Saturday, 15 July 2006

Maps of Cryogenic Conditions and Phenomena in Soils of Russia.

Tatiana V. Ananko, Dmitry Ye. Konyushkov, Yevgeny M. Naumov, Ilia A. Sokolov, and Tatiana Ye. Yakusheva. V.V. Dokuchaev Soil Science Institute, Pyzhevskii per. 7, Moscow, 119017, Russia

1. Cryogenic soil processes (soil cryogenesis) are the processes occurring in soils under the influence of subzero temperatures and phase transitions of soil water. They are subdivided into the groups of physicochemical and structure-forming (cryometamorphic) and physico-mechanical (cryodynamic) processes. Factors of soil cryogenesis are specified by climatic parameters, conditions of heat exchange at the soil-atmosphere interface, and thermophysical properties of soils; the presence and character of permafrost also affect soil cryogenesis. Cryogenic features are the results of cryogenic processes; they are manifested at different levels of soil organization: from the submicrolevel to the levels of soil aggregates, horizons, profiles, and soil cover patterns. Cryogenic features have different characteristic times with respect to their formation and stability in soils. Stable cryogenic features may exist for a long time even when the processes that have shaped them do not operate any more. Thus, paleocryogenic features as indicators of soil evolution and important elements of modern soil functioning are distinguished. Cryomorphic soils are the soils with distinct, stable, and diagnostically meaningful cryogenic features. The effect of soil cryogenesis depends on the intensity, duration, and depth of soil freezing and thawing, as well as on the frequency of phase transitions of soil water, the amount and forms of segregated ice, and the intensity of water migration to the freezing front. With respect to soil temperature regime, all the soils, in which cryogenic processes take place, can be subdivided into the groups of permafrost-affected (or seasonally thawing) soils (all the soils, in which the layer of seasonal freezing-thawing reaches the permafrost table) and seasonally freezing soils, in which the layer with above-zero temperatures is always found below the layer of seasonal freezing (relic permafrost can be present at greater depths). Cryogenic phenomena in soils are diverse and, often, oppositely directed. Cryogenic features are superimposed on other soil features that have similar natures in both freezing and nonfreezing soils. Cryogenic processes per se do not "create" soils; the frozen state retards soil development, and cryodynamic processes disturb the "normal" development of the soil profile. Cryogenic features are important indicators of the past and present environmental conditions; they must be taken into account upon different soil uses. Their separate study and mapping are feasible.

2. On the existing soil maps, information on cryogenic conditions, processes, and features in soils (pedocryological information) is insufficient. It is reasonable to develop pedocryological maps. The analysis of special geocryological and soil maps of Russia (1:2.5 M scale) shows the prospects of using the soil map for the pedocryological interpretation.

3. Small-scale maps of cryogenic conditions and phenomena in soils of Russia are demonstrated. The map of pedocryogenic conditions provides the following information: (I) soil temperature characteristics (mean annual temperature, amplitude of temperatures, minimal soil temperature (0.2 m), presence and depth of permafrost (for permafrost-affected soils), average and maximum depths of soil freezing, unidirectional or two-directional /from the top and from the bottom/), character of soil freezing and thawing, duration of the frozen state of soils, etc; (II) soil moisture characteristics (soil water content before freezing, ice content in the permafrost and in the freezing soil layer, forms of ice segregation); and (III) additional information on soil texture and mineralogy, pebble content, and the presence and thickness of the insulating peat (litter) layer. The map of cryogenic phenomena displays information on the geography of particular forms of soil cryogenesis: cryogenic cracking, different forms of frost polygons, cryoturbation, sorting of coarse fragments, frost heave, solifluction, thermokarst, etc. The development of cryogenic ooidal and platy structures is also shown. A separate group of paleocryogenic features in surface soils is distinguished. The effect of zonal and provincial climatic conditions and regional lithogeomorphic features on the geography of cryogenic conditions and phenomena in Russian soils is discussed.

4. We suggest that a similar approach can be applied to add more detailed pedocryological information to the Circumpolar Soil Map developed under the aegis of the Cryosol working group.

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