Long-term variability of the air-sea CO2 exchange coefficient: Consequences for the CO2 fluxes in the equatorial Pacific ocean

Global distributions of the air-sea CO2 exchange coefficient are deduced from the remotely sensed Geosat and special sensor microwave imager wind speeds from April 1985 to December 1992. The global 8-year average of the air-sea CO2 exchange coefficient is 3.15 10(-2) mol m(-2) yr(-1) mu atm(-1). The peak-to-peak interannual variations are as large as the amplitude of the seasonal cycle in the tropical oceans and in the Antarctic Ocean, whereas in the northern high latitudes the seasonal variability dominates. The exchange coefficient time series is combined with air-sea CO2 partial pressure gradient that we extrapolate between 0 degrees N and 5 degrees S in the equatorial Pacific Ocean, and a zonal distribution of the air-sea CO2 fluxes is presented from 1985 to 1992. While the maximum of the CO2 partial pressure gradient is located in the eastern Pacific, the maximum of the flux is in the central Pacific because of low exchange coefficients in the eastern Pacific. The largest interannual variation, 3.5 mol m(-2) yr(-1), occurs in the central Pacific between 1987 and 1989 because the 1986-1987 El-Nino event drives ocean partial pressure close to equilibrium with the atmosphere and the 1988-1989 La Nina event brings about both high partial pressure gradient and strong exchange coefficient.