Ocean acidification

Ocean acidification is the ongoing decrease in seawater pH, driven mainly by ocean uptake of atmospheric carbon dioxide. It also reduces the availability of carbonate ions used by many marine organisms to build shells and skeletons.

Ocean carbonate system: The linked chemical equilibria among dissolved carbon dioxide, bicarbonate, carbonate, and hydrogen ions in seawater. It explains how added carbon dioxide lowers pH and shifts carbonate availability.
Pteropods: Small swimming marine snails whose shells are commonly made of aragonite. Their thin aragonite shells can show damage in waters with low saturation states.
Hawaii Ocean Time-series: A long-running program measuring physical, chemical, and biological conditions in the North Pacific near Hawaii. Its repeated measurements document rising dissolved carbon and declining pH in open-ocean waters.
Ocean deoxygenation: The decline of dissolved oxygen in ocean waters. It often co-occurs with acidification but involves oxygen loss rather than declining pH.
Carbon dioxide dissolution in seawater: The physical and chemical transfer of carbon dioxide from the atmosphere into seawater. This transfer supplies the carbon that drives most modern ocean acidification.
Coral reefs: Marine ecosystems built primarily by calcium-carbonate-producing corals. Acidification can slow reef framework construction, compounding other stresses on corals.
Ocean Observatories Initiative: A US research program using instruments and platforms to collect sustained ocean observations. Its coastal and deep-sea sensors help track changing carbonate chemistry over time.
Ocean warming: The long-term increase in the ocean’s heat content and temperature. Warming is a distinct carbon-driven stressor that can interact with acidification.
Carbonic acid: A weak acid formed when dissolved carbon dioxide reacts with water. Its formation begins the seawater reactions that increase hydrogen-ion concentration.
Oyster hatchery: A facility that breeds and raises oysters, often producing larvae for aquaculture. Some hatcheries have faced larval losses when intake water becomes corrosive to young shells.

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