Marine biotopes

Marine biotopes of HT consist of various hydrothermal systems situated at shallow to abyssal depths. Similar to ambient seawater, submarine hydrothermal systems usually contain high concentrations of NaCl and sulfate and exhibit a slightly acidic to alkaline pH (5.0-8.5). Otherwise, the major gases and life-supporting mineral nutrients can be similar to those in terrestrial thermal areas. Shallow submarine hydrothermal systems are found in many parts of the world, mainly on beaches with active volcanism, like at Vulcano Island, Italy, with temperatures of 80 to 105 °C.

Most impressive are the deep sea 'smoker' vents (Figure 7.2), where mineralladen hydrothermal fluids with temperatures up to approximately 400 °C escape into the cold (2.8 °C), surrounding deep sea water and build up huge rock chimneys. Although these hot fluids are sterile, the surrounding porous smoker rock material appears to contain very steep temperature gradients, which provide zones of suitable growth temperatures for HT. Some smoker rocks are teeming with HT (for example 108 cells of Methanopyrus per gram of rock inside a Mid Atlantic Snake Pit hot vent chimney). Deep sea vents are located along submarine tectonic fracture zones (for example the 'TAG' and 'Snake Pit' sites situated at the Mid Atlantic Ridge in a depth of about 4000 m). Another type of submarine high temperature environment is provided by active sea mounts. Close to Tahiti, there is a huge abyssal volcano, Macdonald Seamount (28°58.7' S, 140 °15.5' W), the summit of which is situated approximately 40 meters below the sea surface. Samples taken during an active phase from the submarine eruption plume and rocks from the active crater contained high concentrations of viable HT (Huber et al., 1990).

Fig. 7.2. Abyssal hot 'black smoker' chimneys at the East Pacific Rise, 21 °N.

Depth: 2500 m, maximal fluid temperature: 365 °C.

Fig. 7.2. Abyssal hot 'black smoker' chimneys at the East Pacific Rise, 21 °N.

Depth: 2500 m, maximal fluid temperature: 365 °C.

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