Inter-Annual Variability of Salinity in the Upper Layer of South Eastern Arabian Sea and Its Acoustic Relevance

Abstract

This study investigates the seasonal dynamics and inter-annual variability of low-salinity Bay of Bengal Water (BBW) and Arabian Sea High Salinity Water (ASHSW) in the South Eastern Arabian Sea (SEAS). Using HadISST temperature and salinity data (2016–2020), OSCAR ocean current data, and water mass indices, we analyze the seasonal evolution and interactions of these water masses. During winter, the East India Coastal and North Equatorial Current transport low-saline waters to southern India, forming an anticyclonic eddy that recirculates BBW south-westward. By June, these waters dissipate, replaced by the expansion of ASHSW driven by summer monsoon circulation, with increasing core salinity values observed at shallower depths. Monthly salinity difference plots reveal peak BBW intrusion in November, with spreading occurring south-westward and moving northward along the coast. BBW in the SEAS exhibits strong seasonality with minimal inter-annual variability. Acoustic propagation modeling highlights the significant influence of BBW and ASHSW on sound speed profiles, with deeper sonic layer depth and strong sound speed gradients facilitating long-range ducted propagation during BBW intrusion periods.