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

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Abstract
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‐14C oceanic uptake constraints, additional checks are warranted, particularly at high wind speeds where the enhancement is most pronounced.