The transect from East to West Pacific realized along the equator during the Alize 2 cruise (January-March 1991) offers a unique opportunity to evaluate the effect of the equatorial upwelling on the partial derivative(13)C values of Sigma CO2 in oceanic waters. The surface partial derivative(13)C distribution from 95 degrees W to 165 degrees E is characterized by a general increase from 0.90 to 1.54 parts per thousand which parallels the temperature rise from 23 to 30 degrees C, both giving a signature of the upwelling and of the westward advection of superficial waters: the C-13 depletion in the Sigma CO2 marks the progressive influence of upwelled waters which are rich in C-13-depleted CO2 generated by organic matter remineralization. The vertical partial derivative(13)C distribution from the surface down to 1000 metres shows that the upper thermocline and the oxygen minimum are two major boundaries between which the regeneration of organic matter mainly occurs. Furthermore, the comparison of our measurements with those obtained by Kroopnick in 1970 at the same location (150 degrees W) shows that partial derivative(13)C values in surface waters have decreased by 0.5 parts per thousand during the last twenty years period as a result of anthropogenic CO2 inputs.