Organic matter sources and productivity variations in the southeastern Bay of Bengal in the past 54,000 years

Abstract

Primary productivity in the Bay of Bengal (BoB) has been primarily controlled by salinity stratification driven by the Indian summer monsoon (ISM). The increase in freshwater influx during enhanced ISM periods results in strong salinity stratification, which inhibits the vertical mixing of nutrients and limits primary production. The southern BoB receives relatively less freshwater influx compared to the northern BoB. However, very few studies have been carried out concerning productivity variation in the southern BoB. Hence, to understand the organic matter sources and productivity variation, a sediment core (MGS 22/01) collected from southeastern BoB was analysed for total organic carbon (TOC), total nitrogen (TN), and stable isotopes (δ¹³C, δ¹⁵N), Calcium Carbonate (CaCO₃), Barium (Ba), and for paleoredox condition, Manganese (Mn)/Aluminum (Al) proxy was used. Results indicated relatively more terrestrial-derived organic matter (OM) during ∼54 cal ka BP up to 15 cal ka BP and relatively low input after ∼15 cal ka BP, controlled by sea level and ISM. Low TOC and high Mn/Al indicated prevailing oxic conditions during ∼12 to 6 cal ka BP. High marine productivity was observed during the early MIS 3, LGM, and the mid-late Holocene period. Strong ISM resulted in weaker marine productivity, and weak ISM enhanced marine productivity in the present study area.