Water > Ocean Acidification > Glossary

Glossary of Terms

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pH is related to the concentration of hydrogen ions [H+] in a solution. The pH scale runs from 0 to 14; a value of 7 is neutral; less than 7 is acidic; greater than 7 is basic. Like the Richter scale, the pH scale is logarithmic. This means that a pH of 6 is ten times more acidic than a pH of 7.

pCO2 refers to the amount of dissolved carbon dioxide in seawater. The pH of seawater is affected by pCO2; the higher the pCO2, the lower (more acidic) the pH.

ppm means ‘parts per million’

Hypoxia is the depletion of dissolved oxygen in water. This condition results from an overabundance of nutrients of human or natural origin that stimulates the growth of algae, which in turn die and require large amounts of oxygen as the algae decompose.

Saturation State (Ω) is a measure of the tendency of a mineral, such as calcium carbonate (CaCO3), to dissolve in water. At Ω values greater than 1, CaCO3 does not readily dissolve. Most calcifying organisms live in such waters. The Ω of CaCO3 declines with depth and temperature.

Upwelling is the replacement of surface ocean water by colder, saltier, nutrient and CO2-rich but oxygen-poor, intermediate-depth ocean water.