2 Introduction Current large uncertainties in the air-sea flux of CO 2 prevent us from verifying the partitioning of fossil fuel CO 2 between the ocean and the terrestrial biosphere. This limits our ability to realistically model future atmospheric CO 2 levels.
Techniques are now in hand to improve our estimates of air-sea fluxes.
The GasEx-II study, which will begin in January 2001, will take place in the eastern Equatorial Pacific. The goal of the study is to use direct gas flux measurements to improve our understanding of the forcing functions of the kinetics of air-sea gas exchange. A second goal will be to determine the physical, chemical, and biological factors controlling pCO 2 in the surface water. The questions about mesoscale CO 2 dynamics in this region relate to biological versus physical control, and remote versus local influences. The pCO 2 in the surface water relates directly to upwelling strength but regional fluxes are strongly influenced by remote factors such as the capping off of the upwelling system by the low salinity water advecting from the West.