Lost City Hydrothermal Field

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Lost City Vent Field
A series of vents on the Atlantis Massif.
Lost City (hydrothermal field)02.jpg
The Lost City has numerous carbonate hydrothermal vents, including this chalky-white flange.
Map showing the location of Lost City Vent Field
Map showing the location of Lost City Vent Field
LocationMid-Atlantic Ridge
Coordinates30°07′0″N 42°07′0″W / 30.11667°N 42.11667°W / 30.11667; -42.11667Coordinates: 30°07′0″N 42°07′0″W / 30.11667°N 42.11667°W / 30.11667; -42.11667
Area500 square metres (5,400 sq ft)
Max. elevation−750 metres (−2,460 ft)
Min. elevation−900 metres (−3,000 ft)

The Lost City Vent Field or Lost City is a series of alkaline hydrothermal vents located on the Atlantis Massif at the intersection between the Mid Atlantic Ridge and the Atlantis Transform Fault. It is a long-lived site of active and inactive ultramafic-hosted serpentinization,[1] abiotically producing many molecules such as methane and hydrogen that are fundamental to microbial life. It is a prime location for investigating the origin of life on Earth and other planets similar to it.

Expedition History[edit]

Hercules diving at the Lost City in 2005

The Lost City was identified on the 4th of December, 2000 using DSV Alvin and ROV ArgoII on cruise AT03-60 of the RV Atlantis.[2][3] The cruise lasted 34 days during which photographs and vent chimney samples were taken.[4]

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 to use Alvin and the autonomous vehicle ABE with a greater emphasis on scientific sampling and creating a high-resolution bathymetric map of the field.[5] ABE would do a combined 17 dive expeditions including following visits, creating a bathymetry profile for 3.3 square kilometres (1.3 sq mi) of the massif.[6]

The first visit by the Integrated Ocean Drilling Program took place in late 2004 with Expedition 304, when a series of holes were drilled into the Atlantis Massif to collect large cores of rock from the site.[7][8] Expeditions 305 followed suit in early 2005, and 340T in 2012.[9]

In July 2005, Lost City was explored for 9 days by Hercules and Argus on the NOAA vessel the Ronald H. Brown, with video streamed live to the University of Washington in Seattle.[5][10] 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.[11] The RV Knorr sailed to the Atlantis Massif in May that year for hydoacoustic measurements of potential seismic activity.[12][13]

2015 saw a visit from the International Ocean Discovery Program Expedition 357, which emphasized drilling on the Atlantis Massif to explore off-axis circulation.[14][15] A series of boreholes were left behind after cores from 9 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.

In September 2018, cruise AT42-01 nicknamed 'Return to the Lost City' was undertaken to revisit the vent field, featuring many members of the original discovery team in 2000.[16][17] 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 .[18] 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.

Geography[edit]

Map of the Lost City on the Atlantis Massif

Lost City is located on the seafloor mountain Atlantis Massif approximately the size of Mount Rainier.[19] The site is described as a long-lived vent field, estimated to be older than 120,000 years by carbon dating the oldest chimney deposits of the field.[1] However, this is significantly younger than the age of the Atlantis Massif itself, which may be as old as 2 million years.[20] Lost City is located on a shelf approximately 70 m (70 metres (230 ft)) below the massif summit at a depth of around 750–900 m (2,460–2,950 ft), with an approximate area of 500 square metres (5,400 sq ft).[21] The massif itself may originate 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 bathymetry steepens.[6] Mass-wasting events of the past are evident by bountiful scarps on the slope of the massif. Rubble tends to accumulate at areas no steeper than 60 degrees bounding the field, and can undergo lithification depending on how far it is located from Lost City.

Of the 30 active and inactive vent chimneys, Posidon is the largest and most-studied within the vent field.[19][6] Posidon stands about 60 metres (200 ft) tall and 100 metres (330 ft) wide and has numerous orifices venting hot fluids. The vent nicknamed Beehive for its distinct shape upon discovery, is about a meter tall and located on the south side of Posidon. Furthermore, the IMAX tower stands approximately 8 metres (26 ft) tall on the north side of Posidon, though the chimney has stalagmite-like growths that are as tall as 30 metres (98 ft). IMAX has a large flange which catches hot, escaping fluid and has a very apparent biofilm acting within it.

There are other chimneys, such as Ryan and Nature to the east of Posidon which also have flange and beehive-like structures, though they are significantly smaller and vent significantly less than Posidon. Several inactive vents are located about 100 metres (330 ft) south of Posidon, though they are entirely inactive and only stand a few meters tall.[6]

Since the location of the massif is upon a slow to ultra-slow spreading center, there is a large quantify of faults that run through the vent field.[20] Many faults, especially at the south side, are high-angle normal faults that can be concealed by debris. Most of the vents found tend to run from east to west, likely due to the orientation of fault lines under the field.[6]

Two extinct fields, one about 300 metres (980 ft) west and another 450 metres (1,480 ft) southwest of the central vent field at depths of 1,000 metres (3,300 ft) or more. They have inactive vents similar in profile to Posidon with a talus (scree) deposit separating them from the central vent field, though they have not been as actively explored. It is hypothesized from the ages of samples collected that hot fluid flow migrated from the south to the north where Posidon currently resides.[6]

Strontium, carbon, and oxygen isotope data and radiocarbon ages document at least 30,000 years of hydrothermal activity driven by serpentinization reactions at Lost City, making the Lost City older than known black smoker vents by at least two orders of magnitude.

Geology and Chemistry[edit]

Lost City vents release methane and hydrogen into the surrounding water; they do not produce significant amounts of carbon dioxide, hydrogen sulfide or metals, which are the major outputs of volcanic black smoker vents. The temperature and pH of water surrounding the two types of vent is also significantly different.

Geology and Mineralogy[edit]

The Mid-Atlantic Ridge spreading center pulls the lithosphere apart, creating normal faults which expose sub-surface rocks to seawater.
Olivine, the mineral responsible for Lost City's serpentinization.

The Atlantis Massif is described as an ultramafic oceanic core complex of the Mid-Atlantic Ridge, with upper-mantle rock being exposed to seawater through faulting from tectonic extension associated with ocean spreading centers.[22] The spreading half-rate is approximated to about 12 mm/yr, classifying it as a slow-spreading ridge.[23] Seismic events have been detected at the massif of Richter magnitude 4 and 4.5.[13]

The dominant minerals found at Lost City are ultramafic, composed primarily of olivine and pyroxene with very little silica content. Peridotite (primarily spinel harzburgite) minerals undergo serpentinization and form magnetite and serpentine minerals.[6] Because little to no carbon dioxide or metals are released in the venting fluids, Lost City bears the appearance of a non-smoker, with few particulates to give a smokey appearance.

Once pore waters have permeated the surface and return to the surface, aragonite, brucite, and calcite chimneys as calcium carbonates precipitate out of solution.[24] Younger chimneys are primarily brucite and aragonite, being white and flaky in appearance. As vents mature, porosity decreases as precipitates clog fluid pathways. Mineral compositions change with aragonite succeeded by calcite and brucite being removed through dissolution, and the chimneys darken to a grey or brown color.[25]

On the side of the Atlantis Transform Fault, the Atlantis Massif wall terminates approximately 740 meters below sea level, where rock types deform to various mylonitic rocks with deformation fabric minerals of talc, tremolite, and ribbon serpentine.[6]

Serpentinization[edit]

Lost City is an exemplary location for the study of abiotic methanogenesis and hydrogenesis, as serpentinization reactions produce methane and hydrogen. Supplementing Fischer-Troph reactions;

Olivine(Fe,Mg)2SiO4 + Watern·H2O + Carbon dioxideCO2SerpentineMg3Si2O5(OH)4 + MagnetiteFe3O4 + MethaneCH4

 

 

 

 

(Methanogenesis)

Fayalite (Olivine)3 Fe2SiO4 + water2 H2OMagnetite2 Fe3O4 + Silica (aqueous)3 SiO2 + Hydrogen2 H2

 

 

 

 

(Hydrogenesis)

The reactions are exothermic and warm surrounding waters via reaction heating, though fluid temperatures are still relatively low (40° - 90 °C) when compared to other hydrothermal systems.[26] Furthermore, 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, combined with 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[edit]

Lost City and other vent systems support vastly different lifeforms due to Lost City's unique chemistry.

The Lost City supports a variety of small invertebrates associated with the carbonate structures, including snails, bivalves, polychaetes, amphipods, and ostracods.[citation needed] Large animals, however, such as tube worms and giant clams that are abundant in typical black smoker vents are absent at Lost City. 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 Firmicutes also live inside the vents. External to the vents archaea, including the newly described ANME-1 and bacteria including proteobacteria oxidise methane and sulfur as their primary source of energy.

Significance[edit]

Lost City provides geologists, chemists and biologists a working ecosystem for the study of life and other processes driven by abiotic production of methane and hydrogen by serpentinisation.

Similarities to other locales[edit]

A similar alkaline hydrothermal vent, the Strytan Hydrothermal Field, has been identified off the north coast of Iceland.[27]

Origin of Life[edit]

Speculation has been offered that ancient versions of similar hydrothermal vents in the seas of a young Earth are the birthplace of all life, constituting the original abiogenesis. The free hydrogen, 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 archaea and organic molecule creation.[28][29] Microscopic structures in such alkaline vents "show interconnected compartments that provide an ideal hatchery for the origin of life".[30] 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 the high free energy change of thioesters hydrolysis and corresponding to their low equilibrium constants, it is unlikely that these species could have accumulated abiotically to any significant extant in the Lost City fields.[31]

Trivia[edit]

The first mission to the Atlantis Massif took place in 1996, though they were unable to find the vent field near the summit.[citation needed]

Lost City is featured in the Disney 3-D IMAX film Aliens of the Deep.[32] 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.[33]

Gallery[edit]

References[edit]

  1. ^ a b Ludwig, Kristin A.; Shen, Chuan-Chou; Kelley, Deborah S.; Cheng, Hai; Edwards, R. Lawrence (April 2011). "U–Th systematics and 230Th ages of carbonate chimneys at the Lost City Hydrothermal Field". Geochimica et Cosmochimica Acta. 75 (7): 1869–1888. doi:10.1016/j.gca.2011.01.008.
  2. ^ "A Lost 'City' of the Deep Reveals Unexpected Forms". today.duke.edu. Retrieved 2019-04-11.
  3. ^ Rivizzigno, Pete; Lebon, Geoff T.; Roe, Kevin K.; Schrenk, Matthew O.; Olson, Eric J.; Lilley, Marvin D.; Butterfield, David A.; Früh-Green, Gretchen L.; Blackman, Donna K. (July 2001). "An off-axis hydrothermal vent field near the Mid-Atlantic Ridge at 30° N". Nature. 412 (6843): 145–149. Bibcode:2001Natur.412..145K. doi:10.1038/35084000. ISSN 1476-4687.
  4. ^ Design by J. Morton, V. Ferrini, and S. O'Hara. "IEDA: Marine Geoscience Data System". www.marine-geo.org. Retrieved 2019-04-11.CS1 maint: Multiple names: authors list (link)
  5. ^ a b Kelley, Deborah; Früh-Green, Gretchen; Karson, Jeffrey; Ludwig, Kristin (2007-12-01). "The Lost City Hydrothermal Field Revisited". Oceanography. 20 (4): 90–99. doi:10.5670/oceanog.2007.09.
  6. ^ a b c d e f g h Denny, Alden R.; Kelley, Deborah S.; Früh-Green, Gretchen L. (February 2016). "Geologic evolution of the Lost City Hydrothermal Field". Geochemistry, Geophysics, Geosystems. 17 (2): 375–394. Bibcode:2016GGG....17..375D. doi:10.1002/2015GC005869.
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  22. ^ Blackman, Donna K.; Karson, Jeffrey A.; Kelley, Deborah S.; Cann, Johnson R.; Früh-Green, Gretchen L.; Gee, Jeffrey S.; Hurst, Stephen D.; John, Barbara E.; Morgan, Jennifer (2002). "Geology of the Atlantis Massif (Mid-Atlantic Ridge, 30° N): Implications for the evolution of an ultramafic oceanic core complex". Marine Geophysical Researches. 23 (5/6): 443–469. doi:10.1023/B:MARI.0000018232.14085.75. ISSN 0025-3235.
  23. ^ Zervas, Chris E.; Sempéré, Jean-Christophe; Lin, Jian (1995-06-01). "Morphology and crustal structure of a small transform fault along the Mid-Atlantic Ridge: The Atlantis Fracture Zone". Marine Geophysical Researches. 17 (3): 275–300. doi:10.1007/BF01203466. ISSN 1573-0581.
  24. ^ Cite error: The named reference :2 was invoked but never defined (see the help page).
  25. ^ Ludwig, Kristin A.; Kelley, Deborah S.; Butterfield, David A.; Nelson, Bruce K.; Früh-Green, Gretchen (July 2006). "Formation and evolution of carbonate chimneys at the Lost City Hydrothermal Field". Geochimica et Cosmochimica Acta. 70 (14): 3625–3645. doi:10.1016/j.gca.2006.04.016.
  26. ^ Schrenk, M. O.; Brazelton, W. J.; Lang, S. Q. (13 February 2013). "Serpentinization, Carbon, and Deep Life". Reviews in Mineralogy and Geochemistry. 75 (1): 575–606. doi:10.2138/rmg.2013.75.18.
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  32. ^ "Astrobiologist Kevin Hand helps IMAX director film Aliens of the Deep". Stanford University. 14 January 2005.
  33. ^ "Blue Planet II just showed us where life may have begun". The Independent. 2017-11-06. Retrieved 2019-04-11.

External links[edit]