Арктический лед на севере Аляски резко сократился за несколько недель

Sea ice north of Alaska shifted from above-normal conditions to below-average levels during the first half of August. It went from being significantly above normal in terms of abundance to being below average as measured against a 48-year satellite record in just a couple of weeks. The transformation was most evident in the Chukchi and Beaufort Seas. Those areas experienced rapid ice loss following a dramatic slowdown in melting from late July into early August. During the same period, some of the satellite-based monitoring systems reported differing amounts of remaining ice. The slowdown ended almost overnight across Northern Arctic waters In addition to the seasonal melt that takes place every year, Arctic sea ice will continue to retreat toward its minimum level, which typically occurs in September. According to the Alaska and Arctic Climate Newsletter, in the first half of August, conditions across the Pacific side of the Arctic Ocean changed significantly. Prior to that period, waters north and northwest of Alaska contained relatively high amounts of ice but later experienced a dramatic reduction in coverage. Conditions changed rapidly over the course of a few weeks. In the Chukchi and Beaufort Seas, passive-microwave rankings dropped from very high levels in late July to well below the 48-year median by mid-August. At the same time, MASIE showed substantially more ice remaining in the region due to summer melt ponds and dispersed low-concentration ice. By the end of July, Arctic-wide sea ice losses had slowed dramatically. Following the slowdown, the rate of ice loss increased sharply in waters north of Alaska, producing the shift observed during August. Satellites started telling a very different story about the ice During the same period, researchers encountered a different challenge. Disagreements between passive microwave analysis and MASIE (Multisensor Analyzed Sea Ice Extent) were greatest in the Chukchi and Beaufort Seas. A large expanse of open ocean appeared in passive microwave analyses extending far out over the waters northwest and northeast of Alaska. In contrast, MASIE indicated that ice persisted in nearly all of those areas. This did not necessarily mean that either method was incorrect. Rather, according to the Alaska and Arctic Climate Newsletter, the discrepancy primarily reflects the difficulty of detecting scattered, low-concentration sea ice during the summer months. Small differences in how ice near the 15% concentration threshold is classified can produce different estimates. Surface meltwater on top of sea ice can also contribute to those differences. In some cases, it can cause passive microwave sensors to identify areas as open ocean even when sea ice remains present. This known problem can impact ice extent measurements taken using passive microwave sensors during the summer months. These issues should decrease later in the season as melting occurs further northward and refreezing begins at higher latitudes within the Arctic. Summer melting is not over yet in the Arctic Although there was a short-lived slowdown in sea ice loss, Arctic sea ice extent is currently lower than in many years since the beginning of the satellite record. On August 16th, Arctic-wide rankings differed slightly depending upon whether data was obtained from JAXA or NSIDC. According to NSIDC data, Arctic-wide sea ice extent rankings are currently at their 9th lowest value ever recorded. Meanwhile, JAXA placed it at its 8th lowest position. Other monitoring systems provided similar rankings, illustrating the same measurement challenges seen in waters north of Alaska. Despite the recent slowdown, the report described Arctic sea ice extent as “typically low” for the 2020s. However, the changes north of Alaska occurred so quickly that major monitoring systems produced different estimates of remaining sea ice. The largest differences were reported in the Chukchi and Beaufort Seas, where sea ice conditions changed rapidly during August. Read the whole thing? Get the week's signal, not the noise Our sharpest reporting on energy, climate and nature — free, once a week.