Discussed in this paper are the isotopic-geochemical characteristics of the "axial" and "deep crustal" circulation hydrothermal systems, based on the experimental data available for the isotopic compositions of sulfur and carbon compounds in hot solutions, in sulfide ores, and in the biomass of hydrothermal community organisms in four MAR active fields of different ages 14o, 26o, 29o, and 36o N. The deep crustal systems differ from the axial ones by their higher concentrations of isotopically heavy CH 4d13 C= - 13.4/ - 14.3 in their fluids and petroleum hydrocarbons in sulfide ores. The proved isotopic C org heterogeneity in the sulfide ores proved its polygenetic origin. The main C org constituent in all ores is the "fresh" and/or thermally transformed biomass of hydrothermal community organisms living at the expense of the chemical synthesis of the H 2 S, H 2, and other reconstructed compounds of hydrothermal water, differing from the common C org synthesized in the ocean either by the anomalously light d>13 C -30 or by anomalously heavy d>13 C -11 isotope composition of organic carbon. As distinct from H 2 S and H 2, the methane of the hydrothermal fluids is only partially utilized by the microbe community and, hence, must compose the bulk of the CH 4 dissolved in the deep oceanic water.
sulfur, carbon isotope, active hydrothermal fields, Mid-Atlantic Ridge, isotopic-geochemical characteristics.
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