A cubic relationship between air-sea CO2 exchange and wind speed

Using recent laboratory and field results we explore the possibility of a cubic relationship between gas exchange and instantaneous (or short-term) wind speed, and its impact on global air-sea fluxes. The theoretical foundation for such a dependency is based on retardation of gas transfer at low to intermediate winds by surfactants, which are ubiquitous in the world's oceans, and bubble-enhanced transfer at higher winds. The proposed cubic relationship shows a weaker dependence of gas transfer at low wind speed and a significantly stronger dependence at high wind speed than previous relationships. A long-term relationship derived from such a dependence, combined with the monthly CO2 climatology of Takahashi [1997], leads to an increase in the global annual oceanic CO2 uptake from 1.4 Gigaton C yr(-1) to 2.2 Gigaton C yr(-1). Although a cubic relationship fits within global bomb-C-14 oceanic uptake constraints, additional checks are warranted, particularly at high wind speeds where the enhancement is most pronounced.