Optimum Application of the Radon Deficit Method to Obtain Air-Sea Gas Exchange Rates

Abstract

The radon deficit method determines air-sea gas transfer rates from the amount of ²²²Rn that is deficient in ocean surface water relative to radioactive equilibrium with ²²⁶Ra. The gas transfer signal is contained in the ²²²Rn deficit in time-integrated form (relaxation time = a few days), the relaxation, however, being blurred by depth variations of the ²²²Rn-deficit layer that arise from mixed-layer dynamics. We show from field data and through numerical simulations that this situation makes accounting for the gas transfer signal a difficult task. We conclude that observations drifting with the mixed-layer flow, and in selected areas of the ocean, are necessary, and that under such conditions our instrumentation is capable to provide gas transfer information with a useful precision at some 12 h resolution. Field observations will also require observations of a complete set of the external variables, of which the definition and measurement of appropriate wave parameters are open questions.