Progressive Oxygenation of the North Atlantic Subpolar Gyre
Abstract
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 a novel observation-based data product to analyze large-scale patterns of the air-sea flux of oxygen, finding a mean annual flux of 48.1 (Formula presented.) 14.6 Tmol (Formula presented.) from the atmosphere into the ocean integrated over the SPNA ((Formula presented.) N– (Formula presented.) N). An analysis of a fully-closed oxygen budget from the data-assimilative ECCO-Darwin ocean biogeochemistry model suggests that the net uptake is counteracted by oxygen removal through ocean circulation and mixing. Over an annual cycle, a SPNA oxygen uptake of 63.6 (Formula presented.) 13.8 Tmol at densities greater than 26.7 kg (Formula presented.) drives a wintertime oxygen increase in corresponding mode and deep water layers. 87% of this net annual uptake occurs in the density range of subpolar mode water (SPMW), 26.7 kg (Formula presented.) 27.63 kg (Formula presented.), in the upper branch of the Atlantic Meridional Overturning Circulation (AMOC). Our results demonstrate that oxygen is injected during mode water formation throughout the subpolar gyre's cyclonic pathway from the North Atlantic Current toward the Labrador Sea. Along this path, SPMW becomes progressively denser and more oxygenated, and is ultimately transformed into Labrador Sea Water which exports the accumulated oxygen to the global ocean in the lower branch of the AMOC.
