Abstract
Abstract. Eddy covariance measurements show gas transfer velocity suppression at medium to high wind speed. A wind–wave interaction described by the transformed Reynolds number is used to characterize environmental conditions favoring this suppression. We take the transformed Reynolds number parameterization to review the two most cited wind speed gas transfer velocity parameterizations: Nightingale et al. (2000) and Wanninkhof (1992, 2014). We propose an algorithm to adjust k values for the effect of gas transfer suppression and validate it with two directly measured dimethyl sulfide (DMS) gas transfer velocity data sets that experienced gas transfer suppression. We also show that the data set used in the Nightingale 2000 parameterization experienced gas transfer suppression. A compensation of the suppression effect leads to an average increase of 22 % in the k vs. u relationship. Performing the same correction for Wanninkhof 2014 leads to an increase of 9.85 %. Additionally, we applied our gas transfer suppression algorithm to global air–sea flux climatologies of CO2 and DMS. The global application of gas transfer suppression leads to a decrease of 11 % in DMS outgassing. We expect the magnitude of Reynolds suppression on any global air–sea gas exchange to be about 10 %.
Highlights
Gas flux F between the ocean and the atmosphere is commonly described as the product of the concentration difference C between the liquid phase and the gas phase and the total gas transfer velocity ktotal.C acts as the forcing potential difference and k as the conductance, which includes all processes promoting and suppressing gas transfer. cair and cwater are the respective air-side and water-side concentrations
We test the adjustment of u10 → ualt with two data sets of dimethyl sulfide (DMS) gas transfer velocities, Knorr11 (Bell et al, 2017) and SO234-2/235 (Zavarsky et al, 2018)
Both data sets experienced gas transfer suppression at high wind speed. Using this proof of concept, we quantify the influence of gas transfer suppression on Nightingale et al (2000) parameterization (N00) and Wanninkhof (2014) gas transfer parameterization (W14) and provide unsuppressed estimates
Summary
Gas flux F between the ocean and the atmosphere is commonly described as the product of the concentration difference C between the liquid phase (seawater) and the gas phase (atmosphere) and the total gas transfer velocity ktotal.C acts as the forcing potential difference and k as the conductance, which includes all processes promoting and suppressing gas transfer. cair and cwater are the respective air-side and water-side concentrations. Gas flux F between the ocean and the atmosphere is commonly described as the product of the concentration difference C between the liquid phase (seawater) and the gas phase (atmosphere) and the total gas transfer velocity ktotal. Cair and cwater are the respective air-side and water-side concentrations. F = ktotal · C = ktotal · (cwater − cair · H ) (1). C is typically measured with established techniques, the distance of the measurements from the interface introduces uncertainties in the flux calculation. Parameterizations of k are another source of uncertainty in calculating fluxes. The flux F can be directly measured, e.g., with the eddy covariance technique, together with C in order to derive k and estimate a k parameterization (Eq 2)
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