VARIATIONS AND DISTRIBUTIONS OF CO2 IN AND OVER THE EQUATORIAL PACIFIC DURING THE PERIOD FROM THE 1986/88 EL-NINO EVENT TO THE 1988/89 LA-NINA EVENT

Measurements of pCO2 in the background air and seawater of the equatorial Pacific were made during the period from January 1987 to February 1989 to study variations in CO2 flux between the sea and the air. In January and February 1987, which was within the period of 1986/88 ENSO event, the surface water pCO2 of the central equatorial Pacific decreased due to the reduction of upwelling, but less dramatically than during the 1982/83 ENSO event. In January and February 1989, the pCO2 of the central equatorial Pacific increased with the SST decrease, due to the enhancement of upwelling during the La Nina event. Changes in surface water pCO2 along the equator were well approximated by the effect on pCO2 of the temperature, salinity, biological activity and the CO2 exchange between the sea and the air. In January and February 1987, the CO2 flux in the equatorial Pacific was estimated to be 0.4 Gt-C yr-1, which was low compared to the non-ENSO periods, but remained positive. In January and February 1989, it increased to the level of 1 Gt-C yr-1, mainly due to the increase of surface seawater pCO2 during the La Nina event. The large interannual variation in CO2 flux could affect the growth rate of atmospheric CO2. For the period from January 31, 1987 to January 31, 1989, the concentration of atmospheric CO2 has increased considerably (4.8 ppm). The delta-C-13 of atmospheric CO2 suggests the enhanced releases of CO2 from the biosphere for the period between 1988 and 1987, and a relatively important role of air/sea CO2 exchange between 1989 and 1988.