Dissolved Inorganic Carbon (DIC)

Inorganic carbon refers to the carbonate buffer equilibrium system in water due to the presence of carbon dioxide in the atmosphere. While there is on the order of 500 Gigatonnes of carbon dioxide in the atmosphere, two orders of magnitude MORE is dissolved in the ocean as DIC. The chemical equilibrium:

CO2 + H2O = H2CO3 = H+ + HCO3- = 2H+ + CO3(2-)

This equilibrium system describes that at left there is a balance between carbon dioxide in the atmosphere and dissolved in water as “carbonic acid” or H2CO3; and at right there is a balance between carbonate ions {CO3(2-)} and bicarbonate ions {HCO3-} that involves hydrogen ions (measured by pH). In the contemporary ocean, the majority of carbon is present as bicarbonate ions at pH of about 8.0. As more carbon dioxide dissolves, it forms more carbonic acid which produces more hydrogen ions and the pH tends to decline. This is the fundamental process of ocean acidification.

DIC content of seawater measured by Lueker, T.J., C.D. Keeling, P.R. Guenther, M. Whalen, and W.G. Mook. Inorganic Carbon Variations in Surface Ocean Water near Bermuda. UC San Diego: Scripps Institution of Oceanography. Inorganic Carbon Variations in Surface Ocean Water near Bermuda, 1998. Average: 2045 umol/kg

mass of Earth’s oceans = 1.37E21 kg
mass of DIC = 2045 umol/kg x 12E-9 kg C/umol x 1.37E21 kg = 3.3E16 kg = 33000 Gt as carbon
equivalent mass of CO2 = 33000 Gt x (44 g CO2/12 g C) = 121000 Gt as CO2

{equilibrium constants? fresh or sea?}{carbonate mineral equilibrium}{silicate weathering}