Ocean Acidification Threatens Marine Ecosystems

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Since the beginning of the industrial era, the world's oceans have absorbed approximately one quarter of all carbon dioxide emissions produced by human activity, a process that has provided a significant buffer against even more rapid atmospheric warming but has simultaneously triggered a profound and accelerating chemical transformation of marine environments known as ocean acidification. When carbon dioxide dissolves in seawater it reacts with water molecules to form carbonic acid, which subsequently dissociates to release hydrogen ions, measurably reducing the pH of ocean water and decreasing the availability of carbonate ions that countless marine organisms depend upon to construct their calcium carbonate shells and skeletal structures. Since pre-industrial times, the average pH of surface ocean water has already declined from approximately 8.2 to 8.1, a seemingly modest shift that nonetheless represents a forty percent increase in hydrogen ion concentration due to the logarithmic nature of the pH scale. Coral reefs are among the most severely threatened ecosystems, as acidifying conditions impair the calcification processes of reef-building corals, weakening existing structures and preventing the growth necessary to keep pace with natural erosion. Shellfish, sea urchins, pteropods, and certain species of plankton are similarly vulnerable, and since many of these organisms occupy foundational positions within marine food webs, their decline carries cascading consequences for the productivity and biodiversity of entire ocean ecosystems upon which billions of humans depend for nutrition and economic livelihood.