He and Rn gas exchange experiments in the large wind-wave facility of IMST

In a collaboration between the Laboratoire de Géochimie Isotopique (Centre d'Etudes Nucléaires, Saclay), the Institut de Mécanique Statistique de la Turbulence (IMST, Marseille), and the Institut für Umweltphysik (Heidelberg), for the first time gas exchange experiments have been carried out in the large IMST wind-wave facility. The experiments included simultaneous measurements of Rn and He gas exchange rates, wave slope measurements at four fetches, and bubble measurements. Compared with transfer velocities measured previously in smaller tunnels, our results are considerably lower. This effect can be explained qualitatively by differences in the wave field, which must be taken into account as an important parameter for gas exchange. Wave breaking, starting at 12 m/s wind, was not intense. Consequently, only low bubble densities are obtained, not significantly enhancing gas exchange.