They document a previously unknown subpopulation of polar bears in southeastern Greenland . The animals survive with limited access to sea ice, hunting freshwater ice that pours into the ocean from Greenland’s glaciers. It is a genetically very different population from the rest of polar bears. In addition, it is very well adapted to its environment, which could give us clues about the future of the species in a warming Arctic.
“We wanted to study this region because we didn’t know much about the polar bears of southeastern Greenland, but we never expected to find a new subpopulation living there,” said lead study author Kristin Laidre, a polar scientist at the University of Washington Applied Physics Laboratory. . “We knew there were some bears in the area from historical records and indigenous knowledge. We just didn’t know how special they were.”
The study analyzed data collected on the southeast coast of Greenland for seven years and historical information from the entire east coast of the island covering about 30 years. The southeastern area had not been studied much because of its unpredictable weather, heavy snowfall, and rugged terrain. Newly collected population, movement and genetic data show how these bears use glacial ice to survive with limited access to sea ice.
“Polar bears are threatened by sea ice loss due to climate change . This new population gives us insight into how the species might persist into the future,” said Laidre, who is also an associate professor of aquatic and fisheries sciences at the University of Washington. “But we need to be careful about extrapolating our findings, because the glacial ice that makes bear survival possible in southeastern Greenland is not available in most of the Arctic.”
Genetically, these bears are different from other populations. In fact, the genetic difference between them and their closest neighbors is greater than has been observed in any of the 19 previously known polar bear populations. “They are the most genetically isolated population of polar bears on the entire planet ,” said co-author Beth Shapiro, a professor and geneticist at the University of California, Santa Cruz and a Howard Hughes Medical Institute investigator. “We know that this population has been living separately from other polar bear populations for at least several hundred years, and that their population size has remained small throughout this time.”
Scientists believe these bears are so isolated because they are surrounded on all sides by landforms . By the mountain peaks and the Great Greenland Ice Sheet to the west, by the open waters of the Denmark Strait to the east, and by the rapid East Greenland Coastal Current.
Satellite tracking of adult females showed that, unlike most other polar bears that travel far over sea ice to hunt, those from southeast Greenland stay at home. They walk on ice within sheltered fjords or climb mountains to reach neighboring fjords on the Greenland Ice Sheet. Half of the 27 bears tracked accidentally floated an average of 190 km south on small ice floes caught in the East Greenland Coastal Current. They then jumped off and walked north again overland to their home fjord.
“In a sense, these bears provide insight into how Greenland bears may behave in future climate scenarios ,” Laidre said. “Sea ice conditions in southeast Greenland today resemble what is predicted for northeast Greenland later this century.”
The bears of southeastern Greenland do not always have access to sea ice, but only from February to the end of May. Most of the approximately 26,000 polar bears in the Arctic use the sea ice to hunt seals . The rest of the months that they cannot access these ice, the animals hunt seals from pieces of freshwater ice that break off from the Greenland ice sheet.
“The marine-terminating glaciers of southeastern Greenland are quite a unique environment,” says co-author Twila Moon, deputy senior scientist at the National Snow and Ice Data Center. “These types of glaciers exist elsewhere in the Arctic, but the combination of fjord shapes, high glacial ice production and the large ice reservoir that is available from the Greenland Ice Sheet is what currently provides a constant supply of glacial ice.
The fact that bears can survive in the area suggests that sea-ending glaciers, and especially those that dump ice into the ocean on a regular basis, could become refugia where some polar bears might survive as sea ice in the ocean surface decreases. Similar habitats exist in marine-terminating glaciers elsewhere along the coast of Greenland and on the island of Svalbard, a Norwegian territory east of Greenland. “Even with the rapid changes that are occurring in the ice sheet, this area of Greenland has the potential to continue to produce glacial ice, with a coastline that may look similar to today, for a long time,” Moon said.
Although the finding is undoubtedly good news, the researchers believe that in the future only a few polar bears may survive as the glacier habitat is not large enough to accommodate them all.
Referencia: Laidre, K et. al. 2022. Glacial ice supports a distinct and undocumented polar bear subpopulation persisting in late 21st-century sea-ice conditions. Science. DOI: 10.1126/science.abk2793
