Reduced bottom water oxygenation in the northern Indian Ocean during the Last Glacial Maximum

Reconstructing variations in the past bottom water oxygenation of the oceans is crucial for understanding the current global ocean deoxygenation and increased respired carbon storage. Changes in the deep water circulation have significantly influenced the oxygenation conditions of bottom water in the past. This study tracks the changes in bottom water oxygenation and carbonate dissolution in the northern Indian Ocean for the past 25 kyr BP using a multi-proxy record of surface porosity of epifaunal benthic foraminifera Cibicidoides wuellerstorfi, foraminiferal fragmentation percentage, CaCO3 content, size index, and authigenic uranium concentration in sediments, from a gravity core SSD-044/GC-01 recovered from a water depth of 3160 m. Results suggest that during the Last Glacial Maximum (LGM) and the Heinrich Stadial 1 (HS1), low-O-2 and CO2-rich deep water mass existed in the northern Indian Ocean, probably due to an increased proportion of southern sourced Antarctic Bottom Water (AABW) at the core location, which indicates increased respired carbon storage in the deep water of the northern Indian Ocean, suggesting it was part of a large carbon reservoir. At the onset of the B & oslash;lling-Aller & oslash;d (at around similar to 14.5 kyr BP), there was an incursion of O-2-rich and CO2-poor NADW at the core site. Furthermore, a well-oxygenated deep water mass prevailed in the northern Indian Ocean during the Holocene.