Michael Ivanov

The Trophic Structure and Composition of the Hydrothermal Community Rainbow (36° N, the Mid-Atlantic Ridge)

The modern classification distinguishes two type of hydrothermal circulation systems (HCSs) in the world rift system: the widespread, so-called axial HCS and the deep HCS [1–3]. To date, the hydrothermal activities of only two areas, Rainbow and Logatchev ( 14°45 ′ N), are known to be related to the deep HCSs. Both areas are located on the Mid-Atlantic Ridge (MAR). The main characteristic features of a deep HCS are an absence of volcanic activity at the present time and a relationship between the hydrothermal activity and serpentinization of ultrabasites in the presence of sea water. When ultrabasites are serpentinized, considerably larger amounts of hydrogen and methane and smaller amounts of hydrogen sulfide are formed compared to the usual hydrothermal solution of axial HCSs. This is reflected in the chemical and gas composition of the venting fluids. The concentration of CH 4 in the venting fluids of the Rainbow and Logatchev hydrothermal areas is as high as 2220–2310 μ M, whereas its concentrations in other areas of the MAR vary from 45 to 970 μ M. Water in the Rainbow and Logatchev areas is also unusually rich in CH 4 (its concentration is 5– 20 times higher than background); hydrothermal sulfide ores contain various hydrocarbons [4]. These characteristic features of hydrothermal solutions may affect the vital activity of chemoautotrophs and methanotrophs, which are primary producers in hydrothermal communities.

Changes in the stable isotope composition of gases and minerals as a result of microbial activity

The effect of biological fractionation of carbon and sulfur isotopes is described now for many microbial processes. Stable isotope composition of carbon and sulfur gases and minerals, produced by microorganisms depends on isotope composition of initial substrates, part of substrate consumed by microorganisms and rate of microbial metabolism.