Environmental Radioisotope lab
Department of Geography and Environment, Bar-Ilan University
Applying Radium Isotopes to Permafrost Studies
Permafrost is defined as soil (or rock) that remains below 0°C for at least two consecutive years. Permafrost soils cover more than 20% of the terrestrial area, mostly in high latitudes. The thermal regime of permafrost is determined by a complex of variables, including soil type, organic matter and water content, and surface conditions (e.g. permafrost will not form under glaciers or seawater).
The permafrost layer is covered by an active layer of variable thickness, which thaws annually. The active layer depth changes yearly according to local or zonal physical and biological variables such as air temperature, slope aspect, snow cover, snow timing during autumn, as well as vegetation type and cover.
Permafrost aggrades in two different ways: epigenetic or syngenetic. In epigenetic permafrost, freezing is decoupled from soil formation, sometimes with a lag of thousands or millions of years. Syngenetic permafrost aggrades as a follow-up on soil deposition, which is typical for cold-climate landscapes, dominated by relatively continuous deposition of fluvial or aeolian sediments.
Figure 1: The vertical temperature profile in permafrost and the active layers. (https://en.wikipedia.org).
Figure 2: Map showing areal distribution of permafrost regions in the Northern Hemisphere (Brown et al. 1997, http://nsidc.org/fgdc/ ).