Note on the stability of water stratified by both salt and heat

The stability of water stratified by both salt and heat is considered. A new criterium complementing the one derived earlier by Stern (1960) is found. It is demonstrated that, contrary to ordinary gravitational convection, convection against a stable density gradient will generally occur on a scale limited by internal parameters and not by the dimensions of the vessel. This limits the transporting capacity of the convection and thus reduces its importance. The characteristic scale that will dominate the instability is derived.