Climate, in the Mediterranean there is a new threat

Climate, in the Mediterranean there is a new threat


Looking at the Mediterranean Sea from the coast of Israel, you can see the calm, deep blue waters that have sustained human life for millennia. Under the surface, however, a strange phenomenon is taking place: a process called stratification is altering the way in which the sea processes carbon dioxide (CO 2).

We must think of this part of the Mediterranean as a a kind of liquid cake. Sunlight heats the most superficial level of the water, under which there are colder and deeper layers. In the open ocean, where temperatures are lower, CO 2 dissolves in salt water, allowing the Earth's seas to absorb a total of a quarter of the carbon dioxide emissions that humans release into the atmosphere. But when it warms up in the summer, the eastern Mediterranean Sea is no longer able to absorb CO 2 and instead begins to emit.

Worrying signs

It is the same thing that happens in a bottle containing a carbonated drink: "Usually it is stored in the cold, so that the dissolved gases remain so - explains Or Bialik, a geoscientist at the University of Münster, Germany - if you leave it in the car for a while and then try to open it, all the gases will come out in one fell swoop, because when it heats up, the capacity of the fluid to retain CO 2 decreases ".

In the eastern Mediterranean, this dynamic has much more relevant effects for the climate, since the sea begins to emit large quantities of carbon dioxide, which water can no longer to hold back. As if that weren't enough, Bialik and his colleagues found that these warm, layered waters present a second problem: recently, the team found aragonite crystals in sediment traps. ].

Aragonite is a form of calcium carbonate, which ocean creatures such as sea snails use to build their shells. The problem is that in the increasingly hot eastern Mediterranean, aragonite is forming in an abiotic environment, another sign that the water is getting so hot that it releases its CO 2 load.

In these warm, shallow waters, the surface fluid does not mix as much with the colder layers below, unlike in the deeper areas of the ocean, where the rising phenomenon brings colder water. "The conditions are so extreme that from these waters we can certainly generate calcium carbonate chemically, which was a bit of a shock to us," says Bialik, co-author of a recent article on the discovery published in Scientific Reports magazine. a beaker stood there for a long time, long enough to trigger these reactions and start generating these crystals. "

When it warms up and stratifies, the Mediterranean becomes saturated with carbonate. Bialik and his colleagues are still unable to say exactly how the reactions that lead to the formation of aragonite occur. However, it is possible that the process begins with particles - for example dust grains - which are carried by the wind from the mainland and on which the aragonite layers crystallize.

The effects

It should also be noted that the Mediterranean Sea is one of the most microplastic polluted water bodies in the world: in 2020, scientists reported finding 2 million particles in a single square meter of sediment only 5 centimeters thick.

Bialik doesn't know if aragonite crystals are forming around the microplastics floating in the water column. What Bialik and his colleagues are able to say with certainty, however, is that when these crystals are formed, they emit carbon dioxide. So much so that, according to Bialik's calculations, they are responsible for the 15 percent of CO 2 that the Mediterranean Sea emits into the atmosphere.

When the sea heats up and releases carbon dioxide, both from water and from the crystals, its acidity decreases. This is the opposite of the process that is causing the widespread acidification of the oceans: when humans release more carbon dioxide into the atmosphere, the oceans absorb more carbon dioxide in turn, and the resulting chemical reaction increases acidity. . Acidification makes it more difficult for organisms such as corals and snails (collectively also known as calcifiers) to build calcium carbonate shells or exoskeletons. But as it warms up and releases previously absorbed CO 2 into the atmosphere, the Mediterranean becomes more basic, reversing the acidification process. This shouldn't necessarily be good for calcifiers. "Many of them have specific temperature ranges in which they can build their shell: neither too hot, nor too cold," explains Bialik. So even though the sea becomes less acidic with warming, the heat disturbs these organisms in a different way.

A phenomenon to be better understood

It is not clear whether aragonite crystals are also forming in other areas of the world. Scientists are already aware of the phenomenon known as whiting, in which calcium carbonate gives the waters around the Bahamas and the Persian Gulf a milky color. In the Eastern Mediterranean, however, no obvious similar events were recorded.

"This is a rather unique area and there are a number of conditions that must occur for this to happen - points out marine chemist Andrew Dickson of the Scripps institution of oceanography, who was not involved in the research - the question that arises is: to what extent is this environment really special? Or is it common to all oceans? clear idea about it ".

It may be that the conditions of the eastern Mediterranean are not replicated in many other areas of the planet. So Dickson is inclined to the idea that this environment is not particularly common. But Bialik points out that wherever it occurs, it would pose a potential problem for the climate: the formation of aragonite crystals could hinder the ability of water to absorb atmospheric carbon dioxide, thus interfering with how the ocean reduces. the levels of the gas that warms the planet.

"I cannot say that we fully understand the phenomenon yet and that we understand what governs it, when it is determined and when not - continues Bialik -. We did not even think that this process is would occur on this scale in open water, under normal marine conditions. So we still have a lot to understand. "

This content originally appeared on US.

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