研究者詳細 - 角皆　潤

論文 - 角皆　潤

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Stable carbon and oxygen isotopic analysis of atmospheric carbon monoxide using continuous-flow isotope ratio MS by isotope ratio monitoring of CO 査読有り

Tsunogai, U, Nakagawa, F, Komatsu, DD, Gamo, T

ANALYTICAL CHEMISTRY 74 巻 ( 22 ) 頁： 5695-5700 2002年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

We have developed a rapid and simple measurement system for both content and stable isotopic compositions (C-13 and O-18) of atmospheric CO, using continuous-flow isotope ratio mass spectrometry by simultaneously monitoring the CO+ ion currents at masses 28, 29, and 30. The analytical system consisted sequentially of a sample trapping port (liquid nitrogen temperature silica gel and molecular sieve 5A), a gas dryer, a CO purification column (molecular sieve 5A), a cryofocusing unit, and a final purification column using a GC capillary. Analytical precision of 0.2parts per thousand for C-13 and 0.4parts per thousand for O-18 can be realized for samples that contain as little as 300 pmol of CO within 40 min for one sample analysis. Analytical blanks associated with the method are less than 1 pmol. The extent of analytical error in delta¹³C due to mass-independent fractionation of oxygen in natural CO is estimated to be less than 0.3parts per thousand. Based on this system, we report herein a kinetic isotopic effect during CO consumption in soil.

DOI： 10.1021/ac020290x

Carbon isotopic evidence of methane oxidation through sulfate reduction in sediment beneath cold seep vents on the seafloor at Nankai Trough 査読有り

Tsunogai, U, Yoshida, N, Gamo, T

MARINE GEOLOGY 187 巻 ( 40910 ) 頁： 145-160 2002年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

During the Kaiko-Tokai project, we took a total of 15 near-surface sediment push cores from inside and outside seafloor clam colonies and bacterial mats in the Nankai Trough. In this study, we present the chemical and isotopic composition of pore fluids extracted from the sampled cores, with special emphasis on those taken at the Ryuyo Canyon, and discuss (a) the chemical relation between the seeping fluid and biological communities, and (b) the origin of cold seep fluids. Compared with bottom seawater, up to 5 % depletion of chloride concentration, extremely high CH₄ concentration of more than 300 mumol/kg, and slight deltaD(H2O) depletion are observed in pore fluids at the Ryuyo Canyon, which suggests that the Ryuyo Canyon is an active seep zone of low chloride, CH₄-rich, low deltaD(H2O) fluid from the sea bottom. Remarkable depletion of sulfate and significant enrichment of dissolved inorganic carbon and of hydrogen sulfide are also observed in the pore fluids, particularly those taken within bacterial mats, while the carbon isotopic composition of pore fluid dissolved methane (delta¹³C(CH₄)) shows large heterogeneity (up to 30parts per thousand) in and around the vents. These chemical and isotopic characteristics might be due to active anaerobic methane oxidation and hydrogen sulfide production (methane oxidation through sulfate reduction) in the sedimentary layer just below (within 30 cm) the vents on the seafloor. The carbon isotopic composition of methane can be considered direct evidence of the mediation process between methane-enriched cold seep fluid and the H2S-dependent biological community on the cold seep vent. After correcting for the effect of methane oxidation at the sediment surface, we estimate the end-member carbon isotopic composition of methane as less than -90parts per thousand PDB, and the end-member CH₄/C2H6 ratio as more than 10(3), which suggests a microbial, shallow layer is the origin of methane in the fluid.

DOI： 10.1016/S0025-3227(02)00263-3

Surface expression of fluid venting at the toe of the Nankai wedge and implications for flow paths 査読有り

Henry, P, Lallemant, S, Nakamura, K, Tsunogai, U, Mazzotti, S, Kobayashi, K

MARINE GEOLOGY 187 巻 ( 40910 ) 頁： 119-143 2002年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

Cold seeps have been observed with manned submersibles at many sites on the Tokai margin. Most sites are found on the hanging wall of major thrust faults, within 1-2 km of their outcrop. Few sites relate to purely erosional features. This relationship between thrusting and venting may be explained either by fluid flow along fault zones, by fluid flow along permeable layers outcropping at the fault scarp, or by diffuse upward flow of fluids released during footwall compaction. We use deep-towed side-scan sonar and sediment sounder profiles acquired at the toe of the Nankai accretionary wedge to identify the context of seepage at a smaller scale. Modes of fluid expulsion inferred from observations in this zone include flow channelling along strata, along thrusts, along gravity faults, and along joint fractures as well as diffuse flow. We then combine visual observation and monitoring of electrochemical potential (Eh) to assess the relative importance of seepage sites. We show that bacterial mats are better visual indicators of active seepage than bivalve beds and that the most active seepage sites correlate with outcrops of coarse turbidites, cemented by authigenic carbonates. These were sampled and have permeability high enough to channel fluid flow (1-4 x 10(-14) m(2)). We suggest they are the main conduits near the seafloor. However, seepage sites are also observed directly on the outcrop of major thrusts, indicating that they do play a role as fluid conduits. We observe negative polarity seismic reflections on these faults below 1 km depth and wonder about their significance.

DOI： 10.1016/S0025-3227(02)00262-1

Stable carbon isotopic compositions of light hydrocarbons over the western North Pacific and implication for their photochemical ages 査読有り

Saito, T, Tsunogai, U, Kawamura, K, Nakatsuka, T, Yoshida, N

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 107 巻 ( D4 ) 2002年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

Light hydrocarbons collected over the western North Pacific in canisters during an oceanographic cruise in May 1999 were analyzed for the mixing ratios and the stable carbon isotopic compositions (delta¹³C). Their mixing ratios decreased during the passage of a warm front. By contrast, they increased after the passage of a cold front. The delta¹³C values of ethane were found to be in a range of -26 to -19parts per thousand and to be systematically heavier when the mixing ratios (range of 1.7-0.6 ppbv) became lower. The delta¹³C values of ethane over the open ocean generally showed heavier values than those previously reported in the source regions, suggesting an isotopic fractionation during a long-range atmospheric transport. In contrast, delta¹³C values of i- and n-butanes varied in a wide range (-37 to -16parts per thousand and -37 to -21parts per thousand, respectively); however, their averaged values are comparative to the isotopic source compositions. Likewise, no systematic relationships were found between the mixing ratios and the delta¹³C values of the butane isomers. For n-butane the observed relationship was substantially different from that predicted by kinetic isotope effect by the reaction with OH radicals probably due to the contribution of effective mixing process. From the changes in the delta¹³C values for ethane and n-butane the averaged photochemical ages were calculated to be 49 +/- 26 days and 2 +/- 6 days, respectively. The difference in the estimated ages is attributed to the different reactivity of hydrocarbons. The average ages for n-butane were found to be consistent with numbers of days, which the air mass took for the transport from the continent to the sampling site over the ocean, on the basis of backward trajectory analysis. This study suggests that the photochemical ages are useful for assessing the importance of recent emission in the marine atmosphere.

DOI： 10.1029/2000JD000127

Production mechanism and global budget of N₂O inferred from its isotopomers in the western North Pacific 査読有り

Toyoda, S, Yoshida, N, Miwa, T, Matsui, Y, Yamagishi, H, Tsunogai, U, Nojiri, Y, Tsurushima, N

GEOPHYSICAL RESEARCH LETTERS 29 巻 ( 3 ) 2002年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

We measured the intramolecular distribution of N-15 as well as conventional nitrogen and oxygen isotope ratios in oceanic nitrous oxide (N₂O) in the western North Pacific for the first time. In contrast to a nearly homogeneous vertical distribution of a bulk nitrogen isotope ratio, a wide variation in site preference for intramolecular N-15 distribution was found, suggesting the subsurface and deep source mixing and the production mechanism in the ocean. The oceanic composition of N₂O isotopomers quantitatively outlines the ocean as the most significant source after the terrestrial one.

DOI： 10.1029/2001GL014311

超微量炭素同位体比測定による熱水・冷湧水溶存気体に関する研究（日本地球化学会奨励賞受賞記念論文）招待有り査読有り

角皆　潤

地球化学 36 巻 ( 1 ) 頁： 51-63 2002年

Chemical characteristics of newly discovered black smoker fluids and associated hydrothermal plumes at the Rodriguez Triple Junction, Central Indian Ridge 査読有り

Gamo, T, Chiba, H, Yamanaka, T, Okudaira, T, Hashimoto, J , Tsuchida, S, Ishibashi, J, Kataoka, S, Tsunogai, U, Okamura, K, Sano, Y, Shinjo, R

EARTH AND PLANETARY SCIENCE LETTERS 193 巻 ( 40972 ) 頁： 371-379 2001年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

The chemical characteristics of hydrothermal fluids in the Indian Ocean have been revealed for the first time. A hydrothermal field (called the Kairei field), including active black smoker chimneys, was discovered by ROV Kaiko dives at 25 degrees 19.17'S, 70 degrees 02.40'E ( similar to 2450 to depth) on the southwestern flank of an off-axis knoll located similar to 15 miles north of the Rodriguez Triple Junction, Central Indian Ridge, after detailed tow-yo surveys of the hydrothermal plume distribution. The temperature of the fluid expelled from the most active chimney was almost stable (359-360 degreesC) throughout three successive days of fluid sampling. The endmember fluid has a chemical composition similar to the hydrothermal fluids sampled from sediment-starved mid-ocean ridges in the Pacific and the Atlantic oceans, suggesting typical interactions between hot fluid and mid-ocean ridge basalts in the subseafloor reaction zone.

DOI： 10.1016/S0012-821X(01)00511-8

Carbon isotopic distribution of methane in deep-sea hydrothermal plume, Myojin Knoll Caldera, Izu-Bonin arc: Implications for microbial methane oxidation in the oceans and applications to heat flux estimation 査読有り

Tsunogai, U, Yoshida, N, Ishibashi, J, Gamo, T

GEOCHIMICA ET COSMOCHIMICA ACTA 64 巻 ( 14 ) 頁： 2439-2452 2000年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

The concentration and stable carbon isotopic composition; (delta¹³C) Of methane have been measured for both seafloor hydrothermal venting fluids and effluent plume waters supplied from the vents at the Myojin Knell Caldera, Izu-Bonin are, in the western North Pacific. The hydrothermal end-member concentrations and delta¹³C of methane show near-homogeneity among vents. 41.2 (mu mol/kg) and -16.3 +/- 0.8 (parts per thousand PDB), respectively, while those in the effluent plume are stratified m the caldera and vertically exhibit a large variation (2.1-11 (nmol/kg) and -29.0 to -11.3 ( %BDB), respectively). Comparison of concentration and delta¹³C data between vent fluids and plume waters suggest that the methane is not conserved but microbially oxidized along with the plume. Gradual decrease of diffusive methane flux in proportion to distance from the vent fields supports the occurrence of significant microbial oxidation within the plume. Assuming steady state emission of methane from the vents, (1) kinetic isotope effect due to the microbial oxidation (k(12)/k(13)); (2) methane flux from the vents (F-vents); (3) heat flux from the vents (Q); and (4) average turnover time of hydrothermal methane (T-all) are estimated to be k(12)/k(13) = 1.005 +/- 0.001, F-vents = 90-340 (mol/d), Q = 30-110 (MW), and T-all = 60 -240 (d), respectively. The estimated turnover times, however, are not uniform within the water column. Around the vents, a turnover time of less than 50 d for methane is one of the shortest values in the pelagic ocean, while those at the distant points correspond to values more typical for deep ocean water.

DOI： 10.1016/S0016-7037(00)00374-4

Stable carbon and oxygen isotopic analysis of carbon monoxide in natural waters 査読有り

Tsunogai, U, Nakagawa, F, Hachisu, Y, Yoshida, N

RAPID COMMUNICATIONS IN MASS SPECTROMETRY 14 巻 ( 16 ) 頁： 1507-1512 2000年

記述言語：英語掲載種別：研究論文（学術雑誌）

Techniques have been developed to allow on-line simultaneous analysis of concentration and stable isotopic compositions (C-13 and O-18) of dissolved carbon monoxide (CO) in natural water, using continuous-flow isotope ratio mass spectrometry (CF-IRMS), The analytical system consisted sequentially of a He-sparging bottle of water, a gas dryer, CO2-trapping stage using both Ascarite trap and silica-gel packed gas chromatography (GC), on-line oxidation to CO2 using the Schutze reagent, cryofocusing, GC purification using a capillary column and measurement by CF-IRMS, Each sample analysis takes about 40 minutes. The detection limit with delta¹³C standard deviation of 0.5 parts per thousand is 300 pmol and that with delta(18)O deviation of 1.0 parts per thousand is 750 pmol. Analytical blanks associated with these methods are 21 +/- 9 pmol, The procedures are evaluated through analyses of temporally varying concentration and isotopic compositions of CO in an artificial lake on the university campus. The delta¹³C and delta(18)O values of CO showed wide variation in accordance with diurnal variation of CO concentration, probably due to significant isotopic effects during photochemical production and microbial oxidation of CO in the aquatic environment. The delta¹³C and delta(18)O values of CO should be a useful tool in studies of the mechanism and pathways of CO production and consumption in natural waters.

DOI： 10.1002/1097-0231(20000830)14:16<1507::AID-RCM56>3.3.CO;2-5

Carbon isotopic compositions of C₂-C₅ hydrocarbons and methyl chloride in urban, coastal, and maritime atmospheres over the western North Pacific 査読有り

Tsunogai, U, Yoshida, N, Gamo, T

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 104 巻 ( D13 ) 頁： 16033-16039 1999年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

C-2, - C-5, non-methane hydrocarbons (NMHCs) and methyl chloride in the remote maritime atmosphere over the western North Pacific are analyzed in regard to their variation of mixing ratio and C-13/C-12 ratio (delta¹³C), together with those in polluted urban (Nagoya and Yokohama) and coastal (Tokyo Bay) atmosphere in Japan. NMHCs show large atmospheric mixing ratio and reacts between urban (coastal) and maritime atmospheres probably due to emission from urban areas and degradation within the maritime atmosphere. Reflecting isotopic fractionation during the degradation within the maritime atmosphere, ethane shows large and systematic delta¹³C variation between urban (around -27 parts per thousand ethane Peedee belemnite (PDB)) and maritime atmosphere s (up to -22 parts per thousand PDB). Except for ethane, however, alkanes show small isotopic variation around delta¹³C = -27 +/- 2 parts per thousand PDB (lo) without systematic isotopic differences between urban and maritime atmospheres, suggesting br,th small delta¹³C: variation a ithin major emission sources and also little isotopic fractionation during atmospheric degradation for alkanes other than ethane. Alkenes show large delta¹³C variation from -37 to -12 parts per thousand PDB for ethylene and from -27 to -14 parts per thousand PDB for propylene. Combination of both large delta¹³C differences between major sources (especially between land and maritime sources) and large isotopic fractionation effect during atmospheric degradation call be suggested for alkenes. Methyl chloride also shows large isotopic variation from -44 to -30 parts per thousand PDB in spite of their similar atmospheric mixing ratios from 580 to 710 parts per trillion by volume (pptv), probably due to the contribution of highly C-13-depleted, anthropogenic methyl chloride especially to urban atmospheres, Thr general delta¹³C pattern of NMHCs and methyl chloride in polluted urban city air agrees s strongly with those of biomass (C-3 plant) burning plumes, suggesting that thermal breakdown of C-3 plant (or related organic matter) is one of the representative sources of these hydrocarbons in urban atmospheres. Further investigations of the isotopic signature of source materials as well as laboratory studies of isotopic fractionation processes resulting from atmospheric degradation will improve our understanding of the sources, sinks, and atmospheric distributious of NMHCs and methyl chloride.

DOI： 10.1029/1999JD900217

Carbon isotope measurement of extremely low amounts of CH₄: Application to volcanic gases from Satsuma-Iwojima, Japan 査読有り

Sato, M, Tsunogai, U, Ishibashi, J, Notsu, K, Wakita, H

ANALYTICAL SCIENCES 15 巻 ( 6 ) 頁： 513-516 1999年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

A preconcentration system attached to a GC/C/MS (gas chromatography/combustion/mass spectrometer) was developed to determine the carbon-isotope composition of methane in volcanic gases with extremely low concentration. With this system, we can analyze the carbon isotope ratio (C-13/C-12) of 0.7 - 6 nmol methane with a precision of +/-1.6 parts per thousand, unlike other conventional methods without preconcentration (150 - 1000 nmol CH₄ with a precision of +/-0.2 parts per thousand). This system was tested with volcanic gas samples from Satsuma-Iwojima volcano, suggesting a mixture of magmatic and thermogenic origins for methane.

DOI： 10.2116/analsci.15.513

Origin of ¹³C-enriched methane in the crater lake Towada, Japan 査読有り

Nishimura, R, Tsunogai, U, Ishibashi, J, Wakita, H, Nojiri, Y

GEOCHEMICAL JOURNAL 33 巻 ( 4 ) 頁： 277-283 1999年

記述言語：英語掲載種別：研究論文（学術雑誌）

Concentration and stable carbon isotopic composition (delta¹³C) of CH₄ are determined in a water column of an 327 m deep oxic oligotrophic crater lake, Lake Towada in Japan. The results of CTD measurements show relatively high temperature and high conductivity in the Lower part of the column, possibly derived from hot springs at the crater wall approximately 150 m deep. The vertical profile of CH₄ concentration shows two sharp maxima of 68 and 69 nmol/kg at depths of 20 and 150 m, respectively, The delta¹³C value of CH₄ at 20 m is -55 parts per thousand PDB, suggesting microbial production in and around the lake. In contrast, the delta¹³C value of CH₄ at 150 m is +11 parts per thousand PDB, which suggests some secondary isotopic alternation processes peculiar to hot spring-derived CH₄ in the oxic water column, such as rapid aerobic microbial oxidation.

Methane-rich plumes in the Suruga Trough (Japan) and their carbon isotopic characterization 査読有り

Tsunogai, U, Ishibashi, J, Wakita, H, Gamo, T

EARTH AND PLANETARY SCIENCE LETTERS 160 巻 ( 40910 ) 頁： 97-105 1998年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

The carbon isotopic compositions (delta¹³C(CH₄)) Of the methane-rich buoyant plumes, observed in the oxygenated hemipelagic sea waters of the Suruga Trough, Japan, are discussed in relation to their sources. During a survey made in May 1996, two layers of anomalous methane-rich plumes, both of which centred at the same station about a few tens of kilometres off the coast, were found in the Suruga Trough. The deeper plume (ca. 2100 m depth, with a maximum methane concentration of 13 nmol/kg) had already been detected by a previous survey in 1986 at the same station, whereas the shallower plume (ca, 1000 m depth, with a maximum methane concentration of 10 nmol/kg) was newly discovered. The estimated end-member delta¹³C(CH₄) value (-59 +/- 3 parts per thousand PDB) for the deeper plume suggests a microbial origin of the methane, probably derived from some shallow (surface) layer of sediment. The plume could be supplied from a continuous cold fluid seepage on the sea floor of the Suruga Trough. On the other hand, the shallower plume is characterized by more C-13-enriched end member methane (delta¹³C(CH₄) = -38 +/- 2 parts per thousand PDB), presumably produced by the thermogenic degradation of organic matter. Since thermogenic methane should originate from a deeper part (more than 1000 m) of the sedimentary layer, it is unlikely that the thermogenic methane reaches the sea water by normal transport processes. The shallower plume may be a result of some sudden, catastrophic event on the sea floor, such as earthquakes.

DOI： 10.1016/S0012-821X(98)00075-2

Neutron activation analysis of deep sea sediments from the regions near Japan 査読有り

Minai, Y, Tsunogai, U, Takahashi, H, Ishibashi, J, Matsumoto, R, Tominaga, T

JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY 216 巻 ( 2 ) 頁： 265-277 1997年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

Eighteen trace elements, including seven rare earth elements (REEs), and major and minor elements in the sediment samples from the Japan Sea and the northwestern Pacific near Japan were determined with instrumental neutron activation analysis (INAA). Most REE patterns (chondrite-normalized) of the sediments were nearly identical to the patterns of terrigenous materials without cerium anomaly whereas the La/Yb ratio varied with the site locations. The variation of the La/Yb ratio of the sediments may indicate the regional variation of the mixing proportion of the terrigenous materials from the continent to the materials from the volcanic island area including the Japanese islands. The Th/Sc ratio of the sediments tended to increase with distance from the island-arc volcanism. Regional variation of the Th/Sc ratio may indicate variation of amount of the continental terrigenous materials supplied to the sediments.

DOI： 10.1007/BF02033789

Discrete scaling in earthquake precursory phenomena: Evidence in the Kobe earthquake, Japan 査読有り

Johansen, A, Sornette, D, Wakita, H, Tsunogai, U, Newman, WI , Saleur, H

JOURNAL DE PHYSIQUE I 6 巻 ( 10 ) 頁： 1391-1402 1996年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

We analyze the ion concentrations of groundwater issuing from deep wells located near the epicenter of the recent earthquake of magnitude 6.9 near Kobe, Japan, on January 17, 1995. These concentrations are well fitted by log-periodic modulations around a leading power law. The exponent (real and imaginary parts) is very close to those already found for the fits of precursory seismic activity for Loma Prieta and the Aleutian Islands. This brings further support for the general hypothesis that complex critical exponents are a general phenomenon in irreversible self-organizing systems and particularly in rupture and earthquake phenomena.

DOI： 10.1051/jp1:1996143

Fresh water seepage and pore water recycling on the seafloor: Sagami Trough subduction zone, Japan 査読有り

Tsunogai, U, Ishibashi, J, Wakita, H, Gamo, T, Masuzawa, T , Nakatsuka, T, Nojiri, Y, Nakamura, T

EARTH AND PLANETARY SCIENCE LETTERS 138 巻 ( 40912 ) 頁： 157-168 1996年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

We collected 19 samples of bottom sea water (including 8 samples of shimmering fluid), using the Japanese submersible Shinkni 2000, in the bathyal Calyptogena community area (the Hatsushima area) along Sagami Trough, at the northern end of the Philippine Sea plate, in order to clarify the source of fluid seepage, Shimmering fluid samples showed a maximum temperature of 11.6 degrees C, which is about 9 degrees C higher than the ambient sea water. The fluid chemistry of these samples is summarized as follows: (1) alkalinity, H2S, SiO2, NH4, Sigma CO2 and CH₄ show enrichment and Cl, SO4, K, Na, Mg and Ca show depletion compared with ambient sea water; (2) Cl depletion is about 20 %; and (3) the content and He-3/He-4 ratio of dissolved helium show little anomaly compared with ambient sea water. The observed chemical composition and temperature of the fluid is well explained by mixing of sea water, pore water and land-derived groundwater with a temperature of about 40 degrees C and a seeping flux of about 400 m(3) per day. A preliminary estimation of the global chemical flux implies that groundwater discharge to the ocean (including pore water recycling) is an important factor in controlling ocean chemistry.

DOI： 10.1016/0012-821X(95)00228-5

Anomalous changes in groundwater chemistry - Possible precursors of the 1995 Hyogo-ken Nanbu earthquake, Japan 査読有り

Tsunogai, U and Wakita, H

JOURNAL OF PHYSICS OF THE EARTH 44 巻 ( 4 ) 頁： 381-390 1996年

記述言語：英語掲載種別：研究論文（学術雑誌）

A post-earthquake investigation revealed statistically significant changes in the chemical composition of groundwater pumped from wells located about 20 km east of the epicenter within the aftershock region, preceding the disastrous M7.2 Hyogo-ken Nanbu earthquake in southwestern Japan on January 17, 1995. The chloride ion concentration had increased steadily after August 1994, compared to the constant level since July 1990, and reached an excess of about 10 % just before the earthquake. Groundwater sampled after the earthquake showed much higher Cl- concentrations. Together with the increase in Cl-, sulfate and alkaline earth metal ions (Mg2+, Ca2+, Sr2+, Ba2+) showed similar increases in their concentrations, while sodium ion and silica contents showed decreases. These changes may be the result of shallow groundwater inflow, enriched in chloride, sulfate and alkaline earth metal ions, to the artesian layer of the wells, due to permeability enhancement in the shallow stratum. The observed changes in groundwater chemistry before and after the earthquake are useful clues to understanding the mechanism of the present earthquake.

Precursory chemical changes in ground water - Kobe Earthquake, Japan 査読有り

Tsunogai, U. and Wakita, H.

SCIENCE 269 巻 ( 5220 ) 頁： 61-63 1995年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

Chloride (Cl-) and sulfate (SO42-) ion concentrations of ground water issuing from two wells located near the epicenter of the Kobe earthquake in Japan fluctuated before the disastrous magnitude 7.2 event on 17 January 1995. The samples measured were pumped ground water packed in bottles and distributed in the domestic market as drinking water from 1993 to April 1995. Analytical results demonstrate that Cl- and SO42- concentrations increased steadily from August 1994 to just before the earthquake. Water sampled after the earthquake showed much higher Cl- and SO42- concentrations. The precursory changes in chemical composition may reflect the preparation stage of a large earthquake.

DOI： 10.1126/science.269.5220.61

Peculiar features of Suiyo seamount hydrothermal fluids, Izu-Bonin arc: Differences from subaerial volcanism 査読有り

Tsunogai, U, Ishibashi, J, Wakita, H, Gamo, T, Watanabe, K, Kajimura, T, Kanayama, S, Sakai, H

EARTH AND PLANETARY SCIENCE LETTERS 126 巻 ( 4 ) 頁： 289-301 1994年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

This is the first report of the dissolved gas composition of a deep-sea venting hydrothermal system originating from are volcanism; the origin of dissolved gases in hydrothermal fluids from the Suiyo seamount in the southern Izu-Bonin (Ogasawara) Are is discussed on the basis of chemical and isotopic compositions. Twelve high-temperature (up to 310 degrees C) fluid samples were collected from three vents of the hydrothermal system using the submersible Shinkai 2000. The average He-3/He-4 ratio of the dissolved He is 8.1 (R/R(atm)), which is within the range of values reported for N-MORB. The CO2/He-3 ratio is 12 x 10(9), which is within the range of are volcanic gas values. The delta¹³C values of CO2 and CH₄ are -1 and -8.5 parts per thousand respectively, which is quite high compared with other subaerial are volcanic gases and those from mid-ocean ridges. These results, which do not accord with those from subaerial volcanism, are unlikely to result from fractionation or addition of carbon sources during the fluid circulation, but are regarded as characteristic of the magma source of Suiyo Seamount. A simple mixing of 97 % MORB mantle with 3 % subducting slab explains well the composition of the helium and carbon in the parent magma.

DOI： 10.1016/0012-821X(94)90113-9

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