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Is mechanics driving the Arctic sea ice decline ?
In the Arctic, sea ice is undergoing for several decades a dramatic decline both in terms of spatial extent and average thickness. As sea ice strongly affects the exchanges of energy and momentum between the ocean and the atmosphere, its decline is accompanied by a particularly strong warming in the Arctic. The classical explanation for this combination of phenomena is an albedo feedback loop. This scenario, however, is insufficient to explain the rapidity of the sea ice decline, as illustrated e.g. by its strong underestimation in climate models. In this presentation, I will show that mechanical processes likely play a key role in this recent evolution. A detailed analysis of sea ice kinematics from passive tracers (drifting buoys) allows a characterization of sea ice brittle behavior, and highlights spectacular evolutions of mechanical properties : acceleration of drift and deformation, as well as a mechanical weakening in recent decades as revealed from an increased sensitivity of the ice cover to the Coriolis effect. These mechanisms likely reinforce the classical albedo feedback through an increasing sea ice export out of the Arctic basin and a shortening of the residence time. This calls for an improvement of the representation of sea ice brittle mechanics in ice/ocean coupled models.