Oceanic carbon cycle#Inputs

File:Marine carbon cycle.png

Carbon compounds can be distinguished as either organic or inorganic, and dissolved or particulate, depending on their composition. Organic carbon forms the backbone of key component of organic compounds such as – proteins, lipids, carbohydrates, and nucleic acids. Inorganic carbon is found primarily in simple compounds such as carbon dioxide, carbonic acid, bicarbonate, and carbonate (CO₂, H₂CO₃, HCO₃⁻, CO₃²⁻ respectively).

Marine carbon is further separated into particulate and dissolved phases. These pools are operationally defined by physical separation – dissolved carbon passes through a 0.2 μm filter, and particulate carbon does not.

There are two main types of inorganic carbon that are found in the oceans. Dissolved inorganic carbon (DIC) is made up of bicarbonate (HCO₃⁻), carbonate (CO₃²⁻) and carbon dioxide (including both dissolved CO₂ and carbonic acid H₂CO₃). DIC can be converted to particulate inorganic carbon (PIC) through precipitation of CaCO₃ (biologically or abiotically). DIC can also be converted to particulate organic carbon (POC) through photosynthesis and chemoautotrophy (i.e. primary production). DIC increases with depth as organic carbon particles sink and are respired. Free oxygen decreases as DIC increases because oxygen is consumed during aerobic respiration.

Particulate inorganic carbon (PIC) is the other form of inorganic carbon found in the ocean. Most PIC is the CaCO₃ that makes up shells of various marine organisms, but can also form in whiting events. Marine fish also excrete calcium carbonate during osmoregulation.{{Cite journal|last1=Wilson|first1=R. W.|last2=Millero|first2=F. J.|last3=Taylor|first3=J. R.|last4=Walsh|first4=P. J.|last5=Christensen|first5=V.|last6=Jennings|first6=S.|last7=Grosell|first7=M.|date=2009-01-16|title=Contribution of Fish to the Marine Inorganic Carbon Cycle|journal=Science|language=en|volume=323|issue=5912|pages=359–362|doi=10.1126/science.1157972|issn=0036-8075|pmid=19150840|bibcode=2009Sci...323..359W|s2cid=36321414}}

Some of the inorganic carbon species in the ocean, such as bicarbonate and carbonate, are major contributors to alkalinity, a natural ocean buffer that prevents drastic changes in acidity (or pH). The marine carbon cycle also affects the reaction and dissolution rates of some chemical compounds, regulates the amount of carbon dioxide in the atmosphere and Earth's temperature.{{Cite book|title=Chemical Oceanography and the Marine Carbon Cycle|last=Emerson|first=Steven|publisher=Cambridge University Press|year=2008|isbn=978-0-521-83313-4|location=United Kingdom}}

Like inorganic carbon, there are two main forms of organic carbon found in the ocean (dissolved and particulate). Dissolved organic carbon (DOC) is defined operationally as any organic molecule that can pass through a 0.2 μm filter. DOC can be converted into particulate organic carbon through heterotrophy and it can also be converted back to dissolved inorganic carbon (DIC) through respiration.

Those organic carbon molecules being captured on a filter are defined as particulate organic carbon (POC). POC is composed of organisms (dead or alive), their fecal matter, and detritus. POC can be converted to DOC through disaggregation of molecules and by exudation by phytoplankton, for example. POC is generally converted to DIC through heterotrophy and respiration.

Full article: Solubility pump

File:Dissociation of carbon and henry's law in the oceanic carbon pump nov 2017.jpg

The oceans store the largest pool of reactive carbon on the planet as DIC, which is introduced as a result of the dissolution of atmospheric carbon dioxide into seawater – the solubility pump. Aqueous CO₂, carbonic acid, bicarbonate ion, and carbonate ion concentrations comprise dissolved inorganic carbon (DIC). DIC circulates throughout the whole ocean by Thermohaline circulation, which facilitates the tremendous DIC storage capacity of the ocean.{{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. | last10 = Linder | first10 = S. | last11 = MacKenzie | first11 = F. T. | last12 = Moore III| first12 = B. | last13 = Pedersen | first13 = T. | last14 = Rosenthal | first14 = Y. | last15 = Seitzinger | first15 = S. | last16 = Smetacek | first16 = V. | last17 = Steffen | first17 = W. | title = The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System | doi = 10.1126/science.290.5490.291 | journal = Science | volume = 290 | issue = 5490 | pages = 291–296 | year = 2000 | pmid = 11030643| bibcode = 2000Sci...290..291F }} The chemical equations below show the reactions that CO₂ undergoes after it enters the ocean and transforms into its aqueous form.

File:Annual mean sea surface dissolved inorganic carbon for the 1990s (GLODAP).png

First, carbon dioxide reacts with water to form carbonic acid. concentration in the 1990s (from the GLODAP climatology)]]{{NumBlk|:|CO2(aq) + H2O -> H2CO3|{{EquationRef|1}}}}Carbonic acid rapidly dissociates into free hydrogen ion (technically, hydronium) and bicarbonate.{{NumBlk|:|H2CO3 -> H+ + HCO3^-|{{EquationRef|2}}}}The free hydrogen ion meets carbonate, already present in the water from the dissolution of CaCO₃, and reacts to form more bicarbonate ion.{{NumBlk|:|H+ + CO3^2- -> HCO3^-|{{EquationRef|3}}}}The dissolved species in the equations above, mostly bicarbonate, make up the carbonate alkalinity system, the dominant contributor to seawater alkalinity.

The carbonate pump, sometimes called the carbonate counter pump, starts with marine organisms at the ocean's surface producing particulate inorganic carbon (PIC) in the form of calcium carbonate (calcite or aragonite, CaCO₃). This CaCO₃ is what forms hard body parts like shells. The formation of these shells increases atmospheric CO₂ due to the production of CaCO₃ in the following reaction with simplified stoichiometry:{{Cite web|url=https://aslo.org/page/limnology-%26-oceanography-e-books|title=ASLO : Limnology & Oceanography: e-Books|website=aslo.org|access-date=2017-11-28|archive-date=2017-12-07|archive-url=https://web.archive.org/web/20171207084449/https://aslo.org/page/limnology-%26-oceanography-e-books|url-status=dead}}{{NumBlk|:|Ca^2+ + 2HCO3^- <=> CaCO3 + CO2 + H2O{{Cite journal|last1=Smith|first1=S. V.|last2=Key|first2=G. S.|date=1975-05-01|title=Carbon dioxide and metabolism in marine environments1|journal=Limnology and Oceanography|language=en|volume=20|issue=3|pages=493–495|doi=10.4319/lo.1975.20.3.0493|issn=1939-5590|bibcode=1975LimOc..20..493S|doi-access=free}}|{{EquationRef|4}}}}Coccolithophores, a nearly ubiquitous group of phytoplankton that produce shells of calcium carbonate, are the dominant contributors to the carbonate pump. Due to their abundance, coccolithophores have significant implications on carbonate chemistry, in the surface waters they inhabit and in the ocean below: they provide a large mechanism for the downward transport of CaCO₃.{{Cite book|title=Coccolithophores|last1=Rost|first1=Björn|last2=Riebesell|first2=Ulf|chapter=Coccolithophores and the biological pump: Responses to environmental changes |date=2004|publisher=Springer, Berlin, Heidelberg|isbn=9783642060168|pages=99–125|language=en|doi=10.1007/978-3-662-06278-4_5|citeseerx = 10.1.1.455.2864}} The air-sea CO₂ flux induced by a marine biological community can be determined by the rain ratio - the proportion of carbon from calcium carbonate compared to that from organic carbon in particulate matter sinking to the ocean floor, (PIC/POC). The carbonate pump acts as a negative feedback on CO₂ taken into the ocean by the solubility pump. It occurs with lesser magnitude than the solubility pump.

{{main|Biological pump}}

Particulate organic carbon, created through biological production, can be exported from the upper ocean in a flux commonly termed the biological pump, or respired (equation 6) back into inorganic carbon. In the former, dissolved inorganic carbon is biologically converted into organic matter by photosynthesis (equation 5) and other forms of autotrophy that then sinks and is, in part or whole, digested by heterotrophs.{{cite journal|last1=Kim|first1=S|last2=Kramer|first2=R|last3=Hatcher|first3=P|date=2003|title=Graphical method for analysis of ultrahigh-resolution broadband mass spectra of natural organic matter, the van Krevelen diagram|journal=Analytical Chemistry|volume=75|issue=20|pages=5336–5344|doi=10.1021/AC034415P|pmid=14710810}} Particulate organic carbon can be classified, based on how easily organisms can break them down for food, as labile, semilabile, or refractory. Photosynthesis by phytoplankton is the primary source for labile and semilabile molecules, and is the indirect source for most refractory molecules.{{Cite journal|last1=Brophy|first1=Jennifer E.|last2=Carlson|first2=David J.|title=Production of biologically refractory dissolved organic carbon by natural seawater microbial populations|journal=Deep Sea Research Part A. Oceanographic Research Papers|volume=36|issue=4|pages=497–507|doi=10.1016/0198-0149(89)90002-2|year=1989|bibcode=1989DSRA...36..497B}}{{cite journal|last1=Moran|first1=M|last2=Kujawinski|first2=E|last3=Stubbins|first3=A|last4=Fatland|first4=R|last5=Aluwihare|first5=L|last6=Buchan|first6=A|last7=Crump|first7=B|last8=Dorrestein|first8=P|last9=Dyhrman|first9=S|date=2016|title=Deciphering ocean carbon in a changing world|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=113|issue=12|pages=3143–3151|doi=10.1073/pnas.1514645113|pmid=26951682|last10=Hess|first10=N|last11=Howe|first11=B|last12=Longnecker|first12=K|last13=Medeiros|first13=P|last14=Niggemann|first14=J|last15=Obernosterer|first15=I|last16=Repeta|first16=D|last17=Waldbauer|first17=J|pmc=4812754|bibcode=2016PNAS..113.3143M|doi-access=free}} Labile molecules are present at low concentrations outside of cells (in the picomolar range) and have half-lives of only minutes when free in the ocean.{{cite journal|last1=Azam|first1=F|last2=Malfatti|first2=F|date=2007|title=Microbial structuring of marine ecosystems|journal=Nature Reviews Microbiology|volume=5|issue=10|pages=782–791|doi=10.1038/nrmicro1747|pmid=17853906|s2cid=10055219}} They are consumed by microbes within hours or days of production and reside in the surface oceans, where they contribute a majority of the labile carbon flux.{{cite journal|last1=Moran|first1=X|last2=Ducklow|first2=H|last3=Erickson|first3=M|date=2013|title=Carbon fluxes through estuarine bacteria reflect coupling with phytoplankton|journal=Marine Ecology Progress Series|volume=489|pages=75–85|doi=10.3354/meps10428|bibcode=2013MEPS..489...75M|doi-access=free}} Semilabile molecules, much more difficult to consume, are able to reach depths of hundreds of meters below the surface before being metabolized.{{cite journal|last1=Hansell|first1=D|last2=Carlson|first2=C|date=1998|title=Net community production of dissolved organic carbon|journal=Global Biogeochemical Cycles|volume=12|issue=3|pages=443–453|doi=10.1029/98gb01928|bibcode=1998GBioC..12..443H|doi-access=free}} Refractory DOM largely comprises highly conjugated molecules like Polycyclic aromatic hydrocarbons or lignin. Refractory DOM can reach depths greater than 1000 m and circulates through the oceans over thousands of years.{{cite journal|last1=Follett|first1=C|last2=Repeta|first2=D|last3=Rothman|first3=D|last4=Xu|first4=L|last5=Santinelli|first5=C|date=2014|title=Hidden cycle of dissolved organic carbon in the deep ocean|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=111|issue=47|pages=16706–16711|doi=10.1073/pnas.1407445111|pmid=25385632|pmc=4250131|bibcode=2014PNAS..11116706F|doi-access=free}}{{cite journal|last1=Hansell|first1=D|date=2013|title=Recalcitrant dissolved organic carbon fractions|journal=Annual Review of Marine Science|volume=5|issue=1|pages=421–445|doi=10.1146/annurev-marine-120710-100757|pmid=22881353}} Over the course of a year, approximately 20 gigatons of photosynthetically-fixed labile and semilabile carbon is taken up by heterotrophs, whereas fewer than 0.2 gigatons of refractory carbon is consumed. Marine dissolved organic matter (DOM) can store as much carbon as the current atmospheric CO₂ supply, but industrial processes are altering the balance of this cycle.{{cite journal|last1=Doney|first1=Scott|author-link1=Scott Doney|last2=Ruckelshaus|first2=Mary|last3=Duffy|first3=Emmett|last4=Barry|first4=James|last5=Chan|first5=Francis|last6=English|first6=Chad|last7=Galindo|first7=Heather|last8=Grebmeier|first8=Jacqueline|author-link8=Jacqueline M. Grebmeier|last9=Hollowed|first9=Anne|date=2012|title=Climate change impacts on marine ecosystems|journal=Annual Review of Marine Science|volume=4|issue=1|pages=11–37|doi=10.1146/annurev-marine-041911-111611|pmid=22457967|last10=Knowlton|first10=Nancy|last11=Polovina|first11=Jeffrey|last12=Rabalais|first12=Nancy|last13=Sydeman|first13=William|last14=Talley|first14=Lynne|bibcode=2012ARMS....4...11D|s2cid=35349779}}

{{NumBlk|:|\underset{carbon~dioxide}{6CO2} + \underset{water}{6H2O} ->[\overset{}\text{light energy}] \underset{carbohydrate}{C6H12O6} + \underset{oxygen}{6O2}|{{EquationRef|5}}}}{{NumBlk|:|\underset{carbohydrate}{C6H12O6} + \underset{oxygen}{6O2} -> \underset{carbon~dioxide}{6CO2} + \underset{water}{6H2O} + heat|{{EquationRef|6}}}}

Inputs to the marine carbon cycle are numerous, but the primary contributions, on a net basis, come from the atmosphere and rivers. Hydrothermal vents generally supply carbon equal to the amount they consume.

{{See also|Carbon sequestration#Sequestration in oceans}}

File:CO2 flux IPCC.jpg

File:Carbon cycle processes in high-latitude shelf seas.jpgs{{hsp}}{{cite journal |doi = 10.1016/j.pocean.2020.102319|title = Effect of terrestrial organic matter on ocean acidification and CO2 flux in an Arctic shelf sea|year = 2020|last1 = Capelle|first1 = David W.|last2 = Kuzyk|first2 = Zou Zou A.|last3 = Papakyriakou|first3 = Tim|last4 = Guéguen|first4 = Céline|last5 = Miller|first5 = Lisa A.|last6 = MacDonald|first6 = Robie W.|journal = Progress in Oceanography|volume = 185|page = 102319|bibcode = 2020PrOce.18502319C|doi-access = free|hdl = 1993/34767|hdl-access = free}} 50px Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].}}]]

Before the Industrial Revolution, the ocean was a source of CO₂ to the atmosphere balancing the impact of rock weathering and terrestrial particulate organic carbon; now it has become a sink for the excess atmospheric CO₂.{{cite journal|last1=Raven|first1=J.A.|last2=Falkowskli|first2=P.G.|title=Oceanic sinks for atmospheric CO2 |journal=Global Biogeochemical Cycles|date=2009|volume=23|issue=1|pages=GB1005|doi=10.1029/2008gb003349|bibcode=2009GBioC..23.1005G|hdl=1912/3415|citeseerx=10.1.1.715.9875|s2cid=17471174 |url=http://www.vliz.be/imisdocs/publications/291174.pdf}} Carbon dioxide is absorbed from the atmosphere at the ocean's surface at an exchange rate which varies locally and with time{{cite journal|last1=Takahashi|first1=T|last2=Sutherland|first2=S|last3=Sweeney|first3=C|last4=Poisson|first4=A|last5=Metzl|first5=N|title= Global sea–air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects|date=2002|volume=49|issue=9–10|pages=1601–1622|doi=10.1016/S0967-0645(02)00003-6|journal=Deep Sea Research Part II: Topical Studies in Oceanography|bibcode=2002DSRII..49.1601T}} but on average, the oceans have a net absorption of around 2.9 Pg (equivalent to 2.9 billion metric tonnes) of carbon from atmospheric CO₂ per year.{{Cite journal |last1=Friedlingstein |first1=Pierre |last2=O'Sullivan |first2=Michael |last3=Jones |first3=Matthew W. |last4=Andrew |first4=Robbie M. |last5=Bakker |first5=Dorothee C. E. |last6=Hauck |first6=Judith |last7=Landschützer |first7=Peter |last8=Le Quéré |first8=Corinne |last9=Luijkx |first9=Ingrid T. |last10=Peters |first10=Glen P. |last11=Peters |first11=Wouter |last12=Pongratz |first12=Julia |last13=Schwingshackl |first13=Clemens |last14=Sitch |first14=Stephen |last15=Canadell |first15=Josep G. |date=2023-12-05 |title=Global Carbon Budget 2023 |url=https://essd.copernicus.org/articles/15/5301/2023/ |journal=Earth System Science Data |language=English |volume=15 |issue=12 |pages=5301–5369 |doi=10.5194/essd-15-5301-2023 |doi-access=free |issn=1866-3508|hdl=20.500.11850/665569 |hdl-access=free }} Because the solubility of carbon dioxide increases when temperature decreases, cold areas can contain more CO₂ and still be in equilibrium with the atmosphere; In contrast, rising sea surface temperatures decrease the capacity of the oceans to take in carbon dioxide.{{cite book|last1=Zeebe|first1=R|last2=Wolf-Gladrow|first2=D|title=CO2 in seawater: Equilibrium, Kinetics, Isotopes|date=2001|publisher=Elsevier Science|pages=360}} The North Atlantic and Nordic oceans have the highest carbon uptake per unit area in the world,{{cite journal|display-authors=3 |last1=Takahashi |first1=T |last2=Sutherland |first2=S |last3=Wanninkhof |first3=R |last4=Sweeney |first4=C |last5=Feely |first5=RA |last6=Chipman |first6=DW |last7=Hales |first7=Burke |last8=Friedrich |first8=Gernot |last9=Chavez |first9=Francisco |last10=Sabine |first10=Christopher |last11=Watson |first11=Andrew |last12=Bakker |first12=Dorothee CE |last13=Schuster |first13=Ute |last14=Metzl |first14=Nicolas |last15=Yoshikawa-Inoue |first15=Hisayuki |last16=Ishii |first16=Masao |last17=Midorikawa |first17=Takashi |last18=Nojiri |first18=Yukihiro |last19=de Baar |first19=Hein J.W. |title=Climatological mean and decadal change in surface ocean pCO2, and net sea-air CO2 flux over the global oceans|journal=Deep Sea Research Part II: Topical Studies in Oceanography|date=2009|volume=56|issue=8–10|pages=554–577|doi=10.1016/j.dsr2.2008.12.009|bibcode=2009DSRII..56..554T}} and in the North Atlantic deep convection transports approximately 197 Tg per year of non-refractory carbon to depth.{{cite journal|last1=Fontela|first1=M|last2=Garcia-Ibanez|first2=M|last3=Hansell|first3=D|last4=Mercier|first4=H|last5=Perez|first5=F|title=Dissolved organic carbon in the North Atlantic meridional overturning circulation|journal=Nature|date=2016|volume=6|page=26931|doi=10.1038/srep26931|pmid=27240625|pmc=4886255|bibcode=2016NatSR...626931F}}

The rate of CO₂ absorption by the ocean has been increasing with time as atmospheric CO₂ concentrations have increased due to anthropogenic emissions. However, the ocean carbon sink may be more sensitive to climate change than previously thought, and ocean warming and circulation changes due to climate change could result in the ocean absorbing less CO₂ from the atmosphere in future than expected.{{Cite journal |last1=Gruber |first1=Nicolas |last2=Bakker |first2=Dorothee C. E. |last3=DeVries |first3=Tim |last4=Gregor |first4=Luke |last5=Hauck |first5=Judith |last6=Landschützer |first6=Peter |last7=McKinley |first7=Galen A. |last8=Müller |first8=Jens Daniel |date=24 January 2023 |title=Trends and variability in the ocean carbon sink |url=https://www.nature.com/articles/s43017-022-00381-x |journal=Nature Reviews Earth & Environment |language=en |volume=4 |issue=2 |pages=119–134 |doi=10.1038/s43017-022-00381-x |bibcode=2023NRvEE...4..119G |issn=2662-138X|hdl=20.500.11850/595538 |hdl-access=free }}

{{See also|Carbon dioxide in Earth's atmosphere}}

Ocean-atmospheric exchanges rates of CO₂ depend on the concentration of carbon dioxide already present in both the atmosphere and the ocean, temperature, salinity, and wind speed.{{cite book|last1=Robbins|first1=L.L.|last2=Hansen|first2=M.E.|last3=Kleypas|first3=J.A.|last4=Meylan|first4=S.C.|title=CO2calc—A user-friendly seawater carbon calculator for Windows, Mac OS X, and iOS (iPhone)|date=2010|publisher=U.S. Geological Survey Open-File Report 2010-1280|pages=16}} This exchange rate can be approximated by Henry's law and can be calculated as S = kP, where the solubility (S) of the carbon dioxide gas is proportional to the amount of gas in the atmosphere, or its partial pressure.

Since the oceanic intake of carbon dioxide is limited, CO₂ influx can also be described by the Revelle factor.{{cite journal|last1=Revelle|first1=R|last2=Suess|first2=H|title=Carbon dioxide exchange between atmosphere and ocean and the question of an increase of atmospheric CO2 during the past decades|journal=Tellus|date=1957|volume=9|issue=1|pages=18–27|doi=10.1111/j.2153-3490.1957.tb01849.x|bibcode=1957Tell....9...18R}} The Revelle Factor is a ratio of the change of carbon dioxide to the change in dissolved inorganic carbon, which serves as an indicator of carbon dioxide dissolution in the mixed layer considering the solubility pump. The Revelle Factor is an expression to characterize the thermodynamic efficiency of the DIC pool to absorb CO₂ into bicarbonate. The lower the Revelle factor, the higher the capacity for ocean water to take in carbon dioxide. While Revelle calculated a factor of around 10 in his day, in a 2004 study data showed a Revelle factor ranging from approximately 9 in low-latitude tropical regions to 15 in the southern ocean near Antarctica.{{cite journal|last1=Sabine|first1=C.L.|last2=Feely|first2=R.A.|last3=Gruber|first3=N|last4=Key|first4=R.M.|last5=Lee|first5=K|title= The oceanic sink for anthropogenic CO2|date=2004|volume=305|issue=5682|pages=367–371|doi=10.1126/science.1097403|pmid=15256665|journal=Science|bibcode=2004Sci...305..367S|hdl=10261/52596|s2cid=5607281|url=http://oceanrep.geomar.de/46251/1/1193.full.pdf|hdl-access=free}}

Rivers can also transport organic carbon to the ocean through weathering or erosion of aluminosilicate (equation 7) and carbonate rocks (equation 8) on land,

{{NumBlk|:|2 NaAlSi3O8 + 2 H2CO3 + 9 H2O -> 2 Na+ + 2 HCO3^- + 4 H4SiO4 + Al2Si2O5(OH)4|{{EquationRef|7}}}}

{{NumBlk|:|CaCO3 + H2CO3 -> Ca^2+ + 2 HCO3^-|{{EquationRef|8}}}}

or by the decomposition of life (equation 5, e.g. plant and soil material). Rivers contribute roughly equal amounts (~0.4 GtC/yr) of DIC and DOC to the oceans. It is estimated that approximately 0.8 GtC (DIC + DOC) is transported annually from the rivers to the ocean. The rivers that flow into Chesapeake Bay (Susquehanna, Potomac, and James rivers) input approximately 0.004 Gt (6.5 x 10¹⁰ moles) DIC per year.{{cite journal|last1=Waldbusser|first1=G|last2=Powell|first2=E|last3=Mann|first3=R|title=Ecosystem effects of shell aggregations and cycling in coastal waters: an example of Chesapeake Bay oyster reefs|journal=Ecology|date=2013|volume=94|issue=4|pages=895–903|doi=10.1890/12-1179.1|bibcode=2013Ecol...94..895W|url=https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=2673&context=vimsarticles}} The total carbon transport of rivers represents approximately 0.02% of the total carbon in the atmosphere.{{cite journal|last1=Galy|first1=Valier|last2=Peucker-Ehrenbrink|first2=Bernhard|last3=Eglinton|first3=Timothy|title=Global carbon export from the terrestrial biosphere controlled by erosion|journal=Nature|date=2015|volume=521|issue=7551|pages=204–207|doi=10.1038/nature14400|pmid=25971513|bibcode=2015Natur.521..204G|s2cid=205243485}} Though it seems small, over long time scales (1000 to 10,000 years) the carbon that enters rivers (and therefore does not enter the atmosphere) serves as a stabilizing feedback for greenhouse warming.{{Cite journal|last=Velbel|first=Michael Anthony|date=1993-12-01|title=Temperature dependence of silicate weathering in nature: How strong a negative feedback on long-term accumulation of atmospheric CO2 and global greenhouse warming?|journal=Geology|language=en|volume=21|issue=12|pages=1059–1062|doi=10.1130/0091-7613(1993)021<1059:TDOSWI>2.3.CO;2|issn=0091-7613|bibcode=1993Geo....21.1059V|s2cid=747129}}

File:Fate of Buried Organic Matter.jpg

The key outputs of the marine carbon system are particulate organic matter (POC) and calcium carbonate (PIC) preservation as well as reverse weathering. While there are regions with local loss of CO₂ to the atmosphere and hydrothermal processes, a net loss in the cycle does not occur.

Sedimentation is a long-term sink for carbon in the ocean, as well as the largest loss of carbon from the oceanic system. Deep marine sediments and geologic formations are important since they provide a thorough record of life on Earth and an important source of fossil fuel.{{cite journal|last1=Emerson|first1=S|last2=Hedges|first2=J|date=October 1988|title=Processes Controlling the Organic Carbon Content of Open Ocean Sediments|journal=Paleoceanography|volume=3|issue=5|pages=621–634|doi=10.1029/pa003i005p00621|bibcode=1988PalOc...3..621E}} Oceanic carbon can exit the system in the form of detritus that sinks and is buried in the seafloor without being fully decomposed or dissolved. Ocean floor surface sediments account for 1.75x10¹⁵ kg of carbon in the global carbon cycle.{{cite book |last1= Ciais|first1= Philippe|last2= Sabine |first2=Christopher | title= Climate Change 2013: the physical science basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.|url= http://pubman.mpdl.mpg.de/pubman/item/escidoc:2058766/component/escidoc:2058768/WG1AR5_Chapter06_FINAL.pdf |publisher= Cambridge University Press|date= 2014 |pages= 465–470 }} At most, 4% of the particulate organic carbon from the euphotic zone in the Pacific Ocean, where light-powered primary production occurs, is buried in marine sediments. It is then implied that since there is a higher input of organic matter to the ocean than what is being buried, a large portion of it is used up or consumed within.

Historically, sediments with the highest organic carbon contents were frequently found in areas with high surface water productivity or those with low bottom-water oxygen concentrations.{{Cite book|last1=Fleming|first1=R.H.|last2=Revelle|first2=R.|date=1939|chapter=Physical processes in the oceans|pages=48–141|editor=Trask, P.D.|title=Recent Marine Sediments|location=Tulsa|publisher=American Association of Petroleum Geologists}} 90% of organic carbon burial occurs in deposits of deltas and continental shelves and upper slopes;{{Cite journal|last=Berner|first=Robert A.|date=1989-01-01|title=Biogeochemical cycles of carbon and sulfur and their effect on atmospheric oxygen over phanerozoic time|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|series=The Long Term Stability of the Earth System|volume=75|issue=1|pages=97–122|doi=10.1016/0031-0182(89)90186-7|bibcode=1989PPP....75...97B}} this is due partly to short exposure time because of a shorter distance to the seafloor and the composition of the organic matter that is already deposited in those environments.{{Cite journal|last=Henrichs|first=Susan|date=1992|title=Early diagenesis of organic matter in marine sediments: progress and perplexity|journal=Marine Chemistry|volume=39|issue=1–3|pages=119–149|doi=10.1016/0304-4203(92)90098-U|bibcode=1992MarCh..39..119H }} Organic carbon burial is also sensitive to climate patterns: the accumulation rate of organic carbon was 50% larger during the glacial maximum compared to interglacials.

{{biogeochemical cycle sidebar|carbon}}

POC is decomposed by a series of microbe-driven processes, such as methanogenesis and sulfate reduction, before burial in the seafloor.{{cite book|last1=Claypool|first1=G.E.|last2=Kaplan|first2=I.R.|date=1974|title=Natural Gases in Marine Sediments|publisher=Plenum Press|pages=99–139}}{{cite journal|last1=D'Hondt|first1=S|last2=Rutherford|first2=S|last3=Spivack|first3=A.J.|date=2002|title=Metabolic activity of subsurface life in deep-sea sediments|journal=Science|volume=295|issue=5562|pages=2067–2070|doi=10.1126/science.1064878|pmid=11896277|bibcode=2002Sci...295.2067D|s2cid=26979705}} Degradation of POC also results in microbial methane production which is the main gas hydrate on the continental margins.{{Cite book|last1=Kvenvolden|first1=K.A.|last2=Lorenson|first2=T.D.|date=2001|title=Natural Gas Hydrates: Occurrence, Distribution, and Detection|pages=3–18 |isbn=978-0-875-90982-0|editor1=Charles K. Paull |editor2=William P. Dillon|publisher=American Geophysical Union|series=Geophysical Monograph Series |volume=124}} Lignin and pollen are inherently resistant to degradation, and some studies show that inorganic matrices may also protect organic matter.{{Cite journal|last1=Huguet|first1=Carme|last2=de Lange|first2=Gert J.|last3=Gustafsson|first3=Örjan|last4=Middelburg|first4=Jack J.|last5=Sinninghe Damsté|first5=Jaap S.|last6=Schouten|first6=Stefan|date=2008-12-15|title=Selective preservation of soil organic matter in oxidized marine sediments (Madeira Abyssal Plain)|journal=Geochimica et Cosmochimica Acta|volume=72|issue=24|pages=6061–6068|doi=10.1016/j.gca.2008.09.021|bibcode=2008GeCoA..72.6061H}} Preservation rates of organic matter depend on other interdependent variables that vary nonlinearly in time and space.{{Cite journal|last1=Hedges|first1=John I.|last2=Hu|first2=Feng Sheng|last3=Devol|first3=Allan H.|last4=Hartnett|first4=Hilairy E.|author-link4=Hilairy Hartnett|last5=Tsamakis|first5=Elizabeth|last6=Keil|first6=Richard G.|date=1999|title=Sedimentary organic matter preservation: A test for selective degradation under oxic conditions|url=https://asu.pure.elsevier.com/en/publications/sedimentary-organic-matter-preservation-a-test-for-selective-degr|journal=American Journal of Science|language=en|volume=299|issue=7–9|pages=529|issn=0002-9599|bibcode=1999AmJS..299..529H|doi=10.2475/ajs.299.7-9.529}} Although organic matter breakdown occurs rapidly in the presence of oxygen, microbes utilizing a variety of chemical species (via redox gradients) can degrade organic matter in anoxic sediments. The burial depth at which degradation halts depends upon the sedimentation rate, the relative abundance of organic matter in the sediment, the type of organic matter being buried, and innumerable other variables. While decomposition of organic matter can occur in anoxic sediments when bacteria use oxidants other than oxygen (nitrate, sulfate, Fe³⁺), decomposition tends to end short of complete mineralization.{{Cite journal|last1=Kristensen|first1=Erik|last2=Ahmed|first2=Saiyed I.|last3=Devol|first3=Allan H.|date=1995-12-01|title=Aerobic and anaerobic decomposition of organic matter in marine sediment: Which is fastest?|journal=Limnology and Oceanography|language=en|volume=40|issue=8|pages=1430–1437|doi=10.4319/lo.1995.40.8.1430|issn=1939-5590|bibcode=1995LimOc..40.1430K|doi-access=free}} This occurs because of preferential decomposition of labile molecules over refractile molecules.

Organic carbon burial is an input of energy for underground biological environments and can regulate oxygen in the atmosphere at long time-scales (> 10,000 years).{{Cite journal|last1=Cartapanis|first1=Olivier|last2=Bianchi|first2=Daniele|last3=Jaccard|first3=Samuel|last4=Galbraith|first4=Eric|date=2016-01-21|title=Global pulses of organic carbon burial in deep-sea sediments during glacial maxima|volume=7|pages=10796|journal = Nature Communications|doi=10.1038/ncomms10796|pmid=26923945|pmc=4773493|bibcode=2016NatCo...710796C}} Burial can only take place if organic carbon arrives to the sea floor, making continental shelves and coastal margins the main storage of organic carbon from terrestrial and oceanic primary production. Fjords, or cliffs created by glacial erosion, have also been identified as areas of significant carbon burial, with rates one hundred times greater than the ocean average.{{Cite journal|last1=Smith|first1=Richard|last2=Bianchi|first2=Thomas|last3=Allison|first3=Mead|last4=Savage|first4=Candida|last5=Galy|first5=Valier|date=2015|title=High rates of organic carbon burial in fjord sediments globally|volume=8|issue=6|pages=450|journal = Nature Geoscience|doi=10.1038/ngeo2421|bibcode=2015NatGe...8..450S}} Particulate organic carbon is buried in oceanic sediments, creating a pathway between a rapidly available carbon pool in the ocean to its storage for geological timescales. Once carbon is sequestered in the seafloor, it is considered blue carbon. Burial rates can be calculated as the difference between the rate at which organic matter sinks and the rate at which it decomposes.

The precipitation of calcium carbonate is important as it results in a loss of alkalinity as well as a release of CO₂ (Equation 4), and therefore a change in the rate of preservation of calcium carbonate can alter the partial pressure of CO₂ in Earth's atmosphere. CaCO₃ is supersatured in the great majority of ocean surface waters and undersaturated at depth, meaning the shells are more likely to dissolve as they sink to ocean depths. CaCO₃ can also be dissolved through metabolic dissolution (i.e. can be used as food and excreted) and thus deep ocean sediments have very little calcium carbonate. The precipitation and burial of calcium carbonate in the ocean removes particulate inorganic carbon from the ocean and ultimately forms limestone. On time scales greater than 500,000 years Earth's climate is moderated by the flux of carbon in and out of the lithosphere.{{Cite journal|last1=Kasting|first1=J. F.|last2=Toon|first2=O. B.|last3=Pollack|first3=J. B.|date=1988-02-01|title=How climate evolved on the terrestrial planets|journal=Scientific American|volume=258|issue=2|pages=90–97|doi=10.1038/scientificamerican0288-90|pmid=11538470|issn=0036-8733|bibcode=1988SciAm.258b..90K}} Rocks formed in the ocean seafloor are recycled through plate tectonics back to the surface and weathered or subducted into the mantle, the carbon outgassed by volcanoes.

Oceans take up around 25 – 31% of anthropogenic CO₂.{{Cite journal |last1=Gruber |first1=Nicolas |last2=Clement |first2=Dominic |last3=Carter |first3=Brendan R. |last4=Feely |first4=Richard A. |last5=van Heuven |first5=Steven |last6=Hoppema |first6=Mario |last7=Ishii |first7=Masao |last8=Key |first8=Robert M. |last9=Kozyr |first9=Alex |last10=Lauvset |first10=Siv K. |last11=Lo Monaco |first11=Claire |last12=Mathis |first12=Jeremy T. |last13=Murata |first13=Akihiko |last14=Olsen |first14=Are |last15=Perez |first15=Fiz F. |date=2019-03-15 |title=The oceanic sink for anthropogenic CO 2 from 1994 to 2007 |url=https://www.science.org/doi/10.1126/science.aau5153 |journal=Science |language=en |volume=363 |issue=6432 |pages=1193–1199 |doi=10.1126/science.aau5153 |pmid=30872519 |issn=0036-8075}}{{Cite journal |last1=Gruber |first1=Nicolas |last2=Bakker |first2=Dorothee C. E. |last3=DeVries |first3=Tim |last4=Gregor |first4=Luke |last5=Hauck |first5=Judith |last6=Landschützer |first6=Peter |last7=McKinley |first7=Galen A. |last8=Müller |first8=Jens Daniel |date=24 January 2023 |title=Trends and variability in the ocean carbon sink |url=https://www.nature.com/articles/s43017-022-00381-x |journal=Nature Reviews Earth & Environment |language=en |volume=4 |issue=2 |pages=119–134 |doi=10.1038/s43017-022-00381-x |bibcode=2023NRvEE...4..119G |issn=2662-138X|hdl=20.500.11850/595538 |hdl-access=free }} Because the Revelle factor increases with increasing CO₂, a smaller fraction of the anthropogenic flux will be taken up by the ocean in the future.{{Cite journal|last1=Revelle|first1=Roger|last2=Suess|first2=Hans E.|date=1957-02-01|title=Carbon Dioxide Exchange Between Atmosphere and Ocean and the Question of an Increase of Atmospheric CO2 during the Past Decades|journal=Tellus|language=en|volume=9|issue=1|pages=18–27|doi=10.1111/j.2153-3490.1957.tb01849.x|issn=2153-3490|bibcode=1957Tell....9...18R}} Current annual increase in atmospheric CO₂ is approximately 4–5 gigatons of carbon,{{Cite journal |last1=Friedlingstein |first1=Pierre |last2=O'Sullivan |first2=Michael |last3=Jones |first3=Matthew W. |last4=Andrew |first4=Robbie M. |last5=Bakker |first5=Dorothee C. E. |last6=Hauck |first6=Judith |last7=Landschützer |first7=Peter |last8=Le Quéré |first8=Corinne |last9=Luijkx |first9=Ingrid T. |last10=Peters |first10=Glen P. |last11=Peters |first11=Wouter |last12=Pongratz |first12=Julia |last13=Schwingshackl |first13=Clemens |last14=Sitch |first14=Stephen |last15=Canadell |first15=Josep G. |date=2023-12-05 |title=Global Carbon Budget 2023 |url=https://essd.copernicus.org/articles/15/5301/2023/#section3 |journal=Earth System Science Data |language=English |volume=15 |issue=12 |pages=5301–5369 |doi=10.5194/essd-15-5301-2023 |doi-access=free |issn=1866-3508|hdl=20.500.11850/665569 |hdl-access=free }} about 2–3ppm CO₂ per year.{{Cite web |last=Copernicus Climate Change Service |title=Greenhouse gas concentrations |url=https://climate.copernicus.eu/climate-indicators/greenhouse-gas-concentrations#:~:text=Based%20on%20additional%20data%20sources,contributed%20needs%20to%20be%20investigated. |access-date=2024-09-21 |website=climate.copernicus.eu}}{{Cite web |last=Lindsey |first=Rebecca |date=2024-04-09 |editor-last=Dlugokencky |editor-first=Ed |title=Climate Change: Atmospheric Carbon Dioxide |url=https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide |access-date=2024-09-21 |website=www.climate.gov |language=en}} This induces climate change that drives carbon concentration and carbon-climate feedback processes that modifies ocean circulation and the physical and chemical properties of seawater, which alters CO₂ uptake.{{cite journal|last1=Boer|first1=G|last2=Arora|first2=V|title=Feedbacks in emission-driven and concentration-driven global carbon budgets|journal=Journal of Climate|date=2013|volume=26|issue=10|pages=3326–3341|doi=10.1175/JCLI-D-12-00365.1|bibcode=2013JCli...26.3326B|doi-access=free}}{{cite journal|last1=Gregory|first1=J|last2=Jones|first2=C|last3=Cadule|first3=P|last4=Friedlingstein|first4=P|title=Quantifying carbon cycle feedbacks|journal=Journal of Climate|date=2009|volume=22|issue=19|pages=5232–5250|doi=10.1175/2009JCLI2949.1|bibcode=2009JCli...22.5232G|s2cid=59385833|url=https://hal.archives-ouvertes.fr/hal-03197002/file/Gr199.pdf}} Overfishing and the plastic pollution of the oceans contribute to the degraded state of the world's biggest carbon sink.{{Cite news |last=Harvey |first=Fiona |author-link=Fiona Harvey |date=2019-12-04 |title=Tackling degraded oceans could mitigate climate crisis - report |url=https://www.theguardian.com/environment/2019/dec/04/tackling-ocean |access-date=2019-12-07 |work=The Guardian |language=en-GB |issn=0261-3077}}{{Cite news |last=Harvey |first=Fiona |author-link=Fiona Harvey |date=2019-12-07 |title=Oceans losing oxygen at unprecedented rate, experts warn |url=https://www.theguardian.com/environment/2019/dec/07/oceans-losing-oxygen-at-unprecedented-rate-experts-warn |access-date=2019-12-07 |work=The Guardian |language=en-GB |issn=0261-3077}}

Full article: Ocean acidification

The pH of the oceans is declining due to uptake of atmospheric CO₂.{{Cite journal|last1=Caldeira|first1=Ken|last2=Wickett|first2=Michael E.|date=2003-09-25|title=Oceanography: Anthropogenic carbon and ocean pH|journal=Nature|language=en|volume=425|issue=6956|pages=365|doi=10.1038/425365a|pmid=14508477|issn=1476-4687|bibcode=2003Natur.425..365C|s2cid=4417880|url=https://zenodo.org/record/1233227|doi-access=free}} The rise in dissolved carbon dioxide reduces the availability of the carbonate ion, reducing CaCO₃ saturation state, thus making it thermodynamically harder to make CaCO₃ shell.{{Cite book|title=Ocean acidification|date=2011|publisher=Oxford University Press|last1=Gattuso|first1=Jean-Pierre|last2=Hansson|first2=Lina|isbn=9780199591091|location=Oxford [England]|oclc=823163766}} Carbonate ions preferentially bind to hydrogen ions to form bicarbonate, thus a reduction in carbonate ion availability increases the amount of unbound hydrogen ions, and decreases the amount of bicarbonate formed (Equations 1–3). pH is a measurement of hydrogen ion concentration, where a low pH means there are more unbound hydrogen ions. pH is therefore an indicator of carbonate speciation (the format of carbon present) in the oceans and can be used to assess how healthy the ocean is.

The list of organisms that may struggle due to ocean acidification include coccolithophores and foraminifera (the base of the marine food chain in many areas), human food sources such as oysters and mussels,{{Cite journal|last=Barton|first=Alan|date=2015|title=Impacts of Coastal Acidification on the Pacific Northwest Shellfish Industry and Adaptation Strategies Implemented in Response|journal=Oceanography|volume=25|issue=2|pages=146–159|doi=10.5670/oceanog.2015.38|url=http://ir.library.oregonstate.edu/xmlui/bitstream/1957/56946/1/WaldbusserGeorgeCEOASImpactsCoastalAcidification.pdf|doi-access=free|bibcode=2015Ocgpy..25b.146B }} and perhaps the most conspicuous, a structure built by organisms – the coral reefs. Most surface water will remain supersaturated with respect to CaCO₃ (both calcite and aragonite) for some time on current emissions trajectories, but the organisms that require carbonate will likely be replaced in many areas. Coral reefs are under pressure from overfishing, nitrate pollution, and warming waters; ocean acidification will add additional stress on these important structures.

Full article: Iron Fertilization

Iron fertilization is a facet of geoengineering, which purposefully manipulates the Earth's climate system, typically in aspects of the carbon cycle or radiative forcing. Of current geoengineering interest is the possibility of accelerating the biological pump to increase export of carbon from the surface ocean. This increased export could theoretically remove excess carbon dioxide from the atmosphere for storage in the deep ocean. Ongoing investigations regarding artificial fertilization exist.{{Cite journal|last1=Aumont|first1=O.|last2=Bopp|first2=L.|date=2006-06-01|title=Globalizing results from ocean in situ iron fertilization studies|journal=Global Biogeochemical Cycles|language=en|volume=20|issue=2|pages=GB2017|doi=10.1029/2005gb002591|issn=1944-9224|bibcode=2006GBioC..20.2017A|doi-access=free}} Due to the scale of the ocean and the fast response times of heterotrophic communities to increases in primary production, it is difficult to determine whether limiting-nutrient fertilization results in an increase in carbon export. However, the majority of the community does not believe this is a reasonable or viable approach.{{cite journal|last1=Chisholm|first1=S|last2=Falkowski|first2=P|last3=Cullen|first3=J|title=Dis-crediting ocean fertilization|journal=Science|date=2001|volume=294|issue=5541|pages=309–310|doi=10.1126/science.1065349|pmid=11598285|s2cid=130687109}}

There are over 16 million dams in the world{{cite journal|last1=Lehner|first1=B|last2=Liermann|first2=C|last3=Revenga|first3=C|last4=Vorosmarty|first4=C|last5=Fekete|first5=B|last6=Crouzet|first6=P|last7=Doll|first7=P|last8=Endejan|first8=M|last9=Frenken|first9=K|last10=Magome|first10=J|last11=Nilsson|first11=C|last12=Robertson|first12=J|last13=Rodel|first13=R|last14=Sindorf|first14=N|last15=Wisser|first15=D|title=High-resolution mapping of the world's reservoirs and dams for sustainable river-flow management|journal=Frontiers in Ecology and the Environment|date=2011|volume=9|issue=9|pages=494–502|doi=10.1890/100125|url=http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-49188|doi-access=free|bibcode=2011FrEE....9..494L}} that alter carbon transport from rivers to oceans.{{cite journal|display-authors=3|first1=Pierre |last1=Regnier |first2=Pierre |last2=Friedlingstein |first3=Philippe |last3=Ciais |first4=Fred T. |last4=Mackenzie |first5=Nicolas |last5=Gruber |first6=Ivan A. |last6=Janssens |first7=Goulven G. |last7=Laruelle |first8=Ronny |last8=Lauerwald |first9=Sebastiaan9 |last9=Luyssaert |first10=Andreas J. |last10=Andersson |first11=Sandra |last11=Arndt |first12=Carol |last12=Arnosti |first13=Alberto V. |last13=Borges |first14=Andrew W.|last14=Dale |first15=Angela |last15=Gallego-Sala |first16=Yves|last16=Goddéris |first17=Nicolas |last17=Goossens |first18=Jens |last18=Hartmann |first19=Christoph |last19=Heinze |first20=Tatiana |last20=Ilyina |first21=Fortunat |last21=Joos |first22=Douglas E. |last22=LaRowe |first23=Jens |last23=Leifeld |first24=Filip J. R. |last24=Meysman |first25=Guy |last25=Munhoven |first26=Peter A.|last26=Raymond |first27=Renato|last27=Spahni |first28=Pradava |last28=Suntharalingam |first29=Martin |last29=Thullner|title=Anthropogenic perturbation of the carbon fluxes from land to ocean|journal=Nature Geoscience|date=2013|volume=6|issue=8|pages=597–607|doi=10.1038/ngeo1830|bibcode=2013NatGe...6..597R|url=http://orbi.ulg.ac.be/handle/2268/150126|hdl=10871/18939|s2cid=53418968 |hdl-access=free}} Using data from the Global Reservoirs and Dams database, which contains approximately 7000 reservoirs that hold 77% of the total volume of water held back by dams (8000 km³), it is estimated that the delivery of carbon to the ocean has decreased by 13% since 1970 and is projected to reach 19% by 2030.{{cite journal|last1=Maavara|first1=T|last2=Lauerwald|first2=R|last3=Regnier|first3=P|last4=Van Cappellen|first4=P|date=2016|title=Global perturbation of organic carbon cycling by river damming|journal=Nature|doi=10.1038/ncomms15347|pmid=28513580|pmc=5442313|volume=8|page=15347|bibcode=2017NatCo...815347M}} The excess carbon contained in the reservoirs may emit an additional ~0.184 Gt of carbon to the atmosphere per year{{cite journal|last1=Barros|first1=N|last2=Cole|first2=J|last3=Tranvik|first3=L|last4=Prairie|first4=Y|last5=Bastviken|first5=D|last6=Huszar|first6=V|last7=del Giorgio|first7=P|last8=Roland|first8=F|title=Carbon emission from hydroelectric reservoirs linked to reservoir age and latitude|journal=Nature Geoscience|date=2011|volume=4|issue=9|pages=593–596|doi=10.1038/ngeo1211|bibcode=2011NatGe...4..593B|s2cid=52245758}} and an additional ~0.2 GtC will be buried in sediment. Prior to 2000, the Mississippi, the Niger, and the Ganges River basins account for 25 – 31% of all reservoir carbon burial. After 2000, the Paraná (home to 70 dams) and the Zambezi (home to the largest reservoir) River basins exceeded the burial by the Mississippi. Other large contributors to carbon burial caused by damming occur on the Danube, the Amazon, the Yangtze, the Mekong, the Yenisei, and the Tocantins Rivers.

{{portal|Oceans}}

• Phosphorus cycle

{{reflist}}

• [https://earth.nullschool.net/#current/ocean/surface/currents/overlay=spco2/winkel3 Current global map of the partial pressure of carbon dioxide at the ocean surface]
• [https://earth.nullschool.net/#current/ocean/surface/currents/overlay=fgco2/winkel3 Current global map of the sea-air carbon dioxide flux density]

{{biogeochemical cycle}}

Category:Carbon cycle

Category:Chemical oceanography