VARIATIONS IN THE GLOBAL AIR-SEA TRANSFER VELOCITY FIELD OF CO2

The air-sea exchange of trace gases is critical in modeling the evolution of the compositional changes of the Earth's atmosphere on a variety of time scales. This exchange is controlled by the transfer velocity (Kw) and the air-sea concentration gradient. The interplay between the transfer velocity and extent of local surface ocean CO2 saturation influences the partitioning of carbon and its isotopes between the atmosphere and ocean. Here, the present-day global transfer velocity field of CO2 is computed for January and July with user-defined derived fields based on control runs of the NCAR (National Center for Atmospheric Research) CCMl (Community Climate Model), a 12-layer atmospheric general circulation model. The spatial resolution of these calculations is 4.5 degrees X 7.5 degrees latitude-longitude. The range of KwCO2 variation over the globe is an order of magnitude, varying from 3 to 40 cm h(-1). Equatorial values are generally 310 cm h(-1) and high latitude regions experience values in excess of 30 cm h(-1). The annual variability of the transfer velocity for CO2 in the high-latitude northern hemisphere is larger than in the high-latitude southern hemisphere. The global area-weighted CO2 transfer velocity for both January and July runs is roughly a factor of 1.8 less than the global C-14 mean.