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.