No abstract

Bacterial endospores are dominant members of the marine deep biosphere.

Carbon isotope fluctuations of sedimentary organic matter along the two geological traverses in the Yezo Group, Hokkaido, northern Japan, elucidate a detailed chemostratigraphy for the Cenomanian Stage on the northwestern Pacific margin. Visual characterization of the kerogen from mudstone samples shows that the major constituents of sedimentary organic matter originated as terrestrial higher plants. The atomic hydrogen/carbon ratios of the kerogen suggest that the original d 13 C values of terrestrial organic matter (TOM) have not been affected significantly by thermal diagenesis. The patterns in two d 13 C TOM curves are similar and independent of changes in lithology and total organic carbon contents, which suggests that TOM was mixed sufficiently before the deposition in the Yezo forearc basin for the d 13 C composition having been homogenized. In addition, this implies that the Hokkaido d 13 C TOM profiles represent the averaged temporal d 13 C variations of terrestrial higher-plant vegetation in the hinterlands of northeast Asia during Cenomanian time. Three shorter-term (ca. 0.1 my duration) positive-and-negative d 13 C TOM fluctuations of~1‰ are present in the Lower to Middle Cenomanian interval in the Yezo Group. On the basis of the age-diagnostic taxa (ammonoids, inoceramids and planktic foraminifers), these discrete d 13 C TOM events are interpreted to be correlated with those in the d 13 C curves of pelagic carbonates from European basins. The correlation of d 13 C events between the European and Yezo Group sections suggests that the shorter-term d 13 C fluctuations in Cenomanian ocean-atmosphere carbon reservoirs are useful for global chemostratigraphic correlation of marine strata. In particular, the correlation of d 13 C fluctuations of the so-called 'Mid-Cenomanian event' (MCE) implies: (i) the d 13 C variations of global carbon reservoir during the MCE are precisely recorded in the d 13 C TOM records; and (ii) the MCE d 13 C TOM event is an efficient chronostratigraphic index for the Lower/ Middle Cenomanian boundary of the Mid-Cretaceous sequences.

Stratigraphic fluctuations of carbon isotope values of terrestrial organic matter within the Upper Cretaceous (Cenomanian-Santonian) sequence in the Obira area of Hokkaido, Japan, record distinctive δ 13 C fluctuations for the Cenomanian-Turonian boundary, the Middle Turonian, the upper Turonian-lower Coniacian, and the Santonian. A biostratigraphic framework of the agediagnostic taxa (ammonoids, bivalves and planktic foraminifers) indicates that these δ 13 C fluctuation events are comparable with those recorded in δ 13 C data of terrestrial organic matter in Japan and marine carbonates in Europe. These correlations reinforce the utility of these δ 13 C events in terms of global chemostratigraphy. In particular, the δ 13 C patterns within the overall positive interval of the Cenomanian-Turonian boundary event are highly conformable between marine and terrestrial records. The consistent nature of these different records of δ 13 C fluctuation patterns demonstrates that the terrestrial organic δ 13 C data mirror the global-scale δ 13 C patterns in the carbon reservoir of oceanatmosphere-terrestrial biosphere during the Cenomanian-Turonian boundary event. In addition, global correlation of short-term marine and terrestrial organic δ 13 C fluctuations of the Upper Cretaceous sequence indicate that the magnitude of several terrestrial organic δ 13 C events appears more amplified than that of coeval marine carbonate δ 13 C events. This correlation is interpreted to mean that the effects of local CO 2 emission into the atmosphere by release of terrestrial methane hydrate or biomass burning of terrestrial vegetation in the hinterland of the NE Asian region have been superimposed on the global δ 13 C trend and resulted in the terrestrial organic δ 13 C records of the Yezo Group.

Ferromanganese minerals are widely distributed in subseafloor sediments and on the seafloor in oceanic abyssal plains. Assessing their input, formation and preservation is important for understanding the global marine manganese cycle and associated trace elements. However, the extent of ferromanganese minerals buried in subseafloor sediments remains unclear. Here we show that abundant (108–109 particles cm−3) micrometer-scale ferromanganese mineral particles (Mn-microparticles) are found in the oxic pelagic clays of the South Pacific Gyre (SPG) from the seafloor to the ~100 million-year-old sediments above the basement. Three-dimensional micro-texture, and major and trace element compositional analyses revealed that these Mn-microparticles consist of poorly crystalline ferromanganese oxides precipitating from bottom water. Based on our findings, we extrapolate that 1.5–8.8 × 1028 Mn-microparticles, accounting for 1.28–7.62 Tt of manganese, are globally present in oxic subseafloor sediments. This estimate is at least two orders of magnitude larger than the manganese budget for nodules and crusts on the seafloor. Subseafloor Mn-microparticles thus contribute significantly to the global manganese budget.

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 data of terrestrial organic matter (δ 13 C TOM) obtained in Hokkaido, northern Japan, from the marine Cretaceous Yezo Group along the northwestern Pacifi c 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 fl uctuations in these events show similar patterns in the Yezo Group, indicating that terrestrial organic matter is mixed suffi ciently 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 chemostrati graphic 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 identifi es changes in isotopic difference between δ 13 C TOM and δ 13 C carbonate (Δ TOM-carbonate), which are interpreted to refl ect changes in atmospheric pCO 2 levels, and climate-driven stresses of humidity and soil processes. In earlier stages of Turonian, Δ TOM-carbonate values are increased. Elevated atmospheric pCO 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 pCO 2 or decrease of climate stress related to the diverse paleoclimatic cooling is interpreted to have restored the ocean-atmosphere δ 13 C trends.

Marine sediments are composed of various mineral species and are characterized by micro‐scale grain fabric. The arrangements and interactions of component particles place critical constraints on the physical, chemical, and biological processes that occur in subseafloor environments. However, the observation of nearly intact microstructures is difficult, especially in soft, muddy sediments because of their high water content and the presence of organic molecules. In this study, a modified version of the resin‐embedding method generally used for biological samples was applied to marine sediment sample preparation. The new method was compared with the conventional t‐butyl alcohol freeze‐drying method using microfocus X‐ray computed tomography (µXCT) and scanning electron microscopy (SEM). The µXCT and SEM results showed that all t‐butyl alcohol freeze‐dried sediment samples contained microstructural disturbances (e.g., cracks). In contrast, no cracks were observed in the samples prepared using the new resin‐embedding method, and the microstructural arrangement of the sediment particles were clearly visible. In addition, the porosity visible from SEM images of the resin‐embedded samples was similar to that measured using the moisture and density method, providing additional evidence that the microstructures of the resin‐embedded samples were well preserved. The resin‐embedding method allowed observation of the limited contact of the fine particles in clayey sediments, the clay microaggregates throughout the continental margin to pelagic sediments, and the presence of organic materials in environmental sediments. This modified biological resin‐embedding method is suitable for the detailed observation and characterization of fine‐grained marine sediment microstructure.