Life in extreme environments: Hydrothermal vents

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Eruption of volcanic rocks at the midocean ridges is the major mechanism by which heat is lost from the interior of the Earth. Approximately one-third of the heat is removed from the spreading centers by convective circulation of seawater (1). The magnitude of this heat loss requires that the entire volume of the oceans circulates through the midocean ridges in approximately 10 million years. Seawater interaction with volcanic rocks at near 400°C results in substantial chemical flux and makes an important contribution to buffering the composition of some elements in seawater. Cations from seawater (Mg+2, Ca+2, and Na+) form hydroxyl-bearing alteration minerals in the volcanic rocks, releasing hydrogen ion to solution. The hot, acidic altered-seawater releases metals (Fe, Mn, Zn, and Cu) and reduced sulfur (H2S) from the volcanic rock; these are transported by hydrothermal solutions to the seafloor and form metallic mineral deposits. Seafloor hydrothermal vents support ecosystems with enormous biomass and productivity compared with that observed elsewhere in the deep oceans. What is the energy source that fuels these oases of life, and what adaptations allow them to exist in these extreme environments? Oxidation/reduction (redox) reactions are key to supporting chemosynthesis. The atmosphere and hydrosphere are relatively oxidizing with an abundance of potential electron acceptors (O2, SO4=, and NO3-). In contrast, the basaltic rocks that form the oceanic crust are relatively reduced because of the abundance of ferrous iron. High-temperature fluid/rock interaction forms reduced gases (H2S, H2, and CH4) that dissolve in hydrothermal fluid. Representative redox reactions that produce H2S include: 1 2where talc serves as a proxy for a Mg hydroxide component of alteration minerals such as chlorite and amphibole. Sulfur is a particularly important …

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Bacteria Archaea Cations Oxidation-Reduction Geology Hot Temperature Bacterial Physiological Phenomena Geological Phenomena