Winter Sea Ice Export From the Beaufort Sea as a Preconditioning Mechanism for Enhanced Summer Melt: A Case Study of 2016

During September 2016 an ice-free Beaufort Sea was observed for only the second time. Like previous regional sea ice minima (1998, 2008, and 2012), seasonal preconditioning of the ice pack toward younger, thinner ice types contributed to premature breakup that accelerated the ice-albedo feedback and enhanced summer melt. In 2016, anomalously high sea ice export and ice pack divergence during February and April promoted the unusual widespread formation of new ice within the Beaufort. Thin ice types reached a peak regional concentration of 30% in March, when the ice cover is typically dominated by thick first-year and multiyear sea ice. Combined CryoSat-2 and Soil Moisture and Ocean Salinity (SMOS) data indicate that the regional ice volume plateaued from December to March as export offset ice growth and ultimately culminated in a -30% volume anomaly in April 2016. This atypically thin ice cover broke up 7 weeks earlier than average, with open water forming not only within coastal flaw leads but also within the offshore pack ice. By July 2016, vast areas of open water within the highly fractured ice cover accelerated the ice-albedo feedback and led to rapid melt. Though maintaining a partial ice cover during summer throughout the observational record, significant negative trends in September sea ice area within the Beaufort are now punctuated by two recent ice-free Septembers (2012 and 2016). As the Beaufort transitions toward a seasonally ice-free sea, we examine the role of winter preconditioning through sea ice transport and its growing importance within an increasingly seasonal and mobile Arctic ice cover.