Faculty Profiles - TSUNOGAI Urumu

Papers - TSUNOGAI Urumu

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Liquid CO₂ venting on the seafloor: Yonaguni knoll IV hydrothermal system, Okinawa Trough Reviewed

Konno, Uta, Tsunogai, Urumu, Nakagawa, Fumiko, Nakaseama, Miwako, Ishibashi, Jun-ichiro, Nunoura, Takuro, Nakamura, Ko-ichi

GEOPHYSICAL RESEARCH LETTERS Vol. 33 ( 16 ) 2006.8

Language：English Publishing type：Research paper (scientific journal)

We determined the chemical and isotopic compositions of the liquid CO₂ found on Yonaguni IV knoll hydrothermal site, as well as those in hydrothermal fluid venting from the surrounding chimneys. The delta¹³C of both CO₂ and CH₄ in the liquid CO₂ almost coincide with those in the hydrothermal fluid, suggesting that the liquid CO₂ must be derived from the hydrothermal fluid. While showing homogeneous delta¹³C, the hydrothermal fluids exhibit wide variation in gas contents. Active phase separation must be taking place within the conduits. Besides, H₂-depletion in the liquid CO₂ suggests formation of solid CO₂-hydrate must also precede the venting of liquid CO₂. In conclusion, liquid CO₂ must be produced through following subseafloor processes: phase separation of hydrothermal fluid due to boiling, formation of solid CO₂-hydrate due to cooling of vapor phase, and melting of the solid CO₂-hydrate to liquid CO₂ due to a temperature increase within the sedimentary layer.

DOI： 10.1029/2006GL026115

Molecular phylogenetic and chemical analyses of the microbial mats in deep-sea cold seep sediments at the northeastern Japan Sea Reviewed

Arakawa, Shizuka, Sato, Takako, Sato, Rumi, Zhang, Jing, Gamo, Toshitaka, Tsunogai, Urumu, Hirota, Akinari, Yoshida, Yasuhiko, Usami, Ron, Inagaki, Fumio, Kato, Chiaki

EXTREMOPHILES Vol. 10 ( 4 ) page： 311-319 2006.8

Language：English Publishing type：Research paper (scientific journal)

Microbial communities inhabiting deep-sea cold seep sediments at the northeastern Japan Sea were characterized by molecular phylogenetic and chemical analyses. White patchy microbial mats were observed along the fault offshore the Hokkaido Island and sediment samples were collected from two stations at the southern foot of the Shiribeshi seamount (M1 site at a depth of 2,961 m on the active fault) and off the Motta Cape site (M2 site at a depth of 3,064 m off the active fault). The phylogenetic and terminal-restriction fragment polymorphism analyses of PCR-amplified 16S rRNA genes revealed that microbial community structures were different between two sampling stations. The members of ANME-2 archaea and diverse bacterial components including sulfate reducers within Deltaproteobacteria were detected from M1 site, indicating the occurrence of biologically mediated anaerobic oxidation of methane, while microbial community at M2 site was predominantly composed of members of Marine Crenarchaeota group I, sulfate reducers of Deltaproteobacteria, and sulfur oxidizers of Epsilonproteobacteria. Chemical analyses of seawater above microbial mats suggested that concentrations of sulfate and methane at M1 site were largely decreased relative to those at M2 site and carbon isotopic composition of methane at M1 site shifted heavier (C-13-enriched), the results of which are consistent with molecular analyses. These results suggest that the mat microbial communities in deep-sea cold seep sediments at the northeastern Japan Sea are significantly responsible for sulfur and carbon circulations and the geological activity associated with plate movements serves unique microbial habitats in deep-sea environments.

DOI： 10.1007/s00792-005-0501-0

Development of a multibottle gas-tight fluid sampler WHATS II for Japanese submersibles/ROVs Reviewed

Saegusa, S., Tsunogai, U., Nakagawa, F., Kaneko, S.

GEOFLUIDS Vol. 6 ( 3 ) page： 234-240 2006.8

Language：English Publishing type：Research paper (scientific journal)

This paper summarizes the design and performance of our recently developed gas-tight fluid sampler WHATS II, especially designed to collect seafloor venting gas-rich fluid from submersibles/remotely operated vehicles (ROVs). It consists of four 150-cm(3) stainless steel sample cylinders, eight ball valves, a motor-driven arm, a rail, a peristaltic pump, a control unit, and a flexible Teflon tube connected to a titanium inlet tube. All the parts have been designed to be used at undersea as deep as 4000 m. The motor-driven arm on the rail can open and close each of the four cylinders. By pumping out distilled water that has filled an open cylinder and the dead spaces of the sampler, we can fill the cylinder with sample fluid. WHATS II can take a maximum of four different gas-tight samples in a series. The whole operation can be arranged from the cabin, etc., of a submersible/ROV. Use of only one motor to operate eight valves makes the sampler small, light (21 kg in sea water), and easy to handle. In addition, the sampler is able to collect an almost uncontaminated gas-tight sample from the seafloor. To date, the sampler has been used in more than 90 dive surveys by Japanese submersibles/ROVs, including Shinkai 2000, Shinkai 6500, and Hyper Dolphin, with a success rate of > 90 %.

DOI： 10.1111/j.1468-8123.2006.00143.x

Geomicrobiological exploration and characterization of a novel deep-sea hydrothermal system at the TOTO caldera in the Mariana Volcanic Arc Reviewed

Nakagawa, T, Takai, K, Suzuki, Y, Hirayama, H, Konno, U, Tsunogai, U, Horikoshi, K

ENVIRONMENTAL MICROBIOLOGY Vol. 8 ( 1 ) page： 37-49 2006.1

Language：English Publishing type：Research paper (scientific journal)

Novel hydrothermal activities accompanying effluent white smokers and elemental sulfur chimney structures at the north-east lava dome of the TOTO caldera depression in the Mariana Volcanic Arc have been explored and characterized by geochemical and microbiological surveys. White smoker hydrothermal fluids were observed in the potential hydrothermal activity centre of the field and represented the maximal temperature of 170 degrees C and the lowest pH of 1.6. The chimney structures, all consisting of elemental sulfur (sulfur chimney), were also unique to the TOTO caldera hydrothermal field. Microbial community structures in a sulfur chimney and its formation hydrothermal fluid with a high concentration of hydrogen sulfide (15 mM) have been investigated by culture-dependent and -independent analyses. 16S rRNA gene clone analysis and fluorescence in situ hybridization (FISH) analysis revealed that epsilon-Proteobacteria dominated the microbial communities in the sulfur chimney structure and formed a dense microbial mat covering the sulfur chimney surface. Archaeal phylotypes were consistently minor components in the communities and related to the genera Thermococcus, Pyrodictium, Aeropyrum, and the uncultivated archaeal group of `deep-sea hydrothermal vent euryarchaeotal group'. Cultivation analysis suggested that the chemolithoautotrophs might play a significant ecological role as primary producers utilizing gas and sulfur compounds provided from hydrothermal fluids.

DOI： 10.1111/j.1462-2920.2005.00884.x

Polar and neutral isopranyl glycerol ether lipids as biomarkers of archaea in near-surface sediments from the Nankai Trough Reviewed

Oba, Masahiro, Sakata, Susumu, Tsunogai, Urumu

ORGANIC GEOCHEMISTRY Vol. 37 ( 12 ) page： 1643-1654 2006

Language：English Publishing type：Research paper (scientific journal)

The molecular and carbon isotopic compositions of polar isopranyl glycerol ether lipids, which are direct indicators of viable archaea, and neutral isopranyl glycerol ether lipids, which are derived from polar lipids via hydrolysis, in near-surface sediments from a methane seep in the Nankai Trough (off central Japan) were investigated. Procedures for extracting, separatine and derivatizing polar and neutral ether lipids for detection using gas chromatography were first examined with one sediment sample and a cultivated methanogen. For all sediment samples, archaeol and hydroxyarchaeol were detected in both the polar and neutral ether lipid fractions. Acyclic and cyclic biphytanes were also detected in both types of lipid fractions after treatment with HI/LiAlH4 for ether cleavage and alkylation. The delta C-13 values of archaeol, sn-2-hydroxyarchaeol, and sn-3-hydroxyarchaeol in the sample from 0.82 in below the seafloor were lower than -100 parts per thousand relative to PDB, indicating that diverse living methanotrophic archaea are present in the seep sediments. Biphytanes released from polar ether lipids in the same sample were less depleted in delta C-13 (-71 parts per thousand to -36 parts per thousand). The wide range of delta C-13 values suggests that the biphytanes were derived not only from methanotrophic but also from non-methanotrophic archaea, and that the relative contributions of the methanotrophic and non-methanotrophic archaea differed, depending on the biphytane compound. The vertical profiles and delta C-13 values of the neutral ether lipids were similar to those of the intact polar ether lipids, suggesting that neutral ether lipids derived from fossil archaea in the samples had mainly been lost by the time of sampling.

DOI： 10.1016/j.orggeochem.2006.09.002

Stable isotopic compositions of methane and carbon monoxide in the Suiyo hydrothermal plume, Izu-Bonin arc: Tracers for microbial consumption/production Reviewed

Tsunogai, U, Nakagawa, F, Gamo, T, Ishibashi, J

EARTH AND PLANETARY SCIENCE LETTERS Vol. 237 ( 40972 ) page： 326-340 2005.9

Language：English Publishing type：Research paper (scientific journal)

Effluent hydrothermal water samples in and around the water column of the Suiyo seamount caldera (ca. 2 km diameter), Izu-Bonin arc, were taken to determine concentrations and stable carbon isotopic compositions (delta¹³C) of methane (CH₄) and carbon monoxide (CO) in the plume. Venting fluids on the caldera floor (ca. 1370 m depth) were also examined, using the manned submersible Shinkai 2000, to compare the chemical composition and isotopic composition of CH₄ and CO with those in the hydrothermal plume. Strong CH₄ enrichment was detected not only in the water column within the caldera, but also on those outside the caldera at the depth of ca. I 100 m, the sill depth of the caldera wall. Within the plume, we also detected significant CO enrichment. The delta¹³C of CO in the plume, however, exhibited highly C-13-depleted values (-110 parts per thousand(VPDB) to -60 parts per thousand(VPDB)) compared with those in seafloor venting hydrothermal fluids (around - 31 parts per thousand(VPDB)). Besides, the plume samples exhibited higher CO/CH₄ ratios depending on the distance from the seafloor venting site. We conclude that in situ microbial activity in the plume causes the CO enrichment in the hydrothermal plume. The present results suggest that CO enrichment in deep sea water could act as a new tracer for unidentified seafloor hydrothermal activities, especially for detecting plumes distant from venting sites, as well as for quantifying in situ microbial activity related to CO production in hydrothermal plumes.

DOI： 10.1016/j.epsl.2005.05.042

Geochemical studies on submarine groundwater discharges in Toyama Bay using methane as a tracer Reviewed

Kameyama, S., U. Tsunogai, T. Gamo, J. Zhang, M. Suzuki, and Y. Koyama

Chikyukagaku (Geochemistry) Vol. 39 page： 131-140 2005.8

Language：Japanese Publishing type：Research paper (scientific journal)

We present here a geochemical study on the SGD in the Toyama Bay using CH4 and its carbon isotope ratio as tracers. We found that all SGD fluids and many of land groundwaters contain less methane than natural water in equilibrium with atmospheric CH4. The .DELTA.'13'C values of CH4 in the SGD fluids range from -50 to -20.PERMIL. VPDB, almost comparable or slightly higher than that of atmospheric CH4. The results suggest that most of methane in the SGD fluids had been derived from the atmosphere and a part of the CH4 is oxidized in the course of groundwater flow through the aquifer, with no CH4 production that is usual in highly anoxic groundwater. This is probably due to little organic matter content in the aquifer and/or a short residence time from recharge to discharge on seafloor. The low concentration and high carbon isotopic ratio of CH4 are similar to those in some of the land groundwaters. The SGD fluid in Uozu should be flowing underground along the Katagai River.

An analytical system for determining delta O-17 in CO2 using continuous flow-isotope ratio MS Reviewed

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

ANALYTICAL CHEMISTRY Vol. 77 ( 14 ) page： 4509-4514 2005.7

Language：English Publishing type：Research paper (scientific journal)

We developed a simple measurement system for delta¹⁷O in nanomole quantities of CO2 using continuous flow isotope ratio mass spectrometry (CF-IRMS). The analytical system consisted of a sample injection system, a helium-purged CO2 purification line, a capillary GC, a combustion unit, and CF-IRMS. A unique feature of the system is that we use molecular CO2 to determine the isotopic compositions including delta¹⁷O. The delta¹⁷O Of CO2 in a sample is calculated from the mass ratios of both 45/44 and 46/44 of two different kinds Of CO2, which have been purified quantitatively from different aliquots of a sample. While one aliquot (rCO₂) flows into IRMS directly, the other (eCO₂) flows through a CuO unit (900 degrees C) prior to injection into IRMS, to exchange oxygen atoms in the sample CO2 molecules with those in CuO for which we can assume Delta¹⁷O = 0. In our system, we introduce both rCO₂ and eCO₂ alternately to IRMS repeatedly by using an automatic multianalytical system to improve analytical precision statistically. The standard deviation of 0.35 parts per thousand for Delta¹⁷O can be realized using as little as 8.7 nmol CO2 in a similar to 3-h analysis. Based on this system, we have quantified delta¹⁷O in the stratospheric CO2 over Japan.

DOI： 10.1021/ac050266u

Geochemical studies on the microbial activities within the Suiyo seamount hydrothermal plume, Izu-Bonin arc Invited Reviewed

Ishibashi, J., K. Nakamura, K. Okamura, K. Shitashima, T. Toki, U. Tsunogai

Oceanogr. Japan Vol. 14 ( 2 ) page： 251-266 2005.3

Geochemical studies on the microbial activities within the Suiyo seamount hydrothermal plume, Izu-Bonin arc Invited Reviewed

Tsunogai, U., F. Nakagawa, and K. Okamura

Oceanogr. Japan Vol. 14 ( 2 ) page： 279-295 2005.3

A selective unsaturated hydrocarbon subtraction technique for stable carbon isotopic analysis of atmospheric methyl chloride, methyl bromide, and C(2)-C(5) saturated hydrocarbons using continuous-flow isotope ratio mass spectrometry Reviewed

Komatsu, DD, Tsunogai, U, Yamaguchi, J, Nakagawa, F

RAPID COMMUNICATIONS IN MASS SPECTROMETRY Vol. 19 ( 4 ) page： 477-483 2005

Language：English Publishing type：Research paper (scientific journal)

Using continuous-flow isotope ratio mass spectrometry, we have developed a new analytical system which enables us to determine the stable carbon isotopic composition of CH(3)Cl, CH(3)Br, and C(2)-C(5) saturated hydrocarbons in gas samples even if they contain substantial amounts of unsaturated hydrocarbons, using an I(2)O(5) reagent for their selective subtraction. The analytical precision of the delta¹³C determinations is better than 0.5parts per thousand for >300 pmolC injections and better than 5parts per thousand for 20 pmolC injections. Using the system, delta¹³C values for CH(3)Cl and CH(3)Br were found in burning exhaust that contain a substantial quantity of unsaturated hydrocarbons. CH(3)Cl and CH(3)Br measured in exhaust from burning rice plants exhibit highly ¹³C-depleted values of -56.6 +/- 1.3parts per thousand and -48.6 +/- 3.9parts per thousand, respectively, while saturated hydrocarbons exhibit delta¹³C values (-26.4 to -28.9parts per thousand) that are comparable with the total delta¹³C value of the parent material (rice plant; -28.0parts per thousand). Using the system, we can determine the delta¹³C values of methyl halides and hydrocarbons in many kinds of gas samples.

DOI： 10.1002/rcm.1795

Automobile exhaust as a source of C-13- and D-enriched atmospheric methane in urban areas Reviewed

Nakagawa, F, Tsunogai, U, Komatsu, DD, Yamada, K, Yoshida, N , Moriizumi, J, Nagamine, K, Iida, T, Ikebe, Y

ORGANIC GEOCHEMISTRY Vol. 36 ( 5 ) page： 727-738 2005

Language：English Publishing type：Research paper (scientific journal)

The stable carbon and hydrogen isotopic compositions (delta¹³C and delta D, respectively) of methane (CH₄) in automobile exhaust were determined in order to quantify by mass balance the contribution from this source to atmospheric CH₄ in an urban area of Nagoya, Japan. Both delta¹³C and delta D values of CH₄ in automobile exhaust increased in accordance with the model year of the engine, probably as a result of isotope fractionation effects associated with oxidation over metal catalysts in the catalytic converter of modern vehicles. Thus, CH₄ emissions from recent automobiles exhibit conspicuous C-13 and D enrichment compared to the flux from other major anthropogenic sources, such as natural gas leakage, landfills and rice paddies. Using average delta¹³C and delta D CH₄ values estimated for local sources, automobile exhaust in Nagoya, Japan, was determined to contribute significant amounts (up to 30 %) of CH₄ to the troposphere in the study area.

DOI： 10.1016/j.orggeochem.2005.01.003

Characterization of C-1-metabolizing prokaryotic communities in methane seep habitats at the Kuroshima Knoll, southern Ryukyu arc, by analyzing pmoA, mmoX, mxaF, mcrA, and 16S rRNA genes Reviewed

Inagaki, F, Tsunogai, U, Suzuki, M, Kosaka, A, Machiyama, H , Takai, K, Nunoura, T, Nealson, KH, Horikoshi, K

APPLIED AND ENVIRONMENTAL MICROBIOLOGY Vol. 70 ( 12 ) page： 7445-7455 2004.12

Language：English Publishing type：Research paper (scientific journal)

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： 10.1128/AEM.70.12.7445-7455.2004

Detection of low-chloride fluids beneath a cold seep field on the Nankai accretionary wedge off Kumano, south of Japan Reviewed

Toki, T, Tsunogai, U, Gamo, T, Kuramoto, S, Ashi, J

EARTH AND PLANETARY SCIENCE LETTERS Vol. 228 ( 40910 ) page： 37-47 2004.11

Language：English Publishing type：Research paper (scientific journal)

Chemical and isotopic characteristics were determined for interstitial waters extracted from surface sediments in and around dense biological communities on the seafloor of the Nankai accretionary prism off Kumano, south of Japan. We found the following unique features when compared with usual interstitial water samples of normal seafloor in those of samples from bacterial mats on the Oomine Ridge, one of the outer ridge in the Nankai accretionary prism: (1) significant depletion of chloride concentration (maximum 10% depletion from bottom seawater), (2) high concentrations of CH₄ and SigmaCO₂ (more than 660 mumol/kg and 60 mmol/kg, respectively), (3) sulfate depletion (more than 90% depletion compared to bottom seawater), and (4) deltaDH₂O and delta(18)O(H2O) depletion [more than 4parts per thousand and 0.7parts per thousand depletion, respectively, compared to standard mean ocean water (SMOW)]. The highest CH₄ value among these samples was comparable to the highest value so far reported at one of the most active seep areas in the Nankai Trough, suggesting that these sites should also be regarded as one of the most active seep sites in the Nankai Trough. The chemical compositions of the samples taken from the Oomine Ridge strongly suggest that the fluid originates not from normal sediment-seawater interaction at the sediment surface of hemipelagic environments, but from active seepage of fluids that are rich in CH₄ and SigmaCO₂, depleted in Cl- and SO42-, and low in deltaD(H2O) and delta(18)O(H2O) compared to normal seawater. Values for the carbon isotopic composition (delta¹³C(CH₄)) of the dissolved methane in the interstitial fluid [less than -70parts per thousand PeeDee Belemnite (PDB)] and for the C2H6/CH₄ ratio (less than 10(-3)) suggest that the methane originates from microbial production in a relatively shallow layer of sediment, not from the deep sedimentary layer of higher temperature than 60 degreesC at the depthof more than 300 m below the seafloor. The Cl-=0 mmol/kg extrapolated end-member deltaD(H2O) and delta(18)O(H2O) values of low-chloride fluids were -46+7parts per thousand and -6.3+0.7parts per thousand SMOW, respectively, suggesting that land-derived groundwater could be one of the possible sources for the low-Cl- fluids. Depth profiles of chloride concentrations of interstitial fluids show the heterogeneity of end members ad upward sluid velocities suggest active fluid seepage on the Oomine Ridge seems to be a localized phenomenon. Assuming steady-state emission of fluid from the cold seep vent, upward fluid flow velocities from the seeping vent are estimated to be 40-200 cm year(-1), comparable to the previously reported values within the bacterial mats in Nankai Trough accretionary wedge. Development of bacterial mat might favor slower advection, which might allow longer time for diagenetic reactions in the vent conduits, and consequently, carry more reductive compounds in the fluids.

DOI： 10.1016/j.epsl.2004.09.007

Geochemical and microbiological evidence for a hydrogen-based, hyperthermophilic subsurface lithoautotrophic microbial ecosystem (HyperSLiME) beneath an active deep-sea hydrothermal field Reviewed

Takai, K, Gamo, T, Tsunogai, U, Nakayama, N, Hirayama, H, Nealson, KH, Horikoshi, K

EXTREMOPHILES Vol. 8 ( 4 ) page： 269-282 2004.8

Language：English Publishing type：Research paper (scientific journal)

Subsurface microbial communities supported by geologically and abiologically derived hydrogen and carbon dioxide from the Earth's interior are of great interest, not only with regard to the nature of primitive life on Earth, but as potential analogs for extraterrestrial life. Here, for the first time, we present geochemical and microbiological evidence pointing to the existence of hyperthermophilic subsurface lithoautotrophic microbial ecosystem (HyperSLiME) dominated by hyperthermophilic methanogens beneath an active deep-sea hydrothermal field in the Central Indian Ridge. Geochemical and isotopic analyses of gaseous components in the hydrothermal fluids revealed heterogeneity of both concentration and carbon isotopic compositions of methane between the main hydrothermal vent (0.08 mM and -13.8parts per thousand PDB, respectively) and the adjacent divergent vent site (0.2 mM and -18.5parts per thousand PDB, respectively), representing potential subsurface microbial methanogenesis, at least in the divergent vent emitting more C-13-depleted methane. Extremely high abundance of magmatic energy sources such as hydrogen (2.5 mM) in the fluids also encourages a hydrogen-based, lithoautotrophic microbial activity. Both cultivation and cultivation-independent molecular analyses suggested the predominance of Methanococcales members in the superheated hydrothermal emissions and chimney interiors along with the other major microbial components of Thermococcales members. These results imply that a HyperSLiME, consisting of methanogens and fermenters, occurs in this tectonically active subsurface zone, strongly supporting the existence of hydrogen-driven subsurface microbial communities.

DOI： 10.1007/s00792-004-0386-3

Stable isotopic compositions and fractionations of carbon monoxide at coastal and open ocean stations in the Pacific Reviewed

Nakagawa, F, Tsunogai, U, Gamo, T, Yoshida, N

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS Vol. 109 ( C6 ) 2004.6

Language：English Publishing type：Research paper (scientific journal)

Included in this report are the results of the first isotopic studies of seawater-dissolved carbon monoxide ( CO). Large variations in both carbon and oxygen isotopic compositions (delta¹³C: -44.7 similar to -21.1parts per thousand PDB, and delta(18)O: + 8.7 similar to + 32.9parts per thousandSMOW) were observed in seawater-dissolved CO due to the combination of isotopically light CO production in seawater and the enrichment of heavy isotopes during the microbial consumption of CO. Compared with the total delta¹³C value of dissolved organic matter (DOM), the isotopic compositions of the photochemically produced CO in seawater are depleted in C-13 by more than 20parts per thousand, probably due to large fractionation processes during the photochemical production of CO from DOM. In addition, the isotopic fractionation factors resulting from the microbial oxidation of CO in seawater were estimated to be 1.005 +/- 0.002 and 1.006 +/- 0.002 for carbon (alpha(c)) and oxygen (alpha(o)) based on the incubation experiments. By calculating the weighted mean of the isotopic composition of CO according to the CO concentration observed in surface seawater, the mean delta¹³C and delta(18)O for CO emitted from the oceans were estimated to be -40parts per thousand PDB and + 15parts per thousand SMOW, respectively. Oceanic CO is a unique source of C-13 and O-18-depleted CO relative to that of fossil fuel combustion and biomass burning, which will help us create a better isotopic mass balance for both global and local CO budget.

DOI： 10.1029/2001JC001108

Geophysical and geochemical observations on actively seeping hydrocarbon gases on the south-eastern Yellow Sea continental shelf Reviewed

Jeong, KS, Cho, JH, Kim, SR, Hyun, S, Tsunogai, U

GEO-MARINE LETTERS Vol. 24 ( 1 ) page： 53-62 2004.2

Language：English Publishing type：Research paper (scientific journal)

In the southeastern Yellow Sea, active seepage of hydrocarbon gases has been observed by high-resolution (3.5 kHz) seismic profiling both in 1987 and 2001, occurring through a large number of plumes from the topmost pre-Holocene sedimentary layer. It is strong enough to compensate for current speed, extending vertically up to the sea surface. The gas seepage often appears to be explosive to form craters and diapirs, although pockmarks are rare due to the redistribution of mobile palimpsest sands. In core-top seawater and sediments, the gases are characterized by high amounts of C-2, homogenous delta¹³C(1) values and a large difference (19.7parts per thousand on average) between delta¹³C(1) (-55.2 to -53.6parts per thousand PDB) and delta¹³C(2) (-36.8 to -32.5parts per thousand PDB) values. The gases are considered to be generated with a smaller amount of C-1 at the early thermal cracking stage of labile source materials, after which the C-2 gas is enriched in C-13 by diffusion or biological alternation at the generation or accumulation site. The homogenous delta¹³C(1) values may be one of the geochemical characteristics of gases acquired at depth which are less altered in the case of rapid diffusive gas migration to the seafloor.

DOI： 10.1007/s00367-003-0164-8

Stable carbon and oxygen isotopic determination of sub-microgram quantities of CaCO₃ to analyze individual foraminiferal shells Reviewed

Ishimura, T, Tsunogai, U, Gamo, T

RAPID COMMUNICATIONS IN MASS SPECTROMETRY Vol. 18 ( 23 ) page： 2883-2888 2004

Language：English Publishing type：Research paper (scientific journal)

We have developed an analytical system to determine stable isotopic compositions (delta¹³C and delta¹⁸O) of sub-microgram quantities of CaCO₃ for the purpose of analyzing individual foraminiferal shells, using continuous-flow isotope ratio mass spectrometry (CF-IRMS). The system consists of a microvolume CaCO₃ decomposition tube, stainless steel CO₂ purification vacuum line with a quantity-regulating unit, helium-purged CO₂ purification line, gas chromatograph, and a CF-IRMS system. By using this system, we can determine stable carbon and oxygen isotopic compositions as low as 0.2 µg of CaCO₃, with standard deviations of +/-0.10 parts per thousand for delta¹³C and +/-0.18parts per thousand for delta¹⁸O within a 4-h reaction time and 30-min analysis period.

DOI： 10.1002/rcm.1701

Discovery of a new hydrothermal venting site in the southernmost Mariana Arc: Al-rich hydrothermal plumes and white smoker activity associated with biogenic methane Reviewed

Gamo, T, Masuda, H, Yamanaka, T, Okamura, K, Ishibashi, J , Nakayama, E, Obata, H, Shitashima, K, Nishio, Y, Hasumoto, H, Watanabe, M, Mitsuzawa, K, Seama, N, Tsunogai, U, Kouzuma, F, Sano, Y

GEOCHEMICAL JOURNAL Vol. 38 ( 6 ) page： 527-534 2004

Language：English Publishing type：Research paper (scientific journal)

This paper reports a series of studies leading to the discovery of a submarine hydrothermal field (called Nakayama Field) at an arc seamount (12degrees43' N, 143degrees32' E) in the southernmost part of the Mariana Trough, western Pacific Ocean. We first detected hydrothermal plumes characterized by water column anomalies of temperature, light transmission, Mn, Fe, Al, O-2, CH₄, and delta¹³C of CH₄ above the summit caldera of the seamount. Then deep-tow camera surveys confirmed the existence of hydrothermal activity inside the caldera, and an ROV dive finally discovered white smoker-type fluid venting associated with vent fauna. A high concentration of aluminum in the plume and white smoker-type emissions imply acidic hydrothermal activity similar to that observed at the DESMOS Caldera in the eastern Manus Basin, Papua New Guinea. Anomalously low delta¹³C (CH₄) of -38parts per thousand of a vent fluid sample compared to other arc hydrothermal systems along the Izu-Bonin and Mariana Arcs suggests an incorporation of biogenic methane based on a subsurface microbial ecosystem.

An updated estimation of the stable carbon and oxygen isotopic compositions of automobile CO emissions Reviewed

Tsunogai, U, Hachisu, Y, Komatsu, DD, Nakagawa, F, Gamo, T , Akiyama, K

ATMOSPHERIC ENVIRONMENT Vol. 37 ( 35 ) page： 4901-4910 2003.11

Language：English Publishing type：Research paper (scientific journal)

We estimate up-to-date values of the average isotopic compositions of CO emitted from automobiles. In the estimation, we determined the isotopic compositions of CO in tail pipe exhaust for four gasoline automobiles and two diesel automobiles under varying conditions of both idling and running. While the dependence on the automobile manufacturer is little, each automobile equipped with functional catalytic converter exhibits a large temporal delta¹³C and delta(18)O variation. They tend to show C-13 and O-18 enrichment in accordance with the reduction of CO in exhaust, suggesting that the functional catalytic converter in engines enhances the delta¹³C and delta(18)O values of CO from tail pipes through a kinetic isotope effect during CO destruction. Assuming that automobiles run a modeled driving cycle, we estimated the average delta¹³C and delta(18)O of CO to be -23.8 +/- 0.8parts per thousand(PDB) and +25.3 +/- 1.0parts per thousand(SMOW), respectively, for recent gasoline automobiles, and -19.5 +/- 0.7parts per thousand(PDB) and +15.1 +/- 1.0parts per thousand(SMOW), respectively, for recent diesel automobiles. While the delta¹³C and delta(18)O values of recent gasoline automobiles coincide well with the isotopic compositions of source CO in present trunk road atmosphere estimated in this study, those are +4-+6parts per thousand (delta¹³C) and +1-+3parts per thousand (delta(18)O) higher than those reported previously and also those emitted from old, non-catalyst automobiles determined in this study. Recent improvements in functional catalytic converters have enhanced and will enhance the delta¹³C and delta(18)O values of CO from automobiles.

DOI： 10.1016/j.atmosenv.2003.08.008

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