Reassessing the structure and characteristics of watermass using ship-based repeat observations along the eastern Arabian Sea

The structure and characteristics of watermass along the eastern Arabian Sea (EAS) have been re-evaluated using ship-based monthly repeat measurements along the 2000 m isobath in 2018. Overall, the EAS is identified by various watermasses, viz., Bay of Bengal Water (BBW) and Arabian Sea High Saline Water (ASHSW) in the surface layers (0-150 m) associated with poleward/equatorward West India Coastal Currents, Persian Gulf Water (PGW) in the 200-500 m, Red Sea Waters (RSW) in intermediate depth (500-800 m), Arabian Sea Bottom Water (ASBW) in the bottom layers (1000-2000 m). A salinity minimum was observed along the EAS at a depth of 100-200 m, termed Modified Arabian Sea Waters (MASW). The MASW is formed by mixing different watermasses, viz., BBW, Indian Central Water (ICW), and Indian Ocean Equatorial Water (IOEW) in the south (6-15 degrees N), whereas in the north (15-22 degrees N), it is formed due to the mixing of ASHSW (0-100 m) and PGW (200-500 m). The reanalysis of the current dataset revealed the advection of IOEW (100-200 m) and ICW (200-800 m) associated with poleward undercurrent up to 15 degrees N, restricting the southward penetration of PGW. The region between 12 and 17 degrees N is found to be a mixing zone of these low and high-saline water masses of EAS.