Glacial to Holocene fluctuations in hydrography and productivity along the southwestern continental margin of India

Oxygen isotope and sedimentological records of a sediment core from the southwestern continental margin of India are used to reconstruct the fluctuations in sea surface hydrography and productivity during the last deglaciation. The δ18O records of Globigerinoides ruber and Globigerinoides sacculifer exhibit high amplitude oscillations during the early deglaciation and Holocene. Significant variations in δ18O during the Holocene and a high glacial–interglacial amplitude in δ18O values (Δδ18O ∼2.1‰) suggest large fluctuations in sea surface hydrography related to monsoonal precipitation on land. Our results suggest that although the last deglacial events are coherent in time with the regional and global climatic events, fluctuations in sea surface salinity during Holocene are unique to this region. Maximum monsoonal precipitation appears to have occurred after ∼9–8 ka BP. Unlike the records from the western Arabian Sea, biological productivity was maximum between ∼18 and 15 ka BP and substantially diminished between ∼13 and 6 ka BP. The increased strength in the winter monsoon during the glacial period could have enhanced convective mixing and nutrient injection, leading to high primary production. Reduced surface productivity during the early Holocene may be attributed to the complex dynamics of the circulation system and hydrological cycle along the southwest coast of India.