A Sea State Dependent Gas Transfer Velocity for CO₂ Unifying Theory, Model, and Field Data

Abstract

Wave breaking induced bubbles contribute a significant part of air‐sea gas fluxes. Recent modeling of the sea state dependent CO2 flux found that bubbles contribute up to ∼40% of the total CO2 air‐sea fluxes (Reichl & Deike, 2020, https://doi.org/10.1029/2020gl087267). In this study, we implement the sea state dependent bubble gas transfer formulation of Deike and Melville (2018, https://doi.org/10.1029/2018gl078758) into a spectral wave model (WAVEWATCH III) incorporating the spectral modeling of the wave breaking distribution from Romero (2019, https://doi.org/10.1029/2019gl083408). We evaluate the accuracy of the sea state dependent gas transfer parameterization against available measurements of CO2 gas transfer velocity from 9 data sets (11 research cruises, see Yang et al. (2022, https://doi.org/10.3389/fmars.2022.826421)). The sea state dependent parameterization for CO2 gas transfer velocity is consistent with observations, while the traditional wind‐only parameterization used in most global models slightly underestimates the observations of gas transfer velocity. We produce a climatology of the sea state dependent gas transfer velocity using reanalysis wind and wave data spanning 1980–2017. The climatology shows that the enhanced gas transfer velocity occurs frequently in regions with developed sea states (with strong wave breaking and high significant wave height). The present study provides a general sea state dependent parameterization for gas transfer, which can be implemented in global coupled models.

The Importance of Contemporaneous Wind and pCO2 Measurements for Regional Air‐Sea CO2 Flux Estimates

“…We expect the bubble contribution to the air-sea CO 2 flux to be especially important in the wintertime North Atlantic, which experiences strong, frequent storms that bring high wind speeds and large significant wave heights (Reichl & Deike, 2020;Zhou et al, 2023). One example of a sea-state dependent gas transfer velocity is that by Deike and Melville (2018) (DM18 herein):…”

“…Breaking waves and bubble injection contribute to air‐sea CO 2 exchange in high wind conditions (Brumer et al., 2017; Edson et al., 2011; Woolf, 1997). Wind‐only gas transfer velocity parameterizations, such as in Equation , do not explicitly account for the contribution of breaking waves and bubble injection to the air‐sea CO 2 exchange and underestimate transfer under high wind speeds when compared to observations (Deike & Melville, 2018; Gu et al., 2021; Zhou et al., 2023). Some observational platforms provide data to calculate significant wave height, allowing for the implementation of a sea‐state dependent gas transfer velocity equation.…”

“…Some observational platforms provide data to calculate significant wave height, allowing for the implementation of a sea‐state dependent gas transfer velocity equation. We expect the bubble contribution to the air‐sea CO 2 flux to be especially important in the wintertime North Atlantic, which experiences strong, frequent storms that bring high wind speeds and large significant wave heights (Reichl & Deike, 2020; Zhou et al., 2023). One example of a sea‐state dependent gas transfer velocity is that by Deike and Melville (2018) (DM18 herein): $$$k=\left[{A}_{NB}{u}_{\ast }+\frac{{A}_{B}}{\alpha }\left({u}_{\ast }^{5/3}{\sqrt{g{H}_{s}}}^{4/3}\right)\right]\cdot {\left(\frac{Sc}{660}\right)}^{-1/2}$$$ where A NB and A B are empirical coefficients related to the non‐bubble and bubble components of the gas transfer velocity, respectively.…”