Last 42 Ky Sediment Chemistry of Oxygen Deficient Coastal Region of the Bay of Bengal: Implications for Terrigenous Input and Monsoon Variability

The discharge of terrigenous clastics by seasonal peninsular rivers is known to reach the upper slope of the eastern margin of India, which is presently impinged by the monsoon-sensitive intense oxygen minimum zone (OMZ); however, their mutual behaviour in response to changes in the intensity of past Indian summer monsoons (ISM) is not clear. The δ¹⁸O_G.sacculifer time-series of a sediment core from the upper slope off Chennai exhibits distinct enrichment (~0.4‰) during the last glacial period (30–18 kiloyears BP: ka), and depletion (~-2.2‰) during the Holocene, suggesting a significant shift in ISM intensity. The monotonously increased terrigenous elements (Al, Ti and Mg) content and depleted δ¹⁸O_G.sacculifer during the Holocene suggest tight-coupling between ISM and terrigenous sediment input. Highly depleted redoxsensitive Mn (<0.04%) (lesser than the source sediment content of 0.07%) throughout the last 42 kyr suggests well-sustained intense OMZ irrespective of ISM variation.