Air-sea fluxes of gas play an increasingly visible role in the global ocean-atmosphere balance. Yet, our estimates of air-sea carbon dioxide fluxes, for example, are less than solidly reliable past a narrow range of wind and wave conditions.

We present here an attempt at estimating carbon dioxide transfer velocities over a large range of conditions. To model the water-side turbulence, we use a recently developed air-sea stress model that incorporate independently wind forcing and sea state, including the effect of air-flow separation at high wind speeds. Concentration changes due to molecular and turbulent diffusion through the air-sea interface as well as those due to bubble entrainment are addressed. The empirical relationships may prove to be a good approximation to the physics at low wind speeds, despite not accounting for variable sea states. At high wind speeds, our estimates differ from the extrapolated wind-dependent power laws. We find that these departures are consistent with changes in the controlling physics.