Hydrodynamic states in water below the temperature of the density maximum: the limit to supercooling

Spectra of fluctuations in the total intensity of laser light deflected by supercooled water show that even under carefully controlled conditions large samples give convection when cooled below -0%. This is in agreement with the Rayleigh versus Prandtlnumber relation for supercooled water. Localisation of the temperatures at which transitions in thermal convection occur allowsan estimate of the temperature at which the samples should become fully turbulent. Since the samples always freeze before that point is reached and a turbulent situation is never observed, one is led to the surmise that turbulence drives the transition out of the metastable state.