Title: Effects of Submesoscale Turbulence on Tracer Evolution in the Oceanic Mixed Layer

Peter Hamlington and Katherine Smith

Ocean tracers such as carbon dioxide, nutrients, and plankton evolve primarily in the oceanic 
mixed layer where air-sea gas exchange occurs and light is plentiful for photosynthesis. It is 
well known from prior observational and computational studies that there can be substantial 
heterogeneity, or “patchiness," in the spatial distribution of ocean tracers due to both vertical 
and horizontal turbulent mixing across a wide range of scales. The contribution of submesoscale 
turbulent processes to these distributions remains incompletely understood, however, particularly 
in the sub-kilometer range. Within this range, both large-scale quasi-geostrophic eddies and 
small-scale three-dimensional turbulence are active, resulting in substantial dynamical 
complexity from which tracer heterogeneity can arise. In this talk, results from large eddy 
simulations of the evolution of a large scale temperature front are used to examine the role of 
multi-scale turbulent mixing on distributions of idealized ocean tracers from scales of 20km down 
to 5m. The simulations include the effects of wave-driven Langmuir turbulence by solving the 
wave-averaged Boussinesq equations with an imposed Stokes drift velocity. Tracers with different 
source, initial, and boundary conditions are examined in order to understand the respective roles 
of both small-scale, near-surface vertical mixing and larger-scale upwelling motions typically 
associated with submesoscale eddies. Tracer evolution is characterized using spectra, multiscale 
fluxes, and probability distribution functions, and the implications of the results for 
computational modeling of air-sea gas exchange and upper-ocean tracer transport are outlined.