研究者データベース

平譯 享(ヒラワケ トオル)
水産科学研究院 海洋生物資源科学部門 海洋計測学分野
准教授

基本情報

所属

  • 水産科学研究院 海洋生物資源科学部門 海洋計測学分野

職名

  • 准教授

学位

  • 理学博士(名古屋大学)

ホームページURL

J-Global ID

研究キーワード

  • 海洋生態系   生物生産   植物プランクトン   海洋環境   極域海洋   低温   生物多様性   チャクチ海   ベーリング海   北極海   極球海洋   海氷   南極海   環境変動   海洋生態   極地   高緯度海域   地球規模   春季ブルーム   海氷生態系   海洋基礎生産   衛星海洋学   衛星海色リモートセンシング   海洋光学   Primary productivity   Satellite Oceanography   Satellite ocean color remote sensing   Ocean optics   

研究分野

  • 環境・農学 / 環境動態解析
  • ライフサイエンス / 水圏生産科学
  • 環境・農学 / 環境政策、環境配慮型社会
  • 環境・農学 / 環境影響評価
  • 環境・農学 / 環境動態解析

職歴

  • 2007年04月 - 現在 北海道大学 大学院・水産科学研究院 准教授
  • 1998年04月 - 2007年03月 国立極地研究所 助手・助教

所属学協会

  • 米国海洋学会   水産海洋学会   日仏海洋学会   日本海洋学会   The Oceanographic Sciety of JapanJapanese-French Oceanographic Sciety   

研究活動情報

論文

  • Kan Murakami, Daiki Nomura, Gen Hashida, Shin ichiro Nakaoka, Yujiro Kitade, Daisuke Hirano, Toru Hirawake, Kay I. Ohshima
    Marine Chemistry 225 2020年09月10日 [査読有り][通常論文]
     
    © 2020 Elsevier B.V. Formation of dense shelf water (DSW) in coastal polynyas (open water or thin sea-ice cover) in the sea-ice zone around Antarctica supplies Antarctic Bottom Water (AABW) through overflow down the continental slope. In coastal polynyas, atmospheric carbon dioxide (CO2) is absorbed by the ocean in the early spring because of active primary production, and DSW formation is an important process for transporting this carbon from the sea surface to the deep ocean. However, there have been few quantitative evaluations of carbon consumption by active primary production and transport in coastal polynyas. Here, we examined the carbon dynamics in the Cape Darnley polynya (CDP), East Antarctica during austral summer 2009, by using carbonate system parameters combined with oceanographic mooring data. The partial pressure of CO2 in the CDP surface water was lower than that of the atmosphere and the mean and standard deviation of sea−air CO2 flux was estimated as −6.5 ± 6.9 mmol C m−2 d−1 (a negative value indicates absorption of atmospheric CO2 by the ocean). Vertical profiles of dissolved inorganic carbon (DIC) concentration showed that concentrations in the bottom layer near the ocean floor were lower (by about 20 μmol kg−1) than those in the ambient water (e.g., modified Circumpolar Deep Water, mCDW). The low-DIC in the shelf water was maintained by the strong biological uptake of carbon imported from high-DIC mCDW within the water column. Therefore, low-DIC DSW overflowed down the continental slope, and low-DIC concentrations were maintained through an export pathway to the continental shelf. The annual production of dissolved organic carbon and particulate organic carbon on the shelf was estimated as 0.7 × 1011–1.5 × 1011 mol C using the data for the DIC of DSW and current velocity data from a mooring in the CDP. Our results provide quantitative estimates for the potential role of carbon consumption by the active primary production and carbon transport by dense water formation in Antarctic coastal polynyas.
  • Toru Hirawake, Masaki Uchida, Hiroto Abe, Irene D. Alabia, Tamotsu Hoshino, Shota Masumoto, Akira S. Mori, Jun Nishioka, Bungo Nishizawa, Atsushi Ooki, Akinori Takahashi, Yukiko Tanabe, Motoaki Tojo, Masaharu Tsuji, Hiromichi Ueno, Hisatomo Waga, Yuuki Y. Watanabe, Atsushi Yamaguchi, Youhei Yamashita
    Polar Science in press 100533 - 100533 2020年05月 [査読有り][通常論文]
  • Takao, S., S. Nakaoka,, F. Hashihama, K. Shimada, H. Yoshikawa-Inoue, T Hirawake, J. Kanda, G. Hashida, K. Suzuki
    Deep-Sea Research Part I 2020年03月 [査読有り][通常論文]
  • Daiki NOMURA, Pat WONGPAN, Takenobu TOYOTA, Tomonori TANIKAWA, Yusuke KAWAGUCHI, Takashi ONO, Tomomi ISHINO, Manami TOZAWA, Tetsuya P. TAMURA, Itsuka S. YABE, Eun Yae SON, Frederic VIVIER, Antonio LOURENCO, Marion LEBRUN, Yuichi NOSAKA, Toru HIRAWAKE, Atsushi OOKI, Shigeru AOKI, Brent ELSE, Francois FRIPIAT, Jun INOUE, Martin VANCOPPENOLLE
    Bulletin of Glaciological Research 38 0 1 - 12 2020年 [査読有り][通常論文]
  • Hisatomo Waga, Toru Hirawake, Hiromichi Ueno
    GEOPHYSICAL RESEARCH LETTERS 46 22 13191 - 13198 2019年11月 [査読有り][通常論文]
     
    The impact of mesoscale eddies on phytoplankton communities attracts considerable research attention because phytoplankton play numerous roles in marine ecosystems. Using remote sensing techniques, this study considered a synoptic relationship between phytoplankton size structure, which is a determinant of energy transfer efficiency in marine ecosystems, and mesoscale eddies, which are ubiquitous ocean features. We found clear spatial variation in the impacts of mesoscale eddies on phytoplankton size structure; phytoplankton communities with larger cell sizes were supported by anticyclonic eddies in oligotrophic regions and by cyclonic eddies in eutrophic regions. Differences in the phytoplankton size structure within these two types of mesoscale eddies became greater, accompanied by interannual trends in the phytoplankton size structure for 2003-2014. Our findings are the first to demonstrate the important linkage between mesoscale eddies and phytoplankton size structure on a global scale; this new knowledge might help better predict variability in marine ecosystems.Plain Language Summary Mesoscale eddies are ubiquitous ocean features and they play a significant role in phytoplankton dynamics. This study used satellite remote sensing techniques to examine the impact of mesoscale eddies on phytoplankton size structure, an important factor of marine ecosystems. We found clear regional and temporal variations in the impacts of two types of mesoscale eddies: communities of larger-sized phytoplankton were observed in anticyclonic eddies in oligotrophic regions and in cyclonic eddies in eutrophic regions, and differences in the phytoplankton size structure inside these two eddy types increased during the period 2003-2014. Our findings are the first to demonstrate the important linkage between the cell-size composition of phytoplankton communities and mesoscale eddies on a global scale; this new knowledge might help us to better predict variability in marine ecosystems both now and in the future.
  • Youhei Yamashita, Yuki Yagi, Hiromichi Ueno, Atsushi Ooki, Toru Hirawake
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 124 11 7545 - 7556 2019年11月 [査読有り][通常論文]
     
    Pacific water is an important nutrient source for sustaining biological production in the Chukchi Sea, western Arctic Ocean, which is one of the productive regions in the world. Therefore, to understand the impacts of future environmental changes on biological production in the sea, it is crucial to understand the origins, modification processes, and spatiotemporal variations of the water masses from the Bering Sea with changes in nutrient concentrations. To improve water mass analysis in the shelf regions of the Bering and Chukchi Seas, we observed levels of humic-like fluorescent organic matter (FOMH) by using an in situ fluorometer directly connected to a temperature-salinity sensor during a cruise in the early summer of 2013 and evaluated the potential of FOMH as a third parameter of water mass analysis. The levels of FOMH were different among specific water masses in the region, and FOMH seemed to behave semiconservatively in the shelf regions of the Bering and Chukchi Seas during the early summer of 2013. The distributional pattern of FOMH implies that FOMH estimated by the in situ fluorometer has the potential to (1) separate warm water into riverine-affected Alaskan Coastal Water and historically photobleached summer Bering Basin Water; (2) distinguish the Anadyr Water, which has low FOMH levels and high nutrient concentrations, from the Bering Shelf Water; and (3) determine different formation/modification processes of dense shelf water that contains high nutrient concentrations.
  • Abe Hiroto, Sampei Makoto, Hirawake Toru, Waga Hisatomo, Nishino Shigeto, Ooki Atsushi
    FRONTIERS IN MARINE SCIENCE 6 2019年03月08日 [査読有り][通常論文]
  • Tokuhiro Koki, Abe Yoshiyuki, Matsuno Kohei, Onodera Jonaotaro, Fujiwara Amane, Harada Naomi, Hirawake Toru, Yamaguchi Atsushi
    POLAR SCIENCE 19 94 - 111 2019年03月 [査読有り][通常論文]
  • Alabia Irene D, Molinos Jorge Garcia, Saitoh Sei-Ichi, Hirawake Toru, Hirata Takafumi, Mueter Franz J
    DIVERSITY AND DISTRIBUTIONS 24 11 1583 - 1597 2018年11月 [査読有り][通常論文]
  • Amane Fujiwara, Shigeto Nishino, Kohei Matsuno, Jonaotaro Onodera, Yusuke Kawaguchi, Toru Hirawake, Koji Suzuki, Jun Inoue, Takashi Kikuchi
    Polar Biology 41 6 1279 - 1295 2018年06月01日 [査読有り][通常論文]
     
    The recent increasing of atmospheric turbulence has had considerable impact on the oceanic environment and ecosystems of the Arctic. To understand its effect on phytoplankton community structure, a Eulerian fixed-point observation (FPO) was conducted on the Chukchi shelf in fall 2013. Temporal and vertical distributions of the phytoplankton community were inferred from algal pigment signatures. A strong wind event (SWE) occurred during the observation term, and significant convection supplied nutrients from the bottom layer to the surface. Before the SWE, pigment composition in the warmer, less saline, and nutrient-poor surface waters was diverse with low concentration of chlorophyll-a (chla). Vertical mixing induced by the SWE weakened the stratification and brought sufficient nutrients to enhance diatom-derived pigment concentrations (e.g., fucoxanthin and chlc3), suggesting increases in diatoms. We also developed a model to predict the distribution of major phytoplankton pigment/chla ratios using a profiling multi-wavelength fluorometer (Multi-Exciter) with higher spatio-temporal resolution. The Multi-Exciter also captured changes in pigment composition with environmental changes at the FPO site and at four observation sites 16 km from the location of the FPO. Furthermore, we investigated the change in grazing rates of the major Arctic copepod Calanus glacialis copepodid stage five to assess the interaction between primary and secondary producers during the fall bloom. Increased diatom biomass caused a significant increase in the grazing rate on microphytoplankton (>  20 µm) and a decrease on nanophytoplankton (2–20 µm), indicative of a strong cascade effect because of the reduction of microzooplankton due to the grazing from C. glacialis. We conclude that SWEs during fall might affect food webs via the alternation of seasonal succession of phytoplankton community structure.
  • Hori, M, H. Murakami, R. Miyazaki, Y. Honda, K. Nasahara, K. Kajiwara, T. Y. Nakajima, H. Irie, M. Toritani, T. Hirawake, T. Aoki
    Transactions of JSASS, Aerospace Technology Japan “ISTS Special Issue” 16 3 218 - 223 2018年 [査読有り][通常論文]
  • Masafumi Natsuike, Rui Saito, Amane Fujiwara, Kohei Matsuno, Atsushi Yamaguchi, Naonobu Shiga, Toru Hirawake, Takashi Kikuchi, Shigeto Nishino, Ichiro Imai
    PLOS ONE 12 11 2017年11月 [査読有り][通常論文]
     
    The eastern Bering Sea has a vast continental shelf, which contains various endangered marine mammals and large fishery resources. Recently, high numbers of toxic A. tamarense resting cysts were found in the bottom sediment surface of the eastern Bering Sea shelf, suggesting that the blooms have recently occurred. However, little is known about the presence of A. tamarense vegetative cells in the eastern Bering Sea. This study's goals were to detect the occurrence of A. tamarense vegetative cells on the eastern Bering Sea shelf and to find a relationship between environmental factors and their presence. Inter-annual field surveys were conducted to detect A. tamarense cells and environmental factors, such as nutrients, salinity, chlorophyll a, and water temperature, along a transect line on the eastern Bering Sea shelf during the summers of 2004, 2005, 2006, 2009, 2012, and 2013. A. tamarense vegetative cells were detected during every sampling year, and their quantities varied greatly from year to year. The maximum cell densities of A. tamarense observed during the summers of 2004 and 2005 were much higher than the Paralytic shellfish poisoning warning levels, which are greater than 100-1,000 cells L-1, in other subarctic areas. Lower quantities of the species occurred during the summers of 2009, 2012, and 2013. A significant positive correlation between A. tamarense quantity and water temperature and significant negative correlations between A. tamarense quantity and nutrient concentrations (of phosphate, silicate, and nitrite and nitrate) were detected in every sampling period. The surface- and bottom-water temperatures varied significantly from year to year, suggesting that water temperatures, which have been known to affect the cell growth and cyst germination of A. tamarense, might have affected the cells' quantities in the eastern Bering Sea each summer. Thus, an increase in the Bering Sea shelf's water temperature during the summer will increase the frequency and scale of toxic blooms and the toxin contamination of plankton feeders. This poses serious threats to humans and the marine ecosystem.
  • Jose M. Landeira, Kohei Matsuno, Atsushi Yamaguchi, Toru Hirawake, Takashi Kikuchi
    POLAR BIOLOGY 40 9 1805 - 1819 2017年09月 [査読有り][通常論文]
     
    Crustacean decapods are key components that structure the benthic ecosystems in the Subarctic/Arctic regions and support one of the largest fishery industries, but their larval dynamics are largely unknown. To investigate variability in decapod larvae community in this region, we analysed plankton samples collected during the summers of 2007 and 2008 along the southeastern Bering and Chukchi Seas. Distribution of adult population was studied using bottom trawling during 2008 cruise. Larvae of Pagurus spp., Hyas spp., and the commercially important Chionoecetes bairdi and Chionoecetes opilio were the most abundant species. The distribution of benthic adults linked to those of planktonic larvae and may favour recruitment near suitable habitats and the maintenance of the populations. Earlier larval stages of C. bairdi, C. opilio, and Hyas spp. were more abundant in 2008 than in 2007. The body size of C. opilio showed a significant latitudinal pattern, in which larger sizes occurred at higher latitudes in association with distinct temperature and food conditions. We argue that annual changes in abundance and developmental stage structure of planktonic larvae seemed to be related to the 1 month delay in the sampling period and are not determined by the contrasting environmental conditions observed in both years.
  • Tihomir S. Kostadinov, Anna Cabre, Harish Vedantham, Irina Marinov, Astrid Bracher, Robert J. W. Brewin, Annick Bricaud, Takafumi Hirata, Toru Hirawake, Nick J. Hardman-Mountford, Colleen Mouw, Shovonlal Roy, Julia Uitz
    REMOTE SENSING OF ENVIRONMENT 190 162 - 177 2017年03月 [査読有り][通常論文]
     
    Ocean color remote sensing of chlorophyll concentration has revolutionized our understanding of the biology of the oceans. However, a comprehensive understanding of the structure and function of oceanic ecosystems requires the characterization of the spatio-temporal variability of various phytoplankton functional types (PFTs), which have differing biogeochemical roles. Thus, recent bio-optical algorithm developments have focused on retrieval of various PFTs. It is important to validate and inter-compare the existing PFT algorithms; however direct comparison of retrieved variables is non-trivial because in those algorithms PFTs are defined differently. Thus, it is more plausible and potentially more informative to focus on emergent properties of PFTs, such as phonology. Furthermore, ocean color satellite PFT data sets can play a pivotal role in informing and/or validating the biogeochemical routines of Earth System Models. Here, the phenological characteristics of 10 PFT satellite algorithms and 7 latest-generation climate models from the Coupled Model Inter-comparison Project (CMIPS) are inter compared as part of the International Satellite PFT Algorithm Inter-comparison Project. The comparison is based on monthly satellite data (mostly SeaWiFS) for the 2003-2007 period. The phonological analysis is based on the fraction of microplankton or a similar variable for the satellite algorithms and on the carbon biomass due to diatoms for the climate models. The seasonal cycle is estimated on a per-pixel basis as a sum of sinusoidal harmonics, derived from the Discrete Fourier Transform of the variable time series. Peak analysis is then applied to the estimated seasonal signal and the following phenological parameters are quantified for each satellite algorithm and climate model: seasonal amplitude, percent seasonal variance, month of maximum, and bloom duration. Secondary/double blooms occur in many areas and are also quantified. The algorithms and the models are quantitatively compared based on these emergent phenological parameters. Results indicate that while algorithms agree to a first order on a global scale, large differences among them exist; differences are analyzed in detail for two Longhurst regions in the North Atlantic: North Atlantic Drift Region (NADR) and North Atlantic Subtropical Gyre West (NASW). Seasonal cycles explain the most variance in zonal bands in the seasonally-stratified subtropics at about 30 latitude in the satellite PFT data. The CMIP5 models do not reproduce this pattern, exhibiting higher seasonality in mid and high-latitudes and generally much more spatially homogeneous patterns in phenological indices compared to satellite data. Satellite data indicate a complex structure of double blooms in the Equatorial region and mid-latitudes, and single blooms on the poleward edges of the subtropical gyres. In contrast, the CMIP5 models show single annual blooms over most of the ocean except for the Equatorial band and Arabian Sea. (C) 2016 Elsevier Inc. All rights reserved.
  • Tomonori Isada, Toru Hirawake, Satoshi Nakada, Tsukuru Kobayashi, Ken'ichi Sasaki, Yoshiyuki Tanaka, Shuichi Watanabe, Koji Suzuki, Sei-Ichi Saitoh
    ESTUARINE COASTAL AND SHELF SCIENCE 188 199 - 211 2017年03月 [査読有り][通常論文]
     
    Phytoplankton community structures and primary productivity were assessed in relation to the oceanographic conditions in the coastal waters of Funka bay and the eastern end of the Tsugaru Strait, adjacent to southwestern Hokkaido, Japan, from April 2010 to January 2012. Phytoplankton community compositions, as estimated from chemotaxonomic analysis based on high-performance liquid chromatography of pigments, showed diatom blooms during spring in both 2010 and 2011. However, spatial heterogeneity of chlorophyll a (Chl a) concentration and primary productivity were found between regions investigated within and outside of Funka Bay during the spring diatom blooms in April 2010. The low Chl a concentrations within Funka Bay in April 2010 were related to the depletion of dissolved inorganic macronutrients, which implies that this difference was related to both the small inflow of the cold Coastal Oyashio Current (COW),into the bay and the development of clockwise circulation caused by discharge of fresh water into the bay. After the spring diatom blooms, the major phytoplankton groups in the study area were Chl b-containing phytoplanktons (chlorophytes and prasinophytes) because of changes in salinity associated with river discharge during the melting season. The results indicate that these phytoplanktons play an important role in the carbon cycle after the spring bloom in Funka Bay and the eastern end of the Tsugaru Strait. The thermohaline fronts created by the COW and the Tsugaru Warm Water in late February produced north south differences in phytoplankton community structures in the eastern end of the Tsugaru Strait. Diatoms with high Chl a concentrations dominated in the northern section of the front. In the southern section, the proportions of chlorophytes and cryptophytes were high. Increases in cyanobacterial abundance and temperature were detected in both regions. Additionally, the contribution of pico-plus nano-sized phytoplanlcton productivity to the total primary productivity at the surface was concomitant with increases in temperature. Our results suggest that small-sized phytoplankton become more important part of the food web during summer, even in the coastal waters. (C) 2017 Elsevier Ltd. All rights reserved.
  • Hisatomo Waga, Toru Hirawake, Amane Fujiwara, Takashi Kikuchi, Shigeto Nishino, Koji Suzuki, Shintaro Takao, Sei-Ichi Saitoh
    REMOTE SENSING 9 3 2017年03月 [査読有り][通常論文]
     
    Species distributions are changing with various rates and directions in response to recent global warming. The velocity of sea surface temperature (SST) has been used to predict species migration and persistence as an expectation of how species track their thermal niches; however, several studies have found that evidence for species shifts has deviated from the velocity of SST. This study investigated whether estimation of the velocity of shifts in phytoplankton size structure using remote sensing data could contribute to better prediction of species shifts. A chlorophyll-a (Chla) size distribution (CSD) model was developed by quantifying the relationships between the size structure of the phytoplankton community and the spectral features of the phytoplankton absorption coefficient (a(ph)()), based on the principal component analysis approach. Model validation demonstrated that the exponent of CSD (hereafter, CSD slope), which can describe the synoptic size structure of a phytoplankton community, was derived successfully with a relative root mean square error of 18.5%. The median velocity of CSD slope across the ocean was 485.2 kmdecade(-1), broadly similar to Chla (531.5 kmdecade(-1)). These values were twice the velocity of SST, and the directions of shifts in CSD slope and Chla were quite different from that of SST. Because Chla is generally covariant with the size structure of a phytoplankton community, we believe that spatiotemporal changes in Chla can explain the variations of phytoplankton size structure. Obvious differences in both rate and direction of shifts were found between the phytoplankton size structure and SST, implying that shifts of phytoplankton size structure could be a powerful tool for assessing the distributional shifts of marine species. Our results will contribute to generate global and regional maps of expected species shifts in response to environmental forcing.
  • Colleen B. Mouw, Nick J. Hardman-Mountford, Séverine Alvain, Astrid Bracher, Robert J. W. Brewin, Annick Bricaud, Aurea M. Ciotti, Emmanuel Devred, Amane Fujiwara, Takafumi Hirata, Toru Hirawake, Tihomir S. Kostadinov, Shovonlal Roy, Julia Uitz
    Frontiers in Marine Science 4 2017年02月21日 [査読有り][通常論文]
     
    Phytoplankton are composed of diverse taxonomical groups, which are manifested as distinct morphology, size, and pigment composition. These characteristics, modulated by their physiological state, impact their light absorption and scattering, allowing them to be detected with ocean color satellite radiometry. There is a growing volume of literature describing satellite algorithms to retrieve information on phytoplankton composition in the ocean. This synthesis provides a review of current methods and a simplified comparison of approaches. The aim is to provide an easily comprehensible resource for non-algorithm developers, who desire to use these products, thereby raising the level of awareness and use of these products and reducing the boundary of expert knowledge needed to make a pragmatic selection of output products with confidence. The satellite input and output products, their associated validation metrics, as well as assumptions, strengths, and limitations of the various algorithm types are described, providing a framework for algorithm organization to assist users and inspire new aspects of algorithm development capable of exploiting the higher spectral, spatial and temporal resolutions from the next generation of ocean color satellites.
  • Achmad Fachruddin Syah, Sei-Ichi Saitoh, Irene D. Alabia, Toru Hirawake
    3RD INTERNATIONAL SYMPOSIUM ON LAPAN-IPB SATELLITE FOR FOOD SECURITY AND ENVIRONMENTAL MONITORING 2016 54 2017年 [査読有り][通常論文]
     
    To evaluate the effects of oceanographic conditions on the formation of the potential fishing zones for Pacific saury in western North Pacific, fishing locations of Pacific saury from Defense Meteorological Satellite Program/Operating Linescan System (DMSP/OLS) and satellite-based oceanographic information were used to construct species habitat models. A 2-level slicing method was used to identify the bright regions as actual fishing areas from OLS images, collected during the peak fishing season of Pacific saury in the North Pacific. Statistical metrics, including the significance of model terms, and reduction in the Akaike's Information Criterion (AIC) were used as the bases for model selection. The selected model was then used to visualize the basin scale distributions of the Pacific saury habitat. The predicted potential fishing zones exhibited spatial correspondence with the fishing locations. The results from generalized additive model revealed that the Pacific saury habitat selection was significantly influenced by the SST ranges from 13-18 degrees C, SSC ranges from 0.5-1.8 mg.m(-3), SSHA ranges from 5-17 cm and EKE ranges from 700-1200 cm(2)s(-2). Moreover, among the set of oceanographic factors examined, SST explained the smallest AIC and is thus, considered to be the most significant variable in the geographic distribution of Pacific saury.
  • Xun Zhang, Sei-Ichi Saitoh, Toru Hirawake
    INTERNATIONAL JOURNAL OF REMOTE SENSING 38 21 6129 - 6146 2017年 [査読有り][通常論文]
     
    The present study used nighttime visible satellite images to identify the daily presence and absence of the fishing vessel aggregations, targeting the Japanese common squid (Todarodes pacificus) in the coastal waters of south-western Hokkaido, Japan. Here, statistical (generalized additive model (GAM) and generalized linear model (GLM)) and machine learning models (boosted regression tree (BRT)) were developed using a 3-year (2000-2002) presence/absence information from squid fishing aggregations and environmental variables (night-time sea surface temperature (SST), chlorophyll-a (Chl-a) concentration, Kd(490) (diffuse attenuation coefficients of downwelling irradiance at 490 nm), and bathymetry). Our findings showed that BRT outperformed the regression-based models in predicting the potential squid fishing zones during the validation period (2003). Results from BRT indicated that potential fishing zones were closely associated with water depth. Both SST and Chl-a concentration were also found highly influential to squid occurrence, while Kd(490), which is related to the water transparency, showed relatively less impact on the squid distribution. The spatial predictions using daily data from 2000 to 2003 revealed the gradual eastward movement of potential fishing zones between June and December, consistent with the pattern of squid fishing activities. Four experimental fishing surveys were further conducted to validate and improve our model predictions against experience-based fishing surveys. The results showed that the squid catches using our model predictions in 2012 substantially exceeded the average catches of experience-based fishing in 2011.
  • Masafumi Natsuike, Kohei Matsuno, Toru Hirawake, Atsushi Yamaguchi, Shigeto Nishino, Ichiro Imai
    HARMFUL ALGAE 61 80 - 86 2017年01月 [査読有り][通常論文]
     
    A high abundance of resting cysts of the toxic dinoflagellate Alexandrium tamarense was recently reported in the vast continental shelf of the Chukchi Sea in the Arctic Ocean, suggesting that the species is widespread in the shelf. Nevertheless, little is known about the occurrence of A. tamarense vegetative cells in the water column of the arctic. Sea ice reduction and the inflow of Pacific summer water (PSW) through the Bering Strait have recently increased owing to warming in the shelf. To determine the spatial and temporal distributions of A. tamarense in the Chukchi Sea shelf and their relationship to the inflow of PSW, field samplings were conducted in the Chukchi Sea and north Bering Sea shelves three times during the summer of 2013 from July to October. Vegetative cells of A. tamarense was detected in both shelves at all sampling periods with a maximum density of 3.55 x 10(3) cells L-1. This species was also observed at the station at 73 degrees N, indicating the northernmost record of this species to date. The center of the A. tamarense distribution was between the north Bering and south Chukchi Sea shelf during the first collection period, and spread to the north Chukchi Sea shelf during the second and third collection periods. The species occurrences were mainly observed at stations affected by the PSW, especially Bering shelf water. Water structure of PSW was characterized by warmer surface and bottom water temperatures, and increased temperatures may have promoted the cell growth and cyst germination of A. tamarense. Therefore, it is suggested that an increase in the PSW inflow owing to warming promotes toxic A. tamarense occurrences on the Chukchi Sea shelf. (C) 2016 Elsevier B.V. All rights reserved.
  • Irene D. Alabia, Mariko Dehara, Sei-Ichi Saitoh, Toru Hirawake
    REMOTE SENSING 8 11 2016年11月 [査読有り][通常論文]
     
    The understanding of the spatio-temporal distributions of the species habitat in the marine environment is central to effectual resource management and conservation. Here, we examined the potential habitat distributions of Japanese common squid (Todarodes pacificus) in the Sea of Japan during a four-year period. The seasonal patterns of preferential habitat were inferred from species distribution models, built using squid occurrences detected from night-time visible images and remotely-sensed environmental factors. The predicted squid habitat (i.e., areas with high habitat suitability) revealed strong seasonal variability, characterized by a reduction of potential habitat, confined off of the southern part of the basin during the winter-spring period (December-May). Apparent expansion of preferential habitat occurred during summer-autumn months (June-November), concurrent with the formation of highly suitable habitat patches in certain regions of the Sea of Japan. These habitat distribution patterns were in response to changes in oceanographic conditions and synchronous with seasonal migration of squid. Moreover, the most important variables regulating the spatio-temporal patterns of suitable habitat were sea surface temperature, depth, sea surface height anomaly, and eddy kinetic energy. These variables could affect the habitat distributions through their impacts on growth and survival of squid, local nutrient transport, and the availability of favorable spawning and feeding grounds.
  • Kohei Matsuno, Jose M. Landeira Sanchez, Atsushi Yamaguchi, Toru Hirawake, Takashi Kikuchi
    POLAR SCIENCE 10 3 335 - 345 2016年09月 [査読有り][通常論文]
     
    From July to August 2007 and June to July 2008, the horizontal/geographical changes in the zooplankton community in the Bering and Chukchi Seas were studied. The geographical patterns, which were common for these two years, were observed for salinity, chlorophyll a (Chl. a), zooplankton chaetognaths, hydrozoans and the whole zooplankton community. Among them, the patterns of salinity and Chl. a were related with the horizontal distribution of the water masses. The distributions of the two carnivorous taxa were correlated with their prey (copepods or barnacle larvae). The analysis of the structural equation model (SEM) revealed that the horizontal distribution of the zooplankton abundance and biomass were governed by the different taxa. Thus, the zooplankton abundance was governed by the numerically dominant but smaller-bodied taxa, such as the barnacle larvae and copepod Pseudocalanus spp., while the zooplankton biomass was determined by the large-bodied copepods, such as Calanus glacialis/marshallae and Eucalanus bungii. (C) 2016 Elsevier B.V. and NIPR.
  • Kazuki Tanaka, Nobuyuki Takesue, Jun Nishioka, Yoshiko Kondo, Atsushi Ooki, Kenshi Kuma, Toru Hirawake, Youhei Yamashita
    SCIENTIFIC REPORTS 6 34123  2016年09月 [査読有り][通常論文]
     
    The spatial distribution of dissolved organic carbon (DOC) concentrations and the optical properties of dissolved organic matter (DOM) determined by ultraviolet-visible absorbance and fluorescence spectroscopy were measured in surface waters of the southern Chukchi Sea, western Arctic Ocean, during the early summer of 2013. Neither the DOC concentration nor the optical parameters of the DOM correlated with salinity. Principal component analysis using the DOM optical parameters clearly separated the DOM sources. A significant linear relationship was evident between the DOC and the principal component score for specific water masses, indicating that a high DOC level was related to a terrigenous source, whereas a low DOC level was related to a marine source. Relationships between the DOC and the principal component scores of the surface waters of the southern Chukchi Sea implied that the major factor controlling the distribution of DOC concentrations was the mixing of plural water masses rather than local production and degradation.
  • Christopher Mulanda Aura, Sei-Ichi Saitoh, Yang Liu, Toru Hirawake, Katsuhisa Baba, Tooru Yoshida
    AQUACULTURE RESEARCH 47 7 2164 - 2182 2016年07月 [査読有り][通常論文]
     
    The determination of the causes for the changes in marine environment in areas with similar oceanic climate forcing on most suitable sites for scallop aquaculture can help to ensure long-term sustainability of the coastal ecosystem. This study assessed aquaculture suitability sites using dominant indicators of marine ecological dynamics on Japanese scallop culture in Funka and Mutsu Bays, Japan as comparative examples. Data sources comprised of Moderate Resolution Imaging Spectroradiometer (MODIS), four dimensional-variational (4D-VAR) data assimilation system, Advanced Land Observing Satellite (ALOS), in situ and buoy measurements. The suitable sites were ranked on a scale of 1 (least suitable) to 8 (most suitable). In the most suitable sites in aquaculture operational areas, Funka Bay had a high proportion (51.1%) than Mutsu Bay (13.7%) for the best performed model. Peaks of aquaculture suitability scores were attributed to potential effects of currents. Extreme sea temperatures (>24 degrees C) in summer 2010 were associated with low performance of the 2010 model in Mutsu Bay and mortality of scallops based on sea temperature-depth visualizations. Future global warming effects are likely to decrease the most suitable culture sites in Funka Bay and loss of similar areas in Mutsu Bay. Thus, change in marine environment influences scallop culture development. Such concepts could form scientific basis for aquaculture planning on designated system of larval distribution and stock management of cultured species to minimize mortality and economic losses.
  • Achmad F. Syah, Sei-Ichi Saitoh, Irene D. Alabia, Toru Hirawake
    FISHERY BULLETIN 114 3 330 - 342 2016年07月 [査読有り][通常論文]
     
    Fishing locations for Pacific saury (Cololabis saira) obtained from images of the Operational Linescan System (OLS) of the U.S. Defense Meteorological Satellite Program, together with maximum entropy models and satellite-based oceanographic data of chlorophylla alpha concentration (chl-alpha), sea-surface temperature (SST), eddy kinetic energy (EKE), and sea-surface height anomaly (SSHA), were used to evaluate the effects of oceanographic conditions on the formation of potential fishing zones (PFZ) for Pacific saury and to explore the spatial variability of these features in the western North Pacific. Actual fishing regions were identified as the bright areas created by a 2-level slicing method for OLS images collected August-December during 2005-2013. The results from a Maxent model revealed its potential for predicting the spatial distribution of Pacific saury and highlight the use of multispectral satellite images for describing PFZs. In all monthly models, the spatial PFZ patterns were explained predominantly by SST (14-16 degrees C) and indicated that SST is the most influential factor in the geographic distribution of Pacific saury. Also related to PFZ formation were EKE and SSHA, possibly through their effects on the feeding grounds conditions. Concentration of chl-a had the least effect among other environmental factors in defining PFZs, especially during the end of the fishing season.
  • Irene D. Alabia, Sei-Ichi Saitoh, Toru Hirawake, Hiromichi Igarashi, Yoichi Ishikawa, Norihisa Usui, Masafumi Kamachi, Toshiyuki Awaji, Masaki Seito
    HYDROBIOLOGIA 772 1 215 - 227 2016年06月 [査読有り][通常論文]
     
    The effects of the El Nio Southern Oscillation (ENSO)-mediated environmental changes to marine resources were long recognized; however, species-specific responses were also reported to vary, possibly more so, under the emerging event-to-event diversity of the ENSO conditions. Hence, the objective of this study is to characterize the potential impacts of the ENSO-regulated environmental variability to squid habitat in the central North Pacific under the different ENSO flavors, using habitat models developed from at least a decade of fishery-dependent dataset and environmental parameters. Our findings revealed that the potential squid habitats were largely influenced by ENSO-forced environmental changes during the squid's spawning and nursery periods, resulting in substantial reduction/enhancement of available habitats in the succeeding summers of Central Pacific El Nio/La Nia, where the latter led to an expansion of favorable spawning and nursery grounds. However, the autumn-winter periods of weaker and short-lived Eastern Pacific El Nio showed elevated potential habitats due to minimal sea surface temperature drop and close proximity of spawning and nursery grounds to optimal feeding environments. The quick, albeit variable, squids' responses to ENSO flavors accentuate their promising potential as ecological beacons under climate changes, aiding the development of adaptive management strategies for commercially exploited fisheries.
  • 松本 健太郎, 有馬 大地, 松野 孝平, 山﨑 康裕, 大西 広二, 大木 淳之, 平譯 享, 山口 篤, 今井 一郎
    北海道大学水産科学研究彙報 66 1 29 - 38 北海道大学大学院水産科学研究院 2016年03月 [査読無し][通常論文]
     
    The spring phytoplankton community in the western North Pacific is characterized by large variability in both the horizontal and verical dimensions. To evaluate this variability, phytoplankton communitiesat 39°30'N-44°00'N along 155°E were investigated in situ using a multi-excitation fluorometer during May 2014. The sea surface chlorophyll a(Chi. a) level was high and composed mainly of diatoms near 43°30'N-42'N, while it was low and composed of dinoflagellates south of 40°N. Based on seven fixed-station investigations, the phytoplanklton communities were classified into 4 types : a low Chl. a level before bloom (44°N), massive diatom bloom(42°N-43°N), low Chl. a level with dinoflagellates(40°N-41°N) and lowest Chl.a(at the southernmost station at 39°30'N). These phytoplankton communities corresponded with the formation of a water mass separating the Subartctic front(SAF) and Subarctic boundary(SAB). Multi-excitation fluorometry data showed a high correlation with Chl. a measurements obtained via Thrmo-salinometer and biovolume microscopic analyses(r²=0.67-0.97,p<0.05). Thus, we concluded that a multi-excitation fluorometer can be applied for the evaluation of detailed spatial and temporal changes in the phytoplankton community at various locations.
  • A. Fujiwara, T. Hirawake, K. Suzuki, L. Eisner, I. Imai, S. Nishino, T. Kikuchi, S. -I. Saitoh
    BIOGEOSCIENCES 13 1 115 - 131 2016年 [査読無し][通常論文]
     
    The size structure and biomass of a phytoplankton community during the spring bloom period can affect the energy use of higher-trophic-level organisms through the predator-prey body size relationships. The timing of the sea ice retreat (TSR) also plays a crucial role in the seasonally ice-covered marine ecosystem, because it is tightly coupled with the timing of the spring bloom. Thus, it is important to monitor the temporal and spatial distributions of a phytoplankton community size structure. Prior to this study, an ocean colour algorithm was developed to derive phytoplankton size index F-L, which is defined as the ratio of chlorophyll a (chl a) derived from cells larger than 5 mu m to the total chl a, using satellite remote sensing for the Chukchi and Bering shelves. Using this method, we analysed the pixel-by-pixel relationships between F-L during the marginal ice zone (MIZ) bloom period and TSR over the period of 1998-2013. The influences of the TSR on the sea surface temperature (SST) and changes in ocean heat content (Delta OHC) during the MIZ bloom period were also investigated. A significant negative relationship between F-L and the TSR was widely found in the shelf region during the MIZ bloom season. However, we found a significant positive (negative) relationship between the SST (Delta OHC) and TSR. Specifically, an earlier sea ice retreat was associated with the dominance of larger phytoplankton during a colder and weakly stratified MIZ bloom season, suggesting that the duration of the nitrate supply, which is important for the growth of large-sized phytoplankton in this region (i.e. diatoms), can change according to the TSR. In addition, under-ice phytoplankton blooms are likely to occur in years with late ice retreat, because sufficient light for phytoplankton growth can pass through the ice and penetrate into the water columns as a result of an increase in solar radiation toward the summer solstice. Moreover, we found that both the length of the ice-free season and the annual median of F-L positively correlated with the annual net primary production (APP). Thus, both the phytoplankton community composition and growing season are important for the APP in the study area. Our findings showed a quantitative relationship between the interannual variability of F-L, the TSR, and the APP, which suggested that satellite remote sensing of the phytoplankton community size structure is suitable to document the impact of a recent rapid sea ice loss on the ecosystem of the study region.
  • Mega Syamsuddin, Sei-Ichi Saitoh, Toru Hirawake, Fadli Syamsudin, Mukti Zainuddin
    INTERNATIONAL JOURNAL OF REMOTE SENSING 37 9 2087 - 2100 2016年 [査読有り][通常論文]
     
    Remotely derived environmental variables, including sea surface height anomaly (SSHA), sea surface temperature (SST), chlorophyll-a (chl-a), eddy kinetic energy (EKE), mixed layer data set of argo float (MLD), Nino 3.4 index, and bigeye tuna catch data for the period 1997-2008, were used to analyse ocean climate variability and how they relate to the hotspots of bigeye tuna catch in the eastern Indian Ocean off Java. The empirical orthogonal function (EOF) was performed to obtain a more detailed structure of the spatio-temporal ocean variability in the region. The results showed that the first EOF modes of chl-a, SSHA, and SST accounted for 42.8%, 36.5%, and 27.4% of total variance, respectively, and these corresponded to the interannual signal. The maps of spatial patterns of the first EOF modes of SSHA, SST, and chl-a gave very typical values for cold-water SSHA, low SST, and high chl-a concentration along the southern coast of the Indonesian archipelago; and warm-water SSHA, high SST, and low chl-a concentration in the offshore region to make frontal areas along the latitudinal line around 10-12 degrees S. The EOF analysis further revealed a strong relationship between the El Nino event and favourable oceanographic conditions, resulting in a significant increase in bigeye tuna catch. The average hook rate of 0.71 (0.43) was recorded during El Nino (La Nina). Major hotspots were located away from the confluence region and frontal areas around 11-16 degrees S and 110-118 degrees E and were thus demonstrated as the most favourable oceanographic conditions for bigeye tuna fishing in the eastern Indian Ocean off Java.
  • Shigeto Nishino, Takashi Kikuchi, Amane Fujiwara, Toru Hirawake, Michio Aoyama
    BIOGEOSCIENCES 13 8 2563 - 2578 2016年 [査読有り][通常論文]
     
    We analysed mooring and ship-based hydrographic and biogeochemical data obtained from a Hope Valley biological hotspot in the southern Chukchi Sea. The moorings were deployed from 16 July 2012 to 19 July 2014, and data were captured during spring and autumn blooms with high chlorophyll a concentrations. Turbidity increased and dissolved oxygen decreased in the bottom water at the mooring site before the autumn bloom, suggesting an accumulation of particulate organic matter and its decomposition (nutrient regeneration) at the bottom. This event may have been a trigger for the autumn bloom at this site. The bloom was maintained for 1 month in 2012 and for 2 months in 2013. The maintenance mechanism for the autumn bloom was also studied by hydrographic and biogeochemical surveys in late summer to autumn 2012 and 2013. Nutrient-rich water from the Bering Sea supplied nutrients to Hope Valley, although a reduction in nutrients occurred in 2012 by the influence of lower-nutrient water that would have remained on the Chukchi Sea shelf. In addition, nutrient regeneration at the bottom of Hope Valley could have increased nutrient concentrations and explained 60% of its nutrient content in the bottom water in the autumn of 2012. The high nutrient content with the dome-like structure of the bottom water may have maintained the high primary productivity via the vertical nutrient supply from the bottom water, which was likely caused by wind-induced mixing during the autumn bloom. Primary productivity was 0.3 g C m(-2) d(-1) in September 2012 and 1.6 g C m(-2) d(-1) in September 2013. The lower productivity in 2012 was related to strong stratification caused by the high fraction of surface sea ice meltwater.
  • Yang Liu, Sei-Ichi Saitoh, Yu Ihara, Satoshi Nakada, Makoto Kanamori, Xun Zhang, Katsuhisa Baba, Yoichi Ishikawa, Toru Hirawake
    ICES JOURNAL OF MARINE SCIENCE 72 9 2684 - 2699 2015年11月 [査読有り][通常論文]
     
    The Japanese scallop (Patinopecten (Mizuhopecten) yessoensis) is an important commercial species in Funka Bay, Japan, where it is farmed using the hanging culture method. Our study was based on 6 years (from 2006 to 2011) of monthly in situ observations of scallop growth at Yakumo station. To produce a basic spatial distribution dataset, we developed an interpolation solution for the shortage of Chl-a concentration data available from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite. Additionally, we integrated four-dimensional variational (4D-VAR) assimilation water temperature data from ocean general circulation models (OGCMs), with four vertical levels (6, 10, 14, and 18 m) from the sea surface. Statistical models, including generalized additive models (GAMs) and generalized linear models, were applied to in situ observation data, satellite data, and 4D-VARdata to identify the influence of environment factors (interpolated Chl-a, temperature, and depth) on the growth of scallops, and to develop a three-dimensional growth prediction model for the Japanese scallops in Funka Bay. We considered three methods to simulate the growth process of scallops (accumulation, summation, and product), and used them to select the most suitable model. All the interpolated Chl-a concentrations and 4D-VAR temperature data were verified by shipboard data. The results revealed that GAM, using an accumulation method that was based on a combination of integrated temperature, integrated log Chl-a, depth, and number of days, was best able to predict the vertical and spatial growth of the Japanese scallop. The predictions were verified by in situ observations from different depths (R-2 = 0.83-0.94). From the distribution of three-dimensional predicted scallop growth maps at each depth, it was suggested that the growth of the Japanese scallop was most favourable at 6 m and least favourable at 18 m, although variations occurred in each aquaculture region in different years. These variations were probably due to the ocean environment and climate variation.
  • S. Nishino, T. Kikuchi, A. Fujiwara, T. Hirawake, M. Aoyama
    Biogeosciences Discuss 12 1 - 38 2015年10月 [査読有り][通常論文]
  • Younjoo J. Lee, Patricia A. Matrai, Marjorie A. M. Friedrichs, Vincent S. Saba, David Antoine, Mathieu Ardyna, Ichio Asanuma, Marcel Babin, Simon Belanger, Maxime Benoit-Gagne, Emmanuel Devred, Mar Fernandez-Mendez, Bernard Gentili, Toru Hirawake, Sung-Ho Kang, Takahiko Kameda, Christian Katlein, Sang H. Lee, Zhongping Lee, Frederic Melin, Michele Scardi, Tim J. Smyth, Shilin Tang, Kevin R. Turpie, Kirk J. Waters, Toby K. Westberry
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 120 9 6508 - 6541 2015年09月 [査読有り][通常論文]
     
    We investigated 32 net primary productivity (NPP) models by assessing skills to reproduce integrated NPP in the Arctic Ocean. The models were provided with two sources each of surface chlorophyll-a concentration (chlorophyll), photosynthetically available radiation (PAR), sea surface temperature (SST), and mixed-layer depth (MLD). The models were most sensitive to uncertainties in surface chlorophyll, generally performing better with in situ chlorophyll than with satellite-derived values. They were much less sensitive to uncertainties in PAR, SST, and MLD, possibly due to relatively narrow ranges of input data and/or relatively little difference between input data sources. Regardless of type or complexity, most of the models were not able to fully reproduce the variability of in situ NPP, whereas some of them exhibited almost no bias (i.e., reproduced the mean of in situ NPP). The models performed relatively well in low-productivity seasons as well as in sea ice-covered/deep-water regions. Depth-resolved models correlated more with in situ NPP than other model types, but had a greater tendency to overestimate mean NPP whereas absorption-based models exhibited the lowest bias associated with weaker correlation. The models performed better when a subsurface chlorophyll-a maximum (SCM) was absent. As a group, the models overestimated mean NPP, however this was partly offset by some models underestimating NPP when a SCM was present. Our study suggests that NPP models need to be carefully tuned for the Arctic Ocean because most of the models performing relatively well were those that used Arctic-relevant parameters.
  • Kohei Matsuno, Atsushi Yamaguchi, Toru Hirawake, Shigeto Nishino, Jun Inoue, Takashi Kikuchi
    POLAR BIOLOGY 38 7 1075 - 1079 2015年07月 [査読無し][通常論文]
     
    The species composition of Arctic zooplankton differs greatly from that of the zooplankton of the North Pacific and Bering Sea. Particularly with greater warming from sea-ice retreat, the reproduction of North Pacific species transported into the Chukchi Sea and beyond may lead to changes in the Arctic pelagic ecosystem. We report the egg production and hatching of the Pacific copepod Neocalanus flemingeri in the Chukchi Sea based on shipboard experiments performed in September 2013. The reproductive capability of N. flemingeri observed in the Chukchi Sea resembled that reported in the Pacific, with the exception of a lower hatching success. Only 7.5 % of N. flemingeri eggs hatched compared with 93 % in Pacific experiments. Low hatching success is considered to be caused by failures of fertilization. The potential recruitment number for N. flemingeri suggests that it is unlikely to establish expatriate Arctic populations in the near future.
  • Kohei Matsuno, Atsushi Yamaguchi, Toru Hirawake, Shigeto Nishino, Jun Inoue, Takashi Kikuchi
    POLAR BIOLOGY 38 7 1075 - 1079 2015年07月 [査読有り][通常論文]
     
    The species composition of Arctic zooplankton differs greatly from that of the zooplankton of the North Pacific and Bering Sea. Particularly with greater warming from sea-ice retreat, the reproduction of North Pacific species transported into the Chukchi Sea and beyond may lead to changes in the Arctic pelagic ecosystem. We report the egg production and hatching of the Pacific copepod Neocalanus flemingeri in the Chukchi Sea based on shipboard experiments performed in September 2013. The reproductive capability of N. flemingeri observed in the Chukchi Sea resembled that reported in the Pacific, with the exception of a lower hatching success. Only 7.5 % of N. flemingeri eggs hatched compared with 93 % in Pacific experiments. Low hatching success is considered to be caused by failures of fertilization. The potential recruitment number for N. flemingeri suggests that it is unlikely to establish expatriate Arctic populations in the near future.
  • Detection of Squid and Pacific Saury fishing vessels around Japan using VIIRS Day/Night Band image
    Liu Y, Saitoh S-I, Hirawake T, Igarashi, H, Ishikawa, Y
    Proceedings of the Asia-Pacific Advanced Network 39 28 - 39 2015年06月 [査読有り][通常論文]
  • 堀 雅裕, 村上 浩, 宮崎 理紗, 本多 嘉明, 梶原 康司, 奈佐原 顕郎, 中島 孝, 入江 仁士, 虎谷 充浩, 平譯 享, 青木 輝夫
    大会講演予講集 107 社団法人日本気象学会 2015年04月30日 [査読無し][通常論文]
  • Shengqiang Wang, Joji Ishizaka, Toru Hirawake, Yuji Watanabe, Yuanli Zhu, Masataka Hayashi, Sinjae Yoo
    OPTICS EXPRESS 23 8 10301 - 10318 2015年04月 [査読有り][通常論文]
     
    Phytoplankton size structure plays an important role in ocean biogeochemical processes. The light absorption spectra of phytoplankton provide a great potential for retrieving phytoplankton size structure because of the strong dependence on the packaging effect caused by phytoplankton cell size and on different pigment compositions related to phytoplankton taxonomy. In this study, we investigated the variability in light absorption spectra of phytoplankton in relation to the size structure. Based on this, a new approach was proposed for estimating phytoplankton size fractions. Our approach use the spectral shape of the normalized phytoplankton absorption coefficient (a(ph)(lambda)) through principal component analysis (PCA). Values of a(ph)(lambda) were normalized to remove biomass effects, and PCA was conducted to separate the spectral variance of normalized a(ph)(lambda) into uncorrelated principal components (PCs). Spectral variations captured by the first four PC modes were used to build relationships with phytoplankton size fractions. The results showed that PCA had powerful ability to capture spectral variations in normalized a(ph)(lambda), which were significantly related to phytoplankton size fractions. For both hyperspectral a(ph)(lambda) and multiband a(ph)(lambda), our approach is applicable. We evaluated our approach using wide in situ data collected from coastal waters and the global ocean, and the results demonstrated a good and robust performance in estimating phytoplankton size fractions in various regions. The model performance was further evaluated by a(ph)(lambda) derived from in situ remote sensing reflectance (R-rs(lambda)) with a quasi-analytical algorithm. Using R-rs(lambda) only at six bands, accurate estimations of phytoplankton size fractions were obtained, with R-2 values of 0.85, 0.61, and 0.76, and root mean-square errors of 0.130, 0.126, and 0.112 for micro-, nano-, and picophytoplankton, respectively. Our approach provides practical basis for remote estimation of phytoplankton size structure using a(ph)(lambda) derived from satellite observations or rapid field instrument measurements in the future. (C)2015 Optical Society of America
  • Shigeto Nishino, Yusuke Kawaguchi, Jun Inoue, Toru Hirawake, Amane Fujiwara, Ryosuke Futsuki, Jonaotaro Onodera, Michio Aoyama
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 120 3 1975 - 1992 2015年03月 [査読無し][通常論文]
     
    A fixed-point observation station was set up in the northern Chukchi Sea during autumn 2013, and for about 2 weeks conductivity-temperature-depth (CTD)/water samplings (6 h) and microstructure turbulence measurements (2 to 3 times a day) were performed. This enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity. There have been no such fixed-point observations in this region, where incoming low-salinity water from the Pacific Ocean, river water, and sea-ice meltwater promote a strong pycnocline (halocline) that stabilizes the water column. Previous studies have suggested that because of the strong pycnocline, wind-induced ocean mixing could not change the stratification to impact biological activity. However, the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind-induced inertial motion and turbulent mixing caused by intense gale-force winds (>10 m s(-1)) did result in increases in upward nutrient fluxes, primary productivity, and phytoplankton biomass, particularly large phytoplankton such as diatoms. Convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there. For diatom production at the fixed-point observation station, it was essential that silicate was supplied from a subsurface silicate maximum, a new feature that we identified during autumn in the northern Chukchi Sea. Water mass distributions obtained from wide-area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the Canada Basin.
  • Shigeto Nishino, Yusuke Kawaguchi, Jun Inoue, Toru Hirawake, Amane Fujiwara, Ryosuke Futsuki, Jonaotaro Onodera, Michio Aoyama
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 120 3 1975 - 1992 2015年03月 [査読有り][通常論文]
     
    A fixed-point observation station was set up in the northern Chukchi Sea during autumn 2013, and for about 2 weeks conductivity-temperature-depth (CTD)/water samplings (6 h) and microstructure turbulence measurements (2 to 3 times a day) were performed. This enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity. There have been no such fixed-point observations in this region, where incoming low-salinity water from the Pacific Ocean, river water, and sea-ice meltwater promote a strong pycnocline (halocline) that stabilizes the water column. Previous studies have suggested that because of the strong pycnocline, wind-induced ocean mixing could not change the stratification to impact biological activity. However, the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind-induced inertial motion and turbulent mixing caused by intense gale-force winds (>10 m s(-1)) did result in increases in upward nutrient fluxes, primary productivity, and phytoplankton biomass, particularly large phytoplankton such as diatoms. Convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there. For diatom production at the fixed-point observation station, it was essential that silicate was supplied from a subsurface silicate maximum, a new feature that we identified during autumn in the northern Chukchi Sea. Water mass distributions obtained from wide-area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the Canada Basin.
  • Tomonori Isada, Toru Hirawake, Tsukuru Kobayashi, Yuichi Nosaka, Masafumi Natsuike, Ichiro Imai, Koji Suzuki, Sei-Ichi Saitoh
    REMOTE SENSING OF ENVIRONMENT 159 134 - 151 2015年03月 [査読有り][通常論文]
     
    Identification of phytoplankton functional groups is key to understanding marine biogeochemical cycles. For more accurate understanding of phytoplankton community structure and its implications for ocean color remote sensing applications, we investigated seasonal changes in phytoplankton pigments with high-performance liquid chromatography (HPLC), hyperspectral absorption coefficients of detritus (a(d)(lambda)), phytoplankton (a(ph)(lambda)), and colored dissolved organic matter (a(CDOM)(lambda)), and hyperspectral a(ph)(X) derived from remote sensing reflectance (a(ph_Rrs-derived)(lambda)) in the coastal waters of Funka Bay from 2010 to 2012. Chlorophyll a (Chl a) concentrations measured by HPLC ranged from 029 to 8.6 mg m(-3). Phytoplankton community compositions, as estimated by chemotaxonomic analysis (CHEMTAX) based on HPLC phytoplanIcton pigments, showed a seasonal succession of diatoms, chlorophyll b-containing phytoplankton (chlorophytes and prasinophytes), and cyanobacteria. Additonally, to identify the dominant type of phytoplankton with an alternative technique to CHEMTAX analysis, we employed a derivative spectroscopy/similarity index (SI) approach for a(ph)(X) as an optical detection technique for discriminating between different types of phytoplankton. In particular for diatom-dominated stations, SI values relative to the second derivative spectra of a(ph)(lambda) of diatom cultures, isolated from our study region, were significantly higher than those for chlorophyll b-containing phytoplankton- and cyanobacteriadominated stations. Furthermore, we found a strong relationship between the SI values calculated from the second derivative spectra and the composition of diatoms as estimated by CHEMTAX. These results suggest that the two different methods validated each other's performance and precision in estimating relative diatom abundance from bulk samples and that it is possible to optically discriminate the dominance of diatoms using derivative spectra of a(ph)(lambda). We extended this combination approach to hyperspectral a(ph_Rrs_derived)(lambda), using a quasi-analytical algorithm within 400-546 nm range. We found a significant correlation between SI values obtained from the second derivative spectra of a(ph_Rrs-derived)(lambda)/a(ph_Rrs-derived)(443) and the composition of diatoms derived by CHEMTAX, but it was not as high as for a(ph)(lambda) measured by filter-pad analysis. These results indicate that using hyperspectral optical data of a(ph)(lambda) and R-rs(lambda) with derivative spectroscopy is potentially a promising approach to identify seasonal variability in the composition of diatoms in coastal waters. Furthermore, a hyperspectral approach in combination with CHEMTAX analysis as a reference for phytoplankton community structure has proven useful in improving our understanding of phytoplankton community structure in the coastal waters of Funka Bay. (C) 2014 Elsevier Inc All rights reserved.
  • Yang Liu, Sei-Ichi Saitoh, Satoshi Nakada, Xun Zhang, Toru Hirawake
    SUSTAINABILITY 7 2 1263 - 1279 2015年02月 [査読有り][通常論文]
     
    We provide an overview of selected recent operational applications of satellite remote sensing and marine Geographic Information Systems (GIS) procedures to the practice of sustainable aquaculture in southern Hokkaido, Japan, focusing mainly on kelp and scallop aquaculture. We also developed a suitable aquaculture site-selection model (SASSM) for suspension culture of Gagome (a kelp species) in the same region. Models for Japanese kelp and Gagome showed that the distributions of the most suitable areas for both species overlapped. Competition between kelps was especially marked along the coastline between Hakodate and Esan. In addition, we examined the impact of oceanographic environmental changes and atmospheric events on scallop and kelp aquaculture sites, demonstrating that variations in the coastal Oyashio Current and the Tsugaru Warm Current significantly influenced the growth and harvesting seasons of scallops and kelps in Funka Bay and other sections of southern Hokkaido. Because a strong El Nino event occurred in 2010, January of that year was extremely cold. The proportion of suitable areas for both scallops and kelps during their respective growing seasons contracted in 2010. Thus, shifts in oceanographic and atmospheric conditions should be incorporated into sustainability management planning for coastal scallop and kelp aquaculture in southern Hokkaido.
  • Shintaro Takao, Toru Hirawake, Gen Hashida, Hiroshi Sasaki, Hiroshi Hattori, Koji Suzuki
    POLAR BIOLOGY 37 11 1563 - 1578 2014年11月 [査読無し][通常論文]
     
    Phytoplankton population dynamics play an important role in biogeochemical cycles in the Southern Ocean during austral summer. However, the relationship between phytoplankton community composition and primary productivity remains elusive in this region. We investigated the community composition and photosynthetic physiology of surface phytoplankton assemblages in the Australian sector of the Southern Ocean from December 2010 to January 2011. There were significant latitudinal variations in hydrographic and biological parameters along 110A degrees E and 140A degrees E. Surface (5 m) chlorophyll a (chl a) concentrations measured with high-performance liquid chromatography varied between 0.18 and 0.99 mg m(-3). The diatom contribution to the surface chl a biomass increased in the south, as estimated with algal chemotaxonomic pigment markers, while the contributions of haptophytes and chlorophytes decreased. In our photosynthesis-irradiance (P-E) curve experiment, the maximum photosynthetic rate normalized to chl a (), initial slope (alpha (*)), the maximum quantum yield of carbon fixation (I broken vertical bar (c max)), and the photoinhibition index (beta (*)) were higher in the region where diatoms contributed > 50 % to the chl a biomass. In addition, there were statistically significant correlations between the diatom contribution to the chl a biomass and the P-E parameters. These results suggested that the changes in the phytoplankton community composition, primarily in diatoms, could strongly affect photosynthetic physiology in the Australian sector of the Southern Ocean.
  • Shintaro Takao, Toru Hirawake, Gen Hashida, Hiroshi Sasaki, Hiroshi Hattori, Koji Suzuki
    POLAR BIOLOGY 37 11 1563 - 1578 2014年11月 [査読有り][通常論文]
     
    Phytoplankton population dynamics play an important role in biogeochemical cycles in the Southern Ocean during austral summer. However, the relationship between phytoplankton community composition and primary productivity remains elusive in this region. We investigated the community composition and photosynthetic physiology of surface phytoplankton assemblages in the Australian sector of the Southern Ocean from December 2010 to January 2011. There were significant latitudinal variations in hydrographic and biological parameters along 110A degrees E and 140A degrees E. Surface (5 m) chlorophyll a (chl a) concentrations measured with high-performance liquid chromatography varied between 0.18 and 0.99 mg m(-3). The diatom contribution to the surface chl a biomass increased in the south, as estimated with algal chemotaxonomic pigment markers, while the contributions of haptophytes and chlorophytes decreased. In our photosynthesis-irradiance (P-E) curve experiment, the maximum photosynthetic rate normalized to chl a (), initial slope (alpha (*)), the maximum quantum yield of carbon fixation (I broken vertical bar (c max)), and the photoinhibition index (beta (*)) were higher in the region where diatoms contributed > 50 % to the chl a biomass. In addition, there were statistically significant correlations between the diatom contribution to the chl a biomass and the P-E parameters. These results suggested that the changes in the phytoplankton community composition, primarily in diatoms, could strongly affect photosynthetic physiology in the Australian sector of the Southern Ocean.
  • Kenshi Kuma, Ryohei Sasayama, Nanako Hioki, Yuichiroh Morita, Yutaka Isoda, Tohru Hirawake, Keiri Imai, Takafumi Aramaki, Tomohiro Nakamura, Jun Nishioka, Naoto Ebuchi
    JOURNAL OF OCEANOGRAPHY 70 4 377 - 387 2014年08月 [査読無し][通常論文]
     
    In the southwestern Okhotsk Sea, the cold water belt (CWB) is frequently observed on satellite images offshore of the Soya Warm Current flowing along the northeastern coast of Hokkaido, Japan, during summertime. It has been speculated that the CWB is upwelling cold water that originates from either subsurface water of the Japan Sea off Sakhalin or bottom water of the Okhotsk Sea. Hydrographic and chemical observations (nutrients, humic-type fluorescence intensity, and iron) were conducted in the northern Japan Sea and southwestern Okhotsk Sea in early summer 2011 to clarify the origin of the CWB. Temperature-salinity relationships, vertical distributions of chemical components, profiles of chemical components against density, and the (NO3 + NO2)/PO4 relationship confirm that water in the CWB predominantly originates from Japan Sea subsurface water.
  • Yang Liu, Sei-Ichi Saitoh, I. Nyoman Radiarta, Hiromichi Igarashi, Toru Hirawake
    AQUACULTURE 422 172 - 183 2014年02月 [査読有り][通常論文]
     
    The Japanese scallop (Mizuhopecten yessoensis) is an important commercial species in the Dalian coastal area. The present study employed a suitable aquaculture site-selection model (SASSM) and used satellite remote-sensing data to analyze the spatiotemporal distribution of suitable areas for Japanese scallop aquaculture in the Dalian coastal area from 2003 to 2012. The study area was divided into four marine zones. The results demonstrated that the suitability scores of scallop aquaculture areas were high in May and low in February. The Changhai County (Zone II) and Lushunkou areas (Zone III) exhibited high potential for Japanese scallop aquaculture development. The results of the suitability models were consistent with the existing scallop aquaculture in the study area. These zones, combined with climatic events [the winter East Asian Monsoon (EAM) and El Nino/La Nina-Southern Oscillation (ENSO) events], were used to examine the impact of climate variability on scallop aquaculture. Results suggest that the suitability scores in Zone III were more sensitive to changes in environmental factors (e. g., sea surface temperature, chlorophyll-a, and suspended sediment) and climate changes, whereas the correlations among these factors were not significant in Zone II. Adaptation to these changes should be considered when developing plans and management strategies for scallop aquaculture. (C) 2013 Elsevier B. V. All rights reserved.
  • 平田 貴文, 平譯 享, 境田 太樹, 山口 寿史, 鈴木 光次, 石坂 丞二, 小林 拓, 村上 浩, 虎谷 充浩, 藤原 周, 齊藤 誠一
    日本リモートセンシング学会誌 34 4 278 - 285 The Remote Sensing Society of Japan 2014年 [査読無し][通常論文]
     
    Several ocean algorithms have been developed for the Second-Generation Global Imager (SGLI) on the Global Climate Observation Mission - Climate (GCOM-C) satellite (planned launch, 2016). Here we present verification of the ocean algorithms designed to retrieve the inherent optical properties, phytoplankton functional types and primary productivity. The satellite algorithm verification is defined here to evaluate accuracy of target variables using input parameter(s) obtained from in situ measurements rather than from satellite measurements. The verification of inherent optical properties (IOP) algorithms showed RMSE of 0.12, 0.22, and 0.05 for the absorption coefficient of phytoplankton, detrital materials plus colored dissolved organic materials, and the backscattering coefficient of suspended particles, respectively. Verification of the primary production algorithm indicated that it almost satisfied the values measured in situ by a factor of 2. Other algorithms such as phytoplankton functional types (PFTs) and size classes (PSCs) algorithms, which can be derived from the optical properties of phytoplankton rather than from chlorophyll a concentration, showed RMSE of 10.1-11.6 % in a relative abundance of PFTs/PSCs. Towards validation of the ocean algorithms, a radiometer called the Compact-Optical Profiling System (C-OPS), as well as another compact radiometer system specifically designed for turbid waters, were configured for in situ observation. The latter was found to reduce shelf-shading error to within 10 %. Furthermore, Ultra-High Performance Liquid Chromatography systems (UHPLC) have been developed for rapid measurements (7 min) of phytoplankton pigments in a water sample (conventional HPLC takes 30 min). This new system significantly increases spatio-temporal coverage of in situ data required for algorithm validation.
  • Atsushi Yamaguchi, Tomoe Homma, Rui Saito, Kohei Matsuno, Hiromichi Ueno, Toru Hirawake, Ichiro Imai
    Plankton and Benthos Research 8 3 116 - 123 2014年 [査読無し][通常論文]
     
    © The Plankton Society of Japan.Stratified zooplankton sampling was conducted in the subarctic Pacific in June 2009 at four stations along 47°N from 0 to 3,000 m depth to evaluate longitudinal changes in population structure and vertical distribution of the dominant copepod species. At the westernmost station (160°E), the population structure of Eucalanus bungii and Metridia pacifica was dominated by early copepodid stages. In E. bungii, nauplii were abundant and adult females had developed ovaries at 160°E, while at the three stations to the east (167°E, 174°E and 179°W), no E. bungii nauplii were collected, and the resting stages were dominant. This suggests the species was reproducing near 160°E and in diapause in the east. In all three Neocalanus species analyzed (N. cristatus, N. flemingeri and N. plumchrus), late copepodid stages were dominant at the eastern three stations. Lipid accumulation in the fifth copepodid stage of Neocalanus spp. was greater in the west than in the east. This probably resulted from better food conditions and lower temperatures in the west, where copepods could consume more food during development than in the east.
  • Yang Liu, Sei-Ichi Saitoh, Hiromichi Igarashi, Toru Hirawake
    INTERNATIONAL JOURNAL OF REMOTE SENSING 35 11-12 4422 - 4440 2014年 [査読有り][通常論文]
     
    Climate changes affect coastal environments and aquaculture, threatening food security and economic growth. Japanese scallop (Mizuhopecten yessoensis) culture is economically important for the coastal communities of Dalian, China, and Funka Bay, Japan. In this study, we combined satellite remote-sensing data, in situ observations, and a suitable aquaculture site selection model to explore the interactions between marine environments and climate variability over a recent 10-year period (2003-2012). Our selection of appropriate zones in these two Far Eastern regions and our analyses of climatic event (Arctic Oscillation (AO), winter East Asian monsoon (EAM), and El Nino/La Nina Southern Oscillation (ENSO)) and meteorological (precipitation, temperature, and wind) data allowed us to determine the impacts of climate change on regional coastal environments and prospects for scallop aquaculture. These analyses showed that AO and EAM strongly influenced the aquaculture areas on the Dalian coast through their effects on temperature during winter. We also determined that wind was the main driving force behind regional environmental changes during spring. Conversely, ocean conditions and suitable areas in Funka Bay changed rapidly relative to oceanic and atmospheric circulation. In Funka Bay, areas appropriate for scallop aquaculture and variations in chlorophyll-a concentration (which reflect the availability of algal food for scallops) were strongly correlated with ENSO, precipitation, and air temperature. These correlations demonstrate the influence of oceanic and atmospheric parameters on the productivity of scallop aquaculture in Funka Bay. Adaptation to oceanic and atmospheric changes should be considered when developing plans and management strategies for coastal scallop aquaculture in northeast Asia.
  • A. Fujiwara, T. Hirawake, K. Suzuki, I. Imai, S. -I. Saitoh
    BIOGEOSCIENCES 11 7 1705 - 1716 2014年 [査読無し][通常論文]
     
    This study assesses the response of phytoplankton assemblages to recent climate change, especially with regard to the shrinking of sea ice in the northern Chukchi Sea of the western Arctic Ocean. Distribution patterns of phytoplankton groups in the late summers of 2008-2010 were analysed based on HPLC pigment signatures and, the following four major algal groups were inferred via multiple regression and cluster analyses: prasinophytes, diatoms, haptophytes and dinoflagellates. A remarkable interannual difference in the distribution pattern of the groups was found in the northern basin area. Haptophytes dominated and dispersed widely in warm surface waters in 2008, whereas prasinophytes dominated in cold water in 2009 and 2010. A difference in the onset date of sea ice retreat was evident among years-the sea ice retreat in 2008 was 1-2 months earlier than in 2009 and 2010. The spatial distribution of early sea ice retreat matched the areas in which a shift in algal community composition was observed. Steel-Dwass's multiple comparison tests were used to assess the physical, chemical and biological parameters of the four clusters. We found a statistically significant difference in temperature between the haptophyte-dominated cluster and the other clusters, suggesting that the change in the phytoplankton communities was related to the earlier sea ice retreat in 2008 and the corollary increase in sea surface temperatures. Longer periods of open water during the summer, which are expected in the future, may affect food webs and biogeochemical cycles in the western Arctic due to shifts in phytoplankton community structure.
  • Yang Liu, Sei-Ichi Saitoh, I. Nyoman Radiarta, Tomonori Isada, Toru Hirawake, Hiroyuki Mizuta, Hajime Yasui
    ICES JOURNAL OF MARINE SCIENCE 70 7 1460 - 1470 2013年11月 [査読有り][通常論文]
     
    Japanese kelp (Saccharina japonica) is one of the most valuable cultured and harvested kelp species in Japan. In this study, we added a physical parameter, sea surface nitrate (SSN) estimated from satellite remote sensing data, to develop a suitable aquaculture site-selection model (SASSM) for hanging cultures of Japanese kelp in southern Hokkaido, Japan. The local algorithm to estimate SSN was developed using satellite measurements of sea surface temperature and chlorophyll-a. We found a high correlation between satellite-and ship-measured data (r(2) = 0.87, RMSE = 1.39). Multi-criteria evaluation was adapted to the SASSM to rank sites on a scale of 1 (least suitable) to 8 (most suitable). Wefound that 64.4% of the areas were suitable (score above 7). Minamikayabe was identified as the most suitable area, and Funka Bay also contained potential aquaculture sites. In addition, we examined the impact of El Nino/La Nina-Southern Oscillation (ENSO) events on Japanese kelp aquaculture and site suitability from 2003-2010. During El Nino events, the number of suitable areas (scores 7 and 8) decreased significantly, indicating that climatic conditions should be considered for future development of marine aquaculture.
  • Mega L. Syamsuddin, Mega L. Syamsuddin, Sei Ichi Saitoh, Toru Hirawake, Bachri Samsul, Agung B. Harto
    Fishery Bulletin 111 2 175 - 188 2013年 [査読有り][通常論文]
     
    The effects of El Niño-Southern Oscillation events on catches of Bigeye Tuna (Thunnus obesus) in the eastern Indian Ocean (EIO) off Java were evaluated through the use of remotely sensed environmental data (sea-surface-height anomaly [SSHA], sea-surface temperature [SST], and chlorophyll-a concentration), and Bigeye Tuna catch data. Analyses were conducted for the period of 1997-2000, which included the 1997-98 El Niño and 1999-2000 La Niña events. The empirical orthogonal function (EOF) was applied to examine oceanographic parameters quantitatively. The relationship of those parameters to variations in catch distribution of Bigeye Tuna was explored with a generalized additive model (GAM). The mean hook rate was 0.67 during El Niño and 0.44 during La Niña, and catches were high where SSHA ranged from-21 to 5 cm, SST ranged from 24°C to 27.5°C, and chlorophyll-a concentrations ranged from 0.04 to 0.16 mg m-3. The EOF analysis confirmed that the 1997-98 El Niño affected oceanographic conditions in the EIO off Java. The GAM results indicated that SST was better than the other environmental factors (SSHA and chlorophyll-a concentration) as an oceanographic predictor of Bigeye Tuna catches in the region. According to the GAM predictions, the highest probabilities (70-80%) for Bigeye Tuna catch in 1997-2000 occurred during oceanographic conditions during the 1997-98 El Niño event.
  • Toru Hirawake, Katsuhito Shinmyo, Amane Fujiwara, Sei-ichi Saitoh
    ICES JOURNAL OF MARINE SCIENCE 69 7 1194 - 1204 2012年09月 [査読有り][通常論文]
     
    Ocean colour remote sensing has been utilized for studying primary productivity in the Arctic Ocean. However, phytoplankton chlorophyll a (Chl a) is not predicted accurately because of the interference of coloured dissolved organic matter (CDOM) and non-algal particles (NAP). To enhance the estimation accuracy, a phytoplankton absorption-based primary productivity model (ABPM) was applied to the Bering and Chukchi Seas. The phytoplankton absorption coefficient was determined correctly from sea surface remote sensing reflectance (R-rs) and reduced the effect of CDOM and NAP in primary productivity (PPeu) estimates. PPeu retrieved from in situ R-rs using the ABPM satisfied a factor of 2 of measured values. PPeu estimated from the Moderate Resolution Imaging Spectroradiometer R-rs data were within the range of historical values. These estimated PPeu values were less than half of those of the model based on Chl a, and the difference between the two models reflected the influence of CDOM and NAP absorptions. Interannual variation in August and September over the period 2002-2010 showed an increase in primary productivity. The increase in 2007 was especially large, by a factor of 1.51-2.71, compared with 2006. The significant temporal increase in productivity detected here differs from earlier studies that detected little, if any, change in the region.
  • S. Takao, T. Hirawake, S. W. Wright, K. Suzuki
    BIOGEOSCIENCES 9 10 3875 - 3890 2012年 [査読無し][通常論文]
     
    Phytoplankton population dynamics play an important role in biogeochemical cycles in the Southern Ocean during austral summer. Recent environmental changes such as a rise in sea surface temperature (SST) are likely to impact on net primary productivity (NPP) and phytoplankton community composition. However, their spatiotemporal relationships are still unclear in the Southern Ocean. Here we assessed the relationships between NPP, dominant phytoplankton groups, and SST in the Indian sector of the Southern Ocean over the past decade (1997-2007) using satellite remote sensing data. As a result, we found a statistically significant reduction in NPP in the polar frontal zone over the past decade during austral summer. Moreover, the decrease in NPP positively correlated with the dominance of diatoms (Kendall's rank correlation tau = 0.60) estimated by a phytoplankton community composition model, but not correlated with SST. In the seasonal ice zone, NPP correlated with not only the dominance of diatoms positively (tau = 0.56), but also the dominance of haptophytes (tau = -0.54) and SST (tau = -0.54) negatively. Our results suggested that summer NPP values were strongly affected by the phytoplankton community composition in the Indian sector of the Southern Ocean.
  • Kohei Matsuno, Atsushi Yamaguchi, Toru Hirawake, Ichiro Imai
    POLAR BIOLOGY 34 9 1349 - 1360 2011年09月 [査読有り][通常論文]
     
    A recent drastic decrease in sea ice cover area was observed in the western Arctic Ocean during summer, yet little information is available for its effect on zooplankton community. To evaluate the effect of sea ice reduction on zooplankton, we studied year-to-year changes of zooplankton community structure in the Chukchi Sea during summers of 1991, 1992 (when sea ice extended), 2007, and 2008 (when sea ice reduced). Zooplankton abundance ranged from 4,000 to 316,000 ind. m(-2) (mean: 70,000) and was greater north of Lisburne Peninsula in 2008. Zooplankton biomass ranged from 0.07 to 286 g wet mass m(-2) (mean: 36) and was greater south of Lisburne Peninsula in 2007. Cluster analysis based on zooplankton abundance showed a division of the zooplankton community into four groups. Occurrence of each group was separated geographically and interannually, and geographic distributions of each group in 1991 and 1992 were similar but those in 2007 and 2008 were shifted northward. Abundance and biomass in 2007/2008 were higher than in 1991/1992, indicating that further sea ice reduction would have a positive effect on zooplankton production (e.g. invasion of large Pacific species and temperature effects on their growth rate). The northern shift in geographic distribution of the zooplankton community in 2007/2008 indicates that sea ice reduction would have a negative effect on the zooplankton community (loss of characteristic Arctic species) in part of the Chukchi Sea. These apparently contradictory effects of sea ice reduction on zooplankton community emphasize the critical need for continued monitoring in this area.
  • Shigeto Nishino, Takashi Kikuchi, Michiyo Yamamoto-Kawai, Yusuke Kawaguchi, Toru Hirawake, Motoyo Itoh
    JOURNAL OF OCEANOGRAPHY 67 3 305 - 314 2011年06月 [査読有り][通常論文]
     
    The biological pump is a central process in the ocean carbon cycle, and is a key factor controlling atmospheric carbon dioxide (CO2). However, whether the Arctic biological pump is enhanced or reduced by the recent loss of sea ice is still unclear. We examined if the effect was dependent on ocean circulation. Melting of sea ice can both enhance and reduce the biological pump in the Arctic Ocean, depending on ocean circulation. The biological pump is reduced within the Beaufort Gyre in the Canada Basin because freshwater accumulation within the gyre limits nutrient supply from deep layers and shelves hence inhibits the growth of large-bodied phytoplankton. Conversely, the biological pump is enhanced outside the Beaufort Gyre in the western Arctic Ocean because of nutrient supply from shelves and greater light penetration, enhancing photosynthesis, caused by the sea ice loss. The biological pump could also be enhanced by sea ice loss in the Eurasian Basin, where uplifted isohaline surfaces associated with the Transpolar Drift supply nutrients upwards from deep layers. New data on nitrate uptake rates are consistent with the pattern of enhancement and reduction of the Arctic biological pump. Our estimates indicate that the enhanced biological pump can be as large as that in other oceans when the sea ice disappears. Contrary to a recent conclusion based on data from the Canada Basin alone, our study suggests that the biological CO2 drawdown is important for the Arctic Ocean carbon sink under ice-free conditions.
  • Sei-Ichi Saitoh, Robinson Mugo, I. Nyoman Radiarta, Shinsuke Asaga, Fumihiro Takahashi, Toru Hirawake, Yoichi Ishikawa, Toshiyuki Awaji, Teiji In, Shigeki Shima
    ICES JOURNAL OF MARINE SCIENCE 68 4 687 - 695 2011年03月 [査読有り][通常論文]
     
    An overview of satellite remote-sensing (SRS) operational applications in fisheries is presented, and includes two case studies illustrating the societal benefits of SRS. The first describes the use of satellite-based vessel monitoring systems (VMS) and SRS data in a skipjack tuna (Katsuwonus pelamis) fishery, including a simple algorithm for determining fishing activity from vessel speed. The second case study illustrates the application of remotely sensed information in determining the impact of climate change on site suitability for scallop (Mizuhopecten yessoensis) aquaculture. Global warming simulated according to Intergovernmental Panel on Climate Change scenarios had a significant impact on sites with the greatest suitability for scallop aquaculture. Some challenges in the field of fisheries information systems are also discussed.
  • Toru Hirawake, Shintaro Takao, Naho Horimoto, Takashi Ishimaru, Yukuya Yamaguchi, Mitsuo Fukuchi
    POLAR BIOLOGY 34 2 291 - 302 2011年02月 [査読有り][通常論文]
     
    Recent global environmental changes such as an increase in sea surface temperature (SST) are likely to impact primary productivity of phytoplankton in the Southern Ocean. However, models to estimate net primary production using satellite data use SST and uncertain estimation of chlorophyll a (chl-a) concentration. A primary productivity model for satellite ocean color data from the Southern Ocean, which is based on the light absorption coefficient of phytoplankton to reduce uncertainties of sea surface chl-a estimations and bias in optimal values of chl-a normalized productivity derived from SST, has been developed. The new model was able to estimate net primary productivity in the water column (PP(eu)) without dependency on temperature when in the range of -2 to 25 degrees C, and it explained 51% of the observed variability in PP(eu) with a root mean square error (RMSE) of 0.15. Application of the model revealed that the SST dependent model has overestimated PP(eu) in warmer waters around the Subtropical Front, and underestimated PP(eu) in colder waters poleward of the Sub-Antarctic Front. This absorption-based primary productivity model contributes to a study of the relationship among spatio-temporal variations in the physical environment, and biogeochemical cycles in the Southern Ocean.
  • A. Fujiwara, T. Hirawake, K. Suzuki, S. -I. Saitoh
    BIOGEOSCIENCES 8 12 3567 - 3580 2011年 [査読無し][通常論文]
     
    Recent ocean warming and subsequent sea ice decline resulting from climate change could affect the northward shift of the ecosystem structure in the Chukchi Sea and Bering Sea shelf region (Grebmeier et al., 2006b). The size structure of phytoplankton communities provides an index of trophic levels that is crucial to understanding the mechanisms underlying such ecosystem changes and their implications for the future. This study proposes a new ocean color algorithm for deriving this characteristic by using the region's optical properties. The size derivation model (SDM) estimates the phytoplankton size index F-L on the basis of size-fractionated chlorophyll-a (chl-a) using the light absorption coefficient of phytoplankton, a(ph)(lambda), and the backscattering coefficient of suspended particles including algae, b(bp)(lambda). F-L was defined as the ratio of algal biomass attributed to cells larger than 5 mu m to the total. It was expressed by a multiple regression model using the a(ph)(lambda) ratio, a(ph)(488)/a(ph)(555), which varies with phytoplankton pigment composition, and the spectral slope of b(bp)(lambda), gamma, which is an index of the mean suspended particle size. A validation study demonstrated that 69% of unknown data are correctly derived within F-L range of +/- 20 %. The spatial distributions of F-L for the cold August of 2006 and the warm August of 2007 were compared to examine application of the SDM to satellite remote sensing. The results suggested that phytoplankton size was responsive to changes in sea surface temperature. Further analysis of satellite-derived F-L values and other environmental factors can advance our understanding of ecosystem structure changes in the shelf region of the Chukchi and Bering Seas.
  • 小林 拓, 平譯 享, 矢吹 正教, 上田 沙也子, 長田 和雄, 塩原 匡貴, 福地 光男, コバヤシ ヒロシ, ヒラワケ トオル, ヤブキ マサタカ, ウエダ サヤコ, オサダ カズオ, シオバラ マサタカ, フクチ ミツオ, Hiroshi Kobayashi, Toru Hirawake, Masanori Yabuki, Sayako Ueda, Kazuo Osada, Masataka Shiobara, Mitsuo Fukuchi
    南極資料 54 0 465 - 473 2010年12月28日 [査読無し][通常論文]
     
    東京海洋大学「海鷹丸」の南極海研究航海において,大気エアロゾルの光学的厚さ(AOT)の観測を実施した.南極海インド洋セクターでの500 nmでのAOTは,0.02-0.12の範囲であった.南極大陸沿岸域でのAOTは比較的低く,0.02前後であった.40-60゜Sの海域では,0.1以上の値を示すことがあった.インド洋低中緯度帯でのAOTは,0.05-0.15の範囲であった.風速とAOTとに正の相関がみられたことから,南極海では光学的に海塩粒子が卓越し,風速がAOTに影響を及ぼしていると考えられる.AOTが高くなるにつれ,オングストローム指数は減少した.AOTの波長スペクトルにおいて,380 nmと870 nmのAOTはべき関数からずれる傾向がみられた.レイリーの光学的厚さの算出方法を比較したところ,ずれが大幅に改善される可能性が示された.今後,より観測精度を高めていくためには,機器定数の精度を把握するとともに,レイリーの光学的厚さの算出方法の見直しなどが必要である.Aerosol optical thickness (AOT) was measured during Antarctic research cruises of R V Umitaka-Maru. The measured AOTs at 500 nm in the Indian sector of the Antarctic Ocean ranged from 0.02 to 0.12. In Antarctic coastal waters, the AOTs were as low as around 0.05. On the other hand, the some AOTs were higher than 0.1 from 40゜S to 60゜S. In middle and low latitude regions of the Indian Ocean, the AOTs ranged from 0.05 to 0.15. The AOTs were correlated with wind speed. It is indicated that sea-salt particles, generated by wind, dominated optically and wind speed affected the AOT in the Antarctic Ocean. Angstro¨m exponent decreased with increasing AOT. In the AOT wavelength spectra, some AOTs in 380 nm and 870 nm tended to deviate from the power function. Comparing calculation methods of Rayleigh optical thickness suggested a possibility of reducing the deviations of these AOTs. In the future, accuracy check of the instrument constant and review of the calculation method of Rayleigh optical thickness are recommended to enhance the accuracy of maritime AOT measurement.
  • Fuminori Hashihama, Haruko Umeda, Chiaki Hamada, Sakae Kudoh, Toru Hirawake, Kazuhiko Satoh, Mitsuo Fukuchi, Yasuhiro Kashino
    MARINE BIOLOGY 157 10 2263 - 2278 2010年10月 [査読有り][通常論文]
     
    In high-latitude waters such as the Southern Ocean, the primary production of phytoplankton supports the ecosystem. To understand the photo-acclimation strategy of such phytoplankton within cold environments, the vertical distribution profile of photosynthetic pigments was analyzed in the Southern Ocean. Samples were taken along 110A degrees E during the austral summer, and along 150A degrees E and around the edge of the seasonal sea ice of the Antarctic Continent during the austral autumn. Pigment extraction methods were optimized for these samples. The standing crop of chlorophyll a was larger in the region along the edge of the seasonal sea ice than at sampling stations in open ocean areas. Chlorophyll concentration seemed to be dependent on the formation of thermo- and haloclines along the edge of the seasonal sea ice, but not in the open ocean where such clines are less pronounced. The marker pigments fucoxanthin and/or 19'-hexanoyloxyfucoxanthin were dominant at most sampling stations throughout the water column, while other marker pigments such as alloxanthin were quite low. This indicated that diatoms and/or haptophytes were the major phytoplankton in this area. Comparison of the relative ratio of fucoxanthin with that of 19'-hexanoyloxyfucoxanthin allowed some stations to be characterized as either diatom-dominant or haptophyte-dominant. The relative ratio of xanthophyll-cycle pigments (diadinoxanthin plus diatoxanthin) to chlorophyll a was high in surface waters and decreased gradually with depth. This suggests that near the ice edge during summer in the Southern Ocean, both diatoms and haptophytes acclimate to their light environments to protect their photosystems under high-light conditions.
  • Suguru Okamoto, Toru Hirawake, Sei-Ichi Saitoh
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 57 17-18 1608 - 1617 2010年09月 [査読有り][通常論文]
     
    Inter-annual variability in the magnitude and timing of the spring bloom was investigated for the Oyashio region (40 degrees-48 degrees N, 143 degrees E-152 degrees E) using 10 years (from 1998 to 2007) of satellite ocean-color data. Geostrophic currents were examined using satellite altimeter data. Early spring blooms ( > 1.5 mg m(-3)) occurred in early April 2001 and late March 2002. The 2001 bloom continued for one month. Late blooms occurred from mid-May 1999, early June 2004 and late April 2006, continuing for about 1 month, 8 days and 16 days, respectively. A strong bloom (4.7 mg m(-3)) also occurred in midApril 1998; however, it terminated in early May. We classified the Oyashio region based on the pattern of temporal variation of Chl-a concentration from March to June. The spatio-temporal variability in Chl-a concentration during spring was different among years. The area where Chl-a concentration was highest in April was more extensive in 2001, 2002 and 2006 than usual. In 1999, the area where Chl-a concentration was highest in May was the widest among the 10 years. Mesoscale eddies and currents with high velocity were frequently observed in the area of high Chl-a concentration east of Hokkaido, propagating Coastal Oyashio Water of low salinity and low density into the oceanic region. That strengthened stratification in the surface layer. We suggest that this seaward transfer of coastal water could be one of the important factors for phytoplankton distribution in two ways: (1) horizontal advection of water with high Chl-a concentration and (2) enhancement of stratification in the oceanic region. (C) 2010 Elsevier Ltd. All rights reserved.
  • Philippe Koubbi, Catherine Ozouf-Costaz, Anne Goarant, Masato Moteki, Percy-Alexander Hulley, Romain Causse, Agnes Dettai, Guy Duhamel, Patrice Pruvost, Eric Tavernier, Alexandra L. Post, Robin J. Beaman, Stephen R. Rintoul, Toru Hirawake, Daisuke Hirano, Takashi Ishimaru, Martin Riddle, Graham Hosie
    POLAR SCIENCE 4 2 115 - 133 2010年08月 [査読有り][通常論文]
     
    Ecoregions are defined in terms of community structure as a function of abiotic or even anthropogenic forcing. They are meso-scale structures defined as the potential habitat of a species or the predicted communities geographic extent. We assume that they can be more easily defined for long-lived species, such as benthos or neritic fish, in the marine environment. Uncertainties exist for the pelagic realm because of its higher variability, plus little is known about the meso-and bathypelagic zones. A changing environment and modification of habitats will probably drive new communities from plankton to fish or top predators. We need baseline studies, such as those of the Census of Antarctic Marine Life, and databases like SCAR-MarBIN as tools for integrating all of these observations. Our objective is to understand the biodiversity patterns in the Southern Ocean and how these might change through time. (C) 2010 Elsevier B.V. and NIPR. All rights reserved.
  • Chiba Sanae, Hirawake T, Ishizaki S, Ito S, Kamiya H, Kaeriyama M, Kuwata A, Midorikawa T, Minobe S, Okamoto S, Okazaki Y, Ono T, Saito H, Saitoh S, Sasano D, Tadokoro K, Takahashi K, Takatani Y, Watanabe Y, Watanabe Y.W, Watanuki Y, Yamamuro O, Yamashita N, Yatsu A, McKinnell S.M, Dagg M.J
    Marine ecosystems of the North Pacific Ocean, 2003-2008. [PICES Special Publication No 4.] 302 - 329 2010年 [査読有り][通常論文]
  • A. McMinn, H. Hattori, T. Hirawake, A. Iwamoto
    POLAR BIOLOGY 31 8 1011 - 1015 2008年07月 [査読無し][通常論文]
     
    Okhotsk Sea pack ice from Shiretoko in northern Hokkaido, sampled in March 2007, contained microalgal communities dominated by the centric diatoms Thalassiosira nordenskioeldi and T. punctigera. Domination by this genus is very unusual in sea ice. Communities from nearby fast ice at Saroma-ko lagoon were dominated by Detonula conferavea and Odontella aurita. Average microalgal biomass of the Okhotsk Sea pack ice (surface and bottom) was 1.59 +/- 1.09 mu g chla l(-1) and for fast ice (bottom only) at nearby Saroma-ko lagoon, 16.5 +/- 3.2 mu g l(-1) (=31.1 +/- 5.0 mg chla m(-2)). Maximum quantum yield of the Shiretoko pack ice algal communities was 0.618 +/- 0.056 with species-specific data ranging between 0.211 and 0.653. These community values are amongst the highest recorded for sea ice algae. Rapid light curves (RLC) on individual cells indicated maximum relative electron transfer rates (relETR) between 20.8 and 60.6, photosynthetic efficiency values (alpha) between 0.31 and 0.93 and onset of saturation values (E(k)) between 33 and 91 mu mol photons m(-2) s(-1). These data imply that the pack ice algal community at Shiretoko was healthy and actively photosynthesising. Maximum quantum yield of the Saroma-ko fast ice community was 0.401 +/- 0.086, with values for different species between 0.361 and 0.560. RLC data from individual Saroma-ko fast ice algal cells indicated relETR between 55.3 and 60.6, alpha values between 0.609 and 0.816 and E (k) values between 74 and 91 mu mol photons m(-2) s(-1) which are consistent with measurements in previous years.
  • HASHIHAMA Fuminori, HIRAWAKE Toru, KUDOH Sakae, KANDA Jota, FURUYA Ken, YAMAGUCHI Yukuya, ISHIMARU Takashi
    Polar Science 2 2 109 - 120 2008年06月25日 [査読無し][通常論文]
     
    We investigated the size fraction and pigment-derived class compositions of phytoplankton within the euphotic zone of the Antarctic marginal ice zone between 63.3°S and 66.5°S along the 140°E meridian on two consecutive cruises in the late austral summer and early austral autumn of 2003. We observed significant temporal and spatial variations in phytoplankton size and taxonomic composition, although chlorophyll a concentrations were generally below 1 μg l-1 during both periods. Microphytoplankton (> 20 μm), mainly diatoms, were prominent in the euphotic zone in the southernmost area around 66.5°S during late summer. In the rest of the study area during both cruises, the phytoplankton community was dominated by pico- and nano-sized populations (< 20 μm) throughout the euphotic zone. The small-size populations mostly consisted of diatoms and haptophytes, although chlorophytes were dominant in extremely cold water (-1.5°C) below the overlying warm water around 65.5°S during late summer. From late summer to early autumn, chlorophytes declined in abundance, probably due to increasing temperature within the euphotic zone (-1 to 0°C). These pico- and nano-phytoplankton-dominated populations were often accompanied by relatively high concentrations of ammonium, suggesting the active regeneration of nutrients within the small-size plankton community. © 2008 Elsevier B.V. and NIPR.
  • Tukimat Lihan, Sei-Ichi Saitoh, Takahiro Iida, Toru Hirawake, Kohji Iida
    ESTUARINE COASTAL AND SHELF SCIENCE 78 2 237 - 249 2008年06月 [査読有り][通常論文]
     
    River plumes have important effects on marine ecosystems. Variation in the extent and dispersal of river plumes is often associated with river discharge, wind characteristics and ocean circulation. The objectives of this study were to identify the Tokachi River plume by satellite, determine its relationship with river discharge and clarify its temporal and spatial dynamics. SeaWiFS multispectral satellite data (normalized water-leaving radiance: nL(w)) with 1.1 km spatial resolution were used to determine the spatial and temporal variability of the plume during 1998-2002. Supervised maximum likelihood classification using six channels of nL(w) at 412, 443, 490, 510, 555 and 670 nm with each band's spectral signature statistic was used to define classes of surface water and to estimate the plume area. Supervised maximum likelihood classification separated three to four classes of coastal water based on optical characteristics as a result of wind stress events. The satellite-observed plume area was correlated with the amount of river discharge from April to October. The plume distribution patterns were influenced by wind direction and magnitude, the occurrences of a near-shore eddy field and surface currents. Empirical orthogonal function (EOF) was used to express the spatial and temporal variability of the plume using anomalies of nL(w)(555) monthly averaged images. The first mode (44% of variance) showed the turbid plume distribution resulting from re-suspension by strong wind mixing along the coast during winter. This mode also showed the plume was distributed along-shelf direction in spring to early autumn. The second mode (17% of variance) showed spring pattern across-shelf direction. EOF analysis also explained the interannual variability of the plume signature, which might have been affected by the flow of the Oyashio Current and the occurrence of a near-shore eddy field. (C) 2007 Elsevier Ltd. All rights reserved.
  • Shigeru Aoki, Daisuke Fukai, Toru Hirawake, Shuki Ushio, Stephen R. Rintoul, Hiroshi Hasumoto, Takashi Ishimaru, Hideharu Sasaki, Takashi Kagimoto, Yoshikazu Sasai, Humio Mitsudera
    Journal of Geophysical Research: Oceans 112 5 2007年05月08日 [査読有り][通常論文]
     
    The spatial and temporal characteristics of cyclonic eddies in the Antarctic Divergence off Adélie Coast are described using repeated in situ observations between 2001 and 2003, satellite observations, and results of a high-resolution ocean general circulation model. Satellite ocean color images and altimetry clearly revealed a series of cyclonic eddies, with diameters of about 100-150 km that were separated by about 150 km in the zonal direction. The eddies are found at almost the same locations and can be traced for at least two months in the spring-summer period. Cold and fresh anomalies were found throughout the water column in the cores of the cyclonic eddies. The water properties in the core of the eddies are similar to water found over the continental slope, 150-200 km to the south. The geopotential anomaly of the cold features was smaller than the sea level anomaly detected with satellite altimetry, indicating that significant barotropic flow is associated with the eddies. The Ocean general circulation model for the Earth Simulator (OFES) reproduces a series of cyclonic eddies similar to those observed, including a significant barotropic component. In the model, the series of eddies appear to originate further west over the continental slope region with no consistent phase propagation. The combination of repeat in situ observations, remote sensing and high-resolution model results confirms the existence of persistent cyclonic eddies near 140°E and suggests the eddies play an important role in the exchange of water across the Antarctic Divergence. Copyright 2007 by the American Geophysical Union.
  • Shigeru Aoki, Daisuke Fukai, Toru Hirawake, Shuki Ushio, Stephen R. Rintoul, Hiroshi Hasumoto, Takashi Ishimaru, Hideharu Sasaki, Takashi Kagimoto, Yoshikazu Sasai, Humio Mitsudera
    Journal of Geophysical Research: Oceans 112 C5 C05019, doi:10.1029/2006JC003712  2007年05月 [査読有り][通常論文]
     
    The spatial and temporal characteristics of cyclonic eddies in the Antarctic Divergence off Adélie Coast are described using repeated in situ observations between 2001 and 2003, satellite observations, and results of a high-resolution ocean general circulation model. Satellite ocean color images and altimetry clearly revealed a series of cyclonic eddies, with diameters of about 100-150 km that were separated by about 150 km in the zonal direction. The eddies are found at almost the same locations and can be traced for at least two months in the spring-summer period. Cold and fresh anomalies were found throughout the water column in the cores of the cyclonic eddies. The water properties in the core of the eddies are similar to water found over the continental slope, 150-200 km to the south. The geopotential anomaly of the cold features was smaller than the sea level anomaly detected with satellite altimetry, indicating that significant barotropic flow is associated with the eddies. The Ocean general circulation model for the Earth Simulator (OFES) reproduces a series of cyclonic eddies similar to those observed, including a significant barotropic component. In the model, the series of eddies appear to originate further west over the continental slope region with no consistent phase propagation. The combination of repeat in situ observations, remote sensing and high-resolution model results confirms the existence of persistent cyclonic eddies near 140°E and suggests the eddies play an important role in the exchange of water across the Antarctic Divergence. Copyright 2007 by the American Geophysical Union.
  • Susanne Preunkert, Michel Legrand, Bruno Jourdin, Cyril Moulin, Sauveur Belviso, Nobue Kasamatsu, Mitsuo Fukuchi, Toru Hirawake
    Journal of Geophysical Research Atmospheres 112 6 D06306, doi:10.1029/2006JD007585  2007年03月27日 [査読有り][通常論文]
     
    A multiple year-round study of atmospheric dimethyl sulfide (DMS) (from December 1998 to April 2003) as well as sulfur-derived aerosols (methanesulfonic acid (MSA) and non-sea-salt sulfate) (from March 1991 to February 2003) was conducted at Dumont d'Urville, coastal Antarctica. The three sulfur-derived species exhibit a seasonal cycle characterized by maxima in midsummer (January). Whereas the interannual variability of winter levels remains low, a strong interannual variability is shown in summer, particularly for DMS and MSA, and to a lesser extent for non-sea-salt sulfate. Over the 1998-2003 time period, January 2002 stands out with high values for all sulfur species. These interannual variabilities of atmospheric summer levels are examined in the light of seawater chlorophyll a content derived from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data (themselves compared to field measurements made south of 60°S), oceanic DMS levels estimated from chlorophyll a SeaWiFS data, and various sea-ice indices. Copyright 2007 by the American Geophysical Union.
  • Susanne Preunkert, Michel Legrand, Bruno Jourdain, Cyril Moulin, Sauveur Belviso, Nobue Kasamatsu, Mitsuo Fukuchi, Toru Hirawake
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 112 D6 2007年03月 [査読有り][通常論文]
     
    A multiple year-round study of atmospheric dimethyl sulfide (DMS) (from December 1998 to April 2003) as well as sulfur-derived aerosols (methanesulfonic acid (MSA) and non-sea-salt sulfate) (from March 1991 to February 2003) was conducted at Dumont d'Urville, coastal Antarctica. The three sulfur-derived species exhibit a seasonal cycle characterized by maxima in midsummer (January). Whereas the interannual variability of winter levels remains low, a strong interannual variability is shown in summer, particularly for DMS and MSA, and to a lesser extent for non-sea-salt sulfate. Over the 1998-2003 time period, January 2002 stands out with high values for all sulfur species. These interannual variabilities of atmospheric summer levels are examined in the light of seawater chlorophyll a content derived from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data (themselves compared to field measurements made south of 60 degrees S), oceanic DMS levels estimated from chlorophyll a SeaWiFS data, and various sea-ice indices.
  • Distribution of Copepoda along 140°E in the Indian sector of the Southern Ocean
    Polar Bioscience 20 140 - 146 2006年 [査読無し][通常論文]
  • Unusual abundance of appendicularians in the seasonal ice zone (140°E) of the Southern Ocean
    Polar Bioscience 19 133 - 141 2006年 [査読無し][通常論文]
  • T Hirawake, S Kudoh, S Aoki, T Odate, M Fukuchi
    INTERNATIONAL JOURNAL OF REMOTE SENSING 26 10 2035 - 2044 2005年05月 [査読無し][通常論文]
     
    Inter-annual variability in chlorophyll a (ch a) and sea-ice concentration in the Antarctic Divergence (AD) region near 140 degrees E was examined using satellite sensor data in order to derive a quantitative relationship between the two. Sea-viewing Wide Field-of-view Sensor (SeaWiFS) derived chl a and Special Sensor Microwave/Imager (SSM/I) derived sea-ice concentration data during 1997-2003 were analysed. Mean chl a concentration south of 64 degrees S during the period between September and April (from austral spring to autumn) of each year was calculated. The mean chl a in 2001/2002 was extremely high (1.08 mg m(-3)) within the six periods between 1997/1998 and 2002/2003. Simply integrated indices on sea-ice amount, such as the maximum sea-ice extent in the winter season, annual integration of coverage area over ice edge to coast, were not able to explain inter-annual variation of chl a, especially the highest chl a value in 2001/2002. We found a high correlation between the chl a south of 64 degrees S and the sea-ice index, which might be due to the surface meltwater of the sea-ice from the AD zone as a result of eddies. The quantitative relationship might have contributed to the prediction of phytoplankton blooms in this coastal region and demonstrated the impact of the sea-ice extent on the Antarctic marine ecosystem.
  • A McMinn, T Hirawake, T Hamaoka, H Hattori, M Fukuchi
    JOURNAL OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM 85 2 283 - 289 2005年04月 [査読無し][通常論文]
     
    Benthic microalgal communities usually make a major contribution to the primary production of estuaries and shallow seas. Pulse amplitude modulation (PAM) fluorometry was used to investigate the contribution of benthic microalgae to the primary production of the Okhotsk Sea coast and Saroma Ko Lagoon in northern Hokkaido. In general the benthic communities had a relatively high biomass but low photosynthetic activity. This led to estimates of 29.2% and 64.5% for the benthic contributions for the 9 in and 3 m depth sites at Mombetsu and 13.1% for Saroma Ko. Sea ice algae provided the greatest contribution at Saroma Ko.
  • T Hirawake, T Odate, M Fukuchi
    GEOPHYSICAL RESEARCH LETTERS 32 5 1 - 4 2005年03月 [査読無し][通常論文]
     
    [1] The variation in the phytoplankton biomass over a decadal time scale, and its relationship with the Antarctic Circumpolar Wave (ACW) and climate change, has been poorly interpreted because of the limited satellite chlorophyll a (chl a) data compared with the physical parameters from satellite. We analyzed a long-term chl a data set along the Japanese Antarctic Research Expedition (JARE) cruise tracks since 1965 to investigate inter-annual variation of phytoplankton biomass. In the Southern Ocean, increasing trends of chl a and the spreading of higher chl a area to the north with 3-7 year cycles were found. Although relationships between the decadal change in chl a and climate change such as variation of sea ice extent and the El Nino are still obscure, large variation of primary production in proportion to the chl a is implied.
  • A simple method for estimating phytoplankton abundance using a surface seawater monitoring system off Syowa Station during austral summer
    Polar Bioscience 18 28 - 34 2005年 [査読無し][通常論文]
  • Yoriko Arai, Yoriko Arai, Toru Hirawake, Toru Hirawake, Tsuneo Odate, Tsuneo Odate, Kentaro Watanabe, Kentaro Watanabe, Mitsuo Fukuchi, Mitsuo Fukuchi
    Polar Bioscience 16 - 27 2005年01月01日 [査読無し][通常論文]
     
    We investigated the distribution of chlorophyll-a (Chl-a) and sea surface temperature (SST) off the sea ice region south of 64°S in East Antarctica between 20°E and 60°E during austral summers, 1998-2002. We used satellite multi-sensor remote sensing datasets including ocean color Chl-a, SST and sea ice concentration. High concentrations of Chl-a (>0.5 mg m-3) were generally observed in colder water below 0°C. Phytoplankton blooms were extended into shallow areas along the isobath. SST distribution exhibited two patterns. In the first pattern, warm water located to the north of this region associated with polynya in early spring. The second pattern was characterized by distribution of cold water throughout the study area. A shift of the Antarctic Circumpolar Current (ACC) is considered to affect this difference between SST distributions. The cold water from the Antarctic coastal current mixed with meltwater was expected to provide vertical stability of the water column for phytoplankton blooms. These results suggest that the phytoplankton blooms in this study area during austral summer can be attributed to water conditions affected by melting sea ice, movement of the ACC and sea floor topography. © 2005 National Institute of Polar Research.
  • T Hirawake, S Kudoh, S Aoki, Rintoul, SR
    Geophysical Research Letters 30 9 1458, doi:10.1029/2003GL016996  2003年05月 [査読無し][通常論文]
     
    [1] Eddy-like distributions of chlorophyll a were clearly detected in the Antarctic Divergence zone around 140degreesE by SeaWiFS ocean color images. The distribution was also supported by in-situ measurements. The eddy-like structure was associated with changes in surface and subsurface water mass properties. Extremely high levels of chlorophyll in coastal areas were transported and redistributed horizontally offshore by these eddies, and a significant effect of the huge biomass on the biological processes in the investigated area was expected. The lateral exchange between coastal and offshore waters driven by these eddies, may be an essential factor in the observed patchy structures in this region.
  • T Odate, T Hirawake, S Kudoh, B Klein, B LeBlanc, M Fukuchi
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 49 22-23 4947 - 4958 2002年 [査読無し][通常論文]
     
    Temperature, salinity, and in vivo fluorescence of surface seawater in the North Water were recorded continuously, using a CTD + fluorometer, in August 1997, April-July 1998 and August-October 1999. The phytoplankton bloom started in the polynya on the Greenland side in April. In April and May, high phytoplankton biomass coincided with saline water on the Greenland side, while biomass was low on the Ellesmere Island (Canada) side where a deep mixed layer prevailed. High phytoplankton biomass extended over the whole polynya in June, when surface temperature increased due to solar heating and salinity decreased due to freshwater input. The initiation of the bloom was about 2 months earlier on the Greenland than the Canadian side. In July and August, phytoplankton biomass became low in the southern survey area, indicating that the phytoplankton bloom had ended. In September, relatively saline and warm water occurred in the southeastern part of the study area where, consistent with the change in water properties, high concentrations of chlorophyll a were observed again. These results imply that both the earlier start of the algal bloom in spring and the eventual increase in phytoplankton biomass in summer contribute to the high annual primary production along the Greenland side, thus influencing the structure and biological productivity of the entire North Water ecosystem. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • Y Kashino, S Kudoh, Y Hayashi, Y Suzuki, T Odate, T Hirawake, K Satoh, M Fukuchi
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 49 22-23 5049 - 5061 2002年 [査読無し][通常論文]
     
    During the 1999 expedition of the International North Water Polynya Study in northern Baffin Bay, the photosynthetic characteristics of phytoplankton were measured using pulse-amplitude-modulated (PAM) fluorescence methods. We focused mainly on the functioning of the diadinoxanthin cycle, which was expected to be an effective protection system of photosystems from high irradiance under low temperature. In spite of the low temperature (ca. 0degreesC), the diadinoxanthin cycle was very active, as monitored by the change of non-photochemical quenching of fluorescence (NPQ). The extent of NPQ became larger when phytoplankton were exposed to higher irradiance, and seemed to be in good correlation with the total amount of diadinoxanthin plus diatoxanthin, which are responsible for the diadinoxanthin cycle. The NPQ was more active in the surface phytoplankton community than in the phytoplankton living at the bottom of the euphotic zone, which had less xanthophyll pigments. These results indicate that the diadinoxanthin cycle actively drains out excess light energy as non-radiative heat and protects photosystems under high irradiance. The active NPQ reduced the effective irradiance; the effective quantum yield of photosystem 11 became smaller under higher irradiance. Reflecting these features, the resulting rate of photosynthesis in surface phytoplankton tended to be smaller than that of phytoplankton at the bottom of the euphotic zone. The irradiance at the onset of light saturation (I-k) was generally higher than the reported values for polar phytoplankton and ice algae, probably because of the presence of a water-water cycle and/or other metabolic pathways. Our work also shows the usefulness of PAM measurements for ecological and biochemical studies of psychrophilic phytoplankton in polar regions. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • 岸野 元彰, 古谷 研, 田口 哲, 平譯 享, 鈴木 光次, 田中 昭彦
    海の研究 10 6 537 - 559 日本海洋学会 2001年11月01日 [査読無し][通常論文]
     
    海水の光吸収係数は, 海洋の基礎生産や海色リモートセンシングの研究において重要なパラメータの1つである。今まで, その測定法について多くの提案がなされてきた。本稿は, まず吸収係数の定義を明確に定義し, その海洋学における意義を述べた。引き続き, オパールグラス法, グラスファイバー法, 光音響法, 積分球法の原理を述べると共に問題点を挙げた。また, 採水処理しなくて済む現場法についてその原理と問題点をまとめた。引き続き吸収係数の組成分離法について直接分離法と実測値から求めた半理論的分離法を紹介した。最後に人工衛星によるリモートセンシングによる推定法に言及した。
  • JARE-39, 40 しらせ航路に沿った夏季南大洋インド洋区における表層水中の動物プランクトン現存量
    南極資料 45 3 279 - 296 2001年 [査読無し][通常論文]
  • 平譯 享, 鈴木 光次, 岸野 元彰, 古谷 研, 田口 哲, 齋藤 誠一, 才野 敏郎, 松本 和彦, 播本 孝史, 佐々木 宏明, 藤木 徹一, 古原 慎一, 柏 俊行
    海の研究 10 6 471 - 484 The Oceanographic Society of Japan 2001年 [査読無し][通常論文]
     
    植物プランクトンの光吸収係数は, 海洋の基礎生産や海色リモートセンシングの研究において必要不可欠なパラメータの一つである。その測定法を標準化するために開いたワークショップの成果として, 植物プランクトンの光吸収係数を測定するためのプロトコルを作成した。過去3回のワークショップにおいて, 吸収係数測定法の一つであるQFT法(Quantitative Filter Technique)を中心に, 分光光度計間の比較, 補正式の検討, 植物色素の抽出法の検討を行った。また, 現場型の水中分光吸光度計の利用についても評価を行った。それらの結果をもとに, ろ過方法, 測定方法, さらにデータ管理に至るまで, 推奨するべき方法を提言した。このプロトコルに従って植物プランクトンの光吸収係数を測定することにより, 研究者間の測定値の相互比較が容易となると考えられる。
  • Toru Hirawake, Hiroo Satoh, Takashi Ishimaru, Yukuya Yamaguchi, Motoaki Kishino
    Journal of Oceanography 56 3 245 - 260 2000年06月 [査読無し][通常論文]
     
    Both historic and currently operational chlorophyll algorithms of the satellite-borne ocean color sensors, such as SeaWiFS, were evaluated for in situ spectral radiation and chlorophyll data in some Case I waters, including the waters in the Indian Ocean sector of the Southern Ocean. Chlorophyll a concentration of the data set (n = 73) ranged from 0.04 to 1.01 mg m-3. The algorithms had higher accuracy for the low- and mid-latitude waters (RMSE: 0.163-0.253), specifically the most recently developed algorithms of OCTS and SeaWiFS showed 0.163 and 0.170 of Root Mean Square Errors, respectively. However, these algorithms had large errors (0.422-0.621) for the Southern Ocean data set and underestimated the surface chlorophyll by more than a factor of 2.6. The absorption coefficients in the blue spectral region retrieved from remote sensing reflectance varied in a nonlinear manner with chlorophyll a concentration, and the value in the Southern Ocean was significantly lower than that in the low- and mid-latitude waters for each chlorophyll a concentration. The underestimation of chlorophyll a concentration in the Southern Ocean with these algorithms was caused by the lower specific absorption coefficient in the region compared with the low- and mid-latitude waters under the same chlorophyll a concentration.
  • S Chiba, T Hirawake, S Ushio, N Horimoto, R Satoh, Y Nakajima, T Ishimaru, Y Yamaguchi
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 47 12-13 2589 - 2613 2000年 [査読無し][通常論文]
     
    suggesting the need for constructing local algorithms appropriate For Antarctic Waters. (C) 2000 Elsevier Science Ltd. All rights reserved.suggesting the need for constructing local algorithms appropriate For Antarctic Waters. (C) 2000 Elsevier Science Ltd. All rights reserved.suggesting the need for constructing local algorithms appropriate For Antarctic Waters. (C) 2000 Elsevier Science Ltd. All rights reserved.A biological/oceanographic survey was conducted around the Antarctic Divergence AD) off Adelie Land, Antarctica by the RTV Umitaka-Maru III of Tokyo University of Fisheries in the 1995/1996 Austral summer. Investigations were included (1) characteristics of oceanic structure, (2) primary production and related upper water mass structure, (3) phytoplankton community structure, (4) zooplankton community structure, (5) distribution of Antarctic krill, and (6) optical properties and development of biooptical algorithms for future use of ocean color remote sensing in monitoring phytoplankton biomass. The existence of dense water on the continental slope suggests that the survey area is one of major sources of the Antarctic Bottom Water. We observed a southward meandering of ACC, which allowed the warmer, saline offshore water to intrude south in the eastern part of the area. This east-west gradient in water mass seemed to influence the formation of the local trophic structure in the research area. In the western area, primary productivity was high, and diatoms and copepods dominated, particularly around the AD. The eastern part, however, showed low primary productivity, with a relative dominance of pico- and nanophytoplankton and high abundance of salps. Antarctic krill was distributed mostly in the south of the AD, and its biomass was low compared to previous records, both from adjacent areas and from other Antarctic regions. A biooptical algorithm obtained from this study did not agree with the conventional global algorithm,suggesting the need for constructing local algorithms appropriate for Antartic Waters.(C) 2000 Elsevier Science Ltd.All rights reserved.
  • Photosynthetic characteristics of phytoplankton off Adelie Land, Antarctica, during the austral summer
    Polar Bioscience 13 28 - 42 2000年 [査読無し][通常論文]
  • S Chiba, T Hirawake, S Ushio, N Horimoto, R Satoh, Y Nakajima, T Ishimaru, Y Yamaguchi
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 47 12-13 2589 - 2613 2000年 [査読無し][通常論文]
     
    suggesting the need for constructing local algorithms appropriate For Antarctic Waters. (C) 2000 Elsevier Science Ltd. All rights reserved.suggesting the need for constructing local algorithms appropriate For Antarctic Waters. (C) 2000 Elsevier Science Ltd. All rights reserved.suggesting the need for constructing local algorithms appropriate For Antarctic Waters. (C) 2000 Elsevier Science Ltd. All rights reserved.A biological/oceanographic survey was conducted around the Antarctic Divergence AD) off Adelie Land, Antarctica by the RTV Umitaka-Maru III of Tokyo University of Fisheries in the 1995/1996 Austral summer. Investigations were included (1) characteristics of oceanic structure, (2) primary production and related upper water mass structure, (3) phytoplankton community structure, (4) zooplankton community structure, (5) distribution of Antarctic krill, and (6) optical properties and development of biooptical algorithms for future use of ocean color remote sensing in monitoring phytoplankton biomass. The existence of dense water on the continental slope suggests that the survey area is one of major sources of the Antarctic Bottom Water. We observed a southward meandering of ACC, which allowed the warmer, saline offshore water to intrude south in the eastern part of the area. This east-west gradient in water mass seemed to influence the formation of the local trophic structure in the research area. In the western area, primary productivity was high, and diatoms and copepods dominated, particularly around the AD. The eastern part, however, showed low primary productivity, with a relative dominance of pico- and nanophytoplankton and high abundance of salps. Antarctic krill was distributed mostly in the south of the AD, and its biomass was low compared to previous records, both from adjacent areas and from other Antarctic regions. A biooptical algorithm obtained from this study did not agree with the conventional global algorithm,suggesting the need for constructing local algorithms appropriate for Antartic Waters.(C) 2000 Elsevier Science Ltd.All rights reserved.
  • Distribution of turbidity in the ROPME Sea Area
    Offshore Environment of the ROPME Sea Area after the War - related Oil Spill - Results of the 1993-4 Umitaka-Maru cruises 49 - 63 1998年 [査読無し][通常論文]
  • Primary production in the ROPME Sea Area
    Offshore Environment of the ROPME Sea Area after the War - related Oil Spill - Results of the 1993-4 Umitaka-Maru cruises 181 - 191 1998年 [査読無し][通常論文]
  • Photosynthetic characteristics and primary productivity of phytoplankton in the Arabian Sea and the Indian Ocean during the NE monsoon season
    La mer 35 4 157 - 167 1997年 [査読無し][通常論文]

書籍

  • Bio/Chemiluminescence and its Application to Photosynthesis
    Research Signpost 2005年

その他活動・業績

教育活動情報

主要な担当授業

  • 大学院共通授業科目(一般科目):自然科学・応用科学
    開講年度 : 2018年
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : 北極、地球観測、衛星リモートセンシング
  • 衛星海洋学
    開講年度 : 2018年
    課程区分 : 学士課程
    開講学部 : 水産学部
    キーワード : 地球観測衛星、リモートセンシング、海洋環境、海洋光学、クロロフィルa濃度、基礎生産、海面水温、海面高度、海上風、海面塩分、海氷
  • 海洋計測学
    開講年度 : 2018年
    課程区分 : 学士課程
    開講学部 : 水産学部
    キーワード : 電磁波,測位,電波測位,衛星測位,衛星リモートセンシング,CTD,音波,測深,音響測深,魚群探知機,ソナー,ドップラー流向流速計
  • 環境と人間
    開講年度 : 2018年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 海洋環境,海洋生態系,環境変化,プランクトン,ベントス,魚類,イカ・タコ類,鯨類,海鳥類,海獣類,海藻,衛星海洋学,生態系モデル,人間活動,地球温暖化,海洋動物の保全・保護


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