Future Model Projections of Ocean Acidification Markers

Carbonate Chemistry

The different carbonate chemistry species involved in the ocean acidification process are presented here, in its individual form as well as the chemical reactions leading to the production of hydrogen ions and hence changes in seawater pH.

Bicarbonate Ions

Bicarbonate is an intermediate form of the carbonic acid. It has a negative charge. It is soluble in water and it is the dominant form of dissolved inorganic carbon in seawater and therefore and important sink in the global carbon cycle.

Hydrogen Ions

Hydrogen ions cannot exist freely in solution and it bonds quickly with other compounds and molecules. It is charged positively. It is commonly known also as Hydron, as a positive ion of any hydrogen isotope.

Carbon Dioxide

Formed by a carbon atom bonded to two oxygen atoms, it is produced in a variety of environments such as volcanoes, hot springs and carbonate rocks. It can be also found in seawater, groundwater, rivers, lakes and ice sheets. Deposits of petroleum and natural gas also contain carbon dioxide.


Water is formed by two atoms of hydrogen bonded to one atom of oxygen. It is the most abundant substance on Earth in its three states of matter (solid, liquid and gas). Under standard conditions water is basically a liquid.

Carbonic Acid

Once carbon dioxide is dissolved in water, it becomes carbonic acid. In seawater, carbonic acid exists in equilibrium with carbon dioxide. Its two protons can be dissociated from the parent molecule, forming bicarbonate ion and a hydrogen ion.

CO2 + H2O  =  H2CO3

The first reaction is that of producing carbonic acid when carbon dioxide is dissolved in water.

H2CO3 =   HCO3- + H+

The second reaction takes places when the carbonic acid dissociates into bicarbonate ion and hydrogen ions.

H+ + CO3 = HCO3

Ultimately, hydrogen ions can combine with carbonate ions and generate molecules of bicarbonate ions. The removal of the available carbonate hampers the development of shells by marine organisms that require carbonate to build their shells.