The Mediterranean Sea is so hot that carbonate crystals are formed

It’s also worth noting that the Mediterranean Sea is one of the most microplastic-contaminated bodies of water in the world: in 2020, scientists reported finding 2 million particles in a single square meter of sediment that was just 5 centimeters thick. Bialik does not know whether aragonite crystals form around microplastics that float in the water column. “They could probably form around any nucleation center,” Bialik says. “I suspect that microplastics are also possible. But as scientists like to say, more research is needed.”

What Bialik and his colleagues can What we can say, however, is that when these crystals form, they produce CO . hand off2. So much so, Bialik calculates, that they make up perhaps 15 percent of the gas emitted by the Mediterranean into the atmosphere.

As the sea warms and its CO . loses2both the regurgitation of the water and the expanding crystals really dissipate its acidity down. This is the opposite process to the process that causes widespread ocean acidification: as humans use more CO. spit out2 in the atmosphere, the oceans absorb more of it, and the resulting chemical reaction increases acidity. Acidification makes it more difficult for organisms such as corals and snails (which are collectively known as calcifiers), to build shells or exoskeletons from calcium carbonate. But as the Mediterranean warms and releases its absorbed carbon back into the atmosphere, it becomes basic, reversing that acidification.

That should be good for the calcifiers, right? Not necessary. “Many of them have specific temperature ranges in which to build their shells — not too hot, not too cold,” Bialik says. So even if the sea becomes less acidic as it gets warmer, that heat puts a different strain on these organisms. (Not to mention the stress of being constantly exposed to extreme levels of microplastics.)

It is not clear whether aragonite crystals form in more places in the world. Scientists are already aware of “whiting events,” where calcium carbonate precipitates in much more obvious ways, turning the waters around the Bahamas and in the Persian Gulf a milky color. In the Eastern Mediterranean, Bialik and his colleagues had no apparent whiting event. Instead, they stumbled upon the crystals in their sediment traps.

“This is a somewhat unique area with a variety of conditions needed for this to work,” said marine chemist Andrew Dickson of the Scripps Institution of Oceanography, who was not involved in the study. “The question then is, to what extent is that environment really special, or is it common around the oceans? And I don’t have a clear picture of that.”

Conditions in the eastern Mediterranean may not be replicated in many other places, so Dickson is leaning towards the idea that this may not be particularly common. But Bialik points out that wherever it happens, it could create a climate problem: The formation of aragonite crystals could disrupt the water’s ability to absorb atmospheric CO.2thus interfering with how the ocean lowers the levels of the planet-warming gas.

“I won’t say we fully understand this yet and fully understand what it controls — when it turns on and when it shuts down,” Bialik says. “We didn’t even think that this process would take place on this scale in open water, under normal marine conditions. And so we still have a lot to understand about it.”

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