CHANGES IN EQUATORIAL CO2 FLUX AND NEW PRODUCTION ESTIMATED FROM CO2 AND NUTRIENT LEVELS IN PACIFIC SURFACE WATERS DURING THE 1986/87 EL-NINO

The seasonal variabilities of the CO2 system and dissolved nutrients (nitrate, phosphate, and silicate) in surface seawater of the central tropical Pacific Ocean before and during the 1986/1987 El Nino/Southern Oscillation (ENSO) warm event were observed as part of a ship-of-opportunity program. Beginning in late 1986 and continuing through 1987, there was a gradual increase in sea surface temperature (SST) and slight decrease of surface seawater salinity around the central equatorial region. These changes were accompanied by decreasing levels of dissolved nutrients, ocean-surface PCO2, dissolved inorganic carbon (SIGMA CO2) and net CO2 evasion. In September 1987, equatorial SST was warmest while CO2 evasion, PCO2, SIGMA CO2, and the dissolved nutrients reached their Lowest levels. In September 1987, owing to the weakened equatorial upwelling, the supply of SIGMA CO2 from deeper waters was reduced by about 97-194 mM m-2 d-1, while the low replenishment of nitrate represented a loss of about 17-34 mM C m-2 d-1 in new production. The evasion of CO2 from the central equatorial Pacific between 5-degrees-S and 5-degrees-N [10-degrees-S and 10-degrees-N] was estimated to be about 1.2 M CO2 m-2 yr-1 [0.9 M CO2 m-2 yr-1] prior to the 1987 El Nino, but only 0.2 M CO2 m-2 yr-1 [0.2 M CO2 m-2 yr-1] during the El Nino.