Lower Glacial Oxygen in the Eastern Equatorial Pacific Concentrated in the Deep Sea

Abstract Oxygen in the global oceans has declined since the 1960s, including in the Eastern Equatorial Pacific (EEP). Reconstructions of EEP glacial oxygenation help advance understanding of current and projected ocean deoxygenation. Previous estimates of the glacial oxygen deficient zones (ODZs) in the upper EEP are poorly constrained. Here we include sediment cores that extend shallower into the ODZ and quantitatively reconstruct the glacial oxygen depth profile. We find glacial oxygen levels were similar or slightly lower than modern in the upper‐intermediate ocean and much lower in the deep EEP. We estimate ∼95% of the lower glacial oxygen occurred in the deep EEP. This contrasts with modern, where only 67% of oxygen loss is in the deep ocean, and could be due to a smaller role of temperature‐dependent oxygen solubility in modulating oxygen on longer timescales and/or a longer ocean response time to record oxygen changes at depths during glacial times.