Ocean Acidification

Class notes:

The Ocean and Carbonate Chemistry

Acidity is a measure of H+ concentrations;  the more free H+ ions, the lower the solution’s pH and the greater the acidity.  Temperature change by itself cannot add H+ ions.  Where do they come from?

CO2 + H2O –> H2CO3

Carbon dioxide + water → carbonic acid

H2CO3→ H+  +  HCO3-

Carbonic acid almost instantly dissociates in seawater, releasing H+ ions and bicarbonate molecules.

H+  +  HCO3- → 2 H+  +  CO32-

The bicarbonate ions also dissociate, releasing additional hydrogen ions and forming carbonate ions.

Marine organisms that build calcareous shells use calcium carbonate in the form of the minerals, calcite or argonite.  That calcium carbonate is formed when some of the free bicarbonate ions react calcium ions in the water to form calcium bicarbonate, which is then used to form calcium carbonate, with carbonic acid as a byproduct.

Ca+2 + 2HCO3- → Ca(HCO3)2

Ca(HCO3)2→  CaCO3  +  HCO3  +  H+