For many years, carbon dioxide (CO2) in Earth’s atmosphere has been increasing. Regardless of the reasons for this increase, the ocean is a “sink” for CO2, so as levels of atmospheric CO2 have increased, dissolved carbon dioxide in the ocean has increased as well.
When CO2 is absorbed by seawater, chemical reactions occur that reduce seawater pH, carbonate ion concentration, and saturation states of biologically important calcium carbonate minerals. These chemical reactions are termed "ocean acidification."
Calcium carbonate minerals are an important building block for the skeletons and shells of many marine organisms. Decreases in carbonate ions can make building and maintaining shells and other calcium carbonate structures difficult for calcifying organisms such as oysters, clams, sea urchins, shallow water corals, deep-sea corals, and calcareous plankton.
Changes in ocean chemistry can affect the behavior of non-calcifying organisms as well. For example, the ability of certain fish, like pollock, to detect predators is decreased in more acidic waters, and recent studies have shown that decreased pH levels also affect the ability of larval clownfish to locate suitable habitat.
Ocean acidification is currently affecting all ocean areas, including coastal estuaries and waterways. As the pace of ocean acidification accelerates, scientists, resource managers, and policymakers continue to recognize the urgent need to strengthen science as a basis for sound decision making and action.