Dependence of Beaufort Sea Low Ice Condition in the Summer of 1998 on Ice Export in the Prior Winter

Abstract

Four events of distinctly low summer ice coverage in the Beaufort Sea, in 1998, 2008, 2012, and 2016, have been identified using satellite-observed concentration between 1979 and 2017. Previous studies have revealed that these four minima were impacted by preconditioning of the ice cover, and specifically the 1998 event was preconditioned toward thinner ice by anomalous southeasterly winds during winter. This study further investigates the 1998 event through analyzing the solution of a coupled ocean and sea ice model. Compared with the mean condition during 1995–2015, the net ice loss in the melt season (May–September) of 1998 was not particularly high. In the preceding fall (October–December 1997), the ice conditions and processes contributing to ice changes were neither significantly different from the mean condition nor unique in the time series during 1995–2015. In the preceding winter (January–April 1998), over the southeastern part of the Beaufort Sea, the ice was 1.5 m thinner than the mean condition on average, and the increase in ice thickness due to freezing was nearly offset by the decrease due to lateral advection, which was the result of high westward ice export and limited southerly import. The dynamic process in preceding winter was also the cause of low ice in summer 2016 according to a recent study. Model analyses suggest that the 2008 event was due to the small regional ice volume at the end of summer 2007 and ice export during the preceding fall, whereas the 2012 event was caused by the excessive summer melting.