvin waves and the East India Coastal Current, facilitating transport of low-salinity waters through the “River-in-the-Sea”(RIS) pathway. These results highlight the sensitivity of EAS salinity to coupled local and remote freshwater processes and demonstrate the importance of multi-sensor satellite SSS products for monitoring climate-driven hydrological variability.