Millennial‐Scale Deoxygenation in the Southern California Oxygen Minimum Zone Over the Last Glacial Cycle

Past variability of oxygen minimum zones (OMZs) provides key insights into future ocean deoxygenation. However, California margin OMZ records remain temporally limited, restricting evaluation of mechanisms across full glacial–interglacial cycles. Here, we reconstruct high‐resolution bottom water oxygen (BWO) over the past ∼140,000 years using redox‐sensitive trace metals from ODP Site 1017E in the Southern California OMZ. BWO was lower during interglacial intervals (Last Interglacial and Holocene) than during glacial periods (Penultimate Glacial and Last Glacial Maximum). However, BWO exhibits previously unresolved millennial‐scale fluctuations during the glacial inception, including repeated deoxygenation events approaching interglacial conditions. This variability cannot be explained by local productivity or temperature‐driven oxygen solubility. Instead, it reflects changes in intermediate water ventilation, likely driven by shifting contributions of North Pacific and Equatorial Pacific intermediate waters. These results demonstrate that BWO in the Southern California is highly dynamic and may have been primarily controlled by ocean circulation.