SURFACE-WATER FCO(2) IN THE EASTERN EQUATORIAL PACIFIC DURING THE 1992-1993 EL-NINO

The fugacity of CO2 in surface water (fCO(2W)) was measured in the eas tern equatorial Pacific (EEP) during the boreal spring and fall of 199 2 and in the spring of 1993. A prolonged El Nino occurred during this period with anomalously warm sea surface temperatures (SST) during the spring of 1992 and 1993. Correspondingly, the fCO(2W) values were low er than historical non-El Nino values at the equator. However, the fCO (2W) in the spring of 1993 was up to 50 mu atm higher than in the spri ng of 1992, despite similar SSTs. The trend is attributed to the slowe r response times of factors causing fCO(2W) decrease compared to rapid increase of fCO(2W) by upwelling of cold water with high carbon conte nt and subsequent heating. During the fall of 1992, SSTs south of the equator were 5 degrees C cooler than in the spring, which is indicativ e of vigorous upwelling of water with high CO, content from below the thermocline. Decreases in fCO(2W) due to net biological productivity a nd gas exchange take of the order of months, causing the fCO(2W) level s during the spring of 1993 to be elevated compared to the spring of t he previous year. Our data and data obtained in 1986 and 1989 along 11 0 degrees W suggest that fCO(2W) maxima in the equatorial Pacific can be either associated with temperature minima or temperature maxima. De spite the multitude of factors which influence fCO(2W), most of the va riance can be accounted for with changes in nitrate and SST. A multili near regression of fCO(2W) with SST and nitrate for the 1992 data has a standard error in predicted fCO(2W) of 10 mu atm. Air-sea fluxes of CO2 in the EEP were estimated to be 30% higher in the spring of 1993 a nd 10% higher in the fall of 1992 than in the spring of 1992.