Scientists have discovered opal pools of high carbon dioxide concentration within the volcanic crater of Santorini, located in the Aegean Sea near Greece, at a depth of 250 m. Santorini is the site of the second largest volcanic eruption in human history. The eruption wiped out the Minoan civilization along the Aegean Sea in 1600 B.C.
This is one of the most active areas of the Hellenic Volcanic Arc. A volcanic arc is a chain of volcanoes strung together, much like the Japanese islands or the Aleutian islands above a subduction zone (where two tectonic plates collide and the more dense plate slides under the less dense plate). In this case, the African plate is subducting under the Eurasian plate.
These newly discovered opalescent pools called Kallisti Limnes (Greek for “Beautiful lake”) may give us information on deep sea carbon storage and monitoring future volcanic eruptions. Geologists have seen pools within the ocean before, but they are usually brine pools, where excess salt is introduced into the seawater from geologic formations. The saltier, more dense water stays separated from the surrounding, less salty seawater.
In this case, carbon dioxide is believed to be making the water denser and separating it from the surrounding seawater. The carbon dioxide is likely a byproduct of the subduction zone that the volcano sits atop. The opal pools have a low pH, making them very acidic, suggesting that the opal was formed from silica-based organisms (such as diatoms), rather than calcite-based organisms (like most seashells and coral).
Geologists knew that carbon dioxide was released into the ocean during subduction events, but they thought that when it was released into the ocean it was even distributed throughout the water. This is the first time that they are seeing the carbon dioxide pool and collect in groups. The implications of these finding are extremely timely because more studies are suggesting that deep sea carbon storage is an acceptable means of trapping the greenhouse gas and not allowing it to be released into the atmosphere.