The Lost City Hydrothermal Field, often called Lost City, is a location in the Atlantic Ocean where underwater vents release alkaline water. It is found 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 involving certain types of rocks naturally creating simple molecules like methane and hydrogen. These molecules are important for the survival of tiny living things. Because of this, scientists study Lost City to learn more about how life began on Earth and on other planets similar to it.
Expedition history
The Lost City was first discovered on December 4, 2000, using the DSV Alvin and ROV ArgoII during cruise AT03-60 of the RV Atlantis. The cruise lasted 34 days, and scientists collected photographs and samples of vent chimneys.
The discovery led the National Science Foundation to fund a second 32-day voyage (AT07-34) to the site in 2003. This expedition used Alvin and the autonomous vehicle ABE to focus on scientific sampling and creating a detailed map of the vent field. ABE participated in 17 dive expeditions, including follow-up visits, to map 3.3 square kilometers (1.3 square miles) of the massif.
The first visit by the Integrated Ocean Drilling Program occurred during Expedition 304 in late 2004. Scientists drilled holes into the Atlantis Massif to collect rock cores. Expedition 305 followed in early 2005, and another expedition, 340T, took place in 2012.
In July 2005, the Lost City was explored for nine days using Hercules and Argus on 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 exploration took place during cruise 50 of the Akademik Mstislav Keldysh, which focused on areas south of the vent field. The RV Knorr visited the Atlantis Massif in May 2005 to measure potential seismic activity. Additionally, the French EXOMAR cruise on the vessel L'Atalante studied life forms in extreme deep-ocean environments during July and August 2005.
In 2015, the International Ocean Discovery Program Expedition 357 visited the Atlantis Massif to investigate off-axis circulation. Scientists collected rock cores from nine sites and used Niskin bottles to sample fluids. Borehole plugs were placed on two sites to allow future sampling of fluids.
In July and August 2018, the French TRANSECT cruise on 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 collected photographs, gases, rock, vent fluid, and seawater samples using the ROV Jason II and a CTD Niskin rosette. The mission aimed to study energy sources for microbial life and sample fluids from holes drilled in 2015.
In March 2023, the first cruise of the RV Falkor Too deployed a new methane sensor to search 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 called Atlantis Massif, which is about the same size as Mount Rainier. The site is known as a long-lasting vent field, estimated to be older than 120,000 years based on dating 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 top 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 a place with steep cliffs to the south, chimneys, and mounds made of carbonate material that forms as chimneys age and collapse. As one moves away from the field, rocks such as breccia, gabbros, and peridotites become more common. These rocks are prone to sliding or falling as the underwater landscape becomes steeper. Evidence of past landslides or rockfalls can be seen as large, steep slopes on the massif. Rubble tends to collect in areas that are no steeper than 60 degrees, and this rubble may turn into rock over time depending on its distance from Lost City.
Among the 30 active and inactive vent chimneys, Poseidon is the largest and most studied. Poseidon is about 60 meters (200 feet) tall and 100 meters (330 feet) wide, with many openings that release hot fluids. Another chimney, called Beehive because of its shape, is about 1 meter tall and is located on the south side of Poseidon. On the north side of Poseidon, the IMAX tower is approximately 8 meters (26 feet) tall, but it has growths resembling stalagmites that can be as tall as 30 meters (98 feet). IMAX has a wide edge that traps hot fluid and contains a visible layer of living microorganisms.
Other chimneys, such as Ryan and Nature, are located east of Poseidon and also have edges and beehive-like shapes, though they are smaller and release less fluid. Several inactive vents are found about 100 meters (330 feet) south of Poseidon, but they are only a few meters tall.
Because the massif is located on a slow to ultra-slow spreading center, there are many faults running through the vent field. Many of these faults, especially on the south side, are steep normal faults that can be covered by debris. Most vents are aligned from east to west, likely due to the direction of fault lines beneath the field.
Two inactive vent fields are located about 300 meters (980 feet) west and 450 meters (1,480 feet) southwest of the main vent field, at depths of 1,000 meters (3,300 feet) or more. These fields have inactive vents similar to Poseidon, but they are separated from the main field by a layer of loose rock. These areas have not been studied as much as the central field. Scientists believe that hot fluid flow moved from the south to the north, where Poseidon now exists.
Isotope data from strontium, carbon, and oxygen, along with radiocarbon dating, show that hydrothermal activity at Lost City has been happening for at least 30,000 years. This activity is driven by chemical reactions called serpentinization, making Lost City older than all known black smoker vents by at least 100 times.
Geology and chemistry
Alkaline hydrothermal vents, such as those found at Lost City, are not very 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 hydrogen gas into the surrounding water, while they do not produce large amounts of carbon dioxide, hydrogen sulfide, or metals, which are major outputs of black smoker vents. The temperature and pH of the water around the two types of vents are also very different.
The Atlantis Massif is a type of underwater mountain located on the Mid-Atlantic Ridge. It is part of an oceanic core complex where upper mantle rock is exposed to seawater due to faulting caused by tectonic extension at spreading centers. The spreading rate is about 12 millimeters per year, which classifies it as a slow-spreading ridge. Earthquakes with magnitudes of 4 and 4.5 have been recorded at the massif.
The main minerals found at Lost City are ultramafic, consisting mostly of olivine and pyroxene with very little silica. Peridotite minerals, which are primarily spinel harzburgite, undergo a process called serpentinization, forming magnetite and serpentine minerals. Because little to no carbon dioxide or metals are released in the venting fluids, Lost City appears similar to a non-smoker vent, with few particles that create a smoky look.
When water moves through the rock, aragonite, brucite, and calcite chimneys form as calcium carbonate solidifies from the solution. Younger chimneys are mainly made of brucite and aragonite, appearing white and flaky. As the vents age, the spaces inside the chimneys become smaller because the solid deposits block fluid pathways. Over time, the mineral composition changes, with aragonite being replaced by calcite, and brucite dissolving. This causes the chimneys to darken to a grey or brown color.
On the Atlantis Transform Fault, the Atlantis Massif wall ends approximately 740 meters (2,430 feet) below sea level. At this depth, the rock types change into mylonitic rocks, which contain minerals like talc, tremolite, and ribbon serpentine. These minerals show the way the rocks were shaped by intense pressure and movement.
Lost City is an important place for studying abiotic methanogenesis and hydrogenesis, as serpentinization reactions create methane and hydrogen gas. These reactions release heat, warming the surrounding water, but the fluid temperatures remain relatively low (40°–90 °C) compared to other hydrothermal systems. The local pH also increases to over 9, which helps calcium carbonate form. Because serpentinization is widespread, carbon dioxide levels are very low. The low temperature, low carbon dioxide levels, and low amounts of hydrogen sulfide and metals in the vent plumes make the vents harder to detect using CTD measurements or optical backscatter methods.
Biology
The Lost City and other hydrothermal vent systems support very different kinds of life because of the Lost City's special chemical conditions. Many types of microorganisms live inside, on, and around the vents. Methanosarcinales-like archaea create thick layers of biofilms 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. Animals like tube worms and giant clams, which are common in typical black smoker vents, are not found at the Lost City. Other animals, such as crabs, shrimp, sea fans, and jellyfish, have also been observed at the site.
Large animals, called macrofauna, are rarely found near the vent field, though some larger organisms visit occasionally. These visitors include wreckfish, grenadiers, and sharks. Arrowtooth Eels have been seen at the Lost City field, and these fish can live in water as shallow as −120 meters (−390 feet) or as deep as −4,800 meters (−15,700 feet).
Significance
Lost City is a place where scientists such as geologists, chemists, and biologists study life in extreme environments. It is also a location where processes like the creation of methane and hydrogen gas occur naturally through a process called serpentinization.
The Lost City vent field has similarities to the Prony Bay vent field near New Caledonia in the Pacific Ocean. Both locations produce large amounts of hydrogen gas and methane, and both have moderate temperatures. Prony Bay is much closer to the ocean surface, at less than 50 meters (160 feet) deep, compared to Lost City, which is about 800 meters (2,600 feet) deep. Prony Bay is home to unique life forms, including a special type of microbe called 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 there mainly comes from land.
The Von Damm Vent Field, found in the Caribbean Sea, is located on a specific type of underwater structure called an ocean core complex.
Some scientists believe that ancient versions of these alkaline hydrothermal vents in the early Earth’s oceans may have been the first places where life began. The presence of free hydrogen gas, metal catalysts that match an iron-sulfur world theory, the physical structure of the vent towers, and the energy from hydrothermal activity could have created conditions suitable for the development of early life processes and the formation of organic molecules. Tiny structures in these vents show connected spaces that could have helped life begin.
These vents also continuously produce molecules called acetyl thioesters, which are important for forming more complex organic molecules and providing energy. However, researchers from the Earth-Life Science Institute in Tokyo, Japan, suggested that these molecules are unlikely to have formed naturally in significant amounts in the Lost City due to the chemical properties of thioester hydrolysis.
The conditions at Lost City are unique because it hosts a variety of extremophiles—microbes that can survive in extreme environments. These microbes are polyextremophiles, meaning they can live in high pH, moderate pressure, and high temperature conditions, even without sunlight. The combination of these traits suggests that life at Lost City may be more extreme than in other locations, making it an important area for studying the requirements for life.
Since serpentinization only needs olivine and seawater, places like Lost City could potentially exist on other celestial bodies with liquid water, such as Europa and Enceladus.
In popular culture
Lost City appears in the Disney 3-D IMAX movie Aliens of the Deep. Before the documentary was released, the IMAX flange had no name, but it is easily seen in the film and later received the nickname for the type of movie shown in theaters.
Lost City is also shown in episode 2 of the BBC series Blue Planet II.