The subpolar North Atlantic (SPNA) is one of the few regions where the deep ocean is in direct contact with the atmosphere, making it a key location for interior ocean ventilation through gas exchange. We use observational data to analyze large-scale patterns of mean annual air-sea flux, biological production and consumption, and physical transport of oxygen for the subpolar North Atlantic Ocean (45N-65N), finding a net annual flux of 48.1±14.6 Tmol (1Tmol = 10^12 mol) of oxygen from the atmosphere into the ocean, largely balanced by a removal of oxygen through physical transport. Wintertime increases in oxygen content in isopycnal layers match the location and magnitude of net oxygen uptake from the atmosphere, supporting the connection between air-sea gas exchange at the surface and ventilation of deeper layers. Integrated over the whole SPNA, 90% of the net oxygen influx and 80% of the seasonal oxygen content increase occur at densities of σ0 < 27.6 kg m-3, in the upper branch of the Atlantic Meridional Overturning Circulation (AMOC). The subpolar gyre (SPG) is ventilated with oxygen largely at these lower densities, accumulating oxygen along its cyclonic pathway from the North Atlantic Current towards the Labrador Sea. Our results thus suggest that the subpolar gyre is oxygenated cumulatively throughout the SPNA, as mode waters formed each winter become progressively denser and more oxygenated along the SPG’s path, culminating in the oxygen-rich Labrador Sea Water which is ultimately exported to the rest of the ocean in the lower branch of the AMOC.

Anthropogenic carbon emissions and associated climate change are driving rapid warming, acidification, and deoxygenation in the ocean, which increasingly stress marine ecosystems. On top of long-term trends, short term variability of marine stressors can have major implications for marine ecosystems and their management. As such, there is a growing need for predictions of marine ecosystems on monthly, seasonal, and multi-month timescales. Previous studies have demonstrated the ability to make reliable predictions of the surface ocean physical and biogeochemical state months to years in advance, but few studies have investigated forecasts of multiple stressors simultaneously or assessed the forecast skill below the surface. Here, we use the Community Earth System Model (CESM) Seasonal to Multiyear Large Ensemble (SMYLE) along with novel observation-based biogeochemical and physical products to quantify the predictive skill of dissolved inorganic carbon, dissolved oxygen, and temperature in the surface and subsurface ocean. CESM SMYLE demonstrates high physical and biogeochemical predictive skill multiple months in advance in key oceanic regions and frequently outperforms persistence forecasts. We find up to 10 months of skillful forecasts, with particularly high skill in the Northeast Pacific (Gulf of Alaska and California Current Large Marine Ecosystems) for temperature, surface DIC, and subsurface oxygen. Our findings suggest that dynamical marine ecosystem prediction could support actionable advice for decision making.