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Glacial Ice Offers Polar Bears a Precarious Climate Refuge

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Discovered in the fjords of southeastern Greenland, the world’s most genetically isolated polar bear subpopulation has an unusual relationship to ice. Whereas most polar bears rely on sea ice, the bears recently found prowling Greenland’s southernmost tip also hunt on glacial mélange—the jumble of floating glacial ice that spills into fjords when glaciers come apart against the sea.

These unusual fjord dwellers might be a glimpse of their species’ future in the melting Arctic, researchers said. Ice is already as short-lived in the fjords as it is expected to be in the High Arctic by the end of the century. And as sea ice grows ever scarcer, polar bears will be driven farther back into a shrinking handful of climate change refugia, such as fjords.

A multiyear effort to study the bears and their environment was described in Science and will be presented at AGU’s Fall Meeting 2022.

Unexpected Discovery

The research team wasn’t expecting to find a new subpopulation of polar bears hunting on fjord ice, said ecologist Kristin Laidre of the University of Washington. The team’s project started in 2011 as a multiyear effort to survey the broader eastern Greenland population, which hadn’t been studied closely in more than a decade.

“[Southeastern Greenland] definitely wasn’t thought to be a place that would support a population of polar bears,” said Laidre. “But we took one or two trips down there and it kind of struck me. Coming into the fjords, we were seeing a high density of bears, and I didn’t really expect that.”

Southeastern Greenland is incredibly remote, and doing fieldwork there was a yearslong logistical challenge, Laidre recalled. Helicopter fuel and supplies were cached years in advance, and the team had to get creative with campsites if they wanted to avoid a daily 4-hour commute to the fjords.

“We lived in abandoned mining camps. We lived in abandoned weather stations. We slept in a sheep farm with a couple hundred sheep,” said Laidre. The small team had to carry noisemakers, flares, and rifles to protect themselves from the polar bears they were there to study.

Striking out by helicopter, Laidre and her colleagues scouted the fjords to find and “capture” bears using sedative darts so they could safely land and approach the animals to collect health data. They’d also fit adult females with tracking collars. When capture wouldn’t be safe for the researchers or for the bears, the team used biopsy darts to collect small tissue samples for genetic analysis instead.

In addition to the fieldwork, the team used satellite imagery to track the ice conditions in the bears’ habitats. But because fjords are so narrow and small, the normal automated tools used to track Arctic sea ice just wouldn’t work, Laidre said. The team’s ice scientists had to analyze daily satellite images of the fjords by hand.

Isolated Homebodies

Polar bears need sea ice to hunt but can endure between 100 and 180 ice-free days every year. That’s one reason why Laidre was so surprised to find a substantial population of bears in southeastern Greenland at all; the sub-Arctic region has more than 250 days without sea ice every year.

The southeastern Greenland bears survive by hunting from the glacial mélange, which flows into the fjords year-round. The strategy gives the bears plenty of food to eat, but also seems to restrict their movements.

“These bears are kind of homebodies.”

“These bears are kind of homebodies,” said Laidre. “[They] would stay in one or two fjords for 3–5 years. They’d move, on average, 10 or 15 square kilometers. Bears in other parts of the Arctic will move 1,000 kilometers…they really are just stuck in little pockets.”

This, as well as their habitat’s remote location, might explain the bears’ incredible isolation—the southeastern Greenland bears are the most genetically isolated polar bears in the Arctic, said Laidre.

Although there are other polar bear populations that are genetically isolated, have small ranges, or hunt from glacial mélange, the southeastern Greenland bears are unique in having all three of these characteristics, said University of Alberta ecologist Andrew Derocher, who was not involved in the study.

Symptom of Climate Change

The discovery of this unique bear population shows that glaciers that flow into the sea offer polar bears a refuge from melting sea ice. But although it might be tempting to see the southeastern Greenland bears as a new hope for their species in our warming world, it’s not that simple.

Lifestyles such as those of the Greenland bears are “a symptom of climate change,” said Derocher. “In a warming Arctic, this is a scenario that we’re going to see played out in many, many different places where…groups of bears become more isolated.”

“Polar bears are still at risk from climate change.”

Sea-terminating glaciers such as those in southeastern Greenland aren’t common in most of the Arctic, which includes northern Canada and Russia, where most polar bears live. And ice conditions in the Arctic can be erratic, said Derocher, adding that one or two unusually warm winters could “blink out” a small, isolated population such as the one in the study.

So rather than being a saving grace for the bears’ species, said Laidre, southeastern Greenland’s fjords are better understood as a glimpse of the future—and a potential opportunity for scientists to better understand the specific challenges climate change will bring.

“Polar bears are still at risk from climate change,” she said. “This small group of bears is going to teach us a lot about the future of the species, but [the way they live] is not going to save polar bears.”

—Elise Cutts (@elisecutts), Science Writer

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Citation: Cutts, E. (2022), Glacial ice offers polar bears a precarious climate refuge, Eos, 103, https://doi.org/10.1029/2022EO220563. Published on 9 December 2022.
Text © 2022. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

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