Abstract

The thermodynamics and kinetics of air–sea exchange are discussed in terms of the underlying theory and on the basis of numerical calculations. The thermodynamic driving force for gas exchange is dependent on the air–sea temperature difference as well as on the partial pressure or concentration difference across the interface. The kinetics of the exchange process are strongly affected by the surface temperature of the water, as controlled by the fluxes of sensible and latent heat. The results of calculations for a model which incorporates a turbulent air layer are compared with the experimental data of Liss et al. (1981), Smith and Jones (1985) and Smith et al. (1991). This comparison clearly demonstrates the importance of coupling, in the sense of Onsager's irreversible thermodynamics, of the fluxes of sensible heat and matter across the interface. The calculations also suggest a possible new approach to the measurement of air–water exchange rates for trace gases such as carbon dioxide.

Introduction

The rate of air–sea exchange of carbon dioxide is a topic which has been the subject of some controversy in recent years. This exchange rate, which is of great practical importance in connection with global warming, is very difficult to determine experimentally, and the difficulty is compounded by the need to obtain values for both the long-term average of the rate on a global scale and the local exchange rate at a particular instant.