研究者詳細 - 角皆　潤

論文 - 角皆　潤

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Hydrothermal Methane Venting and Its Microbial Oxidation Along the Eastern Southwest Indian Ridge, 63.5°–68°E 査読有り国際共著国際誌 Open Access

Surya Prakash L., John Kurian P., Sen K., Tsunogai U., Linsy P., Shuhail M., Roy P.

Geophysical Research Letters 52 巻 ( 2 ) 2025年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Geophysical Research Letters

Methane concentration and its stable carbon isotope ratio studies were carried out in deep waters of ultraslow-spreading eastern Southwest Indian Ridge (eSWIR), 63.5°–68°E, to identify hydrothermal plumes and associated biogeochemical processes. High methane concentrations (1.0–37.8 nmol/kg) confirm the presence of 11 hydrothermal plumes along the ∼500 km long section of eSWIR. Among these 11 plumes, eight are reporting for the first time. Detailed investigations near 67.67°E; 26.61°S show the presence of three plumes at various depths and their dispersion >100 km along the ridge in east-west directions. Stable carbon isotope ratios of these plumes show lighter and heavier isotope enrichment (−40‰ to −3‰). Lighter isotope enrichment may indicate that methane could be derived from a combination of abiotic and thermogenic sources and, heavier isotope enrichment is mainly because of microbial methane oxidation. We report strong evidence for the presence of an active hydrothermal field at 67.67°E; 26.61°S in the eSWIR for the first time.

DOI： 10.1029/2024GL110958

Bias in calculating gross nitrification rates in forested catchments using the triple oxygen isotopic composition (<mml:msup>Δ17</mml:msup>O) of stream nitrate 査読有り国際誌 Open Access

Ding, WT; Tsunogai, U; Nakagawa, F

BIOGEOSCIENCES 21 巻 ( 21 ) 頁： 4717 - 4722 2024年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Biogeosciences

A novel method has been proposed and applied in recent studies to quantify gross nitrification rate (GNR) in forested catchments using the triple oxygen isotopic composition (Δ17O) of stream nitrate. However, the equations used in these calculations assume that the Δ17O value of nitrate consumed through assimilation or denitrification in forest soils is equal to the Δ17O value of stream nitrate. The GNR estimated from the Δ17O value of stream nitrate was significantly higher than the GNRs in our simulated calculations for a forested catchment where the soil nitrate had Δ17O values higher than those the stream nitrate. Given that most reported soil nitrate in forested catchments showed Δ17O values higher than those of the stream nitrate, we concluded that the GNR estimated from the Δ17O value of stream nitrate was, to an extent, an overestimate of the actual GNR.

DOI： 10.5194/bg-21-4717-2024

Influences of topography on nitrate export from forested watersheds on Yakushima Island, a Natural World Heritage site. 査読有り国際誌

Shinozuka K, Nagafuchi O, Nakazawa K, Tsunogai U, Nakagawa F, Tetsuka K, Tetsuka N, Ebise S

RSC advances 14 巻 ( 41 ) 頁： 29860 - 29872 2024年9月

Estimating emission flux of H2S from fumarolic fields using vertical sensor array system 査読有り国際誌 Open Access

Miyagi, Y; Tsunogai, U; Watanabe, K; Ito, M; Nakagawa, F; Kazahaya, R

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 450 巻頁： 108090 - 108090 2024年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Volcanology and Geothermal Research

The emission flux of volatiles from each fumarolic field in volcanic and geothermal areas can be used to evaluate the current state of magmatic activity and predict its future trends. The emission flux of SO2 has been quantified in many fumarolic fields using remote sensing techniques, such as differential optical absorption spectroscopy (DOAS). However, most of these remote sensing techniques are inapplicable to fumarolic fields emitting volatiles depleted in SO2 to which most of the geothermal fields are classified. In this study, we developed a vertical sensor array system to quantify the emission flux of H2S from each fumarolic field by integrating the cross-sectional distributions of H2S concentrations in the volcanic plume using the vertical sensor array system. In Iwo-yama of the Kirishima volcanic complex, the cross-sectional distribution of H2S concentrations was determined using the walking traverse method by moving the vertical sensor array system in the plume perpendicular to the direction of plume transport. The emission flux of SO2 (2.2 ± 0.4 ton SO2/day) was estimated from that of H2S using the walking traverse method (2.6 ± 0.5 ton H2S/day) and the molar ratio of the plume (SO2/H2S=0.45) corresponds well with that estimated optically by JMA. We concluded that the emission flux quantified using the vertical sensor array system was reliable. In the Oyunuma pond in the Kuttara volcano, the emission flux of H2S was quantified as 2.0 ton H2S/day through the fixed point method, wherein the vertical sensor array system was fixed in one point, whereas the cross sectional distribution of H2S in the plume was estimated using the natural variation in wind direction. The topography is often irregular and wind direction is variable in most fumarolic fields; thus, in general, the fixed point method should be more suitable to determine the emission flux of H2S from fumarolic fields, wherein H2S occupies a major portion of the total sulfur emission.

DOI： 10.1016/j.jvolgeores.2024.108090

Archaeal lipid biomarkers in near-surface sediments at a giant colony of the bivalve<i> Calyptogena:</i> Molecular records of a massive methane release event associated with methane hydrate dissociation 査読有り国際誌 Open Access

Sakata, S; Tsunogai, U; Oba, M; Ujiie, T; Tanahashi, M

ORGANIC GEOCHEMISTRY 188 巻頁： 104739 - 104739 2024年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Organic Geochemistry

To investigate the possibility that dissociation of subsurface methane hydrate (MH) in the eastern Nankai Trough, offshore of Japan, led to the formation of a giant colony of the bivalve Calyptogena (currently mostly dead), the carbon isotope ratios (δ13C) of archaeal lipids and methane were measured in near-surface core sediments at Daini-Tenryu Knoll. The irregular variation of porewater methane δ13C with depth (from −75 ‰ to −26 ‰) suggested that originally low δ13C microbial methane was degraded in different proportions by anaerobic methane oxidation. Consistent with this inference, biomarkers of anaerobic methanotrophic archaea (ANME), namely, crocetane (2,6,11,15-tetramethylhexadecane), PMI (2,6,10,15,19-pentamethylicosane), and diethers (archaeol and hydroxyarchaeols), were detected in lipid extracts. The low diether δ13C values (−121 ‰ to −104 ‰) were characteristic of ANME, but less variable than the methane δ13C values, and the relationships between diethers and methane δ13C values deviated from regression lines derived using worldwide data from modern methane seep sites. In contrast, δ13C values of the ANME source methane predicted from those regression lines and the diether δ13C values agreed well with methane δ13C values in MH samples obtained by nearby deep drilling. This result strongly suggests that most of the diethers were produced by ANME that proliferated during a past massive methane release event associated with MH dissociation. The crocetane δ13C value, measured in a mixture with phytane and estimated from the correlation of the δ13C of the mixture with the mole fraction of crocetane, was about −127 ‰. More than half of the PMI δ13C values were greater than −100 ‰, suggesting the background presence of fossil PMI from methanogens.

DOI： 10.1016/j.orggeochem.2024.104739

Stable isotopic evidence for the excess leaching of unprocessed atmospheric nitrate from forested catchments under high nitrogen saturation 査読有り国際誌

Ding W., Tsunogai U., Nakagawa F., Sambuichi T., Chiwa M., Kasahara T., Shinozuka K.

Biogeosciences 20 巻 ( 3 ) 頁： 753 - 766 2023年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Biogeosciences

Owing to the elevated loading of nitrogen through atmospheric deposition, some forested ecosystems become nitrogen saturated, from which elevated levels of nitrate are exported. The average concentration of stream nitrate eluted from upstream and downstream of the Kasuya Research forested catchments (FK1 and FK2 catchments) in Japan were more than 90 μM, implying that these forested catchments were under nitrogen saturation. To verify that these forested catchments were under the nitrogen saturation, we determined the export flux of unprocessed atmospheric nitrate relative to the entire deposition flux (Matm/Datm ratio) in these catchments; because the Matm/Datm ratio has recently been proposed as a reliable index to evaluate nitrogen saturation in forested catchments. Specifically, we determined the temporal variation in the concentrations and stable isotopic compositions, including δ17O, of stream nitrate in the FK catchments for more than 2 years. In addition, for comparison, the same parameters were also monitored in the Shiiba Research forested catchment (MY catchment) in Japan during the same period, where the average stream nitrate concentration was low, less than 10 μM. While showing the average nitrate concentrations of 109.5, 90.9, and 7.3 μM in FK1, FK2, and MY, respectively, the catchments showed average δ17O values of +2.6 ‰, +1.5 ‰, and +0.6 ‰ in FK1, FK2, and MY, respectively. Thus, the average concentration of unprocessed atmospheric nitrate ([NO3-atm]) was estimated to be 10.8, 5.1, and 0.2 μM in FK1, FK2, and MY, respectively, and the Matm/Datm ratio was estimated to be 14.1 %, 6.6 %, and 1.3 % in FK1, FK2, and MY, respectively. The estimated Matm/Datm ratio in FK1 (14.1 %) was the highest ever reported from temperate forested catchments monitored for more than 1 year. Thus, we concluded that nitrogen saturation was responsible for the enrichment of stream nitrate in the FK catchments, together with the elevated NO3-atm leaching from the catchments. While the stream nitrate concentration ([NO3-]) can be affected by the amount of precipitation, the Matm/Datm ratio is independent of the amount of precipitation; thus, the Matm/Datm ratio can be used as a robust index for evaluating nitrogen saturation in forested catchments.

DOI： 10.5194/bg-20-753-2023

First Measurements on Triple Oxygen Isotopes of Dissolved Inorganic Phosphate in the Hydrosphere. 査読有り国際誌

Sambuichi T, Tsunogai U, Ito M, Nakagawa F

Environmental science & technology 57 巻 ( 8 ) 頁： 3415 - 3424 2023年2月

Tracing the sources of excess methane in Ise and Mikawa bays using dual stable isotopes as tracers 査読有り

Lan, H; Tsunogai, U; Nakagawa, F; Ito, M; Shingubara, R; Miyoshi, Y; Hara, S

GEOCHEMICAL JOURNAL 57 巻 ( 2 ) 頁： 59 - 72 2023年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Geochemical Journal

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.

DOI： 10.2343/geochemj.GJ23005

Geochemical distribution of helium, hydrogen, carbon dioxide, and methane in Sakhalin Island mud volcanoes, hot springs, and cold seeps 査読有り国際共著国際誌

Syrbu, NS; Snyder, GT; Shakirov, RB; Kholmogorov, AO; Zharkov, RV; Tsunogai, U

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 431 巻 2022年11月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Volcanology and Geothermal Research

The Asian-Pacific - continental margins have been the object of intensive geochemical research in recent years, as areas within this zone have been found to contain large hydrocarbon deposits in a variety of forms including: oil, natural gas, gas condensate, and gas hydrates. One such area is Sakhalin Island, located in Russia's Far Eastern Federal District. Genetically, the territory of Sakhalin Island is a part of the shelf of the Hokkaido-Sakhalin fold area, therefore, the nature of the sub-vertical gas migration is controlled by deep faults, along which the concentrations of natural gases change, and is also influenced by high seismotectonic activity of the Okhotsk region. This paper presents data regarding the distribution of helium, hydrogen, carbon dioxide and methane from mud volcanoes, thermal springs, mineral waters and other seep types on Sakhalin island and the surrounding marine margins, along with an interpretation of the geological and tectonic factors that have likely led to the present distribution of these gases. In general, the results of geothermometry equations based on the concentration and stable isotopic composition of carbon dioxide indicate much higher temperatures than equations involving the saturation concentrations of hydrogen gas. We interpret this to indicate that deeply-sourced carbon dioxide does not reequilibrate at near-surface conditions, whereas the equilibration time for hydrogen gas is relatively rapid. Areas on the island which are observed to have active degassing, coupled with high apparent reservoir temperatures also provide indicators of geodynamics along the regional tectonic structures. Mud volcanoes to the south of the island are predominantly situated at the juncture between NW-SE trending faults which extend the entire length of Sakhalin and continue as far south as Hokkaido Island, and more recently developed NE-SW trending faults. Despite the relatively low water temperatures of these mud volcanoes, the high reservoir temperatures indicated by gas chemistry suggest a source of fluids and gas at several km from the surface.

DOI： 10.1016/j.jvolgeores.2022.107667

Volatile-Rich Hydrothermal Plumes Over the Southern Central Indian Ridge, 24°49’S: Evidence for a New Hydrothermal Field Hosted by Ultramafic Rocks 査読有り国際共著国際誌

Surya Prakash L., John Kurian P., Resing J.A., Tsunogai U., Srinivas Rao A., Sen K., Lupton J.E., Baumberger T., Prajith A., Roy P.

Geochemistry, Geophysics, Geosystems 23 巻 ( 10 ) 2022年10月

Tracing the source of nitrate in a forested stream showing elevated concentrations during storm events 査読有り国際誌

Weitian Ding, Urumu Tsunogai, Fumiko Nakagawa, Takashi Sambuichi, Hiroyuki Sase, Masayuki Morohashi, Hiroki Yotsuyanagi

BIOGEOSCIENCES 19 巻 ( 13 ) 頁： 3247 - 3261 2022年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Sampling Volcanic Plume Using a Drone-Borne SelPS for Remotely Determined Stable Isotopic Compositions of Fumarolic Carbon Dioxide 招待有り査読有り国際誌

Urumu Tsunogai, Ryo Shingubara, Yuhei Morishita, Masanori Ito, Fumiko Nakagawa, Shin Yoshikawa, Mitsuru Utsugi, Akihiko Yokoo

Frontiers in Earth Science 10 巻 2022年3月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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 (SO<sub>2</sub>) sensor triggered a pump to collect plume samples when the SO<sub>2</sub> 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 SO<sub>2</sub> 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 <sup>2</sup>H/<sup>1</sup>H ratios of H<sub>2</sub>, <sup>18</sup>O/<sup>16</sup>O ratios of CO<sub>2</sub>, and <sup>13</sup>C/<sup>12</sup>C ratios of CO<sub>2</sub> within the plume samples. Based on the isotopic ratios of fumarolic H<sub>2</sub> (δ<sup>2</sup>H = −239 ± 6‰) and fumarolic CO<sub>2</sub> (δ<sup>13</sup>C = −3.58 ± 0.85‰ and δ<sup>18</sup>O = +22.01 ± 0.68‰) determined from the linear correlations, we estimated the apparent equilibrium temperatures (AETs) with magmatic H<sub>2</sub>O simultaneously and precisely for the first time in erupting volcanoes, assuming hydrogen isotope exchange equilibrium between H<sub>2</sub> and H<sub>2</sub>O (AET<sub>D</sub> = 629 ± 32°C) and oxygen isotope exchange equilibrium between CO<sub>2</sub> and H<sub>2</sub>O (AET<sub>18O</sub> = 266 ± 65°C). We found that the AET<sub>18O</sub> was significantly lower than the AET<sub>D</sub> 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<sub>D</sub> and AET<sub>18O</sub> in eruptive volcanoes, wherein fumaroles are inaccessible. Simultaneous and precise determination of both the AET<sub>18O</sub> and AET<sub>D</sub> 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

Nitrogen saturation of forested catchments in central Japan-Progress or recovery? 査読有り国際誌

Sase Hiroyuki, Takahashi Masamichi, Matsuda Kazuhide, Yamashita Naoyuki, Tsunogai Urumu, Nakagawa Fumiko, Morohashi Masayuki, Yotsuyanagi Hiroki, Ohizumi Tsuyoshi, Sato Keiichi, Kurokawa Junichi, Nakata Makoto

SOIL SCIENCE AND PLANT NUTRITION 68 巻 ( 1 ) 頁： 5 - 14 2022年1月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Soil Science and Plant Nutrition

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

High-precision Δ′<sup>17</sup>O measurements of geothermal H<sub>2</sub>O and MORB on the VSMOW-SLAP scale: evidence for active oxygen exchange between the lithosphere and hydrosphere 査読有り国際誌

Takashi Sambuichi, Urumu Tsunogai, Kazushige Kura, Fumiko Nakagawa, Takeshi Ohba

GEOCHEMICAL JOURNAL 55 巻 ( 6 ) 頁： e25 - e33 2021年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Determination of the triple oxygen isotopic composition of tropospheric ozone in terminal positions using a multistep nitrite‐coated filter‐pack system 査読有り国際誌

Hao Xu, Urumu Tsunogai, Fumiko Nakagawa, Yijun Li, Masanori Ito, Keiichi Sato, Hiroshi Tanimoto

Rapid Communications in Mass Spectrometry 35 巻 ( 15 ) 頁： e9124 2021年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Development of a drone-borne volcanic plume sampler 招待有り査読有り国際誌

Ryo Shingubara, Urumu Tsunogai, Masanori Ito, Fumiko Nakagawa, Shin Yoshikawa, Mitsuru Utsugi, Akihiko Yokoo

Journal of Volcanology and Geothermal Research 412 巻頁： 107197 - 107197 2021年4月

Vertical Changes in the Flux of Atmospheric Nitrate From a Forest Canopy to the Surface Soil Based on Delta O-17 Values 査読有り国際誌

Inoue Takahiro, Nakagawa Fumiko, Shibata Hideaki, Tsunogai Urumu

JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES 126 巻 ( 4 ) 2021年4月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Behavior of magmatic components in fumarolic gases related to the 2018 phreatic eruption at Ebinokogen Ioyama volcano, Kirishima Volcanic Group, Kyushu, Japan 査読有り国際誌

Ohba Takeshi, Yaguchi Muga, Tsunogai Urumu, Ito Masanori, Shingubara Ryo

EARTH PLANETS AND SPACE 73 巻 ( 1 ) 2021年3月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Earth, Planets and Space

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. [Figure not available: see fulltext.]

DOI： 10.1186/s40623-021-01405-4

その他リンク： http://link.springer.com/article/10.1186/s40623-021-01405-4/fulltext.html

Geological features for the formation of gas-geochemical fields, including helium and hydrogen, in the water and sediments at the Vietnamese part of the South-China Sea 査読有り国際共著国際誌

Syrbu N.S., Cuong D.H., Iakimov T.S., Kholmogorov A.O., Telegin Y.A., Tsunogai U.

Georesursy 23 巻 ( 3 ) 頁： 132 - 142 2021年

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Variation of volcanic gas composition at a poorly accessible volcano: Sakurajima, Japan 査読有り国際誌

Shinohara H., Kazahaya R., Ohminato T., Kaneko T., Tsunogai U., Morita M.

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 407 巻頁： 107098 - 107098 2020年12月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Volcanology and Geothermal Research

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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