  We use concepts from statistical physics to transform the original evolution
equation for the sea ice thickness distribution $g(h)$ due to Thorndike et al.,
(1975) into a Fokker-Planck like conservation law. The steady solution is $g(h)
= {\cal N}(q) h^q \mathrm{e}^{-~ h/H}$, where $q$ and $H$ are expressible in
terms of moments over the transition probabilities between thickness
categories. The solution exhibits the functional form used in observational
fits and shows that for $h \ll 1$, $g(h)$ is controlled by both thermodynamics
and mechanics, whereas for $h \gg 1$ only mechanics controls $g(h)$. Finally,
we derive the underlying Langevin equation governing the dynamics of the ice
thickness $h$, from which we predict the observed $g(h)$. The genericity of our
approach provides a framework for studying the geophysical scale structure of
the ice pack using methods of broad relevance in statistical mechanics.
