A note on the energetics of a double-diffusive system

Abstract

Adjacent oceanic water masses with the same density but different concentrations of heat and salt generate interleaving accompanied by double-diffusive processes. Laboratory experiments with salt and sugar concentrations are used to study the interleaving process. Most double-diffusive studies have treated vertical configurations in which one of the two components contains a destabilizing feature, salt above fresh water for salt fingers or warm underlying cold for the diffusive case. However, when the fluid lacks any gravitationally unstable feature, i.e. no gravitational potential energy is available in either component, the question arises as to what the source of energy is to drive the system. Such a case is discussed here and it is shown that the ultimate source of the energy is the chemical potential associated with the different property distributions. Diffusion creates a destabilizing property distribution and then enables the resulting potential energy to be released.