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IN DEPTH Thermokarst ponds (seen here in summer) release CO2 and methane, two potent greenhouse gases. polystyrene or a good quilted jacket,” he explains. “In winter, it acts as a buffer between the permafrost and the outside air, preventing the ground from cooling as much as the air. However, its insulating properties vary according to its thickness, density, and structure. A very thick layer of snow provides greater protection than a thinner layer, while low-density snow is a better shield against the cold than compact snow.” Dominé pulls out his snow probe: the layer is a mere 12 centimeters deep at the top of the palsa. He then sticks a temperature probe into the snow. At the interface with the permafrost, the temperature reaches -9°C, which is 15°C warmer than the air temperature. Using a small shovel of known capacity (100 cm3), he gathers some snow, weighs it on a scale, and works out its density. “It’s still fairly light,” he observes. The demonstration is repeated at the foot of the palsa, where the snow is considerably thicker, reaching a depth of 80 centimeters. The temperature of the permafrost where it comes into contact with the snow is -1°C. It is on the verge of melting. There is a reason for his demonstration: with climate change, not only do air temperatures rise but precipitation (rain and snow) also increases as a result of greater evaporation. “It’s counter-intuitive: everyone in the Arctic can see that there are fewer days of snow,” Dominé points out. “Yet when snow does fall, it does so in much larger amounts than it used to and tends to become deeper, causing the permafrost to warm up.” Another factor to take into account for understanding the effects of the snow cover is vegetation. With rising air temperatures, plant cover expands while trees and bushes migrate northwards. And more vegetation means deeper snow. “Windblown snow tends to accumulate in the presence of vegetation, especially under trees,” Dominé explains. In addition, vegetation, which is dark, reduces the reflectivity of snow (sending less heat and solar radiation back into space), and substantially alters its optical properties. All these parameters will be accurately measured as part of the APT project. … © CEN/TAKUVIK 36 CNRS INTERNATIONAL MAGAZINE


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