Laboratory studies have been conducted in two circular wind wave flumes to
investigate the relationship between air-sea transfer velocities of weakly
soluble, nonreactive gases and wind-generated surface waves over clean wate
r surfaces and in the presence of surface films. Detailed surface wave meas
urements have been made using a scanning laser slope gauge. In the circular
tanks, longer gravity waves (wavenumber below 12 rad/m) are hardly affecte
d by surfactant, while shorter waves (above 100 rad/m) are significantly re
duced. With higher surfactant concentrations, waves above 200-300 rad/m may
be completely eliminated. Because of the absence of narrow-banded fetch-li
mited gravity waves, the wave fields in the circular tanks are significantl
y different from those in linear wind wave flumes. At a given wind friction
velocity, the transfer velocity may decrease by as much as 60% because of
surface films. Regardless of the surfactant concentrations, the transfer ve
locity shows a reasonable correlation with the total mean square slope and
With the mean square slope of shorter wind waves (wavenumber above 200 rad/
m). However, it shows a poor correlation with the mean square slope of long
er wind waves (wavenumber below 50 rad/m). These observations suggest that
short wind waves play an important role in air-sea gas exchange.