Seasonal spreading of the Persian Gulf Water mass in the Arabian Sea

The characteristics of the subsurface salinity maximum associated with the Persian Gulf Water mass (PGW) are used to quantify the spreading and mixing of PGW in the thermocline of the Arabian Sea based on a bimonthly climatol ogy of temperature and salinity. Examination of the seasonal cycles of heat and freshwater fluxes in the Persian Gulf region indicates that PGW forms as a result of elevated evaporative cooling in conjunction with reduced ins olation during winter. Maps are presented of the distributions of depth, sa linity, and geostrophic flow on sigma (theta) = 26.5, which nearly coincide s with the core of the PGW. After intense mixing in the Strait of Hormuz, t he property fields suggest that warm (> 17 degreesC) and high-salinity (> 3 6.2 psu) PGW enters the Arabian Sea to form a subsurface salinity extremum between 200 and 300 m. We have found variability in the distribution of PGW in the Arabian Sea associated with monsoonal changes in the Arabian Sea ci rculation. During the winter monsoon, there is southward spreading of PGW a long the western boundary; during summer it is not present. Lateral mixing with low-salinity water from the Bay of Bengal in the region south of 10 de greesN and along the west coast of India during winter accounts for changes in the characteristics of PGW along these paths. Associated with the Findl ater Jet during summer, the entire thermohaline structure is vertically dis placed along the coasts of Somalia and Arabia. Ekman convergence in the cen tral Arabian Sea accounts for deepening of the PGW. Either lateral or verti cal mixing would cause changes in PGW :properties in these regions. During this time, PGW spreads predominantly southward along the central Arabian Se a, as indicated by a tongue of high salinity.