Newly discovered polar bears found a way to survive without sea ice

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An earlier version of this article incorrectly stated that polar bears have been isolated in southeastern Greenland for hundreds of thousands of years. Bears have been isolated for hundreds of years. The article has been corrected.

For centuries, sea ice was considered essential to the survival of polar bears. Generations of Arctic bears have ventured onto sheets of floating ice to travel long distances and hunt unsuspecting seals. As climate change lowered sea ice concentrations, many of these populations struggled to thrive.

But now researchers have discovered a new genetic population of polar bears in Greenland that don’t rely on sea ice to hunt, rewriting how we think about sea bears and their ability to adapt to a warming planet. Scientists described their discovery of this 20th subpopulation of polar bears in a study released Thursday in the journal Science.

“This was just a totally unexpected discovery,” said lead author Kristin Laidre in an interview. “They are the most genetically isolated polar bears in the world and are unlike any other 19 currently accepted subpopulations around the Arctic.”

Much of the population’s uniqueness comes from its remote location. in the southeastern corner of Greenland. The Greenland ice sheet limits them to the west, while the open ocean limits them to the east, limiting their travel and interaction with other polar bear populations. The team isn’t sure how the bears got there, but the data suggests they’ve likely been isolated in the region for hundreds of years. Their unique genetic makeup may have evolved over several hundred years of isolation.

Laidre said this new subpopulation – estimated at just hundreds – lives at the southern end of the polar bear distribution, technically in the subarctic region. As a result, this region also experiences shorter sea ice seasons than other polar bear habitats on the island.

“They are very local bears. They don’t move very far. They stay in the same fjord for years,” Laidre said. “They have sea ice on average about 100 days a year, and we know that’s too short for a polar bear to survive.”

Rather than relying solely on sea ice, polar bears have adapted and hunt on glacial ice that protrudes from the ice sheet. While other polar bear populations must move to new locations during ice-free seasons, these bears move to the back of fjords against the fronts of glaciers. They use these glaciers as a platform to hunt seals throughout the year.

The study authors say the discovery of this unusual behavior is enlightening, especially as climate change continues to shrink the region’s sea ice.

“When we’re looking to the future and an ice-free Arctic, we ask, ‘Where are the places that polar bears can hang? Where could they survive or persist?’ – said Laidre.

Rising global temperatures have reduced Arctic sea ice concentrations by 13% every decade since 1979. Climate models project sea ice conditions in densely populated regions of polar bears in the High Arctic will deteriorate even more so at the end of this century. The sea ice season could become as sparse as is currently seen in this region of southeastern Greenland, which is ice-free for more than eight months a year.

Earth is now losing 1.2 trillion tons of ice each year. And it will get worse.

“What’s cool about this population is that they’re actually living in a habitat that we thought was beyond the physiological ability of these bears to survive,” said Beth Shapiro, study author and an evolutionary biologist at the University of California, Santa Cruz. Shapiro said the team doesn’t know whether the bears have a specific genetic mutation that helps them adapt to this habitat, but would like to investigate any links in the future.

Despite this adaptation, bears are not immune to climate change. Just as the Greenland ice sheet is losing mass each year, the glaciers around the ice sheet are also retreating. But projections show the southeastern edge of the ice sheet and nearby glaciers not retreating as quickly as other areas heavily populated by bears.

“Some changes that we anticipate with climate change may occur more quickly than we expected, while others may occur more slowly,” said Twila Moon, study author and researcher at the National Snow and Ice Data Center at the University of Colorado Boulder. in an email. “As sea ice continues to decline, glacial ice may remain available longer.”

Greenland ice sheet experiences record loss of glacier melt and ocean melt in 2021

Even though glacial ice has been available for longer, the researchers said there are few places in the Arctic where this type of glacial ice is accessible to polar bears. Such environments exist only in this region of Greenland and in Svalbard, Norway.

“There are a limited number of places in the Arctic where this type of glacial ice is available, however using glacial ice is not an option for many Arctic polar bear populations,” Moon wrote.

John Whiteman, who serves as chief scientist for the nonprofit Polar Bears International and was not involved in the study, agreed that this discovery does not change the fate of polar bears.

“This article reinforces that polar bears rely exclusively on ice; what’s unique here is that the source of the ice is a glacier rather than sea ice,” Whiteman said. in an email. “This strategy does not provide a long-term home for polar bears.”

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