Changes in equatorial CO2 flux and new production estimated from CO2 and nutrient levels in Pacific surface waters during the 1986/87 El Niño

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 pC0₂ , dissolved inorganic carbon (Σ CO₂) and net CO₂ evasion. In September 1987, equatorial SST was warmest while CO₂ evasion, pCO₂ , Σ: CO₂ , and the dissolved nutrients reached their lowest levels. In September 1987, owing to the weakened equatorial upwelling, the supply of Σ: 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 Cm ^-2 d^-1 in new production. The evasion of CO₂ from the central equatorial Pacific between 5°S and 5°N [l0°S and l0°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 Nifio, but only 0.2 M CO₂ m^-2 yr^-1 [0.2 M CO₂ m^-2 yr^-1] during the El Niño.