Spatial variability of the CO2 sink in the Sargasso Sea

Spatial fields of the partial pressure of carbon dioxide (pCO2) were derived for the entire Sargasso Sea from three-day composite satellite images of sea-surface temperature (SST) and established empirical relationships between surface pCO2 and SST. Application of the retrieval method from summer of 1994 through fall of 1996 faithfully reproduced the annual cycle of surface pCO2 at the US JGOFS Bermuda Atlantic Time-Series Study (BATS) site, with a cross-validated root-mean-square (rms) error of 11–14 μatm. Estimates of air–sea CO2 exchange were made using satellite-derived surface pCO2 and surface wind distributions from global analysis products. Present estimates of air–sea CO2 exchange at the BATS site agreed well with previous determinations made using in situ data sets. The Sargasso Sea offshore of the Gulf Stream was found to be a net annual sink for CO2 (north of 29°N at the western end of the study area, and north of ∼26°N at the eastern end). Interannual variability in the net CO2 exchange was not large (<5%) when integrated over the entire study area, but significant interannual differences existed in the meridional and zonal gradients of CO2 flux. These were largely driven by interannual differences in seasonal spatial wind distribution. The BATS site was found to be in a region of the strongest spatial gradients of air–sea CO2 flux. The present study illustrates the importance of spatial data sets to extrapolating point determinations of the CO2 flux to regional scales.