A group of polar bears in southeastern Greenland have adapted to melting sea ice by hunting from freshwater ice that pours into the ocean from glaciers.
The population – which is genetically distinct and adapted to its environment – could offer a glimpse of the future for polar bears in a warming Arctic, researchers believe.
Lead author Professor Kristin Laidre, a polar scientist at the University of Washington's Applied Physics Laboratory, said: "We wanted to survey this region because we didn't know much about the polar bears in southeast Greenland, but we never expected to find a new subpopulation living there.
"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 is based on seven years of new data collected along the southeastern coast of Greenland, plus 30 years of historical data from the island's whole east coast.
The remote southeast region had been poorly studied because of its unpredictable weather, jagged mountains and heavy snowfall.
The newly-collected genetic, movement and population data show how these bears use glacier ice to survive with limited access to sea ice.
Professor Laidre said: "Polar bears are threatened by sea ice loss due to climate change. This new population gives us some insight into how the species might persist into the future.
"But we need to be careful about extrapolating our findings, because the glacier ice that makes it possible for southeast Greenland bears to survive is not available in most of the Arctic."
The genetic difference between this group of bears and its nearest genetic neighbour is bigger than that observed for any of the 19 previously known polar bear populations.
Co-author Beth Shapiro, a professor and geneticist at the University of California, Santa Cruz, said: "They are the most genetically isolated population of polar bears anywhere on the planet.
"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 throughout this time has remained small."
Part of the reason the population is so isolated, the researchers believe, is that the bears are hemmed in on all sides – by the sharp mountain peaks and massive Greenland Ice Sheet to the west, the open water of the Denmark Strait to the east, and by the fast-flowing East Greenland coastal current that poses a hazard offshore.
The satellite tracking of adult females shows that, unlike most other polar bears that travel far over sea ice to hunt, southeast Greenland bears walk on ice inside protected fjords or scramble up mountains to reach neighbouring fjords over the Greenland Ice Sheet.
Half of the 27 tracked bears accidentally floated an average of 120 miles south on small ice floes caught in the East Greenland coastal current, but then hopped off and walked back north on land to their home fjord.
Laidre said: "In a sense, these bears provide a glimpse into how Greenland's bears may fare under future climate scenarios.
"The sea ice conditions in southeast Greenland today resemble what's predicted for northeast Greenland by late this century."
Southeast Greenland bears have access to sea ice for only four months, between February and late May.
Sea ice provides the platform that most of the Arctic's roughly 26,000 polar bears use to hunt seals.
For two-thirds of the year, the southeast Greenland polar bears hunt seals from chunks of freshwater ice breaking off the Greenland Ice Sheet.
Laidre cautioned, however, that longer-term monitoring is needed to know the future viability of southeast Greenland bears and to understand what happens to polar bear subpopulations as they become increasingly cut off from the rest of the Arctic by declining sea ice.
He said: "If you're concerned about preserving the species, then yes, our findings are hopeful – I think they show us how some polar bears might persist under climate change.
"But I don't think glacier habitat is going to support huge numbers of polar bears. There's just not enough of it. We still expect to see large declines in polar bears across the Arctic under climate change."
Watch: Polar bears fight for survival as sea ice disappears