Abstract

In 1994 Cryosols were introduced in the Draft WRB, defined as:

“Soils having permafrost within 100 cm of the mineral soil surface and which are saturated with water during the thawing period; showing features of cryoturbation at the surface or in the solum; having no diagnostic horizons other than a histic or ochric horizon; lacking gleyic or stagnic properties.”

This definition limited the occurrence of Cryosols to a very restricted area with permafrost-affected soils:

•        No dry permafrost-affected soils

•        No reduction-oxidation features

•        No diagnostic horizons other than histic or ochric

 

In 1998 the definition of Cryosols in WRB changed into:

“Soils having one or more cryic horizons within 100 cm of the soil surface.”

A cryic horizon (from Gr. kryos, cold) is defined by the following diagnostic criteria:

1. Soil temperature at or below 0⁰ C for two or more years in succession; and

2. a. In presence of sufficient interstitial soil water, evidence of cryoturbation, frost heave, cryogenic sorting, thermal cracking, or ice segregation; or

b. In absence of sufficient interstitial soil moisture, evidence of thermal contraction of the frozen soil material; and

3. Platy or blocky macrostructure resulting from vein ice development, and orbicular, conglomeratic and banded microstructures resulting from sorting of coarse soil material.

In 2006 the definition of Cryosols in the revised WRB changes into:

“Soils having

1.  One or more cryic horizons within 100 cm of the mineral soil surface; or
2.  One or more cryic horizons within 200 cm of the mineral soil surface and evidence of cryoturbation from the mineral soil surface down to the shallowest cryic horizon.”

Modification in the cryic horizon definition:

1. Soil temperature at or below 0⁰ C for two or more years in succession; and
2. a. In presence of sufficient interstitial soil water, evidence of cryoturbation, frost heave, cryogenic sorting, thermal cracking, or ice segregation; or

            b. In absence of sufficient interstitial soil moisture, evidence of thermal contraction of the frozen soil material; and

3. Platy or blocky macrostructure, orbicular, conglomerate-like and banded microstructure, or sorting of coarse soil material.

Conclusion

The Cryosol area in the world according to WRB has expanded from small areas in 1994, to larger areas in 1998, including all soils with cryic horizons within 1 m depth, to even larger areas in 2006, incorporating also soils with cryic horizons between 1 and 2 m depth. Yes, Cryosols are on the move.