AIR-SEA EXCHANGE OF CO2 IN THE CENTRAL AND WESTERN EQUATORIAL PACIFIC IN 1990

Measurements of CO2 in marine boundary air and in surface seawater of the central and western Pacific west of 150 degrees W were made during the period from September to December 1990. The meridional section along 150 degrees W showed pCO(2)(sea) maximum over 410 mu atm between the equator and 3 degrees S due to strong equatorial upwelling. In the equatorial Pacific between 150 degrees W and 179 degrees E, pCO(2)(sea) decreased gradually toward the west as a result of biological CO2 uptake and surface sea temperature increase. Between 179 degrees E and 170 degrees E, the pCO(2)(sea) decreased steeply from 400 mu atm to 350 mu atm along with a decrease of salinity. West of 170 degrees E, where the salinity is low owing to the heavy rainfall, pCO(2)(sea) was nearly equal to pCO(2)(air). The distribution of the atmospheric CO2 concentration showed a considerable variability (+/- 3 ppm) in the area north of the Intertropical Convergence Zone due to the regional net source-sink strength of the terrestrial biosphere. The net CO2 flux from the sea to the atmosphere in the equatorial region of the central and western Pacific (15 degrees S-10 degrees N, 140 degrees E-150 degrees W) was evaluated from the Delta pCO(2) distribution and the several gas transfer coefficients reported so far. It ranged from 0.13 GtC year(-1) to 0.29 GtC year(-1). This CO2 outflux is thought to almost disappear during the period of an El Nino event.