Ocean acidification is a process in which the pH of the ocean decreases over an extended period of time, caused primarily by the uptake of carbon dioxide (CO2) from the atmosphere. When CO2 is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions. This increase causes the seawater to become more acidic and causes carbonate ions to be relatively less abundant. Carbonate ions are an important building block of structures such as sea shells and coral skeletons. Decreases in carbonate ions can make building and maintaining shells and other calcium carbonate structures difficult for calcifying organisms such as oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton.
The primary cause of ocean acidification is carbon dioxide emissions from human activities, with atmospheric carbon dioxide levels exceeding 410 ppm (in 2020) . Oceans absorb about 30% of the CO2 that is released in the atmosphere, and as levels of atmospheric CO2 increase, so do the levels in the ocean. This process is making it harder for marine calcifiers to build a shell or skeletal structure, endangering coral reefs and the broader marine ecosystems.
Ocean acidification is already impacting many ocean species, especially organisms like oysters and corals that make hard shells and skeletons. It is affecting the entire worlds oceans, including coastal estuaries and waterways, and threatens marine ecosystems, which also affects populations who rely on the ocean as a source of income and diet.
