Salt fingers in the presence of grid-generated turbulence

Abstract

The transport of heat and salt across a density interface containing salt fingers is investigated when turbulence produced by vertically oscillating horizontal grids is imposed on the deeper layers above and below the interface. The fluxes of heat and salt are measured as functions of the stirring frequency. The results are discussed with reference to the parameter $\lambda = w^2/(\overline{u})^2$ , where w is the velocity of the fluid in the fingers in the undisturbed state and $\overline{u}$ is the r.m.s. horizontal velocity of the turbulence. It is found that the salt flux has a minimum (as a function of the stirring frequency) when Λ ∼ 0·3 and that when Lambda; [lsim ] 0·05 the transport across the interface is dominated by mechanical mixing. The ratio r of the contributions of heat and salt to the buoyancy flux increases with decreasing Λ and r > 1 when Λ [lsim ] 1·3. The latter result implies that if turbulent intensities are such that Λ [lsim ] 1·3 in a particular oceanic situation, mechanical mixing will affect the vertical transport of heat and salt in such a way that the salt finger mechanism will be unable to produce layered temperature and salinity microstructure in the manner described by Turner (1967).