研究者詳細 - 角皆　潤

論文 - 角皆　潤

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Microbial carbon isotope fractionation to produce extraordinarily heavy methane in aging hydrothermal plumes over the southwestern Okinawa Trough 査読有り

Gamo, Toshitaka, Tsunogai, Urumu, Ichibayashi, Shinsuke, Chiba, Hitoshi, Obata, Hajime, Oomori, Tamotsu, Noguchi, Takuro, Baker, Edward T., Doi, Takashi, Maruo, Masahiro, Sano, Yuji

GEOCHEMICAL JOURNAL 44 巻 ( 6 ) 頁： 477-487 2010年

記述言語：英語掲載種別：研究論文（学術雑誌）

Within neutrally buoyant hydrothermal plumes derived from the Yonaguni Knoll IV hydrothermal field (24 degrees 51' N, 122 degrees 42' E D = 1 370-1 385 m) in the southwestern Okinawa Trough back arc basin we obtained profiles of dissolved manganese (Mn), helium isotopes ((3)He/(4)He) methane (CH₄) and its stable carbon isotope ratio (delta¹³C(PDB)) in young to old plume waters We first mapped the spatial distribution of hydrothermal plumes by towing a fixed array of optical sensors (Miniature Autonomous Plume Recorders MAPRs) above the field We then made water column observations and samplings using a CTD (Conductivity Temperature and Depth sensors)-Carousel package with a transmissometer and Niskin-X bottles at five locations with distances between 0 6 and 6 1 km horn the hydrothermally active center so far discovered Vertical profiles of light transmission and chemical tracers indicated triple-layered plumes the centers of which were at depths of 700-800 m similar to 1 050 m and similar to 1 200 m The CH₄ concentrations and delta¹³C value for the 1 200-m plume ranged between 1,026 and 10 nmol/kg, and between -22 4 and +40 4 parts per thousand (the highest delta¹³C value yet reported for oceanic CH₄) respectively indicating active microbial CH₄ oxidation accompanied by the delta¹³C increase for residual CH₄ The delta¹³C(CH₄) was shown to be useful for tracing such a ``microbial plume whose CH₄ concentration has already fallen to almost the background level By applying the Rayleigh distillation equation for a closed system we estimated the kinetic isotope fractionation factor of 1.012 for the CH₄ oxidation process occurring within the hydrothermal plumes deeper than 1 000 m.

Gas geochemical characteristics of hydrothermal plumes at the HAKUREI and JADE vent sites, the Izena Cauldron, Okinawa Trough 査読有り

Kawagucci, Shinsuke, Shirai, Kotaro, Lan, Tefang Faith, Takahata, Naoto, Tsunogai, Urumu, Sano, Yuji, Gamo, Toshitaka

GEOCHEMICAL JOURNAL 44 巻 ( 6 ) 頁： 507-518 2010年

記述言語：英語掲載種別：研究論文（学術雑誌）

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 delta(3)He covary with each other above the HAKUREI site but only CH₄ and delta(3)He 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 delta¹³C value of -32 parts per thousand in the HAKUREI fluid was obtained Both the plumes above the HAKUREI and JADE sites showed C(1)/C(2) ratios between 10(3)similar to 10(4) Only the bottom water around the HAKUREI site showed significant N(2)O excess with isotopically light delta¹⁵N and delta(18)O, suggesting N(2)O input from microbial activity in the sediment A linear con elation 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.

Sources of pore water in a Tanegashima mud volcano inferred from chemical and stable isotopic studies 査読有り

Nakayama, Noriko, Ashi, Juichiro, Tsunogai, Urumu, Gamo, Toshitaka, Tanahashi, Michiro

GEOCHEMICAL JOURNAL 44 巻 ( 6 ) 頁： 561-569 2010年

記述言語：英語掲載種別：研究論文（学術雑誌）

Pore waters at the depths of 0-590 cm below seafloor (bsf) were collected from four core samples at four different sites in a mud volcano off Tanegashima Island between Ryukyu trench and Ryukyu arc of Japan Concentrations of Cl(-), SO(4)(2-), CH₄ C(2)H(6) and stable isotopic composition of delta¹³C(CH₄), delta(18)O(H2O) delta D(H2O) in the pore waters vary as a function of distance from seafloor This paper reports and discusses the pore waters collected at the summit (CV) site The concentration, of Cl(-) decrease from 540 at the seafloor to 375 mmol/kg at a depth of similar to 200 cm and remain constant at around 350 mmol/kg (64 % of the concentration of seawater) below the depth The concentrations of CH₄ are two to three orders of magnitude higher than those at other sites and have a maximum value of 715 mu mol/kg at around 120-140 cm bsf Core samples collected at depths deeper than 180 cm bsf show collapsing gas bubbles and empty voids when they were split open It was also observed that liquid seeped out from the surface of the split core Considering the physical condition is favorable for the, formation of methane hydrate, the observations suggest the existence of methane hydrates High concentration of C2H6 which had similar depth profile to that of CH₄ was also observed C(2)H(6)/CH₄ ratio remained larger than 10(-3) and delta¹³C(CH₄) also remained around -45 parts per thousand below 180 cm bsf The data suggest presence of thermogenic methane in the CV site delta(18)O(H2O) and delta D(H2O) profiles exhibited an opposite depth dependence and only delta D(H2O) showed a decreasing depth profile similar to the concentration profile of Cl- They were inversely correlated with the concentration of Cl- The data of these two isotope compositions suggest a dilute fluid originates mainly from clay mineral dehydration but meteoric water A simple mixing model of fluids from three sources (ambient seawater water dissociated from methane hydrates and diagenetic water ascending from deeper depth) with isotopic fraction during methane hydrate dissociation was applied for the observation result below 280 cm bsf to constrain ranges of delta(18)O(H2O) and delta D(H2O) of diagenetic water Using the observed depth profile of Cl(-) as a conservative component of ambient seawater contribution of ambient seawater is estimated to be 64 % whereas 36 % from other two sources Considering an isotopic fractionation during methane hydrate dissociation and using the estimated source fractions and observed isotopic composition of pore water delta(18)O(H2O) and delta D(H2O) of the diagenetic water were estimated to range from +15 to +22 parts per thousand and from -103 to -43 parts per thousand respectively which are in good agreement with isotopic compositions of water formed from clay minerals during their dehydration but quite different from those of meteoric water, supporting negligible contribution of meteoric water in the Tanegashima mud volcano fluid.

Tracing the fate of atmospheric nitrate deposited onto a forest ecosystem in Eastern Asia using Δ¹⁷O 査読有り

Tsunogai, U., Komatsu, D. D., Daita, S., Kazemi, G. A., Nakagawa, F., Noguchi, I., Zhang, J.

ATMOSPHERIC CHEMISTRY AND PHYSICS 10 巻 ( 4 ) 頁： 1809-1820 2010年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

The stable isotopic compositions of nitrate in precipitation (wet deposition) and groundwater (spring, lake, and stream water) were determined for the island of Rishiri, Japan, so as to use the ¹⁷O anomalies (Δ¹⁷O) to trace the fate of atmospheric nitrate that had deposited onto the island ecosystem, which is a representative background forest ecosystem for eastern Asia. The deposited nitrate had large ¹⁷O anomalies with Δ¹⁷O values ranging from +20.8 parts per thousand to +34.5 parts per thousand (n = 32) with +26.2 parts per thousand being the annual average. The maximum Δ¹⁷O value of + 34.5 parts per thousand, obtained for precipitation on the 23rd to 24th of February 2007, was an extraordinarily large value among values for all samples of precipitation in Rishiri. Most nitrate in the sample might have been produced via NO(3) radical in a highly polluted air mass that had been supplied from megacities on the eastern coast of the Asian continent. On the other hand, nitrate in groundwater had small Δ¹⁷O values ranging from + 0.9 parts per thousand to 3.2 parts per thousand (n = 19), which corresponds to an mixing ratio of atmospheric nitrate to total nitrate of (7.4 +/- 2.6) %. Comparing the inflow and outflow of atmospheric nitrate in groundwater within the island, we estimated that the direct drainage accounts for (8.8 +/- 4.6) % of atmospheric nitrate that has deposited on the island and that the residual portion has undergone biological processing before being exported from the forest ecosystem.

DOI： 10.5194/acp-10-1809-2010

三酸素同位体組成を指標に用いた大気沈着窒素ー森林生態系間相互作用の定量的評価法査読有り

角皆潤, 小松大祐, 代田里子, 中川書子, 野口泉, 張勁

低温科学 68 巻頁： 107-120 2010年

Determination of total N₂ fixation rates in the ocean taking into account both the particulate and filtrate fractions 査読有り

Konno, U., Tsunogai, U., Komatsu, D. D., Daita, S., Nakagawa, F., Tsuda, A., Matsui, T., Eum, Y. -J., Suzuki, K.

BIOGEOSCIENCES 7 巻 ( 8 ) 頁： 2369-2377 2010年

記述言語：英語掲載種別：研究論文（学術雑誌）

Using the ¹⁵N(2) tracer method and high-sensitivity delta¹⁵N analytical systems, we determined N(2) fixation rates for ocean samples by dividing them into particulate (> 0.7 mu m) and filtrate (< 0.7 mu m) fractions. While N(2) fixation in the filtrate fraction had been ignored in previous studies, we found a significant N(2) fixation rates in the filtrate fraction in our study. The areal N(2) fixation rates in the western North Pacific Ocean estimated from the particulate fraction varied from < 1 to 160 mu mol N m(-2) d(-1), and those rates estimated from the filtrate fraction ranged from < 0.5 to 54 mu mol N m(-2) d(-1). Thus, N(2) fixation in the filtrate fraction accounts for on average 50 % (ranging from < 10 % to 84 %) of the total N(2) fixation rates. If these results are confirmed generally in the ocean, the new total N(2) fixation flux, which includes fixation in the filtrate fraction, possibly doubles the original estimates; therefore, the revised influx may reduce the imbalance in the global oceanic fixed nitrogen budget.

DOI： 10.5194/bg-7-2369-2010

Unique distribution of deep groundwater bacteria constrained by geological setting 査読有り

Kato, Kenji, Nagaosa, Kazuyo, Kimura, Hiroyuki, Katsuyama, Chie , Hama, Katsuhiro, Kunimaru, Takanori, Tsunogai, Urumu, Aoki, Kazuhiro

ENVIRONMENTAL MICROBIOLOGY REPORTS 1 巻 ( 6 ) 頁： 569-574 2009年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

P>We collected groundwater samples at depths of up to 482 m from three boreholes drilled into sedimentary rock within two formations in Hokkaido, Japan. The prokaryotic community in each subsurface groundwater sample was analysed by microscopic counts and cloning-sequencing the 16S rRNA genes. On total direct counts, there were between 4.61 x 104 and 5.06 x 106 prokaryote cells ml-1 in the samples, which is similar to the numbers observed at the marine subsurface. However, the vertical distribution of the prokaryotes did not show a simple decrease in abundance with increasing depth. A high abundance of cells with significant amounts of RNA was identified in the domain Bacteria using fluorescence in situ hybridization, with a high frequency of dividing cells at the transition zone between the two sedimentary rock formations. Cloning-sequencing analysis showed the predominance of gamma-Proteobacteria at this transition zone at 281-312 m. The horizontal heterogeneity of the microbial distribution in the subsurface environment was also demonstrated by a relatively high density of members of the domain Archaea in borehole HDB-4, drilled only 1.5 km northeast of HDB-6 and in the same formation.

DOI： 10.1111/j.1758-2229.2009.00087.x

Enrichment of nitrous oxide in the water columns in the area of the Bering and Chukchi Seas 査読有り

Hirota, A., Ijiri, A., Komatsu, D. D., Ohkubo, S. B., Nakagawa, F., Tsunogai, U.

MARINE CHEMISTRY 116 巻 ( 40912 ) 頁： 47-53 2009年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

We found N2O enrichment of up to 157% saturation in continental shelf water columns in the Bering and Chukchi Seas at water depths less than 66 m. The N2O enrichment exhibited a linear relationship with N* depletion. We also observed that the stable isotopic characteristics of N2O are an enrichment of 18O and a depletion of 15N relative to atmospheric N2O. We conclude that N2O in the area is primarily produced through denitrification in sediments. By using the observed instantaneous N2O emission rate, we estimated the annual emission rate from the surface to the atmosphere in the area to be 0.097 +/- 0.065 Tg N year-1, which corresponds to 0.6% to 10% of the total oceanic emission. The area of the Bering and Chukchi Seas could be very important in understanding global oceanic N2O emission.

DOI： 10.1016/j.marchem.2009.09.001

Molecular Characterization of Potential Nitrogen Fixation by Anaerobic Methane-Oxidizing Archaea in the Methane Seep Sediments at the Number 8 Kumano Knoll in the Kumano Basin, Offshore of Japan 査読有り

Miyazaki, Junichi, Higa, Ryosaku, Toki, Tomohiro, Ashi, Juichiro, Tsunogai, Urumu, Nunoura, Takuro, Imachi, Hiroyuki , Takai, Ken

APPLIED AND ENVIRONMENTAL MICROBIOLOGY 75 巻 ( 22 ) 頁： 7153-7162 2009年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

The potential for microbial nitrogen fixation in the anoxic methane seep sediments in a mud volcano, the number 8 Kumano Knoll, was characterized by molecular phylogenetic analyses. A total of 111 of the nifH (a gene coding a nitrogen fixation enzyme, Fe protein) clones were obtained from different depths of the core sediments, and the phylogenetic analysis of the clones indicated the genetic diversity of nifH genes. The predominant group detected (methane seep group 2), representing 74 % of clonal abundance, was phylogenetically related to the nifH sequences obtained from the Methanosarcina species but was most closely related to the nifH sequences potentially derived from the anoxic methanotrophic archaea (ANME-2 archaea). The recovery of the nif gene clusters including the nifH sequences of the methane seep group 2 and the subsequent reverse transcription-PCR detection of the nifD and nifH genes strongly suggested that the genetic components of the gene clusters would be operative for the in situ assimilation of molecular nitrogen (N(2)) by the host microorganisms. DNA-based quantitative PCR of the archaeal 16S rRNA gene, the group-specific mcrA (a gene encoding the methyl-coenzyme M reductase alpha subunit) gene, and the nifD and nifH genes demonstrated the similar distribution patterns of the archaeal 16S rRNA gene, the mcrA groups c-d and e, and the nifD and nifH genes through the core sediments. These results supported the idea that the anoxic methanotrophic archaea ANME-2c could be the microorganisms hosting the nif gene clusters and could play an important role in not only the in situ carbon (methane) cycle but also the nitrogen cycle in subseafloor sediments.

DOI： 10.1128/AEM.01184-09

Equilibrator Inlet-Proton Transfer Reaction-Mass Spectrometry (EI-PTR-MS) for Sensitive, High-Resolution Measurement of Dimethyl Sulfide Dissolved in Seawater 査読有り

Kameyama, Sohiko, Tanimoto, Hiroshi, Inomata, Satoshi, Tsunogai, Urumu, Ooki, Atsushi, Yokouchi, Yoko, Takeda, Shigenobu, Obata, Hajime, Uematsu, Mitsuo

ANALYTICAL CHEMISTRY 81 巻 ( 21 ) 頁： 9021-9026 2009年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

We developed an equilibrator inlet-proton transfer reaction-mass spectrometry (EI-PTR-MS) method for fast detection of dimethyl sulfide (DAIS) dissolved in seawater. Dissolved DMS extracted by bubbling pure nitrogen through the sample was continuously directed to the PTR-MS instrument. The equilibration of DMS between seawater and the carrier gas, and the response time of the system, were evaluated in the laboratory. DMS reached equilibrium with an overall response time of 1 min. The detection limit (50 pmol L(-1) at 5 s integration) was sufficient for detection of DMS concentrations in the open ocean. The EI-PTR-MS instrument was deployed during a research cruise in the western North Pacific Ocean. Comparison of the EI-PTR-MS results with results obtained by means of membrane tube equilibrator-gas chromatography/mass spectrometry agreed reasonably well on average (R(2) = 0.99). EI-PTR-MS captured temporal variations of dissolved DMS concentrations, including elevated peaks associated with patches of high biogenic activity. These results demonstrate that the EI-PTR-MS technique was effective for highly time-resolved measurements of DMS in the open ocean. Further measurements will improve our understanding of the biogeochemical mechanisms of the production, consumption, and distribution of DMS on the ocean surface and, hence, the air-sea flux of DMS, which is a climatically important species.

DOI： 10.1021/ac901630h

Enrichment of adsorbed methane in authigenic carbonate concretions of the Japan Trench 査読有り

Ijiri, Akira, Tsunogai, Urumu, Gamo, Toshitaka, Nakagawa, Fumiko, Sakamoto, Tatsuhiko, Saito, Saneatsu

GEO-MARINE LETTERS 29 巻 ( 5 ) 頁： 301-308 2009年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

Substantial amounts of adsorbed methane were detected in authigenic carbonate concretions recovered from sedimentary layers from depths between 245 and 1,108 m below seafloor during Ocean Drilling Program Leg 186 to ODP sites 1150 and 1151 on the deep-sea terrace of the Japan Trench. Methane contents were almost two orders of magnitude higher in the concretions (291-4,528 nmol/g wet wt) than in the surrounding bulk sediments (5-93 nmol/g wet wt), whereas methane/ethane ratios and stable carbon isotopic compositions were very similar. Carbonate content of surrounding bulk sediments (0.02-3.2 wet wt %) and methane content of the surrounding bulk sediments correlated positively. Extrapolation of the carbonate contents of bulk sediments suggests that 100 wt % carbonate would correspond to 1,886 +/- 732 nmol methane per g bulk sediment, which is similar to the average value observed in the carbonate concretions (1,321 +/- 1,067 nmol/g wet wt, n = 13). These data support the hypothesis that, in sediments, adsorbed hydrocarbon gases are strongly associated with authigenic carbonates.

DOI： 10.1007/s00367-009-0143-9

Theoretical and experimental evaluation of the isotope effect of NDIR analyzer on atmospheric CO₂ measurement 査読有り

Tohjima, Yasunori, Katsumata, Keiichi, Morino, Isamu, Mukai, Hitoshi, Machida, Toshinobu, Akama, Isao, Amari, Taketo, Tsunogai, Urumu

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 114 巻 2009年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

Nondispersive infrared (NDIR) CO₂ analyzer could produce erroneous CO₂ mole fraction measurements for an air sample when CO₂-in-air mixtures having different isotopic compositions than atmospheric CO₂ are used as the NDIR calibration gases. This is because (1) an optical band-pass filter equipped in a typical NDIR analyzer to minimize the interference effect from the other infrared-active species is basically designed to transmit only the absorption band of (12)C(16)O(2) and (2) absorption bands for the other CO₂-related isotopologues, for example, ¹³C(16)O(2), are shifted to lower wave numbers depending on their isotope effects. To evaluate the effect of the isotopic composition on the NDIR response, we computed the theoretical relative molar response of the instrument to each isotopologue based on the infrared absorptance by the individual isotopologues. We then prepared a gravimetric ¹³CO₂-in-air mixture with CO₂ mole fraction of 380 ppm to experimentally determine the optical filter property. The apparent mole fractions of the ¹³CO₂-in-air mixture determined by three NDIR analyzers used in this study were 46, 94, and 27 ppm, indicating that the optical filters in these instruments substantially reduced the response to ¹³C(16)O(2). Based on these theoretical and experimental analyses, we evaluated the apparent difference in the CO₂ mole fraction determined by the three NDIR analyzers from the true value when isotopically lighter CO₂-in-air mixtures (delta¹³C = -32.4 parts per thousand and delta(18)O = +11.7 parts per thousand), as compared to atmospheric CO₂ (delta¹³C = similar to -8 parts per thousand and delta(18)O = similar to +40 parts per thousand), are used as calibration gases. The estimated difference varied with NDIR analyzers, ranging from -0.04 to -0.08 ppm for air samples with 380 ppm CO₂.

DOI： 10.1029/2009JD011734

Enrichment of alkanes within a phytoplankton bloom during an in situ iron enrichment experiment in the western subarctic Pacific 査読有り

Kameyama, Sohiko, Tsunogai, Urumu, Nakagawa, Fumiko, Sasakawa, Motoki, Komatsu, Daisuke D., Ijiri, Akira, Yamaguchi, Junko, Horiguchi, Takeo, Kawamura, Hiroshi, Yamaguchi, Aika, Tsuda, Atsushi

MARINE CHEMISTRY 115 巻 ( 40910 ) 頁： 92-101 2009年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

During the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study II (SEEDS-II), we monitored variations in the concentrations of non-methane hydrocarbons (NMHCs), CH(3)Cl. N(2)O. and CH₄ within a phytoplankton bloom. Stable isotopic compositions were also determined to evaluate the sources of the variations. Although there was little variation in either the concentrations or the stable isotopic compositions of alkenes, CH(3)Cl, N(2)O. and CH₄ during the 23-day observation period, alkane concentrations increased substantially as the phytoplankton bloomed. The column-integrated quantities of alkanes increased to 3 times pre-bloom levels for C(2)H(6), 5 times for C(3)H(8). and 20 times for n-C(4)H(10). The delta¹³C values of both C(2)H(6) and C(3)H(8) remained almost constant while concentrations increased, whereas that of n-C(4)H(10) increased by about 12 parts per thousand. To evaluate the sources of the alkanes produced during the bloom, we compared their delta¹³C values with those of alkanes produced in axenic phytoplankton cultures in our laboratory. We concluded that during the SEEDS-II experiment the major portions of C(2)H(6) and C(3)H(8) were produced during the autolysis of diatoms cells, whereas n-C(4)H(10) was produced during autolysis of other phytoplankton cells such as cryptophytes and dinoflagellates.

DOI： 10.1016/j.marchem.2009.06.009

Photochemical histories of nonmethane hydrocarbons inferred from their stable carbon isotope ratio measurements over east Asia 査読有り

Saito, Takuya, Kawamura, Kimitaka, Tsunogai, Urumu, Chen, Tai-Yih, Matsueda, Hidekazu, Nakatsuka, Takeshi, Gamo, Toshitaka, Uematsu, Mitsuo, Huebert, Barry J.

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 114 巻 2009年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

The first airborne measurements of stable carbon isotope ratios (delta¹³C) of nonmethane hydrocarbons (NMHCs) were made over east Asia and its downwind regions as part of the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia). The measured delta¹³C values for ethane, n-butane, and n-pentane varied from approximately -30 parts per thousand to -20 parts per thousand. In contrast, acetylene showed much higher delta¹³C with a wide variation (-10 parts per thousand to +20 parts per thousand). These are consistent with the high delta¹³C values of combustion-derived acetylene and a significant isotopic fractionation due to photochemical removal process. Vertical profiles of delta¹³C-derived photochemical ages of NMHCs differed from one NMHC to another: less reactive ethane and acetylene showed linear increases in age with altitude (similar to 8 days below 1 km to similar to 20 days at about 6 km altitude), whereas more reactive n-butane and n-pentane (similar to 4 days) had no age gradient. This suggests that less reactive NMHCs in high-altitude air are transported from upwind source regions and mixed with fresh emissions from east Asia, while reactive NMHCs, even in the free troposphere, have recently been emitted. Thus vertical profiles are caused by the mixing of fresh emissions with aged air masses containing reactivity-determined amounts of photochemically aged NMHCs. This mixing causes the difference in the photochemical ages calculated by two methods (the ``hydrocarbon clock'' method using n-butane/ethane ratios and the ``isotopic hydrocarbon clock'' method using delta¹³C values of ethane).

DOI： 10.1029/2008JD011388

The living triserial planktic foraminifer Gallitellia vivans (Cushman): Distribution, stable isotopes, and paleoecological implications 査読有り

Kimoto, Katsunori, Ishimura, Toyoho, Tsunogai, Urumu, Itaki, Takuya, Ujiie, Yurika

MARINE MICROPALEONTOLOGY 71 巻 ( 40910 ) 頁： 71-79 2009年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

Gallitellia vivans (Cushman) is the only triserial coiling species among modern planktic foraminifera. Although previous studies suggested that G. vivans is a planktic species, it was unreported for a long time because of its small test and its low abundance in the water column and deep-sea sediments. Therefore, its distribution and ecology are poorly understood. In November 2006 we collected numerous specimens of living G. vivans by towed plankton net at three stations in the Tsushima Strait, located between the East China Sea and Japan Sea, and we performed faunal assemblage and isotopic analyses. G. vivans were commonly observed in the water column, and this species accounted for 1.4-63.1 % of all living planktic foraminifera, but plankton tow samples contained both living and resuspended shells. Stable oxygen isotopic values of G. vivans ranged from -1.14 parts per thousand to -2.85 parts per thousand. VPDB and indicated that their habitat is definitely planktic and that they may live at the surface. On the other hand, carbon isotope ratios ranged from -2.4 parts per thousand to -3.2 parts per thousand, distinctly lower than values for other planktic species. This may indicate isotopic disequilibrium between ambient seawater and the shells of G. vivans during shell formation. The geographic distribution and stable isotopic features of G. vivans are shared among the multiserial planktic species that have appeared in geological history, and they should also share similar ecologies and habitats. The study of the ecology of G. vivans is important when considering the paleoecology of primitive forms of planktic foraminifera and their surrounding environments along continental margins.

DOI： 10.1016/j.marmicro.2009.01.006

Biogeochemical profiles in deep sedimentary rocks in an inland fore-arc basin, Central Japan 査読有り

Suzuki, Yohey, Suko, Takeshi, Yoshioka, Hideyoshi, Takahashi, Masaaki, Nanba, Kenji, Tsunogai, Urumu, Takeno, Naoto, Ito, Kazumasa

CHEMICAL GEOLOGY 259 巻 ( 40972 ) 頁： 107-119 2009年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

Microorganisms thrive in the deep subsurface, but their extent and distribution, type and rate of metabolism are not well constrained, at least in part, owing to geochemical, lithological, hydrological and tectonic variations. We obtained deep sedimentary rocks from a tectonically stable inland basin in central Japan by drilling with minimized microbial and geochemical disturbance. Along with hydrogeological and microbial characterizations, geochemical properties of drilled cores from depths between similar to 200 and similar to 350 m were investigated. Except for a depth of 202 m, nitrate and/or nitrite were present in pore-water at all depths investigated in the present study. In most of the pore-water samples, the levels of dissolved Fe and H₂S were low. Additionally, the presence of microbially reducible Fe(III) was not evident in most of the core samples. Based on the acetylene blockage method, it was revealed the denitrification potential was high at depths of 302 and 351 m where pore-water was depleted in nitrate and enriched in nitrite, while the denitrification potential was relatively low at depths of 300 and 340 m where nitrate and nitrite were both detected in pore-water. Potential rates of methane production via CO₂ reduction were higher than those via acetate fermentation in the 302- and 350-m deep core samples. In the silty sandstone interval at depths of 340 and 351 m where permeability was relatively low, isotopically light methane of microbial origin was slightly enriched with sodium and chloride in pore-water. As a moderately mineralized fluid similarly enriched in sodium and chloride is entrained in the deeper subsurface with a depth over 1200 m around the drilling site, the increase in dissolved aqueous species is attributed to the remnant of the mineralized groundwater after the circulation of meteoric groundwater. The ubiquity of type of the sedimentary rocks suggests that the biogeochemical processes presented in this study might not be limited to the terrestrial sedimentary basin in central Japan.

DOI： 10.1016/j.chemgeo.2008.10.028

Geological background of the Kairei and Edmond hydrothermal fields along the Central Indian Ridge: Implications of their vent fluids' distinct chemistry 査読有り

Kumagai, H., Nakamura, K., Toki, T., Morishita, T., Okino, K., Ishibashi, J. -I., Tsunogai, U., Kawagucci, S., Gamo, T. , Shibuya, T., Sawaguchi, T., Neo, N., Joshima, M., Sato, T., Takai, K.

GEOFLUIDS 8 巻 ( 4 ) 頁： 239-251 2008年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

Hydrogen-rich hydrothermal areas, such as those in the Indian Ocean, may have had an influence on early evolution of life on Earth and thus have attracted interest because they may be a proxy for ancient ecosystems. The Kairei and Edmond hydrothermal fields in the Indian Ocean are separated by 160 km, but exhibit distinct fluid chemistry: Kairei fluids are hydrogen-rich; Edmond fluids are hydrogen-poor. At this region, the Central Indian Ridge shows an intermediate spreading rate, 48 mm year(-1) as full rate, where the hydrothemal fields occur. Kairei field vent fluids show persistently high concentrations of H₂. The Kairei field seems to be unique among hydrogen-enriched hydrothermal regions: most similar hydrogen-rich hydrothermal activity occurs along slowly spreading ridge, < 40 mm year(-1). The geological and tectonic aspects of the Kairei and Edmond hydrothermal fields were studied to try to elucidate geological constraints on hydrogen production. Visual observations of the seafloor near Kairei from a submersible revealed olivine-rich plutonic rocks with olivine gabbro-troctolite-dunite assemblages exposed within 15 km of the vent field, with serpentinized ultramafic mantle rocks on the Oceanic Core Complex (OCC). The OCC area might be a recharge zone of Kairei hydrothermal activity producing H₂-rich vent fluids. The chaotic seafloor within 30 km of the Kairei field reflects a magma-starved condition persisting there for 1 Myr. Asymmetric geomagnetic and gravity anomalies near the Kairei field can be used to infer that patchy olivine-rich intrusions are scattered within mantle ultramafics, where infiltrated seawater reacts with magma and ultramafic rocks or olivine-rich rocks. The heterogeneous uppermost lithosphere containing shallow olivine-rich rock facies surrounding the Kairei field provides abundant H₂ into the vent fluid through serpentinization. The hydrogen-rich Kairei field is hosted by basalt, with mafic-ultramafic olivine-rich lithology; the ordinary, hydrogen-poor Edmond field is hosted by a normal basaltic lithology. The contrasting geochemical signatures of the two fields reported here can also be found in ancient rocks from a juvenile Earth. This suggests that lithology-controlled generation of hydrogen may have operated for a long time and be relevant to the origin of life on Earth.

DOI： 10.1111/j.1468-8123.2008.00223.x

Methane, manganese, and helium-3 in newly discovered hydrothermal plumes over the Central Indian Ridge, 18°-20° S 査読有り

Kawagucci, Shinsuke, Okamura, Kei, Kiyota, Kaoru, Tsunogai, Urumu, Sano, Yuji, Tamaki, Kensaku, Gamo, Toshitaka

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 9 巻 2008年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

We have investigated newly discovered submarine hydrothermal plumes over the Central Indian Ridge, 18° - 20° S. Onshore chemical analyses of methane, its carbon isotope, manganese, and helium-3 in seawater samples obtained from the plumes revealed their detailed geochemical characteristics. One of the newly discovered hydrothermal plumes located over the western wall of the axial valley at Segment 15B (19°33' S), called the Roger Plateau, showed constant CH₄/Mn and CH₄/³He ratios throughout the plume. The CH₄/³He ratio (4*10⁶) and delta13C (-17.5 per mil) are consistent with those of basalt-hosted sediment-free hydrothermal systems, although the CH₄/Mn ratio (~1) is moderately higher. These features are thought to indicate a metal-depleted fluid chemistry. The other hydrothermal field is located within the axial valley at the northern part of the smooth lava plain at Segment 16 (18°20' S), called the Dodo Great Lava Plain, where several plumes were detected.The CH₄/Mn and CH₄/³He ratios showed large variation through the plumes while delta13C values were almost constant. Geochemical characteristics of venting fluid estimated from those of the plumes were apparently high CH₄/Mn (>6) and CH₄/³He (>60*10⁶) ratios and low delta13C values (<-27.5 per mil), suggesting possible influences of several methane input processes to the fluid chemistry.

DOI： 10.1029/2008GC002082

A multi-isotope study of deep-sea mussels at three different hydrothermal vent sites in the northwestern Pacific 査読有り

Naraoka, Hiroshi, Naito, Taku, Yamanaka, Toshiro, Tsunogai, Urumu, Fujikura, Katsunori

CHEMICAL GEOLOGY 255 巻 ( 40910 ) 頁： 25-32 2008年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

To investigate symbiotic bacterial ecosystems at different deep-sea hydrothermal systems in the northwestern Pacific, compound-specific carbon and hydrogen isotope analyses of lipid biomarkers have been performed in addition to bulk C, H, N, S and O isotope analyses on Bathymodiolus mussels from the Hatoma seamount (B. platifrons), the Daiyon-Yonaguni (Yonaguni) knoll (B. platifrons), and the Suiyo seamount (B. septemdierum). The two B. platifrons contain large amounts of diploptene, while no hopanoid is detected in B. septemdierum, suggesting that B. platifrons and B. septemdierum harbors methanotrophic and thiotrophic bacteria, respectively. In spite of the same symbiont, the large bulk delta C-13 difference between the Hatoma (-44.8 parts per thousand) and Yonaguni (-24.5 parts per thousand) mussels reflects isotopically distinct hydrothermal CH₄ (Hatoma: similar to-48 parts per thousand, Yonaguni: similar to-26 parts per thousand) as a carbon source. Fatty acids of the Hatoma and Yonaguni mussels are more enriched in D (-144 to -101 parts per thousand) than the Suiyo mussel (-265 to -162 parts per thousand), suggesting that D-depleted magmatic water or D-enriched hydrogen derived from CH₄ could be a partial hydrogen source for methanotrophy or thiotrophy, respectively. Apparent positive correlations are observed between delta C-13 and delta D of the bulk and biomarkers for each mussel due to similar biochemical processes during de novo synthesis. The compound-specific delta C-13 and delta D variations have provided much information on not only distinct carbon and hydrogen sources but also the lipid synthesis with respect to different symbiotic bacterial ecosystems.

DOI： 10.1016/j.chemgeo.2008.05.015

Methane enrichment in low-temperature hydrothermal fluids from the Suiyo Seamount in the Izu-Bonin Arc of the western Pacific Ocean 査読有り

Toki, Tomohiro, Tsunogai, Urumu, Ishibashi, Jun-ichiro, Utsumi, Motoo, Gamo, Toshitaka

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 113 巻 ( B8 ) 2008年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

The gas geochemistries of high-temperature and low-temperature hydrothermal fluids (HTHFs and LTHFs, respectively) were studied for the Suiyo Seamount hydrothermal system (140 degrees 39'E, 28 degrees 33'N) in the southern Izu-Bonin (Ogasawara) Arc of the western Pacific Ocean. HTHFs (290 +/- 20 degrees C) were collected from four active vents using a gastight fluid sampler, which prevented the loss of volatile components through degassing during sample processing. The end-member CH₄ concentrations were homogeneous across the vent fields. LTHFs were collected from four diffuse flow zones using a funnel, which was deployed on the seafloor with replacement of the seawater inside the funnel by the LTHF. Strong linear relationships were found among the concentrations of CH₄, Sigma CO₂, and Si of the obtained samples, which ensured that the end-member chemical composition of the LTHFs could be accurately estimated. While the Sigma CO₂ concentrations of the HTHFs and LTHFs were similar, all four LTHFs showed enrichment of CH₄ as compared to the HTHFs. The carbon isotopic composition of CH₄ also revealed a significant difference: the LTHFs (delta¹³C(CH₄) = -4.8 +/- 0.3 parts per thousand PDB) showed ¹³C enrichment, as compared to the HTHFs (delta¹³C(CH₄) = -5.8 +/- 0.4 parts per thousand PDB). The ¹³C enrichment can be explained by a combination of microbial CH₄ production and oxidation after formation of the LTHFs. On the basis of the observed differences in CH₄ concentrations and carbon isotopic compositions of the HTHFs and LTHFs, microbial methane oxidation and production are estimated to have comparable impacts. These results support the notion of a subseafloor microbial consortium of methanogens and methanotrophs.

DOI： 10.1029/2007JB005476

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