Rapid Global Oxygen Shifts and Delayed OMZ Response: Pulse and Memory of the Pacific Decadal Oscillation

Abstract Natural decadal variability often obscures anthropogenic trends in ocean deoxygenation. Using a global observational oxygen reconstruction (1965–2022), we investigate the role of the Pacific Decadal Oscillation (PDO) in modulating decadal oxygen variability. We show that the global oxygen inventory and upper‐ocean hypoxic boundaries closely track the rate of PDO change, with a coupling dominated by Northern Hemisphere dynamics . This produces rapid hypoxic boundary shifts during PDO transitions via fast upper‐ocean adjustments (isopycnal heave and ventilation). In contrast, deep Oxygen Minimum Zones (OMZs) track the time‐integrated PDO state, acting as reservoirs that accumulate ventilation anomalies over decadal timescales, with the strongest signal in the North Indian Ocean. This dual pulse–memory response reveals that surface ecosystems respond to the pace of PDO transitions, whereas the deep ocean retains a persistent imprint of prolonged PDO forcing.