The Mediterranean Sea is now so acidic that it dissolves plankton!

Effect of increase in CO₂ The atmosphere is not limited to global warming. We must remember that the interaction between air and ocean is particularly important. Thus, any increase in CO₂ impacts the environment chemistrychemistry Of the ocean. Since the Industrial Revolution, we assume 25% of CO₂ Emissions from human activities have been absorbed by the world’s oceans, resulting in a decrease in the pH of the water. In other words, it becomes an ocean. acidacid,

Better and better foraminifera tests

A development that is not without affecting marine fauna and flora. Among the organisms most affected, foraminifera. These unicellular planktonic species actually have a thin covering of calcium carbonate (we talk about a test). However, acids attack the limestone and promote its dissolution.

Critical situation in the Mediterranean

A new study, the results of which were published communication earth and environment, shows how serious the situation is becoming in the Mediterranean Sea, particularly affected by this increasing acidification. The pH has dropped by 0.08 units in a century. Degradation sufficient to affect the process of become hardbecome hard Foraminifera. Sediment analysis shows that since the Industrial Revolution, foraminiferal tests have gradually become better and better. a development that makes these microorganismsmicroorganisms is located at the base of food chainfood chain Too unsafe. Beyond plankton populations, therefore, all marine ecosystems find themselves threatened by this evolution of marine chemistry.

Ocean acidification hinders calcification of marine animals

article from Jean-Luc GaudetJean-Luc Gaudet Published March 11, 2009

According to an Australian study, tiny ShellsShells Tiny planktonic organisms, foraminifera, are about a third thinner than their ancestors. Researchers demonstrate that it is associated with an increase in the amount of thinning yardyard carbon dioxide inAtmosphereAtmosphere and resulting acidification of seawater. This is confirmation of a suspected but poorly quantified phenomenon.

The laws of chemistry easily explain why CO₂ (carbon dioxide or carbon dioxidecarbon dioxide) present in the atmosphere affects the acidity or alkalinity (we call pH) of sea water. When it dissolves, CO₂ Can react with it and give carbonate, HCO₃^, etcco₃^2-And ionsions h^,, i.e. acid. We would therefore expect an increase in atmospheric carbon dioxide content to result in a decline in pH (acidification) of the entire oceans, averaging slightly more than 8 (ocean water is slightly less so). alkalinealkaline,

We also know that organisms that survive in limestone formations struggle to reproduce in more acidic (or less alkaline) waters. This is the situation of corals, molluscsmolluscs With shells and many small creatures.

In practice and at the quantitative level, the question is much less clear. It is estimated that the pH of the global ocean has decreased by about 0.1 since pre-industrial times, from 8.16 to 8.01 and, importantly, continued increases in the atmospheric gas content carbon dioxide will drive it down further. The current results presented during the Eleventh Inter-Congress of Pacific Sciences, held in Papeete (Tahiti), lead us to believe that the average ocean pH may drop to 7.9 or 7.8 at the end of this century.

Ocean acidification is now under surveillance. Recently, four hundred researchers are working for ICRI (International Coral Reef Initiative) established a worrying assessment of the health of the planet’s corals and indicated the acidification of ocean waters as one of the factors of a significant regression (19% of corals have already disappeared). Last January, 150 researchers from around the world signed a text called monaco declaration And its purpose was to alert political decision makers to the problem of ocean water acidification and its rapid growth.

50,000 years of archives

The new Australian study contributes to this debate, which is growing in scope. William Howard, Andrew Moy and colleagues at the University of Tasmania (Antarctic Climate and Ecosystem Cooperative Research CenterACE CRC) has just published an article nature geology Showing the results of measuring the weight of small spheres (as we call testing). sea ​​urchinssea ​​urchins) Small planktonic organisms, globigerines. Like all foraminifera, these unicellular organisms protect themselves in limestone tests pierced by holes (or stomastoma, hence the name of the group). They are found almost everywhere in the planet’s oceans where they represent vast biomassbiomass And play a big role in carbon sequestration in the ocean. It is estimated that they represent between a quarter and half of the carbonate flux. Foraminifera in general and Globigerines in particular have existed for a very long time archaeologistarchaeologist They are highly appreciated because they can monitor populations over long periods of time.

The University of Tasmania team weighed in on the globigerin tests (Globigerina bulloides) of today and tomorrow, is found in marine sediments on the ocean floor AntarcticAntarctic, According to him, current Globigerin tests are 30 to 35% lighter than their ancestors! The team went ahead and – seemingly for the first time – demonstrated a relationship of more than 50,000 years between atmospheric carbon dioxide content and the thickness of the tests.

What conclusion to draw? At the biological level, the authors ignore the consequences of this thinness on survival speciesspecies And that of other foraminifera. Currently, globigerins haveAirAir to be well. On the other hand, at the global oceanic scale, declines in foraminiferal populations may affect ecosystemsecosystems and reduce the ability toabsorptionabsorption Carbon dioxide in the atmosphere.