The Mediterranean Sea is so hot, it’s forming carbonate crystals


If you stand on the coast of Israel and gaze out across the Mediterranean Sea, you’ll spy deep-blue, calm waters that have sustained humans for millennia. Beneath the surface, though, something odd is unfolding: A process called stratification is messing with the way the sea processes carbon dioxide.

Think of this part of the Mediterranean as a cake made of liquid, essentially. Fierce sunlight heats the top layer of water that sits on cooler, deeper layers below. Out in the open ocean, where water temperatures are lower, CO2 dissolves in saltwater—which is what allows Earth’s seas to collectively absorb a quarter of the carbon emissions that humans pump into the atmosphere. But as the eastern Mediterranean Sea heats up in the summer, it can no longer absorb that gas and instead starts releasing it.

It’s the same thing that happens in a bottle of soda that is carbonated with carbon dioxide. “You usually keep it cold, so the dissolved gasses will stay dissolved,” says Or Bialik, a geoscientist at the University of Münster in Germany. “If you leave it in your car for a while and try to open it, all the gasses are going to pop out at once, because when it warms, the capacity of the fluid to hold CO2 goes down.” Boomfizz, you’ve got a mess on your hands. 

In the Eastern Mediterranean, this dynamic is rather more consequential for the climate than a sticky car interior, as the sea begins burping up great quantities of CO2 that the water can no longer hold. And Bialik and his colleagues have discovered that these warming, stratifying waters teem with a second carbon problem: The team recently caught aragonite crystals in sediment traps. Aragonite is a form of calcium carbonate, which oceanic creatures like snails use to build their shells. Except in the increasingly hot Eastern Mediterranean, the aragonite is forming abiotically. That’s another sign that the water is getting so warm that it’s releasing its carbon load.

In these hot, shallow, stable waters, the fluid on top doesn’t mix much with the underlying colder layers, in contrast to deeper parts of the ocean, where upwelling brings up cooler H2O. “The conditions are so extreme that we can definitely generate calcium carbonate chemically from these waters, which was kind of a shock for us,” says Bialik, who coauthored a recent paper describing the discovery in the journal Scientific Reports. (He did the research while at the University of Malta and University of Haifa.) “It’s basically like a beaker that sits there for a very long time, and it’s long enough to get these reactions going and start generating these crystals.”

Matt Simon, 4 October 2022, Wired. Full article.

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