What is ocean acidification? What causes it? What are its consequences? How can ocean acidification be reduced?
Ocean acidification is the gradual decline in the pH of the oceans. This acidification is the result of the pollution that’s particularly, directly or indirectly, caused by human action. As the ocean becomes more and more acidic, oceanic ecosystems start getting affected.
In this way, we can say ocean acidification is a complex phenomenon with multiple consequences for the global ecosystem equilibrium. In fact, more and more scientists are worried about the acceleration of ocean acidification.
Like all fluids, the oceans have a pH, i.e., a hydrogen potential. This pH is a way of measuring the activity of the hydrons in the fluid, i.e., the degree of acidity and basicity of the liquid. While a low the pH means a more acidic fluid, the higher the pH the more alkaline it is.
The average pH of the oceans is normally around 8.25: this is this level that allows for optimal development of marine life as we know it today. The problem is that for several decades, the pH of the oceans tends to decrease: it has now a pH of around 8.14.
The causes of oceans’ acidification are manifold. The three main ones are:
It is mainly the CO2 absorbed by the ocean that’s responsible for the global acidification of the oceans. Indeed, since the industrial revolution, human societies have been releasing significant amounts of greenhouse gases, prominently CO2, in the atmosphere, causing, among other things global warming. But all this CO2 does not stay in the atmosphere: some of it is absorbed by plants and trees, but most of it is absorbed by the oceans (about a third).
CO2 gradually dissolves in the water and this produces (among other things) carbonic acidic which reduces the pH of the water. For 250 years the ocean has absorbed hundreds of millions of tons of CO2 globally, and all this CO2 surplus has greatly contributed to increase the oceans’ level of acidity.
Human activities and in particular agricultural activities contribute to the emission into the atmosphere of large quantities of nitrogen compounds, represented in particular by N 2 O (nitrous oxide). When these nitrogenous compounds dissolve in the ocean, they also have acidifying properties and contribute to the global acidification of the oceans.
Compared to the acidification caused by the increase in CO2 emissions, that generated by the disruption of the nitrogen cycle is rather low, but it is starting to become a subject of concern, especially near shorelines where agricultural activities are important.
Acidification is a serious ecological problem. Although a drop of 0.1 pH point may seem derisory in itself, such a change can have significant consequences on the ecosystem.
One of the major consequences of ocean acidification is that it affects the ability of ocean plankton to renew. Indeed, many species of plankton need a specific pH to grow. If the pH is too low (the ocean is too acidic) these species no longer manage to structure their calcareous skeletons and have trouble developing.
But plankton is at the base of the marine ecosystem. It serves as a foundation for the food chain, but most importantly, it contributes to the oxygenation of the oceans. And, by extension, plankton also contributes to the production of oxygen in the atmosphere.
In summary: the more acidic the ocean becomes, less plankton there is growing and less oxygen is produced for the oceanic and atmospheric equilibrium. Ultimately, if plankton populations collapse, this could affect the amount of oxygen in the air we breathe.
In the same way, scientists believe that ocean acidification affects corals. Corals are animals with often calcareous structures, which are the basis of ecological environments very rich in biodiversity: the coral reefs. Like plankton, in an acidic environment, the coral finds it harder to develop its calcareous structures, making it more vulnerable.
It’s believed that much of the world’s coral degradation is attributable to ocean acidification. By disappearing, coral often takes away with it a whole ecosystem of fish, algae and endemic organisms that constitute an important chain of the marine world.
Acidification of ocean waters also has diverse impacts on marine biodiversity. Fish, crustaceans, algae and marine organisms all react differently to the evolution of pH.
Scientists have shown that some fish experience changes in their behavior or metabolism when the pH decreases. Some stay more fragile, and others start having trouble finding their food and leave to other places, disturbing the local balance.
For now, it is difficult to assess all the effects of ocean acidification on marine life, but it is likely to have very significant long-term consequences.
Ocean acidification may also have other consequences for marine ecosystems which are still hard to perfectly understand. From ocean circulation to crustacean mortality, toxicity or erosion, ocean acidification is a systemic ecological threat that is sometimes hard to quantify.
The main way of fighting ocean acidification is to reduce CO2 emissions of human origin. If the amount of CO2 released into the atmosphere decreases, the CO2 dissolved in the ocean will also decrease, which will slow down the acidification phenomenon.
As well, limiting nitrogen and sulfur emissions is also a way to reduce ocean acidification, although the impact of these releases is minimal compared to the impact of CO2.
The problem is that these measures involve redefining our economic system in depth. Indeed, to reduce global CO2 emissions, we must massively reduce our energy consumption, change our consumption patterns, and reduce our dependence on fossil fuels. It is, therefore, a real ecological transition project that needs to be implemented urgently.
In 2014, a study conducted by a team of researchers at Columbia University’s Lamont-Doherty Earth Observatory sought to map the phenomenon of ocean acidification around the globe.
The results show that all the oceans of the planet are affected by the phenomenon. Geographically, it is particularly the equatorial zones and the oceans closer to the poles that are affected. The equatorial Pacific is largely affected but more significantly in its northern part, close to the Russian and North American coasts. Overall, the areas near the coast are strongly affected by ocean acidification.