Permafrost: Difference between revisions

Permafrost
Map showing extent and types of permafrost in the Northern Hemisphere
Used in	International Permafrost Association
Climate	High latitudes, alpine regions

Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface is underlain by permafrost,^[1], with the total area of around 18 million km².^[2]. This includes substantial areas of Alaska, Greenland, Canada and Siberia. It can also be located on mountaintops in the Southern Hemisphere and beneath ice-free areas in the Antarctic.

Permafrost does not have to be the first layer that is on the ground. It can be from an inch to several miles deep under the Earth's surface. It frequently occurs in ground ice, but it can also be present in non-porous bedrock. Permafrost is formed from ice holding various types of soil, sand, and rock in combination.^[3]

Permafrost contains large amounts of biomass and decomposed biomass that has been stored as methane and carbon dioxide, making tundra soil a

In contrast to the relative dearth of reports on frozen ground in North America prior to World War II, a vast literature on basic permafrost science and the engineering aspects of permafrost was available in Russian. Some Russian authors relate permafrost research with the name

Permafrost is

The extent of permafrost is displayed in terms of permafrost zones, which are defined according to the area underlain by permafrost as continuous (90%–100%), discontinuous (50%–90%), sporadic (10%–50%), and isolated patches (10% or less).[13] These permafrost zones cover together approximately 22% of the Northern Hemisphere. Continuous permafrost zone covers slightly more than half of this area, discontinuous permafrost around 20 percent, and sporadic permafrost together with isolated patches little less than 30 percent.^[14] Because permafrost zones are not entirely underlain by permafrost, only 15% of the ice-free area of the Northern Hemisphere is actually underlain by permafrost.^[1] Most of this area is found in Siberia, northern Canada, Alaska and Greenland. Beneath the active layer annual temperature swings of permafrost become smaller with depth. The deepest depth of permafrost occurs where geothermal heat maintains a temperature above freezing. Above that bottom limit there may be permafrost with a consistent annual temperature—"isothermal permafrost".^[15]

Continuity of coverage

Permafrost typically forms in any climate where the mean annual air temperature is lower than the freezing point of water. Exceptions are found in humid boreal forests, such as in Northern Scandinavia and the North-Eastern part of European Russia west of the Urals, where snow acts as an insulating blanket. Glaciated areas may also be exceptions. Since all glaciers are warmed at their base by geothermal heat, temperate glaciers, which are near the pressure-melting point throughout, may have liquid water at the interface with the ground and are therefore free of underlying permafrost.^[16] "Fossil" cold anomalies in the Geothermal gradient in areas where deep permafrost developed during the Pleistocene persist down to several hundred metres. This is evident from temperature measurements in boreholes in North America and Europe.^[17]

Discontinuous permafrost

The below-ground temperature varies less from season to season than the air temperature, with mean annual temperatures tending to increase with depth as a result of the geothermal crustal gradient. Thus, if the mean annual air temperature is only slightly below 0 °C (32 °F), permafrost will form only in spots that are sheltered—usually with a northern or southern aspect (in north and south hemispheres respectively) —creating discontinuous permafrost. Usually, permafrost will remain discontinuous in a climate where the mean annual soil surface temperature is between −5 and 0 °C (23 and 32 °F). In the moist-wintered areas mentioned before, there may not be even discontinuous permafrost down to −2 °C (28 °F). Discontinuous permafrost is often further divided into extensive discontinuous permafrost, where permafrost covers between 50 and 90 percent of the landscape and is usually found in areas with mean annual temperatures between −2 and −4 °C (28 and 25 °F), and sporadic permafrost, where permafrost cover is less than 50 percent of the landscape and typically occurs at mean annual temperatures between 0 and −2 °C (32 and 28 °F).^[18] In soil science, the sporadic permafrost zone is abbreviated SPZ and the extensive discontinuous permafrost zone DPZ.^[19] Exceptions occur in un-glaciated Siberia and Alaska where the present depth of permafrost is a relic of climatic conditions during glacial ages where winters were up to 11 °C (20 °F) colder than those of today.

Continuous permafrost

At mean annual soil surface temperatures below −5 °C (23 °F) the influence of aspect can never be sufficient to thaw permafrost and a zone of continuous permafrost (abbreviated to CPZ) forms. A line of continuous permafrost in the

Alpine permafrost occurs at elevations with low enough average temperatures to sustain perennially frozen ground; much alpine permafrost is discontinuous.[25] Estimates of the total area of alpine permafrost vary. Bockheim and Munroe^[20] combined three sources and made the tabulated estimates by region, totaling 3,560,000 km² (1,370,000 sq mi).

Alpine permafrost in the Andes has not been mapped.^[26] Its extent has been modeled to assess the amount of water bound up in these areas.^[27] In 2009, a researcher from Alaska found permafrost at the 4,700 m (15,400 ft) level on Africa's highest peak, Mount Kilimanjaro, approximately 3° south of the equator.^[28]

Subsea permafrost

Subsea permafrost occurs beneath the seabed and exists in the continental shelves of the polar regions.^[29] These areas formed during the last ice age, when a larger portion of Earth's water was bound up in ice sheets on land and when sea levels were low. As the ice sheets melted to again become seawater, the permafrost became submerged shelves under relatively warm and salty boundary conditions, compared to surface permafrost. Therefore, subsea permafrost exists in conditions that lead to its diminishment. According to Osterkamp, subsea permafrost is a factor in the "design, construction, and operation of coastal facilities, structures founded on the seabed, artificial islands, sub-sea pipelines, and wells drilled for exploration and production."^[30] It also contains gas hydrates in places, which are a "potential abundant source of energy" but may also destabilize as subsea permafrost warms and thaws, producing large amounts of methane gas, which is a potent greenhouse gas.^[30][31][32] Scientists report with high confidence that the extent of subsea permafrost is decreasing, and 97% of permafrost under Arctic ice shelves is currently thinning.^[33][34]

Manifestations

Base depth

Permafrost extends to a base depth where geothermal heat from the Earth and the mean annual temperature at the surface achieve an equilibrium temperature of 0 °C.

Calculations indicate that the time required to form the deep permafrost underlying Prudhoe Bay, Alaska was over a half-million years.^[35][39] This extended over several glacial and interglacial cycles of the Pleistocene and suggests that the present climate of Prudhoe Bay is probably considerably warmer than it has been on average over that period. Such warming over the past 15,000 years is widely accepted.^[35] The table to the right shows that the first hundred metres of permafrost forms relatively quickly but that deeper levels take progressively longer.

Massive ground ice

When the ice content of a permafrost exceeds 250 percent (ice to dry soil by mass) it is classified as massive ice. Massive ice bodies can range in composition, in every conceivable gradation from icy mud to pure ice. Massive icy beds have a minimum thickness of at least 2 m and a short diameter of at least 10 m.^[40] First recorded North American observations were by European scientists at Canning River, Alaska in 1919.^[41] Russian literature provides an earlier date of 1735 and 1739 during the Great North Expedition by P. Lassinius and Kh. P. Laptev, respectively.^[42] Two categories of massive ground ice are buried surface ice and intrasedimental ice^[43] (also called constitutional ice).^[42]

Buried surface ice may derive from snow, frozen lake or sea ice, aufeis (stranded river ice) and—probably the most prevalent—buried glacial ice.^[44]

Intrasedimental ice forms by in-place freezing of subterranean waters and is dominated by segregational ice which results from the crystallizational differentiation taking place during the freezing of wet sediments, accompanied by water migrating to the freezing front.^[42]

Intrasedimental or constitutional ice has been widely observed and studied across Canada and also includes intrusive and injection ice.^[41][42]

Additionally, ice wedges—a separate type of ground ice—produce recognizable patterned ground or tundra polygons. Ice wedges form in a pre-existing geological substrate and were first described in 1919.^[41][42]

Landforms

Permafrost processes manifest themselves in large-scale land forms, such as palsas and pingos^[45] and smaller-scale phenomena, such as patterned ground found in arctic, periglacial and alpine areas.^[46] In ice-rich permafrost areas, melting of ground ice initiates thermokarst landforms such as thermokarst lakes, thaw slumps, thermal-erosion gullies, and active layer detachments.^[47][48]

• 
  A group of palsas, as seen from above, formed by the growth of ice lenses.
• 
  A peat plateau complex south of Fort Simpson, Northwest Territories
• 
  Pingos near Tuktoyaktuk, Northwest Territories, Canada
• 
  Ground polygons
• 
  Stone rings on Spitsbergen
• 
  Ice wedges seen from top
• 
  Solifluction on Svalbard
• 
  Contraction crack (ice wedge) polygons on Arctic sediment.
• 
  Cracks forming at the edges of the Storflaket permafrost bog in Sweden.

Carbon cycle in permafrost

The

Arctic permafrost has been diminishing for decades. Globally, permafrost warmed by about 0.3 °C between 2007 and 2016, with stronger warming observed in the continuous permafrost zone relative to the discontinuous zone.

At the

By definition, permafrost is ground that remains frozen for two or more years.^[3] The ground can consist of many substrate materials, including bedrock, sediment, organic matter, water or ice. Frozen ground is that which is below the freezing point of water, whether or not water is present in the substrate. Ground ice is not always present, as may be the case with nonporous bedrock, but it frequently occurs and may be present in amounts exceeding the potential hydraulic saturation of the thawed substrate.

During thaw, the ice content of the soil melts and, as the water drains or evaporates, causes the soil structure to weaken and sometimes become viscous until it regains strength with decreasing moisture content. Thawing can also influence the rate of change of soil gases with the atmosphere.^[61] One visible sign of permafrost degradation is the random displacement of trees from their vertical orientation in permafrost areas.^[62]

• 
  Thawing permafrost in Herschel Island, Canada, 2013
• 
  Permafrost and ice in Herschel Island, Canada, 2012
• 
  Permafrost thaw ponds on peatland in Hudson Bay, Canada in 2008.^[63]

Effect on slope stability

Over the past century, an increasing number of alpine rock slope failure events in mountain ranges around the world have been recorded. It is expected that the high number of structural failures is due to permafrost thawing, which is thought to be linked to climate change. Permafrost thawing is thought to have contributed to the 1987 Val Pola landslide that killed 22 people in the Italian Alps.^[64] In mountain ranges, much of the structural stability can be attributed to glaciers and permafrost. As climate warms, permafrost thaws, which results in a less stable mountain structure, and ultimately more slope failures.^[65]

McSaveney^[66] reported massive rock and ice falls (up to 11.8 million m³), earthquakes (up to 3.9 Richter), floods (up to 7.8 million m³ water), and rapid rock-ice flow to long distances (up to 7.5 km at 60 m/s) caused by “instability of slopes” in high mountain permafrost. Instability of slopes in permafrost at elevated temperatures near freezing point in warming permafrost is related to effective stress and buildup of pore-water pressure in these soils.^[67] Kia and his co-inventors^[68] invented a new filter-less rigid piezometer (FRP) for measuring pore-water pressure in partially frozen soils such as warming permafrost soils. They extended the use of effective stress concept to partially frozen soils for use in slope stability analysis of warming permafrost slopes. The use of effective stress concept has many advantages such as ability to extend the concepts of "Critical State Soil Mechanics" into frozen ground engineering.^{[citation needed]}

In high mountains rockfalls may be caused by thawing of rock masses with permafrost.^[69]

Frozen debris lobes

According to the

In the northern circumpolar region, permafrost contains 1700 billion tons of organic material equaling almost half of all organic material in all soils.[74] This pool was built up over thousands of years and is only slowly degraded under the cold conditions in the Arctic. The amount of carbon sequestered in permafrost is four times the carbon that has been released to the atmosphere due to human activities in modern time.^[75] One manifestation of this is yedoma, which is an organic-rich (about 2% carbon by mass) Pleistocene-age loess permafrost with ice content of 50–90% by volume.^[76]

Formation of permafrost has significant consequences for ecological systems, primarily due to constraints imposed upon rooting zones, but also due to limitations on den and

The number of bacteria in permafrost soil varies widely, typically from 1 to 1000 million per gram of soil.[78] Most of these bacteria and fungi in permafrost soil cannot be cultured in the laboratory, but the identity of the microorganisms can be revealed by DNA-based techniques.

Global warming has been increasing permafrost slope disturbances and sediment supplies to fluvial systems, resulting in exceptional increases in river sediment. ^[79]

Climate change feedback

This section is an excerpt from Permafrost carbon cycle § Carbon release from the permafrost.[edit]

Carbon is continually cycling between soils, vegetation, and the atmosphere. As climate change increases mean annual air temperatures throughout the Arctic, it extends permafrost thaw and deepens the active layer, exposing old carbon that has been in storage for decades to millennia to biogenic processes which facilitate its entrance into the atmosphere. In general, the volume of permafrost in the upper 3 m of ground is expected to decrease by about 25% per 1 °C (1.8 °F)of global warming.^[80]: 1283 According to the IPCC Sixth Assessment Report, there is high confidence that global warming over the last few decades has led to widespread increases in permafrost temperature.^[80]: 1237 Observed warming was up to 3 °C (5.4 °F) in parts of Northern Alaska (early 1980s to mid-2000s) and up to 2 °C (3.6 °F) in parts of the Russian European North (1970–2020), and active layer thickness has increased in the European and Russian Arctic across the 21st century and at high elevation areas in Europe and Asia since the 1990s.^[80]: 1237 In Yukon, the zone of continuous permafrost might have moved 100 kilometres (62 mi) poleward since 1899, but accurate records only go back 30 years. Based on high agreement across model projections, fundamental process understanding, and paleoclimate evidence, it is virtually certain that permafrost extent and volume will continue to shrink as global climate warms.^[80]: 1283

Carbon emissions from permafrost thaw contribute to the same warming which facilitates the thaw, making it a

positive climate change feedback. The warming also intensifies Arctic water cycle, and the increased amounts of warmer rain are another factor which increases permafrost thaw depths.^[81] The amount of carbon that will be released from warming conditions depends on depth of thaw, carbon content within the thawed soil, physical changes to the environment^[82] and microbial and vegetation activity in the soil. Microbial respiration is the primary process through which old permafrost carbon is re-activated and enters the atmosphere. The rate of microbial decomposition within organic soils, including thawed permafrost, depends on environmental controls, such as soil temperature, moisture availability, nutrient availability, and oxygen availability.^[83] In particular, sufficient concentrations of iron oxides in some permafrost soils can inhibit microbial respiration and prevent carbon mobilization: however, this protection only lasts until carbon is separated from the iron oxides by Fe-reducing bacteria, which is only a matter of time under the typical conditions.^[84] Depending on the soil type, Iron(III) oxide can boost oxidation of methane to carbon dioxide in the soil, but it can also amplify methane production by acetotrophs: these soil processes are not yet fully understood.^[85]

Altogether, the likelihood of the entire carbon pool mobilizing and entering the atmosphere is low despite the large volumes stored in the soil. Although temperatures will increase, this does not imply complete loss of permafrost and mobilization of the entire carbon pool. Much of the ground underlain by permafrost will remain frozen even if warming temperatures increase the thaw depth or increase thermokarsting and permafrost degradation.

adsorb some of the mobilized soil carbon before it reaches the atmosphere, and they are particularly prominent in the mineral sand layers which often overlay permafrost.^[87] On the other hand, once the permafrost area thaws, it will not go back to being permafrost for centuries even if the temperature increase reversed, making it one of the best-known examples of tipping points in the climate system

.

Preservation of organisms in permafrost

Microbes

Scientists predict that up to 10²¹ microbes, including fungi and bacteria in addition to viruses, will be released from melting ice per year. Often, these microbes will be released directly into the ocean. Due to the migratory nature of many species of fish and birds, it is possible that these microbes have a high transmission rate.^[101]

Permafrost in eastern Switzerland was analyzed by researchers in 2016 at an alpine permafrost site called “Muot-da-Barba-Peider”.This site had a diverse microbial community with various bacteria and eukaryotic groups present. Prominent bacteria groups included phylum Acidobacteriota, Actinomycetota, AD3, Bacteroidota, Chloroflexota, Gemmatimonadota, OD1, Nitrospirota, Planctomycetota, Pseudomonadota, and Verrucomicrobiota. Prominent eukaryotic fungi included Ascomycota, Basidiomycota, and Zygomycota. In the present species, scientists observed a variety of adaptations for sub-zero conditions, including reduced and anaerobic metabolic processes.^[102]

A 2016 outbreak of anthrax in the Yamal Peninsula is believed to be due to thawing permafrost.^[103] Also present in Siberian permafrost are two species of virus: Pithovirus sibericum^[104] and Mollivirus sibericum.^[105] Both of these are approximately 30,000 years old and considered giant viruses due to the fact that they are larger in size than most bacteria and have genomes larger than other viruses. Both viruses are still infective, as seen by their ability to infect Acanthamoeba, a genus of amoebas.^[105]

Freezing at low temperatures has been shown to preserve the infectivity of viruses. Caliciviruses, influenza A, and enteroviruses (ex. Polioviruses, echoviruses, Coxsackie viruses) have all been preserved in ice and/or permafrost. Scientists have determined three characteristics necessary for a virus to successfully preserve in ice: high abundance, ability to transport in ice, and ability to resume disease cycles upon being released from ice. A direct infection from permafrost or ice to humans has not been demonstrated; such viruses are typically spread through other organisms or abiotic mechanisms.^[101]

A study of late Pleistocene Siberian permafrost samples from Kolyma Lowland (an east siberian lowland) used DNA isolation and gene cloning (specifically 16S rRNA genes) to determine which phyla these microorganisms belonged to. This technique allowed a comparison of known microorganisms to their newly discovered samples and revealed eight phylotypes, which belonged to the phyla Actinomycetota and Pseudomonadota.^[106]

Plants

In 2012, Russian researchers proved that permafrost can serve as a natural repository for ancient life forms by reviving of

Sources

• Fox-Kemper, Baylor; Hewitt, Helene T.; Xiao, Cunde; Aðalgeirsdóttir, Guðfinna; et al. (2021). "Chapter 9: Ocean, cryosphere, and sea level change" (PDF). IPCC AR6 WG1 2021.
• IPCC (2021). Masson-Delmotte, V.; Zhai, P.; Pirani, A.; Connors, S. L.; et al. (eds.). Climate Change 2021: The Physical Science Basis (PDF). Contribution of Working Group I to the Sixth Assessment Report
  of the Intergovernmental Panel on Climate Change. Cambridge University Press (In Press).

External links

Look up permafrost in Wiktionary, the free dictionary.

Wikimedia Commons has media related to Permafrost.

• Permafrostwatch University of Alaska Fairbanks
• Infographics about permafrost
• International Permafrost Association (IPA)
• Alpine permafrost monitoring network - permanet
• Center for Permafrost
• Map of permafrost in Antarctica.
• Permafrost – what is it? – YouTube (Alfred Wegener Institute)