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The Chemistry

Coastal and ocean acidification chemistry involves three main components that are found in the ocean and coastal zone, both naturally and through human contributions. These component, seen below, are Carbon Dioxide, Water, and Carbonate Ions. Acidification can occur when the naturally occurring chemical reactions are thrown off balance. Read below for a primer on acidification chemistry. More resources can be found on our Resources Page.


NOAA Ocean Acidification Program

When carbon dioxide (CO2) is absorbed by seawater (H2O), it forms carbonic acid (H2CO3). Carbonic acid quickly breaks apart to form hydrogen ions (H+) and bicarbonate (HCO3-). The amount of hydrogen ions in the seawater will tell us the pH, or how acidic or basic the water is. When there are more hydrogen ions, the water becomes more acidic, ultimately through the production of free hydrogen ions that are released from bicarbonate. It is important to note that seawater will still be basic for the foreseeable future, but as we add CO2 the pH goes down. Carbon dioxide can come from many sources but one is from the burning of fossil fuels. The changes to seawater chemistry caused by absorption of carbon dioxide from the atmosphere is called ocean acidification. 


NOAP Pacific Marine Environmental Laboratory

There is naturally a lot of carbonate in seawater, which absorbs (attaches to) hydrogen ions to buffer against changes in pH. Antacids actually do the same thing for our stomachs. Freshwater, from the coastal ocean, doesn't have a lot of carbonate (or "antacids"). This is why freshwater runoff can cause large swings in pH. Large storm events or impervious surfaces (like concrete that prevents rain from being absorbed into the ground) can contribute to large influxes of freshwater that temporarily lower the pH. 

CO2 not only comes from the atmosphere, it also comes from mixing with deep waters from off the shelf. Deeper waters have higher concentrations of CO2 because over time, organic material is decomposed and CO2 is released during this process called respiration. Mixing and upwelling are the physical processes that bring the CO2 onto the self either from the coastal zone or deep waters. Conversely, CO2 can also be exported to the open ocean as water moves offshore due to tides or wind. 

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