Acidification Alters Ocean Chemistry and Calcification

Acidic ocean water decreases the ability of aquatic organisms to form shells or exoskeletons, while also dissolving the shells and coral that have already been formed. Normal seawater has an average pH of around 8.2, meaning it is slightly basic.

Carbon dioxide (CO₂) acidifies the ocean. Atmospheric CO₂ levels rise as humans use fossil fuels and increase deforestation.

CO₂ enters the ocean from the atmosphere. In the ocean, CO₂ reacts with water. The result is bicarbonate (HCO₃^-) and a hydrogen ion (H⁺). As H⁺ ions are released, the ocean acidifies and the pH drops.

Meanwhile, other reactions occur in the ocean to form the shells of marine species. Carbonate (CO₃^2-) binds with calcium (Ca²⁺) to form the calcium carbonate of shells.

As oceans acidify H⁺ ions, instead, react with CO₃^2- ions and shells grow more slowly.

Increasing acid levels also attack shells that have already been formed. Shells release calcium and HCO₃^-, become thin, and disintegrate.