Hydrogen and carbon isotope systematics in hydrogenotrophic methanogenesis under H2-limited and H2-enriched conditions: implications for the origin of methane and its isotopic diagnosis

Compilation of hydrogen and carbon isotope systematics from incubation and observation. Description of data: Type of ecosystem, name of ecosystem, temperature of methanogen growth (Celsius), approximate timescale for growth, fractionation factors of the carbon isotope ratio between CH4 and CO2 ( α C C H 4 – C O 2 {\upalpha^{\mathrm{C}}}_{{\mathrm{C}\mathrm{H}}_4\hbox{--} {\mathrm{C}\mathrm{O}}_2} ), fractionation factors of the hydrogen isotope ratio between CH4 and H2O ( α H C H 4 – H 2 O {\upalpha^{\mathrm{H}}}_{{\mathrm{CH}}_4\hbox{--} {\mathrm{H}}_2\mathrm{O}} ), and references. (XLSX 53 kb

Identification of paleomagnetic remanence carriers in ca. 3.47 Ga dacite from the Duffer Formation, the Pilbara Craton

金沢大学理工研究域地球社会基盤学系The ca. 3.47 Ga Duffer Formation has been considered to carry one of the oldest paleomagnetic records. Yet, the lack of rock magnetic data limits the interpretation of the nature of the remanence. We conducted a rock magnetic and paleomagnetic investigation on columnar dacite of the Duffer Formation. The main magnetic minerals are phenocrysts of titanomagnetite and magnetite, and secondary hematite in groundmass. Detailed thermal demagnetization revealed more complex natural remanence than previously estimated, consisting of four components with typical unblocking temperature of 200–350, 200–500, 590, and 690 °C. Combined with alternating field demagnetization and rock magnetic data, they are attributed to titanomagnetite, coarse-grained magnetite, fine-grained magnetite, and hematite, respectively. The comparison of unblocking temperature and coercivity suggests that the previously proposed secondary component is carried by fine-grained magnetite as well as hematite, while the putative primary component is carried by coarse-grained magnetite and titanomagnetite. Microscopic observations showed that coarse-grained magnetite and titanomagnetite are primary crystals, although this does not necessarily indicate they preserve primary remanence. The remanence directions of all components revealed higher scatter than the previous studies, suggesting the need for caution in interpretation. The low unblocking temperature of titanomagnetite suggests that if their remanence is truly primary, the rocks must have kept below ~ 250 °C for ~3.47 billion years. © 2020 Elsevier B.V.Embargo Period 24 month

Evaluation of nutrient and energy sources of the deepest known serpentinite-hosted ecosystem using stable carbon, nitrogen, and sulfur isotopes.

The Shinkai Seep Field (SSF) in the southern Mariana forearc discovered in 2010 is the deepest (~5,700 m in depth) known serpentinite-hosted ecosystem dominated by a vesicomyid clam, Calyptogena (Abyssogena) mariana. The pioneering study presumed that the animal communities are primary sustained by reducing fluid originated from the serpentinization of mantle peridotite. For understanding the nutrient and energy sources for the SSF community, this study conducted four expeditions to the SSF and collected additional animal samples such as polychaetes and crustaceans as well as sediments, fragments of chimneys developing on fissures of serpentinized peridotite, seeping fluid on the chimneys, and pore water within the chimneys. Geochemical analyses of seeping fluids on the chimneys and pore water of the chimneys revealed significantly high pH (~10) that suggest subseafloor serpentinization controlling fluid chemistry. Stable isotope systematics (carbon, nitrogen, and sulfur) among animals, inorganic molecules, and environmental organic matter suggest that the SSF animal community mostly relies on the chemosynthetic production while some organisms appear to partly benefit from photosynthetic production despite the great depth of SSF

Temperature-independency in Oxygen Isotopic Fractionation between Carbonate and Water

Oxygen isotopic composition of carbonate has been considered as the most reliable thermometer for ancient water environments because of temperature-dependency of the fractionation factor between carbonate and water. However, the temperature-dependency is not always guaranteed, and the fractionation factor is variable with pH that controls relative abundance among different dissolved carbonate species. This chemical systematics was first verified by a German geochemist, Eberhard Usdowski. We review his work on temperature-independency in oxygen isotopic fractionation, and note that our data from an Indonesian hot spring are consistent with his model