The spectacular evolution of the Arctic sea-ice cover over the last few decades is not restricted to sea-ice thinning or the decline of the September minimum. From a statistical analysis of the buoy trajectories of the International Arctic Buoy Project (IABP) dataset, recorded from February 1979 to December 2008, we analyzed the evolution of sea-ice drift speed, deformation and mechanical behaviour over the last three decades. Calculating the monthly averages of buoy speed over the Arctic basin, we observed a significant increasing trend of +9% per decade, superimposed to a strong annual cycle. As Arctic sea ice is essentially confined into a basin, one expects on average an increasing deformation rate as a consequence of increasing ice speed. Using the dispersion rate of buoys as a proxy of sea-ice strain rate, we obtained increasing trends of more than +50% per decade for both summer and winter deformation rates. We argue that this spectacular evolution is unlikely (or marginally) the consequence of an increase of the wind forcing over the period, but instead results from a coupling between sea-ice thickness and fracturing-induced deformation. A thinner sea-ice cover means a decreasing mechanical strength and so an increase of deformation and associated fracturing. More fracturing means more lead opening, hence stronger melting during summer and a delayed refreezing in early winter, thus a thinner ice. As a fragmented ice cover is easier to deform and drag, this explains the acceleration of its drift and may facilitate the export from the Arctic basin. To further test this scenario, we developed an original method to estimate an ‘internal friction’ of the ice cover from the average magnitude of inertial oscillations: a more fragmented less cohesive ice cover will, on average, exhibit larger inertial oscillations, whereas these oscillations will be entirely damped within a highly cohesive cover. This inertial oscillation magnitude is calculated from the amplitude of the Fourier spectrum of the velocity records of the buoys measured at f = –2sin(latitude) d^–1, then appropriately averaged over specific time and/or spatial scales to analyse the evolution of sea-ice mechanical behaviour over the last three decades. We observed a significant evolution towards larger inertial oscillations, i.e. a weaker less cohesive Arctic sea-ice cover in both summer and winter. This evolution is particularly remarkable since 2000 and in the eastern Arctic regions where the sea-ice decline has been especially marked. This re-asserts the importance of mechanical processes for the future of Arctic sea ice.