Lost City (hydrothermal field)

Lost City is the name of an area of hot springs, or hydrothermal vents at the Atlantis Massif, an oceanic mountain range in the mid-Atlantic.

This massif is part of the Mid-Atlantic Ridge, the volcanically active mountain range that runs through the ocean on the entire length from north to south. Lost City is significantly different from other hydrothermal areas, such as the well-known since the late 1970s, black smoker - vents. It consists of a box with about 30 chimneys composed mainly of calcium carbonate (lime ) and have 30 meters to 60 meters high. In addition, there is a number of small vents. Geologists, chemists and biologists can explore where the abiotic processes and the ways of life of a previously unknown ecosystem, based on methane and hydrogen as an energy source.

Lost City was discovered in December 2000 during an expedition of the National Science Foundation. A second expedition, which was fitted in 2003, used the submarine Alvin to explore the vents. A third expedition, by the National Oceanic and Atmospheric Administration ( NOAA) followed in 2005, with the submarines Hercules and Argus. The details of the unusual chemistry and biology of hydrothermal area were published in March 2005.

The vents give mainly methane and hydrogen into the surrounding water. These gases come from highly alkaline fluids, which are concentrated solutions which emerge there with a pH of 9 to 11, and temperatures between 40 ° C and 90 ° C. These fluids caused by the fact that sea water reacts with the rock peridotite in an exothermic process together and it converts to serpentine ( serpentinization ), where ( H2) can be generated in addition methane (CH4), hydrogen sulfide ( H2S) and hydrogen gas. This is possible because the peridotite was raised by tectonic processes from the depths close to the seabed. Other effects include a decrease in the density of the rock and an increase in volume of 20 to 40 %, thereby creating additional cracks in the rock and caused sea water can penetrate into previously unaffected areas of the peridotite.

However, in contrast to the black smokers these fluids promote only insignificant amounts of carbon dioxide or metals. The temperatures and pH values ​​of the black smoker fluids are also significantly different.

The isotope ratios of strontium, carbon and oxygen, as well as radiocarbon datings occupy at least 30,000 years of hydrothermal activity at the Lost City, so it is older by at least two orders of magnitude, than the previously known black smokers. Correspondingly, the life forms in the two types of hydrothermal areas differ enormously. The chimneys of the Lost City can be the high biomass of microorganisms miss that are typical of the Black Smoker. Nevertheless Lost City hosts a variety of small invertebrates that reside primarily on the calcified structures, including snails, clams, polychaete worms, amphipods and ostracods ( Ostracoda ). Inside the vents live Methanosarcina -like archaea that oxidize the escaping methane, in addition to relatives of Firmicutes. Outside the vents oxidize other archaebacteria both methane and sulfur and hydrogen, such as the recently described new ANME 1 and other bacteria, including Proteobacteria.

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