Late Quaternary Magnetofossils Record of Indian Ocean Productivity and Upwelling Driven by Ice Sheet and Indian Summer Monsoon Feedbacks

Ocean upwelling and vertical mixing have played a crucial role in regulating atmospheric carbon dioxide (pCO2) during the Pleistocene glacial-interglacial cycles. Important uncertainties remain on the spatial response of the ocean to these cycles because the impact of some important upwelling areas, such as the equatorial Indian Ocean, remain understudied due to scarcity of reliable records. Here, we present systematic environmental magnetic and geochemical results derived from marine core CJ02-01 over the past 200 thousand years (kyr) in the western equatorial Indian Ocean. Our results indicate a mixture of magnetofossils and detrital magnetic particles in the studied sediments, being magnetofossils dominant during interglacial periods and being detrital magnetic particles more abundant during glacial intervals. The increase of magnetofossils abundance during interglacials indicates an enhanced export productivity supply driven by intensified upwelling. Magnetofossils abundance can be served as reliable proxies for the reconstruction of ocean upwelling variability in the equatorial Indian Ocean. Primary variations in the upwelling closely correlate with glacial-interglacial cycles, which demonstrates that global ice sheet plays a key role in controlling the export production and nutrient upwelling in the western equatorial Indian Ocean. Specifically, enhanced upwelling as a result of weaken stratification was driven by the intensification of North Atlantic Deep Water (NADW), accompanied by reduced oxygen-rich Antarctic Bottom Water (AABW) during low ice volume stages. Secondary variations in upwelling also are closely linked to precession forcing. We interpret that the northward migration of the Indian summer monsoon front, resulting from a combination of low ice volume and minima in precession, promoted enhanced upwelling of nutrient-rich subsurface water and the release of previously sequestered CO2 from the equatorial Indian Ocean to the atmosphere.