Scaling the Bubble Penetration Depth in the Ocean

• Published in: Journal of geophysical research. Oceans 2023-09, Vol.128 (9), p.n/a
• Main Authors: Cifuentes‐Lorenzen, A., Zappa, C. J., Randolph, K., Edson, J. B.
• Format: Article
• Language: English
• Subjects: Acoustic backscatter; Acoustic Doppler Current Profiler; air‐sea interaction; Atmospheric forcing; Atmospheric models; Atmospheric waves; Backscatter; Boundary layers; Breaking waves; bubble plume penetration depth; Bubbles; Dissipation; Doppler sonar; effective wavelength; Energy balance; Gases; Geophysics; Kinetic energy; Langmuir circulation; Mixed layer; Momentum; Momentum transfer; Ocean surface; Oceans; Parameter identification; Parameterization; Penetration depth; Phase velocity; Plankton; Plumes; Scaling; Significant wave height; Turbulent kinetic energy; wave boundary layer; Wave breaking; Wave height; Wavelength; Wavelengths; Whitecaps; Wind
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2022JC019582

Bubble plume penetration depths have been identified as a key parameter linking subsurface turbulent kinetic energy (TKE) dissipation rates and whitecaps. From data collected in the Atlantic sector of the Southern Ocean, nominally 50°S 40°W, bubble plume penetration depths were estimated from Acoustic Doppler Current Profiler measurements of the acoustic backscatter anomaly. Bubble presence at depth was corroborated using independent measurements of optical scattering. Here, an effective wavelength, observations of significant wave height and atmospheric forcing were used to scale penetration depths of breaking waves under open ocean conditions. The parameterization was developed assuming a correlation between the observed penetration depth and an estimate of the TKE dissipation rate enhancement under breaking waves. The effective wavelength was defined from the effective phase speed based on a momentum and energy balance across the atmospheric wave boundary layer and was considered to be the largest actively wind‐coupled wave and representative of large‐scale breaking for wave ages ranging from 15 to 35 (i.e., 15 ≤ 〈cp/u*〉 ≤ 35). This yields a dimensional penetration depth parameterization in terms of inverse wave age and the length scales under consideration. The parameterization captures the bubble plume penetration depth with stronger forcing leading to deeper injections, reaching up to 9 m. Both length scales are effective at defining the depth of a wave‐affected layer in terms of bubble presence with the effective wavelength better collapsing the data under mixed conditions with deeper plumes associated to larger fractional whitecap coverage. Plain Language Summary The depth to which waves breaking at the ocean surface influence oceanic processes in the mixed layer, including the transfer of momentum, heat and gases between the atmosphere and ocean, is an ongoing and active area of research. Parameterizations and observations describing the vertical extent of wave‐driven effects, including whitecaps and vertical jets associated with Langmuir circulation, are relevant for numerical circulation models and our understanding of wave breaking and dissipation dynamics. Here, observations of atmospheric and oceanic conditions, principally wind, wave, and inferred bubble plume penetration depths collected in the Atlantic sector of the Southern Ocean were used to build a parameterization for estimating the vertical extent of bubble injections and for inferrin