Some Properties of the Trace Metal Biogeochemistry in the Deep-Sea Hydrothermal Ecosystems at the Mid-Atlantic Ridge (MAR) and East Pacific Rise (EPR)

Some features of the trace metal biogeochemistry in some deep-sea hydrothermal ecosystems were studied at the Menez Gwen, Lost City, Rainbow, Broken Spur at the Mid–Atlantic Ridge (MAR), as well as the 9o50' N of the East Pacific Rise (EPR) and the Guaymas Basin (Gulf of California). These hydrothermal fields differ in depth of their location, spreading velocitiy of the ocean crust (<6 cm year -1 at the MAR, > 11 cm year-1 at EPR), geological structure, composition of rocks, etc. The significant differences in trace metal metals (Fe, Mn, Zn, Cu, Ni, Cr, Co, As, Pb, Cd, Ag, Hg) concentrations in the biotope water were found between the low- and high-temperature hydrothermal fields.
Distribution patterns of trace metals in different taxa gave an evidence of the influence of environmental and biological parameters on their bioaccumulation in organisms. Among the animals a particular “champion” with respect to the trace metal content was found to be a polychaeta Alvinella pompejana that inabits the hottest places of the vent sulphide chimneys of the 9o50’N field, EPR.
New data on the trace metal behaviour during the biomineralization in case of carbonate shells of Bathymodiolus spp. mussels and Calyptogena magnifica clams were obtained. From calculations of trace metal partition between soft tissues and carbonate shells (based on their weight proportion in the whole body) we have found that Mn, Ni, Pb, Co, Cr, Se, and Fe are predominantly accumulated (>70% of the total content in the whole body) in the carbonate shells. Mn having a geochemical affinity to Ca, is almost completely (on average 97%) associated with carbonate shell. More than 50% of total amount of Cu, As, Zn, Ag, Hg, and Cd is accumulated in the soft tissues.
Inter-site comparison of the trace metal partitioning in different organs of the Bathymodiolus spp. mussels (soft tissues and carbonate shells) showed that a significant difference occurred only between the high-temperature vent sites (Rainbow, Broken Spur) on the one hand, and low-temperature Menez Gwen (MAR) vent site, on the other hand.
Our measurement of the organic carbon (Corg) content in 115 samples of the hydrothermal animals have shown that in different soft tissues it varies from 21,5 to 62,8% with an average of 43,7%. It is interesting to understand if there is any relationship between the Corg and trace metal content in the organisms. The maximal content of both the trace metals and Corg contents were detected in the Bathymodiolus mussel gills, where the high metal/Corg ratio was calculated also. Taking into account that the mussel gills contain chemoautotrophic bacteria, these peak values can be more likely attributed to a very specific hydrocarbon composition: predominance of high-molecular hydrocarbon with almost equal content of even and odd homologs (ΣC10-22/ΣC23-35 = 0.71, OEP17-19 = 1.53, CPI = 1.14, data of N.Shulga).
Owing to the large biomasses of hydrothermal bottom organisms (up to 60 kg per m2, Demina, Galkin, 2010) they may be considered an efficient local deep-water biological filter of the ocean.

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Shirshov Institute of Oceanology, Russian academy of science, Moscow
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Shirshov Institute of Oceanology, Russian academy of science, Moscow
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