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 (C-org), 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 C-org and CaCO3 contents are associated with the MIS 1/2 and mid-MIS 3, indicating reduced productivity. The 8180 values in planktonic foraminifera range between -2.7 parts per thousand and -0.1 parts per thousand, with a large glacial interglacial amplitude Delta delta O-18 of similar to 2.6 parts per thousand, suggesting changes related to monsoonal precipitation/runoff. The delta N-15 values fluctuate between 5.4 parts per thousand and 7.3 parts per thousand, signifying variation in denitrification intensity. The delta N-15 indicates an overall increase in denitrification intensity during MIS 1 and MIS 3 and, reduced intensity during MIS 1/2, LGM and mid-MIS 3. Higher 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.