Microscale wave breaking and air-water gas transfer

Laboratory results showing that the air-water gas transfer velocity k is co rrelated with mean square wave slope have been cited as evidence that a wav e-related mechanism regulates k at low to moderate wind speeds [Jahne et al ,, 1987; Beck et al., 1999]. Csanady [1990] has modeled the effect of micro scale wave breaking on air-water gas transfer with the result that k is pro portional to the fractional surface area covered by surface renewal generat ed during the breaking process. In this report we investigate the role of m icroscale wave breaking in gas transfer by determining the correlation betw een k and Ag, the fractional area coverage of microscale breaking waves. Si multaneous, colocated infrared (IR) and wave slope imagery is used to verif y that Ag detected using IR techniques corresponds to the fraction of surfa ce area covered by surface renewal in the wakes of microscale breaking wave s. Using measurements of k and Ag made at the University of Washington wind -wave tank at wind speeds from 4.6 to 10.7 m s(-1), we show that k is linea rly correlated with Ag, regardless of the presence of surfactants. This res ult is consistent with Csanady's [1990] model and implies that microscale w ave breaking is likely a fundamental physical mechanism contributing to gas transfer.