Fluctuations in productivity and denitrification in the Southeastern Arabian Sea during the Late Quaternary

• Main Authors: Kessarkar, Pratima M., Purnachandra Rao, V., Naqvi, S. W. A., Chivas, Allan R., Saino, T.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Current Science Association 2010
• Subjects: QE Geology; Planktonic foraminifera
• Online Access: http://repository.ias.ac.in/38669/; http://repository.ias.ac.in/38669/1/33_pub.pdf; http://www.ias.ac.in/currsci/25aug2010/485.pdf

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 (CaCO 3 ) 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 CaCO 3 contents are associated with the MIS ½ and mid-MIS 3, indicating reduced productivity. The δ 18 O values in planktonic foraminifera range between - 2.7% and - 0.1%, with a large glacial-interglacial amplitude Δδ 18 O of ∼2.6%, suggesting changes related to monsoonal precipitation/ runoff. The δ 15 N values fluctuate between 5.4% and 7.3%, signifying variation in denitrification intensity. The δ 15 N indicates an overall increase in denitrification intensity during MIS 1 and MIS 3 and, reduced intensity during MIS ½, 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 ½ and mid-MIS 3 might be the effect of enhanced precipitation associated with the intensified southwest monsoon fortifying near-surface stratification.