Ainley thinks the ice was so extensive this year because the winter and spring winds were much calmer than normal. As a result, McMurdo Sound was not blown clear of sea ice, and open areas in the pack ice of the southern Ross Sea did not appear.
"A horrendous four-day storm in December broke up a lot of the fast ice," said Kooyman.
The unusual sea ice conditions were compounded by two giant icebergs, which scientists named B-15A and C-16.
B-15A, which is 20 miles wide by 100 miles long (37 kilometers by 161 kilometers), was originally part of an iceberg about the size of Connecticutthe largest iceberg ever recordedthat calved off the Ross Ice Shelf in March 2000.
Pushed by ocean winds, B-15A bumped along the edge of the continent. As it migrated westward, B-15A rammed into the jutting edge of the ice shelf and created a second large berg, named C-16, that extends ten miles by 30 miles (18.5 kilometers by 55 kilometers).
C-16 ran aground north of Ross Island in November 2000. Two months later, the drifting B-15A grounded itself alongside C-16.
Both of the icebergs are large enough to have upset the currents and winds of the Ross Sea, disrupting the movement of pack ice and the formation of fast ice, according to the U.S. National Ice Center.
"It looked like the berg might be acting as a dam almost, backing up circulation," said Kooyman.
As it was moving toward C-16, the iceberg B-15A bumped against Cape Crozier, pushing sea ice into piles at the shoreline. These piles of ice have made it difficult for the penguins to move between their colony and the ocean, said Ainley.
Penguin Colonies at Risk?
Two colonies at Cape Crozier, one of Adélie penguins and the other of Emperor penguins, have been seriously affected by the giant bergs and unusually abundant sea ice.
The colony of about 1,200 Emperor penguins at Cape Crozier failed to raise any chicks this year.
Emperor penguins don't use nests. Once the females have laid eggs, the males incubate them on their feet while the females return to the sea for the roughly 65 days it takes the eggs to hatch.
Kooyman thinks there were no chicks this year because the eggs failed to hatch. "By the time we got there, it was difficult to tell what happened," he said.
"What we saw was just the tip of the evidence because so much of the ice was destroyedjust ground up and crumbling away," he said. "It looks like the birds got there before the berg arrived, and then were caught by surprise."
"They're probably en route to the eastern Ross Sea now to molt," he added.
The Adélie penguin colony at Cape Crozierthe sixth largest Adélie colony in the worldis home to about 140,000 breeding pairs. Unlike Emperors, male and female Adélie penguins share incubation and chick-rearing duties.
Breeding Emperor adults travel three to 50 miles (five to 80 kilometers) from their colonies to catch food for their chicks. The trips can extend from a few hours long to as much as four days.
"Normally an Adélie penguin colony is within a mile or less of open water," said Ainley. "The total migration for the Adélie penguins from their wintering area is on the order of several hundred miles, much of which they cover by swimming.
"Owing to extensive pack ice," he added, "migration was delayed for many individuals who arrived at colonies too late to breed. About 30 percent of the normal number of pairs laid eggs."
A smaller colony of Adélies at Cape Royds completely failed to reproduce this year because of the massive amount of fast ice in McMurdo Sound during the spring, said Ainley.
Looking to the Future
Ainley and his colleagues are now tracking Adélies that are wearing tiny radio transmitters, and are banding more penguins so researchers can identify them in future studies.
Ainley and Kooyman both said they have learned more about the life histories and migrating patterns of the birds.
Penguins can live up to 20 years, and the failure of one breeding season does not necessarily spell doom for the colonies affected by the ice this year. But whether the unusual icy conditions and the obstacles they pose are part of a trend that could have serious effects on Antarctic penguin populations in the future is unclear.
"We've never seen icebergs this big," said Kooyman, who believes the events may be associated with global warming. "The Ross Ice Shelf is developing cracks, and there's some evidence that the decay of the West Antarctica ice shelf could be very rapid.
"It gives you pause," he said, "to think about what we are witnessing."
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