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Periglacial Environments

Periglacial environments are characterized by intense frost, often combined with the presence of perennially frozen ground, or permafrost. Periglacial environments are restricted to areas that experience cold, but essentially nonglacial, climates. They include (a) the polar deserts and semideserts of the High Arctic and the icefree areas of Antarctica; (b) the extensive tundra zones of high latitudes; (c) the northern parts of the boreal forests of North America and Eurasia; (d) the alpine zones that lie above the timberline and below the snowline in mid- and low-latitude mountains; (e) the high-elevation montane environments of Central Asia, the largest of which is the Qinghai-Xizang (Tibet) Plateau of China; and (f) small oceanic islands in the high latitudes of both the polar regions.

In climatic terms, periglacial environments are areas where the mean annual air temperature is less than +3 °C. This can be subdivided into environments where frost action dominates (mean annual air temperature less than −2 °C) and those areas in which frost action occurs but does not necessarily dominate (mean annual air temperature between −2 °C and +3 °C). Fundamental to most periglacial environments is the freezing of water and its associated frost heaving and ice segregation.

Periglacial environments occupy approximately 20% of the world's land area. However, their human population is only 7 to 9 million, mostly living in Russia, or only 0.3% of the world's population. Thus, the larger importance of periglacial environments lies not in their spatial extent but in their natural resources. For example, the old Pre-cambrian basement rocks that outcrop as huge tablelands in both Canada and Siberia contain precious minerals, such as gold and diamonds, and sizable deposits of lead, zinc, and copper, while the sedimentary basins of Western Siberia, Northern Alaska, and the Canadian High Arctic contain large hydrocarbon reserves. A second reason why periglacial environments are of significance is their place within the cryosphere (i.e., snow, ice, frozen ground, sea ice) and the critical role that the cryosphere plays in global climate change.

Periglacial Ecosystems

The most extensive periglacial environments are those of the high northern latitudes (Figure 1). These can be regarded as either arctic or subarctic in nature. The boundary between the two approximates the northern limit of trees, the so-called tree line. This is a zone, 30 to 150 kilometers in extent, north of which trees are no longer able to survive. North of the tree line, the terrain is perennially frozen, and the surface thaws for a period of only 2 to 3 months each summer to depths that, in vegetated areas, may be as little as 30 to 50 centimeters. Ecologists refer to the vegetated but treeless arctic as tundra (see lowland tundra photo). Where Precambrian basement rocks occur, as in the tablelands of Northern Canada and Siberia, the tundra is barren. At higher latitudes, the tundra progressively changes into semi-desert and, ultimately, into polar desert terrain (a “frost-rubble” zone) in the high latitudes of Arctic Canada, Northeast Greenland, Svalbard, and Novaya Zemblya.

The alpine environments of the midlatitudes are less extensive but equally distinct, being dominated by both diurnal and seasonal effects and by much higher solar radiation. In such environments, the timberline constitutes the boundary between the alpine and subalpine. Alpine environments are dominated by steep slopes, tundra (alpine) plants, rock outcrops, and snow and ice. The montane environments of Central Asia differ from the alpine environments in that they are more extensive, are far more arid, and consist of steppe grasslands and intervening desert-like uplands. In Antarctica, the relatively small ice-free areas are unusual, being essentially polar deserts or rock-rubble surfaces that are kept free of snow and ice by sublimation from strong katabatic winds that flow outward from the Antarctic ice sheet.

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