Analysis and Modeling of Surfzone Turbulence and Bubbles

Turbulence in the surfzone mixes momentum vertically, transmits stress to the sea bed, influences the structure of the crossand alongshore currents, and controls the suspension of sediment from the sea bed. In many coastal and shelf environments, the sea-bed is the primary source of tur­ bulence due to bottom induced shear. In the surfzone, the breaking-wave generated turbulence dominates over bottom generated turbulence. Wave breaking is also the source of bubbles in the surfzone. The dynamics of turbulence under breaking waves in the surfzone is poorly understood. The potentially major impacts of vertical buoyancy fluxes due to air entrainment and bubbles are also unknown and have not been considered. Both the distribution and dynamics of breaking-wave generated bubbles and turbulence, and how they are linked are poorly understood. Bubble injected into the water column dissolve and are a major mechanism for air-sea gas fluxes (Keeling, 1993). However, uncertainties in bubble dynamics (generation and evolution) and their interaction with the turbulence generated by breaking waves preclude understanding oxygen or carbon dioxide airsea fluxes induced during various sea-states. Quantitative estimates of the bubble-induced air-sea gas fluxes are important to constraining the global oxygen and carbon dioxide cycles. Bubbles are also scatterers of light and sound. While the effect of bubbles on the acoustics of the upper ocean has long been of interest, more recently bubble induced optical scattering has been shown to highly variable and often exceeds the scattering due to chlorophyll concentrations (Terrill et al., 2001). An improved understanding of bubble dynamics under breaking waves will result in improved un­ derstanding of air-sea gas fluxes, organic carbon budgets, and the acoustics and optics of the upper ocean.