Laboratory experiments on CO2 gas exchange with wave breaking

The CO2 gas transfer velocity (KCO2) at air-water interface in a wind-wave flume was estimated at the circumstance of wave breaking. Three types of dynamic processes in the flume were created: monochromatic waves generated by wavemaker, mechanically-generated monochromatic waves with superimposed wind forcing, pure wind waves with 10-meter wind speed ranging from 4.5 m/s to 15.5 m/s. Without wind forcing, KCO2 correlated with the wave breaking probability, wave height of breakers and energy loss due to wave breaking. With superimposed wind, wind speed was found to influence KCO2 both in the coupled wind/mechanical wave experiments and in pure wind waves, but wave breaking still played a significant role in CO2 gas exchange. Therefore, wave properties should be considered directly in parameterization of KCO2. A non-dimensional empirical formula was established in which KCO2 is expressed as a function of wave breaking probability, a modified Reynolds number and an enhancement factor to account for wind speed.