April 5, 2006
Several biological changes in the northern Bering Sea ecosystem appear to be caused by increasing air and seawater temperature changes, according to U.S. and Canadian researchers. The changes may have lasting and irreversible effects on wildlife and residents in the area.
The northern Bering Sea is experiencing a shift from arctic to sub-arctic conditions, noted the researchers in an article published in the March 10 issue of Science.
“We’re seeing that a change in the physical conditions is driving a change in the ecosystems,” said Jackie Grebmeier, a researcher at the University of Tennessee and one of the paper’s co-authors. Grebmeier is also chief scientist for the Western Shelf-Basin Interactions research project, which has studied changes in the carbon balance of offshore areas of the Alaskan Arctic and related effects on the food chain.
The northern Bering Sea provides critical habitat for large populations of sea ducks, gray whales, bearded seals and walruses, all of which depend on small bottom-dwelling creatures for sustenance. These bottom-dwellers are accustomed to cold water temperatures and long periods of extensive sea ice cover.
The shift from arctic to sub-arctic conditions favors both water-column and bottom-feeding fish and other animals that previously have stayed in more southerly, warmer sea waters.
As a result, the ranges of region’s typical inhabitants can be expected to move northward and away from the small, isolated Native communities on the Bering Sea coast that subsist on the animals.
The report, said Grebmeier, considers the potential effects of a changing Arctic climate primarily from a life-sciences perspective, instead of focusing on the physics of climate change. “It’s a biology-driven, integrated look at what’s going on,” said Grebmeier.
Other researchers in the area supported by the National Science Foundation and the National Oceanic and Atmospheric Administration contributed data collected by the Bering Strait Environmental Observatory, which annually samples waters in the northern Bering Sea to assess the biological status of productive animal communities on the sea floor.
These highly productive waters, according to NSF, act as “sponges” for carbon dioxide, absorbing quantities of the gas that otherwise would remain in the atmosphere where it would be expected to contribute to warming.
If the biological trends observed by the researchers in the northern Bering Sea persist and are not reversible, the accompanying shift in species and ecosystem structure could have important implications for the role of the sea as a “carbon sink,” said the NSF.
The changes researchers are observing are not uniform throughout the Bering Sea. “The northern Bering Sea ecosystem is changing as well as that in the southeast,” said James Overland, a co-author of the paper and an oceanographer at NOAA’s Pacific Marine Environmental Laboratory. “In the southeast, fish population and (bottom-dweller) changes are happening in the context of a complete loss of sea ice. But in the northern Bering Sea, ecological changes are occurring in the context of shifts in the quality of the sea ice. The ice there is broken and thin compared with ice floes that were more the norm.”
Satellite observations and other measurements, for example, combined with observations of native Yupik hunters, confirm that sea ice extent and thickness have become greatly reduced in recent years.
Additionally, observations by scientists on the 2004 Western Shelf-Basin Interactions research expeditions confirm that walrus mothers were leaving their pups when sea ice normally used as a summer resting platform retreated to the north.
Shifts in fish populations have also been observed, including the appearance much farther north of juvenile pink salmon in rivers that drain into the Arctic Ocean. Salmon feed on pollock, a species that is beginning to appear in larger numbers in the northern Bering Sea, possibly in response to warmer ocean temperatures.
“What we are seeing,” said Grebmeier concluded, “is a change in the boundary between the sub-Arctic and the Arctic ecosystem. The potential is real for an ecosystem shift that will be felt father north.”
However, Overland noted that continued observations are needed to fully understand the scope and potential permanence of the changes. “Both physical and biological indicators need to be watched closely over the next few years to track the persistence of changes in the context of natural variability,” he said.
Source: National Science Foundation.