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 = 1012 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.