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Thaw slump of high Arctic permafrost rises

13 Aug 2019
Permafrost thaw slump
Permafrost thaw slump (Image courtesy: Melissa Ward Jones)

Situated around 800 km from the North Pole, Eureka is one of the coldest inhabited places in the world. With a mean annual air temperature of -19.7° C and polar night lasting from mid-October until the end of February, this Arctic weather station on Ellesmere Island has just a handful of residents. Now research shows that climate change is biting even here.

Ellesmere and Axel Heiberg Islands are the two most northerly islands in the Canadian high Arctic. Permafrost here is over half a kilometre thick and has a mean annual temperature of -16.5°C at its surface. It’s been this way for thousands of years; people assumed that the cold temperatures would keep permafrost in the region safe.

Wayne Pollard from McGill University, Canada, has monitored this permafrost since 1989, flying the same transect from the Eureka Weather Station by helicopter every summer. He scans the landscape beneath for the tell-tale features where permafrost thaw has made horseshoe-shaped “bites” known as retrogressive thaw slumps.

Combining this long-term record with high-resolution satellite imagery showed that high Arctic permafrost is not as stable as we thought.

Until 2003 Pollard generally spotted somewhere between 50 and 100 slump features every summer. Since then numbers have increased; on three occasions there have been over 200 slumps each year.

Pollard used GPS measurements and satellite imagery to measure the rate of headwall retreat for some of the more recent slumps, working with colleagues from McGill University and University of Alaska Fairbanks, US. These features are growing fast, the team found, at up to 26 m per year.

“These are dramatic landforms as they appear suddenly and grow quickly,” says Melissa Ward Jones of McGill University. “The land surface lowers as ground ice melts and releases large volumes of sediments that get displaced downslope and can enter water bodies and impact aquatic ecosystems. They also impact terrestrial ecosystems because often vegetation that grows after the disturbance is different.”

Comparing slump frequency with average July temperatures suggests that recent record summer warmth – with average air temperatures of 7 °C or more – has been a trigger. “The widespread increases [in slumps] we’ve seen in the last 16 years is likely attributed to increases in summer air temperatures,” says Ward Jones.

These exceptionally warm summers appear to have driven permafrost thaw despite average annual temperatures remaining fairly steady over time.

“I think we should approach these high Arctic observations as a warning sign to changes that will be experienced in southern areas, because an area we think of as being really cold and stable is undergoing rapid change,” says Ward Jones.

The team published the study in Environmental Research Letters (ERL).

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