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 from satellite observations of sea ice concentration between 1979-2017. Previous studies have revealed that these 4 minima were impacted by preconditioning of the ice cover, and specifically the 1998 event was shown to be preconditioned toward thinner ice by anomalous southeasterly winds during winter. This study further investigate the 1998 event through analyzing the simulation results 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 proceeding 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 proceeding 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 proceeding winter was also the cause of low ice condition in the summer of 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 proceeding fall, while the 2012 event was caused by the excessive melting in summer.