Form of the Temperature-Salinity Relationship in the Central Water: Evidence for Double-Diffusive Mixing

Abstract

Abstract Ingham (1966) reported that the temperature-salinity relationships in the Central Waters were much better described by a curve of constant density ratio (Rρ = αΔT/βΔS) than by a straight line. His result is quantitatively verified and a simple, but powerful, double-diffusive mechanism is proposed to explain the observed constancy of Rρ in the main thermocline. The mechanism is based on the evidence from theory, experiment and observation that the intensity of salt-finger convection is a strong function of Rρ. This dependence, plus the fact that more salt than heat is transferred by the fingers, causes any deviation from a constant Rρ to be the site of convergence or divergence of the vertical salt flux that acts to remove the perturbation in Rρ. A linear treatment of the mechanism shows that Rρ can be “diffused” with an effective diffusivity that is much greater than the diffusivities of heat or mass. A few numerical examples illustrate the predicted effects of salt fingering on the T-S relation,...