Seasonality of pCO2 and air-sea CO2 fluxes in the Central Labrador Sea

The Labrador Sea in the subpolar North Atlantic is known for its large air-to-sea CO 2 fluxes, which can be around 40% higher than in other regions of intense ocean uptake like the Eastern Pacific and within the Northwest Atlantic. This region is also a hot-spot for storage of anthropogenic CO 2 . Deep water is formed here, so that dissolved gas uptake by the surface ocean directly connects to deeper waters, helping to determine how much atmospheric CO 2 may be sequestered (or released) by the deep ocean. Currently, the Central Labrador Sea acts as a year-round sink of atmospheric CO 2 , with intensification of uptake driven by biological production in spring and lasting through summer and fall. Observational estimates of air-sea CO 2 fluxes in the region rely upon very limited, scattered data with a distinct lack of wintertime observations. Here, we compile surface ocean observations of p CO 2 from moorings and underway measurements, including previously unreported data, between 2000 and 2020, to create a baseline seasonal climatology for the Central Labrador Sea. This is used as a reference to compare against other observational-based and statistical estimates of regional surface p CO 2 and air-sea fluxes from a collection of global products. The comparison reveals systematic differences in the representation of the seasonal cycle of p CO 2 and uncertainties in the magnitude of air-sea CO 2 fluxes. The analysis reveals the paramount importance of long-term, seasonally-resolved data coverage in this region in order to accurately quantify the size of the present ocean sink for atmospheric CO 2 and its sensitivity to climate perturbations.