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The need for action in response to ocean acidification

Underwater sun through the water surface seen from a rocky bottom.
Credit: Damsea / Shutterstock
Soleil sous-marin à travers la surface de l'eau vue depuis un fond rocheux.
  • Soleil sous-marin à travers la surface de l'eau vue depuis un fond rocheux.
  • Nos émissions de CO2 acidifie les océans.
  • CO2 d’origine volcanique à l’île d’Ischia, Italie, une fenêtre ouverte sur notre futur?
The need for action in response to ocean acidification

If this last year of pandemic has in fact taught us anything, it’s that we’re able, all together, to take strong action to get us out of a crisis situation.

We can do the same in tackling the environmental crisis ‒ the troubling increase in our greenhouse gas emissions, that is, including especially CO2. The amount of atmospheric CO2 climbed from 310 ppm (parts per million) in 1950 to 405 ppm in 2017. If nothing is done, we could reach 900 ppm in 2100.

We can be gratified that the oceans capture from 25 to 30 percent of the surplus CO2, which accounts for 25 million tons of CO2 per day. Without that effect, we’d reach a rate of atmospheric CO2 of 460 ppm (instead of 405 ppm), and the consequences for the global climate would be even more severe. Unfortunately, the continually greater increase in the amount of CO2 dissolved in the oceans comprises a very serious threat for marine ecosystems by bringing about their acidification.

Ocean acidification, the other CO2 problem

Ocean acidification happens when CO2 is in contact with water molecules. That chemical reaction produces among other things carbonic acid and H+ hydrogen ions affecting the acidity of seawater: that acidity has risen by 30 percent over the last 100 years, with the pH dropping from 8.2 to 8.1. And that’s just the start of a curve that could take us, in 2100, to a rise in acidity of 170% (its pH at that point would be 7.8), with catastrophic effects for marine ecosystems.

Consequences of acidification

With seawater acidity, H+ hydrogen ions are more numerous in the environment. But that surplus causes a drop in carbonate (CO3-2) ions. And these, when bonded with Ca2 + (calcium) ions, are essential for a number of marine organisms, entering into the composition of their carapaces, their shells or their “limestone” skeletons (aragonite). Among those animals should be mentioned almost all mollusks (mussels, oysters, clams, scallops, periwinkles, etc.), crustaceans (crabs, lobsters, shrimp, krill, etc.), many echinoderms (urchins and starfish), and corals. The dearth of carbonate ions risks producing first of all a thinning of the shell or the carapace, then a reduction in it. The animal will have to expend more energy for making it, which translates to weaker size and reproduction rate.

The estimate is that coral reefs form ecosystems that support 25 percent of marine species. The acidity level anticipated for 2100 risks producing the complete dissolution of the coral reefs and the disappearance of the species that depend on them.

Plankton forms the basis of the oceans’ food web. However, an important part of this is threatened by ocean acidification. As it happens, a number of planktonic forms also produce a shell or “limestone” carapace highly sensitive to acidity change. Among these we find numerous marine invertebrate larvae that must go through this free stage to complete their life cycle.

As for fish and squid, they’ll have to expend more energy to avoid too significant a concentration of CO2 in their blood. In consequence, they have less energy available for their growth and their reproduction. Moreover, this state may lead to a weakening of the immune system and alter their senses (hearing and smell). These animals need calcium carbonate to manufacture their statoliths, essential elements for their balance and orientation.

Acting for the future

The current excessive consumption of fossil fuels is in the process of causing a serious environmental crisis, and at a speed far superior to the other major crises that the Earth has known. On the other hand, we’ve also seen what solidarity and determination can do to overcome crises that affect us. The environmental crisis threatening us is even more important. Will we be able to demonstrate the same energy and the same determination in acting together for our future?

To find out more:

Ocean acidification by Fisheries and Oceans Canada

Ocean acidification. by Smithsonian

Ocean acidification - The other CO2 problem. by Tom Marshall. 5 January 2009 UK research and Innovation (Natural Environment Research Council)

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