Shear and Convective Turbulence in a Model of Thermohaline Intrusions

Thermohaline interleaving is an important mechanism for laterally fluxing salt, heat, and nutrients between water masses. Interleaving is driven by a release of potential energy resulting from the differing diffusivities of heat and salt in seawater. The flows are composed of stacked intrusions that flux more buoyant and less buoyant water in opposite directions. In this paper, we investigate the role of shear instability caused by this juxtaposed motion. The model described in Walsh and Ruddick (1998) is modified to include effects of shear induced turbulence and also an improved convective mixing parameterization. Shear and convective mixing play a similar and significant role in interleaving dynamics. In the absence of either instability, cross-front fluxes are increased by approximately 30%. While in situ observations of horizontal diffusivity due to interleaving are not yet precise enough to calibrate the parameterizations independently, parameter values based on independent lab and numerical studies lead to diffusivity predictions that are within error of the observations.