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研究者情報

マスター

アカウント（マスター）

  • 氏名

    大木　淳之(オオキ　アツシ), オオキ　アツシ

所属（マスター）

  • 水産科学研究院　海洋生物資源科学部門　海洋環境科学分野

所属（マスター）

  • 水産科学研究院　海洋生物資源科学部門　海洋環境科学分野

独自項目

syllabus

  • 2021, 一般教育演習(ﾌﾚｯｼｭﾏﾝｾﾐﾅｰ), Freshman Seminar, 学士課程, 全学教育, 海洋環境、水圏生態、水産資源、海洋物理学、海洋化学、プランクトン、イカ、耳石
  • 2021, 海洋生物地球化学, Marine Biogeochemistry, 学士課程, 水産学部, 地球化学、海洋化学、生物生産、環境化学
  • 2021, 洋上実習Ⅰ, Field Training on Board Ⅰ, 学士課程, 水産学部, 乗船実習　おしょろ丸　北太平洋西部　流し網　海洋観測　プランクトン　海水分析　サケ　外洋　生態系　目視調査　操船
  • 2021, 化学海洋学, Chemical Oceanography, 学士課程, 水産学部, 栄養塩、基礎生産、物質循環、炭素循環、窒素循環、植物プランクトン、微量金属
  • 2021, 分析化学, Analytical Chemistry, 学士課程, 水産学部, データ処理，環境分析，海水分析，底質分析
  • 2021, 海洋生物科学実験Ⅰ, Marine Science Biology I - Laboratory, 学士課程, 水産学部, 分析化学，環境分析，基礎?産，岩礁海岸の生物相
  • 2021, 環境と人間, Environment and People, 学士課程, 全学教育, 海洋物理，海洋化学、海洋生態系，気候変化，プランクトン，ベントス，カレイ，サケ、深海魚、イカ・タコ類，鯨類，海鳥類，海獣類，衛星海洋学，人間活動，地球温暖化，海洋動物の保全・保護

researchmap

プロフィール情報

学位

  • 博士（理学）（東京大学）

プロフィール情報

  • プロフィール

    1973年埼玉県出身。
    海洋環境を調べる研究をしている。実習船や研究船で野外観測し、実験室にて分析する仕事である。北海道大学水産学部では、海洋生物科学科の教員として主に化学系の授業を受け持っている。


    現在の主な研究テーマは、海洋植物が放出する有機ハロゲンガスの分布に関する研究である。最近は、マコンブ有機物の分解特性を調べている。


    2006年頃までは、大気中の黄砂粒子の動態や海水への溶け具合、大気中粒子の水溶性イオン成分に挙動に関する研究を行っていた。とくに、粒子の粒径分布の特徴を解析するのが好きである。最近は、大気中粒子の仕事はしていないが、大気中オゾンと海水の反応で生成されるヨウ素化合物の研究も（学生任せで）やっている。

    2019年度より、北海道大学の「バランスドオーシャン事業」（https://repun-app.fish.hokudai.ac.jp/）に携わっている。海の分野のオンライン教材を集積して、北大の学生や一般に提供するものである。LASBOS（Learning And Study by Balance de Ocean System）から、オンライン教材を公開している。かなりのコンテンツ数になってきた。SDGsとの関係を記述して、SDGsマッピングの機能を持たせるようにしている。SDGsを軸にして、教育や大学広報にも力を入れている。SDGsの授業では、学生グループ（チーム藻場）が藻場の大事さを訴えていた。これに触発されて、以下、大型藻類の研究に取り組み始めた。

    2022年度より、函館市と北大院水産との共同プロジェクト、函館マリンカルチャープロジェクトにて、サーモン養殖とマコンブ養殖の環境調査を始めている。マコンブ養殖に関係して、マコンブのブルーカーボン効果を調べている。研究を始めたところ、明らかにしなくてはならないことが山ほどあることがわかった。これに真面目に取り組もう。流行りのブルーカーボンに便乗するわけではない。ブルーカーボン研究の問題点が見えてきたから、これを正しい方向に導きたいからである。

    これまで大気、海水、堆積物と色々な研究テーマに取り組んできて、今は、サーモンやコンブである。目の前にある楽しいテーマがあれば、何でもよい。色々なリンクが見えてくるのが楽しいのである。

    趣味は、函館にてゴーヤと椎茸を栽培すること。初夏（7月）の函館は涼しく、北海道の中でもゴーヤ栽培に不向きな場所である。函館の６－７月は親潮の影響で、平均気温が札幌より１℃ほど低い。この１℃の差がゴーヤには致命的である。函館では、ポットで発芽させ、6月中は毎晩家の中に入れ、7月はビニールチューブで育て、８月に大きく成育、9月にようやく収穫できる。2020年には、毎日6本、3か月間、ゴーヤを収穫した。大学内で、同僚教員や学生にゴーヤを配るのに忙しい。（一度でも、「ゴーヤ美味しい」と口を滑らせると、毎週のようにゴーヤが届けられるようになるので要注意）

    当研究室では、海の研究をしたい学生を募集しています。研究室HPを見てください。
    北大水産学部HPからリンクしています。

  • 姓

    大木, オオキ

  • 名

    淳之, アツシ

  • ID各種

    201301090636511285

対象リソース

業績リスト

研究キーワード

  • VOC   ハロカーボン   ブロモホルム   揮発性有機化合物   臭化メチル   海洋起源   揮発性有機ハロゲン化合物   海洋植物プランクトン   ジブロモメタン   海洋大気   混合層   植物プランクトン   大気観測   塩化メチル   生成メカニズム   ヨウ化メチル   海洋観測   

研究分野

  • 環境・農学 / 環境動態解析

経歴

  • 2011年04月 - 現在 北海道大学 水産科学研究科(研究院) 准教授
  • 2006年09月 - 2011年03月 国立研究開発法人国立環境研究所 NIESポスドクフェロー
  • 2006年04月 - 2006年09月 北海道区水産研究所 支援研究員
  • 2003年04月 - 2006年03月 北海道大学 地球環境科学研究科 学振PD

学歴

  • 2000年04月 - 2003年03月   東京大学   理学系研究科   地球惑星科学専攻博士課程
  • 1997年04月 - 1999年03月   東京理科大学   理学研究科   物理学専攻修士課程
  • 1993年04月 - 1997年03月   東京理科大学   理学部   物理学科

論文

  • Sachi Umezawa, Manami Tozawa, Yuichi Nosaka, Daiki Nomura, Hiroji Onishi, Hiroto Abe, Tetsuya Takatsu, Atsushi Ooki
    Biogeosciences 20 2 421 - 438 2023年01月27日 
    Abstract. We conducted repetitive observations in Funka Bay,Hokkaido, Japan, on 15 February, 4 and 15 March, and 14 April 2019. Thediatom spring bloom peaked on 4 March and started declining on 15 March.Funka Bay winter water remained below 30 m depth, which was below thesurface mixed-layer and dark-layer depth (0.1 % of the surface photosynthetically active radiation, PAR, depth) on 4and 15 March. In the subsurface layer at depths of 30–50 m, concentrationsof NO3-, PO43-, and Si(OH)4 decreased by halfbetween these dates, even in the dark. Incubation experiments using thediatom Thalassiosira nordenskioeldii showed that this diatom could consume added nutrients in the dark atsubstantial rates after pre-culturing to deplete nutrients. Incubationexperiments using natural seawater collected in the growing phase of the bloom on 8 March 2022 also showed that nutrient-depleted phytoplankton could consumeadded nutrients in the dark. We excluded three physicalprocess – water mixing, diffusive transport, and subduction – as possible mainreasons for the decrease in nutrients in the subsurface layer. We concludethat the nutrient reduction in the subsurface layer (30–50 m) between 4 and15 March 2019 could be explained by nutrient consumption by diatoms in the dark in thatlayer.
  • H. Abe, Y. Yahiro, T. Hasegawa, T. Hirawake, H. Onishi, A. Ooki, T. Takatsu, K. Sasaki, M. Wakita, H. Kaneko, S. Watanabe, T. Tanaka, T. Okunishi, S. Ohno, S. Hashizume
    Journal of Oceanography 2023年01月09日
  • Takumi Teraoka, Kanako Amei, Yutaka Fukai, Kohei Matsuno, Hiroji Onishi, Atsushi Ooki, Tetsuya Takatsu, Atsushi Yamaguchi
    Plankton and Benthos Research 17 4 369 - 382 2022年11月30日
  • Atsushi Ooki, Keita Minamikawa, Fanxing Meng, Naoya Miyashita, Toru Hirawake, Hiromichi Ueno, Yuichi Nosaka, Tetsuya Takatsu
    Communications Earth & Environment 3 1 2022年08月12日 [査読有り]
     
    Abstract The surface ocean is an important source of longer-lived volatile organic iodine compounds, such as methyl and ethyl iodide. However, their production in deep waters is poorly constrained. Here, we combine shipborne seawater and sediment core analyses to investigate the temporal and vertical distribution of methyl and ethyl iodide concentrations in the Bering and Chukchi Seas in July 2017 and 2018, and Funka Bay, Japan, between March 2018 and December 2019. We find the highest methyl and ethyl iodide concentrations in sediment porewaters and at the sediment surface. In Funka Bay, concentrations in the sediment and bottom waters strongly increased following the spring bloom and subsequent settling of phytodetritus to the seafloor. Dark incubation experiments suggest that diatom aggregates are a source of methyl and ethyl iodide to the ambient water. Our findings suggest that phytodetritus at the seafloor is a potential source of volatile organic iodine compounds to the water column in polar and subpolar coastal oceans.
  • Hyojin Ahn, Yusuke Asano, Shota Suzuki, Atsushi Ooki
    Environmental DNA 4 3 661 - 673 2022年05月 [査読有り][通常論文]
  • Sachi Umezawa, Manami Tozawa, Yuichi Nosaka, Daiki Nomura, Hiroji Onishi, Hiroto Abe, Tetsuya Takatsu, Atsushi Ooki
    2022年01月06日 
    Abstract. We conducted time-series observations in Funka Bay, Hokkaido, Japan, from 15 February to 14 April 2019. The diatom spring bloom peaked on 4 March and started declining on 15 March. Funka Bay winter water remained below 30-m depth, which was below the surface mixed-layer and dark-zone depths on both dates. At depths of 30–50 m, concentrations of NO3–, PO43–, and Si(OH)4 decreased by half between these dates even in darkness. Incubation experiments using the diatom Thalassiosira nordenskioeldii showed that this diatom could consume nutrients in darkness at substantial rates. We conclude that the nutrient reduction in the subsurface layer (30–50 m) could be explained by dark consumption by diatoms that had been growing in the surface waters and then sank to the subsurface layer. We believe that this is the first study to present observational evidence for the consumption of the main nutrients by diatoms in the dark subsurface layer during the spring bloom. Nutrient consumption in this layer might have a substantial influence on the primary production during and after the spring bloom.
  • Atsushi Ooki, Naoya Miyashita, Sachi Umezawa, Manami Tozawa, Yuichi Nosaka, Daiki Nomura, Hiroji Onishi, Hiroto Abe, Tetsuya Takatsu
    GEOCHEMICAL JOURNAL 56 5 142 - 150 2022年
  • Daiki NOMURA, Hiroki IKAWA, Yusuke KAWAGUCHI, Naoya KANNA, Tatsuya KAWAKAMI, Yuichi NOSAKA, Sachi UMEZAWA, Manami TOZAWA, Takahito HORIKAWA, Reishi SAHASHI, Taichi NOSHIRO, Ibuki KABA, Makoto OZAKI, Fumiyoshi KONDO, Keisuke ONO, Itsuka S. YABE, Eun Yae SON, Takahiro TOYODA, Sohiko KAMEYAMA, Changqing WANG, Hajime OBATA, Atsushi OOKI, Hiromichi UENO, Akihide KASAI
    Bulletin of Glaciological Research 40 1 - 17 2022年 [査読有り]
  • Toru Hirawake, Joji Oida, Youhei Yamashita, Hisatomo Waga, Hiroto Abe, Jun Nishioka, Daiki Nomura, Hiromichi Ueno, Atsushi Ooki
    Progress in Oceanography 197 102641 - 102641 2021年09月 [査読有り][通常論文]
     
    The northern Bering Sea (NBS) and southern Chukchi Sea (SCS) contain several water masses with different characteristics that have been conventionally classified using temperature and salinity data. However, recent warming and sea ice decline can change these water properties, which suggests that classifying water masses using temperature–salinity diagrams could be problematic for this region. We used the light absorption coefficient of chromophoric dissolved organic matter (CDOM), aCDOM, as an alternative way to classify water masses. The aCDOM spectra of several water depths were measured in the NBS, the Gulf of Anadyr included, and SCS in July 2017 and 2018, and August 2018. Optical parameters that indicate CDOM quantity and quality, aCDOM(350) and spectral slopes (S275–295 and S350–400), were calculated for each sample; water masses were classified using cluster analysis. When surface waters in the NBS and SCS are classified on the basis of the conventional method using a temperature–salinity diagram, they are mistakenly identified as Alaskan Coastal Water because of warmer temperatures. However, our cluster analysis using CDOM parameters evenly classified seven water masses with reasonable distributions. A water mass with the highest aCDOM(350) and lowest S275–295 was found along the coast of the Gulf of Anadyr and Alaska mainland, which suggests that freshwater originates from the Anadyr and Yukon rivers and is transported by the Anadyr Current and Alaskan Coastal Current, respectively. A CDOM-based water mass with high S275–295, indicating CDOM degradation by ultraviolet radiation, was present at the sea surface. A water mass with low S275–295 was found at deeper water depths and river mouths. These results suggest that classification with CDOM parameters is consistent with geographical features. In addition, we recognized a water mass with high nitrate concentrations, which is likely Anadyr Water that originates in the region from the Bering Slope to the Gulf of Anadyr. Overall, this study reveals that water mass classification using CDOM parameters is useful in coastal sea areas in which water mass mixing is complex.
  • Daiki Nomura, Hiroto Abe, Toru Hirawake, Atsushi Ooki, Youhei Yamashita, Aiko Murayama, Kazuya Ono, Jun Nishioka
    PROGRESS IN OCEANOGRAPHY 196 2021年08月 [査読有り]
     
    We analyzed temperature and salinity data and oxygen isotope ratios (818O) in summer 2018 in order to quantify the formation of dense shelf water (DSW) associated with sea ice freezing in the Gulf of Anadyr in the northwestern Bering Sea. Salinity and 818O displayed a strong linear relationship in samples upstream (southwest) of the Gulf of Anadyr. However, in bottom water (>26.5 00) in the northern Gulf of Anadyr, where a large polynya is the site of high sea ice production in winter, salinity was clearly higher than in the upstream water, whereas 818O was in the same range. This deviation is consistent with the formation of sea ice through brine rejection and subsequent DSW formation, causing an increase of salinity without changing 818O. A mass balance calculation based on these results yielded an estimated production of sea ice equivalent to a thickness 0.7 m, a result that matched an independent estimate of 2018 annual ice production based on satellite data. Even though the winter of 2018 had a historically low sea ice extent in the Bering Sea, including the Gulf of Anadyr, our results indicate continued DSW formation in the Gulf of Anadyr.
  • Ryo Dobashi, Hiromichi Ueno, Yuki Okada, Takahiro Tanaka, Jun Nishioka, Toru Hirawake, Atsushi Ooki, Sachihiko Itoh, Daisuke Hasegawa, Yoshikazu Sasai, Hideharu Sasaki, Ichiro Yasuda
    JOURNAL OF OCEANOGRAPHY 77 2 229 - 242 2021年04月 [査読有り][通常論文]
     
    We conducted a ship observation of two anticyclonic mesoscale eddies (Eddies A and B) between June and July 2016 in the offshore region of the western subarctic North Pacific to clarify the impact of anticyclonic eddies on biological production. Analysis of satellite data reveals that Eddy A formed south of the Alaskan Peninsula on May 2011 while Eddy B formed in the observation area on November 2015. Iron concentration was low both inside and outside Eddies A and B, and there were no large differences between chlorophyll a (chl-a) concentration inside and outside eddies. Satellite-derived chl-a concentration inside Eddy A had been high compared with that in the surrounding area when the eddy was located along the Aleutian Islands and just after it detached from the islands, suggesting that iron originating from the coastal region was consumed during the two-year journey from the coastal region to the observation area. Field measurements also reveal that vertical diffusivity was low both inside and outside Eddies A and B, which could be another factor underlying low iron both inside and outside Eddies A and B and small differences between chl-a concentration inside and outside the eddies.
  • Toru Hirawake, Masaki Uchida, Hiroto Abe, Irene D. Alabia, Tamotsu Hoshino, Shota Masumoto, Akira S. Mori, Jun Nishioka, Bungo Nishizawa, Atsushi Ooki, Akinori Takahashi, Yukiko Tanabe, Motoaki Tojo, Masaharu Tsuji, Hiromichi Ueno, Hisatomo Waga, Yuuki Y. Watanabe, Atsushi Yamaguchi, Youhei Yamashita
    POLAR SCIENCE 27 2021年03月 [査読有り]
     
    Arctic ecosystems are altered profoundly by climate changes. However, the responses of Arctic marine and terrestrial ecosystems as well as their biodiversity to global warming remain largely unknown. This article provides comprehensive insights into the results and major findings from the Arctic Challenge for Sustainability (ArCS) Project ? an Arctic region research program initiated in Japan, which aims to address and advance our understanding of these uncertainties. Marine ecosystem studies have identified several biogeochemical processes that are associated with sea ice decline and northward transport and shift of marine species across multiple trophic levels over the Bering and Chukchi Sea shelves. Studies of the terrestrial ecosystem have identified factors that are important for the understanding of terrestrial biodiversity and ecosystems, including Arctic lakes, under the presence of global warming. Novel fungal species from the Arctic terrestrial ecosystem have also been isolated and described. Overall, these results could contribute to the conservation and sustainable management of the Arctic ecosystem services.
  • Atsushi Yamaguchi, Fumihiko Kimura, Yuri Fukai, Yoshiyuki Abe, Kohei Matsuno, Atsushi Ooki, Toru Hirawake
    POLAR SCIENCE 27 2021年03月 [査読有り]
     
    In the northern Bering Sea, ice coverage and retreat timing were low and early, respectively, in the 2017?2018 winter. To evaluate the effect of these anomalous ice conditions, we quantified various environmental parameters (temperature, salinity, mixed-layer depth, nutrients) and the standing stocks of various planktonic taxa (phytoplankton counts, meso- and macrozooplankton mass, jellyfish abundance) during July of 2017 and 2018. For each year, the interaction between each parameter was evaluated by structural equation modelling (SEM) analysis. Large yearly differences were detected for the interactions between environmental parameters and planktonic stocks. Thus, for 2017, a total of fifteen interactions were present between environmental parameters and various planktonic stocks. In 2018, however, only eight interactions were present. Among the interactions, four were common to the two years. It is notable that the path coefficients of these four interactions were all lower in 2018 than in 2017. These findings suggest that the small magnitude and short pulse of the phytoplankton bloom in 2018 may have failed to transfer production and energy to a higher trophic level even within the planktonic food web. Indeed, in 2018, mass mortality was reported for seabirds (two murre species) feeding on planktivorous fishes.
  • Pat Wongpan, Daiki Nomura, Takenobu Toyota, Tomonori Tanikawa, Klaus M. Meiners, Tomomi Ishino, Tetsuya P. Tamura, Manami Tozawa, Yuichi Nosaka, Toru Hirawake, Atsushi Ooki, Shigeru Aoki
    ANNALS OF GLACIOLOGY 61 83 454 - 463 2020年12月 [査読有り]
     
    Sea ice, which forms in polar and nonpolar areas, transmits light to ice-associated (sympagic) algal communities. To noninvasively study the distribution of sea-ice algae, empirical relations to estimate its biomass from under-ice hyperspectral irradiance have been developed in the Arctic and Antarctica but lack for nonpolar regions. This study examines relationships between normalised difference indices (NDI) calculated from hyperspectral transmittance and sympagic algal biomass in the nonpolar Saroma-ko Lagoon. We analysed physico-biogeochemical properties of snow and land-fast sea ice supporting 27 paired bio-optical measurements along three transects covering an area of over 250 m x 250 m in February 2019. Snow depth (0.08 +/- 0.01 m) and ice-bottom brine volume fraction (0.21 +/- 0.02) showed low (0.06) and high (0.58) correlations with sea-ice core bottom section chlorophyll a (Chl. a), respectively. Spatial analyses unveiled the patch size of sea-ice Chl. a to be similar to 65 m, which is in the same range reported from previous studies. A selected NDI (669, 596 nm) explained 63% of algal biomass variability. This reflects the bio-optical properties and environmental conditions of the lagoon that favour the wavelength pair in the orange/red part of the spectrum and suggests the necessity of a specific bio-optical relationship for Saroma-ko Lagoon.
  • Hiromichi Ueno, Mizuki Komatsu, Zhaoqianyi Ji, Ryo Dobashi, Miaki Muramatsu, Hiroto Abe, Keiri Imai, Atsushi Ooki, Toru Hirawake
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 181 2020年12月 [査読有り]
     
    We investigated spatial and interannual variation in the physical environment in the northern Bering Sea focusing on stratification, which is one factor affecting biological production in Arctic/subarctic regions. In particular, we analyzed in situ data obtained onboard the training ship Oshoro Maru in early summer in 2017 and 2018. We found that stratification in the areas just north of St. Lawrence Island (around 64.5 degrees N and west of 168.5 degrees W) and south/southwest of St. Lawrence Island was significantly weaker in 2018 than in 2017. These results are consistent with the extremely low sea-ice extent present in the winter of 2017/2018, which would have resulted in less freshwater being supplied to the surface layers and a warmer and less saline bottom water. Conversely, stratification was as strong in 2018 as in 2017 in the area close to the Alaska mainland, including the Bering Strait area, suggesting that the Alaskan Coastal Water dominates stratification in this area in early summer. Moreover, we found that the weakly stratified water column in the Bering Strait area stratified quickly shortly after the occurrence of strong northerly winds, likely because of the Ekman transport of warm and low-salinity Alaskan Coastal Water from the east.
  • Daiki NOMURA, Pat WONGPAN, Takenobu TOYOTA, Tomonori TANIKAWA, Yusuke KAWAGUCHI, Takashi ONO, Tomomi ISHINO, Manami TOZAWA, Tetsuya P. TAMURA, Itsuka S. YABE, Eun Yae SON, Frederic VIVIER, Antonio LOURENCO, Marion LEBRUN, Yuichi NOSAKA, Toru HIRAWAKE, Atsushi OOKI, Shigeru AOKI, Brent ELSE, Francois FRIPIAT, Jun INOUE, Martin VANCOPPENOLLE
    Bulletin of Glaciological Research 38 0 1 - 12 2020年 [査読有り][通常論文]
  • 氷河と海氷の融解減少が北極海表層の物質循環過程に与える影響
    野村大樹, 漢那直也, 大木淳之
    地球化学 2020年01月 [査読有り][通常論文]
  • 北極域における臭素および有機硫黄化合物の生物地球化学
    亀山宗彦, 大木淳之, 野村大樹
    地球化学 2020年01月 [査読有り][通常論文]
  • 「北極域の地球化学」特集序文
    大木淳之, 亀山宗彦
    地球化学 53 2020年01月 [査読有り][通常論文]
  • Atsushi Ooki, Ryuta Shida, Masashi Otsu, Hiroji Onishi, Naoto Kobayashi, Takahiro Iida, Daiki Nomura, Kota Suzuki, Hideyoshi Yamaoka, Tetsuya Takatsu
    Journal of Oceanography 75 6 485 - 501 2019年12月 [査読有り][通常論文]
  • Youhei Yamashita, Yuki Yagi, Hiromichi Ueno, Atsushi Ooki, Toru Hirawake
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 124 11 7545 - 7556 2019年11月 [査読有り][通常論文]
     
    Pacific water is an important nutrient source for sustaining biological production in the Chukchi Sea, western Arctic Ocean, which is one of the productive regions in the world. Therefore, to understand the impacts of future environmental changes on biological production in the sea, it is crucial to understand the origins, modification processes, and spatiotemporal variations of the water masses from the Bering Sea with changes in nutrient concentrations. To improve water mass analysis in the shelf regions of the Bering and Chukchi Seas, we observed levels of humic-like fluorescent organic matter (FOMH) by using an in situ fluorometer directly connected to a temperature-salinity sensor during a cruise in the early summer of 2013 and evaluated the potential of FOMH as a third parameter of water mass analysis. The levels of FOMH were different among specific water masses in the region, and FOMH seemed to behave semiconservatively in the shelf regions of the Bering and Chukchi Seas during the early summer of 2013. The distributional pattern of FOMH implies that FOMH estimated by the in situ fluorometer has the potential to (1) separate warm water into riverine-affected Alaskan Coastal Water and historically photobleached summer Bering Basin Water; (2) distinguish the Anadyr Water, which has low FOMH levels and high nutrient concentrations, from the Bering Shelf Water; and (3) determine different formation/modification processes of dense shelf water that contains high nutrient concentrations.
  • Hideyoshi Yamaoka, Tetsuya Takatsu, Kota Suzuki, Naoto Kobayashi, Atsushi Ooki, Mitsuhiro Nakaya
    Fisheries Science 2019年09月 [査読有り][通常論文]
  • Abe, Hiroto, Sampei, Makoto, Hirawake, Toru, Waga, Hisatomo, Nishino, Shigeto, Ooki, Atsushi
    FRONTIERS IN MARINE SCIENCE 6 2019年03月 [査読有り][通常論文]
     
    Bering Strait is the single gateway between the Arctic and Pacific Oceans, and has localized strong currents, which can exceed 100 cm s(-1). Although massive spring phytoplankton blooms and the subsequent production of particulate organic matter that sinks to the seafloor are observed in the surrounding regions of the Bering Strait, the impact of the locally strong current on the horizontal and vertical transport of the particles remains unclear. Therefore, we conducted year-round mooring measurements from 2016 to 2017 by focusing on near-bottom processes associated with ocean currents. Our time-series analysis showed that high-turbidity events, triggered by strong barotropic currents, occurred near the seafloor in all seasons. Consequently, the fluorescence sensor detected highly concentrated chlorophyll a in the resuspended sediment; however, the amount of chlorophyll a release was seasonal, with large and small amounts being released during the warm and cold seasons, respectively. The small amounts of chlorophyll a may be attributed to small amounts of phytoplankton in the sediment owing to less input of fresh phytoplankton from the overlaying water column and organic matter decomposition in the sediments under no-light conditions. The barotropic currents were modulated by surface winds associated with an intercontinental atmospheric pattern having a 5000-km spatial scale on a timescale of 6 days. The locally strong ocean current in the Bering Strait, driving the upward transport of sediment and the subsequent horizontal transport, may play a vital role in supplying particulate organic matter/phytoplankton/nutrients to the downstream region of the southern Chukchi Sea where the formation of biological hotspots is reported.
  • Takafumi Kataoka, Atsushi Ooki, Daiki Nomura
    Microbes and Environments 34 2 215 - 218 2019年 [査読有り][通常論文]
  • Ryohei Sasayama, Nanako Hioki, Yuichiroh Morita, Yutaka Isoda, Keiri Imai, Atsushi Ooki, Kenshi Kuma
    Journal of Oceanography 74 4 1 - 13 2018年02月16日 [査読有り][通常論文]
     
    We studied the behavior of chemical substances in the upper 300 m of the water column across the continental shelf–slope interface in the East China Sea off the Okinawa Trough. The behaviors of iron, inorganic nutrients, and humic-like fluorescent dissolved organic matter were strongly influenced by the extensive water exchange between the East China Sea and the Kuroshio Current across the shelf break and slope via upwelling and frontal processes. We attributed the high humic-like fluorescent intensity at the subsurface of the shelf break and slope regions to the lateral supply of humic-like fluorescent dissolved organic matter from the shelf sediments to the outer shelf region due to the intrusion of shelf water into Kuroshio subsurface water. We found that the behavior of iron at the continental shelf–slope was remarkably different from the conservative mixing of inorganic nutrients and humic-like fluorescent dissolved organic matter. In deep and bottom waters at the shelf–slope, high total iron concentrations, which were closely related to water transmittance, possibly resulted from the swept transport of iron-rich resuspended sediments over the shelf floor from the slope by the invading Kuroshio Intermediate Water close to the bottom.
  • Yuichiroh Morita, Kei Yamagata, Atsuki Oota, Atsushi Ooki, Yutaka Isoda, Kenshi Kuma
    GEOCHIMICA ET COSMOCHIMICA ACTA 215 33 - 50 2017年10月 [査読有り][通常論文]
     
    We studied the seasonal variations in Fe(II), Fe(III), humic-like dissolved organic matter (DOM), nitrate and nitrite (NO3+ NO2), and silicate (Si(OH)(4)) in river waters of three subarctic rivers flowing into Hakodate Bay in southwestern Hok-kaido, Japan from May 2010 to February 2014. High Fe(II) concentrations were detected in winter at the sampling sites where the river bottom was comprised of sandy or silty sediment, primarily the lower and middle reaches of the rivers. Conversely, from early spring to late autumn Fe(II) levels were low or undetectable. We infer that soluble Fe(II) concentration in these subarctic river waters is driven by the balance between the influx of Fe(II) to the river and the Fe(II) oxidation rates that determines the dynamics in Fe(II) concentration in the river water. The Fe(II) may originate from reductive dissolution of Fe(III) in the river sediment or from Fe(II)-bearing groundwater. The latter seems to be the most likely source during winter time. The high Fe(II) concentrations during winter is predominantly attributed to the extremely slow oxidation rate of Fe(II) to Fe(III) at low water temperature rather than to an actual increase in the flux of reduced Fe(II). Nevertheless, we propose that the flux of reduced Fe(II) from river sediments and groundwater in lowland area of the catchment to overlying river waters might be the most important sources of iron in river waters. This provides an important insight into the role of river processes and the interaction between climate and river morphology in determining the inputs of iron to subarctic coastal marine waters. (C) 2017 Elsevier Ltd. All rights reserved.
  • Yusaku Shimizu, Atsushi Ooki, Hiroji Onishi, Tetsuya Takatsu, Seiji Tanaka, Yuta Inagaki, Kota Suzuki, Naoto Kobayashi, Yoshihiko Kamei, Kenshi Kuma
    JOURNAL OF ATMOSPHERIC CHEMISTRY 74 2 205 - 225 2017年06月 [査読有り][通常論文]
     
    Volatile organic iodine compounds (VOIs) emitted from the ocean surface to the air play an important role in atmospheric chemistry. Shipboard observations were conducted in Funka Bay, Hokkaido, Japan, bimonthly or monthly from March 2012 to December 2014, to elucidate the seasonal variations of VOI concentrations in seawater and their sea-to-air iodine fluxes. The bay water exchanges with the open ocean water of the North Pacific twice a year (early spring and autumn). Vertical profiles of CH2I2, CH2ClI, CH3I, and C2H5I concentrations in the bay water were measured bimonthly or monthly within an identified water mass. The VOI concentrations began to increase after early April at the end of the diatom spring bloom, and represented substantial peaks in June or July. The temporal variation of the C2H5I profile, which showed a distinct peak in the bottom layer from April to July, was similar to the PO4 (3-) variation profile. Correlation between C2H5I and PO4 (3-) concentrations (r = 0.93) suggests that C2H5I production was associated with degradation of organic matter deposited on the bottom after the spring bloom. CH2I2 and CH2ClI concentrations increased substantially in the surface and subsurface layers (0-60 m) in June or July resulted in a clear seasonal variation of the sea-to-air iodine flux of the VOIs (high in summer or autumn and low in spring).
  • 大津 将史, 大木 淳之, 野村 大樹
    日本地球化学会年会要旨集 64 230 - 230 一般社団法人日本地球化学会 2017年 

    北海道噴火湾にて、2014-16年に渡り、表面0 mから底層90 mまでの計14層において、計24回の海洋観測を行った。ジブロモメタンCH2Br2、ブロモホルムCHBr3、イソプレンC5H8をパージ&トラップ-ガスクロマトグラフ-質量分析法にて測定した。化合物の濃度は、ブルーム期に低く、ブルームの終焉2ヶ月以上経過後の5-8月に最大濃度を示した(ジブロモメタン：4.3-19.1 pmol L-1, ブロモホルム：13.0-34.0 pmol L-1, イソプレン: 67.8-133.3 pmol L-1)。鉛直分布の極大が表層混合層直下(5月50 m, 8月20 m)に一致して見られ、これは、表面混合による大気放出から免れたことと、混合層直下に存在する植物プランクトンが放出されたものが蓄積されたものと考えられた。

  • Yoshiko Kondo, Hajime. Obata, Nanako Hioki, Atsushi Ooki, Shigeto Nishino, Takashi Kikuchi, Kenshi Kuma
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 116 236 - 252 2016年10月 [査読有り][通常論文]
     
    Distributions of trace metals (Mn, Fe, Ni, Zn and Cd) in the western Arctic Ocean (Chukchi Sea and Canada Basin) in September 2012 were investigated to elucidate the mechanisms behind the transport of these metals from the Chukchi Shelf to the Canada Basin. Filtered (< 0.22 mu m) and unfiltered seawater samples were analyzed to determine dissolved (D) and total dissolvable (TD) trace metal concentrations, respectively. We identified maxima in vertical profiles for the concentrations of D-Fe and TD-Fe, as well as for the other four analyzed trace metals, which occurred in the halocline and/or near-bottom waters. Concentration profiles of all trace metals except for Cd also tended to show peaks near the surface, which suggest that the inflow of low-salinity Pacific-origin water from the Bering Strait, as well as local fresh water inputs such as river water and melting sea-ice, influenced trace metal concentrations. The distribution patterns and concentration ranges were generally similar between the D and TD fractions for Ni, Zn and Cd, which indicate that Ni, Zn and Cd were present mainly in their dissolved forms, whereas the concentrations of TD-Fe and TD-Mn were generally higher than those of D-Fe and D-Mn, respectively. These results are consistent with the results of previous studies of this region. For both Fe and Mn, labile particulate (LP) concentrations (the difference between the TD and D fractions, which is acid-leachable fraction in the particles during storage at pH 1.5-1.6) were highest in the near-bottom waters of the Chukchi Shelf region. The relationships between the distance from the shelf break and the concentrations of trace metals revealed that Fe and Mn concentrations in halocline waters tended to decrease logarithmically with distance, whereas changes in the concentrations of Ni, Zn, Cd and phosphate with distance were small. These results suggest that the distributions of Fe and Mn were controlled mainly by input from shelf sediment and removal through scavenging processes. Based on the phase distributions of Fe and Mn, which were calculated as ratios between the LP and D fractions, different behaviors between Fe and Mn were expressed during lateral transportation. The concentration of TD-Fe declined rapidly via removal of LP-Fe from the water column, whereas the concentration of TD-Mn declined more slowly through the transformation of D-Mn into LP-Mn. In contrast, the concentrations of D-Cd, D-Zn and D-Ni were more strongly correlated with phosphate levels, which suggest that, like phosphate, the distributions of Cd, Zn and Ni were generally controlled by the internal biogeochemical cycles of the ocean interior. Based on the findings of studies that have previously evaluated the concentration maxima of Ni, Zn and Cd within the halocline layer in the Canada Basin near the Canadian Arctic Archipelago, the elevated Ni, Zn and Cd concentrations in the halocline layer may extend across the Canada Basin from the Chukchi Sea shelf-break area. The determination coefficients for correlations with phosphate concentration varied between the concentrations of Ni, Zn and Cd, which suggest that the sources of these trace metals, such as sediments and sea-ice melting, affected their patterns of distributions differently. Our findings reveal the importance and impact of the halocline layer for the transport of trace metals in the western Arctic Ocean during the late summer. The existence of rich and various sources likely sustained the high concentrations of trace metals and their unique profiles in this region. (C) 2016 Elsevier Ltd. All rights reserved.
  • Kazuki Tanaka, Nobuyuki Takesue, Jun Nishioka, Yoshiko Kondo, Atsushi Ooki, Kenshi Kuma, Toru Hirawake, Youhei Yamashita
    SCIENTIFIC REPORTS 6 2016年09月 [査読有り][通常論文]
     
    The spatial distribution of dissolved organic carbon (DOC) concentrations and the optical properties of dissolved organic matter (DOM) determined by ultraviolet-visible absorbance and fluorescence spectroscopy were measured in surface waters of the southern Chukchi Sea, western Arctic Ocean, during the early summer of 2013. Neither the DOC concentration nor the optical parameters of the DOM correlated with salinity. Principal component analysis using the DOM optical parameters clearly separated the DOM sources. A significant linear relationship was evident between the DOC and the principal component score for specific water masses, indicating that a high DOC level was related to a terrigenous source, whereas a low DOC level was related to a marine source. Relationships between the DOC and the principal component scores of the surface waters of the southern Chukchi Sea implied that the major factor controlling the distribution of DOC concentrations was the mixing of plural water masses rather than local production and degradation.
  • A. Ooki, S. Kawasaki, K. Kuma, S. Nishino, T. Kikuchi
    BIOGEOSCIENCES 13 1 133 - 145 2016年 [査読有り][通常論文]
     
    We conducted a shipboard observation over the Chukchi Sea and the Canada Basin in the western Arctic Ocean in September and October 2012 to obtain vertical distributions of four volatile organic iodine compounds (VOIs) in seawater. The VOIs observed in this study were iodomethane (CH3I), iodoethane (C2H5I), diiodomethane (CH2I2), and chloroiodomethane (CH2ClI). Maximum concentrations of the four VOIs were found in the bottom layer water over the Chukchi Sea shelf, in which layer the maximum concentration of ammonium (NH4+) also occurred. A significant correlation was observed between C2H5I and NH4+ (correlation coefficient R = 0.93, P < 0.01, n = 64) and between CH3I and NH4+ (R = 0.77, P < 0.01, n = 64), suggesting that the production of these VOIs increased with the degradation of organic matter. Over the northern Chukchi Sea shelf-slope area, concentration maxima of CH2I2, CH2ClI, and CH3I were found in the subsurface cold, dense water (CDW). A large nitrogen deficit (N deficit = NH4+ + NO3- + NO2- -16PO(4)(3-)) occurred simultaneously in this water, suggesting the production of the three VOIs in the sediment or the bottom layer water over the shelf, probably in association with the degradation of organic matter. We conclude that VOI production over the Chukchi Sea shelf can be largely attributed to the degradation of organic matter that is produced in the highly productive shelf water. High concentrations of CH2ClI were also found in the Alaskan Coastal Water (ACW) from the Bering Strait to the surface of the northern Chukchi slope. The VOIs that originated at the Chukchi Sea shelf are expected to be laterally transported to the Arctic Ocean basin through the CDW and the surface ACW.
  • Nanako Hioki, Kenshi Kuma, Yuichiroh Morita, Daichi Miura, Atsushi Ooki, Seiji Tanaka, Hiroji Onishi, Tetsuya Takatsu, Naoto Kobayashi, Yoshihiko Kamei
    JOURNAL OF OCEANOGRAPHY 71 6 703 - 714 2015年12月 [査読有り][通常論文]
     
    We studied iron remobilization and nutrient regeneration in bottom water of Funka Bay, Japan, bimonthly from August 2010 to December 2011. The bay basin (bottom depth, 92-96 m) is separated from the northwest Pacific Ocean at its mouth by a sill with a depth of 60 m. After a spring phytoplankton bloom during early March-early April, nutrients in bay bottom water tended to accumulate with time until August-September, and to increase gradually with depth during April-October, by the oxidative decomposition of settling particulate organic matter on the bay bottom. In contrast, the process of iron remobilization into bottom water of the bay is remarkably different from nutrient regeneration. The much higher concentrations of dissolved and total dissolvable iron near the bottom and the seasonally variable relationship between dissolved iron concentration and apparent oxygen utilization in bay bottom water likely reflect a balance between dissolved iron input and removal processes within the bay bottom water. The release of soluble Fe(II) from reducing bay sediments might induce the high concentrations of dissolved and total dissolvable iron in deep-bottom waters of Funka Bay and might be one of the most important sources of iron in Funka Bay. The upward transport of iron from the bay bottom to the surface water during the winter vertical mixing may play an important role in the supply of bioavailable iron for phytoplankton growth in the coastal waters.
  • Atsushi Ooki, Daiki Nomura, Shigeto Nishino, Takashi Kikuchi, Yoko Yokouchi
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 120 6 4108 - 4128 2015年06月 [査読有り][通常論文]
     
    Isoprene (C5H8) and three volatile organic iodine compounds (VOIs: CH3I, C2H5I, and CH2ClI) in surface seawater were measured in the western Arctic, Northwest Pacific, Indian, and Southern Oceans during the period 2008-2012. These compounds are believed to play an important role in the marine atmospheric chemistry after their emission. The measurements were performed with high time-resolution (1-6 h intervals) using an online equilibrator gas chromatography mass spectrometer. C5H8 was most abundant in high-productivity transitional waters and eutrophic tropical waters. The chlorophyll-a normalized production rates of C5H8 were high in the warm subtropical and tropical waters, suggesting the existence of a high emitter of C5H8 in the biological community of the warm waters. High concentrations of the three VOIs in highly productive transitional water were attributed to biological productions. For CH3I, the highest concentrations were widely distributed in the basin area of the oligotrophic subtropical NW Pacific, probably due to photochemical production and/or high emission rates from phytoplankton. In contrast, the lowest concentrations of C2H5I in subtropical waters were attributed to photochemical removal. Enhancement of CH2ClI concentrations in the shelf-slope areas of the Chukchi Sea and the transitional waters of the NW Pacific in winter suggested that vertical mixing with subsurface waters by regional upwelling or winter cooling acts to increase the CH2ClI concentrations in surface layer. Sea-air flux calculations revealed that the fluxes of CH2ClI were the highest among the three VOIs in shelf-slope areas; the CH3I flux was highest in basin areas.
  • 清水 悠作, 大木 淳之, 久万 健志, 大西 広二, 亀井 佳彦, 小林 直人
    日本地球化学会年会要旨集 62 89 - 89 一般社団法人日本地球化学会 2015年 
    CH2I2、C2H5Iなど揮発性有機ヨウ素化合物（volatile organoiodine compound:VOI）は、海から大気へヨウ素を供給するキャリアーとして機能する。本研究では、VOIと生物生産性や有機物分解との関係を調べるために、北海道噴火湾で2012年3月から2014年12月の隔月に海水を採取し、海水中VOI濃度をパージ＆トラップ-ガスクロマトグラフ-質量分析法で測定した。
    春季植物プランクトンブルーム終了後の5月以降にVOI濃度は急激に増加し始め、6月から7月に年間ピークに達した。ピーク深度はVOI成分により異なった。このようなピーク深度の違いは、生成メカニズムの違いを示しており、こうした海水中VOIの生成メカニズムの違いは、大気への放出特性にも反映されると考えられる。
  • Nanako Hioki, Kenshi Kuma, Yuichirou Morita, Ryouhei Sasayama, Atsushi Ooki, Yoshiko Kondo, Hajime Obata, Jun Nishioka, Youhei Yamashita, Shigeto Nishino, Takashi Kikuchi, Michio Aoyama
    SCIENTIFIC REPORTS 4 2014年10月 [査読有り][通常論文]
     
    The location and magnitude of oceanic iron sources remain uncertain owing to a scarcity of data, particularly in the Arctic Ocean. The formation of cold, dense water in the subsurface layer of the western Arctic Ocean is a key process in the lateral transport of iron, macronutrients, and other chemical constituents. Here, we present iron, humic-like fluorescent dissolved organic matter, and nutrient concentration data in waters above the continental slope and shelf and along two transects across the shelf-basin interface in the western Arctic Ocean. We detected high concentrations in shelf bottom waters and in a plume that extended in the subsurface cold dense water of the halocline layer in slope and basin regions. At sigma(theta) = 526.5, dissolved Fe, humic-like fluorescence intensity, and nutrient maxima coincided with N* minima (large negative values of N* indicate significant denitrification within shelf sediments). These results suggest that these constituents are supplied from the shelf sediments and then transported laterally to basin regions. Humic dissolved organic matter probably plays the most important role in the subsurface maxima and lateral transport of dissolved Fe in the halocline layer as natural Fe-binding organic ligand.
  • 清水 悠作, 大木 淳之, 久万 健志, 大西 広二, 亀井 佳彦, 小林 直人
    日本地球化学会年会要旨集 61 202 - 202 一般社団法人日本地球化学会 2014年 
    CH2I2などの海水中の揮発性有機ヨウ素化合物(Volatile organoiodine compound；VOI)は、海洋から大気へのヨウ素の主なキャリアーとして知られるが、生成過程などは明らかになっていない。本研究では、VOIと生物生産性や有機物分解との関係を明らかにするため、VOIと生物化学パラメータのモニタリングを行った。北海道噴火湾にて、VOI（CH2I2、CH3I、CH2ClI）濃度や、生物科学パラメータの定点測定を、2012年3月から2014年6月まで行った。春季の植物プランクトンブルームが終焉し、植物プランクトンが老化、死滅する時期に、VOIが多量に生成されることがわかった。CH2I2増分が2013年は2012年の半分であったことより、VOI生成量には経年差がみられた。
  • 近藤 能子, 小畑 元, 大木 淳之, 山下 洋平, 西岡 純, 久万 健志
    日本地球化学会年会要旨集 61 199 - 199 日本地球化学会 2014年 
    過酸化水素は、大気中ではその酸性度を高める物質として、海水中では微量金属の酸化還元反応や溶存有機物の循環および微生物群集の生物生産に影響を与える因子として重要な物質である。海水中の過酸化水素のソースとシンクは光化学反応や生物活動と密接に関わるためその挙動は動的で一様ではない。これまで、海洋における過酸化水素の分布は外洋域・沿岸域様々な海域で報告されているが、北極海におけるデータは限られている。本発表では、これまでの海洋における過酸化水素の分布動態に関するレビューを含め、GRENE北極海研究プロジェクト（http://www.nipr.ac.jp/grene/）の一環として2013年夏期に実施された北海道大学練習船おしょろ丸航海で得られた北極海（チャクチ海）における過酸化水素の分布について紹介する。
  • 野村 大樹, 西岡 純, 川合 美千代, 大木 淳之, 田村 岳史
    日本地球化学会年会要旨集 61 132 - 132 日本地球化学会 2014年 
    我が国におけるこれまでの海氷研究は、主に物理過程を明らかにすることに主眼が置かれ、海氷の物理的動態を実測や衛星観測、モデリングから明らかにする研究が精力的に進められてきた。一方で、海氷に関わる化学過程や生物過程に関しては、これまで十分な研究が展開されていなかった。海氷の生成が生み出す独特の海洋循環を介して、他海域の物質循環にまで多大な影響を与えているシステムの存在が指摘されており、これらのシステムを理解するためには、海氷の存在する時期から消失していくまでの詳細な時系列観測、ポリニヤにおける海氷の生成が起こっている現場での観測が欠かせない。また、地球規模で起こっている環境変動を理解するためには、通年観測する必要があり、海洋研究プラットフォームを生物地球化学分野で最大限活用すると同時に、厳冬期でも観測が続けられる本格的な観測研究用の砕氷船が欠かせないだろう。
  • 大木淳之
    化学工業 64 7 516 - 523 小峰工業出版 2013年07月 [査読無し][通常論文]
  • 大木淳之
    分析化学 62 12 1071 - 1078 2013年 [査読有り][通常論文]
     
    A shipboard observation was conducted in Funka Bay of Hokkaido from October 2011 to August 2012. Volatile organic halogenated compounds (halocarbons) in seawater collected at coastal, basin and sea shore sampling sites were measured by purge and trap GC-MS method. The spatial and temporal distributions of bromoform (CHBr3) were obtained, and we analyzed the origin of the compound. The minimum concentration of bromoform (15 pmol L< sup> -1< /sup> ) was found in December. The bromoform concentration in the basin area increased from 20 pmol L< sup> -1< /sup> to 25 pmol L< sup> -1< /sup> at a rate of 5 pmol L< sup> -1< /sup> month< sup> -1< /sup> during the phytoplankton spring bloom period (March-April). This increase would have been derived from the phytoplankton production of bromoform. The concentration increased from April to August at a rate of 4 pmol L< sup> -1< /sup> month< sup> -1< /sup> , and the maximum concentration of 42 pmol L< sup> -1< /sup> in basin area was found in August. Much higher concentrations were found in the coastal area (125 pmol L< sup> -1< /sup> ) and the sea shore (up to 1800 pmol L< sup> -1< /sup> ). The late summer bromoform maximum found in the basin area would be derived from macro algal production near the sea shore. © 2013 The Japan Society for Analytical Chemistry.
  • Daiki Nomura, Atsushi Ooki, Daisuke Simizu, Mitsuo Fukuchi
    ANTARCTIC SCIENCE 23 6 623 - 628 2011年12月 [査読有り][通常論文]
     
    Bromoform concentrations in water of the slush layer that developed at the interface between snow and sea ice were measured during the seasonal warming in Lutzow-Holm Bay, East Antarctica. Mean bromoform concentration was 5.5 +/- 2.4 pmol l(-1), which was lower than that of the under-ice water (10.9 +/- 3.5 pmol l(-1)). Temporal decrease in bromoform concentrations and salinity with increasing temperature of the slush water suggest that the bromoform concentrations were reduced through dilution with meltwater input from the upper surface of sea ice. In contrast, bromoform concentrations in the under-ice water increased during this period while the salinity of the under-ice water decreased. It is speculated that the sea ice meltwater input contained high bromoform concentrations from the brine channels within the sea ice and from the bottom of the ice that were contributed to the increased bromoform concentrations in the under-ice water.
  • Atsushi Ooki, Yoko Yokouchi
    MARINE CHEMISTRY 124 1-4 119 - 124 2011年03月 [査読有り][通常論文]
     
    We measured partial pressures of CH2Cl2 (dichloromethane) and CCl3F (CFC-11) in air and surface seawater of the Indian and Southern Oceans from November 2009 to January 2010. The excess CH2Cl2 saturation anomaly (Delta SA(CH2Cl2)>0) in surface seawater between 10 degrees S and 40 degrees S, which is the corrected value of saturation anomaly after subtracting the effects of summertime sea-surface temperature increase and of summertime decrease of atmospheric CH2Cl2 level, provides evidence for in-situ production of CH2Cl2. Depth profiles from the South Indian Ocean at 5 degrees S, 20 degrees S and 30 degrees S showed concentration maxima of dihalomethanes (CH(2)l(2), CH(2)Cll and CH2Cl2) and chlorophyll-a in the subsurface layer (20-150 m). Our data suggest that phytoplankton production of dihalomethanes leads to concentration maxima in the subsurface layer and Delta SA(CH2Cl2)>0 in surface seawater between 10 degrees S and 40 degrees S. The average oceanic emission of CH2Cl2 derived from the region between 10 degrees S and 40 degrees S in the South Indian Ocean was calculated to be 0.29-0.43 mu g m(-2) d(-1). (C) 2011 Elsevier B.V. All rights reserved.
  • Yoko Yokouchi, Takuya Saito, Atsushi Ooki, Hitoshi Mukai
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 116 2011年03月 [査読有り][通常論文]
     
    Four iodocarbons, chloroiodomethane (CH2ClI), diiodomethane (CH2I2), methyl iodide (CH3I), and ethyl iodide (C2H5I), were measured with an automated preconcentration gas chromatography-mass spectrometry system at two remote marine sites, Hateruma Island (24.05 degrees N, 123.8 degrees E) in the East China Sea and Cape Ochiishi (43.15 degrees N, 145.5 degrees E) on the eastern coast of Hokkaido, for 17 months, giving the first full-year high-frequency data sets for all these compounds. CH2ClI and CH2I2, which are highly photolyzed, showed remarkable diurnal variation in all seasons, with lower concentrations in the daytime, whereas CH3I and C2H5I showed no significant diurnal changes. At Cape Ochiishi, all of the iodocarbons showed clear seasonal variations and were highest in summer and autumn, which are characterized by algal blooms in the adjacent ocean. At Hateruma Island, which is surrounded by subtropical oligotrophic waters, the seasonal variations were not significant, but C2H5I and CH2I2 showed lower mixing ratios in summer. The nighttime mixing ratio of CH2ClI was strongly and positively correlated with wind speed throughout the observation period at Hateruma Island, suggesting the ubiquitous presence of CH2ClI sources, probably nonbiogenic, in the subtropical ocean. CH3I and C2H5I mixing ratios occasionally increased at Hateruma Island concurrently with winter and spring pollution events from the Asian continent, indicating possible continental anthropogenic sources or emissions from seawater off the continental coast. A rise in the CH3I baseline mixing ratio was also observed at Hateruma Island, when the air mass origin became more southerly, compared with the earlier, easterly source area, suggesting higher concentrations in equatorial regions.
  • Y. Morino, T. Ohara, Y. Yokouchi, A. Ooki
    Journal of Geophysical Research Atmospheres 116 2 2010JD014762  2011年 [査読有り][通常論文]
     
    Source contributions of volatile organic compounds (VOCs) were comprehensively evaluated using an observational data set, two receptor models, and an emission inventory. Hourly concentrations of C< inf> 2< /inf> -C< inf> 8< /inf> nonmethane hydrocarbons (NMHCs) were measured at Saitama, which is near the northern edge of Tokyo, throughout 2007. Estimates of background NMHC concentrations at the Saitama site corresponded well with median NMHC concentrations at a remote island in Japan in winter and spring. Source contributions of ΔNMHCs (differences between ambient and background concentrations) calculated by the chemical mass balance (CMB) model and positive matrix factorization (PMF) corresponded with each other within a factor of 2. The two receptor models estimated that vehicle exhaust, gasoline vapor, liquefied natural gas and liquefied petroleum gas (LPG), and other evaporative sources contributed 14%-25%, 9%-16%, 7%-10%, and 49%-71%, respectively, to total VOC concentrations on a mass basis. These values agreed with the emission inventory except for the LPG values. In addition, the CMB and PMF results explained at least two thirds of the observed total ΔNMHC values. These results suggest that the current emission inventory roughly captures the individual contributions and total amount of VOC emissions. However, characterization of background NMHCs is necessary to fully understand the VOC budget. Copyright 2011 by the American Geophysical Union.
  • Atsushi Ooki, Yoko Yokouchi
    GEOCHEMICAL JOURNAL 45 6 E1 - E7 2011年 [査読有り][通常論文]
     
    The sea-to-air flux of C2H5I (iodoethane) in the Indian Ocean and the Southern Ocean was estimated from the Henry's law constant (K-H) and the measured partial pressures of C2H5I in surface seawater and air. The values of K-H, defined as the ratio of molar concentration (mol l(-1)) to partial pressure (atm), for ten volatile organic compounds (VOCs) (CFCl3 (CFC-11), C5H8 (isoprene), C2H2F4 (HFC-134a), CHF2Cl (HCFC-22), CH3I, CH2Br2, C2H5I, CH2Cl2, CH2ClI, and CHBr3) were measured with an equilibrator and a purge-and-trap system in combination with gas chromatography-mass spectrometry. Ours is the first report of the K-H values for C2H5I and C5H8 as functions of temperature. The K-H values for the other VOCs were in good agreement with previously reported values. We calculated the sea-to-air flux of C2H5I using the newly determined K-H. Large sea-to-air fluxes (average, 0.04 nmol m(-2)h(-1)) were widespread in the Southern Ocean. We suggest that high biological productivity led to a high rate of C2H5I production in the subpolar water, and that the strong winds that frequently blow over the Southern Ocean resulted in the large sea-to-air flux.
  • 大木 淳之, 横内 陽子
    日本地球化学会年会要旨集 58 270 - 270 日本地球化学会 2011年 
    2008年1月～2010年6月に北光丸(HK08-1)、白鳳丸(KH-08-2、KH-09-5、KH-10-1)、淡青丸(KT-09-5)で北西太平洋と南北インド洋で揮発性の有機ヨウ素化合物のフラックス測定を行った。夏季の亜寒帯・亜熱帯はCH3IのフラックスがCH2ClIの10倍以上に達した。いっぽう、春季ブルーム域、秋～冬季の亜熱帯・亜寒帯域ではCH2ClIの寄与が大きくなる傾向が見られた。海水中のCH2ClIは紫外線で分解するので、夏場の表層では濃度が低下する。それに伴い、亜表層にはCH2ClIの濃度極大が形成される。冬場の鉛直混合により亜表層に蓄積されたCH2ClIが表層にもたらされて、大気に放出されることが推測された。
  • Sohiko Kameyama, Hiroshi Tanimoto, Satoshi Inomata, Urumu Tsunogai, Atsushi Ooki, Shigenobu Takeda, Hajime Obata, Atsushi Tsuda, Mitsuo Uematsu
    MARINE CHEMISTRY 122 1-4 59 - 73 2010年10月 [査読有り][通常論文]
     
    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. (C) 2010 Elsevier B.V. All rights reserved.
  • M. K. Kurihara, M. Kimura, Y. Iwamoto, Y. Narita, A. Ooki, Y. J. Eum, A. Tsuda, K. Suzuki, Y. Tani, Y. Yokouchi, M. Uematsu, S. Hashimoto
    Marine Chemistry 118 3-4 156 - 170 2010年02月28日 [査読有り][通常論文]
     
    Biogenic trace gases, especially halomethanes, which are important with respect to atmospheric chemistry, are released from the ocean and carry halogens to the troposphere and stratosphere. The concentrations of 10 halocarbons and isoprene in seawater were measured during the spring of 2007 in the western North Pacific Ocean (37-43° N, 143-146° E). Sea-air fluxes of CH3Cl, CH3Br, CH2ClI, and CH2I2 were also estimated based upon the atmospheric as well as oceanic measurement of these species. Temperature-salinity scatter diagram analyses divided the sampling stations into the Oyashio region, Tsugaru warm current region, and Kuroshio region. Mean (range) concentrations of the gases in the water columns (5-100 m) were 114 (56-150) pmol L- 1 CH3Cl, 6.9 (4.1-19.4) pmol L- 1 CH3Br, 1.7 (0.7-2.9) pmol L- 1 CH3I, 1.9 (0.9-4.1) pmol L- 1 CH2BrCl, 4.8 (3.2-8.1) pmol L- 1 CH2Br2, 1.0 (0.6-1.8) pmol L- 1 CHBrCl2, 1.2 (0.7-2.0) pmol L- 1 CHBr2Cl, 10.8 (4.7-24.5) pmol L- 1 CHBr3, 1.7 (0.7-5.4) pmol L- 1 CH2ClI, 3.0 (< 0.1-22.2) pmol L- 1 CH2I2, and 19.7 (3.8-68.2) pmol L- 1 isoprene. The maximum concentration of isoprene was observed in the Oyashio region, where concentrations of chlorophyll a (maximum: 2.94 μg L- 1) were highest in the present study. However, the peaks of CH3Br, CH2ClI, and CH2I2 were observed in the Tsugaru warm current region, where concentrations of chlorophyll a were not as high (maximum: 0.65 μg L- 1). The results of chlorophyll a size fractionation showed a high occurrence of halomethanes in the stations dominated by pico-sized phytoplankton. These results indicate the importance of picoplankton as a possible source of halocarbon production. Chlorophyll b and prasinoxanthin had a statistically significant positive correlation with CH2I2 (r2 = 0.69 and r2 = 0.71, respectively) and with CH2ClI (r2 = 0.87 and r2 = 0.77, respectively). These results suggest that some species of prasinophytes might contribute to CH2I2 and CH2ClI production. For other compounds, there was no peak in the vertical profile in seawater. In the depth profiles, the peak of CH2ClI was observed above the peak of CH2I2; these profiles suggest that a photochemical reaction could yield CH2ClI from CH2I2 in seawater. The mean mixing ratio and range of CH3Cl, CH3Br, and CH2ClI in the air were measured as 548 (524-609), 12.1 (8.6-19.0), and 0.27 (0.03-0.90) pptv, respectively. CH2I2 was not detected in the atmosphere (< 1 pptv). The saturation anomaly of CH3Br was positive at all stations (the sea surface temperature varied from 1.7 °C to 19 °C). The highest mixing ratio of CH2ClI in air was also observed near the station at which the highest concentration of CH2ClI was observed in seawater; the sea-to-air fluxes of CH2ClI and CH2I2 were 3.8 and 1.6 nmol m- 2 day- 1, respectively. These results suggest that the production of CH2ClI and CH2I2 in seawater is an important source of organic iodine compounds in the remote atmosphere. © 2009 Elsevier B.V. All rights reserved.
  • Atsushi Ooki, Atsushi Tsuda, Sohiko Kameyama, Shigenobu Takeda, Sachihiko Itoh, Toshio Suga, Hirofumi Tazoe, Ayako Okubo, Yoko Yokouchi
    Journal of Geophysical Research: Oceans 115 10 2010年 [査読有り][通常論文]
     
    The partial pressures of methyl halides (CH3X X = Cl, Br, or I) and of CHClF2 (HCFC-22), which are all volatile organic compounds (VOCs), were measured in the air of the marine boundary layer (pVOC air) and in surface seawater (pVOCwater) during a cruise from the subarctic to subtropical regions of the northwest Pacific in summer of 2008. In the northern transition water (TWN) with high biological activity, high levels of the three CH3Xs in surface seawater were frequently observed, probably owing to their enhanced production by phytoplankton. Supersaturation of CH3Br was only present in TW N water, with a saturation anomaly (SCH3Br) of 0.95 [SCH3X = (pCH3Xwater - pCH3X air)/pCH3Xair]. The highest saturation anomalies for CH3Cl (SCH3Cl = 1.6) and CH3I (SCH3I = 91) were found in the southern subtropical water (ST S) with low biological production south of the subtropical front. We found that the molar concentrations of CH3Cl (CCH3Cl) and CH3I (CCH3I) sharply increased with increasing sea surface temperature (SST) in the subtropical waters. The maximum CCH3Cl (144 pmol l-1) was present in STS water at SST = 30°C and is 1.5 times the value extrapolated from the previously reported relationship between CCH3Cl and SST. Photochemical production might have contributed to the production of CH3Cl and CH3I in ST S water. Copyright 2010 by the American Geophysical Union.
  • Sohiko Kameyama, Hiroshi Tanimoto, Satoshi Inomata, Urumu Tsunogai, Atsushi Ooki, Yoko Yokouchi, Shigenobu Takeda, Hajime Obata, Mitsuo Uematsu
    ANALYTICAL CHEMISTRY 81 21 9021 - 9026 2009年11月 [査読有り][通常論文]
     
    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.
  • Atsushi Ooki, Jun Nishioka, Tsuneo Ono, Shinichiro Noriki
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 114 2009年02月 [査読有り][通常論文]
     
    Asian mineral dust was sampled at Hokkaido, northern Japan, in spring 2004 and 2006. Iron solubility of the bulk aerosol, the size-segregated aerosol (0.45 < D < 11 mu m), the snow containing a lot of mineral dust, and a simulated Asian dust standard (CJ-2) were measured by an iron dissolution experiment using a newly developed continuous leaching method. The iron solubility of the bulk aerosol samples was 1.2-2.2%. Within the 1.1 < D < 11 mu m size range, iron solubility (0.52-8.2%) was higher in the smaller fractions of the size-segregated aerosol samples. We considered that the preferential removal of larger mineral dust particles from the air by snow resulted in the low iron solubility of the snow samples. Iron solubility of mineral dust was relatively lower in the 4.7 < D < 11 mu m fraction of the size-segregated aerosol samples (0.52%), in the snow samples (0.20-0.57%), and in the CJ-2 standard (0.33%), which are dominated by large size particles (D > 4.7 mu m). We suggest that an iron solubility of around 0.4% is typical for Asian mineral dust of large particles transported to Hokkaido. In the high-nutrient low-chlorophyll region of the western subarctic North Pacific near the Asian continent, where the mineral dust deposition is dominated by large particles, the iron solubility of the mineral dust entering the ocean is around 0.4%.
  • 大木 淳之, 横内 陽子
    日本地球化学会年会要旨集 56 325 - 325 日本地球化学会 2009年 
    2008～2009年（冬、春、夏）に北西太平洋の親潮-黒潮混合域で大気と海水中の臭素系ハロカーボン分圧の測定を行った。１月に北海道沿岸で海水中のブロモホルム分圧が上昇したのは大型藻類に由来すると考えられる。春季ブルーム時期の５月は外洋域で海水中の分圧が比較的高く、これは植物プランクトンに由来すると考えられる。また、５月は海水に比べて大気中のブロモホルム分圧の方が高かった。表面海水中のブロモホルム分圧の高い海洋上を大気が長距離輸送された結果と考えられる。
  • Atsushi Ooki, Yoko Yokouchi
    ENVIRONMENTAL SCIENCE & TECHNOLOGY 42 15 5706 - 5711 2008年08月 [査読有り][通常論文]
     
    Methods for determining volatile organic compounds (VOCs) in water and air are required so that the VOCs' fluxes in water environments can be estimated. We developed a silicone membrane tube equilibrator for collecting gas-phase samples containing VOCs at equilibrium with natural water. The equilibrator consists of six silicone tubes housed in a polyvinyl chloride pipe. Equilibrated air samples collected from the equilibrator were analyzed with an automated preconcentration gas chromatography-mass spectrometry system for hourly measurements of VOC partial pressures. The partial pressures of all the target VOCs reached equilibrium within 1 h in the equilibrator. The system was used to determine VOC partial pressures in Lake Kasumigaura, a shallow eutrophic lake with a high concentration of suspended particulate matter (SPM). Compressed air was used daily to remove SPM deposited on the inner wall of the equilibrator and to maintain the equilibrium conditions for more than a week without the need to shut the system down. CH(2)Br(2), CHCl(3), CHBrCl(2), CH(2)BrCl, C(2)H(5)l, C(2)Cl(4), CH(3)l and CH(3)Br in the lake were supersaturated with respect to the air, whereas CH(3)Cl was undersaturated. CHCl(3) had the highest flux (6.2 nmol m(-2) hr(-1)) during the observation period.
  • 大木 淳之, 横内 陽子
    日本地球化学会年会要旨集 55 313 - 313 日本地球化学会 2008年 
    大気中の揮発性有機化合物（VOC）は主要な反応性微量気体であり、様々な大気化学反応にかかわっている。大気中で長寿命（＞0.5年）と短寿命（＜0.5年）のハロカーボンは成層圏と対流圏（及び下部成層圏）のオゾンを破壊することがいわれている。短寿命ハロカーボンの多くは海洋の大型藻類や植物プランクトンが主要起源であること、長寿命ハロカーボンのうち塩化メチルと臭化メチルについては陸上や海洋の生物が生成・消滅過程に関与していることが考えられている。本研究では、西部北太平洋亜寒帯におけるハロカーボンの動態とフラックスの特徴を明らかにするため、大気と表面海水中のハロカーボン分圧を連続測定した。表層海水中のハロカーボンを４グループに分け、それらの動態を特徴付けることができた。
  • Atsushi Ooki, Mitsuo Uematsu, Shinichiro Noriki
    ATMOSPHERIC ENVIRONMENT 41 1 81 - 91 2007年01月 [査読有り][通常論文]
     
    Marine background levels of non-sea-salt- (nss-) SO(4)(2-) (5.0-9.7 neq m(-3)), NH(4)(+) (2.1-4.4 neq m(-3)) and elemental carbon (EC) (40-80 ngC m(-3)) in aerosol samples were measured over the equatorial and South Pacific during a cruise by the R/V Hakuho-maru from November 2001 to March 2002. High concentrations of nss-SO(4)(2-) (47-94 neq m-(3)), NH(4)(+) (35-94 neq m(-3)) and EC (130-460 ngC m(-3)) were found in the western North Pacific near the coast of the Asian continent under the influence of the Asian winter monsoon. Particle size distributions of ionic components showed that the equivalent concentrations of nss-SO(4)(2-) were balanced with those of NH(4)(+) in the size range of 0.06 < D < 0.22 mu m, whereas the concentration ratios of NH(4)(+) to nss-SO(4)(2-) in the size range of D > 0.22 mu m were decreased with increase in particle size. We estimated the source contributions of those aerosol components in the marine background air over the equatorial and South Pacific. Biomass burning accounted for the large fraction (80-98% in weight) of EC and the minor fraction (2-4% in weight) of nss-SO(4)(2-). Marine biogenic source accounted for several tens percents of NH(4)(+) and nss-SO(4)(2-). In the accumulation mode, 70% of particle number existed in the size range of 0.1 < D < 0.2 mu m. In the size rage of 0.06 < D < 0.22 mu m, the dominant aerosol component of (NH(4))(2)SO(4) would be mainly derived from the marine biogenic sources. (c) 2006 Elsevier Ltd. All rights reserved.
  • Atsushi Ooki, Mitsuo Uematsu
    Journal of Geophysical Research D: Atmospheres 110 3 1 - 13 2005年02月16日 [査読有り][通常論文]
     
    Acid gas reactions during the passage from the source regions to the western North Pacific modify the chemical characteristics of Asian mineral dust particles as they pass through heavily industrial regions. We conducted aerosol samplings to investigate the interaction of mineral dust particles with acid gases in the western North Pacific region during the high-dust season. The concentration peaks of NO3 - and mineral dust particles were in the coarse mode range (D > 1.25 μm) in all aerosol samples, while non-sea-salt-(nss)-SO42- had an apparent peak in the coarse mode range only in an Asian dust event that experienced rain. Nitrate was the dominant acid substance associated with the mineral dust particles rather than nss-S)42-. In the urban air of Tokyo we also conducted an in situ experiment to react ambient acid gases with mineral dust particle loaded on a filter. The in situ experiment indicated that HNO3 had reacted with mineral dust particles much more efficiently than SO2 had. HNO3 (+NO2) and HCI accounted for large fractions (48% and 40%) of acid gases that reacted with mineral dust particles, while SO2 accounted for a small fraction (12%). The high adsorption of HNO3 on mineral dust particles would change their surface properties from hydrophobic to hygroscopic and form an efficient mechanism to remove nitrogen compounds to the ocean surface layer. Copyright 2005 by the American Geophysical Union.
  • 永尾一平, 宇山悠紀子, 大木淳之, 植松光夫
    Journal of Aerosol Research 19 2 122 - 127 日本エアロゾル学会 2004年 [査読有り][通常論文]
     
    In order to study the chemical composition of marine aerosol and an impact caused by the primary production in spring season, aerosol sampling and measurement of dimethylsulfide (DMS) concentration were carried out on board of R/V Mirai during MR01-K02 cruise from May 14 to 28 2001.
    Based on the relationship between in-situ seawater DMS concentration and chlorophyll-a (CHL-a) estimated from satellite, amount of DMS emitted from the sea surface is estimated along the way of air parcel.
    MSA concentration observed on May 25 and 27 was about 2∼3 times higher than the average MSA concentration of this cruise. This enhancement is supposed to be due to a large amount of DMS supplied from high CHL-a area during an air parcel transport.
    Besides, nss-Ca2+ concentration between May 18 and 20 was about 3∼4 times higher than the average concentration of this cruise. Trajectory analysis and other approaches such as analysis of physical properties of aerosols in this period showed that Kosa particles were observed in the atmospheric marine boundary layer.
    An influence of Kosa particles on the marine production and succeeding sulfur emission should be explored.
  • A Ooki, K Miura, M Uematsu
    JOURNAL OF OCEANOGRAPHY 59 6 799 - 807 2003年12月 [査読有り][通常論文]
     
    During a cruise aboard the R/V Hakuho-maru in the northwestern North Pacific in the summer of 1998 the particle number concentrations and the major ionic components of size fractionated aerosols were measured to investigate the aerosol produced by marine biological activity. Continuous low concentrations of nitrate (<1.8 nmol m(-3)), similar to the marine air background level, were found over the northwestern North Pacific (40-45degreesN) and the Sea of Okhotsk (44-45'N). Over the Sea of Okhotsk, a high concentration of chlorophyll-a (5.4 mg m(-3)) in seawater was observed, and atmospheric concentrations of non sea-salt (nss-)sulfate (44 nmol m(-3)), methane sulfonic acid (MSA) (1.8 nmol m(-3)) and particle number in the size range of 0.1 < D < 0.5 mum (199 cm(-3)) were found to be 9, 7, and 2 times, respectively, higher than those in the background marine air. The increase in particle number concentrations mainly in the size range of 0.2 < D < 0.3 mum was likely caused by the increase of biogenic sulfate over the high productive region of the Sea of Okhotsk. In humid air conditions (R.H. > 96%), the increased biogenic sulfate that condensed the large amount of water vapor would not have sufficient solute mass to activate as cloud condensation nuclei (CNN) and would remain as aerosol particles in the marine air with frequent sea-fogs over the high productive region. Biogenic sulfate originating from dimethyl sulfide (DMS) would gradually grow into the CCN size and continuously supply a great number of CCN to the marine air in the northwestern North Pacific.
  • 大木 淳之
    地球化学 37 3 155 - 155 日本地球化学会 2003年08月 [査読無し][通常論文]
  • SASAKAWA M, OOKI A, UEMATSU M
    J Geophys Res 108 D3 AAC13.1-AAC13.9  2003年02月 [査読有り][通常論文]
  • A Ooki, M Uematsu, K Miura, S Nakae
    ATMOSPHERIC ENVIRONMENT 36 27 4367 - 4374 2002年09月 [査読有り][通常論文]
     
    Concentrations of size fractionated particulate sodium and potassium were measured in both marine and urban air. Marine air sampling was conducted during a cruise on R/V Hakuho-maru in the northwestern North Pacific in the summer of 1998. Urban air sampling was performed in the central part of Tokyo in 1997 and 1998. The fine sodium concentration (D < 1.1 mum) in "Urban" air (180 ng m(-3)) was 3 times higher than that in "Marine" air (56 ng m(-3)). In the urban air samples, the size distributions of sodium and potassium showed bimodal peaks in the fine particle range (D < 1.1 mum) and in the coarse particle range (D > 1.1 mum). The existence of anthropogenic sodium in the fine particle range was detected in the urban air. The K/Na weight ratios in the fine particle range of the urban air (1.8-2.7) was 50-75 times higher than that in seawater (0.036). Potassium in the urban air is thought to be derived largely from anthropogenic sources. In the urban air samples, a high correlation between fine sodium and fine potassium concentrations suggests that they have the same anthropogenic source. Reevaluating the K/Na ratios in marine air to be relatively higher than that in seawater, we can estimate that several percents of anthropogenic sodium can be transported from land to remote marine air. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • K Aranami, S Watanabe, S Tsunogai, A Ohki, K Miura, H Kojima
    JOURNAL OF ATMOSPHERIC CHEMISTRY 41 1 49 - 66 2002年01月 [査読有り][通常論文]
     
    Dimethylsulfide (DMS) in surface seawater and the air, methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO42-) in aerosol, and radon-222 (Rn-222) were measured in the northern North Pacific, including the Bering Sea, during summer (13 July - 6 September 1997). The mean atmospheric DMS concentrations in the eastern region (21.0 +/- 5.8 nmole/m(3) (mean +/- S.D.), n = 30) and Bering Sea (19.9 +/- 9.8 nmole/m(3), n = 10) were higher than that in the western region (11.1 +/- 6.4 nmole/m(3), n = 31) (p<0.05), although these regions did not significantly differ in the mean DMS concentration in surface seawater. Mean sea-to-air DMS flux in the eastern region (21.0 +/- 10.4 mu mole/m(2)/day, n = 19) was larger than those in the western region (11.3 +/- 16.9 mu mole /m(2)/day, n = 22) and Bering Sea (11.2 +/- 7.8 mu mole/m(2)/day, n = 7) (p < 0.05). This suggests that the longitudinal difference in atmospheric DMS was produced by that in DMS flux owing to wind speed, while the possible causes of the higher DMS concentrations in the Bering Sea include (1) later DMS oxidation rates, (2) lower heights of the marine boundary layer, and (3) more inactive convection. The mean MSA concentrations in the eastern region (1.18 +/- 0.84 nmole/m(3), n = 35) and Bering Sea (1.17 +/- 0.87 nmole/m(3), n = 13) were higher than that in the western region (0.49 +/- 0.25 nmole/m(3), n = 28) (p < 0.05). Thus the distribution of MSA was similar to that of DMS, while the nss-SO42- concentrations were higher near the continent. This suggests that nss-SO42- concentrations were regionally influenced by anthropogenic sulfur input, because the distribution of nss-SO42- was similar to that of Rn-222 used as a tracer of continental air masses.

MISC

講演・口頭発表等

所属学協会

  • 日本分析化学会   日本地球化学会   日本海洋学会   

Works（作品等）

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2022年06月 -2025年03月 
    代表者 : 大木 淳之, 野坂 裕一, 亀山 宗彦, 野村 大樹
     
    北海道噴火湾で珪藻が大増殖する春先に、有光層の直下（無光層）にて、海水中の栄養塩が減る現象が捉えられた。北海道噴火湾の珪藻ブルーム時に採取した海水に栄養塩を添加したところ、暗所でも栄養塩が急速に消費されることがわかった。有光層で栄養不足に陥った珪藻が無光層に沈降して、無光層に豊富にある栄養塩を吸収することが考えられた。珪藻ブルームで見られるタラシオシラ・ノルデンスキオルディの無菌培養株を培地で増殖させ、培地中の栄養塩が枯渇したのを確認してから、栄養塩（硝酸イオン、リン酸イオン、ケイ酸）を添加、暗所に移す暗所培養実験を行った。すると、暗所に置いてから３日ほどで、硝酸イオン、リン酸イオン、ケイ酸が枯渇した。暗所にて、珪藻が栄養塩を吸収することが確認された。同様の実験にて、過剰量の栄養塩を添加したところ、硝酸イオンとリン酸イオンの暗所での取り込みは数日で終わった。しかし、ケイ酸については暗所での培養期間中（１１日間）、取り込みが続いた。暗所で栄養塩を吸収させた後、再び明所に置いて増殖する能力があるかを確かめた。１１日間暗所に置いた後では、増殖を確認することができなかった。暗所に置いた時点で、栄養塩枯渇のため死滅しつつあった可能性、暗所で吸収した栄養塩では再増殖に使えない可能性が考えられた。珪藻が浮力を保つ方法として、透明細胞外重合粒子（TEP）を放出することを想定している。自然海水中および培養海水中のTEP濃度を測定する手法を確立した。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 野村 大樹, 薮下 彰啓, 山下 洋平, 大木 淳之
     
    高緯度海域に分布する海氷は、地球規模の気候変動を制御する要因として大きな役割を担っている。従来、海氷は、物質循環の観点において大気と海洋間の「障壁」として認識されてきた。しかし、実際、海氷表面では、結氷による濃縮効果によって溶存物質が高濃度化し、大気に対して放出源になることが予想される。ただ、極域の厳しい環境での観測の難しさにより、海氷表面での「低温化学」に関する反応機構の解明に至っていない。本研究では、自然界で起こる結氷現象を室内でのチャンバー実験で再現し、有機臭素ガス、特にブロモホルムに関して、海氷表面での化学反応機構・大気への放出過程を明らかにすることが目的である。本課題は、極域大気中オゾン濃度の急激な減少を招く有機臭素ガスの発生源が特定されていないことから設定した。本研究で提唱する海氷表面でのブロモホルム生成は、有機臭素ガスの大気への新たな発生源の提案となり、長年謎とされてきた大気中オゾン消失現象の原因解明に一石を投じることとなる。しかし、これまでの応募者らによる観測事実と低温環境での化学反応の新たな知見により、反応仮説を提唱するに至ったが、反応機構は検証されていない。そこで本年度は、チャンバー実験を実施し、本研究の解明に向けてのデータの採取を行った。具体的には、購入したチャンバーを利用した化学反応実験、また、室内での結氷および積雪を再現し、ブロモホルム生成に関する室内実験を実施した。また、これまでの観測データの解析を実施した。これらの解析を実施することにより、当初の目的に向けて順調に研究が進んでいる状況にある。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2016年04月 -2021年03月 
    代表者 : 大木 淳之, 野村 大樹
     
    北海道噴火湾では、春の珪藻ブルームの後、海底付近の海水中でヨードエタンの濃度が高まる現象が発見されていた。有機ヨウ素化合物が海底堆積物から発生すると考え、海洋堆積物の観測を始めた。 噴火湾の堆積物の表面では、春の珪藻ブルーム中から、ヨードエタンとヨードメタンの濃度高まることがわかった。ブルーム期間にプランクトンネットで珪藻凝集物を集め、ガラス瓶に密封して冷暗所に置いた。すると、３日目から、ガラス瓶内でヨードエタンの濃度が高くなることが確認された。珪藻凝集物から、ヨードエタンとヨードメタンが発生することを明らかにした。珪藻の無菌株を使った培養実験でも同様の結果を得ることができた。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2016年04月 -2018年03月 
    代表者 : 大木 淳之
     
    H28年度に実施した海洋観測にて、北太平洋亜寒帯循環域で海洋表面から水深300mの海水を鉛直的に採取し光分解性を有する有機ガス濃度を測定した。さらに、分光放射照度と鉛直拡散係数の測定を行った。H29年度には、光分解性を有する有機ヨウ素ガス種（ジヨードメタンとクロロヨードメタン）の鉛直プロファイルを再現するモデル（光分解と光生成、鉛直輸送、微生物による正味の生成を考慮）を構築した。ジヨードメタンのモデル結果では、微生物による生成に対して、表層混合層内での光分解が卓越するため、混合層内の濃度がモデル開始から数時間内にゼロに収束してしまった。混合層内でのジヨードメタンの濃度を実測値に保つには、日中のみ、ジヨードメタンの光分解を補償するだけの未知の生成過程が存在しなくてはならない。つまり、ジヨードメタンが光分解すると同時に、その減少分を補うだけ光生成していることが示唆された。H29年度の研究では、ジヨードメタンの光生成過程を調べる実験も行ったが、その実験的証拠を得るには至らなかった。そこで、ジヨードメタンの濃度を保つメカニズムは不明のままとして、その濃度が定常状態に保たれていることを仮定し、クロロヨードメタンの鉛直分布モデルを構築した。クロロヨードメタンモデルにおいては、ジヨードメタンの光分解に起因するクロロヨードメタンの光生成の項を加えた（過去の知見を引用）。クロロヨードメタンの光生成項を加えないと、ジヨードメタンと同様に表層での光分解が卓越して表層水中の濃度が速やかにゼロに収束してしまったが、光生成項を加えると実際の濃度をよく再現するモデル結果が得られた。クロロヨードメタンの鉛直プロファイルは、光生成と光分解、鉛直混合により決まることが明らかとなった。これにより、クロロヨードメタンの濃度、光生成と光分解を得れば、鉛直混合を読み解く道筋をつけることができた。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 飯田 高大, 田村 岳史, 茂木 正人, 大木 淳之, 野村 大樹
     
    本研究では、南極海の氷縁域において、海洋生態系と化学物質循環を総合的に観測するプロジェクトを立ち上げ、豪州が代表の砕氷船を用いた国際共同観測に参画する。近年、南極の季節海氷域における生態系変動が化学物質循環のパターンを変え、地球環境変化に大きな影響を及ぼす可能性が指摘されている。しかし、南極域へのアクセスは気象・海況条件が厳しいため現地観測データは乏しく、その影響を評価するにはほど遠い。そこで、地球温暖化の影響が顕著に表れつつある季節海氷域に特化して、海氷融解の物理環境変化がもたらす植物・動物プランクトン群集の変動を解析し、生態系変動により引き起こされる化学物質循環の変化を明らかにし、全球規模での環境応答を予測する。本年度（平成27年度）は、これまで我々が海氷観測のプラットフォーム及び観測サイトとして利用してきた巡視船そうやとサロマ湖において、以下の予備的調査観測を実施した。また、海洋生態系における海氷の役割を解明する目的で、東京海洋大学海鷹丸を用いて南極海季節海氷域において海洋観測を実施した。 1. 巡視船そうや航海観測: オホーツク海の海氷監視にあたる巡視船そうやに乗船し、外洋域の海氷を採取した。海氷中の化学成分、植物及び動物プランクトンの種類同定用サンプルを採取した。現在、分析・解析を実施している。 2. サロマ湖現地観測: 南極海の海氷上での海氷採取作業等を想定し、掘削機器の動作試験と取扱法の習熟、海氷サンプルの採取を行った。オーストリアから訪問した共同研究者とともに本観測を実施した。 3. 南極海での海洋観測：東京海洋大学海鷹丸で、平成28年1月に南極海の南緯60度から65度、東経110度付近において海洋観測を実施した。観測項目は各種ネットによるプランクトン・魚類の採集、海氷の採取、水温・塩分である。現在、分析・解析を実施している。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2012年04月 -2016年03月 
    代表者 : 大木 淳之
     
    メチル基にハロゲンが一つ結合した化合物をモノハロメタンという。対流圏や成層圏のオゾンを破壊する効果をもち、海洋はモノハロメタン発生源の一つと考えられている。本研究では、海洋のモノハロメタン分布を調査した。北極海のチャクチ海陸棚上では、底層水中でモノハロメタン３成分の濃度が高くなった。北海道噴火湾では、有機物分解が進行する時期に中層にてブロモメタンとクロロメタンの濃度が極大を示した。植物プランクトンの培養実験により、対数増殖期にはモノハロメタンの生成は無かったが、定常期から老化・死滅期に生成が確認された。モノハロメタン生成には、植物プランクトンの老化や有機物分解が関与していることが考えられた。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2010年 -2011年 
    代表者 : 大木 淳之, 横内 陽子
     
    北西太平洋の混合域北部(40-42°N, 145-160°E)で表面海水中の臭素系ハロカーボン(CH_3Br, CH_2Br_2, CHBr_3)が高濃度になる現象を捉えた。また、30°Nでは亜表層に顕著な濃度極大が見られたのに対して、45°Nでは表層から亜表層にかけて一様な鉛直分布が見られた。臭素系ハロカーボンの水平・鉛直分布の特徴は、混合層の形成過程、大気への放出、植物プランクトンによる生成のバランスで決まることが考えられた。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2006年 -2010年 
    代表者 : 横内 陽子, 橋本 伸哉, 伊藤 伸哉, 大木 淳之
     
    海洋から大気中に放出されるハロカーボンについてグローバルな大気観測および北西太平洋と南北インド洋における海水中ハロカーボン連続観測によってそれらの分布と変動を明らかにした。また、植物プランクトンの培養実験により、ハロカーボンがクリプト藻やラン藻の培養後期(減少期)に生成されることを示し、さらに、海産性微細藻類の生物学的なヨウ化メチルの生成機構がハライドイオン・チオールメチルトランスフェラーゼ(HTMT)反応に起因することを明らかにすると共に遺伝子の単離にも成功した。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2003年 -2005年 
    代表者 : 大木 淳之
     
    大気から地表面へ沈着する鉱物粒子の粒径分布と粒径別鉱物粒子の鉄溶出率を測定した。大気エアロゾルを海水に抽出して鉄溶出率を測定する手法を確立し、人為起源エアロゾルの鉄溶出率を測定した。 1.粒径別鉱物粒子の鉄溶出率 2001年3月11日に大規模な黄砂現象を北海道札幌市で観測した。大気境界層上部に位置する手稲山頂で積雪中の黄砂粒子を集めた。黄砂粒子を沈降法で1

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