Permafrost is defined on the basis of temperature as ground (i.e. soil and/or rock) that remains at or below 0°C for at least two consecutive years . Permafrost is most commonly associated with various types of ice (ice-bonded permafrost), but if there is insufficient interstitial water the permafrost is dry (dry permafrost).
Permafrost distribution in Canada shows a latitudinal zonation (Figure 1). In the south it is discontinuous, while in the north it is continuous. Two zones are identified in the discontinuous portion, the Sporadic and the Widespread/Extensive Discontinuous Permafrost Zones [16, 18, 24]. In its most southerly occurrence the permafrost is sporadic, occurring under less than 30% of the area , and is found mainly in peatlands as islands in a generally unfrozen terrain (Sporadic Discontinuous Permafrost Zone, SPZ). Farther north the permafrost becomes widespread, occurring under 30-80% of the landscape , and is found in both organic (peatlands) and mineral terrain (Widespread Discontinuous Permafrost Zone, WPZ). In the most northerly regions all land surfaces, even under shallow water bodies, are underlain by permafrost (Continuous Permafrost Zone, CPZ). South of the southern limit of the Discontinuous Permafrost Zone permafrost can occur at high elevations in mountainous areas. These areas belong to the Alpine Permafrost Zone. The thickness of the permafrost varies greatly, depending on location. It is no more than a few meters thick in the southern part of the SPZ, increasing to 30-50 m in the WPZ, and can be as deep as 500 m in the CPZ .
The mean annual air temperatures (MAAT) associated with these permafrost zones in Canada range from 0° to -5.5°C in the SPZ , -5.5° to -8.3°C in the WPZ , and -8.3° to -17.0°C in the CPZ .
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