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

Abstract Surface water mixing in the Bay of Bengal (BOB) inferred from spatio-temporal distribution of δ 18 O and salinity based on synthesis of 194 new samples together with published data is reported. In general, both δ 18 O 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 δ 18 O–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 δ 18 O–salinity relationship is poor. The δ 18 O–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 δ 18 O 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.