Relationship between wind speed and gas exchange over the ocean revisited

Abstract

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-14 CO 2 flux into the ocean remains unchanged. The improved relationship is created using revised global ocean 14 C inventories and improved wind speed products. Empirical relationships of the Schmidt number, which are necessary to determine the fluxes, are extended to 40°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 ( -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.

Intense methane ebullition from open water area of a shallow peatland lake on the eastern Tibetan Plateau

“…Experiments have shown that in addition to other factors including turbulence, boundary layer stability, and surfactants, wind also acts as a key factor for the gas transfer at the air-water interface (Wanninkhof et al, 1992). Generally, the relationship between gas transfer and wind speed is expressed as a quadratic dependency (Sweeney et al, 2007), where gas transfer velocity was nearly zero in condition of wind speed lower than 3 m/s (Wanninkhof et al, 2014). In the region where Lake Medo is located, the mean annual wind speed is 2.4 m/s, which indicated a very low gas transfer velocity and limited diffusive flux of methane.…”

Uncertainty and sensitivity in optode-based shelf-sea net community production estimates

“…The square root of the squared mean was used for wind speed to fit with the quadratic k w parametrisation used. Wanninkhof et al (2009) argue that comprehensive surface forcing models provide little to no improvement over simple wind speed algorithms, and although simple parametrisations cannot capture all the processes that control gas transfer, they appear to capture most.…”

“…The calculation of k w is conservatively assumed to be accurate to ±15 % (Wanninkhof, 2014). The root-mean-square error (RMSE) from regressions between ECMWF and ship anemometer, shown in Fig.…”

“…However Nightingale et al (2000) found no measurable change in k w during a 30-fold increase in chlorophyll during an algal bloom. We, like Wanninkhof et al (2009), consider that practically surfactants are always in effect and are thus incorporated into empirically derived k w parametrisations.…”

The carbon cycle in a changing climate

“…The rate of CO 2 exchange is therefore often parameterized using a quadratic dependence on wind speed that has been determined empirically. 12 As computational capabilities grow, higher-resolution models that include more processes and complexity continue to be developed.…”