地球化学

企画総説「地球化学の最前線」

中性pH付近で生育する鉄酸化菌の生理生態とその生物地球化学的重要性

加藤真悟

2015 年 49 巻 1 号 p. 1-17
発行日: 2015/03/25
公開日: 2015/03/30

DOIhttps://doi.org/10.14934/chikyukagaku.49.1

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Iron is a key element to understand global biogeochemical cycling. Microorganisms are involved in redox cycling of iron in natural environments. In particular, neutrophilic iron-oxidizing microorganisms that grow at circumneutral pH potentially play a significant role in global iron oxidation at redox boundaries. However, little is known about neutrophilic iron-oxidizing microorganisms because only a few cultivated species have been reported to date despite a long research history. In this review, knowledge about neutrophilic iron-oxidizing microorganisms, i.e., phylogeny, physiology, ecology, spatial distribution, and unique extracellular polymeric substances, is summarized, including the most recent reports. This will provide useful information to various scientific fields: not only microbiology, but also geochemistry, astrobiology and environmental engineering.

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報文

213 nm Nd: YAGレーザーアブレーション誘導結合プラズマ質量分析計を用いたジルコンのU–Pb年代測定: Pb/U分別補正にNIST SRM 610を用いるための分析条件最適化

高地吉一, 折橋裕二, 小原北士, 藤本辰弥, 春田泰宏, 山本鋼志

2015 年 49 巻 1 号 p. 19-35
発行日: 2015/03/25
公開日: 2015/03/30

DOIhttps://doi.org/10.14934/chikyukagaku.49.19

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We carried out an optimization of analytical parameters for U–Pb zircon dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using a NIST SRM 610 glass. As a result, we obtained the following optimum analytical parameters: laser energy: 11.7 J/cm², repetition rate: 10 Hz, pre-ablation time: 8 sec, integration time: 10 sec and crater diameter: 25 μm. The average ²⁰⁶Pb/²³⁸U ratio of the NIST SRM 610 glass normalized by a 91500 zircon standard under the conditions mentioned above was 0.2236±0.0044 (1σ, N : 87). The median value of this result matches with that of the literature value within range of the analytical precision. Furthermore, the ²⁰⁶Pb/²³⁸U weighted mean ages of the Plešovice, OD-3 and Fish Canyon Tuff zircons, having the proposed ²⁰⁶Pb/²³⁸U ages of 335.48±0.95 Ma (95% conf., N : 38, MSWD : 1.1), 33.25±0.38 Ma (95% conf., N : 23, MSWD : 1.5), 28.56±0.49 Ma (95% conf., N : 34, MSWD : 5.1), respectively, were measured, normalized by the NIST SRM 610 glass standard. The results were consistent within 1% error range of the recommended values. These results suggest that the matrix effect can be reduced to less than analytical precision on materials with different physical properties under well-optimized analytical conditions.

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非メタン炭化水素測定時に使用する水から放出される非メタン炭化水素とその除去法

猪狩俊一郎

2015 年 49 巻 1 号 p. 37-44
発行日: 2015/03/25
公開日: 2015/03/30

DOIhttps://doi.org/10.14934/chikyukagaku.49.37

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The concentration of atmospheric nonmethane hydrocarbon can be measured by the method of Igari (1995). In the study, water is used. Here I describe a method for measuring the concentration of nonmethane hydrocarbons in water samples. In addition, a method for removing nonmethane hydrocarbons from water was studied. A high concentration of nonmethane hydrocarbons were observed in tap water stored in a water pipe. The concentration of nonmethane hydrocarbon in distilled water was also investigated; water obtained using a new water distillation apparatus contained high nonmethane hydrocarbon concentrations, whereas water obtained using an old water distillation apparatus had relatively low concentrations. Heating water samples for several hours in an electric kettle significantly decreased nonmethane hydrocarbon concentrations. The described method can be used to measure both atmospheric nonmethane hydrocarbon and trace nonmethane hydrocarbon concentrations in natural gases.

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総説

化学風化と河川におけるマグネシウム同位体比の挙動

眞中卓也, 吉村寿紘

2015 年 49 巻 1 号 p. 45-58
発行日: 2015/03/25
公開日: 2015/03/30

DOIhttps://doi.org/10.14934/chikyukagaku.49.45

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Magnesium is a major terrestrial rock element and plays an important role in the global geochemical cycles. In terrestrial waters, dissolved magnesium is derived from the weathering of both siliceous and carbonate rocks. It is then transported to the ocean where it is crucial for the aquatic biota and regulates global climate over geologic time scales. Recently, a technologically advanced multicollector inductively coupled plasma mass spectrometry provided an opportunity to measure the magnesium isotope ratio (δ²⁶Mg) with high accuracy. In this paper we review ongoing researches on the δ²⁶Mg value in the river systems over the world, as well as its controlling factors, including isotope fractionation during chemical weathering, secondary mineral formation, and biological activity. Furthermore, we examine the potential use of δ²⁶Mg as a new tool for the better understanding of chemical weathering processes and the global magnesium cycle, which ultimately controls the Earth's surface environment.

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訂正

訂正

2015 年 49 巻 1 号 p. 59-62
発行日: 2015/03/25
公開日: 2015/03/30

DOIhttps://doi.org/10.14934/chikyukagaku.49.59

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