The Lost City Hydrothermal Field, often referred to simply as Lost City, is an area of marine alkaline hydrothermal vents located on the Atlantis Massif at the intersection between the Mid-Atlantic Ridge and the Atlantis Transform Fault, in the Atlantic Ocean. It is a long-lived site of active and inactive ultramafic-hosted serpentinization, abiotically producing many simple molecules such as methane and hydrogen which are fundamental to microbial life. As such it has generated scientific interest as a prime location for investigating the origin of life on Earth and other planets similar to it.

Expedition history

thumb|Hercules diving at the Lost City in 2005

The Lost City was first identified on December 4, 2000, using DSV Alvin and ROV ArgoII on cruise AT03-60 of the RV Atlantis. The cruise lasted 34 days, during which photographs and vent chimney samples were taken.

The discovery of the Lost City prompted the National Science Foundation to fund a second, 32-day voyage (AT07-34) to the site in 2003 in order to use Alvin and the autonomous vehicle ABE with a greater emphasis on scientific sampling and creating a high-resolution bathymetric map of the vent field. ABE would participate in a combined 17 dive expeditions including follow-up visits, creating a bathymetry profile for of the massif.

The first visit by the Integrated Ocean Drilling Program took place with Expedition 304 in late 2004, when a series of holes were drilled into the Atlantis Massif to collect large cores of rock from the site. Expedition 305 followed suit in early 2005, and 340T in 2012.

In July 2005, Lost City was explored for nine days by Hercules and Argus on the National Oceanic and Atmospheric Administration vessel Ronald H. Brown, with video streamed live to the University of Washington in Seattle. Lost City was also explored on cruise 50 of the Akademik Mstislav Keldysh, which had a greater emphasis on exploring downslope south of the vent field. The RV Knorr sailed to the Atlantis Massif in May that year for hydroacoustic measurements of potential seismic activity. Furthermore, the French EXOMAR cruise on the vessel L'Atalante was conducted in July and August 2005 to study extremophile biodiversity in deep-ocean environments.

2015 saw a visit from the International Ocean Discovery Program Expedition 357, which emphasized drilling on the Atlantis Massif to explore off-axis circulation. A series of boreholes were left behind after cores from nine different sites were taken, which were sampled by Niskin bottles. Borehole plugs were installed on two sites to allow future endeavors to sample borehole fluids.

thumb|Instruments on the ROV Jason in 2018

In July and August 2018, the French TRANSECT cruise was conducted on L'Atalante utilizing the ROV VICTOR to collect a variety of measurements and samples. The following month, American cruise AT42-01, nicknamed Return to the Lost City, was undertaken to revisit the vent field after many years, featuring many members of the original discovery team in 2000. Photographs, ambient gases, cells for cultures, rock, vent fluid, and ambient seawater samples were collected using the ROV Jason II and a CTD Niskin rosette. The mission's key objectives were to collect biological and geochemical samples for researching sources of energy for microbial life. They also followed up on the 2015 borehole expedition by attempting to sample from the drilled holes for access to residual fluids.

In March 2023, the first cruise of the RV Falkor Too was undertaken to deploy a new in-situ methane sensor to search for hydrothermal activity similar to that of Lost City along the Mid-Atlantic Ridge. ROV dives were live-streamed to the Schmidt Ocean Institute's website. The cruise concluded on April 11, having identified new black-smoker vents.

Geography

thumb|Map of the Lost City on the [[Atlantis Massif]]

Lost City is located in the North Atlantic Ocean on the seafloor mountain Atlantis Massif, which is approximately the size of Mount Rainier. The site is described as a long-lived vent field, estimated to be older than 120,000 years by radiocarbon dating the oldest chimney deposits of the field. Lost City is located on a shelf approximately below the massif summit at a depth of around , with an approximate area of . The massif itself may have originated in a similar manner to many other ocean core complexes.

Lost City is a location dominated by steep cliffs to the south, chimneys, and mounds of carbonate material deposited from chimneys that collapse as they age. Breccia, gabbros, and peridotites are dominating rock types as one maneuvers away from the field, which are prone to mass wasting as the bathymetry steepens. The spreading half-rate is approximated to about 12 mm/yr, classifying it as a slow-spreading ridge. Seismic events of Richter magnitude 4 and 4.5 have been detected at the massif.

On the side of the Atlantis Transform Fault, the Atlantis Massif wall terminates approximately below sea level, where rock types deform to various mylonitic rocks with deformation fabric minerals of talc, tremolite, and ribbon serpentine. Furthermore, local pH is increased to values of over 9, which enables calcium carbonate precipitation. Since serpentinization is particularly extensive, carbon dioxide concentrations are also very low. Low temperature, carbon dioxide concentrations, as well as the low hydrogen sulfide and metal content of the plume make the vents more difficult to identify from CTD measurements or optical backscatter methods.

Biology

thumb|upright|Desmophyllum have been observed at the Lost City field

Lost City and other hydrothermal vent systems support vastly different lifeforms due to Lost City's unique chemistry. A variety of microorganisms live in, on, and around the vents. Methanosarcinales-like archaea form thick biofilms inside the vents where they subsist on hydrogen and methane; bacteria related to the Bacillota also live inside the vents. External to the vents, archaea, including the newly described ANME-1, and bacteria, including Pseudomonadota, oxidise methane and sulfur as their primary sources of energy.

Lost City also supports a variety of small invertebrates associated with the carbonate structures, including small corals, snails, bivalves, polychaetes, amphipods, and ostracods. Desmophyllum corals and nematode worms have been observed living on the carbonate chimneys. Other animals such as tube worms and giant clams that are abundant in typical black smoker vents, however, are absent from Lost City. A variety of crabs, shrimp, sea fans, and jellyfish have also been observed at the field.

Macrofauna are rare around the vent field, though larger organisms do visit the field on occasion. Visitors can include wreckfish, grenadiers, and even sharks. Arrowtooth Eel have been observed at the Lost City field, which have a massive depth range of to .

Another alkaline hydrothermal vent, the Strytan Hydrothermal Field, has been identified off the north coast of Iceland. It is significantly shallower and fluids are primarily supplied by fresh, terrestrial water.

The Von Damm Vent Field found in the Caribbean Sea is also situated atop an ocean core complex.

Origin of life

Speculation has been offered that ancient versions of similar alkaline hydrothermal vents in the seas of a young Earth were the birthplace of all life, constituting the planet's original abiogenesis. The free hydrogen gas produced, metallic catalysts consistent with an iron-sulfur world theory, micro-cellular physical structure of the towers, and available hydrothermal energy might plausibly have provided an environment for the beginnings of non-photosynthetic energy cycles common to the most primitive microorganisms and organic molecule creation. Microscopic structures in such alkaline vents "show interconnected compartments that provide an ideal hatchery for the origin of life".

These alkaline hydrothermal vents also continuously generate acetyl thioesters, providing both the starting point for more complex organic molecules and the energy needed to produce them. However, this notion was rejected by Japanese researchers from Earth-Life Science Institute (ELSI), Tokyo Institute of Technology. They showed that because of the high free energy change of thioester hydrolysis and their corresponding low equilibrium constants, it is unlikely that these species could have accumulated abiotically to any significant extent in the Lost City fields.

The conditions at Lost City are of particular concern because of the different types of extremophiles present. Lost City microbes are polyextremophiles, fitting the description of alkaliphiles, moderate piezophiles, and thermophiles in an environment without sunlight. The combination of different extremophile elements suggests that Lost City organisms are more extreme than at other locations, making them particularly interesting subjects of study on the requirements for life.

Given the only requirements for serpentinization are olivine and seawater, locations like Lost City could theoretically exist on extraterrestrial bodies with liquid water such as Europa and Enceladus.

thumb|A visiting shark at the Lost City field

Lost City is featured in the Disney 3-D IMAX film Aliens of the Deep. The IMAX flange was unnamed prior to the documentary's release, but is extremely recognizable in the film and subsequently picked up the nickname of the video format played in theaters.

Lost City is also featured in episode 2 of the BBC's documentary Blue Planet II.

Protection

The carbonate spires of the Lost City Hydrothermal Field are on UNESCO's protection wish list.

References

  • The site for the original UW expedition
  • University of Washington, Lost City Expedition
  • The official page for the 2018 mission
  • The PMEL vents program
  • The InterRidge Vents Database
  • 2023 Falkor mission