Central role of Labrador Sea convection for transport of oxygen into the deep North Atlantic Ocean

Convection in the subpolar North Atlantic feeds highly oxygenated water into the lower limb of the Atlantic Meridional Overturning Circulation (AMOC), sustaining deep-sea organisms across a vast expanse of the ocean. Yet, the rates and processes responsible for this oxygenation have remained largely hidden by a lack of direct measurements. Here we apply newly developed calibration protocols for multi-year oxygen measurements to quantify oxygen transport across a mooring array spanning the Labrador Sea. The results show that Labrador Sea deep convection results in a substantial export of oxygen to the lower limb of the AMOC. Specifically, local air–sea exchange adds ~4.1 Tmol yr−1 of oxygen to dense Labrador Sea waters, while deep convection moves ~23.5 Tmol yr−1, added to lighter waters upstream in the eastern subpolar North Atlantic, to those same dense waters. We estimate that this export is sufficient to balance biological respiration across much of the deep North Atlantic, making processes in the Labrador Sea critical to North Atlantic oxygenation despite their small contribution to the densification of the AMOC lower limb. This finding shows that future risk of deep North Atlantic deoxygenation depends not only on the processes that drive overturning, but also on Labrador Sea deep convection. The Labrador Sea plays a crucial role in transporting oxygen into the deep limb of the Atlantic Meridional Overturning Circulation, despite its limited contribution to density transformation, according to an analysis of 2 years of mooring data.