Fluctuations in productivity and denitrification in the southeastern Arabian Sea during the late Quaternary

Sedimentological and stable isotopic characteristics of sediments have been studied in a core from the southeastern Arabian Sea containing records of the past 70 ka. Palaeoproductivity proxies such as organic carbon (Corg), total nitrogen (TN) and calcium carbonate (CaCO3) contents, show high values at the core top and during the Last Glacial Maximum (LGM) and marine isotope stage (MIS) 4, suggesting high productivity, whereas low Corg and CaCO3 contents are associated with the MIS 1/2 and mid-MIS 3, indicating reduced productivity. The δ18O values in planktonic foraminifera range between - 2.7‰ and - 0.1‰, with a large glacial-interglacial amplitude Δδ18O of ~ 2.6‰, suggesting changes related to monsoonal precipitation/runoff. The δ15N values fluctuate between 5.4‰ and 7.3‰, signifying variation in denitrification intensity. The δ15N indicates an overall increase in denitrification intensity during MIS 1 and MIS 3 and, reduced intensity during MIS 1/2, LGM and mid-MISHigher primary productivity and reduced denitrification intensity during LGM and MIS 4 might be due to convective winter mixing and more oxygenated subsurface waters. Reduced primary productivity during MIS 1/2 and mid-MIS 3 might be the effect of enhanced precipitation associated with the intensified southwest monsoon fortifying near-surface stratification.