New stable isotope records of sediment cores from the SE Arabian Sea - inferences on the variations in monsoon regime during the late Quaternary

Abstract

We reconstruct here the changes in regional hydrography related to the fluctuations in Indian monsoons during the late Quaternary based on the stable isotope composition of the foraminifers and organic matter in three sediment cores from the upper continental slope of western India. The planktic foraminiferal δ¹⁸O contrast between the Last Glacial Maximum (LGM) and Holocene (Δδ¹⁸O), after correcting for the global 'ice effect' is relatively high (0.8–1.0‰), suggesting notable changes in the sea surface conditions. This includes a moderate sea surface cooling (~2°C) and an enhanced evaporation (increasing salinity by ~2.5 p.s.u.) during the LGM and/or increased precipitation during the early Holocene. The diminished Δδ¹⁸O value of benthic records (~1.0‰) appears to be a basin-wide phenomenon along the shallow depths of the upper continental slope and is related to the eustatic sea level fluctuations. Carbon isotope composition of the organic matter suggests that primary productivity was the main source of organic carbon along this margin throughout the late Quaternary.