Biogenic Magnetite Indicating Millennial‐Scale Evolution of Bottom Water Oxygenation in the Northern South China Sea Since About 30 ka

Abstract Previous studies indicate that bottom‐water oxygenation (BWO) during glacial–interglacial transitions varies complexly, particularly on millennial timescales. Here we reconstruct millennial‐scale BWO variations since ∼30 ka using biogenic magnetite preserved in sediments from the northern South China Sea. Magnetofossil proxies reveal a four‐stage evolution: low oxygenation (∼28–18 ka), a rapid deglacial increase (18–11 ka), an early–mid Holocene maximum (11–5.8 ka), and a gradual decline thereafter. This pattern parallels oxygenation records from the Pacific and Indian Oceans and broadly tracks atmospheric CO 2 , suggesting coupling between deep‐ocean oxygenation and the carbon cycle. Our results suggest that Western Pacific circulation exerted a primary control on long‐term BWO evolution. Low BWO during the Last Glacial Maximum likely reflects an enhanced influence of oxygen‐depleted deep waters through the Luzon Strait, followed by increased ventilation and oxygen‐rich BWO since the deglacial. On millennial timescales, however, biogeochemical oxygen consumption influenced dissolved oxygen variability. This coherent coupling between BWO and atmospheric CO 2 provides insights into future climate change under ongoing global warming.