The pH scale is a chemical property that measures a substance’s acidity or alkalinity, ranging from 0 to 14. A pH of 7 is neutral; values below 7 are acidic, and values above 7 are alkaline (basic). This measurement helps understand natural systems’ chemical environment.
Understanding Ocean pH
Ocean water is naturally alkaline, with a typical pH range of 8.0 to 8.3. Its chemical stability comes from a natural buffering system, primarily dissolved inorganic carbon like carbonate and bicarbonate ions. This system regulates pH by neutralizing excess acids or bases, keeping it relatively stable.
When carbon dioxide dissolves in seawater, it forms carbonic acid, which then dissociates into hydrogen ions and bicarbonate ions. The presence of carbonate ions acts as a buffer, preventing large fluctuations in pH. This inherent alkalinity supports the ocean’s chemical balance and marine life.
Life Thrives on pH Balance
The ocean’s pH is important for the survival and well-being of marine life. Marine organisms are sensitive to minor pH fluctuations. Many species, including corals, shellfish, and plankton, use carbonate ions for calcification, building their shells and skeletons. These structures are primarily composed of calcium carbonate.
When pH shifts, carbonate ion availability decreases, making it harder for calcifying organisms to build and maintain their protective structures. Even small pH changes impact growth, reproduction, and survival of marine species. This delicate balance supports the intricate web of marine ecosystems.
The Changing Ocean pH
Ocean water is naturally alkaline, but its pH is gradually decreasing due to human activities, known as ocean acidification. This change is primarily driven by the ocean’s absorption of excess atmospheric carbon dioxide (CO2), largely from fossil fuel burning. The ocean has absorbed about 30% of CO2 released since the Industrial Revolution.
When CO2 dissolves in seawater, it forms carbonic acid. This acid releases hydrogen ions, increasing water acidity and lowering pH. Surface ocean pH has already fallen by about 0.1 units, a 30% acidity increase since pre-industrial times. Projections indicate surface ocean pH could further decrease, potentially reaching around 7.8 by century’s end.
This ongoing pH shift has significant consequences for marine ecosystems. Calcifying organisms like corals, oysters, clams, and pteropods struggle to build and maintain shells and skeletons due to reduced carbonate ion availability and increased acidity. This leads to slower growth, weakened structures, and even dissolution of existing shells. Such impacts ripple through marine food webs, affecting fish populations and threatening overall biodiversity and ecosystem function.