The hydrothermal mounts or hydrothermal chimneys , or smokers , are hydrothermal vents located near the dorsal S oceanic. They are a consequence of the movements of the tectonic plates. They evacuate part of the internal heat of the Ground. It is in 1977 that the black smokers and the luxuriant life which is associated for them were discovered by the American submarine Alvin. This ecosystem is based on a primary production ensured by chimiosynthetic Bactéries which live free or in Symbiose with the organizations.
Formation of the hydrothermal systems
The movements of the Tectonic plates cause phenomena of extension and Accrétion to the level of the oceanic dorsals, generating anfractuosities on the level of the oceanic crust. The sea water can infiltrate and warms up near the magma. Under the effect of the temperature and pressure, the fluid goes up towards the ocean floor. It is acidified and taken care in metal elements in contact with the surrounding rocks, by solubilization (the very high temperatures and the pressure increase the capacity solvent of water). Then, during the emission, in contact with the cold sea, the minerals of the fluid precipitates and form mineral buildings thus comparable with chimneys.
The hydrothermal fluid is rich in dissolved gas (H2S, CH4, CO, CO2, H2) and in metals (If, mn, Fe, Zn). The composition and the physicochemical characteristics of the hydrothermal fluid are function of the temperature and the type of crossed rocks. It is possible to distinguish the black smokers and the smokers blancs.
The black smokers, and in particular smokers, represent true oases of lives at the bottom of the oceans. Organizations adapted to exploit the Chaleur and the Soufre emitted by these hydrothermal sources.
The life is localized around the points of emission of the hydrothermal fluids which mix with sea water. There exists a variation in temperature as one moves away from the point of emission of the fluids, and one can find communities animal of pole hot and animal communities of poles tepid. Micro-organisms (Bacterium S and Archaea) can multiply with more close to the chimney at very high temperatures and are described as Extrémophile S.
Micro-organisms hyperthermophile S live in free form in the hydrothermal fluid. It is the case of the Thermococcales like the kinds Pyrococcus and Thermococcus and of the Archaeoglobales.
Various organizations live near the smokers, in water between 4 and 50°C.
With the hot pole (20-50°C), nearest to the chimneys, one can find Annélides polychètes of the kinds Alvinella and Paralvinella , as well as crabs (for example of the kind Cyanagraea ).
Further, the tepid pole (10-20°C) is occupied by Vestimentifères ( Riftia pachyptila , Lamellibrachia barhami ), crabs, fish…
Lastly, with the cold pole (inter alia) bivalves live: Bathymodiolus (moulds depths), Calyptogena .
One can find also there the Galathée yéti, species recently discovered…
Organizations surprising like the worm Riftia pachyptila , the annélide Alvinella pompejana , the shrimp Rimicaris exoculata are used like models and very studied by various laboratories.
Simple: Hydrothermal wind
The structures evolve/move during time and the smokers are transitory: they can last from 10 to 100 years. They can indeed collapse, or the conduit can be clogged by precipitation of minerals. The active zone along the dorsal can move and involve the training of new smokers and the disappearance of old.
Thus, a site located by scientists at the time of a mission can have disappeared before a new mission is gone back there.
Various hydrothermal structures
Ecosystem of the hydrothermal sources
Before 1977, the underwater funds were regarded as desert because stripped of primary production photosynthetic. The discovery of the ecosystem associated with the hydrothermal sources upset knowledge in biology of the time and in particular the conviction that the life was impossible without lumière.
The level of the hydrothermal sources, the primary production is ensured by Chimiosynthèse thanks to micro-organisms. Instead of using solar energy by photosynthesis as the plants do it, of the bacteria exploit the geothermal energy which emerges from the sources by chemosynthesis. They use the chemical energy provided by the fluid and thus form the first link of the food chain. The primary education consumers nourish primary production. One finds also associations symbiotic in which the symbion brings energy to the host.
Bacteria more mésophiles develop on the surrounding rocks forming of the carpets like Beggiatoa and Thiothrix .
Micro-organisms develop in ecto- or endo-symbiosis with fauna colonizing the surroundings of the chimneys.
See too
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