A fCO₂ sensor, based on a colorimetric method used for the CARIOCA buoys, has been installed on a Pilot Research Moored Array in the Tropical Atlantic (PIRATA) mooring at 6°S, 10°W, in the gulf of Guinea, in June 2006 during the EGEE 3 cruise. Hourly fCO₂ data recorded from June to December 2006 are presented. An alkalinity-salinity relationship has been determined using data from different cruises, which allows the calculation of dissolved inorganic carbon. Although the tropical Atlantic is an important source of CO₂, an unexpected area of low CO₂ concentrations is observed in the South Equatorial Counter Current with fCO₂ values close to equilibrium conditions or even slightly undersaturated with respect to the atmospheric fCO₂ value of 367.7 μatm measured during the cruise. At the end of June, an increase of seawater fCO₂ to 400 μatm is consistent with the beginning of the upwelling season occurring from July to September. Although the mooring is not located within the upwelling area, the spreading of the cold tongue explains the large CO₂ outgassing. The monthly CO₂ flux ranges from 1.19 mmol m^-2 d^-1 in June to a maximum of 8.37 mmol m^-2 d^-1 in October, when high fCO₂ values above 420 μatm are maintained by the warming of surface water. Most of the fCO₂ distribution can be explained by physical processes and a strong relationship between fCO₂ and SST is determined for the upwelling season. From mid-September, diurnal cycles can be detected. Using a dissolved inorganic carbon budget, periods where net community production or diurnal warming and cooling dominates are observed.