Sea ice is a major component of polar environments, especially in the
Arctic where it covers the entire Arctic Ocean throughout most of the
year. However, in the context of climate change, the Arctic sea ice
cover has been declining significantly over the last decades, either in
terms of its concentration or thickness. The sea ice cover evolution and
climate change are strongly coupled through the albedo positive
feedback, thus possibly explaining the Arctic amplification of climate
warming. In addition to thermodynamics, sea ice kinematics (drift,
deformation) appears as an essential factor in the evolution of the ice
cover through a reduction of the average ice age (and consequently of
the cover's thickness), or ice export out of the Arctic. This is a first
motivation for a better understanding of the kinematical and mechanical
processes of sea ice. A more upstream, theoretical motivation is a
better understanding of the brittle deformation of geophysical objects
across a wide range of scales. Indeed, owing to its very strong
kinematics, compared e.g. to the Earth's crust, an unrivaled kinematical
data set is available for sea ice from in situ (e.g. drifting buoys) or
satellite observations. Here, we review the recent advances in the
understanding of sea ice drift, deformation and fracturing obtained from
these data. We focus particularly on the scaling properties in time and
scale that characterize these processes, and we emphasize the analogies
that can be drawn from the deformation of the Earth's crust. These
scaling properties, which are the signature of long-range elastic
interactions within the cover, constrain future developments in the
modeling of sea ice mechanics. We also show that kinematical and
rheological variables such as average velocity, average strain-rate or
strength have significantly changed over the last decades, accompanying
and actually accelerating the Arctic sea ice decline.
