VARIABILITY OF DELTA-C-13 OF SIGMA-CO2 IN OCEAN WATERS OF THE EQUATORIAL PACIFIC

The transect from East to West Pacific realized along the equator duri ng the Alize 2 cruise (January-March 1991) offers a unique opportunity to evaluate the effect of the equatorial upwelling on the partial der ivative(13)C values of Sigma CO2 in oceanic waters. The surface partia l derivative(13)C distribution from 95 degrees W to 165 degrees E is c haracterized by a general increase from 0.90 to 1.54 parts per thousan d which parallels the temperature rise from 23 to 30 degrees C, both g iving a signature of the upwelling and of the westward advection of su perficial waters: the C-13 depletion in the Sigma CO2 marks the progre ssive influence of upwelled waters which are rich in C-13-depleted CO2 generated by organic matter remineralization. The vertical partial de rivative(13)C distribution from the surface down to 1000 metres shows that the upper thermocline and the oxygen minimum are two major bounda ries between which the regeneration of organic matter mainly occurs. F urthermore, the comparison of our measurements with those obtained by Kroopnick in 1970 at the same location (150 degrees W) shows that part ial derivative(13)C values in surface waters have decreased by 0.5 par ts per thousand during the last twenty years period as a result of ant hropogenic CO2 inputs.