Part of a series on the
Carbon cycle
By regions Terrestrial Marine Atmospheric Deep carbon Soil Permafrost Boreal forest Geochemistry
Carbon dioxide In the atmosphere Ocean acidification Removal Satellite measurements
Forms of carbon Total carbon (TC) Total organic carbon (TOC) Total inorganic carbon (TIC) Dissolved organic carbon (DOC) Dissolved inorganic carbon (DIC) Particulate organic carbon (POC) Particulate inorganic carbon (PIC) Primary production marine Black carbon Blue carbon Kerogen
Metabolic pathways Photosynthesis Chemosynthesis Calvin cycle Reverse Krebs cycle Carbon fixation C3 C4
Carbon respiration Ecosystem respiration Net ecosystem production Photorespiration Soil respiration
Carbon pumps Biological pump Martin curve Solubility pump Lipid pump Marine snow Microbial loop Viral shunt Jelly pump Whale pump Continental shelf pump
Carbon sequestration Carbon sink Soil carbon storage Marine sediment pelagic sediment
Methane Atmospheric methane Methanogenesis Methane emissions Arctic Wetland Aerobic production Clathrate gun hypothesis Carbon dioxide clathrate
Biogeochemical Marine cycles Nutrient cycle Carbonate–silicate cycle Carbonate compensation depth Great Calcite Belt Redfield ratio
Other Climate reconstruction proxies Carbon-to-nitrogen ratio Deep biosphere Deep Carbon Observatory Global Carbon Project Carbon capture and storage Carbon cycle re-balancing Territorialisation of carbon governance Total Carbon Column Observing Network C4MIP CO2SYS
Category
v t e

Total inorganic carbon (C_T orTIC) is the sum of the inorganiccarbon species.

Carbon compounds can be distinguished as eitherorganic orinorganic, anddissolved orparticulate, depending on their composition. Organic carbon forms the backbone of key components of organic compounds such asproteins,lipids,carbohydrates, andnucleic acids. Inorganic carbon is found primarily in simple compounds such ascarbon dioxide (CO₂),carbonic acid (H₂CO₃),bicarbonate (HCO−3), andcarbonate (CO2−3).

The aquatic inorganic carbon system is composed of the various ionic, dissolved, solid, and/or gaseous forms of carbon dioxide in water. These species includedissolved carbon dioxide,carbonic acid,bicarbonateanion,carbonate anion,calcium carbonate,magnesium carbonate, and others. The relative amounts of each species in a body of water depends on physical variables including temperature and salinity, as well as chemical variables like pH and gas partial pressure. Variables like alkalinity and dissolved (or total) inorganic carbon further define a mass and charge balance that constrains the total state of the system.^[1][2]

Given any two of the four central inorganic carbon system parameters (pH, alkalinity, dissolved inorganic carbon, partial pressure of carbon dioxide) the remainder may be derived by solving a system of equations that adhere to the principles ofchemical thermodynamics.^[2]

For most of the 20th century, chemical equilibria in marine and freshwater systems were calculated according to various conventions, which led to discrepancies among laboratories' calculations and limited scientific reproducibility.^[3] Since 1998, a family ofsoftware programs calledCO2SYS has been widely used. This software calculatechemical equilibria foraquaticinorganic carbon species and parameters. Their core function is to use any two of the four central inorganic carbon system parameters (pH,alkalinity,dissolved inorganic carbon, andpartial pressure of carbon dioxide) to calculate various chemical properties of the system. The programs are widely used byoceanographers andlimnologists to understand and predictchemical equilibria in natural waters.^[4]

The inorganic carbon species includecarbon dioxide,carbonic acid,bicarbonateanion, andcarbonate.^[5] It is customary to express carbon dioxide and carbonic acid simultaneously asCO₂*.C_T is a key parameter when making measurements related to thepH of natural aqueous systems,^[6] and carbon dioxide flux estimates.

${\displaystyle C_T=[{\text{CO}}_2^{\star }]+[{\text{HCO}}_3^{-}]+[{\text{CO}}_3^{2-}]}$

where,

• C_T is the total inorganic carbon
• [CO₂*] is the sum of carbon dioxide and carbonic acid concentrations ([CO₂*] = [CO₂] + [H₂CO₃])
• [HCO−3] is the bicarbonate concentration
• [CO2−3] is the carbonate concentration

Each of these species are related by the following pH-driven chemical equilibria:

The concentrations of the different species of DIC (and which species is dominant) depends on the pH of the solution, as shown by aBjerrum plot.

Total inorganic carbon is typically measured by theacidification of the sample which drives theequilibria toCO₂. This gas is thensparged from solution and trapped, and the quantity trapped is then measured, usually byinfrared spectroscopy.

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 (HCO⁻
  ₃), carbonate (CO²⁻
  ₃) 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 toparticulate organic carbon (POC) through photosynthesis andchemoautotrophy (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 inwhiting events. Marine fish also excrete calcium carbonate duringosmoregulation.^[7]

Some of the inorganic carbon species in the ocean, such asbicarbonate andcarbonate, are major contributors toalkalinity, a natural ocean buffer that prevents drastic changes in acidity (orpH). 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.^[8]

• Chemical oceanography
• Analytical chemistry
• Carbon

• CS1 maint: location missing publisher
• Articles with short description
• Short description matches Wikidata
• Pages that use a deprecated format of the chem tags