Ocean acidification is the process by which oceanic waters progressively become more and more acidic, mostly as a result of absorption of atmospheric carbon dioxide. To put that another way, as atmospheric carbon dioxide levels increase, the process of ocean acidification will increase as well. To a point anyways.

Acidic in this case is actually something of a slight misnomer, though, as the “acidification” is actually more of a move to pH-neutral conditions, from the generally slightly basic (pH >7) condition’s of the earth’s oceans.

This move to pH-neutral conditions will have a profound impact on the myriad lifeforms found within the oceans though, as witnessed during previous ocean acidification events such as “The Great Dying” (~252 million years ago), rather than being a trivial process.

Impacts that can be reliably expected are: major changes to plankton distribution, types, and numbers; increasingly common mass coral bleaching events; associated extinctions; depressed metabolic rates and immunity in some types of marine animals, as well as behavioral changes; fishery collapses; and increasingly common red tide events.

To go back over that earlier point a bit more — seawater is generally slightly basic (pH>7), as it absorbs carbon dioxide (CO2) from the atmosphere, or from elsewhere (carbon seeps, etc), some of the absorbed CO2 reacts to form carbonic acid (H2CO3), and leads as well to carbonate (HCO3−) and bicarbonate (CO32−) formation. The carbonate and bicarbonate formation results in increased hydrogen ion (H+) concentrations in the ocean water (acidity) — as they are the “leftovers” of the formation process.
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