What is ocean acidification?
Ocean acidification refers to a reduction in the pH of ocean water, caused primarily by uptake of carbon dioxide from the atmosphere, but also by other chemical additions or subtractions from the ocean.
Limacina helicina, a free-swimming planktonic snail. These snails, known as pteropods, form a calcium carbonate shell and are an important food source in many marine food webs. As levels of dissolved carbon dioxide in seawater rise, skeletal growth rates of pteropods and other calcium-secreting organisms will be reduced due to the effects of dissolved carbon dioxide on ocean acidity. Image courtesy of Russ Hopcroft, UAF/NOAA. Download image (jpg, 38 KB).
For many years, carbon dioxide (CO2) in Earth’s atmosphere has been increasing due to anthropogenic (human-caused) emissions. Currently the ocean is a “sink” for CO2, meaning it absorbs more CO2 than it releases. Because of this, 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.