Geoscience Reference
In-Depth Information
develops as a result of the movement of two freezing fronts (downward from the
surface and upward from the permafrost table) during freeze-back periods. These
two freezing fronts draw water from the unfrozen soil layer between the two fronts
and compact this layer because of the cryostatic pressure they exert.
Fine-textured cryosols commonly have high moisture content, especially above
the permafrost layer; resulting in gleying and other redoximorphic features. Salt
crusts also form on the surface of cryosols, especially those developed from marine
clays and shale-derived parent materials.
Dilatancy is common in cryosols with high silt content. This property leads to the
creation of a very unstable soil surface that liquefies when subjected to mechanical
vibration. When these soils dry, a characteristic vesicular structure develops.
2.2.3.3
Chemical Properties
Cryoturbation within the active layer has marked effects on chemical properties such
as the distribution and turnover of soil organic C and N, Fe and Mn redox relations,
hydrogeochemistry of seasonal flow regimes (Pecher
1994
), and epigenic salt accu-
mulation. The effect of sporadic permafrost on chemical soil properties was exam-
ined in the eastern Swiss Alps (Zollinger et al.
2013
). Although there were no
significant differences in C stocks on permafrost and non-permafrost sites, the stable
C-fraction was greater in the non-permafrost sites, enabling greater turnover of SOC.
One of the unique properties of cryosols, especially those affected cryoturbation,
is the large amount of SOC in both the active and transitional layers (Bockheim
et al.
1998
). Even though permafrost-affected ecosystems produce much less bio-
mass than do temperate ecosystems, permafrost-affected mineral soils that are sub-
ject to cryoturbation are able to sequester a large portion of this organic matter
(Bockheim
2007
). Although permafrost-affected mineral soils cover a much greater
area than permafrost-affected organic soils, the organic cryosols are able to seques-
ter SOC at much greater rates as a result of their gradual build-up process.
2.2.3.4
Mineralogical Properties
Putkonen (
1998
) pointed out that the thermal regime of the active layer is important
because all chemical, biological and physical processes are concentrated there.
Moreover, thermal conduction, the phase change of soil water at 0 ﾰC, and changes
in unfrozen water content are the primary thermal processes that control soil
temperature and weathering rates. Alekseev et al. (
2003
) compared mineral
transformations in the active layer versus that in the near-surface permafrost. Illite
and dioctahedral (Fe) chlorite were altered at the cryogenic barrier to lepidocrocite.
They identified the boundary between the active layer and permafrost as an important
geochemical barrier. Borden et al. (
2010
) compared the clay mineralogy of soils in
moist acidic tundra (MAT) and moist nonacidic tundra (MNT) of arctic Alaska.
They reported that the proportion of vermiculite to illite was higher in MAT than in
MNT because of differences in acidity and its relation to weathering processes.
