Deep-sea organisms living without sunlight and feeding off toxic "mud volcanoes" have been discovered by a team of Irish and international scientists on board the State's research ship Celtic Explorer.
The scientists have nicknamed the area "Chimney-henge" after Stonehenge in England, because of the resemblance of the circular arrangement of carbonate chimneys in the volcanic deep seabed area to the Neolithic monuments.
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.
Expedition leader Dr Jens Carlsson of University College Dublin said the aim was to explore and take samples from mud volcanoes, which are similar to volcanoes on land.
Instead of lava, they emit liquefied mud with methane and the highly toxic hydrogen sulphite and can reach several hundred metres in height at depths extending to 5,000 metres.
The ROV focused on three mud volcanoes, named Hesperides, Anastasia and Gazul, and spent a considerable time on the sea floor at depths ranging from 1,200m to 400m, sending live video feeds back to the ship.
Dr Carlsson said one of the most surprising finds on the cruise 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,” he said. “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.”
Chemical reactions
The chimneys were formed as a side effect of chemosynthetic microorganisms over thousands of years of activity, he said. Unlike photosynthesis, which uses sunlight to make food by converting carbon dioxide and water into sugar and oxygen in plants, chemosynthesis uses the energy released by chemical reactions to make sugar.
Undersea hot springs provide habitats for the most extensive chemosynthesising communities, a fact only known since 1977 when the first such observation was made on a deep sea vent.
The abundance of carbonate chimneys in “Chimney-henge” shows volcanic mud eruptions were supporting life here for a long time, Dr Carlsson said.
The Deep-Links project aims to track where chemosynthetic energy goes. “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.”
The team included researchers from NUI Galway, Galway-Mayo Institute of Technology and the Geological Survey of Ireland.
