Researcher Profile and Settings

Master

Affiliation (Master)

• Faculty of Fisheries Sciences　Marine Bioresource and Environmental Science　Marine Environmental Science

Affiliation (Master)

• Faculty of Fisheries Sciences　Marine Bioresource and Environmental Science　Marine Environmental Science

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Profile and Settings

Profile and Settings

• Name (Japanese)

  Onishi

• Name (Kana)

  Hiroji

• Name

  200901050742078472

Alternate Names

https://www.facebook.com/hirojionishi
http://a-stream3.fish.hokudai.ac.jp

Achievement

Research Interests

• 海洋物理学   水産海洋学   Physical Oceanography(4402)   Marine Science(6301)   

Research Areas

• Natural sciences / Atmospheric and hydrospheric science
• Life sciences / Aquaculture

Education

•        - 1992  Hokkaido University
•        - 1992  Hokkaido University  Graduate School, Division of Fisheries
•        - 1990  Hokkaido University  School of Fisheries Sciences
•        - 1990  Hokkaido University  Faculty of Fisheries
•        - 1989  Hokkaido University  School of Fisheries Sciences
•        - 1989  Hokkaido University  Faculty of Fisheries

Awards

• 2001/04 The Oceanography Society of Japan The Hidaka Outstanding-Publication Award
   

  受賞者: ONISHI Hiroji

Published Papers

• Significant nutrient consumption in the dark subsurface layer during a diatom bloom: a case study on Funka Bay, Hokkaido, Japan

  Sachi Umezawa, Manami Tozawa, Yuichi Nosaka, Daiki Nomura, Hiroji Onishi, Hiroto Abe, Tetsuya Takatsu, Atsushi Ooki

  Biogeosciences 20 (2) 421 - 438 2023/01/27 

  Abstract. We conducted repetitive observations in Funka Bay,Hokkaido, Japan, on 15 February, 4 and 15 March, and 14 April 2019. Thediatom spring bloom peaked on 4 March and started declining on 15 March.Funka Bay winter water remained below 30 m depth, which was below thesurface mixed-layer and dark-layer depth (0.1 % of the surface photosynthetically active radiation, PAR, depth) on 4and 15 March. In the subsurface layer at depths of 30–50 m, concentrationsof NO3-, PO43-, and Si(OH)4 decreased by halfbetween these dates, even in the dark. Incubation experiments using thediatom Thalassiosira nordenskioeldii showed that this diatom could consume added nutrients in the dark atsubstantial rates after pre-culturing to deplete nutrients. Incubationexperiments using natural seawater collected in the growing phase of the bloom on 8 March 2022 also showed that nutrient-depleted phytoplankton could consumeadded nutrients in the dark. We excluded three physicalprocess – water mixing, diffusive transport, and subduction – as possible mainreasons for the decrease in nutrients in the subsurface layer. We concludethat the nutrient reduction in the subsurface layer (30–50 m) between 4 and15 March 2019 could be explained by nutrient consumption by diatoms in the dark in thatlayer.
• Seasonal changes in taxonomic, size composition, and Normalised Biomass Size Spectra (NBSS) of mesozooplankton communities in the Funka Bay, southwestern Hokkaido: Insights from ZooScan analysis

  Takumi Teraoka, Kanako Amei, Yutaka Fukai, Kohei Matsuno, Hiroji Onishi, Atsushi Ooki, Tetsuya Takatsu, Atsushi Yamaguchi

  Plankton and Benthos Research 17 (4) 369 - 382 1880-8247 2022/11/30
• Late Holocene centennial to millennial-scale variability in lower trophic level productivity off southern Hokkaido, Japan, and its response to dissolved iron-replete Coastal Oyashio dynamics

  Michinobu Kuwae, Narumi Tsugeki, Bruce P. Finney, Yukinori Tani, Jonaotaro Onodera, Mako Kiyoto, Mitsukuni Kusaka, Takuya Sagawa, Yugo Nakamura, Hiroji Onishi, Hiroshi Kuroda, Noboru Okuda, Tamihisa Ohta, Minoru Ikehara, Tomohisa Irino

  Quaternary Research 107 27 - 42 0033-5894 2022/05 

  Abstract Little is known about the dynamics of marine food chains spanning primary to higher trophic levels on centennial and longer timescales, especially where the supply of dissolved iron limits primary productivity. To elucidate the long-term dynamics of biological productivity in the Coastal Oyashio (CO), which is a major pathway for transporting dissolved iron into the western North Pacific from winter to spring, we reconstructed the lower trophic level productivity over the last 3000 years in the CO. Our results demonstrate that the concentrations and mass accumulation rates of both Chl-a (chlorophyll a and its derivatives) and biogenic opal used as proxies of primary productivity, and steryl chlorin esters (SCEs) used as that of zooplankton productivity, show a millennial-scale increasing trend and centennial-scale variability beginning ca. AD 400. SCEs were positively correlated with Chl-a, indicating that changes in zooplankton productivity were induced by bottom-up control of primary productivity. The Chl-a and SCEs showed synchronous centennial-scale patterns with a relative abundance of sea-ice-associated diatom species transported by CO, and with a ventilation index in the Okhotsk Sea Intermediate Water. This synchronous pattern indicates that lower trophic-level productivity during the spring bloom responded to the intensity of iron-replete CO.
• Nutrient consumption by diatoms in the dark subsurface layer of Funka Bay, Hokkaido, Japan

  Sachi Umezawa, Manami Tozawa, Yuichi Nosaka, Daiki Nomura, Hiroji Onishi, Hiroto Abe, Tetsuya Takatsu, Atsushi Ooki

  2022/01/06 [Refereed]
   

  Abstract. We conducted time-series observations in Funka Bay, Hokkaido, Japan, from 15 February to 14 April 2019. The diatom spring bloom peaked on 4 March and started declining on 15 March. Funka Bay winter water remained below 30-m depth, which was below the surface mixed-layer and dark-zone depths on both dates. At depths of 30–50 m, concentrations of NO3–, PO43–, and Si(OH)4 decreased by half between these dates even in darkness. Incubation experiments using the diatom Thalassiosira nordenskioeldii showed that this diatom could consume nutrients in darkness at substantial rates. We conclude that the nutrient reduction in the subsurface layer (30–50 m) could be explained by dark consumption by diatoms that had been growing in the surface waters and then sank to the subsurface layer. We believe that this is the first study to present observational evidence for the consumption of the main nutrients by diatoms in the dark subsurface layer during the spring bloom. Nutrient consumption in this layer might have a substantial influence on the primary production during and after the spring bloom.
• Isoprene production in the water column and sediment in Funka Bay, Hokkaido, Japan

  Atsushi Ooki, Naoya Miyashita, Sachi Umezawa, Manami Tozawa, Yuichi Nosaka, Daiki Nomura, Hiroji Onishi, Hiroto Abe, Tetsuya Takatsu

  GEOCHEMICAL JOURNAL 56 (5) 142 - 150 0016-7002 2022
• The potential role of thermohaline-shear instability in turbulence production in the Bering Sea and the subarctic North Pacific

  Mamoru Tanaka, Jiro Yoshida, Keunjong Lee, Yasutaka Goto, Takahiro Tanaka, Hiromichi Ueno, Hiroji Onishi, Ichiro Yasuda

  JOURNAL OF OCEANOGRAPHY 77 (3) 431 - 446 0916-8370 2021/06 

  A recent linear stability analysis and a numerical simulation suggest that diffusive convection (DC), a regime of the double-diffusive convection, plays a potential role in onset of thermohaline-shear instability, implying that DC could contribute to turbulence production in the oceans. However, an existence of such a thermohaline-shear instability has not been examined in real oceans. We examine if this newly proposed instability mechanism exists in the subarctic North Pacific by analyzing our fine- and micro-scale turbulence measurement data. Vertical inversions were cautiously detected in seawater density profiles and used as a proxy for instability events for gradient Richardson number larger than the critical value of 1/4. We found that a portion of inversions were associated with active DC. Such DC-related inversions exhibited elevated levels of turbulent kinetic energy dissipation rate even for gradient Richardson number largely exceeding 1/4. Our estimate suggested that the thermohaline-shear instability contributes to roughly only 10% of the dissipation of turbulent kinetic energy in the diffusively convective layer in our observation site.
• Influence of monsoon-forced Ekman transport on sea surface height in the Gulf of Thailand

  M. Higuchi, M. Anongponyoskun, J. Phaksopa, H. Onishi

  Agriculture and Natural Resources 54 (2) 2468-1458 2020 [Refereed]
  
• Isoprene production in seawater of Funka Bay, Hokkaido, Japan

  Atsushi Ooki, Ryuta Shida, Masashi Otsu, Hiroji Onishi, Naoto Kobayashi, Takahiro Iida, Daiki Nomura, Kota Suzuki, Hideyoshi Yamaoka, Tetsuya Takatsu

  Journal of Oceanography 75 2019/06 [Refereed][Not invited]
  
• Seabird densities and species and hydrographic features across Amchitka Pass, Aleutian Islands

  Bungo Nishizawa, Hiroji Onishi, Yutaka Watanuki

  Fisheries Science 85 (1) 53 - 60 0919-9268 2019/01 [Refereed]
  
• Seasonal variation of volatile organic iodine compounds in the water column of Funka Bay, Hokkaido, Japan

  Shimizu Yusaku, Ooki Atsushi, Onishi Hiroji, Takatsu Tetsuya, Tanaka Seiji, Inagaki Yuta, Suzuki Kota, Kobayashi Naoto, Kamei Yoshihiko, Kuma Kenshi

  JOURNAL OF ATMOSPHERIC CHEMISTRY 74 (2) 205 - 225 0167-7764 2017/06 [Refereed][Not invited]
   

  Volatile organic iodine compounds (VOIs) emitted from the ocean surface to the air play an important role in atmospheric chemistry. Shipboard observations were conducted in Funka Bay, Hokkaido, Japan, bimonthly or monthly from March 2012 to December 2014, to elucidate the seasonal variations of VOI concentrations in seawater and their sea-to-air iodine fluxes. The bay water exchanges with the open ocean water of the North Pacific twice a year (early spring and autumn). Vertical profiles of CH2I2, CH2ClI, CH3I, and C2H5I concentrations in the bay water were measured bimonthly or monthly within an identified water mass. The VOI concentrations began to increase after early April at the end of the diatom spring bloom, and represented substantial peaks in June or July. The temporal variation of the C2H5I profile, which showed a distinct peak in the bottom layer from April to July, was similar to the PO4 (3-) variation profile. Correlation between C2H5I and PO4 (3-) concentrations (r = 0.93) suggests that C2H5I production was associated with degradation of organic matter deposited on the bottom after the spring bloom. CH2I2 and CH2ClI concentrations increased substantially in the surface and subsurface layers (0-60 m) in June or July resulted in a clear seasonal variation of the sea-to-air iodine flux of the VOIs (high in summer or autumn and low in spring).
• Distribution of Dall's Porpoise, Phocoenoides dalli, in the North Pacific and Bering Sea, Based on T/S Oshoro Maru 2012 Summer Cruise Data

  Sachiko Suzuki, Keiko Sekiguchi, Yoko Mitani, Hiroji Onishi, Takehiko Kamito

  Zoological Science 33 (5) 491 - 491 0289-0003 2016/10/01 [Refereed]
  
• Subsurface hydrographic structures and the temporal variations of Aleutian eddies

  Saito Rui, Yasuda Ichiro, Komatsu Kosei, Ishiyama Hiromu, Ueno Hiromichi, Onishi Hiroji, Setou Takeshi, Shimizu Manabu

  OCEAN DYNAMICS 66 (5) 605 - 621 1616-7341 2016/05 [Refereed][Not invited]
   

  Aleutian eddies are mesoscale anticyclonic eddies formed within the Alaskan Stream region between 180A degrees meridian and 170A degrees E south of the Aleutian Islands. They propagate southwestward after the isolation from the Alaskan Stream and pass through the Western Subarctic Gyre. We compared hydrographic structures of three Aleutian eddies observed during summer, west of 170A degrees E (Eddy A) and east of 170A degrees E (Eddies B and C). In each eddy, a subsurface dichothermal water (3.0-4.0 A degrees C) was observed above a subsurface mesothermal water (4.0-4.5 A degrees C). The minimum temperature in the dichothermal water at around a depth of 100 m was colder in Eddy A (2.8 A degrees C) than in Eddies B and C (3.0-3.2 A degrees C). This difference could be ascribed to wintertime cooling and influence of surrounding waters during spring warming period. The wintertime cooling makes the dichothermal water colder for eddies isolated from the Alaskan Stream region for a longer time. Particle-tracking experiments using re-analysis products from a data-assimilative eddy resolving ocean model suggested that the dichothermal water within Eddy A was cooled by the entrainment of surrounding colder water even during the spring warming period. The mesothermal waters at depth around 250 m demonstrated similarity among the observed eddies, and the maximum temperature in the mesothermal water within Eddy A (4.3 A degrees C) was close to that of Eddies B and C (4.2 A degrees C) in the in situ observations. These results indicated that the dichothermal water of Aleutian eddies modifies over time, whereas the mesothermal water maintains the original feature as they propagate southwestward from the Alaskan Stream region to the Western Subarctic Gyre.
• べーリング海南東部陸棚縁辺域での潮汐混合と溶存鉄輸送

  田中雄大, 安田一郎, 久万健志, 西岡純, 田中祐希, 大西広二, 上野洋路, 増島雅親

  月刊海洋 号外 58 47 - 55 2016 [Not refereed][Not invited]
  
• Regeneration dynamics of iron and nutrients from bay sediment into bottom water of Funka Bay, Japan

  Hioki Nanako, Kuma Kenshi, Morita Yuichiroh, Miura Daichi, Ooki Atsushi, Tanaka Seiji, Onishi Hiroji, Takatsu Tetsuya, Kobayashi Naoto, Kamei Yoshihiko

  JOURNAL OF OCEANOGRAPHY Springer 71 (6) 703 - 714 0916-8370 2015/12 [Refereed][Not invited]
   

  We studied iron remobilization and nutrient regeneration in bottom water of Funka Bay, Japan, bimonthly from August 2010 to December 2011. The bay basin (bottom depth, 92-96 m) is separated from the northwest Pacific Ocean at its mouth by a sill with a depth of 60 m. After a spring phytoplankton bloom during early March-early April, nutrients in bay bottom water tended to accumulate with time until August-September, and to increase gradually with depth during April-October, by the oxidative decomposition of settling particulate organic matter on the bay bottom. In contrast, the process of iron remobilization into bottom water of the bay is remarkably different from nutrient regeneration. The much higher concentrations of dissolved and total dissolvable iron near the bottom and the seasonally variable relationship between dissolved iron concentration and apparent oxygen utilization in bay bottom water likely reflect a balance between dissolved iron input and removal processes within the bay bottom water. The release of soluble Fe(II) from reducing bay sediments might induce the high concentrations of dissolved and total dissolvable iron in deep-bottom waters of Funka Bay and might be one of the most important sources of iron in Funka Bay. The upward transport of iron from the bay bottom to the surface water during the winter vertical mixing may play an important role in the supply of bioavailable iron for phytoplankton growth in the coastal waters.
• Observations of current and mixing around the shelf break in Pribilof Canyon in the Bering Sea

  T. Tanaka, I. Yasuda, H. Onishi, H. Ueno, M. Masujima

  JOURNAL OF OCEANOGRAPHY 71 (1) 1 - 17 0916-8370 2015/02 [Refereed][Not invited]
   

  Tide-induced vertical mixing along the shelf break in the eastern Bering Sea is considered one of the main physical processes that sustain local summertime high biological production. However, observations based on microstructure measurements that show enhanced tidal mixing are scarce. In this study, repeated casts of current and turbulence in the vicinity of the shelf break within Pribilof Canyon were conducted over a day in June 2012, enabling us to evaluate the representativeness of the vertical mixing intensity during one day and to detect the relationship between turbulence and tidal current. The cross-sectional distributions of the one-day averaged vertical diffusivity and the turbulent energy dissipation rate showed that strong vertical mixing occurred at the subsurface within about 15 km of the shelf break and near the seabed of the outer shelf. This result agrees with prior observations that were made by us and based on a single profile at each station, which indicated that the observed spatial pattern of turbulence is robust. Diurnal and semidiurnal tidal currents dominated the flow variations off the shelf break, and a statistically significant positive correlation was detected between the vertical shear of the horizontal tidal currents and the turbulent energy dissipation rate. This result suggests that the high turbulent energy dissipation and the enhanced vertical mixing off the shelf break were induced by the strong vertical shear of tidal currents.
• Production and sea-to-air flux of organic iodine gases associated with degradation of organic matter after diatom bloom in coastal sea area

  Shimizu Yusaku, Ooki Atsushi, Kuma Kenshi, Onishi Hiroji, Kamei Yoshihiko, Kobayashi Naoto

  Abstracts of Annual Meeting of the Geochemical Society of Japan 一般社団法人日本地球化学会 62 89 - 89 2015 

  CH₂I₂、C₂H₅Iなど揮発性有機ヨウ素化合物（volatile organoiodine compound:VOI）は、海から大気へヨウ素を供給するキャリアーとして機能する。本研究では、VOIと生物生産性や有機物分解との関係を調べるために、北海道噴火湾で2012年3月から2014年12月の隔月に海水を採取し、海水中VOI濃度をパージ＆トラップ-ガスクロマトグラフ-質量分析法で測定した。
  春季植物プランクトンブルーム終了後の5月以降にVOI濃度は急激に増加し始め、6月から7月に年間ピークに達した。ピーク深度はVOI成分により異なった。このようなピーク深度の違いは、生成メカニズムの違いを示しており、こうした海水中VOIの生成メカニズムの違いは、大気への放出特性にも反映されると考えられる。
• Sightings of the western stock of North Pacific right whales (Eubalaena japonica) in the far southeast of the Kamchatka Peninsula

  Keiko Sekiguchi, Hiroji Onishi, Hiroko Sasaki, Shota Haba, Yuka Iwahara, Daisuke Mizuguchi, Mayuko Otsuki, Daisuke Saijo, Bungo Nishizawa, Hirona Mizuno, Naoki Hoshi, Takehiko Kamito

  MARINE MAMMAL SCIENCE 30 (3) 1199 - 1209 0824-0469 2014/07 [Refereed][Not invited]
  
• Time series observation of volatile organoiodide compounds in Funka Bay, Hokkaido

  Shimizu Yusaku, Ooki Atsuhi, Kuma Kenshi, Oonishi Hiroji, Kamei Yoshihiko, Kobayashi Naoto

  Abstracts of Annual Meeting of the Geochemical Society of Japan 一般社団法人日本地球化学会 61 202 - 202 2014 

  CH₂I₂などの海水中の揮発性有機ヨウ素化合物(Volatile organoiodine compound；VOI)は、海洋から大気へのヨウ素の主なキャリアーとして知られるが、生成過程などは明らかになっていない。本研究では、VOIと生物生産性や有機物分解との関係を明らかにするため、VOIと生物化学パラメータのモニタリングを行った。北海道噴火湾にて、VOI（CH₂I₂、CH₃I、CH₂ClI）濃度や、生物科学パラメータの定点測定を、2012年3月から2014年6月まで行った。春季の植物プランクトンブルームが終焉し、植物プランクトンが老化、死滅する時期に、VOIが多量に生成されることがわかった。CH2I2増分が2013年は2012年の半分であったことより、VOI生成量には経年差がみられた。
• Influences of mesoscale anticyclonic eddies on the zooplankton community south of the western Aleutian Islands during the summer of 2010

  Rui Saito, Atsushi Yamaguchi, Ichiro Yasuda, Hiromichi Ueno, Hiromu Ishiyama, Hiroji Onishi, Ichiro Imai

  JOURNAL OF PLANKTON RESEARCH 36 (1) 117 - 128 0142-7873 2014/01 [Refereed][Not invited]
   

  Mesoscale anticyclonic eddies have been observed south of the Aleutian Islands. Eddies farther east, in the Gulf of Alaska, are known to transport coastal water and coastal zooplankton to the offshore open ocean. The impacts of mesoscale anticyclonic eddies formed south of the western Aleutian Islands (Aleutian eddies) on the zooplankton community are not fully understood. In the present study, we describe zooplankton population structures within an Aleutian eddy and outside the eddy during July 2010. Based on the sea-level anomaly, the Aleutian eddy was formed south of Attu Island (172 degrees 54'E) in February 2010, and it moved southeastward in the next 5 months. Large oceanic copepods, Neocalanus cristatus, Eucalanus bungii and Metridia pacifica were more abundant inside the eddy than the outside. Inside the eddy, the life stage distribution of N. cristatus was more advanced than that outside, and Neocalanus spp. had accumulated more lipids. These conditions probably reflect the greater primary production in the eddy, production enhanced by nutrients advected into the eddy. The Aleutian eddy contained mostly oceanic copepods because it was formed in the offshore water and/or eddy-eddy interaction occurred after its formation. The sufficient food condition in the eddy presumably resulted in higher growth and survival rates of these oceanic copepods, resulting in the greater abundance, advanced development stages and greater lipid accumulation.
• Modification of a Kenai eddy along the Alaskan Stream

  Hiromichi Ueno, Ichiro Yasuda, Sachihiko Itoh, Hiroji Onishi, Yutaka Hiroe, Toshio Suga, Eitarou Oka

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 117 2169-9275 2012/08 [Not refereed][Not invited]
   

  A Kenai eddy was studied through analyses of satellite altimeter data and hydrographic data from shipboard and Argo float observations. This eddy formed in December 2006 south of the Kenai Peninsula and propagated southwestward along the Alaskan Stream. The eddy held horizontally uniform warm core water in January 2007. In late winter 2007, this core water was cooled from the top and a subsurface temperature maximum was formed around 26.5 sigma(theta). Two years later in summer 2009, warm and low-dissolved-oxygen (low- DO) water characterized by a temperature maximum around 26.5 sigma(theta) was observed again in the eddy core and was likely the remnant of original core water. At the same time, cold and high-DO water intrusions occurred in the eddy core, suggesting that strong modification of core water was ongoing. After summer 2009, the core water was fully changed through interaction with another eddy.
• Modification of a Kenai eddy along the Alaskan Stream

  UENO Hiromichi, YASUDA Ichiro, ITOH Sachihiko, ONISHI Hiroji, HIROE Yutaka, SUGA Toshio, OKA Eitarou

  J Geophys Res 117 (C8) C08032-C08032-11 - n/a 0148-0227 2012/08 [Refereed][Not invited]
  
• Observations on a school of ocean sunfish and evidence for a symbiotic cleaning association with albatrosses

  Takuzo Abe, Keiko Sekiguchi, Hiroji Onishi, Kota Muramatsu, Takehiko Kamito

  Marine Biology 159 (5) 1173 - 1176 0025-3162 2012/05 [Refereed]
  
• 潮汐混合とオホーツク海・ベーリング海の物理・化学・生物過程―白鳳丸KH09‐4航海・おしょろ丸・クロモフ2006/2007シンセシス―Kenai渦の変質過程

  上野洋路, 安田一郎, 伊藤幸彦, 大西広二, 廣江豊, 廣江豊, 須賀利雄, 須賀利雄, 岡英太郎

  月刊海洋 43 (12) 756 - 762 0916-2011 2011/12 [Not refereed][Not invited]
  

MISC

• GEOTRACES計画エンジン全開ヘ―躍進する微量元素海洋学―ベーリング海南東部陸棚縁辺域での潮汐混合と溶存鉄輸送

  田中雄大, 安田一郎, 久万健志, 西岡純, 田中祐希, 大西広二, 上野洋路, 増島雅親  月刊海洋  47‐55  2016/11/01  [Not refereed][Not invited]
  
• The Spatial and Vertical Distributions of a Spring Phytoplankton Community along 155°E in the Western North Pacific : An In Situ Multi-Excitation Fluorometer Analysis

  松本健太郎, 有馬大地, 松野孝平, 山?康裕, 大西広二, 大木淳之, 平譯享, 山口篤, 今井一郎  北大水産彙報  66-  (1)  29  -38  2016  [Not refereed][Not invited]
   

  The spring phytoplankton community in the western North Pacific is characterized by large variability in both the horizontal and verical dimensions. To evaluate this variability, phytoplankton communitiesat 39°30'N-44°00'N along 155°E were investigated in situ using a multi-excitation fluorometer during May 2014. The sea surface chlorophyll a(Chi. a) level was high and composed mainly of diatoms near 43°30'N-42'N, while it was low and composed of dinoflagellates south of 40°N. Based on seven fixed-station investigations, the phytoplanklton communities were classified into 4 types : a low Chl. a level before bloom (44°N), massive diatom bloom(42°N-43°N), low Chl. a level with dinoflagellates(40°N-41°N) and lowest Chl.a(at the southernmost station at 39°30'N). These phytoplankton communities corresponded with the formation of a water mass separating the Subartctic front(SAF) and Subarctic boundary(SAB). Multi-excitation fluorometry data showed a high correlation with Chl. a measurements obtained via Thrmo-salinometer and biovolume microscopic analyses(r²=0.67-0.97,p<0.05). Thus, we concluded that a multi-excitation fluorometer can be applied for the evaluation of detailed spatial and temporal changes in the phytoplankton community at various locations.
• アリューシャン渦の水塊構造と特性

  齋藤類, 安田一郎, 小松幸生, 石山宙夢, 上野洋路, 大西広二, 山口篤  日本海洋学会大会講演要旨集  2014-  102  2014/03/10  [Not refereed][Not invited]
  
• 夏季の西部アリューシャン列島南岸域における中規模高気圧性渦が動物プランクトンの分布に与える影響

  齋藤類, 山口篤, 安田一郎, 上野洋路, 石山宙夢, 大西広二, 今井一郎  日本ベントス学会・日本プランクトン学会合同大会講演要旨集  2013-  115  2013/09/26  [Not refereed][Not invited]
  
• 夏季のアラスカンストリーム流域における大型カラヌス目カイアシ類の空間分布

  齋藤類, 山口篤, 安田一郎, 上野洋路, 大西広二, 今井一郎  日本海洋学会大会講演要旨集  2013-  237  2013/08/30  [Not refereed][Not invited]
  
• Seasonal variations of bromoform distribution in the Funka Bay

  Atsushi Ooki, Kazuji Miwa, Hiroji Onishi, Yoshihiko Kamei, Naoto Kobayashi, Kenshi Kuma  Bunseki Kagaku  62-  (12)  1071  -1078  2013  [Not refereed][Not invited]
   

  A shipboard observation was conducted in Funka Bay of Hokkaido from October 2011 to August 2012. Volatile organic halogenated compounds (halocarbons) in seawater collected at coastal, basin and sea shore sampling sites were measured by purge and trap GC-MS method. The spatial and temporal distributions of bromoform (CHBr3) were obtained, and we analyzed the origin of the compound. The minimum concentration of bromoform (15 pmol L< sup> -1< /sup> ) was found in December. The bromoform concentration in the basin area increased from 20 pmol L< sup> -1< /sup> to 25 pmol L< sup> -1< /sup> at a rate of 5 pmol L< sup> -1< /sup> month< sup> -1< /sup> during the phytoplankton spring bloom period (March-April). This increase would have been derived from the phytoplankton production of bromoform. The concentration increased from April to August at a rate of 4 pmol L< sup> -1< /sup> month< sup> -1< /sup> , and the maximum concentration of 42 pmol L< sup> -1< /sup> in basin area was found in August. Much higher concentrations were found in the coastal area (125 pmol L< sup> -1< /sup> ) and the sea shore (up to 1800 pmol L< sup> -1< /sup> ). The late summer bromoform maximum found in the basin area would be derived from macro algal production near the sea shore. © 2013 The Japan Society for Analytical Chemistry.
• 2010年夏季のアラスカンストリーム海域における動物プランクトン群集:中規模渦の影響

  齋藤類, 山口篤, 上野洋路, 大西広二, 今井一郎  日本海洋学会大会講演要旨集  2012-  76  2012/03/13  [Not refereed][Not invited]
  
• 北太平洋中部亜寒帯Station SAおよびベーリング海Station ABにおける長期時系列沈降粒子フラックス観測,1990‐2010年

  高橋孝三, 朝日博史, 小野寺丈尚太郎, 岡崎裕典, 筒井英人, 池上隆仁, 兼松芳幸, 大西広二  日本海洋学会大会講演要旨集  2012-  72  2012/03/13  [Not refereed][Not invited]
  
• アルゴ時代の海洋物理船舶観測 おしょろ丸北洋航海における海洋物理観測

  上野洋路, 大西広二  月刊海洋  44-  (12)  2012
• Impact of Alaskan Stream Eddies on Chlorophyll Distribution in the North Pacific

  Hiromichi Ueno, William R. Crawford, Hiroji Onishi  JOURNAL OF OCEANOGRAPHY  66-  (3)  319  -328  2010/06  [Not refereed][Not invited]
   

  The impact of the Alaskan Stream (AS) eddies on the chlorophyll a (chl-a) distribution in the central subarctic North Pacific was investigated through analysis of chl-a and altimetry data from satellite observations. Altimetry observations provided the locations of mesoscale eddies in time and space within the maps of chlorophyll distributions. The climatological chl-a distributions averaged in the area and time showing presence of AS eddies suggested that AS eddies contributed significantly to the chl-a distribution in the deep-sea region of the subarctic North Pacific. The chl-a distribution was closely related to the AS eddies regardless of whether the eddy was located in or detached from the AS. A combination of two or three AS eddies sometimes formed high chl-a concentration belts that injected chlorophyll and coastal nutrient-rich waters southward from the Aleutian Islands far into the deep-sea region of the subarctic North Pacific. These results indicate that chl-a distribution in the central subarctic North Pacific was strongly impacted by AS eddies.
• Kenai渦の変質過程

  月刊海洋・海洋出版株式会社  2010  [Not refereed][Not invited]
  
• アラスカンストリームの流域特性と変動

  月刊海洋・海洋出版株式会社  2010  [Not refereed][Not invited]
  
• Current property and variability of the Alaskan Stream

  2010  [Not refereed][Not invited]
  
• Anticyclonic Eddies in the Alaskan Stream

  Hiromichi Ueno, Howard J. Freeland, William R. Crawford, Hiroji Onishi, Eitarou Oka, Kanako Sato, Toshio Suga  JOURNAL OF PHYSICAL OCEANOGRAPHY  39-  (4)  934  -951  2009/04  [Not refereed][Not invited]
   

  Anticyclonic eddies propagating southwestward in the Alaskan Stream (AS) were investigated through analysis of altimetry data from satellite observations during 1992-2006 and hydrographic data from profiling float observations during 2001-06. Fifteen long-lived eddies were identified and categorized based on their area of first appearance. Three eddies were present at the beginning of the satellite observations; another three formed in the eastern Gulf of Alaska off Sitka, Alaska; and four were first detected at the head of the Gulf of Alaska near Yakutat, Alaska. The other five eddies formed along the AS between 157 degrees and 169 degrees W, and were named AS eddies. While the eddies that formed in the Gulf of Alaska mainly decayed before exiting the Gulf of Alaska, the AS eddies mostly crossed the 180 degrees meridian and reached the western subarctic gyre. Four of five AS eddies formed under negative or weakly positive wind stress curls, which possibly caused AS separation from the coast. Comparison of eddy propagation speeds in the AS with the bottom slope showed that eddies propagated faster over steeper slopes, although eddy speeds were slower than those predicted by the topographic planetary wave dispersion relation. An AS eddy was observed by profiling floats in the western subarctic gyre after it detached from the AS. Intermediate-layer water near the eddy center had low potential vorticity compared with the surrounding water, suggesting that AS eddies provided the western subarctic gyre with water just south of the Aleutian Islands.
• Diatom floral fluxes at Stations AB and SA in the Bering Sea and the northern Subarctic Pacific, 1990-1998

  ONODERA Jonaotaro, TAKAHASHI Kozo, ONISHI Hiroji, YANADA Mitsuru, Jonaotaro Onodera, Kozo Takahashi, Hiroji Onishi, Mitsuru Yanada, Center for Advanced Marine Core Research Kochi University, Department of Earth and Planetary Sciences Kyushu University, Graduate School of Fisheries Science Hokkaido University, Graduate School of Fisheries Science Hokkaido University  Oceanography in Japan  18-  (5)  307  -322  2009  [Not refereed][Not invited]
   

  珪藻沈降群集フラックスと海洋環境変動との対応関係を探るために,Station AB(ベーリング海)とStation SA(北太平洋北部中央亜寒帯)において,1990年8月から1999年1月上旬までに得られたセディメントトラップ試料を分析した。全珪藻フラックス変動の極大は,多くの年は両Stationともに春と秋のどちらか年一回か,春と秋の年2回観察された。しかし,年によっては特異なフラックス変動が観測され,そのタイミングはStations ABとSAで異なっていた。これらの経年変動は,おそらく冬季鉛直混合と,それに引き続く夏季成層構造の発達度合いとタイミングの違いが影響していると思われる。珪藻沈降群集の優占種はNeodenticula seminaeで,8年間を通した平均優占率はABで80%,SAで82%に達した。8年間を通して,珪藻沈降群集組成に若干の変化が両Stationで見られたが,これらの変動傾向が長期的な海洋環境変動と関係しているかどうかについては,9年目以降の試料分析を通して考察する必要がある。In order to decipher the relationship between the changes in diatom floral fluxes and the oceanographic conditions, we've deployed sediment traps at Stations AB (the Aleutian Basin) and SA (the central subarctic Pacific) from August of 1990 to the present. For the first eight years, we've conducted a diatom flux study. Total diatom fluxes (TDF) at both stations usually showed spring and/or fall peaks in a year. However, significant interannual variations of TDF were observed at both stations. At Station SA, significant correlation coefficient was obtained between mean TDF of each year and Pacific Decadal Oscillation index. These interannual variations are possibly due to the differences in the strength and timing of winter mixing and the subsequent summer stratification. The dominant species at both stations was Neodenticula seminae with mean abundances of 80% (Station AB) and 82% (Station SA) of TDF throughout the sampled duration. Coastal species were more abundant at Station AB than Station SA. At Station SA, relatively small numbers of Chaetoceros resting spores occurred in summers of some years as the result of lateral advection from the Aleutian Islands. During the eight years, the slight changes of diatom sinking flora were observed at both stations. Whether or not these trends suggest the changes in oceanographic condition for long-term, a further observation is warranted and to be continued.
• Estimation of water circulation in Otsuchi Bay, Japan inferred from ADCP observation

  OTOBE Hirotaka, ONISHI Hiroji, INADA Masakatsu, MICHIDA Yutaka, TERAZAKI Makoto  Coastal marine science  33-  (1)  78  -86  2009  [Not refereed][Not invited]
   

  In order to understand the seasonal water circulation system of Otsuchi Bay, direct current measurements were taken by using bottom-mounted Acoustic Doppler Current Profilers (ADCPs) during two periods, from October 2003 to March 2004 and from May 2004 to October 2004. During the first observation period, a remarkable estuary-type vertical circulation was observed. An anti-clockwise circulation, flowing into the bay along the northern coast and out along the southern coast was dominant during the second observation period. It was found that this clear seasonal variation was generated by both seasonal changes of wind and tide-induced residual current.
• Diatom floral fluxes at Stations AB and SA in the Bering Sea and the northern Subarctic Pacific, 1990-1998

  ONODERA Jonaotaro, TAKAHASHI Kozo, ONISHI Hiroji, YANADA Mitsuru, Jonaotaro Onodera, Kozo Takahashi, Hiroji Onishi, Mitsuru Yanada, Center for Advanced Marine Core Research Kochi University, Department of Earth and Planetary Sciences Kyushu University, Graduate School of Fisheries Science Hokkaido University, Graduate School of Fisheries Science Hokkaido University  Oceanography in Japan  18-  (5)  307  -322  2009  [Not refereed][Not invited]
   

  珪藻沈降群集フラックスと海洋環境変動との対応関係を探るために,Station AB(ベーリング海)とStation SA(北太平洋北部中央亜寒帯)において,1990年8月から1999年1月上旬までに得られたセディメントトラップ試料を分析した。全珪藻フラックス変動の極大は,多くの年は両Stationともに春と秋のどちらか年一回か,春と秋の年2回観察された。しかし,年によっては特異なフラックス変動が観測され,そのタイミングはStations ABとSAで異なっていた。これらの経年変動は,おそらく冬季鉛直混合と,それに引き続く夏季成層構造の発達度合いとタイミングの違いが影響していると思われる。珪藻沈降群集の優占種はNeodenticula seminaeで,8年間を通した平均優占率はABで80%,SAで82%に達した。8年間を通して,珪藻沈降群集組成に若干の変化が両Stationで見られたが,これらの変動傾向が長期的な海洋環境変動と関係しているかどうかについては,9年目以降の試料分析を通して考察する必要がある。In order to decipher the relationship between the changes in diatom floral fluxes and the oceanographic conditions, we've deployed sediment traps at Stations AB (the Aleutian Basin) and SA (the central subarctic Pacific) from August of 1990 to the present. For the first eight years, we've conducted a diatom flux study. Total diatom fluxes (TDF) at both stations usually showed spring and/or fall peaks in a year. However, significant interannual variations of TDF were observed at both stations. At Station SA, significant correlation coefficient was obtained between mean TDF of each year and Pacific Decadal Oscillation index. These interannual variations are possibly due to the differences in the strength and timing of winter mixing and the subsequent summer stratification. The dominant species at both stations was Neodenticula seminae with mean abundances of 80% (Station AB) and 82% (Station SA) of TDF throughout the sampled duration. Coastal species were more abundant at Station AB than Station SA. At Station SA, relatively small numbers of Chaetoceros resting spores occurred in summers of some years as the result of lateral advection from the Aleutian Islands. During the eight years, the slight changes of diatom sinking flora were observed at both stations. Whether or not these trends suggest the changes in oceanographic condition for long-term, a further observation is warranted and to be continued.
• Evaluation of the fall rates of the present and developmental XCTDs

  Shoichi Kizu, Hiroji Onishi, Toshio Suga, Kimio Hanawa, Tomowo Watanabe, Hiroshi Iwamiya  DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS  55-  (4)  571  -586  2008/04  [Not refereed][Not invited]
   

  The fall rates of the current types of expendable conductivity-temperature-depth (XCTD) profilers and one under development are evaluated based on a series of co-located measurements with conventional conductivity-temperature-depth (CTD) profilers in the North Pacific. The types of probes investigated are the XCTD-1, the XCTD-2, the XCTD-3, and the XCTD-5 manufactured by Tsurumi Seiki Co., Ltd. It is confirmed that the present manufacturer's fall-rate coefficients for the XCTD-1/2 satisfy the accuracy guarantee of 2% of depth, at depth greater than 20 in. The coefficients of all XCTD types tested Lire dependent on water temperature, and the probes tend to fall slightly faster in warmer water. New sets of coefficients are given for the individual types, in a form that includes a correction for water temperature. It is also found that the ring hood structure of the XCTD-1/2 is effective in stabilizing the fall rates. The newer XCTD-3/5, which lack the hood, show larger scatter in the fall rate and occasionally violates the guaranteed depth accuracy. (c) 2008 Elsevier Ltd. All rights reserved.
• 表層水塊および成層構造の時空間変動に関する研究の進展と今後の展開

  須賀利雄, 上野洋路, 大西広二, 林和彦, 斎藤寛子, 鋤柄千穂, 遠山勝也  月刊海洋  39-  (7)  2007/07  [Not refereed][Not invited]
  
• Formation and variation of temperature inversions in the eastern subarctic North Pacific

  Hiromichi Ueno, Eitarou Oka, Toshio Suga, Hiroji Onishi, Dean Roemmich  GEOPHYSICAL RESEARCH LETTERS  34-  (5)  L05603  -L05603  2007/03  [Not refereed][Not invited]
   

  Hydrographic data from profiling float observations for 2001 - 2005 and from expendable bathythermograph observations for 1993 - 2005 were analyzed to study the formation and variation of temperature inversions (T-inversions) in the eastern subarctic North Pacific ( SNP). The formation and variation of T-inversions differed significantly between the northern and southern regions of the eastern SNP. In the northern region, the temperature minimum (T-min) at the top of T-inversions outcropped to the sea surface and was cooled in the mixed layer nearly every winter. This process caused a seasonal cycle in the magnitude of T-inversions (DT), with a maximum in winter. In the southern region, the winter T-min outcropped relatively infrequently and the DT did not exhibit a significant maximum in winter during most years. The T-min in the southern region was likely to outcrop upstream near the date line roughly one year earlier and was then advected to the southern region.
• Comparison of the current measured by electromagnetic current meter and bottom mounted ADCP in Otsuchi bay

  Coastal Marine Science  30-  (2)  459  -463  2006  [Not refereed][Not invited]
  
• Seasonal and interannual variability of temperature inversions in the subarctic North Pacific

  H Ueno, E Oka, T Suga, H Onishi  GEOPHYSICAL RESEARCH LETTERS  32-  (20)  L20603  -L20603  2005/10  [Not refereed][Not invited]
  
• 1994-2002年夏季におけるアラスカ湾の水温極小

  橋本 洋平, 磯田 豊, 大西 広二, 坂岡 桂一郎  海の研究  14-  (4)  513  -525  2005  [Not refereed][Not invited]
  
• 北太平洋亜寒帯海域におけるArgoデータの利用

  月刊海洋・海洋出版株式会社  2005  [Not refereed][Not invited]
  
• Spatial and temporal variability in a vertical section across the Alaskan Stream and Subarctic Current

  Hiroji Onishi  海の研究 = Umi no Kenkyu (Oceanography in Japan)  11-  (2)  358  -358  2002/03/05  

  北太平洋中央部の亜寒帯海域において,北海道大学のおしょろ丸によるCTD観測が毎年6月の下旬に行われている。1990～1998年の9年間,180°の経度線に沿って,48°N～51.2°Nの間に9観測点が設けられた。このデータセットを用いて,水温,塩分,密度,地衡流速(3,000m基準)についての平均断面図や標準偏差断面図などを作成した。さらにEOF解析を用いて断面構造における空間分布と時間変動の解析を行った。流速断面のEOF第1モード(寄与率37.6%)は,西向きのアラスカンストリームと東向きの亜寒帯海流の強弱を表わす空間分布を示した。このモードの振幅関数では,1991年と1997年に正の極大値を持ち,亜寒帯海流の東向き輸送量の変動とよい一致を示した。また,この変動は,Ridge Domainにおける深層水の湧昇の度合いが強く関与していることが示された。
• Spatial and temporal variability in a vertical section across the Alaskan stream and subarctic current

  H. Onishi  Journal of Oceanography  57-  (1)  79  -91  2001  [Not refereed][Not invited]
   

  In the central North Pacific Subarctic Gyre, CTD hydrographic measurements were carried out yearly in late June from 1990 to 1998 at 9 stations along 180° meridian from 48°N to 51.2°N. Vertical sections of 9-year means, anomalies for each year and others of potential temperature, salinity, potential density and geostrophic velocity (referred to 3000 m) were calculated based on this data set. Empirical Orthogonal Function (EOF) analysis was adopted in the investigation of spatial characteristics and its temporal variation in vertical sections. The spatial distribution of the 1st mode EOF of velocity shows the westward Alaskan Stream and the eastward Subarctic Current. This mode explains 37.6% of the total variance. Two positive maxims appear in its amplitude in 1991 and 1997, which is similar to the variation in volume transport of the eastward Subarctic Current. These variations are closely related to the vertical movement of Ridge Domain deep water.
• Anticyclonic, Baroclinic Eddies along 145^.W in the Gulf of Alaska in 1994-1999

  ONISHI Hiroji, OHTSUKA Shintaro, ANMA Gen  Bulletin of the Faculty of Fisheries, Hokkaido University  51-  (1)  31  -43  2000  [Not refereed][Not invited]
  
• On seasonal and year to year variation in flow of the Alaskan Stream in the central North Pacific

  Hiroji Onishi, Kiyotaka Ohtani  Journal of Oceanography  55-  (5)  597  -608  1999/10  [Not refereed][Not invited]
   

  The Alaskan Stream is the westward boundary current of the North Pacific subarctic gyre. In the central region of the North Pacific, the Alaskan Stream serves as a connection between the Alaskan gyre, Western subarctic gyre and Bering Sea gyre. Its volume transport is very important in estimating the magnitude of the subarctic circulation in the North Pacific. In order to clarify its seasonal and interannual variation, we conducted observations along a north-south section at 180°during June from 1990 to 1997. Moorings were deployed from 1995 to 1997. Hydrographic casts were made at intervals of ~37 km to a depth of 3000 m. Moorings were set between CTD stations, with Moor1 (Moor2) at the center (southern edge) of the Alaskan Stream. Geostrophic volume transport (referred to 3000 m) revealed large interannual variability in the Alaskan Stream. Average volume transport over the 8 years was 27.5 x 106 m3s-1 with a standard deviation of 6.5 x 106 m3s-1. Maximum transport was 41.0 x 106 m3s-1 (1997) and minimum was 21.7 x 106 m3s-1 (1995). Stable westward flows were observed at Moor1 1500 m (259°, 11.7 cm s-1) and 3000 m (240°, 3.7 cm s-1, 1996-1997 year average). The ratio of eddy to mean kinetic energy (KE'/KE) was very small (< 0.6) throughout the year. A relatively weak and unstable westward flow was observed at Moor2 at 3000 m depth. Conversely, the average flow direction at Moor2 5000 m was eastward.
• Seasonal and interannual variability of the Alaskan Stream in the central North Pacific

  IOC-WESPAC The Fourth International Sciencetific Symposium, Okinawa, Japan  43  -52  1998  [Not refereed][Not invited]
  
• Baroclinic Flow Referred to the 3000m Reference Level across the 180° Transect in the Subarctic Pacific

  Bull. Fac. Fish. Hokkaido Univ.  48-  53  -64  1997  [Not refereed][Not invited]
  
• 「北太平洋西部亜寒帯海域の平均海洋構造と変動」

  『水産海洋研究』  60-  78  -83  1996  [Not refereed][Not invited]
  
• 北太平洋亜寒帯循環の東西輸送

  月刊海洋・海洋出版株式会社  1992  [Not refereed][Not invited]
  

Association Memberships

• 日本海洋学会   水産海洋学会   海洋気象学会   

Works

• 大西先生の流体力学の実験教室⑧

  北海道大学大学院水産科学研究院マリンラーニング事務局 Youtubeウェッブページ 2020/09 - Today
• 大西先生の流体力学の実験教室⑦

  北海道大学大学院水産科学研究院マリンラーニング事務局 Youtubeウェッブページ 2020/09 - Today
• 大西先生の流体力学の実験教室⑥

  北海道大学大学院水産科学研究院マリンラーニング事務局 Youtubeウェッブページ 2020/09 - Today
• 大西先生の流体力学の実験教室⑤

  北海道大学大学院水産科学研究院マリンラーニング事務局 Youtubeウェッブページ 2020/09 - Today
• 大西先生の流体力学の実験教室④

  北海道大学大学院水産科学研究院マリンラーニング事務局 Youtubeウェッブページ 2020/08 - Today
• 大西先生の流体力学の実験教室③

  北海道大学大学院水産科学研究院マリンラーニング事務局 Youtubeウェッブページ 2020/08 - Today
• 大西先生の流体力学の実験教室②

  北海道大学大学院水産科学研究院マリンラーニング事務局 Youtubeウェッブページ 2020/08 - Today
• 大西先生の流体力学の実験教室①

  北海道大学大学院水産科学研究院マリンラーニング事務局 Youtubeウェッブページ 2020/08 - Today

Research Projects

• Optimization of polyculture in Sanriku ria coasts based on comparative coastal oceanography

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2006 -2008 

  Author : FURUYA Ken, KUROKURA Hisashi, TAKEDA Shigenobu, KISHI Michio, ONISHI Hiroji, OGAWA Hisao

   

  三陸沿岸域におけるホタテ、マガキなどの無給餌養殖生産の内湾環境依存性を、大槌湾と大船渡湾の対比から明らかにした。大船渡湾では、大槌湾よりも閉鎖性が強いため湾内外の海水交換が悪く、湾外からの栄養塩供給は湾奥には至らない。両湾ともに、貝類養殖は現状の養殖密度がほぼ妥当であるが、養殖貝類の成長速度は養殖実施場所によって異なることから、養殖実施場所の選択により増産の可能性があることが明らかになった。
• The annual variation of sinking particles flux corresponding to material transports of North Pacific Subarctic Gyre

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2003 -2006 

  Author : YANADA Mitsuru, TAKAHASHI Kozo, OHISHI Hiroji

   

  The aim of this study is to predict the changes of marine environment in the future by elucidating hydrographic environmental factors, e. g. the Alaskan Stream, which cause the seasonal and annual variations in the processes of primary production in the central subarctic Pacific and the Bering Sea Basin. The deployment and recovery of time-series sediment trap array were carried out by the T/S "Oshoro Maru" belonging to Hokkaido University every year from 2003 to 2007 in the Bering Sea Basin (AB: 53. 5°N, 177. 0°W) and in the central subarctic Pacific (SA: 49. 0°N, 174. 0°W). A part of obtained sinking particles was measured for the determinations of total mass, total carbon, organic carbon, total nitrogen, total amino acids, hexosamine, biogenic opal, calcium carbonate and stable isotope. The other parts of the sinking particles were also observed using a microscope for analysis of diatoms, radiolarians, 〓ccoliths and foraminifera. The variation of hydrographic environments was elucidated by calculations of heat, salts and volume transports of the Alaskan Stream and the Subarctic Current using CTD, XCTD and Argo floats data. As a result, in the Bering Sea Basin a high maximum peak flux of sinking particles with relatively high contribution of diatoms was observed in the spring season of 2003. A time lag of the maximum peak flux of sinking particles composed of coccoliths and foraminifera was also observed in the central subarctic Pacific. These results make us expect some abnormalities on the characteristics of sinking particles during 2003-2007, implying some abnormal sinking processes or production of marine organisms in both AB station and SA station during 2003-2007. These variations for the flux and the characteristics of sinking particles may relate to the variation of surface temperature condition.
• 北太平洋東西亜寒帯循環の繋がりと深層水湧昇域の空間分布解析

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2003 -2005 

  Author : 大西 広二

   

  本年度は研究期間の3年目の最終年にあたり、一昨年度導入した観測機器を利用した夏期の観測準備を行った。また、限られた観測時間の有効利用を図るため、1950m深まで観測可能なXCTD2プローブを購入し、CTD観測の充実を図った。 夏期(6月下旬〜8月下旬)に行われた、北海道大学水産学部附属練習船おしょろ丸の北洋航海には、研究代表者が乗船し、海洋観測に携わった。海洋観測は、時間的制約の中で、アラスカンストリーム海域・亜寒帯海流海域を横断する観測断面を3断面に渡って行うことが出来た。観測結果から、3断面のうちアラスカンストリームの上流域にあたる西経165度と170.5度では流域幅は広いものの流量は少なく、経度180度では流域幅は狭いものの構造が深く、多くの西向き流量が求められた。この結果から、アラスカンストリームが流下方向に増大する傾向は過去の観測結果と一致し、深層水湧昇域の密度傾斜の形状が大きく空間的に変化する事が流速構造や流量の変化に繋がっていることが確かめられた。 この結果を踏まえて、今後は東西循環を繋ぐ流量、外部との流入・流出量に着目し、ADCPデータや水塊分析データを基に解析結果をまとめる予定である。さらにArgoフロートデータ、衛星データや気象データとの対応も図り、本研究で得られた成果がよりグローバルな海洋環境の変化と密接に係わっている事を確かめ、長期にわたるアラスカンストリームのモニター観測を一層重要な物と位置づけて行きたいと考える。 本年度の成果の一部は、2005年日本海洋学会春季大会シンポジウムで発表・報告した。これからも更なる成果を公表し、広く意見を求めて研究のまとめにつなげたい。
• Response of the Key-species in Ecosystem to Multi-decadal Changes in the Subarctic Circulation

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 1996 -1998 

  Author : OHTANHI Kiyotaka, ONISHI Hiroji, MATSUISHI Takashi, SAKURAI Yasunori

   

  Long-term variations in sea condition in the subarctic circulation connected with variation in the Aleutian Low system. Residence time index of the sea ice in the Bering Sea and the Okhotsk Sea indicated decadal changes which showed negative phase between them. Current path and transport in the subarctic circulation and the transition zone also changed inter-annually. Pelagic fishes such as the salmonoid and the squids changed in their distribution and abundance with inter-annual variation in sea conditions. Life history of the saury were discussed with modeling analysis based on catch-at-age data. Useful cohort analysis for the cods based on catch-at-weight data were proposed.
• Joint Study on the Bioclimatology in the Bering Sea

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 1995 -1997 

  Author : OHTANI Kiyotaka, ONISHI Hiroji, SHIGA Nanobu, NAKATANI Toshikuni, SAITOH Sei-ichi, SAKURAI Yasunori

   

  During Bering Sea surveys by the T/S Oshoro-Maru of Hokkaido University in the summers of 1995,1996 and 1997, we conducted a joint study of the bioclimatology in the Bering Ses with sientists from the University of Alaska, Fairbanks. In this study, we examined the relationship between the physical environment, production structure and recruitment of keystone species, including walleye pollock Theragra chalcogramma, related to recent climatic changes in th Bering Sea ecosystem. The results will be published in teh Memories of the Faculty of Fisheries.Hokkaido University, in the summer of 1998. A summary of our joint study is as follows : 1. We studied coastal upwelling in the St.Lawrence Island Polynya in the summers of 1994 and 1995 by satellite and ship observations. 2, We clarified interannual variation and vertical distribution of appendicularians in the St.Lawrence Island Shelf in summer. 3. We examined biophysical processes relevant to recruitment dynamics of walleye pollock in the eastern Bering Sea during the summers of 1995,1996 and 1997. We will present a conceptual model of factors influencing pollock recruitment in this area. 4. We clarified the effect of temperature and salinity on development and survival of eggs and larvae of Arctic cod, Boreogadus saida as an indicator species related to climatic change in the Berin Sea. 5. We studied the bottom fish composition and food habits in the southern water off the St.Lawrence Island in the Bering Sea.
• 北部北太平洋亜寒帯循環の物質・熱輸送量の評価