Underwater volcanic brine pools could be home to extreme life forms

Super-salty underwater lakes rich in carbon dioxide could host extreme life forms unlike any others on Earth.

Water that is rich in salt and other minerals sinks to the bottom of the ocean due to its density and, if it reaches a depression in the sea floor, can collect in a liquid lake that is distinct from the water above. These brine pools have been found in many oceans, and their unique chemical make-up – low in oxygen and rich in certain minerals – makes them places where extreme microorganisms can evolve and thrive.

Now, Froukje van der Zwan at King Abdullah University of Science and Technology in Saudi Arabia and her colleagues have discovered a new type of brine pool that is warm, rich in carbon dioxide and appears to be fed by underwater volcanoes.

On a recent expedition to two underwater volcanoes in the Red Sea, Hatiba Mons and Mabahiss Mons, van der Zwan and her colleagues found several brine pools near the summit of the volcanoes, more than a kilometre above the surrounding sea floor and 5 kilometres away from any mineral deposits that may have increased the water’s salinity. They also found nearby areas with multiple hydrothermal vents that were releasing mineral-rich water at around 60°C (140°F).

Sampling using robotic vehicles showed that the pools were warmer than the surrounding water and had elevated levels of metal elements such as zinc and manganese.

They were also rich in the gases found at the hydrothermal vents. “They’re relatively high in CO2 as well as methane… but in contrast to other hydrothermal vents, where the fluids are really going into the sea water, here they keep contained in the brine, so maybe this is sort of a sink for these gases,” van der Zwan told the Goldschmidt geochemistry conference in Prague, Czech Republic, on 8 July.

The researchers are currently analysing microbial samples taken from the pools, to see how life forms might be adapted to the extreme environment. At the nearby hydrothermal vents, they found thick mats containing microbes much larger than any others known in marine environments, as well as polychaete worms and amphipods.

Life in the salty pools may provide clues as to how life might develop in extreme alien environments, such as in the salty, iron-rich ocean of Jupiter’s moon Europa. There, the ocean is trapped under a thick crust of ice, but if there is hydrothermal activity below it, then it could present a similar scenario to the iron-rich brine pools that van der Zwan and her team found.