Go-Ichiro Uramoto

Biological CO2 conversion to acetate in subsurface coal-sand formation using a high-pressure reactor system

Geological CO2 sequestration in unmineable subsurface oil/gas fields and coal formations has been proposed as a means of reducing anthropogenic greenhouse gasses in the atmosphere. However, the feasibility of injecting CO2 into subsurface depends upon a variety of geological and economic conditions, and the ecological consequences are largely unpredictable. In this study, we developed a new flow-through-type reactor system to examine potential geophysical, geochemical and microbiological impacts associated with CO2 injection by simulating in-situ pressure (0–100 MPa) and temperature (0–70°C) conditions. Using the reactor system, anaerobic artificial fluid and CO2 (flow rate: 0.002 and 0.00001 ml/min, respectively) were continuously supplemented into a column comprised of bituminous coal and sand under a pore pressure of 40 MPa (confined pressure: 41 MPa) at 40°C for 56 days. 16S rRNA gene analysis of the bacterial components showed distinct spatial separation of the predominant taxa in the coal and sand over the course of the experiment. Cultivation experiments using sub-sampled fluids revealed that some microbes survived, or were metabolically active, under CO2-rich conditions. However, no methanogens were activated during the experiment, even though hydrogenotrophic and methylotrophic methanogens were obtained from conventional batch-type cultivation at 20°C. During the reactor experiment, the acetate and methanol concentration in the fluids increased while the δ13Cacetate, H2 and CO2 concentrations decreased, indicating the occurrence of homo-acetogenesis. 16S rRNA genes of homo-acetogenic spore-forming bacteria related to the genus Sporomusa were consistently detected from the sandstone after the reactor experiment. Our results suggest that the injection of CO2 into a natural coal-sand formation preferentially stimulates homo-acetogenesis rather than methanogenesis, and that this process is accompanied by biogenic CO2 conversion to acetate.

Carbon isotope stratigraphy of terrestrial organic matter for the Turonian (Upper Cretaceous) in northern Japan: Implications for ocean-atmosphere δ13C trends during the mid-Cretaceous climatic optimum

Carbon isotope data of terrestrial organic matter (δ 13 C TOM ) obtained in Hokkaido, northern Japan, from the marine Cretaceous Yezo Group along the northwestern Pacific margin elucidated a detailed chemostratigraphy for the Turonian Stage in this region of East Asia. Chemostratigraphic intra-basin correlation reveals three positive δ 13 C TOM events in the Middle–Upper Turonian of the Yezo Group. δ 13 C TOM fluctuations in these events show similar patterns in the Yezo Group, indicating that terrestrial organic matter is mixed sufficiently before deposition in the Yezo Basin. These δ 13 C TOM events are correlated with previously documented δ 13 C carbonate events in Europe (the Lulworth–Round Down, Glynde–Pewsey, and Late Turonian Events) based on global biostratigraphy. Our chemostratigraphic correlations strengthen the use of these δ 13 C events for global correlation of the Turonian marine successions. In addition, global correlation of Turonian marine and terrestrial δ 13 C events identifies changes in isotopic difference between δ 13 C TOM and δ 13 C carbonate (Δ TOM-carbonate ), which are interpreted to reflect changes in atmospheric p CO 2 levels, and climate-driven stresses of humidity and soil processes. In earlier stages of Turonian, Δ TOM-carbonate values are increased. Elevated atmospheric p CO 2 , and increased humidity and soil processes in enhanced greenhouse conditions during mid-Turonian, are interpreted to enlarge Δ TOM-carbonate values. In later stages of Turonian, Δ TOM-carbonate values are at a constant level, and the lowering of atmospheric p CO 2 or decrease of climate stress related to the diverse paleoclimatic cooling is interpreted to have restored the ocean-atmosphere δ 13 C trends.

Cretaceous Carbon Isotope Stratigraphy and Constraints on the Sedimentary Patterns of the Turonian Forearc Successions in Hokkaido, Northern Japan

Abstract We present a summary on the carbon isotope stratigraphy of terrestrial organic matter (δ13CTOM) of the Cretaceous forearc successions in northern Japan. The δ13CTOM profiles of the Turonian (Upper Cretaceous) successions in Japan exhibit similar trends with the δ13C trends of marine carbonates in Europe (on the basis of the biostratiraphic framework of the age diagnostic ammonoids and bivalves). The similarity indicates an isotopic link between the global oceanic and atmospheric carbon reservoirs. In addition, the chemostratigraphic intrabasin correlation of the Middle Turonian successions in Japan suggests that the spatiotemporal variations in sedimentary pattern are related to a prolonged hiatus or tectonically confined basin formation. Cretaceous carbon isotope stratigraphy in northern Japan validates the potential for δ13C records to be used not only for elucidation of global δ13C trend in ocean‒atmosphere systems, but also for examining the interrelationships between tectonics and sedimentary patterns in this East Asian region.