Anatoly M Sagalevich

Isotopic-Geochemical Characteristics of the Lost City Hydrothermal Field

The isotopic (δD, δ18O, δ13C, and 87Sr/86Sr) and geochemical characteristics of hydrothermal solutions from the Mid-Atlantic Ridge and the material of brucite-carbonate chimneys at the Lost City hydrothermal field at 30°N, MAR, were examined to assay the role of the major factors controlling the genesis of the fluid and hydrothermal chimneys of the Lost City field. The values of δD and δ18O in fluid samples indicates that solutions at the Lost City field were produced during the serpentinization of basement ultramafic rocks at temperatures higher than 200°C and at relatively low fluid/rock ratios (<1). The active role of serpentinization processes in the genesis of the Lost City fluid also follows from the results of the electron-microscopic studying of the material of hydrothermal chimneys at this field. The isotopic (δ18O, δ13C, and 87Sr/86Sr) and geochemical (Sr/Ca and REE) signatures indicate that, before its submarine discharging at the Lost City field, the fluid filtered through already cold altered outer zones of the Atlantis Massif and cooled via conductive heat loss. During this stage, the fluid could partly dissolve previously deposited carbonates in veins cutting serpentinite at the upper levels of the Atlantis Massif and the carbonate cement of sedimentary breccias underlying the hydrothermal chimneys. Because of this, the age of modern hydrothermal activity at the Lost City field can be much younger than 25 ka.

Hydrothermal sulfide deposits of the Lucky Strike vent field, Mid-Atlantic Ridge

Several hydrothermal sulfide structures were sampled using Mir manned submersibles in the relatively shallow Lucky Strike vent field, Mid-Atlantic Ridge; the bathymetric position of these structures varies by approximately 100 m. The investigation of the chemical and mineral compositions of hydrothermal ore occurrences led to the conclusion that the initial high-temperature ore-bearing solution ascending toward the surface became unstable and experienced phase separation beneath the ocean floor. The phase separation was responsible for the bathymetric control of hydrothermal ore formation in the ocean.

Carbon Dioxide Assimilation and Methane Oxidation in Various Zones of the Rainbow Hydrothermal Field

Rates of carbon dioxide assimilation and methane oxidation were determined in various zones of the Rainbow Hydrothermal Field (36°N) of the Mid-Atlantic Ridge. In the plume above the hydrothermal field, anomalously high methane content was recorded, the microbial population density (up to 105 cells/ml) was an order of magnitude higher than the background values, and the CO2 assimilation rate varied from 0.01 to 1.1 μg C/(l day). Based on the data on CO2 assimilation, the production of organic carbon due to bacterial chemosynthesis in the plume was calculated to be 930 kg/day or 340 tons/year (about 29% of the organic carbon production in the photic zone). In the black smoke above active smokers, the microbial population density was as high as 106 cells/ml, the rate of CO2 assimilation made up 5–10 μg C/(l day), the methane oxidation rate varied from 0.15 to 12.7 μl/(l day), and the methane concentration ranged from 1.05 to 70.6 μl/l. In bottom sediments enriched with sulfides, the rate of CO2 assimilation was at least an order of magnitude higher than in oxidized metal-bearing sediments. At the base of an active construction, whitish sediment was found, which was characterized by a high methane content (92 μl/dm3) and a high rate of methane oxidation (1.7 μl/(dm3 day)).

Authigenic carbonates in methane seeps from the Norwegian sea: Mineralogy, geochemistry, and genesis

Authigenic carbonates in the caldera of an Arctic (72°N) submarine mud volcano with active CH4bearing fluid discharge are formed at the bottom surface during anaerobic microbial methane oxidation. The microbial community consists of specific methane-producing bacteria, which act as methanetrophic ones in conditions of excess methane, and sulfate reducers developing on hydrogen, which is an intermediate product of microbial CH4 oxidation. Isotopically light carbon (δ13Cav =−28.9%0) of carbon dioxide produced during CH4 oxidation is the main carbonate carbon source. Heavy oxygen isotope ratio (δ18Oav = 5%0) in carbonates is inherited from seawater sulfate. A rapid sulfate reduction (up to 12 mg S dm−3 day−1) results in total exhausting of sulfate ion in the upper sediment layer (10 cm). Because of this, carbonates can only be formed in surface sediments near the water-bottom interface. Authigenic carbonates occurring within sediments occur do notin situ. Salinity, as well as CO32−/Ca and Mg/Ca ratios, correspond to the field of nonmagnesian calcium carbonate precipitation. Calcite is the dominant carbonate mineral in the methane seep caldera, where it occurs in the paragenetic association with barite. The radiocarbon age of carbonates is about 10000 yr.

Geochemistry of hydrothermal solutions from 9°50′ N at the East Pacific Rise (EPR) within twelve years after the eruption of a submarine volcano

Hydrothermal solutions were examined in a circulation system that started to develop after the 1991 volcanic eruption in the axial EPR segment between 9°45′ N and 9°52′ N. Within the twelve years elapsed after the eruption, the diffusion outflow of hot fluid from fractures in basaltic lavas gave way to focused seeps of hot solutions through channels of hydrothermal sulfide edifices. The example of field Q demonstrates that the concentrations of H2S decreased from 86 to 1 mM/kg from 1991 to 2003, and the Fe/H2S ratio simultaneously increased by a factor of 1.7, a fact that can explain the disappearance of the microbial mats, which were widespread at the fields before 1991. The S isotopic composition of H2S is independent of the H2S concentration, a fact testifying to the rapid evolution of the hydrothermal system in the early years of its evolution. Carbon in CH4 from the hot fluid sampled in 2003 is richer in the light 12C isotope than carbon in the fluid from the hydrothermal field at 21° N in EPR, which suggests that methane comes to field Q from more than one source. The composition of particulate matter in the hydrothermal solutions indicates that it was contributed by biological material. Experimental solutions with labeled substrates (t < 70°C) show evidence of the active processes of methane oxidation and sulfate reduction. Our results indicate that, during the 12 years of the evolution of the hydrothermal system, the composition of its solutions evolved and approached the compositions of solutions in mature hydrothermal systems in EPR.

Endemism and Biodiversity of Hydrothermal Vent Fauna

Hydrothermal vent fauna represents a unique source for scientists who are involved in investigations of ecology, zoology, and biochemistry of extremophyles . However, exoskeletal and biomineral-containing structures located within these organisms are of large scientific interest for bioinspired material science and especially for extreme biomimetics . Here, we report about biodiversity, endemism, and trophic specialization and the food web of animals which habituate in these extreme environmental conditions. Numerous underwater images represented in this chapter should help for better understanding of the life near hydrothermal vents.

Initial stage of the hydrothermal ore accumulation within the field at 9°50′ N on the East Pacific Rise

In 2003, several hydrothermal mounds located at 9°50′ N on the East Pacific Rise were described and sampled during the expedition of R/V Akademik Mstislav Keldysh during dives of Mir deep-sea manned submersibles. These hydrothermal mounds were formed during a few recent years after the volcanic activity in this region that occurred in 1991. The studies of the chemical and mineralogical compositions of the hydrothermal deposits of these mounds and of the chemical composition of the principal sulfide minerals helped to describe the initial stage of the formation of the hydrothermal circulation system and the initiation of the hydrothermal ore formation.

Manned Submersibles Mir and the Worldwide Research of Hydrothermal Vents

The role of deep manned submersibles (DMSs) in scientific research of the ocean is considered. The history of development of DMS is introduced, drawing attention on the steps, generated by submarine accident (“Thresher”) and scientific research jumps (hydrothermal vent discovery). Development of the building of DMS in Russia and particularly in P. P. Shirshov Institute of Oceanology, RAS, is considered, concentrating on worldwide research with “Pisces VII” and “Pisces XI” submersibles in 1970–1980s of the twentieth century.