Modeling gas bubbles in the ocean boundary layer

Gas bubbles in the ocean boundary layer play an important role in determining air-sea gas-transfer. In this study, the evolution of the gas bubbles injected by breaking surface waves is modeled using a bin-resolving bubble model. The model is comprised of a set of concentration equations for bubbles of different radius and considers the injection of bubbles by wave breaking, the advection by ambient turbulence, buoyancy, and bubble size change due to gas dissolution. This model is first shown to be consistent with a Lagrangian model (Baschek et al. 2006) that computes the trajectories, sizes and gas contents of individual bubbles. It is then implemented in a Direct Numerical Simulation (DNS) model (Sullivan et al. 2004) to simulate the bubbles after their injection by a single breaking wave. The evolution of bubble size spectrum is in close agreement with laboratory measurements (Deane and Stokes 2002). The model is then coupled with a Large Eddy Simulation (LES) model for ocean boundary layer (Sullivan et al. 2007). It is shown that bubbles substantially enhance gas concentration in the ocean boundary layer and thus air-sea gas fluxes under normal wind conditions.