Introduction to Ocean Acidification


Mona Loa (Hawaï) time series shows a clear increase in atmospheric CO2 concentration.

Modern human activities require lot of energy mainly based on burning of fossil fuels, releasing vast quantities of extra carbon dioxide (CO2) to the Earth’s atmosphere. A proportion of this stays in the atmosphere, raising atmospheric CO2 levels, but much leaves the atmosphere after a time, either to become sequestered in trees and plants or to become absorbed in the ocean. Increasing atmospheric CO2 cause the well known global warming (with other greenhouse gas). In the ocean, this CO2 increase cause the “other CO2 problem”: ocean acidification. The figure on the right, is a very famous atmospheric CO2 time series. Since 1958, in Hawaï atmospheric pCO2 is measured and we clearly see an increase in this isolated island. If you want to learn more about Past, Present and Futur changes click here.


Sceme of the different chemicals species of carbon in the seawater.

When it dissolves in the ocean, CO2 changes the chemistry of the water, making it more acidic. As a result the pH of surface water has fallen by 0.1 units since the industrial revolution, the period in which human activities become high producers of CO2. The illustration on the left, show the “carbonate chemistry system”. More explanation on chemistry here.

How will ocean acidification impact biology and biogeochemistry?

Under the surface, many organisms are living. From virus to whales through phytoplankton and fishes. The impacts of ocean acidification on marine ecosystems are still poorly known but one of the most likely consequences is the slower growth of organisms forming calcareous skeletons or shells, such as corals and molluscs (mussels, oysters, …). More studies have to be done, in laboratories and in situ to understand why and how OA will modify or not biology. You can learn more about the processes and worries here.