Algorithms to estimate the carbon dioxide uptake in the northern North Atlantic using shipboard observations, satellite and ocean analysis data

Observations of the surface-water fugacity of carbon dioxide (fCO2sw) measured during 2005 in the subpolar North Atlantic Ocean (58–62°N, 10–40°W) were used together with in situ ocean data and remotely sensed data to develop algorithms to estimate fCO2sw. Based on multiple regression we found that sea-surface temperature (SST), mixed-layer depth (MLD), and chlorophyll a (chl a) contributed significantly to the fit. Two algorithms were developed for periods depending on the presence of chl a data. The correlation coefficient (r2) and the root-mean-square deviation (rms) for the best fit in the period when chl a was observed (20 March–15 October) were 0.720 and ±10.8 μatm, respectively. The best fit for the algorithm for the period when no chl a was present (16 October–19 March) resulted in a r2 of 0.774 and a rms of ±5.6 μatm. Based on these algorithms we estimated seasonal fields of fCO2sw and the air–sea CO2 flux. The estimated net annual CO2 sink was 0.0058 Gt C yr−1 or 0.6 mol C m−2 yr−1.