Field determination of air-sea gas exchange by continuous measurement of radon-222

Abstract

Equipment has been developed for automatic measurement of the radon dissolved in sea water, with the aim of determining gas exchange rates at sea on the basis of the radon-222 deficiency in the mixed layer with respect to its parent nuclide radium-226. The equipment will be employed to obtain, over an extended period at fixed position, repeated measurements of the vertically integrated radon deficiency. The repetition period will be 2 hours, and sampling will be by a winch-operated submersible pumping system which will continuously scan the radon-deficient layer. The repeated measurements will allow to derive gas exchange rates even under transient meteorological conditions. As opposed to this, radon work carried out to date relied on isolated deficiency measurements and stationary conditions were commonly assumed (the deficiency relaxation time is about 5 days), which, under transient conditions, may lead to considerable errors. Equipment tests have been made at sea and the first integrated-deficiency measurements were obtained on the RSSChallenger in July 1977. Field programs are in preparation for JASIn (Joint Air-Sea Interaction, July–September 1978) and FGGE (First GARP Global Experiment, January–July 1979). The ultimate goal is a parameterization of the gas exchange rate in terms of external parameters, primarily wind speed.