Դիտել Մասնակից:Մելանի/Ավազարկղ էջի աղբյուրը

[[File:Global Oxygen Cycle.jpg|alt=|360px|thumb|Main reservoirs and fluxes — in the [[biosphere]] (green), marine biosphere (blue), [[lithosphere]] (brown), and [[atmosphere]] (grey).
<br>
The major fluxes between these reservoirs are shown in colored arrows, where the green arrows are related to the terrestrial biosphere, blue arrows are related to the marine biosphere, black arrows are related to the lithosphere, and the purple arrow is related to space (not a reservoir, but also contributes to the atmospheric O<sub>2)</sub>.<ref name=":0" />
<br>
The value of photosynthesis or [[net primary productivity]] (NPP) can be estimated through the variation in the abundance and isotopic composition of atmospheric O<sub>2</sub>.<ref name=":1" /><ref name=":4">{{cite journal | vauthors = Keeling RF, Shertz SR | title = Seasonal and interannual variations in atmospheric oxygen and implications for the global carbon cycle. | journal = Nature | date = August 1992 | volume = 358 | issue = 6389 | pages = 723–727 | doi = 10.1038/358723a0 | bibcode = 1992Natur.358..723K | s2cid = 4311084 }}</ref>
<br>
The rate of [[Oceanic carbon cycle#Burial|organic carbon burial]] was derived from estimated fluxes of volcanic and hydrothermal carbon.<ref>{{Cite journal|last=Holland|first=Heinrich D. | name-list-style = vanc |date=2002|title=Volcanic gases, black smokers, and the great oxidation event|journal=Geochimica et Cosmochimica Acta|language=en|volume=66|issue=21|pages=3811–3826|doi=10.1016/S0016-7037(02)00950-X|bibcode=2002GeCoA..66.3811H }}</ref><ref>{{Cite journal|last1=Lasaga|first1=Antonio C.|last2=Ohmoto|first2=Hiroshi| name-list-style = vanc |date=2002|title=The oxygen geochemical cycle: dynamics and stability|journal=Geochimica et Cosmochimica Acta|language=en|volume=66|issue=3|pages=361–381|doi=10.1016/S0016-7037(01)00685-8|bibcode=2002GeCoA..66..361L}}</ref>
]]

Թթվածնի ցիկլը վերաբերում է [[Թթվածին|թթվածնի]] շարժմանը մթնոլորտի (օդի), կենսոլորտի (բույսերի և կենդանիների) և լիթոսֆերայի (երկրակեղևի) միջով: Թթվածնի ցիկլը ցույց է տալիս, թե ինչպես է ազատ թթվածինը հասանելի դառնում այս շրջաններից յուրաքանչյուրում, ինչպես նաև ինչպես է այն օգտագործվում: Թթվածնի ցիկլը թթվածնի ատոմների [[կենսաերկրաքիմիական]] ցիկլն է իոնների, օքսիդների և մոլեկուլների տարբեր օքսիդացման վիճակների միջև՝ Երկիր մոլորակի գնդերի/ջրամբարների ներսում և միջև ռեդոքս ռեակցիաների միջոցով։ Գրականության մեջ թթվածին բառը սովորաբար վերաբերում է թթվածնի ամենատարածված ալոտրոպին՝ տարրական/դիատոմային թթվածին (O2), քանի որ այն ցիկլի ընթացքում շատ կենսաերկրաքիմիական ռեդոքս ռեակցիաների սովորական արտադրանք է կամ ռեակտիվ: Թթվածնի ցիկլում տեղի ունեցող գործընթացները համարվում են կենսաբանական կամ երկրաբանական և գնահատվում են որպես աղբյուր (O2 արտադրություն) կամ խորտակիչ (O2 սպառում): 

Oxygen cycle refers to the movement of oxygen through the [[atmosphere]] (air), [[biosphere]] (plants and animals) and the [[lithosphere]] (the Earth’s crust). The oxygen cycle demonstrates how free oxygen is made available in each of these regions, as well as how it is used. The '''oxygen cycle''' is the [[biogeochemical cycle]] of [[oxygen]] [[atom]]s between different [[oxidation state]]s in [[ion]]s, [[oxide]]s, and [[molecule]]s through [[Redox|redox reactions]] within and between the [[Outline of Earth sciences|spheres/reservoirs]] of the planet Earth.<ref name=":0">{{cite book | first1 = Andrew H | last1 = Knoll | first2 = Donald E | last2 = Canfield | first3 = Kurt | last3 = Konhauser | name-list-style = vanc  |title=Fundamentals of geobiology|date=2012|publisher=John Wiley & Sons .|isbn=978-1-118-28087-4|location=Chichester, West Sussex|pages=93–104|chapter=7|oclc=793103985}}</ref> The word oxygen in the literature typically refers to the most common [[Allotropes of oxygen|oxygen allotrope]], elemental/diatomic oxygen (O<sub>2</sub>), as it is a common [[Product (chemistry)|product]] or [[Reagent|reactant]] of many biogeochemical redox reactions within the cycle.<ref name=":1">{{cite book | vauthors = Petsch ST | chapter = The Global Oxygen Cycle|date=2014 | title =Treatise on Geochemistry|pages=437–473|publisher=Elsevier |doi=10.1016/b978-0-08-095975-7.00811-1|isbn=978-0-08-098300-4 }}</ref> Processes within the oxygen cycle are considered to be [[Biology|biological]] or [[Geology|geological]] and are evaluated as either a [[Source–sink dynamics|source]] (O<sub>2</sub> production) or sink (O<sub>2</sub> consumption).<ref name=":0" /><ref name=":1" />

Oxygen is one of the most common elements on Earth and represents a large portion of each main reservoir. By far the largest reservoir of Earth's oxygen is within the [[Silicate minerals|silicate]] and [[Oxide minerals|oxide]] [[mineral]]s of the [[Crust (geology)|crust]] and [[Mantle (geology)|mantle]] (99.5% by weight).<ref>{{cite journal | vauthors = Falkowski PG, Godfrey LV | title = Electrons, life and the evolution of Earth's oxygen cycle | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 363 | issue = 1504 | pages = 2705–16 | date = August 2008 | pmid = 18487127 | pmc = 2606772 | doi = 10.1098/rstb.2008.0054 }}</ref> The Earth's atmosphere, [[hydrosphere]], and biosphere together hold less than 0.05% of the Earth's total mass of oxygen. Besides O<sub>2</sub>, additional oxygen atoms are present in various forms spread throughout the surface reservoirs in the molecules of [[Biomass (ecology)|biomass]], [[Properties of water|H<sub>2</sub>O]], [[Carbon dioxide|CO<sub>2</sub>]], [[Nitric acid|HNO<sub>3</sub>]], [[Nitric oxide|NO]], [[Nitrogen dioxide|NO<sub>2</sub>]], [[Carbon monoxide|CO]], [[Hydrogen peroxide|H<sub>2</sub>O<sub>2</sub>]], [[Ozone|O<sub>3</sub>]], [[Sulfur dioxide|SO<sub>2</sub>]], [[Sulfuric acid|H<sub>2</sub>SO<sub>4</sub>]], [[Magnesium oxide|MgO]], [[Calcium oxide|CaO]], [[Aluminium oxide|Al2O3]], [[Silicon dioxide|SiO<sub>2</sub>]], and [[Phosphate|PO<sub>4</sub>]].<ref name=":2" />

== Atmosphere ==
The [[Atmosphere of Earth|atmosphere]] is 21% oxygen by volume, which equates to a total of roughly [[Scientific notation|34 × 10<sup>18</sup>]] [[Mole (unit)|mol]] of oxygen.<ref name=":1" /> Other oxygen-containing molecules in the atmosphere include [[ozone]] (O<sub>3</sub>), [[carbon dioxide]] (CO<sub>2</sub>), [[water vapor]] (H<sub>2</sub>O), and [[Sulfur|sulphur]] and [[Nitrogen oxide|nitrogen oxides]] ([[Sulfur dioxide|SO<sub>2</sub>]], [[Nobelium|NO]], [[Nitrous oxide|N<sub>2</sub>O]], etc.).

== Biosphere ==
The [[biosphere]] is 22% oxygen by volume, present mainly as a component of [[Organic compound|organic molecules]] (C<sub>x</sub>H<sub>x</sub>N<sub>x</sub>O<sub>x</sub>) and water.

== Hydrosphere ==
The [[hydrosphere]] is 33% oxygen by volume<ref>{{Cite web |title=hydrosphere - Origin and evolution of the hydrosphere {{!}} Britannica |url=https://www.britannica.com/science/hydrosphere/Origin-and-evolution-of-the-hydrosphere |access-date=2022-07-03 |website=www.britannica.com |language=en}}</ref> present mainly as a component of water molecules, with dissolved molecules including free oxygen and carbolic acids (H<sub>x</sub>CO<sub>3</sub>).

== Lithosphere ==
The [[lithosphere]] is 46.6% oxygen by volume, present mainly as [[Silicon dioxide|silica minerals]] (SiO<sub>2</sub>) and other [[oxide]] minerals.

== Sources and sinks ==
While there are many [[Abiotic component|abiotic]] sources and sinks for O<sub>2</sub>, the presence of the profuse concentration of free oxygen in modern [[Atmosphere of Earth|Earth's atmosphere]] and [[ocean]] is attributed to O<sub>2</sub> production from the [[biological process]] of [[Photosynthesis|oxygenic photosynthesis]] in conjunction with a biological sink known as the [[biological pump]] and a geologic process of [[Carbon sequestration|carbon burial]] involving [[plate tectonics]].<ref>{{cite journal | vauthors = Holland HD | title = The oxygenation of the atmosphere and oceans | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 361 | issue = 1470 | pages = 903–15 | date = June 2006 | pmid = 16754606 | pmc = 1578726 | doi = 10.1098/rstb.2006.1838 }}</ref><ref name=":3">{{cite book | vauthors = Walker JC | title = The Natural Environment and the Biogeochemical Cycles| chapter = The Oxygen Cycle|date=1980|pages=87–104|publisher=Springer Berlin Heidelberg|doi=10.1007/978-3-662-24940-6_5|isbn=9783662229880|series=The Handbook of Environmental Chemistry}}</ref><ref>{{cite book | vauthors = Sigman DM, Haug GH | chapter = The biological pump in the past. | title = Treatise on geochemistry. | edition = 2nd | date = December 2003 | volume = 6 | page = 625 | doi = 10.1016/b978-0-08-095975-7.00618-5 | isbn = 978-0-08-098300-4 }}</ref><ref name=":2">{{cite journal | vauthors = Falkowski PG | title = The biological and geological contingencies for the rise of oxygen on Earth | journal = Photosynthesis Research | volume = 107 | issue = 1 | pages = 7–10 | date = January 2011 | pmid = 21190137 | doi = 10.1007/s11120-010-9602-4 | doi-access = free }}</ref> Biology is the main driver of O<sub>2</sub> [[flux]] on modern Earth, and the [[evolution]] of oxygenic photosynthesis by [[bacteria]], which is discussed as part of [[Great Oxygenation Event|the Great Oxygenation Event]], is thought to be directly responsible for the conditions permitting the development and existence of all [[Multicellular organism|complex]] [[Eukaryote|eukaryotic]] [[metabolism]].<ref>{{cite journal | vauthors = Fischer WW, Hemp J, Johnson JE | title = Evolution of oxygenic photosynthesis. | journal = Annual Review of Earth and Planetary Sciences | date = June 2016 | volume = 44 | issue = 1 | pages = 647–83 | doi = 10.1146/annurev-earth-060313-054810 | bibcode = 2016AREPS..44..647F }}</ref><ref>{{cite journal | vauthors = Lyons TW, Reinhard CT, Planavsky NJ | title = The rise of oxygen in Earth's early ocean and atmosphere | journal = Nature | volume = 506 | issue = 7488 | pages = 307–15 | date = February 2014 | pmid = 24553238 | doi = 10.1038/nature13068 | bibcode = 2014Natur.506..307L | s2cid = 4443958 }}</ref><ref>{{cite journal | vauthors = Reinhard CT, Planavsky NJ, Olson SL, Lyons TW, Erwin DH | title = Earth's oxygen cycle and the evolution of animal life | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 113 | issue = 32 | pages = 8933–8 | date = August 2016 | pmid = 27457943 | pmc = 4987840 | doi = 10.1073/pnas.1521544113 | bibcode = 2016PNAS..113.8933R | doi-access = free }}</ref>

=== Biological production ===
The main source of atmospheric free oxygen is photosynthesis, which produces [[sugar]]s and free oxygen from carbon dioxide and water:

:<math>\mathrm{6 \ CO_2 + 6H_2O + energy \longrightarrow C_6H_{12}O_6 + 6 \ O_2}</math>

Photosynthesizing organisms include the plant life of the land areas, as well as the [[phytoplankton]] of the oceans. The tiny marine [[cyanobacterium]] ''[[Prochlorococcus]]'' was discovered in 1986 and accounts for up to half of the photosynthesis of the open oceans.<ref>{{cite journal | first = Steve | last = Nadis | name-list-style = vanc | title = The Cells That Rule the Seas | journal = Scientific American | volume = 289 | issue = 6 | pages = 52–53 | date = November 2003 | doi = 10.1038/scientificamerican1203-52 | bibcode = 2003SciAm.289f..52N | pmid = 14631732 }}</ref><ref>{{cite journal | vauthors = Morris JJ, Johnson ZI, Szul MJ, Keller M, Zinser ER | year = 2011 | title = Dependence of the Cyanobacterium ''Prochlorococcus'' on Hydrogen Peroxide Scavenging Microbes for Growth at the Ocean's Surface | journal = PLOS ONE | volume = 6 | issue = 2 | pages = e16805 | doi = 10.1371/journal.pone.0016805 | pmid = 21304826 | pmc = 3033426| bibcode = 2011PLoSO...616805M | doi-access = free }}</ref>

=== Abiotic production ===
An additional source of atmospheric free oxygen comes from [[photolysis]], whereby high-energy [[ultraviolet]] radiation breaks down atmospheric water and nitrous oxide into component atoms. The free hydrogen and nitrogen atoms escape into space, leaving O<sub>2</sub> in the atmosphere:   
:<math>\mathrm{2 \ H_2O + energy \longrightarrow 4 \ H + O_2}</math>
:<math>\mathrm{2 \ N_2O + energy \longrightarrow 4 \ N + O_2}</math>

=== Biological consumption ===
The main way free oxygen is lost from the atmosphere is via [[Respiration (physiology)|respiration]] and [[Decomposition|decay]], mechanisms in which [[animal]] life and [[bacteria]] consume oxygen and release carbon dioxide.

== Capacities and fluxes ==
The following tables offer estimates of oxygen cycle reservoir capacities and fluxes. 
These numbers are based primarily on estimates from (Walker, J. C. G.):<ref name=":3" /> More recent research indicates that ocean life ([[marine primary production]]) is actually responsible for more than half the total oxygen production on Earth.<ref name="NalGeo">{{cite news|last=Roach|first=John|date=June 7, 2004|title=Source of Half Earth's Oxygen Gets Little Credit|work=National Geographic News|url=http://news.nationalgeographic.com/news/2004/06/0607_040607_phytoplankton.html|archive-url=https://web.archive.org/web/20040608065449/http://news.nationalgeographic.com/news/2004/06/0607_040607_phytoplankton.html|url-status=dead|archive-date=June 8, 2004|access-date=2016-04-04}}</ref><ref>{{cite journal|last1=Lin|first1=I.|last2=Liu|first2=W. Timothy|last3=Wu|first3=Chun-Chieh|last4=Wong|first4=George T. F.|last5=Hu|first5=Chuanmin|last6=Chen|first6=Zhiqiang|last7=Wen-Der|first7=Liang|last8=Yang|first8=Yih|last9=Liu|first9=Kon-Kee|year=2003|title=New evidence for enhanced ocean primary production triggered by tropical cyclone|url=https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1335&context=oeas_fac_pubs|journal=Geophysical Research Letters|volume=30|issue=13|page=1718|bibcode=2003GeoRL..30.1718L|doi=10.1029/2003GL017141|s2cid=10267488 |doi-access=free}}</ref>

{| class="wikitable"
|----- align="center"
! Reservoir
! Capacity<br>(kg O<sub>2</sub>) 
! Flux in/out<br>(kg O<sub>2</sub> per year)
! Residence time<br>(years)
|----- align="right"
| align="left" | Atmosphere   || {{val|1.4|e=18}}
| {{val|3|e=14}} || {{val|4500}}
|----- align="right"
| align="left" | Biosphere   || {{val|1.6|e=16}}
| {{val|3|e=14}} || 50
|----- align="right"
| align="left" | Lithosphere   || {{val|2.9|e=20}}
| {{val|6|e=11}} || {{val|500000000}}
|}   
<br>
'''Table 2''': Annual gain and loss of atmospheric oxygen (Units of 10<sup>10</sup> kg O<sub>2</sub> per year)<ref name=":0" />

{| class="wikitable"
|- align="right"
| Photosynthesis (land) || 16,500
|- align="right"
| Photosynthesis (ocean) || 13,500
|- align="right"
| Photolysis of N<sub>2</sub>O || 1.3
|- align="right"
| Photolysis of H<sub>2</sub>O || 0.03
|- align="right"
| Total gains || ~30,000      
|-
| colspan="2" | <u>''Losses - respiration and decay''</u>     
|- align="right"
| Aerobic respiration || 23,000
|- align="right"
| Microbial oxidation || 5,100
|- align="right"
| Combustion of fossil fuel (anthropogenic) || 1,200
|- align="right"
| Photochemical oxidation || 600
|- align="right"
| Fixation of N<sub>2</sub> by lightning || 12
|- align="right"
| Fixation of N<sub>2</sub> by industry (anthropogenic) || 10
|- align="right"
| Oxidation of volcanic gases || 5  
|-
| colspan="2" | <u>''Losses - weathering''</u>     
|- align="right"
| Chemical weathering || 50
|- align="right"
| Surface reaction of O<sub>3</sub> || 12 
|- align="right"
| Total losses || ~30,000   
|}

== Ozone ==
{{main|Ozone-oxygen cycle}}
The presence of atmospheric oxygen has led to the formation of [[ozone]] (O<sub>3</sub>) and the [[ozone layer]] within the [[stratosphere]]:

:<math>\mathrm{O_2 + uv~light \longrightarrow 2~O}\qquad(\lambda \lesssim 200~\text{nm})</math>
:<math>\mathrm{O + O_2 \longrightarrow O_3}</math>
:'''O + O<sub>2</sub> :- O<sub>3</sub>'''

The ozone layer is extremely important to modern life as it absorbs harmful [[ultraviolet]] radiation:

:<math>\mathrm{O_3 + uv~light \longrightarrow O_2 + O}\qquad(\lambda \lesssim 300~\text{nm})</math>

== See also ==

* [[Carbon cycle]]
* [[Nitrogen cycle]]
* [[Hydrogen Cycle]]

== References ==
{{Reflist}}

== Further reading ==
{{refbegin}}
* {{cite journal | vauthors = Cloud P, Gibor A | date = September 1970 | title = The oxygen cycle | journal = Scientific American | volume = 223 | issue = 3 | pages = 110–123 | doi = 10.1038/scientificamerican0970-110 | pmid = 5459721 | bibcode = 1970SciAm.223c.110C }}
* {{cite web | vauthors = Fasullo J | title = Substitute Lectures for ATOC 3600 | work = Principles of Climate, Lectures on the global oxygen cycle | url = http://paos.colorado.edu/~fasullo/pjw_class/oxygencycle.html }}
* {{cite web | vauthors = Morris RM | title = OXYSPHERE - A Beginners' Guide to the Biogeochemical Cycling of Atmospheric Oxygen | url = http://seis.natsci.csulb.edu/rmorris/oxy/Oxy.htm | archive-url = https://web.archive.org/web/20041103093231/http://seis.natsci.csulb.edu/rmorris/oxy/Oxy.htm | archive-date = 2004-11-03 }}
{{refend}}

{{Authority control}}

[[Category:Ecology]]
[[Category:Chemical oceanography]]
[[Category:Photosynthesis]]
[[Category:Biogeochemical cycle]]
[[Category:Oxygen|Cycle]]