January 31, 2023

A fjord in Greenland with proglacial blend. A subpopulation of polar bears in southeastern Greenland hunts on glacial rather than sea ice, a recent study finds. Credit: NASA’s Marshall Space Flight Center

Holes in sea ice provide the perfect hunting ground for polar bears looking for their main food source: seals. So when rising temperatures melt sea ice, the existence of polar bears is threatened, making them the poster child for many reports and documentaries on climate change. While every population of polar bears is threatened by the loss of this sea ice, some have evolved adaptations to survive the low ice seasons. In southeastern Greenland, researchers have discovered a unique subpopulation of polar bears that have found a way to live in an area of ​​low sea ice by hunting glacial melange — a floating mixture of icebergs calved from glaciers, sea ice and snow. it forms at the foot of glaciers and survives the warm season.

The discovery was published in June in the journal Science by an international team of Arctic scientists. The population is isolated and genetically distinct from other groups of polar bears, surviving in fjords that are free of sea ice for more than two-thirds of the year.

The Arctic Ocean is a mix of liquid and frozen seawater in the Arctic. This area and the adjacent seas around it are a critical, shrinking habitat for polar bears. Polar bears use sea ice to travel long distances and hunt ringed seals, their favorite prey or other seals and marine mammals. Usually, polar bears wait at holes in the sea ice for their prey to surface for air so they can snatch them out of the water.

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As the sea ice in the Arctic Ocean regained the mass it lost in the summer during the cold, dark winter months, it has been steadily declining for decades. It has lost an average of 27,000 square miles of ice per year since 1979. This is bad news for species that rely on sea ice, such as polar bears, which are now being forced to spend more time on land and fast for longer periods of time. Because the sea ice breaks up and recedes earlier in the summer, many polar bears have little or no access to food during the warmer months, affecting both their physical and reproductive health.

According to the new study, an isolated polar bear population on Greenland’s southeast coast complements the low-ice season by relying on glacial ice for hunting when the sea ice is gone. Unlike sea ice, glaciers form on land, while sea ice forms and melts in the ocean. Glacier mélange is a floating mixture of icebergs calved from glaciers, snow and freshwater ice that forms at the bases of glaciers that end in lakes and rivers in fjords – narrow valleys carved by ancient ice movements. Because glaciers do not completely melt in the summer, they provide a hunting ground for this subpopulation when sea ice is not available.

Lead author Kristin Laidre, an associate professor in the School of Aquatic and Fishery Sciences at the University of Washington, and her team conducted a decade-long study of the polar bears on the east coast of Greenland when they realized they might be looking at two subpopulations. look instead of one. “We were assessing what we thought was a single subpopulation on the 1,800-mile east coast of Greenland when we made this completely unexpected discovery,” Laidre said in an interview with GlacierHub. The decade-long study tracked the movement, genetics and demographics of polar bears along Greenland’s eastern coast. They also surveyed indigenous subsistence hunters from East Greenland and incorporated their traditional ecological knowledge into the study.

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Through genetic and behavioral data, Laidre and her team realized they had found a new subpopulation of polar bears on the southeast coast of Greenland — the “most genetically isolated polar bears in the world,” Laidre said. In other words, while those bears are still the same species as other polar bears, they are genetically and demographically different from other subpopulations. Genetic diversity is important for species because it allows them to adapt to changing environments. While more research needs to be done on the population, a combination of genetic diversity and behavioral adaptation has allowed these bears to hunt glacial ice during low sea ice seasons to supplement their diets.

Laidre stressed that this study does not mean that the bears are not threatened by the loss of sea ice. “Glacier ice can help small numbers of polar bears survive for extended periods under climate warming, but it’s not available to the vast majority of polar bears,” she explained. In the long term, she points to the importance of studying this population and other polar bears to understand where Arctic polar bears can survive and how genetic diversity could help other species threatened by climate change.

Newly documented polar bear population in Southeast Greenland sheds light on the species’ future in a warming Arctic

More information:
Kristin L. Laidre et al, Glacial ice supports a distinct and undocumented polar bear subpopulation persisting in late 21st century sea ice conditions, Science (2022). DOI: 10.1126/science.abk2793

Provided by Earth Institute at Columbia University

This story has been republished courtesy of Earth Institute, Columbia University http://blogs.ei.columbia.edu.