June 4, 2005
Permafrost May Be Shrinking Arctic Lakes
ANCHORAGE, Alaska -- Arctic lakes are shrinking, and melting permafrost brought on by higher temperatures may be the reason, according to a research paper.
California, Alaska and New York researchers compared satellite images spanning 30 years of more than 10,000 large lakes over 200,000 square miles in Siberia. They concluded that lakes where permafrost remains frozen are growing.But where permafrost has thinned or completely melted, lakes are shrinking or disappearing, a change that could affect habitat for migratory birds.
The research is outlined in a paper, "Disappearing Arctic Lakes," published in the journal "Science" on Friday.
Permafrost is ground that remains below freezing temperature all year. It may contain ice, but with or without it, the ground remains impermeable.
As temperatures rise, ice and snow melt and put more water into Arctic lakes. Larry Smith, an associate geography professor at UCLA, said researchers expected to measure more, larger lakes, not fewer.
"We were expecting to see more of the same," he said.
They now believe additional lake surface brought on by melting is just the first part of the process. In the southern parts of the Siberia study area, the permafrost itself is believed to be melting.
Researchers mapped four zones of varying amounts of permafrost. As they looked south, where permafrost thinned or disappeared, lakes were shrinking. That indicates melt water is seeping into soil as permafrost decreases, Smith said.
Larry Hinzman, a University of Alaska Fairbanks researcher, found a similar phenomenon at tundra ponds on Seward Peninsula near Council in western Alaska. Surface pond area there decreased over the last 50 years.
"This is the first paper that demonstrates that the changes we are seeing in Alaskan lakes in response to a warming climate is also occurring in Siberia," Hinzman said.
The latest study was aimed at quantifying the Alaska observations on a larger basis, Smith said.
Small, shallow tundra lakes that rest on permafrost are "ephemeral," coming and going with variations in weather, Smith said. Researchers instead studied lakes of 40 hectares or about 100 acres, Smith said.
The study compared satellite digital images from 1973 to images from 1997-98. Researchers entered images into computers and "co-registered" them with modern data by manually picking control features - structures that can be confidently identified in both photos, Smith said.
The number of 100-acre lakes fell from 10,882 to 9,712, a decline of 1,170 or 11 percent. The scientists said 125 disappeared, replaced by vegetation.
Other lakes shrank. The overall loss of lake surface area was approximately 6 percent, researchers said.
Lakes grew in northern areas of the study, where permafrost remained intact.
Varying effects on lakes is not a conflict but different phases of the process, Smith said.
"We're proposing that it's all part of a continuum," Smith said.
In regions where permafrost has thinned or disappeared, surface soils also become drier as permafrost degrades, Hinzman said.
"The changing lakes are a consistent, measurable indication of the overall changes to hydrology in the Arctic," Hinzman said. "The loss of surface water will inevitably impact local ecosystems, which will have a cascading effect.
Changes could include loss of migratory bird habitat. Huge numbers of migratory waterfowl fly north for breeding.
Changes could affect subsistence hunting activities and local and regional atmospheric conditions, causing more localized wind and more frequent and more severe wildfires, Hinzman said.
Researchers would like to expand their study and will seek funding for lake work in Alaska, Canada and eastern Russia, Smith said.
The other co-authors of the study were Yongwei Sheng, an assistant professor of environmental science and forestry at State University of New York, and Glen MacDonald, chairman of UCLA's geography department.
The study was paid for by the National Science Foundation.
Arctic warming has been documented in both Alaska and Siberia. John Walsh, president's professor at the University of Alaska Fairbanks International Arctic Research Center, said spring temperatures at Nome near Hinzman's research at Council have risen 4.3 degrees since 1950. At locations in Interior Alaska and northern Siberia, the spring warming has been closer to 6 degrees, he said.