The oceans generate much of the air we breathe, absorb greenhouse gases, provide economic livelihoods for millions of people, and are also fundamental to the planet's weather and climate systems and the carbon cycle. For this reason, the profound alteration of their chemical composition due to human activities has become a major problem. Since the late 1980s, 95% of open ocean surface waters have become more acidic because they have absorbed a considerable amount of carbon dioxide (CO2), which has increased to a volume 50% higher than before the industrial revolution.
What is acidification?
The pH is a value that represents the degree of acidity or alkalinity of a liquid solution. It indicates the concentration of hydrogen ions (H+) and hydroxyl ions (OH-) on a scale from 0 to 14.
Pure water has a pH = 7 and is neutral, i.e. it is neither acidic nor alkaline as it has identical H+ and OH- concentrations. Solutions with a pH < 7 are acidic and those with pH > 7 are alkaline.
This is a logarithmic scale in which the acidity increases 10 times with each decrease of one pH unit. For example, a solution with a pH = 3 is 10 times more acidic than a solution with a pH = 4, and if you still don't get the idea, take a look at the picture below:
The ocean is slightly alkaline and, before the industrial revolution, its average pH was 8.2. Today, that figure is 8.1. This does not seem like much of a difference, but it means that the oceans today are 30 percent more acidic than they were then. According to the Intergovernmental Panel on Climate Change (IPCC), by the end of the 21st century, the pH of the oceans will be around 7.8, i.e. 150% more acidic.
What will be the consequences?
Acidification decreases the concentration of carbonate ions (CO32-), a compound that some organisms, such as oysters, crabs, sea urchins, lobsters, and corals, need to form and regenerate their shells and skeletons, which also wear out more easily as pH decreases.
Also, because marine organisms invest energy in coping with a more acidic environment, they may not have enough energy for physiological processes such as reproduction and growth, affecting food chains and the balance of ecosystems.
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