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Watanabe Yutaka

Faculty of Environmental Earth Science　Earth System Science　Marine and Atmospheric GeochemistrySpecially Appointed Associate Professor

Researcher basic information

■ Degree
  • 博士（水産学）, 北海道大学
■ URL
researchmap URLホームページURL■ Various IDs
J-Global ID■ Research Keywords and Fields
Research Keyword
  • 南大洋
  • 地球環境化学
  • 化学海洋学
  • 地球化学
Research Field
  • Environmental Science/Agriculture Science, Environmental dynamic analysis
■ Educational Organization

Research activity information

■ Awards
  • 2003, 2002年度日本海洋学会日高論文賞授賞
    Japan
  • 1997, 1996年度日本海洋学会岡田賞授賞
    Japan
  • 1994, 1993年度日本海洋学会日高論文賞授賞
    Japan
■ Papers
■ Other Activities and Achievements
■ Syllabus
  • 化学海洋学特論, 2024年, 修士課程, 環境科学院
  • 海洋生物地球化学特論, 2024年, 修士課程, 環境科学院
  • 環境と人間, 2024年, 学士課程, 全学教育
■ Affiliated academic society
  • 日本分析化学会
  • 第四紀学会
  • 日本地球化学会
  • 日本海洋学会
  • 日本気象学会
  • American Geophysical Union
■ Research Themes
  • Development of parameterization techniques for next-generation Southern Ocean oceanographic observations
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)
    Apr. 2022 - Mar. 2027
    渡辺 豊
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (S), Hokkaido University, 22H05003
  • 東南極における氷床－海氷－海洋システムの地域特性の解明
    科学研究費助成事業
    05 Apr. 2021 - 31 Mar. 2026
    田村 岳史; 草原 和弥; 溝端 浩平; 平野 大輔; 野村 大樹; 巻 俊宏; 渡辺 豊
    白瀬氷河底面融解量と外洋からの熱供給との比較
    白瀬氷河が存在するリュツォ・ホルム湾で取得した海洋観測データの解析から明らかにした白瀬氷河―海洋相互作用に関する研究結果を、海洋―海氷―棚氷結合モデルによる実験結果と比較・統合し、顕著な季節変動を伴う年間を通じた白瀬氷河舌の底面融解プロセスを明らかにした。海洋―海氷―棚氷結合モデルによる実験結果からは、中層での海流の変動が、沖合の暖水のLH湾湾内への流入の変動の決め手となっている事が示唆された。さらにこの数値モデルの結果からは、LH湾で卓越する存在である沿岸定着氷の存在が、大気海洋間の熱交換を遮断して海氷生成を抑制し、これが沖合から白瀬氷河への暖水流入をより強くする（又は暖かいままにしてたどり着く）要因を作っている事が明らかになった。衛星観測、海洋観測、測地観測、数値モデル結果は全て、白瀬氷河の高い底面融解率を示している。
    ケープダンレー周辺域での海氷生産と外洋からの熱供給との比較
    ケープダンレー周辺域において、顕著な海氷後退が海面での熱貯留を増やし、東風によりアメリ―棚氷下へ押し込まれると同時に棚氷底面を融解させて、ケープダンレー沖の暖水化・淡水化をもたらす一連の過程が現場観測により捉えられた。このケープダンレーからの底層水流出を数値実験で再現するうえで、観測に基づく詳細な現実地形を考慮することが、流出量の絶対値に大きく影響することが明らかになった。
    このように、交付申請書に記載した「研究の目的」及び「研究実施計画」について、上記のように直接的に研究目的に対して成果を上げる事となった。
    日本学術振興会, 基盤研究(A), 国立極地研究所, 21H04931
  • Quasi-real-time dynamics of ocean anthropogenic CO2 in the coastal Southern Ocean
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Apr. 2020 - Mar. 2022
    渡辺 豊
    全海水の40％を占める南極底層水は熱と物質の巨大な貯留槽であり、この底層水形成域である南大洋でのCO2の取り込み量は全球の気候や生態系変動を大きく支配する。南大洋縁辺部で、南極底層水に大気から取り込まれる人為起源CO2は海洋吸収量の40%にもなると推定されているが、飽和平衡量に到達する前（非平衡）に海洋内部へと沈み込み、その非平衡量は30%までになるとの予測もある。しかし、観測を基盤としてこの非平衡量を確かめるには至っていない。その最大の理由は、海洋のCO2吸収を把握するための炭酸系物質（全炭酸：DIC、アルカリ度：Alk、pH)の測定が他の観測成分に比べて煩雑であること、さらに、海洋観測船を基盤とせざるを得ない制約条件によりデータ数が時空間的に疎であるためである。このため、南極底層水への人為起源CO2取り込み量は正確に未だ分かっておらず、全球的な気候変動予測の大きなボトルネックとなっている。
    本申請では「南極底層水に人為起源CO2はどのくらい取り込まれているのか」という最大の問いに答えるために、2020年度は以下の項目を実施した。(1)南大洋縁辺部における炭酸系物質のパラメタリゼーション（炭酸系物質の関数化：DIC, Alk, pH = f (T, S, DO, Pr); T・S・DO・Prによる炭酸系物質の関数化）の開発を行い、高精度なパラメタリゼーションの開発に成功し、これを基盤に南大洋における炭酸系物質の大気海洋間の非平衡量のパラメタリゼーション化も成功した。(2)同海域の既存海洋水理データ群に適用することで、南大洋縁辺域も含めた南緯30度以南の南大洋における全炭酸物質の時空間高解像度なマッピングに成功した。(3)これらを基盤に、南大洋縁辺部に現在展開されている約200個の自動海洋観測ロボットに応用し、南大洋縁辺域の人為起源二酸化炭素濃度の詳細な分布に着手した。
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Hokkaido University, 20H04962
  • Development of a method for predicting the dynamics of ocean acidification in the coastal regions of Japan
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Apr. 2019 - Mar. 2022
    Imai Keiri
    We aimed to develop a parameterization of pH (pH = f (salinity, oxygen, chlorophyll-a, etc.)) that can be applied to the Japanese coastal regions to predict the temporal and spatial changes and magnitude of ocean acidification in the coastal waters of Japan. Since a large amount of pH data is required to understand the dynamics of ocean acidification in coastal waters with large environmental variability, we improved the surface seawater monitoring system equipped with the Oshoro Maru of Hokkaido University, which makes several cruises per year to the Japanese coastal regions (off the coast of Hokkaido and Tohoku), to enable continuous multi-item data acquisition. The system has been improved to enable continuous data acquisition of multiple items.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, Coinvestigator, 19K12292
  • Spatiotemporal high-resolution mapping for ocean carbon system in the Southern Ocean
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Apr. 2018 - Mar. 2021
    Watanabe Yutaka
    In order to answer the question, "How is ocean acidification progressing in the Southern Ocean now?", we developed the parameterization of carbonate species (DIC, Alk, pH) and nitrates in the Southern Ocean, and clarified the detailed distributions of carbonate species and nitrates in the Southern Ocean in quasi-real time. These results indicate that ocean acidification in the Southern Ocean is progressing at a rate of 0.004 pH/year, which is twice as fast as the average for the entire ocean, and that anthropogenic CO2 uptake in the Southern Ocean is responsible for absorbing as much as 40% of the whole ocean.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Hokkaido University, Principal investigator, 18H04131
  • Quasi-real time and high-resolution spatiotemporal distribution of ocean carbon species
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Apr. 2015 - Mar. 2018
    WATANABE Yutaka
    In order to clarify how ocean carbon cycle changes spatiotemporally, we developed the analytical technique for ocean carbon species (alkalinity, dissolved inorganic carbon, pH) along with making parameterization of ocean carbon species in the North Pacific.
    Applying our parameterization to high precision hydrographic data set, we had the detailed spatiotemporal distributions of ocean carbon species in the North Pacific. Additionally, we found out the long-term trend of anthropogenic ocean acidification with -0.002 pH/year over the entire ocean.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, Principal investigator, 15H02799
  • Transfer and accumulation of radioactive material in marine ecosystem
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Jun. 2012 - Mar. 2017
    Kanda Jota; MORIYA Shigeharu; KOBAYASHI Takuya; YOSHIMURA Takeshi; ISHIMARU Takashi; IGARASHI Satoshi; SUGA Jiro; YAMAKAWA Hiroshi; OTSU Hideaki; ITO Yukari; TAKAZAWA Nobue; UCHIYAMA Kaori; KUBO Atshushi
    Radioactive material derived from the Fukushima Daiichi Nuclear Power Plant accident was investigated in marine ecosystem. 1) For radioactive cesium in marine organisms and environment in the coastal area of Fukushima, we obtained a continuous time-series data set by ship observations twice a year. Time-series data set for radioactive cesium in zooplankton was also obtained in several open ocean areas. 2) Examinations of transfer routes of radioactive cesium in coastal rocky seafloor revealed that transition of radioactive cesium from suspended or descending particles, and from organic fraction of sediments was small. 3) Using the on-site observation data, the transition of radioactive cesium in the ecosystem was reproduced by a numerical model, and the model was applied to prediction of the future trend of the radioactivity level of marine organisms.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Tokyo University of Marine Science and Technology, Coinvestigator, 24110005
  • Simultaneous estimation method of denitrification and nitrogen fixation in sea water
    Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    Apr. 2013 - Mar. 2015
    WATANABE Yutaka
    The aims of this study were to develop the high precise and simultaneous method for dissolved nitrogen and argon in the ocean, and to evaluate the oceanic amount of denitrification and nitrogen fixation by using the new approach. Using the above approaches, we found that the generation rate of dinitrification in the Sea of Okhotsk was over 7 micromole/kg/year despite no nitrogen fixation, and it significantly contributed to the oceanic nitrogen cycle in the North Pacific.
    Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Hokkaido University, Principal investigator, 25550004
  • Elucidation of thermohaline/biogeochemical circulation systems connecting the Sea of Okhotsk with subarctic North Pacific Ocean
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)
    Apr. 2010 - Mar. 2015
    WAKATSUCHI Masaaki; MITSUDERA Humio; NISHIOKA Jun; NAKAMURA Tomohiro; EBUCHI Naoto; WATANABE Yutaka; SUZUKI Koji; KURODA Hiroshi; OHSHIMA Keiichiro; TSUMUNE Daisuke; MATOBA Sumito
    We investigated the thermohaline/biogeochemical circulation systems, connecting the Sea of Okhotsk with the North Pacific, to elucidate a ‘miraculous mechanism’ that supports abundant fisheries resources in the Okhotsk and Oyashio regions. Salinity of the dense shelf water (DSW) over the northern shelf of the Okhotsk Sea controls the strength of the thermohaline circulation of the North Pacific Ocean. DSW salinity is determined by relative contribution among the salinity anomaly that propagates long distance from the subarctic gyre, freshwater anomaly by precipitation, and saline water anomaly rejected during sea ice formation. DSW entrains nutrients such as iron, originating in the Amur River and deposited over the continental shelf, and spreads these materials to the North Pacific Ocean. This study has revealed an exquisite thermohaline-biogeochemical system coupled through DSW and tidal mixing, which controls primary production in the large area of the subarctic North Pacific.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (S), Hokkaido University, Coinvestigator, 22221001
  • The feedback system of gas exchange in the ocean
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    2010 - 2012
    WATANABE Yutaka; NISHIOKA Jun; SAKAOKA Keiichiro; YOSHIKAWA Hisayuki; MINAMI Hideki; ONO Tsuneo
    ：In order to clarify how the nitrogen and carbon cycles in the ocean change spatiotemporally, we carried out the developments of the new estimations about these changes with a new sampling system. Applying the new estimations with the new sampling system to ocean observation, we had significant distributions of spatiotemporal distributions of nitrogen and carbon parameters in the North Pacific and the global ocean, indicating a possibility that we can obtain the detailed spatiotemporal distributions of change in ocean biogeochemical cycles.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Hokkaido University, Principal investigator, 22241001
  • Direct observations of tidal mixing and studies on ocean/climate variability synchronized with 18.6-year period nodal tidal cycle
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)
    2008 - 2012
    YASUDA Ichiro; HASUMI Hiroyasu; KOMATSU Kosei; NISHIOKA Jun; WATANABE Yutaka; NAKATSUKA Takeshi; ITOH Sachihiko; TATEBE Hiroaki; KATSUMATA Katsurou; NAKAMURA Tomohiro; HIROE Yutaka; OSAFUNE Satoshi; TANAKA Yuki; IKEYA Tohru; NISHIKAWA Haruka; TOMOSADA Akira
    Intense tide-induced turbulent mixing that reached deep ocean around the Kuril or Aleutian Straits was observationally evidenced. This strong vertical mixing affects marine ecosystem in the subarctic North Pacific through circulations of nutrients such as iron. Furthermore, observations and climate model experiments revealed that oceanic variations originated from the 18.6-year period modulation of the tidal mixing in those regions are amplified by air-sea interactions such as SST east of Japan and the Aleutian Low Pressure system and regulate bi-decadal climate and ocean variations.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (S), The University of Tokyo, Coinvestigator, 20221002
  • Precise estimation for oceanic uptake rate of anthropogenic carbon in the ocean
    Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    2010 - 2011
    WATANABE Yutaka
    The aims of this study were to develop the high precise method forδ^<13> C in the oceanic dissolved inorganic carbon, and to evaluate the oceanic uptake rate of anthropogenic carbon by using the newδ^<13> C approach. Using this approach withδ^<13> C data set, we found that the uptake rate of anthropogenic carbon in the North Pacific high-latitudinal region was 1. 2 times higher than the expected value derived from oceanic equilibration with increasing atmospheric carbon dioxide.
    Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Hokkaido University, Principal investigator, 22651002
  • Long-term changes of greenhouse gases in the ocean and their feedback effects on the climate
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas
    2006 - 2010
    WATANABE Yutaka; YASUDA Ichiro; TSURUSHIMA Nobuo
    In order to clarify the long-term climate change in the North Pacific, we carried out the comprehensive ocean observations with physical-biological-chemical systems. Based on these observations, we had significant quantifications of ocean biogeochmical cycles with the parameterizations of greenhouse gases in this region. In addition, we could reconstruct the long-term climate change in this region by using improved ocean circulation models.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Priority Areas, Hokkaido University, Principal investigator, 18067002
  • Linkages in Biogeochemical Cycles Between Surface Ocean and Lower Atmosphere
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas
    2006 - 2010
    UEMATSU Mitsuo; YOKOUCHI Yoko; WATANABE Yutaka; TAKEDA Shigenobu; YAMANAKA Yasuhiro; TSUDA Atsushi
    The general management group (X00) of the W-PASS project coordinated to clarify the scientific direction of the four research divisions. The X00 group planned and proposed the intensive island observation campaigns and research cruises. Annual plenary meeting for all project members, meetings for principle investigators and advisory committee members were periodically held and discussed how to manage the project activities. The four working groups (WGs) were established to collaborate among the activities of four divisions (i.e., WG for intensive atmospheric observation campaign at Hedo Cape, WG for evaluation of typhoon impacts, WG for long term variability of marine ecosystems, and WG for eddy covariance technique). It functioned quite well to make vivid discussions and to find new approaches for our goals. Over 20 sessions and workshops were organized for presenting our scientific accomplishments during the national and international symposium and society meetings. Young scientists and students to present their study in abroad were encouraged and supported to cover their travel expenses. To this end, 12 grad students earned their PhD degrees under this project. Newsletters were annually published and the W-PASS webpage was popular to the community.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Priority Areas, The University of Tokyo, Coinvestigator, 18067009
  • 窒素とアルゴンとラジウムを用いた高確度な海水中の脱窒速度決定法の開発に関する研究
    Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    2008 - 2009
    渡辺 豊
    H21年度は、以下の項目を実施した。
    実海域における実証試験の実施
    生物生産が高く脱窒の起こっている外洋の親潮海域ならびにオホーツク海において、広域範囲にわたる窒素、アルゴンとラジウムの高頻度サンプリングを実施した。H20年度に完成した方法(海水中の窒素の過剰量と、ラジウムによる海水の滞留時間を組み合わせた方法)を用いて、窒素、アルゴンとラジウムに基づく脱窒速度の見積りと、これまでに定性的であるがよく用いられてきた脱窒の指標N^*を比較したところ、外洋域においては時空間的に有意の差がなく、よく一致していることを明らかとした。
    さらに、この方法に基づき、親潮域をバックグラウンドとし、オホーツク海との窒素過剰量の差を取るとともに、ラジウムから推定されるオホーツク海の滞留時間を組み合わせて、オホーツク海の全域の脱窒速度の平均場を求めた。その結果、オホーツク海の全脱窒速度は約0.39～1.02T mol/年であり、世界で最も大きな脱窒海域アラビア海の2.92T mol/年に次ぐほどの大きな脱窒海域であることを定量化し、北太平洋の窒素循環に大きな影響を与えていることを明らかとした。このことは、今後の温暖化によって、オホーツク海の窒素変動が北太平洋の窒素循環に多大なインパクトを与える可能性をも示唆した。
    この結果は、2010年3月に行われた日本海洋学会で発表し、その内容を査読付英文学術雑誌に投稿するため現在執筆中で、近日中に投稿する予定である。
    Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Hokkaido University, Principal investigator, 20651001
  • Feedback mechanisms between the polar regions as indicators of global change and subpolar areas
    Grants-in-Aid for Scientific Research
    2007 - 2009
    IKEDA Motoyoshi; WATANABE Yutaka; WATANABE Masahiro; SUGIMOTO Atsuko; MINOBE Shoshiro; SASAI Yoshikazu
    The investigation was carried out for exploring important processes for climate change in the polar ocean and atmosphere as well as atmosphere-ocean interactions and bio-geochemical systems. Under the global change, the key findings include the deteriorating carbon cycle associated with reduction both in marine ecosystem production and boreal forests. These results were reported at the international symposia of Hokkaido University in 2008 and 2009.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Hokkaido University, 19201001
  • Iron behavior and sources regulating primary production in marginal seas (Bering Sea, Okhotsk Sea, Japan Sea)
    Grants-in-Aid for Scientific Research
    2006 - 2009
    KUMA Kenshi; SAITOH Seiichi; ISODA Yutaka; NAGAO Seiya; NAKATSUKA Takeshi; SUZUKI Koji; WATANABE yutaka; NISHIOKA Jun
    Surface mixed layer of the basin region in the Bering Sea is under a typical iron-deficient and nutrient-rich condition with low primary production because of low atmospheric iron input. However, phytoplankton bloom (Breen Belt) is observed at the shelf break region of the Southeastern Bering Sea for a long period in summer. It is suggested that the Green Belt is maintained by the supply of nutrient-rich basin water and iron-rich shelf deep water to the surface water of the shelf break. The tidal mixing in the straits of the Kuril Islands is an important role on supplying nutrient and iron to the surface water of the northwestern North Pacific Ocean and maintaining the high primary production in the Oyashio region. On the contrary, the surface mixed layer in the Japan Sea is characterized by low nutrient and high iron concentrations, resulting from high atmospheric iron input to nutrient-depleted surface water of the Japan Sea close to the Asian continent.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Hokkaido University, 18201001
  • 千島列島・アリューシャン列島付近潮汐混合の実態解明と北太平洋海洋・気候変動
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    2008 - 2008
    安田 一郎; 小松 幸生; 渡辺 豊; 中塚 武
    淡青丸KT-08-7次研究航海(2008年4月23日~5月7日)において、伝導度-水温-水深プロファイラ(CTD)、垂下式超音波流速計(LADCP)、および鉛直微細構造プロファイラ(乱流計)等を用い、房総半島沖合の親潮系低塩分水が貫入した直後の黒潮続流域において2000mまでのグリッド観測を実施した(安田一郎・伊藤幸彦)。この研究航海ではまた、鉛直方向に詳細な硝酸分布が取得できる硝酸塩連続プロファイラをレンタルして使用した。硝酸計データと乱流計データと組み合わせると硝酸の鉛直フラックスが算出でき、これにより本研究における栄養塩・生態系観測研究の基礎が構築されつつある。2009年に予定されている白鳳丸アリューシャン・ベーリング海観測を行うために、5/22-23にシンポジウムを開催し観測計画のとりまとめを行った。2006/2007ロシア船観測によって千島列島海域で得られた観測データの解析を進め、密度逆転からの乱流強度評価手法の開発(院生D1:八木雅宏)、千島列島付近での乱流による栄養塩鉛直輸送の評価(院生D1:金子)を行った。鉄分布観測データの検討(西岡純)、化学トレーサ観測データの解析(渡辺豊)を行った。海洋観測長期データを用いた解析(院生D3:長船哲史)により潮汐18.6年振動がベーリング海にも現れることを明らかにした千島列島付近の潮汐混合を変動させた大気・海洋・海氷結合モデルを開発し、エルニーニョ・南方振動(ENSO)を通じて気候にも影響を与えうることが明らかにされた(羽角・安田・建部)。
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), The University of Tokyo, Coinvestigator, 20253004
  • DMS flux in the North Pacific subpolar region
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    2006 - 2008
    WATANABE Yutaka; ONO Tsuneo; NIKI Takushi; NORIKI Shinichiro
    北太平洋高度海域の沿岸・外洋において、地球温暖化抑制物質であるDMS(ジメチルサルファイド)濃度について、植物プランクトン・クロロフィル・色素データと炭酸物質等とともに、世界で初めての周年規模の時系列観測を試みた。その結果、DMSの北太平洋における月別の詳細な空間分布を描き出すことに成功し、さらに、北太平洋全体でその表層濃度ならびに大気への逃散速度がここ30年で増加して傾向にあることを明らかとした。
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, Principal investigator, 18310001
  • 窒素とアルゴンを用いた高確度な海水年齢決定法の開発に関する研究
    Grants-in-Aid for Scientific Research Grant-in-Aid for Exploratory Research
    2006 - 2007
    渡辺 豊
    H18年度に確立した分析法と以下の計算方法を用いて、H19年度にはその信憑性を明らかにするために北太平洋高緯度海域で季節毎に得た海水試料の分析し、鉛直的な気泡貫入量の見積もりを行った。
    A項(真の飽和度)とB項(気泡貫入量)推定式:
    N_<2(obs)>=A_・N_<2(s)>+0.780・B(1),Ar_<(obs)>=A_・(k_/k_)・Ar_<(s)>+0.009・B(2)
    A_:窒素の飽和度(%)、N_<2(s)>とAr_<(s)>:現場の水温・塩分・大気組成比から求められるN_2とArのそれぞれの飽和濃度、k_、k_:窒素とアルゴンの気体交換速度、B:気泡が直接溶け込んだ量、0.789及び0.009:N_2とArのそれぞれの大気混合比。
    その結果、気泡貫入量は水深1000m以深では変動せず、その上層、表層・中層において季節的に10-50μmol/kgの範囲内で変動することを明らかにした。
    さらに、この方法を、年代決定に用いられているCFCsが観測されている南半球40度付近を一周する数十点の観測点試料について、窒素とアルゴンを測定し、気泡貫入の程度を計算した。その結果、年代は5-10年程度補正する必要があることが明らかになった。
    Japan Society for the Promotion of Science, Grant-in-Aid for Exploratory Research, Hokkaido University, Principal investigator, 18651002
  • Direct turbulence observation around Kuril Straits and studies on the impact of the tidal mixing on the North Pacific
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    2005 - 2007
    YASUDA Ichiro; HIBIYA Toshiyuki; KEIICHIRO Oshima; YASUHIRO Kawasaki; WATANABE Yutaka
    North Pacific marine ecosystem including tuna and small pelagic fish as sardine and anchovy is known to be related with inter-decadal ocean-climate variability. However, multi-decadal time-scale ocean-climate variability and mechanism remain unclear and thus unpredictable. Present studies discovered the relationship between the 18.6-year period nodal tidal cycle caused by lunar orbital variation and the bi-decadal variability of water-masses in the northwestern subarctic Pacific and of the North Pacific climate indices as winter NPI (North Pacific Index), PDO (Pacific Decadal Oscillation Index) and MOI (east-Asian Monsoon Index). Direct turbulence observations by the Russian Vessel Khromov evidenced the strong tidal mixing around the Kuril Straits; the vertical diffusivity reached over 1000 cm2/s, which is roughly 10,000 times the value (0.1 cm^<2>/s) in ordinary open ocean intermediate depths. Changes in this strong tidal mixing associated with the 18.6-year period tidal cycle probably change the surface salinity in the Okhotsk Sea and then intermediate water formation (sinking) rate in the northwestern shelf region. This explains the observed bidecadal variations in the intermediate waters in the Okhotsk Sea and Oyashio. The isopycnal depth changes observed around the Kuril Straits and along the east coast of Hokkaido and Tohoku propagate as coastally trapped wave and may change the Kuroshio intensity and heat transport. This coastal change may reach the equator and may influence the ENSO. These changes in the ocean could lead to the changes in the Aleutian Low Pressure, through atmospheric teleconnection. The present study linked the astronomically predictable 18.6-year period tidal cycle and with small-scale ocean mixing phenomena, and explained the surface to intermediate depths water-mass bi-decadal variability in the North Pacific subarctic regions. This study also proposed the link with the oceanic circulation and North Pacific climate variability. These open the predictability of multi-decadal scale ocean-climate-ecosystem variability. Since the tidal mixing considerably changes temporally and spatially, we need further observation of turbulence in mixing hot spots to make clear the strong mixing mechanism and to quantify the mixing. Studies are going on about the vertical transport of nutrients and influence on long-term marine ecosystem variability and diapycnal water transport and influence on the ocean circulation and climate.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), The University of Tokyo, Coinvestigator, 17253004
  • Observational research for iron, biological productivity, and carbon cycle in the subarctic northwestern Pacific
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    2004 - 2006
    ONO Tsuneo; KASAI Hiromi; NISHIOKA Jun; WATANABE Yutaka; YOSHIMURA Takeshi
    2-D iron distribution in the subarctic northwestern Pacific was investigated repeatedly from 2003 to 2006 with high spacio-temporal resolution equally to major nutrients. Seasonal and interannual variations of iron observed in the Oyashio domain brought us the following information :
    1] Monthly-mean concentration of dissolved iron (DFe) in the Oyashio mixed layer varies in parallel with nitrate, with its maximum anteceding the Kosa season. Ratio of DFe to the nitrate is fairly constant throughout the year (ΔDFe/ΔN=27×10^<-6>[mol/mol]), and this ratio resembles those of North Pacific intermediate water (NPIW). Based on these observation results and a simple model calculation, it is concluded that the seasonal variation of Dfe in the Oyashio mixed layer is mainly governed by spring-summer biological consumption and winter recirculation from the NPIW. Iron input from the dust deposition is implied to have small effect to the mixed-layer iron cycle, although small-scale high iron patch might sometimes be generated by local iron deposition.
    2] More than half of the DFe data observed in Oyashio mixed layer at the bloom-termination period shows roughly constant value of 0.25 nM, implying that the bloom-forming diatoms incur significant iron limitation below this iron level. In spring, iron reaches this lower-limit faster than nitrate, forming iron-limited ecosystem conditions at the end of spring bloom. In summer, however, the ultimate depletion of mixed layer nitrate occurs faster than that of DFe at July, forming nitrate-limited ecosystem in the summer Oyashio domain.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Fisheries Research Agency, Coinvestigator, 16310019
  • 海洋・大気間の物質相互作用研究計画(IGBP/SOLAS)の準備調査
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    2004 - 2004
    植松 光夫; 梶井 克純; 津田 敦; 渡辺 豊; 武田 重信; 山中 康裕
    本研究では、海洋・大気間の物質相互作用研究計画(IGBP/SOLAS)の特定領域研究申請に向けて、各プロジェクトの具体的な共同研究体制や戦略、国際的な協力体制を確立するため、国内研究立案集会を2004年7月1-2日に東大海洋研にて開催した。
    その後、10月6日にDMS関係のデータ、情報交換を含めたSOLAS-Japan DMSワークショップを開催した。ワークショップ終了後、"Dr.Sauveur BELVISO(CEN de Saclay, France)とDr.Dileep KUMAR(National Institute of Oceanography, India)を招待して、それぞれ"Recent progresses of DMS biogeochemistry in the Southern Ocean"と"Dimethylsulphide in the monsoon driven Indian Ocean"というタイトルでセミナーを開催した。
    11月15-16日には東大海洋研において「大気・海洋間の生物地球化学的循環過程」について国内SOLASシンポジウムを開催し、30件を越える成果と研究提案の発表があった。
    2005年1月20-21日に名古屋大においてSOLAS-Japanワークショップを開催し、来年度の研究計画や長期の航海計画申請について意見を集約した。
    国際的な活動として、ノルウェーのベルゲンで開催された国際SOLAS SSC meetingに植松(SSC委員)と武田(SSC委員)が出席し、日本を中心としたアジア域での取り組みについて取りまとめた。2005年には東京で国際SOLAS SSC meetingを開催することに決まった。また、この東京会議に引き続いてAsia SOLAS Workshopの開催を計画した。
    2004年10月にカナダ、ハリファックスで開催される国際SOLASシンポジウムに我が国から15名の研究者が発表した。津田がキーノートスピーカーとして招待された。本研究費から4名の発表者に旅費の援助を行った。
    この間、特定領域研究申請に向けて作業を行い、2004年11月に「海洋表層・大気下層間の物質循環リンケージ」(大気海洋物質循環)を申請した。
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), The University of Tokyo, Coinvestigator, 16631003
  • Reconstruction of climate change using tropical peat deposit in Indonesia.
    Grants-in-Aid for Scientific Research
    2000 - 2003
    NARITA Hisashi; OHOTA Keiichi; TANOUE Eiichiro; WATANABE Yutaka
    Peat core (3.60 m, 7428 cal.yr BP) collected from Rawa Danau, West Java, Indonesia, were studied to reconstruct past vegetation and forest fire related in the climate changes in the tropical area. Vertical profiles for TOG, TN, these isotopes, water content, elemental carbon, other geochemical data and core lithology reflected dry and wet cycles in this area. The lignin phenol vegetation index shows four major vegetation change events since the mid-late Holocene. The profiles of elemental carbon reveals tow or three large forest fire events during same period. The geochemical records form peat core indicated the change of vegetation changes and frequency of forest fire in response to climate change during last 8 kyr.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), HOKKAIDO UNIVERSITY, 12480144