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Orders: Cryosolic

Soils of the Cryosolic order occur throughout northern Canada (CRYOSOL CANADA MAP) and are the dominant soil type throughout most of the territories (northern Yukon, Northwest Territories, and Nunavut). Cryosols are also common in the regions around the Hudson Bay and Hudson Strait, particularly in northeastern Manitoba, northwestern Ontario, and the northernmost part of Quebec (the Ungava peninsula in Nunavik). These regions are characterized by long, cold winters and short, cool summers. As a consequence, the mean annual soil temperature is at or below 0°C, resulting in permafrost conditions, where the ground remains frozen for two or more consecutive years. The frequent freeze-thaw cycles associated with these cold environments contribute not only to the presence of permafrost near the soil surface but also to a suite of soil-forming processes known as cryoturbation. Cryoturbation refers to soil movement that arises from frost action, and is sometimes also referred to as “frost churning”.

There are a few different commonly accepted models to explain how cryoturbation occurs; just a few examples are listed here. In the cryostatic model, a freezing front advancing from both above (cold air) and below (permafrost) can exert pressure on the soil of the active layer. In the convective cell equilibrium model, heave-subsidence processes occurring at both the top and bottom of the active layer move soil upward and outward. Both the formation and subsequent melting of ice lenses within the active layer can give rise to the characteristic broken or irregular soil horizons commonly associated with cryoturbation. Where changes in temperature and moisture contribute to cracking in the soil, ice and/or sand wedges can develop.

Generally, cryoturbation is most common in soils with finer textures (fine sand to silt) and wet conditions, but has been observed under other environmental conditions as well. The relative importance of a given cryoturbation mechanism or model in developing a particular Cryosolic profile will depend on the environmental conditions at that particular location.

Although many of the same soil-forming processes that occur in other orders also take place in Cryosols (for example, the reduction-oxidation processes associated with Gleysols or the build-up of organic material associated with the Organic order), the near-surface permafrost contributes to a particular suite of soil properties that include, but are not limited to, horizons that have been affected by cryoturbation. The diagnostic horizons associated with the Cryosolic order are represented by the suffixes ‘y’ (for horizons with evidence of cryoturbation) and ‘z’ (for frozen material, i.e., permafrost). These suffixes can be used alone with a major horizon (O, A, B, C) or together with another suffix to reflect a combination of soil-forming processes.

In those regions of Canada where the active layer is thicker (such as the discontinuous permafrost zone), Cryosols may be found in association with other soil orders. Soils of the Gleysolic and Organic orders may be found in wetter, low-lying areas of the landscape where the active layer is greater than 1 m thick. Similarly, Brunisolic and Regosolic soils may be found on well-drained knolls and slopes, particularly south-facing slopes. Relict Cryosols (i.e., soils with evidence of cryoturbation but that no longer meet the permafrost criteria for the Cryosolic order) can be found in some southern environments, such as the boreal forest, reflecting a historically colder soil-forming environment. These features are generally not well represented in the Canadian System of Soil Classification.

The information presented above reflects some of the extensive research done by cryopedologists such as Charles Tarnocai (Agriculture and Agri-Food Canada) and James Bockheim (University of Wisconsin).

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