For polar bears and co. It is getting tighter: An arctic region, which is considered a refuge for ice-dependent animal species, is less resistant to global warming than previously assumed. This emerges from an analysis of the record melting of the pack ice that hit part of this region in the summer of 2020. According to this, an unusual weather situation was the main cause, but the consequences of climate change also led to the drastic loss of ice cover in the study area, the researchers report.
Climate change is noticeable all over the world – but especially in the far north: In the summer half of the year, the Arctic sea ice melts so much that only a comparatively small ocean surface remains covered. This is not only a clear sign of global warming – the loss of ice itself has critical consequences: In addition to feedback effects on the climate, the changes also threaten the animals of the complex ecosystems of the Arctic Ocean, because many species depend on the floating ice surfaces in summer. This is especially true for the mammals of this lifelong dream: polar bears hunt from the ice, seal species need it to build caves for their young and walruses use the ice as a platform for foraging.
The “Last Ice Area” at a glance
Until now, it has been hoped that at least one region could serve as a refuge for ice-dependent animal species if the conditions in the surrounding areas become inhospitable. These are the area north of Greenland and the islands of the Canadian-Arctic archipelago. “The sea ice circulates through the Arctic and follows a certain pattern: It naturally ends with it piling up off Greenland and the northern Canadian coast,” explains first author Axel Schweiger from the University of Washington in Seattle. “In climate models, if you let them run forward over the next hundred years, there is a tendency in this area that the pack ice will last the longest there in summer,” explains Schweiger. This area has long been considered the primary refuge for the ice-dependent animal species.
But the researchers’ results now indicate that at least in parts of this “last ice area”, a decline in summer sea ice is already becoming apparent. As part of their study, they investigated the background to the previously strongest known melt of summer sea ice cover in part of the sea ice refuge: the Wandelsee in northern Greenland. While this marginal sea of the Arctic Ocean usually remains largely covered with ice in summer, gigantic bodies of water appeared in summer 2020. The German research ship “Polarstern” had found this on site and satellite images then showed: On August 14th there was a record low of only 50 percent sea ice cover, report Schweiger and his colleagues. By evaluating satellite data and sea ice models, they have now also investigated the question of which factors led to the record low.
Unusual weather – but also climate change
The bottom line is that the scientists come to the conclusion that around 80 percent of the effect was due to unusual weather constellations. But the other 20 percent was a consequence of the longer-term thinning of the sea ice due to global warming. As the team reports, the ice loss initially seemed surprising because the average ice thickness at the beginning of summer 2020 was actually close to the norm. The model simulations from June 1 to August 16 then made it clear, however, that unusual winds had moved the sea ice and thus fragmented it particularly intensely.
However, the thinning trend of recent years and thus global warming have also made a significant contribution to ice loss, emphasize the researchers: “During winter and spring 2020 there were patches of older, thicker ice that had drifted into this area of the sea, but existed enough thinner, newer ice that melted to expose the open ocean, ”explains Schweiger. “This started a cycle of absorbing thermal energy to melt more ice, despite the fact that there was also some thicker ice. If, in some years, the ice cover in this region fills up with older and thicker ice, this seems to have a less protective effect than one might expect, ”explains the scientist.
As he and his colleagues point out, the results are cause for concern – but to what extent the entire region, which is considered to be the last ice hideaway, remains unclear. Thus, according to them, there is now a need for further research. This also applies to questions about how increasingly open water bodies in this region could affect the ice-dependent animal species in the short and long term. “We know very little about the marine mammals in the Last Ice Area,” says senior author Kristin Laidre of the University of Washington. “We have almost no historical or current data, and the reality is that there are many more questions than answers about the future of these animal populations,” concludes the scientist.
Source: University of Washington, Article: Commun Earth Environ, doi: 10.1038 / s43247-021-00197-5