"Satellite image analysis is a great tool to measure the landscape patterns created by permafrost thaw over large spatial scales," Fay Belshe of the University of Florida told environmentalresearchweb. "We demonstrated that it is possible to detect rather small permafrost thaw features using high-resolution imagery. Previous work has been limited to detecting relatively large and visually distinct features."

This is an important step, the researchers say, because a diversity of landscape features can form as permafrost thaws, and scientists must be able to quantify these changes accurately.

Together with colleagues from the University of Florida and the University of Fairbanks, Belshe used images from the IKONOS satellite with a resolution of around 3 m. In this way, the scientists analysed 10.4 square km of land featuring discontinuous permafrost in the Eight Mile Lake watershed in an upland region of Interior Alaska. They also carried out assessments in the field.

The satellite images indicated that 12% of the Eight Mile Lake watershed had become thermokarst, mainly in valleys containing tussock tundra, where the soil organic layer is relatively thick. The team estimated that 35% of the 3.7 square km the satellite images revealed to be tussock tundra had transitioned to thermokarst.

 The thermokarst features were generally gullies 300–700 m long and 1–5 m wide draining from the valleys towards the lake, and containing ground subsidence less than 1 metre. Subsided ground tends to contain more water, increasing the soil's thermal conductivity.

"Our finding that permafrost thaw features are developing in the carbon-rich areas of the watershed and altering the hydrology of the landscape in ways to increase the seasonal thawing of soil has very important implications for the carbon balance of the ecosystem," said Belshe. "By exposing more previously frozen carbon to above-freezing temperatures and extending the time it remains unfrozen (because it takes longer to refreeze the greater volume of soil), permafrost thaw is increasing the vulnerability of the soil carbon pool."

According to Belshe, vast quantities of organic carbon are currently stored in permafrost soils due to the long, harsh winters of the region and poorly drained soils, which create conditions that slow decomposition relative to plant production. Release of this stored carbon to the atmosphere by permafrost thaw could create a strong positive feedback to climate change.

"Now that we have demonstrated the feasibility of detecting small, irregular thaw features with high-resolution imagery, we hope this methodology can be extended to other areas," said Belshe, detailing, as an example, the 64,000 ha Toklat Basin to the west of the team's study site. "Additionally, Guido Grosse has a highly active research group at the University of Alaska, Fairbanks that is doing cutting-edge research using remote sensing to detect the impacts of climate change in Arctic and Subarctic terrestrial environments."

The team reported the results in Environmental Research Letters (ERL) .

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