研究者詳細 - 栗田　直幸

論文 - 栗田　直幸

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Characteristics of tritium, stable isotopes and chemical components in monthly precipitation at Hiroshima, Japan.

Yamada R, Kuwata H, Kheamsiri K, Ohno K, Kitayama Y, Yoshinaka Y, Yoshinaga S, Kurita N, Akata N

Radiation protection dosimetry 200 巻 ( 16-18 ) 頁： 1797 - 1801 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：Radiation Protection Dosimetry

This article mainly discusses tritium concentrations in monthly precipitation at Hiroshima City during 2021. The tritium concentrations, which were measured with a low background liquid scintillation counter, fluctuated from 0.16 to 0.78 Bq L−1. Additionally, hydrogen and oxygen stable isotopes and ionic species were measured in order to characterize precipitation, and their trends including tritium concentrations were compared with data collected in other regions of Japan in previous studies. Although the results showed the characteristics of precipitation were similar to those observed in the other regions, the tritium concentrations were found to be contrary to behavior expected from the latitude effect and some of the observed ionic components were suggested to be continental in origin. Since these results are not common at other sites in Japan, the tritium concentration in the westernmost region of Honshu, including Hiroshima City, may be influenced by Asian continental influences.

DOI： 10.1093/rpd/ncae024

Scopus

PubMed

Near-Surface Air Temperature Records over the Past 30 Years in the Interior of Dronning Maud Land, East Antarctica

Kurita N., Kameda T., Motoyama H., Hirasawa N., Mikolajczyk D., Welhouse L.J., Keller L.M., Weidner G.A., Lazzara M.A.

Journal of Atmospheric and Oceanic Technology 41 巻 ( 2 ) 頁： 179 - 188 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：Journal of Atmospheric and Oceanic Technology

The interior of Dronning Maud Land (DML) in East Antarctica is one of the most data-sparse regions of Antarctica for studying climate change. A monthly mean near-surface temperature dataset for the last 30 years has been compiled from the historical records from automatic weather stations (AWSs) at three sites in the region (Mizuho, Relay Station, and Dome Fuji). Multiple AWSs have been installed along the route to Dome Fuji since the 1990s, and observations have continued to the present day. The use of passive-ventilated radiation shields for the temperature sensors at the AWSs may have caused a warm bias in the temperature measurements, however, due to insufficient ventilation in the summer, when solar radiation is high and winds are low. In this study, these warm biases are quantified by comparison with temperature measurements with an aspirated shield and subsequently removed using a regression model. Systematic error resulting from changes in the sensor height due to accumulating snow was insignificant in our study area. Several other systematic errors occurring in the early days of the AWS systems were identified and corrected. After the corrections, multiple AWS records were integrated to create a time series for each station. The percentage of missing data over the three decades was 21% for Relay Station and 28% for Dome Fuji. The missing rate at Mizuho was 49%, more than double that at Relay Station. These new records allow for the study of temperature variability and change in DML, where climate change has so far been largely unexplored. SIGNIFICANCE STATEMENT: Antarctic climate change has been studied using temperature data at staffed stations. The staffed stations, however, are mainly located on the Antarctic Peninsula and in the coastal regions. Climate change is largely unknown in the Antarctic plateau, particularly in the western sector of the East Antarctic Plateau in areas such as the interior of Dronning Maud Land (DML). To fill the data gap, this study presents a new dataset of monthly mean near-surface climate data using historical observations from three automatic weather stations (AWSs). This dataset allows us to study temperature variability and change over a data-sparse region where climate change has been largely unexplored.

DOI： 10.1175/JTECH-D-23-0092.1

Scopus

Regional variations in mineralogy of dust in ice cores obtained from northeastern and northwestern Greenland over the past 100 years

Naoko Nagatsuka, Kumiko Goto-Azuma, Koji Fujita, Yuki Komuro, Motohiro Hirabayashi, Jun Ogata, Kaori Fukuda, Yoshimi Ogawa-Tsukagawa, Kyotaro Kitamura, Ayaka Yonekura, Fumio Nakazawa, Yukihiko Onuma, Naoyuki Kurita, Sune Olander Rasmussen, Giulia Sinnl, Trevor James Popp, Dorthe Dahl-Jensen

2023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：Copernicus GmbH

Abstract. To investigate regional and temporal variations in the sources and atmospheric transport processes for mineral dust deposited on the Greenland Ice Sheet, we analysed the morphology and mineral composition of dust in an ice core from northeastern Greenland (East Greenland Ice-Core Project, EGRIP), representing the period from 1910 to 2013, using scanning electron microscopy and energy-dispersive X-ray spectroscopy, and compared the results with those previously obtained for an ice core from northwestern Greenland (SIGMA-D). The composition of the SIGMA-D ice-core dust, comprising mostly silicate minerals, varied on a multi-decadal timescale due to an increased contribution of minerals originating from local ice-free areas during recent warming periods. In contrast, for the EGRIP ice-core dust, also consisting mostly of silicate minerals, there was relatively low compositional variation among the samples, suggesting that the mineral sources have not changed dramatically over the past 100 years. The subtle variation in the EGRIP ice-core mineral composition is likely due to a minor contribution of local dust. The type of silicate minerals differed significantly between the two ice cores; micas and chlorite, which form in cold dry regions, were abundant in the EGRIP ice core, whereas kaolinite, which forms in warm humid regions, was abundant in the SIGMA-D ice core. This indicates that the EGRIP ice-core dust likely originated from different geological sources than those for the SIGMA-D dust. A back-trajectory analysis indicated that the ice-core dust was transported from Northern Eurasia and North America to the EGRIP site, and that the contribution from each source was likely smaller and larger, respectively, than those for the SIGMA-D ice core. Furthermore, the higher illite content in the EGRIP ice core suggests dust transportation from Asian deserts. Although the back-trajectory analysis suggests that most of the air mass that arrived at the EGRIP site came from the Greenland coast, the mineral grain size and composition results showed that the local dust contribution was likely small.

DOI： 10.5194/egusphere-2023-1666

Verification of Estimated Cosmic Neutron Intensities Using a Portable Neutron Monitoring System in Antarctica

Yasuda H., Kurita N., Yajima K.

Applied Sciences (Switzerland) 13 巻 ( 5 ) 2023年3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：Applied Sciences (Switzerland)

Featured Application: A portable neutron-monitoring system can be effectively applied to verification of the models used for estimating cosmic radiation intensities over a wide range of altitudes in a harsh environment such as in Antarctica. Many ongoing studies for predicting the production rates of cosmogenic nuclides, forecasting changes of atmospheric compositions and climate, assessing the cosmic-radiation exposure of aircraft crew, and the effects on precise electronic devices use numerical models that estimate cosmic-radiation intensities in the atmosphere. Periodic verifications of those models are desirable to be performed for assuring the reliability of the study outcomes. Here, we investigated an application of a portable neutron-monitoring system composed of an extended-energy-range neutron monitor and a small data logger for monitoring of cosmic-neutron intensities in a polar region. As a result of measurements in the east Antarctica region covering a wide range of altitudes (from 30 m to 3762 m) and comparisons with the model calculations performed with an analytical model based on comprehensive Monte Carlo simulations (PARMA), it was demonstrated that the portable neutron-monitoring system could be effectively applied for periodic verification of cosmic-neutron intensities that would improve the reliability of related studies.

DOI： 10.3390/app13053297

Scopus

Temporal variations of surface mass balance over the last 5000 years around Dome Fuji, Dronning Maud Land, East Antarctica

Oyabu I., Kawamura K., Fujita S., Inoue R., Motoyama H., Fukui K., Hirabayashi M., Hoshina Y., Kurita N., Nakazawa F., Ohno H., Sugiura K., Suzuki T., Tsutaki S., Abe-Ouchi A., Niwano M., Parrenin F., Saito F., Yoshimori M.

Climate of the Past 19 巻 ( 2 ) 頁： 293 - 321 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：Climate of the Past

We reconstructed surface mass balance (SMB) around Dome Fuji, Antarctica, over the last 5000 years using the data from 15 shallow ice cores and seven snow pits. The depth-age relationships for the ice cores were determined by synchronizing them with a layer-counted ice core from West Antarctica (WAIS Divide ice core) using volcanic signals. The reconstructed SMB records for the last 4000 years show spatial patterns that may be affected by their locations relative to the ice divides around Dome Fuji, proximity to the ocean, and wind direction. The SMB records from the individual ice cores and snow pits were stacked to reconstruct the SMB history in the Dome Fuji area. The stacked record exhibits a long-term decreasing trend at -0.037±0.005g€¯kgg€¯m-2 per century over the last 5000 years in the preindustrial period. The decreasing trend may be the result of long-term surface cooling over East Antarctica and the Southern Ocean and sea ice expansion in the water vapor source areas. The multidecadal to centennial variations of the Dome Fuji SMB after detrending the record shows four distinct periods during the last millennium: a mostly negative period before 1300g€¯CE, a slightly positive period from 1300 to 1450g€¯CE, a slightly negative period from 1450 to 1850g€¯CE with a weak maximum around 1600g€¯CE, and a strong increase after 1850g€¯CE. These variations are consistent with those of previously reconstructed SMB records in the East Antarctic plateau. The low accumulation rate periods tend to coincide with the combination of strong volcanic forcings and solar minima for the last 1000 years, but the correspondence is not clear for the older periods, possibly because of the lack of coincidence of volcanic and solar forcings or the deterioration of the SMB record due to a smaller number of stacked cores.

DOI： 10.5194/cp-19-293-2023

Scopus

東シベリア・レナ川の水安定同位体比とトリチウム濃度の季節変化：端成分混合解析による河川水の成分分離の可能性

檜山哲哉, 本間朝香, 栗田直幸, 浅井和由, 朴昊澤

水文・水資源学会研究発表会要旨集 36 巻 ( 0 ) 頁： 340 2023年

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：水文・水資源学会

温暖化と北極海氷縮小の影響を受け、北ユーラシアの水循環は大きく変化している。北極海を取り囲む陸域（環北極陸域）における水循環変動を永久凍土融解と河川への地下水流出を含めて理解することを目的に、東シベリア・レナ川のタバガ観測点において2020年4月から2021年3月の1年間、河川水を採取し、その水安定同位体比とトリチウム濃度の季節変化を得た。水安定同位体比とトリチウム濃度は明瞭な季節変化を示し、河川水位との関係も明瞭であった。水安定同位体比は河川水位が高い融雪期に低く、暖候期に最も高くなった。一方トリチウム濃度は河川が凍結する冬季に低く、融雪期に上昇した後、暖候期に最も高い値を示した。興味深いことに、水安定同位体比とトリチウム濃度の季節変化には明瞭なヒステリシスが見られた。したがって冬季には地下水（または地下氷融解水）が、融雪期には融雪水が、暖候期には降雨起源の土壌水が、それぞれ河川に流出すると考えられた。そして端成分混合解析により、各季節における各起源水の河川流出への寄与率が推定できることを見出した。

DOI： 10.11520/jshwr.36.0_340

CiNii Research

Spatial variations of 10Be in surface snow along the inland traverse route of Japanese Antarctic Research Expeditions

Horiuchi K., Kato S., Ohtani K., Kurita N., Tsutaki S., Nakazawa F., Motoyama H., Kawamura K., Tazoe H., Akata N., Yamagata T., Matsuzaki H.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 533 巻頁： 61 - 65 2022年12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：Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

To contribute further to understanding of the nature of 10Be deposition in Antarctica, we determined 10Be concentrations in surface snow samples obtained along the inland traverse route of the 59th and 60th Japanese Antarctic Research Expeditions (JAREs) in eastern Dronning Maud Land. The 10Be concentrations ranged between 3.7 × 103 and 8.6 × 104 atoms/g. When plotted against latitude, they showed a clear trend of increasing concentration southward with an upward inflection point at around 75°S (elevation 3.5 km) for the 59th JARE. Comparison with both snow accumulation rate and δ18O data suggests that the inflection point divides the dominant deposition regime into two different groups: wet deposition (north of 75°S) and dry deposition with slight enhancement of 10Be fallout further inland (south of 75°S). Additional factors associated with 10Be transport from the stratosphere are also proposed.

DOI： 10.1016/j.nimb.2022.10.018

Scopus

Monthly Precipitation Collected at Hirosaki, Japan: Its Tritium Concentration and Chemical and Stable Isotope Compositions

Kuwata H., Akata N., Okada K., Tanaka M., Tazoe H., Kurita N., Otashiro N., Negami R., Suzuki T., Tamakuma Y., Shiroma Y., Hosoda M.

Atmosphere 13 巻 ( 5 ) 2022年5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：Atmosphere

Monthly precipitation samples were collected at Hirosaki, Aomori Prefecture from January 2018 to December 2020 to measure the ion species and stable hydrogen and oxygen isotope ratios in order to understand the regional properties. The tritium concentration ranged from 0.28 to 1.20 Bq/L, with mean values (±S.D.) of 0.52 ± 0.18, 0.67 ± 0.25 and 0.63 ± 0.21 Bq/L in 2018, 2019 and 2020, respectively. This concentration level was almost the same as for Rokkasho, Aomori Prefecture. The tritium concentration had clear seasonal variation: high in the spring and low in the summer. This trend was thought to arise from seasonal fluctuations in the atmospheric circulation. On the other hand, the pH tended to be low, and the electrical conductivity (EC) tended to be high from the winter to the spring. The ion components, which major ion species contained in sea salt, also tended to be high in the winter, and these components had a strong influence on EC. The d-excess values were high in the winter and low in the summer, and when this trend was considered from the viewpoint of the wind direction data in Hirosaki, these dust components were attributed to the northwest monsoon in the winter to the spring coming from the Asian continent.

DOI： 10.3390/atmos13050848

Scopus

Comparison of Ventilated and Unventilated Air Temperature Measurements in Inland Dronning Maud Land on the East Antarctic Plateau

Morino S., Kurita N., Hirasawa N., Motoyama H., Sugiura K., Lazzara M., Mikolajczyk D., Welhouse L., Keller L., Weidner G.

Journal of Atmospheric and Oceanic Technology 38 巻 ( 12 ) 頁： 2061 - 2070 2021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 Atmospheric and Oceanic Technology

Surface temperature measurements with naturally ventilated (NV) sensors over the Antarctic Plateau are largely subject to systematic errors caused by solar radiative heating. Here we examined the radiative heating error in Dronning Maud Land on the East Antarctic Plateau using both the newly installed automatic weather stations (AWSs) at NDF and Relay Station and the existing AWSs at Relay Station and Dome Fuji. Two types of NV shields were used in these AWSs: a multiplate radiation shield and a simple cylinder-shaped shield. In austral summer, the temperature bias between the force-ventilated (FV) sensor and the NV sensor never reached zero because of continuous sunlight. The hourly mean temperature errors reached up to 8°C at noon on a sunny day with weak wind conditions. The errors increased linearly with increasing reflected shortwave radiation and decreased nonlinearly with increasing wind speed. These features were observed in both the multiplate and the cylinder-shaped shields. The magnitude of the errors of the multiplate shield was much larger than that of the cylinder-shaped shield. To quantify the radiative errors, we applied an existing correction model based on the regression approach and successfully reduced the errors by more than 70% after the correction. This indicates that we can use the corrected temperature data instead of quality controlled data, which removed warm bias during weak winds in inland Dronning Maud Land.

DOI： 10.1175/JTECH-D-21-0107.1

Scopus

Isotope and chemical composition of monthly precipitation collected at Sapporo, northern part of Japan during 2015-2019

Fusion Engineering and Design 168 巻 2021年7月

Climate response of oxygen isotopic compositions in tree-ring cellulose in java: Evaluation using a proxy system model

Atmosphere 12 巻 ( 3 ) 2021年3月

AWSの積雪深計が観測する南極氷床表面堆積量の時間変化査読有り

平沢尚彦、本山秀明、山田恭平、杉浦幸之助、栗田直幸

日本雪氷学会誌雪氷 83 巻 ( 1 ) 頁： 67 - 77 2021年1月

AWSの積雪深計が観測する南極氷床表面堆積量の時間変化

平沢尚彦, 本山秀明, 山田恭平, 杉浦幸之助, 栗田直幸

雪氷 83 巻 ( 1 ) 頁： 67 - 77 2021年

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：公益社団法人日本雪氷学会

超音波積雪深計を搭載したAWS（Automatic Weather Station）を，2016 年1 月から2019 年10 月にかけて4 つの地点に新設した．それらの地点は，海岸域のH128，カタバ風が発達する大陸斜面域のMD78，大陸斜面上部の内陸高地域のNRP，氷床頂上部のNDF である．この観測システムの目的は，広域にわたる南極氷床の地域特性を把握しながら，総観規模擾乱や日変化による堆積の時間変化を明らかにすることである．本論文はこれらの4地点で観測された雪面レベルの時間変動について調べた．その結果以下のことが分かった．1）雪面レベルの時間変化には階段状の変動とパルス状の変動がある．雪面レベルの上昇は主に階段状の上昇によりもたらされる．2）H128 及びNRP の比較によって広域に同時に雪面レベルの変動が表れた4 つの事例が見いだされた．これらの事例では総観規模擾乱に伴う雲域が氷床上に侵入していたことがNOAA の赤外画像から示唆された．3）雪面レベルの比較的大きな変動は異なる地点で同じ日に起こっていないことの方が圧倒的に多い．4）NRP 以外の3地点において，暖候期にゆっくりとした雪面レベルの低下が観測された．

DOI： 10.5331/seppyo.83.1_67

イラン北西部のトラバーチン湧水中のヒ素を含む微量元素の起源解析

金子将己, 淺原良浩, 南雅代, 栗田直幸, Azizi Hossein, Rasouli―Amin Hadi, 張玉博

日本地球化学会年会要旨集 68 巻 ( 0 ) 頁： 125 2021年

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：一般社団法人日本地球化学会

イラン北西部の地域にはジュラ系～白亜系の石灰岩が広く分布するとともに、第三紀〜第四紀に形成されたトラバーチン(石灰岩質沈殿岩)も広く産出する。この地域は第三紀～第四紀の火山活動が活発であり、金属・非金属の鉱床も多く存在する。この地域のトラバーチン湧水(地下水)にはヒ素などの重金属元素を高濃度に含むものがある。生活環境や健康の面からの水質調査が行われているが、この地域のトラバーチン湧水のヒ素を含む様々な溶存元素についての詳細な地球化学的検討はなされていない。本研究では、イラン北西部地域のトラバーチン湧水の溶存元素の起源解析を主要・微量元素の定量分析と同位体分析を利用して行った。その結果、湧水およびその溶存元素は石灰岩から溶解した成分に火山由来の成分が付加して形成されていることが推察された。

DOI： 10.14862/geochemproc.68.0_125

CiNii Research

グリーンランドEGRIP浅層コアの年代決定及び固体粒子解析

小室悠紀, 中澤文男, 東久美子, 平林幹啓, 尾形純, 福田かおり, 栗田直幸, 北村享太郎, 米倉綾香, Popp Trevor J., Dahl-Jensen Dorthe

雪氷研究大会講演要旨集 2021 巻 ( 0 ) 頁： 22 - 22 2021年

Atmospheric factors controlling stable isotope variations in modern precipitation of the tropical region of Bangladesh.

Ahmed N, N. Kurita, Chowdhury MAM, Gao J, Hassan SMQ, Mannan MA, Mallik MAK, Choudhury SA, Bhuiyan MAQ, Karim MM

Isotopes in environmental and health studies 56 巻 ( 3 ) 頁： 220-237 2020年6月

イラン北西部のトラバーチン湧水の同位体地球化学的評価

金子将己, 淺原良浩, 南雅代, 栗田直幸, Hossein Azizi, Hadi Amin-Rasouli, 張玉博

日本地球化学会年会要旨集 67 巻 ( 0 ) 2020年

掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本地球化学会

イラン北西部の地域にはジュラ系～白亜系の石灰岩が広く分布するとともに、第三紀〜第四紀に形成されたトラバーチン(石灰岩質沈殿岩)も広く産出する。この地域は第三紀～第四紀の火山活動が活発であり、金属・非金属の鉱床も多く存在する。この地域のトラバーチン湧水(地下水)にはヒ素などの重金属元素を高濃度に含むものがある。生活環境や健康の面からの水質調査が行われているが、この地域のトラバーチン湧水のヒ素を含む様々な溶存元素についての詳細な地球化学的検討はなされていない。本研究では、イラン北西部地域のトラバーチン湧水の溶存元素の起源解析を主要・微量元素の定量分析と同位体分析を利用して行った。その結果、湧水中のヒ素濃度は、鉄や硫酸濃度との相関関係が見られ、特に火成活動が活発な地域においてヒ素濃度が高いことが明らかとなった。

DOI： 10.14862/geochemproc.67.0_126

Data Descriptor: Daily observations of stable isotope ratios of rainfall in the tropics.

Scientific reports 9 巻 ( 1 ) 頁： 14419 2019年10月

Tritium, hydrogen and oxygen isotope compositions in monthly precipitation samples collected at toki, Japan

Akata N.

Radiation Protection Dosimetry 184 巻 ( 3-4 ) 頁： 338-341 2019年10月

Deciphering key processes controlling rainfall isotopic variability during extreme tropical cyclones.

Nature communications 10 巻 ( 1 ) 頁： 4321 2019年9月

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