Stable isotopes and salinity in the surface waters of the Bay of Bengal: Implications for water dynamics and palaeoclimate

Surface water mixing in the Bay of Bengal (BOB) inferred from spatio-temporal distribution of δ18O and salinity based on synthesis of 194 new samples together with published data is reported. In general, both δ18O and salinity have low values in northern part of the BOB, progressively increasing towards SW. The lowest values are observed during July–September (southwest monsoon season) and the highest in pre-monsoon. The most prominent δ18O–salinity relationship is seen for samples collected during June to October when the Himalayan river influx dominates. When this influx decreases in other seasons the δ18O–salinity relationship is poor.The δ18O–δD regression of samples north of 10°N is similar to the GMWL. However, for samples south of ~ 10°N, this regression has a significantly lower slope. This is interpreted as due to absence of direct riverine inflow in this region of the BOB, coupled with –ve (P − E; Precipitation minus Evaporation) almost throughout the year.This study shows that the seasonal distribution of δ18O and salinity over the northern BOB is dominantly governed by the variation in the (P + R − |E|) in spite of the fact that ocean currents transfer several times more water between the two basins of northern Indian Ocean.

► Lack of strong δ18O–S relation in the Bay of Bengal due to multi-end member mixing
► δ18O and S depend on (P + R − |E|) due to formation of stratified meteoric water layer
► Different δ18O–δD relation in equatorial oceans from global ocean surface water
► Thinning of stratified meteoric water layer in BOB may affect south Asian rainfall