Ocean Acidification

February 14th, 2019

Ocean Acidification

Ocean acidification is caused by an influx of C02

A rise in CO2 increases the number of hydrogen ions in the water, reducing pH and CO32- levels

CO2 + H2O <–> H2CO3

H2CO3 <–> (H+) + HCO3-

HCO3- <–> (H+) + CO32-

*this reaction can shift either way

At an oceanic pH of 8.3, carbonate levels are high enough for coral building. As CO2 increases and pH decreases, carbonate levels will quickly drop below optimum levels.

Calcium carbonate, CaCO3, is a necessary ingredient in building corals, shells and exoskeletons for many aquatic creatures.

As CO2 levels increase, the availability of carbonate (CO3²⁻ )  decreases

As CO3²⁻ levels decrease, it becomes more difficult for marine creatures to build their shells.

CO2 + H2O + CO3²⁻ <–> 2HCO3-

Stony corals begin to bleach and deteriorate as carbonate ion and pH levels fall.

Carbon Dioxide levels have rapidly increased since the industrial revolution from both natural and anthropogenic sources, putting stress on marine organisms’ ability to survive.

In the last 100 years, this increase in CO2 has increased the hydrogen ion concentration in the World’s oceans by 26%1

As atmospheric CO2 increases, dissolved CO2 will increase and the pH of water will decrease. (data: NOAA/ESRL and University of Hawaii; credit: SERC EarthLabs)

Since 1989, the spectrophotometric pH method has been used due to its far greater accuracy1

Spectrophotometric pH measurements are taken by adding a pH-sensitive dye into a water sample. This dye changes color as the pH fluctuates

Then a spectrophotometer measures the light from an LED as it passes through the dyed water. The wavelength absorption characteristics of the dye give an indicator of the pH of the water sample2

While the oceans will never become “acidic” (with a pH of less than 7), even decreasing pH a slight amount stresses saltwater organisms and increases mortality rates

Although ocean acidification proves to be a threat to coral reef communities, scientists around the world have begun to combat this problem.

For instance, the Central Caribbean Marine Institute (CCMI) have created coral nurseries around the Cayman Islands to assist a new generation of corals.

Organizations around the world have also adopted this strategy, and are joining in the fight to save coral reefs from ocean acidification.



1.NOAA. (n.d.). Retrieved February 21, 2019, from https://www.pmel.noaa.gov/co2/story/Quality of pH Measurements in the NODC Data Archives

2.Leibniz Institute for Baltic Sea Research. (n.d.). Retrieved February 21, 2019, from https://www.io-warnemuende.de/spectrophotometric-ph-measurements.html

3.Loucaides, S., Rèrolle, V. M., Papadimitriou, S., Kennedy, H., Mowlem, M. C., Dickson, A. G., . . . Achterberg, E. P. (2017, May 30). Characterization of meta -Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures. Retrieved February 21, 2019, from https://www.nature.com/articles/s41598-017-02624-0

All references can be viewed in the reference section of the Fondriest Environmental Website “Learning Center” under “References”



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