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  1. The air–sea exchange of carbon dioxide (CO2) on a global scale is a key factor in understanding climate change and predicting its effects. The magnitude of sea spray’s contribution to this flux is currently highly uncertain. Constraining CO2’s diffusion in sea spray droplets is important for reducing error margins in global estimates of oceanic CO2 uptake and release. The timescale for CO2 gas diffusion within sea spray is known to be shorter than the timescales for the droplets’ physical changes to take place while aloft. However, the rate of aqueous carbonate reactions relative to these timescales has not been assessed. This study investigates the timescales of droplet physical changes to those of chemical transformations across the H2CO3/HCO3−/CO32− sequence. We found that physical timescales are rate limiting and that evaporation drives carbonate species into gaseous CO2, promoting the production and evasion of CO2 from sea spray droplets. This has important implications for carbon cycling and feedback in the surface ocean. 
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    Free, publicly-accessible full text available July 1, 2025
  2. Abstract

    Surface gravity wave effects on currents (WEC) cause the emergence of Langmuir cells (LCs) in a suite of high horizontal resolution (Δx= 30 m), realistic oceanic simulations in the open ocean of central California. During large wave events, LCs develop widely but inhomogeneously, with larger vertical velocities in a deeper mixed layer. They interact with extant submesoscale currents. A 550-m horizontal spatial filter separates the signals of LCs and of submesoscale and larger-scale currents. The LCs have a strong velocity variance with small density gradient variance, while submesoscale currents are large in both. Using coarse graining, we show that WEC induces a forward cascade of kinetic energy in the upper ocean up to at least a 5-km scale. This is due to strong positive vertical Reynolds stress (in both the Eulerian and the Stokes drift energy production terms) at all resolved scales in the WEC solutions, associated with large vertical velocities. The spatial filter elucidates the role of LCs in generating the shear production on the vertical scale of Stokes drift (10 m), while submesoscale currents affect both the horizontal and vertical energy fluxes throughout the mixed layer (50–80 m). There is a slightly weaker forward cascade associated with nonhydrostatic LCs (by 13% in average) than in the hydrostatic case, but overall the simulation differences are small. A vertical mixing schemeK-profile parameterization (KPP) partially augmented by Langmuir turbulence yields wider LCs, which can lead to lower surface velocity gradients compared to solutions using the standard KPP scheme.

     
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  3. Abstract

    We present an investigation of the azimuthal bimodality of the wind-wave spectrum for waves shorter than the dominant scale comparing numerical model solutions of developing waves from idealized experiments using WAVEWATCH III (WW3). The wave solutions were forced with the “exact” Webb–Resio–Tracy (WRT) nonlinear energy fluxes and the direct interaction approximation (DIA) with three different combinations of wind input and breaking dissipation parameterizations. The WRT gives larger azimuthal bimodal amplitudes compared to the DIA regardless of wind input/dissipation. The widely used wind input/dissipation parameterizations (i.e., ST4 and ST6) generally give narrow directional distributions with relatively small bimodal amplitudes and lobe separations compared to field measurements. These biases are significantly improved by the breaking dissipation of Romero (R2019). Moreover, the ratio of the resolved cross- to downwind mean square slope is significantly lower for ST4 and ST6 compared to R2019. The overlap integral relevant for the prediction of microseisms is several orders of magnitude smaller for ST4 and ST6 compared to R2019, which nearly agrees with a semiempirical model.

    Significance Statement

    Spectral gravity wave models generally cannot accurately predict the directional distribution which impacts their ability to predict the resolved down- and crosswind mean square slopes and the generation of microseisms. Our analysis shows that a directionally narrow spectral energy dissipation, accounting for long-wave–short-wave modulation, can significantly improve the directional distribution of the wind-wave spectrum by coupling to the nonlinear energy fluxes due to wave–wave interactions, which has important implications for improved predictions of the mean square slopes and the generation of microseisms.

     
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  4. Abstract

    Wave breaking modulates air‐sea fluxes of energy, momentum, heat, and gases. Building on recent advances in the modeling of CO2gas exchange and wave breaking, we investigate the variability of bubble‐mediated gas transfer coefficients due to wave‐current interactions. Submesoscale current gradients strongly modulate wave breaking, which can enhance the bubble‐mediated gas transfer coefficient along temperature fronts and cold filaments. The enhancement of the gas transfer coefficient is over relatively small areas averaging out over larger regions. However, the correlation between positively anomalous gas transfer coefficients and regions with strong downwelling could potentially enhance CO2exchange over regions with increased submesoscale activity. An empirical scaling based on the mean wave period, root‐mean‐square current gradients, and friction velocity can explain the root‐mean‐square differences of gas transfer coefficients computed from solutions with and without current forcing.

     
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  5. Abstract

    A set of realistic coastal simulations in California allows for the exploration of surface gravity wave effects on currents (WEC) in an active submesoscale current regime. We use a new method that takes into account the full surface gravity wave spectrum and produces larger Stokes drift than the monochromatic peak-wave approximation. We investigate two high-wave events lasting several days—one from a remotely generated swell and another associated with local wind-generated waves—and perform a systematic comparison between solutions with and without WEC at two submesoscale-resolving horizontal grid resolutions (dx= 270 and 100 m). WEC results in the enhancement of open-ocean surface density and velocity gradients when the averaged significant wave heightHsis relatively large (>4.2 m). For smaller waves, WEC is a minor effect overall. For the remote swell (strong waves and weak winds), WEC maintains submesoscale structures and accentuates the cyclonic vorticity and horizontal convergence skewness of submesoscale fronts and filaments. The vertical enstrophyζ2budget in cyclonic regions (ζ/f> 2) reveals enhanced vertical shear and enstrophy production via vortex tilting and stretching. Wind-forced waves also enhance surface gradients, up to the point where they generate a small-submesoscale roll-cell pattern with high vorticity and divergence that extends vertically through the entire mixed layer. The emergence of these roll cells results in a buoyancy gradient sink near the surface that causes a modest reduction in the typically large submesoscale density gradients.

     
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