View source for Marine biogeochemical cycles

{{Use British English|date=August 2021}}
{{Use dmy dates|date=August 2021}}
{{multiple image
 | header   = Marine biogeochemical cycles
 | total_width = 400px
 | image1   = Earth Pacific jul 30 2010.jpg
 | alt1     = 
 | caption1 = The dominant feature of the planet viewed from space is water – oceans of liquid water flood most of the surface while water vapour swirls in atmospheric clouds and the poles are capped with ice. Taken as a whole, the oceans form a single marine system where liquid water – the "universal solvent" – dissolves nutrients and substances containing elements such as oxygen, carbon, nitrogen and phosphorus. These substances are endlessly cycled and recycled, chemically combined and then broken down again, dissolved and then precipitated or evaporated, imported from and exported back to the land and the atmosphere and the ocean floor. Powered both by the biological activity of marine organisms and by the natural forces of the Sun and tides and movements within the Earth's crust, these are the marine biogeochemical cycles.
}}
{{marine life sidebar}}

'''Marine biogeochemical cycles''' are [[biogeochemical cycle]]s that occur within [[Marine habitat|marine environments]], that is, in the [[saline water|saltwater]] of seas or oceans or the [[brackish]] water of coastal [[Estuary|estuaries]]. These biogeochemical cycles are the pathways [[chemical substance]]s and [[chemical element|elements]] move through within the marine environment. In addition, substances and elements can be imported into or exported from the marine environment. These imports and exports can occur as exchanges with the atmosphere above, the ocean floor below, or as runoff from the land.

There are [[biogeochemistry|biogeochemical]] cycles for the elements [[calcium cycle|calcium]], [[carbon cycle|carbon]], [[hydrogen cycle|hydrogen]], [[mercury cycle|mercury]], [[nitrogen cycle|nitrogen]], [[oxygen cycle|oxygen]], [[phosphorus cycle|phosphorus]], [[selenium cycle|selenium]], and [[sulfur cycle|sulfur]]; molecular cycles for [[water cycle|water]] and [[silica cycle|silica]]; macroscopic cycles such as the [[rock cycle]]; as well as human-induced cycles for synthetic compounds such as [[polychlorinated biphenyl]] (PCB). In some cycles there are reservoirs where a substance can be stored for a long time. The cycling of these elements is interconnected.

[[Marine organisms]], and particularly [[marine microorganisms]] are crucial for the functioning of many of these cycles. The forces driving biogeochemical cycles include [[metabolism|metabolic processes]] within organisms, geological processes involving the Earth's mantle, as well as [[chemical reaction]]s among the substances themselves, which is why these are called biogeochemical cycles. While chemical substances can be broken down and recombined, the chemical elements themselves can be neither created nor destroyed by these forces, so apart from some losses to and gains from outer space, elements are recycled or stored (sequestered) somewhere on or within the planet.

==Overview==
Energy flows directionally through ecosystems, entering as sunlight (or inorganic molecules for chemoautotrophs) and leaving as heat during the many transfers between trophic levels. However, the matter that makes up living organisms is conserved and recycled. The six most common elements associated with organic molecules—carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur—take a variety of chemical forms and may exist for long periods in the atmosphere, on land, in water, or beneath the Earth's surface. Geologic processes, such as weathering, erosion, water drainage, and the subduction of the continental plates, all play a role in this recycling of materials. Because geology and chemistry have major roles in the study of this process, the recycling of inorganic matter between living organisms and their environment is called a biogeochemical cycle.<ref name=OpenStax>[https://cnx.org/contents/ZdFkREJc@7/Biogeochemical-Cycles Biogeochemical Cycles], ''OpenStax'', 9 May 2019. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

The six aforementioned elements are used by organisms in a variety of ways. Hydrogen and oxygen are found in water and organic molecules, both of which are essential to life. Carbon is found in all organic molecules, whereas nitrogen is an important component of nucleic acids and proteins. Phosphorus is used to make nucleic acids and the phospholipids that comprise biological membranes. Sulfur is critical to the three-dimensional shape of proteins. The cycling of these elements is interconnected. For example, the movement of water is critical for leaching sulfur and phosphorus into rivers which can then flow into oceans. Minerals cycle through the biosphere between the biotic and abiotic components and from one organism to another.<ref name=Fisher2019>Fisher M. R. (Ed.) (2019) ''Environmental Biology'', [https://openoregon.pressbooks.pub/envirobiology/chapter/3-2-biogeochemical-cycles/ 3.2 Biogeochemical Cycles], OpenStax. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

{{clear}}

==The water cycle==
[[File:Water cycle.png|thumb|upright=1.5| Interaction of terrestrial and atmospheric water cycles with the marine water cycle]]
{{main|water cycle}}
{{further|Gulf Stream|thermohaline circulation}}

Water is the medium of the oceans, the medium which carries all the substances and elements involved in the marine biogeochemical cycles. 
Water as found in nature almost always includes dissolved substances, so water has been described as the "universal solvent" for its ability to dissolve so many substances.<ref>{{Greenwood&Earnshaw2nd|page=620}}</ref><ref>{{cite web |title=Water, the Universal Solvent |url=http://water.usgs.gov/edu/solvent.html |website=[[USGS]] |access-date=27 June 2017 |archive-url=https://web.archive.org/web/20170709141251/https://water.usgs.gov/edu/solvent.html |archive-date=9 July 2017 |url-status=live  }}</ref> This ability allows it to be the "[[solvent]] of life"<ref>{{Cite book |title=Campbell Biology |last=Reece |first=Jane B. |date=31 October 2013 |publisher=[[Pearson Education|Pearson]] |isbn=9780321775658 |edition=10th |page=48 }}</ref>  Water is also the only common substance that exists as [[ice|solid]], liquid, and [[water vapor|gas]] in normal terrestrial conditions.<ref>{{Cite book |title=Campbell Biology |last=Reece |first=Jane B. |date=31 October 2013 |publisher=[[Pearson Education|Pearson]] |isbn=9780321775658 |edition=10th |page=44 }}</ref> Since liquid water flows, ocean waters cycle and flow in currents around the world. Since water easily changes phase, it can be carried into the atmosphere as water vapour or frozen as an iceberg. It can then precipitate or melt to become liquid water again. All marine life is immersed in water, the matrix and womb of life itself.<ref>Collins J. C. (1991) [https://books.google.com/books?id=Rm_wAAAAMAAJ&q=%22materund+matrix%22 ''The Matrix of Life: A View of Natural Molecules from the Perspective of Environmental Water''] Molecular Presentations. {{ISBN|9780962971907}}.</ref> Water can be broken down into its constituent hydrogen and oxygen by metabolic or abiotic processes, and later recombined to become water again.

While the water cycle is itself a [[biogeochemical cycle]], flow of water over and beneath the Earth is a key component of the cycling of other biogeochemicals.<ref>{{cite web |publisher=The Environmental Literacy Council |url=http://www.enviroliteracy.org/subcategory.php/198.html |title=Biogeochemical Cycles |url-status=live |archive-url=https://web.archive.org/web/20150430133927/http://enviroliteracy.org/subcategory.php/198.html |archive-date=2015-04-30 |access-date=2006-10-24}}</ref> Runoff is responsible for almost all of the transport of [[erosion|eroded]] [[sediment]] and [[phosphorus]] from land to [[waterbody|waterbodies]].<ref>{{Cite web |url=https://enviroliteracy.org/air-climate-weather/biogeochemical-cycles/phosphorus-cycle/ |title=Phosphorus Cycle |publisher=The Environmental Literacy Council |access-date=2018-01-15 |url-status=live |archive-url=https://web.archive.org/web/20160820012731/http://enviroliteracy.org/air-climate-weather/biogeochemical-cycles/phosphorus-cycle/|archive-date=2016-08-20}}</ref> Cultural [[eutrophication]] of lakes is primarily due to phosphorus, applied in excess to [[field (agriculture)|agricultural fields]] in [[fertilizer]]s, and then transported overland and down rivers. Both runoff and groundwater flow play significant roles in transporting nitrogen from the land to waterbodies.<ref>{{cite web |publisher=Ohio State University |website=Extension Fact Sheet |url=http://ohioline.osu.edu/aex-fact/0463.html |title=Nitrogen and the Hydrologic Cycle |url-status=dead |archive-url=https://web.archive.org/web/20060901071850/http://ohioline.osu.edu/aex-fact/0463.html |archive-date=2006-09-01 |access-date=2006-10-24}}</ref> The [[dead zone (ecology)|dead zone]] at the outlet of the [[Mississippi River]] is a consequence of [[nitrate]]s from fertilizer being carried off agricultural fields and funnelled down the [[river system]] to the [[Gulf of Mexico]]. Runoff also plays a part in the [[carbon cycle]], again through the transport of eroded rock and soil.<ref>{{cite web |publisher=NASA |date=2011-06-16 |website=Earth Observatory |title=The Carbon Cycle |url=http://earthobservatory.nasa.gov/Library/CarbonCycle/ |access-date=2006-10-24 |url-status=dead |archive-url=https://web.archive.org/web/20060928223836/http://earthobservatory.nasa.gov/Library/CarbonCycle/ |archive-date=2006-09-28}}</ref>

===Ocean salinity===
{{see also|Temperature–salinity diagram}}

[[Ocean salinity]] is derived mainly from the weathering of rocks and the transport of dissolved salts from the land, with lesser contributions from [[hydrothermal vent]]s in the seafloor.<ref name=noaasalt>[https://oceanservice.noaa.gov/facts/whysalty.html Why is the ocean salty?] ''NOAA''. Last updated: 26 February 2021. {{PD-notice}}</ref> Evaporation of ocean water and formation of sea ice further increase the salinity of the ocean. However these processes which increase salinity are continually counterbalanced by processes that decrease salinity, such as the continuous input of fresh water from rivers, precipitation of rain and snow, and the melting of ice.<ref name=nasasalt>[https://science.nasa.gov/earth-science/oceanography/physical-ocean/salinity#:~:text=Evaporation%20of%20ocean%20water%20and,snow%2C%20and%20melting%20of%20ice. Salinity] ''NASA''. Last updated: 7 April 2021. {{PD-notice}}</ref> The two most prevalent ions in seawater are chloride and sodium. Together, they make up around 85 per cent of all dissolved ions in the ocean. Magnesium and sulfate ions make up most of the rest. Salinity varies with temperature, evaporation, and precipitation. It is generally low at the equator and poles, and high at mid-latitudes.<ref name=noaasalt />

<gallery mode=packed style=float:left; heights=260px>
File:SeaSurfaceSalinity.jpg| Annual mean sea surface salinity, measured in 2009 in [[Practical Salinity Unit|practical salinity units]]{{hsp}}<ref>[https://svs.gsfc.nasa.gov/vis/a000000/a003600/a003652/ Sea Surface Temperature, Salinity and Density] ''NASA Scientific Visualization Studio'', 9 October 2009.</ref>
</gallery>

<gallery mode=packed style=float:left; heights=200px>
File:Vertical differences in ocean salinity (0 to 300m).png| Vertical differences in sea salinity between the surface and a depth of 300 metres. Salinity increases with depth in red regions and decreases in blue regions.<ref name=Sundby2015>Sundby, S. and Kristiansen, T. (2015) "The principles of buoyancy in marine fish eggs and their vertical distributions across the world oceans". ''PLOS ONE'', '''10'''(10): e0138821. {{doi|10.1371/journal.pone.0138821}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>
</gallery>

{{clear}}

===Sea spray===
[[File:Ocean mist and spray 2.jpg|thumb|upright=1.3 |right| Sea spray containing [[marine microorganism]]s, and all the substances and elements contained in their bodies, can be swept high into the atmosphere. There they become [[aeroplankton]] and can travel the globe before falling back to Earth.]]

A stream of airborne microorganisms circles the planet above weather systems but below commercial air lanes.<ref>[https://www.smithsonianmag.com/science-nature/living-bacteria-are-riding-earths-air-currents-180957734/ Living Bacteria Are Riding Earth’s Air Currents] ''Smithsonian Magazine'', 11 January 2016.</ref> Some peripatetic microorganisms are swept up from terrestrial dust storms, but most originate from marine microorganisms in [[sea spray]]. In 2018, scientists reported that hundreds of millions of viruses and tens of millions of bacteria are deposited daily on every square meter around the planet.<ref>{{cite news |last=Robbins |first=Jim |title=Trillions Upon Trillions of Viruses Fall From the Sky Each Day |url=https://www.nytimes.com/2018/04/13/science/virosphere-evolution.html |date=13 April 2018 |work=[[The New York Times]] |access-date=14 April 2018 }}</ref><ref name="ISME-2018">{{cite journal |last1=Reche |first1=Isabel |last2=D’Orta |first2=Gaetano |last3=Mladenov |first3=Natalie |last4=Winget |first4= Danielle M |last5=Suttle |first5= Curtis A |title=Deposition rates of viruses and bacteria above the atmospheric boundary layer |journal=ISME Journal |volume=12 |issue=4 |pages=1154–1162 |date=29 January 2018 |doi=10.1038/s41396-017-0042-4 |pmid=29379178 |pmc=5864199 }}</ref> This is another example of water facilitating the transport of organic material over great distances, in this case in the form of live microorganisms.

Dissolved salt does not evaporate back into the atmosphere like water, but it does form [[sea salt aerosol]]s in [[sea spray]]. Many [[physical process]]es over ocean surface generate sea salt aerosols. One common cause is the bursting of [[air bubble]]s, which are entrained by the wind stress during the [[Wind wave|whitecap]] formation. Another is tearing of drops from wave tops.<ref name="levin">{{Cite book|title=Aerosol Pollution Impact on Precipitation|year=2009|isbn=978-1-4020-8689-2|editor-last=Levin|editor-first=Zev|doi=10.1007/978-1-4020-8690-8|editor-last2=Cotton|editor-first2=William R.}}</ref> The total sea salt flux from the ocean to the atmosphere is about 3300 Tg (3.3 billion tonnes) per year.<ref>IPCC Third Assessment Report: Climate Change 2001 (TAR)</ref>

===Ocean circulation===
{{see also|continental shelf pump}}
[[File:Convection cycle.png|thumb| {{center|[[Convection]] cycle}}]]
{{multiple image
 | align = right
 | direction = 
 | header            = [[Upwelling]]
 | header_align      = 
 | background color  = 
 | total_width = 400px
 | image1    = Figure 44 02 04.png
 | alt1      = 
 | caption1  = Upwelling caused by an offshore wind in friction with the ocean surface
 | image2    = Upwelling-labels-en.svg
 | alt2      = 
 | caption2  = Upwelling can be caused if an alongshore wind moves towards the equator, inducing [[Ekman transport]]
 | footer            = Two mechanisms which result in [[upwelling]]. In each case, if the wind direction were reversed it would induce [[downwelling]].<ref>[http://oceanmotion.org/html/background/upwelling-and-downwelling.htm Wind Driven Surface Currents: Upwelling and Downwelling] ''NASA''. Accessed 17 June 2020.</ref>
 | footer_align      = 
 | footer_background = 
}}
{{multiple image
 | align = right
 | direction = 
 | header            = Ventilation of the deep ocean
 | header_align      = 
 | background color  = 
 | total_width = 400px
 | image1    = Antarctic bottom water.svg
 | alt1      = 
 | caption1  = {{center|[[Antarctic bottom water]]}}
 | image2    = Antarctic Circumpolar Current.png
 | alt2      = 
 | caption2  = {{center|Antarctic Circumpolar Current, with branches connecting to the global conveyor belt}}
 | footer            = 
 | footer_align      = 
 | footer_background = 
}}
[[File:Overturning circulation of the global ocean.jpg|thumb|400px| {{center|[[Global conveyor belt]]}}]]

Solar radiation affects the oceans: warm water from the Equator tends to circulate toward the [[geographical pole|pole]]s, while cold polar water heads towards the Equator.  The surface currents are initially dictated by surface wind conditions.  The [[trade winds]] blow westward in the tropics,<ref>{{cite web |title=trade winds |work=Glossary of Meteorology |publisher=American Meteorological Society |year=2009 |access-date=2008-09-08 |url=http://amsglossary.allenpress.com/glossary/search?id=trade-winds1 |url-status=dead |archive-url=https://web.archive.org/web/20081211050708/http://amsglossary.allenpress.com/glossary/search?id=trade-winds1 |archive-date=2008-12-11 }}</ref> and the [[westerlies]] blow eastward at mid-latitudes.<ref>Glossary of Meteorology (2009). [http://amsglossary.allenpress.com/glossary/search?id=westerlies1 Westerlies.] {{webarchive|url=https://web.archive.org/web/20100622073904/http://amsglossary.allenpress.com/glossary/search?id=westerlies1 |date=2010-06-22 }} [[American Meteorological Society]]. Retrieved on 2009-04-15.</ref>  This wind pattern applies a [[stress (physics)|stress]] to the subtropical ocean surface with negative [[curl (mathematics)|curl]] across the [[Northern Hemisphere]],<ref>Matthias Tomczak and J. Stuart Godfrey (2001). [http://www.es.flinders.edu.au/~mattom/regoc/pdffiles/colour/double/04P-Ekman-left.pdf Regional Oceanography: an Introduction.] {{webarchive|url=https://web.archive.org/web/20090914120630/http://www.es.flinders.edu.au/~mattom/regoc/pdffiles/colour/double/04P-Ekman-left.pdf |date=2009-09-14 }} Matthias Tomczak, pp. 42. {{ISBN|81-7035-306-8}}. Retrieved on 2009-05-06.</ref> and the reverse across the [[Southern Hemisphere]].  The resulting [[Sverdrup transport]] is equatorward.<ref>Earthguide (2007). [http://earthguide.ucsd.edu/parkerprogram/berger/pdf/OcnBasLesson06.pdf Lesson 6: Unraveling the Gulf Stream Puzzle - On a Warm Current Running North.] {{webarchive|url=https://web.archive.org/web/20080723104316/http://earthguide.ucsd.edu/parkerprogram/berger/pdf/OcnBasLesson06.pdf |date=2008-07-23 }} [[University of California]] at San Diego. Retrieved on 2009-05-06.</ref>  Because of conservation of [[potential vorticity]] caused by the poleward-moving winds on the [[subtropical ridge]]'s western periphery and the increased relative vorticity of poleward moving water, transport is balanced by a narrow, accelerating poleward current, which flows along the western boundary of the ocean basin, outweighing the effects of friction with the cold western boundary current which originates from high latitudes.<ref>Angela Colling (2001). [https://books.google.com/books?id=tFJRLhSez_YC&pg=PA90 Ocean circulation.] {{webarchive|url=https://web.archive.org/web/20180302144439/https://books.google.com/books?id=tFJRLhSez_YC&pg=PA90 |date=2018-03-02 }} Butterworth-Heinemann, pp. 96. Retrieved on 2009-05-07.</ref>  The overall process, known as [[western intensification]], causes currents on the western boundary of an ocean basin to be stronger than those on the eastern boundary.<ref>National Environmental Satellite, Data, and Information Service (2009). [http://www.science-house.org/nesdis/gulf/background.html Investigating the Gulf Stream.] {{webarchive|url=https://web.archive.org/web/20100503013457/http://www.science-house.org/nesdis/gulf/background.html |date=2010-05-03 }} [[North Carolina State University]]. Retrieved on 2009-05-06.</ref>

As it travels poleward, warm water transported by strong warm water current undergoes evaporative cooling. The cooling is wind driven: wind moving over water cools the water and also causes [[evaporation]], leaving a saltier brine. In this process, the water becomes saltier and denser. and decreases in temperature.  Once sea ice forms, salts are left out of the ice, a process known as brine exclusion.<ref>{{cite web |last=Russel |first=Randy |title=Thermohaline Ocean Circulation |url=http://www.windows.ucar.edu/tour/link=/earth/Water/thermohaline_ocean_circulation.html |publisher=University Corporation for Atmospheric Research |access-date=2009-01-06 |url-status=dead |archive-url=https://web.archive.org/web/20090325062339/http://www.windows.ucar.edu/tour/link=/earth/Water/thermohaline_ocean_circulation.html |archive-date=2009-03-25 }}</ref>  These two processes produce water that is denser and colder.  The water across the northern [[Atlantic Ocean]] becomes so dense that it begins to sink down through less salty and less dense water. This downdraft of heavy, cold and dense water becomes a part of the [[North Atlantic Deep Water]], a southgoing stream.<ref>{{cite web |last=Behl |first=R. |title=Atlantic Ocean water masses |url=http://seis.natsci.csulb.edu/rbehl/NADW.htm |publisher=[[California State University]] Long Beach |access-date=2009-01-06|archive-url = https://web.archive.org/web/20080523170145/http://seis.natsci.csulb.edu/rbehl/NADW.htm |archive-date = May 23, 2008|url-status=dead}}</ref>

Winds drive ocean currents in the upper 100 meters of the ocean's surface. However, ocean currents also flow thousands of meters below the surface. These deep-ocean currents are driven by differences in the water's density, which is controlled by temperature (thermo) and salinity (haline). This process is known as thermohaline circulation. In the Earth's polar regions ocean water gets very cold, forming sea ice. As a consequence the surrounding seawater gets saltier, because when sea ice forms, the salt is left behind. As the seawater gets saltier, its density increases, and it starts to sink. Surface water is pulled in to replace the sinking water, which in turn eventually becomes cold and salty enough to sink. This initiates the deep-ocean currents driving the global conveyor belt.<ref>[https://oceanservice.noaa.gov/education/tutorial_currents/05conveyor1.html Thermohaline Circulation]  National Ocean Service, NOAA. Retrieved: 20 May 2020. {{PD-notice}}</ref>

Thermohaline circulation drives a global-scale system of currents called the “global conveyor belt.” The conveyor belt begins on the surface of the ocean near the pole in the North Atlantic. Here, the water is chilled by Arctic temperatures. It also gets saltier because when sea ice forms, the salt does not freeze and is left behind in the surrounding water. The cold water is now more dense, due to the added salts, and sinks toward the ocean bottom. Surface water moves in to replace the sinking water, thus creating a current. This deep water moves south, between the continents, past the equator, and down to the ends of Africa and South America. The current travels around the edge of Antarctica, where the water cools and sinks again, as it does in the North Atlantic. Thus, the conveyor belt gets "recharged." As it moves around Antarctica, two sections split off the conveyor and turn northward. One section moves into the Indian Ocean, the other into the Pacific Ocean. These two sections that split off warm up and become less dense as they travel northward toward the equator, so that they rise to the surface (upwelling). They then loop back southward and westward to the South Atlantic, eventually returning to the North Atlantic, where the cycle begins again. The conveyor belt moves at much slower speeds (a few centimeters per second) than wind-driven or tidal currents (tens to hundreds of centimeters per second). It is estimated that any given cubic meter of water takes about 1,000 years to complete the journey along the global conveyor belt. In addition, the conveyor moves an immense volume of water—more than 100 times the flow of the Amazon River (Ross, 1995). The conveyor belt is also a vital component of the global ocean nutrient and carbon dioxide cycles. Warm surface waters are depleted of nutrients and carbon dioxide, but they are enriched again as they travel through the conveyor belt as deep or bottom layers. The base of the world's food chain depends on the cool, nutrient-rich waters that support the growth of algae and seaweed.<ref>[https://oceanservice.noaa.gov/education/tutorial_currents/05conveyor2.html The Global Conveyor Belt]  National Ocean Service, NOAA. Retrieved: 20 May 2020. {{PD-notice}}</ref>

{| class="wikitable collapsible collapsed" style="margin-left:1em; text-align:center" align="right" width=320px 
! colspan=2 | Average reservoir residence times <ref name="PHYS">{{Cite book |author=Pidwirny, M. |via=PhysicalGeography.net |chapter-url=http://www.physicalgeography.net/fundamentals/8b.html |chapter=Chapter 8: Introduction to the Hydrosphere |archive-url=https://web.archive.org/web/20160126072955/http://www.physicalgeography.net/fundamentals/8b.html |archive-date=2016-01-26 |access-date=2006-10-24 |url-status=live |title=Fundamentals of Physical Geography |edition=2nd |at=8(b) The Hydrologic Cycle |date=2006}}</ref>
|-
! style="text-align:left" | Reservoir 
! Average residence time
|-
| style="text-align:left" | Antarctica
| 20,000 years
|-
| style="text-align:left" | Oceans
| 3,200 years
|-
| style="text-align:left" | Glaciers
| 20 to 100 years
|-
| style="text-align:left" | Seasonal snow cover
| 2 to 6 months
|-
| style="text-align:left" | Soil moisture
| 1 to 2 months
|-
| style="text-align:left" | Groundwater: shallow
| 100 to 200 years
|-
| style="text-align:left" | Groundwater: deep
| 10,000 years
|-
| style="text-align:left" | Lakes (see [[lake retention time]])
| 50 to 100 years
|-
| style="text-align:left" | Rivers
| 2 to 6 months
|-
| style="text-align:left" | Atmosphere
| 9 days
|}

The global average residence time of a water molecule in the ocean is about 3,200 years. By comparison the average residence time in the atmosphere is about nine days. If it is frozen in the Antarctic or drawn into deep groundwater it can be sequestered for ten thousand years.<ref name="PHYS"/><ref>Van Der Ent, R.J. and Tuinenburg, O.A. (2017) "The residence time of water in the atmosphere revisited". ''Hydrology and Earth System Sciences'', '''21'''(2): 779–790. {{doi|10.5194/hess-21-779-2017}}.</ref>

{{clear}}

==Cycling of key elements==
{| class="wikitable collapsible"
|-
! colspan=3| Some key elements involved in marine biogeochemical cycles
|-
! {{align|left|Element}}
! Diagram
! Description
|-
! {{align|left|Carbon}}
| [[File:Marine carbon cycle.jpg|220px]]
| The [[marine carbon cycle]] involves processes that exchange [[carbon]] between various pools within the ocean as well as between the atmosphere, Earth interior, and the [[Seabed|seafloor]]. The [[carbon cycle]] is a result of many interacting forces across multiple time and space scales that circulates carbon around the planet, ensuring that carbon is available globally. The marine carbon cycle is a central to the global carbon cycle and contains both [[Total inorganic carbon|inorganic]] carbon (carbon not associated with a living thing, such as carbon dioxide) and [[Organic matter|organic]] carbon (carbon that is, or has been, incorporated into a living thing). Part of the marine carbon cycle transforms carbon between non-living and living matter. Three main processes (or pumps) that make up the marine carbon cycle bring atmospheric [[carbon dioxide]] (CO<sub>2</sub>) into the ocean interior and distribute it through the oceans.  These three pumps are: (1) the solubility pump, (2) the carbonate pump, and (3) the biological pump.  The total active pool of carbon at the Earth's surface for durations of less than 10,000 years is roughly 40,000 gigatons C (Gt C, a gigaton is one billion tons, or the weight of approximately 6 million [[blue whale]]s), and about 95% (~38,000 Gt C) is stored in the ocean, mostly as dissolved inorganic carbon.<ref name="H. 2013">{{Cite book|title=Biogeochemistry: an analysis of global change |last=Schlesinger |first=William H. |last2=Bernhardt |first2=Emily S. |date=2013 |publisher=Academic Press |isbn=9780123858740 |edition=3rd |location=Waltham, MA |oclc=827935936}}</ref><ref name="Falkowski 291–296">{{Cite journal |last1=Falkowski |first1=P. |last2=Scholes |first2=R. J. |last3=Boyle |first3=E. |last4=Canadell |first4=J. |last5=Canfield |first5=D. |last6=Elser |first6=J. |last7=Gruber |first7=N. |last8=Hibbard |first8=K. |last9=Högberg |first9=P. |date=2000-10-13 |title=The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System |journal=Science |language=en |volume=290 |issue=5490 |pages=291–296 |doi=10.1126/science.290.5490.291 |issn=0036-8075 |pmid=11030643 |bibcode=2000Sci...290..291F}}</ref>  The speciation of dissolved inorganic carbon in the marine carbon cycle is a primary controller of [[Acid-base reaction|acid-base chemistry]] in the oceans.
|-
! {{align|left|Oxygen}}
| [[File:Oxygen Cycle.jpg|220px]]
| The [[oxygen cycle]] involves biogeochemical transitions 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=Andrew2012>{{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 [[molecular oxygen]] (O<sub>2</sub>) since it is the common [[Product (chemistry)|product]] or [[Reagent|reactant]] of many biogeochemical redox reactions within the cycle.<ref name=Petsch2014>{{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=Andrew2012 /><ref name=Petsch2014 />
|-
! {{align|left|Hydrogen}}
| [[File:CHO-cycles en.png|220px]]
| The [[hydrogen cycle]] consists of [[hydrogen]] exchanges between [[Life|biotic]] (living) and [[Abiotic component|abiotic]] (non-living) sources and sinks of hydrogen-containing compounds. Hydrogen (H) is the most abundant element in the universe.<ref>{{cite journal| vauthors = Cameron AG |date=1973|title=Abundances of the elements in the solar system|journal=Space Science Reviews|language=en|volume=15|issue=1|pages=121|doi=10.1007/BF00172440|issn=0038-6308|bibcode=1973SSRv...15..121C|s2cid=120201972}}</ref> On Earth, common H-containing inorganic molecules include water (H<sub>2</sub>O), hydrogen gas (H<sub>2</sub>), [[methane]] (CH<sub>4</sub>), [[hydrogen sulfide]] (H<sub>2</sub>S), and [[ammonia]] (NH<sub>3</sub>). Many organic compounds also contain H atoms, such as [[hydrocarbon]]s and [[organic matter]]. Given the ubiquity of hydrogen atoms in inorganic and organic chemical compounds, the hydrogen cycle is focused on molecular hydrogen (H<sub>2</sub>). 
|-
! {{align|left|Nitrogen}}
| [[File:Marine Nitrogen Cycle.jpg|220px]]
| The [[nitrogen cycle]] is the process by which [[nitrogen]] is converted into multiple chemical forms as it circulates among [[atmosphere]], [[terrestrial ecosystem|terrestrial]], and [[marine ecosystems]]. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include [[nitrogen fixation|fixation]], [[ammonification]], [[nitrification]], and [[denitrification]]. 78% of the [[Earth's atmosphere]] is molecular nitrogen (N<sub>2</sub>),<ref name="CarrollSalt2004p93">{{Cite book|title=Ecology for gardeners|author1=Steven B. Carroll|author2=Steven D. Salt|publisher=Timber Press|year=2004|isbn=978-0-88192-611-8|page=93|url=https://books.google.com/books?id=aM4W9e5nmsoC&pg=PA93|access-date=2016-10-23|archive-url=https://web.archive.org/web/20180201122648/https://books.google.com/books?id=aM4W9e5nmsoC&pg=PA93|archive-date=2018-02-01|url-status=live}}</ref> making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a [[scarcity]] of usable nitrogen in many types of [[ecosystems]]. The nitrogen cycle is of particular interest to [[ecologist]]s because nitrogen availability can affect the rate of key ecosystem processes, including [[primary production]] and [[decomposition]]. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically [[Human impact on the nitrogen cycle|altered the global nitrogen cycle]].<ref name="Kuypers 2011">{{cite journal |last1=Kuypers |first1= MMM |last2=Marchant |first2=HK |last3=Kartal |first3=B |title=The Microbial Nitrogen-Cycling Network |journal=Nature Reviews Microbiology |volume=1 |issue=1 |pages=1–14 |year=2011 |pmid=29398704 |doi=10.1038/nrmicro.2018.9 |hdl= 21.11116/0000-0003-B828-1 |s2cid= 3948918 |hdl-access=free }}</ref><ref name="Galloway 2004">{{cite journal|last1=Galloway|first1=J. N.|title=Nitrogen cycles: past, present, and future generations |journal=Biogeochemistry|volume=70|issue=2|pages=153–226|year=2004|doi=10.1007/s10533-004-0370-0|s2cid=98109580|display-authors=etal}}</ref><ref name="Reis 2016">{{Cite journal|last1=Reis|first1=Stefan|last2=Bekunda|first2=Mateete|last3=Howard|first3=Clare M|last4=Karanja|first4=Nancy|last5=Winiwarter|first5=Wilfried|last6=Yan|first6=Xiaoyuan|last7=Bleeker|first7=Albert|last8=Sutton|first8=Mark A|date=2016-12-01|title=Synthesis and review: Tackling the nitrogen management challenge: from global to local scales|journal=Environmental Research Letters|volume=11|issue=12|pages=120205|doi=10.1088/1748-9326/11/12/120205|issn=1748-9326|bibcode=2016ERL....11l0205R|doi-access=free}}</ref> Human modification of the global nitrogen cycle can negatively affect the natural environment system and also human health.<ref name="Gu 2012">{{Cite journal|last1=Gu|first1=Baojing|last2=Ge|first2=Ying|last3=Ren|first3=Yuan|last4=Xu|first4=Bin|last5=Luo|first5=Weidong|last6=Jiang|first6=Hong|last7=Gu|first7=Binhe|last8=Chang|first8=Jie|date=2012-08-17|title=Atmospheric Reactive Nitrogen in China: Sources, Recent Trends, and Damage Costs|journal=Environmental Science & Technology|volume=46|issue=17|pages=9420–9427|doi=10.1021/es301446g|pmid=22852755|issn=0013-936X|bibcode=2012EnST...46.9420G}}</ref><ref name="Kim 2017">{{Cite journal|last1=Kim|first1=Haryun|last2=Lee|first2=Kitack|last3=Lim|first3=Dhong-Il|last4=Nam|first4=Seung-Il|last5=Kim|first5=Tae-Wook|last6=Yang|first6=Jin-Yu T.|last7=Ko|first7=Young Ho|last8=Shin|first8=Kyung-Hoon|last9=Lee|first9=Eunil|date=2017-05-11|title=Widespread Anthropogenic Nitrogen in Northwestern Pacific Ocean Sediment|journal=Environmental Science & Technology|volume=51|issue=11|pages=6044–6052|doi=10.1021/acs.est.6b05316|pmid=28462990|issn=0013-936X|bibcode=2017EnST...51.6044K}}</ref>
|-
! {{align|left|Phosphorus}}
| [[File:Phosphorus cycle.png|220px]]
| The [[phosphorus cycle]] is the movement of [[phosphorus]] through the [[lithosphere]], [[hydrosphere]], and [[biosphere]]. Unlike many other biogeochemical cycles, the [[Earth's atmosphere|atmosphere]] does not play a significant role in the movement of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth. The production of [[phosphine]] gas occurs in only specialized, local conditions. Therefore, the phosphorus cycle should be viewed from whole Earth system and then specifically focused on the cycle in terrestrial and aquatic systems. Locally, transformations of phosphorus are  chemical, biological and microbiological: the major long-term transfers in the global cycle, however, are driven by [[tectonic plate|tectonic]] movements in [[geologic time]].<ref name="Schlesinger_1991">{{cite book | vauthors = Schlesinger WH | title = Biogeochemistry: An analysis of global change | date = 1991 }}</ref> Humans have caused major changes to the global phosphorus cycle through shipping of phosphorus minerals, and use of phosphorus [[fertilizer]], and also the shipping of food from farms to cities, where it is lost as effluent.
|-
! {{align|left| Sulphur}}
| [[File:Schematic-figure-of-the-sulfur-cycle.jpg|220px]]
| The [[sulfur cycle]] is the collection of processes by which [[sulfur]] moves between rocks, waterways and living systems. Such biogeochemical cycles are important in [[geology]] because they affect many minerals. Biochemical cycles are also important for life because sulfur is an [[essential element]], being a constituent of many [[protein]]s and [[cofactor (biochemistry)|cofactor]]s, and sulfur compounds can be used as oxidants or reductants in microbial respiration.<ref name=Brock>{{cite book |title=Brock Biology of Microorganisms | year=2006| vauthors = Madigan MT, Martino JM | edition=11th |page=136 |publisher=Pearson |isbn=978-0-13-196893-6}}</ref>  The global [[sulfur]] cycle involves the transformations of sulfur species through different oxidation states, which play an important role in both geological and biological processes. Earth's main sulfur sink is the oceans SO<sub>4</sub><sup>2−</sup>, where it is the major [[oxidizing agent]].<ref>{{cite journal | vauthors = Bickle MJ, Alt JC, Teagle DA | date = 1994 | title = Sulfur transport and sulphur isotope fractionations in ocean floor hydrothermal systems | journal = Mineralogical Magazine | volume = 58A | issue = 1 | pages = 88–89 | doi = 10.1180/minmag.1994.58A.1.49 | bibcode = 1994MinM...58...88B }}</ref>
|-
! {{align|left| Iron}}
| [[File:Iron cycle.svg|220px]]
| The [[iron cycle]] (Fe) is the biogeochemical cycle of [[iron]] through the [[atmosphere]], [[hydrosphere]], [[biosphere]] and [[lithosphere]]. While Fe is highly abundant in the Earth's crust,<ref name=Taylor1964>{{cite journal| vauthors = Taylor SR |date=1964|title=Abundance of chemical elements in the continental crust: a new table|journal=Geochimica et Cosmochimica Acta|volume=28|issue=8|pages=1273–1285|doi=10.1016/0016-7037(64)90129-2|bibcode=1964GeCoA..28.1273T}}</ref> it is less common in oxygenated surface waters. Iron is a key micronutrient in [[primary productivity]],<ref name = "Tagliabue_2017">{{cite journal | vauthors = Tagliabue A, Bowie AR, Boyd PW, Buck KN, Johnson KS, Saito MA | title = The integral role of iron in ocean biogeochemistry | journal = Nature | volume = 543 | issue = 7643 | pages = 51–59 | date = March 2017 | pmid = 28252066 | doi = 10.1038/nature21058 | bibcode = 2017Natur.543...51T | s2cid = 2897283 | url = https://eprints.utas.edu.au/24469/2/115577%20-%20postprint.pdf }}</ref> and a limiting nutrient in the Southern ocean, eastern equatorial Pacific, and the subarctic Pacific referred to as [[High-nutrient, low-chlorophyll regions|High-Nutrient, Low-Chlorophyll (HNLC) regions]] of the ocean.<ref name="Iron deficiency limits phytoplankto">{{cite journal| vauthors = Martin JH, Fitzwater SE  |date=1988 |title=Iron deficiency limits phytoplankton growth in the north-east Pacific subarctic |journal=Nature |volume=331 |issue=6154 |pages=341–343 |doi=10.1038/331341a0|bibcode=1988Natur.331..341M |s2cid=4325562 }}</ref> Iron exists in a range of [[oxidation states]] from -2 to +7; however, on Earth it is predominantly in its +2 or +3 redox state and is a primary redox-active metal on Earth.<ref>{{cite journal | vauthors = Melton ED, Swanner ED, Behrens S, Schmidt C, Kappler A | title = The interplay of microbially mediated and abiotic reactions in the biogeochemical Fe cycle | journal = Nature Reviews. Microbiology | volume = 12 | issue = 12 | pages = 797–808 | date = December 2014 | pmid = 25329406 | doi = 10.1038/nrmicro3347 | s2cid = 24058676 }}</ref> The cycling of iron between its +2 and +3 oxidation states is referred to as the iron cycle. This process can be entirely [[abiotic]] or facilitated by [[microorganisms]], especially [[iron-oxidizing bacteria]]. The abiotic processes include the [[rust]]ing of iron-bearing metals, where Fe<sup>2+</sup> is abiotically oxidized to Fe<sup>3+</sup>  in the presence of oxygen, and the reduction of Fe<sup>3+</sup> to Fe<sup>2+</sup> by iron-sulfide minerals. The biological cycling of Fe<sup>2+</sup> is done by iron oxidizing and reducing microbes.<ref>{{cite journal| vauthors = Schmidt C, Behrens S, Kappler A |date=2010 |title=Ecosystem functioning from a geomicrobiological perspective – a conceptual framework for biogeochemical iron cycling|journal=Environmental Chemistry |volume=7 |issue=5 |pages=399 |doi=10.1071/EN10040 |doi-access=free }}</ref><ref>Kappler, Andreas; Straub, Kristina L. (2005-01-01). "Geomicrobiological Cycling of Iron". ''Reviews in Mineralogy and Geochemistry''. '''59''' (1): 85–108. [[Doi (identifier)|doi]]:10.2138/rmg.2005.59.5. [[ISSN (identifier)|ISSN]]&nbsp;1529-6466.</ref>
|-
! {{align|left| Calcium}}
| [[File:Equilibrium of carbonic acid in the oceans .png|220px]]
| The [[calcium cycle]] is a transfer of calcium between [[Solubility|dissolved]] and [[solid]] phases. There is a continuous supply of [[Calcium|calcium ions]] into waterways from [[Rock (geology)|rocks]], [[organism]]s, and [[soil]]s.<ref name=Walker1981>{{Cite journal|last1=Walker|first1=James C. G.|last2=Hays|first2=P. B.|last3=Kasting|first3=J. F.|date=1981|title=A negative feedback mechanism for the long-term stabilization of Earth's surface temperature|journal=Journal of Geophysical Research|volume=86|issue=C10|pages=9776|doi=10.1029/jc086ic10p09776|issn=0148-0227|bibcode=1981JGR....86.9776W}}</ref><ref>{{Cite journal|last=Berner|first=R. A.|date=2004-05-01|title=A model for calcium, magnesium and sulfate in seawater over Phanerozoic time|journal=American Journal of Science|volume=304|issue=5|pages=438–453|doi=10.2475/ajs.304.5.438|issn=0002-9599|bibcode=2004AmJS..304..438B|doi-access=free}}</ref> Calcium ions are consumed and removed from aqueous environments as they react to form insoluble structures such as [[calcium carbonate]] and calcium silicate,<ref name=Walker1981/><ref>{{Cite journal|last1=Ridgwell|first1=Andy|last2=Zeebe|first2=Richard E.|date=2005-06-15|title=The role of the global carbonate cycle in the regulation and evolution of the Earth system|journal=Earth and Planetary Science Letters|volume=234|issue=3–4|pages=299–315|doi=10.1016/j.epsl.2005.03.006|issn=0012-821X}}</ref> which can deposit to form sediments or the [[exoskeleton]]s of organisms.<ref name=Raisman2013>{{Cite book|title=Ocean acidification: Elements and Considerations|last1=Raisman|first1=Scott|last2=Murphy|first2=Daniel T.|publisher=Nova Science Publishers, Inc|year=2013|isbn=9781629482958|location=Hauppauge, New York}}</ref> Calcium ions can also be utilized [[Calcium in biology|biologically]], as calcium is essential to biological functions such as the production of [[bone]]s and [[Tooth|teeth]] or cellular function.<ref name="Nordin 1988">{{Cite book|title=Calcium in Human Biology|last=Nordin|first=B. E. C|date=1988|publisher=Springer London|isbn=9781447114376|location=London|language=en|oclc=853268074|doi = 10.1007/978-1-4471-1437-6|series = ILSI Human Nutrition Reviews|s2cid=9765195}}</ref><ref name="Calcium in Biological Systems">{{Cite book|url=https://books.google.com/books?id=gdrTBwAAQBAJ&q=Biological+use+of+Calcium+review&pg=PR5|title=Calcium in Biological Systems|last1=Rubin|first1=Ronald P.|last2=Weiss|first2=George B.|last3=Putney|first3=James W. Jr|date=2013-11-11|publisher=Springer Science & Business Media|isbn=9781461323778|language=en}}</ref> The calcium cycle is a common thread between terrestrial, marine, geological, and biological processes.<ref>{{Cite journal|last1=Fantle|first1=Matthew S.|last2=Tipper|first2=Edward T.|date=2014|title=Calcium isotopes in the global biogeochemical Ca cycle: Implications for development of a Ca isotope proxy|url=https://www.sciencedirect.com/science/article/pii/S0012825213001700|journal=Earth-Science Reviews|volume=131|pages=148–177|doi=10.1016/j.earscirev.2014.02.002|issn=0012-8252|via=Elsevier ScienceDirect}}</ref> The marine calcium cycle is affected by changing [[Carbon dioxide in Earth's atmosphere|atmospheric carbon dioxide]] due to [[ocean acidification]].<ref name=Raisman2013 /> 
|-
! {{align|left| Silicon}}
| [[File:Silica cycle-draft.jpg|220px]]
| The [[silica cycle]] involves the transport of [[silica]] between the Earth's systems. [[Opal]] silica (SiO<sub>2</sub>), also called [[silicon dioxide]], is a chemical compound of [[silicon]]. Silicon is a bioessential element and is one of the most abundant elements on Earth.<ref>{{cite journal|last1=Hunt|first1=J. W.|last2=Dean|first2=A. P.|last3=Webster|first3=R. E.|last4=Johnson|first4=G. N.|last5=Ennos|first5=A. R.|date=2008|title=A Novel Mechanism by which Silica Defends Grasses Against Herbivory|journal=Annals of Botany|volume=102|issue=4|pages=653–656|doi=10.1093/aob/mcn130|pmid=18697757|pmc=2701777|issn=1095-8290}}</ref><ref>{{cite journal|last=Conley|first=Daniel J.|date=December 2002|title=Terrestrial ecosystems and the global biogeochemical silica cycle|journal=Global Biogeochemical Cycles|volume=16|issue=4|pages=68–1–68–8|doi=10.1029/2002gb001894|issn=0886-6236|bibcode=2002GBioC..16.1121C|s2cid=128672790 |doi-access=free}}</ref> The silica cycle has significant overlap with the [[carbon cycle]] (see the [[carbonate–silicate cycle]]) and plays an important role in the sequestration of carbon through continental [[weathering]], biogenic export and burial as [[Siliceous ooze|oozes]] on geologic timescales.<ref>{{cite journal|last1=Defant|first1=Marc J.|last2=Drummond|first2=Mark S.|date=October 1990|title=Derivation of some modern arc magmas by melting of young subducted lithosphere|journal=Nature|volume=347|issue=6294|pages=662–665|doi=10.1038/347662a0|issn=0028-0836|bibcode=1990Natur.347..662D|s2cid=4267494}}</ref>
|}

==Box models==
{{see also|Climate box models}}

[[File:Simple box model.png|thumb|upright=1|right| {{center|'''Basic one-box model'''}} Box models are widely used to illustrate [[flux]]es in biogeochemical cycles{{hsp}}<ref name=Bianchi2007>[[Thomas S. Bianchi|Bianchi, Thomas]] (2007) [https://books.google.com/books?id=3no8DwAAQBAJ&q=%22Biogeochemistry+of+Estuaries%22 ''Biogeochemistry of Estuaries''] page 9, Oxford University Press. {{ISBN|9780195160826}}.</ref>]]

Box models are widely used to model biogeochemical systems.<ref name=Sarmiento1984>{{cite journal| author = Sarmiento, J.L.|author2=Toggweiler, J.R.| year = 1984| title = A new model for the role of the oceans in determining atmospheric P CO 2| journal = Nature| volume = 308| pages = 621–24| doi = 10.1038/308621a0| issue=5960 |bibcode = 1984Natur.308..621S |s2cid=4312683}}</ref> Box models are simplified versions of complex systems, reducing them to boxes (or storage [[Thermodynamics#Instrumentation|reservoir]]s) for chemical materials, linked by material [[flux]]es (flows). Simple box models have a small number of boxes with properties, such as volume, that do not change with time. The boxes are assumed to behave as if they were mixed homogeneously.<ref name=Bianchi2007 /> These models are often used to derive analytical formulas describing the dynamics and steady-state abundance of  the chemical species involved.

The diagram at the right shows a basic one-box model. The reservoir contains the amount of material ''M'' under consideration, as defined by chemical, physical or biological properties. The source ''Q'' is the flux of material into the reservoir, and the sink ''S'' is the flux of material out of the reservoir. The budget is the check and balance of the sources and sinks affecting material turnover in a reservoir. The reservoir is in a [[steady state]] if ''Q'' = ''S'', that is, if the sources balance the sinks and there is no change over time.<ref name=Bianchi2007 />

{{Quote box
 |title = Measurement units
 |quote = Global biogeochemical box models usually measure:<br />{{space|12}}— ''reservoir masses'' in petagrams (Pg)<br />{{space|12}}— ''flow fluxes'' in petagrams per year (Pg yr<sup>−1</sup>)<br />{{space|11}}Diagrams in this article mostly use these units<br />________________________________________________<br />
<small>&nbsp;one [[petagram]] = 10<sup>15</sup> grams = one [[gigatonne]] = one [[billion]] (10<sup>9</sup>) [[tonne]]s</small>
 |source = 
 |align = right
 |width = 360px
 |border = 
 |fontsize = 
 |bgcolor = 
 |style = 
 |title_bg = 
 |title_fnt = 
 |tstyle = 
 |qalign =
 |qstyle = 
 |quoted = 
 |salign = 
 |sstyle = 
}}

The [[turnover time]] (also called the renewal time or exit age) is the average time material spends resident in the reservoir. If the reservoir is in a steady state, this is the same as the time it takes to fill or drain the reservoir. Thus, if τ is the turnover time, then τ = M/S.<ref name=Bianchi2007 /> The equation describing the rate of change of content in a reservoir is

::<math> \frac{dM}{dt} = Q - S = Q - \frac{M}{\tau}</math>

When two or more reservoirs are connected, the material can be regarded as cycling between the reservoirs, and there can be predictable patterns to the cyclic flow.<ref name=Bianchi2007 /> More complex [[multi-compartment model|multibox models]] are usually solved using numerical techniques.

[[File:Simplified budget of carbon flows in the ocean.png|thumb|upright=1.2|left| {{center|'''Simplified budget of ocean carbon flows''' <small>example of a three box model{{hsp}}<ref name=Middelburg2019>Middelburg, J.J.(2019) ''Marine carbon biogeochemistry: a primer for earth system scientists'', page 5, Springer Nature. {{ISBN|9783030108229}}. {{doi|10.1007/978-3-030-10822-9}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref></small>}}]]

[[File:Simplified diagram of the global carbon cycle.jpg|thumb|upright=2|right| {{center|'''Export and burial rates of terrestrial organic carbon in the ocean'''<br /><small>example of a more complex model with many interacting boxes</small>}} Reservoir masses here represents ''carbon stocks'', measured in Pg C. Carbon exchange fluxes, measured in Pg C yr<sup>−1</sup>, occur between the atmosphere and its two major sinks, the land and the ocean. The black numbers and arrows indicate the reservoir mass and exchange fluxes estimated for the year 1750, just before the [[Industrial Revolution]]. The red arrows (and associated numbers) indicate the annual flux changes due to anthropogenic activities, averaged over the 2000–2009 time period. They represent how the carbon cycle has changed since 1750. Red numbers in the reservoirs represent the cumulative changes in anthropogenic carbon since the start of the Industrial Period, 1750–2011.<ref>{{cite journal |doi=10.1063/1.1510279 |title=Sinks for Anthropogenic Carbon |year=2002 |last1=Sarmiento |first1=Jorge L. |last2=Gruber |first2=Nicolas |journal=Physics Today |volume=55 |issue=8 |pages=30–36 |bibcode=2002PhT....55h..30S |s2cid=128553441 |doi-access=free}}</ref><ref>{{cite book |doi=10.13140/2.1.1081.8883 |year=2013 |last1=Chhabra |first1=Abha |chapter=Carbon and Other Biogeochemical Cycles |pages=465–570 |title=CLIMATE CHANGE 2013 The Physical Science Basis, WORKING GROUP I CONTRIBUTION TO THE FIFTH ASSESSMENT REPORT OF THE INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE |editor1=Stocker, T.F. |editor2=Qin, D. |editor3=Plattner, G.-K. |editor4=Tignor, M. |editor5=Allen, S.K. |editor6=Boschung, J. |editor7=Nauels, A. |editor8=Xia, Y. |editor9=Bex, V. |editor10=Midgley, P.M. |edition=1st |publisher=Cambridge University Press}}</ref><ref>{{cite journal |doi=10.3389/fmars.2016.00259 |title=Perspectives on the Terrestrial Organic Matter Transport and Burial along the Land-Deep Sea Continuum: Caveats in Our Understanding of Biogeochemical Processes and Future Needs |year=2016 |last1=Kandasamy |first1=Selvaraj |last2=Nagender Nath |first2=Bejugam |journal=Frontiers in Marine Science |volume=3 |s2cid=30408500 |doi-access=free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

{{clear left}}

The diagram above shows a simplified budget of ocean carbon flows. It is composed of three simple interconnected box models, one for the [[euphotic zone]], one for the [[Aphotic zone|ocean interior]] or dark ocean, and one for [[ocean sediment]]s. In the euphotic zone, net [[phytoplankton production]] is about 50 Pg C each year. About 10 Pg is exported to the ocean interior while the other 40 Pg is respired. Organic carbon degradation occurs as [[Particulate organic carbon|particles]] ([[marine snow]]) settle through the ocean interior. Only 2 Pg eventually arrives at the seafloor, while the other 8 Pg is respired in the dark ocean. In sediments, the time scale available for degradation increases by orders of magnitude with the result that 90% of the organic carbon delivered is degraded and only 0.2 Pg C yr<sup>−1</sup> is eventually buried and transferred from the biosphere to the geosphere.<ref name=Middelburg2019 />

{{clear}}

==Dissolved and particulate matter==
{{further|Dissolved organic carbon|Particulate organic carbon}}

[[File:DOC net production, transport and export in the ocean.png|thumb|upright=1.7|left| {{center|'''DOC net production, transport and export in the ocean'''}} Regions of significant net DOC production (broad arrows) include coastal and equatorial upwelling regions that support much of the global new production. DOC is transported into and around the subtropical gyres with the wind-driven surface circulation. Export takes place if exportable DOC (elevated concentrations indicated by dark blue fields) is present during overturning of the water column. precursor for deep and intermediate water mass formation. DOC is also exported with subduction in the gyres. In regions where DOCenriched subtropical water is prevented by polar frontal systems from serving as a precursor for overturning circulation (such as at the sites of Antarctic Bottom Water formation in the Southern Ocean) DOC export is a weak component of the biological pump. Waters south of the Antarctic Polar Front lack significant exportable DOC (depicted by light blue field) during winter.<ref>Hansell DA and Craig AC (2015) "Marine Dissolved Organic Matter and the Carbon Cycle". ''Oceanography'', '''14'''(4): 41–49. {{doi|10.5670/oceanog.2001.05}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

[[File:Forms of organic matter.webp|thumb|upright=1.7|right| {{center|'''Dissolved organic matter (DOM)'''}} Venn diagram of various forms of [[dissolved organic matter]] (DOM) found in water. Total organic matter (TOM), [[total organic carbon]] (TOC), dissolved organic carbon (DOC), [[particulate organic carbon]] (POC), dissolved organic nitrogen (DON), and dissolved organic phosphorus (DOP) are represented. DOC can be further broken down to its humic ([[humic acid]], [[fulvic acid]], and [[humin]]) and non-humic material.<ref>Pagano, T., Bida, M. and Kenny, J.E. (2014) "Trends in levels of allochthonous dissolved organic carbon in natural water: a review of potential mechanisms under a changing climate". ''Water'', '''6'''(10): 2862–2897. {{doi|10.3390/w6102862}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

[[File:Size and classification of marine particles.png|thumb|upright=1.7| {{center|'''Size and classification of marine particles<ref>Monroy, P., Hernández-García, E., Rossi, V. and López, C. (2017) "Modeling the dynamical sinking of biogenic particles in oceanic flow". ''Nonlinear Processes in Geophysics'', '''24'''(2): 293–305. {{doi|10.5194/npg-24-293-2017}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 International License].</ref>'''<br /><small>Adapted from Simon et al., 2002.<ref>Simon, M., Grossart, H., Schweitzer, B. and Ploug, H. (2002) "Microbial ecology of organic aggregates in aquatic ecosystems". ''Aquatic microbial ecology'', '''28''': 175–211. {{doi|10.3354/ame028175}}.</ref></small>}}]]

{{clear}}

==Biological pumps==
{{multiple image
 | align = right
 | direction = horizontal
 | total_width = 400px
 | header    = Importance of Antarctic krill in biogeochemical cycles
 | image1    = Importance of Antarctic krill in biogeochemical cycles.png
 | caption1  = {{center|'''Processes in the biological pump'''}}{{center|<small> Numbers given are carbon fluxes (Gt C yr−1) in white boxes<br />and carbon masses (Gt C) in dark boxes</small>}}
Phytoplankton convert {{CO2}}, which has dissolved from the atmosphere into the surface oceans into particulate organic carbon (POC) during primary production. Phytoplankton are then consumed by krill and small zooplankton grazers, which in turn are preyed upon by higher trophic levels. Any unconsumed phytoplankton form aggregates, and along with zooplankton faecal pellets, sink rapidly and are exported out of the mixed layer. Krill, zooplankton and microbes intercept phytoplankton in the surface ocean and sinking detrital particles at depth, consuming and respiring this POC to {{CO2}} (dissolved inorganic carbon, DIC), such that only a small proportion of surface-produced carbon sinks to the deep ocean (i.e., depths > 1000 m). As krill and smaller zooplankton feed, they also physically fragment particles into small, slower- or non-sinking pieces (via sloppy feeding, coprorhexy if fragmenting faeces), retarding POC export. This releases dissolved organic carbon (DOC) either directly from cells or indirectly via bacterial solubilisation (yellow circle around DOC). Bacteria can then remineralise the DOC to DIC ({{CO2}}, microbial gardening). Diel vertically migrating krill, smaller zooplankton and fish can actively transport carbon to depth by consuming POC in the surface layer at night, and metabolising it at their daytime, mesopelagic residence depths. Depending on species life history, active transport may occur on a seasonal basis as well.<ref>Cavan, E.L., Belcher, A., Atkinson, A., Hill, S.L., Kawaguchi, S., McCormack, S., Meyer, B., Nicol, S., Ratnarajah, L., Schmidt, K. and Steinberg, D.K. (2019) "The importance of Antarctic krill in biogeochemical cycles". ''Nature communications'', '''10'''(1): 1–13. {{doi|10.1038/s41467-019-12668-7}}.  [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>
}}
{{further|Biological pump}}

The [[biological pump]], in its simplest form, is the ocean's biologically driven sequestration of [[carbon]] from the atmosphere to the ocean interior and [[seafloor sediments]].<ref name="Sigman DM 2006. pp. 491-528">{{cite book |vauthors=Sigman DM, Haug GH |date=2006 |chapter=The biological pump in the past |title=Treatise on Geochemistry |volume=6 |publisher=Pergamon Press |pages=491–528}}</ref> It is the part of the [[oceanic carbon cycle]] responsible for the cycling of [[organic matter]] formed mainly by [[phytoplankton]] during [[photosynthesis]] (soft-tissue pump), as well as the cycling of [[calcium carbonate]] (CaCO<sub>3</sub>) formed into shells by certain organisms such as [[plankton]] and [[mollusks]] (carbonate pump).<ref name="Hain et al 2014 ToG">{{cite book |chapter=The Biological Pump in the Past |title=Treatise on Geochemistry |edition=2nd |year=2014 |vauthors=Hain MP, Sigman DM, Haug GH |volume=8 |pages=485–517 |doi=10.1016/B978-0-08-095975-7.00618-5  |url=https://earth-system-biogeochemistry.net/wp-content/uploads/2021/05/Hain_et_al_2014_ToG.pdf |access-date=2015-06-01 |isbn=9780080983004}}</ref>

The biological pump can be divided into three distinct phases,<ref name="Rocha CL 2006. pp. 83-111">De La Rocha CL. 2006. The Biological Pump. In: Treatise on Geochemistry; vol. 6, (ed.). Pergamon Press, pp. 83-111</ref> the first of which is the production of fixed carbon by planktonic [[phototrophs]] in the [[euphotic]] (sunlit) surface region of the ocean. In these surface waters, [[phytoplankton]] use [[carbon dioxide]] (CO<sub>2</sub>), [[nitrogen]] (N), [[phosphorus]] (P), and other trace elements ([[barium]], [[iron]], [[zinc]], etc.) during photosynthesis to make [[carbohydrates]], [[lipids]], and [[proteins]]. Some plankton, (e.g. [[coccolithophores]] and [[foraminifera]]) combine calcium (Ca) and dissolved carbonates ([[carbonic acid]] and [[bicarbonate]]) to form a calcium carbonate (CaCO<sub>3</sub>) protective coating.

{{multiple image
 | align = left
 | direction = horizontal
 | total_width = 550
 | header    = 
 | image1    = CO2 pump hg.svg
 | caption1  = {{center|[[Biological pump]]}}
 | image2    = WhalePump.jpg
 | caption2  = {{center|The oceanic whale pump where whales cycle nutrients through the water column}}
}}

{{clear left}}

Once this carbon is fixed into soft or hard tissue, the organisms either stay in the euphotic zone to be recycled as part of the regenerative [[nutrient cycle]] or once they die, continue to the second phase of the biological pump and begin to sink to the ocean floor. The sinking particles will often form aggregates as they sink, greatly increasing the sinking rate. It is this aggregation that gives particles a better chance of escaping predation and decomposition in the water column and eventually make it to the sea floor.

The fixed carbon that is either decomposed by bacteria on the way down or once on the sea floor then enters the final phase of the pump and is remineralized to be used again in [[primary production]]. The particles that escape these processes entirely are sequestered in the sediment and may remain there for millions of years. It is this sequestered carbon that is responsible for ultimately lowering atmospheric CO<sub>2</sub>.

{{ external media
| float  = right
| width  = 280px
| video1 = [https://www.youtube.com/watch?v=qSUX8hhyP98 Marine oxygen and carbon dioxide cycles]
}}

* Brum JR, Morris JJ, Décima M and Stukel MR (2014) "Mortality in the oceans: Causes and consequences". ''Eco-DAS IX Symposium Proceedings'',  Chapter 2, pages 16–48. Association for the Sciences of Limnology and Oceanography. {{ISBN|978-0-9845591-3-8}}.
* Mateus, M.D. (2017) "Bridging the gap between knowing and modeling viruses in marine systems—An upcoming frontier". ''Frontiers in Marine Science'', '''3''': 284. {{doi|10.3389/fmars.2016.00284}}
* Beckett, S.J. and Weitz, J.S. (2017) "Disentangling niche competition from grazing mortality in phytoplankton dilution experiments". ''PLOS ONE'', '''12'''(5): e0177517. {{doi|10.1371/journal.pone.0177517}}.

{{clear}}

==Role of microorganisms==
{{see also|marine microorganisms|microbial loop|viral shunt|marine microbial symbiosis}}
{{multiple image
 | align = left
 | direction = horizontal
 | total_width = 720
 | header            = DOM, POM and the viral shunt
 | header_align      = <!-- left/right/center -->
 | footer            = 
 | footer_align      = <!-- left/right/center -->
 | footer_background = 
 | background color  = 
 | image1    = Marine connections between the living and the nonliving.png
 | alt1      = 
 | caption1  = Connections between the different compartments of the living (bacteria/viruses and phyto−/zooplankton) and the nonliving (DOM/POM and inorganic matter) environment<ref>Heinrichs, M.E., Mori, C. and Dlugosch, L. (2020) "Complex Interactions Between Aquatic Organisms and Their Chemical Environment Elucidated from Different Perspectives". In: ''YOUMARES 9-The Oceans: Our Research, Our Future '', pages 279–297. Springer. {{doi|10.1007/978-3-030-20389-4_15}}.</ref>
 | image2    = Viral shunt.jpg
 | alt2      = 
 | caption2  = The [[viral shunt pathway]] facilitates the flow of [[dissolved organic matter]] (DOM) and [[particulate organic matter]] (POM) through the marine food web
}}

{{clear}}

==Carbon, oxygen and hydrogen cycles==
{{further|ocean carbon cycle|blue carbon|oxygen cycle|hydrogen cycle}}

The [[marine carbon cycle]] is composed of processes that exchange [[carbon]] between various pools within the ocean as well as between the atmosphere, Earth interior, and the [[Seabed|seafloor]]. The [[carbon cycle]] is a result of many interacting forces across multiple time and space scales that circulates carbon around the planet, ensuring that carbon is available globally. The Oceanic carbon cycle is a central process to the global carbon cycle and contains both [[Total inorganic carbon|inorganic]] carbon (carbon not associated with a living thing, such as carbon dioxide) and [[Organic matter|organic]] carbon (carbon that is, or has been, incorporated into a living thing). Part of the marine carbon cycle transforms carbon between non-living and living matter.

{{multiple image
 | align = right
 | direction = vertical
 | header    = 
 | total_width = 240px
 | image1    = OceanCarbonCycle.jpg
 | caption1  = {{center|[[Oceanic carbon cycle|Marine carbon cycle]]<ref name=Prentice_etal_2001>{{Cite web|last=Prentice|first=I.C.|title=The carbon cycle and atmospheric carbon dioxide|url =http://ir.anet.ua.ac.be/irua/handle/10067/381670151162165141?show=full|publisher=Climate change 2001: the scientific basis: contribution of Working Group I to the Third Assessment Report of the Intergouvernmental Panel on Climate Change / Houghton, J.T. [edit.]|year=2001|access-date=31 May 2012 }}</ref>}}
 | image2    = Oxygen cycle.svg
 | caption2  = {{center|[[Oxygen cycle]]}}
}}

Three main processes (or pumps) that make up the marine carbon cycle bring atmospheric [[carbon dioxide]] (CO<sub>2</sub>) into the ocean interior and distribute it through the oceans.  These three pumps are: (1) the solubility pump, (2) the carbonate pump, and (3) the biological pump.  The total active pool of carbon at the Earth's surface for durations of less than 10,000 years is roughly 40,000 gigatons C (Gt C, a gigaton is one billion tons, or the weight of approximately 6 million [[blue whale]]s), and about 95% (~38,000 Gt C) is stored in the ocean, mostly as dissolved inorganic carbon.<ref name="H. 2013"/><ref name="Falkowski 291–296"/>  The [[Ion speciation|speciation]] of dissolved inorganic carbon in the marine carbon cycle is a primary controller of [[Acid-base reaction|acid-base chemistry]] in the oceans.

{| class="wikitable collapsible"
|-
! colspan=4| Forms of carbon <ref>[https://www.ck12.org/book/cbse_biology_book_class_xii/section/18.7/ Biogeochemical Cycles]  ''CK-12 Biology''. Accessed: 2 June 2020.</ref>
|-
! Carbon form	
! Chemical formula
! State
! Main reservoir
|-
| [[carbon dioxide]]
| CO<sub>2</sub>
| gas
| atmosphere
|-
| [[carbonic acid]]
| H<sub>2</sub>CO<sub>3</sub>
| liquid
| ocean
|-
| [[bicarbonate ion]]
| HCO<sub>3</sub>−
| liquid<br />(dissolved [[ion]])
| ocean
|-
| [[organic compound]]s
| ''Examples:''<br />C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> (glucose)<br />CH<sub>4</sub> (methane)
| solid<br />gas
| [[marine organisms]]<br />[[organic sediment]]s<br />([[fossil fuel]]s)
|-
| other carbon compounds
| ''Examples:''<br />CaCO<sub>3</sub> (calcium carbonate)<br />CaMg(CO<sub>3</sub>)<sub>2</sub><br />(calcium magnesium carbonate)
| solid
| shells<br />[[sedimentary rock]]
|}

{{clear}}

==Nitrogen and phosphorus cycles==

[[File:Aquatic Dead Zones.jpg|thumb|upright=1.7|right| Dead zones occur in the ocean when phosphorus and nitrogen from fertilizers in [[land runoff]] cause excessive growth of microorganisms, which depletes oxygen and kills fauna. Worldwide, large dead zones are found in coastal areas with high human population density.<ref name=OpenStax>[https://cnx.org/contents/ZdFkREJc@7/Biogeochemical-Cycles Biogeochemical Cycles], ''OpenStax'', 9 May 2019. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

[[File:Interactions between marine biogeochemical carbon, nitrogen and phosphorus cycles.pdf|thumb|upright=1.7|right| {{center|Interactions between marine biogeochemical<br />carbon, nitrogen and phosphorus cycles}}
----
{{center|<small>RDOC: recalcitrant [[dissolved organic carbon]]{{space|50}}<br />DOM: [[Dissolved organic carbon|dissolved organic material]]{{space|16}}POM: [[Particulate organic carbon|particulate organic material]]</small>}}]]
{{further|Nitrogen cycle#Marine nitrogen cycle|Phosphorus cycle}}

The nitrogen cycle is as important in the ocean as it is on land. While the overall cycle is similar in both cases, there are different players and modes of transfer for nitrogen in the ocean.<ref name="Moulton 2016">{{cite journal |last1=Moulton |first1=Orissa M |last2=Altabet |first2=Mark A |last3=Beman |first3=J Michael |last4=Deegan |first4=Linda A |last5=Lloret |first5=Javier |last6=Lyons |first6=Meaghan K |last7=Nelson |first7=James A |last8=Pfister |first8=Catherine A |title=Microbial associations with macrobiota in coastal ecosystems: patterns and implications for nitrogen cycling |journal=Frontiers in Ecology and the Environment |date=May 2016 |volume=14 |issue=4 |pages=200–208 |doi=10.1002/fee.1262 |language=en |issn=1540-9295|hdl=1912/8083 |hdl-access=free}}</ref> Nitrogen enters the ocean through precipitation, runoff, or as N<sub>2</sub> from the atmosphere. Nitrogen cannot be utilized by [[phytoplankton]] as N<sub>2</sub> so it must undergo [[nitrogen fixation]] which is performed predominantly by [[cyanobacteria]].<ref name="Miller 2008" /> Without supplies of fixed nitrogen entering the marine cycle, the fixed nitrogen would be used up in about 2000 years.<ref name=Gruber2008>{{cite book|last=Gruber|first=Nicolas|title=Nitrogen in the Marine Environment|year=2008|publisher=Elsevier|location=Burlington, MA |isbn=978-0-12-372522-6|pages=1–35}}</ref> Phytoplankton need nitrogen in biologically available forms for the initial synthesis of organic matter. [[Ammonia]] and [[urea]] are released into the water by excretion from plankton. Nitrogen sources are removed from the [[Photic zone|euphotic zone]] by the downward movement of the organic matter. This can occur from sinking of phytoplankton, vertical mixing, or sinking of waste of vertical migrators. The sinking results in ammonia being introduced at lower depths below the euphotic zone. Bacteria are able to convert ammonia to [[nitrite]] and [[nitrate]] but they are inhibited by light so this must occur below the euphotic zone.<ref name="Miller 2008">{{cite book|last=Miller|first=Charles|title=Biological oceanography |year=2008 |publisher=Blackwell Publishing |location=Malden, MA |isbn=978-0-632-05536-4|pages=60–62}}</ref> Ammonification or [[Mineralization (geology)|mineralization]] is performed by bacteria to convert organic nitrogen to ammonia. [[Nitrification]] can then occur to convert the ammonium to nitrite and nitrate.<ref name=Boyes2011>{{cite web|last=Boyes |last2=Elliot |first=Susan |first2=Michael |title=Learning Unit: Nitrogen Cycle Marine Environment |url=http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/16/uc/vlus/nitrogenmarine.vlu.html|access-date=22 October 2011|url-status=dead |archive-url=https://web.archive.org/web/20120415123617/http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/16/uc/vlus/nitrogenmarine.vlu.html |archive-date=15 April 2012}}</ref> Nitrate can be returned to the euphotic zone by vertical mixing and [[upwelling]] where it can be taken up by phytoplankton to continue the cycle. N<sub>2</sub> can be returned to the atmosphere through [[denitrification]].

Ammonium is thought to be the preferred source of fixed nitrogen for phytoplankton because its assimilation does not involve a [[redox]] reaction and therefore requires little energy. Nitrate requires a redox reaction for assimilation but is more abundant so most phytoplankton have adapted to have the enzymes necessary to undertake this reduction ([[nitrate reductase]]). There are a few notable and well-known exceptions that include most ''[[Prochlorococcus]]'' and some ''[[Synechococcus]]'' that can only take up nitrogen as ammonium.<ref name=Gruber2008 />

{{multiple image
 | align = left
 | direction = vertical
 | header    = 
 | total_width = 360px
 | image1    = Marine Nitrogen Cycle.jpg
 | caption1  = {{center|[[Nitrogen cycle#Marine nitrogen cycle|Marine nitrogen cycle]]}}
 | image2    = Phosphorus cycle.png
 | caption2  = {{center|Marine [[phosphorus cycle]]}}
}}

{{clear}}

Phosphorus is an essential nutrient for plants and animals. Phosphorus is a [[Limiting factor|limiting nutrient]] for aquatic organisms. Phosphorus forms parts of important life-sustaining molecules that are very common in the biosphere. Phosphorus does enter the atmosphere in very small amounts when the dust is dissolved in rainwater and seaspray but remains mostly on land and in rock and soil minerals. Eighty per cent of the mined phosphorus is used to make fertilizers. Phosphates from fertilizers, sewage and detergents can cause pollution in lakes and streams. Over-enrichment of phosphate in both fresh and inshore marine waters can lead to massive [[algae bloom]]s which, when they die and decay leads to [[eutrophication]] of freshwaters only. Recent research suggests that the predominant pollutant responsible for algal blooms in saltwater estuaries and coastal marine habitats is nitrogen.<ref>{{cite web|url=https://www.soils.org/discover-soils/soils-in-the-city/green-infrastructure/important-terms/eutrophication|title=Eutrophication - Soil Science Society of America|website=www.soils.org|url-status=dead|archive-url=https://web.archive.org/web/20140416123353/https://www.soils.org/discover-soils/soils-in-the-city/green-infrastructure/important-terms/eutrophication|archive-date=2014-04-16|access-date=2014-04-14}}</ref>

Phosphorus  occurs most abundantly in nature as part of the [[orthophosphate]] ion (PO<sub>4</sub>)<sup>3−</sup>, consisting of a P atom and 4 oxygen atoms. On land most phosphorus is found in rocks and minerals. Phosphorus-rich deposits have generally formed in the ocean or from guano, and over time, geologic processes bring ocean sediments to land. [[Weathering]] of rocks and minerals release phosphorus in a soluble form where it is taken up by plants, and it is transformed into organic compounds.  The plants may then be consumed by [[herbivore]]s and the phosphorus is either incorporated into their tissues or excreted. After death, the animal or plant decays, and phosphorus is returned to the soil where a large part of the phosphorus is transformed into insoluble compounds. [[Runoff (water)|Runoff]] may carry a small part of the phosphorus back to the [[ocean]].<ref>{{cite journal | vauthors = Peltzer DA, Wardle DA, Allison VJ, Baisden WT, Bardgett RD, Chadwick OA, Condron LM, Parfitt RL, Porder S, Richardson SJ, Turner BL | display-authors = 6 | title = Understanding ecosystem retrogression. | journal = Ecological Monographs | date = November 2010 | volume = 80 | issue = 4 | pages = 509–29 | doi = 10.1890/09-1552.1 }}</ref>

==Nutrient cycle==
[[File:Nutrient cycle.jpg|thumb|upright=1.5|right| {{center|'''Flow of energy and cycling of nutrients'''}} Dark green lines represent movement of nutrients and dashed lines represent movement of energy. Nutrients remain within the system while energy enters via photosynthesis and leaves the system primarily as heat energy, a non-biologically useful form of energy.<ref>Bear R and Rintoul D (2018) [https://cnx.org/contents/24nI-KJ8@27.4:D-ygu4Ty@13/Biogeochemical-Cycles "Biogeochemical Cycles"]. In: Bear R, Rintoul D, Snyder B, Smith-Caldas M, Herren C and Horne E (Eds) ''Principles of Biology'' OpenStax.</ref>]]
{{further|Nutrient cycle}}

A [[nutrient cycle]] is the movement and exchange of [[organic matter|organic]] and [[inorganic]] matter back into the [[Productivity (ecology)|production]] of matter. The process is regulated by the pathways available in [[marine food webs]], which ultimately decompose organic matter back into inorganic nutrients. Nutrient cycles occur within ecosystems. Energy flow always follows a unidirectional and noncyclic path, whereas the movement of [[mineral nutrients]] is cyclic. Mineral cycles include the [[carbon cycle]], [[oxygen cycle]], [[nitrogen cycle]], [[phosphorus cycle]] and [[sulfur cycle]] among others that continually recycle along with other mineral nutrients into [[Productivity (ecology)|productive]] ecological nutrition.

There is considerable overlap between the terms for the [[biogeochemical cycle]] and nutrient cycle. Some textbooks integrate the two and seem to treat them as synonymous terms.<ref name="Levin09">{{cite book|last1=Levin|first1=Simon A|last2=Carpenter|first2=Stephen R|last3=Godfray|first3=Charles J|last4=Kinzig|first4=Ann P|last5=Loreau|first5=Michel|last6=Losos|first6=Jonathan B|last7=Walker|first7=Brian|last8=Wilcove|first8=David S|title=The Princeton Guide to Ecology|date=27 July 2009|publisher=Princeton University Press|isbn=978-0-691-12839-9|page=330|url=https://books.google.com/books?id=4MS-vfT89QMC&pg=PA330 |display-editors=etal}}</ref> However, the terms often appear independently. Nutrient cycle is more often used in direct reference to the idea of an intra-system cycle, where an ecosystem functions as a unit. From a practical point, it does not make sense to assess a terrestrial ecosystem by considering the full column of air above it as well as the great depths of Earth below it. While an ecosystem often has no clear boundary, as a working model it is practical to consider the functional community where the bulk of matter and energy transfer occurs.<ref name="Bormann67">{{cite journal | last1=Bormann | first1=F. H. | last2=Likens | first2=G. E. | year=1967 | title=Nutrient cycling | journal=[[Science (journal)|Science]] | volume=155 | issue=3761 | pages=424–429 | doi=10.1126/science.155.3761.424 | pmid=17737551 | url=http://www.biology.duke.edu/upe302/pdf%20files/Emily_BormannLikens1967.pdf | bibcode=1967Sci...155..424B | s2cid=35880562 | url-status=dead | archive-url=https://web.archive.org/web/20110927182833/http://www.biology.duke.edu/upe302/pdf%20files/Emily_BormannLikens1967.pdf | archive-date=2011-09-27 }}</ref> Nutrient cycling occurs in ecosystems that participate in the "larger biogeochemical cycles of the earth through a system of inputs and outputs."<ref name="Bormann67" />{{rp|425}}

===Dissolved nutrients===
Nutrients dissolved in seawater are essential for the survival of marine life. Nitrogen and phosphorus are particularly important. They are regarded as [[limiting nutrient]]s in many marine environments, because primary producers, like algae and marine plants, cannot grow without them. They are critical for stimulating [[Marine primary production|primary production]] by [[phytoplankton]]. Other important nutrients are  silicon, iron, and zinc.<ref name="PenState/NASSA">[https://www.e-education.psu.edu/earth103/node/838 Dissolved Nutrients] ''Earth in the Future'', PenState/NASSA. Retrieved 18 June 2020.</ref>

The process of cycling nutrients in the sea starts with [[#biological pumping|biological pumping]], when nutrients are extracted from surface waters by phytoplankton to become part of their organic makeup. Phytoplankton are either eaten by other organisms, or eventually die and drift down as [[marine snow]]. There they decay and return to the dissolved state, but at greater ocean depths. The fertility of the oceans depends on the abundance of the nutrients, and is measured by the [[Marine primary production|primary production]], which is the rate of fixation of carbon per unit of water per unit time. "Primary production is often mapped by satellites using the distribution of chlorophyll, which is a pigment produced by plants that absorbs energy during photosynthesis. The distribution of chlorophyll is shown in the figure above. You can see the highest abundance close to the coastlines where nutrients from the land are fed in by rivers. The other location where chlorophyll levels are high is in upwelling zones where nutrients are brought to the surface ocean from depth by the upwelling process..."<ref name="PenState/NASSA" />
{{clear right}}

{{multiple image
 | align = right
 | direction = <!-- horizontal/vertical -->
 | total_width = 400
 | image1 = Nutrient-cycle hg.png |caption1 = Ocean [[nutrient cycle]]
 | image2 = Nutrient flux.png |caption2 = Ocean nutrient flux
}}

{{multiple image
 | align = right
 | direction = <!-- horizontal/vertical -->
 | total_width = 400
 | header            = Land runoff drains nutrients and pollutants to the ocean
 | header_align      = center
 | header_background = 
 | footer            = 
 | footer_align      = 
 | footer_background = 
 | background color  = 
 | image1    = Ocean drainage.png
 | alt1      = 
 | caption1  = The drainage basins of the principal oceans and seas of the world are marked by [[continental divide]]s. The grey areas are [[endorheic basin]]s that do not drain to the ocean.
}}
"Another critical element for the health of the oceans is the dissolved oxygen content. Oxygen in the surface ocean is continuously added across the air-sea interface as well as by photosynthesis; it is used up in respiration by marine organisms and during the decay or oxidation of organic material that rains down in the ocean and is deposited on the ocean bottom. Most organisms require oxygen, thus its depletion has adverse effects for marine populations.  Temperature also affects oxygen levels as warm waters can hold less dissolved oxygen than cold waters. This relationship will have major implications for future oceans, as we will see... The final seawater property we will consider is the content of dissolved {{CO2}}. {{CO2}} is nearly opposite to oxygen in many chemical and biological processes; it is used up by plankton during photosynthesis and replenished during respiration as well as during the oxidation of organic matter. As we will see later, {{CO2}} content has importance for the study of deep-water aging."<ref name="PenState/NASSA" />

[[File:Global_N-P_Ratio.gif|thumb|upright=1.7|left| Nitrogen to phosphorus ratio at the ocean surface. Nutrients are available in the three HNLC ([[High-nutrient, low-chlorophyll regions|high-nutrient, low-chlorophyll]]) regions in sufficient [[Redfield ratio]]s for biological activity.]]
{{clear}}

==Marine sulfur cycle==
[[File:Biogeochemical sulfur cycle of marine sediments.jpg|thumb|upright=1.7|right| {{center|'''Biogeochemical sulfur cycle of marine sediments'''}} Arrows indicate fluxes and pathways of biological or chemical processes. Microbial dissimilatory sulfate reduction to sulfide is a predominant terminal pathway of organic matter mineralization in the anoxic seabed. Chemical or microbial oxidation of the produced sulfide establishes a complex network of pathways in the sulfur cycle, leading to intermediate sulfur species and partly back to sulfate. The intermediates include elemental sulfur, polysulfides, thiosulfate, and sulfite, which are all substrates for further microbial oxidation, reduction or disproportionation. New microbiological discoveries, such as long-distance electron transfer through sulfide oxidizing [[cable bacteria]], add to the complexity. Isotope exchange reactions play an important role for the stable isotope geochemistry and for the experimental study of sulfur transformations using radiotracers. Microbially catalyzed processes are partly reversible whereby the back-reaction affects our interpretation of radiotracer experiments and provides a mechanism for isotope fractionation.<ref name="Jørgensen2019">Jørgensen, B.B., Findlay, A.J. and Pellerin, A. (2019) "The biogeochemical sulfur cycle of marine sediments". ''Frontiers in microbiology'', '''10''': 849. {{doi|10.3389/fmicb.2019.00849}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]
{{further|sulfur cycle}}

[[File:Sulfur cycle - English.jpg|thumb|upright=1.5|left| {{center|Sulfur cycle}}]]
Sulfate reduction in the seabed is strongly focused toward near-surface sediments with high depositional rates along the ocean margins. The benthic marine sulfur cycle is therefore sensitive to anthropogenic influence, such as ocean warming and increased nutrient loading of coastal seas. This stimulates photosynthetic productivity and results in enhanced export of organic matter to the seafloor, often combined with low oxygen concentration in the bottom water (Rabalais et al., 2014; Breitburg et al., 2018). The biogeochemical zonation is thereby compressed toward the sediment surface, and the balance of organic matter mineralization is shifted from oxic and suboxic processes toward sulfate reduction and methanogenesis (Middelburg and Levin, 2009).<ref name="Jørgensen2019"/>
{{clear left}}

* [[cable bacteria]]

The sulfur cycle in marine environments has been well-studied via the tool of [[Isotopes of sulfur|sulfur isotope systematics]] expressed as δ<sup>34</sup>S. The modern global oceans have sulfur storage of 1.3 × 10<sup>21</sup> g,<ref>{{Cite book |title=Treatise on Geochemistry |last=Brimblecombe |first=Peter |author1-link=Peter Brimblecombe |publisher=Elsevier |year=2014 |isbn=9780080983004 |volume=10 |location=Amsterdam |pages=559–591 |chapter=The global sulfur cycle|doi=10.1016/B978-0-08-095975-7.00814-7}}</ref> mainly occurring as sulfate with the δ<sup>34</sup>S value of +21‰.<ref name="Fike_2015">{{Cite journal |last1=Fike |first1=David A. |last2=Bradley |first2=Alexander S. |last3=Rose |first3=Catherine V. |name-list-style=vanc |date=2015 |title=Rethinking the Ancient Sulfur Cycle |journal=Annual Review of Earth and Planetary Sciences |volume=43 |issue=1 |pages=593–622 |doi=10.1146/annurev-earth-060313-054802 |bibcode=2015AREPS..43..593F |s2cid=140644882}}</ref> The overall input flux is 1.0 × 10<sup>14</sup> g/year with the sulfur isotope composition of ~3‰.<ref name="Fike_2015"/> Riverine sulfate derived from the terrestrial weathering of sulfide minerals (δ<sup>34</sup>S = +6‰) is the primary input of sulfur to the oceans. Other sources are metamorphic and volcanic degassing and hydrothermal activity (δ<sup>34</sup>S = 0‰), which release reduced sulfur species (e.g., H<sub>2</sub>S and S<sup>0</sup>). There are two major outputs of sulfur from the oceans. The first sink is the burial of sulfate either as marine evaporites (e.g., gypsum) or carbonate-associated sulfate (CAS), which accounts for 6 × 10<sup>13</sup> g/year (δ<sup>34</sup>S = +21‰). The second sulfur sink is pyrite burial in shelf sediments or deep seafloor sediments (4 × 10<sup>13</sup> g/year; δ<sup>34</sup>S = -20‰).<ref>{{Cite journal| vauthors=Canfield DE |date=2004 |title=The evolution of the Earth surface sulfur reservoir |journal=American Journal of Science |language=en |volume=304 |issue=10 |pages=839–861 |doi=10.2475/ajs.304.10.839 |bibcode=2004AmJS..304..839C |doi-access=free}}</ref> The total marine sulfur output flux is 1.0 × 10<sup>14</sup> g/year which matches the input fluxes, implying the modern marine sulfur budget is at steady state.<ref name="Fike_2015"/> The residence time of sulfur in modern global oceans is 13,000,000 years.<ref>{{cite journal |vauthors=Kah LC, Lyons TW, Frank TD |title=Low marine sulphate and protracted oxygenation of the Proterozoic biosphere |journal=Nature |volume=431 |issue=7010 |pages=834–8 |date=October 2004 |pmid=15483609 |doi=10.1038/nature02974 |bibcode=2004Natur.431..834K |s2cid=4404486 |url=https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1098&context=geosciencefacpub}}</ref>

In modern oceans, ''[[Hydrogenovibrio crunogenus]]'', ''[[Halothiobacillus]]'', and ''[[Beggiatoa]]'' are primary sulfur oxidizing bacteria,<ref name="Sievert_2008" /><ref>Jiang, L., Lyu, J. and Shao, Z. (2017) "Sulfur metabolism of ''Hydrogenovibrio thermophilus'' strain s5 and its adaptations to deep-sea hydrothermal vent environment". ''Frontiers in microbiology'', '''8''': 2513. {{doi|10.3389/fmicb.2017.02513}}.</ref> and form chemosynthetic symbioses with animal hosts.<ref>{{cite journal | vauthors = Klotz MG, Bryant DA, Hanson TE | title = The microbial sulfur cycle | language = en | journal = Frontiers in Microbiology | volume = 2 | pages = 241 | date = 2011 | pmid = 22144979 | pmc = 3228992 | doi = 10.3389/fmicb.2011.00241 | doi-access = free }}</ref> The host provides metabolic substrates (e.g., CO<sub>2</sub>, O<sub>2</sub>, H<sub>2</sub>O) to the symbiont while the symbiont generates organic carbon for sustaining the metabolic activities of the host. The produced sulfate usually combines with the leached calcium ions to form [[gypsum]], which can form widespread deposits on near mid-ocean spreading centers.<ref>{{cite journal | vauthors = Pedersen RB, Rapp HT, Thorseth IH, Lilley MD, Barriga FJ, Baumberger T, Flesland K, Fonseca R, Früh-Green GL, Jorgensen SL | display-authors = 6 | title = Discovery of a black smoker vent field and vent fauna at the Arctic Mid-Ocean Ridge | journal = Nature Communications | volume = 1 | pages = 126 | date = November 2010 | issue = 8 | pmid = 21119639 | pmc = 3060606 | doi = 10.1038/ncomms1124 | bibcode = 2010NatCo...1..126P }}</ref>

[[Hydrothermal vent]]s emit hydrogen sulfide that support the carbon fixation of [[Hydrothermal vent microbial communities|chemolithotrophic bacteria]] that oxidize hydrogen sulfide with oxygen to produce elemental sulfur or sulfate.<ref name="Sievert_2008">{{Cite book|last1=Sievert|first1=Stefan M.|last2=Hügler|first2=Michael|last3=Taylor|first3=Craig D.|last4=Wirsen|first4=Carl O.|title=Microbial Sulfur Metabolism |chapter=Sulfur Oxidation at Deep-Sea Hydrothermal Vents |date=2008|editor-last=Dahl|editor-first=Christiane|editor2-last=Friedrich|editor2-first=Cornelius G. | name-list-style = vanc |language=en|publisher=Springer Berlin Heidelberg|pages=238–258|doi=10.1007/978-3-540-72682-1_19|isbn=978-3-540-72679-1}}</ref>

{{clear}}

==Iron cycle and dust==
[[File:Iron cycle7.png|alt=Iron cycle|thumb|upright=2|right| Biogeochemical iron cycle: Iron circulates through the atmosphere, [[lithosphere]], and oceans. Labeled arrows show flux in Tg of iron per year.<ref name=osch>{{cite journal| vauthors = Nickelsen L, Keller D, Oschlies A |date=2015-05-12 |title=A dynamic marine iron cycle module coupled to the University of Victoria Earth System Model: the Kiel Marine Biogeochemical Model 2 for UVic 2.9 |journal=Geoscientific Model Development |volume=8 |issue=5 |pages=1357–1381 |doi=10.5194/gmd-8-1357-2015 |bibcode=2015GMD.....8.1357N |doi-access=free }}</ref><ref name = "Jickells_2005">{{cite journal | vauthors = Jickells TD, An ZS, Andersen KK, Baker AR, Bergametti G, Brooks N, Cao JJ, Boyd PW, Duce RA, Hunter KA, Kawahata H, Kubilay N, laRoche J, Liss PS, Mahowald N, Prospero JM, Ridgwell AJ, Tegen I, Torres R | display-authors = 6 | title = Global iron connections between desert dust, ocean biogeochemistry, and climate | journal = Science | volume = 308 | issue = 5718 | pages = 67–71 | date = April 2005 | pmid = 15802595 | doi = 10.1126/science.1105959 | bibcode = 2005Sci...308...67J | s2cid = 16985005 }}</ref><ref>{{cite journal| vauthors = Raiswell R, Canfield DE |date=2012|title=The iron biogeochemical cycle past and present|url=https://www.geochemicalperspectives.org/wp-content/uploads/2011/12/GPv1n1_online.pdf|journal=Geochemical Perspectives|volume=1|issue=1 |pages=1–232|doi=10.7185/geochempersp.1.1|bibcode=2012GChP....1....1R }}</ref><ref name = "Wang_2007">{{cite journal| vauthors = Wang T, Müller DB, Graedel TE |date=2007-07-01|title=Forging the Anthropogenic Iron Cycle |journal=Environmental Science & Technology|volume=41|issue=14|pages=5120–5129|doi=10.1021/es062761t |pmid=17711233|bibcode=2007EnST...41.5120W}}</ref>]]
{{further|Iron cycle|Aeolian dust|Iron fertilization|Iron-oxidizing bacteria}}

The [[iron cycle]] (Fe) is the biogeochemical cycle of [[iron]] through the [[atmosphere]], [[hydrosphere]], [[biosphere]] and [[lithosphere]]. While Fe is highly abundant in the Earth's crust,<ref>{{cite journal| vauthors = Taylor SR |date=1964|title=Abundance of chemical elements in the continental crust: a new table|journal=Geochimica et Cosmochimica Acta|volume=28|issue=8|pages=1273–1285|doi=10.1016/0016-7037(64)90129-2|bibcode=1964GeCoA..28.1273T}}</ref> it is less common in oxygenated surface waters. Iron is a key micronutrient in [[primary productivity]],<ref name = "Tagliabue_2017"/> and a [[limiting nutrient]] in the Southern ocean, eastern equatorial Pacific, and the subarctic Pacific referred to as [[High-nutrient, low-chlorophyll regions|High-Nutrient, Low-Chlorophyll (HNLC) regions]] of the ocean.<ref name="Iron deficiency limits phytoplankto"/>

Iron in the ocean cycles between plankton, aggregated particulates (non-bioavailable iron), and dissolved (bioavailable iron), and becomes sediments through burial.<ref name=osch /><ref>{{cite journal | vauthors = Völker C, Tagliabue A | title = Modeling organic iron-binding ligands in a three-dimensional biogeochemical ocean model. | journal = Marine Chemistry | date = July 2015 | volume = 173 | pages = 67–77 | doi = 10.1016/j.marchem.2014.11.008 | bibcode = 2015MarCh.173...67V | url = https://epic.awi.de/id/eprint/36980/1/Voelker14MC_preprint.pdf }}</ref><ref name = "Matsui_2018">{{cite journal | vauthors = Matsui H, Mahowald NM, Moteki N, Hamilton DS, Ohata S, Yoshida A, Koike M, Scanza RA, Flanner MG | title = Anthropogenic combustion iron as a complex climate forcer | journal = Nature Communications | volume = 9 | issue = 1 | pages = 1593 | date = April 2018 | pmid = 29686300 | pmc = 5913250 | doi = 10.1038/s41467-018-03997-0 | bibcode = 2018NatCo...9.1593M }}</ref> [[Hydrothermal vent]]s release ferrous iron to the ocean<ref>{{cite journal | vauthors = Emerson D | title = The Irony of Iron - Biogenic Iron Oxides as an Iron Source to the Ocean | journal = Frontiers in Microbiology | volume = 6 | pages = 1502 | date = 2016 | pmid = 26779157 | pmc = 4701967 | doi = 10.3389/fmicb.2015.01502 | doi-access = free }}</ref> in addition to oceanic iron inputs from land sources. Iron reaches the atmosphere through volcanism,<ref>{{cite journal| vauthors = Olgun N, Duggen S, Croot PL, Delmelle P, Dietze H, Schacht U, Oskarsson N, Siebe C, Auer A, GarbeSchnberg D | display-authors = 6 |date=2011|title=Surface ocean iron fertilization: The role of airborne volcanic ash from subduction zone and hot spot volcanoes and related iron fluxes into the Pacific Ocean |journal=Global Biogeochemical Cycles|volume=25|issue=4| pages = n/a |doi=10.1029/2009GB003761 | bibcode = 2011GBioC..25.4001O | s2cid = 53356668 | url = http://oceanrep.geomar.de/10133/1/2009GB003761.pdf }}</ref> [[Aeolian processes|aeolian]] wind,<ref>{{cite journal| vauthors = Gao Y, Kaufman YJ, Tanre D, Kolber D, Falkowski PG |date=2001-01-01|title=Seasonal distributions of aeolian iron fluxes to the global ocean|journal=Geophysical Research Letters|volume=28|issue=1|pages=29–32|doi=10.1029/2000GL011926|bibcode=2001GeoRL..28...29G|s2cid=128762758 |doi-access=free}}</ref> and some via combustion by humans. In the [[Anthropocene]], iron is removed from mines in the crust and a portion re-deposited in waste repositories.<ref name = "Wang_2007" /><ref name = "Matsui_2018" />

[[File:Trichodesmium interact with bacteria to acquire iron from dust.webp|thumb|upright=2.25|left| {{center|'''Colonies of marine cyanobacteria ''Trichodesmium''<br />interact with other bacteria to acquire iron from dust'''}} '''a.''' The N<sub>2</sub>-fixing ''[[Trichodesmium]]'' spp., which commonly occurs in tropical and sub-tropical waters, is of large environmental significance in fertilizing the ocean with important nutrients.<br />'''b.''' ''Trichodesmium'' can establish massive blooms in nutrient poor ocean regions with high dust deposition, partly due to their unique ability to capture dust, center it, and subsequently dissolve it.<br />'''c.''' Proposed dust-bound Fe acquisition pathway: Bacteria residing within the colonies produce [[siderophore]]s (C-I) that react with the dust particles in the colony core and generate dissolved Fe (C-II). This dissolved Fe, complexed by siderophores, is then acquired by both ''Trichodesmium'' and its resident bacteria (C-III), resulting in a mutual benefit to both partners of the [[Microbial consortium|consortium]].<ref>{{cite journal |doi = 10.1038/s42003-019-0534-z|title = Colonies of marine cyanobacteria Trichodesmium interact with associated bacteria to acquire iron from dust|year = 2019|last1 = Basu|first1 = Subhajit|last2 = Gledhill|first2 = Martha|last3 = De Beer|first3 = Dirk|last4 = Prabhu Matondkar|first4 = S. G.|last5 = Shaked|first5 = Yeala|journal = Communications Biology|volume = 2|page = 284|pmid = 31396564|pmc = 6677733}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

[[File:Role of marine animals in the cycling of iron in the Southern Ocean.jpg|thumb|upright=2| {{center|Role of [[marine animals]] in the cycling of iron in the [[Southern Ocean]]{{hsp}}<ref name=Ratnarajah2018>{{cite journal |doi = 10.3389/fmars.2018.00109|title = Pelagic Iron Recycling in the Southern Ocean: Exploring the Contribution of Marine Animals|year = 2018|last1 = Ratnarajah|first1 = Lavenia|last2 = Nicol|first2 = Steve|last3 = Bowie|first3 = Andrew R.|journal = Frontiers in Marine Science|volume = 5|s2cid = 4376458|doi-access = free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>}}]]

{{multiple image
 | align = right
 | direction = horizontal
 | header            = global dust
 | header_align      = 
 | footer            = 
 | footer_align      = 
 | footer_background = 
 | background color  = 
 | total_width = 450px
 | image1    = Dust2017.png
 | alt1      = 
 | caption1  = {{center|Map of dust in 2017}}
 | image2    = DustDeposition.png
 | alt2      = 
 | caption2  = {{center|Global oceanic distribution of dust [[Deposition (geology)|deposition]]}}
}}

{{clear left}}

Iron is an essential micronutrient for almost every life form. It is a key component of hemoglobin, important to nitrogen fixation as part of the [[Nitrogenase]] enzyme family, and as part of the iron-sulfur core of [[ferredoxin]] it facilitates electron transport in chloroplasts, eukaryotic mitochondria, and bacteria. Due to the high reactivity of Fe<sup>2+</sup> with oxygen and low solubility of Fe<sup>3+</sup>, iron is a limiting nutrient in most regions of the world.

{{clear}}

==Calcium and silica cycles==
{{further|calcium cycle|silica cycle|carbonate–silicate cycle|lysocline|carbonate compensation depth|diatom|ocean acidification#Calcification}}

[[File:Carbonate-Silicate Cycle (Carbon Cycle focus).jpg|thumb|upright=1.7| {{center|[[Carbonate-silicate cycle]] (carbon cycle focus)}}]]
{{Carbon cycle|Biogeochemical}}

The [[calcium cycle]] is a transfer of calcium between [[Solubility|dissolved]] and [[solid]] phases. There is a continuous supply of [[Calcium|calcium ions]] into waterways from [[Rock (geology)|rocks]], [[organism]]s, and [[soil]]s.<ref name="Walker1981"/><ref name=":23">{{Cite journal|last=Berner|first=R. A.|date=2004-05-01|title=A model for calcium, magnesium and sulfate in seawater over Phanerozoic time|journal=American Journal of Science|volume=304|issue=5|pages=438–453|doi=10.2475/ajs.304.5.438|issn=0002-9599|bibcode=2004AmJS..304..438B|doi-access=free}}</ref> Calcium ions are consumed and removed from aqueous environments as they react to form insoluble structures such as [[calcium carbonate]] and calcium silicate,<ref name="Walker1981"/><ref name=":8">{{Cite journal|last1=Ridgwell|first1=Andy|last2=Zeebe|first2=Richard E.|date=2005-06-15|title=The role of the global carbonate cycle in the regulation and evolution of the Earth system|journal=Earth and Planetary Science Letters|volume=234|issue=3–4|pages=299–315|doi=10.1016/j.epsl.2005.03.006|issn=0012-821X}}</ref> which can deposit to form sediments or the [[exoskeleton]]s of organisms.<ref name=Raisman2013 /> Calcium ions can also be utilized [[Calcium in biology|biologically]], as calcium is essential to biological functions such as the production of [[bone]]s and [[Tooth|teeth]] or cellular function.<ref name="Nordin 1988"/><ref name="Calcium in Biological Systems"/> The calcium cycle is a common thread between terrestrial, marine, geological, and biological processes.<ref name=":62"/> Calcium moves through these different media as it cycles throughout the Earth. The marine calcium cycle is affected by changing [[Carbon dioxide in Earth's atmosphere|atmospheric carbon dioxide]] due to [[ocean acidification]].<ref name=Raisman2013 />

Biogenic calcium carbonate is formed when marine organisms, such as [[coccolithophore]]s, [[coral]]s, [[Pteropoda|pteropods]], and other [[Mollusca|mollusks]] transform calcium ions and [[bicarbonate]] into shells and [[exoskeleton]]s of [[calcite]] or [[aragonite]], both forms of calcium carbonate.<ref name=Raisman2013 /> This is the dominant sink for dissolved calcium in the ocean.<ref name=":62">{{Cite journal|last1=Fantle|first1=Matthew S.|last2=Tipper|first2=Edward T.|date=2014|title=Calcium isotopes in the global biogeochemical Ca cycle: Implications for development of a Ca isotope proxyy|url=https://www.sciencedirect.com/science/article/pii/S0012825213001700|journal=Earth-Science Reviews|volume=131|pages=148–177|doi=10.1016/j.earscirev.2014.02.002|issn=0012-8252|via=Elsevier ScienceDirect}}</ref> Dead organisms sink to the bottom of the ocean, depositing layers of shell which over time cement to form [[limestone]]. This is the origin of both marine and terrestrial limestone.<ref name=Raisman2013 />

Calcium precipitates into calcium carbonate according to the following equation:

Ca<sup>2+</sup> + 2HCO<sub>3</sub><sup>−</sup> → CO<sub>2</sub>+ H<sub>2</sub>O + CaCO<sub>3</sub><ref name=":23"/>

The relationship between dissolved calcium and calcium carbonate is affected greatly by the levels of carbon dioxide (CO<sub>2</sub>) in the atmosphere.

Increased carbon dioxide leads to more [[Bicarbonate buffer system|bicarbonate]] in the ocean according to the following equation:

CO<sub>2</sub> + CO<sub>3</sub><sup>2−</sup> + H<sub>2</sub>O → 2HCO<sub>3</sub><sup>−</sup> <ref>{{Cite book|title=Ocean Acidification : Elements and Considerations|last1=Raisman|first1=Scott|last2=Murphy|first2=Daniel T.|publisher=Nova Science Publishers, Inc|year=2013|isbn=9781629482958|location=Hauppauge, New York}}</ref>

[[File:Equilibrium of carbonic acid in the oceans .png|thumb|upright=1.7|left| {{center|Equilibrium of [[carbonic acid]] in the oceans}}]]

[[File:The carbonate cycle in the water environment.jpg|thumb|upright=1.7|right| {{center|The carbonate cycle in the water environment{{hsp}}<ref>{{cite journal |doi = 10.1016/j.jprot.2013.09.016|title = Carbon acquisition and accumulation in microalgae Chlamydomonas: Insights from "omics" approaches|year = 2013|last1 = Winck|first1 = Flavia Vischi|last2 = Páez Melo|first2 = David Orlando|last3 = González Barrios|first3 = Andrés Fernando|journal = Journal of Proteomics|volume = 94|pages = 207–218|pmid = 24120529}}</ref><ref>{{cite journal |doi = 10.3390/w9110859|title = Effects of Climate Change on 2-Methylisoborneol Production in Two Cyanobacterial Species|year = 2017|last1 = Zhang|first1 = Junzhi|last2 = Li|first2 = Luwei|last3 = Qiu|first3 = Lijia|last4 = Wang|first4 = Xiaoting|last5 = Meng|first5 = Xuanyi|last6 = You|first6 = Yu|last7 = Yu|first7 = Jianwei|last8 = Ma|first8 = Wenlin|journal = Water|volume = 9|issue = 11|page = 859|doi-access = free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>}}]]

{{clear left}}

With its close relation to the [[carbon cycle]] and the effects of greenhouse gasses, both calcium and carbon cycles are predicted to change in the coming years.<ref>{{Cite journal|last1=Komar|first1=N.|last2=Zeebe|first2=R. E.|date=January 2016|title=Calcium and calcium isotope changes during carbon cycle perturbations at the end-Permian|journal=Paleoceanography|language=en|volume=31|issue=1|pages=115–130|doi=10.1002/2015pa002834|issn=0883-8305|bibcode=2016PalOc..31..115K|s2cid=15794552|doi-access=free}}</ref> Tracking calcium isotopes enables the prediction of environmental changes, with many sources suggesting increasing temperatures in both the atmosphere and marine environment. As a result, this will drastically alter the breakdown of rock, the pH of oceans and waterways and thus calcium sedimentation, hosting an array of implications on the calcium cycle.

Due to the complex interactions of calcium with many facets of life, the effects of altered environmental conditions are unlikely to be known until they occur. Predictions can however be tentatively made, based upon evidence-based research. Increasing carbon dioxide levels and decreasing ocean pH will alter calcium solubility, preventing corals and shelled organisms from developing their calcium-based exoskeletons, thus making them vulnerable or unable to survive.<ref>{{Cite web|url=https://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification?|title=PMEL {{CO2}} - Carbon Dioxide Program|website=www.pmel.noaa.gov|access-date=2018-10-29}}</ref><ref>{{Cite web|url=https://ocean.si.edu/ocean-life/invertebrates/ocean-acidification|title=Ocean Acidification|website=Smithsonian Ocean|date=30 April 2018 |language=en|access-date=2018-10-29}}</ref>

Most biological production of [[biogenic silica]] in the ocean is driven by [[diatom]]s, with further contributions from [[radiolaria]]ns. These microorganisms extract dissolved [[silicic acid]] from surface waters during growth, and return this by recycling throughout the [[water column]] after they die. Inputs of silicon to the ocean from above arrive via rivers and [[dust|aeolian dust]], while those from below include seafloor sediment recycling, weathering, and [[hydrothermal vent|hydrothermal activity]].<ref name="AAAS1">{{cite journal |doi=10.1126/science.268.5209.375 |pmid=17746543 |title=The Silica Balance in the World Ocean: A Reestimate |journal=Science |volume=268 |issue=5209 |pages=375–9 |year=1995 |last1=Treguer |first1=P. |last2=Nelson |first2=D. M. |last3=Van Bennekom |first3=A. J. |last4=Demaster |first4=D. J. |last5=Leynaert |first5=A. |last6=Queguiner |first6=B. |bibcode=1995Sci...268..375T |s2cid=5672525 }}</ref>

[[File:Oceanic Silicon Cycle Budget.svg|thumb|upright=1.35|left| {{center|'''Modern oceanic silicon cycle'''}} showing major flows and magnitudes<br/><small>Fluxes in [[Tera-|T]] [[Mole (unit)|mol]] Si y<sup>−1</sup> = 28 million [[tonne]]s of silicon per year</small>]]

[[File:Pterapod shell dissolved in seawater adjusted to an ocean chemistry projected for the year 2100.jpg|thumb|upright=1.7|right| Effects of an acidic ocean (with pH projected for the year 2100) on a pteropod shell made of calcite - the shell progressively dissolves in the lower pH as calcium is drawn out of the shell]]

{{clear left}}

===Biomineralization===
{{further|biomineralization}}
[[File:LimestoneWithFossilUSGOV.jpg|thumb|right| {{center|Deposition of calcifying organisms/shells on the ocean floor}}]]

"Biological activity is a dominant force shaping the chemical structure and evolution of the earth surface environment. The presence of an oxygenated atmosphere-hydrosphere surrounding an otherwise highly reducing solid earth is the most striking consequence of the rise of life on earth. Biological evolution and the functioning of ecosystems, in turn, are to a large degree conditioned by geophysical and geological processes. Understanding the interactions between organisms and their abiotic environment, and the resulting coupled evolution of the biosphere and geosphere is a central theme of research in biogeology. Biogeochemists contribute to this understanding by studying the transformations and transport of chemical substrates and products of biological activity in the environment."<ref name=VanCappellen2003>Van Cappellen, P. (2003) "Biomineralization and global biogeochemical cycles". ''Reviews in mineralogy and geochemistry'', '''54'''(1): 357–381. {{doi|10.2113/0540357}}.</ref>

"Since the Cambrian explosion, mineralized body parts have been secreted in large quantities by biota. Because calcium carbonate, silica and calcium phosphate are the main mineral phases constituting these hard parts, biomineralization plays an important role in the global biogeochemical cycles of carbon, calcium, silicon and phosphorus"<ref name=VanCappellen2003 />

{{clear}}

==Deep cycling==
[[File:Reservoirs and fluxes of carbon in deep Earth.png|thumb |upright=1.7|right|{{center|[[Deep carbon cycle|Deep earth carbon]]}}]]
{{further|deep water cycle|deep carbon cycle|deep biosphere}}

Deep cycling involves the exchange of materials with the [[mantle (geology)|mantle]]. The [[deep water cycle]] involves exchange of water with the mantle, with water carried down by [[Subduction|subducting]] oceanic plates and returning through volcanic activity, distinct from the [[water cycle]] process that occurs above and on the surface of Earth. Some of the water makes it all the way to the [[Lower mantle (Earth)|lower mantle]] and may even reach the [[outer core]]. 
{{biogeochemical cycle sidebar|marine}}

In the conventional view of the water cycle (also known as the ''hydrologic cycle''), water moves between reservoirs in the [[Atmosphere of Earth|atmosphere]] and Earth's surface or near-surface (including the [[World ocean|ocean]], [[river]]s and [[lake]]s, [[glacier]]s and [[polar ice cap]]s, the [[biosphere]] and [[groundwater]]). However, in addition to the surface cycle, water also plays an important role in geological processes reaching down into the [[Crust (geology)|crust]] and [[Mantle (geology)|mantle]]. Water content in [[magma]] determines how explosive a volcanic eruption is; hot water is the main conduit for economically important minerals to concentrate in [[hydrothermal mineral deposit]]s; and water plays an important role in the formation and migration of [[petroleum]].<ref name=Bodnar>{{cite book |last1=Bodnar |first1=R.J. |last2=Azbej |first2=T. |last3=Becker |first3=S.P. |last4=Cannatelli |first4=C. |last5=Fall |first5=A. |last6=Severs |first6=M.J. |chapter=Whole Earth geohydrologic cycle, from the clouds to the core: The distribution of water in the dynamic Earth system |doi=10.1130/2013.2500(13) |editor-last1=M.E. |editor-first1=Bickford |title=The Web of Geological Sciences: Advances, Impacts, and Interactions: Geological Society of America Special Paper 500 |date=2013 |publisher=The Geological Society of America |isbn=9780813725000 |pages=431–461 |chapter-url=https://gsa.confex.com/gsa/2013AM/webprogram/Handout/Paper219836/2013_Bodnar_GSA_125th.pdf |access-date=19 April 2019}}</ref> Petroleum is a [[fossil fuel]] derived from ancient [[fossilized]] [[organic material]]s, such as [[zooplankton]] and [[algae]].<ref>{{cite journal|doi=10.1016/j.orggeochem.2005.09.001|title=Organic geochemistry – A retrospective of its first 70 years|year=2006|last1=Kvenvolden|first1=Keith A.|journal=Organic Geochemistry|volume=37|issue=1 |pages=1–11|bibcode=2006OrGeo..37....1K |s2cid=95305299 |url=https://zenodo.org/record/1000677}}</ref><ref name=":0">{{Cite book|title=Chemistry of fossil fuels and biofuels|last=Schobert|first=Harold H.|publisher=Cambridge University Press|year=2013|isbn=978-0-521-11400-4|location=Cambridge|pages=103–130|oclc=795763460}}</ref>

Water is not just present as a separate phase in the ground. Seawater percolates into oceanic crust and [[Mineral hydration|hydrates]] igneous rocks such as [[olivine]] and [[pyroxene]], transforming them into hydrous minerals such as [[Serpentine subgroup|serpentines]], [[talc]] and [[brucite]].<ref>{{cite journal |last1=Peacock |first1=Simon M. |last2=Hyndman |first2=Roy D. |title=Hydrous minerals in the mantle wedge and the maximum depth of subduction thrust earthquakes |journal=Geophysical Research Letters |date=15 August 1999 |volume=26 |issue=16 |pages=2517–2520 |doi=10.1029/1999GL900558|bibcode=1999GeoRL..26.2517P |s2cid=128800787 |doi-access=free }}</ref> In this form, water is carried down into the mantle. In the [[upper mantle (Earth)|upper mantle]], heat and pressure dehydrates these minerals, releasing much of it to the overlying [[mantle wedge]], triggering the melting of rock that rises to form [[volcanic arc]]s.<ref name=Rupke2004>{{cite journal |last1=Rüpke |first1=L |last2=Morgan |first2=Jason Phipps |last3=Hort |first3=Matthias |last4=Connolly |first4=James A. D. |title=Serpentine and the subduction zone water cycle |journal=Earth and Planetary Science Letters |date=June 2004 |volume=223 |issue=1–2 |pages=17–34 |doi=10.1016/j.epsl.2004.04.018 |bibcode=2004E&PSL.223...17R}}</ref> However, some of the "nominally anhydrous minerals" that are stable deeper in the mantle can store small concentrations of water in the form of [[hydroxyl]] (OH<sup>−</sup>),<ref name=Bell>{{cite journal |last1=Bell |first1=D. R. |last2=Rossman |first2=G. R. |title=Water in Earth's Mantle: The Role of Nominally Anhydrous Minerals |journal=Science |date=13 March 1992 |volume=255 |issue=5050 |pages=1391–1397 |doi=10.1126/science.255.5050.1391 |pmid=17801227 |bibcode=1992Sci...255.1391B |s2cid=26482929 |url=https://www.researchgate.net/publication/6039715 |access-date=23 April 2019}}</ref> and because they occupy large volumes of the Earth, they are capable of storing at least as much as the world's oceans.<ref name=Bodnar/>

[[File:Carbon Outgassing (Dasgupta 2011).png|thumb|upright=2|left| {{center|Carbon outgassing processes<ref>{{Cite conference |url=http://www.deep-earth.org/postAGU2011/Dasgupta-cider-agu2011.ppt |title=The Influence of Magma Ocean Processes on the Present-day Inventory of Deep Earth Carbon |last=Dasgupta |first=Rajdeep |date=December 10, 2011|conference=Post-AGU 2011 CIDER Workshop |archive-url=https://web.archive.org/web/20160424031155/http://www.deep-earth.org/postAGU2011/Dasgupta-cider-agu2011.ppt |archive-date=24 April 2016 |access-date=20 March 2019}}</ref>}}]]

{{clear left}}

The conventional view of the ocean's origin is that it was filled by outgassing from the mantle in the early [[Archean]] and the mantle has remained dehydrated ever since.<ref name=KepplerP22>{{cite book |first=Hans |last=Keppler |chapter=Volatiles under high pressure |editor-last1=Karato |editor-first1=Shun-ichiro |editor-last2=Karato |editor-first2=Shun'ichirō |title=Physics and chemistry of the deep Earth |date=2013 |publisher=John Wiley & Sons |isbn=9780470659144 |pages=22–23 |doi=10.1002/9781118529492.ch1}}</ref> However, subduction carries water down at a rate that would empty the ocean in 1–2 billion years. Despite this, changes in the [[Eustatic sea level|global sea level]] over the past 3–4 billion years have only been a few hundred metres, much smaller than the average ocean depth of 4 kilometres. Thus, the fluxes of water into and out of the mantle are expected to be roughly balanced, and the water content of the mantle steady. Water carried into the mantle eventually returns to the surface in eruptions at [[mid-ocean ridge]]s and [[hotspot (geology)|hotspots]].<ref name=Hirschmann2006>{{cite journal |last1=Hirschmann |first1=Marc M. |title=Water, melting, and the deep Earth H<sub>2</sub>O cycle |journal=Annual Review of Earth and Planetary Sciences |date=2006 |volume=34 |pages=629–653 |doi=10.1146/annurev.earth.34.031405.125211 |bibcode=2006AREPS..34..629H |url=https://www.researchgate.net/publication/228364911}}</ref> {{rp|646}} Estimates of the amount of water in the mantle range from {{frac|4}} to 4 times the water in the ocean.<ref name=Hirschmann2006 />{{rp|630–634}}

The [[deep carbon cycle]] is the movement of [[carbon]] through the Earth's [[mantle (geology)|mantle]] and [[Structure of the Earth#Core|core]].
It forms part of the [[carbon cycle]] and is intimately connected to the movement of carbon in the Earth's surface and atmosphere. By returning carbon to the deep Earth, it plays a critical role in maintaining the terrestrial conditions necessary for life to exist. Without it, carbon would accumulate in the atmosphere, reaching extremely high concentrations over long periods of time.<ref>{{Cite web|url=https://deepcarbon.net/feature/deep-carbon-cycle-and-our-habitable-planet|title=The Deep Carbon Cycle and our Habitable Planet|website=Deep Carbon Observatory|date=3 December 2015|access-date=2019-02-19|archive-date=27 July 2020|archive-url=https://web.archive.org/web/20200727084309/https://deepcarbon.net/feature/deep-carbon-cycle-and-our-habitable-planet|url-status=dead}}</ref>

{{clear}}

==Rock cycle==
[[File:Rock cycle nps.PNG|thumb|350px| {{center|The rock cycle and [[plate tectonics]]}}]]
{{further|rock cycle|marine sediment|fast and slow carbon cycles}}

{{clear}}

==Fossil fuels==
{{further|fossil fuel}}

Aquatic [[phytoplankton]] and [[zooplankton]] that died and sedimented in large quantities under [[anoxic sea water|anoxic conditions]] millions of years ago began forming petroleum and natural gas as a result of [[anaerobic decomposition]] (by contrast, [[terrestrial plant]]s tended to form [[coal]] and methane). Over [[geologic time scale|geological time]] this [[organic compound|organic]] [[matter]], mixed with [[mud]], became buried under further heavy layers of inorganic sediment. The resulting high [[temperature]] and [[pressure]] caused the organic matter to chemically [[diagenesis|alter]], first into a waxy material known as [[kerogen]], which is found in [[oil shale]]s, and then with more heat into liquid and gaseous hydrocarbons in a process known as [[catagenesis (geology)|catagenesis]].
Such organisms and their resulting fossil fuels typically have an age of millions of years, and sometimes more than 650 million years,<ref>Paul Mann, Lisa Gahagan, and Mark B. Gordon, "Tectonic setting of the world's giant oil and gas fields", in [[Michel T. Halbouty]] (ed.) [https://books.google.com/books?id=mrghwzjeU-AC&pg=PA50 ''Giant Oil and Gas Fields of the Decade, 1990–1999''], Tulsa, Okla.: [[American Association of Petroleum Geologists]], p. 50, accessed 22 June 2009.</ref> the energy released in combustion is still photosynthetic in origin.<ref name="thermochemistry of formation">{{cite web|title= thermochemistry of fossil fuel formation|url= http://www.geochemsoc.org/files/6214/1261/1770/SP-2_271-284_Sato.pdf}}</ref>

{{clear}}

==Other cycles==
Such as trace minerals, micronutrients, human-induced cycles for synthetic compounds such as [[polychlorinated biphenyl]] (PCB).
<gallery mode=packed heights=180px>
File:Lead Cycle.jpg| {{center|Lead cycle}}
File:MercuryFoodChain.svg|{{center|[[Mercury cycle]]}}
</gallery>

{{clear}}

==References==
{{reflist}}

==Further references==
* James, Rachael and Open University (2005) [https://books.google.com/books?id=jiQ6Gjdn_7oC&q=%22marine+biogeochemical+cycles%22 ''Marine Biogeochemical Cycles''] Butterworth-Heinemann. {{ISBN|9780750667937}}.

{{biogeochemical cycle|state=expanded}}

[[Category:Biogeochemical cycle]]
[[Category:Geochemistry]]
[[Category:Biogeography]]
[[Category:Marine organisms]]
[[Category:Oceanography]]