The seasonal evolution of sea ice motion in the Beaufort Sea and the ice packs response to atmospheric forcing

Abstract:

Through spring the ice pack of the Beaufort Sea transitions from an extensive, consolidated ice state in late winter to a less extensive, weaker, marginal ice zone in summer. Using an array of autonomous instruments deployed in early April 2012 along the periphery of the multiyear ice pack, we highlight the seasonal evolution of ice drift as the ice pack broke up and individual ice floes entered a state of free drift. Coincident hourly observations of ice drift, surface winds, and ice mass balance were collected from early April to the end of July 2012 when the autonomous equipment failed. During this period ice drift speeds tripled, meander coefficients increased, ice drift became less correlated across increasingly small length scales, inertial oscillations developed along the ice floe trajectories and ice floes became increasingly responsive to surface winds, as indicated by increasing scaling factors and turning angles. Given that monthly mean wind speeds remained around 4 m/s throughout the study, we ascribe the seasonal change in ice drift characteristics to the seasonal mechanical weakening of the ice pack. Using a combination of in situ and remotely sensed observations we highlight the seasonal decline of local and regional ice concentrations, declining ice floe flexural strengths, substantial surface melt and bottom ablation and a seasonal tendency towards smaller floe sizes. Collectively these observations represent the mechanical weakening of the ice pack which fostered a seasonal increase in the responsiveness of the ice pack to atmospheric forcing.