Glacial- deglacial bottom oxygen condition in the western Bay of Bengal and its relation to the monsoon related export productivity

Changes in composition of benthic foraminiferal assemblages in a sediment core SK 218/1 retrieved from Bay of Bengal (14°02’06” lat; 82°00’12” long, W.D. 3307m) are investigated to decipher variations ocean bottom condition for the last 45 Kyr BP. The age model of the core is based on 8 AMS radiocarbon dates and stable oxygen isotope stratigraphy. The benthic foraminifera show specific species microhabitat preferences within sediments depending on their adaptation capabilities to the changing bottom environment governed mainly by the Organic Carbon flux and oxygen condition. We have classified benthic foraminiferal assemblages into various morphotype categories based on their distinct morphological features i.e. Rounded – Trochospiral, Biconvex – Trochospiral, Planoconvex – Trochospiral and Miliolids) with epifaunal habitat and Spherical, Tapered/Cylindrical, Rounded – Planispiral, Flattened – Tapered and Flattened - Ovoid with infaunal habitat.

High abundances of infaunal benthic foraminifera signal oxygen poor condition, whereas the peak abundances of epifaunal benthic foraminifera indicate high levels of bottom oxygenation. The microhabitat patterns (epifauna vs infauna) of the examined core reveal that ocean bottom oxygen level has considerably varied in the past with high - oxic condition during the periods equivalent to the northern hemisphere cold Heinrich events. Interestingly, during the Younger Dryas and Holocene period (except latest Holocene), our data show low-oxic bottom condition. A strong coupling of pelagic and benthic environments evidenced from the record suggests that bottom oxygen condition at the core site is primarily governed by the monsoon related export productivity at photic zone.