Gas Transfer by Breaking Waves

Abstract

The transfer of gases at the ocean‐atmosphere interface impacts weather and climate from local to global scales, with carbon dioxide (CO2) key to marine life and ecosystems, and dimethyl sulfide affecting aerosols and atmospheric processes. However, the bubble‐mediated gas transfer, associated with breaking waves has remained poorly constrained. We present a spectral framework for bubble‐mediated gas transfer, computed from a mechanistic model for air bubble entrainment at the breaking wave scale combined with a chemical model. Gas transfer is upscaled to the ocean scale by evaluating air entrainment at all wave scales using wave and wave breaking statistics. The obtained CO2 gas transfer velocity reproduces the variability of historical parameterizations and recent field measurements, with very good accuracy. We propose a wind‐wave parameterization that collapses all available data, which can be directly implemented in ocean‐wave models or used with remote sensing of the ocean surface to infer gas transfer.

Air–sea gas exchange at wind speeds up to 85 m s−1

“…Therefore, it appears logical that wave breaking in the ocean could be more intense than in a short-fetch wind-wave tank and thus would start to become significant at considerably lower wind speeds. This is supported by the estimation of air entrainment by breaking waves by Deike et al (2017). They estimated maximum air entrainment velocities V a = k r up to about 50 cm h −1 , as we did (Fig.…”

“…It is the effective velocity (volume flux per water surface area) averaged over all bubble sizes, with which the air volume is being submerged by breaking waves and rises towards the surface again. Deike et al (2017) call this quantity the air entrainment velocity V a . The transition solubility, at which the constant bubblemediated transfer velocity for low solubility k c,low α changes into the transfer velocity decreasing with increasing solubil-ity can be computed by setting both values equal:…”

“…where in the second term u 5/3 * ,a (gH s ) 2/3 is replaced by the simpler term u 2 * ,a c p using the Toba (1972) relation for fetchlimited waves. The term A b u 2 * ,a c p is the air entrainment velocity V a = k r , which, according to Deike and Melville (2018), is increasing with the phase speed c p of the peak wave or its significant weight height H s , respectively. Surprisingly, Deike et al (2017) found the air entrainment velocity decreasing with the wave age c p /u * ,a by estimating the air entrainment velocity directly based on a model for a single breaking wave and the statistics of breaking waves as measured in the field.…”

Distribution of Surface Wave Breaking Fronts

“…The model results show good agreement with Deike et al (). The air entrainment rate computations within WW3 can be easily extended to model the bubble‐mediated gas transfer of CO 2 based on the work by Deike and Melville ().…”

Surface Gravity Waves and Their Role in Ocean‐Atmosphere Coupling in the Gulf of Mexico

“…Breaking waves mediate air‐sea interaction. Therefore, wave age is also a parameter determining the energy flux from waves to ocean (e.g., Terray et al, 1996), the subsurface distribution of gas bubbles (e.g., Liang, McWilliams, Sullivan, et al, 2012), and the role of gas bubbles on air‐sea gas transfer (e.g., Brumer et al, 2017; Deike & Melville, 2018; Liang et al, 2017). The significance of wave age in quantifying these processes makes it important to understand its spatial and temporal distribution over the GoM.…”