Response of the Air-Sea CO₂ Flux to Climate Events in the Pacific Ocean

The variations of the air-sea CO₂ exchange flux with time in various regions of the Pacific Ocean from 1960 to 2000 are analyzed with a basinwide ocean general circulation model coupled with a simple biogeochemical carbon model. The simulated results show that the equatorial Pacific Ocean is a source of atmospheric CO₂, while both the North and South Pacific Ocean (from 15°N or 15°S to the northern or southern boundary of the model) are sinks of atmospheric CO₂. Variations of the air-sea CO₂ flux with time are obtained to be significant in these three regions, in which the variation in the equatorial Pacific Ocean is the most intense. The responses of the variations of the flux to the climate events in the three regions are different. During El Niño years, the intensity of cool tongue, total dissolved inorganic carbon concentrations, and export production in the equatorial Pacific Ocean are reduced because of a weakening of upwelling, while during La Niña years all variables that can control the air-sea carbon flux are enhanced. These phenomena do not exist in the North and South Pacific Ocean, and the responses of export production in these regions to the El Niña and La Niña events are similar. The relationship between sea surface temperature (SST) and the air-sea CO₂ flux shows that in the equatorial Pacific Ocean, the influence of the upwelling on the concentration of sea surface total dissolved inorganic carbon is a main factor controlling the air-sea CO₂ flux. In other regions, particularly in the subtropical regions, SST plays a more important role in the variations of the air-sea CO₂ flux.