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Planet Earth's nine lives: Our planet's limits

Acid oceans: the seas are becoming hostile to animals with shells

You know what acid is, don't you? Vinegar is a weak acid but it burns your throat if you take a swig of it! Maybe you've heard that the oceans are getting more acid. Most people probably haven't and so don't know why it's happening or why it's important.

Carbon dioxide from the air dissolves in seawater and makes it more acidInformationNow for some simple chemistry!Fizzy water is made by squirting carbon dioxide into it under pressure. The CO2 dissolves in the water and when you take the top off the bottle, there's a fizz and lots of bubbles of CO2 form in the water. But this carbonated (=fizzy) water is a weak acid. So if you drop a sea shell from the beach into it, it will begin to dissolve in the acid. [Sea shells are made of the same stuff as limestone: a mineral called calcium carbonate. So are coral reefs and the shells of all shellfish.] The same happens with rain which absorbs CO2 from the air. And the same happens with the oceans. . With ever more CO2 in the air, more dissolves in the oceans so the more acid they become.

What does it matter if the oceans get a bit more acidic? There are 3 reasons

Shellfish and corals are animals which build their shells or skeletons out of calcium carbonateInformationWhat is calcium carbonate?This is a very common mineral which exists in two forms: calcite and aragonite, chemical formula CaCO3. Limestones are all made of it and it's useful because it 'locks away' carbon. Sea creatures which use it for their skeletons are helping to remove carbon from the air and sea. The animals make this by using calcium and CO2 both dissolved in the seawater. If the seas get too acid the sea creatures can't build their shells and skeletons and they will die. So these zillions of tiny creatures are providing us with a free means of getting carbon out of both the atmosphere and the sea and locking it away safely into what will become limestone rock (mostly calcium carbonate). The shell-building plankton whose tiny bodies sink to the bottom of the sea when they die also become another type of limestone rock.

The acidity of surface ocean waters - which is where all the planktonInformationWhy plankton are so importantPlankton are very tiny but very numerous; so numerous that you can see them from space when they form 'blooms'. They are bottom of the food chain which means that all larger sea creatures depend on them, directly or indirectly, for their food. Without plankton, there'd be no fish and no corals. and corals live - has increased by one third since humans started burning fossil fuels on a grand scale. Scientists reckon things will be critical in some oceans by mid-century. We are getting close to the boundary but we're not there yet. There's still time to stop the damage from happening. How? By quitting burning fossil fuels and getting the energy you need from other sources like renewables and nuclear power.



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