A polar desert is a biome with precipitation below 250 millimeters per annum and a mean temperature during the warmest month of less than 10 degrees Celsius. Typically occurring at higher latitudes than tundra biomes, polar deserts occupy approximately 5,000,000 square kilometers of land surface, chiefly comprised of exposed bedrock, talus or rocky plains. In the northern hemisphere this biome is often termed the High Arctic. The soils regime of the polar desert is generally characterized by occurrence of permafrost. Remarkably, the reddish soils of much of the Antarctic montane region suggest that the McMurdo Dry Valleys are a relict of an earlier, much warmer climate.
In the paleoclimate view of Earth, Polar deserts were much more common during previous Ice ages in areal extent than at present, not only because of the expansive cold regime, but also because of the prevailing aridity common to Ice age environments.
A prominent feature of the polar desert is the complete absence of sunlight over a period of nine to ten months; corresponding the growing season is a maximum of two and one half months. Sand seas (dunes) are not prominent features in these deserts, although snow dunes occur commonly in areas where precipitation is more plentiful. Temperatures of polar deserts commonly oscillate around the freezing point of water, producing patterned textures on the ground resulting from freeze-thaw cycles; these distinctive topographic features may have patterns as as five meters in diameter.
For the Antarctic polar desert the temperature of the coldest months typcially has a mean of minus 29 to minus 30 degrees Celsius; the warmest month realizes temperatures of a few degrees Celsius to about minus one degree Celsius. Annual precipitation of the Antarctic polar desert is less than 40 millimeters, and summer relative humidity ranges from 45 to 80 percent. There is almost no presence of surface liquid water, except for scattered hypersaline lakes, some of which never freeze due to the high salinity content. Often there are atmospheric (Earth's atmosphere) salts prominent in the Antarctic polar desert air; in the coastal zone chlorides are dominant, where atmospheric nitrates dominate these salts on old plateaus in montane areas.
Vegetation and soils
Not surprisingly density of soil organic material increases from Polar deserts as one moves toward more temperate climate zones. Permafrost soils pervade most of the polar desert, e.g. soils where the subsurface and surface are below zero degrees Celsius for a period longer than 24 months continuously.
Sometmes in the Arctic, the polar desert is combined with tundra to compile statistics of these biomes, likely due to subtle intergrading of these two biomes in parts of the Arctic. When considered together these two Arctic biomes have a comparable plant biodiversity to the coniferous forests and taiga at lower latitudes.
In the Arctic approximately one to five percent of the polar desert ground surface has plant cover, consisting of approximately 350 vascular species. Bryophytes are abundant here, with crustose and foliose lichens being common; moreover, fructose lichens present a minor occurrence. The growth forms of plants are typically graminoid, cushion and rosette. Shrubs present a height ranging from five to 100 centimeters, while forbs have a stature ranging from two to ten centimeters. Studies conducted in the polar desert component in the former Soviet Union reveal carbon storage and carbon fluxes in polar desert much smaller than other biomes of tundra, taiga and steppe. For example total carbon flux from polar desert below ground mortmass (dead wood) was estimated at merely 0.2 Tgram carbon per year, and biomass litter decomposition at 0.1 Tgram per year, both values three orders of magnitude below that of tundra, taiga or steppe.
Most of the interior of Antarctica is polar desert, despite the thick ice cover. Conversely, the McMurdo Dry Valleys of Antarctica, although in some areas, they have been ice-free for thousands of years, are not necessarily all polar desert: they are maintained in an arid condition by katabatic winds.
An interesting element of the polar desert of Antarctica is the formation of hypersaline lakes. In such cases the extreme aridity and high wind velocities often lead to a pond or lake of salinity greater than ocean water. A specific example of the most saline lake on Earth is found in the McMurdo Dry Valleys: Don Juan Pond. This small lake is not only notable for its very high salinity, but also for the occurrence of extremophile organisms that can survive in the high salinity and extremely low temperature.
Prevalent Antarctic soils in the polar desert have a geological ages ranging from thousands to millions of years; soil material is sporadic compared to the larger expanses of cobble, boulder, outcrop and talus formations, principally comprised of grantiic rock. Chief soil types are Aridi Gelic, Solonchak Lithic, Cryosol, Cryosol Aridi Salic, Cryosol Calcisalic, Cryosol Saliturbic, and Cryosol Eutriturbic. Humus content of soils ranges from .002 to .700 percent. Soils generally exhibit a permanent high salinity.
Fauna, fungi and bacteria
The extreme cold along with sparse vegetative cover are demanding circumstances for both carnivores and omnivores in the polar desert biome. Complete lack of sunlight over much of the year also deprives the use of typical sensory means of finding and tracking prey, or even vegetation in the case of herbivores.
Several large fauna are found in the Arctic polar desert. The polar bear is the quintessential mammal designed for survival in the Arctic. This well insulated animal sleeps during the long winter and is built for foraging on pack ice during the summer months. A number of high latitude occurring pinnipeds are found hauling out in [[coastal zone]s] along the polar desert; for example, ribbon seals are found in the north Pacific Ocean and in the seas bordering Alaska and Russia: Bering Sea, Chukchi Sea, Beaufort Sea and Okhotsk Sea. Walrus are found around many of the Arctic Seas including the White, Pechora and Laptev Seas.
In the Maudlandia Antarctic Desert, the largest element of the Antarctic polar desert, the landscape was once deemed to be biologically barren; howver, in the 1970s microbiologists found communities of microscopic algae, fungi, and bacteria living protected inside rocks. These organisms live in tiny gaps between grains of sandstone, near the surface of the semi-translucent rock where they can garner some sunlight (Solar radiation) and moisture, and also receive nourishment from the minerals in that rock stratum. These organisms are known as cryptoendolithic microorganisms. Other such algal species as Hemichloris antarctica, are specially adapted to repeated freezing and re-thawing. Recently discovered by divers, the bottom of some lakes support a microbial mat made up of many species of blue-green algae, similar to those thought to be the earliest life-forms and the original sources of oxygen on Earth. The improbable top predator within the Dry Valleys is a bacteria-eating nematode that can survive multiple years of being freeze-dried—entering a state called anhydrobiosis. Certain lichen species, for example, Buellia frigida, might grow as little as one centimetre in a millennium. The area's harsh conditions and the organisms here are thought to be Earth's closest proxy to life that may exist on Mars.
Astoundingly several terrestrial bird species have adapted to the polar desert, notably penguins such as the Emperor penguin and Adelie penguin. Seabirds breeding in Maudlandia include the southern fulmar (Fulmaras glacialoides), southern giant fulmar (Macronectes giganteus), cape pigeon (Daption capense), snow petrel (Pagodroma nivea), Wilson’s storm petrel (Oceanites oceanicus), south polar skua (Catharacta maccormicki), and Antarctic petrel (Thalassoica antarctica). Several Maudlandia locales have been given protected status due to large colonies of breeding seabirds.
Examples of polar desert ecoregions
There are a number of distinct geographic ecoregions, some or all of which qualify as polar desert. The following are examples of such ecoregions:
- Brooks Range, North America (Extreme northern portion)
- Maudlandia Antarctic Desert
- Kalaalit Nunaat High Arctic Tundra, northern Greenland
- High Arctic Tundra (Middle Arctic tundra), North America (Northern portion)
- V.D.Aleksandrova. 1988. Vegetation of the Soviet polar desert. Cambridge University Press. Cambridge, England
- Michael G. Barbour, William Dwight Billings. North American terrestrial vegetation
- M.J.Bovis, and R.G.Barry. 1974. A climatological analysis of north polar desert areas. In:T.L.Smiley and J.H.Zumberge (eds.). Polar Deserts and Modern Man . University of Arizona Press
- Peter T.Doran, W.Berry Lyons, Diane M.McKnight. 2010. Life in Antarctic deserts and other cold dry environments: astrobiological analogs. Cambridge University Press. 307 pages
- G.E.Fogg G. E. 1998. The Biology of Polar Habitats. Oxford University Press, New York, N.Y. ISBN: 0198549539
- Headland, R. K. 1996. Protected Areas in the Antarctic Treaty Region. Scott Polar Research Institute.
- John M. Kimble. 2004. Cryosols: permafrost-affected soils (Google eBook) Springer. 726 page
- R. Lal. 1995. Soil management and greenhouse effect. CRC Press. 385 pages
- Chris Woodford. 2010. Arctic Tundra and Polar Deserts. Heinemann-Raintree Library. 64 pages