研究者詳細 - 角皆　潤

論文 - 角皆　潤

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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

Cell proliferation at 122 degrees C and isotopically heavy CH₄ production by a hyperthermophilic methanogen under high-pressure cultivation 査読有り

Takai, Ken, Nakamura, Kentaro, Toki, Tomohiro, Tsunogai, Urumu , Miyazaki, Masayuki, Miyazaki, Junichi, Hirayama, Hisako, Nakagawa, Satoshi, Nunoura, Takuro, Horikoshi, Koki

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 105 巻 ( 31 ) 頁： 10949-10954 2008年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

We have developed a technique for cultivation of chemolithoautotrophs under high hydrostatic pressures that is successfully applicable to various types of deep-sea chemolithoautotrophs, including methanogens. It is based on a glass-syringe-sealing liquid medium and gas mixture used in conjunction with a butyl rubber piston and a metallic needle stuck into butyl rubber. By using this technique, growth, survival, and methane production of a newly isolated, hyperthermophilic methanogen Methanopyrus kandleri strain 116 are characterized under high temperatures and hydrostatic pressures. Elevated hydrostatic pressures extend the temperature maximum for possible cell proliferation from 116 degrees C at 0.4 MPa to 122 degrees C at 20 MPa, providing the potential for growth even at 122 C under an in situ high pressure. In addition, piezophilic growth significantly affected stable carbon isotope fractionation of methanogenesis from CO₂. Under conventional growth conditions, the isotope fractionation of methanogenesis by M. kandleri strain 116 was similar to values (-34 parts per thousand to-27 parts per thousand) previously reported for other hydrogenotrophic methanogens. However, under high hydrostatic pressures, the isotope fractionation effect became much smaller (<-12 parts per thousand), and the kinetic isotope effect at 122 degrees C and 40 MPa was -9.4 parts per thousand, which is one of the smallest effects ever reported. This observation will shed light on the sources and production mechanisms of deep-sea methane.

DOI： 10.1073/pnas.0712334105

Grain-scale heterogeneities in the stable carbon and oxygen isotopic compositions of the international standard calcite materials (NBS 19, NBS 18, IAEA-CO-1, and IAEA-CO-8) 査読有り

Ishimura, Toyoho, Tsunogai, Urumu, Nakagawa, Fumiko

RAPID COMMUNICATIONS IN MASS SPECTROMETRY 22 巻 ( 12 ) 頁： 1925-1932 2008年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

We determined grain-scale heterogeneities (from 6 to 88 mu g) in the stable carbon and oxygen isotopic compositions (delta¹³C and delta(18)O) of the international standard calcite materials (NBS 19, NBS 18, IAEA-CO-1, and IAEA-CO-8) using a continuous-flow isotope ratio mass spectrometry (CF-IRMS) system that realizes a simultaneous determination of the delta¹³C and the delta(18)O values with standard deviations (S.D.) of less than 0.05 parts per thousand for CO₂ gas. Based on the S.D. of the delta¹³C and delta(18)O values determined for CO₂ gases evolved from the different grains of the same calcite material, we found that NBS 19, IAEA-CO-1, and IEAE-CO-8 were homogeneous for delta¹³C (less than 0.10 parts per thousand S.D.), and that only NBS 19 was homogeneous for delta(18)O (less than 0.14 parts per thousand S.D.). On the level of single grains, we found that both IAEA-CO-1 and IAEA-CO-8 were heterogeneous for delta(18)O (1.46 parts per thousand and 0.76 parts per thousand S.D., respectively), and that NBS 18 was heterogeneous for both delta¹³C and delta(18)O (0.34 parts per thousand and 0.54 parts per thousand S.D., respectively). Closer inspection of NBS 18 grains revealed that the highly deviated isotopic compositions were limited to the colored grains. By excluding such colored grains, we could also obtain the homogeneous delta¹³C and delta(18)O values (less than 0.18 parts per thousand and less than 0.16 parts per thousand S.D., respectively) for NBS 18. We conclude that NBS 19, IAEA-CO-1, or pure grains in NBS 18 are suitable to be used as the standard reference material for delta¹³C, and that either NBS 19 or pure grains in NBS 18 are suitable to be used as the reference material for delta(18)O during the grain-scale isotopic analyses of calcite.

DOI： 10.1002/rcm.3571

Determination of the ¹⁵N/¹⁴N, ¹⁷O/¹⁶O, and ¹⁸O/¹⁶O ratios of nitrous oxide by using continuous-flow isotope-ratio mass spectrometry 査読有り

omatsu, D.D., T. Ishimura, F. Nakagawa, U. Tsunogai

RAPID COMMUNICATIONS IN MASS SPECTROMETRY 22 巻 ( 10 ) 頁： 1587-1596 2008年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

We developed a rapid, sensitive, and automated analytical system to determine the delta¹⁵N, delta¹⁸O, and Δ¹⁷O values of nitrous oxide (N₂O) simultaneously in nanomolar quantities for a single batch of samples by continuous-flow isotope-ratio mass spectrometry (CF-IRMS) without any cumbersome and time-consuming pretreatments. The analytical system consisted of a vacuum line to extract and purify N₂O, a gas chromatograph for further purification of N₂O, an optional thermal furnace to decompose N₂O to O₂, and a CF-IRMS system. We also used pneumatic valves and pneumatic actuators in the system so that we could operate it automatically with timing software on a personal computer. The analytical precision was better than 0.12 parts per thousand for delta¹⁵N with >4 nmol N₂O injections, 0.25 parts per thousand for delta¹⁸O with >4 nmol N₂O injections, and 0.20 parts per thousand for Δ¹⁷O with >20 nmol N₂O injections for a single measurement. We were also easily able to improve the precision (standard errors) to better than 0.05 parts per thousand for delta¹⁵N, 0.10 parts per thousand for delta¹⁸O, and 0.10 parts per thousand for Δ¹⁷O through multiple analyses with more than four repetitions with 190 nmol samples using the automated analytical system. Using the system, the delta¹⁵N, delta¹⁸O, and Δ¹⁷O values of N₂O can be quantified not only for atmospheric samples, but also for other gas or liquid samples with low N₂O content, such as soil gas or natural water. Here, we showed the first ever Δ¹⁷O measurements of soil N₂O.

DOI： 10.1002/rcm.3493

Radiocarbon-based carbon source quantification of anomalous isotopic foraminifera in last glacial sediments in the western North Pacific 査読有り

Uchida, Masao, Ohkushi, Ken'ichi, Kimoto, Katsunori, Inagaki, Fumio, Ishimura, Toyoho, Tsunogai, Urumu, TuZino, Taqumi, Shibata, Yasuyuki

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 9 巻 2008年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

A previous study interpreted extremely ¹³C-depleted excursions of planktonic and benthic foraminifera in last glacial sediments (17,500 to 25,400 cal years B. P.) of the core retrieved from off Shimokita Peninsula and off Hokkaido, Japan, as evidence for periodic releases of methane, arising from the dissociation of methane hydrate. To better understand the formation process of the ¹³C-depleted excursions, we conducted high-resolution natural radiocarbon measurements and biogeochemical analyses. We found highly depleted 13 C excursions ranging from -10.2 % to -1.6 % and -6.8 % to -1.6 % in planktonic and benthic foraminifera, respectively. Most of the foraminiferal tests in these horizons were brown, most likely as a result of postdepositional alteration, reflecting the formation of authigenic carbonate on the surface of tests. These alterations were also supported by high levels of Mg-calcite and the acid-leaching test for anomalous foraminifera. To evaluate the carbon sources in the altered foraminifera tests, we quantified the relative contributions of (14)C-free methane-derived carbon sources to the formation of authigenic carbonates in foraminifera with depleted 13 C excursions using a coupled mass balance isotopic model ((14)C/C and ¹³C/(12)C). The radiocarbon ages of both planktonic and benthic ¹³C-depleted foraminifera were approximately 600 to 2000 years older than those of normal tests from nearby horizons. The relative contributions of authigenic carbonates derived from the methane oxidizing process reached to -22 wt % for planktonic foraminifera and -15 wt % for benthic foraminifera. The delta¹³C values of methane calculated from the mass balance model were between -29 % and -68 % for planktonic foraminifera and between -40 % and -108 % for benthic foraminifera, consistent with delta¹³C values reported for thermogenic and abiogenic methane in global methane hydrate reservoirs. These data consistently suggest that methane-related drastic environmental change occurred in the horizons that included delta¹³C anomalies. This study provides important information for interpreting geological records of the methane hydrate instability associated with climate.

DOI： 10.1029/2006GC001558

Carbon isotopic characterization for the origin of excess methane in subsurface seawater 査読有り

Sasakawa, Motoki, Tsunogai, Urumu, Kameyama, Sohiko, Nakagawa, Fumiko, Nojiri, Yukihiro, Tsuda, Atsushi

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 113 巻 ( C3 ) 2008年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

We collected samples of seawater, zooplankton, and sinking particles in the northwestern North Pacific to determine the source of excess CH₄ over the saturation value in equilibrium with the atmospheric CH₄ in the oxygenated open ocean, using stable carbon isotope as a tracer. We found that subsurface (similar to 100 m depth) seawater is supersaturated (up to 12 %) with ¹³C-enriched CH₄ (up to -33.1 %) relative to surface seawater in equilibrium with the atmosphere (-47 %), suggesting that in situ addition of ¹³C-enriched CH₄ must be responsible for CH₄ enrichment at depth. The delta¹³C of CH₄ emitted from sinking particles (from -36.7 +/- 1.2 % to +5.9 +/- 7.5 %) is within the range of that of excess CH₄ in seawater, suggesting that the major source of subsurface excess CH₄ is sinking particles. The unusually ¹³C-enriched delta¹³C composition of CH₄ emitted from sinking particles suggests that active microbial CH₄ oxidation occurs within the oxic/anoxic boundary of these particles. On the basis of the Rayleigh equation, we estimated that at least 62 % of CH₄ produced within the anoxic center of sinking particles is oxidized within 100 m of the surface.

DOI： 10.1029/2007JC004217

Sensitive determinations of stable nitrogen isotopic composition of organic nitrogen through chemical conversion into N₂O 査読有り

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

Rapid Communications in Mass Spectrometry 22 巻 ( 3 ) 頁： 345-354 2008年1月

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）

We present a method for high-sensitivity nitrogen isotopic analysis of particulate organic nitrogen (PON) in seawater and freshwater, for the purpose of determining the aquatic nitrogen fixation rate through the ¹⁵N(2) tracer technique for samples that contain a low abundance of organisms. The method is composed of the traditional oxidation/reduction methods, such as the oxidation of PON to nitrate (NO(3)) using persulfate, the reduction of NO(3) to nitrite (NO(2)) using spongy cadmium, and further reduction of NO(2) to nitrous oxide (N(2)O) using sodium azide. Then, N(2)O is purged from the water and trapped cryogenically with subsequent release into a gas chromatography column to analyze the stable nitrogen isotopic composition using continuous-flow isotope ratio mass spectrometry (CF-IRMS) by simultaneously monitoring the NO(+) ion currents at masses 30,31, and 32. The nitrogen isotopic fractionation was consistent within each batch of analysis. The standard deviation of sample measurements was less than 0.3 %. for samples containing PON of more than 50 nmolN, and 0.5 parts per thousand for those of more than 20 nmolN, by subtracting the contribution of blank nitrogen, 8 +/- 2 nmol at final N(2)O. By using this method, we can determine delta¹⁵N for lower quantities of PON better than by other methods, so we can reduce the quantities of water samples needed for incubation to determine the nitrogen fixation rate. In addition, we can expand the method to determine the nitrogen isotopic composition of organic nitrogen in general, such as that of total dissolved nitrogen (TDN; sum of NO(3), NO(2), ammonium, and DON), by applying the method to filtrates.

DOI： 10.1002/rcm.3368

Diverse range of mineralization induced by phase separation of hydrothermal fluid: Case study of the Yonaguni Knoll IV hydrothermal field in the Okinawa Trough back-arc basin 査読有り

Suzuki, Ryohei, Ishibashi, Jun-Ichiro, Nakaseama, Miwako, Konno, Uta, Tsunogai, Urumu, Gena, Kaul, Chiba, Hitoshi

RESOURCE GEOLOGY 58 巻 ( 3 ) 頁： 267-288 2008年

記述言語：英語掲載種別：研究論文（学術雑誌）

The Yonaguni Knoll IV hydrothermal vent field (24 degrees 51'N, 122 degrees 42'E) is located at water depths of 1370-1385 m near the western edge of the southern Okinawa Trough. During the YK03-05 and YK04-05 expeditions using the submersible Shinkai 6500, both hydrothermal precipitates (sulfide/sulfate/carbonate) and high temperature fluids (Tmax = 328 degrees C) presently venting from chimney-mound structures were extensively sampled. The collected venting fluids had a wide range of chemistry (Cl concentration 376-635 mmol kg(-1)), which is considered as evidence for sub-seafloor phase separation. While the Cl-enriched smoky black fluids were venting from two adjacent chimney-mound structures in the hydrothermal center, the clear transparent fluids sometimes containing CO₂ droplet were found in the peripheral area of the field. This distribution pattern could be explained by migration of the vapor-rich hydrothermal fluid within a porous sediment layer after the sub-seafloor phase separation. The collected hydrothermal precipitates demonstrated a diverse range of mineralization, which can be classified into five groups: (i) anhydrite-rich chimneys, immature precipitates including sulfide disseminations in anhydrite; (ii) massive Zn-Pb-Cu sulfides, consisting of sphalerite, wurtzite, galena, chalcopyrite, pyrite, and marcasite; (iii) Ba-As chimneys, composed of barite with sulfide disseminations, sometimes associated with realgar and orpiment overgrowth; (iv) Mn-rich chimneys, consisting of carbonates (calcite and magnesite) and sulfides (sphalerite, galena, chalcopyrite, alabandite, and minor amount of tennantite and enargite); and (v) pavement, silicified sediment including abundant native sulfur or barite. Sulfide/sulfate mineralization (groups i-iii) was found in the chimney-mound structure associated with vapor-loss (Cl-enriched) fluid venting. In contrast, the sulfide/carbonate mineralization (group iv) was specifically found in the chimneys where vapor-rich (Cl-depleted) fluid venting is expected, and the pavement (group v) was associated with diffusive venting from the seafloor sediment. This correspondence strongly suggests that the subseafloor phase separation plays an important role in the diverse range of mineralization in the Yonaguni IV field. The observed sulfide mineral assemblage was consistent with the sulfur fugacity calculated from the FeS content in sphalerite/wurtzite and the fluid temperature for each site, which suggests that the shift of the sulfur fugacity due to participation of volatile species during phase separation is an important factor to induce diverse mineralization. In contrast, carbonate mineralization is attributed to the significant mixing of vapor-rich hydrothermal fluid and seawater. A submarine hydrothermal system within a back-arc basin in the continental margin may be considered as developed in a geologic setting favorable to a diverse range of mineralization, where relatively shallow water depth induces sub-seafloor phase separation of hydrothermal fluid, and sediment accumulation could enhance migration of the vapor-rich hydrothermal fluid.

DOI： 10.1111/j.1751-3928.2008.00061.x

Long-term observation of mass-independent oxygen isotope anomaly in stratospheric CO₂ 査読有り

Kawagucci, S., Tsunogai, U., Kudo, S., Nakagawa, F., Honda, H., Aoki, S., Nakazawa, T., Tsutsumi, M., Gamo, T.

ATMOSPHERIC CHEMISTRY AND PHYSICS 8 巻 ( 20 ) 頁： 6189-6197 2008年

記述言語：英語掲載種別：研究論文（学術雑誌）

Stratospheric and upper tropospheric air samples were collected during 1994-2004 over Sanriku, Japan and in 1997 over Kiruna, Sweden. Using these archived air samples, we determined the triple oxygen-isotope composition of stratospheric CO₂ and the N(2)O mixing ratio. The maximum Delta¹⁷O(CO2) value of +12.2 parts per thousand, resembling that observed previously in the mesosphere at 60 km height, was found in the middle stratosphere over Kiruna at 25.6 km height, suggesting that upper stratospheric and mesospheric air descended to the middle stratosphere through strong downward advection. A least-squares regression analysis of our observations on a delta(18)O(CO2)-delta¹⁷O(CO2) plot (r(2)> 0.95) shows a slope of 1.63 +/- 0.10, which is similar to the reported value of 1.71 +/- 0.06, thereby confirming the linearity of three isotope correlation with the slope of 1.6-1.7 in the mid-latitude lower and middle stratosphere. The slope decrease with increasing altitude and a curvy trend in three-isotope correlation reported from previous studies were not statistically significant. Using negative linear correlations of Delta¹⁷O(CO2) and delta(18)O(CO2) with the N(2)O mixing ratio, we quantified triple oxygen-isotope fluxes of CO₂ to the troposphere as +48 parts per thousand GtC/yr (Delta¹⁷O(CO2))and +38 parts per thousand GtC/yr (delta(18)O(CO2)) with similar to 30 % uncertainty. Comparing recent model results and observations, underestimation of the three isotope slope and the maximum Delta¹⁷O(CO2) value in the model were clarified, suggesting a smaller O(2) photolysis contribution than that of the model. Simultaneous observations of delta(18)O(CO2), delta¹⁷O(CO2), and N(2)O mixing ratios can elucidate triple oxygen isotopes in CO₂ and clarify complex interactions among physical, chemical, and photochemical processes occurring in the middle atmosphere.

Determination of formaldehyde mixing ratios in air with PTR-MS: laboratory experiments and field measurements 査読有り

Inomata, S., Tanimoto, H., Kameyama, S., Tsunogai, U., Irie, H., Kanaya, Y., Wang, Z.

ATMOSPHERIC CHEMISTRY AND PHYSICS 8 巻 ( 2 ) 頁： 273-284 2008年

記述言語：英語掲載種別：研究論文（学術雑誌）

Formaldehyde (HCHO), the most abundant carbonyl compound in the atmosphere, is generated as an intermediate product in the oxidation of nonmethane hydrocarbons. Proton transfer reaction mass spectrometry (PTR-MS) has the capability to detect HCHO from ion signals at m/z 31 with high time-resolution. However, the detection sensitivity is low compared to other detectable species, and is considerably affected by humidity, due to back reactions between protonated HCHO and water vapor prior to analysis. We performed a laboratory calibration of PTR-MS for HCHO and examined the detection sensitivity and humidity dependence at various field strengths. Subsequently, we deployed the PTR-MS instrument in a field campaign at Mount Tai in China in June 2006 to measure HCHO in various meteorological and photochemical conditions; we also conducted intercomparison measurements by Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS). Correction of interference in the m/z 31 signals by fragments from proton transfer reactions with methyl hydroperoxide, methanol, and ethanol greatly improves agreement between the two methods, giving the correlation [HCHO]MAX-DOAS=(0.99±0.16) [HCHO]PTR-MS+(0.02±0.38), where error limits represent 95% confidence levels.

Geochemical studies of pore fluid in surface sediment on the Daini Atsumi Knoll 査読有り

Toki, T., Tsunogai, U., Gamo, T., Tanahashi, M.

JOURNAL OF GEOCHEMICAL EXPLORATION 95 巻 ( 40911 ) 頁： 29-39 2007年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

We collected sediment samples and pore water samples from the surface sediment on the Daini Atsumi Knoll, and analyzed the sediments for CH₄, C2H6, and delta C-13(CH₄), and the pore fluids for CH₄, C2H6, delta C-13(CH₄), Cl-, SO42- delta O-18(H2O), and delta D-H2O, respectively. A comparison of the measured concentration and isotopic composition of methane in pore water samples with those in sediment samples revealed that methane was present in the sediment samples at a higher concentration and was isotopically heavier than those in the pore water samples. It suggests that the effect of the release of a sorbed gas bound to organic particles when heated prior to analysis of hydrocarbons was larger than that of the degassing process. A large amount of a sorbed gas would be a significant source of natural gas. Two striking features are the chemical and isotopic composition of the pore water samples taken from the different sites around the Daini Atsumi Knoll. In the KL09, KL10, and KP07 samples, Cl- concentrations in the pore water samples showed depletion to a minimum of 460 mmol/kg, correspond to similar to 17 % dilution of seawater, however the latter was not enriched in CH₄. The isotopic compositions of pore water samples suggested the low-Cl- fluids in the pore water were not derived from dissociation of methane hydrate, but were derived from input of meteoric water. In contrast, in the KP05 samples from the north flank of the Daini Atsumi Knoll, pore water were characterized by CH₄ enrichment more than 370 mu mol/kg, but not depleted in Cl- concentrations. The observed methane concentration in the KP05 samples is not sufficient for methane hydrate to form in situ, indicating that the existence of methane hydrate in the surface sediment is negligible, as supported by Cl- concentration. Based on the stable carbon isotope ratio of methane in the pore fluid from the KP05 site (delta C-13(CH₄) <-50 parts per thousand PDB), methane is thought to be of microbial origin. The pore waters in the surface sediments in the north flank of the Daini Atsumi Knoll were not directly influenced by upward fluid bearing methane of thermogenic origin from a deeper part of the sedimentary layer. However, extremely high methane concentration in the north flank site as compared with the concentration of pore water taken from the normal seafloor suggests that the north flank site is not the normal seafloor. We hypothesize that upward migration of chemically-reduced fluids from a deeper zone of the sedimentary layer reduces chemically-oxidized solutes in the surface sediment. As a consequence methane production replaced sulfate reduction as the microbial metabolism in the reduced environment of the surface sediment.

DOI： 10.1016/j.gexplo.2007.05.009

Assessment of winter fluxes of CO₂ and CH₄ in boreal forest soils of central Alaska estimated by the profile method and the chamber method: a diagnosis of methane emission and implications for the regional carbon budget 査読有り

Kim, Yongwon, Ueyama, Masahito, Nakagawa, Fumiko, Tsunogai, Urumu, Harazono, Yoshinobu, Tanaka, Noriyuki

TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY 59 巻 ( 2 ) 頁： 223-233 2007年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

This research was carried out to estimate the winter fluxes of CO₂ and CH₄ using the concentration profile method and the chamber method in black spruce forest soils in central Alaska during the winter of 2004/5. The average winter fluxes of CO₂ and CH₄ by chamber and profile methods were 0.24 +/- 0.06 (SE; standard error) and 0.21 +/- 0.06 gCO₂-C/m(2)/d, and 21.4 +/- 5.6 and 21.4 +/- 14 mu gCH₄-C/m(2)/hr. This suggests that the fluxes estimated by the two methods are not significantly different based on a one-way ANOVA with a 95 % confidence level. The hypothesis on the processes of CH₄ transport/production/emission in underlying snow-covered boreal forest soils is proven by the pressure differences between air and in soil at 30 cm depth. The winter CO₂ emission corresponds to 23 % of the annual CO₂ emitted from Alaska black spruce forest soils, which resulted in the sum of mainly root respiration and microbial respiration during the winter based on the delta(CO₂)-C-13 of -22.5 parts per thousand. The average wintertime emissions of CO₂ and CH₄ were 49 +/- 13 gCO₂-C/m(2)/season and 0.11 +/- 0.07 gCH₄-C/m(2)/season, respectively. This implies that winter emissions of CO₂ and CH₄ are an important part of the annual carbon budget in seasonally snow-covered terrain of typical boreal forest soils.

DOI： 10.1111/j.1600-0889.2006.00233.x

Geochemical characterization of the organic matter, pore water constituents and shallow methane gas in the eastern part of the Ulleung Basin, East Sea (Japan Sea) 査読有り

Kim, Ji-Hoon, Park, Myong-Ho, Tsunogai, Urumu, Cheong, Tae-Jin , Ryu, Byong-Jae, Lee, Young-Joo, Han, Hyun-Chul, Oh, Jae-Ho , Chang, Ho-Wan

ISLAND ARC 16 巻 ( 1 ) 頁： 93-104 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

Geochemical analyses of sediments, pore water and headspace gas of the piston cores taken from the eastern part of Ulleung Basin of the East Sea (Japan Sea) were carried out to assess the origin of the sedimentary organic matter and interstitial fluid. Several tephra layers within the core are identified as the Ulleung-Oki (10.1 ka), the Aira-Tanzawa (23 ka) and the Ulleung-Yamato (30.9 ka) tephras. With the exception of these volcanic layers, the cores consist predominantly of muddy sediments that contain > 0.5 % total organic carbon. Atomic C/N ratios and delta C-13(org) values suggest that the organic matter originated from marine algae rather than from land vascular plants, whereas Rock-Eval pyrolysis suggests that the organic matter is thermally immature and comes from a land vascular plant (Type III). These conflicting results seem to be caused by the heavy oxidization of the marine organic matter. Sulphate concentration profiles of pore waters show strongly linear depletion (r(2) > 0.97) with sediment depth. The estimated sulphate-methane interface (SMI) depth using the sulphate concentration gradient was nearly 3.5 m below seafloor (mbsf) in the southern part of the study area, and deeper than 6 mbsf in the northern part of the area. The difference in SMI depths is likely associated with the amount of the methane flux. The methane concentration below the SMI in the two southern cores increases rapidly, implying the occurrence of methanogenesis and anaerobic methane oxidation (AMO). In contrast, the two northern cores have a low methane concentration below the SMI. delta C-13(CH₄) values measured from all cores were in the range of -83.5 to -69.5 parts per thousand, which suggests that the methane derives from a methanogenic microbe. delta C-13(CH₄) values become decreased toward SMI, but increased below SMI; therefore, delta C-13(CH₄) has eventually the minimum value near the SMI. The delta C-13(CH₄) values are also decreased when the methane concentration is increased. These phenomena support the typical occurrence of AMO in the study area.

DOI： 10.1111/j.1440-1738.2007.00560.x

Chemical and isotopic characteristics of interstitial fluids within the Taiwan Chelungpu fault 査読有り

Hirono, Tetsuro, Tsunogai, Urumu, Maegawa, Kenji, Toki, Tomohiro, Tanimizu, Masaharu, Soh, Wonn, Lin, Weiren, Yeh, En-Chao, Song, Sheng-Rong, Wang, Chien-Ying

GEOCHEMICAL JOURNAL 41 巻 ( 2 ) 頁： 97-102 2007年

記述言語：英語掲載種別：研究論文（学術雑誌）

We determined chloride and sulfate concentrations and (delta D-H2O and delta O-18(H2O) isotope ratios of interstitial fluids extracted from cores from two fault zones within the Taiwan Chelungpu fault. The fluids had higher concentrations of chloride and sulfate and higher delta D-H2O and delta O-18(H2O) values than the local meteoric water. We concluded that the higher (delta D-H2O) and delta O-18(H2O) values were the result of either entry of surface meteoric water at low altitude via fault zones, or isotopic fractionation by depletion at 50 degrees C in a shallower fault zone, and at 125 degrees C in the deeper fault zone. The high temperature in the deeper fault zone might have been earthquake-related frictional heating, which led to isotopic fractionation. However, neither of the above hypotheses explains the high concentrations of Cl- and SO42-. We concluded that the high concentrations of Cl- and SO42- might have resulted from mixing with seawater and dissolution of pyrite, respectively.

Rare earth elements in the hydrothermal system at Okinawa Trough back-arc basin 査読有り

Hongo, Yayoi, Obata, Hajime, Gamo, Toshitaka, Nakaseama, Miwako , Ishibashi, Junichiro, Konno, Uta, Saegusa, Shunsuke, Ohkubo, Satoru, Tsunogai, Urumu

GEOCHEMICAL JOURNAL 41 巻 ( 1 ) 頁： 40923 2007年

記述言語：英語掲載種別：研究論文（学術雑誌）

We present novel data sets of rare earth element (REE) distributions in a hydrothermal vent field at Yonaguni Knoll IV in the Okinawa Trough. Vertical REE profiles in three water columns showed horizontal variation of REE concentrations within 1000-1200 m. Hydrothermal plumes were discovered by anomalous values of methane, manganese and transmissometry at that site. Europium anomalies in the North Pacific deep water (NPDW) (Nozaki et al., 1999) normalized pattern decreased with distance from the hydrothermal vent site, indicating that the dilution of hydrothermal fluid in the plume can be traced using REE. The horizontal variation of negative Ce-anomalies represents the continuous scavenging of REE by suspended matter in the plume. In addition, we measured nine hydrothermal fluid samples. The REE geochemistry of hydrothermal vent systems had been investigated intensively at sediment-starved mid-oceanic ridges, but few studies had examined sediment-hosted hydrothermal systems like those of the Okinawa Trough. The chondrite-normalized REE patterns of the fluids collected at Yonaguni Knoll IV show typical lighter rare earth elements (LREE) and Eu enrichment similar to at the Mid-ocean Ridge sites. A remarkable characteristic of the Yonaguni Knoll IV fluid pattern is its higher concentrations of heavier rare earth elements (HREE) and La composition than the hydrothermal fluids of the sediment-starved East Pacific Rise and Trans-Atlantic Geotraverse. Such a feature is explainable by influences of covering sediments in the back-arc basin Okinawa Trough. At the hydrothermal vent, lighter REE (LREE) in the fluid was reduced systematically during fluid mixing with seawater within the chimney. Light REE elimination resembles fractionation caused by particle scavenging within the water column. However, the lack of Ce depletion, which is a typical REE feature in the water column, along with distinctive Eu reduction, were unique in the Yonaguni Knoll IV fluid, suggesting that fluid REE fractionation at the vent site was induced predominantly by coprecipitation with hydrothermally originated minerals (e.g. sulfate and carbonate), not by adhesive removal by Fe and/or Mn oxide particles. Previous studies had shown that REE removal and fractionation of the hydrothermal system were observed only in deposit samples. Results of this study elucidated REE fractionation in fluid samples using previous analytical data. We were also able to distinguish REE removal mechanisms occurring at the vent site and water column using REE pattern characteristics.

Microbial community in a sediment-hosted CO₂ lake of the southern Okinawa Trough hydrothermal system 査読有り

Inagaki, Fumio, Kuypers, Marcel M. M., Tsunogai, Urumu, Ishibashi, Jun-ichiro, Nakamura, Ko-ichi, Treude, Tina, Ohkubo, Satoru, Nakaseama, Miwako, Gena, Kaul, Chiba, Hitoshi, Hirayama, Hisako, Nunoura, Takuro, Takai, Ken, Jorgensen, Bo B. , Horikoshi, Koki, Boetius, Antje

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 103 巻 ( 38 ) 頁： 14164-14169 2006年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

Increasing levels Of CO₂ in the atmosphere are expected to cause climatic change with negative effects on the earth's ecosystems and human society. Consequently, a variety of CO₂ disposal options are discussed, including injection into the deep ocean. Because the dissolution Of CO₂ in seawater will decrease ambient pH considerably, negative consequences for deep-water ecosystems have been predicted. Hence, ecosystems associated with natural CO₂ reservoirs in the deep sea, and the dynamics of gaseous, liquid, and solid CO₂ in such environments, are of great interest to science and society. We report here a biogeochemical and microbiological characterization of a microbial community inhabiting deep-sea sediments overlying a natural CO₂ lake at the Yonaguni Knoll IV hydrothermal field, southern Okinawa Trough. We found high abundances (> 10(9) CM(-3)) of microbial cells in sediment pavements above the CO₂ lake, decreasing to strikingly low cell numbers (107 CM-3) at the liquid CO₂/CO₂-hydrate interface. The key groups in these sediments were as follows: (i) the anaerobic methanotrophic archaea ANME-2c and the Eel-2 group of Deltaproteobacteria and (ii) sulfur-metabolizing chemolithotrophs within the Gamma- and Epsilonproteobacteria. The detection of functional genes related to one-carbon assimilation and the presence of highly ¹³C-depleted archaeal and bacterial lipid biomarkers suggest that microorganisms assimilating CO₂ and/or CH₄ dominate the liquid CO₂ and CO₂-hydrate-bearing sediments. Clearly, the Yonaguni Knoll is an exceptional natural laboratory for the study of consequences of CO₂ disposal as well as of natural CO₂ reservoirs as potential microbial habitats on early Earth and other celestial bodies.

DOI： 10.1073/pnas.0606083103

Origins of hydrocarbons in the Sagara oil field, central Japan 査読有り

Toki, Tomohiro, Gamo, Toshitaka, Tsunogai, Urumu

ISLAND ARC 15 巻 ( 3 ) 頁： 285-291 2006年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

We collected free-gas and in situ fluid samples up to a depth of 200.6 m from the Sagara oil field, central Japan (34 degrees 44'N, 138 degrees 15'E), during the Sagara Drilling Program (SDP) and measured the concentrations and stable carbon isotopic compositions of CH₄ and C2H6 in the samples. A combination of the CH₄/C2H6 ratios with the carbon isotope ratios of methane indicates that the hydrocarbon gases are predominantly of thermogenic origin at all depths. The isotope signature of hydrocarbon gases of delta C-13(CH₄)< delta C-13(C2H4) suggests that these gases in the Sagara oil field are not generated by polymerization, but by the decomposition of organic materials.

DOI： 10.1111/j.1440-1738.2006.00528.x

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