Physically driven patchy O2 changes in the North Atlantic Ocean simulated by the CMIP5 Earth system models

Abstract

AbstractThe subpolar North Atlantic is a key region for the oceanic uptake of heat, oxygen, and carbon dioxide. Centennial oxygen (O2) changes are investigated in the upper 700 m of the North Atlantic Ocean using a subset of Earth system models (ESMs) included in the Coupled Model Intercomparison Project phase 5. The climatological distributions of dissolved O2 averaged for the recent past period (1975–2005) are generally well captured, although the convective activity differs among the models in space and strength, and most models show a cold bias south of Greenland. By the end of the twenty‐first century, all models predict an increase in depth‐integrated temperature of 2–3°C, resultant solubility decrease, weakened vertical mass transport, decreased nutrient supply into the euphotic layer, and weakened export production. Despite an overall tendency of the North Atlantic to lose oxygen, patchy regions of O2 increase are observed due to the weakening of the North Atlantic Current (NAC) causing a regional solubility increase (the warming hole effect) and a decrease in the advection of subtropical, low‐O2 waters into the subpolar regions (the nutrient stream effect). Additionally, a shift in the NAC position contributes to localized O2 changes near the boundaries of water masses. The net O2 change reflects the combination of multiple factors leading to highly heterogeneous and model‐dependent patterns. Our results imply that changes in the strength and position of the NAC will likely play crucial roles in setting the pattern of O2 changes in future projections.