Thawing permafrost causes ground to sink in cold regions

Thawing permafrost causes ground to sink in cold regions

More needs to be done to better understand rapidly changing Arctic landscapes that are sinking as climate-driven permafrost thaw penetrates deeper, according to new research by University of Alaska Fairbanks scientists and others.

International climate monitoring organizations have no uniform standard for measuring ground subsidence, leading to an underestimation of thaw depth and therefore an underestimation of how permafrost responds to climate change, the international team writes in a research review published Jan. 7 in Environmental Research Letters.

Thaw-driven subsidence can lead to the release of carbon into the atmosphere, damage to infrastructure, and changes in water flow, among other impacts.

The team analyzed thaw subsidence data collected from sites in Alaska, Canada and Russia as part of long-term permafrost monitoring by others.

The researchers add that an international standardized method for measuring permafrost thaw ground subsidence is needed.

The report is authored by Dmitry Streletskiy of George Washington University. The 11 co-authors include three from UAF: research assistant professor Louise Farquharson of the Geophysical Institute, assistant professor Simon Zwieback of the Geophysical Institute and College of Natural Science and Mathematics, and research assistant professor Go Iwahana of the International Arctic Research Center.

"Permafrost thaw subsidence is important because it has major implications for society, the economy and the environment," Zwieback said. "It threatens infrastructure such as homes, schools, roads and runways."

"The costs to maintain, repair and insure infrastructure affected by permafrost thaw are projected to continue to increase rapidly in Alaska and across the Arctic," he said.

The authors write that determining thaw subsidence estimates through regular field studies, remote sensing measurements and improved modeling is critically needed for assessing the permafrost response to climate change.

Farquharson notes that the Fairbanks North Star Borough in Alaska, for example, is expected to see significant subsidence over coming decades as warming leads to the melt of large ice wedges at the base slopes of valleys. Few annual ground subsidence measurements are taken in the Fairbanks region, however, so knowledge about where that subsidence will occur is limited, she said.

The team's analysis of previously published data found widespread long-term subsidence at permafrost-affected Northern Hemisphere landscapes that were undisturbed by infrastructure or other development.

Subsidence rates generally range from 0.2 to 2 centimeters annually. Rates of 3 centimeters or greater were found in areas with significant ground ice near the top of permafrost and a thin protective organic layer that allows heat through, the review found.

"Permafrost thaw subsidence can inform us about where massive ground ice is," Farquharson said. "A major limitation in our understanding of future Arctic landscape response to thaw is that our understanding of massive ground ice distribution is very limited."

The amount of subsurface ground ice varies greatly, Farquharson said.

"By looking at the location and magnitude of subsidence, we can make inferences about ground ice distribution and explore how it relates to above-ground properties," she said.

Thaw subsidence in areas with large amounts of excess ground ice can promote development of thermokarst, a rapid thaw process. "Excess" means the ground ice exceeds the pore space available in the soil or sediment. It is a common condition in permafrost regions.

A significant increase in thaw subsidence is usually associated with natural or human-caused surface disturbance, such as vegetation removal, the addition of surface gravel or concrete, or snow accumulation, the authors write. Seasonal subsidence at a site on Alaska's North Slope with tundra disturbed by Dalton Highway construction was 8.6 to 19.9 centimeters, for example, which is 1.3 to 1.9 times higher than at a nearby undisturbed tundra location.

The team did not attempt to describe how subsidence varies by location and over time across the Northern Hemisphere, leaving that for additional studies.

The authors conclude with a warning: "It is evident that permafrost thaw subsidence will play an increasingly important role under warming climatic conditions."

ADDITIONAL CONTACTS: Simon Zwieback, 907-474-5549, [email protected]; Louise Farquharson, 907-474-5623, [email protected]

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