Numerical Simulations of the Competition Between Restratification and Mixing Induced by Submesoscale Instabilities

Previous work has suggested that submesoscales play an important role in setting the stratification of the upper ocean; such scales are believed to be associated with large vertical velocities and therefore capable of modifying biological productivity. In this study, the feedbacks between submesoscales and small-scale turbulence are explored using very high resolution numerical simulations. Modelling an idealised domain representative of the upper mixed layer, we find submesoscale motions generated via symmetric and baroclinic instability. These, in turn, via the emergence of secondary instabilities, are able to generate significant small-scale turbulence and mixing even in the absence of surface wind and buoyancy forcing. Using comparison with lower resolution simulations in the same domain we are able to quantify the extent to which fully resolving these submesoscale features and the resulting small scale turbulence impacts on instability growth rates, mixing and dissipation, restratification of the mixed layer and vertical fluxes.