MEASUREMENTS OF ATMOSPHERIC AND OCEANIC CO2 IN THE TROPICAL ATLANTIC - 10 YEARS AFTER THE 1982-1984 FOCAL CRUISES

Measurements of CO2 parameters in and over the tropical Atlantic ocean have been made during the CITHER 1 cruise (January to March 1993). These observations are compared to the results obtained a decade earlier in the same area during the FOCAL experiment (1982-1984). The increase of atmospheric CO2 (1.3 to 1,5 ppm yr(-1)) is in agreement with the secular trend, The variation of CO2 fugacity, fCO(2), in surface seawater is analysed and compared with variations of hydrographic conditions. The apparent increase of ocean surface fCO(2) is somewhat higher than the atmospheric increase: during the 9-year period, the apparent increase of oceanic fCO(2) is found to range from 22.5 to 24.9 mu atm. A new estimate of air-sea CO2 nux in the Atlantic equatorial belt indicates that the oceanic source is enhanced in 1993 compared to 1984. An interannual change in total inorganic carbon, TCO2, through the accumulation of CO2 in the mixed layer is assessed and analysed in comparison with the fCO(2) increase, The agreement between the evolutions of the two parameters of the oceanic CO2 system is acceptable by taking into account the uncertainties to estimate these evolutions.