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NAME: Frozen ground activity
(With contributions from O. Humlun, E. Melnikov, M. Rasch, N.N. Romanovskii. Revised March 2004)
BRIEF DESCRIPTION: Permafrost is present in 13% (18 million km2) of the world's soils, and beneath nearly 25% of the total land surface. In permafrost and other cryogenic (periglacial) areas, and in temperate regions where there is extensive seasonal freezing and thawing of soils, a wide range of processes lead to a variety of surface expressions, many of which have profound effects on human structures and settlements, as well as on ecosystems. These sensitive periglacial features are found around glaciers, in high mountains (even at low-latitudes) and throughout the polar regions. The development (aggradation) or degradation of permafrost is a sensitive and early indicator of climate change [see subsurface temperature regime]. Important abiotic parameters related to permafrost regions include:
SIGNIFICANCE: Permafrost is an agent of environmental change, which influences human settlements and natural and managed ecosystems, including forests, grasslands and rangelands, mountains and wetlands, and their hydrological systems. The thawing of permafrost may enhance climate change by the release of carbon and other greenhouse gases. It is estimated that about 12% of the world's soil carbon is tied up in dead organic mater in the active layer and in permafrost: long-term climate warming would facilitate decomposition and drying, releasing huge quantities of gas hydrates and CO2 [see wetlands extent, structure and hydrology]. Permafrost can result in serious and costly disruptions from ground subsidence, slope failure, icings, and other cryogenic processes.
HUMAN OR NATURAL CAUSE: The freezing and thawing of soils and surficial materials and the consequent ground changes are natural processes controlled by climatic conditions. They can be modified by human actions in and around settlements and engineering works.
ENVIRONMENT WHERE APPLICABLE: High latitudes and high altitudes (arctic and cold deserts, tundra, taiga, mountains) where ground freezing is extensive.
TYPES OF MONITORING SITES: Vegetated polar regions, high altitude locations, areas of obvious disturbance of the active layer (e.g. icings, polygons, failing slopes, areas of frost heaving).
SPATIAL SCALE: patch to mesoscale / regional to continental
METHOD OF MEASUREMENT: There are many approaches to the monitoring of permafrost activity:
FREQUENCY OF MEASUREMENT: Depends on the kind of disturbance being monitored, as detailed above. Certain features need to be checked weekly to several times during a summer season, others on an annual or decadal basis.
LIMITATIONS OF DATA AND MONITORING: It is difficult to do field work in areas of active thawing without disturbing mobile soils and landforms or without endangering sensitive ecosystems. In response to highly variable local conditions, grids installed to monitor polygon development should be left in place or extended from year to year.
APPLICATIONS TO PAST AND FUTURE: Permafrost and cryogenic features are selective recorders of climate change through their thermal and stratigraphic record. Fossil features formed during previous freeze and thaw episodes can be used to indicate and even date the former presence of permafrost, whereas degradational landforms in current permafrost areas indicate either former warm periods or current thermal instability.
POSSIBLE THRESHOLDS: The freeze-thaw transition is a major threshold that, once crossed, may lead to the development of various landforms, some of which (e.g. thermokarst) are irreversible, at least on time scales of less than centuries. Many frozen ground features are closely linked to the ground thermal regime, and changes in moisture conditions or in vegetation or snow cover can offset changes in air temperature [see subsurface temperature regime].
French, H.M. 1996: The periglacial environment. 2nd edition. Harlow: Longman, 341p.
Romanovskii, N., G.F.Gravis, M.O.Leibman & E.Melnikov 1996. Periglacial processes as geoindicators in the cryolithozone. In Berger, A.R. & W.J.Iams (eds). Geoindicators: Assessing rapid environmental changes in earth systems: p.33-54. Rotterdam: A.A. Balkema. (see also paper in same volume by Rasch et al.)
Williams, P.J. & M.W.Smith 1989. The frozen Earth - fundamentals of geocryology. Cambridge: Cambridge University Press.
Wolfe, S.A. (ed.) (1998). Living with frozen ground - A field guide to permafrost in Yellowknife. Geological Survey of Canada, Miscellaneous Report 64, 71 pp
OTHER SOURCES OF INFORMATION: Canadian Permafrost Monitoring Network, Circumpolar Active Layer Monitoring Program Network, Frozen Ground Data Center (US National Snow and Ice Data Center), International Permafrost Association, International Tundra Experiment, World Data Center A for Glaciology.
RELATED ENVIRONMENTAL AND GEOLOGICAL ISSUES: Thawing effects are hazardous to animal and human habitation, and permafrost ecosystems are easily disturbed. Permafrost terrains may contain gas hydrates, ice-like substances composed of water and natural gas, which when released by melting may enhance climate warming.
OVERALL ASSESSMENT: Frozen ground (permafrost and periglacial) activity is sensitive to local climate, hydrology, and vegetation cover. Apart from the thickness of the active layer, which is a most useful indicator of local environmental change, most frozen ground features reflect regional change about the freezing point and require much effort to monitor.
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