Researcher Database

Yasuhiro Yamanaka
Faculty of Environmental Earth Science Integrated Environmental Science Practical and Earth Sciences for Environment
Professor

Researcher Profile and Settings

Affiliation

  • Faculty of Environmental Earth Science Integrated Environmental Science Practical and Earth Sciences for Environment

Job Title

  • Professor

Degree

  • Doctor of Science(The University of Tokyo)
  • Master of Science(The University of Tokyo)

J-Global ID

Research Interests

  • Development Education   総合的な探究の時間   Biogeochemical Cycles   Elderly welfare   climate change   Tourism   生物多様性   大気光学現象   海洋生態系   数値シミュレーション   ESD   CSR   地域活性   環境教育   持続可能な開発   SDGs   IR   Atmospheric Science   Higher Education   Practical Science for the Environment   Ocean Science   

Research Areas

  • Natural sciences / Space and planetary science
  • Humanities & social sciences / Tourism studies
  • Environmental science/Agricultural science / Environmental materials/recycling technology
  • Environmental science/Agricultural science / Recycling systems and society
  • Natural sciences / Atmospheric and hydrospheric science
  • Humanities & social sciences / Educational technology
  • Environmental science/Agricultural science / Environmental dynamics

Academic & Professional Experience

  • 2010/10 - Today Hokkaido University Faculty of Environmental Earth Science
  • 1998/04 - 2010/09 北海道大学大学院地球環境科学研究科/研究院 助教授/准教授
  • 2007/11 - 2008/02 英国イーストアングリア大学環境科学部 Visiting fellow
  • 2007 - 2008 Visiting Fellow,School of Environmental Science, University of East Anglia, UK
  • 1997/04 - 1998/03 米国プリンストン大学大気海洋プログラム Visiting Researcher
  • 1997 - 1998 Visiting Researcher,Atmosphere and Ocean Science Program, Princeton University, USA
  • The University of Tokyo Center for Climate System Research

Education

  •        - 1991  The University of Tokyo
  •        - 1991  The University of Tokyo  Graduate School, Division of Science
  •        - 1989  The University of Tokyo  Faculty of Science
  •        - 1989  The University of Tokyo  Faculty of Science

Association Memberships

  • THE GEOCHEMICAL SOCIETY OF JAPAN   JAPAN GEOSCIENCE UNION   THE JAPANESE SOCIETY FOR ENVIRONMENTAL EDUCATION   IDE大学協会   the Meteorological Society of Japan   THE OCEANOGRAPHIC SOCIETY OF JAPAN   Development Education Association and Resource Center   JAPAN CURRICULUM RESEARCH AND DEVELOPMENT ASSOCIATION   American Geophysical Union   European Geosciences Union   European Geosciences Union   

Research Activities

Published Papers

  • Yukari Higuchi, Yasuhiro Yamanka
    Tourism Review 74 (2) 166 - 177 2019/04 [Refereed][Not invited]
  • Naoyuki Ohara, Yasuhiro Yamanaka, Gregory Trencher
    Environmental Communication Informa {UK} Limited 13 (8) 1053 - 1058 2019/02 [Refereed][Not invited]
     
    his study examined the intent, preparatory processes and challenges of nature photographers mainly shooting plants and animals in northern Japan. Findings revealed that they actively absorb scientific knowledge that relates to their subjects during the preparatory process. A core intention for them is to record and demonstrate their understanding about their subject. They combine their acquisition of knowledge from the natural sciences with in-depth understanding gained from first-hand field observations. In constructing their self-identity and attributing a sense of purpose to their work, they are grappling with internal tensions and contradictions when deciding the optimal distance to place between their work and related professions such as stock photography and artistic expression. We also observed some cases where the original intentions of photography are masked or erased as images are taken up by stock photo agencies. The public would experience greater difficulties in accessing photographs based from natural science.
  • How universities provide education relevant to interdisci-plinary studies? – Environmental studies courses in re-search university as IR survey using education support system
    Yasuhiro Yamanaka, Shota Mitsui, Michiyo Shimamura
    International Journal of Institutional Research and Management International Institute of Applied Informatics 2 (1) 受理  2019/01 [Refereed][Not invited]
  • A lesson plan for development education designed by a Chinese graduate student: Practices at two elementary schools in Shimukappu, Hokkaido
    Ying Liu, Kai Takahashi, Yasuhiro Yamanaka
    Development Education 65 121 - 129 2018/12 [Refereed][Not invited]
  • Naoki H. Kumagai, Jorge García Molinos, Hiroya Yamano, Shintaro Takao, Masahiko Fujii, Yasuhiro Yamanaka
    Proceedings of the National Academy of Sciences of the United States of America 115 8990 - 8995 0027-8424 2018/09 [Refereed][Not invited]
     
    © 2018 National Academy of Sciences. All Rights Reserved. Coral and macroalgal communities are threatened by global stressors. However, recently reported community shifts from temperate macroalgae to tropical corals offer conservation potential for corals at the expense of macroalgae under climate warming. Although such community shifts are expanding geographically, our understanding of the driving processes is still limited. Here, we reconstruct long-term climate-driven range shifts in 45 species of macroalgae, corals, and herbivorous fishes from over 60 years of records (mainly 1950–2015), stretching across 3,000 km of the Japanese archipelago from tropical to subarctic zones. Based on a revised coastal version of climate velocity trajectories, we found that prediction models combining the effects of climate and ocean currents consistently explained observed community shifts significantly better than those relying on climate alone. Corals and herbivorous fishes performed better at exploiting opportunities offered by this interaction. The contrasting range dynamics for these taxa suggest that ocean warming is promoting macroalgal-to-coral shifts both directly by increased competition from the expansion of tropical corals into the contracting temperate macroalgae, and indirectly via deforestation by the expansion of tropical herbivorous fish. Beyond individual species’ effects, our results provide evidence on the important role that the interaction between climate warming and external forces conditioning the dispersal of organisms, such as ocean currents, can have in shaping community-level responses, with concomitant changes to ecosystem structure and functioning. Furthermore, we found that community shifts from macroalgae to corals might accelerate with future climate warming, highlighting the complexity of managing these evolving communities under future climate change.
  • タンクモデルを参考にした小学校高学年向けの地下水学習の教材開発
    岩井尚人, 山中康裕, 根岸淳二郎, 山田朋人
    水利科学 364 59 - 80 2018/08 [Refereed][Not invited]
     
    地下水の持続可能な利用は,その保全にとって必要である。地下水を保全す る態度を育むために,小学校教育の中で地下水について学ぶ機会を作ることは,重要なことである。本研究では,小学校高学年生が地下水涵養に関する森 林の機能などの地下水に関する基本的知識を学べる教材を,タンクモデルを参 考にして開発した。教材は,3 段タンクで構成され,森林領域の下にある帯水 層に設置したスポンジが水を貯留し,その水は装置外へゆっくりと流出するよ うになっている。教材で表現したのは,森林は主要な地下水の涵養域であるこ と,地下水は地表水に比べて滞留時間が長いことの 2 つである。教材を用いた 散水実験では,3 段のタンクそれぞれからの流出ピークのタイムラグや滞留時 間の違いなど,上記 2 点を定量的に確認した。小学校等の教員13名を対象に実 施した教材の実演と,彼らに対する聞き取り調査では,多くの教員は,小学校 児童にとって,上記 2 点が分かりやすいと判断した。
  • Michiyo Shimamura, Yukinori Kobayashi, Yasuhiro Yamanaka
    Proceedings - 2018 7th International Congress on Advanced Applied Informatics, IIAI-AAI 2018 408 - 413 2018/07/02 [Refereed][Not invited]
     
    © 2018 IEEE. To correspond to drastic change in international society such as 'globalization', graduate education plays a key role in development of human resources. The new trans-graduate-school education program called 'Nitobe School' was launched in 2015 as one of the main education projects of 'Top Global University Project' in Hokkaido University. This is a trial case report of the comparison of commercial Transferable Skill test for the Graduate School students. We employed about 50 students from the various graduate schools in Hokkaido University, and they took same commercial Transferable Skill tests (Career Approach, PROG and SEQ), then its result was discussed in here.
  • Yasuhiro Hoshiba, Takafumi Hirata, Masahito Shigemitsu, Hideyuki Nakano, Taketo Hashioka, Yoshio Masuda, Yasuhiro Yamanaka
    Ocean Science 14 (3) 371 - 386 1812-0792 2018/06/01 [Refereed][Not invited]
     
    Ecosystem models are used to understand ecosystem dynamics and ocean biogeochemical cycles and require optimum physiological parameters to best represent biological behaviours. These physiological parameters are often tuned up empirically, while ecosystem models have evolved to increase the number of physiological parameters. We developed a three-dimensional (3-D) lower-trophic-level marine ecosystem model known as the Nitrogen, Silicon and Iron regulated Marine Ecosystem Model (NSI-MEM) and employed biological data assimilation using a micro-genetic algorithm to estimate 23 physiological parameters for two phytoplankton functional types in the western North Pacific. The estimation of the parameters was based on a one-dimensional simulation that referenced satellite data for constraining the physiological parameters. The 3-D NSI-MEM optimized by the data assimilation improved the timing of a modelled plankton bloom in the subarctic and subtropical regions compared to the model without data assimilation. Furthermore, the model was able to improve not only surface concentrations of phytoplankton but also their subsurface maximum concentrations. Our results showed that surface data assimilation of physiological parameters from two contrasting observatory stations benefits the representation of vertical plankton distribution in the western North Pacific.
  • Gregory Trencher, Shirley Vincent, Kyle Bahr, Shogo Kudo, Kate Markham, Yasuhiro Yamanaka
    Journal of Cleaner Production 181 829 - 841 0959-6526 2018/04/20 [Refereed][Not invited]
     
    Interest in and understanding of the various competencies that university sustainability and environmental graduate degree programs should aim for has increased in recent years. Yet empirical efforts that assess the effectiveness of programs from a competency building perspective have visibly lacked—particularly from a macro-perspective examining multiple cases. This study fills this gap in the literature by conducting a novel comparative assessment of different types of master's degrees in a sample of 14 programs from top-performing universities in Europe, Asia and North America. Our study uses quantitative and qualitative approaches to assess the effectiveness of differing types of programs at building key sustainability competencies defined in the literature, and to understand the defining characteristics of programs, innovative competency building approaches, challenges encountered, and potential countermeasures. Using a typological methodology, this study classifies programs into three categories: research-oriented, neutrally-oriented and practice-oriented and then examined the competency building effectiveness of each category through questionnaires administered to faculty (n = 40) and students (n = 205). Results revealed low success in all program types at equipping graduates with anticipatory competencies. Statistically significant differences were also observed between research-oriented and practice-oriented programs, with the latter demonstrating higher success in building interpersonal, strategic and normative competencies. Qualitative questionnaire responses revealed a widespread student demand for more practice-orientated learning and collaborative projects with societal stakeholders. However they also highlight the important role of research-oriented programs at equipping students with theoretical and conceptual knowledge. From a sustainability competency building perspective, the findings point to a need for research-oriented programs to integrate practice-based didactic approaches for building skills and methods via real-world learning projects with external stakeholders. They also prompt a reconsideration of the special importance of research-oriented sustainability and environmental degree programs in a higher education landscape increasingly shaped by vocational and job market expectations.
  • Establishing the Brand-New Trans-Graduate Education Frame: Challenges of Hokkaido University “Nitobe School Program"
    YAMANAKA Yasuhiro, SHIMAMURA Michiyo
    International Journal of Institutional Research and Management International Institute of Applied Informatics 1 (2) 37 - 53 2018/03 [Refereed][Not invited]
  • Gregory Trencher, Achim Geissler, Yasuhiro Yamanaka
    Urban Living Labs: Experimenting with City Futures 167 - 188 2018/01 [Refereed][Not invited]
     
    © 2018 selection and editorial matter, Simon Marvin, Harriet Bulkeley, Lindsay Mai, Kes McCormick and Yuliya Voytenko Palgan; individual chapters, the contributors. The effectiveness of global and national responses to climate change largely hinges on the collective contributions of individual cities (Bulkeley, 2015; Trencher et al., 2016). Accordingly, cities are increasingly expected to pave the way by experimenting with and demonstrating innovative technologies and social arrangements addressing sustainability challenges. Urban living laboratories (ULL) are a powerful enabling paradigm to this end (Voytenko, McCormick, Evans and Schliwa, 2016). Historically, scientific experimentation was limited to the confines of laboratories or field observations (Evans and Karvonen, 2011). In ULL however, messy, uncontrollable and “living” urban environments are targeted by ambitious cross-organisational collaborations to trial and deploy cutting-edge technical and social solutions to advance societal progress towards greater sustainability and prosperity (Evans, Karvonen and Raven, 2016; Voytenko et al., 2016).
  • Yamamoto, Akitomo, Abe-Ouchi, Ayako, Yamanaka, Yasuhiro
    Biogeosciences 15 (13) 4163 - 4180 1726-4170 2018 [Refereed][Not invited]
     
    © Author(s) 2018. <p>Global warming is expected to significantly decrease oceanic carbon uptake and therefore increase atmospheric CO2 and global warming. The primary reasons given in previous studies for such changes in the oceanic carbon uptake are the solubility reduction due to seawater warming and changes in the ocean circulation and biological pump. However, the quantitative contributions of different processes to the overall reduction in ocean uptake are still unclear. In this study, we investigated multi-millennium responses of oceanic carbon uptake to global warming and quantified the contributions of the physical and biological pumps to these responses using an atmosphere-ocean general circulation model and a biogeochemical model. We found that global warming reduced oceanic CO2 uptake by 13ĝ€% (30ĝ€%) in the first 140 years (after 2000 model years), consistent with previous studies. Our sensitivity experiments showed that this reduction is primarily driven by changes in the organic matter cycle via ocean circulation change and solubility change due to seawater warming. These results differ from most previous studies, in which circulation changes and solubility change from seawater warming are the dominant processes. The weakening of biological production and carbon export induced by circulation change and lower nutrient supply, diminishes the vertical DIC gradient and substantially reduces the CO2 uptake. The weaker deep-ocean circulation decreases the downward transport of CO2 from the surface to the deep ocean, leading to a drop in CO2 uptake in high-latitude regions. Conversely, weaker equatorial upwelling reduces the upward transport of natural CO2 and therefore enhances the CO2 uptake in low-latitude regions. Because these effects cancel each other out, circulation change plays only a small direct role in the reduction of CO2 uptake due to global warming but a large indirect role through nutrient transport and biological processes.</p>.
  • Shota Mitsui, Michiyo Shimamura, Yasuhiro Yamanaka
    Proceedings - 2017 6th IIAI International Congress on Advanced Applied Informatics, IIAI-AAI 2017 142 - 146 2017/11/15 [Refereed][Not invited]
     
    For tuning education programs in the higher education, we should identify the status of courses (lectures) in education programs provided by target institutes such as graduate schools, or domestic and international universities relevant to target discipline. As a trial, we chose the courses relevant to environmental science in Hokkaido University, one of the 11 leading research universities in Japan. We extracted 240 syllabuses from 3,006 syllabuses of courses relevant to environmental science listed in an educational support system called ELMS, through the partial matching of Kankyo, a Japanese word of environment, in their course titles or keywords in all syllabuses. We clarified that the courses relevant to environmental science are provided by many graduate schools such as the Graduate Schools of Engineering, Agriculture, Science as well as the Graduate School of Environmental Science. We also found some critical issues when we used ELMS as an Institutional Research (IR) tool, such as duplicate /triplicate syllabuses for the same course, and duplicately/triplicately named courses for the same class due to inconsistency of their syllabuses and no policy for their naming convention of courses.
  • Michiyo Shimamura, Yasuhiro Yamanaka
    Proceedings - 2017 6th IIAI International Congress on Advanced Applied Informatics, IIAI-AAI 2017 153 - 157 2017/11/15 [Refereed][Not invited]
     
    To correspond to drastic change in international society such as globalization, graduate education plays a key role in development of human resources. The new trans-graduate-school education program called Nitobe School was launched in 2015 as one of the main education projects of Top Global University Project in Hokkaido University. This is a trial case report of the comparison of commercial English test for the Graduate School students. We employed about 50 students from the various graduate schools in Hokkaido University, and they took same commercial English tests (TOEIC and TOEFL), then its result is discussed in here. As a result, it was turnout that students need to take same type of English placement test before and after the program. Also depend on the students future career and/or English ability, student themselves need to choose TOEIC or TOEFL as a placement test at the beginning.
  • Shotaro Imai, Michiyo Shimamura, Ankit A. Ravankar, Hisashi Haga, Yukinori Kobayashi, Yasuhiro Yamanaka
    Proceedings - 2017 6th IIAI International Congress on Advanced Applied Informatics, IIAI-AAI 2017 147 - 152 2017/11/15 [Refereed][Not invited]
     
    To correspond to current trend in the international society which is rapidly adopting to the notion of globalization, the graduate education plays a key role in development of human resources for the future. A new trans-graduate-school education program called Nitobe School was launched in 2015 as one of the main education projects of Top Global University Project at Hokkaido University, Japan. To foster the overall development of graduate students and to track their progress throughout the program, Nitobe School introduced a student e-portfolio called NITOBE Portfolio. This portfolio is accessible to the registered students until their graduation. The student can freely interact with the instructors, discuss with fellow students, submit assignments on the e-portfolio and most importantly track individual progress during the course. This paper reports the impact of utilization of student e-portfolio in the program for evaluation, and discusses the system development assuming wide-spread use of such e-portfolio systems for research university in the future.
  • Shotaro Imai, Ankit Ravankar, Michiyo Shimamura, Taichi Takasuka, Go Chiba, Yasuhiro Yamanaka
    International Journal of Institutional Research and Management 1 (2) 17 - 35 2432-3683 2017/09 [Refereed][Not invited]
  • Yasuhiro Hoshiba, Takafumi Hirata, Masahito Shigemitsu, Hideyuki Nakano, Taketo Hashioka, Yoshio Masuda, Yasuhiro Yamanaka
    Ocean Science Discussions Copernicus {GmbH} 1  2017/05 [Refereed][Not invited]
  • Shigemitsu, M., Yamamoto, A., Oka, A., Yamanaka, Y.
    Global Biogeochemical Cycles 31 (5) 2017 [Refereed][Not invited]
  • Yukari Higuchi, Yasuhiro Yamanaka
    JOURNAL OF SUSTAINABLE TOURISM 25 (10) 1456 - 1473 0966-9582 2017 [Refereed][Not invited]
     
    Nature-based tourism (NBT) practitioners urgently need to develop more and better quality products through including the findings of tourism and other scientific researchers. However, in many cases, NBT enterprises do not have enough resources to invest in building a sustainable relationship with such researchers. This paper reports on the long-term involvement of university researchers in value co-creation - producing a new value in tourist experiences - jointly with tourism practitioners, encouraging significant and innovative NBT outcomes. It articulates how knowledge sharing was achievable between these parties in their shared practices, focusing on the importance of tacit knowledge sharing. A case study approach was complemented by long-term monitoring from 2011 to 2015; data was collected by interview and participant observation and qualitatively analysed. The results vividly depict that the key factor for effective tacit knowledge sharing and long-term co-creation is largely related to embeddedness, and also to trust, long-term partnerships, and the creation of win-win situations for all sides. Although limited to one set of actors and one socio-cultural context, one Japanese university and one enterprise, this study pioneers empirical research on the relationships between co-creation, knowledge sharing, and embeddedness in sustainable tourism that could be replicated in other situations.
  • Yoshio Masuda, Yasuhiro Yamanaka, Takafumi Hirata, Hideyuki Nakano
    ECOLOGICAL MODELLING 343 1 - 14 0304-3800 2017/01 [Refereed][Not invited]
     
    To advance our understanding of competition and coexistence in phytoplankton species within a functional group, such as a diatom group, we developed a numerical model composed of 240 within tropic-level virtual species that can actually or potentially compete. We then explored how the phytoplankton assembly is structured by deterministic or stochastic processes, where the former process is typically represented using the traditional niche theory and the latter process is highlighted using the neutral theory. Because we used eddy-resolving resolution, phytoplankton dispersion and the resultant dispersal limitation were explicitly represented, where the dispersal limitation prevents the most competitive species from using its appropriate niche and subsequently enhances stochastic effects. In the simulation results, all surviving species have an oceanic volume in which the phytoplankton species has the highest specific growth rate in all the 240 species. The abundance in the most competitive space has a strong, positive correlation with the relative species abundance. Moreover, of the phytoplankton types whose abundances in the most competitive space are nearly equal, the survival of a species is affected by its residence time within its habitat; the surviving phytoplankton species tend to have larger residence times compared to the non-persistent species. These results led us to conclude that deterministic processes had significant contributions to a formation of phytoplankton assembly. This was supported by the result that a structure of phytoplankton assembly represented by species rank in abundance was invariant with time and hardly dependent on initial conditions of phytoplankton composition. (C) 2016 The Author(s). Published by Elsevier B.V.
  • Naoki H. Kumagai, Hiroya Yamano, Masahiko Fujii, Yasuhiro Yamanaka
    ECOLOGICAL RESEARCH 31 (6) 759 - 759 0912-3814 2016/11 [Refereed][Not invited]
     
    This paper describes the flora of habitat-forming seaweeds (fucoids and temperate kelps) at 7673 sites of the Japanese coast encompassing its warm to cold temperate zone, recorded from 1887 to 2014. The data set includes 86 species (21,168 presence and 20,845 absence records), compiled from 355 literature sources, most of which were written in Japanese and published as grey literature in local journals or individual reports. Scientific names were consolidated under currently-accepted nomenclature based on Algaebase. The data set compiled the seaweed flora at each study site each year, the geographical location and the scientific names. Additionally, three supporting data sets were created respectively including name of each site, synonyms of the seaweeds, and the corresponding literature list. This rich collection of data can be used to study the biogeography and long-term changes of particular species and the diversity of habitat-forming seaweeds of the Japanese coast.
  • Yasuhiro Hoshiba, Yasuhiro Yamanaka
    CONTINENTAL SHELF RESEARCH 117 20 - 29 0278-4343 2016/04 [Refereed][Not invited]
     
    Riverine input often leads to high biological productivity in coastal areas. In coastal areas termed as region of freshwater influence (ROFI), horizontal anticyclonic gyres and vertical circulation form by density differences between buoyant river water and sea water. Previous physical oceanography studies have shown that the horizontal pattern of anticyclonic gyres and the strength of vertical circulation are dependent on the bottom topography of ROFI. However, the dependencies of biogeochemical cycles such as the net primary production (NPP) on the bottom topography have not been verified. In order to clarify how the bottom topography affects the NPP in phytoplankton blooms caused by riverine input through the physical processes in ROFI, we used an ocean general circulation model (OGCM) including a simple ecosystem model and conducted several case studies varying the bottom slope angle in the ideal settings. We estimated NPP categorized into three nutrients supplied from the river, the sea-subsurface layer and via regeneration: RI-NPP, S-NPP and RE-NPP. S-NPP and RE-NPP are larger and smaller with a steeper slope, respectively, while RI-NPP is not affected by the slope angle. As a result, total NPP is weakly dependent on the slope angle, i.e., because S- and RE-NPPs cancel each other out through two physical processes, (1) S-NPP is controlled by the strength of the vertical circulation and (2) RE-NPP is controlled by the shape of the horizontal gyre, which both vary with the bottom slope angle. We also conducted realistic simulations for Ishikari Bay, Japan and confirmed a similar dependency to that in the above ideal settings. That is, the simulation results are consistent with the regime of ideal settings and show that RI and RE-NPPs are important variables for Ishikari Bay which has a gentle slope. (C) 2016 The Authors. Published by Elsevier Ltd.
  • M. Shigemitsu, N. Gruber, A. Oka, Y. Yamanaka
    GLOBAL BIOGEOCHEMICAL CYCLES 30 (4) 576 - 594 0886-6236 2016/04 [Refereed][Not invited]
     
    Using a global ocean biogeochemical model, we investigate the suitability of the N-2/Ar supersaturation ratio (N-2/Ar) as a tracer of marine nitrogen fixation and denitrification, i.e., the main biological processes that add or remove fixed nitrogen to or from the ocean. In a series of factorial simulations, we demonstrate that, in regions away from the oxygen minimum zones (OMZs), the N-2/Ar characteristics are mostly determined by benthic denitrification occurring in the deep ocean with minor contributions from benthic and water column denitrification at shallower depths. In the OMZs, the subsurface maxima of N-2/Ar are mainly determined by water column denitrification. In contrast, nitrogen fixation has little impact on N-2/Ar owing to the rapid loss of the N-2 supersaturation signal through air-sea exchange. We thus conclude that N-2/Ar can act as a powerful constraint on water column and benthic denitrification occurring in intermediate to deep waters, but it cannot be used to estimate nitrogen fixation. A comparison between the currently very limited observations of the N-2/Ar with our model results shows an acceptable level of agreement, suggesting that the model's prescribed rates and distributions of benthic and water column denitrification (i.e., 140 and 52TgNyr(-1), respectively) are reasonable and confirm the results derived from other constraints.
  • 海洋生態系モデル(Marine Ecosystem Model:MEM)の概要
    重光雅仁, 山中康裕
    月刊海洋 548 281 - 290 2016 [Not refereed][Not invited]
  • Yara, Y, H. Yamano, M. Steinacher, M. Fujii, M. Vogt, N. Gruber, Y. Yamanaka
    Aquatic Biodiversity Conservation and Ecosystem Services 41 - 56 2016 [Refereed][Not invited]
     
    Using the results from the NCAR CSM1.4-coupled global carbon cycle?climate model under the Intergovernmental Panel on Climate Change (IPCC) emission scenarios SRES A2 and B1, we estimated the effects of both global warming and ocean acidification on the future habitats of corals in the seas around Japan during this century. As shown by Yara et al. (Biogeosciences 9:4955?4968, 2012), under the high-CO2-emission scenario (SRES A2), coral habitats will be sandwiched and narrowed between the northern region, where the saturation state of the carbonate mineral aragonite (Ωarag) decreases, and the southern region, where coral bleaching occurs. We found that under the low-emission scenario SRES B1, the coral habitats will also shrink in the northern region by the reduced Ωarag but to a lesser extent than under SRES A2, and in contrast to SRES A2, no bleaching will occur in the southern region. Therefore, coral habitats in the southern region are expected to be largely unaffected by ocean acidification or surface warming under the low-emission scenario. Our results show that potential future coral habitats depend strongly on CO2 emissions and emphasize the importance of reducing CO2 emissions to prevent negative impacts on coral habitats.
  • Ankit A. Ravankar, Shotaro Imai, Michiyo Shimamura, Go Chiba, Taichi Takasuka, Yasuhiro Yamanaka
    PROCEEDINGS 2016 5TH IIAI INTERNATIONAL CONGRESS ON ADVANCED APPLIED INFORMATICS IIAI-AAI 2016 542 - 546 2016 [Refereed][Not invited]
     
    The present university education system has been designed to make graduate students good problem solvers such that they can contribute to society through the skills acquired in the graduate schools. With focus on developing critical thinking and reasoning to solve local and global problems such programs have gained immense popularity among teachers and professors in schools and universities and termed as "Problem-Based-Learning" (PBL). However, there has been very few programs that encourage students to become better Problem finders. This study is based on our own experience of teaching problem-finding as an important skill for a special graduate program in university education and our findings on its implication on students ability to comprehend real world problems.
  • Michiyo Shimamura, Shotaro Imai, Ankit A. Ravankar, Yasuhiro Yamanaka
    PROCEEDINGS 2016 5TH IIAI INTERNATIONAL CONGRESS ON ADVANCED APPLIED INFORMATICS IIAI-AAI 2016 547 - 551 2016 [Refereed][Not invited]
     
    This is a report the change of postgraduate student's English ability through the new trans-graduate-school education program "Nitobe School" in Hokkaido University. In the Nitobe School program, students need to take English placement test before and after the program. Students choose TOEIC or TOEFL as a placement test at the beginning and take same test after the program. Also they can know its result within one month after took a test. Therefore we conducted questioner survey of student's motivation against English study and analyzed the relationship between their motivation and the change of English ability through the program period.
  • Shotaro Imai, Ankit A. Ravankar, Michiyo Shimamura, Taichi E. Takasuka, Go Chiba, Yasuhiro Yamanaka
    PROCEEDINGS 2016 5TH IIAI INTERNATIONAL CONGRESS ON ADVANCED APPLIED INFORMATICS IIAI-AAI 2016 537 - 541 2016 [Refereed][Not invited]
     
    The new graduate school education program Nitobe School was launched in 2015 as one of main education projects of "Top Global University Project" in Hokkaido University. This new graduate program is aimed to supply currently undermined skill-set to students from different home graduate or professional school. The scope of the Nitobe School program is to foster students to be a global leader who might contribute not only for local societies but also internationally by Team-Based-Learning (TBL) and Project-Based-Learning (PBL) methods. Since students have different expertise including the area of STEM and humanity, teachers cannot guide classes with their field, rather teachers need to educate students using a general topics. This general education program apparently requires different approaches from the conventional one. After completion of the first year of Nitobe School, we took place the survey that asked students how they felt about our new teaching methods. Overall, students appreciated with the new methods that we carried out, but there are some spaces for further improvement. In this report, we suggest potential ways to improve the Nitobe School program, which will be able to enhance further educating students, and at the same time educate teachers toward the TBL and PBL.
  • Yasuhiro Yamanaka, Michiyo Shimamura
    PROCEEDINGS 2016 5TH IIAI INTERNATIONAL CONGRESS ON ADVANCED APPLIED INFORMATICS IIAI-AAI 2016 533 - 536 2016 [Refereed][Not invited]
     
    To correspond to drastic change in international society such as "globalization", graduate education plays a key role in development of human resources to nurture competencies such as transferable skills as well as their advanced specialty. We report a new trans-graduate-school educational program called the "Nitobe School" in Hokkaido University, which has unique trials and mechanisms: "3+1 Competencies", "Microcosm of international society", "NITOBE Portfolio", and "Systems of Mentors and Advisors". Nitobe School give students supportive push to respect and understand different discipline, nationalities, cultures, and discussing in suitable language. Especially, "Microcosm of international society", i.e. various students having different background learn together in a class room, works well for the students for whom English is not the first language and discuss with diverse students. We spent one year to prepare the coursework as "microcosm of international society" and applied many different mechanisms for promoting students' proactive learning and quality assurance of Nitobe School. In order to realize "microcosm of international society", it is required for professors as well as students to deeply respect and understand key differences. With these skills and understandings, a good platform can be build for faculty development and student guidance.
  • Xuanrui Xiong, Yoshio Masuda, Taketo Hashioka, Tsuneo Ono, Yasuhiro Yamanaka
    JOURNAL OF OCEANOGRAPHY 71 (6) 685 - 701 0916-8370 2015/12 [Refereed][Not invited]
     
    We used an eddy-permitting three-dimensional ocean ecosystem model and applied it in the western North Pacific to understand the seasonal variations and horizontal distributions of the air-sea CO2 flux and difference in the partial pressure between sea water and the atmosphere (a dagger pCO(2)). The high-resolution model reproduced the observed zonal belt of strong CO2 uptake in the mid-latitude (30-45A degrees N) western North Pacific including the Kuroshio extension and mixed water regions, which was difficult to show in previous coarse-resolution models. The East Asian winter monsoon, an important phenomenon in the western North Pacific, affects the seasonal CO2 air-sea gas exchange with a high (low) gas transfer coefficient in winter (summer). In the subtropical region, a dagger pCO(2) is negative in winter and positive in summer as a result of the temperature effect. Combination of seasonal change in gas transfer coefficient with a dagger pCO(2) suppresses CO2 release in the subtropical region, and vice versa in the subarctic region (i.e., suppresses CO2 uptake). That is, the East Asian winter monsoon in the western North Pacific contributes to the reduction of the annual CO2 flux through the seasonal change in the gas transfer coefficient, leading to an overall annual CO2 uptake in the subtropical region and CO2 release in the subarctic region.
  • S. Takao, H. Yamano, K. Sugihara, N. H. Kumagai, M. Fujii, Y. Yamanaka
    CORAL REEFS 34 (4) 1125 - 1137 0722-4028 2015/12 [Refereed][Not invited]
     
    The poleward expansion of coral habitats has been observed along the Japanese coast since the 1930s. Previous modeling studies have projected a poleward expansion using decadal-mean sea surface temperatures (SSTs) in the coldest months. However, this poleward expansion could be affected by the inter-annual variation of SST in the coldest months, which has not been considered before. In this study, the simulated pattern of poleward expansion was compared between cases where coral mortality was considered based on the inter-annual variation of SST and the decadal-mean SST in the coldest months. Modeled monthly mean SSTs for historical and future global warming simulations from the most recent climate projection model (MIROC4h) were used. The poleward expansion of corals simulated by considering mortality based on the inter-annual variation of SST in the coldest months better reproduced the observed poleward expansion speed compared to the simulations without such a consideration. Our results show the importance of considering coral mortality based on the inter-annual variation of seawater temperature to produce a more realistic poleward expansion of coral habitats.
  • Akemi Tanaka, Kiyoshi Takahashi, Yuji Masutomi, Naota Hanasaki, Yasuaki Hijioka, Hideo Shiogama, Yasuhiro Yamanaka
    SCIENTIFIC REPORTS 5 2045-2322 2015/09 [Refereed][Not invited]
     
    Agricultural adaptation is necessary to reduce the negative impacts of climate change on crop yields and to maintain food production. However, few studies have assessed the course of adaptation along with the progress of climate change in each of the current major food producing countries. Adaptation pathways, which describe the temporal sequences of adaptations, are helpful for illustrating the timing and intensity of the adaptation required. Here we present adaptation pathways in the current major wheat-producing countries, based on sequential introduction of the minimum adaptation measures necessary to maintain current wheat yields through the 21st century. We considered two adaptation options: (i) expanding irrigation infrastructure; and (ii) switching crop varieties and developing new heat-tolerant varieties. We find that the adaptation pathways differ markedly among the countries. The adaptation pathways are sensitive to both the climate model uncertainty and natural variability of the climate system, and the degree of sensitivity differs among countries. Finally, the negative impacts of climate change could be moderated by implementing adaptations steadily according to forecasts of the necessary future adaptations, as compared to missing the appropriate timing to implement adaptations.
  • Shintaro Takao, Naoki H. Kumagai, Hiroya Yamano, Masahiko Fujii, Yasuhiro Yamanaka
    ECOLOGY AND EVOLUTION 5 (1) 213 - 223 2045-7758 2015/01 [Refereed][Not invited]
     
    Seaweed beds play a key role in providing essential habitats and energy to coastal areas, with enhancements in productivity and biodiversity and benefits to human societies. However, the spatial extent of seaweed beds around Japan has decreased due to coastal reclamation, water quality changes, rising water temperatures, and heavy grazing by herbivores. Using monthly mean sea surface temperature (SST) data from 1960 to 2099 and SST-based indices, we quantitatively evaluated the effects of warming seawater on the spatial extent of suitable versus unsuitable habitats for temperate seaweed Ecklonia cava, which is predominantly found in southern Japanese waters. SST data were generated using the most recent multiple climate projection models and emission scenarios (the Representative Concentration Pathways or RCPs) used in the Coupled Model Intercomparison Project phase 5 (CMIP5). In addition, grazing by Siganus fuscescens, an herbivorous fish, was evaluated under the four RCP simulations. Our results suggest that continued warming may drive a poleward shift in the distribution of E.cava, with large differences depending on the climate scenario. For the lowest emission scenario (RCP2.6), most existing E.cava populations would not be impacted by seawater warming directly but would be adversely affected by intensified year-round grazing. For the highest emission scenario (RCP8.5), previously suitable habitats throughout coastal Japan would become untenable for E.cava by the 2090s, due to both high-temperature stress and intensified grazing. Our projections highlight the importance of not only mitigating regional warming due to climate change, but also protecting E.cava from herbivores to conserve suitable habitats on the Japanese coast.
  • Yamamoto, A., Abe-Ouchi, A., Shigemitsu, M., Oka, A., Takahashi, K., Ohgaito, R., Yamanaka, Y.
    Global Biogeochemical Cycles 29 (10) 1801 - 1815 2015 [Refereed][Not invited]
  • Michiyo Shimamura, Yasuhiro Yamanaka
    2015 IIAI 4TH INTERNATIONAL CONGRESS ON ADVANCED APPLIED INFORMATICS (IIAI-AAI) 455 - 457 2015 [Refereed][Not invited]
     
    The circumstances of graduate education have been changed significantly from 1990s in Japan. Especially the case of national universities, the numbers of graduate student increased dramatically, however the basic financial support from the government has been decreased from middle 2000's. As a result, dependence of competitive funding projected by the Japanese government was increased, and the requirements of evidence for the application and evaluation after selection were also increased. These required evidence data include research activities both faculties and graduate students. From the historical changes of requirement, it considered how we make assessment of graduate educational outcomes, because the research activities of graduate students are not only research outcomes, but also educational outcomes of graduate education.
  • 島村 道代, 山中 康裕
    年会論文集 日本教育情報学会 (31) 186 - 187 2015 [Refereed][Not invited]
     
    近年,高等教育におけるIR (Institutional Research)の重要性・必要性が高まっている。このため各大学ではIR組織の設置が進んでいるが,機関によって求められる貢献や方向性が多様であると言える。そこで本発表では,特に求められる業務タイプを念頭に,IR人材の在り方およびIR人材育成の在り方について,教職開発の観点から提言させて頂き議論を行いたい。
  • 柴野良太, 藤井賢彦, 山中康裕, 山野博哉, 髙尾信太郎
    Bulletin of the Japanese Society of Fisheries Oceanography 78 (4) 259 - 267 0916-1562 2014/11 [Refereed][Not invited]
  • Natural coast management by divers actors for conservation and recreational use of Ishikari coast, Hokkaido
    MATSUSHIMA Hajime, TAKEDA Shota, YAMANAKA Yasuhiro
    Landscape Research Japan 78 (2) 95 - 96 2014/07 [Not refereed][Invited]
  • Yumiko Yara, Masahiko Fujii, Hiroya Yamano, Yasuhiro Yamanaka
    HYDROBIOLOGIA 733 (1) 19 - 29 0018-8158 2014/07 [Refereed][Not invited]
     
    We quantitatively evaluated the effects of rising sea surface temperature (SST) on coral bleaching and the uncertainties resulting from differences in global warming projections. To do so, we used monthly SSTs in the twenty-first century obtained from 23 climate models under the A1B scenario (from the Special Report on Emissions Scenarios) and SST-based indices for coral bleaching. All of the projections indicated that severe bleaching or death of corals will be common and severe in wide areas of the tropical and subtropical oceans by the middle of this century. However, decadal oscillation could modify the exact timing by around +/- 10 years. Such projections are important for conserving marine biodiversity and designing future strategies to avoid tropical and subtropical coral extinction. To obtain more reliable projections and reduce uncertainties, climate models should be improved by using higher spatiotemporal resolutions, and more realistic biological indices should be embedded into existing models.
  • 佐藤 志穂, 山中 康裕, 敷田 麻実
    日本地域政策研究 日本地域政策学会 (12) 9 - 17 1348-5539 2014/03 [Refereed][Not invited]
     
    Collaboration with exogenous actor is an important factor for the community development through tourism. For creative resourceuse, it is also crucial to construct of prosperous coexistence relationship between exogenous and local actors . We report a case ofcollaboration of exogenous resort with local farmers for local resource uses in Shimukappu, Hokkaido. Through focusing changes inthe consciousness and series of stakeholder s action of the resort in the collaboration process, we examined construction ofrelationship between exogenous actors and farmers. The stakeholders of the resort endeavored to develop one-on-one relationshipwith farmers, to construct sustainable and mutualistic relationships with farmers. The results of this study indicate that exogenousactor has potential contributing to local endogenous development.
  • Akemi Tanaka, Tomonori Sato, Manabu Nemoto, Yasuhiro Yamanaka
    JOURNAL OF AGRICULTURAL METEOROLOGY 70 (1) 25 - 40 0021-8588 2014 [Refereed][Not invited]
     
    In Hokkaido, in northern Japan, rice yields are frequently affected by cool summers in the present climate. Recently, several studies have noted the possibility that cool summer damage may not be reduced even with global warming due to earlier rice phenology. We examined the changes in the range of rice sterility associated with rising temperatures focusing on inter-annual variation in temperature. By raising daily mean and daily maximum temperatures uniformly, we calculated the sterility rate of the Kirara397 variety locally planted in Hokkaido. Generally, long-term mean rice sterility decreases with rising temperatures. However, in each year and with each transplanting date, rice sterility remains identical to the present or even worsens in some cases. We called those cases "accelerated cool summer damage'' (ACSD). In the cases of rising temperature, the growth rate is accelerated, and the period of vulnerability to low temperatures become earlier. When the temperature during the earlier period of vulnerability is equal to or less than that during the original period of vulnerability in the present, ACSD occurs. Future rice sterility that induces cool summer damage may remain even if the temperatures rise associated with global warming, since the increase in temperature during the period of vulnerability is smaller than the range of inter-annual variation in temperature. We also found that there is a possibility that extremely high rice sterility is increased in a warmer climate if the range of inter-annual variation in temperature expands. This finding suggests that rice sterility may be increased by the inter-annual variation in temperature, even if the long-term mean sterility decreases as the temperature rises.
  • Yamamoto, A., Yamanaka, Y., Oka, A., Abe-Ouchi, A.
    Geophysical Research Letters 41 (14) 5075 - 5083 2014 [Refereed][Not invited]
  • Masahito Shigemitsu, J. Nishioka, Y. W. Watanabe, Y. Yamanaka, T. Nakatsuka, Y. N. Volkov
    MARINE CHEMISTRY 157 41 - 48 0304-4203 2013/12 [Refereed][Not invited]
     
    We have found that the ratio of Fe to Al in suspended particulate matter (SPM) in the intermediate layer Of the Okhotsk Sea increases to the open ocean from the dense shelf water on the northwestern continental shelf, which is the source of southward-flowing Okhotsk Sea Intermediate Water (OSIW). The SPM concentration and the Al content of the SPM decrease along the course of the OSIW, whereas the ratios of Ba and Mn to Al increase. The SPM samples on the continental shelf were collected in waters characterized by low N* (the deviation from the stoichiometric relationship between nitrogenous nutrients and phosphate). These low N* values imply that sedimentary denitrification occurs on the continental shelf, and both Fe and Mn are concomitantly reduced in the sediments and diffuse from the sediments to the overlying waters, where they are subsequently oxidized and precipitate. We assume that the SPM in the intermediate layer is influenced mainly by horizontal transport from the continental shelf to the ocean interior and that Ba can be used as a proxy for organic matter. Based on these assumptions, the reults could reflect the following processes: 1) a gradual loss of denser lithogenic matter, evidenced by the decreases of the SPM concentration and of the Al content of the SPM, and 2) a relative increase of the Fe and Mn fractions associated with the organic matter in the SPM, which is derived from the continental shelf. The organic matter-related Fe and Mn could also be affected by the precipitation of both Fe and Mn just above the reduced sediments of the continental shelf. Our results show that the particulate Fe associated with organic matter is preferentially transported from the northwestern continental shelf to the open ocean. (C) 2013 Elsevier B.V. All rights reserved.
  • Yasuhiro Hoshiba, Yasuhiro Yamanaka
    JOURNAL OF OCEANOGRAPHY 69 (6) 753 - 767 0916-8370 2013/12 [Refereed][Not invited]
     
    Rivers transport nutrients and suspended sediment matter (SSM) as well as fresh water from land to coastal regions, where the biological productivity is high. In the coastal area, the buoyancy of fresh water leads to the formation of horizontal anticyclonic gyres and vertical circulations, which affect the variation of biological production such as plankton blooms. However, the primary production caused by the 3-D dynamics have not been quantitatively discussed, and observations can hardly capture the daily temporal variations of phytoplankton blooms. We developed an ocean general circulation model including a simple ecosystem model, to investigate the 3-D and temporal changes in phytoplankton blooms caused by riverine input such as flooding. The distribution patterns of nutrients and phytoplankton differ significantly from that of fresh water. The phytoplankton maxima shift from the downstream (right-hand side of the river mouth) to the upstream regions (left-hand side of the river mouth). The shift that occurs is categorized by the different nitrate origins: (1) river-originated nitrate is dominant in the downstream region; (2) subsurface-originated nitrate is dominant in the upstream region, and is transported by upwelling associated with vertical circulation and horizontal anticyclonic gyre; and (3) regenerated nitrate is dominant in the upstream region. The total primary production in phytoplankton blooms is maintained not only by river-originated nitrate but also by subsurface-originated nitrate that is 1.5 times larger than the river-originated. Several case studies (e.g., including SSM) were conducted in this study.
  • Anne B. Hollowed, Manuel Barange, Richard J. Beamish, Keith Brander, Kevern Cochrane, Kenneth Drinkwater, Michael G. G. Foreman, Jonathan A. Hare, Jason Holt, Shin-ichi Ito, Suam Kim, Jacquelynne R. King, Harald Loeng, Brian R. MacKenzie, Franz J. Mueter, Thomas A. Okey, Myron A. Peck, Vladimir I. Radchenko, Jake C. Rice, Michael J. Schirripa, Akihiko Yatsu, Yasuhiro Yamanaka
    ICES JOURNAL OF MARINE SCIENCE 70 (5) 1023 - 1037 1054-3139 2013/09 [Refereed][Not invited]
     
    This paper reviews current literature on the projected effects of climate change on marine fish and shellfish, their fisheries, and fishery-dependent communities throughout the northern hemisphere. The review addresses the following issues: (i) expected impacts on ecosystem productivity and habitat quantity and quality; (ii) impacts of changes in production and habitat on marine fish and shellfish species including effects on the community species composition, spatial distributions, interactions, and vital rates of fish and shellfish; (iii) impacts on fisheries and their associatedcommunities; (iv) implications for food security and associated changes; and (v) uncertainty andmodelling skill assessment. Climate change will impact fish and shellfish, their fisheries, and fishery-dependent communities through a complex suite of linked processes. Integrated interdisciplinary research teams are forming in many regions to project these complex responses. National and international marine research organizations serve a key role in the coordination and integration of research to accelerate the production of projections of the effects of climate change on marine ecosystems and to move towards a future where relative impacts by region could be compared on a hemispheric or global level. Eight research foci were identified that will improve the projections of climate impacts on fish, fisheries, and fishery-dependent communities.
  • Akihiko Yatsu, Sanae Chiba, Yasuhiro Yamanaka, Shin-ichi Ito, Yugo Shimizu, Masahide Kaeriyama, Yoshioro Watanabe
    ICES JOURNAL OF MARINE SCIENCE 70 (5) 922 - 933 1054-3139 2013/09 [Refereed][Not invited]
     
    The Kuroshio and Oyashio, western boundary currents in the North Pacific, greatly influence climate, ecosystems, and fisheries in the western North Pacific and its adjacent waters. The Kuroshio/Oyashio ecosystem (KOE) shows interannual and decadal variability including regime shifts. Under a collaboration of the Climate Forcing and Marine Ecosystem Response (CFAME) Task Team and Working Group 20 (Evaluations of Climate Change Projections) of PICES, we analysed the observed time-series of physics, nutrients, chlorophyll, zooplankton abundance and phenology, and productivity, biomass, and catch of commercially important species to assess the impacts of Intergovernmental Panel on Climate Change's global change scenarios on KOE. Mechanistic linkages from climate forcing to fish population dynamics were explored for the Japanese common squid (Todarodes pacificus), Japanese sardine (Sardinops melanostictus), walleye pollock (Theragra chalcogramma), and chum salmon (Oncorhynchus keta). Future scenarios of zooplankton, commercial species, and ecosystem changes were presented based on the empirical mechanistic linkages and results of projections for physical conditions and primary production in KOE derived from both empirical knowledge and three-dimensional ecosystem-biogeochemical models. Associated data gaps, uncertainties, and implications for managers were also discussed.
  • S. F. Sailley, M. Vogt, S. C. Doney, M. N. Aita, L. Bopp, E. T. Buitenhuis, T. Hashioka, I. Lima, C. Le Quere, Y. Yamanaka
    ECOLOGICAL MODELLING 261 43 - 57 0304-3800 2013/07 [Refereed][Not invited]
     
    Dynamic Green Ocean Models (DGOMs) include different sets of Plankton Functional Types (PFTs) and equations, thus different interactions and food webs. Using four DGOMs (CCSM-BEC, PISCES, NEMURO and PlankTOM5) we explore how predator-prey interactions influence food web dynamics. Using each model's equations and biomass output, interaction strengths (direct and specific) were calculated and the role of zooplankton in modeled food webs examined. In CCSM-BEC the single size-class adaptive zooplankton preys on different phytoplankton groups according to prey availability and food preferences, resulting in a strong top-down control. In PISCES the micro- and meso-zooplankton groups compete for food resources, grazing phytoplankton depending on their availability in a mixture of bottom-up and top-down control. In NEMURO macrozooplankton controls the biomass of other zooplankton PFTs and defines the structure of the food web with a strong top-down control within the zooplankton. In PlankTOM5, competition and predation between micro- and meso-zooplankton along with strong preferences for nanophytoplankton and diatoms, respectively, leads to their mutual exclusion with a mixture of bottom-up and top-down control of the plankton community composition. In each model, the grazing pressure of the zooplankton PFTs and the way it is exerted on their preys may result in the food web dynamics and structure of the model to diverge from the one that was intended when designing the model. Our approach shows that the food web dynamics, in particular the strength of the predator-prey interactions, are driven by the choice of parameters and more specifically the food preferences. Consequently, our findings stress the importance of equation and parameter choice as they define interactions between PFTs and overall food web dynamics (competition, bottom-up or top-down effects). Also, the differences in the simulated food-webs between different models highlight the gap of knowledge for zooplankton rates and predator-prey interactions. In particular, concerted effort is needed to identify the key growth and loss parameters and interactions and quantify them with targeted laboratory experiments in order to bring our understanding of zooplankton at a similar level to phytoplankton. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
  • Yoshio Masuda, Yasuhiro Yamanaka, Yoshikazu Sasai
    JOURNAL OF MARINE SCIENCE AND TECHNOLOGY 18 (2) 220 - 228 0948-4280 2013/06 [Refereed][Not invited]
     
    In moving-ship type CO2 ocean sequestration, liquid CO2 is discharged into a domain in a water column. Since the maximum CO2 concentration that is reached depends on the horizontal shape of the water column and the depths of release, it is very important to optimize these parameters for each injection site in order to minimize the biological impact. We conducted numerical experiments using an offline Oceanic General Circulation Model with a horizontal resolution of 0.1 degree x 0.1 degree. Experiments using a different horizontal site shape show that a site elongated in the meridional direction is effective to reduce the CO2 concentration. This is because CO2 has a tendency to be transported in a zonal direction. Optimization of the vertical distribution of CO2 injections is inherently determined by the balance of the following two factors; (1) dilution effect by eddy activity which decreases with depth, and the (2) predicted no effect concentration (PNEC), a criterion concentration causing no effect on biota, which increases with depth. Based on superposition of simulated CO2 concentration, we determined the optimized vertical distribution of CO2 injection which keeps the ratio of a simulated maximum CO2 concentration to PNEC constant.
  • J. N. Negishi, S. Nagayama, M. Kume, S. Sagawa, Y. Kayaba, Y. Yamanaka
    ECOLOGICAL INDICATORS 24 127 - 137 1470-160X 2013/01 [Refereed][Not invited]
     
    We tested the hypothesis that globally imperiled freshwater mussels (Order: Unionoida) can be used as an indicator of fish communities in lowland aquatic systems for relatively small geographic areas (i.e., <100 km(2)). The survey was conducted in 13 reaches within a network of agricultural drainage channels and in 9 floodplain backwaters in Central Japan. In each site, the fish community was examined on four seasonal occasions (spring to early summer, mid-summer, fall to early winter, and winter) and related to the mussel community. Total abundance, taxon richness, and diversity index were used to characterize fish communities. Mussel community variables predicted some aspects of fish communities, but such patterns were seasonally limited. In both systems, mussel community variables had no predictive power for the total abundance of fishes. In drainage channels, taxon richness of mussels was a good predictor of all fish community variables except for total abundance in early summer. In winter, mussel abundance predicted well the taxon richness of the fish community, while taxon richness predicted the diversity index of the fish community. In backwaters, mussel abundance was a good predictor of fish community variables except total abundance in mid-summer. A relatively minor portion (<23%) of fish-mussel relationships was attributable to direct commensalism between mussels and bitterlings. A conceptual framework was provided to help identify the mechanisms behind fish-mussel relationships. Our findings validated the use of mussels as an indicator of high-quality summer rearing habitats in backwaters and wintering and reproduction habitats of fishes in drainage channels. (C) 2012 Elsevier Ltd. All rights reserved.
  • T. Hashioka, M. Vogt, Y. Yamanaka, C. Le Quere, E. T. Buitenhuis, M. N. Aita, S. Alvain, L. Bopp, T. Hirata, I. Lima, S. Sailley, S. C. Doney
    BIOGEOSCIENCES 10 (11) 6833 - 6850 1726-4170 2013 [Refereed][Not invited]
     
    We investigated the mechanisms of phytoplankton competition during the spring bloom, one of the most dramatic seasonal events in lower-trophic-level ecosystems, in four state-of-the-art plankton functional type (PFT) models: PISCES, NEMURO, PlankTOM5 and CCSM-BEC. In particular, we investigated the relative importance of different ecophysiological processes on the determination of the community structure, focusing both on the bottom-up and the top-down controls. The models reasonably reproduced the observed global distribution and seasonal variation of phytoplankton biomass. The fraction of diatoms with respect to the total phytoplankton biomass increases with the magnitude of the spring bloom in all models. However, the governing mechanisms differ between models, despite the fact that current PFT models represent ecophysiological processes using the same types of parameterizations. The increasing trend in the percentage of diatoms with increasing bloom magnitude is mainly caused by a stronger nutrient dependence of diatom growth compared to nanophytoplankton (bottom-up control). The difference in the maximum growth rate plays an important role in NEMURO and PlankTOM5 and determines the absolute values of the percentage of diatoms during the bloom. In CCSM-BEC, the light dependency of growth plays an important role in the North Atlantic and the Southern Ocean. The grazing pressure by zooplankton (top-down control), however, strongly contributes to the dominance of diatoms in PISCES and CCSM-BEC. The regional differences in the percentage of diatoms in PlankTOM5 are mainly determined by top-down control. These differences in the mechanisms suggest that the response of marine ecosystems to climate change could significantly differ among models, even if the present-day ecosystem is reproduced to a similar degree of confidence. For further understanding of plankton competition and for the prediction of future change in marine ecosystems, it is important to understand the relative differences in each physiological rate and life history rate in the bottom-up and the top-down controls between PFTs.
  • Takafumi Hirata, Stephane Saux-Picart, Taketo Hashioka, Maki Aita-Noguchi, Hiroshi Sumata, Masahito Shigemitsu, J. Icarus Allen, Yasuhiro Yamanaka
    Journal of Marine Systems 109-110 129 - 137 0924-7963 2013/01 [Refereed][Not invited]
     
    Phytoplankton functional types (PFTs) derived from a global 3D marine ecosystem model, MEM-OU, are compared with those observed by satellite. The climatological field of the large phytoplankton (diatoms) and small phytoplankton (nano- and picoplankton) showed the model and satellite observation generally agrees in their spatial distribution but showed some biases in the equatorial oceans and higher latitudes. Grid-by-grid correlation derived from the time series of the model and satellite observation showed a significant dependence on latitude, and it was found that lower (higher) correlation coefficients were not necessarily found in the regions where higher (lower) bias was found. Spatial PCA analysis of monthly climatology of PFTs showed that a major spatial pattern of PFTs results from a steady state distribution superimposed by regional seasonal distribution. The model and the satellite observation both showed such seasonality, but we found that the model remarkably showed strong seasonality in the Southern Oceans and the equatorial oceans. The wavelet pattern comparison analysis was applied to quantify the spatial scale(s) at which the agreement in spatial distributions of PFTs can be obtained. The objective skill score determined using the pattern matching/mismatching analysis by the wavelet showed that the model has a skill to represent observed spatial patterns at horizontal scales over 1800 km (i.e. basin and global scale). The agreement is found even at the spatial scales down to 200. km (i.e. meso-scales), when the pigment biomass of the PFTs at the scales is relatively small. Our comparison enabled an objective and quantitative examination of the validity and weakness of the model by clarifying the spatial scale(s) to which the present PFT model has skill, and adds a value on conventional comparison procedure based on univariate statistics. © 2012 Elsevier B.V.
  • Takeshi Okunishi, Shin-ichi Ito, Taketo Hashioka, Takashi T. Sakamoto, Naoki Yoshie, Hiroshi Sumata, Yumiko Yara, Naosuke Okada, Yasuhiro Yamanaka
    Climatic Change 115 (3-4) 485 - 503 0165-0009 2012/11 [Refereed][Not invited]
     
    We developed a multi-trophic level ecosystem model by coupling physical, biogeochemical-plankton and fish models. An oceanic general circulation model was coupled with a lower trophic level ecosystem model and a Japanese sardine migration model, and applied to the western North Pacific. To investigate the impact of global warming on the pelagic fish ecosystem, such as Japanese sardine, we conducted numerical experiments of growth and migration of Japanese sardine using physical fields for the present day and future with a global warming scenario simulated by a high-resolution climate model. The model results demonstrated possible impacts of global warming on the growth and migration pattern of Japanese sardine. The growths of fish in the current main spawning region under the global warming scenario were significantly slower than those under the present climate scenario. Fish in this region will be at disadvantage for their recruitment under the global warming condition. Prey conditions in the spawning region were projected not to markedly change under global warming condition while water temperature increased. As a result sardine spawning ground was projected to shift towards more north areas. During the feeding migration period in summer, geographical distribution of juveniles fish was projected to shift northwards by one to two degrees latitude under the global warming condition following the change in the distribution of optimal temperature region for feeding. However, this northwards shift of the optimal temperature for feeding was minimized adjacent to the western North Pacific by the cooler water supply by the intensification of the Oyashio. © 2012 Springer Science+Business Media B.V.
  • ONITSUKA GO, ONITSUKA GO, YANAGI TETSUO, UNO ITSUSHI, KAWAMURA HIDEYUKI, YOON JONG-HWAN, YAMANAKA YASUHIRO
    沿岸海洋研究 50 (1) 45-51  1342-2758 2012/08 [Refereed][Not invited]
  • YAMAGISHI Natsuko, TANAKA Daisuke, SATO Daisuke, NAKAMURA Kazuki, YAMANAKA Yasuhiro, SATO Shiho
    日本雪工学会誌 : journal of snow engineering 28 (3) 231 - 234 0913-3526 2012/07 [Refereed][Not invited]
  • M. Shigemitsu, T. Okunishi, J. Nishioka, H. Sumata, T. Hashioka, M. N. Aita, S. L. Smith, N. Yoshie, N. Okada, Y. Yamanaka
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 117 (6) 0148-0227 2012/06 [Refereed][Not invited]
     
    To investigate the iron cycle at Station A4 in the Oyashio region of the western subarctic Pacific, we developed a 1-D ecosystem model consisting of 14 components including the iron cycle. The parameters associated with the iron cycle were optimized by assimilating monthly averaged data from time series observations for depth-integrated net primary production, nitrate, silicate, dissolved and particulate iron within the surface mixed layer (ML) and at two depths (200 and 300 m depth). The model successfully reproduced the observations and demonstrated that (1) on an annual basis, winter mixing of subsurface water supplies more dissolved iron (Fe-d) to the ML than does dust dissolution, (2) Fe-d concentration in the ML rapidly declines to near-depletion during the peak period of the diatom bloom in spring, which results in an increasing consumption ratio of silicate to nitrogenous nutrients by diatoms as they become more iron-limited, causing a more rapid decrease of silicate compared to that of nitrogenous nutrients in the ML, followed by the silicate limitation of diatoms, and (3) Fe-d supplied to the ML by dust dissolution and desorption from particulate iron, by alleviating iron limitation of phytoplankton, supports their continuous utilization of nitrate from spring to fall even though Fe-d concentration in the ML remains low after the peak spring bloom. The model explained quantitatively the above behavior of Fe-d and other nutrients associated with Fe-d over the annual cycle in the Oyashio region.
  • M. Shigemitsu, T. Okunishi, J. Nishioka, H. Sumata, T. Hashioka, M. N. Aita, S. L. Smith, N. Yoshie, N. Okada, Y. Yamanaka
    Journal of Geophysical Research: Oceans 117 (6) 2169-9291 2012 [Refereed][Not invited]
     
    To investigate the iron cycle at Station A4 in the Oyashio region of the western subarctic Pacific, we developed a 1-D ecosystem model consisting of 14 components including the iron cycle. The parameters associated with the iron cycle were optimized by assimilating monthly averaged data from time series observations for depth-integrated net primary production, nitrate, silicate, dissolved and particulate iron within the surface mixed layer (ML) and at two depths (200 and 300 m depth). The model successfully reproduced the observations and demonstrated that (1) on an annual basis, winter mixing of subsurface water supplies more dissolved iron (Fed) to the ML than does dust dissolution, (2) Fed concentration in the ML rapidly declines to near-depletion during the peak period of the diatom bloom in spring, which results in an increasing consumption ratio of silicate to nitrogenous nutrients by diatoms as they become more iron-limited, causing a more rapid decrease of silicate compared to that of nitrogenous nutrients in the ML, followed by the silicate limitation of diatoms, and (3) Fed supplied to the ML by dust dissolution and desorption from particulate iron, by alleviating iron limitation of phytoplankton, supports their continuous utilization of nitrate from spring to fall even though Fed concentration in the ML remains low after the peak spring bloom. The model explained quantitatively the above behavior of Fed and other nutrients associated with Fed over the annual cycle in the Oyashio region. © 2012 American Geophysical Union. All Rights Reserved.
  • Akemi TANAKA, Kiyoshi TAKAHASHI, Yonghee SHIN, Yuji MASUTOMI, Yasuhiro YAMANAKA, Tomonori SATO
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) Japan Society of Civil Engineers 68 (5) I{\_}237  2185-6648 2012 [Refereed][Not invited]
  • Y. Yara, M. Vogt, M. Fujii, H. Yamano, C. Hauri, M. Steinacher, N. Gruber, Y. Yamanaka
    BIOGEOSCIENCES 9 (12) 4955 - 4968 1726-4170 2012 [Refereed][Not invited]
     
    Using results from four coupled global carbon cycle-climate models combined with in situ observations, we estimate the effects of future global warming and ocean acidification on potential habitats for tropical/subtropical and temperate coral communities in the seas around Japan. The suitability of coral habitats is classified on the basis of the currently observed regional ranges for temperature and saturation states with regard to aragonite (Omega(arag)). We find that, under the "business as usual" SRES A2 scenario, coral habitats are projected to expand northward by several hundred kilometers by the end of this century. At the same time, coral habitats are projected to become sandwiched between regions where the frequency of coral bleaching will increase, and regions where Omega(arag) will become too low to support sufficiently high calcification rates. As a result, the habitat suitable for tropical/subtropical corals around Japan may be reduced by half by the 2020s to 2030s, and is projected to disappear by the 2030s to 2040s. The habitat suitable for the temperate coral communities is also projected to decrease, although at a less pronounced rate, due to the higher tolerance of temperate corals for low Omega(arag). Our study has two important caveats: first, it does not consider the potential adaptation of the coral communities, which would permit them to colonize habitats that are outside their current range. Second, it also does not consider whether or not coral communities can migrate quickly enough to actually occupy newly emerging habitats. As such, our results serve as a baseline for the assessment of the future evolution of coral habitats, but the consideration of important biological and ecological factors and feedbacks will be required to make more accurate projections.
  • A. Yamamoto, M. Kawamiya, A. Ishida, Y. Yamanaka, S. Watanabe
    BIOGEOSCIENCES 9 (6) 2365 - 2375 1726-4170 2012 [Refereed][Not invited]
     
    The largest pH decline and widespread undersaturation with respect to aragonite in this century due to uptake of anthropogenic carbon dioxide in the Arctic Ocean have been projected. The reductions in pH and aragonite saturation state in the Arctic Ocean have been caused by the melting of sea ice as well as by an increase in the concentration of atmospheric carbon dioxide. Therefore, future projections of pH and aragonite saturation in the Arctic Ocean will be affected by how rapidly the reduction in sea ice occurs. The observed recent Arctic sea-ice loss has been more rapid than projected by many of the climate models that contributed to the Intergovernmental Panel on Climate Change Fourth Assessment Report. In this study, the impact of sea-ice reduction rate on projected pH and aragonite saturation state in the Arctic surface waters was investigated. Reductions in pH and aragonite saturation were calculated from the outputs of two versions of an Earth system model with different sea-ice reduction rates under similar CO2 emission scenarios. The newer model version projects that Arctic summer ice-free condition will be achieved by the year 2040, and the older version predicts ice-free condition by 2090. The Arctic surface water was projected to be undersaturated with respect to aragonite in the annual mean when atmospheric CO2 concentration reaches 513 (606) ppm in year 2046 (2056) in new (old) version. At an atmospheric CO2 concentration of 520 ppm, the maximum differences in pH and aragonite saturation state between the two versions were 0.1 and 0.21 respectively. The analysis showed that the decreases in pH and aragonite saturation state due to rapid sea-ice reduction were caused by increases in both CO2 uptake and freshwater in-put. Thus, the reductions in pH and aragonite saturation state in the Arctic surface waters are significantly affected by the difference in future projections for sea-ice reduction rate. Our results suggest that the future reductions in pH and aragonite saturation state could be significantly faster than previously projected if the sea-ice reduction in the Arctic Ocean keeps its present pace.
  • Takeshi Okunishi, Shin-Ichi Ito, Daisuke Ambe, Akinori Takasuka, Takahiko Kameda, Kazuaki Tadokoro, Takashi Setou, Kosei Komatsu, Atsushi Kawabata, Hiroshi Kubota, Tadafumi Ichikawa, Hiroya Sugisaki, Taketo Hashioka, Yasuhiro Yamanaka, Naoki Yoshie, Tomowo Watanabe
    FISHERIES OCEANOGRAPHY 21 (1) 44 - 57 1054-6006 2012 [Refereed][Not invited]
     
    A two-dimensional individual-based fish movement model coupled with fish bioenergetics was developed to simulate the observed migration and growth of Japanese sardine (Sardinops melanostictus) in the western North Pacific. In the model, derived from the observed oceanenvironmental data as the driving force, fish movement was adapted as a kinesis behavior. The model successfully simulated the observed transport patterns during the egg and larval stages and the northward migrations during the juvenile stage in 2005, 2006 and 2007. The model results showed that both temperature during the larval stage in the Kuroshio Extension and the prey availability during the early juvenile stage in the KuroshioOyashio transitional area are important factors for growth of Japanese sardine. In autumn, the observed juvenile sardine were mainly distributed in the subarctic water region off the Kuril Islands, which is an area (158165 degrees E, 4347 degrees N) with a high chlorophyll-a (Chl-a) concentration. The model reproduced the fish distribution, which has a high density in this region. The high Chl-a concentration area in autumn may contribute to increasing the survival rate of Japanese sardine by cascading up the food chain, from the high primary production, and is an important habitat for recruitment success of Japanese sardine.
  • Ryota Shibano, Yasuhiro Yamanaka, Naosuke Okada, Takashi Chuda, Shin-ichi Suzuki, Hiroshi Niino, Mitsuhiro Toratani
    GEOPHYSICAL RESEARCH LETTERS 38 (18) 0094-8276 2011/09 [Refereed][Not invited]
     
    Strong phytoplankton blooms are occasionally observed around a recurvature point of typhoon tracks in the western subtropical Pacific. These are noteworthy events in subtropical regions where both nutrient concentrations and biological production are persistently low. We investigated the response of phytoplankton to typhoon passage using a numerical model with/without biogeochemical processes. The model reproduced the observed patch-like phytoplankton bloom around a recurvature point of Typhoon Keith in 1997. The strong bloom is caused by the typhoon-centered upwelling of nutrient-rich water from below the euphotic layer, which supplies the nutrients required for phytoplankton growth, resulting in higher chlorophyll-a concentrations. Biogeochemical processes then play essential roles in determining the response after the passage of typhoons in subtropical regions. Citation: Shibano, R., Y. Yamanaka, N. Okada, T. Chuda, S. Suzuki, H. Niino, and M. Toratani (2011), Responses of marine ecosystem to typhoon passages in the western subtropical North Pacific, Geophys. Res. Lett., 38, L18608, doi:10.1029/2011GL048717.
  • YAMANAKA Yasuhiro
    Journal of the Japan Society for Computational Engineering and Science 日本計算工学会 16 (3) 2590 - 2593 1341-7622 2011/07 [Refereed][Not invited]
  • SHIGEMATSU Masahito, YAMANAKA Yasuhiro
    Chikyukagaku 日本地球化学会 45 (1) 1 - 28 0386-4073 2011/03 [Refereed][Not invited]
     
    The importance of an ecosystem model as a tool to analyse ocean biogeochemical data has recently been increasing. That is because an ecosystem model can be used as a tool (1) to test hypotheses to explain observational data at hand, (2) to combine the generally scarce ocean observations into a more coherent picture and (3) to indirectly obtain some information about immeasurable process by a data-assimilative approach. In this review, we first show the basic model equations to construct a relatively simple ecosystem model. Then, we introduce some researches which use the above usefulness of...
  • 気候変動に伴う北海道の雪質変化推定手法の開発
    中村一樹, 佐藤友徳, 山中康裕, 西村浩一
    寒地技術シンポジウム論文集 27 80 - 85 2011 [Not refereed][Not invited]
  • Yara, Y, K. Oshima, M. Fujii, H. Yamano, Y. Yamanaka, N. Okada
    Galaxea 13 (1) 11 - 20 2011 [Refereed][Not invited]
     
    Using projected monthly mean sea surface tem-perature (SST) in the 21st century obtained by multiple climate models and SST-based indices for the poleward range expansions of three types of coral habitats, we quantitatively evaluated the effects of SST warming on potential northern limit of coral habitats in seas close to Japan and their uncertainty in the global warming pro-jections. The uncertainty in the timing of temperate coral community formation due to global warming was no less than 30 years, with a modulation of ±10 years due to decadal climate variability. Tropical-subtropical and tem-perate coral communities and coral occurrence in seas close to Japan were predicted to shift poleward by a few hundred kilometers by the end of the 21st century. The average estimated speeds of the shifts were 1, 2, and 4 km/year for the tropical-subtropical coral community, temper-ate coral community, and coral occurrence, respectively. The simulated speeds were relatively slower than those previously observed (up to 14 km/year; Yamano et al. 2011), indicating that there are time lags between the new recruitment of coral colonies and the establishment of coral communities. Hence, monitoring of coral dynamics in response to SST warming is required. Collaboration between monitoring and modeling would enhance the reliability of future projections of changes in coral ha-bitats. Such projections are important for conserving marine biodiversity and developing plans for human societies to adapt to global warming.
  • T. Hirata, N. J. Hardman-Mountford, R. J. W. Brewin, J. Aiken, R. Barlow, K. Suzuki, T. Isada, E. Howell, T. Hashioka, M. Noguchi-Aita, Y. Yamanaka
    BIOGEOSCIENCES 8 (2) 311 - 327 1726-4170 2011 [Refereed][Not invited]
     
    Error-quantified, synoptic-scale relationships between chlorophyll-a (Chl-a) and phytoplankton pigment groups at the sea surface are presented. A total of ten pigment groups were considered to represent three Phytoplankton Size Classes (PSCs, micro-, nano- and picoplankton) and seven Phytoplankton Functional Types (PFTs, i.e. diatoms, dinoflagellates, green algae, prymnesiophytes (haptophytes), pico-eukaryotes, prokaryotes and Prochlorococcus sp.). The observed relationships between Chl-a and PSCs/PFTs were well-defined at the global scale to show that a community shift of phytoplankton at the basin and global scales is reflected by a change in Chl-a of the total community. Thus, Chl-a of the total community can be used as an index of not only phytoplankton biomass but also of their community structure. Within these relationships, we also found nonmonotonic variations with Chl-a for certain pico-sized phytoplankton (pico-eukaryotes, Prokaryotes and Prochlorococcus sp.) and nano-sized phytoplankton (Green algae, prymnesiophytes). The relationships were quantified with a leastsquare fitting approach in order to enable an estimation of the PFTs from Chl-a where PFTs are expressed as a percentage of the total Chl-a. The estimated uncertainty of the relationships depends on both PFT and Chl-a concentration. Maximum uncertainty of 31.8% was found for diatoms at Chla = 0.49 mg m(-3). However, the mean uncertainty of the relationships over all PFTs was 5.9% over the entire Chl-a range observed in situ (0.02< Chl-a < 4.26 mg m(-3)). The relationships were applied to SeaWiFS satellite Chl-a data from 1998 to 2009 to show the global climatological fields of the surface distribution of PFTs. Results show that microplankton are present in the mid and high latitudes, constituting only similar to 10.9% of the entire phytoplankton community in the mean field for 1998-2009, in which diatoms explain similar to 7.5%. Nanoplankton are ubiquitous throughout the global surface oceans, except the subtropical gyres, constituting similar to 45.5%, of which prymnesiophytes (haptophytes) are the major group explaining similar to 31.7% while green algae contribute similar to 13.9%. Picoplankton are dominant in the subtropical gyres, but constitute similar to 43.6% globally, of which prokaryotes are the major group explaining similar to 26.5% (Prochlorococcus sp. explaining 22.8%), while pico-eukaryotes explain similar to 17.2% and are relatively abundant in the South Pacific. These results may be of use to evaluate global marine ecosystem models.
  • Hiroshi Sumata, Taketo Hashioka, Tatsuo Suzuki, Naoki Yoshie, Takeshi Okunishi, Maki N. Aita, Takashi T. Sakamoto, Akio Ishida, Naosuke Okada, Yasuhiro Yamanaka
    JOURNAL OF MARINE SYSTEMS 83 (1-2) 67 - 87 0924-7963 2010/10 [Not refereed][Not invited]
     
    Hindcast experiment with an eddy-permitting ocean ecosystem model was performed in order to investigate the process of nutrient supply into the euphotic zone by vertical and horizontal fluxes with multiple time scales. The model reasonably reproduced the basin-scale spatial pattern of biological production and its seasonal cycles with eddy fields, statistically consistent with those observed in the satellite images. The model results illustrated the nutrient cycle in the euphotic zone with mesoscale eddies, in which the vertical advection with mesoscale spatial variation and convection with relatively large spatial variation supply nutrients into the euphotic zone, and the horizontal advection redistributes them within the euphotic zone, thereby fueling biological production. The vertical advection associated with mean flow supplies a substantial part of nutrients from the aphotic zone, and contributions from time-varied vertical fluxes are limited within the tropical region and regions where strong meandering currents exist. Horizontal advection due to seasonal and eddy fluctuations plays an important role in the redistribution process, in addition to that effected by temporal-mean advection. The relative importance of these fluctuations strongly depends on the horizontal scales of vertical nutrient supply, in contrast to the relatively small effects eddy fields have on heat or fresh-water transport in the global ocean. (C) 2010 Elsevier B.V. All rights reserved.
  • Masahito Shigemitsu, Yutaka W. Watanabe, Yasuhiro Yamanaka, Hajime Kawakami, Makio C. Honda
    JOURNAL OF OCEANOGRAPHY 66 (5) 697 - 708 0916-8370 2010/10 [Refereed][Not invited]
     
    We used time-series sediment trap data for four major components, organic matter and ballast minerals (CaCO3, opal, and lithogenic matter) from 150, 540, and 1000 m in the western subarctic Pacific (WSAP), where opal is the predominant mineral in sinking particles, to develop four simple models for settling particles, including the "ballast model". The ballast model is based on the concept that most of the organic matter "rain" in the deep sea is carried by the minerals. These four models are designed to simultaneously reproduce the flux of each major component of settling particles at 540 and 1000 m by using the data for each component at 150 m as initial values. Among the four models, the ballast model, which considers the sinking velocity increase with depth, was identified as the best using the Akaike information criterion as a measure of the model fit to data. This model successfully reproduced the flux of organic matter at 540 and 1000 m, indicating that the ballast model concept works well in the shallow zone of the WSAP on a seasonal timescale. This also suggests that ballast minerals not only physically protect the organic matter from degradation during the settling process but also enhance the sinking velocity and reduce the degree of decomposition.
  • Takasumi Kurahashi-Nakamura, Ayako Abe-Ouchi, Yasuhiro Yamanaka
    CLIMATE DYNAMICS 35 (4) 713 - 719 0930-7575 2010/09 [Not refereed][Not invited]
     
    Based on LGM experiments with an atmosphere-ocean general circulation model, we systematically investigated the effects of physical changes in the ocean and induced biological effects as well on the low atmospheric CO2 concentration (pCO(2)) at the last glacial maximum (LGM). Numerical experiments with an oceanic carbon-cycle model showed that pCO(2) was lowered by similar to 30 ppm in the LGM ocean. Most of the pCO(2) reduction was explained by the change in CO2 solubility in the ocean due to lower sea surface temperature (SST) during the LGM. Moreover, we found that SST changes in the high-latitude Northern Atlantic could explain more than one-third of the overall change in pCO(2) induced by global SST change, suggesting an important feedback between the Laurentide ice sheet and pCO(2).
  • Shin-ichi Ito, Kenneth A. Rose, Arthur J. Miller, Ken Drinkwater, Keith Brander, James E. Overland, Svein Sundby, Enrique Curchitser, James W. Hurrell, Yasuhiro Yamanaka
    Marine Ecosystems and Global Change 287 - 322 2010/05/01 [Not refereed][Not invited]
     
    Available evidence of recent climate-induced physical and chemical changes in the oceans is summarized, including changes in sea temperatures, nutrient supply, mixing and circulation, trace element supply, acidification, and sea-level rise. The biological responses in the marine environment to these documented physical changes are then presented by trophic level. Our ability to project ecosystem responses to likely future global change is discussed, including numerous examples of existing projections for several regions of the world's oceans. This chapter concludes with a discussion of a vision of the next steps that are needed to develop better models capable of improving our projections of ecosystem responses to global change.
  • Masahito Shigemitsu, Yasuhiro Yamanaka, Yutaka W. Watanabe, Nobuhiro Maeda, Shinichiro Noriki
    EARTH AND PLANETARY SCIENCE LETTERS 293 (1-2) 180 - 190 0012-821X 2010/04 [Not refereed][Not invited]
     
    We used moored time-series sediment traps to collect settling particles at station KNOT (44 degrees N, 155 degrees E; trap depth 770 m) in the western subarctic Pacific (WSAP) from October 1999 to May 2006. Particulate nitrogen content (PN) and isotope ratios (delta(15)N(PN)) were measured in the samples collected. The general pattern of variation in delta(15)N(PN) results showed lower values during the spring bloom periods and summer, and higher values during winter. To interpret the processes controlling such variations quantitatively and reveal some implications for paleoceanographic use of delta(15)N(PN), we developed an ecosystem model that included nitrogen isotopes. This model was validated with an observed data set and successfully reproduced the seasonal variations of delta(15)N(PN). In simulations, the lower delta(15)N(PN) during the spring bloom period was caused mainly by the highest proportion of dead large phytoplankton (diatom) in PN within a year. the highest f-ratio of the year, and phytoplankton assimilation of nitrate with the lowest delta(15)N of the year. The lower delta(15)N(PN) in summer was due to the high relative proportion of dead non-diatom small phytoplankton and microzooplankton fecal pellet with the lowest delta(15)N values among all the PN components in our model. The higher delta(15)N(PN) in winter was mainly caused by the highest proportion of zooplankton components in PN, with higher delta(15)N values than phytoplankton components, and the enhanced delta(15)N values of ammonium induced by nitrification and its subsequent assimilation by phytoplankton. Our identification of nitrification as one cause of higher delta(15)N(PN) in winter is consistent with previous findings in a proximal marginal sea, the Okhotsk Sea, with an ecosystem model simpler than our model. This might indicate that the cause of higher delta(15)N(PN) in winter is common in the WSAP. In our model, we optimized the isotope effect of each process using our observational data of delta(15)N(PN) and delta(15)N of nitrate published elsewhere as constraints, and investigated the sensitivity of the annual flux-weighted mean of delta(15)N(PN) to the isotopic fractionation effects. As a result, we found that the isotope effects of nitrate assimilation appear to be different for non-diatom small phytoplankton and large diatom, and the annual flux-weighted mean of delta(15)N(PN) can be influenced to some extent by the isotope effect of nitrification. (C) 2010 Elsevier B.V. All rights reserved.
  • S. Lan Smith, Naoki Yoshie, Yasuhiro Yamanaka
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 57 (3) 394 - 408 0967-0637 2010/03 [Not refereed][Not invited]
     
    During the SERIES iron-enrichment experiment in the eastern subarctic Pacific, after addition of iron and its subsequent depletion, the Si:N drawdown ratio increased at approximately the time that diatoms became iron limited. Laboratory studies have reported that this results from a decrease in the rate of N uptake together with a more moderate decrease in the rate of Si uptake for iron-limited cultures compared to iron-replete cultures. However, for SERIES Boyd et al. (Limnol. Oceanogr. 50 (2005)) reported an unexplained increase in the rate of Si uptake at the onset of iron limitation and suggested that studies of nutrient uptake kinetics should be undertaken in search of an explanation. We compare the classic Michealis-Menten (MM) kinetics to the recently developed optimal uptake (OU) kinetics (the SPONGE: Smith and Yamanaka. Limnol. Oceanogr. 52 (2007)) within a variable-composition model, which employs cell quotas for each relevant nutrient, applied to the multielement (C, N, Si, Fe) dynamics during SERIES. Using the Monte Carlo Markov Chain, we fit two versions of the model (differing only in the equations for nutrient uptake) to the available data for nutrient concentrations, chlorophyll, biogenic silica and particulate organic carbon and specific growth rates. With either uptake kinetics, the model reproduces observed concentrations well for nutrients and somewhat less well for chlorophyll. The different uptake kinetics yield greater differences in modeled elemental composition of phytoplankton and biomass of phytoplankton and zooplankton, which are not directly constrained by data. MM kinetics cannot reproduce the observed increase in Si uptake rate as a function of the decreasing trend in concentration of silicic acid, and it predicts Si limitation throughout nearly all of the experiment after iron-fertilization. In contrast, OU kinetics reproduces the increase in Si uptake rate and matches the observation-based estimate for the timing of the return to iron limitation. The key assumption of the SPONGE, that uptake rates of all nutrients depend on physiological acclimation by phytoplankton as a function of the ambient concentration of the growth-limiting nutrient, was originally formulated for modeling chemostat experiments. We show that it also agrees with the observations from this field experiment and provides an explanation for the increases in Si uptake rate and Si:N drawdown ratio. (C) 2009 Elsevier Ltd. All rights reserved.
  • Keith B. Rodgers, Robert M. Key, Anand Gnanadesikan, Jorge L. Sarmiento, Olivier Aumont, Laurent Bopp, Scott C. Doney, John P. Dunne, David M. Glover, Akio Ishida, Masao Ishii, Andrew R. Jacobson, Claire Lo Monaco, Ernst Maier-Reimer, Herle Mercier, Nicolas Metzl, Fiz F. Perez, Aida F. Rios, Rik Wanninkhof, Patrick Wetzel, Christopher D. Winn, Yasuhiro Yamanaka
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 114 (12) 0148-0227 2009/12 [Refereed][Not invited]
  • Akira Oka, Hiroyasu Hasumi, Hajime Obata, Toshitaka Gamo, Yasuhiro Yamanaka
    GLOBAL BIOGEOCHEMICAL CYCLES 23 GB4025  0886-6236 2009/11 [Not refereed][Not invited]
     
    Observed vertical profiles of rare earth elements (REEs) in the North Pacific Ocean show a systematic change from lighter to heavier REEs. Their source and sink consist of external fluxes coming from the surface and the bottom of the ocean and internal recycling within the ocean. In order to evaluate the role of each source and sink in controlling the vertical profiles of REEs, we conduct numerical simulations of REEs by using an ocean general circulation model. These simulations demonstrate that the shape of their vertical profiles is not directly related to the external sources from river runoff, atmospheric dust deposition, and coastal regions but is sensitive to the internal recycling processes within the ocean. Nutrient-like treatment where REEs are removed at the surface and released in the deep ocean is suitable for simulating the vertical profiles of lighter REEs but not for heavier REEs. When the irreversible scavenging is considered as a sink term and particle dissolution is taken into consideration as a source term, the vertical profiles of heavier REEs can be reproduced but those of lighter REEs cannot. The observed difference in the vertical profiles among REEs can be reproduced only when the reversible scavenging process is incorporated into the model. Only the reversible scavenging process accounts for the observed vertical profiles of different REEs in comprehensive manner.
  • Taketo Hashioka, Takashi T. Sakamoto, Yasuhiro Yamanaka
    GEOPHYSICAL RESEARCH LETTERS 36 (20) L20604  0094-8276 2009/10 [Refereed][Not invited]
     
    Using an eddy-permitting ecosystem model with a projected physical environment from a high-resolution climate model, we explored the potential impact of global warming on spring blooms in the western North Pacific. We focused on statistically significant signals compared with natural variability. Considering 2xCO(2) conditions, maximum biomass during the spring bloom is found to occur 10 to 20 days earlier due to strengthened stratification, and in the subarctic region, the bloom to decrease in magnitude relative to pre-industrial simulation. However, in the northern part of the Kuroshio extension region where photosynthesis is not strongly limited by nutrients, the maximum biomass increases by 20 to 40% associated with rising temperatures, even though the annually averaged biomass slightly decreases. Our results reveal that even if global warming weakly affects annually averaged quantities, it could strongly affect certain species and biogeochemical processes which depend on seasonal events such as blooms. Citation: Hashioka, T., T. T. Sakamoto, and Y. Yamanaka (2009), Potential impact of global warming on North Pacific spring blooms projected by an eddy-permitting 3-D ocean ecosystem model, Geophys. Res. Lett., 36, L20604, doi: 10.1029/2009GL038912.
  • Keith B. Rodgers, Robert M. Key, Anand Gnanadesikan, Jorge L. Sarmiento, Olivier Aumont, Laurent Bopp, Scott C. Doney, John P. Dunne, David M. Glover, Akio Ishida, Masao Ishii, Andrew R. Jacobson, Claire Lo Monaco, Ernst Maier-Reimer, Herle Mercier, Nicolas Metzl, Fiz F. Perez, Aida F. Rios, Rik Wanninkhof, Patrick Wetzel, Christopher D. Winn, Yasuhiro Yamanaka
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 114 0148-0227 2009/09 [Refereed][Not invited]
     
    Here we use observations and ocean models to identify mechanisms driving large seasonal to interannual variations in dissolved inorganic carbon (DIC) and dissolved oxygen (O-2) in the upper ocean. We begin with observations linking variations in upper ocean DIC and O-2 inventories with changes in the physical state of the ocean. Models are subsequently used to address the extent to which the relationships derived from short-timescale (6 months to 2 years) repeat measurements are representative of variations over larger spatial and temporal scales. The main new result is that convergence and divergence (column stretching) attributed to baroclinic Rossby waves can make a first-order contribution to DIC and O-2 variability in the upper ocean. This results in a close correspondence between natural variations in DIC and O-2 column inventory variations and sea surface height (SSII) variations over much of the ocean. Oceanic Rossby wave activity is an intrinsic part of the natural variability in the climate system and is elevated even in the absence of significant interannual variability in climate mode indices. The close correspondence between SSII and both DIC and O-2 column inventories for many regions suggests that SSII changes (inferred from satellite altimetry) may prove useful in reducing uncertainty in separating natural and anthropogenic DIC signals (using measurements from Climate Variability and Predictability's CO2/Repeat Hydrography program).
  • Kazuhiro Misumi, Yasuhiro Yamanaka, Eiichi Tajika
    EARTH AND PLANETARY SCIENCE LETTERS 286 (1-2) 316 - 323 0012-821X 2009/08 [Not refereed][Not invited]
     
    Response of biogeochemical cycles in the atmosphere and ocean to a major episode Of CO2 release event was investigated using numerical simulations. The results are applied to examine a previously proposed scenario for the Ocean Anoxic Event-1a (OAE-1a) caused by an episodic CO2 release due to the Ontong Java Plateau (OJP) formation in the mid-Cretaceous. We developed an atmosphere-ocean biogeochemical cycle model that includes geochemical input to and output from the atmosphere and ocean due to submarine volcanic activity, continental weathering and sedimentation. We made a reference state, and then the state was perturbed in 42 cases of episodic CO2 release with different rates and periods. In all cases, the elevated atmospheric CO2 level results in an increase in phosphate concentration in the ocean caused by intensified weathering. Variations in the marine carbon isotope ratio are characterized by negative-to-positive excursions with a longer timescale for the latter. The deep water becomes anoxic in the cases with the release of a large amount Of CO2. These features are also seen in the geological records of OAE-1a. From quantitative comparisons, we found that the amount Of CO2 release required to cause OAE-1a is about 8 x 10(18) mol, and atmospheric CO2 increases by a factor of three or more (>3600 ppm) in these cases. The amount can be accounted for by CO2 released due to the OJP formation, if the original magma contained a large CO2 fraction. Therefore, we conclude that the OJP formation possibly caused OAE-1a. (C) 2009 Elsevier B.V. All rights reserved.
  • A. Yamamoto, Y. Yamanaka, E. Taiika
    EARTH AND PLANETARY SCIENCE LETTERS 284 (3-4) 590 - 598 0012-821X 2009/07 [Refereed][Not invited]
     
    Massive methane release from sea-floor sediments due to decomposition of methane hydrate, and thermal decomposition of organic matter by volcanic outgassing, is a potential contributor to global warming. However, the degree of global warming has not been estimated due to uncertainty over the proportion of methane flux from the sea-floor to reach the atmosphere. Massive methane release from a large sea-floor area would result in methane-saturated seawater, thus some methane would reach the atmosphere. In this study, we discussed the possibility of the methane release from a large sea-floor area to the atmosphere focusing on methane saturation in the water column necessary for a methane bubble to reach the atmosphere. Using a one-dimensional numerical model integrated over time, we predict methane bubbles and methane concentration in the water column under the condition of continuous methane input from the sea-floor to the water column. We found that some methane bubbles reach the atmosphere even when the methane saturation fraction in the water column is much lower than 100%. We compared the methane input from the sea-floor required for a methane bubble to reach the atmosphere to the amount of methane in the sediment in the form of methane hydrate and free gas. In most cases, our results suggest that the typical amount of methane in the sediment (i.e., typical hydrate fraction of similar to 2% and free gas of two-thirds of the amount of hydrate) is significantly lower than the required minimum methane input. It is, therefore, suggested that, except in the case of an extraordinary methane flux, the massive quantity of methane bubbles released from sea-floor gas hydrate would not reach the atmosphere directly but would be dissolved in the seawater. With regard to global warming due to human activities, the release of methane bubbles due to methane hydrate decomposition may not be enough to significantly accelerate total global warming. In the case of metamorphic methane release during PETM, there is the possibility that the released methane resulted in methane-sa tu rated seawater, allowing some methane to reach the atmosphere. (C) 2009 Elsevier B.V. All rights reserved.
  • S. Lan Smith, Yasuhiro Yamanaka, Markus Pahlow, Andreas Oschlies
    MARINE ECOLOGY PROGRESS SERIES 384 1 - 12 0171-8630 2009/05 [Not refereed][Not invited]
     
    Phytoplankton supply the base of the marine food web and drive the biogeochemical cycles of carbon and nutrients. Over much of the ocean, their growth is limited by their uptake of nitrogen (as nitrate), which has most commonly been described by the hyperbolic Michaelis-Menten (MM) equation. However, the lack of a theory to explain variations in MM constants has hindered our ability to predict the response of marine ecosystems to changes in environmental conditions. The MM equation fits data from short-term experiments well, but does not agree with steady-state experiments over wide ranges of nutrient concentrations. In contrast, the recently developed optimal uptake kinetics (OU) does agree with the latter and can also describe the observed pattern of MM half-saturation constants from field. experiments. OU kinetics explains the observed pattern of N uptake as the result of a general physiological trade-off between nutrient uptake capacity and affinity. The existence of a general trade-off would imply a relatively high degree of predictability in the response of nutrient uptake to changing nutrient concentrations and thus provide a basis for predicting effects of climate change on marine ecosystems and biogeochemical cycles.
  • Megumi O. Chikamoto, Katsumi Matsumoto, Yasuhiro Yamanaka
    JOURNAL OF OCEANOGRAPHY 65 (2) 209 - 221 0916-8370 2009/04 [Not refereed][Not invited]
     
    The responses of atmospheric pCO(2) and sediment calcite content to changes in the export rain ratio of calcium carbonate to organic carbon are examined using a diffusion-advection ocean biogeochemical model coupled to a one-dimensional sediment geochemistry model. Our model shows that a 25% reduction in rain ratio decreases atmospheric pCO(2) by 59 ppm. This is caused by alkalinity redistribution by a weakened carbonate pump and an alkalinity increase in the whole ocean via carbonate compensation with decreasing calcite burial. The steady state responses of sedimentary calcite content and calcite preservation efficiency are rather insensitive to the deepening of the saturation horizon of 1.9 km. This insensitivity is a result of the reduced deposition flux that decreases calcite burial, counteracting the saturation horizon deepening that increases calcite burial. However, in the first 10,000 years the effect of reduced calcite deposition on the burial change is more prominent; while after 10,000 years, the effect of saturation horizon deepening is more dominant. The lowering of sediment calcite content for the first 10,000 years is effectively decoupled from the 1.9 km downward shift of the saturation horizon. Our results are in part a consequence of the more dominant role that respiration CO2 plays in sediment calcite dissolution over bottom water chemistry in our control run and support the decoupling of calcite lysocline depth and saturation horizon shifts, as suggested originally by Archer and Maier-Reimer (1994) and Archer et al. (2000).
  • Alan F. Koropitan, Motoyoshi Ikeda, Ario Damar, Yasuhiro Yamanaka
    ICES JOURNAL OF MARINE SCIENCE 66 (2) 336 - 348 1054-3139 2009/03 [Refereed][Not invited]
     
    A coupled physical-ecosystem model is applied to Jakarta Bay to examine the role of physical processes on the ecosystem. The simulated physical processes include tides, river discharge, and monsoon winds. The potential sources of nitrogen to Jakarta Bay are through river inputs and wet deposition flux. The model separates the detritus compartment into pelagic and benthic components, based on cohesive sediment processes. Physical model results agree well with the observed tidal amplitude and phase, as well as tidal currents. The biological model can produce reasonable spatial and temporal patterns in lower trophic level characteristics of the ecosystem in some areas of the bay, although a lack of observed data limits confidence in model predictions. Model results show that the physical processes associated with monsoons produce an intensification of ChI a and nutrient concentrations in the eastern and western parts of the bay during northwest monsoon and southeast monsoon, respectively. The physical and biological characteristics of bay waters are controlled by influxes from offshore; the influence of river discharge is limited to the coastal area. The sensitivity of model predictions to the open boundary, river fluxes, and benthic detritus is discussed.
  • Takeshi Okunishi, Yasuhiro Yamanaka, Shin-ichi Ito
    ECOLOGICAL MODELLING 220 (4) 462 - 479 0304-3800 2009/02 [Not refereed][Not invited]
     
    A two-dimensional individual-based model coupled with fish bioenergetics was developed to simulate migration and growth of Japanese sardine (Sardinops melanostictus) in the western North Pacific. In the model, fish movement is controlled by feeding and spawning migrations with passive transport by simulated ocean current. Feeding migration was assumed to be governed by search for local optimal habitats, which is estimated by the spatial distribution of net growth rate of a sardine bioenergetics model. The forage density is one of the most important factors which determines the geographical distributions of Japanese sardine during their feeding migrations. Spawning migration was modeled by an artificial neural network (ANN) with an input layer composed of five neurons that receive environmental information (surface temperature, temperature change experienced, current speed, day length and distance from land). Once the weight of the ANN was determined, the fish movement was solved by combining with the feeding migration model. To obtain the weights of the ANN, three experiments were conducted in which (1) the ANN was trained with back propagation (BP) method with optimum training data, (2) genetic algorithm (GA) was used to adjust the weights and (3) the weights of the ANN were decided by the GA with BP, respectively BP is a supervised learning technique for training ANNs. GA is a search technique used in computing to find approximate solutions, such as optimization of parameters. Condition factor of sardine in the model is used as a factor of optimization in the GA works. The methods using only BP or GA did not work to search the appropriate weights in the ANN for spawning migration. in the third method, which is a combined approach of GA with BP, the model reproduced the most realistic spawning migration of Japanese sardine. The changes in temperature and day length are important factors for the orientation cues of Japanese sardine according to the sensitivity analysis of the weights of the ANN. (C) 2008 Elsevier B.V All rights reserved.
  • L. Cao, M. Eby, A. Ridgwell, K. Caldeira, D. Archer, A. Ishida, F. Joos, K. Matsumoto, U. Mikolajewicz, A. Mouchet, J. C. Orr, G. -K. Plattner, R. Schlitzer, K. Tokos, I. Totterdell, T. Tschumi, Y. Yamanaka, A. Yool
    BIOGEOSCIENCES 6 (3) 375 - 390 1726-4170 2009 [Not refereed][Not invited]
     
    We compare modeled oceanic carbon uptake in response to pulse CO2 emissions using a suite of global ocean models and Earth system models. In response to a CO2 pulse emission of 590 Pg C (corresponding to an instantaneous doubling of atmospheric CO2 from 278 to 556 ppm), the fraction of CO2 emitted that is absorbed by the ocean is: 37 +/- 8%, 56 +/- 10%, and 81 +/- 4% (model mean +/- 2 sigma) in year 30, 100, and 1000 after the emission pulse, respectively. Modeled oceanic uptake of pulse CO2 on timescales from decades to about a century is strongly correlated with simulated present-day uptake of chlorofluorocarbons (CFCs) and CO2 across all models, while the amount of pulse CO2 absorbed by the ocean from a century to a millennium is strongly correlated with modeled radiocarbon in the deep Southern and Pacific Ocean. However, restricting the analysis to models that are capable of reproducing observations within uncertainty, the correlation is generally much weaker. The rates of surface-to-deep ocean transport are determined for individual models from the instantaneous doubling CO2 simulations, and they are used to calculate oceanic CO2 uptake in response to pulse CO2 emissions of different sizes pulses of 1000 and 5000 Pg C. These results are compared with simulated oceanic uptake of CO2 by a number of models simulations with the coupling of climate-ocean carbon cycle and without it. This comparison demonstrates that the impact of different ocean transport rates across models on oceanic uptake of anthropogenic CO2 is of similar magnitude as that of climate-carbon cycle feed-backs in a single model, emphasizing the important role of ocean transport in the uptake of anthropogenic CO2.
  • Keith B. Rodgers, Robert M. Key, Anand Gnanadesikan, Jorge L. Sarmiento, Olivier Aumont, Laurent Bopp, Scott C. Doney, John R Dunne, David M. Glover, Akio Ishida, Masao Ishii, Andrew R. Jacobson, Claire Lo Monaco, Ernst Maier-Reimer, Herlé Mercier, Nicolas Metzl, Fiz F. Pérez, Aida F. Rios, Rik Wanninkhof, Patrick Wetzel, Christopher D. Winn, Yasuhiro Yamanaka
    Journal of Geophysical Research: Oceans 114 (9) 2169-9291 2009 [Refereed][Not invited]
     
    Here we use observations and ocean models to identify mechanisms driving large seasonal to interannual variations in dissolved inorganic carbon (DIC) and dissolved oxygen (O2) in the upper ocean. We begin with observations linking variations in upper ocean DIC and O2 inventories with changes in the physical state of the ocean. Models are subsequently used to address the extent to which the relationships derived from short-timescale (6 months to 2 years) repeat measurements are representative of variations over larger spatial and temporal scales. The main new result is that convergence and divergence (column stretching) attributed to baroclinic Rossby waves can make a first-order contribution to DIC and O2 variability in the upper ocean. This results in a close correspondence between natural variations in DIC and O2 column inventory variations and sea surface height (SSH) variations over much of the ocean. Oceanic Rossby wave activity is an intrinsic part of the natural variability in the climate system and is elevated even in the absence of significant interannual variability in climate mode indices. The close correspondence between SSH and both DIC and O2 column inventories for many regions suggests that SSH changes (inferred from satellite altimetry) may prove useful in reducing uncertainty in separating natural and anthropogenic DIC signals (using measurements from Climate Variability and Predictability's CO2/Repeat Hydrography program.
  • L. Cao, M. Eby, A. Ridgwell, K. Caldeira, D. Archer, A. Ishida, F. Joos, K. Matsumoto, U. Mikolajewicz, A. Mouchet, J. C. Orr, G. -K. Plattner, R. Schlitzer, K. Tokos, I. Totterdell, T. Tschumi, Y. Yamanaka, A. Yool
    BIOGEOSCIENCES 6 (3) 375 - 390 1726-4170 2009 [Refereed][Not invited]
     
    We compare modeled oceanic carbon uptake in response to pulse CO2 emissions using a suite of global ocean models and Earth system models. In response to a CO2 pulse emission of 590 Pg C (corresponding to an instantaneous doubling of atmospheric CO2 from 278 to 556 ppm), the fraction of CO2 emitted that is absorbed by the ocean is: 37 +/- 8%, 56 +/- 10%, and 81 +/- 4% (model mean +/- 2 sigma) in year 30, 100, and 1000 after the emission pulse, respectively. Modeled oceanic uptake of pulse CO2 on timescales from decades to about a century is strongly correlated with simulated present-day uptake of chlorofluorocarbons (CFCs) and CO2 across all models, while the amount of pulse CO2 absorbed by the ocean from a century to a millennium is strongly correlated with modeled radiocarbon in the deep Southern and Pacific Ocean. However, restricting the analysis to models that are capable of reproducing observations within uncertainty, the correlation is generally much weaker. The rates of surface-to-deep ocean transport are determined for individual models from the instantaneous doubling CO2 simulations, and they are used to calculate oceanic CO2 uptake in response to pulse CO2 emissions of different sizes pulses of 1000 and 5000 Pg C. These results are compared with simulated oceanic uptake of CO2 by a number of models simulations with the coupling of climate-ocean carbon cycle and without it. This comparison demonstrates that the impact of different ocean transport rates across models on oceanic uptake of anthropogenic CO2 is of similar magnitude as that of climate-carbon cycle feed-backs in a single model, emphasizing the important role of ocean transport in the uptake of anthropogenic CO2.
  • Yoshio Masuda, Yasuhiro Yamanaka, Yoshikazu Sasai, Michimasa Magi, Takashi Ohsumi
    INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL 3 (1) 67 - 76 1750-5836 2009/01 [Refereed][Not invited]
     
    Site selection in CO2 ocean sequestration is examined based on the idea that a site where injected CO2 is efficiently diluted is favourable in reducing/avoiding biological impacts. Simulations Of CO2 injection into several sites by an eddy-resolving oceanic general circulation model (OGCM) show that the maximum CO2 concentration differs by a factor of 10 among sites. The distribution of eddy activity is the most important causative factor producing the geographical differences in CO2 dilution. Based on the relationship between the maximum CO2 concentration and eddy activity, we estimated the distribution of the maximum CO2 injection rate by a proposed method, which does not cause chronic impacts on biota. Around Japan, extensive ocean volume has the potential to dilute 20 million tonnes per year without chronic impacts, and some areas can be injected with 80 million tonnes per year. (C) 2008 Elsevier Ltd. All rights reserved.
  • Kazuhiro Misumi, Yasuhiro Yamanaka
    CRETACEOUS RESEARCH 29 (5-6) 893 - 900 0195-6671 2008/10 [Not refereed][Not invited]
     
    The mid-Cretaceous is well known for its ocean anoxic events. The causal mechanisms are controversial: stagnant deepwater, high biological productivity in the surface waters, and other possibilities have been suggested. Our study simulated the mid-Cretaceous ocean, using general circulation models combined with a marine biogeochemical cycle model to explore the relationship between thermohaline circulation and biogeochemical cycles and investigate the causes of ocean anoxic events. The simulated thermohaline circulation shows an unsteady inactive state. Oxygen concentrations in the deepwater decrease under the inactive state, but a horizontal gradient develops, with higher oxygen concentrations in the Tethys and lower concentrations in eastern Panthalassa. This is not due to the different ages of the deepwater but rather to the differences in biological productivity in the surface water, meaning that the relationship between thermohaline circulation and biogeochemical cycles under the inactive state is different from that in the present ocean. In the standard simulation, assuming the present level of the total amount of phosphate in the ocean, 29% of the bottom water is anoxic. The experiments increasing the amount of phosphate show its high sensitivity for extending the anoxic region with global-scale anoxia simulated under the doubled amount of phosphate. The high amount of phosphate would be reasonable because the inactive state would induce an imbalance of phosphate between riverine input and sediment output. Therefore, both the inactive thermohaline circulation and the increase in the total amount of phosphate in the ocean induce the global-scale anoxic condition in the deepwater. (c) 2008 Elsevier Ltd. All rights reserved.
  • Chisato Yoshikawa, Michio Kawamiya, Tomomichi Kato, Yasuhiro Yamanaka, Taroh Matsuno
    Journal of Geophysical Research: Biogeosciences 113 (3) G03002  0148-0227 2008/09/28 [Refereed][Not invited]
     
    We examined climate-carbon cycle feedback by performing a global warming experiment using MIROC-based coupled climate-carbon cycle model. The model showed that by the end of the 21st century, warming leads to a further increase in carbon dioxide (CO2) level of 123 ppm by volume (ppmv). This positive feedback can mostly be attributed to land-based soil-carbon dynamics. On a regional scale, Siberia experienced intense positive feedback, because the acceleration of microbial respiration due to warming causes a decrease in the soil carbon level. Amazonia also had positive feedback resulting from accelerated microbial respiration. On the other hand, some regions, such as western and central North America and South Australia, experienced negative feedback, because enhanced litterfall surpassed the increased respiration in soil carbon. The oceanic contribution to the feedback was much weaker than the land contribution on global scale, but the positive feedback in the northern North Atlantic was as strong as those in Amazonia and Siberia in our model. In the northern North Atlantic, the weakening of winter mixing caused a reduction of CO2 absorption at the surface. Moreover, weakening of the formation of North Atlantic Deep Water caused reduced CO2 subduction to the deep water. Understanding such regional-scale differences may help to explain disparities in coupled climate-carbon cycle model results. Copyright 2008 by the American Geophysical Union.
  • Yoshikawa Chisato, Kawamiya Michio, Kato Tomomichi, Yamanaka Yasuhiro, Matsuno Taroh
    JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES 113 (G3) 2169-8953 2008/07/04 [Refereed][Not invited]
  • Takasumi Kurahashi-Nakamura, Ayako Abe-Ouchi, Yasuhiro Yamanaka
    GEOCHIMICA ET COSMOCHIMICA ACTA 72 (12) A505 - A505 0016-7037 2008/07 [Refereed][Not invited]
  • Takasumi Kurahashi-Nakamura, Ayako Abe-Ouchi, Yasuhiro Yamanaka
    GEOCHIMICA ET COSMOCHIMICA ACTA 72 (12) A505 - A505 0016-7037 2008/07 [Refereed][Not invited]
  • MASUDA Yoshio, YAMANAKA Yasuhiro, SASAI Yoshikazu, FUJII Masahiko
    Journal of Advanced Marine Science and Technology Society 海洋理工学会 14 (1) 81 - 87 1341-2752 2008/07 [Refereed][Not invited]
  • Noriko Nakayama, Yasuhiro Yamanaka, Toshitaka Gamo
    JOURNAL OF OCEANOGRAPHY 64 (3) 451 - 457 0916-8370 2008/06 [Refereed][Not invited]
     
    Concentration and stable isotopic compositions (delta(18)O) of dissolved O(2) were measured in seawater samples collected from the Philippine Sea in June 2006. The in-situ O(2) consumption rate and the isotopic fractionation factor (alpha(r)) during dissolved O(2) consumption were obtained from field observations by applying a vertical one-dimensional advection diffusion model to the deep water mass of about 1000-4000 m. The average O(2) consumption rate and alpha(r) were, respectively, 0.11 +/- 0.07 mu mol kg(-1) yr(-1) and 0.990 +/- 0.001. These estimated values agree well with values from earlier estimations of Pacific deep water. The in-situ 02 consumption rates are two or more times higher north of 20 degrees N, although the value of alpha(r) was not significantly different between the north and south. Its levels varied rapidly in the water mass of less about 2000 m depth. These results suggest that organic matter from the continent imparts a meaningful contribution to the upper water in the northern part of the area; it might produce the strong O(2) minimum that is evident in the water mass from about 1000-2000 m in the northern part of the Philippine Sea.
  • Effects of storms on primary productivity and air-sea CO2 exchange in the subarctic western North Pacific: a modeling study
    M. Fujii, Y. Yamanaka
    BIOGEOSCIENCES 5 (4) 1189 - 1197 1726-4170 2008 [Not refereed][Not invited]
     
    Biogeochemical responses of the open ocean to storms and their feedback to climate are still poorly understood. Using a marine ecosystem model, we examined biogeochemical responses to the storms in the subarctic western North Pacific. The storms in summer through early autumn enhance net community production by wind-induced nutrient injections into the surface waters while the storms in the other seasons reduce net community production by intensifying light limitation on the phytoplankton growth due to vertical dilution of the phytoplankton. The two compensating effects diminish the storm-induced annual change of net community production to only 1%. On the contrary, the storms reduce the annual oceanic uptake of the atmospheric CO2 by 3%, resulting from storm-induced strong winds. Our results suggest that previous studies using climatological wind, sea level pressure, and CO2 data probably overestimated the air-to-sea CO2 influx during storms in the subarctic western North Pacific, and therefore, continuous high-frequent observations of these variables are required to reduce uncertainties in the global oceanic CO2 uptake.
  • Yoshio Masuda, Yasuhiro Yamanaka
    OCEANS 2008 - MTS/IEEE KOBE TECHNO-OCEAN, VOLS 1-3 779 - 781 0197-7385 2008 [Refereed][Not invited]
     
    To evaluate whether chronic impacts on biota are caused by continuous 50 Mton CO(2) injection per year into the ocean, we simulated transport and dilution of the injected CO(2) using an offline ocean general circulation model (OGCM) with a horizontal resolution of 0.1 by 0.1 degrees. Carbon dioxide is continuously injected during 30 years into a site with one degree in longitude and three degrees in latitude. Since most of CO(2) dissolved water is transported in the longitudinal direction, its broad latitudinal width is effective to decrease CO(2) concentration in order to reduce/avoid biological impacts. CO(2) concentration increases in the first several to 10 years, but it has an upper limit after the initial increase. Since the simulated maximum CO(2) concentration is 80 percents of the "predicted no effect concentration" (PNEC), an index to estimate concentration causing no effects on biota, we can expect that continuous 50Mton/year CO(2) injection causes no chronic impacts.
  • Yoshio Masuda, Yasuhiro Yamanaka, Yoshikazu Sasai, Michimasa Magi, Takashi Ohsumi
    INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL 2 (1) 89 - 94 1750-5836 2008/01 [Refereed][Not invited]
     
    To evaluate chronic impacts Of CO2 ocean sequestration, we simulated the distribution of injected CO2 using an oceanic general circulation model (OGCM) with a horizontal resolution of 0.1 degrees. The model can explicitly express transport and dispersion of dissolved CO2 by mesoscale eddies. The CO2 which is continuously injected by a moving ship dissolves and accumulates within the first several to 10 years, but the CO2 concentration has an upper limit after its initial increase as a result of the dilution effect of mesoscale eddies which counterbalances the accumulation effect of injection. We can estimate the CO2 injection flux with the CO2 maximum concentration below the "Predicted No Effect Concentration" (PNEC), an index to estimate concentration causing no effects on biota. (C) 2007 Elsevier Ltd. All rights reserved.
  • M. Fujii, Y. Yamanaka
    BIOGEOSCIENCES 5 (4) 1189 - 1197 1726-4170 2008 [Refereed][Not invited]
     
    Biogeochemical responses of the open ocean to storms and their feedback to climate are still poorly understood. Using a marine ecosystem model, we examined biogeochemical responses to the storms in the subarctic western North Pacific. The storms in summer through early autumn enhance net community production by wind-induced nutrient injections into the surface waters while the storms in the other seasons reduce net community production by intensifying light limitation on the phytoplankton growth due to vertical dilution of the phytoplankton. The two compensating effects diminish the storm-induced annual change of net community production to only 1%. On the contrary, the storms reduce the annual oceanic uptake of the atmospheric CO2 by 3%, resulting from storm-induced strong winds. Our results suggest that previous studies using climatological wind, sea level pressure, and CO2 data probably overestimated the air-to-sea CO2 influx during storms in the subarctic western North Pacific, and therefore, continuous high-frequent observations of these variables are required to reduce uncertainties in the global oceanic CO2 uptake.
  • Y. Sasai, H. Sasaki, K. Sasaoka, A. Ishida, Y. Yamanaka
    GEOPHYSICAL RESEARCH LETTERS 34 (23) L23601  0094-8276 2007/12 [Refereed][Not invited]
     
    We have simulated the seasonal variability of marine biology in the eastern tropical Pacific using a global eddy-resolving coupled physical-biological model. Using high-resolution satellite wind fields, the model reproduces the seasonal variability of surface chlorophyll influenced by the meso-scale eddies and upwelling associated with the strong offshore wind jets. In winter, upwelling generated by the wind jets in the Gulfs of Tehuantepec, Papagayo, and Panama brings up cold and nitrate-rich waters from subsurface layer, where the tropical spring bloom occurs and is transported offshore. In summer, the intertropical convergence zone moves northward, and these jets weaken. The Costa Rica Dome develops with wind fields west of the Gulf of Papagayo. The dome in the open ocean supports high chlorophyll by the nutrient supply with upwelling. The westward expansion of surface chlorophyll of dome is response to the thermocline variation with the westward propagation of Rossby waves.
  • T. Kurahashi-Nakamura, A. Abe-Ouchi, Y. Yamanaka, K. Misumi
    GEOPHYSICAL RESEARCH LETTERS 34 (20) L20708  0094-8276 2007/10 [Not refereed][Not invited]
     
    The cause of low atmospheric CO2 concentrations during the Last Glacial Maximum (LGM) is important for understanding the role of the carbon cycle in climatic variation. We used an ocean general circulation model, coupled with a biogeochemical model, to examine the effect of sea-ice expansion in the Southern Ocean on atmospheric CO2 concentration. We newly considered a possible additional effect of sea-ice expansion in reducing biological activity as well as the effect of reduced gas-exchange. We propose that the new effect might have had an opposite operation and canceled the gas-exchange effect. Although there are some uncertainties arising from the absence of explicit sea-ice model in this study, these results suggest that sea-ice expansion might be far from the principal mechanism for low CO2 concentration during the LGM.
  • Akio Ishida, Yoshikazu Sasai, Yasuhiro Yamanaka
    JOURNAL OF PHYSICAL OCEANOGRAPHY 37 (10) 2491 - 2508 0022-3670 2007/10 [Refereed][Not invited]
     
    In this study the global distribution and transport of chlorofluorocarbons ( CFCs) in the oceans are investigated using a high-resolution numerical model. The authors focus on the effects of wind-driven processes such as subduction and ventilation on the distribution of CFC-11 within surface and thermocline layers. Local maxima of tracer inventory are identified in oceanic regions. Two major absorption regions in the South Pacific Ocean are located west of South America and northeast of New Zealand in boundary latitudes between subtropical and subantarctic areas. In the North Pacific and south Indian Oceans, the positions of the local maxima of tracers migrate west-east with increasing density. The relationship between water formation and tracer distribution is discussed by comparing the wintertime mixed layer depth and mean circulation. The contributions of mean and eddy transport of the meridional overturning cells to tracer transport are analyzed. Stationary eddies have a large impact in the Southern Ocean, while transient eddies are crucial for the compensation of mean transport in the equatorial oceans. Mean and seasonal variability components of meridional tracer transport are dominant in the subtropics; however, eddy transport also plays a significant role.
  • R. G. Najjar, X. Jin, F. Louanchi, O. Aumont, K. Caldeira, S. C. Doney, J. -C. Dutay, M. Follows, N. Gruber, F. Joos, K. Lindsay, E. Maier-Reimer, R. J. Matear, K. Matsumoto, P. Monfray, A. Mouchet, J. C. Orr, G. -K. Plattner, J. L. Sarmiento, R. Schlitzer, R. D. Slater, M. -F. Weirig, Y. Yamanaka, A. Yool
    GLOBAL BIOGEOCHEMICAL CYCLES 21 (3) GB3007  0886-6236 2007/08 [Not refereed][Not invited]
     
    Results are presented of export production, dissolved organic matter (DOM) and dissolved oxygen simulated by 12 global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project. A common, simple biogeochemical model is utilized in different coarse-resolution ocean circulation models. The model mean (+/- 1 sigma) downward flux of organic matter across 75 m depth is 17 +/- 6 Pg C yr(-1). Model means of globally averaged particle export, the fraction of total export in dissolved form, surface semilabile dissolved organic carbon (DOC), and seasonal net outgassing (SNO) of oxygen are in good agreement with observation-based estimates, but particle export and surface DOC are too high in the tropics. There is a high sensitivity of the results to circulation, as evidenced by (1) the correlation of surface DOC and export with circulation metrics, including chlorofluorocarbon inventory and deep-ocean radiocarbon, (2) very large intermodel differences in Southern Ocean export, and (3) greater export production, fraction of export as DOM, and SNO in models with explicit mixed layer physics. However, deep-ocean oxygen, which varies widely among the models, is poorly correlated with other model indices. Cross-model means of several biogeochemical metrics show better agreement with observation-based estimates when restricted to those models that best simulate deep-ocean radiocarbon. Overall, the results emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.
  • Takasumi Kurahashi-Nakamupa, Ayako Abe-Ouchi, Yasuhiro Yamanaka
    GEOCHIMICA ET COSMOCHIMICA ACTA 71 (15) A531 - A531 0016-7037 2007/08 [Refereed][Not invited]
  • R. G. Najjar, X. Jin, F. Louanchi, O. Aumont, K. Caldeira, S. C. Doney, J. -C. Dutay, M. Follows, N. Gruber, F. Joos, K. Lindsay, E. Maier-Reimer, R. J. Matear, K. Matsumoto, P. Monfray, A. Mouchet, J. C. Orr, G. -K. Plattner, J. L. Sarmiento, R. Schlitzer, R. D. Slater, M. -F. Weirig, Y. Yamanaka, A. Yool
    GLOBAL BIOGEOCHEMICAL CYCLES 21 (3) 0886-6236 2007/08 [Refereed][Not invited]
     
    Results are presented of export production, dissolved organic matter (DOM) and dissolved oxygen simulated by 12 global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project. A common, simple biogeochemical model is utilized in different coarse-resolution ocean circulation models. The model mean (+/- 1 sigma) downward flux of organic matter across 75 m depth is 17 +/- 6 Pg C yr(-1). Model means of globally averaged particle export, the fraction of total export in dissolved form, surface semilabile dissolved organic carbon (DOC), and seasonal net outgassing (SNO) of oxygen are in good agreement with observation-based estimates, but particle export and surface DOC are too high in the tropics. There is a high sensitivity of the results to circulation, as evidenced by (1) the correlation of surface DOC and export with circulation metrics, including chlorofluorocarbon inventory and deep-ocean radiocarbon, (2) very large intermodel differences in Southern Ocean export, and (3) greater export production, fraction of export as DOM, and SNO in models with explicit mixed layer physics. However, deep-ocean oxygen, which varies widely among the models, is poorly correlated with other model indices. Cross-model means of several biogeochemical metrics show better agreement with observation-based estimates when restricted to those models that best simulate deep-ocean radiocarbon. Overall, the results emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.
  • S. Lan Smith, Yasuhiro Yamanaka
    LIMNOLOGY AND OCEANOGRAPHY 52 (4) 1545 - 1558 0024-3590 2007/07 [Not refereed][Not invited]
     
    We present a new, optimization- based model for uptake kinetics of multiple nutrients, which has the same number of parameters ( two for each nutrient) as the Michaelis - Menten model. We fit this model and an existing inhibition- based model to data from chemostat experiments at various flow rates ( under extreme limitation by both nitrogen [ N] and phosphorus [ P]) and compared these models and the Michaelis - Menten model to an independent data set for the same species in a chemostat at various N: P input ratios ( at constant flow rate). Our model fit the data well, with a slightly higher square error than the much more complex inhibition model. We also successfully applied our model to a data set for a different species under various degrees of vitamin B12- and Plimitation. Our model agrees with measured cell quotas of nonlimiting nutrients when supply ratios differ greatly from the optimal ratio for phytoplankton, whereas the Michaelis - Menten model greatly overestimates the uptake of nonlimiting nutrients at these extreme nutrient supply ratios. The key to our model's success is the optimization of uptake for the limiting nutrient, which results in distinct behavior for limiting versus nonlimiting nutrients, without additional parameters; phytoplankton allocate their internal resources ( nitrogen) to optimize uptake of the limiting nutrient, but not in response to changes in ambient nutrient ratios.
  • Katsumi Matsumoto, Taketo Hashioka, Yasuhiro Yamanaka
    Journal of Geophysical Research: Biogeosciences 112 (2) G02007  0148-0227 2007/06/28 [Not refereed][Not invited]
     
    Extendingy an almost universal observation that the rate of microbial activity increases with temperature, we propose that marine microbial activity was suppressed during previous glacial periods and allowed proportionally more organic carbon to be exported out of the surface ocean. A stronger organic carbon pump and therefore lower rain ratios of CaCO3 to organic carbon may have contributed to the low atmospheric CO2 content during the Last Glacial Maximum. Previous study of temperature-dependent export production (Laws et al., 2000) and our map of data-based, global distribution of the rain ratios lend support to today's rain ratios being controlled at least partly by temperature. A close examination with a high-resolution regional ocean ecosystem model indicates that the correlation between rain ratio and temperature is caused indeed by preferential remineralization of organic matter, but a part of the correlation is also driven by temperature-dependent community composition. An extrapolation of these results to the globe using a global carbon cycle box model with a module for sediments indicates that the drawdown of atmospheric CO2 by the proposed mechanism is approximately 30 ppm. While this estimate is subject to uncertainty, the fact that it represents nearly one third of the glacial-interglacial variation in atmosphere pCO2 suggests the potential importance of the new mechanism. Given the historical difficulty in explaining the full CO2 amplitude with a single cause, we suggest that a set of multiple mechanisms were responsible and that the temperature-dependent POC degradation rate is one of them. We discuss two possible difficulties with our proposal that have to do with the potentially important role that ballasts play in organic carbon export and the possibility that enhanced biological pump is self limiting. Copyright 2007 by the American Geophysical Union.
  • Hiroaki Yamagishi, Marian B. Westley, Brian N. Popp, Sakae Toyoda, Naohiro Yoshida, Shuichi Watanabe, Keisuke Koba, Yasuhiro Yamanaka
    JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES 112 (G2) G02015-G02015-15  0148-0227 2007/05 [Refereed][Not invited]
     
    [1] Nitrous oxide (N2O) is an important atmospheric greenhouse gas and is involved in stratospheric ozone depletion. Analysis of the isotopomer ratios of N2O (i.e., the intramolecular distribution of N-15 within the linear NNO molecule and the conventional N and O isotope ratios) can elucidate the mechanisms of N2O production and destruction. We analyzed the isotopomer ratios of dissolved N2O at a site in the eastern tropical North Pacific (ETNP) and a site in the Gulf of California (GOC). At these sites, the flux of N2O to the atmosphere is extremely high but denitrification activity in the oxygen minimum zone (OMZ) also reduces N2O to N-2. We estimated the isotopomeric enrichment factors for N2O reduction by denitrification. The factor was - 11.6 +/- 1.0 parts per thousand for the bulk ( average) N, - 19.8 +/- 2.3 parts per thousand for the center N (alpha-site nitrogen), - 3.4 +/- 0.3 parts per thousand for the end N (beta-site nitrogen), and - 30.5 +/- 3.2 parts per thousand for the O-18 of N2O. Isotopomer analysis of N2O suggests that nitrifiers should contribute to N2O production more than denitrifiers at the oxycline above the OMZs in the ETNP ( 50 - 80 m) and in the GOC ( 80 - 300 m). In contrast, denitrifiers should largely contribute to the N2O production and consumption in the OMZs both in the ETNP ( 120 - 130 m) and in the GOC ( 600 - 800 m). The N2O isotopomer analysis will be a useful tool for resolving the distribution of water masses that carry a signal of N loss by denitrification.
  • Katsumi Matsumoto, Taketo Hashioka, Yasuhiro Yamanaka
    JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES 112 (G2) 2169-8953 2007/04 [Refereed][Not invited]
     
    [ 1] Extendingy an almost universal observation that the rate of microbial activity increases with temperature, we propose that marine microbial activity was suppressed during previous glacial periods and allowed proportionally more organic carbon to be exported out of the surface ocean. A stronger organic carbon pump and therefore lower rain ratios of CaCO3 to organic carbon may have contributed to the low atmospheric CO2 content during the Last Glacial Maximum. Previous study of temperature-dependent export production ( Laws et al., 2000) and our map of data-based, global distribution of the rain ratios lend support to today's rain ratios being controlled at least partly by temperature. A close examination with a high-resolution regional ocean ecosystem model indicates that the correlation between rain ratio and temperature is caused indeed by preferential remineralization of organic matter, but a part of the correlation is also driven by temperature-dependent community composition. An extrapolation of these results to the globe using a global carbon cycle box model with a module for sediments indicates that the drawdown of atmospheric CO2 by the proposed mechanism is approximately 30 ppm. While this estimate is subject to uncertainty, the fact that it represents nearly one third of the glacial-interglacial variation in atmosphere pCO(2) suggests the potential importance of the new mechanism. Given the historical difficulty in explaining the full CO2 amplitude with a single cause, we suggest that a set of multiple mechanisms were responsible and that the temperature-dependent POC degradation rate is one of them. We discuss two possible difficulties with our proposal that have to do with the potentially important role that ballasts play in organic carbon export and the possibility that enhanced biological pump is self limiting.
  • Masahiko Fujii, Yasuhiro Yamanaka, Yukihiro Nojiri, Michio J. Kishi, Fei Chai
    Ecological Modelling 202 (1-2) 52 - 67 0304-3800 2007/03/24 [Not refereed][Not invited]
     
    A NEMURO-based 16-compartment marine ecosystem model is applied to Stations A7 (41.5°N, 145.5°E) and KNOT (44°N, 155°E) in the subarctic western North Pacific and Station PAPA (50°N, 145°W) in the subarctic eastern North Pacific. Model results show significant west-east differences in seasonal characteristics of physical environmental conditions and biogeochemistry, such as larger seasonal amplitudes in sea surface temperature, mixed layer depth, surface nutrients, chlorophyll and partial pressure of CO2 at the sea surface (pCO2)sea, and higher primary productivity, at Stations A7 and KNOT than at Station PAPA. The modeled annual-mean e-ratios are higher at Stations A7 (0.32) and KNOT (0.33) than at Station PAPA (0.27) due to higher plankton biomass and mortality in the western North Pacific. Modeled annual-mean f-ratios are systematically higher than e-ratios under the influence of nitrification. The f-ratios are lower at Stations A7 (0.57) and KNOT (0.58) than at Station PAPA (0.64) because of higher ammonium concentrations in the western North Pacific. The e-ratio increases and f-ratio decreases with primary productivity, and the relationships can be described by exponential functions at any of the sites. The sea-to-air CO2 flux increases at Stations A7 and KNOT when calculated using daily wind data, instead of climatological wind data, which have been used in most of the previous studies. The increase is attributed to the strong winds in late winter in the daily wind data, suggesting that the sea-to-air CO2 flux was probably underestimated in previous studies and that frequent monitoring of winds and (pCO2)sea is necessary to reduce uncertainties in estimating air-sea CO2 flux. Phytoplankton growth is severely limited by light at any of the stations throughout the year. Diatom growth is regulated by silicate rather than nitrate and ammonium at each site, particularly in late summer and early autumn at Stations A7 and KNOT. We conclude that the west-east differences in the biogeochemistry are primarily caused by differences in the physical environmental conditions. The biogeochemical differences are also suggested to be caused by differences in the ecosystem dynamics resulting from differences in the iron bioavailability among the stations. © 2006 Elsevier B.V. All rights reserved.
  • Bernard A. Megrey, Kenneth A. Rose, Shin-ichi Ito, Douglas E. Hay, Francisco E. Werner, Yasuhiro Yamanaka, Maki Noguchi Aita
    ECOLOGICAL MODELLING 202 (1-2) 196 - 210 0304-3800 2007/03 [Not refereed][Not invited]
     
    We present a modeling approach where we use one common model formulation of a 11 state variable lower trophic level model that includes two groups of phytoplankton, three groups of zooplankton, and representations of nitrogen and silicate embedded in a three-dimensional ocean general circulation model (OGCM) and forced with a common climate forcing. Results are applied to a fish bioenergetics model for two geographically distinct ocean regions off Japan including the Oyashio, mixed, and Kuroshio subregions and off California including the subarctic, transition and subtropical subregions. The model is applied to two fish species (Pacific saury: Cololabis saira and Pacific herring: Clupea harengus pallasi) with different life histories in each region and the influence of three different "regime shift" periods was explored. With this approach, we narrow the observed biological response and model dynamics to reflect local conditions and eliminate differences related to the model formulations in each region. In general, the trend in temperature was negatively correlated with trends in the zooplankton community. Out-of-phase herring growth trends were observed between the Japan and California regions (r = -0.259, p = 0.02). In-phase growth trends between herring and saury were observed at the California region (r = 0.61, p < 0.01). We did note some evidence of a basin-scale PDO mode response. During 1980-1985, simulated saury and herring in both regions showed a consistent increase in weight-at-age. In the Oyashio subregion, temperature decreased and all three zooplankton groups increased beginning around 1980. The same pattern of a decrease in temperature and an increase in zooplankton densities was observed between 1980 and 1985 in the subarctic subregion of California. Results are discussed in the context of ecosystem-based fisheries management. (c) 2006 Elsevier B.V. All rights reserved.
  • Michio J. Kishi, Makoto Kashiwai, Daniel M. Ware, Bernard A. Megrey, David L. Eslinger, Francisco E. Werner, Maki Noguchi-Aita, Tomonori Azumaya, Masahiko Fujii, Shinji Hashimoto, Daji Huang, Hitoshi Iizumi, Yukimasa Ishida, Sukyung Kang, Gennady A. Kantakov, Hyun-cheol Kim, Kosei Komatsu, Vadim V. Navrotsky, S. Lan Smith, Kazuaki Tadokoro, Atsushi Tsuda, Orio Yamamura, Yasuhiro Yamanaka, Katsumi Yokouchi, Naoki Yoshie, Jing Zhang, Yury I. Zuenko, Vladimir I. Zvalinsky
    ECOLOGICAL MODELLING 202 (1-2) 12 - 25 0304-3800 2007/03 [Not refereed][Not invited]
     
    The PICES CCCC (North Pacific Marine Science Organization, Climate Change and Carrying Capacity program) MODEL Task Team achieved a consensus on the structure of a prototype lower trophic level ecosystem model for the North Pacific Ocean, and named it the North Pacific Ecosystem Model for Understanding Regional Oceanography, "NEMURO". Through an extensive dialog between modelers, plankton biologists and oceanographers, an extensive review was conducted to define NEMURO's process equations and their parameter values for distinct geographic regions. We present in this paper the formulation, structure and governing equations of NEMURO as well as examples to illustrate its behavior. NEMURO has eleven state variables: nitrate, ammonium, small and large phytoplankton biomass, small, large and predatory zooplankton biomass, particulate and dissolved organic nitrogen, particulate silica, and silicic acid concentration. Several applications reported in this issue of Ecological Modelling have successfully used NEMURO, and an extension that includes fish as an additional state variable. Applications include studies of the biogeochemistry of the North Pacific, and variations of its ecosystem's lower trophic levels and two target fish species at regional and basin-scale levels, and on time scales from seasonal to interdecadal. (c) 2006 Elsevier B.V. All rights reserved.
  • Maki Noquchi Aita, Yasuhiro Yamanaka, Michio J. Kishi
    ECOLOGICAL MODELLING 202 (1-2) 81 - 94 0304-3800 2007/03 [Not refereed][Not invited]
     
    Regime shifts, consisting of decadal-scale oscillations in atmosphere-ocean systems, have recently been the focus of many marine ecosystem studies. These 'regime shifts' effect the sea surface temperature and mixed layer depth (MLD), changing the environment for marine ecosystems. We simulated changes in the marine ecosystem caused by interdecadal climate variability, using data from 1948 to 2002 to drive an ecosystem model, NEMURO, embedded in a global three-dimensional physical-biological coupled model, '3D-NEMURO'. The results were consistent with observations. Comparing before and after the late 1970s regime shift, primary production and biomass of phytoplankton increased in the north central Pacific but decreased in the sub-tropical northwestern and eastern Pacific. This corresponds to the Pacific decadal oscillation (PDO) index that indicates interdecadal climate variability in the sub-tropical and tropical Pacific. In the north central Pacific, biomass correlated positively with PDO while that in the north eastern and western Pacific correlated negatively with PDO. (c) 2006 Elsevier B.V. All rights reserved.
  • Shin-Ichi Ito, Bernard A. Megrey, Michio J. Kishi, Daiki Mukai, Yutaka Kurita, Yasuhiro Ueno, Yasuhiro Yamanaka
    ECOLOGICAL MODELLING 202 (1-2) 174 - 183 0304-3800 2007/03 [Not refereed][Not invited]
     
    To elucidate the interannual response of Pacific saury growth to climate variability, a simple 3-box model of NEMURO.FISH was forced by observed sea surface temperature (SST) from 1950 to 2002. In the model, fish wet weight is calculated according to a fish bioenergetics equation. The observed condition factor of Pacific saury showed large decadal variability with significant year-to-year variability. in the model, wet weight of Pacific saury also showed decadal and year-to-year variability, however the amplitude of decadal variability was much smaller than observed. The cause of the model failure is suggested to be the absence of a multi-species fish formulation in the model. The Japanese sardine population, which has a large biomass that exhibits great decadal fluctuations, is proposed as potentially affecting zooplankton density in the saury migration region. We also investigated differences of interannual growth variability between spawning seasons. Since Pacific saury spawns from autumn to the following spring, we consider three seasonal (autumn, winter and spring) cohorts in the model. The amplitude of growth variability is largest for the spring-spawned cohort and smallest in the winter-spawned cohort. This difference is caused by the difference of life history of each spawned cohort. The spring-spawned cohort spawns only once in their life-cycle, however other cohorts spawn twice. During the (autumn) fishery season, age 1 spring-spawned cohort has not yet spawned, while the other cohorts have spawned once. As a result, the spring-spawned cohorts retain the memory of the environmental influence during the early life stages while the other cohorts, through their spawning, have erased that memory. Hence, the spring-spawned cohort shows a larger fluctuation in wet weight than other cohorts. (c) 2006 Elsevier B.V. All rights reserved.
  • Naoki Yoshie, Yasuhiro Yamanaka, Kenneth A. Rose, David L. Eslinger, Daniel M. Ware, Michio J. Kishi
    ECOLOGICAL MODELLING 202 (1-2) 26 - 37 0304-3800 2007/03 [Not refereed][Not invited]
     
    We investigated the parameter sensitivity of the NEMURO ecosystem model calibrated to field at two typical Stations (A7 and P) in the subarctic North Pacific. The NEMURO model follows various forms of nitrogen and silicon, and the daily biomasses of two phytoplankton and three zooplankton groups for multiple years. Previously calibrated versions to data at two stations provided the basis for comparing parameter sensitivities under different environmental and biological conditions. Four sensitivity analysis experiments were performed involving 72 parameters: 3 experiments used Monte Carlo methods and 1 experiment used a 1-parameter-at-a-time approach. Normalized sensitivities and correlation were used as sensitivity measures for comparison among the four experiments. Monte Carlo and one-parameter-at-a-time methods that used relatively small variations in parameter values (less than or equal to +/- 10%) yielded very similar rankings of the top five parameters. Parameter rankings from the Monte Carlo analysis that used relatively large variation in parameters (-50% to +100%) differed slightly from the rankings obtained with the small variations. Additional examination of the 10% results showed that parameters deemed important differed among prognostic variables and differed between Stations A7 and P. For example, annual small phytoplankton biomass was most sensitive to the maximum grazing rate of small zooplankton at both stations, while large phytoplankton biomass was most sensitive to its own maximum photosynthetic rate parameter. While at Station A7 large phytoplankton was sensitive to zooplankton parameters, at Station P it was more sensitive to phytoplankton parameters. A few of certain phytoplankton parameters were consistently important in all sensitivity experiments. Despite sometimes complex relationships between prognostic variables and parameters, our analyses showed that the NEMURO model was generally well-behaved and was robust to parameter variation and to the method used for the sensitivity analysis. Extensions of our analysis could involve computing the sensitivity measure over time through the year, and the use other types of prognostic variables than biomass such as the timing of the phytoplankton bloom. Sensitivity analyses, such as those performed here, are useful tools for applying the NEMURO to other locations and for helping to interpret and diagnose existing NEMURO applications. (c) 2006 Elsevier B.V. All rights reserved.
  • Taketo Hashioka, Yasuhiro Yamanaka
    ECOLOGICAL MODELLING 202 (1-2) 68 - 80 0304-3800 2007/03 [Not refereed][Not invited]
     
    We developed a 3D ecosystem-biogeochemical model using NEMURO (North Pacific Ecosyslem Model Used for Regional Oceanography) and applied it to the western North Pacific in order to understand how seasonal and horizontal variations of phytoplankton groups are determined by top-down and bottom-up controls. Our model shows that the annually averaged biomass of diatoms represented as percentage of total phytoplankton is 50-60% in the subarctic and less than 30% in the subtropical regions, which is consistent with the observed values. From the viewpoint of bottom-up control, we investigated which limitation factor of photosynthetic rate (i.e., nutrients, temperature and light) determines the annually averaged P/B ratio and the dominant phytoplankton group. In oligotrophic regions, nutrient concentrations determine the dominant phytoplankton group through the difference in the P/B ratio of each group. However, in the subarctic region, as the P/B ratio of diatoms is almost the same as that of the other small phytoplankton, the difference in the P/B ratio does not contribute in determining the dominant phytoplankton group. We also investigated how the seasonal variation of the percentage of diatoms is determined by both bottom-up and top-down controls at three typical sites (Kuroshio extension, subarctic and subtropical sites). At the Kuroshio extension and subarctic sites, from winter to the beginning of spring bloom, diatoms have a high growth rate without grazing pressure by zooplankton, and the percentage of diatoms rapidly increases over 70%. From the end of the spring bloom to summer the percentage of diatoms decreases to 30%, as a consequence of the copepods' return to the surface from deep waters (and their grazing preferentially on diatoms rather than the other small phytoplankton), and as silicate concentrations limit the photosynthesis' by diatoms. Therefore, at these sites, the seasonal variation of the percentage of diatoms is not only regulated by nutrient concentration, but also by grazing preferences by zooplankton. At the oligotrophic subtropical site, the percentage of diatoms is determined mainly by nutrient concentrations throughout the year. (c) 2006 Elsevier B.V. All rights reserved.
  • S. Lan Smith, Yasuhiro Yamanaka
    ECOLOGICAL MODELLING 201 (3-4) 547 - 552 0304-3800 2007/03 [Not refereed][Not invited]
     
    Photoacclimation models for marine phytoplankton describe the changes in their composition (typcially C, N and chlorophyll) and growth in response to changing light and nutrient environment. We compared two such models: that of Geider et al. (Geider, R.J., MacIntyre, H.L., Kana, T.M., 1998. A dynamic regulatory model of phytoplankton acclimation to light, nutrients, and temperature. Limnol. Oceanogr. 43, 679-694), hereafter the G model, and that of Pahlow (Pahlow, M., 2005. Linking chlorophyll-nutrient dynamics to the redfield N:C ratio with a model of optimal phytoplankton growth. Mar. Ecol. Prog. Ser. 287, 33-43), hereafter the P model. Using the Monte Carlo Markov Chain method, we fitted both models to the data set from an incubation experiment by Flynn et al. (Flynn, K.J., Davidson, K., Leftley, J.W, 1994. Carbon-nitrogen relations at whole-cell and free amino-acid levels, during batch growth of isochrysis galbanna (prymnesiophyceae) under conditions of alternating light and dark. Mar. Biol. 118, 229-237). Data consisted of measured concentrations for particulate organic N, particulate organic C, chlorophyll and ammonium. The authors of the G model began their simulation from day 5 for this experiment, claiming that their model could not reproduce the initial lag phase (slow growth during the first few days of the experiment). The author of the P model claimed that its ability to reproduce this initial lag phase (starting from the beginning of the experiment) was a significant improvement over previous models. Our fitting revealed that the G model can reproduce this initial lag phase as well as the P model, and that both models simulate the data set well. In the best-fits of both models, chlorophyll synthesis during the initial lag phase was limited by the rate of carbon assimilation, even though the G model was designed to have chlorophyll synthesis limited only by the rate of N assimilation. The requirement of organic carbon for energy to assimilate nitrogen results in this indirect limitation of chlorophyll synthesis by C assimilation in the G model, whereas chlorophyll synthesis is explicitly limited by the rate of C assimilation in the P model. This suggests that chlorophyll synthesis is in fact limited by the rate of C assimilation during the initial lag phase. As in the hand-tuned simulations previously published, the P model simulated the initial decrease in Chl:N ratio (as observed) whereas the G model simulated an initial increase in this ratio (contrary to the observations). We also discuss the relative merits of the two models for applications at large scales. Although data assimilation is not perfectly objective, because it requires certain choices such as weights for various data types and which data to include when fitting, our results show the advantage of mathematically rigorous fitting as opposed to hand-tuning of models. Our best-fits were significantly better than the hand-tuned fits originally published, especially for the G model, and this yielded insight into the mechanism responsible for the initial lag in phytoplankton growth. (c) 2006 Elsevier B.V. All rights reserved.
  • Kenneth A. Rose, Francisco E. Werner, Bernard A. Megrey, Maki Noguchi Aita, Yasuhiro Yamanaka, Douglas E. Hay, Jake F. Schweigert, Matthew Birch Foster
    ECOLOGICAL MODELLING 202 (1-2) 184 - 195 0304-3800 2007/03 [Refereed][Not invited]
     
    The infrequent occurrence of climate regime shifts and the long-lived life history of many harvested fish species imply that quantitative understanding of the effects of climate shifts on fish will require long-term data spanning decades. We use the output of the 3-dimensional (3D) NEMURO nutrient-phytoplankton-zooplankton model applied to the Nor-them Pacific as input to a Pacific herring (Clupea pallasi) bicenergetics model, and predict herring weights-at-age and growth from 1948 to 2000 for the West Coast Vancouver Island (WCVI), Prince William Sound (PWS), and Bering Sea (BS) locations. The feeding parameters of the bioenergetics model were calibrated from steady-state predictions of herring weights-at-age at each location compared to observed mean weights-at-age. Herring weights-at-age were then simulated from 1948 to 2000 using the 3D-NEMURO generated time series of monthly temperature and zooplankton densities. Herring growth rates, annual temperature, and zooplankton density time series were analyzed statistically for coincident shifts in their mean values. We also simulated herring growth rates using the 1948-2000 time series and averaged (climatological) temperature and zooplankton densities to determine the relative importance of temperature and zooplankton to predicted herring growth responses. All three locations showed a shift in herring growth during the mid and late 1970s. Herring growth decreased in WCVI and PWS, and increased in BS; these changes were coincident with a warming of temperature and a decrease in predatory zooplankton density. Herring growth responses in PWS and BS were more complex than those predicted for WCVI, with additional shifts predicted besides the late 1970s shift. Interannual variation in zooplankton densities caused the herring growth response for WCVI. Temperature and zooplankton densities affected the herring growth responses in both Alaskan locations, with zooplankton dominating the response for PWS and temperature dominating the response for BS. We compare our simulated herring growth responses to observed responses, and discuss the advantages and drawbacks of using the output of broadly applied lower trophic model as input to fish models in order to examine long-term responses to regime shifts at multiple locations. (c) 2006 Elsevier B.V. All rights reserved.
  • Taketo Hashioka, Yasuhiro Yamanaka
    ECOLOGICAL MODELLING 202 (1-2) 95 - 104 0304-3800 2007/03 [Refereed][Not invited]
     
    We developed a 3D ecosystem-biogeochemical model based on NEMURO (North Pacific Ecosystem Model Used for Regional Oceanography) and applied it to the western North Pacific in order to predict the effects of global warming on ecosystem dynamics and biogeochemical cycles. Using datasets of observed climatology and simulated fields according to a global warming scenario, IS92a (CO-AGCM developed by CCSR/NIES) as boundary conditions for our ecosystem model, we conducted present-day and global warming experiments and compared their results. Model results in the global warming experiment show increases in vertical stratification due to rising temperatures. As a result, the predicted nutrient and chlorophyll-a concentrations in the surface water decrease at the end of the 21st century and the dominant phytoplankton group shifts from diatoms to other small phytoplankton. The P/B ratio slightly increases from that in the present as a result of favorable temperature conditions, although nutrient conditions become worse. The increase in the P/B ratio causes increases in the NPP and GPP, although new and export productions decrease. Increases in the regeneration rates (i.e., decrease in the e-ratio) also contribute to increases in NPP and GPP through nutrient supplies within the surface water. Changes in seasonal variations of biomass and the dominant phytoplankton group in the subarctic-subtropical transition region associated with the global warming are large in all regions. in the global warming scenario, the onset of the diatom spring bloom is predicted to take place 1.5 month earlier than in the present-day simulation due to strengthened stratification. The maximum biomass in the spring bloom is predicted to decrease drastically compared to the present due to the decreases in nutrient concentration. In contrast, the biomass maximum of the other small phytoplankton at the end of the diatom spring bloom is the same as the present, because they can adapt to the low nutrient conditions due to their small half-saturation constant. Therefore, a change in the dominant phytoplankton group appears notably at the end of spring bloom. Since the present nutrient concentrations and phytoplankton biomass from summer to winter are low compared with those in spring, these changes associated with the global warming are small. That is, it is interesting that the changes do not occur uniformly in all seasons, but occur dramatically at the end of the spring and in the fall bloom. (c) 2006 Elsevier B.V. All rights reserved.
  • A Comparison of Simulated Particle Fluxes Using NEMURO and Other Ecosystem Models in the Western North Pacific
    Michio J. Kishi, Takeshi Okunishi, Yasuhiro Yamanaka
    Journal of Oceanography 60 (1) 63 - 73 2007/02 [Refereed][Not invited]
  • S. Lan Smith, B. E. Casareto, M. P. Niraula, Y. Suzuki, J. C. Hargreaves, J. D. Annan, Y. Yamanaka
    JOURNAL OF MARINE SYSTEMS 64 (1-4) 135 - 152 0924-7963 2007/01 [Not refereed][Not invited]
     
    We examined the flows of nitrogen in two batch incubations of plankton assemblages under controlled conditions, using mesopelagic seawater from different depths. Observations included concentrations of nutrients, organic matter (particulate and dissolved) and plankton (biomass by species). Because nitrogen flows were not observed directly (as is generally the case), we examined them using a multi-element ecosystem model developed to simulate these experiments. Dynamic changes in the observed bulk POC/PON ratio (C/N ratio of particulate organic matter, POM) were consistent with a quota model for phytoplankton. To relate these changes to the regeneration of nitrogen, we included such a quota model and all major planktonic groups observed. By assimilating the data (all observations of carbon and nitrogen concentrations, including living carbon biomasses) into the model using the Monte Carlo Markov Chain, we accurately simulated the changes in bulk POC/PON ratio and its difference between incubations. Changes in phytoplankton composition dominated the changes in bulk POC/PON ratio. Bacteria dominated the regeneration of nitrogen in both incubations, and changes in bacterial regeneration strongly affected the bulk POC/PON ratio. After nitrate depletion, gross nitrogen regeneration varied inversely with observed POC/PON ratio and was constrained by this ratio. Thus, we have demonstrated a powerful new approach to constraining the flows of nutrients through ecosystems. Our results suggest that simultaneous observations of POC and PON could place an additional constraint on the supply of inorganic nitrogen in models of the oligotrophic ocean. (c) 2006 Elsevier B.V. All rights reserved.
  • 生態系モデル”eNEMURO”の開発と時系列観測研究への応用
    Yoshie, N, Y. Yamanaka, T. Hashioka, M. Fujii
    Kaiyo Monthly 39 (2) 2 - 10 2007 [Not refereed][Not invited]
  • Chisato Yoshikawa, Yasuhiro Yamanaka, Takeshi Nakatsuka
    JOURNAL OF OCEANOGRAPHY 62 (4) 511 - 525 0916-8370 2006/08 [Not refereed][Not invited]
     
    To understand the processes transporting nitrate to the surface layer of the western and central equatorial Pacific, we measured the nitrogen isotopic ratio of nitrate (delta(NO3-)-N-15) which is a very useful tracer of the source of nitrate, above 200 m depth in this region in December 1999. delta(NO3-)-N-15 is higher (about 13.0 parts per thousand) in the surface water than in the subsurface water (where it is about 6.5 parts per thousand) due to isotopic fractionation during nitrate uptake by phytoplankton. The delta(NO3-)-N-15 value has a roughly linear relationship with the natural logarithm of nitrate concentration (In[NO3-]). However, for values above 150 m depth, the intercept of this linear relationship varies with position from east to west. On the other hand, the data at 200 m depth at all observation stations are concentrated around a single point (In[NO3-] = 2.5 and delta(NO3-)-N-15 = 6.5 parts per thousand) and do not fit the linear relationships for the shallower values. To examine the meaning of the observed distributions of delta(NO3-)-N-15 and nitrate concentration we developed a box model including nitrogen and nitrogen isotopic cycles. By reproducing the observed relationship between delta(NO3-)-N-15 and nitrate concentration using this model we found that most nitrate is transported horizontally from the eastern equatorial Pacific. We also conducted case studies and investigated the effects of differences in pathways of nitrate transport on the distributions of delta(NO3-)-N-15 and nitrate concentration. From these studies we concluded that the observed linear relationships between delta(NO3-)-N-15 and In[NO3-], having a common slope around 6 parts per thousand but different intercepts at each station, are evidence of the significant horizontal transport of nitrate to the surface water in this area.
  • Yoshikazu Sasai, Akio Ishida, Hideharu Sasaki, Shintaro Kawahara, Hitoshi Uehara, Yasuhiro Yamanaka
    SIMULATION-TRANSACTIONS OF THE SOCIETY FOR MODELING AND SIMULATION INTERNATIONAL 82 (7) 467 - 474 0037-5497 2006/07 [Not refereed][Not invited]
     
    Physical influences on a marine ecosystem in the open ocean are investigated using a simplified four-component ecosystem model embedded in an eddy-resolving ocean general-circulation model (OGCM). The annual cycle of temperature, nitrate, and phytoplankton in the upper ocean is well reproduced with the climatological monthly mean forcing. A comparison with satellite ocean color data shows that the model is capable of a realistic description of the annual mean and regional patterns of surface chlorophyll. Simulated chlorophyll distribution at the surface shows a pattern influenced by the western boundary current (Kuroshio) and meso-scale eddies. Nitrate distribution in the upper ocean in the northwestern Pacific is mainly controlled by physical processes, especially meso-scale variability, including many anticyclonic and cyclonic eddies, fine-scale fronts, and filaments. The warm-core eddy entrains high-nitrate water from the surrounding filaments, creating conditions for the high production in spring.
  • Mary-Elena Carr, Marjorie A. M. Friedrichs, Marjorie Schmeltz, Maki Noguchi Aita, David Antoine, Kevin R. Arrigo, Ichio Asanuma, Olivier Aumont, Richard Barber, Michael Behrenfeld, Robert Bidigare, Erik T. Buitenhuis, Janet Campbell, Aurea Ciotti, Heidi Dierssen, Mark Dowell, John Dunne, Wayne Esaias, Bernard Gentili, Watson Gregg, Steve Groom, Nicolas Hoepffner, Joji Ishizaka, Takahiko Kameda, Corinne Le Quere, Steven Lohrenz, John Marra, Frederic Melin, Keith Moore, Andre Morel, Tasha E. Reddy, John Ryan, Michele Scardi, Tim Smyth, Kevin Turpie, Gavin Tilstone, Kirk Waters, Yasuhiro Yamanaka
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 53 (5-7) 741 - 770 0967-0645 2006 [Not refereed][Not invited]
     
    The third primary production algorithm round robin (PPARR3) compares output from 24 models that estimate depth-integrated primary production from satellite measurements of ocean color, as well as seven general circulation models (GCMs) coupled with ecosystem or biogeochemical models. Here we compare the global primary production fields corresponding to eight months of 1998 and 1999 as estimated from common input fields of photosynthetically-available radiation (PAR), sea-surface temperature (SST), mixed-layer depth, and chlorophyll concentration. We also quantify the sensitivity of the ocean-color-based models to perturbations in their input variables. The pair-wise correlation between ocean-color models was used to cluster them into groups or related output, which reflect the regions and environmental conditions under which they respond differently. The groups do not follow model complexity with regards to wavelength or depth dependence, though they are related to the manner in which temperature is used to parameterize photosynthesis. Global average PP varies by a factor of two between models. The models diverged the most for the Southern Ocean, SST under 10 degrees C, and chlorophyll concentration exceeding 1 mg Chlm(-3). Based on the conditions under which the model results diverge most, we conclude that current ocean-color-based models are challenged by high-nutrient low-chlorophyll conditions, and extreme temperatures or chlorophyll concentrations. The GCM-based models predict comparable primary production to those based on ocean color: they estimate higher values in the Southern Ocean, at low SST, and in the equatorial band, while they estimate lower values in eutrophic regions (probably because the area of high chlorophyll concentrations is smaller in the GCMs). Further progress in primary production modeling requires improved understanding of the effect of temperature on photosynthesis and better parameterization of the maximum photosynthetic rate. (c) 2006 Elsevier Ltd. All rights reserved.
  • 山中 康裕
    沿岸域学会誌 日本沿岸域学会 19 (1) 41 - 43 1349-6123 2006 [Not refereed][Not invited]
  • S. Takeda, N. Yoshie, P. W. Boyd, Y. Yamanaka
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 53 (20-22) 2297 - 2326 0967-0645 2006 [Refereed][Not invited]
     
    Numerical modeling experiments were conducted to examine the reasons for observed changes in the silicic acid ([Si(OH)(4)]) to nitrate ([NO(3)(-)]) drawdown ratio after the onset of algal iron stress during SERIES. During phytoplankton blooms and immediately after them, cells encounter a range of iron stress (between iron-replete and iron-deplete) and therefore show a range of growth rates. For these reasons, the potential influence of phytoplankton growth rate, under conditions of algal iron stress, on silicic acid and nitrate depletion were investigated in numerical experiments by altering the timing of a shift in the [Si(OH)(4)]:[NO(3)(-)] uptake ratio. These simulations suggested that the continued growth of iron-stressed phytoplankton at sub-maximum rates, with an elevated [Si(OH())]:[NO(3)(-)] uptake ratio, induced depletion of silicic acid in the surface water and resulted in simultaneous limitation of growth by both iron and silicic-acid supply. Therefore, bottom-up control played an important role in terminating the phytoplankton bloom in SERIES. In the model simulations, the enhancement of diatom silicification due to increased rates of biomass-normalized silicic-acid uptake, led to increases in the export flux of opal after the onset of algal iron-stress and, consequently, it stimulated the silica pump. The regulation of both the [Si(OH)(4)]:[NO(3)(-)] uptake ratio and the growth rate of phytoplankton by iron supply are important factors that determine the relative consumption of silicic acid and nitrate upon iron stress, although the potential influence of a floristic shift in the diatom assemblage cannot be ruled out. These findings offer insights into the impact of iron fertilization, both artificial and natural, on the biogeochemical cycling of nutrients in high-nitrate, low-chlorophyll waters. (c) 2006 Elsevier Ltd. All rights reserved.
  • N Yoshie, Y Yamanaka
    JOURNAL OF OCEANOGRAPHY 61 (6) 1059 - 1073 0916-8370 2005/12 [Refereed][Not invited]
     
    Two processes are generally explained as causes of temporal changes in the stoichiometric silicon/nitrogen (Si/N) ratios of sinking particles and of nutrient consumption in the surface water during the spring diatom bloom: (1) physiological changes of diatom under the stress of photosynthesis of diatom and (2) differences of regeneration between silicon and nitrogen. We investigated which process plays an important role in these changes using a one-dimensional ecosystem model that explicitly represents diatom and the other non-siliceous phytoplankton. The model was applied to station A7 (41 degrees 30'N, 145 degrees 30'E) in the western North Pacific, where diatom regularly blooms in spring. Model simulations show that the SUN ratios of the flux exported by the sinking particles at 100 m depth and of nutrient consumptions in the upper 100 m surface water have their maxima at the end of the spring diatom bloom, the values and timings of which are significantly different from each other. Analyses of the model results show that the differences of regeneration between silicon and nitrogen mainly cause the temporal changes of the SUN ratios. On the other hand, the physiological changes of diatoms under stress can hardly cause these temporal changes, because the effect of the change in the diatom's uptake ratio of silicon to nitrogen is cancelled by that in its sinking rate.
  • M Fujii, M Ikeda, Y Yamanaka
    JOURNAL OF OCEANOGRAPHY 61 (5) 803 - 815 0916-8370 2005/10 [Refereed][Not invited]
     
    To evaluate the contribution of biogeochemical processes to the oceanic carbon cycle and to calculate the ratio of calcium carbonate to organic carbon downward export, we have incorporated biological and alkalinity pumps in the yoked high-latitude exchange/interior diffusion-advection (YOLDA) model. The biogeochemical processes are represented by four parameters. The values of the parameters are tuned so that the model can reproduce the observed phosphate and alkalinity distributions in each oceanic region. The sensitivity of the model to the biogeochemical parameters shows that biological production rates in the euphotic zone and decomposition depths of particulate matters significantly influence horizontal and vertical distributions of biogeochemical substances. The modeled vertical fluxes of particulate organic phosphorus and calcium carbonate are converted to vertical carbon fluxes by the biological pump and the alkalinity pump, respectively. The downward carbon flux from the surface layer to the deep layer in the entire region is estimated to be 3.36 PgC/yr, which consists of 2.93 PgC/yr from the biological pump and 0.43 PgC/yr from the alkalinity pump, which is consistent with previous studies. The modeled rain ratio is higher with depth and higher in the Pacific and Indian Oceans than in the Atlantic Ocean. The global rain ratio at the surface layer is calculated to be 0.14 to 0.15. This value lies between the lower and higher ends of the previous estimates, which range widely from 0.05 to 0.25. This study indicates that the rain ratio is unlikely to be higher than 0.15, at least in the surface waters.
  • C Yoshikawa, Y Yamanaka, T Nakatsuka
    JOURNAL OF OCEANOGRAPHY 61 (5) 921 - 942 0916-8370 2005/10 [Refereed][Not invited]
     
    We have developed an ecosystem model including two nitrogen isotopes (N-14 and N-15), and validated this model using an actual data set. A study of nitrogen isotopic ratios (delta N-15) using a marine ecosystem model is thought to be most helpful in quantitatively understanding the marine nitrogen cycle. Moreover, the model study may indicate a new potential of delta N-15 as a tracer. This model has six compartments: phytoplankton, zooplankton, particulate organic nitrogen, dissolved organic nitrogen, nitrate and ammonium in a two-box model, and has biological processes with/without isotopic fractionation. We have applied this model to the Sea of Okhotsk and successfully reproduced the delta N-15 of nitrate measured in seawater and the seasonal variations in delta N-15 of sinking particles obtained from sediment trap experiments. Simulated delta N-15 of phytoplankton are determined by delta N-15 of nitrate and ammonium, and the nitrogen f-ratio, defined as the ratio of nitrate assimilation by phytoplankton to total nitrogenous nutrient assimilation. Detailed considerations of biological processes in the spring and autumn blooms have demonstrated that there is a significant difference between simulated delta N-15 values of phytoplankton, which assimilates only nitrate, and only ammonium, respectively. We suggest that observations of delta N-15 values of phytoplankton, nitrate and ammonium in the spring and autumn blooms may indicate the ratios of nutrient selectivity by phytoplankton. In winter, most of the simulated biogeochemical fluxes decrease rapidly, but nitrification flux decreases much more slowly than the other biogeochemical fluxes. Therefore, simulated delta N-15 values and concentrations of ammonium reflect almost only nitrification. We suggest that the nitrification rate can be parameterized with observations of delta N-15 of ammonium in winter and a sensitive study varying the parameter of nitrification rate.
  • JC Orr, VJ Fabry, O Aumont, L Bopp, SC Doney, RA Feely, A Gnanadesikan, N Gruber, A Ishida, F Joos, RM Key, K Lindsay, E Maier-Reimer, R Matear, P Monfray, A Mouchet, RG Najjar, GK Plattner, KB Rodgers, CL Sabine, JL Sarmiento, R Schlitzer, RD Slater, IJ Totterdell, MF Weirig, Y Yamanaka, A Yool
    NATURE 437 (7059) 681 - 686 0028-0836 2005/09 [Refereed][Not invited]
     
    Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms - such as corals and some plankton - will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean - carbon cycle to assess calcium carbonate saturation under the IS92a 'business-as-usual' scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.
  • MO Chikamoto, Y Yamanaka
    JOURNAL OF OCEANOGRAPHY 61 (4) 733 - 746 0916-8370 2005/08 [Refereed][Not invited]
     
    A one-dimensional sediment model was developed by introducing the CIP-CSL2 scheme in the advection term. This enables us to represent fluctuations of the vertical profiles of 100 cm depth, which needs integrations on a longer timescale than 10 kyr, because this scheme avoids smoothing of the vertical profiles due to no numerical diffusion, instead of a commonly used forward scheme. Using the models with 10 and 100 cm depths (hereafter, called the 10 cm model and the 100 cm model, respectively) to predict the contents of biogenic silica and clay, we have evaluated the sedimentary responses to an abrupt change in the biogenic silica rain flux. When the rain flux of biogenic silica abruptly decreases, the 10 cm model underestimates the dissolution flux of biogenic silica compared with the 100 cm model. T his is because only clay is supplied from the bottom boundary associated with excess dissolution and also because dissolution of biogenic silica below 10 cm depth is neglected by the 10 cm model. When we consider dissolved matter inputs from sediments to marine biogiochemical cycles, simulations by the 100 cm model would lead to more realistic responses in sediments.
  • SL Smith, Y Yamanaka, MJ Kishi
    JOURNAL OF OCEANOGRAPHY 61 (1) 1 - 23 0916-8370 2005/02 [Refereed][Not invited]
     
    We used a one dimensional, multi-element model to simulate the primary production (PP), recycling and export of organic matter at Stn. ALOHA, near Hawaii. We compared versions of the model with and without the cycling of dissolved organic matter (DOM) via the Microbial Food Web (MFW). We incorporated recently published measurements of high C:N ratios for uptake by diazotrophs. For other phytoplankton we included a formulation for overflow production of dissolved organic carbon (DOC), which occurs under nutrient-limited, light-replete conditions. We were able to match the observed mean DOC profile near the surface with both models, by tuning only the fraction of overflow DOC that is labile. The simulated bulk C:N remineralization ratio from the MFW model agreed well with a data-based estimate for the North Pacific subtropical gyre, but that from the Base model was too low. This is because the MFW model includes bacteria, with their low-C:N biomass. Simulated mean PP was lower than observed by 10% (Base) and 27% (MFW). This is consistent with the expectation that the C-14-method measures something greater than net production. DOC accounted for approximately half of simulated PP, most of this being overflow DOC. We find that overflow production and the MFW are key processes for reconciling the various data and PP measurements at this oligotrophic site. The impact of bacteria on the C:N remineralization ratio is an important link between ecosystem structure and the cycling of carbon.
  • Yoshikawa, C., Y. Yamanaka and T. Nakatsuka: An ecosystem model including nitrogen isotopes: Perspectives on a study of the marine nitrogen cycle. J. Oceanogr., 61:912-942(2005)*
    2005 [Not refereed][Not invited]
  • Sasai Y, A. Ishida, H. Sasaki, S. Kawahara, H. Uehara and Y. Yamanaka: Spreading of Antarctic Bottom Water examined using the CFC-11 distribution simulated by an eddy-resolving OGCM. Polar Meteorol. Glaciol., 19: 15-27(2005)*
    2005 [Not refereed][Not invited]
  • Chikamoto O. M. and Y. Yamanaka: Sedimentary responses an abrupt change of silicate flux using a sediment model with long time series. J. Oceanogr., 61:733-746(2005)*
    2005 [Not refereed][Not invited]
  • Smith, S. L., Y. Yamanaka and M. J. Kishi: Attempting Consistent Simulations of Stn. ALOHA with a Multi-Element Ecosystem Model. J. Oceanog., 61:1-23(2005)*
    2005 [Not refereed][Not invited]
  • Yoshie, N. and Y. Yamanaka: Processes causing the temporal changes in Si/N ratios of nutrient consumptions and export flux during the spring diatom bloom. J. Oceanogr., 61:1059-1073(2005)*
    2005 [Not refereed][Not invited]
  • Fujii, M., N. Yoshie, Y. Yamanaka and F. Chai: Simulated biogeochemical responses to iron enrichments in three high nutrient, low chlorophyll (HNLC) regions. Progr. Oceanogr., 64:307-324, doi:10.1016/j.pocean.2005.02.017. 2005.(2005)*
    2005 [Not refereed][Not invited]
  • Yoshie, N., M. Fujii and Y. Yamanaka: Ecosystem changes after the SEEDS iron fertilization in the western North Pacific simulated by a one-dimensional ecosystem model. Progr. Oceanogr., 64:283-306, doi:10.1016/j.pocean.2005.02.014.(2005)*
    2005 [Not refereed][Not invited]
  • Sasai, Y., A. Ishida, H. Sasaki, S. Kawahara, H. Uehara and Y. Yamanaka: A global eddy-resolving coupled physical-biological model: Physical influences on a marine ecosystem in the North Pacific, In: Open International Conference on Modeling and Simula・・・
    2005 [Not refereed][Not invited]
     
    Sasai, Y., A. Ishida, H. Sasaki, S. Kawahara, H. Uehara and Y. Yamanaka: A global eddy-resolving coupled physical-biological model: Physical influences on a marine ecosystem in the North Pacific, In: Open International Conference on Modeling and Simulation – OICMS 2005 Edited by Hill, D. R. C., V. Barra., and M. K. Troer, Blaise Pascal University, France, pp.129-138(2005)*
  • Orr, J., V. J. Fabry, O. Aumont, L. Bopp, S. C. Doney, R. M. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R. M. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray, A. Mouchet, R. G. Najjar, G.-K. Plattner, K. B. Rodgers, C. L. Sabine, J.・・・
    2005 [Not refereed][Not invited]
     
    Orr, J., V. J. Fabry, O. Aumont, L. Bopp, S. C. Doney, R. M. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R. M. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray, A. Mouchet, R. G. Najjar, G.-K. Plattner, K. B. Rodgers, C. L. Sabine, J. L. Sarmiento, R. Schlitzer, R. D. Slater, I. J. Totterdell, M.-F. Weirig, Y. Yamanaka, and A. Yool: Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature, 437:681-686, doi:10.1038/nature04095(2005)*
  • Fujii, M., M. Ikeda and Y. Yamanaka: Roles of biogeochemical processes in the carbon cycle using a simple coupled physical-biogeochemical model. J. Oceanogr., 61:803-815(2005)*
    2005 [Not refereed][Not invited]
  • M Fujii, N Yoshie, Y Yamanaka, F Chai
    PROGRESS IN OCEANOGRAPHY 64 (2-4) 307 - 324 0079-6611 2005 [Refereed][Not invited]
     
    To fill temporal gaps in iron-enrichment experimental data and gain further understanding of marine ecosystem responses to iron enrichments, we apply a fifteen-compartment ecosystem model to three iron-enrichment sites, namely SEEDS (the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study; 48.5 degrees N, 165 degrees E) in the western North Pacific, SOIREE (the Southern Ocean Iron RElease Experiment; 61 degrees S, 140 degrees E) in the Southern Ocean, and IronExII (the second mesoscale iron enrichment experiment; 3.5 degrees S, 104 degrees W) in the Equatorial Pacific. The ecological effects of iron in the model are represented by changing two photosynthetic parameters during the iron-enrichment period. The model results successfully reproduce the observed biogeochemical responses inside and outside the iron patch at each site, such as rapid increases in plankton biomass and biological productivity, and decreases in surface nutrients and pCO(2), inside the patch. However, the modeled timing and magnitude of changes differ among the sites because of differences in both physical environments and plankton species. After the iron enrichment, the diatom productivity is strongly controlled by light at SOIREE and by silicate at IronExII and SEEDS. Light limitation due to self-shading by the phytoplankton is significant during the bloom at all sites. Sensitivity analysis of the model results to duration of the iron enrichment reveals that long-term multiple infusions over more than a week would not be effective at SEEDS because of strong silicate limitation on diatom growth. Sensitivity of the model to water temperature shows that export production is higher at lower temperatures, because of slower recycling of particulate organic carbon. Therefore, the e-ratio (the ratio of export production to primary production) is inversely correlated with temperature, and the relationship can be described with a linear function. Through this study, we conclude that ecosystem modeling is a powerful tool to help design future iron-enrichment experiments and observational plans. (c) 2005 Elsevier Ltd. All rights reserved.
  • N Yoshie, M Fujii, Y Yamanaka
    PROGRESS IN OCEANOGRAPHY 64 (2-4) 283 - 306 0079-6611 2005 [Refereed][Not invited]
     
    We have developed a one-dimensional ecosystem model considering explicitly two groups of diatoms: centric and pennate. The model was applied to the iron-enrichment experiment, SEEDS (Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study) in the western North Pacific (48.5 degrees N, 165 degrees E). We assumed that the permate diatoms are not stressed by the iron limitation, but that the centric diatoms are significantly stressed and their photosynthetic rate is high when released from iron limitation. The iron-enrichment experiment was conducted by changing the physiological parameters for diatoms (the initial slope of the photosynthetic rate and the potential maximum photosynthetic rate). The model successfully reproduced the time-series of CO2 fugacity and the vertical distributions of chlorophyll-a and nutrients observed in SEEDS. The simulated results in the two-group model, especially the starting time of the diatom bloom, are better than those in the one-group model. We find that it is the transition of dominance, from permate to centric diatoms, rather than a physiological response of each group that causes the lag between iron-enrichment and the diatom bloom. In the simulations, the added iron's effect on the ecosystem continues for about 40 days. The model results suggest that the export flux during the observation period is only about 20% of the total export flux generated by iron-enrichment. For SEEDS, our simulated uptake of atmospheric CO2 and the export of particulate organic carbon at 100 m depth are 0.57 and 1.29 mol C m(-2), respectively, which are converted to 1720 and 3880 tC by assuming the patch's area to be 250 km(2), and to 4.90 and 11.1 tC kg(-1) Fe with the addition of 350 kg of iron. (c) 2005 Elsevier Ltd. All rights reserved.
  • Yoshio Masuda, Yasuhiro Yamanaka, Taketo Hashioka, Michimasa Magi, Shigeo Murai, Takashi Ohsumi
    Greenhouse Gas Control Technologies 819 - 827 2005 [Refereed][Not invited]
     
    A high-resolution model with a Lagrangian method is used to simulate the distribution and concentration of CO2 injected into the mid-depth ocean over timescales ranging from a week to a few years. A high-resolution model with a Lagrangian tracer enables effects of eddy activities on dispersion of particles to be well represented. Comparison of Lagrangian with Eulerian tracers shows that the Lagrangian tracer avoids artificial diffusion and enables CO2 maximum concentration at specific sites to be predicted, which helps in assessing CO2 impact on the marine ecosystem. Ensemble experiments using high-resolution models explicitly deal with dispersion by advection due to mesoscale eddies which cannot be achieved by coarse-resolution models with implicit eddy diffusion, and enable the distribution of CO2 maximum concentrations to be predicted. A high resolution model is demonstrated with this method is a powerful tool for assessing the effects of CO2 injection on the marine environment. © 2005 Elsevier Ltd. All rights reserved.
  • S Ito, MJ Kishi, Y Kurita, Y Oozeki, Y Yamanaka, BA Megrey, FE Werner
    FISHERIES OCEANOGRAPHY 13 (1) 111 - 124 1054-6006 2004/12 [Refereed][Not invited]
     
    A fish bioenergetics model coupled with an ecosystem model was developed to reproduce the growth of Pacific saury. The model spatially covers three different oceanographic spatial domains corresponding to the Kuroshio, Oyashio, and interfrontal (mixed water) regions. In this coupled model, three (small, large, and predatory) zooplankton densities which were derived from the lower trophic level ecosystem model were input to the bioenergetics model of saury as the prey densities. Although certain model parameters were imposed from other species' bioenergetics, several model parameters were estimated from observational data specific to Pacific saury. The integrated model results reproduced appropriate growth rates of Pacific saury. Model sensitivities to water temperature and prey density are examined and observational methods to evaluate the model parameters are discussed.
  • SC Doney, K Lindsay, K Caldeira, JM Campin, H Drange, JC Dutay, M Follows, Y Gao, A Gnanadesikan, N Gruber, A Ishida, F Joos, G Madec, E Maier-Reimer, JC Marshall, RJ Matear, P Monfray, A Mouchet, R Najjar, JC Orr, GK Plattner, J Sarmiento, R Schlitzer, R Slater, IJ Totterdell, MF Weirig, Y Yamanaka, A Yool
    GLOBAL BIOGEOCHEMICAL CYCLES 18 (3) 0886-6236 2004/09 [Refereed][Not invited]
     
    A suite of standard ocean hydrographic and circulation metrics are applied to the equilibrium physical solutions from 13 global carbon models participating in phase 2 of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2). Model-data comparisons are presented for sea surface temperature and salinity, seasonal mixed layer depth, meridional heat and freshwater transport, 3-D hydrographic fields, and meridional overturning. Considerable variation exists among the OCMIP-2 simulations, with some of the solutions falling noticeably outside available observational constraints. For some cases, model-model and model-data differences can be related to variations in surface forcing, subgrid-scale parameterizations, and model architecture. These errors in the physical metrics point to significant problems in the underlying model representations of ocean transport and dynamics, problems that directly affect the OCMIP predicted ocean tracer and carbon cycle variables (e.g., air-sea CO2 flux, chlorofluorocarbon and anthropogenic CO2 uptake, and export production). A substantial fraction of the large model-model ranges in OCMIP-2 biogeochemical fields (+/-25-40%) represents the propagation of known errors in model physics. Therefore the model-model spread likely overstates the uncertainty in our current understanding of the ocean carbon system, particularly for transport-dominated fields such as the historical uptake of anthropogenic CO2. A full error assessment, however, would need to account for additional sources of uncertainty such as more complex biological-chemical-physical interactions, biases arising from poorly resolved or neglected physical processes, and climate change.
  • SASAI Yoshikazu, ISHIDA Akio, YAMANAKA Yasuhiro, SASAKI Hideharu
    海と空 海洋気象学会 80 (1) 3 - 8 0503-1567 2004/07 [Refereed][Not invited]
  • JC Dutay, P Jean-Baptiste, JM Campin, A Ishida, E Maier-Reimer, RJ Matear, A Mouchet, IJ Totterdell, Y Yamanaka, K Rodgers, G Madec, JC Orr
    JOURNAL OF MARINE SYSTEMS 48 (1-4) 15 - 36 0924-7963 2004/07 [Refereed][Not invited]
     
    We compare simulations of the injection of mantle helium-3 into the deep ocean from six global coarse resolution models which participated in the Ocean Carbon Model Intercomparison Project (OCMIP). We also discuss the results of a study carried out with one of the models, which examines the effect of the subgrid-scale mixing parameterization. These sensitivity tests provide useful information to interpret the differences among the OCMIP models and between model simulations and the data. We find that the OCMIP models, which parameterize subgrid-scale mixing using an eddy-induced velocity, tend to underestimate the ventilation of the deep ocean, based on diagnostics with delta(3)He. In these models, this parameterization is implemented with a constant thickness diffusivity coefficient. In future simulations, we recommend using such a parameterization with spatially and temporally varying coefficients in order to moderate its effect on stratification. The performance of the models with regard to the formation of AABW confirms the conclusion from a previous evaluation with CFC-11. Models coupled with a sea-ice model produce a substantial bottom water formation in the Southern Ocean that tends to overestimate AABW ventilation, while models that are not coupled with a sea-ice model systematically underestimate the formation of AABW We also analyze specific features of the deep He-3 distribution (He-3 plumes) that are particularly well depicted in the data and which put severe constraints on the deep circulation. We show that all the models fail to reproduce a correct propagation of these plumes in the deep ocean. The resolution of the models may be too coarse to reproduce the strong and narrow currents in the deep ocean., and the models do not incorporate the geothermal heating that may also contribute to the generation of these currents. We also use the context of OCMIP-2 to explore the potential of mantle helium-3 as a tool to compare and evaluate modeled deep-ocean circulations. Although the source function of mantle helium is known with a rather large uncertainty, we find that the parameterization used for the injection of mantle helium-3 is sufficient to generate realistic results, even in the Atlantic Ocean where a previous pioneering study [J. Geophys. Res. 100 (1995) 3829] claimed this parameterization generates inadequate results. These results are supported by a multi-tracer evaluation performed by considering the simulated distributions of both helium-3 and natural C-14, and comparing the simulated tracer fields with available data. (C) 2004 Elsevier B.V. All rights reserved.
  • Y Sasai, A Ishida, Y Yamanaka, H Sasaki
    GEOPHYSICAL RESEARCH LETTERS 31 (12) 0094-8276 2004/06 [Refereed][Not invited]
     
    We have investigated the pathway of Antarctic Bottom Water (AABW) using simulated chlorofluorocarbons (CFCs) distribution in a global eddy-resolving OGCM. Our goal is to improve our understanding of the processes and pathways determining the distribution of CFCs in the Southern Ocean, where much of this tracer is entrained by formation of the deep and bottom water. The model exhibits considerable skill in reproducing the section along the Greenwich Meridian (AJAX) and 170degreesW (WOCE P15S). In the South Atlantic, the model indicates two pathways transporting CFC-11 from the Weddell Sea to the AJAX section: an upper pathway through the Scotia Sea, and a lower pathway south along the South Scotia Ridge. The simulated CFC-11 inventory along the two sections is much like that observed.
  • K Matsumoto, JL Sarmiento, RM Key, O Aumont, JL Bullister, K Caldeira, JM Campin, SC Doney, H Drange, JC Dutay, M Follows, Y Gao, A Gnanadesikan, N Gruber, A Ishida, F Joos, K Lindsay, E Maier-Reimer, JC Marshall, RJ Matear, P Monfray, A Mouchet, R Najjar, GK Plattner, R Schlitzer, R Slater, PS Swathi, IJ Totterdell, MF Weirig, Y Yamanaka, A Yool, JC Orr
    GEOPHYSICAL RESEARCH LETTERS 31 (7) 0094-8276 2004/04 [Refereed][Not invited]
     
    New radiocarbon and chlorofluorocarbon-11 data from the World Ocean Circulation Experiment are used to assess a suite of 19 ocean carbon cycle models. We use the distributions and inventories of these tracers as quantitative metrics of model skill and find that only about a quarter of the suite is consistent with the new data-based metrics. This should serve as a warning bell to the larger community that not all is well with current generation of ocean carbon cycle models. At the same time, this highlights the danger in simply using the available models to represent the state-of-the-art modeling without considering the credibility of each model.
  • Y Yamanaka, N Yoshie, M Fujii, MN Aita, MJ Kishi
    JOURNAL OF OCEANOGRAPHY 60 (2) 227 - 241 0916-8370 2004/04 [Refereed][Not invited]
     
    A model based on that of Kishi et al. (2001) has been extended to 15 compartments including silicon and carbon cycles. This model was applied to Station A7 off Hokkaido, Japan, in the Northwestern Pacific. The model successfully simulated the observations of: 1. a spring bloom of diatoms; 2. large seasonal variations of nitrate and silicate concentrations in the surface water; and 3. large inter-annual variations in chlorophyll-a. It also reproduced the observed features of the seasonal variations of carbon dioxide partial pressure (pCO(2))-a peak in pCO(2) in winter resulting from deep winter convection, a rapid decrease in pCO(2) as a result of the spring bloom, and an almost constant pCO(2) from summer through fall (when the effect of increasing temperature cancels the effect of biological production). A comparison of cases with and without silicate limitation shows that including silicate limitation in the model results in: 1. decreased production by diatoms during summer; and 2. a transition in the dominant phytoplankton species, from diatoms to other species that do not take up silicate. Both of these phenomena are observed at Station A7, and our results support the hypothesis that they are caused by silicate limitation of diatom growth.
  • MJ Kishi, T Okunishi, Y Yamanaka
    JOURNAL OF OCEANOGRAPHY 60 (1) 63 - 73 0916-8370 2004/02 [Refereed][Not invited]
     
    JGOFS has revealed the importance of marine biological activity to the global carbon cycle. Ecological models are valuable tools for improving our understanding of biogeochemical cycles. Through a series of workshops, the North Pacific Marine Science Organization (PICES) developed NEMURO (North Pacific Ecosystem Model Understanding Regional Oceanography) a model, specifically designed to simulate the lower trophic ecosystem in the North Pacific Ocean. Its ability to simulate vertical fluxes generated by biological activities has not yet been validated. Here compare NEMURO with several other lower trophic level models of the northern North Pacific. The different ecosystem models are each embedded in a common three-dimensional physical model, and the simulated vertical flux of POM and the biomass of phytoplankton are compared. The models compared are: (1) NEMURO, (2) the Kishi and Nakata Model (Kishi et al., 1981), (3) KKYS (Kawamiya et al., 1995, 2000a, 2000b), and (4) the Denman model (Denman and Pena, 2002). With simple NPZD models, it is difficult to describe the production of POM (Particulate Organic Matter) and hence the simulations of vertical flux are poor. However, if the parameters are properly defined, the primary production can be well reproduced, even though none of models we used here includes iron limitation effects. On the whole, NEMURO gave a satisfactory simulation of the vertical flux of POM in the northern North Pacific.
  • Ito, S., M. J. Kishi, Y. Kurita, Y. Oozaki, Y. Yamanaka, B. A. Megrey and F.E. Werner: "A fish bioenergetics model application to Pacific saury coupled with a lower trophic ecosystem model." Fisheries Oceanog., 13, 111-124 (2004)*
    2004 [Not refereed][Not invited]
  • Kishi, M. J., T. Okunishi and Y. Yamanaka: "Comparing primary production and vertical flux using different ecosystem models in the western North Pacific.", J. Oceanogr., 60, 63-73 (2004)*
    2004 [Not refereed][Not invited]
  • Doney, S. C., K. Lindsay, K. Caldeira, J.-M. Campin, H. Drange, J.-C. Dutay, M. Follows, Y. Gao, N. Gruber, A. Ishida, F. Joos, G. Madec, E.Maier-Reimer, J.C. Marshall, R.J. Matear, P. Monfray, R. Najjar, J.C. Orr, G.-K. Plattner, J. Sarmiento, R. Schl・・・
    2004 [Not refereed][Not invited]
     
    Doney, S. C., K. Lindsay, K. Caldeira, J.-M. Campin, H. Drange, J.-C. Dutay, M. Follows, Y. Gao, N. Gruber, A. Ishida, F. Joos, G. Madec, E.Maier-Reimer, J.C. Marshall, R.J. Matear, P. Monfray, R. Najjar, J.C. Orr, G.-K. Plattner, J. Sarmiento, R. Schlitzer, R. Slater, I.J. Totterdell, M.-F. Weirig, Y. Yamanaka and A. Yool: "Evaluating global ocean carbon models: The importance of realistic physics.", Global Biogeochem. Cycle, 18, GB3017, doi:10.1029/2003GB002150, (2004)*
  • Sasai, Y., A. Ishida, Y. Yamanaka, and H. Sasaki: "Chlorofluorocarbons in a global ocean eddy-resolving OGCM : Pathway and formation of Antarctic Bottom Water.", Geophys. Res. Lett, 31, L12305, doi:10.1029/2604GL019895 (2004)*
    2004 [Not refereed][Not invited]
  • H Sasaki, Y Sasai, S Kawahara, M Furuichi, F Araki, A Ishida, Y Yamanaka, Y Masumoto, H Sakuma
    OCEANS '04 MTS/IEEE TECHNO-OCEAN '04, VOLS 1- 2, CONFERENCE PROCEEDINGS, VOLS. 1-4 3 1535 - 1541 2004 [Refereed][Not invited]
  • N Yoshie, Y Yamanaka, MJ Kishi, H Saito
    JOURNAL OF OCEANOGRAPHY 59 (5) 563 - 571 0916-8370 2003/10 [Refereed][Not invited]
     
    A one-dimensional ecosystem model has been used to investigate the processes relevant to the spring diatom bloom which play important roles in the biogeochemical cycle in the western subarctic Pacific. The model represents the plankton dynamics and the nutrient cycles in the spring diatom bloom; its results show the importance of dilution by deep mixing in winter. It is supposed that the vertically integrated biomass of phytoplankton decreases in the winter due to the decrease of photosynthesis, because the deep mixing transports phytoplankton to a layer with a low light level. However, the observed integrated diatom biomass increases as the mixed layer deepens. This is because the decrease of concentration due to dilution by mixing causes the diatom grazed pressure to be less significant than diatom photosynthesis. In other words, the effect of dilution on the grazed rate is more significant than the effect on the photosynthesis rate because the grazed rate depends on the concentrations of both diatom and grazer, whereas the photosynthesis rate depends only diatom concentration. The average specific diatom grazed rate, defined as grazed rate divided by diatom biomass, decreases by 35% associated with the deepening, while the average specific photosynthesis rate of diatom decreases by 11%. As a result, the average specific net diatom growth rate during the deep mixing is about 70% of its maximum during the spring diatom bloom. The deep mixing significantly affects the amplitude of the spring diatom bloom not only by the supply of nutrients but also by the dilution which drastically decreases the grazed pressure.
  • Tajika E, Yamanaka Y
    Fossils 日本古生物学会 0 (74) 27 - 35 0022-9202 2003/09/20 [Refereed][Not invited]
     
    Global warming during the mid-Cretaceous is investigated using a carbon geochemical cycle model. The atmospheric CO_2 level may have increased owing to enhanced volcanic activity during the mid-Cretaceous, while the organic carbon burial rate increased during the same period and may have suppressed further warming. Mantle plume activity, forming large igneous provinces (LIPs), would have released a large amount of CO_2 to the atmosphere, but the effects of this on the climate may have been small compared to those of increased seafloor spreading rates. However, the effects of plume activity ...
  • MN Aita, Y Yamanaka, MJ Kishi
    FISHERIES OCEANOGRAPHY 12 (4-5) 284 - 290 1054-6006 2003/09 [Refereed][Not invited]
     
    We developed a global three-dimensional physical biological coupled model and applied it in simulations with and without ontogenetic seasonal vertical migration of large zooplankton (copepods). The annual cycle of phytoplankton behaviour is well reproduced by this model with the seasonal vertical migration of zooplankton. A comparison of the two cases shows that in the northwestern Pacific and subarctic southern ocean, primary production is higher in the case with vertical migration. In these regions, large phytoplankton ( diatoms) dominate, and the presence of large zooplankton throughout the year reduces primary production by large phytoplankton ( diatoms). This effect is greatest for the diatom bloom. On the other hand, for regions where small phytoplankton dominate, primary production is higher in the case without vertical migration. This is because small zooplankton are suppressed by grazing pressure from large zooplankton, reducing grazing pressure on small phytoplankton.
  • Yoshie, N., Y. Yamanaka, M. J. Kishi and H. Saito: "One dimensional ecosystem model simulation of the effects of vertical dilution by the winter mixing on the spring diatom bloom.", J. Oceanogr., 59:563-571 (2003)*
    2003 [Not refereed][Not invited]
  • "白亜紀における地球システム変動."
    化石(日本古生物学会誌) 74 25 - 33 2003 [Not refereed][Not invited]
  • Aita, M. N., Y. Yamanaka and M. J. Kishi: "Effect of ontogenetic vertical migration of zooplankton on the results of NEMURO embedded in a general circulation model.", Fisheries Oceanog., 12:284-290 (2003)*
    2003 [Not refereed][Not invited]
  • Yamanaka Yasuhiro
    Planetary People 日本惑星科学会 11 (1) 20 - 28 0918-273X 2002/03/01 [Not refereed][Not invited]
  • 「海洋無酸素事変と海洋循環停滞」
    『遊星人(日本惑星科学会誌)』 11 20 - 28 2002 [Not refereed][Not invited]
  • J. -C. Dutay, J. L. Bullister, S. C. Doney, J. C. Orr, R. Najjar, K. Caldeira, J. -M. Campin, H. Drange, M. Follows, Y. Gao, N. Gruber, M. W. Hecht, A. Ishida, F. Joos, K. Lindsay, G. Madec, E. Maier-Reimer, J. C. Marshall, R. J. Matear, P. Monfray, A. Mouchet, G. -K. Plattner, J. Sarmiento, R. Schlitzer, R. Slater, I. J. Totterdell, M. -F. Weirig, Y. Yamanaka, A. Yool
    OCEAN MODELLING 4 (2) 89 - 120 1463-5003 2002 [Refereed][Not invited]
     
    We compared the 13 models participating in the Ocean Carbon Model Intercomparison Project (OCMIP) with regards to their skill in matching observed distributions of CFC-11. This analysis characterizes the abilities of these models to ventilate the ocean on timescales relevant for anthropogenic CO(2) uptake. We found a large range in the modeled global inventory (+/- 30%), mainly due to differences in ventilation from the high latitudes. In the Southern Ocean, models differ particularly in the longitudinal distribution of the CFC uptake in the intermediate water, whereas the latitudinal distribution is mainly controlled by the subgrid-scale parameterization. Models with isopycnal diffusion and eddy-induced velocity parameterization produce more realistic intermediate water ventilation. Deep and bottom water ventilation also varies substantially between the models. Models coupled to a sea-ice model systematically provide more realistic AABW formation source region; however these same models also largely overestimate AABW ventilation if no specific parameterization of brine rejection during sea-ice formation is included. In the North Pacific Ocean, all models exhibit a systematic large underestimation of the CFC uptake in the thermocline of the subtropical gyre, while no systematic difference toward the observations is found in the subpolar gyre. In the North Atlantic Ocean, the CFC uptake is globally underestimated in subsurface. In the deep ocean, all but the adjoint model, failed to produce the two recently ventilated branches observed in the North Atlantic Deep Water (NADW). Furthermore, simulated transport in the Deep Western Boundary Current (DWBC) is too sluggish in all but the isopycnal model, where it is too rapid. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • M Fujii, Y Nojiri, Y Yamanaka, MJ Kishi
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 49 (24-25) 5441 - 5461 0967-0645 2002 [Refereed][Not invited]
     
    A vertically one-dimensional ecosystem model is applied to Station KNOT (Kyodo North Pacific Ocean Time series; 44degreesN, 155degreesE). This model has 15 compartments, including two categories of phytoplankton (diatoms and non-diatom small phytoplankton) and three categories of zooplankton (small, large and predatory zooplankton). Observed seasonal cycles of ecosystem dynamics at Station KNOT, such as surface nutrient concentrations and column-integrated chlorophyll-a, are successfully reproduced by the model. Observed significant seasonality of a total primary production is also reproduced, but its amount is overestimated by more than 50%, especially during summer. The simulated spring diatom bloom seems to occur I month earlier than in reality, considering dramatic decreases in the observed surface silicate in May and June, but it is impossible to determine the time of the actual bloom more precisely because of lack of data in April. Sensitivity studies for several important parameters are described. The Ekman upwelling velocity strongly affects the amount of the total primary production. Stoichiometry of silicon to nitrogen for diatoms strongly determines the amount of the primary production by small phytoplankton. Maximum photosynthetic rate for diatoms contributes to set both the timing and strength of the spring diatom bloom. Maximum rate of grazing on diatoms by large zooplankton controls the timing of the end of the spring diatom bloom and the strength of the autumn diatom bloom. While most of the parameters can be set to the same values as those for Station A7 (41.5degreesN, 145.5degreesE), in the Northwestern Pacific like Station KNOT, some values need to be modified. The modification of the parameter values may be partly caused by the difference in the ecosystem dynamics between Stations KNOT and AT Observations of the mixed-layer depth and surface nutrient concentrations in March and April, when they reach their maxima, are strongly required to reduce uncertainty of the parameter values. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • Y Yamanaka, R Furue, H Hasumi, N Suginohara
    JOURNAL OF PHYSICAL OCEANOGRAPHY 30 (9) 2439 - 2451 0022-3670 2000/09 [Refereed][Not invited]
     
    The authors compare two classical advection schemes, the centered difference and weighted upcurrent, for coarse-resolution OGCMs. using an idealized ocean basin and a realistic World Ocean topography. For the idealized basin, three experiments are run, one with 12 vertical levels and the centered difference scheme, one with 12 levels and the weighted upcurrent scheme, and the other with 800 levels and the centered scheme. The last experiment perfectly satisfies the grid Peclet number stability criterion and is regarded as the "true solution." Comparison of the coarse vertical resolution experiments with the true solution indicates 1) that with the centered scheme, when strong vertical motion crosses a strong stratification, false density values are created in the coarse resolution model and this leads to false convective adjustment, which transports those false density values downward; and 2) that because of computational diffusion, the weighted upcurrent scheme leads to a less dense deep water with a stronger stratification than those of the true solution. These characteristics also apply even to the World Ocean model with relatively small grid Peclet numbers (moderately high vertical resolution and relatively large vertical diffusivity): the centered scheme leads to artificial convective adjustment near the surface in the equatorial Pacific, creating an artificial circulation, and the weighted upcurrent scheme leads to a warmer deep water and more diffuse thermocline. Deep equatorial "stacked jets" are found in all idealized-basin experiments, in particular, in the super-high vertical resolution case. Horizontal diffusion is found to dominate the density balance at the bottom jet in the super-high-resolution model, as previously found in an OGCM with a moderately high vertical resolution. This is consistent with the hypothesis that the jets exist owing to diapycnal mixing.
  • Y Yamanaka, R Furue, H Hasumi, N Suginohara
    JOURNAL OF PHYSICAL OCEANOGRAPHY 30 (9) 2439 - 2451 0022-3670 2000/09 [Refereed][Not invited]
     
    The authors compare two classical advection schemes, the centered difference and weighted upcurrent, for coarse-resolution OGCMs. using an idealized ocean basin and a realistic World Ocean topography. For the idealized basin, three experiments are run, one with 12 vertical levels and the centered difference scheme, one with 12 levels and the weighted upcurrent scheme, and the other with 800 levels and the centered scheme. The last experiment perfectly satisfies the grid Peclet number stability criterion and is regarded as the "true solution." Comparison of the coarse vertical resolution experiments with the true solution indicates 1) that with the centered scheme, when strong vertical motion crosses a strong stratification, false density values are created in the coarse resolution model and this leads to false convective adjustment, which transports those false density values downward; and 2) that because of computational diffusion, the weighted upcurrent scheme leads to a less dense deep water with a stronger stratification than those of the true solution. These characteristics also apply even to the World Ocean model with relatively small grid Peclet numbers (moderately high vertical resolution and relatively large vertical diffusivity): the centered scheme leads to artificial convective adjustment near the surface in the equatorial Pacific, creating an artificial circulation, and the weighted upcurrent scheme leads to a warmer deep water and more diffuse thermocline. Deep equatorial "stacked jets" are found in all idealized-basin experiments, in particular, in the super-high vertical resolution case. Horizontal diffusion is found to dominate the density balance at the bottom jet in the super-high-resolution model, as previously found in an OGCM with a moderately high vertical resolution. This is consistent with the hypothesis that the jets exist owing to diapycnal mixing.
  • M. Fujii, M. Ikeda, Y. Yamanaka
    Journal of Oceanography 56 (6) 655 - 666 0916-8370 2000 [Refereed][Not invited]
     
    A simplified physical model is proposed in this article to describe differences among basins in substance distributions which were not well described by previous simplified models. In the proposed model, the global ocean is divided into the Pacific/Indian Ocean (PI), the Atlantic Ocean (AT), the Southern Ocean and the Greenland/Iceland/Norwegian Sea. The model is consisted of five physical parameters, namely the air-sea gas exchange, the thermohaline circulation, the horizontal and vertical diffusions, and the deep convection in the high-latitude regions. Individual values of these parameters are chosen by optimizing model distribution of natural 14C as a physical tracer. The optimal value for a coefficient of vertical diffusion in the low-latitude region is 7.5 x 10-5 [m2s-1]. Vertical transports by the Antarctic Bottom Water and the North Atlantic Deep Water are estimated at 1.0 Sv and 9.0 Sv. Global-mean air-sea gas exchange time is calculated at 9.0 years. Using these optimal values, vertical profiles of dissolved inorganic carbon without biological production in PI and AT are estimated. Oceanic responses to anthropogenic fluctuations in substance concentrations in the atmosphere induced by the industrialization and nuclear bomb are also discribed, i.e., the effects appear significantly in AT while a signal is extremely weak in PI. A time-delay term is effective to make the PI water older near the bottom boundary.
  • Y Yamanaka, E Tajika
    GLOBAL BIOGEOCHEMICAL CYCLES 11 (4) 599 - 612 0886-6236 1997/12 [Refereed][Not invited]
     
    A biogeochemical general circulation model which includes production and consumption processes of dissolved organic matter (DOM) is developed. The semilabile and the refractory DOM are taken into account. The vertical distribution of the dissolved organic carbon (DOC) concentration and the Delta(14)C value obtained in our model compares well with the recent observations. It is found that the double DOC maximum zone (DDMZ) extends in the east-west direction in the equatorial Pacific. Case studies, which change the decay time and production ratio constant, show that the horizontal distribution of DOC in the surface layer can be reproduced only when the decay time of the semilabile DOM is about half a year. The semilabile DOM exists only above a depth of 400 m, and its vertical and horizontal transport plays an important role in the marine biogeochemical cycle in the surface layer. However, below that depth, only the inert refractory DOM exists, and the role of the refractory DOM in the biogeochemical cycle is not important. The global export production due to the particulate organic matter (POM) and DOM at a depth of 100 m is estimated to be about 8 Gt C/yr and about 3 Gt C/yr, respectively. The vertical transport below 400 m is due almost entirely to POM.
  • Kawamiya M, Kishi M.J, Yamanaka Y, Suginohara N
    Journal of Oceanography 53 (4) 397 - 402 1997 [Refereed][Not invited]
  • Y Yamanaka, E Tajika
    GLOBAL BIOGEOCHEMICAL CYCLES 10 (2) 361 - 382 0886-6236 1996/06 [Refereed][Not invited]
     
    Distributions of chemical tracers in the world ocean are well reproduced in an ocean general circulation model which includes biogeochemical processes (biogeochemical general circulation model, B-GCM). The difference in concentration of tracers between the surface and the deep water depends not only on the export production but also on the remineralization depth. Case studies changing the vertical profile of particulate organic matter (POM) flux and the export production show that the phosphate distribution can be reproduced only when the vertical profile of POM flux observed by sediment traps is used. The export production consistent with the observed distribution of phosphate is estimated to be about 10 GtC/yr. Case studies changing the vertical profile of calcite flux and the rain ratio, a ratio of production rate of calcite against that of particulate organic carbon (POC), show that the rain ratio should be smaller than the widely used value of 0.25. The rain ratio consistent with the observed distribution of alkalinity is estimated to be 0.08 to approximately 0.10. This value can be easily understood in a two-box model where the difference of remineralization depth between POC and calcite is taken into account.
  • Michio Kawamiya, Michio J. Kishi, Yasuhiro Yamanaka, Nobuo Suginohara
    Journal of Oceanography 51 (6) 635 - 664 0916-8370 1995/11 [Refereed][Not invited]
     
    A vertical one-dimensional ecosystem model was constructed and applied to Station Papa. The model has seven compartments (phytoplankton, nitrate, ammonium, zooplankton, particulate organic matters, dissolved organic matters, dissolved oxygen) and was coupled with a mixed layer model for calculating diffusion coefficient which appears in the governing equations. The mixed layer model was driven by SST, SSS data observed at Station Papa in 1980 and ECMWF wind data for 1980, and the ecosystem model was driven by fixing nitrate concentration in deep layer to an observational value. The phytoplankton maximum in March was reproduced by the model although the maximum in fall-winter could not be reproduced. The model also suggests the importance of studying nitrification. As a whole, the model could reproduce characteristic features at Station Papa such as the summer ammonium maximum at 50 m depth, the summer dissolved oxygen maximum at 70 m depth and the absence of remarkable phytoplankton bloom. © 1995 Journal of the Oceanographic Society of Japan.
  • I. Ishikawa, Y. Yamanaka, N. Suginohara
    Journal of Oceanography 50 (3) 247 - 263 0916-8370 1994/05 [Refereed][Not invited]
     
    Effects of the presence of a circumpolar region on buoyancy-driven circulation are investigated by using an idealized numerical ocean model. Comparison of circulation and meridional density (heat) transport is made between a closed ocean and an ocean with a cyclic gap near its southern boundary. The presence of the circumpolar region leads to disconnection of the meridional overturning across the circumpolar region. And the circumpolar eastward flow reaches the bottom of the ocean. It is essential for this that the pycnocline is deeper than the bottom of the gap. Since the amount of the mass transported northward must return southward at the levels deeper than the bottom of the cyclic gap, the weak stratification, hence weak vertical geostrophic shear, at the deeper levels leads to inactive communication across the circumpolar region. Meridional heat transport across the circumpolar region is made mainly by horizontal diffusion for the ocean with the cyclic gap, while the contribution of the advection is dominant for the closed ocean. Sensitivity of meridional heat transport to change in horizontal diffusivity is studied. The meridional heat transport for the ocean with the cyclic gap is more sensitive than for the closed ocean. The change in heat transport occurs not only in the circumpolar region but also in the rest of the ocean. It is suggested that subgrid scale phenomena, especially mesoscale eddies, in the circumpolar region controls the whole ocean to a great extent. © 1994 Oceanographic Society of Japan.

Books etc

  • 北海道から見る地球温暖化
    岩波書店 2008

Conference Activities & Talks

MISC

Research Grants & Projects

  • 地球温暖化における海洋による人為起源二酸化炭素吸収と海洋生態系変動の解明と予測

Educational Activities

Teaching Experience

  • Exercise in Practical Science for Environment II
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 研究倫理 統計 プレゼンテーション アカデミックスキル Research ethics, statistics, presentation, academic skills
  • Field Work in Practical Science for Environment II
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : サービスラーニング、プロジェクト・マネジメント、企画、ファシリテーション、プレゼンテーション、文章作成 Service learning, Project Management, Planing, facilitation, presentation, writing
  • Introduction to Practical Science for Environment I
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 地球温暖化, 地球システム, 適応, 緩和,京都議定書, 気候変化, 人為影響, 気候変動に関する政府間パネル(IPCC), 気候変動枠組み条約 Global Warming, Earth System, Adaptation, Mitigation, Kyoto Protocol, Climate Change, Anthropogenic effects, IPCC, UNFCCC
  • Introduction to Practical Science for Environment II
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : アクティブラーニング、実践環境科学、科学コミュニケーション、地域コミュニティー、地球環境、市民科学 Active Learning, Practical Science for Environment, science communication, community activities, global environment, citizen science
  • Advanced Course in Practical Science for Environment
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : アクティブラーニング、実践環境科学、科学コミュニケーション、地域コミュニティー、地球環境、市民科学 Active Learning, Practical Science for Environment, science communication, community activities, global environment, citizen science
  • Internship in Practical Science for Environment I
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 提案型インターンシップ、インターンシップ、多様な人との協働、地域活性、環境科学、実践 Self-proposed Internship, Internship, collaboraion with various people, regional revitalization, environmental science, Practice
  • Internship in Practical Science for Environment II
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 提案型インターンシップ、インターンシップ、多様な人との協働、地域活性、環境科学、実践 Self-proposed Internship, Internship, collaboraion with various people, regional revitalization, environmental science, Practice
  • Exercise in Practical Science for Environment I
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : チーム学習、TBL、プロジェクト・マネジメント、企画、PDCAサイクル、事業、ファシリテーション、プレゼンテーション Team-based learning, TBL, Project Management, Planing, PDCA cycle, facilitation, presentation
  • Field Work in Practical Science for Environment I
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : チーム学習、TBL、プロジェクト・マネジメント、企画、PDCAサイクル、事業、ファシリテーション、プレゼンテーション Team-based learning, TBL, Project Management, Planing, PDCA cycle, facilitation, presentation
  • Inter-Graduate School Classes(General Subject):Inter-Disciplinary Sciences
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : チーム学習、TBL、プロジェクト・マネジメント、企画、PDCAサイクル、事業、ファシリテーション、プレゼンテーション
  • Inter-Graduate School Classes(General Subject):Inter-Disciplinary Sciences
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : チーム学習、TBL、プロジェクト・マネジメント、企画、PDCAサイクル、事業、ファシリテーション、プレゼンテーション
  • Introduction to Environmental Science
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 環境科学、持続可能な開発目標(SDGs)、気候変動、環境保全、自然共生社会、環境保全、異なる立場の理解、キャリアパス、大学院
  • Inter-Graduate School Classes(General Subject):Natural and Applied Sciences
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : 環境科学、持続可能な開発目標(SDGs)、気候変動、環境保全、自然共生社会、環境保全、異なる立場の理解、キャリアパス、大学院
  • Environment and People
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 持続可能な社会、低炭素社会、環境リスク、生態系サービス、エコツーリズム、持続可能な開発目標(SDGs)

Campus Position History

  • 2013年4月1日 
    2016年3月31日 
    サステイナビリティ学教育研究センター長
  • 2013年5月27日 
    2015年3月31日 
    研究戦略室室員
  • 2015年4月1日 
    2017年3月31日 
    研究戦略室室員

Position History

  • 2013年4月1日 
    2016年3月31日 
    サステイナビリティ学教育研究センター長
  • 2013年5月27日 
    2015年3月31日 
    研究戦略室室員
  • 2015年4月1日 
    2017年3月31日 
    研究戦略室室員


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