研究者データベース

鈴木 光次(スズキ コウジ)
地球環境科学研究院 地球圏科学部門 化学物質循環学分野
教授

基本情報

所属

  • 地球環境科学研究院 地球圏科学部門 化学物質循環学分野

職名

  • 教授

学位

  • 博士(理学)(名古屋大学)

ホームページURL

科研費研究者番号

  • 40283452

ORCID ID

J-Global ID

研究キーワード

  • 海洋植物プランクトン   海氷微細藻類(アイスアルジー)   一次生産   生物海洋学   海洋生物地球化学   藻類生態生理学   

研究分野

  • 環境・農学 / 環境動態解析 / 生物海洋学
  • 環境・農学 / 環境動態解析 / 海洋生物地球化学
  • ライフサイエンス / 水圏生産科学 / 一次生産

職歴

  • 2016年10月 - 現在 北海道大学 大学院地球環境科学研究院 教授
  • 2007年04月 - 2016年09月 北海道大学 大学院地球環境科学研究院 准教授
  • 2002年12月 - 2007年03月 北海道大学 大学院地球環境科学研究科 助教授
  • 2001年04月 - 2002年11月 名古屋大学 地球水循環研究センター 助手
  • 1996年04月 - 2001年03月 名古屋大学 大気水圏科学研究所 助手
  • 1993年04月 - 1996年03月 日本学術振興会 特別研究員(DC1)

所属学協会

  • American Geophysical Union   Phycological Society of America   Association for the Sciences of Limnology and Oceanography   日本海洋学会   日本分析化学会   日本地球化学会   European Geosciences Union   

研究活動情報

論文

  • Kaori Kawana, Yuzo Miyazaki, Yuko Omori, Hiroshi Tanimoto, Sara Kagami, Koji Suzuki, Youhei Yamashita, Jun Nishioka, Yange Deng, Hikari Yai, Michihiro Mochida
    Journal of Geophysical Research: Atmospheres 2022年09月23日 [査読有り]
  • Yuri Fukai, Kohei Matsuno, Amane Fujiwara, Koji Suzuki
    Frontiers in Marine Science 9 2022年09月15日 [査読有り]
     
    Diatoms form dense blooms in the Pacific Arctic region from spring to summer, supporting the unique benthic-pelagic coupling ecosystems. Although the Arctic has a severe light-limited season from autumn to winter, diatoms can proliferate in spring when sufficient light becomes available for photosynthesis. One of the crucial strategies for diatoms to survive in unfavorable growing conditions is to form resting stages. Because of enhanced primary and export production in the Pacific Arctic shelves, many viable diatom resting stages can be detected in the surface sediments. However, little is known about the photophysiological response of viable diatom cells, including resting stages, in sediments to light availability. We conducted a laboratory experiment investigating the photophysiological capabilities of the diatom cells containing resting stages using surface sediments from the Chukchi Sea shelf. As a result, diatoms grew dramatically after light exposure, and Chaetoceros socialis complex highly contributed to the enhanced diatom abundance. Their photophysiological changes were also evident from the maximum quantum efficiency (Fv/Fm) of photochemistry in photosystem II, 13C-based photosynthetic-energy (PE) parameters, diadinoxanthin (DD)-diatoxanthin (DT) pool size, and the de-epoxidation state (DES) of DD. Even after the excess light exposure suppressed the photosynthetic activity in the microalgal cells, the diatoms recovered quickly, indicating the high photophysiological plasticity to dynamic light changes. Therefore, our results suggest that diatoms in surface sediments have a high seeding potential for blooms in the Pacific Arctic shelf region.
  • Shunyan Cheung, Kailin Liu, Kendra A. Turk-Kubo, Jun Nishioka, Koji Suzuki, Michael R. Landry, Jonathan, P. Zehr, Szeki Leung, Lixia Deng, Hongbin Liu
    Limnology and Oceanography Letters 2022年07月05日 [査読有り]
  • Takako Masuda, Keisuke Inomura, Taketoshi Kodama, Takuhei Shiozaki, Satoshi Kitajima, Gabrielle Armin, Takato Matsui, Koji Suzuki, Shigenobu Takeda, Mitsuhide Sato, Ondrej Prasil, Ken Furuya
    Microbiology Spectrum 2022年06月30日 [査読有り]
     
    Crocosphaera watsonii is as a key nitrogen (N) supplier in marine ecosystems, and it has been estimated to contribute up to half of oceanic N 2 fixation. Conversely, a recent study reported that Crocosphaera can assimilate combined N and proposed that unicellular diazotrophs can be competitors with non-N 2 fixing phytoplankton for combined N.
  • Ryosuke Futsuki, Toru Hirawake, Amane Fujiwara, Hisatomo Waga, Takashi Kikuchi, Shigeto Nishino, Tomonori Isada, Koji Suzuki, Yutaka W. Watanabe
    Journal of Oceanography 2022年06月08日 [査読有り]
  • Dong Yan, Jun Nishioka, Takenobu Toyota, Koji Suzuki
    Progress in Oceanography 204 102806 - 102806 2022年06月 [査読有り]
  • Yudai Segawa, Masanobu Yamamoto, Michinobu Kuwae, Kazuyoshi Moriya, Hitoshi Suzuki, Koji Suzuki
    Journal of Geophysical Research: Biogeosciences 127 6 2022年05月27日 [査読有り]
  • Koh Yokouchi, Koji Suzuki, Takeo Horiguchi
    Journal of Phycology 2022年05月04日 [査読有り]
  • Tomonori Isada, Stanford B. Hooker, Yukiko Taniuchi, Koji Suzuki
    Journal of Oceanography 2022年02月23日 [査読有り]
  • Stanford B. Hooker, Henry F. Houskeeper, Randall N. Lind, Raphael M. Kudela, Koji Suzuki
    Remote Sensing 2022年02月23日 [査読有り]
  • Hisatomo Waga, Amane Fujiwara, Toru Hirawake, Koji Suzuki, Kazuhiro Yoshida, Hiroto Abe, Daiki Nomura
    Progress in Oceanography 201 102738 - 102738 2022年02月 [査読有り]
     
    The western subarctic Pacific and adjacent Bering Sea are recognized as one of the most productive regions supported by spring diatom bloom among the world's oceans. Yet, phytoplankton growth and photosynthesis are often suppressed during summer. Little is known about factors controlling the summer primary productivity and phytoplankton community structure in the western subarctic Pacific and the Bering Sea, especially along the Russian coast extending from the Kuril Islands to the Gulf of Anadyr. A total of 24 stations belonging to two cruises conducted in June 2014 and August 2018 was categorized into three groups using hierarchical cluster analysis for physical properties such as seawater temperature, salinity, and mixed layer depth. Based on the biogeochemical characteristics of each cluster, we defined clusters 1, 2, and 3 as bloom, post-bloom, and pre-bloom conditions, respectively. Cluster 1, observed near the Kuril Islands and the Kamchatka Peninsula, was characterized by nutrient-rich cold water that supported the predominance of diatoms. Nutrient-depleted warm waters associated with shallow mixed-layer and small diatom populations were grouped into cluster 2, distributed in the Gulf of Anadyr and near the Kamchatka Peninsula. The deepest mixed layer depth was found in cluster 3, accompanied by the low proportions of diatoms. The spatial distribution of cluster 3 showed broad geographical coverages extending from the Kuril Islands to the Aleutian Basin. Thus, this study identified the relationships between summer primary productivity, phytoplankton community composition, and environmental variables in surface waters of the subarctic Pacific along the Russian coast. Overall, the present study addressed the shortcoming of in situ data in phytoplankton communities and environmental variables in the western subarctic Pacific and the Bering Sea.
  • Zhimeng Xu, Shunyan Cheung, Hisashi Endo, Xiaomin Xia, Wenxue Wu, Bingzhang Chen, Ngai Hei Ernest Ho, Koji Suzuki, Meng Li, Hongbin Liu
    mSystems 2022年01月04日 [査読有り]
     
    Phytoplankton are diverse and abundant as primary producers in the ocean, with diversity and community compositions varying spatially. How fundamental processes (e.g., selection, dispersal, and drift) regulate their global biogeography remains to be comprehensively explored.
  • Atsushi Matsuoka, Janet W. Campbell, Stanford B. Hooker, François Steinmetz, Kazunori Ogata, Takafumi Hirata, Hiroto Higa, Victor S. Kuwahara, Tomonori Isada, Koji Suzuki, Toru Hirawake, Joji Ishizaka, Hiroshi Murakami
    Journal of Oceanography 2021年10月23日 [査読有り]
  • Koji Suzuki, Yuta Yoshino, Yuichi Nosaka, Jun Nishioka, Stanford B. Hooker, Toru Hirawake
    Progress in Oceanography 199 102692 - 102692 2021年10月22日 [査読有り]
  • Stanford B. Hooker, Henry F. Houskeeper, Randall N. Lind, Koji Suzuki
    Sensors 21 16 5384 - 5384 2021年08月09日 [査読有り]
  • Yuri Fukai, Kohei Matsuno, Amane Fujiwara, Koji Suzuki, Mindy L. Richlen, Evangeline Fachon, Donald M. Anderson
    Journal of Geophysical Research: Oceans 126 7 2021年06月17日 [査読有り]
  • Shunyan Cheung, Jonathan P. Zehr, Xiaomin Xia, Chihiro Tsurumoto, Hisashi Endo, Shin-ichiro Nakaoka, Wingkwan Mak, Koji Suzuki, Hongbin Liu
    Environmental Microbiology 2021年05月27日 [査読有り]
  • Stanford B. Hooker, Henry F. Houskeeper, Raphael M. Kudela, Atsushi Matsuoka, Koji Suzuki, Tomonori Isada
    Continental Shelf Research 219 104357 - 104357 2021年04月 [査読有り]
  • Kazuhiro Yoshida, Andreas Seger, Matthew Corkill, Petra Heil, Kristen Karsh, Andrew McMinn, Koji Suzuki
    Frontiers in Marine Science 8 2021年03月22日 [査読有り]
     
    Sea-ice algae play a crucial role in the ecology and biogeochemistry of sea-ice zones. They not only comprise the base of sea-ice ecosystems, but also seed populations of extensive ice-edge blooms during ice melt. Ice algae must rapidly acclimate to dynamic light environments, from the low light under sea ice to high light within open waters. Recently, iron (Fe) deficiency has been reported for diatoms in eastern Antarctic pack ice. Low Fe availability reduces photosynthetic plasticity, leading to reduced ice-algal primary production. We developed a low-Fe ice tank to manipulate Fe availability in sea ice. Over 20 days in the ice tank, the Antarctic ice diatom Fragilariopsis cylindrus was incubated in artificial low-Fe sea ice ([total Fe] = 20 nM) in high light (HL) and low light (LL) conditions. Melted ice was also exposed to intense light to simulate light conditions typical for melting ice in situ. When diatoms were frozen in, the maximum photochemical quantum efficiency of photosystem II (PSII), Fv/Fm, was suppressed by freezing stress. However, the diatoms maintained photosynthetic capability throughout the ice periods with a stable Fv/Fm value and increased photoprotection through non-photochemical quenching (NPQ) via photoprotective xanthophyll cycling (XC) and increased photoprotective carotenoid levels compared to pre-freeze-up. Photoprotection was more pronounced in the HL treatment due to greater light stress. However, the functional absorption cross section of PSII, σPSII, in F. cylindrus consistently increased after freezing, especially in the LL treatment (σPSII > 10 nm2 PSII–1). Our study is the first to report such a large σPSII in ice diatoms at low Fe conditions. When the melted sea ice was exposed to high light, Fv/Fm was suppressed. NPQ and XC were slightly upregulated, but not to values normally observed when Fe is not limiting, which indicates reduced photosynthetic flexibility to adapt to environmental changes during ice melt under low Fe conditions. Although ice algae can optimize their photosynthesis to sea-ice environments, chronic Fe starvation led to less flexibility of photoacclimation, particularly in low light conditions. This may have detrimental consequences for ice algal production and trophic interactions in sea-ice ecosystems if the recent reduction in sea-ice extent continues.
  • Yuzo Miyazaki, Koji Suzuki, Eri Tachibana, Youhei Yamashita, Astrid Müller, Kaori Kawana, Jun Nishioka
    Scientific Reports 10 1 2020年12月 [査読有り][通常論文]
     
    Abstract Linking the amount of organic matter (OM) in sea spray aerosols (SSAs) to biological processes in ocean surface is essential for understanding marine aerosol formation and their potential to affect cloud formation. To date, chlorophyll (Chl) a concentration has been widely used as a surrogate for surface phytoplankton biomass or productivity to predict the relative abundance of OM in SSAs (OMSSA). Here we show a new index to present OMSSA using concentrations of Chl a and chlorophyllide (Chllide) a, which is a breakdown product of Chl a and has been used as a biomarker of senescent algal cells. The index was compared with submicrometer OMSSA, based on surface seawater and aerosol samples obtained during the pre-bloom in the western subarctic Pacific. Our results showed that the OMSSA was highly correlated with this unique index, suggesting that the OMSSA was closely linked with senescent algal cells and/or cell lysis. Furthermore, the hygroscopicity parameters κ derived from water-extracted SSA samples implied a reduction in the SSA hygroscopicity with increasing senescent status of phytoplankton. The index can represent OMSSA on a timescale of a day during the pre-bloom period, which should be further examined over different oceanic regions.
  • Kazuhiro Yoshida, Hiroshi Hattori, Takenobu Toyota, Andrew McMinn, Koji Suzuki
    Polar Biology 43 11 1873 - 1885 2020年11月25日 [査読有り][通常論文]
     
    Sea ice algae, comprised mainly of diatoms, are the main primary producers in polar ecosystems, and they are generally distributed with the highest biomass at the bottom of ice. The taxonomy of ice algae has been traditionally investigated using light microscopy, but molecular techniques, including pigment analysis, have recently provided new insights into the diversity and physiology of ice algae. However, no comparative taxonomic survey has been conducted for ice algae thus far. Here, we investigated differences and similarities in (1) the diversity and (2) the photosynthetic strategies of diatom communities in sea ice and the underlying seawater of Saroma-Ko Lagoon, Hokkaido, Japan, using algal pigment signatures determined by ultra-high performance liquid chromatography, light and scanning electron microscopy and Ion Torrent next-generation sequencing techniques targeting the 18S rRNA gene (i.e., DNA barcoding). Ice algae typically possessed greater biomass (> 20-fold) and chlorophyll (Chl)abreakdown products than under-ice phytoplankton, suggesting that the ice algae formed blooms, and cell senescence and disruption could be significant mitigating factors. At the genus level, the diversity of diatoms in sea ice was higher than in under-ice seawater, although the evenness was comparable or lower in ice algae than in under-ice phytoplankton. Ice algae had a larger xanthophyll pool size and a higher ratio of photoprotective to photosynthetic pigments (11-fold and 4.5-fold higher, respectively) than under-ice phytoplankton. The results indicated that ice algae were well adapted to changes in the light regime, which could partly support their survival capability and high taxonomic diversity.
  • Kailin Liu, Koji Suzuki, Bingzhang Chen, Hongbin Liu
    Limnology and Oceanography 2020年10月19日 [査読有り][通常論文]
  • Shuji Goto, Yuya Tada, Koji Suzuki, Youhei Yamashita
    Frontiers in Microbiology 11 584419 - 584419 2020年10月15日 [査読有り][通常論文]
     
    A large part of marine dissolved organic matter (DOM) is considered to be recalcitrant DOM (RDOM) produced by marine bacteria. However, it is still unclear whether differences in bacterial species and/or physiology control the efficiency of RDOM production. Here, batch culture experiments with glucose as the sole carbon source were carried out using three model marine bacterial strains, namely, Alteromonas macleodii (Alt), Vibrio splendidus (Vib), and Phaeobacter gallaeciensis (Pha). Dissolved organic carbon (DOC) concentrations drastically decreased during the exponential growth phases of these bacteria due to the consumption of glucose. The efficiency of bacterial DOC production at the end of incubation was largely different among the strains and was higher for Vib (20%) than for the other two strains (Alt, 4%; Pha, 6%). All strains produced fluorescent DOM (FDOM), including humic-like FDOM which is considered as recalcitrant component in the ocean, even though the composition of bacterial FDOM was also different among the strains. The efficiency of humic-like FDOM production during the exponential growth phase was different among the bacterial strains; that is, Pha produced humic-like FDOM efficiently compared with the other two species. The efficiency of humic-like FDOM production with mineralization of organic matter was lower during the exponential growth phase than during the stationary phase of Alt and Pha. Four processes for the production of bacterially derived recalcitrant humic-like FDOM are suggested from this study: (1) production during active growing (in all strains), (2) production with the reutilization of bacterial DOM (Alt), (3) production with the consumption of cellular materials (Pha), and (4) release from lysis (Vib). Our results suggest that bacterial species and physiology can regulate RDOM production and accumulation in the ocean.
  • Kazuhiro Yoshida, Andreas Seger, Fraser Kennedy, Andrew McMinn, Koji Suzuki
    Journal of Phycology 56 5 1323 - 1338 2020年10月07日 [査読有り][通常論文]
     
    Sea ice algae contribute up to 25% of the primary productivity of polar seas and seed large-scale ice-edge blooms. Fluctuations in temperature, salinity, and light associated with the freeze/thaw cycle can significantly impact the photophysiology of ice-associated taxa. The effects of multiple co-stressors (i.e., freezing temperature and high brine salinity or sudden high light exposure) on the photophysiology of ice algae were investigated in a series of ice tank experiments with the polar diatomFragilariopsis cylindrusunder different light intensities. When algal cells were frozen into the ice, the maximum quantum yield of photosystem II photochemistry (PSII;F-v/F-m) decreased possibly due to the damage of PSII reaction centers and/or high brine salinity stress suppressing the reduction capacity downstream of PSII. Expression of therbcL gene was highly up-regulated, suggesting that cells initiated strategies to enhance survival upon freezing in. Algae contained within the ice-matrix displayed similar levels ofF(v)/F(m)regardless of the light treatments. Upon melting out, cells were exposed to high light (800 mu mol photons center dot m(-2) center dot s(-1)), resulting in a rapid decline inF(v)/F(m)and significant up-regulation of non-photochemical quenching (NPQ). These results suggest that ice algae employed safety valves (i.e., NPQ) to maintain their photosynthetic capability during the sudden environmental changes. Our results infer that sea ice algae are highly adaptable when exposed to multiple co-stressors and that their success can, in part, be explained by the ability to rapidly modify their photosynthetic competence - a key factor contributing to algal bloom formation in the polar seas.
  • Shunyan Cheung, Risa Nitanai, Chihiro Tsurumoto, Hisashi Endo, Shin‐ichiro Nakaoka, Wee Cheah, Jaime Färber Lorda, Xiaomin Xia, Hongbin Liu, Koji Suzuki
    Global Biogeochemical Cycles 34 9 2020年09月02日 [査読有り][通常論文]
  • Fukutaro Karu, Toru Kobari, Taiga Honma, Takeru Kanayama, Koji Suzuki, Naoki Yoshie, Gen Kume
    Fisheries Oceanography 29 5 442 - 456 2020年09月 [査読有り][通常論文]
     
    © 2020 John Wiley & Sons Ltd Many migratory fishes reproduce and recruit around the Kuroshio, and their survival of early life stages is supported by mesozooplankton. Mesozooplankton standing stocks and productivity equivalent to those on the continental shelf have been found in the Kuroshio; however, there is limited information on trophic sources and linkages to support the mesozooplankton community. Here, we evaluate mesozooplankton feeding on protists and their trophodynamics importance by removal bottle experiments in the Kuroshio of the East China (ECS-Kuroshio). Pico- and nano-autotrophs dominated chlorophyll a concentrations throughout the study sites across the continental shelf, within the Kuroshio path and in adjacent waters. Calanoid and poecilostomatoid copepods comprised more than 85% of mesozooplankton biomass. Significant mesozooplankton ingestion rates were found for nano-autotrophs based on size-fractionated chlorophyll; for haptophytes, chrysophytes, chlorophytes, and diatoms from pigment-based phytoplankton analysis; and for naked ciliates in the microzooplankton. Based on the estimates of individual carbon budgets, nano-autotrophs and naked ciliates ingested by mesozooplankton composed 39% of their food requirements, suggesting other available prey like nano-heterotrophs. These results imply that mesozooplankton ingestion in the ECS-Kuroshio has great impacts on protozoan and phytoplankton communities and their major trophic pathways are from nano-sized auto- and heterotrophs and ciliates to copepods.
  • Takeru Kanayama, Toru Kobari, Koji Suzuki, Naoki Yoshie, Taiga Honma, Fukutaro Karu, Gen Kume
    Deep Sea Research Part I: Oceanographic Research Papers 163 103337 - 103337 2020年09月 [査読有り][通常論文]
     
    © 2020 Elsevier Ltd Many foraging fishes spend their vulnerable life stages with low food availability in the oligotrophic Kuroshio. Although they are likely dependent on microbial production as their energy source, there is limited knowledge of the trophodynamics of the planktonic food web in the Kuroshio of the East China Sea (ECS-Kuroshio). Here, we demonstrate energy sources and feeding impacts of microzooplankton on the phytoplankton community based on size-fractionated dilution experiments in the ECS-Kuroshio. Naked ciliates were the most predominant among micro-sized heterotrophs biomass throughout the study area. Pico- to nano-phytoplankton such as Prochlorococcus and haptophytes contributed to total chlorophyll a concentrations. The apparent growth rates in non-diluted bottles without nutrient enrichment were significantly negative for Prochlorococcus and haptophytes. Microzooplankton grazing rates were higher for nano-phytoplankton (0.17–1.45 d−1) compared with those for pico- (0.18–1.23 d−1) and micro-phytoplankton (0.06–0.92 d−1). The community grazing impacts accounted for up to 122% of primary production. These results suggest that one major pathway at lower trophic levels in the ECS-Kuroshio is from pico- and nano-phytoplankton to microzooplankton. This pathway could support energy transfer to higher trophic levels through food resources of mesozooplankton and fish larvae.
  • Dong Yan, Kazuhiro Yoshida, Jun Nishioka, Masato Ito, Takenobu Toyota, Koji Suzuki
    Frontiers in Marine Science 7 2020年07月24日 [査読有り][通常論文]
  • Yingshun Cui, Shu-Kuan Wong, Ryo Kaneko, Ayako Mouri, Yuya Tada, Ippei Nagao, Seong-Jun Chun, Hyung-Gwan Lee, Chi-Yong Ahn, Hee-Mock Oh, Yuki Sato-Takabe, Koji Suzuki, Hideki Fukuda, Toshi Nagata, Kazuhiro Kogure, Koji Hamasaki
    Frontiers in Microbiology 11 2020年07月13日 [査読有り][通常論文]
  • Sohiko Kameyama, Maki Otomaru, Andrew McMinn, Koji Suzuki
    Journal of Phycology 2020年06月05日 [査読有り][通常論文]
  • Shintaro Takao, Shin-Ichiro Nakaoka, Fuminori Hashihama, Keishi Shimada, Hisayuki Yoshikawa-Inoue, Toru Hirawake, Jota Kanda, Gen Hashida, Koji Suzuki
    Deep Sea Research Part I: Oceanographic Research Papers 160 103263 - 103263 2020年06月 [査読有り][通常論文]
     
    The Southern Ocean is a vast net sink for atmospheric carbon dioxide (CO2), with marine phytoplankton playing a crucial role in CO2 fixation. We assessed how changes in the dominant phytoplankton community and net primary productivity (NPP) affected variations in the partial pressure of CO2 in surface water (pCO(2)(sw)) in the Indian sector of the Southern Ocean during austral summer. pCO2sw was negatively correlated with total phytoplankton and diatom abundances, as estimated from pigment signatures, in the zone south of the Antarctic Circumpolar Current; however, pCO(2)(sw) was not correlated with haptophyte abundance. Additionally, a stronger correlation was found between pCO(2)(sw) and total phytoplankton NPP than between chlorophyll a concentration and pCO(2)(sw). We reconstructed pCO(2)(sw) at inter-annual scale using satellite data and assessed the inter-annual variability of air-sea CO2 flux. Over the period from 1997 to 2007, the integrated CO2 fluxes over the study region showed very large variations from a small source to a strong sink. Variations in the integrated CO2 fluxes were also correlated with changes in satellite-derived phytoplankton community in the Indian sector of the Southern Ocean and changes in the dominant phytoplankton community may control CO2 dynamics in the marginal ice zone.
  • Toru Kobari, Taiga Honma, Daisuke Hasegawa, Naoki Yoshie, Eisuke Tsutsumi, Takeshi Matsuno, Takeyoshi Nagai, Takeru Kanayama, Fukutaro Karu, Koji Suzuki, Takahiro Tanaka, Xinyu Guo, Gen Kume, Ayako Nishina, Hirohiko Nakamura
    Biogeosciences 17 9 2441 - 2452 2020年05月06日 [査読有り][通常論文]
     
    The Kuroshio Current has been thought to be biologically unproductive because of its oligotrophic conditions and low plankton standing stocks. Even though vulnerable life stages of major foraging fishes risk being entrapped by frontal eddies and meanders and encountering low food availability, they have life cycle strategies that include growing and recruiting around the Kuroshio Current. Here we report that phytoplankton growth and consumption by microzooplankton are stimulated by turbulent nitrate flux amplified by the Kuroshio Current. Oceanographic observations demonstrate that the Kuroshio Current topographically enhances significant turbulent mixing and nitrate influx to the euphotic zone. Graduated nutrient enrichment experiments show that growth rates of phytoplankton and microheterotroph communities were stimulated within the range of the turbulent nitrate flux. Results of dilution experiments imply significant microzooplankton grazing on phytoplankton. We propose that these rapid and systematic trophodynamics enhance biological productivity in the Kuroshio.
  • Kazuhiro Yoshida, Suzu Nakamura, Jun Nishioka, Stanford B. Hooker, Koji Suzuki
    Journal of Geophysical Research: Biogeosciences 125 3 2020年03月11日 [査読有り][通常論文]
  • Stanford B. Hooker, Atsushi Matsuoka, Raphael M. Kudela, Youhei Yamashita, Koji Suzuki, Henry F. Houskeeper
    Biogeosciences 17 2 475 - 497 2020年01月30日 [査読有り][通常論文]
     
    Abstract. This study establishes an optical inversion scheme for deriving the absorption coefficient of colored (or chromophoric, depending on the literature) dissolved organic material (CDOM) at the 440 nm wavelength, which can be applied to global water masses with near-equal efficacy. The approach uses a ratio of diffuse attenuation coefficient spectral end-members, i.e., a short- and long-wavelength pair. The global perspective is established by sampling “extremely” clear water plus a generalized extent in turbidity and optical properties that each span 3 decades of dynamic range. A unique data set was collected in oceanic, coastal, and inland waters (as shallow as 0.6 m) from the North Pacific Ocean, the Arctic Ocean, Hawaii, Japan, Puerto Rico, and the western coast of the United States. The data were partitioned using subjective categorizations to define a validation quality subset of conservative water masses (i.e., the inflow and outflow of properties constrain the range in the gradient of a constituent) plus 15 subcategories of more complex water masses that were not necessarily evolving conservatively. The dependence on optical complexity was confirmed with an objective methodology based on a cluster analysis technique. The latter defined five distinct classes with validation quality data present in all classes, but which also decreased in percent composition as a function of increasing class number and optical complexity. Four algorithms based on different validation quality end-members were validated with accuracies of 1.2 %–6.2 %, wherein pairs with the largest spectral span were most accurate. Although algorithm accuracy decreased with the inclusion of more subcategories containing nonconservative water masses, changes to the algorithm fit were small when a preponderance of subcategories were included. The high accuracy for all end-member algorithms was the result of data acquisition and data processing improvements, e.g., increased vertical sampling resolution to less than 1 mm (with pressure transducer precision of 0.03–0.08 mm) and a boundary constraint to mitigate wave-focusing effects, respectively. An independent evaluation with a historical database confirmed the consistency of the algorithmic approach and its application to quality assurance, e.g., to flag data outside expected ranges, identify suspect spectra, and objectively determine the in-water extrapolation interval by converging agreement for all applicable end-member algorithms. The legacy data exhibit degraded performance (as 44 % uncertainty) due to a lack of high-quality near-surface observations, especially for clear waters wherein wave-focusing effects are problematic. The novel optical approach allows the in situ estimation of an in-water constituent in keeping with the accuracy obtained in the laboratory.
  • 野坂裕一, 鈴木光次
    日本プランクトン学会報 67 1 - 18 2020年01月 [査読有り][通常論文]
  • Shunyan Cheung, Koji Suzuki, Xiaomin Xia, Hongbin Liu
    Journal of Geophysical Research: Biogeosciences 124 9 2680 - 2693 2019年09月 [査読有り][通常論文]
  • Dong Yan, Hisashi Endo, Koji Suzuki
    Journal of Phycology 55 3 700 - 713 2019年06月09日 [査読有り][通常論文]
  • Okazaki, Y, H. Miyamoto, K. Suzuki, H. Saito, K. Hidaka, T. Ichikawa
    Kuroshio Current: Physical, Biogeochemical, and Ecosystem Dynamics 245 - 256 2019年04月 [査読有り][通常論文]
  • Endo, H, K. Suzuki
    Kuroshio Current: : Physical, Biogeochemical, and Ecosystem Dynamics 207 - 221 2019年04月 [査読有り][通常論文]
  • Isada, T., Hattori-Saito, A., Saito, H., Kondo, Y., Nishioka, J., Kuma, K., Hattori, H., McKay, R. M. L., Suzuki, K.
    Limnology and Oceanography 64 1 197 - 216 2019年 [査読有り][通常論文]
  • Xia, X., Cheung, S., Endo, H., Suzuki, K., Liu, H.
    Microb Ecol 77 2 333 - 342 2019年 [査読有り][通常論文]
  • Iizuka, Yoshinori, Miyamoto, Chihiro, Matoba, Sumito, Iwahana, Go, Horiuchi, Kazuho, Takahashi, Yoshio, Kanna, Naoya, Suzuki, Koji, Ohno, Hiroshi
    Earth and Planetary Science Letters 515 58 - 66 2019年 [査読有り][通常論文]
     
    © 2019 Elsevier B.V. For atmospheric gases and aerosols, snow and ice provide a useful archive of paleoenvironmental history. In the northern hemisphere, this archive has been largely limited to Greenland ice, but promising pioneering work has been done recently using chronology of an ice wedge in Barrow, northern Alaska. Here, we investigate past aerosols at the same ice-wedge sampling site, reconstructing the sea-ice fluctuations in the adjacent Beaufort Sea during the Bølling/Allerød (BA) and Younger Dryas (YD) periods. We confirm the integrity of methanesulfonate ion (MS − ) concentrations in the BIWS as marine proxies, and then find that the ice wedge has a high MS − concentration through the beginning (coldest) YD periods. The high MS − concentration indicates that even during the coldest YD periods (12,900–12,700 yrBP), the near-shore region in the Alaskan Beaufort Sea near Barrow may not have been completely filled by permanent sea ice.
  • Yuzo Miyazaki, Youhei Yamashita, Kaori Kawana, Eri Tachibana, Sara Kagami, Michihiro Mochida, Koji Suzuki, Jun Nishioka
    Scientific Reports 8 1 2018年12月 [査読有り][通常論文]
  • Hisashi Endo, Hiroyuki Ogata, Koji Suzuki
    Scientific Reports 8 1 10916  2018年12月 [査読有り][通常論文]
  • Mizuno, Yu, Nishioka, Jun, Tanaka, Takahiro, Tada, Yuya, Suzuki, Koji, Tsuzuki, Yuta, Sugimoto, Atsuko, Yamashita, Youhei
    Journal of Oceanography 74 5 1 - 13 2018年 [査読有り][通常論文]
     
    Coastal Oyashio Water (COW), defined as a water mass with a temperature lower than 2 °C and a salinity lower than 33.0, is distributed in the North Pacific Ocean off southeastern Hokkaido, Japan, from winter to spring. COW is rich in macronutrients and dissolved iron and is thus considered to affect the spring phytoplankton blooms in the Oyashio region. Although river water and sea-ice melt water have been considered freshwater end-members of COW, the contributions of these freshwater sources to COW have not been well described. In this study, the humic-like components in dissolved organic matter were first applied as a parameter to evaluate the freshwater end-members of COW in March 2015. Linear regressions with negative slopes were determined between the humic-like components and the salinity of COW. The intercepts of the regressions against the humic-like components were within the ranges of those observed for the local rivers of Hokkaido but were very different from those of sea ice. These findings suggest that river water contributed to the COW observed here as a freshwater end-member, although the contribution of sea-ice melt water to COW could not be evaluated. This novel approach also highlighted two different less-saline water masses in COW. The first was characterized by a lower temperature and relatively high levels of humic-like components, while the second was higher in temperature and had higher levels of humic-like components. It is suggested that these different characteristics are due to the contributions of water from different rivers and/or different effects of sea-ice melt water.
  • Yoshida, Kazuhiro, Endo, Hisashi, Lawrenz, Evelyn, Isada, Tomonori, Hooker, Stanford B., Prášil, Ondřej, Suzuki, Koji
    Estuarine, Coastal and Shelf Science 212 80 - 94 2018年 [査読有り][通常論文]
     
    Globally, the western subarctic Pacific is known as the region with the largest seasonal drawdown in the partial pressure of CO2 due to biological activity, i.e., high spring primary production and particulate organic carbon flux. These distinctive features are mainly caused by intense spring diatom blooms in coastal Oyashio (COY) and Oyashio (OY) waters. Although phytoplankton assemblages in OY waters are rather well studied, little is known about COY waters. In this study, photophysiological properties and phytoplankton community composition in COY waters were investigated during the pre-bloom and bloom periods from March to April 2015. Next-generation sequencing targeting the 18S rRNA gene revealed that the diatom Thalassiosira generally dominated the phytoplankton community and showed distinct differences in the diatom communities in shelf and offshore waters of the COY. Additionally, the relative contribution of Thalassiosira to the total diatom assemblages showed a positive correlation with maximum photosynthetic rates (P-max(B)) occurring throughout this study. Chlorophyll a concentration and primary productivity were also positively correlated with sea surface temperature, suggesting that temperature was a critical factor for bloom development. Short-term on-deck incubation experiments were carried out to examine the role of temperature in determining planktonic photosynthetic processes. Our results showed an increase in P-max(B) with rising temperature in assemblages from the shelf COY waters. Similarly, transcription levels of the diatom-specific rbcL gene, which encodes the large subunit of RuBisCO, also increased with rising temperature in the shelf assemblages. In contrast, temperature had little effect on the maximum photochemical quantum efficiency (F-v/F-m) of photosystem II. The results suggested that the transcription activity of the diatom-specific rbcL gene was upregulated by the increase in temperature, and that led to the higher P-max(B) values and the spring diatom bloom in the shelf COY region.
  • Fujiwara, Amane, Nishino, Shigeto, Matsuno, Kohei, Onodera, Jonaotaro, Kawaguchi, Yusuke, Hirawake, Toru, Suzuki, Koji, Inoue, Jun, Kikuchi, Takashi
    Polar Biology 41 6 1279 - 1295 2018年 [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.
  • Nagao, Ippei, Eum, Young-Joon, Iwamoto, Yoko, Tada, Yuya, Suzuki, Koji, Tsuda, Atsushi, Toratani, Mitsuhiro, Hamasaki, Koji, Uematsu, Mitsuo
    Progress in Oceanography 165 145 - 157 2018年 [査読有り][通常論文]
     
    The distributions of seawater dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) in and around a phytoplankton bloom off the east coast of northern Japan were investigated using seawater samples collected at ten stations from 14 to 28 April 2007. The seawater samples were collected from the sea surface to a depth of 100 m at each station, and the concentrations of particulate DMSP (DMSPp), DMS, chlorophyll a (Chl a), phytoplankton pigments, nutrients and suspended particulate matter were measured on board the R/V Tansei-maru (KT-07-7). The stations belonged to three water masses: the Tsugaru warm current water system (TW), the Oyashio water system (OW) and the Kuroshio water system (KW). Differences in the seawater parameters were observed among these water masses. At OW stations, an intensive phytoplankton bloom mainly consisted of large diatoms and characterized by high concentrations in Chl a, DMSP and DMS was observed. In addition, differences in DMSPp and DMS concentrations at OW stations could be attributed to differences in bloom stage. At KW stations, although Chl a was low, high DMSPp and DMS concentrations were observed at Stn 11 in this water mass, presumably due to the presence of high DMSP producers such as prymnesiophytes. At TW stations, several low DMSP producers were relatively abundant, resulting in low DMSPp and DMS concentrations. Using these data obtained from ten stations located in these three water masses, the relationship between DMS and Chl a/mixed layer depth (MLD) were tested for six MLD criteria. The best relationship was obtained when the same criteria of MLD as being adopted by Simo and Dachs (2002). Then, we proposed the new Fp ratios representing the fractions of high and low DMSP producers among phytoplankton to predict the DMSPp: Chl a ratio, and our results showed an improvement when comparing with the results using the traditional Fp ratio.
  • Kataoka, T., Suzuki, K., Irino, T., Yamamoto, M., Higashi, S., Liu, H.
    Arch Microbiol 200 2 329 - 342 2018年 [査読有り][通常論文]
     
    Microbial nitrification is a key process in the nitrogen cycle in the continental shelf ecosystems. The genotype compositions and abundance of the ammonia monooxygenase gene, amoA, derived from ammonia-oxidizing archaea (AOA) and bacteria (AOB) in two size fractions (2–10 and 0.2–2 µm), were investigated in the East China Sea (ECS) in May 2008 using PCR-denaturing gradient gel electrophoresis (DGGE) and quantitative PCR (qPCR). Four sites were selected across the continental shelf edge: continental shelf water (CSW), Kuroshio branch water (KBW), transition between CSW and KBW (TCSKB) and coastal KBW (CKBW). The gene copy numbers of AOA-amoA were higher than those of AOB-amoA in ECS. The relative abundance of amoA to the total 16S rRNA gene level reached approximately 15% in KBW and CKBW for the free-living fraction of AOA, whereas the level was less than 0.01% throughout ECS for the AOB. A cluster analysis of the AOA-amoA-DGGE band pattern showed distinct genotype compositions in CSW in both the size fractions and in the surface of the TCSKB and KBW. Sequences of the DGGE bands were assigned to two clades. One of the clades exclusively consisted of sequences derived from the 2–10-µm fraction. This study revealed that AOA-amoA abundance dominated over AOB-amoA throughout the ECS, whereas the genotype composition of AOA-amoA were distributed heterogeneously across the water masses. Additionally, this is the first report showing the distribution of AOA-amoA genotypes characteristic to particle-associated AOA in the offshore of the East China Sea.
  • Li, Yingdong, Jing, Hongmei, Xia, Xiaomin, Cheung, Shunyan, Suzuki, Koji, Liu, Hongbin
    Frontiers in Microbiology 9 2018年 [査読有り][通常論文]
     
    The composition and metabolic functions of prokaryotic communities in the western subarctic Pacific (WSP), where strong mixing of waters from the Sea of Okhotsk and the East Kamchatka Current result in transfer to the Oyashio Current, were investigated using a shotgun metagenome sequencing approach. Functional metabolic genes related to nutrient cycling of nitrogen, sulfur, carbohydrates, iron and amino acids were differently distributed between the surface and deep waters of the WSP. Genes related to nitrogen metabolism were mainly found in deep waters, where Thaumarchaeaota, Sphingomonadales, and Pseudomonadales were closely associated and performing important roles in ammonia oxidation, assimilatory nitrate reduction, and dissimilatory nitrate reduction processes, respectively. In addition, orders affiliated to Spingobacteria and Alphaproteobacteria were crucial for sulfate reduction and abundant at 3000 m, whereas orders affiliated to Gammaproteobacteria, which harbored the most sulfate reduction genes, were abundant at 1000 m. Additionally, when compared with the East Kamchatka Current, the prokaryotes in the Oyashio Current were likely to consume more energy for synthesizing cellular components. Also, genes encoding iron transport and siderophore biosynthesis proteins were in low abundance, indicating that the iron was not a limiting factor in the Oyashio current. In contrast, in the East Kamchatka Current, prokaryotes were more likely to directly utilize the amino acids and absorb iron from the environment. Overall, our data indicated that the transformation from the East Kamchatka Current to the Oyashio Current reshapes not only the composition of microbial community, but also the function of the metabolic processes. These results extended our knowledge of the microbial composition and potential metabolism in the WSP.
  • 衛星による海洋基礎生産力の推定
    平譯享, 高尾信太郎, 鈴木光次, 西岡純, 渡邉豊, 伊佐田智規
    海の研究 26 65 - 77 2017年05月 [査読有り][通常論文]
  • Koji Sugie, Koji Suzuki
    Limnology and Oceanography 62 3 884 - 897 2017年05月01日 [査読有り][通常論文]
     
    The diversity, biogeography, and size distribution of diatoms in the North Pacific and underlying mechanisms shaping those patterns have little been characterized despite their importance in marine ecosystems. Here, we examined the community structure of diatoms in the surface and subsurface chlorophyll a maximum (SCM) layers of the North Pacific using light and scanning electron microscopy. Diatom carbon biomass in both the subarctic and temperate coastal regions was higher than that in the open subtropical and tropical waters. Species density was high in the temperate coastal region and certain open ocean stations where coastal water could be intruded. Diversity was generally higher in the SCM layer than that in the surface layer without a clear latitudinal trend. All diatom species in the open subtropical waters were observed in the temperate coastal waters, suggesting that the coastal regions act as a species bank. Certain indigenous species in the subarctic waters were considered as cryophilic species. We found that the general patterns of the size spectrum were nearly identical among different geographical regions of the North Pacific, irrespective of the species composition, environmental conditions, and seasonality. Our results provide mechanistic insights indicating that the diatom biodiversity in the species bank around the coastal region and the following current systems from the coastal to oceanic regions could principally determine biodiversity patterns in the North Pacific. The species-specific ecophysiological traits of diatoms and environmental conditions may further modify the biodiversity patterns and size distribution of diatoms.
  • Cheung, S., Suzuki, K., Saito, H., Umezawa, Y., Xia, X., Liu, H.
    PLoS One 12 10 e0186875  2017年 [査読有り][通常論文]
     
    In this study, we used 454-pyrosequencing to report the highly diverse diazotroph communities in the Kuroshio and its adjacent waters along a transect across the Tokara Strait, Japan. Terrestrial input from the islands resulted in a highly heterogeneous diazotroph community within a relatively small geographic region, which was presumably caused by the remarkably different responses of UCYN-A2, UCYN-C and Trichodesmium to the steep environmental gradient. On the other hand, most major cyanobacterial OTUs found in this study were also detected in an unpublished dataset from the upstream Kuroshio, which suggests transportation of diazotrophs by the Kuroshio in large geographic scale. A significant amount of UCYN-C was found in the Kuroshio and offshore stations, suggesting the importance of this potentially overlooked group in the western North Pacific Ocean (WNPO). Moreover, a novel sublineage of UCYN-B was defined, which was predominant in an oligo-trophic water sample; and it was also found to be widely distributed in oceanic waters. In addition, the apparent increase in relative abundance of UCYN-A2 from offshore to near-shore water provides evidence for the earlier and under-debating view that UCYN-A2 prefers coastal conditions. Our report provides new knowledge for understanding the phylogeny and ecology of unicellular cyanobacterial diazotrophs in WNPO.
  • Endo, Hisashi, Hattori, Hiroshi, Mishima, Tsubasa, Hashida, Gen, Sasaki, Hiroshi, Nishioka, Jun, Suzuki, Koji
    Polar Biology 40 11 2143 - 2159 2017年 [査読有り][通常論文]
     
    The ongoing rise in atmospheric CO2 concentration is causing rapid increases in seawater pCO(2) levels. However, little is known about the potential impacts of elevated CO2 availability on the phytoplankton assemblages in the Southern Ocean's oceanic regions. Therefore, we conducted four incubation experiments using surface seawater collected from the subantarctic zone (SAZ) and the subpolar zone (SPZ) in the Australian sector of the Southern Ocean during the austral summer of 2011-2012. For incubations, FeCl3 solutions were added to reduce iron (Fe) limitation for phytoplankton growth. Ambient and high (similar to 750 mu atm) CO2 treatments were then prepared with and without addition of CO2-saturated seawater, respectively. Non-Fe-added (control) treatments were also prepared to assess the effects of Fe enrichment (overall, control, Fe-added, and Fe-and-CO2-added treatments). In the initial samples, the dominant phytoplankton taxa shifted with latitude from haptophytes to diatoms, likely reflecting silicate availability in the water. Under Fe-enriched conditions, increased CO2 level significantly reduced the accumulation of biomarker pigments in haptophytes in the SAZ and AZ, whereas a significant decrease in diatom markers was only detected in the SAZ. The CO2-related changes in phytoplankton community composition were greater in the SAZ, most likely due to the decrease in coccolithophore biomass. Our results suggest that an increase in CO2, if it coincides with Fe enrichment, could differentially affect the phytoplankton community composition in different geographical regions of the Southern Ocean, depending on the locally dominant taxa and environmental conditions.
  • Goto, S., Tada, Y., Suzuki, K., Yamashita, Y.
    Front Microbiol 8 507 - 507 2017年 [査読有り][通常論文]
     
    The recalcitrant fraction of marine dissolved organic matter (DOM) plays an important role in carbon storage on the earth's surface. Bacterial production of recalcitrant DOM (RDOM) has been proposed as a carbon sequestration process. It is still unclear whether bacterial physiology can affect RDOM production. In this study, we conducted a batch culture using the marine bacterial isolate Alteromonas macleodii, a ubiquitous gammaproteobacterium, to evaluate the linkage between bacterial growth and DOM production. Glucose (1 mmol C L-1) was used as the sole carbon source, and the bacterial number, the DOM concentration in terms of carbon, and the excitationemission matrices (EEMs) of DOM were monitored during the 168-h incubation. The incubation period was partitioned into the exponential growth (0-24 h) and stationary phases (24-168 h) based on the growth curve. Although the DOM concentration decreased during the exponential growth phase due to glucose consumption, it remained stable during the stationary phase, corresponding to approximately 4% of the initial glucose in terms of carbon. Distinct fluorophores were not evident in the EEMs at the beginning of the incubation, but DOM produced by the strain exhibited five fluorescent peaks during exponential growth. Two fluorescent peaks were similar to protein-like fluorophores, while the others could be categorized as humiclike fluorophores. All fluorophores increased during the exponential growth phase. The tryptophan-like fluorophore decreased during the stationary phase, suggesting that the strain reused the large exopolymer. The tyrosine-like fluorophore seemed to be stable during the stationary phase, implying that the production of tyrosine containing small peptides through the degradation of exopolymers was correlated with the reutilization of the tyrosine-like fluorophore. Two humic-like fluorophores that showed emission maxima at the longer wavelength (525 nm) increased during the stationary phase, while the other humic-like fluorophore, which had a shorter emission wavelength (400 nm) and was categorized as recalcitrant, was stable. These humic-like fluorophore behaviors during incubation indicated that the composition of bacterial humic-like fluorophores, which were unavailable to the strain, differed between growth phases. Our results suggest that bacterial physiology can affect RDOM production and accumulation in the ocean interior.
  • Xia, X., Partensky, F., Garczarek, L., Suzuki, K., Guo, C., Yan Cheung, S., Liu, H.
    Environ Microbiol 19 1 142 - 158 2017年 [査読有り][通常論文]
     
    The widespread unicellular cyanobacteria Synechococcus are major contributors to global marine primary production. Here, we report their abundance, phylogenetic diversity (as assessed using the RNA polymerase gamma subunit gene rpoC1) and pigment diversity (as indirectly assessed using the laterally transferred cpeBA genes, encoding phycoerythrin-I) in surface waters of the northwestern Pacific Ocean, sampled over nine distinct cruises (2008-2015). Abundance of Synechococcus was low in the subarctic ocean and South China Sea, intermediate in the western subtropical Pacific Ocean, and the highest in the Japan and East China seas. Clades I and II were by far the most abundant Synechococcus lineages, the former dominating in temperate cold waters and the latter in (sub)tropical waters. Clades III and VI were also fairly abundant in warm waters, but with a narrower distribution than clade II. One type of chromatic acclimater (3dA) largely dominated the Synechococcus communities in the subarctic ocean, while another (3dB) and/or cells with a fixed high phycourobilin to phycoerythrobilin ratio (pigment type 3c) predominated at mid and low latitudes. Altogether, our results suggest that the variety of pigment content found in most Synechococcus clades considerably extends the niches that they can colonize and therefore the whole genus habitat.
  • Isada, Tomonori, Hirawake, Toru, Nakada, Satoshi, Kobayashi, Tsukuru, Sasaki, Ken'ichi, Tanaka, Yoshiyuki, Watanabe, Shuichi, Suzuki, Koji, Saitoh, Sei-Ichi
    Estuarine, Coastal and Shelf Science 188 199 - 211 2017年 [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.
  • Jing, Hongmei, Cheung, Shunyan, Xia, Xiaomin, Suzuki, Koji, Nishioka, Jun, Liu, Hongbin
    Frontiers in Microbiology 8 2017年 [査読有り][通常論文]
     
    Community composition and abundance of ammonia-oxidizing archaea (AOA) in the ocean were affected by different physicochemical conditions, but their responses to physical barriers (such as a chain of islands) were largely unknown. In our study, geographic distribution of the AOA from the surface photic zone to the deep bathypelagic waters in the western subarctic Pacific adjacent to the Kuril Islands was investigated using pyrosequencing based on the ammonia monooxygenase subunit A (amoA) gene. Genotypes of clusters A and B dominated in the upper euphotic zone and the deep waters, respectively. Quantitative PCR assays revealed that the occurrence and ammonia-oxidizing activity of ammonia-oxidizing archaea (AOA) reached their maxima at the depth of 200 m, where a higher diversity and abundance of actively transcribed AOA was observed at the station located in the marginal sea exposed to more terrestrial input. Similar community composition of AOA observed at the two stations adjacent to the Kuril Islands maybe due to water exchange across the Bussol Strait. They distinct from the station located in the western subarctic gyre, where sub-cluster WCAII had a specific distribution in the surface water, and this sub-cluster seemed having a confined distribution in the western Pacific. Habitat-specific groupings of different WCB sub-clusters were observed reflecting the isolated microevolution existed in cluster WCB. The effect of the Kuril Islands on the phylogenetic composition of AOA between the Sea of Okhotsk and the western subarctic Pacific is not obvious, possibly because our sampling stations are near to the Bussol Strait, the main gateway through which water is exchanged between the Sea of Okhotsk and the Pacific. The vertical and horizontal distribution patterns of AOA communities among stations along the Kuril Islands were essentially determined by the in situ prevailing physicochemical gradients along the two dimensions.
  • Nosaka, Yuichi, Yamashita, Youhei, Suzuki, Koji
    Frontiers in Marine Science 4 2017年 [査読有り][通常論文]
     
    The seasonal biological drawdown of the partial pressure of CO2 (pCO2) in the surface waters of the Oyashio region of the western subarctic Pacific is one of the greatest among the world's oceans. This is attributable to spring diatom blooms. Transparent exopolymer particles (TEPs) are known to affect efficiency of the biological carbon pump, and higher TEP levels are frequently associated with massive diatom blooms. However, TEP dynamics in the Oyashio region remain unclear. We investigated the TEP distribution from three cruises during the spring diatom bloom periods in 2010 and 2011. TEP concentrations varied from < 15 to 196 ± 71 μg xanthan gum equiv. L-1 above 300 m and generally declined with depth. Vertical TEP concentrations were significantly related not only to chlorophyll a concentrations but also to bacterial abundance. Average TEP concentrations within the mixed layer (> 30 m) were significantly higher during the bloom (155 ± 12 μg xanthan gum equiv. L-1) than in the post-bloom phase (90 ± 32 μg xanthan gum equiv. L-1). In contrast, bacteria abundance within the mixed layer changed little during the bloom to post-bloom phases. These results suggest that the abundance of phytoplankton greatly contributed to dynamics of the TEP distribution. To evaluate the ability of the phytoplankton to produce TEP, an axenic strain of the diatom Thalassiosira nordenskioeldii, which is a representative species of Oyashio blooms, was examined within a batch culture system. Cell abundance-normalized TEP and dissolved organic carbon (DOC) production rates changed simultaneously with growth of the strain. Although these production rates were significantly higher in the stationary phase than in the exponential growth period, values of the TEP/DOC ratio changed little throughout incubation. These findings suggest that TEP production in the Oyashio region may be enhanced by an increase in DOC production from spring diatoms.
  • Tada, Yuya, Nakaya, Rie, Goto, Shuji, Yamashita, Youhei, Suzuki, Koji
    Journal of Experimental Marine Biology and Ecology 495 119 - 128 2017年 [査読有り][通常論文]
     
    Dissolved organic matter derived from phytoplankton (DOMP) can affect the bacterial growth and community composition, with concomitant changes in DOM characteristics, of aquatic ecosystems. Here, we examined the chemical and fluorescent characteristics of DOMPs derived from the diatom Thalassiosira weissflogii and the dinoflagellate Heterocapsa triquetra, and the community and diversity responses of free-living bacteria to these DOMPs. The DOMP quality was evaluated based on amino acid composition and excitation -emission matrix (EEM) analyses. In addition, EEM analysis was used to examine compositional changes in DOMPs. The total hydrolysable and free amino acid (THAA and FAA, respectively) compositions of each DOMP differed between phytoplankton strains. In addition, THAA and FAA compositions in diatom DOMPs were slightly different between the exponential and stationary growth phases. Terminal restriction fragment -length polymorphism (TRFLP) analysis with 16S rRNA genes revealed that the community shifts varied significantly with different DOMP additions. Furthermore, the specific amino acids in the diatom and dinoflagellate DOMPs potentially affected the bacterial community shifts. Similarity percentage analysis with 16S rRNA gene deep -sequencing revealed that distinct DOMP additions caused the community and diversity shifts with the growth of some specific bacterial lineages. Alteromonas (class Gammaproteobacteria) and Bacteroidetes lineages were strongly associated with the diatom DOMPs, whereas the proportion of Rhodobacteraceae sequences (class Alphaproteobacteria) among the total sequences increased in response to the addition of the dinoflagellate DOMP. EEM analysis revealed that the fluorescent DOM (FDOM) compositions of the diatom and dinoflagellate DOMPs changed in association with shifts in the bacterial community. Especially, a decrease in the fluorescence intensities of DOM was observed from the dinoflagellate treatment with the growth of Rhodobacteraceae lineage. These results indicate that there was a strong linkage between FDOM dynamics and Rhodobacteraceae lineage in the coastal water. This study suggests that DOMPs from different phytoplankton constitute a primary factor that alters the dominant bacterial groups with compositional changes in FDOM in coastal environments.
  • Waga, Hisatomo, Hirawake, Toru, Fujiwara, Amane, Kikuchi, Takashi, Nishino, Shigeto, Suzuki, Koji, Takao, Shintaro, Saitoh, Sei-Ichi
    Remote Sensing 9 3 222 - 222 2017年 [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.
  • Tada, Y., Shiozaki, T., Ogawa, H., Suzuki, K.
    Journal of Oceanography 73 2 145 - 158 2017年 [査読有り][通常論文]
     
    In the present study, we used catalyzed reporter deposition-fluorescence in situ hybridization to quantify the abundance of five bacterial (Alphaproteobacteria, SAR11, Gammaproteobacteria, SAR86, and Bacteroidetes) and two archaeal (Crenarchaeota and Euryarchaeota) phylotypes in the epipelagic layer (0-200 m) of the Central South Pacific Ocean along 170A degrees W from 0A degrees to 40A degrees S. We found that the distribution patterns of these phylotypes differed from each other. All phylotypes except Gammaproteobacteria were particularly abundant at the surface water of the equatorial region, whereas Gammaproteobacteria was relatively abundant in the area from the southern part of the South Pacific Ocean. SAR11, affiliated with Alphaproteobacteria was the dominant phylotype at all depths, throughout the study area. The abundance of SAR11 significantly increased with chlorophyll a concentration, suggesting that phytoplankton could affect their distribution pattern. There was a positive correlation between Bacteroidetes abundance and water temperature, suggesting that the temperature gradient could be a critical factor determining their distribution in the South Pacific Ocean. Crenarchaeota and Euryarchaeota were more abundant at the equatorial region than in other study areas. Euryarchaeota abundance significantly decreased with depth, and increased with chlorophyll a concentration. This suggests that there was ecological interaction between Euryarchaeota and phytoplankton in the equatorial surface. Our data indicate that distinct hydrographic properties such as seawater temperature, salinity, and the concentrations of chlorophyll a and nutrients can principally control the basin-scale distribution of different prokaryotic phylotypes in the epipelagic layer of the Central South Pacific Ocean.
  • A. Fujiwara, T. Hirawake, K. Suzuki, L. Eisner, I. Imai, S. Nishino, T. Kikuchi, S.-I. Saitoh
    Biogeosciences 13 1 115 - 131 2016年01月15日 [査読有り][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.
  • Tada, Y., Suzuki, K.
    FEMS Microbiology Ecology 92 7 2016年 [査読有り][通常論文]
     
    Dissolved organic matter derived from phytoplankton (DOMP) can affect the bacterial biomass and community structure in aquatic ecosystems. Here, we examined the community response of free-living heterotrophic bacteria, with respect to cellular nucleic acid levels, to the DOMP lysates derived from three phytoplankton strains in the open tropical Pacific. The free amino acid (FAA) composition of each DOMP lysate differed among the microalgal strains. Terminal restriction fragment-length polymorphism analyses with 16S rRNA genes revealed that the community shifts of high nucleic acid (HNA) and low nucleic acid (LNA) bacteria varied significantly with the different DOMP lysate treatments. Furthermore, the FAA composition in DOMP lysates significantly affected the bacterial community shifts in HNA and LNA. Similarity percentage analysis using 16S rRNA gene deep-sequencing revealed that the DOMP lysates from the pelagophyte Pelagomonas calceolata caused relatively large community shifts with Alcaligenes predominating in the HNA fraction. In contrast, the DOMP lysate from the diatom Thalassiosira oceanica induced a community shift in the LNA fraction with a predominance of uncultured Actinobacteria. Thus, the data indicate that the DOMP lysates from different microalgae constitute a primary factor altering the dominant bacterial groups in the open ocean.
  • Endo, H., Sugie, K., Yoshimura, T., Suzuki, K.
    PLoS One 11 4 e0154291  2016年 [査読有り][通常論文]
     
    Next-generation sequencing (NGS) technologies have enabled us to determine phytoplankton community compositions at high resolution. However, few studies have adopted this approach to assess the responses of natural phytoplankton communities to environmental change. Here, we report the impact of different CO2 levels on spring diatoms in the Oyashio region of the western North Pacific as estimated by NGS of the diatom-specific rbcL gene (DNA), which encodes the large subunit of RubisCO. We also examined the abundance and composition of rbcL transcripts (cDNA) in diatoms to assess their physiological responses to changing CO2 levels. A short-term (3-day) incubation experiment was carried out on-deck using surface Oyashio waters under different pCO(2) levels (180, 350, 750, and 1000 mu atm) in May 2011. During the incubation, the transcript abundance of the diatom-specific rbcL gene decreased with an increase in seawater pCO(2) levels. These results suggest that CO2 fixation capacity of diatoms decreased rapidly under elevated CO2 levels. In the high CO2 treatments (750 and 1000 mu atm), diversity of diatom-specific rbcL gene and its transcripts decreased relative to the control treatment (350 mu atm), as well as contributions of Chaetocerataceae, Thalassiosiraceae, and Fragilariaceae to the total population, but the contributions of Bacillariaceae increased. In the low CO2 treatment, contributions of Bacillariaceae also increased together with other eukaryotes. These suggest that changes in CO2 levels can alter the community composition of spring diatoms in the Oyashio region. Overall, the NGS technology provided us a deeper understanding of the response of diatoms to changes in CO2 levels in terms of their community composition, diversity, and photosynthetic physiology.
  • Koji Suzuki, Akiko Kamimura, Stanford B. Hooker
    Marine Chemistry 176 96 - 109 2015年11月 [査読有り][通常論文]
     
    We developed a rapid and highly sensitive analytical method for chlorophylls and carotenoids derived from marine phytoplankton using ultra-high performance liquid chromatography (UHPLC). High-performance liquid chromatography (HPLC) has been widely used in phytoplanlcton pigment analysis since the 1980s for estimating the abundance, composition, and photosynthetic physiology of natural algal assemblages or laboratory cultures. However, the run-time of the HPLC analyses is generally ca. 30 min or more, which is time-consuming for analysts. Our UHPLC technique enabled us to complete the separations of chlorophylls and carotenoids from marine phytoplankton within 7 min with similar resolution as conventional HPLC methods. The analytical method was tested on authentic pigment standards, marine phytoplankton cultures, and field samples that were collected from the central tropical and subarctic Pacific plus the neritic Bering Sea. Critical pigment pairs that generally co-eluted as a single peak were successively resolved by obtaining the first derivative spectrum chromatograms (FDSCs) with a photodiode array (PDA) detector based on differences in pigment absorption spectra, e.g., chlorophyll (Chl) c(2) and Mg 2,4 divinyl (DV) pheoporphyrin a(5) monomethyl ester (MgDVP), as well as DVChl b and Chl b. Because the maximum injection volume of UHPLC is generally lower than that of HPLC to minimize the unwanted broadening of chromatographic peaks, the detection sensitivity needed to be increased, especially for oligotrophic seawater samples with low pigment concentration. To overcome this sensitivity issue, a PDA detector equipped with an 85 mm path length capillary cell was used with a fluorescence detector. As a result, the limit of quantitation (LOQ) as determined by absorbance was of the order of 0.1 ng for chlorophylls and carotenoids. Furthermore, a bead-beating technique using N,N-dimethylformamide (DMF) and zirconia beads was utilized to minimize the volume of the organic solvent used for pigment extraction. Our UHPLC method can replace the conventional HPLC techniques, and allows us to yield high-throughput data of the chlorophylls and carotenoids derived from marine phytoplankton. (C) 2015 Elsevier B.V. All rights reserved.
  • Koji Sugie, Koji Suzuki
    DIATOM RESEARCH 30 3 237 - 245 2015年07月 [査読有り][通常論文]
     
    A new marine planktonic diatom Thalassionema kuroshioensis sp. nov., was described based on morphological comparison with five other extant Thalassionema species. Thalassionema kuroshioensis was found in coastal to offshore regions of the Kuroshio current in the temperate to subtropical western North Pacific. Morphological characteristics of T. kuroshioensis were identified using light and scanning electron microscopic observations and include isopolar valves, high density of areolae, cross- to club-shaped occluding bars, apical excavations, and sternum traversed across both ends of apices on the valve face. One rimoportula is located at the end of both valve apices connecting with the external opening slit in the deeply excavated apex. The outline of the valve is linear or slightly inflated. We provide size ranges and a key to the species of all known extant Thalassionema species, including the new species.
  • Koji Sugie, Koji Suzuki
    PLOS ONE 10 6 2015年06月 [査読有り][通常論文]
     
    Traditionally, biodiversity has often been estimated on the basis of abundance partly due to the need for complicated measurements of biomass. Here, we conducted robust measurements of the community composition and of the size structure of diatoms in the North Pacific to evaluate the importance of biomass on the biodiversity. We found that the two most useful evenness indices increased in most cases where small species were numerically dominant when calculations were based on biomass compared with those on abundance. Size-abundance spectra of diatoms revealed that numerically dominant small species rarely dominated in terms of biomass. On the other hand, intermediate to large diatom species generally played a dominant role in terms of biomass in diatom community. The results suggest that the size of the dominant species is a crucial factor in determining the role of diatoms in the ecosystem functioning. Because such size variability can also be observed in other organisms, we need to pay attention to the effect of size structures on biodiversity.
  • 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.
  • H. Endo, K. Sugie, T. Yoshimura, K. Suzuki
    BIOGEOSCIENCES 12 7 2247 - 2259 2015年 [査読有り][通常論文]
     
    Iron (Fe) can limit phytoplankton productivity in approximately 40% of the global ocean, including in high-nutrient, low-chlorophyll (HNLC) waters. However, there is little information available on the impact of CO2-induced seawater acidification on natural phytoplankton assemblages in HNLC regions. We therefore conducted an on-deck experiment manipulating CO2 and Fe using Fe-deficient Bering Sea water during the summer of 2009. The concentrations of CO2 in the incubation bottles were set at 380 and 600 ppm in the non-Fe-added (control) bottles and 180, 380, 600, and 1000 ppm in the Fe-added bottles. The phytoplankton assemblages were primarily composed of diatoms followed by haptophytes in all incubation bottles as estimated by pigment signatures throughout the 5-day (control) or 6-day (Fe-added treatment) incubation period. At the end of incubation, the relative contribution of diatoms to chlorophyll a biomass was significantly higher in the 380 ppm CO2 treatment than in the 600 ppm treatment in the controls, whereas minimal changes were found in the Fe-added treatments. These results indicate that, under Fe-deficient conditions, the growth of diatoms could be negatively affected by the increase in CO2 availability. To further support this finding, we estimated the expression and phylogeny of rbcL (which encodes the large subunit of RuBisCO) mRNA in diatoms by quantitative reverse transcription polymerase chain reaction (PCR) and clone library techniques, respectively. Interestingly, regardless of Fe availability, the transcript abundance of rbcL decreased in the high CO2 treatments (600 and 1000 ppm). The present study suggests that the projected future increase in seawater pCO(2) could reduce the RuBisCO transcription of diatoms, resulting in a decrease in primary productivity and a shift in the food web structure of the Bering Sea.
  • Takeshi Yoshimura, Koji Sugie, Hisashi Endo, Koji Suzuki, Jun Nishioka, Tsuneo Ono
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 94 1 - 14 2014年12月 [査読有り][通常論文]
     
    Increase in seawater pCO(2) and the corresponding decrease in pH caused by the increasing atmospheric CO2 concentration (i.e., ocean acidification) may affect organic matter production by phytoplankton communities. Organic matter production forms the basis of marine food webs and plays a crucial role in oceanic CO2 uptake through the biological carbon pump, and hence will potentially affect future marine ecosystem dynamics. However, responses of organic matter production in open ocean plankton ecosystems to CO2 increase have not been fully examined. We conducted on-deck microcosm experiments using high nutrient, low chlorophyll (HNLC) waters in the western subarctic Pacific and oceanic Bering Sea basin in summer 2008 and 2009, respectively, to examine the impacts of elevated CO2 on particulate and dissolved organic matter (i.e., POM and DOM, respectively) production. Iron deficient natural plankton communities were incubated for 7-14 days under multiple CO2 levels with and without iron enrichments (hereafter +Fe and -Fe treatments, respectively). By combining with our previous experiments at two sites, we created a comprehensive dataset on responses of organic matter production to CO2 increase during macronutrient replete conditions in HNLC waters. Significant differences in net particulate organic carbon production among CO2 treatments were observed only in the -Fe treatments, whereas that in net dissolved organic carbon production were mainly observed in the +Fe treatments, suggesting that CO2 may affect different processes depending on the Fe nutritional status. However, impacts of CO2 were not consistent among experiments and were much smaller than the consistent positive effects of Fe enrichment. In contrast, no significant differences among the CO2 treatments were observed for organic carbon partitioning into POM and DOM, and carbon to nitrogen ratio of net produced POM. We conclude that CO2 does not play a primary role, but could have secondary effects on controlling the organic matter production under macronutrient replete conditions in HNLC waters. On the other hand, in a nutrient-depleted, declining phase of the phytoplankton bloom induced by Fe enrichment, carbon overconsumption was found in an experiment with elevated CO2 conditions suggesting that CO2 impacts might become more significant in such environments. (C) 2014 Elsevier Ltd. All rights reserved.
  • 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.
  • Rumi Sohrin, Kunimatsu Imanishi, Yoshimi Suzuki, Kenshi Kuma, Ichiro Yasuda, Koji Suzuki, Takeshi Nakatsuka
    PROGRESS IN OCEANOGRAPHY 126 168 - 179 2014年08月 [査読有り][通常論文]
     
    The Okhotsk Sea is considered the only ventilation source area for North Pacific Intermediate Water (NPIW), which is widely distributed in the low and middle latitudes of the North Pacific. Previous studies have confirmed high levels of dissolved organic carbon (DOC) in NPIW, yet the amounts and the processes driving DOC export from the Okhotsk Sea are poorly understood. In this study, concentrations of DOC and dissolved organic nitrogen (DON) were measured in the western Okhotsk Sea during the summer of 2006, and additional DOC measurements were made during the late spring of 2010. Results indicate that DOC transport to the intermediate waters (26.7-27.0 sigma(theta)) occurs through two processes. The first process involves the spread of water discharged from the continental shelf (Dense Shelf Water), which contributes to a DOC and turbidity maxima in the 250-300 m layer of Okhotsk Sea Mode Water (OSMW) located off the eastern Sakhalin coast. The second process involves diapycnal mixing in the Kuril Basin and the Bussol' Strait, where DOC is transported to a depth greater than 800 m. The ratio of DOC:DON in OSMW was significantly higher in the Kuril Basin and Bussol' Strait than off of the Sakhalin coast, which suggests that the transport of terrigenous organic matter from the bottom occurs in the former regions. DOC and DON efflux from the Okhotsk Sea to the intermediate layer in the North Pacific water (26.7-27.0 sigma(theta)) were estimated to be 68-72 Tg C yr(-1) and 5.4 Tg N yr(-1), respectively, for which the DOC transported by diapycnal mixing accounts for 37%. We conclude that diapycnal mixing in the Kuril Basin and Bussol' Strait regions could play a significant role in regulating the quality and quantity of DOC exported to the intermediate water in the North Pacific. (C) 2014 Elsevier Ltd. All rights reserved.
  • Shintaro Takao, Takahiro Iida, Tomonori Isada, Sei-Ichi Saitoh, Takafumi Hirata, Koji Suzuki
    PROGRESS IN OCEANOGRAPHY 126 233 - 241 2014年08月 [査読有り][通常論文]
     
    The Sea of Okhotsk is one of the most productive ocean regions in the world. However, the in situ bio-optical properties, which are crucial for satellite ocean-color of the productivity, remain uncertain in this region because little data have been available. We conducted an in situ observation and evaluated the bio-optical properties in terms of chlorophyll a (ChI a) concentration, spectral remote sensing reflectance (R-rs), and the light absorption coefficients of phytoplankton (a(j)), non-algal particles (a(NAP)), and chromophoric dissolved organic matter (a(CDOM)) in the summer of 2006. The data covered a wide range of Chl a levels in surface waters from 0.3 to 8.5 mg m(-3). At 443 nm, a(CDOM) dominated (64% on average) the total non-water absorption (a(t-w)) in this study area. Based on the in situ R-rs data, surface Chl a concentrations that were estimated using the sea-viewing wide field-of-view sensor (SeaWiFS) OC4v6 and the moderate-resolution imaging spectroradiometer (MOD'S) OC3M algorithms were significantly higher than the in situ data by more than 160% and 260%, respectively. In particular, the largest overestimation occurred in the region where a(CDOM) at 443 nm accounted for more than 80% of a(t-w) near the mouth of the Amur River. However, except the CDOM-rich stations, the performance of the OC4v6 and OC3M algorithms became better (i.e., their mean normalized biases were reduced to 50% and 66%, respectively). We conclude that the operational global algorithms were applicable to the summer season in the Sea of Okhotsk except the CDOM-rich region, in which new approaches for ocean-color algorithms (i.e., local algorithms) would be required. (C) 2014 Elsevier Ltd. All rights reserved.
  • Sohiko Kameyama, Satoshi Yoshida, Hiroshi Tanimoto, Satoshi Inomata, Koji Suzuki, Hisayuki Yoshikawa-Inoue
    JOURNAL OF OCEANOGRAPHY 70 3 225 - 239 2014年06月 [査読有り][通常論文]
     
    We measured dissolved isoprene (2-methyl-1,3-butadiene; C5H8) concentrations in a broad area of the southern Indian Ocean and in the Indian sector of the Southern Ocean from 35A degrees S to 64A degrees S and from 37A degrees E to 111A degrees E during austral summer 2010-2011. Isoprene concentrations were continuously measured by use of a proton-transfer-reaction mass spectrometer combined with a bubbling-type equilibrator. Concentrations of isoprene and its emission flux throughout the study period ranged from 0.2 to 395 pmol L-1 and from 181 to 313 nmol m(-2) day(-1), respectively, the averages being generally higher than those of previous studies. Although we found a significant linear positive relationship between isoprene and chlorophyll-a concentrations (r (2) = 0.37, n = 36, P < 0.001), the correlation coefficient was lower than previously reported. In contrast, in the high-latitude area (> 53A degrees S) we identified a significant negative correlation (r (2) = 0.59, n = 1263, P < 0.001) between isoprene and the temperature-normalized partial pressure of carbon dioxide (n-pCO(2)), used as an indicator of net community production in this study. This suggests that residence times and factors controlling variations in isoprene and n-pCO(2) are similar within a physically stable water column.
  • Yuki Sato-Takabe, Koji Hamasaki, Koji Suzuki
    MICROBES AND ENVIRONMENTS 29 1 100 - 103 2014年04月 [査読有り][通常論文]
     
    This paper describes the photosynthetic response of a Roseobacter strain of marine aerobic anoxygenic phototrophic bacteria to an organic substrate limitation. In batch cultures, higher values of the spheroidenone/bacteriochlorophyll a ratio were observed under substrate-deficient conditions. Interestingly, the maximum photochemical quantum efficiencies of the photosystem under substrate-deficient conditions using blue or green excitation were significantly higher than those under substrate-replete conditions. These results indicate that spheroidenone, which can absorb green light, may play an important role in their photosynthesis as a light-harvesting antenna pigment, and the photosynthetic competence of the Roseobacter strain can increase in an organic substrate-deficient environment.
  • Yuichi Nosaka, Tomonori Isada, Isao Kudo, Hiroaki Saito, Hiroshi Hattori, Atsushi Tsuda, Koji Suzuki
    JOURNAL OF OCEANOGRAPHY 70 1 91 - 103 2014年02月 [査読有り][通常論文]
     
    We investigated the water-column light utilization efficiency (I) of phytoplankton photosynthesis in the Western Subarctic Gyre (WSG) of the North Pacific during summer 2008. The I values (0.64-1.86 g C [g Chl a](-1) [mol photon](-1) m(2)) obtained were observed to increase significantly with decreasing daily photosynthetic available radiation (PAR) and were generally higher than those of previous studies, not only from the subarctic Pacific but also from the world's oceans. To examine the effect of iron availability on I in the WSG, I values were estimated from the data of two in situ iron fertilization experiments: the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study I (SEEDS-I) and II (SEEDS-II). We found that iron availability did not affect I values. Overall, this study revealed that I values changed remarkably in the WSG during the summer, and that higher values were found at the stations where moderate PAR levels (ca. 10-30 mol photons m(-2) day(-1)) were observed and where autotrophic flagellates predominated in the phytoplankton assemblages.
  • T. Hirata, T. Hirawake, F. Sakaida, H. Yamaguchi, K. Suzuki, H. Murakami, J. Ishizaka, H. Kobayashi, A. Fujiwara, M. Toratani, S.-I. Saitoh
    Journal of the Remote Sensing Society of Japan 34 4 278 - 285 2014年 [査読有り][通常論文]
  • A. Fujiwara, T. Hirawake, K. Suzuki, I. Imai, S. -I. Saitoh
    BIOGEOSCIENCES 11 7 1705 - 1716 2014年 [査読有り][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.
  • K. Suzuki, A. Hattori-Saito, Y. Sekiguchi, J. Nishioka, M. Shigemitsu, T. Isada, H. Liu, R. M. L. McKay
    BIOGEOSCIENCES 11 9 2503 - 2517 2014年 [査読有り][通常論文]
     
    The Sea of Okhotsk is known as one of the most biologically productive regions among the world's oceans, and its productivity is supported in part by the discharge of iron (Fe)-rich water from the Amur River. However, little is known about the effect of riverine-derived Fe input on the physiology of the large diatoms which often flourish in surface waters of the productive continental shelf region. We conducted diatom-specific immunochemical ferredoxin (Fd) and flavodoxin (Fld) assays in order to investigate the spatial variability of Fe nutritional status in the microplanktonsized (20-200 mu m; hereafter micro-sized) diatoms. The Fd index, defined as the proportion of Fd to the sum of Fd plus Fld accumulations in the cells, was used to assess their Fe nutritional status. Additionally, active chlorophyll fluorescence measurements using pulse-amplitude-modulated (PAM) fluorometry were carried out to obtain the maximum photochemical quantum efficiency (F-v / F-m) of photosystem II for the total micro-sized phytoplankton assemblages including diatoms. During our observations in the summer of 2006, the micro-sized diatoms were relatively abundant (> 10 mu g C L-1) in the neritic region, and formed a massive bloom in Sakhalin Bay near the mouth of the Amur River. Values of the Fd index and F-v / F-m were high (> 0.9 and > 0.65, respectively) near the river mouth, indicating that Fe was sufficient for growth of the diatoms. However, in oceanic waters of the Sea of Okhotsk, the diatom Fd index declined as cellular Fld accumulation increased. These results suggest that there was a distinct gradient in Fe nutritional status in the micro-sized diatoms from near the Amur River mouth to open waters in the Sea of Okhotsk. A significant correlation between dissolved Fe (D-Fe) concentration and the Fd index was found in waters off Sakhalin Island, indicating that D-Fe was a key factor for the photophysiology of this diatom size class. In the vicinity of the Kuril Islands between the Sea of Okhotsk and the Pacific Ocean, micro-sized diatoms only accumulated Fld (i.e., Fd index = 0), despite strong vertical mixing consistent with elevated surface D-Fe levels (> 0.4 nM). Since higher Fe quotas are generally required for diatoms growing under low-light conditions, the micro-sized diatoms off the Kuril Islands possibly encountered Fe and light co-limitations. The differential expressions of Fd and Fld in micro-sized diatoms helped us to understand how these organisms respond to Fe availability in the Sea of Okhotsk in connection with the Amur River discharge.
  • 浜崎 恒二, 石坂 丞二, 齊藤 宏明, 杉崎 宏哉, 鈴木 光次, 高橋 一生, 千葉 早苗
    海の研究 = Umi no Kenkyu (Oceanography in Japan) 22 6 253 - 272 日本海洋学会 2013年11月15日 [査読有り][通常論文]
     
    海洋生物を中心とする視点から,海洋学の過去10年程度の研究の進展を総括するとともに,今後10年間でわが国として取り組むべき研究の方向性と必要とされる研究基盤について論じた。特に,「生物多様性」を生物海洋学,海洋生物学を特徴づけるに最もふさわしい言葉として,その解明ならびに地球システムとの関係について重要と考えられる課題毎に論じた。生物多様性の解明においては,動植物プランクトン及び微生物群集多様性の解明,鍵種の生物学,非優占種の役割,多様性と生物間相互作用を重要課題とした。生物多様性と地球システムとの関係については,気候変動による影響と気候へのフィードバック,複合生態系としての沿岸域,生物多様性とモニタリング,生態系・生物地球化学統合モデルを重要課題とした。Progress in oceanographic research in the past decade is reviewed and future directions and required infrastructures in the Japanese oceanographic research in the next decade are discussed, mainly from the biological oceanographic perspective. Particularly, we chose "Biodiversity" as the best keyword representing the nature of biological oceanography and marine biology, and discussed important issues in the study of biodiversity and its relation to the Earth system. In the study of biodiversity, important issues to reveal are the diversity of phytoplankton, zooplankton and microbial communities, biology of key species, the role of minor species and biological interaction. In the study of relationship between biodiversity and the Earth system, important issues are the effect of climate change and feedbacks to the climate, integrated ecosysetms in the coastal area, monitoring biodiversity, and integrated ecosystem-biogeochemical models.
  • Hongmei Jing, Xiaomin Xia, Koji Suzuki, Hongbin Liu
    PLOS ONE 8 11 2013年11月 [査読有り][通常論文]
     
    Community composition of Bacteria in the surface and deep water layers were examined at three oceanic sites in the Pacific Ocean separated by great distance, i.e., the South China Sea (SCS) in the western tropical Pacific, the Costa Rica Dome (CRD) in the eastern tropical Pacific and the western subarctic North Pacific (SNP), using high throughput DNA pyrosequencing of the 16S rRNA gene. Bioinformatic analysis rendered a total of 143600 high quality sequences with an average 11967 sequences per sample and mean read length of 449 bp. Phylogenetic analysis showed that Proteobacteria dominated in all shallow and deep waters, with Alphaproteobacteria and Gammaproteobacteria the two most abundant components, and SAR11 the most abundant group at family level in all regions. Cyanobacteria occurred mainly in the surface euphotic layer, and the majority of them in the tropical waters belonged to the GpIIa family including Prochlorococcus and Synechococcus, whilst those associated with Cryptophytes and diatoms were common in the subarctic waters. In general, species richness (Chao1) and diversity (Shannon index H') were higher for the bacterial communities in the intermediate water layers than for those in surface and deep waters. Both NMDS plot and UPGMA clustering demonstrated that bacterial community composition in the deep waters (500 m similar to 2000 m) of the three oceanic regions shared a high similarity and were distinct from those in the upper waters (5 m similar to 100 m). Our study indicates that bacterial community composition in the DOC-poor deep water in both tropical and subarctic regions were rather stable, contrasting to those in the surface water layers, which could be strongly affected by the fluctuations of environmental factors.
  • K. Sugie, H. Endo, K. Suzuki, J. Nishioka, H. Kiyosawa, T. Yoshimura
    Biogeosciences 10 10 6309  Copernicus {GmbH} 2013年10月 [査読有り][通常論文]
  • Takeshi Yoshimura, Koji Suzuki, Hiroshi Kiyosawa, Tsuneo Ono, Hiroshi Hattori, Kenshi Kuma, Jun Nishioka
    JOURNAL OF OCEANOGRAPHY 69 5 601 - 618 2013年10月 [査読有り][通常論文]
     
    Response of phytoplankton to increasing CO2 in seawater in terms of physiology and ecology is key to predicting changes in marine ecosystems. However, responses of natural plankton communities especially in the open ocean to higher CO2 levels have not been fully examined. We conducted CO2 manipulation experiments in the Bering Sea and the central subarctic Pacific, known as high nutrient and low chlorophyll regions, in summer 2007 to investigate the response of organic matter production in iron-deficient plankton communities to CO2 increases. During the 14-day incubations of surface waters with natural plankton assemblages in microcosms under multiple pCO(2) levels, the dynamics of particulate organic carbon (POC) and nitrogen (PN), and dissolved organic carbon (DOC) and phosphorus (DOP) were examined with the plankton community compositions. In the Bering site, net production of POC, PN, and DOP relative to net chlorophyll-a production decreased with increasing pCO(2). While net produced POC:PN did not show any CO2-related variations, net produced DOC:DOP increased with increasing pCO(2). On the other hand, no apparent trends for these parameters were observed in the Pacific site. The contrasting results observed were probably due to the different plankton community compositions between the two sites, with plankton biomass dominated by large-sized diatoms in the Bering Sea versus ultra-eukaryotes in the Pacific Ocean. We conclude that the quantity and quality of the production of particulate and dissolved organic matter may be altered under future elevated CO2 environments in some iron-deficient ecosystems, while the impacts may be negligible in some systems.
  • Sohiko Kameyama, Hiroshi Tanimoto, Satoshi Inomata, Hisayuki Yoshikawa-Inoue, Urumu Tsunogai, Atsushi Tsuda, Mitsuo Uematsu, Masao Ishii, Daisuke Sasano, Koji Suzuki, Yuichi Nosaka
    GEOPHYSICAL RESEARCH LETTERS 40 15 3986 - 3990 2013年08月 [査読有り][通常論文]
     
    Although much attention has been paid to describing the distribution of oceanic dimethyl sulfide (DMS) concentrations, establishing robust relationships between DMS concentrations and biological, physical, and chemical variables is still challenging. Previous studies have proposed semiempirical parameterizations by combining multiple physical and biogeochemical parameters to better understand and reproduce the global distribution of sea surface DMS. However, none of these parameterization schemes could reconcile regionally elevated DMS peaks found in high-resolution DMS measurements made in the western subarctic Pacific. Here we found that DMS concentrations are highly correlated with the net community production, a parameter that integrates biological activity over time. We anticipate that this relationship may be exportable to other regions with high primary productivity, such as the Southern Ocean or upwelling regions, and can be used as an important parameterization scheme, combined with solar radiation dose relationship.
  • Tomonori Isada, Takahiro Iida, Hongbin Liu, Sei-Ichi Saitoh, Jun Nishioka, Takeshi Nakatsuka, Koji Suzuki
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 118 4 1995 - 2013 2013年04月 [査読有り][通常論文]
     
    We investigated the photosynthetic parameters of phytoplankton in the Sea of Okhotsk during the late summer of 2006 to characterize their spatiotemporal variability and to test the hypothesis that discharge from the Amur River could influence the algal photophysiology. The highest maximum quantum yield of carbon fixation in photosynthesis (phi cmax; 0.098mol C mol photons-1) was found near the Amur River mouth, where nitrate was depleted. However, none of the photosynthetic parameters, including primary productivity (PP) at the surface, were correlated with temperature, daily photosynthetically available radiation (PAR), or ambient nutrient concentrations. Variations in phi cmax depended on the variations in not only the mean chlorophyll a specific absorption coefficient of phytoplankton (*ph) but also the slope index of the absorption coefficient of phytoplankton (aph slope), an indicator for the ratio of nonphotosynthetic carotenoids to photosynthetic carotenoids. These results indicated that the phytoplankton assemblages acclimated to the ambient light conditions by regulating their cellular pigments. Additionally, *ph and euphotic depth (Zeu) were significantly correlated with salinity, suggesting that photoacclimation of the phytoplankton assemblages observed in this study could be induced by discharge of Amur River. Because spatiotemporal variations in PP were concomitant with phi cmax, *ph, and the chlorophyll a concentration, PP models based on inherent optical property (IOP) were suitable for estimating PP in the Sea of Okhotsk. This study is the first to investigate the factors controlling phytoplankton photophysiology in the Sea of Okhotsk, one of the highest primary production areas in the world.
  • J. Peloquin, C. Swan, N. Gruber, M. Vogt, H. Claustre, J. Ras, J. Uitz, R. Barlow, M. Behrenfeld, R. Bidigare, H. Dierssen, G. Ditullio, E. Fernandez, C. Gallienne, S. Gibb, R. Goericke, L. Harding, E. Head, P. Holligan, S. Hooker, D. Karl, M. Landry, R. Letelier, C. A. Llewellyn, M. Lomas, M. Lucas, A. Mannino, J. C. Marty, B. G. Mitchell, F. Muller-Karger, N. Nelson, C. O'Brien, B. Prezelin, D. Repeta, W. O. Smith Jr., D. Smythe-Wright, R. Stumpf, A. Subramaniam, K. Suzuki, C. Trees, M. Vernet, N. Wasmund, S. Wright
    Earth System Science Data 5 1 109 - 123 2013年03月25日 [査読有り][通常論文]
     
    A global pigment database consisting of 35 634 pigment suites measured by high performance liquid chromatography was assembled in support of the MARine Ecosytem DATa (MAREDAT) initiative. These data originate from 136 field surveys within the global ocean, were solicited from investigators and databases, compiled, and then quality controlled. Nearly one quarter of the data originates from the Laboratoire d'Océanographie de Villefranche (LOV), with an additional 17% and 19% stemming from the US JGOFS and LTER programs, respectively. The MAREDAT pigment database provides high quality measurements of the major taxonomic pigments including chlorophylls a and b, 19'-butanoyloxyfucoxanthin, 19'-hexanoyloxyfucoxanthin, alloxanthin, divinyl chlorophyll a, fucoxanthin, lutein, peridinin, prasinoxanthin, violaxanthin and zeaxanthin, which may be used in varying combinations to estimate phytoplankton community composition. Quality control measures consisted of flagging samples that had a total chlorophyll a concentration of zero, had fewer than four reported accessory pigments, or exceeded two standard deviations of the log-linear regression of total chlorophyll a with total accessory pigment concentrations. We anticipate the MAREDAT pigment database to be of use in the marine ecology, remote sensing and ecological modeling communities, where it will support model validation and advance our global perspective on marine biodiversity. The original dataset together with quality control flags as well as the gridded MAREDAT pigment data may be downloaded from PANGAEA: http://doi.pangaea.de/10.1594/PANGAEA.793246. © 2013 Author(s).
  • Yoshiko Kondo, Shigenobu Takeda, Jun Nishioka, Mitsuhide Sato, Hiroaki Saito, Koji Suzuki, Ken Furuya
    JOURNAL OF OCEANOGRAPHY 69 1 97 - 115 2013年02月 [査読有り][通常論文]
     
    The influence of organic ligands on natural phytoplankton growth was investigated in high-nitrate low-chlorophyll (HNLC) waters and during a phytoplankton bloom induced by a mesoscale iron enrichment experiment (SEEDS II) in the western subarctic Pacific. The growth responses of the phytoplankton in the treatments with iron complexed with model ligand were compared with those with inorganic iron or a control. Desferrioxamine B and protoporphyrin IX were used as models for hydroxamate-type siderophore and tetrapyrrole-type cell breakdown ligand, respectively. In the HNLC water, iron associated with protoporphyrin IX especially stimulated smaller phytoplankton (< 10 mu m) growth, 1.5-fold more than did inorganic iron. Surprisingly, only the addition of protoporphyrin IX stimulated small phytoplankton growth, suggesting that these cell breakdown ligands might be more bioavailable for them. The protoporphyrin IX's stimulatory effect on small phytoplankton was not observed during bloom decline phase. The growth of phytoplankton was inhibited in the treatment with desferrioxamine B-complexed iron, suggesting its low bioavailability for the natural phytoplankton community. Its inhibitory effects were particularly pronounced in pico-eukaryotic phytoplankton. During the iron-induced bloom, the phytoplankton's iron-stress response gradually increased with the desferrioxamine B concentration, suggesting that the competition for iron complexation between natural ligands and desferrioxamine B affected phytoplankton growth. However, the pico-eukaryotes did seem better able to utilize the desferrioxamine B-complexed iron during the bloom-developing phase. These results indicate that the iron bioavailability for phytoplankton differs between bloom-developing and bloom-decline phases.
  • H. Endo, T. Yoshimura, T. Kataoka, K. Suzuki
    Journal of Experimental Marine Biology and Ecology 439 160 - 175 2013年01月 [査読有り][通常論文]
     
    On-deck CO2-Fe-manipulated incubation experiments were conducted using surface seawater collected from the Western Subarctic Gyre of the NW Pacific in the summer of 2008 to elucidate the impacts of ocean acidification and Fe enrichment on the abundance and community composition of phytoplankton and eubacteria in the study area. During the incubation, excluding the initial period, the mean partial pressures of CO2 in non-Fe-added bottles were 230, 419, 843, and 1124μatm, whereas those in Fe-added treatments were 152, 394, 791, and 1008μatm. Changes in the abundance and community composition of phytoplankton were estimated using HPLC pigment signatures with the program CHEMTAX and flow cytometry. A DGGE fingerprint technique targeting 16S rRNA gene fragments was also used to estimate changes in eubacterial phylotypes during incubation. The Fe addition induced diatom blooms, and subsequently stimulated the growth of heterotrophic bacteria such as Roseobacter, Phaeobacter, and Alteromonas in the post-bloom phase. In both the Fe-limited and Fe-replete treatments, concentrations of 19'-hexanoyloxyfucoxanthin, a haptophyte marker, and the cell abundance of coccolithophores decreased at higher CO2 levels (750 and 1000ppm), whereas diatoms exhibited little response to the changes in CO2 availability. The abundances of Synechococcus and small eukaryotic phytoplankton (< 10μm) increased at the higher CO2 levels. DGGE band positions revealed that Methylobacterium of Alphaproteobacteria occurred solely at lower CO2 levels (180 and 380ppm) during the post-bloom phase. These results suggest that increases in CO2 level could affect not only the community composition of phytoplankton but also that of eubacteria. As these microorganisms play critical roles in the biological carbon pump and microbial loop, our results indicate that the progression of ocean acidification can alter the biogeochemical processes in the study area. © 2012 Elsevier B.V.
  • Y. Yamashita, Y. Nosaka, K. Suzuki, H. Ogawa, K. Takahashi, H. Saito
    BIOGEOSCIENCES 10 11 7207 - 7217 2013年 [査読有り][通常論文]
     
    Chromophoric dissolved organic matter (CDOM) ubiquitously occurs in marine environments and plays a significant role in the marine biogeochemical cycles. Basin scale distributions of CDOM have recently been surveyed in the global ocean and indicate that quantity and quality of oceanic CDOM are mainly controlled by in situ production and photobleaching. However, factors controlling the spectral parameters of CDOM in the UV region, i.e., spectral slope of CDOM determined at 275-295 nm (S275-295) and the ratio of two spectral slope parameters (S-R); the ratio of S275-295 to S350-400, have not been well documented. To evaluate the factor controlling the spectral characteristics of CDOM in the UV region in the open ocean, we determined the quantitative and qualitative characteristics of CDOM in the subarctic and subtropical surface waters (5-300 m) of the western North Pacific. Absorption coefficients at 320 nm in the subarctic region were higher than those in the subtropical region throughout surface waters, suggesting that magnitudes of photobleaching were different between the two regions. The values of S275-295 and SR were also higher in the subtropical region than the subarctic region. The dark microbial incubation showed biodegradation of DOM little affected S275-295, but slightly decreased SR. On the other hand, increases in S275-295 and relative stableness of SR were observed during photo-irradiation incubations respectively. These experimental results indicated that photobleaching of CDOM mainly induced qualitative differences in CDOM at UV region between the subarctic and subtropical surface waters. The results of this study imply that S275-295 can be used as a tracer of photochemical history of CDOM in the open ocean.
  • Yuko Omori, Hiroshi Tanimoto, Satoshi Inomata, Sohiko Kameyama, Shintaro Takao, Koji Suzuki
    Limnology and Oceanography: Methods 11 549 - 560 2013年 [査読有り][通常論文]
     
    New, highly time-resolved techniques for measuring dimethyl sulfide (DMS) concentrations in seawater provide the opportunity to greatly increase the size of the DMS concentration database. However, lack of community-level quality control raises concerns about the quality of data obtained by these new techniques and their consistency with data obtained by existing techniques. One of the concerns is that the new techniques use a continuous flow of unfiltered seawater as a sample. Phytoplankton in unfiltered seawater might produce DMS in the sample, resulting in inaccurate DMS concentrations. Here, in our equilibrator inlet-proton transfer reaction-mass spectrometry technique, unfiltered seawater is continuously supplied to the equilibrator, and dissolved DMS is extracted into a bubbling gas and detected by the mass spectrometry. To investigate the possible artifact from using unfiltered seawater and the magnitude of its effects, we conducted laboratory experiments in a closed system at equilibrium, focusing on the effects of sample filtration and gas bubbling on the temporal variation of DMS concentrations in coastal seawater samples dominated by diatoms. With N2 as the bubbling gas, DMS concentration increased with time in unfiltered seawater but not in filtered seawater. DMS concentration increased when unfiltered seawater was bubbled with N2 but not when it was bubbled with air, and the increase occurred just after dissolved O2 was depleted in the seawater in the equilibrator. These results indicate that O2 depletion artificially increased DMS concentrations in unfiltered seawater bubbled with N2. This artifact could be avoided by maintaining aerobic conditions in the equilibrator. © 2013, by the American Society of Limnology and Oceanography, Inc.
  • Yuki Sato-Takabe, Koji Hamasaki, Koji Suzuki
    Archives of Microbiology 194 5 331 - 341 2012年05月 [査読有り][通常論文]
  • S. Takao, T. Hirawake, S. W. Wright, K. Suzuki
    BIOGEOSCIENCES 9 10 3875 - 3890 2012年 [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. 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.
  • Osamu Yoshida, Hisayuki Y. Inoue, Shuichi Watanabe, Koji Suzuki, Shinichiro Noriki
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 116 2011年07月 [査読有り][通常論文]
     
    Oceanic methane (CH4) was examined in the South Pacific and the Southern Ocean from December 2001 to February 2002. From the oligotrophic South Pacific (10 degrees S) to the Subtropical Front (STF), we observed the maximum concentrations of CH4 in the subsurface layer which ranged from 2.7 to 3.9 nmol kg(-1). South of the STF, higher levels of CH4 were often detected in both the surface and the subsurface layers. Elevated surface CH4 concentrations (3.4-6.1 nmol kg(-1)) south of the STF tended to be higher than those north of the STF. Higher CH4 were often concomitant with an increase in chlorophyll a levels in the Seasonal Ice Zone (SIZ). Considering that phytoplankton does not generate methane directly, the high CH4 production probably resulted from the grazing processes of Antarctic krill and/or zooplankton fed on phytoplankton and the subsequent microbial methanogenesis in addition to the aerobic CH4 production in the water column. Present results showed a good relation between surface CH4 data (<50 m) and sigma(theta) between 10 degrees S and the Polar Front (PF), which allow us to provide interpolation/extrapolation schemes for CH4 concentration and sea-air CH4 flux in the wide area ([CH4] = 0.15 sigma(theta) - 0.98 (RMS = 0.21 nmol kg(-1), r = 0.68, n = 49, p < 0.001). The sea-air fluxes estimated during our survey were from 2.4 to 4.9 mol CH4 km(-2) d(-1) between 10 degrees S and the PF (54 degrees S), and from 0.8 to 2.3 mol CH4 km(-2) d(-1) south of the PF, where the sea-air CH4 flux was largely affected by the wind speed.
  • Koji Suzuki, Akira Kuwata, Naoki Yoshie, Akira Shibata, Kyoko Kawanobe, Hiroaki Saito
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 58 5 575 - 589 2011年05月 [査読有り][通常論文]
     
    We characterized the community composition of phytoplankton in the western subarctic Pacific from the pre-bloom to the decline phase of the spring bloom with special reference to decreases in the silicic acid concentration in surface waters as an index for diatom bloom development. Furthermore, responses of heterotrophic bacteria and viruses to the spring bloom were also concomitantly investigated. Under pre-bloom conditions when nutrients were abundant but the surface mixed layer depth was relatively deep, chlorophyll (Chl) a concentrations were consistently low and green algae (chlorophytes and prasinophytes), cryptophytes, and diatoms were predominant in the phytoplankton assemblages as estimated by algal pigment signatures. Together with the shallowing of the mixed layer depth and the decrease in silicic acid concentration, diatoms bloomed remarkably in the Oyashio region, though the magnitude of the bloom in the Kuroshio-Oyashio transition (hereafter Transition) region was relatively small. A total of 77 diatom species were identified, with the bloom-forming diatoms mainly consisting of Thalassiosira, Chaetoceros, and Fragilariopsis species. It has become evident that the carotenoid fucoxanthin can serve as a strong indicator of the diatom carbon biomass during the spring diatom bloom. Differences in the species richness of diatoms among stations generally enabled us to separate the Oyashio bloom stations from the Transition and the Oyashio pre-bloom stations. Relatively high values of the Shannon-Wiener index for the diatom species were also maintained during the Oyashio bloom, indicating that a wide variety of species then shared dominance. In the decline phase of the Oyashio bloom when surface nutrient concentrations decreased, senescent diatom cells increased, as inferred from the levels of chlorophyllide a. Although the cell density of heterotrophic bacteria changed little with the development of the diatom bloom, viral abundance increased toward the end of the bloom, suggesting an increased likelihood of mortality among organisms including diatoms resulting from viral infection. This is the first report on the microbial trophodynamics, including viruses, during the spring diatom bloom in the western subarctic Pacific. (C) 2011 Elsevier Ltd. All rights reserved.
  • Satomi Ushizaka, Kenshi Kuma, Koji Suzuki
    FISHERIES SCIENCE 77 3 411 - 424 2011年05月 [査読有り][通常論文]
     
    The significance of Mn and Fe for the growth of the coastal marine diatom Thalassiosira weissflogii was investigated by culture experiments in the presence of precipitated Fe(III) hydroxide [am-Fe(III)] and EDTA-Fe(III) complex with or without Mn addition. The culture experiments in all media without any added Mn(II) resulted in the very low phytoplankton growth for cell density and chlorophyll a (Chl a) concentration. In contrast, sufficient Mn addition (25 nM) induced the maximum growth both for cell generation and Chl a production. By using an approach in which further iron uptake by T. weissflogii from external iron in the culture media is prevented by adding hydroxamate siderophore desferrioxamine B (DFB) during cultivation, we examined the ability of T. weissflogii to grow on intracellularly stored Fe after the DFB addition. The addition of DFB after 3- and 5-days of cultivation resulted in the lower growth rate and lower maximum yields for cell density and Chl a concentration in solid 7-day-aged am-Fe(III) medium than in freshly precipitated am-Fe(III) medium. The longer aging time of am-Fe(III) in medium reduced the supply of bioavailable iron in the medium by the slower dissolution rate of am-Fe(III) with the longer aging time. In addition, phytoplankton growth for cell generation in EDTA-Fe(III) complex media in the presence of insufficient Mn (0 and 5 nM) is strongly influenced by the bioavailable iron supply through the dissociation of EDTA-Fe(III). These results may suggest that T. weissflogii in longer aged am-Fe(III) medium and in EDTA-Fe(III) medium with a higher ratio of EDTA:Fe(III) is in Fe-limitation of growth, which probably increases the production rate of the reactive oxygen species (ROS), and the corresponding up-regulation of the superoxide dismuting enzyme Mn-SOD increases the requirement for Mn.
  • Koji Sugie, Kenshi Kuma, Satoshi Fujita, Satomi Ushizaka, Koji Suzuki, Tsutomu Ikeda
    JOURNAL OF OCEANOGRAPHY 67 2 183 - 196 2011年04月 [査読有り][通常論文]
     
    We report on the ability for luxury Fe uptake and the potential for growth utilizing intracellular Fe pools for 4 coastal centric diatom isolates and in situ phytoplankton assemblages, mainly composed of diatoms. Iron uptake of the diatom isolates and natural phytoplankton assemblages in the Oyashio region during spring blooms were prevented by adding hydroxamate siderophore desferrioxamine B (DFB). After the addition of DFB, intracellular Fe in the diatom isolates supported 2.4-4.2 cell divisions with 1.2-2.6 Chl a doublings. The intracellular Fe was primarily used for cell generation rather than Chl a production, leading to a reduction in the Chl a cell quota in the Fe-starved cells with time. The metabolic properties of the Fe-starved cells with their cell morphologies were different among species or genera. An on-deck incubation experiment also exhibited 1.9 cell divisions and 0.81 Chl a doublings of phytoplankton after the addition of DFB, also indicating the preference of cell generation over Chl a production. A decrease in the level of cellular Chl a, a main light-harvesting pigment in Fe-starved diatoms, may become a superior survival strategy to protect the cells from high irradiance that can cause photo-oxidative damages through photosynthesis. Such relatively low-Fe with high-light conditions could often occur in surface waters of the Oyashio region from spring to summer.
  • T. Hirata, N. J. Hardman-Mountford, R. J. W. Brewin, J. Aiken, R. Barlow, K. Suzuki, T. Isada, E. Howell, T. Hashioka, M. Noguchi-Aita, Y. Yamanaka
    BIOGEOSCIENCES 8 2 311 - 327 2011年 [査読有り][通常論文]
     
    Error-quantified, synoptic-scale relationships between chlorophyll-a (Chl-a) and phytoplankton pigment groups at the sea surface are presented. A total of ten pigment groups were considered to represent three Phytoplankton Size Classes (PSCs, micro-, nano- and picoplankton) and seven Phytoplankton Functional Types (PFTs, i.e. diatoms, dinoflagellates, green algae, prymnesiophytes (haptophytes), pico-eukaryotes, prokaryotes and Prochlorococcus sp.). The observed relationships between Chl-a and PSCs/PFTs were well-defined at the global scale to show that a community shift of phytoplankton at the basin and global scales is reflected by a change in Chl-a of the total community. Thus, Chl-a of the total community can be used as an index of not only phytoplankton biomass but also of their community structure. Within these relationships, we also found nonmonotonic variations with Chl-a for certain pico-sized phytoplankton (pico-eukaryotes, Prokaryotes and Prochlorococcus sp.) and nano-sized phytoplankton (Green algae, prymnesiophytes). The relationships were quantified with a leastsquare fitting approach in order to enable an estimation of the PFTs from Chl-a where PFTs are expressed as a percentage of the total Chl-a. The estimated uncertainty of the relationships depends on both PFT and Chl-a concentration. Maximum uncertainty of 31.8% was found for diatoms at Chla = 0.49 mg m(-3). However, the mean uncertainty of the relationships over all PFTs was 5.9% over the entire Chl-a range observed in situ (0.02< Chl-a < 4.26 mg m(-3)). The relationships were applied to SeaWiFS satellite Chl-a data from 1998 to 2009 to show the global climatological fields of the surface distribution of PFTs. Results show that microplankton are present in the mid and high latitudes, constituting only similar to 10.9% of the entire phytoplankton community in the mean field for 1998-2009, in which diatoms explain similar to 7.5%. Nanoplankton are ubiquitous throughout the global surface oceans, except the subtropical gyres, constituting similar to 45.5%, of which prymnesiophytes (haptophytes) are the major group explaining similar to 31.7% while green algae contribute similar to 13.9%. Picoplankton are dominant in the subtropical gyres, but constitute similar to 43.6% globally, of which prokaryotes are the major group explaining similar to 26.5% (Prochlorococcus sp. explaining 22.8%), while pico-eukaryotes explain similar to 17.2% and are relatively abundant in the South Pacific. These results may be of use to evaluate global marine ecosystem models.
  • A. Fujiwara, T. Hirawake, K. Suzuki, S. -I. Saitoh
    BIOGEOSCIENCES 8 12 3567 - 3580 2011年 [査読有り][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.
  • Sohiko Kameyama, Hiroshi Tanimoto, Satoshi Inomata, Koji Suzuki, Daisuke D. Komatsu, Akinari Hirota, Uta Konno, Urumu Tsunogai
    GEOCHEMICAL JOURNAL 45 5 355 - 363 2011年 [査読有り][通常論文]
     
    Emission of trace gases from the marine diatom Thalassiosira pseudonana (CCMP 1335) was continuously monitored with a proton transfer reaction-mass spectrometry (PTR-MS) in an axenic batch culture system under a 13:11-h light:dark cycle. Substantial increases in the signals at m/z 49, 63, and 69, attributable to methanethiol, dimethyl sulfide (DMS), and isoprene, respectively, were observed in response to increases in cell density. Signals at m/z 69 showed diurnal variations throughout the experiment whereas those at m/z 49 were more pronounced at the beginning of the incubation. Interestingly, the signals at m/z 49 and 69 changed immediately following the light-dark and dark-light transitions, suggesting that light plays a crucial role in the production of methanethiol and isoprene. However, in the latter half of the experiment, methanethiol showed negligible diurnal variations regardless of light conditions, suggesting the production of methanethiol from enzymatic cleavage of DMS. The trend ill signals at m/z 63 was similar to that of the abundance of senescent cells plus cell debris rather than vegetative cells. The results suggest that aging or death of phytoplankton cells could also substantially control DMS production in natural waters along with the other microbial processes related to bacteria and zooplankton.
  • Takeshi Yoshimura, Jun Nishioka, Koji Suzuki, Hiroshi Hattori, Hiroshi Kiyosawa, Yutaka W. Watanabe
    JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 395 1-2 191 - 198 2010年11月 [査読有り][通常論文]
     
    Increasing CO2 in seawater (i.e. ocean acidification) may have various and potentially adverse effects on phytoplankton dynamics and hence the organic carbon dynamics. We conducted a CO2 manipulation experiment in the Sea of Okhotsk in summer 2006 to investigate the response of the organic carbon dynamics. During the 14-day incubation of nutrient depleted and 200 mu atm in situ pCO(2) surface water with a natural plankton assemblage under 150, 280, 480, and 590 mu atm pCO(2), the amount of net dissolved organic carbon accumulation was significantly lower at >480 mu atm pCO(2) than at 150 mu atm pCO(2), while differences in net particulate organic carbon accumulation between the treatments were small and did not show a clear relationship with the pCO(2). This is the first report to show a decreased net organic carbon production of natural plankton community under elevated pCO(2). Phytoplankton pigment analysis suggests that the relative contribution of fucoxanthin-containing phytoplankton such as diatoms to the phytoplankton biomass was lower at >280 mu atm pCO(2) than at 150 mu atm pCO(2). Different pCO(2) conditions may alter the organic carbon dynamics through changes in plankton processes. We conclude that the continuing increase in atmospheric CO2 in a time scale from the last half century to the end of this century has potential to affect the carbon cycle in nutrient depleted subpolar surface waters. (C) 2010 Elsevier B.V. All rights reserved.
  • Tomonori Isada, Ai Hattori-Saito, Hiroaki Saito, Tsutomu Ikeda, Koji Suzuki
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 57 17-18 1653 - 1664 2010年09月 [査読有り][通常論文]
     
    Despite large diatom blooms occurring in the Oyashio region of the NW Pacific every spring, our knowledge of factors controlling primary productivity in the region during that season remains incomplete. Therefore, we investigated phytoplankton abundance, size structure, and primary productivity from April to June 2007. Significant changes were observed. Chlorophyll a (Chl a) concentrations in surface waters fluctuated between 0.37 and 17 mg m(-3). Micro-sized (> 10 mu m) phytoplankton dominated the phytoplankton community when Chl a was > 1 mg m(-3). Depth-integrated daily primary production within the euphotic layer ranged between 328 and 3231 mg C m(-2) d(-1). Higher values of the water-column light utilization index (Psi) for phytoplankton photosynthesis were observed in May and June. Although no significant relationships were found between surface primary productivity and macronutrient concentrations or photosynthetically available radiation (PAR), surface primary productivity correlated significantly with Chl a concentration during April, indicating that algal productivity depended on phytoplankton biomass. Furthermore, significant linear relationships were found throughout the observations of phytoplankton absorption coefficient to surface primary productivity and of that coefficient to the optimum algal photosynthetic rate normalized by Chl a level (P-opt(B)) in the water column. Modeling P-opt(B) with the empirical equations of Behrenfeld and Falkowski (1997) or Kameda and lshizaka (2005) did not accurately reproduce in situ P-opt(B). These results suggest that the phytoplankton absorption properties could become useful indicators for estimating primary productivity in the Oyashio region during spring. (C) 2010 Elsevier Ltd. All rights reserved.
  • M. K. Kurihara, M. Kimura, Y. Iwamoto, Y. Narita, A. Ooki, Y. -J. Eum, A. Tsuda, K. Suzuki, Y. Tani, Y. Yokouchi, M. Uematsu, S. Hashimoto
    MARINE CHEMISTRY 118 3-4 156 - 170 2010年02月 [査読有り][通常論文]
     
    Biogenic trace gases. especially halomethanes, which are important with respect to atmospheric chemistry, are released from the ocean and carry halogens to the troposphere and stratosphere. The concentrations of 10 halocarbons and isoprene in seawater were measured during the spring of 2007 in the western North Pacific Ocean (37-43 degrees N. 143-146 degrees E). Sea-air fluxes of CH(3)Cl, CH(3)Br, CH(2)ClI, and CH(2)I(2) were also estimated based upon the atmospheric as well as oceanic measurement of these species. Temperature-salinity scatter diagram analyses divided the sampling stations into the Oyashio region, Tsugaru warm current region, and Kuroshio region. Mean (range) concentrations of the gases in the water columns (5-100 m) were 114 (56150) pmol L(-1) CH(3)Cl, 6.9 (4.1-19.4) pmol L(-1) CH(3)Br, 1.7 (0.7-2.9) pmol L(-1) CH(3)l, 1.9 (0.9-4.1) pmol L(-1) CH(2)BrCl, 4.8 (3.2-8.1) pmol L(-1) CH(2)Br(2), 1-0 (0.6-1.8) pmol L(-1) CHBrCl(2), 1.2 (0.7-2.0) pmol L(-1) CHBr(2)Cl, 10.8 (4.7-24.5) pmol L(-1) CHBr(3), 1.7 (0.7-5.4) pmol L(-1) CH(2)ClI, 3.0 (<0.1-22.2) pmol L(-1) CH(2)I(2), and 19.7 (3.8-68.2) pmol L(-1) isoprene. The maximum concentration of isoprene was observed in the Oyashio region, where concentrations of chlorophyll a (maximum: 2.94 mu g L(-1)) were highest in the present study. However, the peaks of CH(3)Br, CH(2)ClI, and CH(2)I(2) were observed in the Tsugaru warm current region, where concentrations of chlorophyll a were not as high (maximum: 0.65 mu g L(-1)). The results of chlorophyll a size fractionation showed a high occurrence of halomethanes in the stations dominated by pico-sized phytoplankton. These results indicate the importance of picoplankton as a possible source of halocarbon production. Chlorophyll b and prasinoxanthin had a statistically significant positive correlation with CH(2)I(2) (r(2) = 0.69 and r(2) = 0.71, respectively) and with CH(2)ClI (r(2) = 0.87 and r(2) = 0.77, respectively). These results suggest that some species of prasinophytes might contribute to CH(2)I(2) and CH(2)ClI production. For other compounds, there was no peak in the vertical profile in seawater. In the depth profiles. the peak of CH(2)ClI was observed above the peak of CH(2)I(2); these profiles suggest that a photochemical reaction could yield CH(2)ClI from CH(2)I(2) in seawater. The mean mixing ratio and range of CH(3)CI, CH(3)Br. and CH(2)ClI in the air were measured as 548 (524-609), 12.1 (8.6-19.0), and 0.27 (0.03-0.90) pptv, respectively. CH(2)I(2) was not detected in the atmosphere (<1 pptv). The saturation anomaly of CH3Br was positive at all stations (the sea surface temperature varied from 1.7 degrees C to 19 degrees C). The highest mixing ratio of CH(2)ClI in air was also observed near the station at which the highest concentration of CH2CII was observed in seawater; the sea-to-air fluxes of CH(2)ClI and CH(2)I(2) were 3.8 and 1.6 nmol m(-2) day(-1). respectively. These results suggest that the production of CH(2)ClI and CH(2)I(2) in seawater is an importat source of organic iodine compounds in the remote atmosphere. (c) 2009 Elsevier B.V. All rights reserved.
  • Hongmei Jing, Hongbin Liu, Koji Suzuki, Rumi Sohrin, Jun Nishioka
    AQUATIC MICROBIAL ECOLOGY 61 2 191 - 204 2010年 [査読有り][通常論文]
     
    We investigated spatial variations of the bacterial and archaeal community composition in surface waters of the Sea of Okhotsk during summer of 2006, using denaturing gradient gel electrophoresis (DGGE). We determined phylogenetic assemblages, including Actinobacteria, Bacteroidetes, Cyanobacteria, Alpha-and Gammaproteobacteria, and Marine Group II Euryarchaea, and successfully revealed their spatial distribution patterns. At most stations, Bacteria had higher diversity than Archaea, indicated by the relatively higher Shannon-Weaver indexes and numbers of operational taxonomic units (OTUs). Canonical correspondence analysis (CCA) and redundancy analysis (RDA) demonstrated that the community compositions of bacterial populations in the Sea of Okhotsk were closely associated with total prokaryote abundance, while the spatial distributions of bacterial phylogenetic groups were more related to both the concentration of dissolved organic nitrogen (DON) and the ratio of DON versus dissolved organic carbon concentration (DOC:DON). On the other hand, the spatial variation of the community composition of Archaea had no significant association with environmental parameters.
  • Ai Hattori-Saito, Jun Nishioka, Tsuneo Ono, R. Michael L. McKay, Koji Suzuki
    Journal of Oceanography 66 1 105 - 115 2010年01月 [査読有り][通常論文]
     
    In order to detect iron (Fe) stress in micro-sized (20-200 μm) diatoms in the Oyashio region, western subarctic Pacific during spring, immunological ferredoxin/flavodoxin assays were applied to samples collected from the surface layer in May 2005. Concomitantly, the community composition of the micro-sized phytoplankton and hydrographic conditions, including dissolved Fe and macronutrient concentrations, were also examined. Chlorophyll (Chl) a concentrations were < 2 mg m-3 at all sampling stations, except at a station where the Chl a level was 9.0 mg m-3 and a micro-sized diatom bloom occurred. A high abundance of ferredoxin in micro-sized diatoms was detected only at a rather near-shore station where dissolved Fe and macronutrient concentrations were higher, indicating that the micro-sized diatoms did not suffer from iron deficiency. On the other hand, flavodoxin in micro-sized diatoms was often observed at the other stations, including the bloom station, where macronutrients were replete but dissolved Fe concentration was low (0.31 nM). A significant amount of chlorophyllide a, a degradation product of Chl a, was also observed at the bloom station, suggesting a decline of the diatom bloom. The micro-sized phytoplankton species at all the stations were mainly composed of the diatoms Thalassiosira, Chaetoceros, and Fragilariopsis spp. Our study indicates that micro-sized diatoms were stressed by Fe bioavailability during the spring season in the Oyashio region © Springer Science+Business Media B.V. 2010.
  • Naoki Yoshie, Koji Suzuki, Akira Kuwata, Jun Nishioka, Hiroaki Saito
    MARINE ECOLOGY PROGRESS SERIES 399 39 - 52 2010年 [査読有り][通常論文]
     
    Variations in photosynthetic parameters of phytoplankton during the spring bloom were investigated in the western subarctic Pacific. Light-saturated maximum photosynthesis rate (P-max(B)) and light-limited slope (alpha(B)) in the photosynthesis-irradiance (P-E) curve were almost constant in the first half of the bloom and then concurrently increased by 5 times in the latter half with a constant light-saturation index (E-k = p(max)(B)/alpha(B)). In contrast, the maximum photochemical quantum efficiency (F-v/F-m) of the algal photosystem II increased in the first half and thereafter decreased. Water temperature significantly affected the covariation in P-max(B) and alpha(B) (i.e. E-k-independent variability), suggesting that dark reaction processes in photosynthesis mainly regulated the changes in the P-E parameters. Although influences of nitrate, silicic acid, and dissolved iron on the P-E parameters were not observed, the elevated ammonium levels found in the latter half of the bloom could contribute to the E-k-independent variability. There was no significant relationship among algal net growth rate, P-max(B), and alpha(B) throughout the observations. Since most ecosystem models have used a constant alpha(B), parallel changes in P-max(B) and alpha(B) should be taken into account in models reproducing ecosystem dynamics during spring diatom blooms.
  • Hongbin Liu, Mianrun Chen, Koji Suzuki, Chong Kim Wong, Bingzhang Chen
    MARINE ECOLOGY PROGRESS SERIES 407 111 - 123 2010年 [査読有り][通常論文]
     
    Phytoplankton community composition and mesozooplankton selective feeding on different phytoplankton taxa were studied by HPLC pigment analysis at 2 sites with contrasting hydrography in the coastal areas of Hong Kong. The site (WE) on the western part of Hong Kong is located in the Pearl River estuary, whereas the site (EO) on the eastern part of Hong Kong is influenced by oceanic waters. Despite the strong difference in hydrographic conditions, diatoms were the dominant phytoplankton at both sites throughout most months of the year, contributing on average more than 40% of the total phytoplankton in terms of chlorophyll a (chl a). Cryptophytes were the second most abundant phytoplankton group at both sites, whereas contributions from haptophytes, green algae, cyanobacteria and dinoflagellates were small. Diatoms and cryptophytes, the 2 most dominant phytoplankton groups, accounted for about 80 and 75% of the diets of mesozooplankton at EO and WE, respectively. One consistent pattern observed throughout the study period was that mesozooplankton assemblages strongly preferred dinoflagellates over other types of phytoplankton, especially in estuarine waters, even though dinoflagellates only contributed to a small fraction of total chl a. On the other hand, phytoplankton groups with relative small cell sizes, such as green algae and cyanobacteria, were not efficiently ingested. Overall, mesozooplankton feeding selectivity in subtropical eutrophic coastal waters, where planktonic food is sufficient, appears to be influenced by a combination of different factors, including the compositions of predators and the size and quality of the prey.
  • U. Konno, U. Tsunogai, D. D. Komatsu, S. Daita, F. Nakagawa, A. Tsuda, T. Matsui, Y. -J. Eum, K. Suzuki
    BIOGEOSCIENCES 7 8 2369 - 2377 2010年 [査読有り][通常論文]
     
    Using the N-15(2) tracer method and high-sensitivity delta N-15 analytical systems, we determined N-2 fixation rates for ocean samples by dividing them into particulate (> 0.7 mu m) and filtrate (< 0.7 mu m) fractions. While N-2 fixation in the filtrate fraction had been ignored in previous studies, we found a significant N-2 fixation rates in the filtrate fraction in our study. The areal N-2 fixation rates in the western North Pacific Ocean estimated from the particulate fraction varied from < 1 to 160 mu mol N m(-2) d(-1), and those rates estimated from the filtrate fraction ranged from < 0.5 to 54 mu mol N m(-2) d(-1). Thus, N-2 fixation in the filtrate fraction accounts for on average 50% (ranging from < 10% to 84%) of the total N-2 fixation rates. If these results are confirmed generally in the ocean, the new total N-2 fixation flux, which includes fixation in the filtrate fraction, possibly doubles the original estimates; therefore, the revised influx may reduce the imbalance in the global oceanic fixed nitrogen budget.
  • Atsushi Tsuda, Kimio Fukami, Hiroshi Kiyosawa, Koji Suzuki, Shigenobu Takeda, Jun Nishioka, Masayuki Takahashi, Keith Johnson, Chi-Shing Wong
    Plankton and Benthos Research 5 4 144 - 155 2010年 [査読有り][通常論文]
     
    The roles of heterotrophic organisms (microzooplankton, mesozooplankton, bacteria and heterotrophic nanoflagellates) were examined during a nutrient enrichment experiment using a mesocosm in Saanich Inlet, British Columbia, Canada. Grazing rates of microzooplankton, copepods, and Noctiluca scintillans were respectively estimated by the dilution method, from the egg production, and the apparent growth rate. The primary production increased by about 11 times during the initial 3 days, and the grazing rate by zooplankton also increased by 7.4 times. The primary production exceeded the grazing rate during the initial 5 days, after that, almost balanced rates were observed. Biomass peaks of bacteria and HNFs (heterotrophic nanoflagellates) were observed after the decline of the phytoplankton bloom. Bacterial production and HNF bacterivory gradually increased from the beginning to the end of the experiment. Microzooplankton consistently removed about half of the primary production. The contribution of microzooplankton to grazing was largest during the initial 7 days. Heterotrophic dinoflagellates were the most dominant component of the microzooplankton, but oligotrich ciliates showed the fastest growth response to phytoplankton production. Noctiluca scintillans became an important grazer after the bloom. Overall, the contribution of microzooplankton grazing was the largest of the processes through which phytoplankton were lost. Cell sinking was a minor component contributing to loss of phytoplankton. Thus, oligotrich ciliates and heterotrophic dinoflagellates were the most plausible organisms contributing to the steady state of phytoplankton concentrations. © The Plankton Society of Japan.
  • Takafumi Kataoka, Koji Suzuki, Maki Hayakawa, Isao Kudo, Seigo Higashi, Atsushi Tsuda
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 56 26 2779 - 2787 2009年12月 [査読有り][通常論文]
     
    Little is known about the effects of iron enrichment in high-nitrate low-chlorophyll (HNLC) waters on the community composition of heterotrophic bacteria, which are crucial to nutrient recycling and microbial food webs. Using denaturing gradient gel electrophoresis (DGGE) of 16S rDNA fragments, we investigated the heterotrophic eubacterial community composition in surface waters during an in situ iron-enrichment experiment (SEEDS-II) in the western subarctic Pacific in the summer of 2004. DGGE fingerprints representing the community composition of eubacteria differed inside and outside the iron-enriched patch. Sequencing of DGGE bands revealed that at least five phylotypes of alpha-proteobacteria including Roseobacter, Cytophaga-Flavobacteria-Bacteroides (CFB), gamma-proteobacteria, and Actinobacteria occurred in almost all samples from the iron-enriched patch. Diatoms did not bloom during SEEDS-II, but the eubacterial composition in the iron-enriched patch was similar to that in diatom blooms observed previously. Although dissolved organic carbon (DOC) accumulation was not detected in surface waters during SEEDS-II, growth of the Roseobacter clade might have been particularly stimulated after iron additions. Two identified phylotypes of CFB were closely related to the genus Saprospira, whose algicidal activity might degrade the phytoplankton assemblages increased by iron enrichment. These results suggest that the responses of heterotrophic bacteria to iron enrichment could differ among phylotypes during SEEDS-II. (C) 2009 Elsevier Ltd. All rights reserved.
  • Ippei Nagao, Shinya Hashimoto, Koji Suzuki, Shuji Toda, Yasushi Narita, Atsushi Tsuda, Hiroaki Saito, Isao Kudo, Shungo Kato, Yoshizumi Kajii, Mitsuo Uematsu
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 56 26 2899 - 2917 2009年12月 [査読有り][通常論文]
     
    Simultaneous measurements of dimethylsulfide (DMS) in the seawater and atmosphere were conducted during SEEDS-II to investigate the responses of DMS to iron (Fe) fertilization in the subarctic North Pacific. No significant increases in the seawater DMS (DMSw) concentration were observed inside the fertilized patch compared to those outside the patch, while particulate dimethylsulfioniopropionate (DMSPp) concentration inside the patch increased 2-fold compared to those outside the patch in the phytoplankton bloom of major DMSP producers such as prasinophytes, cryptophytes, diatoms and prymnesiophytes. In the decline phase of the bloom, maximum DMSw was observed both inside the patch (ca. 6.2 nM) and outside the patch (ca. 9.3 nM). In this period, increases in mesozooplankton and decreases in the DMSP producers (prymnesiophytes and diatoms) were observed both sides of the patch, but larger inside the patch than outside the patch. Large decreases in the DMSPp inside the patch, which was probably related to the large increases in mesozooplankton inside the patch, did not result in increases in the DMSw concentration. Considering biological and nonbiological parameters, we discussed these results, although they could not be completely explained. Unfortunately, the impact of Fe fertilization on the atmospheric DMS (DMSa) concentration was not detected due to no significant changes in DMSw. However, it is noted that DMSa concentrations were dependent on the sea-air DMS flux in the air from higher latitudes and/or the Eurasian continent, though the DMS flux was a minor role to the budget of DMSw. Therefore if DMSw were significantly changed by Fe fertilization, DMSa might be affected through changes in the sea-air flux in this condition. (C) 2009 Elsevier Ltd. All rights reserved.
  • Shinya Hashimoto, Shuji Toda, Koji Suzuki, Shungo Kato, Yasusi Narita, Michiko K. Kurihara, Yoko Akatsuka, Hiroshi Oda, Takahiro Nagai, Ippei Nagao, Isao Kudo, Mitsuo Uematsu
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 56 26 2928 - 2935 2009年12月 [査読有り][通常論文]
     
    Iron could play a key role in controlling phytoplankton biomass and productivity in high-nutrient, low-chlorophyll regions. As a part of the iron fertilization experiment carried out in the western subarctic Pacific from July to August 2004 (Subarctic Pacific iron Experiment for Ecosystem Dynamics Study II-SEEDS II), we analysed the concentrations of trace gases in the seawater for 12 d following iron fertilization. The mean concentrations of chlorophyll a in the mixed layer (5-30m depth) increased from 0.94 to 2.81 mu g L(-1) for 8 d in the iron patch. The mean concentrations of methyl bromide (CH(3)Br; 5-30 in depth) increased from 6.4 to 13.4 pmol L(-1) for 11 d; the in-patch concentration increased relative to the out-patch concentration. A linear correlation was observed between the concentrations of 19'-hexanoyloxyfucoxanthin, which is a biomarker of several prymnesiophytes, and CH(3)Br in the seawater. After fertilization, the air-sea flux of CH(3)Br inside the patch changed from influx to efflux from the ocean. There was no clear evidence for the increase in saturation anomaly of methyl chloride (CH(3)Cl) due to iron fertilization. Furthermore, CH(3)Cl fluxes did not show a tendency to increase after fertilization of the patch. In contrast to CH(3)Br, no change was observed in the concentrations of bromoform (in-patch day 11 and out-patch day 11: 1.7 and 1.7 pmol L(-1)), dibromomethane (2.1 and 2.2 pmol L(-1)), and dibromochloromethane (1.0 and 1.2 pmol L(-1), respectively). The concentration of isoprene, which is known to have a relationship with chlorophyll a, did not change in this study. The responses of trace gases during SEEDS II differed from the previous findings (in situ iron enrichment experiment-EisenEx, Southern Ocean iron experiment-SOFeX, and Subarctic Ecosystem Response to Iron Enrichment Study-SERIES). Thus, in order to estimate the concomitant effect of iron fertilization on the climate, it is important to assess the induction of biological activity and the distributions/air-sea fluxes of trace gases by iron addition. (C) 2009 Published by Elsevier Ltd.
  • Isao Kudo, Yoshifumi Noiri, William P. Cochlan, Koji Suzuki, Takafumi Aramaki, Tsuneo Ono, Yukihiro Nojiri
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 56 26 2755 - 2766 2009年12月 [査読有り][通常論文]
     
    Primary productivity (PP), bacterial productivity (BP) and the uptake rates of nitrate and ammonium were measured using isotopic methods ((13)C, (3)H, (15)N) during a mesoscale iron (Fe)-enrichment experiment conducted in the western subarctic Pacific Ocean in 2004 (SEEDS 11). PP increased following Fe enrichment, reached maximal rates 12 days after the enrichment, and then declined to the initial level on day 17. During the 23-day observation period, we observed the development and decline of the Fe-induced bloom. The surface mixed layer (SML) integrated PP increased by 3-fold, but was smaller than the 5-fold increase observed in the previous Fe-enrichment experiment conducted at almost the same location and season during 2001 (SEEDS). Nitrate uptake rates were enhanced by Fe enrichment but decreased after day 5, and became lower than ammonium uptake rates after day 17. The total nitrogenous nutrient uptake rate declined after the peak of the bloom, and accumulation of ammonium was obvious in the euphotic layer. Nitrate utilization accounted for all the requirements of N for the massive bloom development during SEEDS, whereas during SEEDS II, nitrate accounted for >90% of total N utilization on day 5, declining to 40% by the end of the observation period. The SML-integrated BP increased after day 2 and peaked twice on days 8 and 21. Ammonium accumulation and the delayed heterotrophic activity suggested active regeneration occurred after the peak of the bloom. The SML-integrated PP between days 0 and 23 was 19.0g Cm(-2). The SML-integrated BP during the same period was 2.6 g C m(-2), which was 14% of the SML-integrated PR Carbon budget calculation for the whole experimental period indicated that 33% of the whole (particulate plus dissolved) PP (21.5 gCm(-2)) was exported below the SML and 18% was transferred to the meso-zooplankton (growth). The bacterial carbon consumption (43% of the whole PP) was supported by DOC or POC release from phytoplankton, zooplankton, protozoa and viruses. More than a half (56%) of the whole PP in the Fe patch was consumed within the SML by respiration of heterotrophic organisms and returned to CO(2). (C) 2009 Elsevier Ltd. All rights reserved.
  • Martine Lizotte, Maurice Levasseur, Isao Kudo, Koji Suzuki, Atsushi Tsuda, Ronald P. Kiene, Michael G. Scarratt
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 56 26 2889 - 2898 2009年12月 [査読有り][通常論文]
     
    The effect of added iron on bacterial cycling of the climate-active gas dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) was tested during the second Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study (SEEDS II) from 19 July to 21 August 2004 aboard the R/V Hakuho-Maru. The study area in the northwest Pacific Ocean (48 degrees N 165 degrees E) was enriched with Fe and the conservative tracer, SF(6), allowing the fertilized patch to be tracked. Microbial DMSP cycling rates were determined in the surface mixed layer (5 m) during incubations using the (35)S-DMSP technique. The addition of iron resulted in a 4-fold increase in concentrations of chlorophyll a (chl a) within the surface mixed layer (5 m depth), and the length of the sampling period allowed the observation of both bloom and post-bloom conditions. Inside the fertilized patch, the alleviation of resource limitation gave rise to the concurrent increase in bacterial abundance and production. Changes in the phytoplankton community within the Fe-enriched patch translated into a sustained decrease in chl a-normalized particulate DMSP (DMSP(p)) concentrations, suggesting a preferential stimulation of the growth of DMSP(p)-poor phytoplankton species. Despite short-lived peaks of DMSPp within the Fe-enriched area, concentrations of DMSPp generally remained stable during the entire sampling period inside and outside the fertilized patch. During the Fe-induced bloom, microbial DMSP-sulfur (DMSP-S) assimilation efficiency increased 2.6-fold inside the Fe-enriched area, which indicated that as bacterial production increased, a greater proportion of DMSP-S was assimilated and possibly diverted away from the bacterial cleavage pathway (i.e. production of DMS). Our results suggest that iron-induced stimulation of weak DMSP(p)-producers and DMSP-assimilating bacteria may diminish the potential production of DMS and thus limit its flux towards the atmosphere over the subarctic Pacific Ocean. (C) 2009 Elsevier Ltd. All rights reserved.
  • Koji Suzuki, Hiroaki Saito, Tomonori Isada, Ai Hattori-Saito, Hiroshi Kiyosawa, Jun Nishioka, R. Michael. L. McKay, Akira Kuwata, Atsushi Tsuda
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 56 26 2733 - 2744 2009年12月 [査読有り][通常論文]
     
    Temporal changes in the abundance, community composition, and photosynthetic physiology of phytoplankton in surface waters were investigated during the second in situ iron (Fe) fertilization experiment in the NW subarctic Pacific (SEEDS-II). Surface chlorophyll a concentration was 0.75 mg m(-3) on the day before the first Fe enrichment (i.e. Day 0), increased ca. 3-fold until Day 13 after two Fe additions, and thereafter declined with time. The photochemical quantum efficiency (F-v/F-m) and functional absorption cross-section (sigma(PSII)) of photosystem II for total phytoplankton in surface waters increased and decreased inside the Fe-enriched patch through Day 13, respectively. These results indicate that the photosynthetic physiological condition of the phytoplankton improved after the Fe infusions. However, the maximum F-v/F-m value of 0.43 and the maximum quantum yield of carbon fixation (phi(max)) of 0.041 mol C (mol photon)(-1) during the development phase of the bloom were rather low, compared to their theoretical maximum of ca. 0.65 and 0.10 mol C (mol photon)(-1), respectively. Diatoms, which were mainly composed of oceanic species, did not bloom, and autotrophic nanoflagellates such as cryptophytes and prasinophytes became predominant in the phytoplankton community inside the Fe-enriched patch. In ferredoxin/flavodoxin assays for micro-sized (20-200 mu m in cell length) diatoms, ferredoxin was not detected but flavodoxin expressions consistently occurred with similar levels both inside and outside the Fe-enriched patch, indicating that the large-sized diatoms were stressed by Fe bioavailability inside the Fe-enriched patch even after the Fe enrichments. Our data suggest that the absence of a Fe-induced large-sized diatom bloom could be partly due to their Fe stress throughout SEEDS-II. (C) 2009 Elsevier Ltd. All rights reserved.
  • Hiroaki Saito, Atsushi Tsuda, Yukihiro Nojiri, Takafumi Aramaki, Hiroshi Ogawa, Takeshi Yoshimura, Keiri Imai, Isao Kudo, Jun Nishioka, Tsuneo Ono, Koji Suzuki, Shigenobu Takeda
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 56 26 2852 - 2862 2009年12月 [査読有り][通常論文]
     
    Biogeochemical cycles of N and Si were examined in the surface mixed layer during the mesoscale iron-enrichment (IE) experiment in the high-nutrient low-chlorophyll (HNLC) western subarctic Pacific (SEEDS-II). Although the IEs increased nitrate uptake, silicic acid utilization was not stimulated. The nitrate drawdown in the iron-patch (IN-patch, 140.3 mmol m(-2) in the surface mixed layer, 0-30 in) was only 25% of the initial inventory, which was 1/3-2/5 of the previous IE experiments in the subarctic Pacific. This relatively weak response of nutrient drawdown to IEs was due to the high biomass of mesozooplankton (MZ) dominated by copepod Neocalanus; plumchrus. Feeding of MZ (247.2 mmol m(-2) during Day 0-21 from the first IE) in the IN-patch was higher than the nitrate drawdown and prevented further development of the phytoplankton bloom. In the later period of the experiment (Day 14-21) the increase in the feeding activity and resultant decrease in phytoplankton biomass induced the accumulation of dissolved organic nitrogen (DON) and ammonium. Among total growth of MZ (81.6 mmol N m(-2)), 89% (72.8 mmol N m(-2)) was transported to the depth by the ontogenetic downward migration of N. plumchrus. Although silicic acid drawdown was not increased by the IEs, Si export flux increased by 2.7 times. The increase in Si export was also due to the increase in MZ, which egested faecal pellets with higher Si:N ratio and faster sinking speed than diatoms. The export efficiency (78% of new production) and total amount of export flux (143.8 mmol N m(-2) 1392 mmol C m(-2)) were highest records within the IE experiments despite weak responses of nutrient drawdown to the IE. During SEEDS-II, the high biomass of MZ reduced the phytoplankton response and nutrient drawdown to the IEs but via grazing and ontogenetic vertical migration accelerated the export flux as well as accumulations of dissolved forms of N. Results of the present and previous IE experiments indicate that the ecosystem and biogeochemical responses to IEs in the HNLC region are quite sensitive to the ecosystem components, especially for grazers of diatoms such as copepods and heterotrophic dinoflagellates. More attention needs to be paid to the ecosystem components and their biogeochemical functions as well as physical and chemical properties of the ecosystems in order to hindcast or forecast the impacts of changes in atmospheric iron deposition. (C) 2009 Elsevier Ltd. All rights reserved.
  • Tomonori Isada, Akira Kuwata, Hiroaki Saito, Tsuneo Ono, Masao Ishii, Hisayuki Yoshikawa-Inoue, Koji Suzuki
    JOURNAL OF PLANKTON RESEARCH 31 9 1009 - 1025 2009年09月 [査読有り][通常論文]
     
    Diel and seasonal changes in the photosynthetic physiology of phytoplankton and primary productivity were investigated during 2005, together with community composition in the Oyashio (OY) and Kuroshio-Oyashio transition (TR) regions of the northwest Pacific. In both regions, diel changes in the maximum photosynthetic rate (P*(max)) and the light saturation index (E-k) in the photosynthesis-irradiance (P-E) curve were observed, due to diel differences in photo-physiology. In the OY region, the highest values of chlorophyll a concentration, depth-integrated primary production and the maximum quantum yield of carbon fixation in photosynthesis (Phi(c max)) were observed in May when diatom blooms occurred. Furthermore, a higher water-column light utilization efficiency (Psi) of photosynthesis for phytoplankton was found in the OY region in both May and September. In contrast, in the TR and warm-core ring regions, Phi(c max) was nearly constant, while depth-integrated primary production in May was significantly lower than in the OY region. These results show that the spring phytoplankton assemblages in OY waters had a higher light utilization ability during photosynthesis. Such a high photosynthetic property would contribute to the highest seasonal biological drawdown of surface pCO(2) among the world's oceans (Takahashi, T., Sutherland, S. C., Sweeney, C. et al. (2002) Global sea-air CO2 flux based on climatological surface ocean pCO(2), and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601-1622).
  • Takafumi Kataoka, Yoshikuni Hodoki, Koji Suzuki, Hiroaki Saito, Seigo Higashi
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 95 2 108 - 116 2009年05月 [査読有り][通常論文]
     
    In order to evaluate the effects of solar ultraviolet radiation (UVR) on eubacterial community composition, we examined the tolerance of eubacterial phylotypes to solar UV radiation in surface waters of the western North Pacific during September 2005. Bromodeoxyuridine (BrdU), a halogenated thymine analogue, was used for labeling newly synthesized DNA in proliferating cells. Thymine dimers (TD), which are specifically formed in DNA by biologically harmful ultraviolet B radiation (UVBR; 280315 nm), were also applied to detect UVB damaged genomes selectively. PCR-denaturing gradient gel electrophoresis (PCR-DGGE) on the labeled samples revealed that UVBR-resistant cells showing active synthesis of DNA without accumulating TD, varied among phylotypes. In addition, UVBR-sensitive band positions with TD indicated inter-specific variations in sensitivity to UVBR. Phylogenetic analysis revealed that 12 DNA sequences were classified into eight phylogenetic groups: three Rosecbacter, one Sphingomonas, two Gammaproteobacteria, one Actinobacteria, one Synechococcus, two Prochlorococcus, one plastid and one another group. A UVBR-resistant phylotype was affiliated to Erythrobacter sp. (previously designated as Sphingomonas sp.), which was distributed in warmer waters from the south of Oyashio to Kuroshio regions. A UVBR-sensitive phylotype was affiliated to Pseudoalteromonas sp. in Gammaproteobacteria. Dominant heterotrophic eubacteria were composed of both sensitive and resistant phylotypes. This is the first report on TD accumulated eubacterial phylotypes in oceanic surface waters. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
  • Takafumi Kataoka, Yoshikuni Hodoki, Koji Suzuki, Hiroaki Saito, Seigo Higashi
    JOURNAL OF MARINE SYSTEMS 77 1-2 197 - 207 2009年04月 [査読有り][通常論文]
     
    In the western North Pacific, where subarctic Oyashio waters encounter subtropical Kuroshio waters, phylotype composition of heterotrophic bacteria was estimated by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified bacterial 16S ribosomal DNA. Total bacterial abundance was also measured by flow cytometry. The study area was divided into four water masses: coastal, Oyashio, Kuroshio, and the Kuroshio-Oyashio transition. Abundances of heterotrophic bacteria in the Oyashio, Kuroshio, and Kuroshio-Oyashio transition regions ranged from 0.2x10(5) cells mL(-1) to 1.4x10(5) cells mL(-1) and were not significantly different, except in the Oyashio region during September. Bacterial compositions were distinct in each water mass. Furthermore, phylotype distributions differed between surface and subsurface waters in the Kuroshio-Oyashio transition region. Out of 61 DGGE bands obtained, 41 were successfully identified as 31 phylotypes: 22 Gammaproteobacteria, 4 Alphaproteobacteria, 2 unknown bacteria, 2 cyanobacteria, and 1 plastid. Although the Gammaproteobacteria OM60 clade was eurytopic in the study area, Psychrobacter glacincola and the uncultured Gammaproteobacteria SAR92 clade were often observed in the Oyashio region. Overall, our results indicated that Gammaproteobacteria were predominant in the bacterial community, which was influenced by the hydrographic properties of each water mass in the study area. (C) 2008 Elsevier B.V. All rights reserved.
  • Hongbin Liu, Koji Suzuki, Jun Nishioka, Rumi Sohrin, Takeshi Nakatsuka
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 56 4 561 - 570 2009年04月 [査読有り][通常論文]
     
    The Sea of Okhotsk is one of the most productive marine basins in the world ocean and plays an important role in transport of organic carbon and iron to the western subarctic Pacific. We report the first measurements of phytoplankton growth and microzooplankton grazing rates in the Sea of Okhotsk, in late summer of 2006. The study area can be divided into two areas: nutrient-sufficient waters on the continental shelf along the east coast of Sakhalin Island and in the vicinity of Bussol Strait, and surface nutrient-depleted waters beyond the shelf break and in the vicinity of Sakhalin Bay. Phytoplankton growth rate in the studied area was strongly affected by nutrient availability, with high phytoplankton growth rate (0.55 +/- 0.14 d(-1)) in the nutrient-replete region and severely depressed growth (0.03 +/- 0.05 d(-1)) in the nutrient-depleted region. On the other hand, microzooplankton grazing rates in both the nutrient-replete and nutrient-depleted regions were approximately the same (0.26 +/- 0.20 d(-1) vs. 0.27 +/- 0.24 d(-1)). Consequently, microzooplankton grazing consumed <50% of the phytoplankton growth in nutrient-rich waters but >3 times the phytoplankton growth in nutrient-depleted waters. Phytoplankton physiological condition as measured by the maximum photochemical quantum efficiency (F-v/F-m.) of algal photosystem II (PS II) showed a general trend in agreement with the in situ growth rate of phytoplankton. In contrast to the phytoplankton community, picophytoplankton, especially the cyanobacteria Synechococcus, showed no nutrient effect on their growth, and the growth and mortality rates were well balanced, suggesting that they have a low nutrient requirement and their biomass was controlled principally by microzooplankton grazing. (C) 2008 Elsevier Ltd. All rights reserved.
  • Hongmei Jing, Hongbin Liu, Koji Suzuki
    AQUATIC MICROBIAL ECOLOGY 56 1 55 - 63 2009年 [査読有り][通常論文]
     
    The phylogenetic composition of marine Synechococcus spp. populations from 5 stations, 4 in the Sea of Okhotsk and 1 in the western subarctic Pacific, representing a wide range of hydrographic and ecological conditions, was examined using internal transcribed spacer (ITS) clone libraries and phylogenetic analysis. Synechococcus spp. at Stn G9, an estuarine station near the Amur River, belonged to Subcluster 5.2 phylotypes, while the other 4 stations were composed exclusively of Subcluster 5.1 Synechococcus spp. and dominated by phylotypes of Clades I and IV; this is in agreement with the general global distribution pattern of marine Synechococcus spp. lineages. Additionally, novel phylotypes that are not clustered to any existing clades were found, and sub-clades that exclusively contain phylotypes from the Sea of Okhotsk were also formed within respective clades, demonstrating the occurrence of unique Synechococcus spp. assemblages in the high-latitude marginal sea. Furthermore, distinct Synechococcus spp. populations were found at different stations with different hydrographic conditions, suggesting that the spatial variations in the phylogenetic composition of Synechococcus spp. were strongly affected by the physical-chemical parameters of the seawater. Overall, our study adds significant new insights into the diversity of Synechococcus spp. populations in the subpolar marginal sea and supports the conclusion drawn by Zwirglmaier et al. (2008; Environ Microbiol 10: 147-161) that Synechococcus spp. phylogeography is driven by environmental conditions rather than by geographical proximity.
  • Maki Hayakawa, Koji Suzuki, Hiroaki Saito, Kazutaka Takahashi, Shin-ichi Ito
    JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 360 2 63 - 70 2008年06月 [査読有り][通常論文]
     
    Cell viabilities of phytoplankton in the Oyashio and Kuroshio-Oyashio transition regions of the northwest Pacific Ocean were examined in September 2003 (late summer) and May 2005 (spring) using a membrane permeability test. Specific lysis rates of the phytoplankton during late summer were also assessed by an esterase activity assay. In late summer, cyanobacteria Synechococcus spp. were >2 x 10(4) cells ml(-1) and numerically dominated the phytoplankton communities. The cell viabilities of Synechococcus spp. and eukaryotic ultraphytoplankton (<10 mu m in size) were 60-79% and 26-41% in surface waters, respectively. The specific lysis rates of the phytoplankton were 0.12-0.67 d(-1) in late summer. By contrast, in spring, eukaryotic cells were predominant in the phytoplankton communities. The cell viabilities of surface eukaryotic ultraphytoplankton in spring were >70% and significantly higher than those in late summer. During spring, Synechococcus spp. only occurred with < 1 x 10(4) Cells ml(-1) in the Kuroshio-Oyashio transition region, and their viabilities were 80%. In the Oyashio region where a spring diatom bloom developed, the viability of fucoxanthin-containing algae (mainly diatoms and prymnesiophytes) was ca. 90%. These results suggested that the cell viability of phytoplankton could vary seasonally with their community structure in the study area. The phytoplankton cell death in late summer was particularly significant for their loss process and could support the microbial food webs by supplying dissolved organic carbon (DOC) derived from the dead cells. (C) 2008 Elsevier B.V. All rights reserved.
  • Atsushi Tsuda, Shigenobu Takeda, Hiroaki Saito, Jun Nishioka, Isao Kudo, Yukihiro Nojiri, Koji Suzuki, Mitsuo Uematsu, Mark L. Wells, Daisuke Tsumune, Takeshi Yoshimura, Tatsuo Aono, Takafumi Aramaki, William P. Cochlan, Maki Hayakawa, Keiri Imai, Tomoshi Isada, Yoko Iwamoto, William K. Johnson, Sohiko Kameyama, Shungo Kato, Hiroshi Kiyosawa, Yoshiko Kondo, Maurice Levasseur, Ryuji J. Machida, Ippei Nagao, Fumiko Nakagawa, Takahiro Nakanish, Seiji Nakatsuka, Akira Narita, Yoshifumi Noiri, Hajime Obata, Hiroshi Ogawa, Kenji Oguma, Tsuneo Ono, Tomofumi Sakuragi, Motoki Sasakawa, Mitsuhide Sato, Akifumi Shimamoto, Hyoe Takata, Charles G. Trick, Yutaka W. Watanabe, Chi Shing Wong, Naoki Yoshie
    JOURNAL OF OCEANOGRAPHY 63 6 983 - 994 2007年12月 [査読有り][通常論文]
     
    mesoscale iron-enrichment study (SEEDS II) was carried out in the western subarctic Pacific in the summer of 2004. The iron patch was traced for 26 days, which included observations of the development and the decline of the bloom by mapping with sulfur hexafluoride. The experiment was conducted at almost the same location and the same season as SEEDS (previous iron-enrichment experiment). However, the results were very different between SEEDS and SEEDS II. A high accumulation of phytoplankton biomass (similar to 18 mg chl m(-3)) was characteristic of SEEDS. In contrast, in SEEDS II, the surface chlorophyll-a accumulation was lower, 0.8 to 2.48 mg m(-3), with no prominent diatom bloom. Photosynthetic competence in terms of F-v/F-m for the total phytoplankton community in the surface waters increased after the iron enrichments and returned to the ambient level by day 20. These results suggest that the photosynthetic physiology of the phytoplankton assemblage was improved by the iron enrichments and returned to an iron-stressed condition during the declining phase of the bloom. Pico-phytoplankton (< 2 mu m) became dominant in the chlorophyll-a size distribution after the bloom. We observed a nitrate drawdown of 3.8 mu M in the patch (day 21), but there was no difference in silicic acid concentration between inside and outside the patch. Mesozooplankton (copepod) biomass was three to five times higher during the bloom-development phase in SEEDS II than in SEEDS. The copepod biomass increased exponentially. The grazing rate estimation indicates that the copepod grazing prevented the formation of an extensive diatom bloom, which was observed in SEEDS, and led to the change to a pico-phytoplankton dominated community towards the end of the experiment.
  • Jun Nishioka, Tsuneo Ono, Hiroaki Saito, Takeshi Nakatsuka, Shigenobu Takeda, Takeshi Yoshimura, Koji Suzuki, Kenshi Kuma, Shigeto Nakabayashi, Daisuke Tsumune, Humio Mitsudera, W. Keith Johnson, Atsushi Tsuda
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 112 C10 2007年10月 [査読有り][通常論文]
     
    Iron is an essential nutrient and plays an important role in the control of phytoplankton growth ( Martin et al., 1989). Atmospheric dust has been thought to be the most important source of iron, supporting annual biological production in the western subarctic Pacific (WSP) (Duce and Tindale, 1991; Moore et al., 2002). We argue here for another source of iron to the WSP. We found extremely high concentrations of dissolved and particulate iron in the Okhotsk Sea Intermediate Water (OSIW) and the North Pacific Intermediate Water (NPIW), and water ventilation processes in this region probably control the transport of iron through the intermediate water layer from the continental shelf of the Sea of Okhotsk to wide areas of the WSP. Additionally, our time series data in the Oyashio region of the WSP indicate that the pattern of seasonal changes in dissolved iron concentrations in the surface-mixed layer was similar to that of macronutrients, and that deep vertical water mixing resulted in higher winter concentrations of iron in the surface water of this region. The estimated dissolved iron supply from the iron-rich intermediate waters to the surface waters in the Oyashio region was comparable to or higher than the reported atmospheric dust iron input and thus a major source of iron to these regions. Our data suggest that the consideration of this source of iron is essential in our understanding of spring biological production and biogeochemical cycles in the western subarctic Pacific and the role of the marginal sea.
  • Shouei Iwade, Kenshi Kuma, Yutaka Isoda, Masahiko Yoshida, Isao Kudo, Jun Nishioka, Koji Suzuki
    AQUATIC MICROBIAL ECOLOGY 43 2 177 - 191 2006年06月 [査読有り][通常論文]
     
    The growth and iron uptake of the coastal marine diatom Chaetoceros sociale were experimentally measured in batch experiments at 10 degrees C to which an acidic Fe(III) stock solution was added. The direct input of Fe(III) into the culture media induced the highest iron uptake rate (similar to 3.4 to 4.2 x 10(-16) mol Fe cell(-1) d(-1)) by C. sociale during the first day of the incubation, resulting from the supply of bioavailable inorganic Fe(III) species at levels above its expected equilibrium value (similar to 0.1 nmol l(-1)) with solid amorphous Fe(III) hydroxide in seawater. The iron uptake rate during the first day of incubation in solid amorphous Fe(Ill) hydroxide medium aged for 1 d at 10 degrees C was approximately 50% lower than that in the direct Fe(III) input media. We used a modified approach in which further iron uptake by C. sociale from external iron in the direct Fe(III) input media was prevented by adding hydroxamate siderophore desferrioxamine B (DFB) during cultivation. After the addition of DFB, the highest growth rate (similar to 0.5 to 0.6 d(-1)) of C. sociale by intracellularly stored Fe in the direct Fe(III) input media was maintained for a few days since no iron uptake was observed after the DFB addition. The growth rate was independent of the amount of intracellularly stored Fe, However, the maximal cell yields appeared to be relatively dependent on the amount of intracellularly stored Fe, suggesting the presence of a critical concentration of intracellular Fe (minimum cellular Fe for growth) for phytoplankton growth (similar to 1 x 10(-16) mol Fe cell(-1) for C. sociale). In the present study, maximal and minimal Fe quotas were 3.4 to 4.2 x 10(-16) and similar to 1 x 10(-16) mol Fe cell(-1) (the maximal/minimal Fe ratio of 3.4 to 4.2), respectively. The high iron uptake and storage capacity in C. sociale allows this species to accumulate excess iron at high concentrations of bioavailable inorganic Fe species and to support up to 1.8 to 2.1 cell divisions without any additional iron uptake. In addition, we attempted to model the effect of luxury uptake on growth, as biodilution of cellular Fe eventually decreases the Fe quota to a critical threshold.
  • H Saito, T Ota, K Suzuki, J Nishioka, A Tsuda
    GEOPHYSICAL RESEARCH LETTERS 33 9 2006年05月 [査読有り][通常論文]
     
    Iron enrichment to high-nutrient low-chlorophyll (HNLC) regions is being considered as a possible way of atmospheric CO2 sequestration to the deep sea. Mesoscale iron-enrichment to the HNLC subarctic Pacific induced a massive diatom bloom and led to a large decrease in pCO(2). In response to the diatom bloom, the heterotrophic dinoflagellate Gyrodinium sp. increased and phagotrophically fed on the diatoms up to 12 times their length. Mathematical simulations show the carbon fixed by diatoms is mostly respired by Gyrodinium sp. in the sea surface. The emergence of initially rare species and their key biogeochemical roles were unexpected due to our limited understanding of food-web components. This indicates that the prediction of ecosystem responses to natural or anthropogenic perturbation remains a challenging issue. Effective carbon sequestration as a geoengineering technique may not be accomplished by purposeful iron-enrichment, at least in the western subarctic Pacific where rapid-growth diatom grazers stand by.
  • T Usui, S Nagao, M Yamamoto, K Suzuki, Kudo, I, S Montani, A Noda, M Minagawa
    MARINE CHEMISTRY 98 2-4 241 - 259 2006年02月 [査読有り][通常論文]
     
    Organic carbon (C) and total nitrogen (N) contents and corresponding isotope ratios were determined in surficial sediment (0-3 cm) at 94 stations ranging from 21 to 1995 m water depth off Tokachi, Hokkaido, Japan, to elucidate the distribution and source of sedimentary organic matter. Suspended particulate organic matter (POM) in the seawater and suspended POM and sediment in the Tokachi River were also examined. delta C-13, delta N-15 and C/N ratios of the samples in the Tokachi River suggest that the spring snowmelt is an important process for the transport of terrestrial organic matter to the coastal waters. delta C-13 values of suspended POM in the Surface seawater were higher in May and November than in August, while delta N-15 values of the POM were higher in May and August than in November. These changes are attributed to seasonal changes in phytoplankton growth rate and nitrate availability. delta C-13 and delta N-15 values in the sediments off Tokachi were lowest near the Tokachi River mouth, and increased offshore to constant values that persisted from 134 to 1995 m water depth. The spatial variation in C/N ratios in the sediment mirrored those of delta C-13 and delta N-15. Comparison of delta C-13, delta N-15 and C/N ratios in the sediments off Tokachi with those in the Tokachi River and seawater indicates that about half of the organic matter in the sediment was of terrestrial origin near the Tokachi River mouth, and the sedimentary organic matter from 134 to 1995 in water depth was of marine origin. The organic C content in the sediment was high near the Tokachi River mouth, and also around 1000 m water depth. The C content was significantly correlated with silt plus clay content, with different regression lines for those stations shallower and deeper than 134 m, owing to several stations of higher C content with the elevated C/N ratio on the inner shelf. These results suggest that transport and deposition of organic-rich fine sediment particles by hydrodynamic processes were major factors controlling C content off Tokachi. In addition, the supply of a fraction of terrestrial organic matter with high C/N probably also affected C content on the inner shelf. (c) 2005 Elsevier B.V. All rights reserved.
  • Hiroaki Saito, Atsushi Tsuda, Yukihiro Nojiri, Jun Nishioka, Shigenobu Takeda, Hiroshi Kiyosawa, Isao Kudo, Yoshifumi Noiri, Tsuneo Ono, Yousuke Taira, Koji Suzuki, Takeshi Yoshimura, Philip W. Boyd
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 53 20-22 2168 - 2181 2006年 [査読有り][通常論文]
     
    This paper reports on the variations in nutrient concentrations and phytoplankton dynamics during the stationary and declining phases of a phytoplankton bloom induced by a mesoscale iron-enrichment conducted in the high-nutrient low-chlorophyll (HNLC) eastern subarctic Pacific. During the 26-d sampling period, the main pycnocline was located between 30 and 45 m with a shallow pycnocline developing at 10 m, 19 d after the first iron-enrichment. The iron-induced bloom dominated by diatoms peaked during days 15 and 18, a period of high chlorophyll a concentrations (ca. 5 mg m(-3)), and declined thereafter. Nitrogenous nutrients and phosphate were not depleted during the whole experiment. In contrast, silicic acid and iron concentrations became very low during the stationary phase of the diatom bloom (days 15-18) and F(v)/F(m) declined. These observations suggest that silicic acid and iron limitation probably prevented further development of the diatom bloom. The decline in chlorophyll a concentrations during days 19-24 was mostly due to the decrease in diatom abundance. On the other hand, cell abundances of pico- and nanophytoplankton exhibited little change until day 24. In the layer located between the main and the shallow pycnocline (10-30 m), ammonium and silicic acid concentration increased during days 19-26, suggesting recycling of these nutrients. The amount of silicic acid recycled during that period was estimated at 71.3-99.2 mmol m(-2), while the dissolution rate of biogenic silica (BSi) was estimated to be 5.9-9.2% d(-1) in the upper 50 m of the water column. These results show that the development of a shallow pycnocline during the experiment accelerated the iron and silicic acid depletion in the upper mixed layer and influenced the recycling of the organic matter assimilated during the iron-induced bloom in the ocean surface. (c) 2006 Elsevier Ltd. All rights reserved.
  • K Suzuki, A Hinuma, H Saito, H Kiyosawa, HB Liu, T Saino, A Tsuda
    PROGRESS IN OCEANOGRAPHY 64 2-4 167 - 187 2005年 [査読有り][通常論文]
     
    To verify the hypothesis that the growth of phytoplankton in the Western Subarctic Gyre (WSG), which is located in the northwest subarctic Pacific, is suppressed by low iron (Fe) availability, an in situ Fe fertilization experiment was carried out in the summer of 2001. Changes over time in the abundance and community structure of phytoplankton were examined inside and outside an Fe patch using phytoplankton pigment markers analyzed by high-performance liquid chromatography (HPLC) and flow cytometry (FCM). In addition, the abundance of heterotrophic bacteria was also investigated by FCM. The chlorophyll a concentration was initially ca. 0.9 μ g l(-1) in the surface mixed layer where diatoms and chlorophyll b-containing green algae (prasinophytes and chlorophytes) were predominant in the chlorophyll biomass. After the iron enrichment, the chlorophyll a concentration increased up to 9.1 μ g l(-1) in the upper 10 m inside the Fe patch on Day 13. At the same time, the concentration of fucoxanthin (a diatom marker) increased 45-fold in the Fe patch, and diatoms accounted for a maximum 69% of the chlorophyll biomass. This result was consistent with a microscopic observation showing that the diatom Chaetoceros debilis had bloomed inside the Fe patch. However, chlorophyllide a concentrations also increased in the Fe patch with time, and reached a maximum of 2.2 μ g l(-1) at 5 m depth on Day 13, suggesting that a marked abundance of senescent algal cells existed at the end of the experiment. The concentration of peridinin (a dinoflagellate marker) also reached a maximum 24-fold, and dinoflagellates had contributed significantly (> 15%) to the chlorophyll biomass inside the Fe patch by the end of the experiment. Concentrations of 19'-hexanoyloxyfucoxanthin (a prymnesiophyte marker), 19'-butanoyloxyfucoxanthin (a pelagophyte market), and alloxanthin (a cryptophyte marker) were only incremented a few-fold increment inside the Fe patch. On the contrary, chlorophyll b concentration reduced to almost half of the initial level in the upper 10 m water column inside the Fe patch at the end of the experiment. A decrease with time in the abundance of eukaryotic ultraphytoplankton (< ca. 5 μ m in size), in which chlorophyll b-containing green algae were possibly included was also observed by FCM. Overall, our results indicate that Fe supply can dramatically alter the abundance and community structure of phytoplankton in the WSG. On the other hand, cell density of heterotrophic bacteria inside the Fe patch was maximum at only ca. 1.5-fold higher than that outside the Fe patch. This indicates that heterotrophic bacteria abundance was little respondent to the Fe enrichment. © 2005 Elsevier Ltd. All rights reserved.
  • H Saito, K Suzuki, A Hinuma, T Ota, K Fukami, H Kiyosawa, T Saino, A Tsuda
    PROGRESS IN OCEANOGRAPHY 64 2-4 223 - 236 2005年 [査読有り][通常論文]
     
    Microzooplankton grazing plays an important role in maintaining the phytoplankton biomass low in HNLC waters where iron depletion limits the phytoplankton growth. When the iron limitation is relieved by natural iron supply or manipulation, phytoplankton biomass increases with a floristic shift because responses of phytoplankton and its grazer to such a perturbation are variable by species. During the first in situ iron fertilization (IF) experiment in the western subarctic Pacific (SEEDS), microzooplankton responses to changes in phytoplankton community structure and biomass were examined. Gross growth rate (GGR) of eukaryotic ultraphytoplankton (EUKU, < ca. 5 μ m in size) increased 2 days after the IF (D2) and that of the cyanobacteria Synechococeus spp. (SYN) peaked on D4 and then decreased gradually with time until D 13, the end of the experiment. Net growth rate (NGR: GGR - grazing rate) increased after the IF however, the GGRs and the grazing rates on EUKU and SYN balanced well at the end of the experiment as well as observed prior to the IF. Total chlorophyll a concentration increased after D4 and increased to > 6 mg m(-3) after D9. Although primary productivity was > 1.6 g C m(-2) d(-1) in the surface mixed layer and GGRs of total phytoplankton were > 0.8 d(-1) during D9 and D13, the total chlorophyll a concentration was more or less steady after D9. This phytoplankton bloom in response to the IF was dominated by a centric diatom Chaetoceros debilis and most of the other diatom species and nano-phytoplankton increased their biomass. Grazing rates on total phytoplankton decreased with the increase in chlorophyll a concentration after the IF from 0.3 d(-1) initially to < 0.2 d(-1) on D9, and then rapidly increased to 0.70 d(-1) on D11. Aloricate ciliates were the most dominant microzooplankton (> 10 μ m) both in abundance and biomass prior to the IF and gradually decreased with the developing diatom bloom. Heterotrophic dinoflagellates, dominated by Gyrodinium spp., increased rapidly after D11. Both the abundance and biomass of heterotrophic dinoflagellates on D 13 were 5 times those prior to the IF, and they were the most dominant micrograzer at the end of the experiment. This indicates that grazing by dinoflagellates prevented further development of the diatom bloom after D9, together with limitations of light and iron bioavailability. The present study showed that micrograzers responded to the floristic shift induced by the IF with a time lag and their grazing was an important controlling factor not only on the pico- and nano-phytoplankton but also on the microphytoplankton including. chain-forming diatoms. It also showed that heterotrophic dinoflagellate grazing has an important role in the food-web dynamics and biogeochemical cycle after natural or manipulated perturbations in the HNLC western subarctic Pacific. © 2005 Elsevier Ltd. All rights reserved.
  • HB Liu, K Suzuki, H Saito
    JOURNAL OF OCEANOGRAPHY 60 1 119 - 137 2004年02月 [査読有り][通常論文]
     
    The phytoplankton community in the western subarctic Pacific (WSP) is composed mostly of pico- and nanophytoplankton. Chlorophyll a (Chl a) in the <2 mum size fraction accounted for more than half of the total Chl a in all seasons, with higher contributions of up to 75% of the total Chl a in summer and fall. The exception is the western boundary along the Kamchatka Peninsula and Kuril Islands and the Oyashio region where diatoms make up the majority of total Chl a during the spring bloom. Among the picophytoplankton, picoeukaryotes and Synechococcus are approximately equally abundant, but the former is more important in term of carbon biomass. Despite the lack of a clear seasonal variation in Chl a concentration, primary productivity showed a large seasonal variation, and was lowest in winter and highest in spring. Seasonal succession in the phytoplankton community is also evident with the abundance of diatoms peaking in May, followed by picoeukaryotes and Synechococcus in summer. The growth of phytoplankton (especially >10 mum cell size) in the western subarctic Pacific is often limited by iron bioavailability, and microzooplankton grazing keeps the standing stock of pico- and nano-phytoplankton low. Compared to the other HNLC regions (the eastern equatorial Pacific, the Southern Ocean, and the eastern subarctic Pacific), iron limitation in the Western Subarctic Gyre (WSG) may be less severe probably due to higher iron concentrations. The Oyashio region has similar physical condition, macronutrient supply and phytoplankton species compositions to the WSG, but much higher phytoplankton biomass and primary productivity. The difference between the Oyashio region and the WSG is also believed to be the results of difference in iron bioavailability in both regions.
  • A Tsuda, S Takeda, H Saito, J Nishioka, Y Nojiri, Kudo, I, H Kiyosawa, A Shiomoto, K Imai, T Ono, A Shimamoto, D Tsumune, T Yoshimura, T Aono, A Hinuma, M Kinugasa, K Suzuki, Y Sohrin, Y Noiri, H Tani, Y Deguchi, N Tsurushima, H Ogawa, K Fukami, K Kuma, T Saino
    SCIENCE 300 5621 958 - 961 2003年05月 [査読有り][通常論文]
     
    We have performed an in situ test of the iron limitation hypothesis in the subarctic North Pacific Ocean. A single enrichment of dissolved iron caused a large increase in phytoplankton standing stock and decreases in macronutrients and dissolved carbon dioxide. The dominant phytoplankton species shifted after the iron addition from pennate diatoms to a centric diatom, Chaetoceros debilis, that showed a very high growth rate, 2.6 doublings per day. We conclude that the bioavailability of iron regulates the magnitude of the phytoplankton biomass and the key phytoplankton species that determine the biogeochemical sensitivity to iron supply of high-nitrate, low-chlorophyll waters.
  • H Kitazato, T Nakatsuka, M Shimanaga, J Kanda, W Soh, Y Kato, Y Okada, A Yamaoka, T Masuzawa, K Suzuki, Y Shirayama
    PROGRESS IN OCEANOGRAPHY 57 1 3 - 16 2003年 [査読有り][通常論文]
     
    Deep-sea benthic ecosystems are mainly sustained by sinking organic materials that are produced in the euphotic zone. "Benthic-pelagic coupling" is the key to understanding both material cycles and benthic ecology in deep-sea environments, in particular in topographically flat open oceanic settings. However, it remains unclear whether "benthic-pelagic coupling" exists in eutrophic deep-sea environments at the ocean margins where areas of undulating and steep bottom topography are partly closely surrounded by land. Land-locked deep-sea settings may be characterized by different particle behaviors both in the water column and in relation to submarine topography. Mechanisms of particle accumulation may be different from those found in open ocean sedimentary systems. An interdisciplinary programme, "Project Sagami", was carried out to understand seasonal carbon cycling in a eutrophic deep-sea environment (Sagami Bay) with steep bottom topography along the western margin of the Pacific, off central Japan. We collected data from ocean color photographs obtained using a sea observation satellite, surface water samples, hydrographic casts with turbidity sensor, sediment trap moorings and multiple core samplings at a permanent station in the central part of Sagami Bay between 1997 and 1998. Bottom nepheloid layers were also observed in video images recorded at a real-time, sea-floor observatory off Hatsushima in Sagami Bay. Distinct spring blooms were observed during mid-February through May in 1997. Mass flux deposited in sediment traps did not show a distinct spring bloom signal because of the influence of resuspended materials. However, dense clouds of suspended particles were observed only in the spring in the benthic nepheloid layer. This phenomenon corresponds well to the increased deposition of phytodetritus after the spring bloom. A phytodetrital layer started to form on the sediment surface about two weeks after the start of the spring bloom. Chlorophyll-a was detected in the top 2 cm of the sediment only when a phytodetritus layer was present. Protozoan and metazoan meiobenthos increased in density after phytodetritus deposition. Thus, "benthic-pelagic coupling" was certainly observed even in a marginal ocean environment with undulated bottom topography. Seasonal changes in features of the sediment-water interface were also documented. (C) 2003 Elsevier Science Ltd. All rights reserved.
  • Yoshihisa Mino, Toshiro Saino, Toshiro Saino, Koji Suzuki, Emilio Maranón
    Global Biogeochemical Cycles 16 4 7 - 1 2002年12月01日 [査読有り][通常論文]
     
    Isotopic composition of suspended particulate nitrogen (δ15Nsus) has been studied in near-surface waters along a transect extending from 50°N to 50°S in the Atlantic Ocean. The δ15Nsus values ranged from -0.8 to +5.4‰ and showed a significant correlation with depth of nitracline (δ15Nsus = -0.047 × DNO3 + 5.706; R2 = 0.81, n = 15) in nutrients-depleted regions (45°N-40°S). This inverse relationship implied that higher uptake of new NO3 - during mesotrophic conditions, characterized by shallower DNO3, derived relatively enriched δ15Nsus. On the other hand, lower 15N signature of the remineralized NH4 + would be mainly imprinted on particulate nitrogen pool in the oligotrophic regions characterized by deep DNO3. The observed inverse δ15Nsus-DNO3 relationship can be modeled by a simple isotopic mass balance equation concerning with the N utilizability of phytoplankton (in terms of f-ratio). The model results that the variations in δ15Nsus reflect the regional differences in nitrogen cycle in the upper ocean. In the region between equator and 15°N, where N2-fixing cyanobacteria (Trichodesmium spp.) were found, the measured δ15Nsus values were about 2‰ lower than those expected from the regression with the DNO3 indicating that over 38% of the suspended particulate nitrogen came through N2-fixation in this region. Regional variations in δ15Nsus in surface waters also correlated with those in water column productivity implying that the δ15Nsus signature can provide an estimate of in situ algal production.
  • K Suzuki, HB Liu, T Saino, H Obata, M Takano, K Okamura, Y Sohrin, Y Fujishima
    LIMNOLOGY AND OCEANOGRAPHY 47 6 1581 - 1594 2002年11月 [査読有り][通常論文]
     
    In the subarctic Pacific and its adjacent waters, the photochemical quantum yield (F-v/F-m) and the functional absorption cross section (sigma(PSN)) of photosystem II for surface phytoplankton were continuously measured during the early summer of 1999 using a fast repetition rate fluorometer. Concentrations of total dissolvable iron (TD-Fe) were also determined at each sampling station. The maximum value (0.61) of F-v/F-m was observed off the Aleutian Peninsula, where TD-Fe concentrations were relatively high. The Western Subarctic Gyre (WSG) and the Alaskan Gyre (AG), located in the northwest and northeast subarctic Pacific, respectively, were in high-nutrient, low-chlorophyll (HNLC) conditions. Surface TD-Fe generally remained in the WSG but was depleted (<0.01 nmol L-1) in the AG. Nighttime F-v/F-m and sigma(PSII) in the WSG were significantly higher (p < 0.01) and lower (p < 0.01), respectively, than in the AG. Iron or nitrogen limitations generally lead to a decrease in F,IF and an increase in sigma(PSII). These results suggested that there was an east-west gradient (WSG > AG) in the photosynthetic competence of phytoplankton in the subarctic Pacific and that the difference was probably caused by iron levels in seawater. Indeed, our iron enrichment experiment in the AG revealed that F-v/F-m increased from 0.27 to 0.49 and sigma(PSII) decreased from 496 X 10(-20) to 365 X 10(-20) m(2) photon(-1) after a 0.8 nmol L-1 iron addition. At the same time, a dramatic floristic shift from phytoflagellates to diatoms was found by pigment signatures. Iron could principally control the photosynthetic physiology of phytoplankton in the whole subarctic Pacific.
  • HB Liu, K Suzuki, C Minami, T Saino, M Watanabe
    MARINE ECOLOGY PROGRESS SERIES 237 1 - 14 2002年07月 [査読有り][通常論文]
     
    We studied picoplankton community structures in the subarctic Pacific Ocean and the Bering Sea during summer 1999 using flow cytometric analysis. The picoplankton community in the studied area was comprised of Synechococcus spp., eukaryotic ultraplankton and heterotrophic bacteria. Prochlorococcus spp. were not detected at any station. Abundances of Synechococcus and eukaryotic ultraplankton were at approximately the same level of 10(3) to 10(4) cells ml(-1) within the upper euphotic layer in the subarctic gyres. An abundance of Synechococcus spp. higher than 5 x 10(4) cells ml(-1) was found at the surface to 40 m depth in the northern Gulf of Alaska, whereas low Synechococcus spp. abundance (about 500 cells ml(-1)) was found in the upper euphotic layer in the Bering Sea. Abundances of heterotrophic bacteria were about 2 orders of magnitude higher than those of Synechococcus spp. and eukaryotic ultraplankton, with higher abundance generally occurring in the area of high autotrophic biomass. Although Synechococcus spp. and eukaryotic ultraplankton occurred at comparable abundance, the latter contributed significantly more to photosynthetic carbon biomass, except in the northern Gulf of Alaska, where the biomass of Synechococcus spp. and eukaryotic ultraplankton were approximately equal. Cellular red fluorescence for Synechococcus spp. and eukaryotic ultraplankton increased by an average 4- and 2-fold, respectively, from the surface to the bottom of the euphotic layer, with the smallest increase occurring in the Bering Sea. Both the red fluorescence and forward light scatter (FSC, related mainly to cell size) per cell varied more than 2-fold spatially, with the highest value occurring in the Bering Sea. These variations were probably caused by differences in physiological conditions and species compositions. Overall, picophytoplankton was the dominant contributor to total autotrophic biomass in the subarctic North Pacific, but contributed only a small fraction to total autotrophic biomass in the Bering Sea. The Western Gyre (WG) and the Alaskan Gyre (AG) possess both similarities and differences in biogeochemical processes and microbial food-web dynamics. The slightly higher phytoplankton biomass, photosynthetic efficiencies and growth rates in WG than AG suggests less severe iron limitation in the WG.
  • K Suzuki, A Tsuda, H Kiyosawa, S Takeda, J Nishioka, T Saino, M Takahashi, CS Wong
    JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 271 1 99 - 120 2002年05月 [査読有り][通常論文]
     
    To investigate the impact of microzooplankton grazing on phytoplankton bloom in coastal waters, an enclosure experiment was conducted in Saanich Inlet, Canada during the summer of 1996. Daily changes in the microzooplankton grazing rate on each phytoplankton group were investigated with the growth rates of each phytoplankton group from the beginning toward the end of bloom using the dilution technique with high-performance liquid chromatography (HPLC). On Day I when nitrate and iron were artificially added, chlorophyll a concentration was relatively low (4.3 mug l(-1)) and 19'-hexanoyloxyfucoxanthin-containing prymnesiophytes were predominant in the chlorophyll biomass. However, both the synthetic rates and concentrations of 19'-hexanoyloxyfucoxanthin declined before bloom, suggesting that 19'-hexanoyloxyfucoxanthin-containing prymnesiophytes weakened. Chlorophyll a concentration peaked at 23 mug l(-1) on Day 4 and the bloom consisted of the small chain-forming diatoms Chaetoceros spp. (4 mum in cell diameter). Diatoms were secondary constituents in the chlorophyll biomass at the beginning of the experiment, and the growth rates of diatoms (fucoxanthin) were consistently high (>0.5 d(-1)) until Day 3. Microzooplankton grazing rates on each phytoplankton group remarkably increased except on alloxanthin-containing cryptophytes after the nutrient enrichments, and peaked with >0.6 d(-1) on Day 3. indicating that >45% of the standing stock of each phytoplankton group was removed per day. Both the growth and mortality rates of alloxanthin-containing cryptophytes were relatively high (>1 and >0.5 d(-1), respectively) until the bloom, suggesting that a homeostatic mechanism might exist between predators and their prey. Overall, microzooplankton grazing showed a rapid response to the increase in phytoplankton abundance after the nutrient enrichments, and affected the magnitude of the bloom significantly. High grazing activity of microzooplankton contributed to an increase in the abundance of heterotrophic dinoflagellates with 7-24 mum in cell size, the fraction of large-sized (>10 mum) chlorophyll a, and stimulated the growth of larger-sized ciliates after the bloom. (C) 2002 Elsevier Science B.V. All rights reserved.
  • 鈴木 光次, 吉川 尚, 古谷 研, 才野 敏郎
    日本プランクトン学会報 49 1 27 - 36 日本プランクトン学会 2002年02月 [査読有り][通常論文]
  • HB Liu, K Suzuki, T Saino
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 49 2 363 - 375 2002年02月 [査読有り][通常論文]
     
    Phytoplankton growth and microzooplankton grazing rates were measured by the dilution technique in the subarctic North Pacific Ocean along a west-east transect during summer 1999. Average phytoplankton growth rates without added nutrients (mu(0)) were 0.33, 0.41, 0.20 and 0.49 d(-1) for the four regions sampled: the Western Gyre, the Bering Sea, the Gulf of Alaska gyre and stations along the Aleutian Trench. Average grazing mortality rates (m) were 0.34, 0.27, 0.20 and 0.49 d(-1). Limitation of phytoplankton growth by macronutrients, such as NO3 and SiO2, was identified only at a few stations, with overall mu(0)/mu(n) (mu(n) is nutrient-enhanced growth rate) averaging 0.9. Phytoplankton growth and microzooplankton grazing were approximately balanced, as indicated by high m/mu(0) ratio, except in the Bering Sea, where the m/mu(0) ratio was 0.65, indicating the relative importance of the diatom-macrozooplankton grazing food chain and possible higher export flux to the deep layer. Flow cytometric analysis revealed that the growth rates of picoplankton (Synechococcus and picoeukaryotes) were usually much lower than the total phytoplankton community growth rates estimated from chlorophyll a, except for stations in the Gulf of Alaska Gyre, where the growth rates for different populations were about the same. Lower than community-average growth rate for picoplankton indicates larger phytoplankters, presumably diatoms, were growing at a much faster rate. Suppressed phytoplankton growth in The Gulf of Alaska was probably a result of iron limitation. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • K Suzuki, C Minami, HB Liu, T Saino
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 49 24-25 5685 - 5704 2002年 [査読有り][通常論文]
     
    The distribution and community structure of phytoplankton were investigated in the subarctic Pacific and the Bering Sea during summer 1999 using chemotaxonomic pigment markers analyzed by HPLC and the CHEMTAX program (Mar. Ecol. Prog. Ser. 144 (1996) 265). In addition, in vivo chlorophyll fluorescence was also applied to the estimation of phytoplankton abundance in the study area. During our survey, chlorophyll a concentrations were consistently low (< 1 mug 1(-1)) in the whole water column of the Western Subarctic Gyre (WSG) and the Alaskan Gyre (AG). In contrast, higher chlorophyll a concentrations (> 1 mug 1(-1)) were sometimes observed in the Bering Sea and a coastal domain near the Aleutian Islands. In the WSG stations, prasinoxanthin-containing prasinophytes consistently predominated (ca. 20-40% in terms of chlorophyll biomass), although prasinophytes have received little attention in previous studies of the subarctic Pacific. Diatoms were a secondary component in terms of chlorophyll biomass in the WSG. Phytoflagellates, such as prymnesiophytes, pelagophytes, and green algae (prasinophytes and chlorophytes), contributed 45-90% to the chlorophyll biomass in the AG stations. Diatoms were predominant in the phytoplankton community of the Bering Sea, but the dominant phytoplankton group was variable in the coastal domain of the Aleutian Islands. When we compared the WSG with the AG in terms of the abundance and community structure of phytoplankton during the study period, the two gyres appeared to be in a similar biogeochemical province: sufficient macronutrients, low-chlorophyll biomass (< 1 mug 1(-1)), and the dominance of small phytoflagellates. These results imply the dominance of a microbial food web, which is responsible for the recycling of biogenic carbon or nutrients in the euphotic zone of the two gyres. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • HB Liu, K Imai, K Suzuki, Y Nojiri, N Tsurushima, T Saino
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 49 24-25 5409 - 5420 2002年 [査読有り][通常論文]
     
    Picoplankton community structure in the upper 200 m at Station KNOT in the western subarctic North Pacific was studied by flow cytometric analysis of the time-series samples collected from June 1998 through June 2000. Phototrophic picoplankton, Synechococcus and picoeukaryotes, displayed a clear seasonal cycle in population abundance during the 2-yr period, where chlorophyll a concentration remained relatively low and constant throughout the year, except in spring when the diatom bloom occurred. High picoplankton abundance occurred after the spring diatom bloom when the water column became more stratified. The maximum abundance of Synechococcus occurred in late June to early August, whereas the peak in picoeukaryotes abundance appeared to take place earlier in May and remained high through the summer. Heterotrophic bacteria abundance also displayed a seasonal variation pattern that was closely related to the picoplankton biomass, but not total chlorophyll biomass. (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 [査読有り][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。
  • 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 [査読有り][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。
  • Yumiko Obayashi, Eiichiro Tanoue, Koji Suzuki, Nobuhiko Handa, Yukihiro Nojiri, Chi Shing Wong
    Deep-Sea Research Part I: Oceanographic Research Papers 48 2 439 - 469 2001年 [査読有り][通常論文]
     
    Particulate matter in surface waters of the northern North Pacific and the southern Bering Sea was analyzed for the spatial and temporal distribution of chlorophyll and carotenoid pigment compositions by high-performance liquid chromatography (HPLC). Samples were collected during 11 ship of opportunity cruises between Canada and Japan from April 1995 to June 1996. The cruises each took 13 days and were conducted every six weeks. Seasonal variability of the concentration of chlorophyll a showed different features among the three areas studied: the Alaskan Gyre (eastern part of the subarctic North Pacific), southern Bering Sea, and the area off the Kuril Islands (western part of the subarctic North Pacific). In the Alaskan Gyre, the concentrations of chlorophyll a were around 0.2-0.4 μg/l without any remarkable seasonal variation, consistent with previous studies. In the Bering Sea and the area off the Kuril Islands, a drastic change in chlorophyll a biomass was observed from spring to early summer, with extremely high levels, > 2 μg/l, being found. The composition of the phytoplankton community was estimated by multiple regression analysis. A high concentration of chlorophyll a exceeding 1 μg/l was always accompanied by a high contribution of fucoxanthin-containing diatoms constituting up to 90% of the total chlorophyll a biomass. Chlorophyll b-containing green algae were one of the important algal groups in the northern North Pacific throughout the year as were fucoxanthin-containing diatoms and 19'-hexanoyloxyfucoxanthin-containing prymnesiophytes. The results give new insights into the phytoplankton community structure of the subarctic North Pacific, namely, an ubiquitous basic structure made up of rather diverse algal groups, and a flourishing diatom population limited by area and season and superimposed on the basic structure. These two structures are thought to play their respective roles in the biogeochemical cycle in the surface of the northern North Pacific. (C) 2000 Elsevier Science Ltd.
  • Y Sohrin, S Iwamoto, M Matsui, H Obata, E Nakayama, K Suzuki, N Handa, M Ishii
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 47 1 55 - 84 2000年01月 [査読有り][通常論文]
     
    The vertical profiles of labile Fe in seawater in the Australian sector of the Southern Ocean (50-65 degrees S along 140 degrees E) were obtained in the austral spring 1994/1995 by concentration with 8-hydroxyquinoline immobilized fluoride containing metal alkoxide glass (MAF-8HQ) followed by determination with chemiluminescence on board. While the concentrations of Fe were low in the surface water column (0.14 +/- 0.12 nM, n = 97 for 0-100 m) and increased in deep water at all stations, the profiles varied depending on the latitude. The Fe concentrations in intermediate and deep water were 0.30 +/- 0.12 (n = 36 for 500-2000 m) between the Antarctic Front (AF) and Antarctic Divergence (AD), and steeply increased south of the AD. The high Fe region (<1.5 nM) extended northwards along the continental slope and coincided with the Antarctic Bottom Water. Another Fe maximum in deep water (similar to 1.2 nM) was located on the north side of the Pacific Antarctic Ridge. The Fe concentrations showed a minimum ( similar to 0.3 nM) at 3000 m depth at 62 degrees S, which was almost coincident with the maximum of SiO(2) ( similar to 125 mu M) in the Lower Circumpolar Deep Water. There were some patchy Fe maximums in shallow water between the AF and AD, which did not coincide with the maximums of PO(4) and NO(3) in the Upper Circumpolar Deep Water. These results indicate that the distribution of Fe is nutrient-like but strongly influenced by local sources and water circulation. The Fe:PO(4) ratios in the surface water column (< 3 x 10(-4)) were lower than the critical value for a phytoplankton bloom (1 x 10(-3)) proposed by de Baar et al. (1990, Marine Ecology Progress Series 65, 105-122). Although the concentrations of Fe did not correlate with those of chlorophyll a, they positively correlated with the indices of primary productivity (growth rate, productivity by simulated in situ (13)C method and monthly integrated net community production). It seems that phytoplankton suffered Fe stress and that Fe was a limiting factor of the primary production. However, it is likely that there were some co-limiting factors, such as grazing at the ice edge and depletion of SiO(2) and critical-depth/mixed-depth relationship in the Permanently Open Ocean Zone and Polar Front Zone. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • H. Kitazato, Y. Shirayama, T. Nakatsuka, S. Fujiwara, M. Shimanaga, Y. Kato, Y. Okada, J. Kanda, A. Yamaoka, T. Masuzawa, K. Suzuki
    Marine Micropaleontology 40 3 135 - 149 2000年 [査読有り][通常論文]
     
    The seasonal carbon cycle was studied in the bathyal environment of Sagami Bay, Japan, to determine whether 'benthic-pelagic coupling' takes place in this eutrophic marginal oceanic setting. Both Japanese sea color observation satellite (ADEOS) photography and sediment trap moorings have been used since 1996 for monitoring sea surface primary production. Video records at a real time deep-sea floor observatory off Hatsushima Island in Sagami Bay were also used to monitor the deposition of phytodetritus on the sea floor. At this location, a spring bloom starts in mid-February and ends in mid-April. About 2 weeks after the start of the spring bloom, phytodetrital material is deposited on the sea floor. Video records clearly show that phytodetritus deposition has taken place in the spring of every year since 1994, even though the exact timing is different from year to year. The population size of benthic foraminifera is highly correlated to this phytodetritus deposition. The phytodetritus triggers rapid, opportunistic reproduction of the shallow infaunal taxa, Bolivina pacifica, Stainforthia apertura and Textularia kattegatensis. Shallow infaunal species mainly occur in the phytodetrital layer or just below this layer during the spring. This indicates that such opportunistic species are key indicators of phytodetrital deposition. The deep infaunal taxa Globobulimina affinis and Chilostomella ovoidea show less pronounced seasonal fluctuations in population size, but nevertheless exhibit some response to phytodetrital deposition. Thus the seasonal flux of organic matter is the most important determinant of population size, microhabitats and reproduction of benthic foraminifera in Sagami Bay. (C) 2000 Elsevier Science B.V.
  • Toshiro Saino, Shaoling Shang, Yoshihisa Mino, Koji Suzuki, Hideaki Nomura, Sei-Ichi Saitoh, Hideo Miyake, Toshiyuki Masuzawa, Koh Harada
    Journal of Oceanography 54 5 583 - 592 1998年 [査読有り][通常論文]
     
    A sediment trap experiment was carried out in conjunction with an over flight of Ocean Color Temperature Scanner (OCTS) on board Advanced Earth Observing Satellite (ADEOS) at 40°N, 143°E off Sanriku in April to May 1997. Short term variability of particle fluxes was examined at depths of 450 m and 600 m from April 6 to May 1 with a sampling interval of two days, and at 450 m with one day interval from 2nd to 10th May. Daily averaged mass flux at 450 m and 600 m was 815 mg m-2d-1 and 862 mg m-2d-1, respectively. A sharp increase in mass flux was observed during the period from April 26 to April 29 with the highest mass flux of 8 g m-2d-1. About 85% of the total mass flux for the entire duration (26 days) was collected within these 4 days. Trapped material during the peak flux period was mainly composed of diatoms dominated by Thalassiosira spp. and resting spores of Chaetoceros spp. This suggested that the peak flux was the result of (a) diatom bloom(s) in the euphotic column. Current meter records at 420 m showed that on April 26 and 27, the period when the peak flux was observed, the southwestward current had diminished in strength and changed its direction northwestward. Low current speeds appeared to have enhanced trap efficiency to help form the peak flux. A time series of OCTS Intensive-LAC (Local Area Coverage: Region B) images from mid-March to early May was examined to detect phytoplankton bloom(s). In the March 26th Chl image, high concentration region was restricted to the southwest off Cape Erimo, but spread around the warm core ring (WCR) 93A by April 10. East of the WCR93A, high Chl concentration remained steady until May, but to the west of the WCR93A, Chl decreased rapidly before the 19th of April. From this observation we suspect that the peak flux observed at the end of April originated from a bloom, which ceased on the 17th or 18th of April, in the region north of 40°N and west of 143°E. Taking the current meter records into account, the source region for the trapped material is most likely around southwest of the Cape Erimo.
  • Koji Suzuki, Motoaki Kishino, Kousei Sasaoka, Sei-Ichi Saitoh, Toshiro Saino
    Journal of Oceanography 54 5 517 - 526 1998年 [査読有り][通常論文]
     
    The variety in shape and magnitude of the in vivo chlorophyll-specific absorption spectra of phytoplankton was investigated in relation to differences in pigment composition off Sanriku, northwestern North Pacific. Site-to-site variations of the absorption coefficients, a*ph(λ), and pigment composition were clearly observed. At warm-streamer stations, higher values of a*ph(440) and a*ph(650) were found with relatively high concentrations of chlorophyll b (a green algae marker). At stations located in the Oyashio (cold streamer), a*ph(440) values were lower and fucoxanthin (a diatom marker) concentrations were higher, compared to the other stations. The peak in the absorption spectra at the Oyashio stations was shifted toward shorter wavelenghts, which was probably due to the presence of phaeopigments. In a Kuroshio warm-core ring, the magnitude of a*ph (440) was in between those at the warm-streamer and Oyashio stations, and the diagnostic pigment was peridinin (a dinoflagellate marker). These findings indicated that major differences in phytoplankton absorption spectra of each water mass were a result of differences in the phytoplankton pigment composition of each water mass, which was probably related to the phytoplankton community.
  • Koji Suzuki, Nobuhiko Handa, Hiroshi Kiyosawa, Joji Ishizaka
    Journal of Oceanography 53 4 383 - 396 Oceanographic Society of Japan 1997年08月01日 [査読有り][通常論文]
     
    The long meridional (175°E, 48°N-8°S) distribution of phytoplankton pigments was investigated in the central Pacific Ocean during the boreal summers of 1992 and 1993 by using high-performance liquid chromatography (HPLC). The sampling periods were under El Niño conditions. The distribution patterns of the chemotaxonomical pigments for eukaryotic phytoplankton were characterised: 19′-hexanoyloxyfucoxanthin (a prymnesiophyte marker) and 19′-butanoyloxyfucoxanthin (a pelagophyte marker) were detected throughout the whole study area, fucoxanthin (a diatom marker) was observed north of Kuroshio Extension, and peridinin (a dinoflagellate marker) was found at the stations both north of the Kuroshio Extension and the equatorial area, and the abundance of these pigments detected was not significantly changed (non-parametric one-way ANOVA, P > 0.05) in the whole study area during the two sampling periods. However, the abundance of prokaryotic photoautotrophs (prochlorophytes and cyanobacteria) at the North Pacific subtropical gyre and the equatorial region during the boreal summers of 1993 was significantly higher (P < 0.001) than that during the boreal summer of 1992 as estimated by their chemotaxonomical marker, zeaxanthin. The high prokaryotic phytoplankton biomass during the boreal summer of 1993 was also calculated by using the algorithm of Letelier et al. (1993) for partioning total chlorophyll a biomass into contributions by major phytoplankton taxa. The North Pacific subtropical gyre has generally been thought to support a homogeneous, stable biological community, but our result suggests that the abundance of prokaryotic phytoplankton in this gyre may be spatially and temporally variable, and these change can affect primary production and zooplankton biomass.
  • K Suzuki, N Handa, T Nishida, CS Wong
    JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 214 1-2 1 - 17 1997年07月 [査読有り][通常論文]
     
    An enclosure experiment was conducted during the summer of 1994 in Saanich Inlet, Canada. In order to simulate phytoplankton dynamics when new nutrients are supplied into oligotrophic waters, the enclosure, in which nitrate was initially depleted, was artificially fertilized with macronutrients (nitrate, phosphate, and silicate). The abundance and composition of phytoplankton assemblages in the enclosure at three integrated depths (0-4 m, 4-8 m, 8-12 m) were estimated by measuring phytoplankton pigments using high-performance liquid chromatography. Chlorophyll a concentration at 0-4 m increased rapidly twelve-fold after the addition of the macronutrients, and thereafter gradually decreased until the end of the experiment. However chlorophyll a abundances at both 4-8 m and 8-12 m layers did not change much. Multiple regression analyses of chlorophyll a and selected accessory pigments at each depth indicated that fucoxanthin-containing algae, which were mostly not diatoms but raphidophytes on the basis of the results of microscopic analysis, dominated the chlorophyll a biomass in the enclosure throughout the experiment (30-70%). In addition, fucoxanthin in the < 20 mu m size-fraction generally accounted for > 60% of the total fucoxanthin at the three depths, suggesting that most of the fucoxanthin-containing algae were probably not microplankton (> 20 mu m) but nanoplankton (< 20 mu m). Peridinin-containing dinoflagellates, which were mostly microplankton, were a secondary component of the phytoplankton community throughout the enclosure (15-50%). Chlorophyll b-containing green algae, which were mostly nanoplankton, were also a secondary constituent at the beginning of the experiment (10-35%), declining rapidly thereafter in the all layers. These results suggest that motile raphidophytes and dinoflagellates can become the most important phytoplankton groups when new nutrients become available in the surface waters of temperate zone coastal areas during the summer. (C) 1997 Elsevier Science B.V.
  • H. Sasaki, H. Suzuki, M. Tanaka, K. Suzuki, N. Handa, S. Kudoh, M. Fukuchi
    Proc. NIPR Symp. Polar Biol. 10 50 - 55 国立極地研究所 1997年 [査読有り][通常論文]
     
    Time-series sediment traps were deployed at depths of 537 m, 796 m, 1259 m, 1722 m and 2727 m at ice edge of the Antarctic Ocean (64°42'S, 139°58'E) from 26 December 1994 to 20 January 1995. During a short period from 7 to 9 January, a sporadic flux increase within a few days in terms of total dry weight of 774 mg m^<-2>d^<-1> at 537 m was observed. The mass of sinking particles forming the flux maximum sank down to the deepest trap (2727 m) within 7-11 days, indicating that about 5% of these particles were transported downward to the bottom with the sinking rate of 199-313 m d^<-1> (mean 243 m d^<-1>). The considerable particle loss rate (13% [100 m]^<-1>) below the mesopelagic layers in a short period suggests the occurrence of consumption processes induced by the sporadic supply of freshly produced particles from above.
  • J. I. Goes, N. Handa, K. Suzuki, S. Taguchi, T. Hama
    Proc. NIPR Symp. Polar Biol. 10 25 - 38 国立極地研究所 1997年 [査読有り][通常論文]
     
    Experiments were conducted during January 1995 in the Southern Ocean to examine the impact of enhanced solar ultraviolet-B radiation (UVBR) on the biosynthesis and composition of organic compounds in Antarctic marine phytoplankton. Our results revealed distinct changes in the biochemical composition of phytoplankton attributable to UVBR exposure. Fatty acid concentrations increased in the presence of UVBR, mainly on account of a large increase in the content of saturated fatty acids within the cells. On the other hand, polyunsaturated fatty acids declined in cells exposed to UVBR. Amino acid concentrations were higher in the UVBR exposed samples, attributable largely to a UVBR induced increase in cellular concentrations of glutamic' acid (glutamic acid+glutamine) and aspartic acid. Monosaccharide constituents of cellular storage and structural carbohydrates, however, showed a decline in the cells exposed to UVBR. Except for the decline in structural monosaccharides, these changes in the patterns of organic compounds observed in Antarctic phytoplankton were remarkably similar but, greater in magnitude in comparison to those observed in temperate phytoplankton exposed to UVBR.
  • J. Ishizaka, K. Harada, K. Ishikawa, H. Kiyosawa, H. Furusawa, Y. Watanabe, H. Ishida, K. Suzuki, N. Handa, M. Takahashi
    Deep-Sea Research Part II: Topical Studies in Oceanography 44 9-10 1927 - 1949 1997年 [査読有り][通常論文]
     
    Size and taxonomic structure of plankton community carbon biomass for the 0.22000 p.m equivalent spherical diameter range were determined at the equator at 175°E in September 1990-1993 and April 1994. Total biomass of the plankton community ranged from 1944 to 3448 mg C m-2. Phytoplankton, zooplankton and bacteria carbon biomasses were 6041669 mg C m-2, 300-797 mg C m-2, and 968-1200 mg C m--2 and the percentages were 31-54%, 15-26%, and 29-54%, respectively. Biomass of heterotrophic bacteria was always the largest fraction and Prochlorococcus biomass was second. Heterotrophic and autotrophic flagellates and dinoflagellates in the nanoplankton size range and copepods (adults and copepodites) in the mesoplankton range were also high. Relatively small biomass was observed in the microplankton size range. The differences in integrated biomass of plankton community for El Nino type oligotrophic conditions of September 1990-1993 and non-El Nino type mesotrophic conditions of April 1994 were generally small compared with the interannual difference during 1990-1993. However, the percentage of Prochlorococcus in phytoplankton carbon biomass was larger in non-El Nino year. Biomasses of cyanobacteria. diatom, dinoflagellates, nauplii of copepods, and crustaceans other than copepods were larger in the non-El Nino year. Primary production increased significantly from El Nino to non-El Nino years. Carbon flow through the plankton food chain was estimated using the plankton carbon biomass data, primary production measurements, and published empirical relationships.
  • Koji Suzuki, Nobuhiko Handa, Hiroshi Kiyosawa, Joji Ishizaka
    Limnology and Oceanography 40 5 983 - 989 1995年 [査読有り][通常論文]
     
    This article is in Free Access Publication and may be downloaded using the “Download Full Text PDF” link at right. © 1995, by the Association for the Sciences of Limnology and Oceanography, Inc.

書籍

  • Takeyoshi Nagai, Hiroaki Saito, Koji Suzuki, Motomitsu Takahashi (担当:共編者(共編著者))
    Wiley - American Geophysical Union 2019年06月 (ISBN: 9781119428428) 1 online resource (x, 312 p., [8] p. of plates)
  • Advances in Above- and In-Water Radiometry, Vol. 3: Hybridspectral Next-Generation Optical Instruments
    Hooker, S.B, R.N. Lind, J.H. Morrow, J.W. Brown, R.M. Kudela, H.F. Houskeeper, K. Suzuki (担当:共著)
    NASA Scientific and Technical Information Program, NASA Goddard Space Flight Center 2018年11月
  • Advances in Above- and In-Water Radiometry, Vol. 2: Autonomous Atmospheric and Oceanic Observing Systems
    Hooker, S.B, R.N. Lind, J.H. Morrow, J.W. Brown, R.M. Kudela, H.F. Houskeeper, K. Suzuki (担当:共著)
    NASA Scientific and Technical Information Program, NASA Goddard Space Flight Center 2018年11月
  • Advances in Above- and In-Water Radiometry, Vol. 1: Enhanced Legacy and State-of-the-Art Instrument Suites
    Hooker, S.B, R.N. Lind, J.H. Morrow, J.W. Brown, K. Suzuki, H.F. Houskeeper, T. Hirawake, E.R. Maúre (担当:共著)
    NASA Scientific and Technical Information Program, NASA Goddard Space Flight Center 2018年11月
  • 日本海洋学会編, 鈴木光次 (担当:分担執筆範囲:植物色素; 基礎生産; 海水中の光)
    日本海洋学会 2018年07月
  • 日本生態学会編, 鈴木光次 (担当:分担執筆範囲:基礎生産過程; 海洋生態系の食物関係)
    共立出版 2016年02月 (ISBN: 9784320057456) xi, 305p, 図版 [4] p
  • 日本分析化学会編, 鈴木光次 (担当:分担執筆範囲:植物プランクトン)
    丸善 2011年01月 (ISBN: 9784621082775) xx, 823p, 図版 [4] p
  • 北海道大学大学院環境科学院編, 鈴木光次 (担当:分担執筆範囲:地球温暖化による海洋生態系の変化)
    北海道大学出版会 2007年03月 (ISBN: 9784832981812) xii, 246p
  • 北海道大学大学院環境科学院編, 鈴木光次 (担当:分担執筆範囲:紫外線による海洋生態系への影響; 水中の放射伝達)
    北海道大学出版会 2007年03月 (ISBN: 9784832981799) vi, 408p
  • 日本化学会編, 鈴木光次 (担当:分担執筆範囲:植物プランクトン)
    丸善 2007年01月 (ISBN: 9784621078068) xiii, 519p
  • 日本分析化学会北海道支部編, 鈴木光次 (担当:分担執筆範囲:クロロフィルa)
    化学同人 2005年06月 (ISBN: 9784759809916) x, 472p
  • 鈴木光次 (担当:分担執筆範囲:逆相高速液体クロマトグラフィーによるクロロフィルとカロチノイドの測定及びフィコビリンタンパク質の測定; 蛍光法による基礎生産速度の測定)
    フジ・テクノシステム 2002年 (ISBN: 4938555891) 3冊

特許

  • 特許第6484572号:濾過採取装置    2019年03月13日
    大江亮一 (25%), 大廣洋 (25%), 鈴木光次 (50%)  東洋濾紙株式会社; 北海道大学

受賞

  • 2017年01月 北海道大学 教育総長賞(奨励賞)
     
    受賞者: 鈴木光次
  • 2016年02月 北海道大学 研究総長賞(奨励賞)
     
    受賞者: 鈴木光次

教育活動情報

主要な担当授業

  • 大気海洋化学基礎論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 大気化学、海洋化学 Atmospheric Chemistry, Marine Chemistry
  • 生物地球化学基礎論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 海洋化学、大気化学、生物地球化学、物質循環、地球環境問題 Marine Chemistry, Atmospheric Chemistry, Biogeochemistry, Material Cycling, Global Environmental Issues
  • 環境と人間
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 大気、海洋、生態系、気候変化、地球環境問題、地球温暖化、成層圏オゾン層破壊、大気汚染

大学運営

委員歴

  • 2021年 - 現在   Frontiers in Marine Science Associate Editor
  • 2021年 - 現在   SCOR Working Group165 MixONET Associate Member
  • 2021年 - 現在   日本学術会議地球惑星科学委員会   GEOTRACES小委員会委員
  • 2019年 - 現在   東京大学大気海洋研究所   共同利用研究運営委員会委員
  • 2018年 - 現在   BioGeoSCAPES Member
  • 2018年 - 現在   日本学術会議環境学委員会   IMBeR小委員会委員
  • 2016年 - 現在   Elsevier   Advisory Panel Member
  • 2009年 - 現在   European Geosciences Union (EGU)   Biogeosciences Associate Editor


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