WHOI PO

Abstract: The subpolar North Atlantic is a hot spot for anthropogenic carbon and oxygen uptake.  However, climate models are unable to reproduce the observed global patterns of oxygen and carbon change, hindered both by a dearth of year-round observations of dissolved gases and an incomplete understanding of the dynamics that govern ventilation, i.e. dissolved gas pathways into the interior ocean. Here we use two years of densely-spaced moored oxygen observations in the western Irminger Sea (2020-2022) to quantify the seasonal changes in boundary current oxygen content and associate them with ventilation processes. We find that the oxygen transport variability is dominated by a deep subpolar mode water, which has its origins in the subtropical North Atlantic and forms near the boundary. While some of these waters are within the boundary current’s winter mixed layer and are oxygenated by direct air-sea exchange, the denser portion appears to be oxygenated by along-isopycnal exchange with mixed layer waters just offshore of the boundary current. An analysis of BGC Argo floats in the region largely corroborates this view, though there are many gaps and exciting directions for future measurements and research. Finally, we place these results in the larger-scale context of ventilation from the subpolar North Atlantic, stressing the role of progressive ventilation along the boundary current as well as convection in the Labrador Sea.