Dissolved inorganic carbon

{{Short description|Sum of inorganic carbon species in a solution}}

File:Annual DOC and DIC fluxes in the Tanguro Ranch watershed.jpg 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].]]

Dissolved inorganic carbon (DIC) is the sum of the aqueous species of inorganic carbon in a solution. Carbon compounds can be distinguished as either organic or inorganic, and as 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, {{chem|HCO|3|-}}, {{chem|CO|3|2-}} respectively). Dissolved inorganic carbon (DIC) includes three major aqueous species, CO₂, {{chem|HCO|3|-}} ,{{chem|CO|3|2-}}, and to a lesser extent their complexes in solution with metal ions.Mackenzie FT and Lerman A (2006) [https://books.google.com/books?id=TiGgJip0l64C&dq=%22Dissolved+Inorganic+Carbon%22&pg=PA11 Carbon in the Geobiosphere: Earth's Outer Shell], Springer Science & Business Media. {{ISBN|9781402042386}}.

Marine ecosystems

=Solubility pump=

Aqueous carbon dioxide reacts with water to form carbonic acid which is very unstable and will dissociate rapidly into hydronium and bicarbonate. Therefore, in seawater, dissolved inorganic carbon is commonly referred to as the collection of bicarbonate, carbonate ions, and dissolved carbon dioxide (CO₂, H₂CO₃, {{chem|HCO|3|-}}, {{chem|CO|3|2-}}).

:CO₂(aq) + H₂O {{eqm}} H₂CO₃ {{eqm}} {{chem|HCO|3|-}} + H⁺ {{eqm}} {{chem|CO|3|2-}} + 2 H⁺

More than 99% of dissolved inorganic carbon is in the form of bicarbonate and carbonate ions meaning that most of the ocean’s carbon storing ability is due to this chemical reactivity.{{cite book |last1=Williams |first1=Richard G. |last2=Follows |first2=Michael J. |title=Ocean Dynamics and the Carbon Cycle: Principles and Mechanisms |date=14 July 2011 |publisher=Cambridge University Press |location=Cambridge, UK |isbn=978-0521843690 |pages=7–9}} Sea-air flux of CO₂ and the resulting dissolved inorganic carbon is affected by physical processes such as strong winds and vertical mixing, and the biological processes of photosynthesis, respiration, and decomposition.{{cite journal |last1=Ma|first1=W |last2=Chai |first2=F |last3=Xiu |first3=P |last4=Tian |first4=J |title=Simulation of export production and biological pump structure in the South China Sea |journal=Geo-Marine Letters |date=2014 |volume=34 |issue=6 |pages=541–554 |doi=10.1007/s00367-014-0384-0|bibcode=2014GML....34..541M |s2cid=129982048 }}

=Biological pump=

Dissolved inorganic carbon is a key component of the biological pump, which is defined as the amount of biologically produced organic carbon flux from the upper ocean to the deep ocean.{{cite journal |last1=Emerson |first1=Steven |title=Annual net community production and the biological carbon flux in the ocean |journal=Global Biogeochemical Cycles |date=2014 |volume=28 |issue=1 |pages=14–28 |doi=10.1002/2013GB004680|bibcode=2014GBioC..28...14E |doi-access=free }} Dissolved inorganic carbon in the form of carbon dioxide is fixed into organic carbon through photosynthesis. Respiration is the reverse process and consumes organic carbon to produce inorganic carbon. Photosynthesis, and the biological pump, is dependent on the availability of inorganic nutrients and carbon dioxide.{{cite journal |last1=Raymond |first1=Peter A. |last2=Bauer |first2=James E. |title=Atmospheric CO₂ evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary |journal=Limnol. Oceanogr. |date=2000 |volume=45 |issue=8 |pages=1707–1717|doi=10.4319/lo.2000.45.8.1707 |bibcode=2000LimOc..45.1707R |doi-access=free }}

:Photosynthesis: 6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂

:Respiration: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy

Oceanographers seek to understand the metabolic state of the ocean, or the efficiency of the biological pump, by estimating the net community production (NCP) which is the gross primary productivity (GPP) minus the community respiration (sum of the respiration of the local autotrophs and heterotrophs).{{cite journal |last1=Ducklow |first1=H.W. |last2=Doney |first2=S.C. |title=What is the Metabolic State of the Oligotrophic Ocean? A Debate. |journal=Annual Review of Marine Science |date=2013 |volume=5 |pages=525–33 |doi=10.1146/annurev-marine-121211-172331|pmid=22809191 |hdl=1912/5282 |hdl-access=free }} An efficient biological pump increases biological export to the deeper ocean which has been hypothesized to suppress CO₂ outgassing in the upper ocean.{{cite journal |last1=Ma|first1=W |last2=Chai |first2=F |last3=Xiu |first3=P |last4=Tian |first4=J |title=Simulation of export production and biological pump structure in the South China Sea |journal=Geo-Marine Letters |date=2014 |volume=34 |issue=6 |pages=541–554 |doi=10.1007/s00367-014-0384-0|bibcode=2014GML....34..541M |s2cid=129982048 }}{{cite journal |last1=Kim |first1=H.J. |last2=Kim |first2=T.-W |last3=Hyeong |first3=K |last4=Yeh |first4=S.-W. |last5=Park |first5=J.-Y. |last6=Yoo |first6=C.M. |last7=Hwang |first7=J. |title=Suppressed CO₂ Outgassing by an Enhanced Biological Pump in the Eastern Tropical Pacific |journal= Journal of Geophysical Research: Oceans|date=2019 |volume=124 |issue=11 |pages=7962–7973 |doi=10.1029/2019JC015287 |bibcode=2019JGRC..124.7962K |s2cid=210611691 }}

{{multiple image

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| footer ={{space|10}} Sea surface DIC concentration (from GLODAP climatology)

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| image1 = Annual mean sea surface dissolved inorganic carbon for the 1990s (GLODAP).png

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| caption1 = {{center|"Present day" (1990s)}}

| image2 = Estimated annual mean sea surface dissolved inorganic carbon for the 1700s (GLODAP).png

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| caption2 = {{center|Pre-Industrial Revolution (1700s)}}

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File:Spatial distribution of ocean surface dissolved inorganic carbon.png 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]. }} Spatial distributions of DIC and nDIC. (a) DIC (normalized to year 2005); (b) salinity-normalized DIC (nDIC, DIC normalized to reference year of 2005 and salinity of 35) in the surface global ocean. The latitudinal trends are clear, particularly for nDIC.]]

=Carbonate pump=

The carbonate pump is sometimes referred to as the “hard tissue” component of the biological pump.{{cite journal |last1=Hain |first1=M.P. |last2=Sigman |first2=D.M. |last3=Haug |first3=G.H |title=The Biological Pump in the Past |journal=Treatise on Geochemistry |date=2014 |volume=8 |pages=485–517|doi=10.1016/B978-0-08-095975-7.00618-5 |isbn=9780080983004 }} Some surface marine organisms, like Coccolithophores, produce hard structures out of calcium carbonate, a form of particulate inorganic carbon, by fixing bicarbonate.{{cite book |last1=Rost |first1=Bjorn |last2=Reibessel |first2=Ulf |title=Coccolithophores and the biological pump: responses to environmental changes |date=2004 |publisher=Springer |location=Berlin, Heidelberg |isbn=978-3-642-06016-8}} This fixation of DIC is an important part of the oceanic carbon cycle.

:Ca²⁺ + 2 {{chem|HCO|3|-}} → CaCO₃ + CO₂ + H₂O

While the biological carbon pump fixes inorganic carbon (CO₂) into particulate organic carbon in the form of sugar (C₆H₁₂O₆), the carbonate pump fixes inorganic bicarbonate and causes a net release of CO₂.{{cite book |last1=Rost |first1=Bjorn |last2=Reibessel |first2=Ulf |title=Coccolithophores and the biological pump: responses to environmental changes |date=2004 |publisher=Springer |location=Berlin, Heidelberg |isbn=978-3-642-06016-8}} In this way, the carbonate pump could be termed the carbonate counter pump. It works counter to the biological pump by counteracting the CO₂ flux from the biological pump.

=Measurement=

Oceanographers and engineers continue to find novel and more accurate methods of measuring carbon content in seawater. One method is to collect water samples and directly measure the DIC by using a TOC analyzer.{{cite journal |last1=Raymond |first1=Peter A. |last2=Bauer |first2=James E. |title=Atmospheric CO₂ evasion, dissolved inorganic carbon production, and net heterotrophy in the York River estuary |journal=Limnol. Oceanogr. |date=2000 |volume=45 |issue=8 |pages=1707–1717|doi=10.4319/lo.2000.45.8.1707 |bibcode=2000LimOc..45.1707R |doi-access=free }} Samples can be combined with stable isotope ratios ¹³C/¹²C, alkalinity measurements, and estimation of physical processes, to create diagnostic techniques.{{cite journal |last1=Gruber |first1=Nicolas |last2=Kneeling |first2=Charles D. |last3=Stocker |first3=Thomas F. |title=Carbon-13 constraints on the seasonal inorganics carbon budget at the BATS site in the northwestern Sargasso Sea |journal=Deep-Sea Research Part I |date=1998 |volume=45 |issue=4–5 |pages=673–717|doi=10.1016/S0967-0637(97)00098-8 |bibcode=1998DSRI...45..673G }} Researchers at Scripps Institution of Oceanography developed a tool that uses flow injection analysis to measures microfluidic samples of seawater and continuously monitor dissolved inorganic carbon content.{{cite journal |last1=Bresnahan |first1=Philip J. |last2=Martz |first2=Todd R. |title=Gas Diffusion Cell Geometry for a Microfluidic Dissolved Inorganic Carbon Analyzer |journal=IEEE Sensors Journal |date=2018 |volume=8 |issue=6 |pages=2211–2217 |doi=10.1109/JSEN.2018.2794882|bibcode=2018ISenJ..18.2211B |s2cid=3475999 |doi-access=free }}

References

Category:Chemical oceanography

Category:Analytical chemistry