Ocean Acidification

By Frank Hall

Scientists who study the Earth describe it as a series of interconnecting components or “systems”. These systems are dynamic, and changing aspects of one system can result in dramatic changes in another. The interconnectivity between the oceanic and atmospheric systems is perhaps the most studied of the Earth Systems and is also of greatest concern among Earth and environmental scientists. In particular, as we express concerns about human activities increasing carbon dioxide in the air, the oceanic system will adapt, perhaps in ways that are negative to us as human beings. The most well known interaction between air and ocean is the documented set of reactions is between water (H2O) and carbon dioxide (CO2).

The chemical reactions between water and carbon dioxide are important for determining the pH of the oceans. Many people remember that pure water has a pH of 7, acids, like vinegar, have pH values less than 7, and bases, such as ammonia, have pH values greater than 7. The oceans, overall, are slightly basic, or alkaline, with a pH vale of ~8.1. The reactions between water and carbon dioxide produce two important compounds: bicarbonate (HCO3-: basic) and carbonic acid (H2CO3: acidic). In “normal” ocean waters, bicarbonate will be more abundant than carbonic acid. However, increasing carbon dioxide concentrations will cause the chemical reactions to favor the creation of carbonic acid.

Why should we care? Coral reef organisms build their shells from calcium carbonate (CaO + CO2 = CaCO3) minerals which remain solids in basic solutions. You can see in the chemical composition of these minerals that carbon dioxide (CO2) is contained within it. Coral reefs are literally taking the gas, CO2, from the air and converting it into a solid. As a solid, it no longer contributes to “global warming”. But, in acidic solutions, these minerals tend to dissolve. Also, many of the world’s fisheries rely on coral reefs as breeding grounds for important food species. Ocean acidification has the potential of ruining these breeding grounds resulting in declines of fisheries.

Of course, many other organisms make their shells out of CaCO3, such as clams and oysters. And, important oxygen-producing organisms, such as coccolithophorids not only convert CO2 to oxygen by photosynthesis, but store CO2 in their shells. The White Cliffs of Dover, for example, is comprised largely of the remains of ancient coccolithophorids. Therefore, our knowledge of the potential impacts of ocean acidification is vital to our understanding of how human beings may be affecting our climate.

Frank Hall, Ph.D. in Oceanography, University of Rhode Island, M.S. in Geology, Lehigh University, & B.A. in Earth Science/Geology, Kean University of New Jersey. Dr. Hall resides in Germantown, Maryland and periodically contributes articles to the Center.


See also: Oceanography