EFFECT OF THE EQUATORIAL PACIFIC UPWELLING ON ATMOSPHERIC CO2 DURING THE 1982-1983 EL NINO

The 1982-1983 El Nino event perturbed the otherwise steady growth in atmospheric CO2 due to fossil fuel combustion. Compared to the recent average growth rate in atmospheric CO2 of about 1.5 ppm per year, the growth rate in late 1982 fell to about zero. During this strong El Nino event, additional sinks for atmospheric CO2 operated. By late 1983, the growth rate rebounded to above average, indicating the presence of new sources. To a large extent, the relative roles of the possible actors have eluded us. In this study, box models of the ocean-atmosphere carbon cycle are used to isolate and estimate the effects of the collapse and return of the upwelling in the equatorial Pacific during an El Nino. The models capture the major trends during the El Nino for sea surface temperature, nutrients, and Delta pCO(2). The drop in Delta pCO(2) in the normally strong source of the equatorial Pacific can account for a partial amount (probably less than 30%) of the decrease in the growth rate in atmospheric CO2 centered around late 1982. The recovery to normal equatorial conditions plays an even smaller and nearly negligible role in any growth rate overshoot later in El Nino. Changes in the higher-latitude oceans and disequilibrium in the terrestrial cycle of photosynthesis and respiration continue as major potential agents behind the perturbation.