Limiting conditions for salt-fingering at an interface

Abstract--Conditions for which salt fingers can be formed at the interface between hot, salty water above colder, fresher water are investigated both experimentally and theoretically. For experimental convenience, two solutes of different diffusivities, rather than heat and salt, were used. It is shown that an infinitesimal instability will occur and develop into a finite amplitude salt finger field provided that Rp <'r,X/v,. Here Rp is the ratio of the increment in specific gravity due to the temperature difference across the interface to that due to the salinity difference and z, is the ratio of the diffusivity of heat to that of salt. For oceanic onstituents ":,~/-r, N 700 while typical values of Rp are very much less than this. There is thus sufficient potential energy stored in the salt field to form salt fingers in all parts of the ocean where hot, salty water overlies colder, fresher water