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

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

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A previous version of this article incorrectly said that polar bears were isolated in southeast Greenland for hundreds of thousands of years. Bears have been isolated for hundreds of years. The article has been corrected.

For centuries, sea ice has been considered essential to the survival of polar bears. Generations of Arctic bears have ventured onto the floating ice floes to travel long distances and prey on unsuspecting seals. As climate change has reduced sea ice concentrations, many of these populations have struggled to thrive.

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

“It was just a completely unexpected discovery,” said lead author Kristin Laidre. in an interview. “They are the most genetically isolated polar bears in the world, and they are different from all 19 other currently accepted subpopulations in the Arctic.”

Much of the population’s uniqueness comes from its remote location in the southeast corner of Greenland. The Greenland Ice Sheet borders them to the west, while the open ocean borders them to the east, limiting their movements and interactions with other polar bear populations. The team doesn’t know how the bears got there, but data suggests they’ve likely been isolated in the area for hundreds of years. Their unique genetic makeup may have evolved over several hundred years of isolation.

Laidre said this new subpopulation — estimated to number in the hundreds — lives on the southernmost reaches of polar bear distribution, technically in the subarctic region. As a result, this area also experiences shorter sea ice seasons than other polar bear habitats on the island.

“These 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 far too short for a polar bear to survive.”

Instead of relying exclusively on sea ice, polar bears have adapted to and hunt from glacial ice protruding from the ice sheet. While other populations of polar bears must move to new locations during ice-free seasons, these bears move backwards from the fjords against the fronts of the glaciers. They use these glaciers as a platform to hunt seals all year round.

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

“When we look to the future and envision an ice-free Arctic, we ask ourselves, ‘Where are the places where polar bears can hang? Where could they survive or persist? “, said Laidré.

Rising global temperatures have reduced Arctic sea ice concentrations by 13% every decade since 1979. Climate models predict that sea ice conditions in heavily polar bear-populated regions of the Extreme -Arctic will deteriorate even later this century. The sea ice season could become as meager as it is now in this region of southeastern Greenland, which is ice-free for more than eight months a year.

Earth now loses 1.2 trillion tons of ice every year. And it will get worse.

“The nice thing about this population is that they’re really living in a habitat that we thought was beyond the physiological ability of these bears to survive,” said study author and biologist Beth Shapiro. of evolution at the University of California at Santa Cruz. Shapiro said the team doesn’t know if the bears hold 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 that the southeastern edge of the ice sheet and nearby glaciers are not retreating as quickly as other heavily bear-populated areas.

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

Greenland ice sheet sees record loss from glacier calving and ocean melt in 2021

Even though glacier ice is 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 is chief researcher at the non-profit organization Polar Bears International and was not involved in the study, agreed that the finding did not change the fate of polar bears.

“This document reinforces the fact that polar bears are exclusively dependent on ice; what’s unique here is that the source of the ice is 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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