Research activity information

• Mar. 2023, 日本水産学会, 水産学技術賞
  我が国沖合海域における海洋プラスチックごみ調査の規準化およびデータベース整備
  内田圭一、萩田隆一、向井徹、今井圭理、清水健一、八木光晴、山中有一、三橋廷央、磯辺篤彦、黒田真央

• Tritium and 137Cs levels in marine fishes and in their host seawater around the Fukushima Daiichi Nuclear Power Plant from 2021 to 2024.
  Hyoe Takata; Toshihiro Wada; Hikaru Miura; Yoshifumi Wakiyama; Takuya Niida; Keiri Imai; Atsushi Ooki
  Journal of environmental radioactivity, 289, 107760, 107760, 28 Jul. 2025, [International Magazine]
  English, Scientific journal, We examined distributions of tritium and cesium-137 (137Cs) activity in marine fishes and in simultaneously collected host seawater in 2021-2024 around the Fukushima Daiichi Nuclear Power Plant (FDNPP). From April 2021 to June 2023 (before water treated by a multi-nuclide removal facility was first released into the ocean, hereafter, "before releases"), the mean tritium activity in bottom layer, host water of fishes, collected offshore (>5 km from the FDNPP) was 0.085 Bq/L. In nearshore water (2 km south of the FDNPP), tritium activity varied with fluvial input in 2021 and 2022 and correlated with dissolved 137Cs. After the start of treated-water releases in August 2023 (hereafter, "after releases"), at both offshore and nearshore sites, several samples deviated from the line of tritium vs dissolved 137Cs before releases, reflecting the input of treated-water-derived tritium. Means of tissue-free-water tritium (TFWT) activities in rockfish and Japanese flounder at offshore site were 0.089 and 0.075 Bq/kg-fresh, respectively, before releases, and 0.081 and 0.13 Bq/kg-fresh, respectively, after. At nearshore site, Japanese flounder TFWT activities after releases were 0.37-0.75 Bq/kg-fresh. The elevated TFWT activities after releases could have been caused by elevated tritium activities in host seawater. There, however, was no difference in the concentration ratios (CRs) of TFWT to host seawater tritium between before releases and after releases, indicating that TFWT quickly responded to changes in host water tritium. Moreover, the CRs of TFWT + total organically bound tritium for rockfish and Japanese flounder offshore after releases were 1 or less, suggesting that tritium was not accumulated in marine fish.
• Quantitative evaluation of <i>Karenia</i> cells using FlowCam: Applying to its distribution in Hidaka Bay, southern Hokkaido, northern Japan during autumn 2022
  Hikaru Kubo; Takahiro Iida; Keiri Imai; Atsushi Ooki; Kohei Matsuno
  Plankton and Benthos Research, 20, 1, 1, 11, The Plankton Society of Japan/The Japanese Association of Benthology, 28 Feb. 2025
  Scientific journal
• Abundance and potential sources of floating polystyrene foam macro- and microplastics around Japan
  Mao Kuroda; Atsuhiko Isobe; Keiichi Uchida; Tadashi Tokai; Toshihide Kitakado; Miho Yoshitake; Yoshinori Miyamoto; Tohru Mukai; Keiri Imai; Kenichi Shimizu; Mitsuharu Yagi; Takahisa Mituhasi; Akimasa Habano
  Science of The Total Environment, 925, 171421, 171421, Elsevier BV, May 2024
  Scientific journal
• Microplastic pollution indexes in the coastal and open ocean areas around Japan
  Haruka Nakano; María Belén Alfonso; Suppakan Jandang; Keiri Imai; Hisayuki Arakawa
  Regional Studies in Marine Science, 69, Jan. 2024
  Scientific journal
• Standardization and database development of marine plastic survey in the offshore areas around Japan
  Keiichi Uchida; Ryuichi Hagita; Tohru Mukai; Keiri Imai; Kenichi Shimizu; Mitsuharu Yagi; Yuichi Yamanaka; Takahisa Mituhasi; Atsuhiko Isobe; Mao Kuroda
  Nippon Suisan Gakkaishi (Japanese Edition), 89, 5, 394, 397, 2023
  Scientific journal
• 日本海の日本海盆底層水と大和海盆底層水の境界に形成される底層前線の水平分布と両底層水の混合による変質過程—Horizontal distribution of the benthic front formed at the boundary between Japan Basin Bottom Water and Yamato Basin Bottom Water in the Japan Sea and modification processes due to mixing of both Bottom Waters
  田谷 浩志郎; 伊藤 海彦; 磯田 豊; 今井 圭理; 小熊 健治; 澤田 光希
  海の研究, 31, 6, 99, 110, 東京 : 日本海洋学会, Dec. 2022
  Japanese
• The reducing rate of radiocesium Cs-137 in the North Pacific surface water after the TEPCO fukushima Dai-ichi nuclear power plant accident
  Keiri Imai; Yutaka W. Watanabe
  JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY, Jul. 2022
  English, Scientific journal
• A multilevel dataset of microplastic abundance in the world’s upper ocean and the Laurentian Great Lakes
  Atsuhiko Isobe; Takafumi Azuma; Muhammad Reza Cordova; Andrés Cózar; Francois Galgani; Ryuichi Hagita; La Daana Kanhai; Keiri Imai; Shinsuke Iwasaki; Shin’ichro Kako; Nikolai Kozlovskii; Amy L. Lusher; Sherri A. Mason; Yutaka Michida; Takahisa Mituhasi; Yasuhiro Morii; Tohru Mukai; Anna Popova; Kenichi Shimizu; Tadashi Tokai; Keiichi Uchida; Mitsuharu Yagi; Weiwei Zhang
  Microplastics and Nanoplastics, 1, 1, Springer Science and Business Media LLC, Dec. 2021
  Scientific journal, Abstract
  
  A total of 8218 pelagic microplastic samples from the world’s oceans were synthesized to create a dataset composed of raw, calibrated, processed, and gridded data which are made available to the public. The raw microplastic abundance data were obtained by different research projects using surface net tows or continuous seawater intake. Fibrous microplastics were removed from the calibrated dataset. Microplastic abundance which fluctuates due to vertical mixing under different oceanic conditions was standardized. An optimum interpolation method was used to create the gridded data; in total, there were 24.4 trillion pieces (8.2 × 10⁴ ~ 57.8 × 10⁴ tons) of microplastics in the world’s upper oceans.
• Crustaceans and fishes collected with drifting algae from off the Pacific coast of Tohoku region
  Hɪɢᴜᴄʜɪ Junya; Kᴀᴡᴀɪ Toshio; Uᴊɪ Toshiki; Iᴍᴀɪ Keiri
  北海道大学水産科学研究彙報, 71, 1, 21, 28, 北海道大学大学院水産科学研究院, 03 Aug. 2021
  Japanese, Research institution, Seven specimens of fishes and three specimens of crabs were collected with drifting algae by T/S Oshoro-maru from off the Pacific coast of Tohoku region, northern Japan. In fishes, a single specimen was identified as Histrio histrio (Linnaeus, 1758), five specimens as Oplegnathus punctatus (Temminck and Schlegel, 1844) and a single specimen as Stephanolepis cirrhifer (Temminck and Schlegel, 1850). In crabs, except a single specimen of megalopa, a single specimen was identified as Guinusia dentipes (De Haan, 1835) and a single specimen as Portunus (Portunus) sanguinolentus sanguinolentus (Herbst, 1783). Because previous northernmost records of P. (P.) sanguinolentus sanguinolentus were reported from Boso Peninsula in the Pacific Ocean and Akita Prefecture in the Sea of Japan, the present specimen represents the northernmost record of the species in the Pacific Ocean.
• The current state of marine debris on the seafloor in offshore area around Japan
  Mao Kuroda; Keiichi Uchida; Tadashi Tokai; Yoshinori Miyamoto; Tohru Mukai; Keiri Imai; Kenichi Shimizu; Mitsuharu Yagi; Yuichi Yamanaka; Takahisa Mituhashi
  Marine Pollution Bulletin, 161, Pt A, 111670, 111670, Dec. 2020, [Peer-reviewed], [International Magazine]
  English, Scientific journal
• Model experiments and observations of Oyashio barotropic flow intruding to Hidaka Trough via steep shelf slope area off Cape Erimo
  Miyake Masato; Isoda Yutaka; Imai Keiri; Oguma Kenji; Sawada Kouki
  北海道大学水産科学研究彙報, 70, 1, 1, 11, 北海道大学大学院水産科学研究院, 24 Aug. 2020
  Japanese, Research institution, The shelf slope off Cape Erimo is very steep, and its slope width (L～30 km) is smaller than the internal radius deformation (λi～50 km). A simple model is used to investigate the dynamic response of Oyashio barotropic flow passing through this local
  steep slope area. Model results suggest that near-bottom Oyashio water cannot intrude from shelf area off Cape Erimo to Hidaka Trough, because inverse flow accompanied by the bottom trapped shelf wave is generated over the steep slope under the physical condition of L <λi. To confirm the existence of such inverse flow, hydrographic data at upstream and downstream both sides of shelf area off Cape Erimo were examined.
• Behavior of water mass beneath the tsushimawarm current in the Japan Sea
  Xiaorong Fang; Yutaka Isoda; Isao Kudo; Takafumi Aramaki; Keiri Imai; Naoto Ebuchi
  Water (Switzerland), 12, 8, Aug. 2020, [Peer-reviewed]
  English, Scientific journal
• Spatiotemporal changes of ocean carbon species in the western North Pacific using parameterization technique
  Yutaka W. Watanabe; Bofeng F. Li; Royce Yamasaki; Shun Yunoki; Keiri Imai; Shigeki Hosoda; Yoshiyuku Nakano
  JOURNAL OF OCEANOGRAPHY, 76, 2, 155, 167, Apr. 2020, [Peer-reviewed]
  English, Scientific journal
• Stratification in the northern Bering Sea in early summer of 2017 and 2018
  Hiromichi Ueno; Mizuki Komatsu; Zhaoqianyi Ji; Ryo Dobashi; Miaki Muramatsu; Hiroto Abe; Keiri Imai; Atushi Ooki; Toru Hirawake
  Deep-Sea Research Part II: Topical Studies in Oceanography, 181-182, 2020, [Peer-reviewed]
  Scientific journal
• Upward transport of iron at the west shelf edge–slope of the Okinawa Trough in the East China Sea
  Ryohei Sasayama; Nanako Hioki; Yuichiroh Morita; Yutaka Isoda; Keiri Imai; Atsushi Ooki; Kenshi Kuma
  Journal of Oceanography, 74, 4, 367, 379, 01 Aug. 2018, [Peer-reviewed]
  English, Scientific journal
• Fukushima-derived radiocesium in the western North Pacific in 2014
  Yuichiro Kumamoto; Michio Aoyama; Yasunori Hamajima; Hisao Nagai; Takeyasu Yamagata; Yoshimi Kawai; Eitarou Oka; Atsushi Yamaguchi; Keiri Imai; Akihiko Murata
  Journal of Radioanalytical and Nuclear Chemistry, 311, 2, 1209, 1217, 01 Feb. 2017, [Peer-reviewed], [International Magazine]
  English, Scientific journal
• Time series of radioactive cesium concentration in the North Pacific surface water after the TEPCO Fukushima Dai-ichi Nuclear Power Plant accident by using T/S "Oshoro-Maru" cruses
  Imai Keiri; Watanabe Yutaka W
  北海道大学水産科学研究彙報, 65, 2, 111, 116, 北海道大学大学院水産科学研究科, Aug. 2015
  Japanese, 2011年3月11日，東北地方太平洋沖地震とそれに伴った大津波の影響で東京電力・福島第一原子力発電所において原子力事故が発生し，原子炉の崩壊および汚染水の意図的な放水によって，大量の放射性物質が大気および海洋へ放出された。この原子力発電所から直接海洋に流入したと推定される放射性セシウム量は，事故後から2ヶ月以内の間に，原子力発電所内部から高放射能汚染水として発電所専用港湾を経由して海洋に流出した部分が大半を占めると報告されている(Tsumune et al.，2013; Kanda，2013; 神田，2013)。また，多くの研究機関によって放射性物質による汚染状況を把握するために，海洋，大気および陸域の調査が行われ，放射性セシウムの測定がなされた(Honda et al.，2012; Aoyama et al.，2013a，b)。同時に数値シミュレーションを用いて，福島第一原子力発電所から大気および海洋へ放出された放射性物質量や，その広がりが予測され(Takemura et al.，2011; Tsumune et al.，2013)。
• fN-Oscillation trapped in the benthic front in the Abyssal Japan Sea
  Yamauchi Yasutaka; Kuma Kenshi; Tateno Manami; Imai Keiri; Owada Maki; Shoji Kenya; Isoda Yutaka; Arita Shun; Kawano Kohei; Fujiwara Shohei; Fang Xiaorong; Asahi Keijiro; Ida Satoki; Yasutaka Yamauchi; Kenya Shoji; Yutaka Isoda; Shun Arita; Kohei Kawano; Shohei Fujiwara; Xiaorong Fang; Keijiro Asahi; Satoki Ida; Kenshi Kuma; Manami Tateno; Keiri Imai; Maki Owada; Graduate School of Env. Earth Science Hokkaido University; Graduate School of Fisheries Science Hokkaido University; Graduate School of Fisheries Science Hokkaido University; Graduate School of Fisheries Science Hokkaido University; Graduate School of Fisheries Science Hokkaido University; Graduate School of Fisheries Science Hokkaido University; Faculty of Fisheries Hokkaido University; Faculty of Fisheries Hokkaido University; Faculty of Fisheries Hokkaido University
  Oceanography in Japan, 24, 4, 147, 169, The Oceanographic Society of Japan, 2015, [Peer-reviewed]
  Japanese,

  Because the vertical homogeneous Bottom Water (BW) with N ～0 (N is the buoyancy frequency) is formed in the Japan Sea, the abyssal water always has a depth of N ～f (f is the inertial frequency) above the BW. In the present study, we propose the theoretical existence of buoyancy/inertial oscillation under the weak stratification with N ～f in the non-hydrostatic dynamics and term it "fN-Oscillation". Based on the dispersion relation of internal inertial waves in the limit of N→f, it is concluded that fN-Oscillation with lateral maximum group velocity fulfills the requirement of a finite spatial scale for a ratio of horizontal/vertical wavenumber k/m＝1/√ 3. In the idealized stratification of N=f, in particular, this oscillation is confined to the generation area because it contains zero group velocity. Testing of numerical model experiments, including a localized front under the stratification with N~f, suggests that some of the fN-Oscillation energy trapped in this front escapes as internal waves. We observed that the benthic front existed stably between the Yamato Basin BW (YBBW) and the Japan Basin BW (JBBW) and was the plausible origin of energetic upward-propagating internal waves. The benthic front has a notably sharp structure with a horizontal scale of several hundreds meters. In the vicinity of this front, the periodic variations of temperature and dissolved oxygen were confirmed according to the internal waves, with the wavenumber satisfying approximately k/m~1/√3. Such disturbances represent indirect evidence for the trapping fN-Oscillation.

• Chemical evidence for the origin of the cold water belt along the northeastern coast of Hokkaido
  Kenshi Kuma; Ryohei Sasayama; Nanako Hioki; Yuichiroh Morita; Yutaka Isoda; Tohru Hirawake; Keiri Imai; Takafumi Aramaki; Tomohiro Nakamura; Jun Nishioka; Naoto Ebuchi
  Journal of Oceanography, 70, 4, 377, 387, Aug. 2014, [Peer-reviewed]
  English, Scientific journal
• Development and assessment of inside-coated glass vials for precision analysis of seawater
  Tsurushima Nobuo; Imai Keiri
  Journal of Advanced Marine Science and Technology Society, 20, 1, 29, 36, Advanced Marine Science and Technology Society, 2014, [Peer-reviewed]
  Japanese, Dissolution of silica from glass bottle sometimes influences accuracy of precision analysis of sea water, e.g. density and pH. We assessed and developed inside-coated glass vials to avoid dissolution of silica from glass at least < 1 mM for seawater sample storage. Seawater storage experiments using specially-treated vials available commercially (sulfur treatment, coating with fluoloresin or inorganic-organic hybrid material or silicone) suggests that dissolution of silica decreases by up to 60–70% related to that in uncoated glass vial at 25–40°C. As a result of storage experiments using test product of thick fluororesin coated vials, we found that dissolution of silica from glass can be avoided by repeating coating process (application and calcination) at least 10 times. We made trial products of thick fluororesin coated vials by this coating process. The results of seawater storage experiments showed that this newly developed vials can avoid dissolution of silica from glass surface at least 163 days at 25–40°C.
• Dynamics and elemental stoichiometry of carbon, nitrogen, and phosphorus in particulate and dissolved organic pools during a phytoplankton bloom induced by in situ iron enrichment in the western subarctic Pacific (SEEDS-II)
  Takeshi Yoshimura; Hiroshi Ogawa; Keiri Imai; Takafumi Aramaki; Yukihiro Nojiri; Jun Nishioka; Atsushi Tsuda
  Deep-Sea Research Part II: Topical Studies in Oceanography, 56, 26, 2863, 2874, 15 Dec. 2009, [Peer-reviewed]
  English, Scientific journal
• Biogeochemical cycling of N and Si during the mesoscale iron-enrichment experiment in the western subarctic Pacific (SEEDS-II)
  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, 15 Dec. 2009, [Peer-reviewed]
  English, Scientific journal
• Behavior of particulate materials during iron fertilization experiments in the Western Subarctic Pacific (SEEDS and SEEDS II)
  Takafumi Aramaki; Yukihiro Nojiri; Keiri Imai
  Deep-Sea Research Part II: Topical Studies in Oceanography, 56, 26, 2875, 2888, 15 Dec. 2009, [Peer-reviewed]
  English, Scientific journal
• Evidence for the grazing hypothesis: Grazing reduces phytoplankton responses of the HNLC ecosystem to iron enrichment in the western subarctic pacific (SEEDS II)
  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 Nakanishi; 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, Dec. 2007, [Peer-reviewed]
  English, Scientific journal
• Microplankton assemblages at Station KNOT in the subarctic western Pacific, 1999-2000
  Chika Komuro; Hisashi Narita; Keiri Imai; Yukihiro Nojiri; Richard W. Jordan
  Deep-Sea Research Part II: Topical Studies in Oceanography, 52, 16-18, 2206, 2217, Aug. 2005, [Peer-reviewed]
  English, Scientific journal
• Effect of iron enrichment on the dynamics of transparent exopolymer particles in the western subarctic Pacific
  Neelam Ramaiah; Shigenobu Takeda; Ken Furuya; Takeshi Yoshimura; Jun Nishioka; Tatsuo Aono; Yukihiro Nojiri; Keiri Imai; Isao Kudo; Hiroaki Saito; Atsushi Tsuda
  Progress in Oceanography, 64, 2-4, 253, 261, 2005, [Peer-reviewed]
  English, Scientific journal
• Export fluxes of particulate organic carbon estimated from ²³⁴Th/²³⁸U disequilibrium during the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study (SEEDS 2001)
  Tatsuo Aono; Masatoshi Yamada; Isao Kudo; Keiri Imai; Yukihiro Nojiri; Atsushi Tsuda
  Progress in Oceanography, 64, 2-4, 263, 282, 2005, [Peer-reviewed]
  English, Scientific journal
• Responses of diatoms to iron-enrichment (SEEDS) in the western subarctic Pacific, temporal and spatial comparisons
  Atsushi Tsuda; Hiroshi Kiyosawa; Akira Kuwata; Mamiko Mochizuki; Naonobu Shiga; Hiroaki Saito; Sanae Chiba; Keiri Imai; Jun Nishioka; Tsuneo Ono
  Progress in Oceanography, 64, 2-4, 189, 205, 2005, [Peer-reviewed]
  English, Scientific journal
• Primary productivity and nitrogenous nutrient assimilation dynamics during the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study
  Isao Kudo; Yoshifumi Noiri; Keiri Imai; Yukihiro Nojiri; Jun Nishioka; Atsushi Tsuda
  Progress in Oceanography, 64, 2-4, 207, 221, 2005, [Peer-reviewed]
  English, Scientific journal
• Seasonal variation in chlorophyll-specific growth and microzooplankton grazing of phytoplankton in Japanese coastal water
  T. Odate; K. Imai
  Journal of Plankton Research, 25, 12, 1497, 1505, Dec. 2003, [Peer-reviewed]
  English, Scientific journal
• Export flux and carbon budget in the iron fertilization experiments in the subarctic North Pacific
  Nojiri Y; Imai K; Saito H; Tsuda A; Whitney F
  Geochimica Et Cosmochimica Acta, 67, 18, A342, Sep. 2003, [Peer-reviewed]
• A mesoscale iron enrichment in the Western subarctic Pacific induces a large centric diatom bloom
  Atsushi Tsuda; Shigenobu Takeda; Hiroaki Saito; Jun Nishioka; Yukihiro Nojiri; Isao Kudo; Hiroshi Kiyosawa; Akihiro Shiomoto; Keiri Imai; Tsuneo Ono; Akifumi Shimamoto; Daisuke Tsumune; Takeshi Yoshimura; Tatsuo Aono; Akira Hinuma; Masatoshi Kinugasa; Koji Suzuki; Yoshiki Sohrin; Yoshifumi Noiri; Heihachiro Tani; Yuji Deguchi; Nobuo Tsurushima; Hiroshi Ogawa; Kimio Fukami; Kenshi Kuma; Toshiro Saino
  Science, 300, 5621, 958, 961, 09 May 2003, [Peer-reviewed], [International Magazine]
  English, Scientific journal
• KNOT: Ocean time-series program in western North Pacific completes first phase
  Tsurushima N; Imai K; Nojiri Y; Murphy P.P
  U. S. JGOFS NEWS, 11, 4, 11, 13, 2002
  English, International conference proceedings
• Bering Sea cyclonic and anticyclonic eddies observed during summer 2000 and 2001
  K Mizobata; SI Saitoh; A Shiomoto; T Miyamura; N Shiga; K Imai; M Toratani; Y Kajiwara; K Sasaoka
  PROGRESS IN OCEANOGRAPHY, 55, 1-2, 65, 75, 2002, [Peer-reviewed]
  English, Scientific journal
• Interannual variation in phytoplankton biomass in the Bering Sea basin in the 1990s
  A Shiomoto; S Saitoh; K Imai; M Toratani; Y Ishida; K Sasaoka
  PROGRESS IN OCEANOGRAPHY, 55, 1-2, 147, 163, 2002, [Peer-reviewed]
  English, Scientific journal
• Temporal and spatial variability of chlorophyll-a in the western subarctic Pacific determined from satellite and ship observations from 1997 to 1999
  K Sasaoka; S Saitoh; Asanuma, I; K Imai; M Honda; Y Nojiri; T Saino
  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY, 49, 24-25, 5557, 5576, 2002, [Peer-reviewed]
  English, Scientific journal
• The biological pump in the northwestern North Pacific based on fluxes and major components of particulate matter obtained by sediment-trap experiments (1997-2000)
  MC Honda; K Imai; Y Nojiri; F Hoshi; T Sugawara; M Kusakabe
  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY, 49, 24-25, 5595, 5625, 2002, [Peer-reviewed]
  English, Scientific journal
• Seasonal changes in nutrients, chlorophyll a and the phytoplankton assemblage of the western subarctic gyre in the Pacific Ocean
  M Mochizuki; N Shiga; M Saito; K Imai; Y Nojiri
  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY, 49, 24-25, 5421, 5439, 2002, [Peer-reviewed]
  English, Scientific journal
• Seasonal variability of picophytoplankton and bacteria in the western subarctic Pacific Ocean at station KNOT
  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, [Peer-reviewed]
  English, Scientific journal
• Seasonal variations of carbon dioxide system and nutrients in the surface mixed layer at station KNOT (44°N, 155°E) in the subarctic western North Pacific
  Nobuo Tsurushima; Yukihiro Nojiri; Keiri Imai; Shuichi Watanabe
  Deep-Sea Research Part II: Topical Studies in Oceanography, 49, 24-25, 5377, 5394, 2002, [Peer-reviewed]
  English, Scientific journal
• Time series of seasonal variation of primary productivity at station KNOT (44°N, 155°E) in the sub-arctic western North Pacific
  Keiri Imai; Yukihiro Nojiri; Nobuo Tsurushima; Toshiro Saino
  Deep-Sea Research Part II: Topical Studies in Oceanography, 49, 24-25, 5395, 5408, 2002, [Peer-reviewed]
  English, Scientific journal
• A possible explanation for the dominance of chlorophyll in pico and nano-size fractions in the waters around the south Shetland Islands
  Kawaguchi S; Shiomoto A; Imai K; Tsuruga Y; Yamaguchi H; Noiri Y; Iguch N; Kameda T
  Ocean and Polar Research, 23, 4, 379, 388, 2001, [Peer-reviewed]
  English, Scientific journal
• Characteristics of standard methods of Norpac net towing in the high latitude sea area II. Overtowing under rough sea conditions and estimation of zooplankton abundance
  ODATE Tsuneo; SAKAOKA Keiitiro; KAJIWARA Yoshiyuki; IMAI Keiri; KOBAYASHI Naoto; MEGURO Toshimi; FUKUTI Mitsuo
  Bulletin of the Plankton Society of Japan, 46, 2, 134, 142, 日本プランクトン学会, 25 Aug. 1999, [Peer-reviewed]
  Japanese
• Fluctuations of nutrients and primary production structure during winter and spring in Funka Bay
  IINUMA Tomoaki; IMAI Keiri; ODATE Tsuneo; MAITA Yoshiaki
  水産海洋研究, 62, 4, 406, 407, 01 Nov. 1998
  Japanese
• 5. Fluctuations of Nutrients and Primary Production Structure during Winter and Spring in Funka Bay
  Iinuma Tomoaki; Imai Keiri; Odate Tsuneo; Maita Yoshiaki
  MEMOIRS OF THE FACULTY OF FISHERIES HOKKAIDO UNIVERSITY, 45, 1, 30, 35, THE FACULTY OF FISHERIES, HOKKAIDO UNIVERSITY, Sep. 1998
  English, Ⅰ. Physical, Chemical Environment, Primary Production, Zooplankton and Their Coupling Model Studies
• Response of Phytoplankton Community to Physico-Chemical Changes in the Neritic Water of Funka Bay in Summer
  IMAI Keiri; ODATE Tsuneo; YANADA Mitsuru; MAITA Yoshiaki
  Bulletin of the Japanese Society of Fisheries Oceanography, 62, 2, 89, 96, 水産海洋学会, 01 May 1998, [Peer-reviewed]
  Japanese
• Chla-specific productivity of picophytoplankton not higher than that of larger phytoplankton off the South Shetland Islands in summer
  A Shiomoto; S Kawaguchi; K Imai; Y Tsuruga
  POLAR BIOLOGY, 19, 5, 361, 364, May 1998, [Peer-reviewed]
  English, Scientific journal
• Relationship Between Water Masses and Chlorophyll a Concentration in Bottom Water on the Northern Bering Shelf in Summer
  Imai Keiri; Yanada Mitsuru; Maita Yoshiaki
  Bulletin of the Faculty of Fisheries,Hokkaido University, 49, 1, 41, 49, FACULTY OF FISHERIES, HOKKAIDO UNIVERSITY, Mar. 1998
  English
• Characteristics of standard methods of Norpac net towing in the high latitude sea area
  ODATE Tsuneo; IMAI Keiri; FUKUCHI Mitsuo
  Bulletin of the Plankton Society of Japan, 45, 1, 1, 8, 日本プランクトン学会, 28 Feb. 1998, [Peer-reviewed]
  Japanese

• 我が国沖合海域における海洋プラスチックごみ調査の規準化およびデータベース整備
  内田圭一; 萩田隆一; 向井徹; 今井圭理; 清水健一; 八木光晴; 山中有一; 三橋廷央; 磯辺篤彦; 黒田真央, 日本水産学会大会講演要旨集(CD-ROM), 2023, 2023
• 2017・2018年北部ベーリング海における成層強度の時空間変動とその要因
  上野洋路; 小松瑞紀; 吉兆千一; 土橋稜; 村松美幌; 村松美幌; 阿部泰人; 今井圭理; 大木淳之; 平譯享, 日本海洋学会大会講演要旨集, 2020, 2020
• 日本周辺沖合域における海底ごみの現状
  黒田 真央; 内山 正樹; 東 隆文; 内田 圭一; 東海 正; 向井 徹; 今井 圭理; 森井 康宏; 八木 光晴; 清水健一 清水健一; 三橋 廷央, 日本水産工学会 学術講演会 学術講演論文集, 2019, 0, 85, 88, 2019
  日本水産工学会, Japanese
• 化学成分からみた宗谷暖流沖冷水帯水塊の起源
  久万健志; 笹山了平; 日置菜々子; 森田雄一朗; 磯田豊; 平譯享; 今井圭理; 荒巻能史; 中村知裕; 西岡純; 江淵直人, 日本海洋学会大会講演要旨集, 2013, 94, 30 Aug. 2013
  Japanese
• Phytoplankton distribution and bio-geochemical character of seawater in sub-arctic North Pacific
  Arisawa Momoko; Zhang Jing; Nishitani Hironobu; Narita Hisashi; Richard Jordan; Saito Seiichi; Imai Keiri, Abstracts of Annual Meeting of the Geochemical Society of Japan, 51, 0, 181, 181, 2004
  微小植物プランクトンの分布特徴とその支配要因を把握するために，北太平洋亜寒帯域，東西165度線上の計15地点で観測を行った（7月初旬，7月下旬，10月初旬）。採取した海水はセルカウント用及びクロロフィルa，栄養塩測定用に分取した。セルカウントは微小植物プランクトンまで分類できるように電子顕微鏡を用いた。その結果，植物プランクトンの計数結果から，各季節における北太平洋亜寒帯域での大まかな植物プランクトン分布が明らかになった。植物プランクトン分布は親潮域，黒潮域を境界に大きく変化していた。また，各緯度における優占種及び細胞密度などから，西部北太平洋亜寒帯域の38.5°N_から_40°Nおいては，大気起源の鉄を含む栄養塩が生物生産を支える上で極めて重要であることがわかった。, GEOCHEMICAL SOCIETY OF JAPAN
• セジメントトラップ実験から推定する北西部北太平洋の生物ポンプ能力 (総特集 現代海洋化学・2) -- (4章 物質循環の広域および時系列モニタリング)
  本多 牧生; 今井 圭理; 野尻 幸宏, 号外海洋, 25, 108, 113, 2001
  海洋出版, Japanese
• 定点KNOTにおける海水中メタン濃度の季節変動
  鶴島修夫; 今井圭理; 野尻幸宏; 吉田尚弘; 角皆潤; 渡邊修一, 2000年度日本地球化学会年会講演要旨集, 169, 2000

• THE OCEANOGRAPHIC SOCIETY OF JAPAN

• Spatio-temporal variations in the bioelement composition of particulate organic matters fractionated by plankton size
  Grants-in-Aid for Scientific Research
  01 Apr. 2025 - 31 Mar. 2028
  芳村 毅; 伊佐田 智規; 今井 圭理
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 25K15414
• Revisit a Redfield ratio as a reference value in marine bioactive element cycles
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
  01 Apr. 2021 - 31 Mar. 2024
  芳村 毅; 工藤 勲; 今井 圭理
  海洋によるCO2の吸収・固定量は植物プランクトンによる炭素と栄養素の利用比率によって変化します。その比率としてレッドフィールド比が良く知られており，気候変化を予測する生態系モデルにおいて固定値として使われていますが，実測データの蓄積は十分ではありません。また，プランクトン群集はサイズの異なる多くの種で形成されますが，それらをひとまとめにした比率しか議論されてきませんでした。海洋環境の変化によりプランクトン群集組成が変化すると予測されていますが，その変化が生態系に与える影響を評価できません。そこで，本研究は有機物粒子のサイズ分画手法を確立したうえで，各サイズ画分の主要4元素組成比（炭素：窒素：リン：ケイ素）に関するデータを取得します。
  研究一年目の2021年度は海水中の有機物粒子をサイズ毎に分画するための手法を検討しました。撹拌式セルを用いた限外ろ過システムを応用した「限外ろ過方式」と，孔径の異なるフィルターに連続的に通過させる「逐次ろ過方式」を並行して検討しました。その結果，限外ろ過方式はフィルター上に粒子が捕捉されてしまい，有機物粒子量を過小評価することがわかりました。有機物粒子のサイズ分画手法としては逐次ろ過方式が適していることがわかりました。逐次ろ過方式はリンおよびケイ素の分析試料を作成するのに適していますが，炭素および窒素を分析するためにはフィルター上に集めた有機物粒子を液体に懸濁させて回収する必要があります。フィルターに付着する有機物粒子を完全に回収する手法を検討した結果，超音波洗浄を利用することで達成できることがわかりました。これらの検討により，孔径の異なるメンブレンフィルターを用いた逐次ろ過方式によって有機物粒子を三つにサイズ分画し，超音波洗浄を活用して回収した有機物粒子の主要4元素を分析することで，各サイズ画分の元素組成比を分析するための道筋が完成しました。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 21K12219
• Development of a method for predicting the dynamics of ocean acidification in the coastal regions of Japan
  Grants-in-Aid for Scientific Research
  01 Apr. 2019 - 31 Mar. 2022
  Imai Keiri
  We aimed to develop a parameterization of pH (pH = f (salinity, oxygen, chlorophyll-a, etc.)) that can be applied to the Japanese coastal regions to predict the temporal and spatial changes and magnitude of ocean acidification in the coastal waters of Japan. Since a large amount of pH data is required to understand the dynamics of ocean acidification in coastal waters with large environmental variability, we improved the surface seawater monitoring system equipped with the Oshoro Maru of Hokkaido University, which makes several cruises per year to the Japanese coastal regions (off the coast of Hokkaido and Tohoku), to enable continuous multi-item data acquisition. The system has been improved to enable continuous data acquisition of multiple items.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 19K12292
• Transfer and accumulation of radioactive material in marine ecosystem
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
  28 Jun. 2012 - 31 Mar. 2017
  Kanda Jota; MORIYA Shigeharu; KOBAYASHI Takuya; YOSHIMURA Takeshi; ISHIMARU Takashi; IGARASHI Satoshi; SUGA Jiro; YAMAKAWA Hiroshi; OTSU Hideaki; ITO Yukari; TAKAZAWA Nobue; UCHIYAMA Kaori; KUBO Atshushi
  Radioactive material derived from the Fukushima Daiichi Nuclear Power Plant accident was investigated in marine ecosystem. 1) For radioactive cesium in marine organisms and environment in the coastal area of Fukushima, we obtained a continuous time-series data set by ship observations twice a year. Time-series data set for radioactive cesium in zooplankton was also obtained in several open ocean areas. 2) Examinations of transfer routes of radioactive cesium in coastal rocky seafloor revealed that transition of radioactive cesium from suspended or descending particles, and from organic fraction of sediments was small. 3) Using the on-site observation data, the transition of radioactive cesium in the ecosystem was reproduced by a numerical model, and the model was applied to prediction of the future trend of the radioactivity level of marine organisms.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Tokyo University of Marine Science and Technology, 24110005