GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
49 巻 , 3 号
選択された号の論文の8件中1~8を表示しています
  • Ayaka Tokumaru, Tatsuo Nozaki, Katsuhiko Suzuki, Kosuke T. Goto, Qing ...
    2015 年 49 巻 3 号 p. 233-241
    発行日: 2015/05/25
    公開日: 2015/06/03
    ジャーナル 認証あり
    Os isotope compositions in ferromanganese crusts (Fe–Mn crusts) have been used for the dating of model ages from present to the Late Cretaceous. This dating method assumes that the Fe–Mn crusts preserve a paleo-seawater Os isotope composition at the timing of Fe–Mn crust deposition. However, available Os isotope data are limited to dredged samples without precise indications of water depths, and the Os isotope variation in relation to water depth remains uncertain. Here, we report on the Os isotope ratio data in the surface layer of Fe–Mn crusts from 956–2987 meters below sea level at the Takuyo Daigo Seamount in the northwestern Pacific Ocean collected by a remotely operated vehicle (ROV). Since the 187Re/188Os ratios of the surface layer samples exhibited low values ranging from 0.020 to 0.0078, the age correction of the 187Os/188Os ratios by subtracting radiogenic 187Os from total 187Os was not necessary for the Takuyo Daigo Fe–Mn crusts. Regardless of water depth, the surface layer samples possessed a narrow range of 187Os/188Os ratio (1.003–1.017). As their Os isotope ratios were very similar to or slightly lower than the present-day seawater value (~1.06), the Fe–Mn crusts are inferred to preserve the modern seawater Os isotope composition at the investigated water depths. Therefore, Os isotope stratigraphy using Fe–Mn crusts is a powerful dating tool in paleoceanography.
  • Akihiro Tamura, Norikatsu Akizawa, Ryo Otsuka, Kyoko Kanayama, Marie P ...
    2015 年 49 巻 3 号 p. 243-258
    発行日: 2015/05/25
    公開日: 2015/06/03
    ジャーナル 認証あり
    Whole-rock chemical compositions are significant for igneous petrology, especially volcanic rock studies. ICP-MS is widely used as a conventional method to determine the trace-element compositions using solutions prepared by digestion of rocks. In the past decades, LA-ICP-MS technique has been well developed to measure whole-rock compositions by using pressed powdered pellet or fused glass of rock samples. In this study, trace-element concentrations (Li, Sc, Ti, V, Cr, Co, Ni, Rb, Sr, Y, Zr, Nb, Cs, Ba, Hf, Ta, Pb, Th, U and REEs) of basaltic and andesitic rocks were determined by using flux-free fused glasses and LA-ICP-MS. The fused glass was prepared by the direct fusion method where the powdered rock sample is melted with an iridium-strip heater. The heating temperature was manually controlled by monitoring the current and the heating lasted less than 30 sec to achieve melting. We evaluated our routine analytical work performed by measurements of 3 random target positions in each fused glass. The data accuracy was evaluated by measurement of 11 fused glasses created from USGS and GSJ international reference materials (BCR-2, BHVO-2, BIR-1a, JB-2, JA-1 and JGb-1). The homogeneity of our fused glasses is represented by less than 5% relative standard deviation (1σ) in most elements. The mean values of most elements are in agreement with the reference values within 10% deviation. However, Pb concentration cannot be reproduced because of strong volatilization during the melting, and Lu, Hf and Ta are occasionally enriched by the elemental contamination/interference from the iridium-strip heater. 9 fused glasses created from selected petrological samples, such as the Ogasawara volcanic rocks and Oman diopsidite, were also measured to examine our routine measurement work and glass preparation method for a wider range of the trace-element abundance, especially the Cr abundance. The analytical results of 20 fused glasses demonstrate that our method is capable of determining the whole-rock trace-element compositions for petrological study.
  • Xuchun Ye, Pingheng Yang, Qi Zhang
    2015 年 49 巻 3 号 p. 259-269
    発行日: 2015/05/25
    公開日: 2015/06/03
    ジャーナル 認証あり
    This study presents an investigation of the hydrogeochemical processes and potential vulnerability of a typical underground river system in southwest China. Physical and chemical data were collected from both traditional manual sampling and continuous automatic monitoring. Analysis of high-frequency monitoring data from the outlet spring, Jiangjiaquan spring (JJQ), of the underground river system suggests the existence of several physico-chemical processes with distinctive characteristic response to storm events. Due to the impacts of sources and migration influencing factors, seasonal variations of major chemical components of the outlet spring are much different. For the entire karst watershed, spatial variability of surface and subsurface water geochemistry was significantly influenced by land use and lithologic characteristics. Principal component analysis (PCA) reveals that agricultural activities, water-rock interactions and soil erosion are potential influencing factors and the main sources for the chemical composition of JJQ spring. Nutrients from agricultural activities can be brought into the underground river by ways of diffuse recharge from leaching of soils, as well as focused recharge from surface flow via sinkholes. Water-rock interactions in the karst aquifer provide the evidence of diffuse recharge that contributed to groundwater quality. Soil erosion mainly causes focused recharge of contaminated water with particulate matters including iron, manganese and aluminum that carried into the underground river from sinkholes via surface flow.
  • Daxiang He, Jianfa Chen, Chen Zhang, Wei Li, Jianxun Zhou
    2015 年 49 巻 3 号 p. 271-282
    発行日: 2015/05/25
    公開日: 2015/06/03
    ジャーナル 認証あり
    Compositions of non-hydrocarbon and noble gases in natural gas samples collected from the Kuqa Depression, Tabei Uplift Belt, North Depression, Tazhong Uplift, and Southeast Depression in the Tarim Basin, China were analyzed to investigate the origin of the natural gases. The results show that the largest component of the natural gases is hydrocarbon gas with a concentration of 33.46% to 99.26%. The non-hydrocarbon gases are mainly composed of CO2 and N2 with concentrations of 0.01% to 17.95% and 0.1% to 52.45%, respectively. The helium content varies from 0.005% to 0.30%. The 3He/4He ratio varies from 0.01 Ra to 0.55 Ra (where Ra denotes atmospheric 3He/4He ratio = 1.4 × 10–6), and the 4He/20Ne ratio varies from 8.3 to 7400. Most of the 3He/4He values are below 0.1 Ra. The low 3He/4He ratios indicate crustal radiation to be the main source of the helium. There are no positive correlations between the 3He/4He ratio and helium abundance, non-hydrocarbon abundance, heat flow, and the age of reservoir formations. The ratios of 3He/4He are related to the time or stage of the natural gas accumulation. The ratios of 3He/4He in the reservoirs that were filled in the later stage (Himalayan period) are lower than those in the reservoirs that were filled in the earlier stage (Yanshan period).
  • Chunmao Zhu, Hisayuki Yoshikawa-Inoue, Yasunori Tohjima, Tomohisa Irin ...
    2015 年 49 巻 3 号 p. 283-294
    発行日: 2015/05/25
    公開日: 2015/06/03
    ジャーナル 認証あり
    Equivalent black carbon (BC) in surface air was measured using an aethalometer on Rishiri Island, northern Japan (45°07ʹ N, 141°12ʹ E), to examine temporal variations in BC between May 15, 2012 and May 8, 2013. Based on the negative relationship observed between BC and 222Rn during the diurnal cycle, the dry deposition velocity of BC was estimated to be between 0.23 and 0.42 cm s–1. High BC events, lasting for hours, occurred from late October to April, and were caused by the long-range transport of air masses that had moved over, or near, high BC emission areas in China. In contrast, air masses associated with low BC events originated near the Sea of Okhotsk and the Bering Sea. The observed slope of the linear regression line between BC and CO (ΔCBC/ΔCCO) during high BC events was between 3.6 and 6.8 ng m–3/ppb, except for an event on April 23, 2013 when the value of ΔCBC/ΔCCO decreased by 6.4 ng m–3/ppb (i.e., from 12.0 ± 0.6 ng m–3/ppb to 5.6 ± 0.5 ng m–3/ppb). It is considered that the dry and wet deposition of BC during transport most likely contributed to the large decrease in values of ΔCBC/ΔCCO.
  • Shigeshi Fuchida, Harue Masuda, Rina Fukuchi, Toshiro Yamanaka
    2015 年 49 巻 3 号 p. 295-307
    発行日: 2015/05/25
    公開日: 2015/06/03
    ジャーナル 認証あり
    The distribution and concentration of hydrolyzable amino acids and acid-extractable free amino acids in seafloor sediments collected from the Izena and Yoron Cauldrons hydrothermal systems, Okinawa Trough, were determined. The total hydrolyzable amino acid (THAA) concentrations were between 2.95 and 20.58 μmol/g, and Gly was the most abundant amino acid, followed by Asp, Ser, Ala, Val, and Phe. The high concentration of Gly suggests that the samples were hydrothermally altered. Small amounts of D-Asp, D-Glu and D-Ala were observed in the hydrolyzable fraction of sediments. The D/L ratios were <0.15, indicating that the amino acids were biogenic. Thus, it was inferred that the source of the amino acids in the Okinawa Trough hydrothermal field is mainly bio-debris of marine planktons, such as radiolarians and foraminifera, which were observed using a scanning electron microscope with energy-dispersive spectroscopy. The acid-extractable free amino acid concentrations were between 8.56 and 104.33 nmol/g and accounted for 0.1–1.1% of the THAA. The content of free basic amino acids was much less than that of acidic and neutral amino acids, indicating that the amino acids were adsorbed on organic functional groups coating the mineral surfaces via chemical bonds. Amino acids are unstable and they rapidly decompose under hydrothermal conditions. However, the stability and survival of amino acids is enhanced via adsorption on minerals and sediment particles. Adsorption plays a role in controlling the distribution and concentration of amino acids in hydrothermal sediments.
  • Fawzy Eissa, Nour El-Hoda Zidan, Hiroshi Sakugawa
    2015 年 49 巻 3 号 p. 309-318
    発行日: 2015/05/25
    公開日: 2015/06/03
    ジャーナル 認証あり
    Diuron contamination of water is a general concern because of the pesticide’s toxicity and persistence in the environment. Thus, TiO2-facilitated remediation of water contaminated with 1 mg·L–1 diuron was studied using a solar simulator, and under various pH conditions and photocatalyst concentrations, and with the addition of electron acceptors besides molecular oxygen. The effect of a combined TiO2/photo-Fenton process was also investigated. Diuron degradation rates were found to be strongly affected by all of the above parameters. Degradation rates increased with increases in pH from 5–9, and decreased when the pH was increased to 11. The degradation rate of diuron increased with increases in TiO2 photocatalyst concentrations, up to a maximum concentration of 1 g·L–1. The decrease in total organic carbon due to diuron mineralization was clearly higher when the combination of TiO2 and peroxydisulfate (10 mM) was used, when compared that obtained with TiO2 alone and TiO2 with hydrogen peroxide (20 mM). The combined solar TiO2/photo-Fenton process was the most effective method for both degradation and mineralization of diuron in water. Eight kinds of intermediate products from diuron degradation were identified by GC-MS analysis.
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