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e-Journal

 

Hydrothermal Vent Communities
(Released May 2006)

 
  by Carolyn Scearce  

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Finding Lost City

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Scientists discovered a new class of hydrothermal vents in the Atlantic as recently as December of 2000. Geologists performing a deep-water camera survey of the terrain near the under-sea mountain known as Atlantis Massif serendipitously recorded the Lost City site (Kelly, 2005). The geological processes that drive venting at Lost City are different from those at other known sites. Consequently, the physical and chemical characteristics are also different. Generally, when searching for hydrothermal sites, scientists concentrate on the margins within 1-5 km of spreading centers.

Atlantic ocean & surrounding continents
Map showing location of Lost City

The Lost City hydrothermal field is located 15 km from the Mid Atlantic Ridge spreading center at the latitude of 30 degrees N. Instead of the black smoker formations built up by the precipitating fluids exposed to basalt, Lost City's formations are composed of large white carbonate chimneys. Here vent fluids are exposed to uplifted peridotites and are serpentinized. The pH is higher-basic rather that acidic-- carbon dioxide levels are extremely low, and the temperature of vent fluids ranges only between 40-90 degrees C rather then in excess of 300 degrees C. Microorganisms acquire their energy from methane and pure hydrogen instead of the oxidation of hydrogen sulfide. Carbon 14 studies indicate that the vent field has been around for approximately 30,000 years. Scientists speculate that these newly discovered vent fields may last for hundreds of thousands of years (Boetius, 2005).

'beehive' deposit
Carbonate chimney from Lost City
Due to differences in the geology and chemistry of this vent site, the nature of the community associated with Lost City is substantially different from black smoker communities. Instead of large clusters of sessile invertebrates, organisms are smaller and are found in less densely aggregated groups (Kelly, 2005). Currently, no evidence suggests the existence of symbiotic relationships between animals and the chemoautotrophic microorganisms forming the bottom of the food chain. Instead it appears that the marine invertebrates gain energy from grazing on vent-associated carbonates and microbial biofilms. Gastropods and amphipods have been found living in channels of actively venting carbonate sites that range in temperatures between 10-40 degrees C. Polycheates, nematodes, ostracods, stromatopods and bivalves inhabit hydrothermally active flanges and spires. Larger, more mobile animals found at the site include wreckfish, cut-throat eels, and geryonid crabs (Kelley et al, 2005).

At this point, no one knows how common serpentine hydrothermal vent systems may be. Peridotites can exist in extensive ranges and, with the right geological conditions, it is possible there may be many as yet undiscovered hydrothermal vent systems and communities similar to those found at Lost City.

GO TO Why study hydrothermal vents?

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