Saturday, October 21, 2017

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Ice wedges in the Arctic, like the ones seen here in Canada's Northwestern Territories, are rapidly melting. (Photo credit: Wikimedia Commons/Adam Jones) Ice wedges in the Arctic, like the ones seen here in Canada's Northwestern Territories, are rapidly melting. (Photo credit: Wikimedia Commons/Adam Jones)
 


Reshaping the Arctic Landscape

Ground-surface polygons in the Arctic known as ice wedges are rapidly melting, which could lead to runaway drainage in some regions.
By UAF Media Relations and SDSU News Team
 

Ice wedges, a common subsurface feature in permafrost landscapes, appear to be rapidly melting throughout the Arctic, according to a new study published this week in the journal Nature Geoscience.

The ice wedges, which are sunk into the ground and can be the size of a house, gradually formed over hundreds or even thousands of years as water seeped into permafrost cracks. From a top-down view, they form polygon shapes on the ground surface roughly 15-30 meters wide—a defining characteristic of northern landscapes.

The topographic features of these polygons affect drainage, snow distribution and the general wetness or dryness of a landscape.

University of Alaska Fairbanks researcher Anna Liljedahl and her coauthors gathered information about the various types of ice-wedge polygons and how they changed over time across the Arctic. Ice wedge degradation has been observed before in individual locations, but this is the first study to determine that rapid melting has become widespread throughout the Arctic.

“The increased degradation of these ice-wedge polygons might have a substantial impact on the greenhouse gas balance of these systems,” said Donatella Zona, a coauthor on the study and assistant professor at San Diego State University and research fellow and lecturer at the University of Sheffield.

The big thaw

Such thawing could also bring significant changes to the hydrology of much of the Arctic as it alters the ground-surface topography. When the ice wedge tops melt, the ground that surrounds the polygons subsides, allowing water drainage from the polygon centers. This can create a connective drainage system that encourages runoff and an overall drying of the landscape.

“It’s really the tipping point for the hydrology,” said Liljedahl, the study’s lead author. “Suddenly you’re draining the landscape and creating more runoff, even if the amount of precipitation remains the same. Instead of being absorbed by the tundra, the snowmelt water will run off into lakes and larger rivers. It really is a dramatic hydrologic change across the tundra landscape.”

A comprehensive satellite image survey hasn’t been done to determine how common polygon ice wedge patterns are in permafrost areas, but as much as two-thirds of the Arctic landscape is suited to their formation, Liljedahl said.

Rapid shifts

Gradual warming of permafrost has been well-documented in the Arctic, but the polygon study indicates that even a brief period of unusual warmth can cause a rapid shift. At the sites that were studied, ice wedge degradation occurred in less than a decade. In some cases, a single unusually warm summer was enough to cause more than 10 centimeters of surface subsidence—enough to result in pooling and runoff in an otherwise relatively flat landscape.

Vladimir Romanovsky, a UAF geophysics professor who monitored ice wedge degradation for the study at a site in Canada, said the overall conclusions of the study were striking.

“We were not expecting to see these dramatic changes,” he said. “We could see some other places where ice wedges were melting, but they were all related to surface disturbances, or it happened a long time ago. Whatever is happening, it’s something new for at least the last 60 years in the Arctic.”


Other contributors to the study include Julia Boike, Alfred Wegener Institute; Ronald P. Daanen, Alaska Department of Natural Resources; Alexander N. Fedorov, Melnikov Permafrost Institute; Gerald V. Frost, ABR Inc. Environmental Research and Services; Guido Grosse, Alfred Wegener Institute; Larry D. Hinzman, UAF; Yoshihiro Iijima, Japan Agency for Marine-Earth Science and Technology; Janet C. Jorgenson, U.S. Fish and Wildlife Service, Arctic National Wildlife Refuge; Nadya Matveyeva, Russian Academy of Sciences; Marius Necsoiu, Southwest Research Institute; Martha K. Raynolds, UAF; Jorg Schulla, Hyrdology Software Consulting; Ken D. Tape, UAF; Donald A. Walker, UAF; Cathy Wilson, Los Alamos National Laboratory; and Hironori Yabuki, Japan Agency of Marine-Earth Science.