Regionalized global budget of the CO2 exchange at the air-water interface in continental shelf seas

Over the past decade, estimates of the atmospheric CO2 uptake by continental shelf seas were constrained within the 0.18-0.45 Pg C yr(-1) range. However, most of those estimates are based on extrapolations from limited data sets of local flux measurements (n<100). Here we propose to derive the CO2 air-sea exchange of the shelf seas by extracting 310(6) direct surface ocean CO2 measurements from the global database SOCAT (Surface Ocean CO2 Atlas), atmospheric CO2 values from GlobalVIEW and calculating gas transfer rates using readily available global temperature, salinity, and wind speed fields. We then aggregate our results using a global segmentation of the shelf in 45 units and 152 subunits to establish a consistent regionalized CO2 exchange budget at the global scale. Within each unit, the data density determines the spatial and temporal resolutions at which the air-sea CO2 fluxes are calculated and range from a 0.5 degrees resolution in the best surveyed regions to a whole unit resolution in areas where data coverage is limited. Our approach also accounts, for the first time, for the partial sea ice cover of polar shelves. Our new regionalized global CO2 sink estimate of 0.190.05 Pg C yr(-1) falls in the low end of previous estimates. Reported to an ice-free surface area of 2210(6)km(2), this value yields a flux density of 0.7mol C m(-2)yr(-1), similar to 40% more intense than that of the open ocean. Our results also highlight the significant contribution of Arctic shelves to this global CO2 uptake (0.07 Pg C yr(-1)).