Mechanisms and Early Detections of Multidecadal Oxygen Changes in the Interior Subpolar North Atlantic

Abstract

The oxygen response in the subpolar North Atlantic (SPNA) to future climate change is poorly understood. We investigate the multidecadal variability in interior oxygen and its association with the subpolar gyre index (a gyre strength proxy) for models and data. During positive phases, persistent strong Labrador Sea (LS) lateral and vertical mixing entrains oxygen-rich water into the interior southern SPNA and vice versa during negative phases. This is indicated by the observed anomalously fresh, cold, and low apparent oxygen utilization, resembling LS water mass during positive phases. We use this relationship to benchmark Earth system models. Under a high CO2 future, the best performing models project a steady decline in SPNA oxygen, driven partly by lower solubility and increases in apparent oxygen utilization. The deoxygenation depends on the sensitivity of the LS mixing to warming. The time of emergence of interior oxygen is projected to be decades earlier than that of temperature and salinity.