Permafrost, or permanently frozen ground, is ground (soil, sediment,or rock) that remains at or below 0°C for at least two years (Permafrost Subcommittee, 1988). It occurs both on land and beneath offshore Arctic continental shelves, and underlies about 22% of the Earth's land surface.
Geographers recognize several types of permafrost:
- Continuous permafrost refers to an environment where more than 80% ofthe ground surface is underlain by permafrost. The southern limit of continuous permafrost corresponds closely to a mean annual isotherm(which is derived from air temperatures) of –8ºC.
- Discontinuous permafrost refers to an environment where 30–80% of theground surface is underlain by permafrost. The southern limit ofdiscontinuous permafrost corresponds closely to a mean annual isotherm of –1ºC.
- Sporadic permafrost refers to an environment where less than 30% of the ground surface is underlain by permafrost. There is no commonly acknowledged thermal criteria for the southern boundary of sporadic permafrost. The presence of sporadic permafrost is often dependent on the presence of organic soils that help preserve the permafrost under milderclimates.
- Continuous permafrost is associated with the Arctic and Polar zones, while discontinuous permafrost is associated with the Subarctic zone.
Source: Bachelor of Circumpolar Studies 311, Module 1: Biophyical Parameters
This permafrost map has been developed by the National Snow and Ice Data Centre. The Google Earth layer for this map and many others are directly available through their Virtual Globes page, and can be viewed also in their Atlas of the Cryosphere.
View this map in Google Earth (select Permafrost from the available layers under the NSIDC set).
Original Data Source Documentation taken from http://www.nsidc.org/data/docs/fgdc/ggd318_map_circumarctic/index.html:
Circum-Arctic Map of Permafrost and Ground Ice Conditions
The Circum-Arctic permafrost and ground ice map is available via ftpin ESRI Shapefile format and Equal-Area Scalable Earth Grid (EASE-Grid)format. See the Format section for an explanation of the files provided via ftp.
The circumpolar permafrost and ground ice data contribute to aunified international data set that depicts the distribution andproperties of permafrost and ground ice in the Northern Hemisphere(20°N to 90°N). The re-gridded data set shows discontinuous, sporadic,or isolated permafrost boundaries. Permafrost extent is estimated inpercent area (90-100%, 50-90%, 10-50%, <10%, and no permafrost).Relative abundance of ground ice in the upper 20 m is estimated inpercent volume (>20%, 10-20%, <10%, and 0%). The data set alsocontains the location of subsea and relict permafrost. the gridded dataare gridded at 12.5 km, 25 km, and 0.5 degree resolution. Theshapefiles were derived from the original 1:10,000,000 paper map (Brown et al. 1997)
Permafrost, or permanently frozen ground, is ground (soil, sediment,or rock) that remains at or below 0°C for at least two years(Permafrost Subcommittee, 1988). It occurs both on land and beneathoffshore arctic continental shelves, and underlies about 22% of theEarth's land surface.
For more information on the creation of the original map, see Heginbottom et al. (1993).The original paper map also includes information on the relativeabundance of ice wedges, massive ice bodies and Pingos, ranges ofpermafrost temperature and thickness (Brown et al. 1997).