Past 100 ky surface salinity-gradient response in the Eastern Arabian Sea to the summer monsoon variation recorded by δ18O of G. sacculifer

The residual-δ18OG. sacculifer contrast varies between ∼0.2‰ at ∼75 ky B.P. (i.e., late-Marine Isotope Stage 5) and ∼0.7‰ at ∼20 ky B.P. (i.e., Last Glacial Maximum), suggesting that the overall salinity difference between the northern- and southern-end of the low-salinity tongue has varied between ∼0.6 and ∼1.6 psu. Considerably reduced difference during the former period than the modern suggests substantially intensified and northward-extended low-salinity tongue due to intense summer monsoons than today. On the other hand, larger difference (∼1.6 psu) during the latter period indicates that the low-salinity tongue was significantly weakened or withdrawn due to weaker summer monsoons. Thus, the salinity-gradient in the eastern Arabian Sea low-salinity tongue can be used to understand the past variations in the Indian summer monsoons.