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Dissolved inorganic carbon (DIC) is the sum of the aqueous species of
inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistr ...
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,
lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...
s, carbohydrates, and
nucleic acid Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main clas ...
s. Inorganic carbon is found primarily in simple compounds such as carbon dioxide, carbonic acid, bicarbonate, and carbonate (CO2, H2CO3, , respectively). Dissolved inorganic carbon (DIC) includes three major aqueous species, CO2, ,, and to a lesser extent their complexes in solution with metal ions.


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, , ). :CO2(aq) + H2O H2CO3 + H+ + 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. 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.


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. Dissolved inorganic carbon in the form of carbon dioxide is fixed into organic carbon is produced 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. :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). An efficient biological pump increases biological export to the deeper ocean which has been hypothesized to suppress CO2 outgassing in the upper ocean.


Carbonate pump

The carbonate pump is sometimes referred to as the “hard tissue” component of the biological pump. Some surface marine organisms, like
Coccolithophore Coccolithophores, or coccolithophorids, are single celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the king ...
s, produce hard structures out of calcium carbonate, a form of
particulate inorganic carbon Particulate inorganic carbon (PIC) can be contrasted with dissolved inorganic carbon (DIC), the other form of inorganic carbon found in the ocean. These distinctions are important in chemical oceanography. Particulate inorganic carbon is someti ...
, by fixing bicarbonate. This fixation of DIC is an important part of the oceanic carbon cycle. :Ca2+ + 2 → 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. 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 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. Samples can be combined with stable isotope ratios 13C/12C, alkalinity measurements, and estimation of physical processes, to create diagnostic techniques. 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.


See also

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Alkalinity Alkalinity (from ar, القلوي, al-qaly, lit=ashes of the saltwort) is the capacity of water to resist acidification. It should not be confused with basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength o ...
(total alkalinity; AT) *
Bjerrum plot A Bjerrum plot (named after Niels Bjerrum; sometimes also known as a Sillén diagram or a Hägg diagram) is a graph of the concentrations of the different species of a polyprotic acid in a solution, as a function of pH, when the solution is at ...
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Dissolved organic carbon Dissolved organic carbon (DOC) is the fraction of organic carbon operationally defined as that which can pass through a filter with a pore size typically between 0.22 and 0.7 micrometers. The fraction remaining on the filter is called partic ...
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Fugacity In chemical thermodynamics, the fugacity of a real gas is an effective partial pressure which replaces the mechanical partial pressure in an accurate computation of the chemical equilibrium constant. It is equal to the pressure of an ideal gas whi ...
(carbon dioxide fugacity; fCO2) *
Ocean acidification Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxide ...
* pH *
Total organic carbon Total organic carbon (TOC) is the amount of carbon found in an organic compound and is often used as a non-specific indicator of water quality or cleanliness of pharmaceutical manufacturing equipment. TOC may also refer to the amount of organic c ...


References

{{DEFAULTSORT:Total Inorganic Carbon Chemical oceanography Analytical chemistry