A new type of double-diffusive instability?

A new type of double-diffusive instability of the oscillatory type is predicted for a statically stable fluid layer with two components which have practically the same diffusivity (for example, two suitable types of salts in a molecular case, heat and salt in a case where mixing is due to small-scale turbulence). It is necessary that one component has the concentration value and the other the flux value fixed at the boundaries. A simple example is worked out in detail. The phenomenon should appear in a properly arranged laboratory experiment, and possibly in the oceans, when warmer, saltier water underlies a surface layer of colder, fresher water, and sufficient vertical turbulent mixing is present.