Researchers have already discovered severe levels of pteropod shell dissolution offsite link in the Southern Ocean, which encircles Antarctica.Įstimates of future carbon dioxide levels, based on business-as-usual emission scenarios, indicate that by the end of this century the surface waters of the ocean could have a pH around 7.8 The last time the ocean pH was this low was during the middle Miocene, 14-17 million years ago. When pteropod shells were placed in sea water with pH and carbonate levels projected for the year 2100, the shells slowly dissolved after 45 days. Pteropods are an important part of many food webs and eaten by organisms ranging in size from tiny krill to whales.

The pteropod, or 'sea butterfly,' is a tiny sea snail about the size of a small pea. If the pH gets too low, shells and skeletons can even begin to dissolve. However, as ocean acidification increases, available carbonate ions (CO32-) bond with excess hydrogen, resulting in fewer carbonate ions available for calcifying organisms to build and maintain their shells, skeletons, and other calcium carbonate structures. Ocean acidification is already impacting many ocean species, especially organisms like oysters and corals that make hard shells and skeletons by combining calcium and carbonate from seawater. Impacts of ocean acidification on shell builders The ocean’s average pH is now around 8.1 offsite link, which is basic (or alkaline), but as the ocean continues to absorb more CO 2, the pH decreases and the ocean becomes more acidic. Water and carbon dioxide combine to form carbonic acid (H 2CO 3), a weak acid that breaks (or “dissociates”) into hydrogen ions (H +) and bicarbonate ions (HCO 3 -).īecause of human-driven increased levels of carbon dioxide in the atmosphere, there is more CO 2 dissolving into the ocean.

Carbon dioxide and seawaterĬarbon dioxide, which is naturally in the atmosphere, dissolves into seawater. The pH scale is an inverse of hydrogen ion concentration, so more hydrogen ions translates to higher acidity and a lower pH. Anything higher than 7 is basic (or alkaline) and anything lower than 7 is acidic. The pH scale runs from 0 to 14, with 7 being a neutral pH. This process has far reaching implications for the ocean and the creatures that live there. When CO 2 is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions. As levels of atmospheric CO 2 increase from human activity such as burning fossil fuels (e.g., car emissions) and changing land use (e.g., deforestation), the amount of carbon dioxide absorbed by the ocean also increases. The ocean absorbs about 30% of the carbon dioxide (CO 2) that is released in the atmosphere.

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Examples of buffers in everyday life