Accelerated Sea Ice Loss from Late Summer Cyclones in the New Arctic

Abstract

Abstract Synoptic-scale cyclones in the Arctic are an important source of short-term sea ice variability during the melt season. This study examines whether recent changes to the Arctic environment have made Arctic cyclones during the summer months more destructive to sea ice on short time scales. We compare the 1–7-day changes in sea ice area and thickness following days in each month with and without cyclones from two decades: 1991–2000 and 2009–18. Only in August do cyclones locally accelerate seasonal sea ice loss on average, and the ability of August cyclones to accelerate ice loss has become more pronounced in the recent decade. The recent increase in ice loss following August cyclones is most evident in the Amerasian Arctic (140°E–120°W), where reanalyses indicate that the average upper-ocean temperature has increased by 0.2°–0.8°C and the average ice thickness has decreased by almost 1 m between the two decades. Such changes promote cyclone-induced ocean mixing and sea ice divergence that locally increase the likelihood for rapid ice loss near cyclones. In contrast, June cyclones in both decades locally slow down seasonal sea ice loss. Moreover, the 7-day sea ice loss in June has increased from the early to the recent decade by 67% more in the absence of cyclones than in the presence of cyclones. The largest increases in June ice loss occur in the Eurasian Arctic (0°–140°E), where substantial reductions in average surface albedo in the recent decade have allowed more of the abundant insolation in the absence of cyclones to be absorbed at the sea surface. Significance Statement This study determines whether Arctic storms during summer have become more destructive to sea ice in recent years. In comparing storms from two periods (1991–2000 vs 2009–18), we find that only storms in August have become more destructive to sea ice in the recent period, because of warmer upper-ocean temperatures and thinner ice, which strong winds move around more easily. In June, clear-sky conditions have become more destructive to sea ice in recent years because declining ice cover has allowed more sunlight to be absorbed at the sea surface, favoring further ice melt. These results suggest that sunny conditions in June followed by stormy conditions in August could cause the first ice-free summer in the Arctic.