Ocean’s acidification

The ocean is deeply connected with our history. The first Homo sapiens villages started near the coasts, and even now most of towns and villages are closed to a water source of some type. Some studies even go further by saying that living next to a water source has therapeutic powers.

But before that, let’s first remember that the oceans cover about 71% of our planet; and they produce about 70–80% of the oxygen in the atmosphere thanks to all the marine plants.

What is acidification ?

Today, human activities are threatening this amazing asset that we have, and destabilize the fragile ecosystem in place.

To understand that, we need to remember that one of the mission of the ocean — other than regulating the climate thanks to marine currents and feeding a huge part of humanity — is to absorb a part of the carbon dioxide in the atmosphere.

Currently it is ¼ of the total carbon emissions that are absorbed by the ocean. And when the carbon dioxide dissolves the pH of the water drop, making the water more and more acidic. We are talking about a rise in acidity of 30% in the last 200 years. And we are expecting a decrease in the pH levels of 0,3–0,4 units before the end of the century. To give you an idea, if the pH levels of a human being decrease by the same units death may occur.

But this acidification of the oceans is by some extend a natural phenomenon. In fact carbon dioxide is a natural chemical element produced by all living beings. And Mother Nature did prepared a process to limit the acidification. This compensating phenomenon is called the “buffering effect”. We all know that rivers go to the ocean, and rivers drag dissolved chemicals from rocks encountered on their way and these waters rejected in the ocean allow to balance out the pH levels. Unfortunately today’s carbon emissions are way higher than what the ocean can absorb even with the buffering effect.

The impact on the ocean life ?

This acidification of the ocean waters has a massive impact on the marine life. To dig in this direction, we need to understand how marine life interacts with its immediate environment, and to do so let’s see a bit of chemistry.

We said earlier that a proportion of carbon emissions is absorbed by the ocean. And this carbon dioxide doesn’t just disappear in the immensity of the big blue. But instead breaks down into smaller molecules. And these molecules interact with marine species.

For instance, the acidification of the seawater causes the dissolution of the shells of some marine animal. But even when it doesn’t cause the dissolution, it prevents marine animals to develop at their full size and rate. The explanation here is also on chemistry. Marine species are sensitive to acidity when it comes to building their skeletons. The shells of those animals are made of a major component: calcium carbonate (CaCO3); and to make this component, marine creatures combine a calcium ion with carbonate. But unfortunately, when carbon dioxide dissolves in seawater extra hydrogen ions are produced; and these hydrogen ions tend to match better with carbonate than calcium ions do resulting in the formation of bicarbonate ion (HCO3-). And marine creatures cannot extract the component they need from the bicarbonate ion, so it is way harder for them to build their shell in an acidic environment. Worst: if the proportion of hydrogen ions is much higher than carbonate proportion, those hydrogen ions will break down existing calcium carbonate (shells) to bond with carbonate; so already existing shells will eventually dissolve.

Some animals are adapting but they have to spend more energy on building their shell or skeleton, and if they managed to do so the growth rate is slower than the usual average. Moreover all of this extra energy spent, and extra time is not spent on doing something else… like reproducing. And in the end animals become smaller, fewer, and we human on top of the pyramid, fiercely eating what Mother Nature may give us are left hungry with a growing population.

acespace.org

Different species are threatened by this phenomenon, such as coral, by limiting their growth and corroding them. Even though some coral can use bicarbonate to develop their skeleton, which give them an extra option, other threats such as pollution or warming water have an even bigger impact on their weakened organism. Other animals such as mussels or oysters will be much smaller by the end of the century (25% smaller for mussels and 10% for oysters).

And it goes the same for fishes that have to spend more energy on balancing out their pH level, having less energy to escape predators (they are less able to smell them) and less time to look for food and a partner, resulting in smaller and fewer fishes…

futurity.org

What’s next ?

Now we understand that overall ocean acidification has negative effect on the ocean life, and most of the time a very negative one. If nothing is done the situation is going to keep deteriorate and ocean full of fishes, shells and corals will become a memory fading away.

One of the solutions will be to cut or drastically reduce carbon emissions. But this seems unrealistic, it has been years that countries and companies have engaged themselves to reduce their emissions but no real result has been seen. Mostly because carbon emissions are a global problem, meaning every single individual, company, and country has to make efforts to achieve results.

But with our today’s technology and biological knowledge others solutions appear. They all can be gathered under the same category: geoingeniering.

One idea would be to use phytoplankton to absorb that excess of carbon dioxide. In fact, phytoplanktons is already feeding on carbon dioxide and store it in their shell and when they die (each of them have a life spent of a couple of days) they sink down on the ocean floor, and become sediments.

And we know how to create « bloom » of phytoplankton by adding specific fertilizers in the oceans and emphasize this natural process.

earthobservatory.nasa.gov : phytoplankton bloom

However, we do not know if increasing these populations will have the expected effect and will cause no harm to other marine species, and if the deep seawater will then keep a balanced pH level or become more acidic. And the fact that phytoplankton reproduces so fast (700 generations in 1 year) can let us hope for a natural evolution…

Maybe Mother Nature will figure out the solution for us. But we need to be conscious of the imbalance we have brought to the ocean and try to reduce our impact on it, so that, hopefully, the situation doesn’t get worst. In the meantime individual actions can be taken to have a more positive impact on the environment globally, such as reduction of plastic use, switch to a more plant based diet and reasonable use of polluting means of transportation.