Glacial to interglacial contrasts in the northern Indian Ocean

Abstract

Differences between the 18O/16O ratios of planktonic foraminifera deposited during the last glacial maximum, about 18,000 yr ago, and those deposited during the Holocene show that in the Indian Ocean, the south-west monsoon was weaker than today but that the north-east monsoon was stronger. The upwelling observed in modern conditions along the southern coast of Arabia had disappeared because of the low speed of the southwestern winds during glacial summers. The reduction in rainfall and runoff over the continent caused a reduction of the salinity gradient in the Bay of Bengal and along the western coast of India. Increased precipitation fell on the sea south of 10° N, while strong evaporation over the northernmost Arabian Sea produced an enhanced salinity gradient in that area.