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 degreesN and 47 degreesN, 20 degreesW and the Iberian Peninsula coast, were used to estimate the anthropogenic carbon (C-ANT) 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 C-ANT down to 2000m 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 C-ANT advected by the Mediterranean Water (MW) is the most important contributor to the total C-ANT 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 C-ant. When MW is formed in the Gulf of Cadiz, 85% of Central Water is entrained by sinking of the Mediterranean Overflow Water. Central Waters have about 50 mu mol kg(-1) of C-ANT thus this entrainment represents 0.07 GtC yr(-1), which is about 26% of the C-ANT transported by the thermohaline circulation in the North Atlantic. (C) 2001 Elsevier Science Ltd. All rights reserved.