As Arctic sea ice vanishes, polar bears go with the floes

Thursday, January 22, 2015, 5:40 PM - As the video above shows, both the amount and the thickness of Arctic sea ice have really been seeing a sharp decline over the past few decades, and polar bears - one of the species seeing the greatest impact of this decline - seem to have worked out a fairly good way to adapt.

They follow the ice.

According to Climate.gov:

This trend of vanishing Arctic sea ice is a big problem for human civilization, due to the indirect effects it has on the weather and climate we experience.

The first effect is that all the sunlight the bright ice would have reflected back into space is now absorbed, where it influences Earth's weather system, and can push more weather events to the extreme. Second, plenty of that excess energy gets trapped in the subsurface water, heating the ocean, and causing the refreezing process to take longer. This means that the ocean water is exposed for longer periods of time during the year, so it absorbs even more energy. Third, when the water does finally freeze, all of that excess energy it had absorbed is then dumped into the atmosphere, to influence the weather (as in the first effect).

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We're all in this together

While that all spells bad news for us, the situation for polar bears is far worse. Although they suffer through the same indirect effects as we do (from the ramped-up weather), the loss of sea ice means a direct loss of habitat. Just as cutting down a forest destroys the habitat of animals, birds and insects that lived there, disrupting their feeding and mating habits, removing sea ice does the same for the bears. 

"In general, polar bears move with their habitat," Elizabeth Peacock, the United States Geological Survey researcher who led a recent study published in PLOS ONE, told Discovery News.

"Sea ice is like a moving sidewalk and they travel with it," she added in the interview. "Bears likely move towards places with better access to prey and mates."

That means areas with larger floes of sea ice, and the study led by Peacock shows that the bears are on the move, migrating away from areas where ice is melting away faster, to areas where floes are wider, thicker and longer-lasting. She and the other researchers identified four different clusters in the population - in the Eastern Polar Basin, Western Polar Basin, Canadian Archipelago and Southern Canada - and it seems that they've all been headed for the Canadian Archipelago over the past few generations, since that's one of the few places left where there's sea ice all year long.

How did her team figure this out? By tracking the 'flow' of the bears' genes.

The direction of polar bear gene flow around the Arctic Ocean. Credit: Peacock et al/PLOS ONE

"By examining the genetic makeup of polar bears, we can estimate levels and directions of gene flow, which represents the past story of mating and movement, and population expansion and contraction," Peacock said in a USGS press release. "Gene flow occurs over generations, and would not be detectable by using data from satellite-collars which can only be deployed on a few polar bears for short periods of time."

This work is turning out to be very important, as it not only confirms the findings of other genetic studies of polar bears (such as their genetic link to brown bears), but is highlighting threats to their population and to conservation efforts.

"The threats, of course, include climate change, and the number one safeguard for climate change is to reduce the carbon in the atmosphere," Peacock told Discovery News. "Other safeguards may be to address other habitat disturbances in this area, including oil/gas development and increased Arctic shipping."