Observations of the CO2 system properties in the tropical Atlantic Ocean

We measured three properties of the carbonate system in seawater during the world ocean circulation experiment (WOCE) cruise A15 in the tropical Atlantic Ocean between 7°30′N and 32°S along 19°W. In surface seawater of the tropical Atlantic Ocean, the observed partial pressure of CO2 (pCO2sea) values are close to those observed a decade ago during the program FOCAL. In the atmosphere pCO2 (pCO2air) increased by approximately 10 μatm. These observations suggest that the upper ocean of this area is becoming a weaker CO2 source to the atmosphere than it was a few years ago. At depth, each water mass is well characterized by different concentrations in total CO2 and total alkalinity. A simple calculation of anthropogenic CO2 in the North Atlantic deep water suggests that TCO2 in this water mass has increased by 38±8 μmol/kg.