  The possibility of hydrodynamic diffusion in a model of grease ice stirred by
the velocity field of a gravity wave is explored. It is argued that mechanical
interactions among ice crystals can induce disturbances in the fluid velocity -
in the form of interstitial flows - analogous to those leading to diffusion in
fixed beds. A two-fluid description of the system is introduced, in which the
ice matrix is treated as a deformable porous medium. Depending on the range of
parameters, the effective diffusivity of the medium can exceed the value which
would be obtained by only keeping into account particle dislocation induced by
contact interactions.
