Permafrost soil

from Wikipedia, the free encyclopedia
Permafrost soil with an ice wedge

A permafrost - and permafrost - frozen all year round. Permafrost is therefore “ soil , sediment or rock that has temperatures below freezing point for at least two years without interruption in different thicknesses and depths under the earth's surface”. Permafrost research is the subject of periglacial research.

distribution

Distribution and types of permafrost in the northern hemisphere

Permafrost soils form where the annual average temperature is −1 ° C and the annual precipitation does not exceed 1000 millimeters. The great permafrost areas of the earth are therefore in the polar regions with the arctic and antarctic tundras , in large parts of the boreal coniferous forest areas , but also in all areas that meet the requirements for permafrost, such as high mountains. The permafrost zone is “the circumpolar area of ​​perpetual freezing, which includes the tundra of the northern continents, the large forest areas and offshore zones of the seabed ”.

Geographically speaking, it is a large part of northern Canada , Alaska , Greenland and eastern Siberia . About 20 to 25% of the earth's land area lies within the permafrost zone. Greenland is 99%, Alaska 80%, Russia 50%, Canada 40 to 50% and China up to 20% in the permafrost zone. To the south, some permafrost areas extend into Mongolia .

A location within the permafrost zone does not automatically mean an underlay of permafrost for each individual location, but a distinction is made between continuous (> 90 area percent), discontinuous (> 50–90 area percent), sporadic (> 10–50 area percent) and isolated zones (<10 percent by area) permafrost.

The permafrost also penetrates the subsoil at different depths: In Siberia depths of up to 1500 meters are reached, in Scandinavia only up to approx. 20 meters. The reasons for this lie in the large continental glaciation of the last ice age ( Vistula glacial period ): Siberia was not glaciated to a large extent, so the ground was permanently exposed to the cold air, so that it could freeze down to very low levels. In contrast, Scandinavia was more or less isolated by the mighty ice sheets underground, which meant that the permafrost could not penetrate as deeply.

There are also permafrost areas in high mountain regions such as the Alps . They were formed during the last Ice Age ( Würm Ice Age ), when the ground froze in places to a depth of several thousand meters. In addition to these fossil permafrost areas in the Alps, recent permafrost formation is also taking place today - even if only to a very limited extent (for example due to the retreat of an isolating glacier or rock glacier , whereby the soil is directly exposed to the cold air and permafrost can form again, provided that the requirements are met). On the other hand, an increase in the mean air temperature causes the permafrost soil to thaw in the Alps. For example, in 2015 the water intake (for drinking water and hydropower) of the Richterhütte at 2,374 m above sea level in the Zillertal Alps was destroyed. The Sonnblick Observatory is also endangered in the long term.

In the southern hemisphere, there are permafrost soils, except in the mountainous region of the Andes , on almost 50,000 km 2 of glacier-free areas in the Antarctic. According to this, permafrost there is only relatively small, aided by the fact that less than 1 percent of the land mass there is ice-free.

In addition, there is also submarine permafrost in the Arctic, i.e. permafrost soils on the sea floor. Due to the density anomaly of the water, it is actually physically impossible, which can be explained as follows: Due to the eustatic sea ​​level fluctuation of the last Ice Age , many continental shelves , which are now under water again, were above sea level, which meant that the soils there could form permafrost down to several 100 meters. The seawater that flooded the shelf again in the warm phase that followed was too cold to thaw the submarine permafrost again. In addition, submarine permafrost can form when sea ice rests on the sea floor in shallow waters and the sediments below freeze. The best-known submarine permafrost areas are in the Laptev Sea in the Arctic Ocean .

Permafrost soils can thaw superficially in summer; the thawing floor (often referred to as the active layer in the literature ) is usually between 30 centimeters and 2 meters deep. The ground below remains frozen. Due to the thawing floor, numerous periglacial denudation processes take place. The periodically frozen upper soil layer formed outside the periglacial areas is called winter frosty soil ; this does not belong to the permafrost soils (for example the topsoil frozen in Central Europe in winter).

Some future forecasts assume that permafrost areas will decrease by 25–44% worldwide with an increase in the global average temperature of 2 K due to increasing global warming  .

Outline of the permafrost

Vertical structure of the permafrost soil
Horizontal layout
  1. Zone of continuous permafrost (90 to 100% of the subsoil of a region is frozen)
  2. Zone of discontinuous permafrost (more than 50% of the subsoil of a region is frozen)
  3. Zone of sporadic permafrost (patchy distribution of the frozen subsoil)

Vertical structure (from top to bottom)

  1. Summer thawing floor ( active layer ), which can be thawed to a greater or lesser extent at higher temperatures (thickness: a few centimeters to several meters)
  2. actual permafrost is always frozen; the surface, i.e. the boundary to the thawed soil, is called the permafrost table
  3. Niefrostboden is unfrozen due to the geothermal heat supply from the interior of the earth and lies in a few decades up to a maximum of 1,500 meters depth

A non-frozen area within the permafrost is called a talik . A distinction is made between open and closed taliki, the latter have no contact with the thawing floor.

Distribution of the vegetation zones during the cold maximum of the last glacial period , in the period 24,500 to 18,000 BC In Europe
white: glaciation ; pink dashed line: southern limit of the tundra; white dotted line: southern limit of the permafrost ground; green line: steppe / tree line; yellow hatching: loess desert

Paleontological importance

Pre-Ice Age fauna and flora were excellently preserved in permafrost . The biological material found is permanently frozen. This also enables DNA analyzes of the finds, which is otherwise not possible with fossils . In 1997 a very well preserved woolly mammoth (the Jarkow mammoth ) was found on the Taimyr Peninsula in northern Siberia by the dolgan Gennadij Jarkow, which was extensively examined.

The toadflax species Silene stenophylla was able to survive in the Siberian permafrost for over 30,000 years. In 2012, researchers from the Russian Academy of Sciences managed to grow plants from frozen remains.

Viruses such as the 30,000 year old Mollivirus sibericum have also been found in the permafrost soil.

In addition, nematodes have been found in Siberia that had been preserved in the permafrost soil since the Pleistocene around 42,000 years ago. Despite the fact that they had been frozen for tens of thousands of years, two types of these worms have been successfully revived.

Carbon storage

In permafrost areas such as the Arctic , Antarctic or high mountains , between 1,300 and 1,600 gigatons of carbon are stored, about twice as much as in the entire earth's atmosphere (around 800 gigatons): When the permafrost soils thaw, accelerated by climate change, this is released as a greenhouse gas, carbon dioxide. The thawing of permafrost is considered to be one of the most important tipping elements of global warming.

The investigation of the carbon dynamics in permafrost-influenced soils and the estimation of the amount of carbon stored there are the subject of current research.

Decline in permafrost soils

Stone rings on Svalbard
The ridges of ice wedges visible on the surface of the earth
Solifluction on Svalbard

In the course of global warming , the permafrost is also warming almost worldwide. A northward migration of the permafrost border in North America , Eurasia and the Arctic has been observed in the last few decades . According to a study by the Alfred Wegener Institute (AWI), the temperature of permafrost soils rose by 0.3 degrees Celsius between 2007 and 2016 . The greatest increase was observed in Siberia , where the temperature rise was almost one degree Celsius in some cases. In addition to higher air temperatures in the discontinuous permafrost zone, a thicker snow cover was also the cause.

In the Garwood Valley on the coast of East Antarctica Victoria Land, thermo karst development accelerated sharply between 2001 and 2012 . The cause is probably more intense solar radiation as a result of changed weather conditions. The thin layer of sediment above the permafrost has accelerated its thawing. It is feared that a warming of the region could lead to an equally rapid thawing of the permafrost.

Farquharson, et al. published a scientific article in 2019 about the changes in the permafrost soil (more precisely: the thermokarst) at three measuring stations in the Canadian high Arctic between 2003 and 2017. According to the authors, the soil in some regions of Canada often thawed as much during the study period as it did in a moderate one Development (according to the IPCC RCP 4.5 scenario ; see also representative concentration path ) was actually only expected for the year 2090 with global warming of around 1.1 to 2.6 ° C. As a result, for example, the ground at the “Mold Bay” weather station on Prince Patrick Island sagged by around 90 centimeters in the period under study. The reason for this development seems to be the thawing of the permafrost; The permafrost table is shifting to ever greater depths due to the frequent, above-average warm summers, as the summer thawing soil has a limited heat buffer capacity and thus insulates the permafrost soil poorly against rising temperatures.

Due to the rise in temperature in the Arctic, the risk of forest fires increases there . If the peat soil in the Arctic becomes drier as a result of the warming, it catches fire more easily and in turn releases greenhouse gases into the atmosphere. Smoke and soot resulting from fires cover water and snow areas and reduce their reflectivity ( albedo ), which leads to greater local warming. Thawed permafrost soils in turn provide more food for fires. In June and July 2019, an unusually high number of forest fires was observed in the Arctic, especially in Alaska, where there was a large period of warmth and drought in 2019 (see also Forest Fires in the Boreal Forests of the Northern Hemisphere in 2019 ). If high temperatures and drought persist for several consecutive years, peat soils become flammable more quickly and underground bog fires occur , which can hardly be extinguished. 2020 occurred due to the heat wave in Siberia in 2020 for diesel oil spill in Norilsk , as permafrost thawed.

Damage to buildings and infrastructure

The direct consequences of a decline in permafrost soil include damage to roads, houses and infrastructure, which, where the permafrost thaws, now only stand on mud and can therefore completely or partially sink. Damage to industrial plants, where there is a risk that large amounts of pollutants will be released into the sensitive arctic ecosystems, which are difficult to regenerate due to the short vegetation period, is particularly ecologically threatening. In 2020, a serious oil spill occurred in the Siberian city of Norilsk when an oil tank for a power plant burst as a result of the thawing permafrost and more than 20,000 tons of oil leaked. About 5,000 tons of oil contaminated the soil, most of the oil ended up in bodies of water, especially the Ambarnaya River . The accident is considered to be the biggest accident to date as a result of the thawing permafrost. According to Greenpeace Russia, it was also the largest oil spill in the Arctic since the Exxon Valdez disaster in 1989. Previously, Siberia had experienced the warmest winter since records began 130 years ago, at up to 6 degrees above the long-term average. In Russia, temperatures between January and May 2020 were 5.3 ° C above the average for 1951–1980; In addition, the previous record was exceeded by 1.9 ° C.

Amplification of climate change

In the long term, thawing is feared to an even greater extent, as the Arctic is warmer than average (→  polar amplification ). Some scientists believe that there will be a positive feedback could come when the permanently frozen soils as biomass -bound carbon is in great quantity present, the during defrosting and degradation of biomass as a greenhouse gas CO 2 would be discharged into the atmosphere.

In addition, in this case, bound methane in permafrost soils will escape into the atmosphere in large quantities . Since the global warming potential of methane is estimated to be around 25 times that of CO 2 (possibly even up to 33 if interactions with atmospheric aerosols are taken into account), this is expected to further intensify global warming.

The economic follow-up costs of the release of methane gas when thawing the permafrost under the East Siberian Sea ( Arctic ) in the course of global warming were estimated at 60 trillion US dollars worldwide. Because of the low extent of permafrost in the Antarctic and because of the fact that "climate changes in the continental Antarctica are much slower" than in the Arctic, the Antarctic permafrost does not represent a climate-relevant risk of greenhouse gas emissions.

According to a study published in Nature in 2018 , previous estimates only took into account the gradual thawing of permafrost near the surface; an abrupt thawing of thermokarst lakes would accelerate the mobilization of frozen carbon and lead, measured in CO 2 equivalents , to significantly increased emissions. Climate models that only take into account the gradual and not the occasional abrupt thawing of permafrost significantly underestimated the carbon emissions caused by the thawing of permafrost.

In addition to carbon dioxide and methane, defrosting also increasingly releases laughing gas, the global warming potential of which is around 300 times higher than that of CO 2 over 100 years . Further warming can transform the Arctic from a previously negligible source into a small but important source of global nitrous oxide emissions.

According to scientists, the influence of methane-forming microorganisms in permafrost has long been underestimated in climate models .

In CMIP5 climate models , greenhouse gas emissions caused by the thawing of permafrost are not taken into account, which leads to a systematic underestimation of global warming. Researchers have therefore tried to add these effects retrospectively using correction factors.

A study by Natali et al. a. (2019) comes to the conclusion that the recent warming in the Arctic, which increased in winter, significantly accelerated the microbial degradation of soil organic matter and the subsequent release of carbon dioxide. To estimate current and future carbon losses in winter from the northern permafrost area, the authors synthesized regional in-situ observations of the CO 2 flow from arctic and boreal soils. They estimated a current loss of the permafrost region of 1,662 TgC per year in the winter season (October – April) . This loss is greater than the average carbon uptake in the growing season in this region, estimated according to process models (–1,032 TgC per year). The extension of the model predictions to warmer conditions up to 2100 indicates an increase in CO 2 emissions in winter with a moderate climate protection scenario ( representative concentration path 4.5) by 17% and with a continuing -as-before-emission scenario (representative concentration path 8.5) 41% there. These results provide a basis for winter CO 2 emissions from northern regions and indicate that increased CO 2 loss in the soil due to warming in winter can offset the carbon uptake in the growing season under future climatic conditions.

Release of mercury

Another danger is the release of large amounts of harmful mercury through the thawing of the permafrost soils. In the frozen biomass of the Arctic permafrost, about twice as much mercury is bound as in all other soils, the atmosphere and the oceans combined. When the permafrost is thawed, biological degradation processes would start, through which the mercury may be released into the environment, where it could be. a. could harm arctic ecosystems, aquatic life in the oceans, and human health.

Changes in topography

The thawing of permafrost has already caused significant and threatening changes in topography. Especially in northern Russia, large flat areas suddenly sank within a short time when the frozen water thawed and lost volume, trapped gas escaped and the perforated soil subsequently collapsed under its own weight. Since then, large areas have been a crater landscape with crooked and uprooted trees and lakes with condensation. The submarine permafrost off the Russian coast is also thawing more quickly due to the influx of warm water and allowing gases to escape.

“Stilt house” in Yakutsk
Thawing soil in permafrost region

The superficial thawing of the soils creates many problems in the construction of buildings. If buildings were built on the frozen ground in winter, they can collapse when it thaws. In areas with permafrost soils, buildings are therefore primarily built on piles that reach down into the permanently frozen areas of the ground and thus stand on solid ground. In addition, air can flow around the sub-floor of the house and carry away the heat emitted by the building so that the floor below does not thaw.

The thawing of the permafrost in the Alps sets entire mountain slopes in motion. In 2007, around four million cubic meters of rock and ice slid towards the valley on the Bliggferner in the Alps.

In mountainous regions in Norway, the permafrost soil has a temperature of 0 to −3 ° C. Therefore, if the global warming continues, massive landslides are likely, as the frozen water acts as a binding agent and holds loose rock, sand and the like together. As a result of landslides and landslides , megatsunamis can arise in narrow fjord gorges with heights of 100 m and more.

Others

The permafrost phenomenon was discovered by the Cossacks . The original English word dates from 1943. The colloquial Russian expression wetschnaja merslota ("forever frozen ground") appeared in a scientific lexicon as early as the middle of the 19th century.

It is believed that the water once abundant on Mars is now at least partly as ice in the ground. So there would also be frozen ground there.

A geothermal -use heat pump system can lead to an artificial permafrost if the extracted heat energy can no longer be adequately replenished by the environment. In this case, a block of frozen ground forms around the heat exchanger coils in the ground, which significantly reduces the heating output.

See also

  • Cryoturbation - mixing of the near-surface subsurface by freezing and thawing
  • Nunavut - territory in northern Canada characterized by permafrost soils
  • Thermokarst - land formation process through superficially thawing permafrost soils

literature

  • A. Strahler & A. Strahler: Physical geography . 2002.
  • MA Summerfield: Global Geomorphology. An Introduction to the Study of Landforms . 1991.
  • H. Zepp: Grundriss Allgemeine Geographie: Geomorphologie . 2004.
  • F. Ahnert: Introduction to Geomorphology . 1996.
  • H. French: The Periglacial Environment . 2004.
  • H. Readers: Geomorphology - The Geographical Seminar . 2003.
  • J. Map: Spatial delimitation and regional differentiation of the periglacial . 1979.
  • A. Semmel: Periglacial morphology . 1985.
  • WD Blümel: Physical geography of the polar regions . 1999.
  • Bernhard Wietek : Permafrost in the summit area. International Cable Car Review 2/2007 . 2007.
  • W. Zech, P. Schad, G. Hintermaier-Erhard: Soils of the world. 2nd edition . Springer Spectrum, Heidelberg 2014, ISBN 978-3-642-36574-4 .

Web links

Commons : Permafrost  - collection of images, videos and audio files
 Wikinews: Siberia: Thawing Permafrost Alerts Climate Scientists  - News
Wiktionary: Permafrost  - explanations of meanings, word origins, synonyms, translations
Wiktionary: permafrost soil  - explanations of meanings, word origins, synonyms, translations

Individual evidence

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  49. ↑ Researchers measure methane outbreak off Siberia for the first time , Spiegel.de March 5, 2010. The article refers to Natalia Shakhova et al .: Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf . Science, March 5, 2010: Vol. 327, Issue 5970, pp. 1246-1250. doi: 10.1126 / science.1182221
  50. ↑ FAZ.net July 27, 2010: When the permafrost melts, the slopes slide
  51. ↑ Permafrost - And then the summit was gone , sueddeutsche.de December 27, 2007 (copy on waltner.co.at)
  52. ↑ Landslide disasters
  53. ↑ "Limet" i bakken forsvinner ( "The" glue "disappears into the ground.") - Message on May 21, 2009 yr.no ( Bokmål , accessed on 23 June 2009)
  54. ^ B. McGuire: Potential for a hazardous geospheric response to projected future climate changes . In: Philosophical Transactions of the Royal Society A . March 2010, doi : 10.1098 / rsta.2010.0080 .
  55. ↑ Bretwood Higman et al. a .: The 2015 landslide and tsunami in Taan Fiord, Alaska . In: Scientific Reports . No. 12993 , September 6, 2018, Table 1, doi : 10.1038 / s41598-018-30475-w .
  56. ↑ “ The cold heart of Siberia is thawing ” in Edition Le Monde diplomatique 2017, No. 20 p. 13.