Spring 2021 sea ice transport in the southern Beaufort Sea occurred during coastal ice opening events

Abstract. Winds blew a record large portion of the Arctic’s multiyear sea ice (MYI) into the southern Beaufort Sea (SBS) in winter 2021. From early March, a network of buoys from the Sea Ice Dynamic Experiment (SIDEx) tracked the MYI as it drifted across the SBS toward the Chukchi Sea. Transport was episodic as the consolidated ice pack interacted with coastal boundaries and repeatedly fractured. We investigated variability in 2021 MYI transport by relating in situ sea ice drift to remotely sensed coastal lead opening events, which have been shown to increase ice drift speeds in winter. Daily ice concentration data show ten opening events occurred throughout March and April 2021. Opening lasted 1–5 days as southeasterly winds pushed the SBS ice pack away from local coastal boundaries. During opening, the ice pack abruptly accelerated and its response to wind forcing stabilized around free drift conditions, drifting at 2.1 % of wind speeds (median rate of 14 km d⁻¹). With this efficient wind-to-ice momentum transfer, nearly all (94 %) SBS MYI transport in March–April 2021 occurred during opening events, despite spanning just half the time. Only 6 % of transport occurred during the other half of days without opening. On these days, the ice was mostly stationary (median 2 km d⁻¹ drift rate, 0.6 % of wind speeds) as northwesterly winds compressed the pack against the coast. Spatiotemporal discontinuities in ice-wind speed ratios were measured across several coastal leads that transected the SIDEx buoy network, providing direct observations of ice drift modulation by coastal lead formation. These results quantify the disproportionate contribution of coastal lead opening events to SBS ice transport during spring 2021, highlighting the critical role these transient events play in patterns of sea ice drift at seasonal timescales.