Where Are Arctic Soils Defrosting? The Thermokarst

Arctic sea ice that survives the summer and remains year round—called perennial sea ice—is melting at the alarming rate of 9 percent per decade, and early findings suggest that summertime melting of Arctic sea ice in 2003 is on pace to rival last year’s low. Satellite measurements show that most of the Arctic warmed significantly in the 1990s compared to the 1980s. Such shifts in the Arctic are likely early indications of a global climate in a state of flux.

Credit: NASA

Unlike previous studies that focused on the small scale of thermokarst, this one spans thousands of kilometers around the Arctic, said David Olefeldt, lead author and a professor at the University of Alberta (Canada). To start to form a picture of where thermokarst has formed or is most likely to form, Olefeldt and colleagues merged maps of land topography, ground ice conditions, and biome types. The new maps pinpoint areas that are most likely to release more greenhouse gases as they thaw. These are also places where habitats will change and infrastructure issues—such as structurally damaged roads and bridges—might arise.

acquired 1990 – 2010

The maps above, which show the northernmost latitudes of North America and Eurasia, were created using data from the study. The map below offers a closer look at Siberia. The different colors reflect the types of landscapes—wetlands, lakes, hillslopes, etc.—where thermokarst is likely to be found today and where it is most likely to form in the future. The darker the color, the higher percentage of the landscape is covered by that landform. Coverage is classified as very high when 60 to 100 percent of the land fits into that category. High means 30 to 60 percent coverage; Moderate is 10 to 30 percent, and low is below 10 percent. Hillslope thermokarst landscapes do not reach very high levels, the researchers found.

In places where the permafrost has melted and become thermokarst, wetlands were the most prevalent landform, accounting for nearly 8 percent of the northern landscape. Lake thermokarst covered 7 percent and hillslope thermokarst was prevalent in 5 percent of the area. However, thermokarst landscapes sometimes overlapped, accounting for the marbled appearance of the maps.

While the three thermokarst landscapes have similar total areas, the paper notes, “their distributions differ with regards to both their spatial concentration and their relations to current climate conditions.” Wetland thermokarst has ‘very high’ coverage in boreal peatland regions like the West Siberian Lowlands and the Mackenzie River Valley. For lake thermokarst, ‘very high’ coverage areas include the Yukon Delta, the Alaska North Slope, and coastal regions along the Kara Sea, Laptev Sea, and East Siberian Sea. The map shows ‘moderate’ and ‘high’ regional coverage of hillslope thermokarst landscapes in tundra regions, including the Seward Peninsula and North Slope of Alaska, the Mackenzie River Valley, and the Canadian Arctic Archipelago.

acquired 1990 – 2010

NASA Earth Observatory maps created by Jesse Allen, using data provided by David Olefeldt, University of Alberta. Caption by Pola Lem.