We know that carbon dioxide concentrations are increasing in Earth’s atmosphere, and that this will increase temperatures on our planet. But, rising CO2 will have another effect—making the oceans more acid.
When carbon dioxide dissolves in water, it creates a weak solution of carbonic acid. That’s why carbonated beverages are slightly acidic. Chemists measure the acidity using a pH scale. A neutral pH is 7.0. Acid solutions are lower. The pH of club soda is between 3.0 and 4.0, and the pH of lemon juice is about 2.0.
Seawater at the ocean’s surface has an alkaline pH of about 8.1. But as CO2 from the atmosphere dissolves in seawater, it will become less alkaline. Already, long-term measurements show that the pH of seawater has dropped about 0.1 units in the past 15 years.
That sounds small, but carbonate minerals, such as those that form the shells of marine organisms and coral, need high pH to form. A lower pH will cause a number of these organisms to go extinct, particularly in high latitude, cold waters, where CO2 is especially soluble in seawater.
Corals may be the first to disappear, followed coccolithophores. Most of us have never seen these creatures, but they are an important part of the marine food web. At times in the Earth’s past, when the oceans were acid, the geologic record shows a dramatic decline in these organisms.
The oceans can no longer be seen as an infinite source of dilution, and action must be taken to ensure that acidification does not leave an irreversible imprint on marine life.
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Photo, taken on March 31, 2013, courtesy of MLU Fotos via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.