A 100-400 km wide region of the coastal Eastern Arabian Sea (EAS), off the west-coast of India, is characterized by a low-salinity tongue formed by the inflow of low-salinity surface water from the Bay of Bengal (BoB). This low-salinity tongue is largely driven by the sea level higher in BoB than in the Arabian Sea and by alongshore pressure gradient between southern-and northern-EAS, and is expected to respond to summer monsoon freshwater flux to the bay. Here, we report past variation in the relative intensity of summer-and winter-monsoons based on changes in the north-south salinity gradient within this low-salinity tongue. The salinity gradient is estimated from paired measurement of δ 18 O and Mg/Ca in Globigerinoides sacculifer extracted from sediment cores collected at northern highsalinity and southern low-salinity locations within this tongue.The Last Glacial Maximum (LGM) to peak-Holocene δ 18 O and sea surface temperature gradients at both locations are ~ −2 ‰ and +2 o C respectively, while the sea surface salinity gradient at northern-EAS is 0.5 psu higher than in the southern-EAS, suggesting distinctly different SSS structure in theLGM-EAS. The north-south surface salinity gradient was also larger by ~0.5 psu during the LGM (1.2 psu) as compared to the gradient during the Holocene (0.7 psu). Increased north-south surface salinity gradient during the LGM suggests diminished flow of low-salinity water into the coastal EAS caused by combined effect of decreased freshening of the BoB and reduced seasonal mountain-rivers discharge into the EAS. Such surface hydrographic conditions in the coastal EAS clearly indicate significantly weakened summer monsoons and strengthened winter monsoons during the LGM.
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