The Lost City Hydrothermal Field, often called Lost City, is a place with special underwater vents in the Atlantic Ocean. It is located on the Atlantis Massif, where the Mid-Atlantic Ridge meets the Atlantis Transform Fault. This area has been active for a long time, with processes that create certain minerals and naturally produce simple molecules like methane and hydrogen. These molecules are important for the survival of tiny living things called microbes. Scientists are interested in this location because it helps them study how life might have started on Earth and other planets that are similar.
Expedition history
The Lost City was first discovered on December 4, 2000, using the DSV Alvin and ROV ArgoII during the AT03-60 cruise of the RV Atlantis. The cruise lasted 34 days, and scientists collected photographs and samples of vent chimneys.
The discovery of the Lost City led the National Science Foundation to fund a second, 32-day voyage (AT07-34) to the site in 2003. This mission used Alvin and the autonomous underwater vehicle ABE to focus on scientific sampling and creating a detailed map of the ocean floor around the vent field. ABE participated in 17 dive missions, including follow-up visits, to map 3.3 square kilometers (1.3 square miles) of the Atlantis Massif.
The first visit by the Integrated Ocean Drilling Program happened during Expedition 304 in late 2004. Scientists drilled holes into the Atlantis Massif to collect large rock samples. Expedition 305 followed in early 2005, and another mission, 340T, took place in 2012.
In July 2005, the Lost City was explored for nine days using the Hercules and Argus vehicles aboard the National Oceanic and Atmospheric Administration vessel Ronald H. Brown. Video from the expedition was streamed live to the University of Washington in Seattle. Another cruise, 50 of the Akademik Mstislav Keldysh, focused on exploring the area south of the vent field. The RV Knorr visited the Atlantis Massif in May 2005 to measure potential seismic activity using sound-based methods. Additionally, the French EXOMAR cruise on the vessel L'Atalante in July and August 2005 studied life forms that live in extreme deep-ocean conditions.
In 2015, the International Ocean Discovery Program Expedition 357 visited the Lost City to drill into the Atlantis Massif and study fluid movement away from the main vent area. Scientists collected rock samples from nine sites and used Niskin bottles to sample fluids. Borehole plugs were placed at two sites to allow future sampling of fluids from the drilled holes.
In July and August 2018, the French TRANSECT cruise on the vessel L'Atalante used the ROV VICTOR to collect measurements and samples. The following month, the American cruise AT42-01, nicknamed "Return to the Lost City," revisited the vent field. Scientists used the ROV Jason II and a CTD Niskin rosette to collect samples of rock, vent fluid, seawater, and biological materials. The mission aimed to study energy sources for microbial life and to sample fluids from holes drilled during the 2015 expedition.
In March 2023, the first cruise of the RV Falkor Too was conducted to test a new sensor that detects methane in the ocean. The mission searched for hydrothermal activity similar to the Lost City along the Mid-Atlantic Ridge. ROV dives were live-streamed to the Schmidt Ocean Institute's website. The cruise ended on April 11 after discovering new black-smoker vents.
Geography
Lost City is located in the North Atlantic Ocean on the seafloor mountain Atlantis Massif, which is about the same size as Mount Rainier. The site is a long-lived vent field, estimated to be older than 120,000 years based on radiocarbon dating of the oldest chimney deposits. However, this is much younger than the Atlantis Massif itself, which may be as old as two million years. Lost City is found on a shelf about 70 meters (230 feet) below the summit of the massif, at a depth of around 750–900 meters (2,460–2,950 feet), covering an area of approximately 500 square meters (5,400 square feet). The massif may have formed in a way similar to other ocean core complexes.
Lost City is dominated by steep cliffs to the south, chimneys, and mounds of carbonate material that form when chimneys collapse over time. As one moves away from the vent field, rocks such as breccia, gabbros, and peridotites become more common. These rocks are prone to mass wasting when the seafloor becomes steeper. Evidence of past mass-wasting events includes visible scarps on the slope of the massif. Rubble tends to collect in areas with slopes no steeper than 60 degrees near the field and may harden into rock depending on its distance from Lost City.
Among the 30 active and inactive vent chimneys, Poseidon is the largest and most studied. It is about 60 meters (200 feet) tall and 100 meters (330 feet) wide, with many openings that release hot fluids. Another chimney, called Beehive due to its shape, is about 1 meter tall and located on the south side of Poseidon. The IMAX tower, approximately 8 meters (26 feet) tall on the north side of Poseidon, has stalagmite-like growths that reach up to 30 meters (98 feet). IMAX has a large flange that traps hot fluid and supports a visible biofilm.
Other chimneys, such as Ryan and Nature, are located to the east of Poseidon and have similar flange and beehive-like structures but are much smaller and release less fluid. Several inactive vents are found about 100 meters (330 feet) south of Poseidon, though they are only a few meters tall.
The Atlantis Massif is located on a slow to ultra-slow spreading center, which creates many faults through the vent field. Many faults, especially on the south side, are high-angle normal faults that may be hidden by debris. Most vents run from east to west, likely because the fault lines under the field are oriented that way.
Two extinct vent fields are located about 300 meters (980 feet) west and 450 meters (1,480 feet) southwest of the central vent field, at depths of 1,000 meters (3,300 feet) or more. These fields have inactive vents similar to Poseidon, separated by a layer of loose rock called talus. They have not been as thoroughly studied as the central field. Scientists believe that hot fluid flow moved from the south to the north, where Poseidon is now located.
Strontium, carbon, and oxygen isotope data, along with radiocarbon ages, show that hydrothermal activity at Lost City has occurred for at least 30,000 years. This activity is driven by serpentinization reactions, making Lost City older than all known black smoker vents by at least two orders of magnitude.
Geology and chemistry
Alkaline hydrothermal vents, such as those at Lost City, are only somewhat similar to volcanic black smoker vents. These two types of vents are better described by their differences than their similarities. Both are often found near oceanic spreading centers, but alkaline hydrothermal vents are not formed by volcanic activity. These vents release methane and diatomic hydrogen into the surrounding water, while they do not produce large amounts of carbon dioxide, hydrogen sulfide, or metals, which are the main outputs of volcanic black smoker vents. The temperature and pH of water around the two types of vents are also very different.
The Atlantis Massif is an ultramafic oceanic core complex of the Mid-Atlantic Ridge. Here, upper mantle rock is exposed to seawater through faulting caused by tectonic extension related to oceanic spreading centers. The spreading half-rate is about 12 mm/yr, which classifies it as a slow-spreading ridge. Seismic events with Richter magnitudes of 4 and 4.5 have been recorded at the massif.
The dominant minerals at Lost City are ultramafic, made mostly of olivine and pyroxene with very little silica. Peridotite, primarily spinel harzburgite, undergoes serpentinization and forms magnetite and serpentine minerals. Because little to no carbon dioxide or metals are released in the venting fluids, Lost City appears like a non-smoker, with few particles to create a smoky look.
When pore waters reach the surface, aragonite, brucite, and calcite chimneys form as calcium carbonates precipitate from the water. Younger chimneys are mainly brucite and aragonite, appearing white and flaky. As vents age, porosity decreases because precipitates block fluid pathways. Over time, mineral compositions change, with aragonite being replaced by calcite and brucite dissolving, causing chimneys to darken to grey or brown.
On the Atlantis Transform Fault, the Atlantis Massif wall ends about 740 meters (2,430 feet) below sea level. Here, rock types deform into various mylonitic rocks with deformation fabric minerals such as talc, tremolite, and ribbon serpentine.
Lost City is an ideal location for studying abiotic methanogenesis and hydrogenesis because serpentinization reactions produce methane and hydrogen. These reactions release heat, warming the surrounding waters, though fluid temperatures remain relatively low (40°–90 °C) compared to other hydrothermal systems. The local pH increases to over 9, enabling calcium carbonate precipitation. Because serpentinization is widespread, carbon dioxide concentrations are very low. The low temperatures, low carbon dioxide levels, and low hydrogen sulfide and metal content in the plume make the vents harder to detect using CTD measurements or optical backscatter methods.
Biology
The Lost City and other hydrothermal vent systems have very different types of life because of the unique chemistry at Lost City. Many microorganisms live inside, on, and around the vents. Methanosarcinales-like archaea form thick layers inside the vents and use hydrogen and methane for energy. Bacteria related to the Bacillota also live inside the vents. Outside the vents, archaea such as the newly discovered ANME-1 and bacteria like Pseudomonadota use methane and sulfur as their main energy sources.
The Lost City also has many small invertebrates that live near the carbonate structures, including small corals, snails, bivalves, polychaetes, amphipods, and ostracods. Desmophyllum corals and nematode worms have been seen living on the carbonate chimneys. However, animals like tube worms and giant clams, which are common at typical black smoker vents, are not found at Lost City. Other animals, such as crabs, shrimp, sea fans, and jellyfish, have also been observed there.
Macrofauna are uncommon near the vent field, but larger animals sometimes visit. These visitors include wreckfish, grenadiers, and sharks. Arrowtooth Eels have been seen at the Lost City field, and they can live at depths ranging from −120 metres (−390 ft) to −4,800 metres (−15,700 ft).
Significance
Lost City offers scientists, including geologists, chemists, and biologists, a natural environment to study life in extreme conditions and processes that create methane and hydrogen through a chemical reaction called serpentinisation.
The Lost City vent field has similarities with the Prony Bay vent field near New Caledonia in the Pacific Ocean. Both locations produce large amounts of hydrogen gas and methane at moderate temperatures. Prony Bay is much shallower, sitting less than 50 metres (160 feet) below the ocean surface, compared to Lost City, which is about 800 metres (2,600 feet) deep. Prony Bay is home to unique life forms, such as the extremophile Alkaliphilus hydrothermalis.
Another alkaline hydrothermal vent, the Strytan Hydrothermal Field, is located off the north coast of Iceland. It is much shallower than Lost City, and the water flowing through it mainly comes from fresh, land-based sources.
The Von Damm Vent Field, found in the Caribbean Sea, is located above an ocean core complex.
Some scientists suggest that ancient versions of these alkaline hydrothermal vents in the early Earth’s oceans may have been where life first began, a process called abiogenesis. The hydrogen gas produced, metal-based catalysts linked to the iron-sulfur world theory, the structure of the vent towers, and the energy from hydrothermal activity may have created conditions suitable for the first non-photosynthetic energy cycles in early microorganisms and the formation of organic molecules. Tiny structures in these vents show connected spaces that could have helped life begin.
These vents also continuously create acetyl thioesters, which serve as the starting materials for more complex organic molecules and provide the energy needed to form them. However, researchers from the Earth-Life Science Institute (ELSI) in Tokyo, Japan, disagreed with this idea. They explained that the high energy required for thioester hydrolysis and their low equilibrium levels make it unlikely that these molecules could have formed in large amounts in places like Lost City without biological processes.
The conditions at Lost City are especially important because of the variety of extremophiles found there. Microbes at Lost City are polyextremophiles, meaning they can survive in highly alkaline environments, moderate pressure, and warm temperatures, even without sunlight. The mix of these traits suggests that life at Lost City may be more extreme than in other locations, making it a key area for studying what conditions are needed for life to exist.
Since serpentinisation only requires olivine and seawater, places like Lost City could potentially exist on other celestial bodies with liquid water, such as the moons Europa and Enceladus.
In popular culture
Lost City is shown in the Disney 3-D IMAX film Aliens of the Deep. The IMAX flange had no name before the documentary came out, but it is very easy to spot in the film. After its release, it got the nickname based on the type of video used in movie theaters.
Lost City is also shown in episode 2 of the BBC's documentary series Blue Planet II.