Concept information
Preferred term
permafrost
Definition
- According to the definition from the International Permafrost Association, permafrost is defined as ground (soil or rock and included ice or organic material) that remains at or below 0°C for at least two consecutive years. According to the above definition, sediments or crystalline rocks below 0°C are in permafrost conditions. Such conditions can occur below the present glacial bed or below the base of glacial ice at the time of Pleistocene glaciations (Laurentide, Fennoscandian, ...). Permafrost is perennially frozen ground which underlies 20–25% of the exposed land surface of the earth in regions with cold climates. Time scales for changes in permafrost thicknesses (and thus occurrences and distribution) range from decades to millennia (Lachenbruch et al., 1982). Permafrost is covered by the active layer (the top layer of ground, typically <1 m in thickness, that freezes and thaws annually) where biological activity occurs. (Adapted from: J. Majorowicz (2012), Bulletin of Geography. Socio-economic Series, Vol. 5, 7–28. and M. C. SERREZE et al. (2000), Climatic Change, 46(1), 159-207.))
- Permafrost (from perma- 'permanent', and frost) is soil or underwater sediment which continuously remains below 0 °C (32 °F) for two years or more: the oldest permafrost had been continuously frozen for around 700,000 years. While the shallowest permafrost has a vertical extent of below a meter (3 ft), the deepest is greater than 1,500 m (4,900 ft). Similarly, the area of individual permafrost zones may be limited to narrow mountain summits or extend across vast Arctic regions. The ground beneath glaciers and ice sheets is not usually defined as permafrost, so on land, permafrost is generally located beneath a so-called active layer of soil which freezes and thaws depending on the season. Permafrost contains large amounts of dead biomass that have accumulated throughout millennia without having had the chance to fully decompose and release their carbon, making tundra soil a carbon sink. As global warming heats the ecosystem, frozen soil thaws and becomes warm enough for decomposition to start anew, accelerating the permafrost carbon cycle. Depending on conditions at the time of thaw, decomposition can either release carbon dioxide or methane, and these greenhouse gas emissions act as a climate change feedback. The emissions from thawing permafrost will have a sufficient impact on the climate to impact global carbon budgets. (Adapted from: https://en.wikipedia.org/wiki/Permafrost)
Broader concept
Narrower concepts
In other languages
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French
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permafrost
URI
http://data.loterre.fr/ark:/67375/QX8-VMJ2BL0N-6
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