Spatiotemporal variations of the δ 18O–salinity relation in the northern Indian Ocean

Abstract

A new data set of oxygen isotopic composition (δ 18O) and salinity ( S) of surface and sub-surface waters of the northern Indian Ocean, collected during the period 1987–2009, is presented. While the results are consistent with positive P− E (excess of precipitation over evaporation) over the Bay of Bengal and negative P− E over the eastern Arabian Sea, a significant spatiotemporal variability in the slope (also intercept) of the δ 18O– S relation is observed in the Bay; the temporal variability is difficult to discern in the Arabian Sea. The slope and intercept are positively and negatively correlated, respectively, with the annual rainfall over India, a rough measure of river runoff. Both the slope and intercept appear to be sensitive to rainfall; the slope (intercept) is higher (lower) during years of stronger monsoon. The observed variability in the δ 18O– S relation implies that caution needs to be exercised in paleosalinity estimations, especially from the Bay of Bengal, based on δ 18O of marine organisms.