Capillary wave gas exchange in the presence of surfactants

The effect of surfactants on gas exchange across an air/water interface pop ulated with capillary waves, is considered. Experiments were conducted on c apillary waves having a wavelength of 2.87 mm in the presence of oleyl alco hol and stearic acid, as well as on surfaces which were surfactant-free. Th e presence of these surfactants decreased the gas exchange rate by at most a factor of two when the energy delivered to the tank was held constant. Th us, even in the presence of surfactants, pure capillary waves still caused significant gas exchange, indicating that partially damped capillary waves may play an important role in air/sea gas exchange. When the gas exchange c oefficient was plotted as a function of mean square slope, the presence of surfactants was found to negligibly affect the gas exchange rate, with the possible exception of the high wave slope regime for stearic acid. This res ult suggests that it is principally the kinematics of wave motion which acc ounts for the enhancement of transport due to the capillary waves investiga ted here. Moreover, these results agree with those obtained from polychroma tic, wind-generated waves, suggesting that, for non-breaking waves, knowled ge of the statistics of the wave field may be all that is required to param eterize the gas exchange coefficient.