著者

Naoto Takahata Yama Tomonaga Yuichiro Kumamoto Masatoshi Yamada Yuji Sano

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.52, no.2, pp.211-217, 2018-03-30 (Released:2018-04-19)

参考文献数

24

被引用文献数

1 24

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In this work we report tritium concentrations determined in seawater samples collected offshore of Fukushima in the northwestern Pacific Ocean, immediately after the Fukushima Dai-ichi Nuclear Power Plant (F1-NPP) accident. We found surface seawater to have high concentrations of tritium (3H) and cesium-137 (137Cs) with respect to the concentrations expected for the investigated region. Tritium concentrations were up to six times the pre-accident level. However, these concentrations were found to be relatively low compared to those of 137Cs and 129I. This is most likely because of the very low production ratio of tritium to 137Cs in the F1-NPP, and the inherently high background concentration of tritium in these environmental waters (mainly ascribed to global fallout from nuclear weapons tests conducted during the 1960s). The tritium distribution in surface seawater showed higher concentrations close to the shore and lower concentrations offshore. Higher tritium concentration areas had spread both northward and southward from the F1-NPP along the coast, indicating that large amounts of tritium were carried by coastal currents. A positive correlation was found to exist between 3H and 137Cs concentrations in the seawater. The calculated 3H/137Cs ratio was similar to the production ratio of these isotopes reported for the broken reactors in the F1-NPP, which indicates that both radionuclides might have originated from the F1-NPP. Direct emission of tritium to the ocean from the F1-NPP was estimated to be approximately 0.05 PBq immediately after the accident, which is much smaller than the total inventory in the environment.

著者

SHINSUKE KAWAGUCCI KOTARO SHIRAI TEFANG FAITH LAN NAOTO TAKAHATA URUMU TSUNOGAI YUJI SANO TOSHITAKA GAMO

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.44, no.6, pp.507-518, 2010-12-20 (Released:2013-03-23)

参考文献数

60

被引用文献数

14 35

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Hydrothermal plumes above the HAKUREI and JADE sites, two high-temperature hydrothermal vent sites in the Izena Cauldron at the mid-Okinawa Trough, were investigated in order to gain a preliminary understanding of gas geochemical characteristics at underlying hydrothermal vent sites. Three geochemical tracers, H2, CH4 and δ3He, covary with each other above the HAKUREI site but only CH4 and δ3He are correlated above the JADE site. The carbon isotope ratio of methane within the Izena Cauldron can be accounted by a combination of the fluid dilution by ambient seawater and microbial consumption with the kinetic carbon isotope effect (KIE) of 1.007. An estimated endmember δ13C value of -32‰ in the HAKUREI fluid was obtained. Both the plumes above the HAKUREI and JADE sites showed C1/C2 ratios between 103∼104. Only the bottom water around the HAKUREI site showed significant N2O excess with isotopically light δ15N and δ18O, suggesting N2O input from microbial activity in the sediment. A linear correlation between H2 and CH4 in the HAKUREI plume gives a H2/CH4 ratio of the HAKUREI fluid of more than 0.022. The estimated H2/CH4 ratio in the HAKUREI fluid is significantly higher than that of the JADE fluid, comparable with those of fluids venting at other sediment-related hydrothermal systems, and also comparable with those of thermogenic gases produced by hydrothermal sediment experiments. These facts suggest that fluid-sediment interaction during fluid upwelling appears to modify gas geochemical characteristics at the HAKUREI site but have little influence at the JADE site. This study demonstrates the availability of the Izena Cauldron hydrothermal field and the HAKUREI and JADE sites as a natural laboratory for investigating the fluid-sediment interaction during fluid upwelling.

著者

Naoto Takahata Reika Yokochi Yoshiro Nishio Yuji Sano

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.37, no.3, pp.299-310, 2003-06-20 (Released:2008-04-08)

参考文献数

32

被引用文献数

9 15 12

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Twenty three gas samples were collected from hot and mineral springs associated with Ontake volcano in central Honshu, Japan from June 1996 to June 2000. The chemical compositions, He, Ar, C and N isotopic ratios were measured using a gas chromatography, noble gas and stable isotope mass spectrometers, respectively. The 3He/4He ratio decreased with increasing distance from the central cone of the volcano to the sampling site, while δ13C value of CO2 increased with the distance. Such trends are consistent with those observed from November 1981 to June 1993 in the literature, suggesting that source of magmatic helium and carbon is located beneath the volcanic cone and they are continuously emitted into surroundings. The δ15N value of N2 increased with the distance while most 40Ar/36Ar ratios were similar to the atmospheric value. Magmatic nitrogen may also be carried by a fluid flowing through the volcanic edifice and diluted by crustal nitrogen. Significant increase of 3He/4He ratio from 1996 to 2000 was observed at the site close to the fault formed by a M6.8 earthquake that occurred in September 1984, which agrees well with the 3He/4He change from November 1981 to June 1993. Anomalous increase of δ13C value was observed at Shirakawa site from June 1993 to June 2000. The change cannot be explained by a simple two-component mixing between magmatic and crustal end-members and may require another model with three end-members, mantle, limestone and sediment.

著者

Narumi Moromoto Yosuke Kawai Kentaro Terada Masaaki Miyahara Naoto Takahata Yuji Sano Naoko Fujikawa Mahesh Anand

出版者

The Mass Spectrometry Society of Japan

雑誌

Mass Spectrometry (ISSN:2187137X)

巻号頁・発行日

vol.12, no.1, pp.A0115, 2023-02-10 (Released:2023-02-10)

参考文献数

41

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Northwest Africa (NWA) 2977 is a lunar basaltic meteorite that was found in 2005 and has been classified as an olivine cumulate gabbro. This meteorite contains a shock melt vein (SMV) induced by an intense shock event. We report herein on an in-situ analysis of phosphates in the host gabbro and the shock vein for the U–Pb dating of NWA 2977 using an ion microprobe, NanoSIMS. The majority of the analyzed phosphates, in both the SMV and host-rock, lie on a linear regression in 238U/206Pb–207Pb/206Pb–204Pb/206Pb three-dimensional space, indicating a total Pb/U isochron age of 3.15±0.12 Ga (95% confidence level), which is consistent ages determined in previous isotopic studies of NWA 2977 (Sm–Nd age of 3.10±0.05 Ga, Rb–Sr age of 3.29±0.11 Ga, and Pb–Pb baddeleyite age of 3.12±0.01 Ga), and identical to the age of the U–Pb phosphate in a paired meteorite NWA 773, 3.09±0.20 Ga, derived from our dataset. There was no clear difference in the formation age between the phosphates found in the SMV and host-rock, although the shape and size of the grains and the Raman spectra show the evidence of intense shock metamorphism. Based on these findings, the cooling rate of the phosphate was very rapid, constrained to be larger than 140 K/s.

著者

WEN HSINYI Naoto Takahata Akizumi Ishida Kentaro Tanaka Yama Tomonaga Takanori Kagoshima Kotaro Shirai Jun-Ichiro Ishibashi Hisayoshi Yokose Urumu Tsunogai Yuji Sano

出版者

日本地球化学会

雑誌

日本地球化学会年会要旨集

巻号頁・発行日

vol.61, 2014

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The aim of this study is to get information of gas geochemical characteristics at hydrothermal vent sites in the adjacent region of Tokara Islands by using helium isotopes and methane concentration and its stable carbon isotope ratio to estimate the 3He flux and understand the mechanism of carbon cycling.

著者

Yuji SANO Kotaro SHIRAI Naoto TAKAHATA Takafumi HIRATA Neil C. STURCHIO

出版者

The Japan Society for Analytical Chemistry

雑誌

Analytical Sciences (ISSN:09106340)

巻号頁・発行日

vol.21, no.9, pp.1091-1097, 2005 (Released:2006-01-10)

参考文献数

34

被引用文献数

43 45

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Concentrations of minor (Mg and Sr) and trace (Ba and U) elements in four natural calcium carbonate samples were first analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after chemical dissolution and calibrated against a standard dolomite. Their homogeneities were checked by in situ laser ablation (LA) ICP-MS with 10 - 20 spots. The carbonate samples were measured by using a high lateral resolution secondary ion mass spectrometer (Nano-SIMS NS50). A ∼4 nA O- primary beam was used to sputter a 5 - 6-µm diameter crater on the sample surface, and secondary positive ions were extracted for mass analysis using an accelerating voltage of 8 kV and a Mattauch-Herzog geometry. A multi-collector system was adjusted to detect 26Mg+, 43Ca+, 88Sr+, 138Ba+, 238U16O+ and 238U16O2+ ions at the same time. A resolving power of 2500 - 5000 at 10% peak height was attained by an entrance slit set at 40 µm, and each exit slit at 50 µm with adequate flat-topped peaks. The observed 26Mg/43Ca, 88Sr/43Ca, 138Ba/43Ca and 238U16O2/43Ca ratios agreed well with those measured by LA-ICP-MS. Foraminifera shells were analyzed at 5 - 6 µm scale by Nano-SIMS. There was a large variation of the Mg/Ca ratios, up to ±38%, even in a single fragment of the shell, suggesting that although the ratios provide a useful paleoceanographic proxy at bulk scale, they may reflect a more complex pattern at <10 µm scale.