Detection of microbial activity at seafloor hydrothermal system by sulfur isotope micro-analysis.

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Elemental Analyzer-continuous flow Isotope Ratio Mass Spectrometer (EA-IRMS) was introduced in our laboratory and checked for the ability of the EA-IRMS on micro-scale sulfur isotope ratio measurement. Seafloor hydrothermal sulfide-sulfate chimney and sulfide are were described in detail from the view points of mineralogy and economic geology in order to prepare the detection of the microbial activity at the seafloor hydrothermal system by the sulfur isotopic ratio.Elemental Analyzer-continuous flow Isotope Ratio Mass Spectrometer (EA-IRMS) was found to be capable to analyze sulfur isotopic compositions of common sulfide and sulfate mineral, such as chalcopyrite, pyrite, sphalerite and barite, in seafloor hydrothermal chimney. The required amount of sample for the measurement is very small, which is 1/100 compared to the amount used by conventional double inlet IRMS. Measurement of reference material during sample analyses and the use of combustion improver made the precision of analysis as accurate as those obtained by the conventional method, though the raw measured sulfur isotope ratios increase during consecutive measurements. Furthermore, Niobium oxide was found to be a good combustion improver instead of the commonly used highly toxic Vanadium oxide.Active and dead seafloor hydrothermal chimneys in Iheya North seafloor hydrothermal system, Okinawa Trough, were mineralogically examined in detail to prepare the detection of microbial activity using their sulfur isotopic ratios. They are mainly consisted of chalcopyrite, pyrite, sphalereite and barite. From the occurrences and texture of these minerals, the seafloor chimney growth model in the Okinawa Trough seafloor hydrothermal system was established.