Paleoredox conditions of bottom water in the northern Indian Ocean since 39 ka

Ocean circulation has undergone significant changes during the glacial and interglacial periods. The redox condition at the sediment-water interface is mainly regulated by export productivity and ventilation of abyssal water mass. The changes in the redox condition associated with bottom water circulation in the Indian Ocean are still unclear. The present study assessed multi redox proxies (Mn/Ti, Mo/Ti, U/Ti, V/Ti, Ni/Ca, Cu/Ca, MnEF, U-EF, and V-EF) and C-org in the sediment core collected from the Arabian Sea (NW Indian Ocean) to investigate the past variations in bottom water redox condition. The bottom water in the Arabian Sea is presently bathed with the Lower Circumpolar Deep Water (LCDW), consisting of a fraction of both North Atlantic Deep Water (NADW) and Antarctic Bottom Waters (AABW). Our results show significant changes in oxygenation conditions in response to changes in ocean circulation. The present study revealed that bottom water in the northern Indian Ocean was more oxic during LGM than the deglacial period. We interpret the variability in the contribution of NADW and AABW influenced the redox condition at the study location. Comparing the current study results with previously reported Nd isotopes suggests that the contribution of AABW to the Indian Ocean increased during LGM, resulting in a higher oxic condition in LCDW.

Automated summary

This study investigates the past variations in bottom water redox condition in the Indian Ocean by analyzing multiple redox proxies and organic carbon in sediment core samples from the Arabian Sea. The results show significant changes in oxygenation conditions in response to changes in ocean circulation, with the bottom water in the northern Indian Ocean being more oxic during the Last Glacial Maximum (LGM) than the deglacial period. It is suggested that the contribution of Antarctic Bottom Waters (AABW) to the Indian Ocean increased during LGM, resulting in higher oxygen conditions.