At the End of the Arctic Summer
19 September 2022
While the sun sinks lower and lower over the horizon, air temperatures over the central Arctic Ocean are dipping toward the freezing point. The further sea-ice retreat will chiefly depend on the ocean temperatures and on wind patterns, which can either condense or disperse the sea ice. As the summer draws to a close, the surface of the central Arctic Ocean is once again beginning to freeze over. The remainder of sea-ice loss will be mainly due to melting within the marginal ice zone, caused by heat stored in the ocean. This ocean-driven melting may continue for several more weeks. Regions with lower ice concentrations may continue to experience melting. In some regions (e.g. the Kara and Barents Seas and along the coast of the Laptev Sea), this year’s melting season began much earlier than normal. How early or late the melting begins is an important aspect for what is referred to as ice-albedo feedback: early melting darkens the surface and reduces its reflectiveness (albedo), which is conducive to the earlier formation of melt ponds and patches of open water, which absorb more solar energy and in turn accelerate further melting. Consequently, the earlier onset of melting in the Laptev, Kara and Barents Seas most likely contributed to more rapid sea-ice retreat in said regions.
The sea-ice conditions in the Arctic are currently within the span of two standard deviations from the long-term average for the years 1981 to 2010 (s. Figure 1). Throughout August, the extent remained above the value for 2021. The monthly mean for July, at 8.2 million km², was well above the long-term trend (s. Figure 2). The ice margin in the northern Barents and Kara Seas has remained comparatively stable since the beginning of August, whereas the sea ice in the northern Chukchi Sea, in the East Siberian Sea northwest of the New Siberian Islands and in the channels of the Canadian Arctic Archipelago has largely retreated. At the regional level, the sea-ice extent in the East Greenland Sea, the northern Kara Sea, the Laptev Sea and the East Siberian Sea remains below the average for the years 2003 to 2014 (Figure 3). In the northern Chukchi Sea and southeast Kara Sea, the sea-ice cover is well below the long-term average. At the end of August, the sea ice along the coastal fringe of the East Siberian Sea retreated and the Northeast Passage along Vilkitsky Strait south of Severnaya Zemlya opened (Figure 4). On the basis of the sea-ice concentration maps (Figure 4), the southern route of the Northwest Passage through the Canadian Arctic Archipelago would also appear to be largely ice-free. You can find a fact sheet on the role of shipping routes in the Arctic here. Just like the previous month, August, with a mean sea-ice extent of 6.0 million km², came in 13th on the list of the monthly lowest sea-ice extents in the Arctic. Accordingly, a new record low in this year is considered highly unlikely.
The Antarctic: Heading for a record low winter sea-ice extent
In summer, observation of the sea-ice development often focuses on the Arctic, where the sea-ice minimum is reached in September. However, this year the sea-ice extent in the Southern Hemisphere – where it is nearing the winter maximum but growing only slowly – is also of considerable interest. June and July were characterised by minima in the long-term trend of monthly mean values. With a mean extent of 17.14 million km², August 2022 was the third-lowest value, after August 2002 (17.08 million km²) and the record low to date in August 1986 (17.02 million km², (Figure 5)). This was due to a persistent temperature anomaly at 925 hPa (circa 760 m) of more than 6° Celsius above the long-term average for the years 1971 to 2000, which slowed ice growth (Figure 6). In addition, northern winds from a pronounced low-pressure cell over the Bellingshausen and Amundsen Seas transported warm air masses to the Central Arctic and drove the ice margin back toward the continent. Through nearly all of the Antarctic – from the Bellingshausen Sea to the Weddell Sea, Cosmonauts Sea and Davis Sea – the ice margin was below the long-term average (Figure 7). Only the Ross Sea and D’Urville Sea had an ice margin extending far to the north, as the ice in the Ross Sea was pushed out northward to open water by the winds from the previously mentioned low-pressure cell. It remains to be seen whether the past minima from September 1986, 2002 and 2017, with monthly mean values of less than 18 million km², will be reached again this year.