Carbon dioxide, seawater chemistry, pH, carbonic acid, hydrogen ions, carbonate ions, aragonite, calcification, shellfish, corals, pteropods, plankton, coastal acidification, nutrients, monitoring, fisheries, and climate change
Ocean acidification
Ocean acidification is the long-term decrease in ocean pH caused mainly by seawater absorbing carbon dioxide from the atmosphere.
What ocean acidification is
Ocean acidification is a long-term reduction in seawater pH. It happens as the ocean absorbs carbon dioxide from the atmosphere, changing the balance of dissolved carbon compounds in seawater.
How carbon dioxide changes seawater
When carbon dioxide dissolves in seawater, chemical reactions form carbonic acid, bicarbonate, and hydrogen ions. More hydrogen ions lower pH and reduce the amount of carbonate ions available to many shell-building organisms.
Why pH matters
The pH scale measures how acidic or basic a solution is. Seawater is naturally slightly basic, so acidification does not mean the ocean has become acid. It means ocean chemistry is shifting toward lower pH.
Effects on shells and skeletons
Many corals, oysters, clams, mussels, plankton, and pteropods use calcium carbonate minerals to build shells or skeletons. Acidification can make calcification more energy-intensive and, under some conditions, can help shells dissolve.
Food webs and fisheries
Ocean acidification can affect organisms at the base of marine food webs and species important to fisheries and aquaculture. Effects vary by species, life stage, local water chemistry, food supply, temperature, and other stressors.
Coastal acidification
Coastal waters can acidify for additional reasons, including nutrient pollution, algal blooms, respiration, freshwater inputs, upwelling, and local circulation. These local drivers can combine with global carbon dioxide uptake.
Monitoring and adaptation
Scientists monitor pH, alkalinity, dissolved carbon dioxide, carbonate saturation, temperature, salinity, and biological responses. Hatcheries, fisheries, and coastal managers use monitoring to reduce risk and plan adaptation.
Why it matters
Ocean acidification links climate change with marine chemistry, food webs, reefs, shellfish, and coastal economies. Reducing carbon dioxide emissions addresses the main global driver, while local pollution control can reduce added stress in coastal waters.