New York: Researchers have discovered iridescent white pools containing high concentrations of carbon dioxide (CO2) at 250 metres depth in the waters off Greece’s Santorini island in the Aegean Sea.

Santorini is also the site of the second largest volcanic eruption in human history.

The results may answer some questions about deep sea carbon storage as well as provide a means of monitoring the volcano for future eruptions.

“The volcanic eruption at Santorini in 1600 B.C. wiped out the Minoan civilisation living along the Aegean Sea,” said one of the researchers, Rich Camilli, scientist at Woods Hole Oceanographic Institution (WHOI) in the US.

“Now these never-before-seen pools in the volcano’s crater may help our civilisation answer important questions about how carbon dioxide behaves in the ocean,” Camilli said.

The results were detailed in the journal Scientific Reports.

The researchers used a series of sophisticated underwater exploration vehicles to locate and characterise the pools, which they call the Kallisti Limnes, from ancient Greek for “most beautiful lakes.”

A prior volcanic crisis in 2011 had led the researchers to initiate their investigation at a site of known hydrothermal activity within the Santorini caldera.

During a preliminary reconnaissance of a large seafloor fault, the autonomous underwater vehicle (AUV) Girona 500 from the University of Girona in Spain identified subsea layers of water with unusual chemical properties.

The researchers then sent a smaller remotely operated vehicle (ROV) to sample the pools’ hydrothermal fluids.

“We have seen pools within the ocean before, but they have always been brine pools, where dissolved salt released from geologic formations below the seafloor creates the extra density and separates the brine pool from the surrounding seawater,” Camilli said.

“In this case, the pools’ increased density is not driven by salt – we believe it may be the carbon dioxide itself that makes the water denser and causes it to pool.”

Sensors installed by the team showed that the Kallisti Limnes temperature was five degree Celsius above that of surrounding waters.

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