SAN FRANCISCO---Dec. 15, 1996--The arctic tundra's vast carbon reservoir has sprung a leak.
Recent experiments on Alaska's North Slope show that carbon molecules have started moving out of the tundra and into the atmosphere via a network of lakes, streams and rivers in larger amounts than ever before.
"Our latest data show that the arctic is no longer a strong sink for carbon," said George W. Kling, University of Michigan assistant professor of biology. "In some years, the tundra is adding as much or more carbon to the atmosphere than it removes, although the total amount of carbon released to the atmosphere is still quite small.
"However, the amount of carbon stored in arctic tundra equals almost one-third of the total carbon in Earth's atmosphere," Kling added. "The concern is what will happen in the future as global warming increases and melting permafrost exposes more of this buried carbon to be respired and released into the atmosphere."
Kling is one of several scientists working on the Gas Flux Study, part of the National Science Foundation's Arctic System Science (ARCSS) Program. Kling's research team studies how carbon dioxide and methane move between land, water and the atmosphere in the Kuparuk River Basin---an 8,100-square-kilometer area of Alaska's North Slope extending from the Brooks Range to the Arctic Ocean.
Kling and other scientists involved in the ARCSS Program presented data from this summer's field research during a special session of the American Geophysical Union meeting held here today.
"We have known for some time that arctic lakes and streams are supersaturated with carbon dioxide and methane, and that this excess gas diffuses into the atmosphere," Kling said. "What we didn't know is just how much carbon is entering the atmosphere through contact with surface waters."
Using new field measurements and computer models developed at the Ecosystems Center in Woods Hole, Mass., ARCSS scientists have been able to quantify for the first time the amount of carbon flux from the arctic tundra into the global ecosystem.
Kling's data show that for each square meter of tundra five grams of carbon are being lost from surface waters annually in the Kuparuk watershed. Of that amount, almost half of the carbon leaching out of the tundra into lakes and rivers is released directly to the atmosphere in the form of carbon dioxide or methane. Rivers carry the other half to the Arctic Ocean.
"Arctic plants are still taking in carbon dioxide from the atmosphere during photosynthesis," Kling explained. "But instead of much of that carbon remaining locked up in soil, more of it is being respired back to the atmosphere." Kling added that scientists still have a great deal to learn about the complex biogeochemistry of the arctic ecosystem. For example, how will rising temperatures affect respiration rates in arctic soils? If the tundra starts to dry out, will that increase the amount of carbon dioxide released to surface waters or the atmosphere? What impact will increasing amounts of carbon dioxide and methane from arctic tundra have on global warming?
"As average global temperatures continue to increase, we expect to see the most dramatic changes occurring in the arctic. To prepare for these changes, we need to know a lot more about controls on the exchange of carbon between land, water and the atmosphere than we do now."
Other scientists working with Kling on his part of the NSF Gas Flux Study include John Hobbie and Ed Rastetter of the Ecosystems Center in Woods Hole, Mass., Terry Chapin of the University of California at Berkeley, and Walter Oechel of San Diego State University.