Ocean acidification

Science

Definition

Ocean acidification is the ongoing decrease in ocean pH caused by the absorption of excess atmospheric CO₂. When CO₂ dissolves in seawater, it forms carbonic acid, which releases hydrogen ions and lowers pH. This threatens marine organisms that build calcium carbonate shells and skeletons.

Examples

  • Coral reefs weakening as lower pH reduces their ability to build calcium carbonate skeletons
  • Oyster larvae failing to form shells in acidified waters along the U.S. Pacific coast
  • Pteropods (sea butterflies) showing dissolving shells in acidic Southern Ocean waters
Key Fact

Ocean pH has dropped from ~8.2 to ~8.1 since the Industrial Revolution — a 26% increase in acidity.

Related Terms

Climate change Greenhouse effect Ph scale Biogeochemical cycles

Study This Concept

Practice ocean acidification with free review games in these units:

AP Environmental Science Unit 9: Global Change