A field of alkaline hydrothermal vents, more than 120  000 years old, located on a dropped-down bench 70 m below the southern wall of the summit of the Atlantis Massif and comprising about thirty carbonate chimneys 30–60 m tall. Hydrothermal activity occurs at Poseidon, a chimney 60 m high and 100 m across, where fluid is vented at up to 91°C and pH 9–11. The field supports a variety of small invertebrates. The field was discovered in 2000.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015GC005869 Geological Evolution of the Lost City Hydrothermal Field.