- As has been so often the case over the last several years, alarming news again arrived from the Arctic a few weeks ago. On 9th September, at the maximum of the summer melting season, the sea ice extent in the Arctic Ocean reached the second lowest value in the satellite record: 4.6 million square kilometers. Increasing areas of open water in the summer mean larger and larger areas where new ice forms in winter. Thick and strong perennial ice gets gradually replaced by thinner seasonal ice, more susceptible to breaking and deformation. What do we know about the dynamics of that increasingly abundant – and thus increasingly important – ice type, composed of separate floes? Incomparably less than about the dynamics of the perennial ice. In this paper, sea ice is viewed as a discontinuous medium built of floes of different sizes moving on the sea surface and colliding with each other. The model presented, deriving from analogies with other granular materials, reproduces a number of hitherto unexplained phenomena observed in sea ice at low concentrations – including the formation of floe clusters (see the attached image), important for the dynamics and freezing/melting of ice – and thus it may contribute to a better performance of state-of-the-art sea-ice and climate models.
