A team of scientists on board the Irish research ship Celtic Explorer has discovered deep-sea organisms that feed off methane and toxic hydrogen sulphite and survive without sunlight.

The researchers have nicknamed the area “Chimney-henge” because of the resemblance of the circular arrangement of the carbonate chimneys in the volcanic deep seabed area to England’s Stonehenge.

The Irish Times reports that the research cruise, named Deep-Links, mapped the sea floor in the Iberian peninsula’s Gulf of Cadiz and used the Marine Institute’s remotely operated vehicle ROV Holland I to gather biological, geological and chemical samples.

The expedition, which included researchers from  NUI Galway, Galway-Mayo Institute of Technology and the Geological Survey of Ireland, was led by Dr Jens Carlsson of University College Dublin, who said they aimed to explore and take samples from mud volcanoes.

The toxic mud volcanoes are similar to volcanoes on land, but instead of lava, they emit liquefied mud with methane and hydrogen sulphite. The volcanoes can reach several hundred  meters in height at depths extending to 5,000 meters.

The ROV focused on three mud volcanoes, named Hesperides, Anastasia and Gazul, and spent a great deal of time on the sea floor at depths ranging from 1,200m to 400m, sending live video feeds back to the ship, the Irish Times reports.

One of the most surprising finds was the presence of large fields of “fallen” carbonate chimneys.

“At first we thought these chimneys were old wood from ships or bones from a whale fall,” said Dr Carlsson. “But as we moved up the flank of the volcano we saw more and more toppled chimneys, and when we got to the peak of the volcano we had standing chimneys all around us.”

He explained that the chimneys were a result of chemosynthetic microorganisms over thousands of years of activity.

Chemosynthesis uses the energy released by chemical reactions to make sugar. Undersea hot springs provide habitats for the most extensive chemosynthesising communities.

“If the sun were to go black, life at the mud volcano would go on,” Dr Carlsson said. 

“These micro organisms are then eaten by other animals like deep-water snails, shrimp and sea cucumbers. They in turn are eaten by other organisms including fish and crabs that might end up on our dinner table.

“However, some animals like mussels, clams and tubeworms even harbour these chemosynthetic micro organisms inside their bodies and get all the energy they need from this symbiotic relationship.”

Dr Carlsson said the abundance of carbonate chimneys in “Chimney-henge” shows volcanic mud eruptions were supporting life here for a long time.