  In seasonally ice-covered seas and along the margins of perennial ice pack,
i.e. in regions with medium ice concentrations, the ice cover typically
consists of separate floes interacting with each other by inelastic collisions.
In this paper, hitherto unexplored analogies between this type of ice cover and
two-dimensional granular gases are used to formulate a model of ice dynamics at
the floe level. The model consists of: (i) momentum equations for floe motion
between collisions, formulated in the form of a Stokes-flow problem, with
floe-size dependent time constant and equilibrium velocity, and (ii) hard-disk
collision model. The numerical algorithm developed is suitable for simulating
particle-laden flow of $N$ disk-shaped floes with arbitrary size distribution.
The model is applied to study clustering phenomena in sea ice with power-law
floe-size distribution. In particular, the influence of the average ice
concentration $\bar{A}$ on the formation and characteristics of clusters is
analyzed in detail. The results show the existence of two regimes, at low and
high ice concentration, differing in terms of the exponents of the cluster-size
distribution and of the size of the largest cluster.
