10:45 AM - 12:15 PM
[BBG01-P07] Connection of deep crustal fluids and surface microbial activities: case studies at non-volcanic hot springs in northeastern Japan
Keywords:crustal fluid, microbial life, hot spring
CO2 and Fe2+-rich hot springs are present in several localities in northern Tohoku district, Japan. Chemistries of these hot spring water are considered as analogue of Archean to early Proterozoic oceans. Microbial activities were high at each hot spring site, and they may have information of early microbial ecosystems. Two sites are examined in the present study to constrain how chemical differences of crustal deep fluids influence on the microbial community formation in the hot springs..
Site 1 (Shin Appi-Nanashigure region) hot spring water are anoxic and extremely rich in B, Li, P and NH3 with some metals. Aragonite and calcite precipitated at the venting sites, often alternating with layers of Fe-(hydro)oxide. Such carbonate precipitating sites may be mimicking evaporitic basins of the early Earth. Geological and geochemical investigations indicate that B, Li and other ions in the fluids were enriched in deep-seated brine pools formed by ancient granite/hydrothermal activities. Activities of chemoautotrophic nitrification and S-metabolism were indicated by stable isotope analyses in the present study. This suggests that evaporitic environments enriched in unusual elements are not hinder but have fertilities for specific microorganisms.
Chemical compositions of hot spring water at site 2 (Kowakubi) are similar to those of site 1, but richer in NH3and Br, I and B. The fluids are from the deep oil reservoirs (but barren). This site is mimicking oil-seeping sedimentary basin, which occurred globally at Paleoproterozoic age. Microbial mats are developing around the venting site with precipitation of calcium carbonates. The presence of different microcosmic communities is indicated by stable isotope analyses. Microbial recycling of C and N were significant at each microcosmic community, although hot spring water continuously supplies HCO3- and NH3. This may be the result of unusual nutrient-rich conditions and rapid environmental change (redox change, Fe2+ concentrations, toxicity from Br and I, etc.) of streaming hot spring water.
All data indicates how microbial activities are sensitive to diverse chemistries of deep crustal fluids. Such diversities in Archean to early Proterozoic crustal fluids may have helped the evolution of microbial life on the early Earth.
Site 1 (Shin Appi-Nanashigure region) hot spring water are anoxic and extremely rich in B, Li, P and NH3 with some metals. Aragonite and calcite precipitated at the venting sites, often alternating with layers of Fe-(hydro)oxide. Such carbonate precipitating sites may be mimicking evaporitic basins of the early Earth. Geological and geochemical investigations indicate that B, Li and other ions in the fluids were enriched in deep-seated brine pools formed by ancient granite/hydrothermal activities. Activities of chemoautotrophic nitrification and S-metabolism were indicated by stable isotope analyses in the present study. This suggests that evaporitic environments enriched in unusual elements are not hinder but have fertilities for specific microorganisms.
Chemical compositions of hot spring water at site 2 (Kowakubi) are similar to those of site 1, but richer in NH3and Br, I and B. The fluids are from the deep oil reservoirs (but barren). This site is mimicking oil-seeping sedimentary basin, which occurred globally at Paleoproterozoic age. Microbial mats are developing around the venting site with precipitation of calcium carbonates. The presence of different microcosmic communities is indicated by stable isotope analyses. Microbial recycling of C and N were significant at each microcosmic community, although hot spring water continuously supplies HCO3- and NH3. This may be the result of unusual nutrient-rich conditions and rapid environmental change (redox change, Fe2+ concentrations, toxicity from Br and I, etc.) of streaming hot spring water.
All data indicates how microbial activities are sensitive to diverse chemistries of deep crustal fluids. Such diversities in Archean to early Proterozoic crustal fluids may have helped the evolution of microbial life on the early Earth.