Polar Bears - On Thin Ice

Ashore on Svalbard, a male polar bear investigates a whale's backbone. Fat reserves from hunting ringed and bearded seals, and sometimes walruses, must carry bears through lean summers.  Photograph by Florian Shultz

 

 

On Thin Ice

The Arctic is warming so fast that by 2050 it may be largely ice free in summer. Without their frozen hunting platform, how will polar bears survive?

By Susan McGrath

Photograph by Florian Schulz

In August 1881 the naturalist John Muir was sailing off Alaska aboard the steamer Thomas Corwin, searching for three vessels that had gone missing in the Arctic. Off Point Barrow he spotted three polar bears, "magnificent fellows, fat and hearty, rejoicing in their strength out here in the bosom of the icy wilderness."

Were Muir to sail off Point Barrow in August today, any polar bears he'd see would not be living in a wilderness of ice but swimming through open water, burning precious fat reserves. That's because the bears' sea-ice habitat is disappearing. And it's going fast.
Polar bears ply the Arctic niche where air, ice, and water intersect. Superbly adapted to this harsh environment, most spend their entire lives on the sea ice, hunting year-round, visiting land only to build maternal birthing dens. They prey mainly on ringed and bearded seals (it's been said that they can smell a seal's breathing hole from more than a mile away) but sometimes catch walruses and even beluga whales.

Sea ice is the foundation of the Arctic marine environment. Vital organisms live underneath and within the ice itself, which is not solid but pierced with channels and tunnels large, small, and smaller. Trillions of diatoms, zooplankton, and crustaceans pepper the ice column. In spring, sunlight penetrates the ice, triggering algal blooms. The algae sink to the bottom, and in shallow continental shelf areas they sustain a food web that includes clams, sea stars, arctic cod, seals, walruses—and polar bears.
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