The Distribution of Permafrost and Its Relation to Air Temperature in Canada and the U.S.S.R.

Permafrost is a widespread phenomenon in the northern parts of North America and Eurasia, and in Antarctica. Between 40 and 50 per cent of Canada's total land surface of 3.8 million square miles is underlain by permafrost. The total land area of the U.S.S.R. exceeds 8 million square miles of which 47 per cent is underlain by permafrost (Tsytovich 1958). Because of the great extent of this phenomenon knowledge of its distribution is of vital concern to both countries. The distribution of permafrost varies from continuous in the north to discontinuous in the south. In the continuous zone permafrost occurs everywhere and is hundreds of feet thick. The continuous zone gives way to the discontinuous zone in which permafrost exists in combination with some areas of unfrozen material. The discontinuous zone is one of transition between continuous permafrost and ground having a mean temperature of above 32°F. In this zone permafrost may vary from a widespread distribution with isolated patches of unfrozen ground to predominantly thawed ground containing islands that remain frozen. In the southern area of this discontinuous zone (called the zone of sporadic permafrost in other countries) the permafrost occurs as scattered patches, is only a few feet thick, and has temperatures close to 32°F. The thickness of permafrost varies with the locality; it is greatest in the Arctic and thins out near its southern limit. In Canada, at Resolute, Cornwallis Island, N.W.T., it is thought to be about 1,280 feet thick (Misener 1955); at Norman Wells, N.W.T. it is about 150 feet thick, and at Hay River, N.W.T. it is only 5 feet thick. In the U.S.S.R. permafrost exceeds 500 metres (1650 feet) in thickness in the Taymyr Peninsula. In southeastern and southwestern Siberia it is less than 25 metres (83 feet) thick (Tsytovich 1958). ... It is evident that there is not a close relationship between permafrost distribution and air temperature. Because so many factors - climatic, surface, and geothermal - affect the occurrence of permafrost, prediction of its distribution cannot be based solely on this one climatic factor. Nevertheless, examination of the southern limit of permafrost as known at present and of air temperature pattern reveals the existence of a very broad relationship. The mapping of the distribution and the delineation of the southern limit of permafrost is a problem with many aspects. What defines the southern boundary and how can it best be shown cartographically? Does a pereletok (a shallow spot of frozen ground that persists for several years), which persists for a number of years and then disappears, belong to the permafrost? How many years must a pereletok persist to be classed perennially frozen ground? Can relict permafrost be distinguished from a pereletok in the field? These and other problems make it difficult to locate the southern limit of permafrost. A large number of field investigations of permafrost and observations of ground temperature are required to give detailed knowledge of its areal distribution and thickness for mapping purposes. In Canada this work is still in the early stages, but already the general areal distribution of the two permafrost zones is becoming evident.