Relationship between wind speed and gas exchange over the ocean revisited

The relationship between gas exchange and wind speed is used extensively for estimating bulk fluxes of atmospheric gases across the air-sea interface. Here, I provide an update on the frequently used method of Wanninkhof (1992). The update of the methodology reflects advances that have occurred over the past two decades in quantifying the input parameters. The general principle of obtaining a relationship constrained by the globally integrated bomb-(CO2)-C-14 flux into the ocean remains unchanged. The improved relationship is created using revised global ocean C-14 inventories and improved wind speed products. Empirical relationships of the Schmidt number, which are necessary to determine the fluxes, are extended to 40 degrees C to facilitate their use in the models. The focus is on the gas exchange of carbon dioxide, but the suggested functionality can be extended to other gases at intermediate winds (approximate to 4-15 m s(-1)). The updated relationship, expressed as k = 0.251 <U-2> (Sc/660)(-0.5) where k is the gas transfer velocity, <U-2> is the average squared wind speed, and Sc is the Schmidt number, has a 20% uncertainty. The relationship is in close agreement with recent parameterizations based on results from gas exchange process studies over the ocean.