The origin of summer high-salinity water in the southern Bay of Bengal and its interannual variabilities

This research investigates the origins of high-salinity water in the southern Bay of Bengal (SBHSW) in summer (June to August) and its interannual variabilities associated with El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). The two distinctive sources of the SBHSW, including the eastern Arabian Sea (AS) origin and the western equatorial Indian Ocean (EIO) origin mentioned in the previous studies are identified. The eastern AS origin has much higher salinity (35.5 PSU vs. 35.2 PSU), shallower isopycnal layers (1023.0-1023.5 kg m(-3) vs. 1024.0-1024.5 kg m(-3)), and intrudes into the Bay of Bengal (BOB) approximately one month later compared to the western EIO origin, while accounting for 53% of the total salinity variability compared to 47% contribution from the western EIO origin. The interannual variabilities of SBHSW are closely linked with ENSO and IOD events, with contributions of approximately 47% and 41%, respectively. During El Nino decaying years, high-salinity water export from the western EIO origin into the southern bay (< 7 degrees N) is enhanced due to the anomalous strong spring Equatorial Undercurrent (EUC) associated with El Nino; while in the north of 7 degrees N, the SBHSW was freshened both by the increased rainfall and by the downwelling associate with the anomalous anticyclonic wind. Similar processes operate but in an opposite direction during La Nina decaying years. In contrast, IOD exerts its influence on the SBHSW primarily through modulating the strength of SMC. Positive (negative) IOD caused the anomalous freshening (salty) SBHSW by weakening (enhancing) SMC and consequently advecting less (more) saline water into the BOB.