The Bering Sea -- which lies just south of the Arctic Circle between Russia and Alaska -- is getting warmer, and the heat is already having a huge impact on marine wildlife there, say scientists in a study published today in the journal Science.
Among the findings is a declining food supply for populations of walrus, gray whales and sea ducks in this northern sea.
It appears that these animals now have to compete with fish populations that have pushed into their territory, said the study's lead author, Jacqueline Grebmeier of the University of Tennessee.
Near-freezing water in the northern Bering Sea has traditionally kept bottom-feeding fish like halibut and flounder farther south in warmer waters. But as temperatures have risen -- as much as 6 degrees Fahrenheit at the sea floor -- the fish have moved farther north, where they eat the food favored by the larger marine mammals.
Because the Bering Sea is relatively shallow -- less than 200 feet deep -- researchers said that that marine life balances can be easily upset by minor changes.
"This demonstrates the biological effect in an area so shallow that it doesn't take much to fundamentally change the system," said Lee Cooper, chemical oceanographer at the University of Tennessee and co-author of the study. "It's a little sobering."
But it also looks as if the animals are trying to adapt to the changes.
The report presents evidence that "gray whales have responded by moving their primary foraging area northward," and cites a "surprising detection" of gray whale calls in the winter of 2003-2004 near Barrow, Alaska, a place where local hunters report "more numerous gray whales than in any time previously."
But there is a limit to how far north the whales and other mammals can go.
"You eventually fall off the continental shelf," Grebmeier said. "They don't have to go very far north of Barrow and they're into that much deeper water basin. And they can't find food that deep."
In addition, the report finds walruses have suffered from a lack of pack ice, where they rest while hunting for clams and shellfish. As the ice retreats, the walruses have to swim farther for food.
The end result, say scientists, is that an Arctic ecosystem is being transformed into a sub-Arctic ecosystem, part of a well-documented warming trend in the Arctic region.
The annual average Arctic temperature has "increased at almost twice the rate as that of the rest of the world over the past few decades," according to the multination Arctic Climate Impact Assessment released in late 2004.
The report also found that "increasing concentrations of carbon dioxide and other greenhouse gasses due to human activities, primarily fossil fuel burning, are projected to contribute to additional Arctic warming" of about 7.2 degrees to 12.6 degrees Fahrenheit.
The Science report was released on the same day that the National Oceanic and Atmospheric Administration released figures showing the 2005-2006 winter season was the fifth-warmest on record for the contiguous United States.