Like the bubbles on a soda bottle – how the Mediterranean returns carbon dioxide

If you watch the Mediterranean Sea from the coast of Israel, the water looks its usual way – blue and calm.

However, something strange is happening beneath the surface, reminiscent of the disappearance of carbon dioxide bubbles from a carbonated drink.

The process is called stratification – layering – the waters of the sea become like layers. The uppermost is overheated by the sun to the point that it cannot “mix” with the lower, cooler waters. As a result, the sea cannot dissolve carbon dioxide, as it does in other salty waters, and instead begins to release it.

The finding could be particularly alarming – about a quarter of the carbon emissions in the atmosphere are absorbed by the ocean. But if warming continues, that share could drop significantly.

The process is the same as what happens in a soda bottle.

“Usually you keep it cold so the dissolved gases stay that way. If you leave it warm and open it, all the gases will come out right away, because as it warms, the liquid’s ability to hold carbon dioxide decreases,” Bialik told The Wired. , a marine geoscientist at the University of Haifa, Israel.

Which means that in the eastern Mediterranean, where warming is 20% faster than the rest of the world, the sea is releasing large amounts of carbon dioxide.

Photo: iStock

However, Bialik and his colleagues have discovered something else – crystals of the mineral aragonite in sediments. Aragonite is a type of calcium carbonate that makes up the shells of ocean animals such as snails.

Aragonite can also form outside of living organisms, and its presence in this part of the Mediterranean indicates that the water is so warm that it releases carbon. Bialik and other marine geologists came to this conclusion, and the result was published in the journal Scientific Reports.

In this part of the Mediterranean, the surface water simply does not mix enough with the lower, cooler, oxygenated waters to cool the surface.

“The conditions are so extreme that we can chemically extract calcium carbonate from these waters,” says the scientist.

What happens is similar to what happens when a large amount of sugar is dissolved in water. Once it warms up and you run a string through it, pieces of crystals will stick to the string. In the same way, the water in the sea is saturated with carbonate.

It’s not clear what might come of this, but it’s possible that patches of crystals can form in the water – around dust cores from land or even around particles of microplastic, which the Mediterranean Sea is full of.

However, it is certain that as such crystals form, they also release carbon dioxide – about 15 percent of the total amount of gas that the sea releases into the atmosphere.

This leads to a decrease in the acidity of the water, which interferes with the organisms in it, as well as the reverse process, which occurs in the oversaturation with carbon dioxide and the increase in acidity.

Scientists are yet to study the problem in other waters.

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However, there are already “bleaching events” in which calcium carbonate becomes saturated in the water, so that it is visible to the naked eye – the water turns milky, as has already happened near the Bahamas and the Persian Gulf.

However, this has not been observed in the Mediterranean Sea, where carbonate is found in sediments.

“This is a unique area where you have the combination of conditions needed for this to happen. The question is to what extent is this environment really special or is it common to the rest of the sea and ocean,” says marine chemist Andrew Dixon from the California Scripps Institution of Oceanography. He does not have a clear answer to this question.

If it turns out that the saturation with aragonite is not isolated only in this part of the sea, the problem is big – it will be more and more difficult for the ocean to absorb carbon dioxide, which will accelerate the warming of the planet.


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