The transfer of weakly soluble gases between the atmosphere and seas or lakes is controlled by liquid-phase molecular and turbulent diffusion mechanisms, which essentially depend on wind velocity and gas Schmidt number. A distinct change in regime is observed around 2-3 m s-1, when capillary waves appear, which present models cannot explain. We suggest relating turbulent diffusivity with (1) possible motions close to a ''free'' liquid-gas interface, (2) mean current distribution in that region, and (3) capillary wave spectra. Resulting transfer velocities explain laboratory and field data at low and moderate wind speeds.