Carbon cycle 47503 225329217 2008-07-13T03:15:40Z SEWilco 18620 Reverted 1 edit by [[Special:Contributions/58.172.17.140|58.172.17.140]] identified as [[WP:VAND|vandalism]] to last revision by [[User:Paleorthid|Paleorthid]]. ([[WP:TW|TW]]) {{for|the thermonuclear reaction involving carbon that helps power stars|CNO cycle}} [[Image:Carbon cycle-cute diagram.svg|thumb|400px||Diagram of the carbon cycle. The black numbers indicate how much carbon is stored in various reservoirs, in billions of tons ("GtC" stands for GigaTons of Carbon and figures are circa 2004). The purple numbers indicate how much carbon moves between reservoirs each year. The sediments, as defined in this diagram, do not include the ~70 million GtC of carbonate rock and kerogen.]] The carbon cycle is the biogeochemical cycle by which carbon is exchanged between the [[biosphere]], [[pedosphere]], [[geosphere]], [[hydrosphere]], and [[Earth's atmosphere|atmosphere]] of the Earth. The cycle is usually thought of as four major reservoirs of carbon interconnected by pathways of exchange. These reservoirs are: * The atmosphere. * The terrestrial biosphere, which is usually defined to include fresh water systems and non-living organic material, such as soil carbon. * The [[ocean]]s, including [[total inorganic carbon|dissolved inorganic carbon]] and living and non-living marine biota, * The [[sediment]]s including [[fossil fuel]]s. The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. The ocean contains the largest active pool of carbon near the surface of the Earth, but the [[deep ocean]] part of this pool does not rapidly exchange with the atmosphere. The '''global carbon budget''' is the balance of the exchanges (incomes and losses) of carbon between the carbon reservoirs or between one specific loop (e.g., atmosphere ↔ biosphere) of the carbon cycle. An examination of the carbon budget of a pool or reservoir can provide information about whether the pool or reservoir is functioning as a source or sink for carbon dioxide. ==In the atmosphere== Carbon exists in the [[Earth's atmosphere]] primarily as the gas [[carbon dioxide]] (CO<sub>2</sub>). Although it is a very tiny percent of the atmosphere (approximately 0.04% on a [[Mole (unit)|molar]] basis, though rising), it plays an important role in supporting life. Other gases containing carbon in the atmosphere are [[methane]] and [[chlorofluorocarbon]]s (the latter is entirely [[anthropogenic]]). The overall atmospheric concentration of these [[greenhouse gas]]es has been increasing in recent decades, contributing to [[global warming]].<ref>[http://www.ipcc.ch/ The Intergovernmental Panel on Climate Change (IPCC)] which represents wide consensus of international scientific opinion.</ref> Carbon is taken from the atmosphere in several ways: * When the sun is shining, [[plant]]s perform [[photosynthesis]] to convert carbon dioxide into [[carbohydrates]], releasing [[oxygen]] in the process. This process is most prolific in relatively new forests where tree growth is still rapid. The effect is strongest in deciduous forests during spring leafing out. This is visible as an annual signal in the [[Keeling curve]] of measured CO<sub>2</sub> concentration. Northern hemisphere spring predominates, as there is far more land in temperate latitudes in that hemisphere than in the southern. * Forests store 86% of the planet's above-ground carbon and 73% of the planet's soil carbon.<ref>Sedjo, Roger.1993. The Carbon Cycle and Global Forest Ecosystem. Water, Air, and Soil Pollution 70, 295-307. (via [http://www.oregonwild.org/oregon_forests/old_growth_protection/forests-global-warming/oregon-wild-report-on-forests-carbon-and-global-warming Oregon Wild Report on Forests, Carbon, and Global Warming])</ref> * At the surface of the oceans towards the poles, [[seawater]] becomes cooler and more [[carbonic acid]] is formed as CO<sub>2</sub> becomes more soluble. This is coupled to the ocean's [[thermohaline circulation]] which transports dense surface water into the ocean's interior (see the entry on the [[solubility pump]]). * In upper ocean areas of high biological productivity, organisms convert reduced carbon to tissues, or carbonates to hard body parts such as shells and tests. These are, respectively, oxidized ([[soft-tissue pump]]) and redissolved ([[carbonate pump]]) at lower average levels of the ocean than those at which they formed, resulting in a downward flow of carbon (see entry on the [[biological pump]]). * The [[weathering]] of silicate rock. Carbonic acid reacts with weathered rock to produce bicarbonate ions. The [[bicarbonate]] ions produced are carried to the ocean, where they are used to make marine carbonates. Unlike dissolved CO<sub>2</sub> in equilibrium or tissues which decay, weathering does not move the carbon into a reservoir from which it can readily return to the atmosphere. Carbon can be released back into the atmosphere in many different ways: * Through the [[respiration]] performed by plants and animals. This is an [[exothermic reaction]] and it involves the breaking down of glucose (or other organic molecules) into carbon dioxide and water. * Through the [[bacterial decay|decay]] of animal and plant matter. [[Fungi]] and [[bacterium|bacteria]] break down the carbon compounds in dead animals and plants and convert the carbon to carbon dioxide if oxygen is present, or [[methane]] if not. * Through [[combustion]] of organic material which [[oxidizes]] the carbon it contains, producing carbon dioxide (and other things, like water vapor). Burning [[fossil fuel]]s such as [[coal]], [[petroleum]] products, and [[natural gas]] releases carbon that has been stored in the geosphere for millions of years. Burning agrofuels also releases carbon dioxide. * Production of [[cement]]. Carbon dioxide is released when [[limestone]] (calcium carbonate) is heated to produce [[calcium oxide|lime]] (calcium oxide), a component of cement. * At the surface of the oceans where the water becomes warmer, dissolved carbon dioxide is released back into the atmosphere. * [[Volcano|Volcanic eruptions]] and [[metamorphism]] release gases into the atmosphere. [[Volcanic gas]]es are primarily [[water vapor]], carbon dioxide and [[sulfur dioxide]]. The carbon dioxide released is roughly equal to the amount removed by silicate weathering; so the two processes, which are the chemical reverse of each other, sum to roughly zero, and do not affect the level of atmospheric carbon dioxide on time scales of less than about 100,000 yr. * Forests and crops in the process of growing absorbs lots of carbon, while old and stable forest consumes as much CO2 during the day as they produce during the night. ==In the biosphere == Around 1,900 [[gigaton]]s of carbon are present in the [[biosphere]]. Carbon is an essential part of life on Earth. It plays an important role in the [[Cytoskeleton|structure]], [[biochemistry]], and [[nutrition]] of all living [[Cell (biology)|cells]]. * [[Autotroph]]s are organisms that produce their own [[organic compound]]s using carbon dioxide from the air or water in which they live. To do this they require an external source of energy. Almost all autotrophs use solar radiation to provide this, and their production process is called [[photosynthesis]]. A small number of autotrophs exploit chemical energy sources in a process called [[chemosynthesis]]. The most important autotrophs for the carbon cycle are [[tree]]s in forests on land and [[phytoplankton]] in the Earth's oceans. Photosynthesis follows the reaction 6CO<sub>2</sub> + 6H<sub>2</sub>O → C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> + 6O<sub>2</sub> * Carbon is transferred within the biosphere as [[heterotroph]]s feed on other organisms or their parts (e.g., fruits). This includes the uptake of dead organic material ([[detritus]]) by fungi and bacteria for [[fermentation (biochemistry)|fermentation]] or [[decay]]. * Most carbon leaves the biosphere through [[Cellular respiration|respiration]]. When oxygen is present, [[aerobic respiration]] occurs, which releases carbon dioxide into the surrounding air or water, following the reaction C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> + 6O<sub>2</sub> → 6CO<sub>2</sub> + 6H<sub>2</sub>O. Otherwise, [[anaerobic respiration]] occurs and releases methane into the surrounding environment, which eventually makes its way into the atmosphere or hydrosphere (e.g., as marsh gas or [[flatulence]]). * Burning of biomass (e.g. forest fires, wood used for heating, anything else organic) can also transfer substantial amounts of carbon to the atmosphere * Carbon may also be circulated within the biosphere when dead organic matter (such as [[peat]]) becomes incorporated in the geosphere. [[Animal shell]]s of [[calcium carbonate]], in particular, may eventually become [[limestone]] through the process of [[sediment]]ation. * Much remains to be learned about the cycling of carbon in the deep ocean. For example, a recent discovery is that [[larvacea]]n [[mucus]] houses (commonly known as "sinkers") are created in such large numbers that they can deliver as much carbon to the deep ocean as has been previously detected by [[sediment trap]]s.<ref>{{cite press release|title="Sinkers" provide missing piece in deep-sea puzzle|publisher=Monterey Bay Aquarium Research Institute (MBARI)|date=[[2005-06-09]]|url=http://www.mbari.org/news/news_releases/2005/sinkers-release.pdf|accessdate=2007-10-07}}</ref> Because of their size and composition, these houses are rarely collected in such traps, so most biogeochemical analyses have erroneously ignored them. Carbon storage in the biosphere is influenced by a number of processes on different time-scales: while [[primary production|net primary productivity]] follows a [[wiktionary:diurnal|diurnal]] and seasonal cycle, carbon can be stored up to several hundreds of years in trees and up to thousands of years in soils. Changes in those long term carbon pools (e.g. through de- or afforestation or through temperature-related changes in soil respiration) may thus affect global climate change. == In the ocean == [[Image:TIC oceans.png|thumb|right|200px|"Present day" (1990s) sea surface [[Total inorganic carbon|dissolved inorganic carbon]] concentration (from the [[Global Ocean Data Analysis Project|GLODAP]] [[climatology]])]] The [[ocean]]s contain around 36,000 [[gigatonne]]s of carbon, mostly in the form of [[bicarbonate]] [[ion]] (over 90%, with most of the remainder being [[carbonate]]).. Inorganic carbon, that is carbon compounds with no carbon-carbon or carbon-hydrogen bonds, is important in its reactions within water. This carbon exchange becomes important in controlling [[pH]] in the ocean and can also vary as a source or sink for carbon. Carbon is readily exchanged between the atmosphere and ocean. In regions of oceanic upwelling, carbon is released to the atmosphere. Conversely, regions of downwelling transfer carbon (CO<sub>2</sub>) from the atmosphere to the ocean. When CO<sub>2</sub> enters the ocean, it participates in a series of reactions which are locally in equilibrium: Solution: ::CO<sub>2</sub>(atmospheric) {{unicode|⇌}} CO<sub>2</sub>(dissolved) Conversion to carbonic acid: ::CO<sub>2</sub>(dissolved) + H<sub>2</sub>O {{unicode|⇌}} H<sub>2</sub>CO<sub>3</sub> First ionization: ::H<sub>2</sub>CO<sub>3</sub> {{unicode|⇌}} H<sup>+</sup> + HCO<sub>3</sub><sup>−</sup> (bicarbonate ion) Second ionization: ::HCO<sub>3</sub><sup>−</sup> {{unicode|⇌}} H<sup>+</sup> + CO<sub>3</sub><sup>−−</sup> (carbonate ion) This set of reactions, each of which has its own equilibrium coefficient determines the form that inorganic carbon takes in the oceans<ref>{{cite book|last=Millero|first=Frank J.|edition=3|title=Chemical Oceanography|publisher=CRC Press|location=|year=2005|isbn=0849322804}}</ref>. The coefficients, which have been determined empirically for ocean water, are themselves functions of temperature, pressure, and the presence of other ions (especially borate). In the ocean the equilibria strongly favor bicarbonate. Since this ion is three steps removed from atmospheric CO<sub>2</sub>, the level of inorganic carbon storage in the ocean does not have a proportion of unity to the atmospheric partial pressure of CO<sub>2</sub>. The factor for the ocean is about ten: that is, for a 10% increase in atmospheric CO<sub>2</sub>, oceanic storage (in equilibrium) increases by about 1%, with the exact factor dependent on local conditions. This buffer factor is often called the "[[Revelle Factor]]", after [[Roger Revelle]]. In the oceans, bicarbonate can combine with [[calcium]] to form [[limestone]] ([[calcium carbonate]], CaCO<sub>3</sub>, with [[silica]]), which precipitates to the [[Seabed|ocean floor]]. Limestone is the largest reservoir of carbon in the carbon cycle. The calcium comes from the weathering of [[Silicate minerals|calcium-silicate rocks]], which causes the [[silicon]] in the rocks to combine with [[oxygen]] to form [[sand]] or [[quartz]] ([[silicon dioxide]]), leaving calcium ions available to form limestone<ref>{{cite web | last = Notes | first = Lecture | title = The Carbon Cycle | work = Department of Atmospheric Sciences | publisher = University of Washington | url = http://www.atmos.washington.edu/2001Q1/211/notes_for_013001_lecture.html | accessdate = 2008-07-08 }}</ref>. == See also == * [[C4MIP]] * [[Carbon footprint]] * [[Global Carbon Project]] * [[Carbon diet]] * [[Low carbon diet]] * [[Ocean acidification]] * [[Primary production]] == References == {{reflist}} ===Further reading=== * {{cite journal|last=Appenzeller|first=Tim|coauthors=|year=2004|title=The case of the missing carbon|url=http://magma.nationalgeographic.com/ngm/0402/feature5/index.html|journal=National Geographic Magazine|issn=|volume=|issue=|pages=|doi=}} - article about the missing carbon sink * {{cite book|last=[[Bert Bolin|Bolin]]|first=Bert|coauthors=Degens, E. T.; Kempe, S.; Ketner, P.|authorlink=|title=The global carbon cycle|edition=|publisher=Published on behalf of the Scientific Committee on Problems of the Environment (SCOPE) of the International Council of Scientific Unions (ICSU) by Wiley|location=Chichester ; New York|year=1979|isbn=0471997102|url=http://www.icsu-scope.org/downloadpubs/scope13/index.html|accessdate=2008-07-08}} * {{cite book|last=Houghton|first=R. A.|chapter=The contemporary carbon cycle|editor=William H Schlesinger (editor)|title=Biogeochemistry|edition=|publisher=Elsevier Science|location=Amsterdam|year=2005|isbn=0080446426|pages=473-513}} * {{cite journal|last=Janzen|first=H. H.|coauthors=|year=2004|title=Carbon cycling in earth systems—a soil science perspective|url=|journal=Agriculture, ecosystems and environment|issn=0167-8809|volume=104|issue=3|pages=399–417|doi=10.1016/j.agee.2004.01.040}} * {{cite book|last=Millero|first=Frank J.|edition=3|title=Chemical Oceanography|publisher=CRC Press|location=|year=2005|isbn=0849322804}} * {{cite book|last=Sundquist|first=Eric|coauthors=[[Wallace S. Broecker|Broecker]], Wallace S.(editors)|title=The Carbon Cycle and Atmospheric CO<sub>2</sub>: Natural variations Archean to Present|publisher=American Geophysical Union|series=Geophysical Monographs Series|number=32|location=|year=1985|isbn=}}<!--Volk, T., and Hoffert, M.J.: Ocean cabron pumps: analysis of relative strengths and efficiencies in ocean-driven atsmopheric pCO2 change--> == External links == * [http://www.carboncyclescience.gov/ Carbon Cycle Science Program] - an interagency partnership. * [http://www.esrl.noaa.gov/gmd/ccgg/index.html NOAA's Carbon Cycle Greenhouse Gases Group] * [http://www.globalcarbonproject.org/ Global Carbon Project - initiative of the Earth System Science Partnership] * [http://www.grida.no/climate/vital/13.htm UNEP - The present carbon cycle - Climate Change] carbon levels and flows {{Biogeochemical cycle}} [[Category:Geochemistry]] [[Category:Chemical oceanography]] [[Category:Photosynthesis]] [[Category:Soil biology]] [[Category:Soil chemistry]] [[Category:Carbon|Cycle]] [[Category:Numerical climate and weather models]] [[Category:Biogeography]] [[af:Koolstofkringloop]] [[ar:دورة كربون]] [[bg:Кръговрат на въглерода]] [[cs:Koloběh uhlíku]] [[cy:Cylchred Garbon]] [[da:Kulstofkredsløb]] [[de:Kohlenstoffzyklus]] [[et:Süsinikuringe]] [[es:Ciclo del carbono]] [[fr:Cycle du carbone]] [[ko:탄소의 순환]] [[id:Siklus karbon]] [[it:Ciclo del carbonio]] [[ka:ნახშირბადის წრებრუნვა]] [[lt:Anglies ciklas]] [[mk:Јаглероден циклус]] [[nl:Koolstofkringloop]] [[ja:炭素循環]] [[no:Karbonkretsløpet]] [[pl:Obieg węgla w przyrodzie]] [[pt:Ciclo do carbono]] [[ro:Circuitul carbonului în natură]] [[ru:Геохимический цикл углерода]] [[su:Daur karbon]] [[fi:Hiilen kiertokulku]] [[sv:Kolcykeln]] [[th:วัฏจักรคาร์บอน]] [[uk:Вуглецевий цикл]] [[zh:碳循環]]