Long-term (1977–1997) measurements of carbon dioxide in the Eastern North Atlantic: evaluation of anthropogenic input

From 1977 to 1997 CO2 parameters were measured in the Eastern North Atlantic Ocean. A data set of 12 cruises carried out between 37°N and 47°N, 20°W and the Iberian Peninsula coast, were used to estimate the anthropogenic carbon (CANT) based on a back-calculation technique, with the aim of evaluating its temporal evolution in that 20-year period. The rate of change of the integrated CANT down to 2000 m was 0.95 mol m−2 yr−1. Half of this input corresponds to a direct uptake of atmospheric CO2 (0.48 mol m−2 yr−1), while the other half enters by advection. The CANT advected by the Mediterranean Water (MW) is the most important contributor to the total CANT advected into the area, representing 59% (0.27±0.09 mol m−2 yr−1), whereas the Labrador Sea Water contributes only 15% (0.07±0.04 mol m−2 yr−1). The particular formation mechanism of MW explains its high content of advected CANT. When MW is formed in the Gulf of Cádiz, 85% of Central Water is entrained by sinking of the Mediterranean Overflow Water. Central Waters have about 50 μmol kg−1 of CANT; thus this entrainment represents 0.07 GtC yr−1, which is about 26% of the CANT transported by the thermohaline circulation in the North Atlantic.