Whales, walruses, seabirds and fish are struggling to survive the changing climate of the Bering Sea, their northern feeding grounds perhaps permanently disrupted by warmer temperatures and melting ice, scientists reported Thursday in the journal Science.
By pulling together a broad range of observations and surveys, an international research team concluded that it is witnessing the transformation of an entire ecosystem in a region home to almost half of U.S. commercial fish production.
All in all, the researchers said, the Arctic climate of the northern Bering Sea is in full retreat, yielding to the sub-Arctic system of the south.
The changes are profound and perhaps irreversible, even if cold weather eventually returns, the researchers said.
"It really is changing," said University of Tennessee ecologist Lee W. Cooper, a coauthor of the Science study. "We can see the impact."
Wildlife experts long have worried about the response of single species to the region's fickle weather patterns, which can fluctuate dramatically from one decade to the next. From season to season, they have cataloged puzzling but apparently unrelated die-offs of seabirds, rare algal blooms and odd migration patterns.
For the first time, however, U.S. and Canadian researchers, led by Jacqueline M. Grebmeier, a specialist in polar biological oceanography at the University of Tennessee, systematically assessed the long-term effect of warmer temperatures on the sea life between the Alaska coast and St. Lawrence Island in the northern Bering Sea.
Funded by the National Science Foundation and the National Oceanic and Atmospheric Administration, the researchers analyzed two decades worth of wildlife observations and tied them to climate records that documented warmer water currents, rising air temperatures and vanishing ice packs.
Overall, the Arctic is warming at twice the average global rate.
Until recently, the northern Bering Sea was dominated by a vast subsurface pool of cold water at a temperature of 32 degrees Fahrenheit.
During the last 12 years, near-freezing water temperatures along the Bering Sea floor have grown steadily warmer.
By 2004, the surface water temperature had reached a high of 50 degrees.
Consequently, the local sea ice melts three weeks earlier than in 1997, records of recent years show. Last year, Arctic ice retreated farther than in 25 years of satellite monitoring.
"Here we put all the pieces of the puzzle together," Grebmeier said.
The researchers found that by 2002, Pacific gray whales were fleeing northward to feed in cooler currents, while pink salmon by the millions swarmed into warmer waters the whales had abandoned.
Bottom-dwelling species, unable to adapt, were destroyed in large numbers. The broken shells of a vanished clam species carpeted the sea floor.
As sea ice diminished, breeding grounds for seals were disrupted and populations plummeted. Polar bears started to drown. Walruses, accustomed to diving in the shallows to feed along the sea bottom, found themselves adrift on broken ice floes in waters 6,500 feet deep. The animals starved.
In its essence, the report confirms the anecdotal evidence of Yupik hunters of St. Lawrence Island. Every winter, they told researchers, the winds have been warmer, the ice pack thinner and more unstable. Every year, there is more open water.
Such widespread disruptions may be a symptom of climate changes throughout the Arctic, Grebmeier said.
"It is symptomatic of what may be happening further north," she said, "and that may have global implications."