Cryogenesis and soil formation along a bioclimate gradient in Arctic North America

Abstract

[1] In arctic tundra, cryoturbation resulting from frost heave, cracking, and other cryogenic processes produces patterned ground such as nonsorted circles, stripes, nonsorted polygons, and earth hummocks. We studied cryogenic structures and morphological properties of soils associated with patterned-ground features along a bioclimate gradient in Arctic Alaska and Canada from north (subzone A) to south (subzone E). Most of these soils have strongly developed cryogenic features, including warped and broken horizons, and organic matter moved into the upper permafrost. The expression of cryoturbation generally increases with the gradient southward. Soil color reflects the lithology of the soil, weathering, and accumulation of organic matter. The organic horizons form around the circles, and gleyed matrix with redoximorphic features develop in the lower active layers due to saturation above the permafrost. Cryostructure development depends more on hydrology controlled by microtopography than position along the gradient. The cryostructures form due to freeze-thaw cycles and ice lens formation, which include granular, platy, lenticular, reticulate, suspended (ataxitic), ice lens, and ice wedges. On the surface, the density of nonsorted circles reached their maximum in subzones C and D. However, once the vegetation cover was removed, the nonsorted pattern grounds reached their optimum stage and become closed packed in subzone E. Frost heave decreases in the south as the vegetation changes from tussocks to shrub tundra. Cryogenesis is the controlling factor in patterned ground formation resulting in cryoturbated soil profiles, cryostructures, and carbon sequestration in arctic tundra soils.

Permafrost soils and carbon cycling

“…Once formed, sorted circles are maintained by continued dynamic circulation within the soil and stone domains. Indeed, the most striking cryoturbation features are associated with patterned ground (especially nonsorted and sorted circles) and include broken, involuted or warped horizons within the soil profile Ping et al, 2008aPing et al, , 2013. These features are caused by differential frost heave processes in the soils.…”

“…When the concentration of SOM is high, reduced Fe (Fe 2+ ) in soil solution is rapidly oxidized upon contact with air, forms a poorly ordered Fe 3+ oxide film on water surfaces, and eventually precipitates as orange-colored deposits called ferrihydrite (Schwertmann and Taylor, 1989). The hydromorphism also results in the gleyed color of the mineral matrix in the lower active layer due to Fe reduction (Ping et al, , 2008a.…”

“…This variation results in the development of an assortment of soil cryogenic structures. On the exposed ground surface of silty mineral soils with no (or only thin) surface organic horizons, crumb and granular structures develop due to needle ice formation (Ping et al, 2008a). Ice crystals form on frozen soil particles or structural units near the surface when water is drawn from below to form or build the needle-like ice crystals that lift and move soil particles or structural units (Brink et al, 1967).…”

“…Permafrost exerts a controlling role on soil physical and morphological properties through cryogenesis, i.e., frost cracking and the formation of ice crystals and lens cryostructures that result in frost heaving and cryoturbation (Konishchev, 1982;Rieger, 1983;Mueller et al, 1999;Ping et al, 2008a). Cryostructures are defined as patterns formed by ice inclusions in the frozen soil .…”

Climate change impacts on the Alpine ecosystem: an overview with focus on the soil

“…The relationship has two faces. On the one hand, climate exercises an indirect influence on the soil structure affecting factors correlated with aggregation such as SOM (Von Lützow, Kögel-Knabner 2009), soluble salts and amorphous iron oxides (Mikutta et al 2006), wetting-drying and freeze-thaw cycles which in turn affect land use (Ping et al 2008), vegetation covers and biological cycles (Six et al 2004). The structural improvement of soil, due to the ped aggregation, will lead to a predominance of humus forms in Mull (Chersich et al 2006).…”