Researchers Database

TAKEOKA, Hidetaka

    Institution for Collaborative Relation Professor
Last Updated :2021/03/05

Researcher Information

Degree

  • Doctor of Science(Kyoto University)

J-Global ID

Research Interests

  • モニタリング   クラゲ   赤潮   貧酸素水塊   養殖   地球環境変動   低次生態系   栄養塩   物質循環   生物生産   滞留時間   海水交換   成層   混合   拡散   物質輸送   密度流   潮流   瀬戸内海   沿岸海洋   海洋   monitoring   jellyfish   red tide   oxygen-deficient water mass   aquaculture   global environmental change   lower level ecosystem   material cycling   biological production   residence time   water exchange   stratification   mixing   diffusion   material transport   density-induced current   tidal current   Seto Inland Sea   coastal ocean   ocean   

Academic & Professional Experience

  • 1977 - 1984  Ehime UniversityFaculty of Engineering
  • 1977 - 1984  Faculty of Engineering, Ehime University工学部

Education

  •        - 1977  Kyoto University  理学研究科  地球物理学専攻
  •        - 1977  Kyoto University  Graduate School, Division of Natural Science  Geophysics Course
  •        - 1976  Kyoto University  理学研究科  地球物理学専攻
  •        - 1976  Kyoto University  Graduate School, Division of Natural Science  Geophysics Course
  •        - 1974  Kyoto University  Faculty of Science
  •        - 1974  Kyoto University  Faculty of Science

Association Memberships

  • 日本海洋学会   水産海洋学会   海洋気象学会   日本沿岸域学会   土木学会   日本海洋学会沿岸海洋研究会   Oceanographic Society of Japan   the Oecanographic Society of Japan   Coastal Oceanography Research Committee   

Books etc

  • Sustainable Development in the Seto Inland Sea, Japan
    Terra Scientific Publishing Company 1997
  • Sustainable Development in the Seto Inland Sea, Japan
    Terra Scientific Publishing Company 1997
  • 瀬戸内海の生物資源と環境
    恒星社厚生閣 1996
  • 瀬戸内海の生物資源と環境
    恒星社厚生閣 1996
  • Deep Ocean Circulation, Physical and Chemical Aspects
    Elsevier 1993
  • 東京湾―100年の環境変遷―
    恒星社厚生閣 1993
  • Deep Ocean Circulation, Physical and Chemical Aspects
    Elsevier 1993
  • 瀬戸内海の環境
    恒星社厚生閣 1985
  • 瀬戸内海の環境
    恒星社厚生閣 1985
  • 瀬戸内海の環境
    恒星社厚生閣 1985
  • 瀬戸内海の環境
    恒星社厚生閣 1985
  • 瀬戸内海の環境
    恒星社厚生閣 1985

Works

  • 原発温排水が付着生物に及ぼす影響の共同研究
    1999
  • Joint Research on Infruence for Sessile Organism by Worm Drain of Atomic Power Prant
    1999

MISC

  • Atsuhiko Isobe, Xinyu Guo, Hidetaka Takeoka  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS  115-  (C04023)  doi:10.1029/2009JC005818  2010/04  
    Prerequisite(s) for ocean circulation models capable of hindcasting "kyucho" occurrence (a sudden coastal temperature rise induced by Kuroshio frontal waves) in the Bungo Channel, Japan, is investigated using long-term observed temperature and sea level time series, archived hydrographic data, and reanalysis data provided by the Japanese Coastal Ocean Predictability Experiment (JCOPE) group. Anticyclonic mesoscale eddies impinging on the Kuroshio front south of the Bungo Channel enhance the frontal sharpness, frontal wave growth, and activity of kyucho phenomena. A kyucho hindcast is carried out to examine the reliability of a numerical model including realistic anticyclonic eddies propagating south of Japan. The Finite Volume Coastal Ocean Model (FVCOM) for which boundary conditions are given by daily JCOPE2 reanalysis data is adopted in the present study. This numerical model does a reasonable job of hindcasting kyucho occurrence in 2003. It is therefore considered that forecasts of kyucho occurrence up to 2 or 3 months ahead are possible by using the FVCOM in conjunction with JCOPE2 forecast data.
  • Atsuhiko Isobe, Xinyu Guo, Hidetaka Takeoka  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS  115-  (C04023)  doi:10.1029/2009JC005818  2010/04  
    Prerequisite(s) for ocean circulation models capable of hindcasting "kyucho" occurrence (a sudden coastal temperature rise induced by Kuroshio frontal waves) in the Bungo Channel, Japan, is investigated using long-term observed temperature and sea level time series, archived hydrographic data, and reanalysis data provided by the Japanese Coastal Ocean Predictability Experiment (JCOPE) group. Anticyclonic mesoscale eddies impinging on the Kuroshio front south of the Bungo Channel enhance the frontal sharpness, frontal wave growth, and activity of kyucho phenomena. A kyucho hindcast is carried out to examine the reliability of a numerical model including realistic anticyclonic eddies propagating south of Japan. The Finite Volume Coastal Ocean Model (FVCOM) for which boundary conditions are given by daily JCOPE2 reanalysis data is adopted in the present study. This numerical model does a reasonable job of hindcasting kyucho occurrence in 2003. It is therefore considered that forecasts of kyucho occurrence up to 2 or 3 months ahead are possible by using the FVCOM in conjunction with JCOPE2 forecast data.
  • 急潮によって引き起こされた夏季法花津湾表層におけるミズクラゲ表層出現頻度の短周期変動
    日本海洋学会海の研究  19-  (1)  1  -19  2010
  • Short-term periodic appearance of moon jellyfish aggregation at surface layer in summertime Hokezu Bay, Japan induced by kyucho
    The Oceanographic Siciety of JapanOceanography in Japan  19-  (1)  1  -19  2010
  • Pil-Hun Chang, Xinyu Guo, Hidetaka Takeoka  Journal of Oceanography  65-  (6)  721  -736  2009/12  
    The seasonal variation of water circulation in the Seto Inland Sea is investigated using a high resolution, three-dimensional numerical ocean model. The model results are assessed by comparison with long-term mean surface current and hydrographic data. The simulated model results are consistent with observations, showing a distinct summer and winter circulation patterns. In summer the sea water is highly stratified in basin regions, while it is well mixed near the straits due to strong tidal mixing there. During this period, a cold dome is formed in several basins, setting up stable cyclonic eddies. The cyclonic circulation associated with the cold dome develops from May and disappears in autumn when the surface cooling starts. The experiment without freshwater input shows that a basin-scale estuarine circulation coexists with cyclonic eddy in summer. The former becomes dominant in autumn circulation after the cold dome disappears. In winter the water is vertically well mixed, and the winter winds play a significant role in the circulation. The northwesterly winds induce upwind (downwind) currents over the deep (shallow) water, forming a "double-gyre pattern" in the Suo-Nada, two cyclonic eddies in Hiuchi-Nada, and anticyclonic circulation in Harima-Nada in vertically averaged current fields. © 2009 Springer Science+Business Media B.V.
  • CHANG Pil‐Hun, GUO Xinyu, TAKEOKA Hidetaka  The Oceanographic Society of JapanJournal of Oceanography  65-  (6)  721  -736  2009
  • 宇和海におけるミズクラゲの集群メカニズム
    沿岸海洋研究  46-  (2)  109  -117  2009
  • Qiang Wang, Xinyu Guo, Hidetaka Takeoka  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS  113-  (C8)  doi:10.1029/2007JC004555  2008/08  
    [1] We investigated the behavior of the Yellow River plume in the Bohai Sea through a year and its controlling mechanisms using a numerical model driven by monthly averaged wind stress, heat flux, and river discharge. The model produced a clear seasonal behavior of the Yellow River plume. In summer, the Yellow River plume extends northeastward into the central Bohai Sea; in autumn, it turns southward and flows into Laizhou Bay along the coast; in winter, most of the diluted water is found around southeastern corner of Laizhou Bay; and in spring, a low-salinity area appears in southwest Laizhou Bay. With the same model, several well-designed numerical experiments were performed to investigate the effect on the behavior of the Yellow River plume of tidal current, river discharge, wind stress, and thermal stratification. The tidal currents promote the offshore spread of diluted water, while the tide-induced residual currents prevent the plume from extending further downstream (in the direction of Kelvin wave propagation). Wind stresses lead to pronounced changes in the path and shape of the plume. In autumn and winter, northwesterly or northerly winds drive the buoyant water into Laizhou Bay along the coast. In summer, the combination of southeasterly winds and thermal stratification drives the plume extend northeastward into the central Bohai Sea. By changing only the magnitude of wind stress or river discharge in the experiments, we examined the sensitivity of summertime plume to the magnitude of wind stress and river discharge.
  • Kayoko Fukumori, Misa Oi, Hideyuki Doi, Daisuke Takahashi, Noboru Okuda, Todd W. Miller, Michinobu Kuwae, Hitoshi Miyasaka, Motomi Genkai-Kato, Yoshitsugu Koizumi, Koji Omori, Hidetaka Takeoka  ESTUARINE COASTAL AND SHELF SCIENCE  79-  (1)  45  -50  2008/08  
    Pinctada fucata martensii mantle tissue and gut contents were examined as baseline indicators of carbon and nitrogen isotope composition at six stations in the Uwa Sea, Japan. Substantial variations in delta C-13 and delta N-15 values of oysters among stations were observed, with delta C-13 being consistently lower at Hiburi Island (-18.1 parts per thousand) than at other stations (-17.2 parts per thousand). Oysters from fish farm sites were enriched in delta N-15 (8.1 parts per thousand) relative to those from unaffected sites (6.8 parts per thousand), suggesting that fish farming tends to increase baseline delta N-15 values. The mean Delta delta C-13 (0.8 parts per thousand) was consistent over space and time, whereas the average Delta delta N-15 slightly increased in summer. The relatively low delta N-15 enrichment compared to the theoretical isotope fractionation factor (3.4 parts per thousand) may be due to oyster-specific physiological attributes. Carbon and nitrogen isotope turnover rates were roughly similar within a tissue, and mantle tissue turnover rate was estimated to be 120-180 days. These results indicated that oysters are long-term integrators of delta C-13 and delta N-15 from their diet and that delta C-13 of oysters is a more accurate bioinclicator of isotopic baselines than delta N-15 for marine ecological studies. (C) 2008 Elsevier Ltd. All rights reserved.
  • Qiang Wang, Xinyu Guo, Hidetaka Takeoka  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS  113-  (C8)  doi:10.1029/2007JC004555  2008/08  
    [1] We investigated the behavior of the Yellow River plume in the Bohai Sea through a year and its controlling mechanisms using a numerical model driven by monthly averaged wind stress, heat flux, and river discharge. The model produced a clear seasonal behavior of the Yellow River plume. In summer, the Yellow River plume extends northeastward into the central Bohai Sea; in autumn, it turns southward and flows into Laizhou Bay along the coast; in winter, most of the diluted water is found around southeastern corner of Laizhou Bay; and in spring, a low-salinity area appears in southwest Laizhou Bay. With the same model, several well-designed numerical experiments were performed to investigate the effect on the behavior of the Yellow River plume of tidal current, river discharge, wind stress, and thermal stratification. The tidal currents promote the offshore spread of diluted water, while the tide-induced residual currents prevent the plume from extending further downstream (in the direction of Kelvin wave propagation). Wind stresses lead to pronounced changes in the path and shape of the plume. In autumn and winter, northwesterly or northerly winds drive the buoyant water into Laizhou Bay along the coast. In summer, the combination of southeasterly winds and thermal stratification drives the plume extend northeastward into the central Bohai Sea. By changing only the magnitude of wind stress or river discharge in the experiments, we examined the sensitivity of summertime plume to the magnitude of wind stress and river discharge.
  • Kayoko Fukumori, Misa Oi, Hideyuki Doi, Daisuke Takahashi, Noboru Okuda, Todd W. Miller, Michinobu Kuwae, Hitoshi Miyasaka, Motomi Genkai-Kato, Yoshitsugu Koizumi, Koji Omori, Hidetaka Takeoka  ESTUARINE COASTAL AND SHELF SCIENCE  79-  (1)  45  -50  2008/08  
    Pinctada fucata martensii mantle tissue and gut contents were examined as baseline indicators of carbon and nitrogen isotope composition at six stations in the Uwa Sea, Japan. Substantial variations in delta C-13 and delta N-15 values of oysters among stations were observed, with delta C-13 being consistently lower at Hiburi Island (-18.1 parts per thousand) than at other stations (-17.2 parts per thousand). Oysters from fish farm sites were enriched in delta N-15 (8.1 parts per thousand) relative to those from unaffected sites (6.8 parts per thousand), suggesting that fish farming tends to increase baseline delta N-15 values. The mean Delta delta C-13 (0.8 parts per thousand) was consistent over space and time, whereas the average Delta delta N-15 slightly increased in summer. The relatively low delta N-15 enrichment compared to the theoretical isotope fractionation factor (3.4 parts per thousand) may be due to oyster-specific physiological attributes. Carbon and nitrogen isotope turnover rates were roughly similar within a tissue, and mantle tissue turnover rate was estimated to be 120-180 days. These results indicated that oysters are long-term integrators of delta C-13 and delta N-15 from their diet and that delta C-13 of oysters is a more accurate bioinclicator of isotopic baselines than delta N-15 for marine ecological studies. (C) 2008 Elsevier Ltd. All rights reserved.
  • Kayoko Fukumori, Misa Oi, Hideyuki Doi, Noboru Okuda, Hitomi Yamaguchi, Michinobu Kuwae, Hitoshi Miyasaka, Kenji Yoshino, Yoshitsugu Koizumi, Koji Omori, Hidetaka Takeoka  ESTUARINE COASTAL AND SHELF SCIENCE  76-  (3)  704  -709  2008/02  
    We estimated the composition of two food sources for the cultured pearl oyster Pinctada fucata martensii using stable isotopes and stomach content analysis in the coastal areas of the Uwa Sea, Japan. The delta C-13 values of oysters (-17.5 to -16.8 parts per thousand) were intermediate between that of particulate organic matter (POM, -20.2 to -19.1 parts per thousand,) and attached microalgae on pearl cages (-13.0 parts per thousand). An isotope mixing model suggested that oysters were consuming 78% POM (mainly phytoplankton) and 22% attached microalgae. The attached microalgal composition of the stomach content showed a strong resemblance to the composition of that estimated through the isotope mixing model, suggesting preferential utilization of specific components is unlikely in this species. These results indicate that P. fucata martensii feed on a mixture of phytoplankton and attached microalgae, and that the attached microalgae on pearl cages can serve as an important additional food source. (C) 2007 Elsevier Ltd. All rights reserved.
  • Kayoko Fukumori, Misa Oi, Hideyuki Doi, Noboru Okuda, Hitomi Yamaguchi, Michinobu Kuwae, Hitoshi Miyasaka, Kenji Yoshino, Yoshitsugu Koizumi, Koji Omori, Hidetaka Takeoka  ESTUARINE COASTAL AND SHELF SCIENCE  76-  (3)  704  -709  2008/02  
    We estimated the composition of two food sources for the cultured pearl oyster Pinctada fucata martensii using stable isotopes and stomach content analysis in the coastal areas of the Uwa Sea, Japan. The delta C-13 values of oysters (-17.5 to -16.8 parts per thousand) were intermediate between that of particulate organic matter (POM, -20.2 to -19.1 parts per thousand,) and attached microalgae on pearl cages (-13.0 parts per thousand). An isotope mixing model suggested that oysters were consuming 78% POM (mainly phytoplankton) and 22% attached microalgae. The attached microalgal composition of the stomach content showed a strong resemblance to the composition of that estimated through the isotope mixing model, suggesting preferential utilization of specific components is unlikely in this species. These results indicate that P. fucata martensii feed on a mixture of phytoplankton and attached microalgae, and that the attached microalgae on pearl cages can serve as an important additional food source. (C) 2007 Elsevier Ltd. All rights reserved.
  • Diurnal tidal current on the eastern shelf of Hidaka Bay―Can juvenile walleye Pollock, Theragra chalcogramma, move southeastward with the diurnal tidal current?―
    La mer  46-  (1・2)  37  -47  2008
  • Miho Hirose, Toshiya Katano, Yuichi Hayami, Atsushi Kaneda, Takeshi Kohama, Hidetaka Takeoka, Shin-ichi Nakano  ESTUARINE COASTAL AND SHELF SCIENCE  76-  (2)  293  -303  2008/01  
    The Bungo Channel in southwestern Japan receives both warm, called Kyucho, and cold deep-water intrusions (bottom intrusion) from the Pacific Ocean. Abundances of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton were monitored from 18 July to 17 August 2001 to clarify whether advected picophytoplankton from the Pacific Ocean can grow in the channel or not. Synechococcus cells were further discriminated into low- and high-PUB types according to their fluorescence property in flow cytometry. From 18 to 25 July, the water temperature decreased by 3 degrees C at a 5-m depth at all stations, indicating the occurrence of a bottom intrusion. From 25 July to 4 August, a Kyucho occurred and the water temperature rapidly increased. From 4 to 17 August, a bottom intrusion and a Kyucho both occurred twice, although the intensities were smaller than those occurring until 4 August. From 18 to 30 July, the abundance of both Prochlorococcus and a high-PUB type of Synechococcus drastically decreased because of a bottom intrusion; however, the abundances rapidly increased due to the advection by a Kyucho. These advected cells increased from 4 to 17 August in the channel and Kitanada Bay. Changes in the abundance of low-PUB type of Synechococcus and eukaryotic picophytoplankton were less noticeable than those in the abundance of Prochlorococcus and high-PUB type. The present study demonstrated that oceanic picophytoplankton advected by the Kyucho could grow in the channel. However, abundances of low-PUB type and eukaryotic picophytoplankton increased higher than those of Prochlorococcus and high-PUB type did. Thus, these oceanic phytoplankters will be excluded when Kyucho does not occur for a long time. The co-occurrence of various types of picophytoplankton found in the channel is probably achieved by both Kyucho event and their growth capability in the channel. (C) 2007 Elsevier Ltd. All rights reserved.
  • Diurnal tidal current on the eastern shelf of Hidaka Bay―Can juvenile walleye Pollock, Theragra chalcogramma, move southeastward with the diurnal tidal current?―
    La mer  2008
  • Miho Hirose, Toshiya Katano, Yuichi Hayami, Atsushi Kaneda, Takeshi Kohama, Hidetaka Takeoka, Shin-ichi Nakano  ESTUARINE COASTAL AND SHELF SCIENCE  76-  (2)  293  -303  2008/01  
    The Bungo Channel in southwestern Japan receives both warm, called Kyucho, and cold deep-water intrusions (bottom intrusion) from the Pacific Ocean. Abundances of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton were monitored from 18 July to 17 August 2001 to clarify whether advected picophytoplankton from the Pacific Ocean can grow in the channel or not. Synechococcus cells were further discriminated into low- and high-PUB types according to their fluorescence property in flow cytometry. From 18 to 25 July, the water temperature decreased by 3 degrees C at a 5-m depth at all stations, indicating the occurrence of a bottom intrusion. From 25 July to 4 August, a Kyucho occurred and the water temperature rapidly increased. From 4 to 17 August, a bottom intrusion and a Kyucho both occurred twice, although the intensities were smaller than those occurring until 4 August. From 18 to 30 July, the abundance of both Prochlorococcus and a high-PUB type of Synechococcus drastically decreased because of a bottom intrusion; however, the abundances rapidly increased due to the advection by a Kyucho. These advected cells increased from 4 to 17 August in the channel and Kitanada Bay. Changes in the abundance of low-PUB type of Synechococcus and eukaryotic picophytoplankton were less noticeable than those in the abundance of Prochlorococcus and high-PUB type. The present study demonstrated that oceanic picophytoplankton advected by the Kyucho could grow in the channel. However, abundances of low-PUB type and eukaryotic picophytoplankton increased higher than those of Prochlorococcus and high-PUB type did. Thus, these oceanic phytoplankters will be excluded when Kyucho does not occur for a long time. The co-occurrence of various types of picophytoplankton found in the channel is probably achieved by both Kyucho event and their growth capability in the channel. (C) 2007 Elsevier Ltd. All rights reserved.
  • Shinya Magome, Tomohiro Yamashita, Takeshi Kohama, Atsushi Kaneda, Yuichi Hayami, Satoru Takahashi, Hidetaka Takeoka  JOURNAL OF OCEANOGRAPHY  63-  (5)  761  -773  2007/10  
    Jellyfish patch formation is investigated by conducting a drifter experiment combined with aerial photography of a sustained patch of the moon jellyfish in Hokezu Bay, Japan. Jellyfish patches are aggregations of individuals that are caused by a combination of swimming (active influence) and advection by currents (passive innuence). The drifter experiment involved the injection of 49 drifters around a distinct surface patch of jellyfish within an area of approximately 300 m x 300 m. The drifters' motion, caused only by the passive influence, was recorded in a series of 38 aerial photographs taken over approximately I h. The ambient uniform current field larger than the patch scale was estimated from the movement of the centroid position of drifters, while the distribution of horizontal divergence and relative vorticity around the patch was estimated from the time-derivative in areas of triangles formed by the drifters. The centroid positions of both drifters and patches moved stably toward the bay head at different speeds. The difference vector between the patch and drifter centroids was directed to the sun, and was opposite to the ambient current. The distributions of vorticity and divergence around patches exhibited inhomogeneity within the patch scale, and the drifters in this nonuniform current field aggregated near the convergence area within 1 h. The results suggest that horizontal patch formation is predominantly influenced by passive factors at the surface of Hokezu Bay. Furthermore, the upward swimming against downwelling may make sustained patch in surface layer.
  • Shinya Magome, Tomohiro Yamashita, Takeshi Kohama, Atsushi Kaneda, Yuichi Hayami, Satoru Takahashi, Hidetaka Takeoka  JOURNAL OF OCEANOGRAPHY  63-  (5)  761  -773  2007/10  
    Jellyfish patch formation is investigated by conducting a drifter experiment combined with aerial photography of a sustained patch of the moon jellyfish in Hokezu Bay, Japan. Jellyfish patches are aggregations of individuals that are caused by a combination of swimming (active influence) and advection by currents (passive innuence). The drifter experiment involved the injection of 49 drifters around a distinct surface patch of jellyfish within an area of approximately 300 m x 300 m. The drifters' motion, caused only by the passive influence, was recorded in a series of 38 aerial photographs taken over approximately I h. The ambient uniform current field larger than the patch scale was estimated from the movement of the centroid position of drifters, while the distribution of horizontal divergence and relative vorticity around the patch was estimated from the time-derivative in areas of triangles formed by the drifters. The centroid positions of both drifters and patches moved stably toward the bay head at different speeds. The difference vector between the patch and drifter centroids was directed to the sun, and was opposite to the ambient current. The distributions of vorticity and divergence around patches exhibited inhomogeneity within the patch scale, and the drifters in this nonuniform current field aggregated near the convergence area within 1 h. The results suggest that horizontal patch formation is predominantly influenced by passive factors at the surface of Hokezu Bay. Furthermore, the upward swimming against downwelling may make sustained patch in surface layer.
  • Agus Sudaryanto, In Monirith, Natsuko Kajiwara, Shin Takahashi, Philippus Hartono, Muawanah, Koji Omori, Hidetaka Takeoka, Shinsuke Tanabe  ENVIRONMENT INTERNATIONAL  33-  (6)  750  -758  2007/08  
    Organochlorines such as PCBs, DDTs, HCHs, CHLs and HCB were determined in pooled whole body homogenized of fish samples collected from five locations during 1998 and 2003 in order to understand their contamination status, temporal and spatial variation in Indonesian waters. PCBs and DDTs were the predominant contaminants with concentrations from 9.7 to 2700 ng/g lipid wt. and 12 to 1100 ng/g lipid wt., respectively, while HCHs (nd-24 ng/g lipid wt.), CHL compounds (nd-81 ng/g lipid wt.) and HCB (0.22-28 ng/g lipid wt.) were one to two orders of magnitude lower. Among the locations, PCBs and CHLs were higher in the samples from highly industrialized and thickly populated-locations, whereas OC pesticides such as DDTs and HCHs were particularly more prominent in suburban and rural areas. Levels of OCs observed in the waters surrounding Java Island were higher than those in Sumatra Island, implying significant use of OCs in highly populated Java Island. Concentrations of PCBs and DDTs in fish from Jakarta Bay were significantly lower in the samples collected in 2003 as compared to fish in 1998, indicating decreasing trend of these compounds in the Indonesian environment. Recent estimated average daily intakes of PCBs (0.81 mu g/person/ day), DDTs (1.1 mu g/person/day), HCHs (0.018 (mu g/person/day), CHLs (0.010 mu g/person/day) were much lower than the threshold values recommended by various agencies, suggesting minimal risk of this compound via fish ingestion to Indonesians. (c) 2007 Elsevier Ltd. All rights reserved.
  • Agus Sudaryanto, In Monirith, Natsuko Kajiwara, Shin Takahashi, Philippus Hartono, Muawanah, Koji Omori, Hidetaka Takeoka, Shinsuke Tanabe  ENVIRONMENT INTERNATIONAL  33-  (6)  750  -758  2007/08  
    Organochlorines such as PCBs, DDTs, HCHs, CHLs and HCB were determined in pooled whole body homogenized of fish samples collected from five locations during 1998 and 2003 in order to understand their contamination status, temporal and spatial variation in Indonesian waters. PCBs and DDTs were the predominant contaminants with concentrations from 9.7 to 2700 ng/g lipid wt. and 12 to 1100 ng/g lipid wt., respectively, while HCHs (nd-24 ng/g lipid wt.), CHL compounds (nd-81 ng/g lipid wt.) and HCB (0.22-28 ng/g lipid wt.) were one to two orders of magnitude lower. Among the locations, PCBs and CHLs were higher in the samples from highly industrialized and thickly populated-locations, whereas OC pesticides such as DDTs and HCHs were particularly more prominent in suburban and rural areas. Levels of OCs observed in the waters surrounding Java Island were higher than those in Sumatra Island, implying significant use of OCs in highly populated Java Island. Concentrations of PCBs and DDTs in fish from Jakarta Bay were significantly lower in the samples collected in 2003 as compared to fish in 1998, indicating decreasing trend of these compounds in the Indonesian environment. Recent estimated average daily intakes of PCBs (0.81 mu g/person/ day), DDTs (1.1 mu g/person/day), HCHs (0.018 (mu g/person/day), CHLs (0.010 mu g/person/day) were much lower than the threshold values recommended by various agencies, suggesting minimal risk of this compound via fish ingestion to Indonesians. (c) 2007 Elsevier Ltd. All rights reserved.
  • Michinobu Kuwae, Noboru Okuda, Hitoshi Miyasaka, Koji Omori, Hidetaka Takeoka, Takashige Sugimoto  ESTUARINE COASTAL AND SHELF SCIENCE  73-  (1-2)  279  -289  2007/06  
    In (order to detect responses of primary productivity in Japanese coastal embayments to climate and watershed changes for the last 500 years, we unraveled sedimentary records of delta C-13, delta N-15, TOC, TN, and C/N ratio in the north basin of Kagoshima Bay (KB). Based on principal component analysis of these geochemical data, primary component (PC) I that explains 65% of the total variance within all the geochemical parameters was identified. The records of delta C-13, delta N-15, TOC, and TN having high loadings on the PCI axis showed centennial-scale variations (low levels during AD 1595-1725 and high levels during AD 1725-1860) and a shift (AD 1725). A comparison between our records and previous studies on the biogeochemical processes suggests that the factor responsible for fluctuations in delta C-13, delta N-15, TOC, and TN is likely to be the changes in primary productivity in the north basin of KB rather than other factors. C/N values, which have high loadings on PC2, are possibly related to input of C-3 land plants to the north basin of KB, suggesting changes in the surrounding forest environments. The centennial-scale decrease in primary productivity that is represented by the TOC record is coincident with a temperature decrease associated with the Little Ice Age, suggesting that the primary productivity in the north basin of KB might have been influenced by global or Northern Hemispheric-scale climate changes. (C) 2007 Elsevier Ltd. All rights reserved.
  • Michinobu Kuwae, Noboru Okuda, Hitoshi Miyasaka, Koji Omori, Hidetaka Takeoka, Takashige Sugimoto  ESTUARINE COASTAL AND SHELF SCIENCE  73-  (1-2)  279  -289  2007/06  
    In (order to detect responses of primary productivity in Japanese coastal embayments to climate and watershed changes for the last 500 years, we unraveled sedimentary records of delta C-13, delta N-15, TOC, TN, and C/N ratio in the north basin of Kagoshima Bay (KB). Based on principal component analysis of these geochemical data, primary component (PC) I that explains 65% of the total variance within all the geochemical parameters was identified. The records of delta C-13, delta N-15, TOC, and TN having high loadings on the PCI axis showed centennial-scale variations (low levels during AD 1595-1725 and high levels during AD 1725-1860) and a shift (AD 1725). A comparison between our records and previous studies on the biogeochemical processes suggests that the factor responsible for fluctuations in delta C-13, delta N-15, TOC, and TN is likely to be the changes in primary productivity in the north basin of KB rather than other factors. C/N values, which have high loadings on PC2, are possibly related to input of C-3 land plants to the north basin of KB, suggesting changes in the surrounding forest environments. The centennial-scale decrease in primary productivity that is represented by the TOC record is coincident with a temperature decrease associated with the Little Ice Age, suggesting that the primary productivity in the north basin of KB might have been influenced by global or Northern Hemispheric-scale climate changes. (C) 2007 Elsevier Ltd. All rights reserved.
  • Michinobu Kuwae, Hitomi Yamaguchi, Narumi K. Tsugeki, Hitoshi Miyasaka, Kayoko Fukumori, Minoru Ikehara, Motomi Genkai-Kato, Koji Omori, Takashige Sugimoto, Shingo Ishida, Hidetaka Takeoka  ESTUARINE COASTAL AND SHELF SCIENCE  72-  (1-2)  348  -358  2007/03  
    In order to elucidate the organic and sulfur geochemical processes of surface sediments associated with oxic/anoxic conditions, we have examined the relationship between the spatial distribution of sedimentary delta C-13, delta N-15, TOC, TN, TS, C/N ratio, and C/S ratio and environmental variables in Beppu Bay, Japan. The results of the principal component analysis and redundancy analysis of these geochemical parameters revealed two dominant patterns in their variations. The first pattern is characterized by variations in delta C-13, delta N-15, and C/N, which are closely related to the distance between the river mouth and sampling sites. This pattern is attributed to the mixing of organic materials from two sources-C-3 land plants and marine phytoplankton-rather than various alternation processes such as diagenesis and eutrophication. The second pattern is characterized by variations in TOC, TN, TS, and C/S. The RDA results showed that these geochemical parameters are closely related to the water depth and DO. Meanwhile, a simple correlation analysis also showed a good correlation of TOC, TN, TS, and C/S with bottom temperature and Eh. In Beppu Bay, a significant negative correlation is observed between the depth and the dissolved oxygen concentration and Eh, indicating that the deeper bottom environments have lower oxygen availability and are more reductive. According to these observations and some findings of previous studies, the spatial variations in TOC and TN are controlled by decomposition rates. This is in contrast to those in TS and C/S, by rate of pyrite formation. Both these rates are possibly influenced by temperature or oxic/anoxic conditions. The RDA results revealed that the two patterns in the variations of the geochemical parameters exhibit a perpendicular relation with respect to RDA axes. This indicates that the two geochemical groups are controlled only by their main factors. It is possible that TOC, TN, TS, and C/S are sensitive to temperature or oxic/anoxic conditions in Beppu Bay; in contrast, delta C-13, delta N-15, and C/N are less sensitive to these conditions. (c) 2006 Elsevier Ltd. All rights reserved.
  • Atsushi Kaneda, Takeshi Kohama, Yuji Kawamura, Hidetaka Takeoka  LIMNOLOGY AND OCEANOGRAPHY  52-  (2)  707  -715  2007/03  
    Gelatinous zooplankton collected and quantified daily at the sluice gate of the Ikata Nuclear Power Station along the coast of Iyo-Nada in the Seto Inland Sea were analyzed for the period 1998-2004 in an effort to correlate the number of these animals with the physical oceanographic conditions. Sudden periodic and nonperiodic increases of gelatinous zooplankton occur repeatedly from early summer to late autumn in nearshore areas. Periodic increases are synchronous with the spring tidal period. Nearshore tide-induced eddy development may play an important role for the aggregation process of gelatinous zooplankton, and the spring-neap tidal variation of the circulation induces increases of the gelatinous zooplankton population in coastal waters of the Iyo-Nada. Nonperiodic increases are attributable to typhoons and other storms. The strong shoreward currents due to the winds caused by these events transport gelatinous zooplankton to nearshore areas.
  • Michinobu Kuwae, Hitomi Yamaguchi, Narumi K. Tsugeki, Hitoshi Miyasaka, Kayoko Fukumori, Minoru Ikehara, Motomi Genkai-Kato, Koji Omori, Takashige Sugimoto, Shingo Ishida, Hidetaka Takeoka  ESTUARINE COASTAL AND SHELF SCIENCE  72-  (1-2)  348  -358  2007/03  
    In order to elucidate the organic and sulfur geochemical processes of surface sediments associated with oxic/anoxic conditions, we have examined the relationship between the spatial distribution of sedimentary delta C-13, delta N-15, TOC, TN, TS, C/N ratio, and C/S ratio and environmental variables in Beppu Bay, Japan. The results of the principal component analysis and redundancy analysis of these geochemical parameters revealed two dominant patterns in their variations. The first pattern is characterized by variations in delta C-13, delta N-15, and C/N, which are closely related to the distance between the river mouth and sampling sites. This pattern is attributed to the mixing of organic materials from two sources-C-3 land plants and marine phytoplankton-rather than various alternation processes such as diagenesis and eutrophication. The second pattern is characterized by variations in TOC, TN, TS, and C/S. The RDA results showed that these geochemical parameters are closely related to the water depth and DO. Meanwhile, a simple correlation analysis also showed a good correlation of TOC, TN, TS, and C/S with bottom temperature and Eh. In Beppu Bay, a significant negative correlation is observed between the depth and the dissolved oxygen concentration and Eh, indicating that the deeper bottom environments have lower oxygen availability and are more reductive. According to these observations and some findings of previous studies, the spatial variations in TOC and TN are controlled by decomposition rates. This is in contrast to those in TS and C/S, by rate of pyrite formation. Both these rates are possibly influenced by temperature or oxic/anoxic conditions. The RDA results revealed that the two patterns in the variations of the geochemical parameters exhibit a perpendicular relation with respect to RDA axes. This indicates that the two geochemical groups are controlled only by their main factors. It is possible that TOC, TN, TS, and C/S are sensitive to temperature or oxic/anoxic conditions in Beppu Bay; in contrast, delta C-13, delta N-15, and C/N are less sensitive to these conditions. (c) 2006 Elsevier Ltd. All rights reserved.
  • Atsushi Kaneda, Takeshi Kohama, Yuji Kawamura, Hidetaka Takeoka  LIMNOLOGY AND OCEANOGRAPHY  52-  (2)  707  -715  2007/03  
    Gelatinous zooplankton collected and quantified daily at the sluice gate of the Ikata Nuclear Power Station along the coast of Iyo-Nada in the Seto Inland Sea were analyzed for the period 1998-2004 in an effort to correlate the number of these animals with the physical oceanographic conditions. Sudden periodic and nonperiodic increases of gelatinous zooplankton occur repeatedly from early summer to late autumn in nearshore areas. Periodic increases are synchronous with the spring tidal period. Nearshore tide-induced eddy development may play an important role for the aggregation process of gelatinous zooplankton, and the spring-neap tidal variation of the circulation induces increases of the gelatinous zooplankton population in coastal waters of the Iyo-Nada. Nonperiodic increases are attributable to typhoons and other storms. The strong shoreward currents due to the winds caused by these events transport gelatinous zooplankton to nearshore areas.
  • Toshiya Katano, Atsushi Kaneda, Naoto Kanzaki, Yumiko Obayashi, Akihiko Morimoto, Goh Onitsuka, Hideichi Yasuda, Sotaro Mizutani, Yoshihide Kon, Kazuhiro Hata, Hidetaka Takeoka, Shin-ichi Nakan  AQUATIC MICROBIAL ECOLOGY  46-  (2)  191  -201  2007/02  
    A 'Kyucho' (an intrusion of warm surface water) occurs in the Bungo Channel, located in southwestern Japan. The abundances of Prochlorococcus and Synechococcus during a Kyucho, together with physical and chemical environmental factors, were investigated from the Kuroshio region to the Seto Inland Sea, via Bungo Channel, from 26 November to 5 December 2003. With the occurrence of the Kyucho, oceanic water intruded from the Kuroshio region into the middle of the Bungo Channel. The abundance of Prochlorococcus was the highest in the Kuroshio region and the southern part of the Bungo Channel (> 25 x 10(3) cells ml(-1)), low in the northern part of the Bungo Channel (< 1 x 10(3) cells ml(-1)), and below detection levels in the Seto Inland Sea. A relatively high abundance of Synechococcus cells (> 15 x 10(3) cells ml(-1)) was detected in the Kuroshio region and in the southern part of the Bungo Channel, but the abundance (< 6 x 10(3) cells ml(-1)) was low in other regions. In the Kuroshio region and the southern part of the Bungo Channel, high-phycourobilin (PUB)-type cells were dominant (> 90%); at this location, most of the available light in the deeper layer (> 25 m depth) was in the 450 to 500 nm range, corresponding to the peak absorbance of PUB. In contrast, the abundance of low-PUB-type cells accounted for > 75% of the total in the northern part of the Bungo Channel and in the Seto Inland Sea, where most of the available light in the deeper layer (> 10 m depth) was in the 480 to 560 nm range, including the peak absorbance of both PUB and phycoerythrobilin (PEB). These results indicate that Synechococcus cells of high-PUB type, which have a higher Ex 495:545 (> 1.5; ratio of orange fluorescence intensity excited at 495 nm to that at 545 nm), as well as Prochlorococcus cells were advected to the Bungo Channel by the Kyucho. The co-occurrence of the 2 pigment types of Synechococcus in coastal waters is highly affected by a physical process, such as the Kyucho.
  • Toshiya Katano, Atsushi Kaneda, Naoto Kanzaki, Yumiko Obayashi, Akihiko Morimoto, Goh Onitsuka, Hideichi Yasuda, Sotaro Mizutani, Yoshihide Kon, Kazuhiro Hata, Hidetaka Takeoka, Shin-ichi Nakan  AQUATIC MICROBIAL ECOLOGY  46-  (2)  191  -201  2007/02  
    A 'Kyucho' (an intrusion of warm surface water) occurs in the Bungo Channel, located in southwestern Japan. The abundances of Prochlorococcus and Synechococcus during a Kyucho, together with physical and chemical environmental factors, were investigated from the Kuroshio region to the Seto Inland Sea, via Bungo Channel, from 26 November to 5 December 2003. With the occurrence of the Kyucho, oceanic water intruded from the Kuroshio region into the middle of the Bungo Channel. The abundance of Prochlorococcus was the highest in the Kuroshio region and the southern part of the Bungo Channel (> 25 x 10(3) cells ml(-1)), low in the northern part of the Bungo Channel (< 1 x 10(3) cells ml(-1)), and below detection levels in the Seto Inland Sea. A relatively high abundance of Synechococcus cells (> 15 x 10(3) cells ml(-1)) was detected in the Kuroshio region and in the southern part of the Bungo Channel, but the abundance (< 6 x 10(3) cells ml(-1)) was low in other regions. In the Kuroshio region and the southern part of the Bungo Channel, high-phycourobilin (PUB)-type cells were dominant (> 90%); at this location, most of the available light in the deeper layer (> 25 m depth) was in the 450 to 500 nm range, corresponding to the peak absorbance of PUB. In contrast, the abundance of low-PUB-type cells accounted for > 75% of the total in the northern part of the Bungo Channel and in the Seto Inland Sea, where most of the available light in the deeper layer (> 10 m depth) was in the 480 to 560 nm range, including the peak absorbance of both PUB and phycoerythrobilin (PEB). These results indicate that Synechococcus cells of high-PUB type, which have a higher Ex 495:545 (> 1.5; ratio of orange fluorescence intensity excited at 495 nm to that at 545 nm), as well as Prochlorococcus cells were advected to the Bungo Channel by the Kyucho. The co-occurrence of the 2 pigment types of Synechococcus in coastal waters is highly affected by a physical process, such as the Kyucho.
  • 豊後水道における海洋環境とマアジの漁獲変動特性
    水産海洋学会水産海洋研究  71-  (1)  1  -8  2007
  • Hiroshi Kuroda, Yutaka Isoda, Hidetaka Takeoka, Satoshi Honda  JOURNAL OF OCEANOGRAPHY  62-  (5)  731  -744  2006/10  
    In order to examine seasonal variation in a coastal current and the dynamics of the current, we carried out a mooring current measurement near the coast on the eastern shelf of Hidaka Bay from December 2002 to July 2003. There seemed to be two current regimes during the observed period; one a southeastward current from December to March, and the other a northwestward current after April. Arrested topographic wave dynamics was used to understand along-shore steady momentum balance at the mooring site. It was found that the friction term was negligible during the former regime, that is, the wind stress term roughly counterbalanced the pressure gradient term. On the other hand, the contribution of each term to the momentum balance was sensitive to the resistance coefficient value during the latter regime. A numerical study showed that wind forcing alone could not reproduce the observed current velocity and momentum balance during the former regime. One possible interpretation of the observed results is superposition of the arrested topographic waves forced by the along-shore wind stress and downstream extension of the Coastal Oyashio. Numerical experiments using combined forcing of the wind stress and an inflow associated with the Coastal Oyashio supported the expected dynamics.
  • Michinobu Kuwae, Azumi Yamashita, Yuichi Hayami, Atsushi Kaneda, Takashige Sugimoto, Yoshio Inouchi, Atsuko Amano, Hidetaka Takeoka  JOURNAL OF OCEANOGRAPHY  62-  (5)  657  -666  2006/10  
    In order to examine the responses of primary productivity in the southern coastal sea of Japan to the Pacific Decadal Oscillation (PDO) in the 20th century, sedimentary records of diatom productivity (diatom valve fluxes) were reconstructed using core samples from the Bungo Channel (BC) in southwest Japan. The record of the Thalassionema spp. flux-the best index of fall primary productivity in the BC-indicated a multidecadal-scale duration with a low flux (1943-1982) and those with a. high flux (1913-1943 and 1982-2001); apparent shifts were recognized in 1943 and 1982. The shift in 1982 was also recognized in the flux records of other early summer to fall predominant genera in the BC and, previously, in the biogenic silica records from a broad region of the southeast BC. This indicates that in our records, this shift reflects a general trend in the primary production in the southeast BC. A comparison among the Thalassionema spp. flux records, meteorological data from an observatory adjacent to the core site, and the PDO index showed that the flux records were more similar to the PDO index than the other meteorological records, which suggests that the multidecadal-scale variability of the BC primary productivity may be associated with some marine-derived forcing. The bottom intrusions of nutrient-rich water that upwelled from the shelf slope into the BC, the axis movement or the transport of the Kuroshio Current off the BC, and a basin-scale wind stress in the North Pacific might play an important role in this forcing and mediate between the BC primary productivity and the PDO.
  • Hiroshi Kuroda, Yutaka Isoda, Hidetaka Takeoka, Satoshi Honda  JOURNAL OF OCEANOGRAPHY  62-  (5)  731  -744  2006/10  
    In order to examine seasonal variation in a coastal current and the dynamics of the current, we carried out a mooring current measurement near the coast on the eastern shelf of Hidaka Bay from December 2002 to July 2003. There seemed to be two current regimes during the observed period; one a southeastward current from December to March, and the other a northwestward current after April. Arrested topographic wave dynamics was used to understand along-shore steady momentum balance at the mooring site. It was found that the friction term was negligible during the former regime, that is, the wind stress term roughly counterbalanced the pressure gradient term. On the other hand, the contribution of each term to the momentum balance was sensitive to the resistance coefficient value during the latter regime. A numerical study showed that wind forcing alone could not reproduce the observed current velocity and momentum balance during the former regime. One possible interpretation of the observed results is superposition of the arrested topographic waves forced by the along-shore wind stress and downstream extension of the Coastal Oyashio. Numerical experiments using combined forcing of the wind stress and an inflow associated with the Coastal Oyashio supported the expected dynamics.
  • Michinobu Kuwae, Azumi Yamashita, Yuichi Hayami, Atsushi Kaneda, Takashige Sugimoto, Yoshio Inouchi, Atsuko Amano, Hidetaka Takeoka  JOURNAL OF OCEANOGRAPHY  62-  (5)  657  -666  2006/10  
    In order to examine the responses of primary productivity in the southern coastal sea of Japan to the Pacific Decadal Oscillation (PDO) in the 20th century, sedimentary records of diatom productivity (diatom valve fluxes) were reconstructed using core samples from the Bungo Channel (BC) in southwest Japan. The record of the Thalassionema spp. flux-the best index of fall primary productivity in the BC-indicated a multidecadal-scale duration with a low flux (1943-1982) and those with a. high flux (1913-1943 and 1982-2001); apparent shifts were recognized in 1943 and 1982. The shift in 1982 was also recognized in the flux records of other early summer to fall predominant genera in the BC and, previously, in the biogenic silica records from a broad region of the southeast BC. This indicates that in our records, this shift reflects a general trend in the primary production in the southeast BC. A comparison among the Thalassionema spp. flux records, meteorological data from an observatory adjacent to the core site, and the PDO index showed that the flux records were more similar to the PDO index than the other meteorological records, which suggests that the multidecadal-scale variability of the BC primary productivity may be associated with some marine-derived forcing. The bottom intrusions of nutrient-rich water that upwelled from the shelf slope into the BC, the axis movement or the transport of the Kuroshio Current off the BC, and a basin-scale wind stress in the North Pacific might play an important role in this forcing and mediate between the BC primary productivity and the PDO.
  • Yuji Kawamura, Yuichi Hayami, Takeshi Kohama, Atsushi Kaneda, Hidetaka Takeoka  GEOPHYSICAL RESEARCH LETTERS  33-  (14)  L14607, doi:10.1029/2006GL025866  2006/07  
    Data of mooring observation in Kitanada Bay, located on the eastern coast of Bungo Channel in Japan, obtained during summer 2001 are analyzed to investigate a modification process of the semidiurnal internal tide by density currents, occasionally occurring in the channel. The mooring data show that the semidiurnal internal tide has the character of low vertical mode standing wave. When the bottom slope near the mooring station is near-critical, the energy of the semidiurnal internal tide in the lower layer reached the maximum value. Since the density current modifies the density stratification occasionally creating the near-critical condition, it strongly affects the intensity of the semidiurnal internal tide energy in the lower layer.
  • Kenji Yoshino, Hitoshi Miyasaka, Yuji Kawamura, Motomi Genkai Kato, Noboru Okuda, Yuichi Hayami, Sayaka Ito, Kayo Kofukumori, Tomohiro Sekiguchi, Hidejiro Ohnish, Koji Ohmori, Hidetaka Takeoka  Plankton and Benthos Research  1-  (3)  155  -163  2006  
    There are many sand banks in Seto Inland Sea, making patchy shallow zones less than 10 m deep. Due to the shallow environment, the surface sediment on the sand banks in the Hojo area, in the southern part of Aki Nada, Shikoku Island, Japan, often has a larger amount of benthic microalgae than other areas. We hypothesized that benthic microalgae contributed to the secondary production of coastal waters around sand bank areas, and investigated the food-web structure of the Hojo area using stable isotopes in early summer, mid summer and fall. Mean carbon isotopic signatures of several consumers in early summer (- 16.9 to - 15.1%₀ for polychaeta #x002D 17.3 to 13.9%₀ for brachyuran crabs #x002D 17.2 to #x002D 15.3 for fish) and fall (#x002D 16.2 to #x002D 14.3%₀ for shrimps #x002D 14.0 to #x002D 11.2%₀ for brachyuran crabs) were more enriched than that of the particulate organic materials of the surface water around sand banks (mainly phytoplankton) (#x002D 20.5 ± 0.0%₀ in early summer and #x002D 18.3 ± 0.1%₀ in fall). Organic materials attached to cobbles, representative of benthic microalgae, showed similar or more enriched signatures than consumers (#x002D 14.7?±0.0%₀ in early summer and #x002D 10.3#x002D 0.0%₀ in fall). These results suggest that benthic microalgae on the sand bank contribute greatly to the secondary or higher production of coastal waters in Hojo area. © 2006, The Plankton Society of Japan, The Japanese Association of Benthology. All rights reserved.
  • 潮汐フロント周辺の前線波動とこれに伴う栄養塩輸送
    日本海洋学会海の研究  15-  (4)  343  -356  2006
  • 豊後水道における外洋起源栄養塩の供給機構とその生態系への影響
    沿岸海洋研究  43-  (2)  143  -149  2006
  • 沿岸域における外洋起源栄養物質量の見積もり法とその問題点
    沿岸海洋研究  43-  (2)  105  -111  2006
  • Kenji Yoshino, Hitoshi Miyasaka, Yuji Kawamura, Motomi Genkai Kato, Noboru Okuda, Yuichi Hayami, Sayaka Ito, Kayo Kofukumori, Tomohiro Sekiguchi, Hidejiro Ohnish, Koji Ohmori, Hidetaka Takeoka  Plankton and Benthos Research  1-  (3)  155  -163  2006  
    There are many sand banks in Seto Inland Sea, making patchy shallow zones less than 10 m deep. Due to the shallow environment, the surface sediment on the sand banks in the Hojo area, in the southern part of Aki Nada, Shikoku Island, Japan, often has a larger amount of benthic microalgae than other areas. We hypothesized that benthic microalgae contributed to the secondary production of coastal waters around sand bank areas, and investigated the food-web structure of the Hojo area using stable isotopes in early summer, mid summer and fall. Mean carbon isotopic signatures of several consumers in early summer (- 16.9 to - 15.1%₀ for polychaeta #x002D 17.3 to 13.9%₀ for brachyuran crabs #x002D 17.2 to #x002D 15.3 for fish) and fall (#x002D 16.2 to #x002D 14.3%₀ for shrimps #x002D 14.0 to #x002D 11.2%₀ for brachyuran crabs) were more enriched than that of the particulate organic materials of the surface water around sand banks (mainly phytoplankton) (#x002D 20.5 ± 0.0%₀ in early summer and #x002D 18.3 ± 0.1%₀ in fall). Organic materials attached to cobbles, representative of benthic microalgae, showed similar or more enriched signatures than consumers (#x002D 14.7?±0.0%₀ in early summer and #x002D 10.3#x002D 0.0%₀ in fall). These results suggest that benthic microalgae on the sand bank contribute greatly to the secondary or higher production of coastal waters in Hojo area. © 2006, The Plankton Society of Japan, The Japanese Association of Benthology. All rights reserved.
  • Processes of nutrient supply from the open ocean and their implications for the ecosystem in the BUngo Channel
    Bulletin on Coastal Oceanography  43-  (2)  143  -149  2006
  • Methods to estimate amounts of ocean-origin nutrients in coastal seas and their difficulties
    Bulletin on Coastal Oceanography  43-  (2)  105  -111  2006
  • Toshiya Katano, Atsushi Kaneda, Hidetaka Takeoka, Shin-Ichi Nakano  Marine Ecology Progress Series  298-  59  -67  2005/08  
    Uchiumi Bay experiences intermittent physical events of 'Kyucho' and bottom intrusion. A Kyucho is an intrusion of warm surface water from the Kuroshio in the Pacific Ocean. Bottom intrusion, which contains a large amount of nitrates, phosphates, and silicates, slips through just above the continental shelf. We investigated seasonal changes in the abundance of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton while monitoring Kyucho and bottom intrusion from March to October 2002. Kyucho and bottom intrusion frequently occurred from June to September. Relatively high concentrations of nitrate + nitrite (> 0.8 μmol N l-1) and phosphate (> 0.1 μmol P l-1) were found when bottom intrusion occurred. The cell densities of Prochlorococcus were relatively high (> 1 × 104 cells ml-1) when Kyucho occurred. Those of Synechococcus were high (2 to 30 × 104 cells ml-1) during the period of thermal stratification except in July, when bottom intrusion occurred. The cell densities of eukaryotic picophytoplankton were high (2 to 8 × 10 4 cells ml-1) in May and July. To examine the effects on picophytoplankton growth of the nutrients supplied by bottom intrusion, we conducted nutrient-enrichment experiments. The growth rates of Prochlorococcus and Synechococcus were not stimulated by the addition of any kinds of nutrients. The growth rates of Prochlorococcus were negative in most cases. In July, the growth rate of eukaryotic picophytoplankton was stimulated by nitrate and phosphate additions. Thus, Prochlorococcus detected in Uchiumi Bay might have been transported by Kyucho from the Pacific Ocean and could therefore not grow vigorously. Synechococcus may have been flushed out by bottom intrusion, and its growth was not limited by the nutrient concentrations. Eukaryotic picophytoplankton was abundant in spring, and its growth might have been limited by the nutrient concentrations in some cases. These results suggest that Kyucho and bottom intrusion have different effects on the abundance and growth rate of the 3 picophytoplankton groups. © Inter-Research 2005.
  • 瀬戸内海における環境の長期変動
    沿岸海洋研究  43-  (1)  45  -50  2005
  • 二村 彰, 武岡 英隆, 郭 新宇  日本海洋学会海の研究  14-  (3)  429  -440  2005
  • 宇和海・北灘湾におけるクロロフィルa濃度の季節・経年変動
    水産海洋学会水産海洋研究  69-  (1)  1  -9  2005
  • T Katano, A Kaneda, H Takeoka, S Nakano  MARINE ECOLOGY PROGRESS SERIES  298-  59  -67  2005  
    Uchiumi Bay experiences intermittent physical events of 'Kyucho' and bottom intrusion. A Kyucho is an intrusion of warm surface water from the Kuroshio in the Pacific Ocean. Bottom intrusion, which contains a large amount of nitrates, phosphates, and silicates, slips through just above the continental shelf. We investigated seasonal changes in the abundance of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton while monitoring Kyucho and bottom intrusion from March to October 2002. Kyucho and bottom intrusion frequently occurred from June to September. Relatively high concentrations of nitrate + nitrite (> 0.8 mu mol N l(-1)) and phosphate (> 0.1 mu mol P l(-1)) were found when bottom intrusion occurred. The cell densities of Prochlorococcus were relatively high (> 1 X 10(4) cells ml(-1)) when Kyucho occurred. Those of Synechococcus were high (2 to 30 x 10(4) Cells ml-1) during the period of thermal stratification except in July, when bottom intrusion occurred. The cell densities of eukaryotic picophytoplankton were high (2 to 8 x 10(4) cells ml(-1)) in May and July. To examine the effects on picophytoplankton growth of the nutrients supplied by bottom intrusion, we conducted nutrient-enrichment experiments. The growth rates of Prochlorococcus and Synechococcus were not stimulated by the addition of any kinds of nutrients. The growth rates of Prochlorococcus were negative in most cases. In July, the growth rate of eukaryotic picophytoplankton was stimulated by nitrate and phosphate additions. Thus, Prochlorococcus detected in Uchiumi Bay might have been transported by Kyucho from the Pacific Ocean and could therefore not grow vigorously. Synechococcus may have been flushed out by bottom intrusion, and its growth was not limited by the nutrient concentrations. Eukaryotic picophytoplankton was abundant in spring, and its growth might have been limited by the nutrient concentrations in some cases. These results suggest that Kyucho and bottom intrusion have different effects on the abundance and growth rate of the 3 picophytoplankton groups.
  • Long-term variations in the marine environments of the Seto Inland Sea
    Bulletin on Coastal Oceanography  43-  (1)  45  -50  2005
  • Akira Futamura, Hidetaka Takeoka, Xinyu Guo  The Oceanographic Society of JapanOceanography in Japan  14-  (3)  429  -440  2005
  • Seasonal and inter-annual variation in chlorophyll a concentration in Kitanada Bay, Uwa Sea
    Japanese Society of Fisheries OceanographyBulletin of the Japanese Society of Fisheries Oceanography  69-  (1)  1  -9  2005
  • XY Guo, A Futamura, H Takeoka  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS  109-  (C12)  doi:10.1029/2003JC00203  2004/12  
    On the basis of the Princeton Ocean Model, a robust diagnostic model is developed to calculate the residual currents in the Hiuchi-Nada, a semi-enclosed bay of the Seto Inland Sea. The input water temperature and salinity data are from six hydrographic surveys in 2002, and the model results in the summer show a clockwise eddy in the western part of the bay and an anticlockwise eddy in the eastern part. The magnitude of two eddies is similar to10 cm/s. The modeled flow pattern is consistent with early observations derived from moored arrays. The two eddies are persistent throughout the summer because winds are usually weak and cannot influence their existence. The tide-induced residual currents are appreciable only in the close vicinity of the Kurushima Strait and Bisan Strait, the two straits connecting the bay to the other bays, and have little affect on the two eddies that are inside the bay. Thus the two density-driven eddies in the Hiuchi-Nada are the basic pattern of circulation in the summer. Using the calculated residual currents, we examined the intrusion route of waters from the Kurushima Strait and Bisan Strait with passive tracer experiments. The results show that the water in the Kurushima Strait intrudes into the bay mainly through the middle and bottom layers while the water in the Bisan Strait intrudes mainly through the surface layer. Furthermore, the tracer cannot reach the center of the anticlockwise eddy in the eastern part of the bay. This indicates that the eddy prevents water exchange between its center and outer edges and provides favorable conditions for the formation of oxygen-deficient waters in the central part of the eddy.
  • S Nakano, Y Tomaru, T Katano, A Kaneda, W Makino, Y Nishibe, M Hirose, M Onji, S Kitamura, H Takeoka  AQUATIC ECOLOGY  38-  (4)  485  -493  2004  
    Seasonal changes in abundance of planktonic microorganisms, together with some physico-chemical variables, were monitored monthly from May 1999 to March 2002 in the surface water of a coastal bay where nutrients are mainly supplied by intermittent intrusions of deeper water (bottom intrusion). No significant bottom intrusion was detected in 1999 but large or frequent bottom intrusions were found from June to October in 2000, and again from mid-June only to late July in 2001. These results indicate that there is a different nutrient supply every year, and peaks in the abundance of dominant eukaryotic phytoplankton (diatoms and dinoflagellates) roughly corresponded to the occurrences of bottom intrusions. By contrast, there was a cyclic seasonal pattern of autotrophic picoplankton (APP) cell density, which reached maxima in August of every year at very similar levels (4.0-5.0 X 10(5) cells ml(-1)). Thus, the seasonal abundance of APP was apparently independent of the occurrence of bottom intrusions. Seasonal changes in cell densities of heterotrophic bacteria showed similar trends to the APP, and temperature-dependent growth of both was indicated. The present study suggests that the matter cycling in the bay varies as a result of shifts in the dominant food linkages, from a microbial food web to a herbivorous food web, due to intermittent nutrient supplies from bottom intrusions.
  • 瀬戸内海における窒素・リンの存在量とその長期変動
    海と空  80-  (2)  75  -78  2004
  • Modeling the effects of periodic intrusions of outer water on the variation in phytoplankton biomass and productivity in a small embayment
    Korean Journal of Limnology  37-  (4)  455  -461  2004
  • S Nakano, Y Tomaru, T Katano, A Kaneda, W Makino, Y Nishibe, M Hirose, M Onji, S Kitamura, H Takeoka  AQUATIC ECOLOGY  38-  (4)  485  -493  2004  
    Seasonal changes in abundance of planktonic microorganisms, together with some physico-chemical variables, were monitored monthly from May 1999 to March 2002 in the surface water of a coastal bay where nutrients are mainly supplied by intermittent intrusions of deeper water (bottom intrusion). No significant bottom intrusion was detected in 1999 but large or frequent bottom intrusions were found from June to October in 2000, and again from mid-June only to late July in 2001. These results indicate that there is a different nutrient supply every year, and peaks in the abundance of dominant eukaryotic phytoplankton (diatoms and dinoflagellates) roughly corresponded to the occurrences of bottom intrusions. By contrast, there was a cyclic seasonal pattern of autotrophic picoplankton (APP) cell density, which reached maxima in August of every year at very similar levels (4.0-5.0 X 10(5) cells ml(-1)). Thus, the seasonal abundance of APP was apparently independent of the occurrence of bottom intrusions. Seasonal changes in cell densities of heterotrophic bacteria showed similar trends to the APP, and temperature-dependent growth of both was indicated. The present study suggests that the matter cycling in the bay varies as a result of shifts in the dominant food linkages, from a microbial food web to a herbivorous food web, due to intermittent nutrient supplies from bottom intrusions.
  • Journal of Geophysical Research  109-  (C12008)  doi:10.1029/2003JC00203  2004
  • Modeling the effects of periodic intrusions of outer water on the variation in phytoplankton biomass and productivity in a small embayment
    Korean Journal of Limnology  37-  (4)  455  -461  2004
  • 有明海におけるM2潮汐の変化に関する論議へのコメント
    沿岸海洋研究  41-  (1)  61  -64  2003
  • Unusual aggregations of the scyphomedusa Aurelia aurita in coastal waters along western Shikoku, Japan
    Plankton Biology and Ecology  50-  (1)  17  -21  2003
  • Comment on the controversy about the change in M2 tidal amplitude of Ariake Bay
    Bulletin on Coastal Oceanography  41-  (1)  61  -64  2003
  • Unusual aggregations of the scyphomedusa Aurelia aurita in coastal waters along western Shikoku, Japan
    Plankton Biology and Ecology  50-  (1)  17  -21  2003
  • RS Balotro, A Isobe, M Shimizu, A Kaneda, T Takeuchi, H Takeoka  JOURNAL OF OCEANOGRAPHY  58-  (6)  759  -773  2002/12  
    An attempt was made to reproduce the circulation pattern in Suo-Nada, Japan during spring and summer season in order to elucidate the water exchange mechanism in the basin. Two hydrographic surveys at the end of each season were conducted covering the entire Suo-Nada area. A three-dimensional hydrodynamic Princeton Ocean Model (POM) was used to compute the current resulting from the observed density and wind field. During spring, a very pronounced counter clockwise gyre is situated near the opening of the basin. This is replaced by a clockwise circulation which seemed to occupy the whole domain during summer. Within each season, however, the vertical distribution of current does not show any remarkable differences, indicating the dominance of horizontal current and a very weak estuarine flow. These observational and numerical results were used to estimate the remnant function and the corresponding average residence time of permanently dissolved matter (PDM) and transformable matter (TM). The results revealed a small difference in the average residence times of materials within each season but a large seasonal variability between spring and summer. Furthermore, calculations based on climatological density fields have indicated a similar trend of variation between the seasonal values of average residence times.
  • RS Balotro, A Isobe, M Shimizu, A Kaneda, T Takeuchi, H Takeoka  JOURNAL OF OCEANOGRAPHY  58-  (6)  759  -773  2002/12  
    An attempt was made to reproduce the circulation pattern in Suo-Nada, Japan during spring and summer season in order to elucidate the water exchange mechanism in the basin. Two hydrographic surveys at the end of each season were conducted covering the entire Suo-Nada area. A three-dimensional hydrodynamic Princeton Ocean Model (POM) was used to compute the current resulting from the observed density and wind field. During spring, a very pronounced counter clockwise gyre is situated near the opening of the basin. This is replaced by a clockwise circulation which seemed to occupy the whole domain during summer. Within each season, however, the vertical distribution of current does not show any remarkable differences, indicating the dominance of horizontal current and a very weak estuarine flow. These observational and numerical results were used to estimate the remnant function and the corresponding average residence time of permanently dissolved matter (PDM) and transformable matter (TM). The results revealed a small difference in the average residence times of materials within each season but a large seasonal variability between spring and summer. Furthermore, calculations based on climatological density fields have indicated a similar trend of variation between the seasonal values of average residence times.
  • A Kaneda, H Takeoka, E Nagaura, Y Koizumi  JOURNAL OF OCEANOGRAPHY  58-  (4)  547  -556  2002/08  
    A cold-water intrusion, called a "bottom intrusion", occurs in the lower layer of the Bungo Channel in Japan. It is an intrusion from the shelf slope region of the Pacific Ocean margin in the south of the channel. In order to reveal the fundamental characteristics of the bottom intrusion, we conducted long-term observations of water temperature at the surface and bottom layers of the channel and 15-day current observations at the bottom of the shelf-break region. The long-term water temperature data indicated that the bottom intrusion occurs repeatedly between early summer and late autumn, and its reiteration between early and mid-summer causes a local minimum of water temperature in the lower layer in mid-summer. Moreover, the data revealed that most of the bottom intrusions occurred in neap tidal periods. The current meter recorded a bottom intrusion with a speed of approximately 15 cm(.)s(-1). The current meter also revealed that the intruded cold water slowly retreated back to the shelf slope region after the intrusion.
  • A Kaneda, H Takeoka, Y Koizumi  ESTUARINE COASTAL AND SHELF SCIENCE  55-  (2)  323  -330  2002/08  
    An Acoustic Doppler Current Profiler (ADCP) was deployed for 83 days at the bottom of Uchiumi Bay in the Bungo Channel, Japan. At the same station, the water temperature was measured at nine layers using a thermistor chain. From the temporal variations of the backscatter signal strength data of ADCP, we found that the backscatter signal intensity occasionally showed day-to-night fluctuations. We deduced that the day-to-night fluctuations suggested characterizations of migration patterns of zooplankton or krill, because the signal intensity became relatively high during the night. The migration pattern tended to occur after a cold-water intrusion from the shelf slope region south of the Bungo Channel, which is known as a "bottom intrusion". The bottom intrusion occurred six times during the observation period, and the tendency for the diurnal signal in the back scatter signal strength to develop after the bottom intrusion was observed in four of six cases. Though specific biological effects caused by the bottom intrusion are still unclear, the occasional diurnal fluctuations in backscatter signal strength may indicate that the bottom intrusion affects the biological environment in Uchiumi Bay, because the diurnal signal tended to intensify only after the bottom intrusion. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • A Kaneda, H Takeoka, E Nagaura, Y Koizumi  JOURNAL OF OCEANOGRAPHY  58-  (4)  547  -556  2002/08  
    A cold-water intrusion, called a "bottom intrusion", occurs in the lower layer of the Bungo Channel in Japan. It is an intrusion from the shelf slope region of the Pacific Ocean margin in the south of the channel. In order to reveal the fundamental characteristics of the bottom intrusion, we conducted long-term observations of water temperature at the surface and bottom layers of the channel and 15-day current observations at the bottom of the shelf-break region. The long-term water temperature data indicated that the bottom intrusion occurs repeatedly between early summer and late autumn, and its reiteration between early and mid-summer causes a local minimum of water temperature in the lower layer in mid-summer. Moreover, the data revealed that most of the bottom intrusions occurred in neap tidal periods. The current meter recorded a bottom intrusion with a speed of approximately 15 cm(.)s(-1). The current meter also revealed that the intruded cold water slowly retreated back to the shelf slope region after the intrusion.
  • A Kaneda, H Takeoka, Y Koizumi  ESTUARINE COASTAL AND SHELF SCIENCE  55-  (2)  323  -330  2002/08  
    An Acoustic Doppler Current Profiler (ADCP) was deployed for 83 days at the bottom of Uchiumi Bay in the Bungo Channel, Japan. At the same station, the water temperature was measured at nine layers using a thermistor chain. From the temporal variations of the backscatter signal strength data of ADCP, we found that the backscatter signal intensity occasionally showed day-to-night fluctuations. We deduced that the day-to-night fluctuations suggested characterizations of migration patterns of zooplankton or krill, because the signal intensity became relatively high during the night. The migration pattern tended to occur after a cold-water intrusion from the shelf slope region south of the Bungo Channel, which is known as a "bottom intrusion". The bottom intrusion occurred six times during the observation period, and the tendency for the diurnal signal in the back scatter signal strength to develop after the bottom intrusion was observed in four of six cases. Though specific biological effects caused by the bottom intrusion are still unclear, the occasional diurnal fluctuations in backscatter signal strength may indicate that the bottom intrusion affects the biological environment in Uchiumi Bay, because the diurnal signal tended to intensify only after the bottom intrusion. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • H Takeoka  JOURNAL OF OCEANOGRAPHY  58-  (1)  93  -107  2002/02  Book review  
    The Seto Inland Sea is a representative coastal sea in Japan with a complicated geometry and thus a variety of marine environments. This sea is, at the same time, one of the most industrialized areas in Japan, and its marine environment has been significantly affected by the anthropogenic impacts over the last four decades. The wide range of marine environments in this sea and the serious environmental issues resulting from these impacts have attracted the attention of Japanese coastal oceanographers. It is believed that the nature and scope of these studies might be an example of the progress of Japanese coastal oceanography. The historical changes in the Seto Inland Sea environment in the last four decades are briefly summarized, and the progress in the studies of the Seto Inland Sea is reviewed with reference to historical changes. Some recent research topics and activities are also mentioned.
  • 黒潮の離接岸が豊後水道の水温に与える影響
    沿岸海洋研究  39-  (2)  181  -188  2002
  • Influence of onshore/offshore movements of the Kuroshio on the water temperature in the Bungo Channel, Japan
    Bulletin on Coastal Oceanography  39-  (2)  181  -188  2002
  • Hidetaka Takeoka  Journal of Oceanography  58-  (1)  93  -107  2002  
    The Seto Inland Sea is a representative coastal sea in Japan with a complicated geometry and thus a variety of marine environments. This sea is, at the same time, one of the most industrialized areas in Japan, and its marine environment has been significantly affected by the anthropogenic impacts over the last four decades. The wide range of marine environments in this sea and the serious environmental issues resulting from these impacts have attracted the attention of Japanese coastal oceanographers. It is believed that the nature and scope of these studies might be an example of the progress of Japanese coastal oceanography. The historical changes in the Seto Inland Sea environment in the last four decades are briefly summarized, and the progress in the studies of the Seto Inland Sea is reviewed with reference to historical changes. Some recent research topics and activities are also mentioned.
  • 瀬戸内海の栄養塩環境の長期変動
    地球環境  6-  3  -12  2001
  • 瀬戸内海の栄養塩環境の長期自動モニタリング
    沿岸海洋研究  38-  91  -97  2001
  • T Yamamoto, H Ikeda, T Hara, H Takeoka  HYDROBIOLOGIA  435-  (1-3)  135  -142  2000/09  
    Movement of water overlying the sediments has not been taken into consideration in most of the experiments conducted to estimate the dissolved material flux from the sediment. Even in recent experiments that incorporated the stirring motion, interpretation of the data is difficult, because the mixing rate used may be different from actual mixing rate in the field. We propose a method to estimate the in situ mixing rate that should be used to set the flow rate in a flow-through core incubation system. The flow rate is calculated from the vertical mixing rate of the water that is deduced from the heat diffusivity. Release rates of NO3+NO2-N obtained from our flow-through incubation system were higher by 1-3 orders of magnitude than those from the conventional diffusion calculation method that estimates the flux from the gradient of nutrient concentration across the sediment-water interface. Increase in NO3+NO2-N flux is considered to be due to intensification of the nitrification process as a result of an increase in dissolved oxygen (DO) supply with the motion of water. DO supply is also considered to be an important factor controlling macrofaunal abundance and consequently their excretory contributions to the fluxes of dissolved organic nitrogen as well as NH4-N. From this point of view, we strongly recommend the application of heat and mass balance theory to estimate nitrogen flux using a flow-through experimental system.
  • T Yamamoto, H Ikeda, T Hara, H Takeoka  HYDROBIOLOGIA  435-  (1-3)  135  -142  2000/09  
    Movement of water overlying the sediments has not been taken into consideration in most of the experiments conducted to estimate the dissolved material flux from the sediment. Even in recent experiments that incorporated the stirring motion, interpretation of the data is difficult, because the mixing rate used may be different from actual mixing rate in the field. We propose a method to estimate the in situ mixing rate that should be used to set the flow rate in a flow-through core incubation system. The flow rate is calculated from the vertical mixing rate of the water that is deduced from the heat diffusivity. Release rates of NO3+NO2-N obtained from our flow-through incubation system were higher by 1-3 orders of magnitude than those from the conventional diffusion calculation method that estimates the flux from the gradient of nutrient concentration across the sediment-water interface. Increase in NO3+NO2-N flux is considered to be due to intensification of the nitrification process as a result of an increase in dissolved oxygen (DO) supply with the motion of water. DO supply is also considered to be an important factor controlling macrofaunal abundance and consequently their excretory contributions to the fluxes of dissolved organic nitrogen as well as NH4-N. From this point of view, we strongly recommend the application of heat and mass balance theory to estimate nitrogen flux using a flow-through experimental system.
  • Tamiji Yamamoto, Toshiya Hashimoto, Hidetaka Takeoka, Tenji Sugiyama, Osamu Matsuda  Journal of Oceanography  56-  (2)  131  -139  2000/04  
    Field observations were conducted to examine the processes governing the phytoplankton distribution and photosynthetic activity in and around a tidal front formed in Iyo Nada, the Seto Inland Sea, Japan. The existence of a middle layer intrusion, which, it has been suggested, moves from the mixed region to the stratified region of the tidal front, was ascertained by the phytoplankton distribution in addition to a T-S diagram. Skeletonema costatum, which originally inhabited the mixed region, was used as the indicator to reveal the intrusion. However, the tip of water containing the S. costatum population did not extend deeply into the stratified region. The velocity of the intrusion seemed to be slow enough to make biological processes, such as nutrient uptake by phytoplankton and subsequent growth, as well as the decrease in cell density due to zooplankton grazing, dominate during the transportation. The patchy distribution of copepod nauplii implied that grazing has an influence on the distribution pattern of phytoplankton. The location of high photosynthetic activity did not coincide spatially with the center of high phytoplankton biomass, suggesting the importance of these biological processes. Therefore, it is considered that the middle layer intrusion plays a role as an inducer of subsequent biological processes at the tidal front by not only supplying nutrients from the mixed region but also by increasing the vertical diffusivity.
  • Tamiji Yamamoto, Toshiya Hashimoto, Hidetaka Takeoka, Tenji Sugiyama, Osamu Matsuda  Journal of Oceanography  56-  (2)  131  -139  2000/04  
    Field observations were conducted to examine the processes governing the phytoplankton distribution and photosynthetic activity in and around a tidal front formed in Iyo Nada, the Seto Inland Sea, Japan. The existence of a middle layer intrusion, which, it has been suggested, moves from the mixed region to the stratified region of the tidal front, was ascertained by the phytoplankton distribution in addition to a T-S diagram. Skeletonema costatum, which originally inhabited the mixed region, was used as the indicator to reveal the intrusion. However, the tip of water containing the S. costatum population did not extend deeply into the stratified region. The velocity of the intrusion seemed to be slow enough to make biological processes, such as nutrient uptake by phytoplankton and subsequent growth, as well as the decrease in cell density due to zooplankton grazing, dominate during the transportation. The patchy distribution of copepod nauplii implied that grazing has an influence on the distribution pattern of phytoplankton. The location of high photosynthetic activity did not coincide spatially with the center of high phytoplankton biomass, suggesting the importance of these biological processes. Therefore, it is considered that the middle layer intrusion plays a role as an inducer of subsequent biological processes at the tidal front by not only supplying nutrients from the mixed region but also by increasing the vertical diffusivity.
  • Year-to-year variation of a kyucho and a bottom intrusion in the Bungo Channel, Japan
    Terra Scientific Publishing CompanyInteractions between Estuaries, Coastal Seas and Shelf Seas  197  -215  2000
  • Year-to-year variation of a kyucho and a bottom intrusion in the Bungo Channel, Japan
    Terra Scientific Publishing CompanyInteractions between Estuaries, Coastal Seas and Shelf Seas  197  -215  2000
  • Sustainable usage of coastal ecosystems
    Land-Ocean Interactions: Managing Coastal Ecosystems  1-  529  -534  1999
  • 豊後水道沿岸域の小規模渦
    沿岸海洋研究  37-  (1)  41  -47  1999
  • 夏季の伊予灘の海洋構造(Ⅰ)
    愛媛大学工学部紀要  18-  359  -366  1999
  • Sustainable usage of coastal ecosystems
    Land-Ocean Interactions: Managing Coastal Ecosystems  1-  529  -534  1999
  • 東京湾のPCB分布・堆積モデル
    沿岸海洋研究  36-  (1)  77  -82  1998
  • Toshiya Hashimoto, Hidetaka Takeoka  Journal of Oceanography  54-  (2)  123  -132  1998  
    A simple model of lower trophic level ecosystem has been created to analyze possible environmental control of primary production in eight sub-areas of the Seto Inland Sea. The primary production rates observed by Hashimoto et al. (1997a) in these sub-areas are well reproduced by the model, including horizontal processes such as horizontal transport of nutrients and vertical processes such as vertical mixing, light intensity and sinking of particulate matter. Without taking account of horizontal processes, the model also successfully reproduces the observed primary production rates in some areas, but it fails to reproduce those in the others. This shows that the relative importance of the horizontal transport on the primary production differs area by area. Two time scales, TZ and TH are introduced to explain this difference. TZ is a vertical cycling time of material, which is defined as the time during which the stock of the material in the water column is utilized for primary production TH is the horizontal transit time of the material. The relative importance of the horizontal process is well explained by the TH/TZ ratio that is, the horizontal transport process is important in the areas where this ratio is small. Further the possible mechanisms of nutrient supply for the primary production in each sub-area are investigated using this model.
  • Toshiya Hashimoto, Hidetaka Takeoka  Journal of Oceanography  54-  (2)  123  -132  1998  
    A simple model of lower trophic level ecosystem has been created to analyze possible environmental control of primary production in eight sub-areas of the Seto Inland Sea. The primary production rates observed by Hashimoto et al. (1997a) in these sub-areas are well reproduced by the model, including horizontal processes such as horizontal transport of nutrients and vertical processes such as vertical mixing, light intensity and sinking of particulate matter. Without taking account of horizontal processes, the model also successfully reproduces the observed primary production rates in some areas, but it fails to reproduce those in the others. This shows that the relative importance of the horizontal transport on the primary production differs area by area. Two time scales, TZ and TH are introduced to explain this difference. TZ is a vertical cycling time of material, which is defined as the time during which the stock of the material in the water column is utilized for primary production TH is the horizontal transit time of the material. The relative importance of the horizontal process is well explained by the TH/TZ ratio that is, the horizontal transport process is important in the areas where this ratio is small. Further the possible mechanisms of nutrient supply for the primary production in each sub-area are investigated using this model.
  • 窒素、燐の流入負荷量の削減に対する水質の応答
    沿岸海洋研究  34-  (2)  183  -190  1997
  • Tidal Fronts Induced by Horizontal Contrast of Vertical Mixing Efficiency
    日本海洋学会  53-  (06)  563  -570  1997
  • Tidal Fronts Induced by Horizontal Contrast of Vertical Mixing Efficiency
    The Oceanographic Society of JapanJournal of Oceanography  53-  (06)  563  -570  1997
  • The stratification variations during spring and neap tidal periods in Deukryang Bay, Korea
    La mer  34-  (3)  183  -191  1996
  • 1993年夏季の豊後水道の低温化現象
    沿岸海洋研究  34-  (1)  71  -78  1996
  • 沿岸海洋と外洋の相互作用
    沿岸海洋研究  34-  (1)  3  -13  1996
  • 底質の酸素消費速度に基づく適正養殖基準の決定法
    水産海洋研究  60-  (1)  45  -53  1996
  • The stratification variations during spring and neap tidal periods in Deukryang Bay, Korea
    La mer  34-  (3)  183  -191  1996
  • Hidetaka Takeoka, Yoshio Tanaka, Yuichi Ohno, Yukiharu Hisaki, Akitsugu Nadai, Hiroshi Kuroiwa  Journal of Oceanography  51-  (6)  699  -711  1995/11  
    Observations of sea surface currents by HF radar were carried out in the Bungo Channel in summer 1992. The current ellipses of M2 constituent obtained by the observational results agree quite well with those obtained by the ADCP observations, showing that the accuracy of the HF radar measurements is of the same level as ADCP. The results revealed the current structures and their change with the Kyucho in detail. The Kyucho is influenced by the complicated coastal geometry and does not propagate straightly into the Bungo Channel. It propagates further inward after charging the coastal bays with warm water. The current directions change largely, since the currents turn around the stagnant region in the bay filled with the warm water. The northward intrusion begins to be weakened in the southern part of the channel, while it still persists in the northern part. The northward current speeds of the observed Kyucho are about 50 cm/s and sometimes attain 60 to 70 cm/s. © 1995 Journal of the Oceanographic Society of Japan.
  • Hidetaka Takeoka, Yoshio Tanaka, Yuichi Ohno, Yukiharu Hisaki, Akitsugu Nadai, Hiroshi Kuroiwa  Journal of Oceanography  51-  (6)  699  -711  1995/11  
    Observations of sea surface currents by HF radar were carried out in the Bungo Channel in summer 1992. The current ellipses of M2 constituent obtained by the observational results agree quite well with those obtained by the ADCP observations, showing that the accuracy of the HF radar measurements is of the same level as ADCP. The results revealed the current structures and their change with the Kyucho in detail. The Kyucho is influenced by the complicated coastal geometry and does not propagate straightly into the Bungo Channel. It propagates further inward after charging the coastal bays with warm water. The current directions change largely, since the currents turn around the stagnant region in the bay filled with the warm water. The northward intrusion begins to be weakened in the southern part of the channel, while it still persists in the northern part. The northward current speeds of the observed Kyucho are about 50 cm/s and sometimes attain 60 to 70 cm/s. © 1995 Journal of the Oceanographic Society of Japan.
  • 潮汐フロント域における一次生産
    沿岸海洋研究ノート  33-  (1)  19  -26  1995
  • K OMORI, T HIRANO, H TAKEOKA  MARINE POLLUTION BULLETIN  28-  (2)  73  -80  1994/02  
    Artificial organic loading of a coastal ecosystem with materials such as urban sewage and aquacultural waste must be confined within the assimilative ability of the ecosystem, which is defined as the capacity for oxygenic degradation of organic matter at the bottom of the system. Suitably restricted loading should allow the sustainable use of a coastal ecosystem. Bed sediments at eight sites in Uwajima Bay, Japan, were sampled with a cylindrical core sampler and were incubated under constant temperature for the measurement of their rates of oxygen uptake. The rate of oxygen uptake was maximal for a particular concentration of sulphide in the substratum, which may have some proportional relationship to the extent of organic loading. The concentration of sulphide at the peak of oxygen uptake ranged from 0.02-0.06 mg S g-1 among sampling sites. A positive relationship between the density of several kinds of benthos and the rate of oxygen uptake by the substratum was also found by multivariate analysis. A model of a coastal ecosystem was constructed, and the effects of environmental factors, such as temperature, depth and vertical mixing rate, on the upper limit of organic loading were investigated. The estimated concentration of reduced substance, as an indicator of the upper limit of organic loading, did not vary, but the upper limit itself varied widely depending on environmental factors.
  • K OMORI, T HIRANO, H TAKEOKA  MARINE POLLUTION BULLETIN  28-  (2)  73  -80  1994/02  
    Artificial organic loading of a coastal ecosystem with materials such as urban sewage and aquacultural waste must be confined within the assimilative ability of the ecosystem, which is defined as the capacity for oxygenic degradation of organic matter at the bottom of the system. Suitably restricted loading should allow the sustainable use of a coastal ecosystem. Bed sediments at eight sites in Uwajima Bay, Japan, were sampled with a cylindrical core sampler and were incubated under constant temperature for the measurement of their rates of oxygen uptake. The rate of oxygen uptake was maximal for a particular concentration of sulphide in the substratum, which may have some proportional relationship to the extent of organic loading. The concentration of sulphide at the peak of oxygen uptake ranged from 0.02-0.06 mg S g-1 among sampling sites. A positive relationship between the density of several kinds of benthos and the rate of oxygen uptake by the substratum was also found by multivariate analysis. A model of a coastal ecosystem was constructed, and the effects of environmental factors, such as temperature, depth and vertical mixing rate, on the upper limit of organic loading were investigated. The estimated concentration of reduced substance, as an indicator of the upper limit of organic loading, did not vary, but the upper limit itself varied widely depending on environmental factors.
  • Hidetaka Takeoka, Hajime Murao  Journal of Oceanography  49-  (5)  491  -501  1993/09  
    In the current record taken in Uchuimi Bay during summer in 1990, we find anomalous features that the tidal currents during spring and neap tides are quite different in both speed and direction, and the transition between them takes place suddenly. Relation between the variation of tidal current and the observed internal tide is examined, but they are poorly correlated. By examining the direction and phase of the current, it is inferred that these anomalous features are caused by the influence of topographic eddies formed perioidically in Uchiumi Bay. © 1993 Journal of the Oceanographic Society of Japan.
  • Hidetaka Takeoka, Hajime Murao  Journal of Oceanography  49-  (5)  491  -501  1993/09  
    In the current record taken in Uchuimi Bay during summer in 1990, we find anomalous features that the tidal currents during spring and neap tides are quite different in both speed and direction, and the transition between them takes place suddenly. Relation between the variation of tidal current and the observed internal tide is examined, but they are poorly correlated. By examining the direction and phase of the current, it is inferred that these anomalous features are caused by the influence of topographic eddies formed perioidically in Uchiumi Bay. © 1993 Journal of the Oceanographic Society of Japan.
  • Hidetaka Takeoka, Hideki Akiyama, Takahiro Kikuchi  Journal of Oceanography  49-  (4)  369  -382  1993/08  
    "Kyucho" is a sudden and swift current which is usually accompanied by rise of water temperature. Several features of the Kyucho in the Bungo Channel, Japan, are presented through field observations. The Kyucho in the Bungo Channel is an intrusion of warm water from the Pacific Ocean into the eastern half of the Bungo Channel, being driven gravitationally and advancing along the eastern coast of the channel. The Kyucho occurs usually in summer and seldom occurs in winter. It occurs at neap tides showing the prominent spring-neap periodicity. The modulation of the vertical mixing intensity associated with the variations of tidal current, wind and surface heating etc. is supposed to be a main cause of springneap and seasonal periodicities. © 1993 Journal of the Oceanographic Society of Japan.
  • Hidetaka Takeoka, Hideki Akiyama, Takahiro Kikuchi  Journal of Oceanography  49-  (4)  369  -382  1993/08  
    "Kyucho" is a sudden and swift current which is usually accompanied by rise of water temperature. Several features of the Kyucho in the Bungo Channel, Japan, are presented through field observations. The Kyucho in the Bungo Channel is an intrusion of warm water from the Pacific Ocean into the eastern half of the Bungo Channel, being driven gravitationally and advancing along the eastern coast of the channel. The Kyucho occurs usually in summer and seldom occurs in winter. It occurs at neap tides showing the prominent spring-neap periodicity. The modulation of the vertical mixing intensity associated with the variations of tidal current, wind and surface heating etc. is supposed to be a main cause of springneap and seasonal periodicities. © 1993 Journal of the Oceanographic Society of Japan.
  • Hidetaka Takeoka, Osamu Matsuda, Tamiji Yamamoto  Journal of Oceanography  49-  (1)  57  -70  1993/02  
    A field survey was undertaken to reveal the structure of the tidal front in Iyo-nada. An obvious tidal front was found between the mixed region around Hayasui Straits and the stratified region in Iyo-Nada. Its structure was typical in the eastern part and was influenced by the river discharge in the western part. An intense chlorophyll a maximum was found in the subsurface layer of the eastern typical front. Analysis using TS diagram suggested that, around the eastern front, there was an intrusion from the mixed water to the middle layer of the stratified water. This intrusion was supposed to be an important process supplying nutrients from the mixed water to the subsurface of the frontal region and causing the intense chlorophyll a maximum. © 1993 Oceanographic Society of Japan.
  • Hidetaka Takeoka, Osamu Matsuda, Tamiji Yamamoto  Journal of Oceanography  49-  (1)  57  -70  1993/02  
    A field survey was undertaken to reveal the structure of the tidal front in Iyo-nada. An obvious tidal front was found between the mixed region around Hayasui Straits and the stratified region in Iyo-Nada. Its structure was typical in the eastern part and was influenced by the river discharge in the western part. An intense chlorophyll a maximum was found in the subsurface layer of the eastern typical front. Analysis using TS diagram suggested that, around the eastern front, there was an intrusion from the mixed water to the middle layer of the stratified water. This intrusion was supposed to be an important process supplying nutrients from the mixed water to the subsurface of the frontal region and causing the intense chlorophyll a maximum. © 1993 Oceanographic Society of Japan.
  • 豊後水道の急潮
    沿岸海洋研究ノート  30-  (1)  16  -26  1992
  • S TANABE, A NISHIMURA, S HANAOKA, T YANAGI, H TAKEOKA, R TATSUKAWA  MARINE POLLUTION BULLETIN  22-  (7)  344  -351  1991/07  
    In view of environmental contamination, the function of tidal and thermohaline fronts was examined in the Seto Inland Sea, Japan. These fronts have a potency to elevate the concentrations of persistent organochlorines not only in surface water but also in organisms and sediments. The enrichment of organochlorines during the formation of the front was more pronounced for lipophilic contaminants with higher particle affinity, probably due to the amassment of oily substances and various particles through the surface convergence. The coastal fronts may play a significant role in determining the fate of persistent contaminants in the marine environment.
  • S TANABE, A NISHIMURA, S HANAOKA, T YANAGI, H TAKEOKA, R TATSUKAWA  MARINE POLLUTION BULLETIN  22-  (7)  344  -351  1991/07  
    In view of environmental contamination, the function of tidal and thermohaline fronts was examined in the Seto Inland Sea, Japan. These fronts have a potency to elevate the concentrations of persistent organochlorines not only in surface water but also in organisms and sediments. The enrichment of organochlorines during the formation of the front was more pronounced for lipophilic contaminants with higher particle affinity, probably due to the amassment of oily substances and various particles through the surface convergence. The coastal fronts may play a significant role in determining the fate of persistent contaminants in the marine environment.
  • H TAKEOKA, A RAMESH, H IWATA, S TANABE, AN SUBRAMANIAN, D MOHAN, A MAGENDRAN, R TATSUKAWA  MARINE POLLUTION BULLETIN  22-  (6)  290  -297  1991/06  
    The residue levels of the insecticide HCH in Vellar estuary, Tamil Nadu, South India were surveyed along with the physical structure of estuary and its hydrokinetic parameters to assess the transport of contaminants in tropical coastal areas. From the flux model it was estimated that most of the HCH applied to the catchment area of Vellar river is removed to the air and only a small part of it was drained to the sea. Compared to the present situation, the flux of HCH to the sea seems to be much larger in the past when the river structure was different from the present. This implies that at present the localized contamination of HCH in the sea is reducing: instead more rapid contamination is advancing on global terms due to the 'long-range atmospheric transport' of residues from the 'point-source' areas.
  • H TAKEOKA, A RAMESH, H IWATA, S TANABE, AN SUBRAMANIAN, D MOHAN, A MAGENDRAN, R TATSUKAWA  MARINE POLLUTION BULLETIN  22-  (6)  290  -297  1991/06  
    The residue levels of the insecticide HCH in Vellar estuary, Tamil Nadu, South India were surveyed along with the physical structure of estuary and its hydrokinetic parameters to assess the transport of contaminants in tropical coastal areas. From the flux model it was estimated that most of the HCH applied to the catchment area of Vellar river is removed to the air and only a small part of it was drained to the sea. Compared to the present situation, the flux of HCH to the sea seems to be much larger in the past when the river structure was different from the present. This implies that at present the localized contamination of HCH in the sea is reducing: instead more rapid contamination is advancing on global terms due to the 'long-range atmospheric transport' of residues from the 'point-source' areas.
  • Hidetaka Takeoka, Yasuhiko Ohno, Norifumi Inahata  Journal of the Oceanographical Society of Japan  47-  (2)  33  -44  1991/04  
    Roles of horizontal processes in the formation of the density stratification in Hiuchi-Nada are investigated by means of a two-dimensional numerical model. In Hiuchi-Nada, vertically mixed and stratified regions are formed due to the regional difference of the tidal currents, and a tidal front is formed between the two regions. The horizontal mixing across the tidal front suppresses the development of the stratification, which is developed too much in the absence of the horizontal mixing. The moderate, realistic stratification cannot be realized in the model without the horizontal mixing. Density currents are formed due to the density distribution associated with the mixed and stratified states. These currents contribute to the horizontal mixing through the shear effect. Horizontal heat transfer from the outside water generates the vertical circulation and causes the stratification. This effect dominantly appears at the early and late stages of the stratified season. The stratification is initiated before the beginning of the surface heating and persists beyond the end, due to the horizontal heat transfer. © 1991 the Oceanographical Society of Japan.
  • Hidetaka Takeoka, Yasuhiko Ohno, Norifumi Inahata  Journal of the Oceanographical Society of Japan  47-  (2)  33  -44  1991/04  
    Roles of horizontal processes in the formation of the density stratification in Hiuchi-Nada are investigated by means of a two-dimensional numerical model. In Hiuchi-Nada, vertically mixed and stratified regions are formed due to the regional difference of the tidal currents, and a tidal front is formed between the two regions. The horizontal mixing across the tidal front suppresses the development of the stratification, which is developed too much in the absence of the horizontal mixing. The moderate, realistic stratification cannot be realized in the model without the horizontal mixing. Density currents are formed due to the density distribution associated with the mixed and stratified states. These currents contribute to the horizontal mixing through the shear effect. Horizontal heat transfer from the outside water generates the vertical circulation and causes the stratification. This effect dominantly appears at the early and late stages of the stratified season. The stratification is initiated before the beginning of the surface heating and persists beyond the end, due to the horizontal heat transfer. © 1991 the Oceanographical Society of Japan.
  • Hidetaka Takeoka  Journal of the Oceanographical Society of Japan  47-  (2)  27  -32  1991/04  
    To examine the effects of the deep ocean circulation on the characteristics of the ocean as a reservoir, age distributions of the material whose source and sink are at the ocean surface are calculated using an idealized vertical two-dimensional model of the ocean. The results show that the large-scale vertical circulation of the deep water accelerates the renewal of deep water and reduces the average age of the material. It is also shown that the multi-layered structures of the deep circulation are more realistic than the one-layered structure and promote the renewal of the deep water. © 1991 the Oceanographical Society of Japan.
  • ADCPによる測流データからの潮流の推定法
    沿岸海洋研究ノート  29-  (1)  76  -81  1991
  • H TAKEOKA  MARINE POLLUTION BULLETIN  23-  41  -44  1991  
    Mechanisms determining the average residence time (ART) of the nitrogen in the Seto Inland Sea, Japan, are examined by using a simple numerical model. The ART of the nitrogen is larger than that of the riverine water by about twice. This is due to the coupled effect of the flow having vertical shear and biochemical processes. Strong vertical mixing at the straits reduces the ART of the nitrogen. Mixing through Naruto Strait also effectively reduces the ART of the nitrogen.
  • 武岡 英隆  日本海洋学会  47-  (2)  27  -32  1991
  • Marine Pollution Bulletine  23-  41  -44  1991
  • H TAKEOKA  CONTINENTAL SHELF RESEARCH  10-  (7)  605  -613  1990/07
  • 養殖漁場としての宇和海の物理環境
    水産海洋研究  54-  (1)  9  -18  1990
  • Applications of the water exchange concepts to some water quality problems
    China Ocean PressPhysics of Shallow Sea  130  -136  1990
  • 海洋のreservoir特性に対する深層海水循環の影響
    愛媛大学工学部紀要  12-  (1)  295  -302  1990
  • Applications of the water exchange concepts to some water quality problems
    China Ocean PressPhysics of Shallow Sea  130  -136  1990
  • Pergamon PressContinental Shelf Research  10-  (7)  605  -613  1990
  • 貧酸素水塊の物理モデル
    沿岸海洋研究ノート  26-  (2)  101  -108  1989
  • 宇和島湾の物理的環境(Ⅲ) -海水交換の季節変動-
    愛媛大学工学部紀要  11-  (4)  257  -262  1989
  • H TAKEOKA, T HASHIMOTO  CONTINENTAL SHELF RESEARCH  8-  (11)  1247  -1256  1988/11
  • Hidetaka Takeoka, Tomotoshi Yoshimura  Journal of the Oceanographical Society of Japan  44-  (1)  6  -16  1988/02  
    The phenomenon of rapid increase in water temperature accompanied by a sudden, swift current (Kyucho) in Uwajima Bay is described on the basis of results of long term observations from July 1985 to September 1986. This phenomenon occurs somewhat periodically with an interval of about 15 days in summer, although it does not occur in winter. The increase in water temperature occasionally reaches about 5°C. This phenomenon results from the intrusion of a warm water mass into the bay. NOAA-9 satellite images show that the warm water mass originates from the Pacific Ocean south of the Bungo Channel. © 1987 Oceanographical Society of Japan.
  • Hidetaka Takeoka, Tomotoshi Yoshimura  Journal of the Oceanographical Society of Japan  44-  (1)  6  -16  1988/02  
    The phenomenon of rapid increase in water temperature accompanied by a sudden, swift current (Kyucho) in Uwajima Bay is described on the basis of results of long term observations from July 1985 to September 1986. This phenomenon occurs somewhat periodically with an interval of about 15 days in summer, although it does not occur in winter. The increase in water temperature occasionally reaches about 5°C. This phenomenon results from the intrusion of a warm water mass into the bay. NOAA-9 satellite images show that the warm water mass originates from the Pacific Ocean south of the Bungo Channel. © 1987 Oceanographical Society of Japan.
  • 第35回海岸工学講演会論文集  277  -281  1988
  • 四国南西海岸の水温急変現象
    水産海洋研究会報  52-  (4)  283  -288  1988
  • ハマチ養殖場の物質循環モデル
    水産海洋研究会報  52-  (3)  213  -220  1988
  • 宇和島湾の物理的環境(Ⅱ) -潮流の季節変動-
    愛媛大学工学部紀要  11-  (3)  261  -267  1988
  • Pergamon PressContinental Shelf Research  8-  (11)  1247  -1256  1988
  • Hidetaka Takeoka  Journal of the Oceanographical Society of Japan  43-  (1)  21  -27  1987/02  
    The average residence time and the remnant function which are quantitative expressions of water exchange in coastal waters are investigated in a timevarying transport field by using a simple model. It is shown that the influence of temporal variation on the average residence time and concentration is small, when the ratio of the period of variation to the average residence time in the average state is small, and the influence is large when the ratio is large. The results are applied to the Seto Inland Sea, Lake Hamana, and Osaka Bay. © 1986 Oceanographical Society of Japan.
  • 瀬戸内海における透明度の分布とその季節変動
    海と空  63-  (1)  15  -27  1987
  • 武岡 英隆  Journal of the Oceanographical Society of Japan  43-  (1)  21  -27  1987
  • 海水交換の調査法と問題点
    沿岸海洋研究ノート  24-  (2)  145  -155  1987
  • 宇和島湾の物理的環境(Ⅰ) -水温急変現象-
    愛媛大学工学部紀要  11-  (2)  233  -240  1987
  • Hidetaka Takeoka, Tadashi Ochi, Kazuhiko Takatani  Journal of the Oceanographical Society of Japan  42-  (1)  12  -21  1986/02  
    Temporal variation of the anoxic water mass in Hiuchi-Nada was investigated. Vertical diffusivities at the thermoclines and oxygen consumption rates in the middle and lower layers were estimated by box model analysis using the results of field observations. On the basis of the obtained diffusivities and consumption rates, the time scale for anoxia and the degree of anoxia were examined for various conditions. It was revealed that the time scale for anoxia is about a week in the case where serious anoxia occurs and the degree of anoxia is sensitive to the diffusivity at 'the second thermocline'. The anoxia which occurred frequently in the 1960's and 1970's is deduced to be caused by oxygen consumption rates a few times larger than the average at present and by diffusivities a few tens of per cent smaller than those under normal conditions. © 1986 Oceanographical Society of Japan.
  • Tadashi Ochi, Hidetaka Takeoka  Journal of the Oceanographical Society of Japan  42-  (1)  1  -11  1986/02  
    Distribution of the anoxic water mass in the eastern part of Hiuchi-Nada was investigated from 1981 to 1983. A cold water mass was found on the bottom of the area concerned in summer, and a second (i.e. lower) thermocline appeared just above the cold water mass. The anoxic water was observed below a second thermocline. The horizontal distribution of the cold water mass coincided with that of the anoxic water mass, and also with a region of high concentration of organic matter in the sediment. These results suggest two important effects of the second thermocline on the generation of the anoxic water mass. Firstly, it prevents supply of dissolved oxygen from the upper to bottom layer of the water column. Secondly, it accelerates settling of particulate material resulting in a large accumulation of organic matter in the bottom water and the sediment which leads to an increase in the rate of oxygen consumption. The net oxygen consumption rate in the bottom layer in this sea was much smaller than that in Mikawa Bay where anoxia occurs at almost the same level as in Hiuchi-Nada. This finding also suggests the important role of the second thermocline. © 1986 Oceanographical Society of Japan.
  • Hidetaka Takeoka, Tadashi Ochi, Kazuhiko Takatani  Journal of the Oceanographical Society of Japan  42-  (1)  12  -21  1986/02  
    Temporal variation of the anoxic water mass in Hiuchi-Nada was investigated. Vertical diffusivities at the thermoclines and oxygen consumption rates in the middle and lower layers were estimated by box model analysis using the results of field observations. On the basis of the obtained diffusivities and consumption rates, the time scale for anoxia and the degree of anoxia were examined for various conditions. It was revealed that the time scale for anoxia is about a week in the case where serious anoxia occurs and the degree of anoxia is sensitive to the diffusivity at 'the second thermocline'. The anoxia which occurred frequently in the 1960's and 1970's is deduced to be caused by oxygen consumption rates a few times larger than the average at present and by diffusivities a few tens of per cent smaller than those under normal conditions. © 1986 Oceanographical Society of Japan.
  • Tadashi Ochi, Hidetaka Takeoka  Journal of the Oceanographical Society of Japan  42-  (1)  1  -11  1986/02  
    Distribution of the anoxic water mass in the eastern part of Hiuchi-Nada was investigated from 1981 to 1983. A cold water mass was found on the bottom of the area concerned in summer, and a second (i.e. lower) thermocline appeared just above the cold water mass. The anoxic water was observed below a second thermocline. The horizontal distribution of the cold water mass coincided with that of the anoxic water mass, and also with a region of high concentration of organic matter in the sediment. These results suggest two important effects of the second thermocline on the generation of the anoxic water mass. Firstly, it prevents supply of dissolved oxygen from the upper to bottom layer of the water column. Secondly, it accelerates settling of particulate material resulting in a large accumulation of organic matter in the bottom water and the sediment which leads to an increase in the rate of oxygen consumption. The net oxygen consumption rate in the bottom layer in this sea was much smaller than that in Mikawa Bay where anoxia occurs at almost the same level as in Hiuchi-Nada. This finding also suggests the important role of the second thermocline. © 1986 Oceanographical Society of Japan.
  • H TAKEOKA  CONTINENTAL SHELF RESEARCH  6-  (5)  627  -638  1986
  • Pergamon PressContinental Shelf Research  6-  (5)  627  -638  1986
  • 瀬戸内海の密度成層
    海と空  60-  (3)  145  -152  1985
  • 播磨灘・大阪湾の塩分、窒素、リン収支
    沿岸海洋研究ノート  22-  (2)  159  -164  1985
  • 第31回海岸工学講演会論文集  685  -689  1984
  • 沿岸海域の海水交換
    沿岸海洋研究ノート  21-  (2)  169  -182  1984
  • H TAKEOKA  CONTINENTAL SHELF RESEARCH  3-  (4)  327  -341  1984
  • H TAKEOKA  CONTINENTAL SHELF RESEARCH  3-  (3)  311  -326  1984
  • Pergamon PressContinental Shelf Research  3-  (4)  327  -341  1984
  • Hidetaka Takeoka  Continental Shelf Research  3-  (3)  311  -326  1984  
    Concepts of age, residence time, transit time, and turn-over time are summarized which are useful for describing the exchange and transport of water or materials in a coastal sea. The age of a particle is defined as a time which has elapsed since it entered the reservoir, and the residence time is defined as a time which will be taken for a particle to reach the outlet. Time scales based on the age are simply related with those based on the residence time. It is shown that a suitable time scale for representing the exchange characteristics is the average residence time and not the turnover time, which has often been used as the exchange time scale. Further, the 'remnant function' which describes the phenomena of exchange or transport is introduced, and is related to the residence time. Exchange and transport time scales in a coastal sea are discussed on the basis of the residence time which can be applied to not only steady-state cases, but also the cases where material is injected instantaneously. The average residence time in a one-dimensional channel and bay is obtained from the solutions of the advection-diffusion equation. If we know a flow speed and diffusion coefficient in a channel or bay regarded as one-dimensional, we can translate them into the average residence time. As an example, the average residence time of the Seto Inland Sea is discussed. © 1984.
  • 松山港の海水交流(Ⅰ)
    愛媛大学工学部紀要  10-  (2)  203  -210  1983
  • Tetsuo Yanagi, Hidetaka Takeoka, Hideshi Tsukamoto  Journal of the Oceanographical Society of Japan  38-  (5)  293  -299  1982/11  
    The tidal volume transport in the Seto Inland Sea is calculated. The cross-section where the volume transport of the M2 tide is zero, is located around the western part of Bisan Strait. The tidal energy dissipation of the M2 tide by friction is 6.30×1016 ergs s-1 in the Seto Inland Sea. The quality factor Q for the M2 tide is 20.2. The total energy dissipation of the M2, S2, K1 and O1 tides is 7.99×1016 ergs s-1. © 1982 Oceanographical Society of Japan.
  • Tetsuo Yanagi, Hidetaka Takeoka, Hideshi Tsukamoto  Journal of the Oceanographical Society of Japan  38-  (5)  293  -299  1982/11  
    The tidal volume transport in the Seto Inland Sea is calculated. The cross-section where the volume transport of the M2 tide is zero, is located around the western part of Bisan Strait. The tidal energy dissipation of the M2 tide by friction is 6.30×1016 ergs s-1 in the Seto Inland Sea. The quality factor Q for the M2 tide is 20.2. The total energy dissipation of the M2, S2, K1 and O1 tides is 7.99×1016 ergs s-1. © 1982 Oceanographical Society of Japan.
  • 来島海峡の潮流に関する研究(Ⅱ)-島陰の渦流について-
    愛媛大学工学部紀要  10-  (1)  201  -206  1982
  • 地形性渦流による小港湾の海水交換
    沿岸海洋研究ノート  19-  (2)  175  -182  1982
  • 海水交換と物質輸送の概念について
    愛媛大学紀要第Ⅲ部工学  9-  (4)  287  -298  1981
  • 来島海峡における測流
    沿岸海洋研究ノート  18-  (1)  29  -36  1980
  • 来島海峡の潮流に関する研究(Ⅰ)
    愛媛大学紀要第Ⅲ部工学  9-  (3)  275  -280  1980
  • 瀬戸内海における海水交流の実験的研究(Ⅲ)
    京都大学防災研究所年報  (22B-2)  625  -630  1979
  • 海峡部における潮流の特性に関する研究
    京都大学防災研究所年報  (21B-2)  129  -135  1978
  • 瀬戸内海の海況変動について
    沿岸海洋研究ノート  15-  (2)  138  -142  1978
  • 松山港における潮流の水理模型実験
    京都大学防災研究所年報  (20B-2)  541  -551  1977
  • 瀬戸内海における海水交流の実験的研究(Ⅱ)
    京都大学防災研究所年報  (19B-2)  411  -421  1976
  • 瀬戸内海における海水交流の実験的研究(Ⅰ)
    京都大学防災研究所年報  (18B)  621  -635  1975

Awards & Honors

  • 2009 平成21年度原子力安全功労者表彰
     JPN
  • 2003 瀬戸内法30周年記念環境大臣表彰
     JPN
  • 2003 県政発足記念日知事表彰
     JPN
  • 1999 日本海洋学会日高論文賞
     JPN
  • 1999 Hidaka Prize of the Oceanographic Society of Japan

Research Grants & Projects

  • クラゲ類の大量発生メカニズム
    Date (from‐to) : 2001
  • mechanisms of jellyfish bloom
    Date (from‐to) : 2001
  • 沿岸環境の長期変動
    Date (from‐to) : 2000
  • long-term variations in coastal envilronments
    Date (from‐to) : 2000
  • 豊後水道の底入り潮
    Date (from‐to) : 1998
  • bottom intrusion in the Bungo Channel
    Date (from‐to) : 1998
  • 瀬戸内海の栄養塩起源
    Date (from‐to) : 1997
  • origin of nutrients in the Seto Inland Sea
    Date (from‐to) : 1997
  • 養殖場の環境保全
    Date (from‐to) : 1994
  • environmental preservation in aquaculture ground
    Date (from‐to) : 1994

Committee Membership

  • 2010   Coastal Oceanography Research Committee, the Oecanographic Society of Japan   Vice Chairman   Coastal Oceanography Research Committee, the Oecanographic Society of Japan


Copyright © MEDIA FUSION Co.,Ltd. All rights reserved.