Atmospheric and oceanic partial pressures of CO2 (pCO2) have been recorded automatically along two Atlantic meridional transects in 1995. The tropical Atlantic ocean (20 ¿S-20 ¿N) is generally a source of CO2 for the atmosphere, but in the region of the North Equatorial Countercurrent an undersaturation of CO2 has been observed. Undersaturations previously reported in the literature are explained by the decrease of salinity due to the high precipitations associated with the Intertropical Convergence Zone. In June 1995, strong CO2 undersaturations (ΔpCO2=-70 μatm) were observed near 8 ¿N, which suggests, in addition of the salinity effect, an uptake of CO2 due to biological activity. This undersaturation, although weaker than in spring, also appeared at other periods of the year 1995. ¿ 1998 American Geophysical Union