Variability of terrigenous input to the Bay of Bengal for the last ~80 kyr: Implications on the Indian monsoon variability

Abstract

Oceanographic processes in the Bay of Bengal (BoB) are strongly impacted by south-westerly and north-easterly winds of the Indian monsoon system during the summer and winter respectively. Variations in calcium carbonate (CaCO3) content and magnetic susceptibility (MS), along with Ba, Ti, and Al, were reconstructed for the past ~80 kyr using a sediment core (MD 161/28) from the northern BoB in order to understand the changes in calcium carbonate deposition and MS signals associated with the Indian monsoon system. Our records infer monsoon-induced dilution through river discharges from different sediment provenance to be the main controlling factor of the CaCO3 variations at the core location. Generally lower CaCO3 content during stronger-southwest monsoon (SWM) interglacial periods (Marine Isotope Stage (MIS) 5a & 1, except 3) and higher CaCO3 content during weaker-SWM glacial periods (MIS 4 & 2) were documented. High MS correspond to MIS 4 & 2 of weakened SWM and strengthened northeast monsoon (NEM) periods caused due to enhanced sediment supply from the Peninsular Indian regions, whereas lower MS values correspond to MIS 5, 3 & 1 of strengthened SWM and weakened NEM derived through Ganges-Brahmaputra from the Himalaya Region. Thus, our records infer coupling of major rivers' discharges to the BoB with the SWM and NEM strengths, which has implications on the linkage with other climatic variations such as East Asian monsoon and Northern Hemisphere climate.