Air-sea exchange of CO₂ in the central and western equatorial Pacific in 1990

Abstract

Measurements of CO₂ in marine boundary air and in surface seawater of the central and western Pacific west of 150°W were made during the period from September to December 1990. The meridional section along 150°W showed pCO₂(sea) maximum over 410 μatm between the equator and 3°S due to strong equatorial upwelling. In the equatorial Pacific between 150°W and 179°E, pCO₂(sea) decreased gradually toward the west as a result of biological CO₂ uptake and surface sea temperature increase. Between 179°E and 170°E, the pCO₂(sea) decreased steeply from 400 μatm to 350 μatm along with a decrease of salinity. West of 170°E, where the salinity is low owing to the heavy rainfall, pCO₂(sea) was nearly equal to pCO₂(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°S-10°N, 140°E-150°W) was evaluated from the ΔpCO₂ 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 Niño event.