Permafrost

Despite of the fact that available data on carbon and nitrogen accumulation values of
pedobionts much less then overall organic matter load in forest permafrost soils (0,001-0,02 %
of carbon and 0,005-0,06 % of nitrogen from overall stocks in the soils of Yenisey region), it
reflects the increasing of role of invertebrates in accumulation of main biogenic element under
soil-climatic condition improvement.
Key words: Permafrost soils, invertebrate biomass, accumulation, carbon, nitrogen
92
Contribution of Thermo-mechanical Ratchetting to the
Formation of Periglacial Environments
James G A Croll, FREng, FICE, FIStructE, FRSA
(University College London)
Abstract: It is widely recognised that when lake-ice or sea-ice becomes grounded any increase
in temperature is in certain circumstances capable of developing massive compressive forces.
These forces constitute major threats to any man made structure which might restrain the free
expansion of the ice. And of course where the restraints are sufficiently massive the ice sheet
itself can undergo many forms of crushing, folding and uplift buckling, associated with
compression induced failures. If during this warming cycle the compression failures have
absorbed much of the thermally induced strain energy within the ice sheet, any subsequent
cooling will fairly quickly result in tensile stresses being developed. With the ice being
relatively weak in tension these stresses will at an early stage start to induce tension cracking.
Water and snow getting into these cracks will be turned to ice so that by the end of the cooling
period a relatively continuous ice sheet, containing low levels of tensile strain energy, will
present itself for the next cycle of thermal warming and compressive action. For sea-ice and
lake-ice the result of this, essentially thermal ratchet, process will be a gradual outward
movement of ice that accumulates at the grounded boundaries. There is evidence that similar
processes are at work in the formation of many geomorphic features in periglacial
environments.
This paper will explore how thermo-mechanical ratchetting could be influencing the
formation of many seasonal features within the active layers and perennial features extending
well into the permafrost layers. While fluctuations in solar energy provide the driving force for
these ratchet processes they will be shown to be made possible by one or other form of
differential property of materials during the tension and compression phase. The gradual
outward movement of relatively dense particles, such as stones and rocks, within or above
relatively compliant soil materials to form sorted and unsorted stone circles, polygons etc will
be reasoned to partly result from differences in visco-plastic creep characteristics when warm
soil and ice is subject to compression compared with that occurring when cold soil and ice is
subject to tension. The gradual upward deformation of frozen and unfrozen soil to form
perennial hummocks, frost mounds, palsas and pingos, etc, will be argued to also be partially
the result of similarly temperature sensitive creep within the material. But additionally in these
cases a major causal factor is suggested to be the differences in the nature of the failure