Double-Diffusive Brine Rejection*

It is common knowledge that hot air rises, so we might expect that hot water will rise above cold water. However, the exact opposite happens in cold lakes, where cold water rises! Through surface cooling and mixing, most seasonally ice-covered lakes transition between the intuitive hot-over-cold temperature stratification in the summer, and the reverse cold-over-warm stratification in the winter. Simultaneously, as ice forms, salts in the water are rejected to the ice-water interface. This surface salt-flux destabilizes the stable reverse temperature stratification. Thus, there is a competition between the unstable salt stratification and the stable temperature stratification.

We will show that this configuration will lead to double-diffusive finger-like instabilities under the ice. We will discuss the key parameters that control the evolution of this double-diffusive instability, taking into account the nonlinear equation of state of water. We will analyze both experimental and numerical observations of this phenomenon.