We compare estimates of the anthropogenic CO2 content of seawater samples from the subpolar North Atlantic Ocean calculated on the basis of a back-calculation technique with measurements of the chlorofluorocarbon CFC-11. Estimated anthropogenic CO2 concentrations are in the range 10–80 µmol kg-1, while CFC-11 concentrations cover the full range from below detection limit to > 5 pmol kg-1 in waters at atmospheric equilibrium. The majority of the data points show a linear correlation between anthropogenic CO2 concentrations and CFC-11 saturation, which can only be explained by the strongly advective nature of the North Atlantic Ocean. Only deep eastern basin samples deviate from this general observation in that they show still significant concentrations of anthropogenic CO2 where CFC-11 is no longer detectable. In order to remove the influence of the Revelle factor reflected in the anthropogenic CO2 concentrations we have calculated 'excess' pCO2, showing an even tighter linear correlation with atmospheric equilibrium concentrations of CFC-11.
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