To explain what is ocean acidification is important to understand basic concepts about basic chemistry. pH is a measure of how acidic/basic water is. The range goes from 0 to 14, with 7 being neutral. pHs of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base. pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water.

In relation to the ocean, the average pH of ocean surface water fell from 8 to 8.3. this feature is due to the greenhouse gases that are in the atmosphere, mainly Carbon Dioxide (CO₂₎, due to the high absorption capacity of CO₂ emissions from the oceans themselves, it is estimated that there is approximately 60 times more CO₂ in the oceans than in the atmosphere.

Nevertheless, the CO₂ absrobed by oceans, reacts with seawater and forms carbonic acid that acidifies the ocean. This would make the ocean more acidic that any time in the past and this is a dangerous trend because is more difficult for preserve the resilience of marine ecosystems.

Therefore, the effect of acidification in the oceans is the result of CO₂ emissions to the atmosphere from human activities, this increase in parts per million of CO₂ is absorbed by the oceans and has led to a decrease in the pH of seawater.

While pH decreases, the availability of carbonate decreases at the same time and it produce changes in the chemistry composition of ocean water.

Original video source:
https://sos.noaa.gov/Datasets/view-movie.html?video=ocean_acid_ph_400

Thus, ocean acidification occurs when high concentrations of CO₂ are absorbed by the oceans, a portion of the carbon dioxide reacts with water to form carbonic acid (H₂CO₃), one of the hydrogens of carbonic acid separates and generates hydrogen ions (H⁺) and bicarbonate ions (HCO₃). Most of that H+ combines with carbonate ion (CO₃), to form more bicarbonate ions HCO₃ , el cuál genera un desequilibrio en la calcificación de algunos organismos como corales, moluscos para formar conchas y otras partes duras.  A medida que el océano absorbe más CO₂, prevents the absorption of CO₃ due to the large amount of hydrogen ions associated with this compound.

Calcium carbonate (aragonite, one of the crystallized forms of CaCO₃), is the main building compound for coral skeleton structure, and provides food, shelter and substrate for other organisms, therefore, corals have been vulnerable to climatic changes, including ocean acidification which reduces the concentration of carbonates that corals need to build their skeletons due to the association with the availability of hydrogen ions present in the ocean.

Aragonite saturation in tropical climates is higher than in polar climates because of the CO₂ is more soluble in cold water. The saturation of aragonite in relation to the increase in high concentrations of CO₂ over the ocean, as well as the increase in ocean surface temperature has led to a decrease in the saturation of aragonite in the oceans, this problem will continue until the necessary chemical conditions of the carbon cycle stabilize with respect to its concentrations, and can maintain stable carbonate ion availability for the calcification of some marine organisms, otherwise, the carbonate ion may disappear as we exceed the concentrations of CO₂  above the atmosphere above 550 ppm.

Original video source:
https://sos.noaa.gov/Datasets/view-movie.html?video=ocean_acid_ph_400

In addition to the rate of calcification, growth and reproduction, ocean acidification affects the symbiotic relationship of the algae Zooxanthellae and their productivity of this association, acidification has contributed more to bleaching events than to the decrease in the rate of calcification, in some laboratory studies the high concentrations of CO₂ and the increase in temperature have reduced the calcification rate and productivity of these ecosystems.

Some studies indicate that high-dose CO₂ and decreased pH disrupt photoproductive mechanisms in zooxanthellae chloroplasts and produce low rates of photorespiration, and increased light levels in some experiments, combined with solar radiation and increased concentrations of CO₂ induce bleaching events.

Whitening, Puerto Morelos, Mexico. Photo: Ximena Lizaola