Some polar bears in far north are getting short-term benefit from
thinning ice

Date:
September 23, 2020
Source:
University of Washington
Summary:
The small subpopulation of polar bears in Kane Basin were doing
better, on average, in recent years than in the 1990s. The bears
are experiencing short-term benefits from thinning and shrinking
multiyear sea ice that allows more sunlight to reach the ocean
surface, which makes the system more ecologically productive.



FULL STORY ==========================================================================
A small subpopulation of polar bears lives on what used to be thick,
multiyear sea ice far above the Arctic Circle. The roughly 300 to 350
bears in Kane Basin, a frigid channel between Canada's Ellesmere Island
and Greenland, make up about 1-2% of the world's polar bears.


==========================================================================
New research shows that Kane Basin polar bears are doing better,
on average, in recent years than they were in the 1990s. The study,
published Sept. 23 in Global Change Biology, finds the bears are healthier
as conditions are warming because thinning and shrinking multiyear sea
ice is allowing more sunlight to reach the ocean surface, which makes
the system more ecologically productive.

"We find that a small number of the world's polar bears that live in
multiyear ice regions are temporarily benefiting from climate change,"
said lead author Kristin Laidre, a polar scientist at the University of Washington Applied Physics Laboratory's Polar Science Center.

If greenhouse gases continue to build up in the atmosphere and the climate keeps warming, within decades these polar bears will likely face the same
fate as their southern neighbors already suffering from declining sea ice.

"The duration of these benefits is unknown. Under unmitigated climate
change, we expect the Kane Basin bears to run into the same situation
as polar bears in the south -- it's just going to happen later,"
Laidre said. "They'll be one of the last subpopulations that will be
negatively affected by climate change." All of the world's 19 polar bear subpopulations, including Kane Basin, are experiencing a shorter on-ice
hunting season, according to a 2016 study led by Laidre. This makes it
hard for the animals, that can weigh more than 1,200 pounds as adults, to
meet their nutritional needs. Polar bears venture out on sea ice to catch seals. In summer when the sea ice melts, the polar bears fast on land.



========================================================================== Laidre led a recent study showing that in the Baffin Bay polar bear subpopulation, which includes about 2,800 bears living just south of
Kane Basin, adult females are thinner and are having fewer cubs as the
summer open- water season -- when they must fast on land -- grows longer.

"Kane Basin is losing its multiyear ice, too, but that doesn't have the
same effect on the polar bears' ability to hunt," Laidre said. "Multiyear
ice becomes annual ice, whereas annual ice becomes open water, which
is not good for polar bears." The new paper looked at Kane Basin bears
using satellite tracking data and direct physical measurements to compare
from 1993 to 1997 with a more recent period, from 2012 to 2016. The body condition, or fatness, improved for all ages of males and females. The
average number of cubs per litter, another measure of the animals'
overall health, was unchanged.

Satellite tags showed the Kane Basin polar bears traveled across larger
areas in recent years, covering twice as much distance and ranging
farther from their home territory.

"They now have to move over larger areas," Laidre said. "The region
is transitioning into this annual sea ice that is more productive but
also more dynamic and broken up." Observations show a profound shift in
the sea ice in Kane Basin between the two study periods. In the 1990s,
about half the area was covered in multiyear ice in the peak of summer,
while in the 2010s the region was almost completely annual ice, which
melts to open water in summer.



==========================================================================
Even though there's now more open water, the marine ecosystem has become
more productive. Annual sea ice allows more sunlight through, so more
algae grow, which supports more fish and in turn attracts seals.

"Two decades ago, scientists hypothesized that climate change could
temporarily benefit polar bears in multiyear ice regions over the short
term, and our observations support that," Laidre said.

The subpopulation on the other side of Ellesmere Island, in Canada's
Norwegian Bay, could be in a similar situation, she said, though no data
exist for those animals.

If conditions continue to warm these northernmost polar bears will likely
face the same fate as their southern neighbors. Kane Basin polar bears
have only much deeper water to turn to farther north.

"It's important not to jump to conclusions and suggest that the High
Arctic, which historically was covered by multiyear sea ice, is going to
turn into a haven for polar bears," said Laidre, who is also an associate professor in the UW School of Aquatic and Fishery Sciences. "The Arctic
Ocean around the North Pole is basically an abyss, with very deep waters
that will never be as productive as the shallower waters to the south
where most polar bears live.

"So we are talking about temporary benefits in a limited area and to a
very small number of bears."

========================================================================== Story Source: Materials provided by University_of_Washington. Original
written by Hannah Hickey. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Kristin L. Laidre, Stephen N. Atkinson, Eric V. Regehr, Harry
L. Stern,
Erik W. Born, O/ystein Wiig, Nicholas J. Lunn, Markus Dyck,
Patrick Heagerty, Benjamin R. Cohen. Transient benefits of climate
change for a high‐Arctic polar bear ( Ursus maritimus )
subpopulation. Global Change Biology, 2020; DOI: 10.1111/gcb.15286 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200923124642.htm

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