Ocean acidification

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The increase in the terrestrial atmosphere’s carbon dioxide levels causes a chemical change in oceans. This consequence is often neglected. Not only are oceans warming up, they are also absorbing gases from the atmosphere including carbon dioxide. And because they cover 71% of the Earth’s surface area, they absorb large amounts of if: almost half of the carbon emitted in the atmosphere since the beginning of the Industrial Revolution in the 18th century has been absorbed by oceans.

The more carbon dioxide there is in the atmosphere, the more of it is dissolved in the oceans. And this affects the cellular metabolism of all types of marine life: when it reacts with water, this excess gas turns into carbonic acid. The acidity of sea water has thus increased by 30% since the beginning of the Industrial Revolution.

The danger is not that seas could become corrosive. The pH (potential Hydrogen) that measures acidity is always higher than 7 – the “neutral” value -, and there is plenty of leeway before it goes below this. But many marine organisms which have a skeleton or a limestone shell are already finding it harder to calcify. This means they are finding it harder to extract the minerals that they need from the surrounding environment. This action depends on the environment’s acidity.

The entire ocean food chain is affected, from phytoplankton to zooplankton, molluscs to starfish and crab to coral. According to researchers, the phenomenon is going to get worse and the disappearance of several species could disrupt marine ecosystems. Indeed, plankton photosynthesise and even though they only represent less than one percent of the planet’s biomass, they absorb almost as much carbon dioxide and produce as much oxygen as all terrestrial vegetation. Acidification adds to global warming. It bleaches coral reefs and ultimately leads to their death. Yet, they provide food and shelter for a quarter of marine species.


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