Spatio-temporal distributions of δ18O, δD and salinity in the Arabian Sea: Identifying processes and controls

Isotopic compositions (δ18O and δD) and salinity (S) of 683 surface water samples from the Arabian Sea (AS) collected during 2008–2010, were measured to understand the factors controlling the spatio-temporal distribution of these parameters. From the distributions of δ18O and salinity (S), and the relationships between δ18O–δD and δ18O–S, the following inferences have been drawn: (1) there is a broad correspondence between the geographic distributions of the δ18O and S; (2) in spite of a large scatter, a statistically significant δ18O–S relationship can be identified in much of the investigated part of the AS; (3) the δ18O–δD regression line for all samples clumped together has a slope of 3.2 (± 0.16), much lower than that (7.37) for the global ocean surface water line (GOSWL), which in the case of the AS is seen only for samples with salinity < 34; (4) the linear relationship between δ18O and δD breaks down completely in the months of March–May; (5) contrary to the adjoining Bay of Bengal (BOB), both δ18O and S progressively increase from the equator northwards; (6) the δ18O–δD and the δ18O–d-excess relationships indicate strong kinetic fractionation due to evaporation from surface waters of the AS throughout the year, with enhancement during summer months.