Evolution of ideas about the energetics of turbulent stratified mixing. (a) Interpretation seemingly following the result of classical energetics arguments based on the three reservoirs , , and ; (b) interpretation proposed by Winters et al. [14] based on the use of Lorenz [15] ideas to separate the gravitational potential energy into an available and unavailable component; (c) new interpretation proposed by Tailleux [1] on the basis of a rigorous analysis of the energetics of compressible Navier-Stokes equations aimed at elucidating the role of internal energy.