Antarctic Mega-Iceberg Suffocates Seals

May 27, 2008 -- Weeks after the controversial listing of polar bears as threatened species, new research graphically demonstrates how changes to polar ice can devastate local animals.

The findings of a grim new study illustrate the direct, and often immediate, effects that climate change can have on the physiology, behavior and survival of wild species.

An Iceberg the Size of Rhode Island

In 1998, ecologist and evolutionary biologist Terrie Williams of the University of California at Santa Cruz and her team began a study on Weddell seals in Antarctica.

Three years later, an enormous iceberg detached near Antarctica's McMurdo Sound. According to Williams and her colleagues, the event was caused by global warming, which has likely been melting and weakening ice at the poles.

The 4,200-square-mile iceberg -- dubbed B-15 -- drifted westward and lodged on nearby Ross Island. The lives of countless animals would soon forever change.

Seals Struggle for Breathing Room

"Our first clue that there was a problem was that the seals were not returning to their usual pupping areas, and that there were fewer seals even later in the season," Williams told Discovery News.

She and her colleagues noticed that the ice around Ross Island did not experience its usual "break-out" that year. Normally the ice thaws, creating thinner areas where diving seals can carve breathing holes in the ice shelf. Instead, the presence of B-15 thickened the surrounding ice.

"We started out with three feet of ice and were up to a nine feet thickness" by 2002, the last year of the study, Williams said.

Filming both above and below the thickened ice, Williams and her colleagues observed seals lining up to breathe at the few holes they were able to make with their front canine teeth. Lacking the energy to swim further, fights ensued in the lines, with animals lashing out at each other for access to air.

Williams explained that after B-15 dislodged, there were 80 miles of ice between McMurdo and the open ocean.

"Weddell seals can only swim four miles under ice before they have to come up to breathe, so you can see the problem," she said.

Physiological Systems Overtaxed

The researchers measured the oxygen consumption of seals that managed to surface, and by analyzing the underwater video, calculated the energy cost of each stroke the seals made during dives.

After comparing these calculations with prior data on seals diving under normal conditions, the researchers found that the new environment simultaneously increased the seals' need for oxygen and reduced their access to air.

Since seals dive to hunt, most were unable to catch enough prey to sustain themselves and their pups.