Country：Japan

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Geochemical Society of Japan  

<p>To clarify the sources and fate of CH₄ enriched in coastal seawaters, we determined the distribution of both the concentrations and dual stable isotope compositions (δ¹³C and δ²H) of dissolved CH₄ in the bays of Ise and Mikawa in Japan during five sampling campaigns from 2013 to 2020, together with those in the major inflows of the Kiso, Nagara, and Yahagi Rivers. Excess CH₄ were found in the surface layer of Ise Bay, and their δ¹³C and δ²H values were close to those of CH₄ enriched in the major inflows, but deviated from those of CH₄ in the sedimentary layer at the bottom of Ise Bay. The oxidation rates of CH₄ in the water columns were negligibly small during the incubation experiments. In conclusion, the excess CH₄ in the surface layer of Ise Bay was derived from the inflows. The CH₄ enrichment in the freshwater sediments of the inflows showing up to four orders of magnitude higher CH₄ concentrations than those in the sediments of Ise Bay supported this conclusion. Similar results were obtained in Mikawa Bay. The total emission flux of CH₄ from the estuary area of Ise Bay was larger than the influx of CH₄ into Ise Bay via the inflows, suggesting that the CH₄ dissolved in the inflows was emitted into the atmosphere immediately after inflowing into the bay water.</p>

DOI： 10.2343/geochemj.GJ23005

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CiNii Research

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jvolgeores.2022.107667

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

DOI： 10.1029/2022GC010452

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：COPERNICUS GESELLSCHAFT MBH  

To clarify the source of nitrate increased during storm events in a temperate forested stream, we monitored temporal variation in the concentrations and stable isotopic compositions including Delta O-17 of stream nitrate in a forested catchment (KJ catchment, Japan) during three storm events: I, II, and III (summer). The stream showed a significant increase in nitrate concentration, from 24.7 to 122.6 mu M, from 28.7 to 134.1 mu M, and from 46.6 to 114.5 mu M, during the storm events I, II, and III, respectively. On the other hand, the isotopic compositions (delta N-15, delta O-18, and Delta O-17) of stream nitrate showed a decrease in accordance with the increase in the stream nitrate concentration, from +2.5 parts per thousand to -0.1 parts per thousand, from +3.0 parts per thousand to -0.5 parts per thousand, and from +3.5 parts per thousand to -0.1 parts per thousand, for delta N-15; from +3.1 parts per thousand to 3.4 parts per thousand, from +2.9 parts per thousand to -2.5 parts per thousand, and from +2.1 parts per thousand to -2.3 parts per thousand for delta O-18; and from +1.6 parts per thousand to +0.3 parts per thousand, from +1.4 parts per thousand to +0.3 parts per thousand, and from +1.2 parts per thousand to +0.5 parts per thousand, for delta O-17 during the storm events I, II, and III, respectively. Besides, we found strong linear relationships between the isotopic compositions of stream nitrate and the reciprocal of stream nitrate concentrations during each storm event, implying that the temporal variation in the stream nitrate can be explained by simple mixing between two distinctive endmembers of nitrate having different isotopic compositions. Furthermore, we found that both concentrations and the isotopic compositions of soil nitrate obtained in the riparian zone of the stream were plotted on the nitrate-enriched extension of the linear relationship. We concluded that the soil nitrate in the riparian zone was primarily responsible for the increase in stream nitrate during the storm events. In addition, we found that the concentration of unprocessed atmospheric nitrate in the stream was stable at 1.6 +/- 0.4, 1.8 +/- 0.4, and 2.1 +/- 0.4 mu M during the storm events I, II, and III, respectively, irrespective of the significant variations in the total nitrate concentration. We concluded that the storm events have fews impacts on the concentration of unprocessed atmospheric nitrate in the stream, and thus the annual export flux of unprocessed atmospheric nitrate relative to the annual deposition flux can be a robust index to evaluate nitrogen saturation in forested catchments, irrespective to the variation in the number of storm events and/or the variation in the elapsed time from storm events to sampling.

DOI： 10.5194/bg-19-3247-2022

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

Both chemical and isotopic compositions of concentrated volcanic plumes are highly useful in evaluating the present status of active volcanoes. Monitoring their temporal changes is useful for forecasting volcanic eruptions as well. Recently, we developed a drone-borne automatic volcanic plume sampler, called SelPS, wherein an output signal from a sulfur dioxide (SO₂) sensor triggered a pump to collect plume samples when the SO₂ concentration exceeded a predefined threshold. In this study, we added a radio transmission function to the sampler, which enabled our operator to monitor real-time SO₂ concentration during flights and thus obtain more concentrated volcanic plume samples through precise adjustment of the hovering position. We attached the improved SelPS to a drone at Nakadake crater, Aso volcano (Japan), and successfully obtained volcanic plume samples ejected from the crater more concentrated than those obtained by using previous version of SelPS in 2019. Additionally, we found a significant linear correlation between the reciprocal of the concentration and isotopic ratios for the ²H/¹H ratios of H₂, ¹⁸O/¹⁶O ratios of CO₂, and ¹³C/¹²C ratios of CO₂ within the plume samples. Based on the isotopic ratios of fumarolic H₂ (δ²H = −239 ± 6‰) and fumarolic CO₂ (δ¹³C = −3.58 ± 0.85‰ and δ¹⁸O = +22.01 ± 0.68‰) determined from the linear correlations, we estimated the apparent equilibrium temperatures (AETs) with magmatic H₂O simultaneously and precisely for the first time in erupting volcanoes, assuming hydrogen isotope exchange equilibrium between H₂ and H₂O (AET_D = 629 ± 32°C) and oxygen isotope exchange equilibrium between CO₂ and H₂O (AET_18O = 266 ± 65°C). We found that the AET_18O was significantly lower than the AET_D in the crater. While the temperature of the magmatic gases was originally 600°C or more, most of the gases cooled just beneath the crater to temperatures around the boiling point of water. The improved SelPS enable us to determine both AET_D and AET_18O in eruptive volcanoes, wherein fumaroles are inaccessible. Simultaneous and precise determination of both the AET_18O and AET_D can provide novel information on each volcano, such as the physicochemical conditions of magma degassing and the development of fluid circulation systems beneath each volcano.

DOI： 10.3389/feart.2022.833733

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Informa {UK} Limited  

Excess inputs of reactive nitrogen (Nr) from the atmosphere will cause disturbances to forest ecosystems, including soil and stream water acidification, plant nutrient imbalances, alterations of species compositions (such as biodiversity losses), and nitrogen (N) leaching into stream water. Central Japan (or Chubu region) has experienced both domestic and transboundary air pollution since the 1950s. Emissions of nitrogen oxides in China peaked in 2011/2012, although the peak of ammonia emissions has not been confirmed. Changes in these emissions have been reflected gradually in atmospheric N deposition rates and the biogeochemical cycle in ecosystems in central Japan. We synthetically analyzed the current N saturation situation for forest ecosystems in central Japan based on our recent publications and the latest available dataset. The stream water in the Lake Ijira catchment (IJR) on the Pacific side in Gifu Prefecture became acidified and N-saturated in the mid-1990s but has begun to recover with a decrease in nitrate (NO3–) concentration since the mid-2000s. The progress and recovery of N saturation appeared to be related to the trends of atmospheric deposition, climatic anomalies (such as the cool and drought summers in 1993/1994), and forest management. The NO3– concentrations in stream water within the forest catchment of Kajikawa (KJK) on the Sea of Japan side in Niigata Prefecture have continued to increase, although the catchment seems to be recovering from acidification owing to a decline in atmospheric sulfur (and probably N) deposition. Finally, the NO3– concentration in stream water in KJK became higher than that in IJR, a direct inversion of the situation in the early 2000s. The recent analysis of 17O excess in NO3– estimated that the export of biologically unprocessed atmospheric NO3– via stream water was larger in KJK than in IJR. The N cycle in soil-plant systems likely does not function as expected under excess atmospheric N input (still over 10 kg ha–1 year–1), especially in KJK. In addition to atmospheric N deposition, reduced N uptake rates as coniferous forests mature, and changing precipitation amounts/patterns appear to accelerate N leaching from forest catchments in central Japan.

DOI： 10.1080/00380768.2021.1991228

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Geochemical Society of Japan  

Recent studies have reported slight but definite differences in Δ′¹⁷O between the lithosphere and hydrosphere. In the present study, we precisely and accurately quantify the Δ′¹⁷O values of geothermal H₂O and mid-ocean ridge basalt (MORB) with normalization on the VSMOW-SLAP scale to further substantiate these differences and to discuss the isotopic evolution of the hydrosphere throughout the geologic time scale. With a Δ′¹⁷O value of -60 ± 13 × 10^-6, the Δ′¹⁷O value of MORB is comparable with that in other silicates reported in previous studies. However, the Δ′¹⁷O value of geothermal H₂O tended to decrease from +31 × 10^-6 to -51 × 10^-6, which are the usual Δ′¹⁷O values in meteoric water and silicates, respectively, in accordance with the ¹⁸OO-enrichment. These results imply an active oxygen isotope exchange between silicates and geothermal H₂O under high-temperature conditions at depth. This is supported by previous studies which report the ¹⁷O-enrichment of silicate altered by hydrothermal H₂O. Considering this direct evidence for depletion of ¹⁷O, we conclude that the ¹⁷O-depleted H₂O has been supplied continuously to the hydrosphere. Additionally, low-temperature interaction between the silicates and H₂O besides high-temperature hydrothermal interaction must be assumed to explain the observed Δ′¹⁷O of the terrestrial hydrosphere. We conclude that the Δ′¹⁷O of the terrestrial hydrosphere should have been variable throughout the geologic time scale owing to the various oxygen exchange interaction between the lithosphere and hydrosphere.

DOI： 10.2343/geochemj.2.0644

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

Rationale: The triple oxygen isotopic composition (Δ17O) of tropospheric ozone (O3) is a useful tracer for identifying the source and is essential for clarifying the atmospheric chemistry of oxidants. However, the single nitrite-coated filter method is inaccurate owing to the nitrate blank produced through the reaction of nitrite and oxygen compounds other than O3. Methods: A multistep nitrite-coated filter-pack system is newly adopted to transfer the O-atoms in terminal positions of O3 to nitrite on each filter to determine the Δ17O of O3 in terminal positions (denoted as Δ17O(O3)term). The NO3− produced by this reaction is chemically converted into N2O, and continuous-flow isotope ratio mass spectrometry (CF-IRMS) is used to determine the oxygen isotopic compositions. Results: The reciprocal of the NO3− quantities on the nitrite-coated filters in each sample showed a strong linear relationship with Δ17O of NO3−. Using the linear relation, we corrected the changes in Δ17O of NO3− on the filters. We verified the accuracy of the new method through the measurement of artificial O3 with known Δ17O(O3)term value that had been determined from the changes in Δ17O of O2. The Δ17O(O3)term of tropospheric O3 was in agreement with previous studies. Conclusions: We accurately determined the δ18O and Δ17O values of tropospheric O3 by blank correction using our new method. Measurements of Δ17O(O3)term of the ambient troposphere showed 1.1 ± 0.7‰ diurnal variations between daytime (higher) and nighttime (lower) due likely to the formation of the temperature inversion layer at night.

DOI： 10.1002/rcm.9124

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jvolgeores.2021.107197

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Geophysical Research: Biogeosciences  

To better understand the factors that control N retention and N export in forested watersheds, it is necessary to understand the relationships among atmospheric nitrogen (N) deposition, internal N cycling within plant-soil systems, and N leaching. The relative contributions of atmospheric nitrate (NO3−atm) and remineralized nitrate produced by microbial nitrification to total nitrate (NO3−) in stream water have been investigated in many studies. However, the dynamics of these two types of NO3− from the forest canopy to the soil are not well understood. Therefore, we determined the changes in the NO3− flux and the 17O excess (Δ17O) of NO3−, a robust tracer of NO3−atm, from bulk deposition to the soil water beneath oak and spruce trees as well as dwarf bamboo-dominated canopy gaps in a natural coniferous-broadleaved mixed forest in northern Japan. The Δ17O values in NO3− dramatically decreased after passing through the forest floor, indicating that the dominant source of NO3− leaching is nitrification in the forest floor. In contrast, a large decrease in NO3−atm flux was observed between bulk deposition and throughfall, especially for oak and spruce, suggesting that the forest canopy is an important sink for deposited NO3−atm. The retention of NO3−atm by the canopy was higher for oak (86.3 ± 10.1%) and spruce (87.7 ± 8.8%) than for Sasa in the canopy gap (49.9 ± 26.6%). Our study demonstrated that the Δ17O value of NO3− is a promising tool for quantifying the atmospheric nitrate dynamics in complex forest N cycling.

DOI： 10.1029/2020JG005876

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>Direct sampling and analysis of fumarolic gas was conducted at Ebinokogen Ioyama volcano, Japan, between December 2015 and July 2020. Notable changes in the chemical composition of gases related to volcanic activity included a sharp increase in SO₂ and H₂ concentrations in May 2017 and March 2018. The analyses in March 2018 immediately preceded the April 2018 eruption at Ioyama volcano. The isotopic ratios of H₂O in fumarolic gas revealed the process of formation. Up to 49% high-enthalpy magmatic vapor mixed with 51% of cold local meteoric water to generate coexisting vapor and liquid phases at 100–160 °C. Portions of the vapor and liquid phases were discharged as fumarolic gases and hot spring water, respectively. The CO₂/SO₂ ratio of the fumarolic gas was higher than that estimated for magmatic vapor due to SO₂ hydrolysis during the formation of the vapor phase. When the flux of the magmatic vapor was high, effects of hydrolysis were small resulting in low CO₂/SO₂ ratios in fumarolic gases. The high apparent equilibrium temperature defined for reactions involving SO₂, H₂S, H₂ and H₂O, together with low CO₂/SO₂ and H₂S /SO₂ ratios were regarded to be precursor signals to the phreatic eruption at Ioyama volcano. The apparent equilibrium temperature increased rapidly in May 2017 and March 2018 suggesting an increased flux of magmatic vapor. Between September 2017 and January 2018, the apparent equilibrium temperature was low suggesting the suppression of magmatic vapor flux. During this period, magmatic eruptions took place at Shinmoedake volcano 5 km away from Ioyama volcano. We conclude that magma sealing and transport to Shinmoedake volcano occurred simultaneously in the magma chamber beneath Ioyama volcano.

DOI： 10.1186/s40623-021-01405-4

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Other Link： http://link.springer.com/article/10.1186/s40623-021-01405-4/fulltext.html

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Georesursy  

The paper presents the results of a complex joint Russian-Vietnamese geological, geophysical and oceanographic expedition in the South-China Sea (R/V “Akademik M.A. Lavrentyev”, cruise 88, 2019), as well as related joint Russian- Vietnamese marine and land researches in the area of north and south Vietnam under a series of local FEB RAS - VAST grants. The organizers of the marine expedition are the V. I. Ilyichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences (POI FEB RAS) and the Institute of Marine Geology and Geophysics of the Vietnam Academy of Science and Technology (IMGG VAST). In comparison with the Sea of Japan and the Sea of Okhotsk, it can be noted that the active bottom degassing on the on the Vietnamese shelf and slope have is a local, although the intensity of gas-geochemical anomalies is comparable to similar zones in the Far Eastern Seas. For the first time, anomalous methane fields (up to 5000 nl/l) were found in the water column of the South- China Sea, which are comparable to anomalies on the oil and gas shelf and the gas-hydrate-bearing slope of Sakhalin Island. Metamorphosed sedimentary and volcanic rocks were discovered for the first time in the southern part of Catba Island (Gulf of Tonkin), which indicates the introduction of an endogenous body into the sedimentary strata and its further transformation. In connection with the discovery in 2020 of the large Ken Bau gas field at the southern end of the sedimentary basin of the Red River, the forecast of POI scientists about the presence of significant hydrocarbon reserves in this area was confirmed. The work was carried out within the framework of the joint Vietnam-Russia Laboratory for Marine Sciences and Technology (V. I. Ilyichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences and the Institute of Marine Geology and Geophysics Vietnam Academy of Science and Technology). The expedition of the R/V “Akademik M.A. Lavrentyev” (cruise 88) is part of a series of expeditions in accordance with the UN Decade dedicated to the Ocean Science for Sustainable Development.

DOI： 10.18599/grs.2021.1.16

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

Volcanic gas compositions are estimated based on volcanic plume measurement with Multi-GAS at a frequently erupting Sakurajima volcano by application of airborne methods and automatic monitoring station on the flank during 2013–2019. The airborne measurements of CO2 and H2O concentrations often suffer from large fluctuation of background likely due to entrainment of the atmosphere derived from different altitude. By removing the background effect, a representative volcanic CO2/SO2 mole ratio is estimated as 0.4 ± 0.1 and we did not observe clear temporal variation. The volcanic H2O/SO2 ratios are estimated as 30–70 with a large uncertainty because of the strong atmospheric perturbation. The SO2/H2S ratios show quite a large variation ranging from 1 to 800. The large SO2/H2S ratios larger than 30 are observed during ash eruption and are suggested as a result of oxidation by atmosphere on hot ashes. The small ratios less than 10 are observed when frequency of explosions is low. Variation of the SO2/H2S ratios of the small values can be caused by variation of degassing pressure, however, the small variation of the CO2/SO2 ratio suggests a limited range of the pressure variation.

DOI： 10.1016/j.jvolgeores.2020.107098

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/lno.11566

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Publishing House for Science and Technology, Vietnam Academy of Science and Technology (Publications)  

Paper presents the results of complex gas-geochemical studies of bottom sediments of the East Siberian Sea along the meridional profile from Cape Billings to the Mendeleev Ridge. Abnormal concentrations of methane (up to 2.4% vol.) and hydrogen (up to 600 ppm) are controlled by neotectonic faults and are typical for the areas of gas hydrate formation. The carbon isotope composition indicates the predominance of the thermogenic component. When studying the chemical composition of sediments, the data helped to identify the permeability zones of neotectonic faults that have favorable conditions for the concentration of a number of elements: Mn, Cu, Ag. Such zones are characterized by the gas anomalies in sediments (methane, hydrogen, etc.). The accumulation of anomalous metal contents is facilitated by specific geological conditions that occur in zones of gas anomalies within tectonically active structures, where fine-grained sediments enriched with organic matter are present. The gas-geochemical fields formed in this pattern can be applied as indicators in forecasting of hydrocarbon accumulations, for mapping permeable fault zones, and for the environmental impact assessing of hydrocarbon anomalies. This approach could be especially effective in the basins with low seismic activity such as seas of East Siberian shelf and some of the marginal seas of Pacific Ocean, for instance, South China Sea (Bien Dong).

DOI： 10.15625/0866-7187/42/4/15492

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

DOI： 10.14862/geochemproc.67.0_132

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

DOI： 10.1016/j.polar.2019.100481

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DOI： 10.1016/j.jvolgeores.2019.07.020

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

DOI： 10.3389/feart.2019.00249

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

DOI： 10.1186/s40623-019-1027-5

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

DOI： 10.5194/bg-15-7025-2018

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

DOI： 10.1007/s00227-018-3398-8

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DOI： 10.1080/16000889.2018.1478594

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DOI： 10.1126/sciadv.aao4631

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

DOI： 10.3390/geosciences8060220

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DOI： 10.5194/acp-18-6381-2018

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DOI： 10.1002/lno.10775

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DOI： 10.1038/ismej.2017.140

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

DOI： 10.1080/10934529.2017.1409026

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

<p>By using the hydrogen isotope exchange equilibrium between molecular hydrogen (H₂) and water vapor, a new method called HIReTS (Hydrogen Isotopes Remote Temperature Sensing) was proposed for remote sensing of fumarole outlet temperatures. In this method, the hydrogen isotopic composition (δD) of fumarolic H₂ is obtained remotely from observation in a volcanic plume, and the outlet temperature is then derived from the obtained δD of fumarolic H₂. The HIReTS method can be used to obtain the fumarolic temperature remotely in active volcanoes when the actual fumaroles are inaccessible. Recent advances in using the ¹⁷O-excess (Δ¹⁷O) of nitrate were summarized as well. Within the possible sources of nitrate in the natural environment, only atmospheric nitrate that is produced from atmospheric NO through photochemical reactions can be characterized by the anomalous enrichment in ¹⁷O, reflecting the transfer of an oxygen atom from ozone. In addition, Δ¹⁷O is stable during partial metabolism—such as denitrification and assimilation, so by using these characteristics of Δ¹⁷O, the author and co-workers were able to trace the fate of atmospheric nitrate deposited onto surface ecosystems. This also allowed the author and co-workers to propose a new method to quantify nitrate dynamics—production rate through nitrification and metabolic rate through assimilation and denitrification—in aquatic environments, using the Δ¹⁷O of nitrate. The Δ¹⁷O method is considered to offer an alternative to the traditional artificial tracer techniques for the determination of nitrate dynamics, including temporal variations.</p>

DOI： 10.14934/chikyukagaku.52.107

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

CiNii Research

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

CiNii Research

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

DOI： 10.1038/ismej.2017.140

Authorship：Lead author   Language：Japanese  

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

DOI： 10.1016/j.jvolgeores.2016.11.018

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DOI： 10.1016/j.apgeochem.2016.11.001

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Agency for Marine-Earth Science and Technology  

<p>We describe in detail the pore water chemistry in the sediments below a white mat around a bunch of bananas at a water depth of 2,200 m in the Tenryu Submarine Canyon. We infer the metabolism of microbes in the sediments around the bananas based on the chemical and isotopic compositions of the pore water. On the basis of the relation between ammonia and total carbonate (ΣCO₂) concentrations in the pore water, we identified that an excess ΣCO₂ was distributed around the bananas that cannot be explained by the decomposition of organic matter derived from marine organisms, indicating that the bananas decomposed to generate the excess ΣCO₂. We conclude that the bananas built a local organic-rich environment, stimulating the activity of organotrophic bacteria.</p>

DOI： 10.5918/jamstecr.25.1

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

DOI： 10.1016/j.chemgeo.2016.11.004

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

DOI： 10.2343/geochemj.2.0449

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DOI： 10.1007/s12542-016-0326-4

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2016GL070838

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

DOI： 10.1002/2016PA002947

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DOI： 10.1016/j.jvolgeores.2016.06.013

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DOI： 10.1038/srep34126

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DOI： 10.1002/2015PA002880

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/bg-2015-627

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

DOI： 10.1111/1758-2229.12379

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

In this paper, recent advances in using stable isotopes of atmospheric nitrate to trace the origin and fate are reviewed. While nitrogen isotopes have been used as the indicators of NOx source contributions to the atmospheric nitrate, cautions must be taken for the isotopic fractionations during the photochemical reactions of NOX in atmosphere. On the other hand, the triple oxygen isotope composition (Δ17O) is a robust tracer for the photochemical reaction path of NOX in atmosphere. Besides, the triple oxygen isotope composition can be applied to trace the fate of atmospheric nitrate and to evaluate biological processing of nitrate within the earth surface ecosystems.

DOI： 10.11203/jar.31.5

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

DOI： 10.1016/j.marchem.2015.04.005

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DOI： 10.1016/j.dsr2.2015.06.003

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DOI： 10.1016/j.dsr2.2015.06.004

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DOI： 10.1007/s00338-014-1235-1

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DOI： 10.1371/journal.pone.0113063

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DOI： 10.1007/978-4-431-54865-2_45

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

DOI： 10.1007/978-4-431-54865-2_40

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

DOI： 10.1186/s40623-014-0137-3

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/bg-11-5411-2014

Authorship：Lead author   Language：Japanese  

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

DOI： 10.1016/j.biortech.2014.04.071

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

DOI： 10.1016/j.tecto.2014.01.035

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DOI： 10.5047/w-pass.a02.001

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DOI： 10.1016/j.jvolgeores.2013.11.017

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

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

DOI： 10.1111/1574-6941.12179

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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

Although much attention has been paid to describing the distribution of oceanic dimethyl sulfide (DMS) concentrations, establishing robust relationships between DMS concentrations and biological, physical, and chemical variables is still challenging. Previous studies have proposed semiempirical parameterizations by combining multiple physical and biogeochemical parameters to better understand and reproduce the global distribution of sea surface DMS. However, none of these parameterization schemes could reconcile regionally elevated DMS peaks found in high-resolution DMS measurements made in the western subarctic Pacific. Here we found that DMS concentrations are highly correlated with the net community production, a parameter that integrates biological activity over time. We anticipate that this elationship may be exportable to other regions with high primary productivity, such as the Southern Ocean or upwelling regions, and can be used as an important parameterization scheme, combined with solar radiation dose relationship.

DOI： 10.1002/grl.50654

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

DOI： 10.1016/j.chemgeo.2013.05.024

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

DOI： 10.5194/bg-10-3547-2013

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DOI： 10.1016/j.jvolgeores.2013.04.007

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DOI： 10.3354/meps10202

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DOI： 10.1007/s00248-013-0184-5

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DOI： 10.1007/s13280-012-0343-9

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

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

We report here the discovery of two methane-enriched plumes in a water column above the Kumano Knoll 5 submarine mud volcano (KK-5) in Nankai Trough during 2004; a slight methane enrichment was observed in this region in 2000 and 2010. The deeper of the two plumes spread horizontally at depths near the top of KK-5, whereas a shallow plume spread at a height of 300 m from the top of KK-5. The end-member d¹³C values of methane in both plumes, -46.1+-4.8 per mil and -51.4+-5.8 per mil in the deep and shallow plumes, respectively, and methane extracted from sediment in KK#5 (-52+-2 per mil) are statistically indistinguishable. We conclude that the plumes were created by massive release of methane from KK#5 and that this event probably occurred in response to the large earthquakes (Mw 7.5) that occurred shortly before our observation in 2004. The discharge rates from submarine mud volcanoes (SMVs) in subduction zones may be highly variable in response to major earthquakes.

DOI： 10.1016/j.epsl.2012.06.004

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

DOI： 10.1016/j.orggeochem.2012.04.004

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

DOI： 10.3389/fmicb.2012.00089

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

The impacts of the M9.0 Tohoku Earthquake on deep-sea environment were investigated 36 and 98 days after the event. The light transmission anomaly in the deep-sea water after 36 days became atypically greater (similar to 35 %) and more extensive (thickness similar to 1500 m) near the trench axis owing to the turbulent diffusion of fresh seafloor sediment, coordinated with potential seafloor displacement. In addition to the chemical influx associated with sediment diffusion, an influx of C-13-enriched methane from the deep sub-seafloor reservoirs was estimated. This isotopically unusual methane influx was possibly triggered by the earthquake and its aftershocks that subsequently induced changes in the sub-seafloor hydrogeologic structures. The whole prokaryotic biomass and the development of specific phylotypes in the deep-sea microbial communities could rise and fall at 36 and 98 days, respectively, after the event. We may capture the snap shots of post-earthquake disturbance in deep-sea chemistry and microbial community responses.

DOI： 10.1038/srep00270

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

We measured dissolved methane (CH₄) and its carbon isotope ratio (C-13/C-12 or delta C-13) from surface to bottom seawaters (maximum depth: 3574 m) for the first time in three major offshore areas of the Japan Sea (East Sea): the eastern Japan Basin, Yamato Basin, and Ulleung Basin. Seawater samples were taken during the KT-07-24 cruise of the R/V Tansei Maru in 2007 as part of a Japan-Korea collaborative study. The CH₄ concentration and its delta C-13(PDB) were obtained by continuous flow isotope ratio mass spectrometry. While the CH₄ concentrations of surface seawater were 2.6-3.8 nmol kg(-1), which was 43( +/- 22) % supersaturated compared to the atmospheric equilibrium values, those in the subsurface (D=30-150 m) showed much higher values up to 9.7 nmol kg(-1) (similar to 300 % supersaturation). This subsurface CH₄ had the minimum delta C-13 value of -54.3 parts per thousand (less than the atmospheric CH₄ value of -47 parts per thousand), implying a contribution from in situ microbial CH₄ production in some anoxic microenvironments. The CH₄ concentration decreased with depth toward minimum values of similar to 1 nmol kg(-1) (delta C-13, -30 to -40 parts per thousand.) at 1500-2000 m depth. Below a depth of 2000 m, we found a clear difference in CH₄ profiles among the three basins; in the eastern Japan Basin the CH₄ concentration remained almost constant down to the seafloor, while it gradually increased with depth up to > 2.0 nmol kg(-1) in the Yamato and Ulleung basins. This CH₄ increase toward the bottom was accompanied by a decrease of delta C-13-CH₄ to less than -50 parts per thousand, suggesting a microbial CH₄ supply from bottom sediment in the Yamato and Ulleung basins. We observed a local CH₄ plume over a deep channel east of the Yamato Basin, indicating unknown submarine CH₄ seepage with a microbial delta C-13 value of about -60 parts per thousand.

DOI： 10.1016/j.marchem.2011.10.006

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

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

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

DOI： 10.5194/bg-9-4353-2012

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

We have developed a new automated analytical system that employs a continuous flow isotope ratio mass spectrometer to determine the stable hydrogen isotopic composition (delta D) of nanomolar quantities of molecular hydrogen (H₂) in an air sample. This method improves previous methods to attain simpler and lower-cost analyses, especially by avoiding the use of expensive or special devices, such as a Toepler pump, a cryogenic refrigerator, and a special evacuation system to keep the temperature of a coolant under reduced pressure. Instead, the system allows H₂ purification from the air matrix via automatic multi-step gas chromatographic separation using the coolants of both liquid nitrogen (77 K) and liquid nitrogen + ethanol (158 K) under 1 atm pressure. The analytical precision of the delta D determination using the developed method was better than 4 parts per thousand for >5 nmol injections (250 mL STP for 500 ppbv air sample) and better than 15 parts per thousand for 1 nmol injections, regardless of the delta D value, within 1 h for one sample analysis. Using the developed system, the delta D values of H₂ can be quantified for atmospheric samples as well as samples of representative sources and sinks including those containing small quantities of H₂, such as H₂ in soil pores or aqueous environments, for which there is currently little delta D data available. As an example of such trace H₂ analyses, we report here the isotope fractionations during H₂ uptake by soils in a static chamber. The delta D values of H₂ in these H₂-depleted environments can be useful in constraining the budgets of atmospheric H₂ by applying an isotope mass balance model.

DOI： 10.1002/rcm.5231

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

Understanding tropical nutrient dynamics is essential for quantifying marine productivity. In tropical and subtropical oceans, however, the spatial and continuous observation of nutrients has been scarce because of low nutrient concentration. The nitrogen isotopes of organic nitrogen in coral skeletons (delta¹⁵Ncoral) could be used to record nitrogenous nutrient origins at oceanic surfaces. Here, we show the intra- and inter-reef variations of delta¹⁵Ncoral in the western Pacific. The zonal distribution of delta¹⁵Ncoral was found inside a coral reef corresponding with delta¹⁵N of seawater nitrate (δ¹⁵N(nitrate)). The extended analysis of delta¹⁵Ncoral among various coral reefs also shows a latitudinal gradient from tropical to temperate in the western Pacific. The delta¹⁵Ncoral records high-resolution dynamics of nitrogenous nutrients through the geologic time scale.

DOI： 10.1029/2011GL049053

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

In high-temperature volcanic fumaroles (>400 degrees C), the isotopic composition of molecular hydrogen (H₂) reaches equilibrium with that of the fumarolic H₂O. In this study, we used this hydrogen isotope exchange equilibrium of fumarolic H₂ as a tracer for the remote temperature at volcanic fumaroles. In this remote sensing, we deduced the hydrogen isotopic composition (delta D value) of fumarolic H₂ from those in the volcanic plume. To ascertain that we can estimate the delta D value of fumarolic H₂ from those in a volcanic plume, we estimated the values in three fumaroles with outlet temperatures of 630 degrees C (Tarumae), 203 degrees C (Kuju), and 107 degrees C (E-san). For this we measured the concentration and delta D value of H₂ in each volcanic plume, along with those determined directly at each fumarole. The average and maximum mixing ratios of fumarolic H₂ within a plume's total H₂ were 97 % and 99 % (at Tarumae), 89 % and 96 % (at Kuju), and 97 % and 99 % (at E-san). We found a linear relationship between the depletion in the delta D values of H₂, with the reciprocal of H₂ concentration. Furthermore, the estimated end-member delta D value for each H₂-enriched component (260 +/- 30 parts per thousand vs. VSMOW in Tarumae, 509 +/- 23 parts per thousand in Kuju, and 437 +/- 14 parts per thousand in E-san) coincided well with those observed at each fumarole (-247.0 +/- 0.6 parts per thousand in Tarumae, -527.7 +/- 10.1 parts per thousand in Kuju, and -432.1 +/- 2.5 parts per thousand in E-san). Moreover, the calculated isotopic temperatures at the fumaroles agreed to within 20 degrees C with the observed outlet temperature at Tarumae and Kuju. We deduced that the dD value of the fumarolic H2 was quenched within the volcanic plume. This enabled us to remotely estimate these in the fumarole, and thus the outlet temperature of fumaroles, at least for those having the outlet temperatures more than 400 degrees C. By applying this methodology to the volcanic plume emitted from the Crater 1 of Mt. Naka-dake (the volcano Aso) where direct measurement on fumaroles was impractical, we estimated that the dD value of the fumarolic H2 to be -172 +/- 16 parts per thousand and the outlet temperature to be 868 +/- 97 degrees C. The remote temperature sensing using hydrogen isotopes developed in this study is widely applicable to many volcanic systems.

DOI： 10.1016/j.gca.2011.05.023

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

A comprehensive study was performed to characterize, for the first time, the mud, water, and gases released from onshore mud volcanoes located in the southern margin of the Junggar Basin, northwestern China. Chemical compositions of mud, along with the geology of the basin, suggest that a source of the mud is Mesozoic or Cenozoic shale. Oxygen and H isotope compositions of the released water suggest a local meteoric origin. Combined with the positive Eu anomalies of the water, a large (18)O shift of the water suggests extensive interaction with rocks. Gases discharged from the mud volcanoes are predominantly thermogenic hydrocarbons, and the high delta¹³C values (>+20 parts per thousand VPDB) for CO₂ gases and dissolved carbonate in muddy water suggest secondary methanogenesis with CO₂ reduction after oil biodegradation. The enrichments of Eu and (18)O in water and the low thermal gradient of the area suggest that the water-rock interactions possibly occur deeper than 3670 +/- 200 m. On the other hand, considering the relationship to the petroleum reservoir around the mud volcanoes, the depth of the gases can be derived from about 3600 m, a depth that is greater than that generally estimated for reservoirs whose gas is characterized by ¹³C-enriched CO₂. Oil biodegradation with CO₂ reduction likely occurs at a shallower depth along the seepage system of the mud volcano. The results contribute to the worldwide data set of gas genesis in mud volcanoes. Moreover, they further support the concept that most terrestrial mud volcanoes release thermogenic gas produced in very deep sediments and may be early indicators of oil biodegradation, an important problem in the petroleum industry.

DOI： 10.1016/j.apgeochem.2011.03.011

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

We analyse the fluid flow regime within sediments on the Eastern levee of the modern Mississippi Canyon using 3D seismic data and downhole logging data acquired at Sites U1322 and U1324 during the 2005 Integrated Ocean Drilling Program (IODP) Expedition 308 in the Gulf of Mexico. Sulphate and methane concentrations in pore water show that sulphate-methane transition zone, at 74 and 94 m below seafloor, are amongst the deepest ever found in a sedimentary basin. This is in part due to a basinward fluid flow in a buried turbiditic channel (Blue Unit, 1000 mbsf), which separates sedimentary compartments located below and above this unit, preventing normal upward methane flux to the seafloor. Overpressure in the lower compartment leads to episodic and focused fluid migration through deep conduits that bypass the upper compartment, forming mud volcanoes at the seabed. This may also favour seawater circulation and we interpret the deep sulphate-methane transition zones as a result of high downward sulphate fluxes coming from seawater that are about 5-10 times above those measured in other basins. The results show that geochemical reactions within shallow sediments are dominated by seawater downwelling in the Mars-Ursa basin, compared to other basins in which the upward fluid flux is controlling methane-related reactions. This has implications for the occurrence of gas hydrates in the subsurface and is evidence of the active connection between buried sediments and the water column.

DOI： 10.1111/j.1468-8123.2010.00304.x

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

The atmospheric mixing ratios of ethane and its stable carbon isotope ratios (delta¹³C) were measured over the North Pacific (2 degrees N to 38 degrees N, 140 degrees E to 90 degrees W) during oceanographic cruises in summer and autumn. The measured mixing ratios were relatively low (mostly < 1 ppbv) over the North Pacific, whereas elevated ethane levels (> 1 ppbv) were observed over the western North Pacific near Japan, with lower delta¹³C values (approximately -25 parts per thousand), suggesting recent emissions from neighboring source regions. The most ¹³C-enriched values of ethane (approximately -16 parts per thousand) were observed over the western equatorial Pacific rather than the central and eastern equatorial Pacific. This is likely caused by the kinetic isotope effect (KIE) for the removal of ethane during the atmospheric transport from potential upwind source regions to the most remote region under the prevailing trade easterly winds. The measurements were compared with the results of a global chemical transport model including two ethane isotopologues ((12)C(2)H(6) and ¹³C(2)H(6)). The model-estimated delta¹³C values were too high compared with the observations. It is likely that this discrepancy is partly due to an approximately 40 % overestimation of the reported KIE for the reaction between ethane and OH radicals.

DOI： 10.1029/2010JD014602

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

Emission of trace gases from the marine diatom Thalassiosira pseudonana (CCMP 1335) was continuously monitored with a proton transfer reaction-mass spectrometry (PTR-MS) in an axenic batch culture system under a 13:11-h light:dark cycle. Substantial increases in the signals at m/z 49, 63, and 69, attributable to methanethiol, dimethyl sulfide (DMS), and isoprene, respectively, were observed in response to increases in cell density. Signals at m/z 69 showed diurnal variations throughout the experiment whereas those at m/z 49 were more pronounced at the beginning of the incubation. Interestingly, the signals at m/z 49 and 69 changed immediately following the light-dark and dark-light transitions, suggesting that light plays a crucial role in the production of methanethiol and isoprene. However, in the latter half of the experiment, methanethiol showed negligible diurnal variations regardless of light conditions, suggesting the production of methanethiol from enzymatic cleavage of DMS. The trend ill signals at m/z 63 was similar to that of the abundance of senescent cells plus cell debris rather than vegetative cells. The results suggest that aging or death of phytoplankton cells could also substantially control DMS production in natural waters along with the other microbial processes related to bacteria and zooplankton.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The stable isotopic compositions of nitrate, including the ¹⁷O anomalies (Delta¹⁷O), were determined twice in 1 yr (June and August 2007) in the oligotrophic water column of Lake Mashu, Japan. These data were then used to quantify the geochemical dynamics of nitrate in the lake, by using the deposition rate of the atmospheric nitrate onto the entire catchment area of the lake. The total amount of nitrate in the lake water decreased from 4.2 to 2.1 Mmol during the period between the observations, while the average Delta¹⁷O values remained uniform at + 2.5 parts per thousand. The Delta¹⁷O values corresponded to an small and uniform mixing ratio of atmospheric nitrate to total nitrate of 9.7 +/- 0.8 %. These results indicate that 0.52 +/- 0.34 Mmol of the remineralized nitrate was fed into the water column through nitrification, while 2.6 +/- 0.4 Mmol of nitrate was simultaneously removed from the water column by assimilation, during the period between the observations. The lake water dissolved nitrate was characterized by rapid removal through assimilation during summer until it was almost completely removed from the euphotic layer, as well as continuous feeding into the lake through nitrification (3.2 +/- 0.3 Mmol a(-1)) and deposition (0.35 +/- 0.2 Mmol a(-1)), regardless of the seasons. The ¹⁵N-depleted nitrogen isotopic compositions of nitrate were as low as -6.5 parts per thousand in June, which also indicates that in-lake nitrification is the major source of nitrate in the lake and suggests that there is low potential for denitrification in and around the lake. Atmospheric nitrate deposited into the lake will be assimilated quickly, having a mean residence time of 1.2 +/- 0.1 yr. In addition, more than 90 % of the assimilated nitrate will be remineralized to nitrate and re-assimilated via active nitrogen cycling in the lake.

DOI： 10.5194/bg-8-687-2011

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

The galatheid crab, Shinkaia crosnieri (Decapoda: Galatheidae), forms dense colonies in the Iheya North and Hatoma Knoll deep-sea hydrothermal fields and has numerous setae covered with filamentous epibiotic microorganisms. Molecular phylogenetic analyses revealed that the epibiotic communities in S. crosnieri consisted mainly of yet-uncultivated phylotypes within Epsilonproteobacteria and Gammaproteobacteria in both hydrothermal vent fields. Uptake experiments using ¹³C-labeled tracers clearly demonstrated that both H¹³CO(3)(-) and ¹³CH₄ were assimilated into not only the epibiotic microbial communities associated with the setae, but also the epibiont-free tissue of living S. crosnieri. In addition, the incorporation of H¹³CO(3)(-) into the microbial cells was strongly stimulated by the presence of reduced sulfur compounds but not by H₂. In conclusion, the uptake experiments suggested that sulfur-oxidizing chemolithoautotrophic and methanotrophic production by the epibionts provides the nutrition for S. crosnieri.

DOI： 10.1264/jsme2.ME10135

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

We developed an equilibrator inlet-proton transfer reaction-mass spectrometry (EI-PTR-MS) system for high-resolution measurement of the concentrations of multiple volatile organic compounds (VOCs) dissolved in seawater. The equilibration of five VOCs (isoprene, propene, acetone, acetaldehyde, and methanol) between seawater samples and the carrier gas, and the response time of the system, were evaluated by means of a series of laboratory experiments. Although equilibrium between the seawater sample and the carrier gas in the equilibrator was not achieved for isoprene and propene (likely because of their low water solubility), the other species did reach equilibrium. The EI-PTR-MS system was deployed during a research cruise in the western North Pacific Ocean. Evaluation of several seawater sampling methods indicated that there was no significant contamination from the sampling apparatus for the target VOCs. For isoprene, comparison of EI-PTR-MS measurements with measurements obtained with a membrane equilibrator-gas chromatography/mass spectrometry system showed generally good agreement (R(2)=0.79). EI-PTR-MS captured the temporal variations of dissolved VOCs, including small-scale variability, which demonstrates that the performance of the EI-PTR-MS system was sufficient for simultaneous and continuous measurements of multiple VOCs of environmental importance in seawater.

DOI： 10.1016/j.marchem.2010.08.003

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

Although deep subterranean crystalline rocks are known to harbor microbial ecosystems, geochemical factors that constrain the biomass, diversity, and metabolic activities of microorganisms remain to be clearly defined. To better understand the geochemical and microbiological relationships, we characterized granitic groundwater collected from a 1,148- to 1,169-m-deep borehole interval at the Mizunami Underground Research Laboratory site, Japan, in 2005 and 2008. Geochemical analyses of the groundwater samples indicated that major electron acceptors, such as NO (3) (-) and SO (4) (2-) , were not abundant, while dissolved organic carbon (not including organic acids), CH₄ and H₂, was moderately rich in the groundwater sample collected in 2008. The total number of acridine orange-stained cells in groundwater samples collected in 2005 and 2008 were 1.1 x 10(4) and 5.2 x 10(4) cells/mL, respectively. In 2005 and 2008, the most common phylotypes determined by 16S rRNA gene sequence analysis were both related to Thauera spp., the cultivated members of which can utilize minor electron donors, such as aromatic and aliphatic hydrocarbons. After a 3-5-week incubation period with potential electron donors (organic acids or CH₄ + H₂) and with/without electron acceptors (O(2) or NO (3) (-) ), dominant microbial populations shifted to Brevundimonas spp. These geomicrobiological results suggest that deep granitic groundwater has been stably colonized by Thauera spp. probably owing to the limitation of O(2), NO (3) (-) , and organic acids.

DOI： 10.1007/s00248-010-9683-9

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

We have developed a rapid, sensitive, and automated analytical system to simultaneously determine the concentrations and stable isotopic compositions (delta¹⁵N, delta(18)O, and delta¹³C) of nanomolar quantities of nitrous oxide (N(2)O) and methane (CH₄) in water, by combining continuous-flow isotope-ratio mass spectrometry and a helium-sparging system to extract and purify the dissolved gases. Our system, which is composed of cold traps and a capillary gas chromatograph that use ultra-pure helium as the carrier gas, achieves complete extraction of N(2)O and CH₄ in a water sample and separation among N(2)O, CH₄, and the other component gases. The flow path following exit from the gas chromatograph was periodically changed to pass the gases through the combustion furnace to convert CH₄ and the other hydrocarbons into CO₂, or to bypass the combustion furnace for the direct introduction of eluted N(2)O into the mass spectrometer, for determining the stable isotopic compositions through monitoring the ions of m/z 44, 45, and 46 of CO₂(+) and N(2)O(+). The analytical system can be operated automatically with sequential software programmed on a personal computer. Analytical precisions better than 0.2 parts per thousand and 0.3 parts per thousand and better than 1.4 parts per thousand and 2.6 parts per thousand were obtained for the delta¹⁵N and delta(18)0 of N(2)O, respectively, when more than 6.7 nmol and 0.2 nmol of N(2)O, respectively, were injected. Simultaneously, analytical precisions better than 0.07 %, and 2.1 parts per thousand were obtained for the delta¹³C of CH₄ when more than 5.5 nmol and 0.02 nmol of CH₄, respectively, were injected. In this manner, we can simultaneously determine stable isotopic compositions of a 120 mL water sample with concentrations as low as 1.7 nmol/kg for N(2)O and 0.2 nmol/kg for CH₄.

DOI： 10.1002/rcm.4483

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

A variety of archaeal lineages have been identified using culture-independent molecular phylogenetic surveys of microbial habitats occurring in deep-sea hydrothermal environments such as chimney structures, sediments, vent emissions, and chemosynthetic macrofauna. With the exception of a few taxa, most of these archaea have not yet been cultivated, and their physiological and metabolic traits remain unclear. In this study, phylogenetic diversity and distribution profiles of the archaeal genes encoding small subunit (SSU) rRNA, methyl coenzyme A (CoA) reductase subunit A, and the ammonia monooxygenase large subunit were characterized in hydrothermally influenced sediments at the Yonaguni Knoll IV hydrothermal field in the Southern Okinawa Trough. Sediment cores were collected at distances of 0.5, 2, or 5 m from a vent emission (90 degrees C). A moderate temperature gradient extends both horizontally and vertically (5 to 69 degrees C), indicating the existence of moderate mixing between the hydrothermal fluid and the ambient sediment pore water. The mixing of reductive hot hydrothermal fluid and cold ambient sediment pore water establishes a wide spectrum of physical and chemical conditions in the microbial habitats that were investigated. Under these different physico-chemical conditions, variability in archaeal phylotype composition was observed. The relationship between the physical and chemical parameters and the archaeal phylotype composition provides important insight into the eco-physiological requirements of uncultivated archaeal lineages in deep-sea hydrothermal vent environments, giving clues for approximating culture conditions to be used in future culturing efforts.

DOI： 10.1128/AEM.00924-09

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

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Seafloor sec ping methane bubbles were successfully sampled on the summit area of the Kuroshima Knoll (depth of ca 640 m) using the gas-tight sampler WHATS attached to the Shinkai 2000 To evaluate the origin of the bubbles and verify that the dissociation of methane hydrate was actually in progress the chemical and isotopic composition of the samples wen analyzed The major component of the gas bubbles was methane (C(1)) with traces of CO₂ (67 +/- 16 ppmv) and helium (11 +/- 1 ppmv (4)He/(20)Ne = 320) having a moderate (3)He/(4)He ratio (0 44R(a)) C(1) was enriched relative to other hydrocarbons (C(1)/(C(2)+C(3)) > 3000) The delta¹³C values for C(1) (-40 1 parts per thousand(VPDB)) C(2) (-28 3 parts per thousand(VPDB)) and C(5) (-28 0 parts per thousand(VPDB)) were similar to those of hydrocarbons produced by thermal decomposition of organic matter The contribution of the mantle derived (3)He enriched component in coexisting helium also supports thermogenic generation On the other hand the other light hydrocarbons showed an unusual ¹³C enrichment in C(3) (-19 1 parts per thousand(VPDB)) ISO-C(4) (-22 4 parts per thousand(VPDB)) and n-C(4) (-19 9 parts per thousand(VPDB)) C(3) and C(4) had been fractionated both chemically and isotopically through subsequent microbial destruction during the long storage from Miocene in the gas reservoir In addition the anaerobic oxidation of CH₄ within shallow sediments removed about 20 % of CH₄, until seepage into ocean water column Regarding the contribution of gases originating from hydrate dissociation to the bubbles observed helium amount in the bubbles suggests that methane hydrate is considered to be a minor contributor to the bubbles at least at present Direct leakage of gases from deep reservoirs is a more plausible for the source Regarding the fate of the hydrocarbons in the bubbles in the water column, all rising bubbles at Kuroshima Knoll dissolved within 140 m of the seafloor After the dissolution the plume spreads horizontally along with the surface of equal density in the water column, while the concentrations decrease through dilution by eddy diffusion rather than by oxidation.

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

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

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

Hydrothermal plumes above the HAKUREI and JADE sites two high-temperature hydrothermal vent sites in the Izena Cauldron at the mid-Okinawa Trough were investigated in order to gain a preliminary understanding of gas geochemical characteristics at underlying hydrothermal vent sites Three geochemical tracers, H₂, CH₄ and delta(3)He covary with each other above the HAKUREI site but only CH₄ and delta(3)He are correlated above the JADE site The carbon isotope ratio of methane within the Izena Cauldron can be accounted by a combination of the fluid dilution by ambient seawater and microbial consumption with the kinetic carbon isotope effect (KIE) of 1 007 An estimated endmember delta¹³C value of -32 parts per thousand in the HAKUREI fluid was obtained Both the plumes above the HAKUREI and JADE sites showed C(1)/C(2) ratios between 10(3)similar to 10(4) Only the bottom water around the HAKUREI site showed significant N(2)O excess with isotopically light delta¹⁵N and delta(18)O, suggesting N(2)O input from microbial activity in the sediment A linear con elation between H₂ and CH₄ in the HAKUREI plume gives a H₂/CH₄ ratio of the HAKUREI fluid of more than 0 022 The estimated H₂/CH₄ ratio in the HAKUREI fluid is significantly higher than that of the JADE fluid comparable with those of fluids venting at other sediment related hydrothermal systems, and also comparable with those of thermogenic gases produced by hydrothermal sediment experiments These facts suggest that fluid sediment interaction during fluid upwelling appears to modify gas geochemical characteristics at the HAKUREI site but have little influence at the JADE site This study demonstrates the availability of the Izena Cauldron hydrothermal field and the HAKUREI and JADE sites as a natural laboratory for investigating the fluid-sediment interaction during fluid upwelling.

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

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

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

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

DOI： 10.5194/acp-10-1809-2010

Authorship：Lead author   Language：Japanese  

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

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

DOI： 10.5194/bg-7-2369-2010

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

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

DOI： 10.1111/j.1758-2229.2009.00087.x

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

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

DOI： 10.1016/j.marchem.2009.09.001

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

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

DOI： 10.1128/AEM.01184-09

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

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

DOI： 10.1021/ac901630h

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

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

DOI： 10.1007/s00367-009-0143-9

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

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

DOI： 10.1029/2009JD011734

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

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

DOI： 10.1016/j.marchem.2009.06.009

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

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

DOI： 10.1029/2008JD011388

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

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

DOI： 10.1016/j.marmicro.2009.01.006

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

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

DOI： 10.1016/j.chemgeo.2008.10.028

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

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

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

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

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

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.

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

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.

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

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

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

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

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

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

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

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.

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

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.

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： 10.1073/pnas.0606083103

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

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

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

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

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

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

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

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

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.

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

Language：Japanese  

Authorship：Lead author   Language：Japanese  

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

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

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

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

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

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

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

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

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.

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

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

We report a newly developed water sampler WHATS (Water and Hydrothermal-fluid Atsuryoku Tight Sampler), for collecting seafloor venting gas-rich fluid (or gas itself) at in situ pressure (Atsuryoku means pressure in Japanese). It consist of four 150 cm3 stainless steel sample cylinders, eight ball valves, a motor-driven arm, a rail, a peristaltic pump, and a flexible Teflon tube connected to a titanium inlet tube. The motor-driven arm on the rail can open one of the four cylinders. Then, by pumping out pure water that has filled the cylinder, we can introduce sample fluid into the cylinder. After completely replacing the pure water with sample fluid, the valves at both ends of the cylinder are tightly closed by moving the motor-driven arm again. At this stage, the next cylinder becomes to be ready for next sampling. We can take maximum 4 different gas-tight samples in series. Whole operation can be arranged inside the submersible cabin. Use of only one motor to operate valves makes the sampler small, light (28 kg in water), and easy to handle. With the sampler, we can collect almost uncontaminated sample because we pump fluid slowly (120 cm3/min.) into the cylinder using the peristaltic pump. To date, the sampler has been used for ca. 40 dives of shinkai 2000 and shinkai 6500 with the success rate of more the 90%. We also evaluate the safety factors in handling highly pressured samples. We conclude that the sampler can be used to the depth of 3,000 m.

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

A putative endosymbiont-based benthic animal community composed of at least two kinds of bivalves has been found atop the South Chamorro serpentine seamount in the Mariana fore-arc, western Pacific. Multiple stable isotopic analyses ( hydrogen, carbon, nitrogen, and sulfur) were carried out on the soft tissues of an undescribed mussel species belonging to the genus Bathymodiolus. Markedly higher stable carbon (delta¹³C: -21.4 to -18.9 % vs. PDB) and lower sulfur (delta(34)S: +10.2 to +10.6 % vs. CDT) isotopic compositions of the mussel tissues suggested that they utilized both methane and sulfide as nutrient sources of carbon and sulfur. Analyses of in situ shimmering water and clayey sediment under the mussel bed supported these findings. These results strongly suggest that the mussels harbored both methanotrophic and thioautotrophic bacterial symbionts in their gills. This is the first stable isotopic evidence of a dual symbiotic Bathymodiolus sp. in the western Pacific. It is proposed that the major substrates for energy acquisition-methane and hydrogen sulfide-may be responsible for results from serpentinization in the lower crust. This abiotic process would be followed by abiotic or archaeal methane production and bacterial sulfate-reduction as evidenced by high delta¹³C value (-14.6 %) of methane in the shimmering water and low delta(34)S value (-32.3 %) of sulfides in the immediate sediments, respectively. Due to the very low organic matter content (0.5 mg C/g dry sediment) of the immediate sediment, it is further proposed that sulfate-reduction occurred using hydrogen (or possibly methane) as an electron donor. Thus, the mussel community living independently of magmatism and sedimentary organic matter is a lithotrophic animal community.

DOI： 10.1080/01490450390206674

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

In June 2000, several eruptions occurred on Miyake-jima Island, accompanied by volcanic and/or hydrothermal activity offshore from the island. In January 2001, water samples were collected from five stations around the island in order to reveal the existence of volcanic activity on the seafloor in the area. Concentrations and stable carbon isotopic compositions of dissolved methane in the water samples, however, showed no sign of submarine volcanic activity over the area. These results indicate that the submarine volcanic activity in the area was not in steady state at least during the sampling program.

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

This paper presents a modified H₂O-CO₂ equilibration method for stable oxygen isotopic composition (delta¹⁸O) analysis of water. This method enables rapid and simple delta¹⁸O analysis of milligram quantities of water, by employing solid reagent NaHCO₃ as the CO₂ Source, a small (0.6 mL) glass vial for the equilibration chamber, and an isotope-monitoring gas chromatography/mass spectrometry (irm-GC/MS) system for delta¹⁸O(CO₂) analysis. This method has several advantages, including simple handling for the H₂O-CO₂ equilibration (without purging and/or evacuation treatments), rapid and easy delta¹⁸O analysis of equilibrated CO₂, and highly sensitive and highly precise delta¹⁸O analysis of H₂O, using samples as small as 10 mg and with a precision of less than +/-0.12parts per thousand. The time needed to attain oxygen isotopic equilibration between CO₂ and water is also comparable (17 h for 10 mg H₂O and 10 h for 100 mg H₂O) to other previous methods using CO₂ gas for the CO₂ source. The extent of delta¹⁸O variation of sample water from its initial delta¹⁸O value due to isotope exchange with added NaHCO₃ is also discussed. It is concluded that the correction needed is negligible (less than 0.1parts per thousand) as long as the oxygen atom ratio (O-NaHCO₃/O-H₂O) is less than 3.3 +/- 10^-3 and provided the delta¹⁸O(H₂O) determination is made by comparing delta¹⁸O of CO₂ equilibrated with sample water and that equilibrated with standard water of a moderately close delta¹⁸O value, less than 30parts per thousand difference.

DOI： 10.1002/rcm.1081

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

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

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

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

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

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

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

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

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

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

Authorship：Lead author   Language：Japanese  

This paper summarizes stable carbon isotopic studies of hydrocarbons, especially methane, in seafloor venting hydrothermal and cold seep fluids, and their effluent methane-enriched plume in water column. Through highly sensitive isotopic analysis using CF-IRMS, we have discussed origin and/or behavior of hydrocarbons in each system. Major results are as follows: (i) methane in cold seep fluids around Japanese islands mostly microbial origin, (ii) methane emitted from cold seep fluids mostly oxidized anaerobically within sediments just before they emitted into ocean, (iii) methane in hydrothermal plume oxidized aerobically in some extent in the water column. Besides, methane flux and heat flux can be calculated for a methane-enriched fluid venting area from δ13C distribution of methane in hydrothermal plume, by using kinetic isotope fractionation which occurs during partial destruction. Similar approach could be also applicable to study origin and behavior of reactive trace components in atmosphere, such as non-methane hydrocarbons and CO. Preliminary results of such studies are also presented.

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

Language：Japanese

Language：Japanese

Language：Japanese

Language：Japanese

Language：Japanese

J-GLOBAL

J-GLOBAL

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

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DOI： 10.14862/geochemproc.64.0_241

CiNii Research

Event date： 2023.9

Language：Japanese   Presentation type：Poster presentation  

Venue：Tokyo University of Marine Science and Technology   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Tokyo University of Marine Science and Technology   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Tokyo University of Marine Science and Technology   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Tokyo University of Marine Science and Technology   Country：Japan  

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Tokyo University of Marine Science and Technology   Country：Japan  

Event date： 2023.5

Language：Japanese  

Venue：幕張メッセ（オンライン）   Country：Japan  

Event date： 2023.5

Language：Japanese   Presentation type：Poster presentation  

Venue：幕張メッセ（オンライン）   Country：Japan  

Event date： 2023.5

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：Makuhari Messe, Chiba   Country：Japan  

Event date： 2023.5

Language：Japanese   Presentation type：Poster presentation  

Venue：Makuhari Messe, Chiba   Country：Japan  

Event date： 2023.5

Language：Japanese  

Venue：幕張メッセ（オンライン）   Country：Japan  

Event date： 2023.4

Language：English   Presentation type：Poster presentation  

Venue：TOKI MESSE, Niigata Convention Center   Country：Japan  

Event date： 2023.4

Language：English   Presentation type：Oral presentation (general)  

Venue：TOKI MESSE, Niigata Convention Center   Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熱海市起雲閣   Country：Japan  

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熱海市起雲閣   Country：Japan  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば国際会議場   Country：Japan  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば国際会議場   Country：Japan  

Event date： 2022.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Kochi University   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Kochi University   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：高知大学   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：高知大学   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：高知大学   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：Kochi University   Country：Japan  

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DOI： 10.14862/geochemproc.69.0_139

CiNii Research

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan  

Event date： 2022.5 - 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari Messe, Chiba   Country：Japan  

Event date： 2022.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Makuhari Messe, Chiba   Country：Japan  

Event date： 2022.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

DOI： 10.14862/geochemproc.67.0_132

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

DOI： 10.14862/geochemproc.67.0_6

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2020.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

DOI： 10.18940/vsj.2020.0_19

Event date： 2020.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

DOI： 10.18940/vsj.2020.0_23

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019

Language：Japanese   Presentation type：Oral presentation (general)  

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DOI： 10.14862/geochemproc.66.0_132

Event date： 2019

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.66.0_131

Event date： 2019

Language：Japanese   Presentation type：Oral presentation (general)  

DOI： 10.18940/vsj.2019.0_76

Event date： 2019

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.66.0_117

Event date： 2019

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.66.0_247

Event date： 2019

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.66.0_248

Event date： 2019

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.66.0_17

Event date： 2018

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.65.0_219

Event date： 2018

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.65.0_217

Event date： 2018

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.65.0_159

Event date： 2018

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.65.0_172

Event date： 2018

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.65.0_218

Event date： 2018

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.65.0_281

Event date： 2017.10

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue： 愛知工業大学本山キャンパス2階多目的室   Country：Japan  

Event date： 2017.10

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：愛知工業大学本山キャンパス2階多目的室  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (keynote)  

Country：Japan  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (keynote)  

Event date： 2017.6

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：うなぎ有本   Country：Japan  

Event date： 2017

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.64.0_232

Event date： 2017

Language：English   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.64.0_241

Event date： 2017

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.64.0_83

Event date： 2017

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.64.0_226

Event date： 2017

Language：Japanese   Presentation type：Oral presentation (general)  

DOI： 10.18940/vsj.2017.0_74

Event date： 2017

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.64.0_220

Event date： 2017

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.64.0_273

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：富山大学, 2014年9月15日.   Country：Japan  

Event date： 2014.7

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：コラボしが21   Country：Japan  

Event date： 2012.11

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：仙台秋保温泉佐勘   Country：Japan  

Event date： 2012.10

Language：English   Presentation type：Oral presentation (invited, special)  

Country：Taiwan, Province of China  

Event date： 2011.11

Language：English   Presentation type：Oral presentation (invited, special)  

Country：Korea, Republic of  

Event date： 2011.5

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2010.5

Language：English   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2009.5

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.69.0_47

CiNii Research

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.69.0_48

CiNii Research

Language：Japanese   Presentation type：Oral presentation (general)  

DOI： 10.18940/vsj.2022.0_52

CiNii Research

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.69.0_160

CiNii Research

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.69.0_142

CiNii Research

Language：Japanese   Presentation type：Oral presentation (general)  

DOI： 10.18940/vsj.2022.0_53

CiNii Research

Language：Japanese   Presentation type：Oral presentation (general)  

<p></p>

DOI： 10.14862/geochemproc.69.0_115

CiNii Research

Language：Japanese   Presentation type：Oral presentation (invited, special)  

DOI： 10.18940/vsj.2023.0_114

CiNii Research

Although the ocean covers more than 70 percent of the surface of our planet, there remain a number of unresolved issues. The ocean is, as it were, the earth's last frontier. This is due to the difficulty in conducting oceanographic observations and the lack of oceanographic observation methods and analytical techniques. In this field seminar, students can experience basic ocean observation through practical training on board the vessel and learn about the current state of the coastal and marine environment and methods for ocean observation. The students will board the training/research vessel Seisui-maru, Faculty of Bioresources, Mie University, and perform observations and sampling of seawater on their own for measurement and data analysis. The main observation areas for the training are Ise Bay and Mikawa Bay. After the training, a session for presenting the research results will be held. Students will improve their ability to analyze the obtained data through the discussions with others.

In this class, you will learn a wide range of topics, focusing on the basics of oceanography, which is one of the major fields of earth and planetary science. Specifically, you will acquire knowledge about the physical and chemical characteristics of seawater, together with the laws governing the advection and/or diffusion of water, chemicals, and heat in ocean. Next, we will systematically and comprehensively understand the role of the ocean in the climate, geochemical cycle, and life evolution of the earth. You will also learn about the historical background that revealed present ocean science. We aim to cultivate deep insight into oceanography and earth and planetary science, and to establish accurate ocean and earth images based on scientific knowledge.