Dissolved inorganic carbon

"Present day" (1990s) sea surface DIC concentration (from the GLODAP climatology).

Pre-industrial (1700s) sea surface DIC concentration (from the GLODAP climatology).

The total inorganic carbon (C_T, or TIC) or dissolved inorganic carbon (DIC) is the sum of inorganic carbon species in a solution. The inorganic carbon species include carbon dioxide, carbonic acid, bicarbonate anion, and carbonate. It is customary to express carbon dioxide and carbonic acid simultaneously as CO₂* . C_T is a key parameter when making measurements related to the pH of natural aqueous systems, and carbon dioxide flux estimates.

C_T = [CO₂*] + [HCO₃⁻] + [CO₃²⁻]

where,

• C_T is the total inorganic carbon
• [CO₂*] is the sum of carbon dioxide and carbonic acid concentrations ( [CO₂*] = [CO₂] + [H₂CO₃])
• [HCO₃⁻] is the bicarbonate concentration
• [CO₃²⁻] is the carbonate concentration

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

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ ⇌ 2H⁺ + CO₃²⁻

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

Total inorganic carbon is typically measured by the acidification of the sample which drives the equilibria to CO₂. This gas is then sparged from solution and trapped, and the quantity trapped is then measured, usually by infrared spectroscopy.

See also

• Alkalinity (total alkalinity; A_T)
• Bjerrum plot
• Fugacity (carbon dioxide fugacity; f_CO2)
• Ocean acidification
• pH
• Total organic carbon