Articles | Volume 11, issue 1
Research article
28 Jan 2015
Research article |  | 28 Jan 2015

Measuring air–sea gas-exchange velocities in a large-scale annular wind–wave tank

E. Mesarchaki, C. Kräuter, K. E. Krall, M. Bopp, F. Helleis, J. Williams, and B. Jähne

Abstract. In this study we present gas-exchange measurements conducted in a large-scale wind–wave tank. Fourteen chemical species spanning a wide range of solubility (dimensionless solubility, α = 0.4 to 5470) and diffusivity (Schmidt number in water, Scw = 594 to 1194) were examined under various turbulent (u10 = 0.73 to 13.2 m s−1) conditions. Additional experiments were performed under different surfactant modulated (two different concentration levels of Triton X-100) surface states. This paper details the complete methodology, experimental procedure and instrumentation used to derive the total transfer velocity for all examined tracers. The results presented here demonstrate the efficacy of the proposed method, and the derived gas-exchange velocities are shown to be comparable to previous investigations. The gas transfer behaviour is exemplified by contrasting two species at the two solubility extremes, namely nitrous oxide (N2O) and methanol (CH3OH). Interestingly, a strong transfer velocity reduction (up to a factor of 3) was observed for the relatively insoluble N2O under a surfactant covered water surface. In contrast, the surfactant effect for CH3OH, the high solubility tracer, was significantly weaker.

Short summary
Our article presents successful gas exchange measurements obtained in a large-scale wind-wave tank. The adopted box model methodology, experimental produce and instrumentation are described in detail. For the first time, parallel measurements of total transfer velocities for 14 individual gases within a wide range of solubility have been achieved. Various wind speed conditions and the effect of surfactant layers have been investigated providing exciting results.