Surface oceanographic changes from ∼ 25,000 to 3500 cal yr BP in the eastern Arabian Sea

Abstract

Multiproxy data of pteropods and planktic foraminifera from Core SK291/GC17 suggest significant surface paleoceanographic shifts from ∼25,000 to 3500 calibrated years before present (cal yr BP) in the eastern Arabian Sea (EAS). Increased values of the global ice-volume free stable oxygen isotope ratio of seawater (δ18Osw IVF) and stable oxygen isotope ratio in pteropod (δ18OH. inflatus IVF), as well as lower percentages of planktic foraminifer Globigerina bulloides from ∼22,000 to 18,000 cal yr BP, correspond to the weak Indian summer monsoon (ISM) during the Last Glacial Maximum (LGM). In the early Holocene, the EAS witnessed an increase in upwelling driven by strong summer monsoon winds, and a decrease in salinity corresponding with enhanced precipitation in the Western Ghats region. From ∼4800 to 4000 cal yr BP, including the 4.2 ka event, a prominent increase in the δ18OH. inflatus IVF values suggest an enhanced intrusion of the Arabian Sea High Saline Water (ASHSW) to the relatively deeper part of the mixed layer. In the same interval, the low representations of G. bulloides and thermocline dwelling planktic foraminifera indicate weakening of the coastal upwelling and a reduction in surface productivity due to weak ISM across the Arabian Sea, with more severe conditions in the EAS.