Sulfur isotopic exchange between chemosynthetic microbes and sulfur-bearing minerals in seafloor hydrothermal systems

点击翻译按钮获取中文摘要

We conducted research to explore seafloor hydrothermal sites, cold seep zone on seafloor, sub-seafloor gas hydrate, and fossil seafloor hydrothermal activity to elucidate the geochemical and microbiological processes. We obtained following conclusions:(1)Sulfate and sulfide minerals in the Suiyo Seamount, Izu-Bonin Arc, Western Pacific are formed from seawater sulfate and magmatic sulfide sulfur, respectively, and no biogenic signature was identified in the sulfide minerals despite the fact that the sulfur reducing bacteria is dominant in the sediments near the hydrothermal area.(2)Hydrogen isotopic analysis of the interstitial water at the Hydrate Ridge, Cascadia Margin of North America indicate that the methane seep is accompanied with fluid which was derived from decomposition of gas hydrate. Therefore, high methane flux of the area does not necessarily indicate high rate of methane hydrate formation at depth.(3)Heavy sulfur isotopic value of pyrite in sediments from McKenzie Delta, Northwestern Territories, Canada suggests its seawater sulfate origin under closed or semi-closed environment. This idea matches with the observation of sea-level rise and fall in the district.(4)Organic geochemical analysis on bacterial matte at methane seep off Tokai coast indicate that the biomarkers are the mixture of algae, aerobic bacteria, and methane-oxidizing Archaea.(5)Kuroko deposit is the fossil seafloor hydrothermal deposit of Japan Arc in Miocene age. So-called Brown Ore which is characterized by its gold and silver-rich assay occurs on the periphery of the massive sulfide ore of the Kuroko deposits affected by microbial activity of the hydrothermal system.(6)All the results indicate that the mass spectroscopic analysis is the most powerful tool to discriminate the biological activity of the hydrothermal system in the past and present-day seafloor.