Modulation of Bubble-Mediated Gas Transfer due to Wave-Current Interactions

This is project will study the spatial variability of gas transfer across the air-sea interface within a comprehensive modeling framework. Theoretical and modeling studies agree at relatively small scales, where the flow becomes less dominated by the rotation of the earth, motion, especially along the vertical direction becomes more energetic, with pronounced impacts on ocean biogeochemistry, and air-sea fluxes.

However, no study has focused on wave breaking variability and related bubble mediate gas transfer due to wave-current interactions. Most parameterizations of gas transfer coefficients today depend on wind speed rather than more detailed representation of wave dynamics, resulting in large uncertainties. Recent parameterizations include wave effects through integral wave parameters such as significant wave height or wave age, neither which can explain the modulation due to wave-current interactions at sharp fronts.

A recently developed model of wave breaking statistics provides a framework to explicitly account for breaking on air entrainment and bubble-mediated gas fluxes. The model is suitable for coupled earth system simulations providing a unique opportunity to study the effect of wave-current interactions on the variability of bubble-mediated gas transfer and fluxes.

The results will have direct applications for climate studies. They can explain the uncertainty of the observed gas fluxes in coastal environments, helping to reduce the uncertainty of global CO2 budgets. Other impacts include training students.

Specifically, an undergraduate student will participate in the research. The project will enhance the participation of underrepresented groups by contributing to the career of a Hispanic, early-career scientist, and by exposing the students at UCSB, a designated Hispanic-Serving Institution, to the research and its results.

The overarching goal of the work is to investigate the modulation of bubble-mediated gas transfer due to wave-current interactions at submesoscales. The modeling is based on recent advances on surface wave breaking and related air-sea fluxes, which provide a physics-based framework to model bubble-mediated gas transfer coefficients. Realistic numerical simulations will be used to investigate the spatial variability of bubble-mediated gas transfer and their impact on gas fluxes (i.e., CO2).

Preliminary model results show that wave breaking statistics forced by realistic winds and currents confirm previous findings from observations and theoretical analysis on the modulation of waves by currents, where wave breaking is enhanced in conditions with winds obliquely aligned with ocean fronts. The wave breaking modulation by currents is enhanced with increasing model resolution at submesoscales.

Submesoscale frontal surface convergence and downwelling velocities overlap with areas with enhanced wave breaking with oblique wind forcing. It is hypothesized that under these conditions air-sea gas fluxes are enhanced. This will be tested with numerical simulations at an eastern boundary current during upwelling conditions.

Upwelling areas have been shown to exhibit significant variability in CO2 concentrations that is not well understood. Dissolved CO2 will be modeled neglecting biological and chemical reactions starting from a background equilibrium level and then forced with realistic fluxes, including bubble-mediated transfer coefficients. The hypothesis will be tested by comparing model solutions at varying resolutions against a control run using standard transfer coefficient parameterizations that depend only on wind speed.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.