Stream Study Detects Thawing Permafrost

ANN ARBOR, Mich., May 5 (UPI) — U.S. researchers say they have developed a test that uses chemical tracers in stream water to detect the thawing of permafrost.

University of Michigan scientists said one of the worrisome environmental effects of global warming is the thawing of arctic permafrost — soil that normally remains at or below freezing for at least a two-year period and often much longer. Monitoring changes in permafrost has been difficult, but the new test resolves the problem, the scientists said.

Overlying permafrost is a thin “active layer” that thaws every summer and increases in thickness over the years, indicating thawing of permafrost. Currently, the main method for determining thaw depth is with a graduated steel probe. “You stick it in the ground and see when it hits frozen material,” said Professors Joel Blum and George Kling, who with former graduate student Katy Keller conducted the research.

“We were studying the chemistry of soils in … northern Alaska, and we found that once we got below the thickness that typically would thaw during summer, the soil chemistry changed dramatically,” said Blum. “Material that has not thawed since it was deposited by glaciers 10,000 to 20,000 years ago is now beginning to thaw, and when it does, it reacts strongly with water, which it’s encountering for the first time.”

Kling obtained stream water samples that had been collected over an 11-year period. When the samples were analyzed, “we saw really significant changes from year-to-year that were consistent with what you would predict from increasing thaw depth,” Kling said.

Although the method can’t show precisely how much permafrost is thawing, it still can be a useful adjunct to current methods, Blum said.

The research appears in the journal Chemical Geology.

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