Some Implications of Ocean Mixing for Ocean Modelling

Abstract

Abstract The importance of vertical mixing in ocean circulation models is briefly reviewed and several methods of estimating vertical mixing activity are discussed. Several aspects of the interpretation of dissipation measurements are discussed. It is pointed out that the two dianeutral advection processes – thermobaricity and cabbeling – are invisible to microstructure dissipation measurements. Formulae are developed for calculating vertical diffusivities of scalars in thermohaline staircases, where the diffusivity of salt can be up to 10 times as large as that given by the normal expression 0.2 e/N2. In deducing the upwelling velocity in the ocean from microstructure measurements, the non-linear terms of the equation of state of sea-water must be included consistently. A simple numerical example shows how large these effects can be. Finally, the water-mass conversion equation written in a neutral-surface reference-frame is used to examine the relative importance of salt-fingering and small-scale turbulence in the Central Water of the World's oceans. While salt-fingering is required to induce and maintain the observed curvature in the S-Θ curve of these water masses, small-scale isotropic turbulent mixing is shown to probably be responsible for larger vertical fluxes of salt, heat and buoyancy.