At about 2,300 feet deep, there is a spot known as the Lost City that causes the deep ocean to look briefly like an architectural edifice: pale towers, and ridges, and fine fingers appearing out of the darkness which will never see the sunlight.
The Lost City Hydrothermal Field is located close to the top of a submerged mountain west of the Mid-Atlantic Ridge, and was first discovered in 2000 during the research work of the research vessel Atlantis. The researchers found not the ragged clouds of conventional black smoker vents, but a skyline of creamy carbonate chimneys- some as large as small stacks, with one which is a monolith more than 60 meters tall. Poseidon is the tallest structure, serving to give Poseidon the sense of scale, and the engineering interest is in the power plant: Lost City operates on no magma.
The majority of hydrothermal vent are volcanically heated and sell themselves with mineral plumes. Lost City exists by serpentinization, which is the process that takes place with the entrance of seawater into revealed mantle rock. The result of that reaction is heat and the creation of hydrogen and methane-chemical energy so rich that it can provide whole communities, and at a relatively low temperature by vent standards. Some of the formations in the earlier descriptions of the field seem to be weeping fluid, and they grow in clumps of the fine, multi-pronged growths of carbonates which stretch outward like the fingers of turned-up hands. The outcome is a vent field, which acts rather as an alkaline reactor, draining limestone-like minerals as it exhalates.
One of the shocks is its lifespan. Isotopic dating dates Lost City to have been in operation at least 120,000 years a lifespan much longer than several volcanic vent fields that fade away on human time scales. What that endurance is useful in is that it transforms the site into a lasting natural laboratory: the same rock-water chemistry long enough to construct towers, to change crust, and to support habitable micro-environment within chimney walls. The chemistry is also uncharacteristically fruitful. Analysts of Lost City fluids have reported vent discharges capable of producing 10-100 times the normal output of hydrogen and methane in normal smoker systems, and alkaline fluids and small organic molecules that assist in contextualizing current speculations as to how early metabolism might have established itself.
Within the chimneys, rich blankets of microbes attach to interiors of carbonates where they thrive off of the energy of hydrogen and methane instead of the sun. Larger animals are found, however, the predominant biomass of the system is microbial, life that has been engineered at the level of pores, fractures and mineral grains. It is that biochemical minimalism that ensures that astrobiologists keep going back to Lost City when discussing ocean worlds. One such line was the cross-planetiveness of microbiologist William Brazelton, who wrote: This is an example of a type of ecosystem that could be running on Encycladus or Europa this second.
Despite the fact that the field is located in international waters with fewer formal protection, the field is used as a template of life without light, as observed in Lost City. The mining interests have received the rights in the surrounding areas and the scientists have cautioned that through sediment plumes or discharges, the sensitive surfaces could be covered and this could be interfering with the chemistry that maintains the system. The contradiction is difficult to overlook: one of the most educative natural reactors on the Earth is at the same time the one of the world importance and structurally weak.
In the meantime, the hunt down of other possible systems, akin to the Lost City has also become an exploration tool proving ground. Under the nest to a workflow, an expedition to the Mid-Atlantic Ridge in 2023 involved mapping, underwater column data, autonomous underwater vehicles and confirmation using remote operated vehicles with a methane sensor that can confirm active venting in real time. The campaign discovered several new black smoker areas, which highlights the prevalence of the volcanic venting, but failed to find a second Lost City comparable. That lack places the original site in a rare class: not merely scenic, but unique in its way in terms of transforming rock, seawater and time into a stable chemical engine of life.
