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)

  Ooki

• Name (Kana)

  atsushi

• Name

  201301090636511285

Alternate Names

https://repun-app.fish.hokudai.ac.jp/course/view.php?id=1834

Achievement

Research Interests

• VOC   ハロカーボン   ブロモホルム   揮発性有機化合物   臭化メチル   海洋起源   揮発性有機ハロゲン化合物   海洋植物プランクトン   ジブロモメタン   海洋大気   混合層   植物プランクトン   大気観測   塩化メチル   生成メカニズム   ヨウ化メチル   海洋観測   

Research Areas

• Environmental science/Agricultural science / Environmental dynamics

Research Experience

• 2011/04 - Today Hokkaido University
• 2006/09 - 2011/03 National Institute for Environmental Studies NIES PostDoc Fellow
• 2006/04 - 2006/09 北海道区水産研究所 支援研究員
• 2003/04 - 2006/03 Hokkaido University Faculty of Environmental Earth Science JSPS PD

Education

• 2000/04 - 2003/03  The University of Tokyo
• 1997/04 - 1999/03  Tokyo University of Science  Graduate School of Science
• 1993/04 - 1997/03  Tokyo University of Science

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.
• Intrusion of Coastal Oyashio water to Funka Bay and Tsugaru Strait occasionally disturbed by Kuroshio-originating warm core ring

  H. Abe, Y. Yahiro, T. Hasegawa, T. Hirawake, H. Onishi, A. Ooki, T. Takatsu, K. Sasaki, M. Wakita, H. Kaneko, S. Watanabe, T. Tanaka, T. Okunishi, S. Ohno, S. Hashizume

  Journal of Oceanography 0916-8370 2023/01/09
• 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
• Marine sediment as a likely source of methyl and ethyl iodides in subpolar and polar seas

  Atsushi Ooki, Keita Minamikawa, Fanxing Meng, Naoya Miyashita, Toru Hirawake, Hiromichi Ueno, Yuichi Nosaka, Tetsuya Takatsu

  Communications Earth & Environment 3 (1) 2022/08/12 [Refereed]
   

  Abstract The surface ocean is an important source of longer-lived volatile organic iodine compounds, such as methyl and ethyl iodide. However, their production in deep waters is poorly constrained. Here, we combine shipborne seawater and sediment core analyses to investigate the temporal and vertical distribution of methyl and ethyl iodide concentrations in the Bering and Chukchi Seas in July 2017 and 2018, and Funka Bay, Japan, between March 2018 and December 2019. We find the highest methyl and ethyl iodide concentrations in sediment porewaters and at the sediment surface. In Funka Bay, concentrations in the sediment and bottom waters strongly increased following the spring bloom and subsequent settling of phytodetritus to the seafloor. Dark incubation experiments suggest that diatom aggregates are a source of methyl and ethyl iodide to the ambient water. Our findings suggest that phytodetritus at the seafloor is a potential source of volatile organic iodine compounds to the water column in polar and subpolar coastal oceans.
• Positive effect of filtration additives for increasing environmental DNA detections in summer and winter oceanic waters

  Hyojin Ahn, Yusuke Asano, Shota Suzuki, Atsushi Ooki

  Environmental DNA 4 (3) 661 - 673 2637-4943 2022/05 [Refereed][Not invited]
  
• 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 

  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
• Atmosphere-sea ice-ocean interaction study in Saroma-ko Lagoon, Hokkaido, Japan 2021

  Daiki NOMURA, Hiroki IKAWA, Yusuke KAWAGUCHI, Naoya KANNA, Tatsuya KAWAKAMI, Yuichi NOSAKA, Sachi UMEZAWA, Manami TOZAWA, Takahito HORIKAWA, Reishi SAHASHI, Taichi NOSHIRO, Ibuki KABA, Makoto OZAKI, Fumiyoshi KONDO, Keisuke ONO, Itsuka S. YABE, Eun Yae SON, Takahiro TOYODA, Sohiko KAMEYAMA, Changqing WANG, Hajime OBATA, Atsushi OOKI, Hiromichi UENO, Akihide KASAI

  Bulletin of Glaciological Research 40 1 - 17 1345-3807 2022 [Refereed]
  
• Water mass distribution in the northern Bering and southern Chukchi seas using light absorption of chromophoric dissolved organic matter

  Toru Hirawake, Joji Oida, Youhei Yamashita, Hisatomo Waga, Hiroto Abe, Jun Nishioka, Daiki Nomura, Hiromichi Ueno, Atsushi Ooki

  Progress in Oceanography 197 102641 - 102641 0079-6611 2021/09 [Refereed][Not invited]
   

  The northern Bering Sea (NBS) and southern Chukchi Sea (SCS) contain several water masses with different characteristics that have been conventionally classified using temperature and salinity data. However, recent warming and sea ice decline can change these water properties, which suggests that classifying water masses using temperature–salinity diagrams could be problematic for this region. We used the light absorption coefficient of chromophoric dissolved organic matter (CDOM), aCDOM, as an alternative way to classify water masses. The aCDOM spectra of several water depths were measured in the NBS, the Gulf of Anadyr included, and SCS in July 2017 and 2018, and August 2018. Optical parameters that indicate CDOM quantity and quality, aCDOM(350) and spectral slopes (S275–295 and S350–400), were calculated for each sample; water masses were classified using cluster analysis. When surface waters in the NBS and SCS are classified on the basis of the conventional method using a temperature–salinity diagram, they are mistakenly identified as Alaskan Coastal Water because of warmer temperatures. However, our cluster analysis using CDOM parameters evenly classified seven water masses with reasonable distributions. A water mass with the highest aCDOM(350) and lowest S275–295 was found along the coast of the Gulf of Anadyr and Alaska mainland, which suggests that freshwater originates from the Anadyr and Yukon rivers and is transported by the Anadyr Current and Alaskan Coastal Current, respectively. A CDOM-based water mass with high S275–295, indicating CDOM degradation by ultraviolet radiation, was present at the sea surface. A water mass with low S275–295 was found at deeper water depths and river mouths. These results suggest that classification with CDOM parameters is consistent with geographical features. In addition, we recognized a water mass with high nitrate concentrations, which is likely Anadyr Water that originates in the region from the Bering Slope to the Gulf of Anadyr. Overall, this study reveals that water mass classification using CDOM parameters is useful in coastal sea areas in which water mass mixing is complex.
• Formation of dense shelf water associated with sea ice freezing in the Gulf of Anadyr estimated with oxygen isotopic ratios

  Daiki Nomura, Hiroto Abe, Toru Hirawake, Atsushi Ooki, Youhei Yamashita, Aiko Murayama, Kazuya Ono, Jun Nishioka

  PROGRESS IN OCEANOGRAPHY 196 0079-6611 2021/08 [Refereed]
   

  We analyzed temperature and salinity data and oxygen isotope ratios (818O) in summer 2018 in order to quantify the formation of dense shelf water (DSW) associated with sea ice freezing in the Gulf of Anadyr in the northwestern Bering Sea. Salinity and 818O displayed a strong linear relationship in samples upstream (southwest) of the Gulf of Anadyr. However, in bottom water (>26.5 00) in the northern Gulf of Anadyr, where a large polynya is the site of high sea ice production in winter, salinity was clearly higher than in the upstream water, whereas 818O was in the same range. This deviation is consistent with the formation of sea ice through brine rejection and subsequent DSW formation, causing an increase of salinity without changing 818O. A mass balance calculation based on these results yielded an estimated production of sea ice equivalent to a thickness 0.7 m, a result that matched an independent estimate of 2018 annual ice production based on satellite data. Even though the winter of 2018 had a historically low sea ice extent in the Bering Sea, including the Gulf of Anadyr, our results indicate continued DSW formation in the Gulf of Anadyr.
• Observations of anticyclonic eddies in the western subarctic North Pacific

  Ryo Dobashi, Hiromichi Ueno, Yuki Okada, Takahiro Tanaka, Jun Nishioka, Toru Hirawake, Atsushi Ooki, Sachihiko Itoh, Daisuke Hasegawa, Yoshikazu Sasai, Hideharu Sasaki, Ichiro Yasuda

  JOURNAL OF OCEANOGRAPHY 77 (2) 229 - 242 0916-8370 2021/04 [Refereed][Not invited]
   

  We conducted a ship observation of two anticyclonic mesoscale eddies (Eddies A and B) between June and July 2016 in the offshore region of the western subarctic North Pacific to clarify the impact of anticyclonic eddies on biological production. Analysis of satellite data reveals that Eddy A formed south of the Alaskan Peninsula on May 2011 while Eddy B formed in the observation area on November 2015. Iron concentration was low both inside and outside Eddies A and B, and there were no large differences between chlorophyll a (chl-a) concentration inside and outside eddies. Satellite-derived chl-a concentration inside Eddy A had been high compared with that in the surrounding area when the eddy was located along the Aleutian Islands and just after it detached from the islands, suggesting that iron originating from the coastal region was consumed during the two-year journey from the coastal region to the observation area. Field measurements also reveal that vertical diffusivity was low both inside and outside Eddies A and B, which could be another factor underlying low iron both inside and outside Eddies A and B and small differences between chl-a concentration inside and outside the eddies.
• Response of Arctic biodiversity and ecosystem to environmental changes: Findings from the ArCS project

  Toru Hirawake, Masaki Uchida, Hiroto Abe, Irene D. Alabia, Tamotsu Hoshino, Shota Masumoto, Akira S. Mori, Jun Nishioka, Bungo Nishizawa, Atsushi Ooki, Akinori Takahashi, Yukiko Tanabe, Motoaki Tojo, Masaharu Tsuji, Hiromichi Ueno, Hisatomo Waga, Yuuki Y. Watanabe, Atsushi Yamaguchi, Youhei Yamashita

  POLAR SCIENCE 27 1873-9652 2021/03 [Refereed]
   

  Arctic ecosystems are altered profoundly by climate changes. However, the responses of Arctic marine and terrestrial ecosystems as well as their biodiversity to global warming remain largely unknown. This article provides comprehensive insights into the results and major findings from the Arctic Challenge for Sustainability (ArCS) Project ? an Arctic region research program initiated in Japan, which aims to address and advance our understanding of these uncertainties. Marine ecosystem studies have identified several biogeochemical processes that are associated with sea ice decline and northward transport and shift of marine species across multiple trophic levels over the Bering and Chukchi Sea shelves. Studies of the terrestrial ecosystem have identified factors that are important for the understanding of terrestrial biodiversity and ecosystems, including Arctic lakes, under the presence of global warming. Novel fungal species from the Arctic terrestrial ecosystem have also been isolated and described. Overall, these results could contribute to the conservation and sustainable management of the Arctic ecosystem services.
• Between-year comparison of interactions between environmental parameters and various plankton stocks in the northern Bering Sea during the summers of 2017 and 2018

  Atsushi Yamaguchi, Fumihiko Kimura, Yuri Fukai, Yoshiyuki Abe, Kohei Matsuno, Atsushi Ooki, Toru Hirawake

  POLAR SCIENCE 27 1873-9652 2021/03 [Refereed]
   

  In the northern Bering Sea, ice coverage and retreat timing were low and early, respectively, in the 2017?2018 winter. To evaluate the effect of these anomalous ice conditions, we quantified various environmental parameters (temperature, salinity, mixed-layer depth, nutrients) and the standing stocks of various planktonic taxa (phytoplankton counts, meso- and macrozooplankton mass, jellyfish abundance) during July of 2017 and 2018. For each year, the interaction between each parameter was evaluated by structural equation modelling (SEM) analysis. Large yearly differences were detected for the interactions between environmental parameters and planktonic stocks. Thus, for 2017, a total of fifteen interactions were present between environmental parameters and various planktonic stocks. In 2018, however, only eight interactions were present. Among the interactions, four were common to the two years. It is notable that the path coefficients of these four interactions were all lower in 2018 than in 2017. These findings suggest that the small magnitude and short pulse of the phytoplankton bloom in 2018 may have failed to transfer production and energy to a higher trophic level even within the planktonic food web. Indeed, in 2018, mass mortality was reported for seabirds (two murre species) feeding on planktivorous fishes.
• Using under-ice hyperspectral transmittance to determine land-fast sea-ice algal biomass in Saroma-ko Lagoon, Hokkaido, Japan

  Pat Wongpan, Daiki Nomura, Takenobu Toyota, Tomonori Tanikawa, Klaus M. Meiners, Tomomi Ishino, Tetsuya P. Tamura, Manami Tozawa, Yuichi Nosaka, Toru Hirawake, Atsushi Ooki, Shigeru Aoki

  ANNALS OF GLACIOLOGY 61 (83) 454 - 463 0260-3055 2020/12 [Refereed]
   

  Sea ice, which forms in polar and nonpolar areas, transmits light to ice-associated (sympagic) algal communities. To noninvasively study the distribution of sea-ice algae, empirical relations to estimate its biomass from under-ice hyperspectral irradiance have been developed in the Arctic and Antarctica but lack for nonpolar regions. This study examines relationships between normalised difference indices (NDI) calculated from hyperspectral transmittance and sympagic algal biomass in the nonpolar Saroma-ko Lagoon. We analysed physico-biogeochemical properties of snow and land-fast sea ice supporting 27 paired bio-optical measurements along three transects covering an area of over 250 m x 250 m in February 2019. Snow depth (0.08 +/- 0.01 m) and ice-bottom brine volume fraction (0.21 +/- 0.02) showed low (0.06) and high (0.58) correlations with sea-ice core bottom section chlorophyll a (Chl. a), respectively. Spatial analyses unveiled the patch size of sea-ice Chl. a to be similar to 65 m, which is in the same range reported from previous studies. A selected NDI (669, 596 nm) explained 63% of algal biomass variability. This reflects the bio-optical properties and environmental conditions of the lagoon that favour the wavelength pair in the orange/red part of the spectrum and suggests the necessity of a specific bio-optical relationship for Saroma-ko Lagoon.
• 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, Atsushi Ooki, Toru Hirawake

  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 181 0967-0645 2020/12 [Refereed]
   

  We investigated spatial and interannual variation in the physical environment in the northern Bering Sea focusing on stratification, which is one factor affecting biological production in Arctic/subarctic regions. In particular, we analyzed in situ data obtained onboard the training ship Oshoro Maru in early summer in 2017 and 2018. We found that stratification in the areas just north of St. Lawrence Island (around 64.5 degrees N and west of 168.5 degrees W) and south/southwest of St. Lawrence Island was significantly weaker in 2018 than in 2017. These results are consistent with the extremely low sea-ice extent present in the winter of 2017/2018, which would have resulted in less freshwater being supplied to the surface layers and a warmer and less saline bottom water. Conversely, stratification was as strong in 2018 as in 2017 in the area close to the Alaska mainland, including the Bering Strait area, suggesting that the Alaskan Coastal Water dominates stratification in this area in early summer. Moreover, we found that the weakly stratified water column in the Bering Strait area stratified quickly shortly after the occurrence of strong northerly winds, likely because of the Ekman transport of warm and low-salinity Alaskan Coastal Water from the east.
• Saroma-ko Lagoon Observations for sea ice Physico-chemistry and Ecosystems 2019 (SLOPE2019)

  Daiki NOMURA, Pat WONGPAN, Takenobu TOYOTA, Tomonori TANIKAWA, Yusuke KAWAGUCHI, Takashi ONO, Tomomi ISHINO, Manami TOZAWA, Tetsuya P. TAMURA, Itsuka S. YABE, Eun Yae SON, Frederic VIVIER, Antonio LOURENCO, Marion LEBRUN, Yuichi NOSAKA, Toru HIRAWAKE, Atsushi OOKI, Shigeru AOKI, Brent ELSE, Francois FRIPIAT, Jun INOUE, Martin VANCOPPENOLLE

  Bulletin of Glaciological Research 38 (0) 1 - 12 1345-3807 2020 [Refereed][Not invited]
  
• Effects of glacier and sea ice melting on the biogeochemical cycles of the surface water in the Arctic Ocean

  Daiki Nomura, Naoya Kanna, Atsushi Ooki

  Chikyukagaku (Geochemistry) 2020/01 [Refereed][Not invited]
  
• Biogeochemistry of bromine and organic sulfur compounds in the Arctic region

  Sohiko Kameyama, Atsushi Ooki, Daiki Nomura

  Chikyukagaku (Geochemistry) 2020/01 [Refereed][Not invited]
  
• Preface to Geochemistry of the Arctic

  Atsushi Ooki, Sohiko Kameyama

  Chikyukagaku (Geochemistry) 53 2020/01 [Refereed][Not invited]
  
• 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 (6) 485 - 501 0916-8370 2019/12 [Refereed][Not invited]
  
• Characterization of the Water Masses in the Shelf Region of the Bering and Chukchi Seas With Fluorescent Organic Matter

  Youhei Yamashita, Yuki Yagi, Hiromichi Ueno, Atsushi Ooki, Toru Hirawake

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 124 (11) 7545 - 7556 2169-9275 2019/11 [Refereed][Not invited]
   

  Pacific water is an important nutrient source for sustaining biological production in the Chukchi Sea, western Arctic Ocean, which is one of the productive regions in the world. Therefore, to understand the impacts of future environmental changes on biological production in the sea, it is crucial to understand the origins, modification processes, and spatiotemporal variations of the water masses from the Bering Sea with changes in nutrient concentrations. To improve water mass analysis in the shelf regions of the Bering and Chukchi Seas, we observed levels of humic-like fluorescent organic matter (FOMH) by using an in situ fluorometer directly connected to a temperature-salinity sensor during a cruise in the early summer of 2013 and evaluated the potential of FOMH as a third parameter of water mass analysis. The levels of FOMH were different among specific water masses in the region, and FOMH seemed to behave semiconservatively in the shelf regions of the Bering and Chukchi Seas during the early summer of 2013. The distributional pattern of FOMH implies that FOMH estimated by the in situ fluorometer has the potential to (1) separate warm water into riverine-affected Alaskan Coastal Water and historically photobleached summer Bering Basin Water; (2) distinguish the Anadyr Water, which has low FOMH levels and high nutrient concentrations, from the Bering Shelf Water; and (3) determine different formation/modification processes of dense shelf water that contains high nutrient concentrations.
• Annual and seasonal changes in the assemblage of planktonic copepods and appendicularians in Funka Bay before and after intrusion of Coastal Oyashio Water

  Hideyoshi Yamaoka, Tetsuya Takatsu, Kota Suzuki, Naoto Kobayashi, Atsushi Ooki, Mitsuhiro Nakaya

  Fisheries Science 2019/09 [Refereed][Not invited]
  
• Sediment-Associated Phytoplankton Release From the Seafloor in Response to Wind-Induced Barotropic Currents in the Bering Strait

  Abe, Hiroto, Sampei, Makoto, Hirawake, Toru, Waga, Hisatomo, Nishino, Shigeto, Ooki, Atsushi

  FRONTIERS IN MARINE SCIENCE 6 2019/03 [Refereed][Not invited]
   

  Bering Strait is the single gateway between the Arctic and Pacific Oceans, and has localized strong currents, which can exceed 100 cm s(-1). Although massive spring phytoplankton blooms and the subsequent production of particulate organic matter that sinks to the seafloor are observed in the surrounding regions of the Bering Strait, the impact of the locally strong current on the horizontal and vertical transport of the particles remains unclear. Therefore, we conducted year-round mooring measurements from 2016 to 2017 by focusing on near-bottom processes associated with ocean currents. Our time-series analysis showed that high-turbidity events, triggered by strong barotropic currents, occurred near the seafloor in all seasons. Consequently, the fluorescence sensor detected highly concentrated chlorophyll a in the resuspended sediment; however, the amount of chlorophyll a release was seasonal, with large and small amounts being released during the warm and cold seasons, respectively. The small amounts of chlorophyll a may be attributed to small amounts of phytoplankton in the sediment owing to less input of fresh phytoplankton from the overlaying water column and organic matter decomposition in the sediments under no-light conditions. The barotropic currents were modulated by surface winds associated with an intercontinental atmospheric pattern having a 5000-km spatial scale on a timescale of 6 days. The locally strong ocean current in the Bering Strait, driving the upward transport of sediment and the subsequent horizontal transport, may play a vital role in supplying particulate organic matter/phytoplankton/nutrients to the downstream region of the southern Chukchi Sea where the formation of biological hotspots is reported.
• Production of Dibromomethane and Changes in the Bacterial Community in Bromoform-Enriched Seawater

  Takafumi Kataoka, Atsushi Ooki, Daiki Nomura

  Microbes and Environments 34 (2) 215 - 218 1342-6311 2019 [Refereed][Not invited]
  
• 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) 1 - 13 1573-868X 2018/02/16 [Refereed][Not invited]
   

  We studied the behavior of chemical substances in the upper 300 m of the water column across the continental shelf–slope interface in the East China Sea off the Okinawa Trough. The behaviors of iron, inorganic nutrients, and humic-like fluorescent dissolved organic matter were strongly influenced by the extensive water exchange between the East China Sea and the Kuroshio Current across the shelf break and slope via upwelling and frontal processes. We attributed the high humic-like fluorescent intensity at the subsurface of the shelf break and slope regions to the lateral supply of humic-like fluorescent dissolved organic matter from the shelf sediments to the outer shelf region due to the intrusion of shelf water into Kuroshio subsurface water. We found that the behavior of iron at the continental shelf–slope was remarkably different from the conservative mixing of inorganic nutrients and humic-like fluorescent dissolved organic matter. In deep and bottom waters at the shelf–slope, high total iron concentrations, which were closely related to water transmittance, possibly resulted from the swept transport of iron-rich resuspended sediments over the shelf floor from the slope by the invading Kuroshio Intermediate Water close to the bottom.
• Subarctic wintertime dissolved iron speciation driven by thermal constraints on Fe(II) oxidation, dissolved organic matter and stream reach

  Yuichiroh Morita, Kei Yamagata, Atsuki Oota, Atsushi Ooki, Yutaka Isoda, Kenshi Kuma

  GEOCHIMICA ET COSMOCHIMICA ACTA 215 33 - 50 0016-7037 2017/10 [Refereed][Not invited]
   

  We studied the seasonal variations in Fe(II), Fe(III), humic-like dissolved organic matter (DOM), nitrate and nitrite (NO3+ NO2), and silicate (Si(OH)(4)) in river waters of three subarctic rivers flowing into Hakodate Bay in southwestern Hok-kaido, Japan from May 2010 to February 2014. High Fe(II) concentrations were detected in winter at the sampling sites where the river bottom was comprised of sandy or silty sediment, primarily the lower and middle reaches of the rivers. Conversely, from early spring to late autumn Fe(II) levels were low or undetectable. We infer that soluble Fe(II) concentration in these subarctic river waters is driven by the balance between the influx of Fe(II) to the river and the Fe(II) oxidation rates that determines the dynamics in Fe(II) concentration in the river water. The Fe(II) may originate from reductive dissolution of Fe(III) in the river sediment or from Fe(II)-bearing groundwater. The latter seems to be the most likely source during winter time. The high Fe(II) concentrations during winter is predominantly attributed to the extremely slow oxidation rate of Fe(II) to Fe(III) at low water temperature rather than to an actual increase in the flux of reduced Fe(II). Nevertheless, we propose that the flux of reduced Fe(II) from river sediments and groundwater in lowland area of the catchment to overlying river waters might be the most important sources of iron in river waters. This provides an important insight into the role of river processes and the interaction between climate and river morphology in determining the inputs of iron to subarctic coastal marine waters. (C) 2017 Elsevier Ltd. All rights reserved.
• Seasonal variation of volatile organic iodine compounds in the water column of Funka Bay, Hokkaido, Japan

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

  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).
• Time-series observation of volatile organobromine compounds and isoprene in the Funka bay

  Ootsu Masashi, Ooki Atsushi, Nomura Daiki

  Abstracts of Annual Meeting of the Geochemical Society of Japan 一般社団法人日本地球化学会 64 230 - 230 2017 

• Transport of trace metals (Mn, Fe, Ni, Zn and Cd) in the western Arctic Ocean (Chukchi Sea and Canada Basin) in late summer 2012

  Yoshiko Kondo, Hajime. Obata, Nanako Hioki, Atsushi Ooki, Shigeto Nishino, Takashi Kikuchi, Kenshi Kuma

  DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 116 236 - 252 0967-0637 2016/10 [Refereed][Not invited]
   

  Distributions of trace metals (Mn, Fe, Ni, Zn and Cd) in the western Arctic Ocean (Chukchi Sea and Canada Basin) in September 2012 were investigated to elucidate the mechanisms behind the transport of these metals from the Chukchi Shelf to the Canada Basin. Filtered (< 0.22 mu m) and unfiltered seawater samples were analyzed to determine dissolved (D) and total dissolvable (TD) trace metal concentrations, respectively. We identified maxima in vertical profiles for the concentrations of D-Fe and TD-Fe, as well as for the other four analyzed trace metals, which occurred in the halocline and/or near-bottom waters. Concentration profiles of all trace metals except for Cd also tended to show peaks near the surface, which suggest that the inflow of low-salinity Pacific-origin water from the Bering Strait, as well as local fresh water inputs such as river water and melting sea-ice, influenced trace metal concentrations. The distribution patterns and concentration ranges were generally similar between the D and TD fractions for Ni, Zn and Cd, which indicate that Ni, Zn and Cd were present mainly in their dissolved forms, whereas the concentrations of TD-Fe and TD-Mn were generally higher than those of D-Fe and D-Mn, respectively. These results are consistent with the results of previous studies of this region. For both Fe and Mn, labile particulate (LP) concentrations (the difference between the TD and D fractions, which is acid-leachable fraction in the particles during storage at pH 1.5-1.6) were highest in the near-bottom waters of the Chukchi Shelf region. The relationships between the distance from the shelf break and the concentrations of trace metals revealed that Fe and Mn concentrations in halocline waters tended to decrease logarithmically with distance, whereas changes in the concentrations of Ni, Zn, Cd and phosphate with distance were small. These results suggest that the distributions of Fe and Mn were controlled mainly by input from shelf sediment and removal through scavenging processes. Based on the phase distributions of Fe and Mn, which were calculated as ratios between the LP and D fractions, different behaviors between Fe and Mn were expressed during lateral transportation. The concentration of TD-Fe declined rapidly via removal of LP-Fe from the water column, whereas the concentration of TD-Mn declined more slowly through the transformation of D-Mn into LP-Mn. In contrast, the concentrations of D-Cd, D-Zn and D-Ni were more strongly correlated with phosphate levels, which suggest that, like phosphate, the distributions of Cd, Zn and Ni were generally controlled by the internal biogeochemical cycles of the ocean interior. Based on the findings of studies that have previously evaluated the concentration maxima of Ni, Zn and Cd within the halocline layer in the Canada Basin near the Canadian Arctic Archipelago, the elevated Ni, Zn and Cd concentrations in the halocline layer may extend across the Canada Basin from the Chukchi Sea shelf-break area. The determination coefficients for correlations with phosphate concentration varied between the concentrations of Ni, Zn and Cd, which suggest that the sources of these trace metals, such as sediments and sea-ice melting, affected their patterns of distributions differently. Our findings reveal the importance and impact of the halocline layer for the transport of trace metals in the western Arctic Ocean during the late summer. The existence of rich and various sources likely sustained the high concentrations of trace metals and their unique profiles in this region. (C) 2016 Elsevier Ltd. All rights reserved.
• The conservative behavior of dissolved organic carbon in surface waters of the southern Chukchi Sea, Arctic Ocean, during early summer

  Kazuki Tanaka, Nobuyuki Takesue, Jun Nishioka, Yoshiko Kondo, Atsushi Ooki, Kenshi Kuma, Toru Hirawake, Youhei Yamashita

  SCIENTIFIC REPORTS 6 2045-2322 2016/09 [Refereed][Not invited]
   

  The spatial distribution of dissolved organic carbon (DOC) concentrations and the optical properties of dissolved organic matter (DOM) determined by ultraviolet-visible absorbance and fluorescence spectroscopy were measured in surface waters of the southern Chukchi Sea, western Arctic Ocean, during the early summer of 2013. Neither the DOC concentration nor the optical parameters of the DOM correlated with salinity. Principal component analysis using the DOM optical parameters clearly separated the DOM sources. A significant linear relationship was evident between the DOC and the principal component score for specific water masses, indicating that a high DOC level was related to a terrigenous source, whereas a low DOC level was related to a marine source. Relationships between the DOC and the principal component scores of the surface waters of the southern Chukchi Sea implied that the major factor controlling the distribution of DOC concentrations was the mixing of plural water masses rather than local production and degradation.
• Concentration maxima of volatile organic iodine compounds in the bottom layer water and the cold, dense water over the Chukchi Sea in the western Arctic Ocean: a possibility of production related to the degradation of organic matter

  A. Ooki, S. Kawasaki, K. Kuma, S. Nishino, T. Kikuchi

  BIOGEOSCIENCES 13 (1) 133 - 145 1726-4170 2016 [Refereed][Not invited]
   

  We conducted a shipboard observation over the Chukchi Sea and the Canada Basin in the western Arctic Ocean in September and October 2012 to obtain vertical distributions of four volatile organic iodine compounds (VOIs) in seawater. The VOIs observed in this study were iodomethane (CH3I), iodoethane (C2H5I), diiodomethane (CH2I2), and chloroiodomethane (CH2ClI). Maximum concentrations of the four VOIs were found in the bottom layer water over the Chukchi Sea shelf, in which layer the maximum concentration of ammonium (NH4+) also occurred. A significant correlation was observed between C2H5I and NH4+ (correlation coefficient R = 0.93, P < 0.01, n = 64) and between CH3I and NH4+ (R = 0.77, P < 0.01, n = 64), suggesting that the production of these VOIs increased with the degradation of organic matter. Over the northern Chukchi Sea shelf-slope area, concentration maxima of CH2I2, CH2ClI, and CH3I were found in the subsurface cold, dense water (CDW). A large nitrogen deficit (N deficit = NH4+ + NO3- + NO2- -16PO(4)(3-)) occurred simultaneously in this water, suggesting the production of the three VOIs in the sediment or the bottom layer water over the shelf, probably in association with the degradation of organic matter. We conclude that VOI production over the Chukchi Sea shelf can be largely attributed to the degradation of organic matter that is produced in the highly productive shelf water. High concentrations of CH2ClI were also found in the Alaskan Coastal Water (ACW) from the Bering Strait to the surface of the northern Chukchi slope. The VOIs that originated at the Chukchi Sea shelf are expected to be laterally transported to the Arctic Ocean basin through the CDW and the surface ACW.
• Regeneration dynamics of iron and nutrients from bay sediment into bottom water of Funka Bay, Japan

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

  JOURNAL OF OCEANOGRAPHY 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.
• A global-scale map of isoprene and volatile organic iodine in surface seawater of the Arctic, Northwest Pacific, Indian, and Southern Oceans

  Atsushi Ooki, Daiki Nomura, Shigeto Nishino, Takashi Kikuchi, Yoko Yokouchi

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 120 (6) 4108 - 4128 2169-9275 2015/06 [Refereed][Not invited]
   

  Isoprene (C5H8) and three volatile organic iodine compounds (VOIs: CH3I, C2H5I, and CH2ClI) in surface seawater were measured in the western Arctic, Northwest Pacific, Indian, and Southern Oceans during the period 2008-2012. These compounds are believed to play an important role in the marine atmospheric chemistry after their emission. The measurements were performed with high time-resolution (1-6 h intervals) using an online equilibrator gas chromatography mass spectrometer. C5H8 was most abundant in high-productivity transitional waters and eutrophic tropical waters. The chlorophyll-a normalized production rates of C5H8 were high in the warm subtropical and tropical waters, suggesting the existence of a high emitter of C5H8 in the biological community of the warm waters. High concentrations of the three VOIs in highly productive transitional water were attributed to biological productions. For CH3I, the highest concentrations were widely distributed in the basin area of the oligotrophic subtropical NW Pacific, probably due to photochemical production and/or high emission rates from phytoplankton. In contrast, the lowest concentrations of C2H5I in subtropical waters were attributed to photochemical removal. Enhancement of CH2ClI concentrations in the shelf-slope areas of the Chukchi Sea and the transitional waters of the NW Pacific in winter suggested that vertical mixing with subsurface waters by regional upwelling or winter cooling acts to increase the CH2ClI concentrations in surface layer. Sea-air flux calculations revealed that the fluxes of CH2ClI were the highest among the three VOIs in shelf-slope areas; the CH3I flux was highest in basin areas.
• 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。
• Laterally spreading iron, humic-like dissolved organic matter and nutrients in cold, dense subsurface water of the Arctic Ocean

  Nanako Hioki, Kenshi Kuma, Yuichirou Morita, Ryouhei Sasayama, Atsushi Ooki, Yoshiko Kondo, Hajime Obata, Jun Nishioka, Youhei Yamashita, Shigeto Nishino, Takashi Kikuchi, Michio Aoyama

  SCIENTIFIC REPORTS 4 2045-2322 2014/10 [Refereed][Not invited]
   

  The location and magnitude of oceanic iron sources remain uncertain owing to a scarcity of data, particularly in the Arctic Ocean. The formation of cold, dense water in the subsurface layer of the western Arctic Ocean is a key process in the lateral transport of iron, macronutrients, and other chemical constituents. Here, we present iron, humic-like fluorescent dissolved organic matter, and nutrient concentration data in waters above the continental slope and shelf and along two transects across the shelf-basin interface in the western Arctic Ocean. We detected high concentrations in shelf bottom waters and in a plume that extended in the subsurface cold dense water of the halocline layer in slope and basin regions. At sigma(theta) = 526.5, dissolved Fe, humic-like fluorescence intensity, and nutrient maxima coincided with N* minima (large negative values of N* indicate significant denitrification within shelf sediments). These results suggest that these constituents are supplied from the shelf sediments and then transported laterally to basin regions. Humic dissolved organic matter probably plays the most important role in the subsurface maxima and lateral transport of dissolved Fe in the halocline layer as natural Fe-binding organic ligand.
• 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。
• Disitribution of hydrogen peroxide in the Arctic Ocean

  Kondo Yoshiko, Obata Hajime, Ooki Atsushi, Yamashita Youhei, Nishioka Jun, Kuma Kenshi

  Abstracts of Annual Meeting of the Geochemical Society of Japan 日本地球化学会 61 199 - 199 2014 

  過酸化水素は、大気中ではその酸性度を高める物質として、海水中では微量金属の酸化還元反応や溶存有機物の循環および微生物群集の生物生産に影響を与える因子として重要な物質である。海水中の過酸化水素のソースとシンクは光化学反応や生物活動と密接に関わるためその挙動は動的で一様ではない。これまで、海洋における過酸化水素の分布は外洋域・沿岸域様々な海域で報告されているが、北極海におけるデータは限られている。本発表では、これまでの海洋における過酸化水素の分布動態に関するレビューを含め、GRENE北極海研究プロジェクト（http://www.nipr.ac.jp/grene/）の一環として2013年夏期に実施された北海道大学練習船おしょろ丸航海で得られた北極海（チャクチ海）における過酸化水素の分布について紹介する。
• Biogeochemical study using icebreaker for sea ice and polar oceans

  Nomura Daiki, Nishioka Jun, Kawai Michiyo, Ooki Atsushi, Tamura Takeshi

  Abstracts of Annual Meeting of the Geochemical Society of Japan 日本地球化学会 61 132 - 132 2014 

  我が国におけるこれまでの海氷研究は、主に物理過程を明らかにすることに主眼が置かれ、海氷の物理的動態を実測や衛星観測、モデリングから明らかにする研究が精力的に進められてきた。一方で、海氷に関わる化学過程や生物過程に関しては、これまで十分な研究が展開されていなかった。海氷の生成が生み出す独特の海洋循環を介して、他海域の物質循環にまで多大な影響を与えているシステムの存在が指摘されており、これらのシステムを理解するためには、海氷の存在する時期から消失していくまでの詳細な時系列観測、ポリニヤにおける海氷の生成が起こっている現場での観測が欠かせない。また、地球規模で起こっている環境変動を理解するためには、通年観測する必要があり、海洋研究プラットフォームを生物地球化学分野で最大限活用すると同時に、厳冬期でも観測が続けられる本格的な観測研究用の砕氷船が欠かせないだろう。
• 地球環境の化学 海洋から大気へ放出される揮発性有機ハロゲン化合物の特徴―気液平衡器‐自動大気濃縮‐GC‐MS法による連続測定システムの開発と応用―

  大木淳之

  化学工業 小峰工業出版 64 (7) 516 - 523 0451-2014 2013/07 [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 0525-1931 2013 [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.
• Bromoform concentrations in slush-layer water in Antarctic fast ice

  Daiki Nomura, Atsushi Ooki, Daisuke Simizu, Mitsuo Fukuchi

  ANTARCTIC SCIENCE 23 (6) 623 - 628 0954-1020 2011/12 [Refereed][Not invited]
   

  Bromoform concentrations in water of the slush layer that developed at the interface between snow and sea ice were measured during the seasonal warming in Lutzow-Holm Bay, East Antarctica. Mean bromoform concentration was 5.5 +/- 2.4 pmol l(-1), which was lower than that of the under-ice water (10.9 +/- 3.5 pmol l(-1)). Temporal decrease in bromoform concentrations and salinity with increasing temperature of the slush water suggest that the bromoform concentrations were reduced through dilution with meltwater input from the upper surface of sea ice. In contrast, bromoform concentrations in the under-ice water increased during this period while the salinity of the under-ice water decreased. It is speculated that the sea ice meltwater input contained high bromoform concentrations from the brine channels within the sea ice and from the bottom of the ice that were contributed to the increased bromoform concentrations in the under-ice water.
• Dichloromethane in the Indian Ocean: Evidence for in-situ production in seawater

  Atsushi Ooki, Yoko Yokouchi

  MARINE CHEMISTRY 124 (1-4) 119 - 124 0304-4203 2011/03 [Refereed][Not invited]
   

  We measured partial pressures of CH2Cl2 (dichloromethane) and CCl3F (CFC-11) in air and surface seawater of the Indian and Southern Oceans from November 2009 to January 2010. The excess CH2Cl2 saturation anomaly (Delta SA(CH2Cl2)>0) in surface seawater between 10 degrees S and 40 degrees S, which is the corrected value of saturation anomaly after subtracting the effects of summertime sea-surface temperature increase and of summertime decrease of atmospheric CH2Cl2 level, provides evidence for in-situ production of CH2Cl2. Depth profiles from the South Indian Ocean at 5 degrees S, 20 degrees S and 30 degrees S showed concentration maxima of dihalomethanes (CH(2)l(2), CH(2)Cll and CH2Cl2) and chlorophyll-a in the subsurface layer (20-150 m). Our data suggest that phytoplankton production of dihalomethanes leads to concentration maxima in the subsurface layer and Delta SA(CH2Cl2)>0 in surface seawater between 10 degrees S and 40 degrees S. The average oceanic emission of CH2Cl2 derived from the region between 10 degrees S and 40 degrees S in the South Indian Ocean was calculated to be 0.29-0.43 mu g m(-2) d(-1). (C) 2011 Elsevier B.V. All rights reserved.
• Diurnal and seasonal variations of iodocarbons (CH2ClI, CH2I2, CH3I, and C2H5I) in the marine atmosphere

  Yoko Yokouchi, Takuya Saito, Atsushi Ooki, Hitoshi Mukai

  JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 116 2169-897X 2011/03 [Refereed][Not invited]
   

  Four iodocarbons, chloroiodomethane (CH2ClI), diiodomethane (CH2I2), methyl iodide (CH3I), and ethyl iodide (C2H5I), were measured with an automated preconcentration gas chromatography-mass spectrometry system at two remote marine sites, Hateruma Island (24.05 degrees N, 123.8 degrees E) in the East China Sea and Cape Ochiishi (43.15 degrees N, 145.5 degrees E) on the eastern coast of Hokkaido, for 17 months, giving the first full-year high-frequency data sets for all these compounds. CH2ClI and CH2I2, which are highly photolyzed, showed remarkable diurnal variation in all seasons, with lower concentrations in the daytime, whereas CH3I and C2H5I showed no significant diurnal changes. At Cape Ochiishi, all of the iodocarbons showed clear seasonal variations and were highest in summer and autumn, which are characterized by algal blooms in the adjacent ocean. At Hateruma Island, which is surrounded by subtropical oligotrophic waters, the seasonal variations were not significant, but C2H5I and CH2I2 showed lower mixing ratios in summer. The nighttime mixing ratio of CH2ClI was strongly and positively correlated with wind speed throughout the observation period at Hateruma Island, suggesting the ubiquitous presence of CH2ClI sources, probably nonbiogenic, in the subtropical ocean. CH3I and C2H5I mixing ratios occasionally increased at Hateruma Island concurrently with winter and spring pollution events from the Asian continent, indicating possible continental anthropogenic sources or emissions from seawater off the continental coast. A rise in the CH3I baseline mixing ratio was also observed at Hateruma Island, when the air mass origin became more southerly, compared with the earlier, easterly source area, suggesting higher concentrations in equatorial regions.
• Comprehensive source apportionment of volatile organic compounds using observational data, two receptor models, and an emission inventory in Tokyo metropolitan area

  Y. Morino, T. Ohara, Y. Yokouchi, A. Ooki

  Journal of Geophysical Research Atmospheres 116 (2) 2010JD014762  0148-0227 2011 [Refereed][Not invited]
   

  Source contributions of volatile organic compounds (VOCs) were comprehensively evaluated using an observational data set, two receptor models, and an emission inventory. Hourly concentrations of C< inf> 2< /inf> -C< inf> 8< /inf> nonmethane hydrocarbons (NMHCs) were measured at Saitama, which is near the northern edge of Tokyo, throughout 2007. Estimates of background NMHC concentrations at the Saitama site corresponded well with median NMHC concentrations at a remote island in Japan in winter and spring. Source contributions of ΔNMHCs (differences between ambient and background concentrations) calculated by the chemical mass balance (CMB) model and positive matrix factorization (PMF) corresponded with each other within a factor of 2. The two receptor models estimated that vehicle exhaust, gasoline vapor, liquefied natural gas and liquefied petroleum gas (LPG), and other evaporative sources contributed 14%-25%, 9%-16%, 7%-10%, and 49%-71%, respectively, to total VOC concentrations on a mass basis. These values agreed with the emission inventory except for the LPG values. In addition, the CMB and PMF results explained at least two thirds of the observed total ΔNMHC values. These results suggest that the current emission inventory roughly captures the individual contributions and total amount of VOC emissions. However, characterization of background NMHCs is necessary to fully understand the VOC budget. Copyright 2011 by the American Geophysical Union.
• Determination of Henry's law constant of halocarbons in seawater and analysis of sea-to-air flux of iodoethane (C2H5I) in the Indian and Southern oceans based on partial pressure measurements

  Atsushi Ooki, Yoko Yokouchi

  GEOCHEMICAL JOURNAL 45 (6) E1 - E7 0016-7002 2011 [Refereed][Not invited]
   

  The sea-to-air flux of C2H5I (iodoethane) in the Indian Ocean and the Southern Ocean was estimated from the Henry's law constant (K-H) and the measured partial pressures of C2H5I in surface seawater and air. The values of K-H, defined as the ratio of molar concentration (mol l(-1)) to partial pressure (atm), for ten volatile organic compounds (VOCs) (CFCl3 (CFC-11), C5H8 (isoprene), C2H2F4 (HFC-134a), CHF2Cl (HCFC-22), CH3I, CH2Br2, C2H5I, CH2Cl2, CH2ClI, and CHBr3) were measured with an equilibrator and a purge-and-trap system in combination with gas chromatography-mass spectrometry. Ours is the first report of the K-H values for C2H5I and C5H8 as functions of temperature. The K-H values for the other VOCs were in good agreement with previously reported values. We calculated the sea-to-air flux of C2H5I using the newly determined K-H. Large sea-to-air fluxes (average, 0.04 nmol m(-2)h(-1)) were widespread in the Southern Ocean. We suggest that high biological productivity led to a high rate of C2H5I production in the subpolar water, and that the strong winds that frequently blow over the Southern Ocean resulted in the large sea-to-air flux.
• Sea to air flux of iodinated halocarbons in NW Pacific and Indian oceans

  OOKI Atsushi, Yokouchi Yoko

  Abstracts of Annual Meeting of the Geochemical Society of Japan 日本地球化学会 58 270 - 270 2011 

  2008年1月～2010年6月に北光丸(HK08-1)、白鳳丸(KH-08-2、KH-09-5、KH-10-1)、淡青丸(KT-09-5)で北西太平洋と南北インド洋で揮発性の有機ヨウ素化合物のフラックス測定を行った。夏季の亜寒帯・亜熱帯はCH3IのフラックスがCH2ClIの10倍以上に達した。いっぽう、春季ブルーム域、秋～冬季の亜熱帯・亜寒帯域ではCH2ClIの寄与が大きくなる傾向が見られた。海水中のCH2ClIは紫外線で分解するので、夏場の表層では濃度が低下する。それに伴い、亜表層にはCH2ClIの濃度極大が形成される。冬場の鉛直混合により亜表層に蓄積されたCH2ClIが表層にもたらされて、大気に放出されることが推測された。
• High-resolution measurement of multiple volatile organic compounds dissolved in seawater using equilibrator inlet-proton transfer reaction-mass spectrometry (EI-PTR-MS)

  Sohiko Kameyama, Hiroshi Tanimoto, Satoshi Inomata, Urumu Tsunogai, Atsushi Ooki, Shigenobu Takeda, Hajime Obata, Atsushi Tsuda, Mitsuo Uematsu

  MARINE CHEMISTRY 122 (1-4) 59 - 73 0304-4203 2010/10 [Refereed][Not invited]
   

  We developed an equilibrator inlet-proton transfer reaction-mass spectrometry (EI-PTR-MS) system for high-resolution measurement of the concentrations of multiple volatile organic compounds (VOCs) dissolved in seawater. The equilibration of five VOCs (isoprene, propene, acetone, acetaldehyde, and methanol) between seawater samples and the carrier gas, and the response time of the system, were evaluated by means of a series of laboratory experiments. Although equilibrium between the seawater sample and the carrier gas in the equilibrator was not achieved for isoprene and propene (likely because of their low water solubility), the other species did reach equilibrium. The EI-PTR-MS system was deployed during a research cruise in the western North Pacific Ocean. Evaluation of several seawater sampling methods indicated that there was no significant contamination from the sampling apparatus for the target VOCs. For isoprene, comparison of EI-PTR-MS measurements with measurements obtained with a membrane equilibrator-gas chromatography/mass spectrometry system showed generally good agreement (R-2=0.79). EI-PTR-MS captured the temporal variations of dissolved VOCs, including small-scale variability, which demonstrates that the performance of the EI-PTR-MS system was sufficient for simultaneous and continuous measurements of multiple VOCs of environmental importance in seawater. (C) 2010 Elsevier B.V. All rights reserved.
• Distributions of short-lived iodocarbons and biogenic trace gases in the open ocean and atmosphere in the western North Pacific

  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 0304-4203 2010/02/28 [Refereed][Not invited]
   

  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° N, 143-146° E). Sea-air fluxes of CH3Cl, CH3Br, CH2ClI, and CH2I2 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 (56-150) pmol L- 1 CH3Cl, 6.9 (4.1-19.4) pmol L- 1 CH3Br, 1.7 (0.7-2.9) pmol L- 1 CH3I, 1.9 (0.9-4.1) pmol L- 1 CH2BrCl, 4.8 (3.2-8.1) pmol L- 1 CH2Br2, 1.0 (0.6-1.8) pmol L- 1 CHBrCl2, 1.2 (0.7-2.0) pmol L- 1 CHBr2Cl, 10.8 (4.7-24.5) pmol L- 1 CHBr3, 1.7 (0.7-5.4) pmol L- 1 CH2ClI, 3.0 (< 0.1-22.2) pmol L- 1 CH2I2, 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 μg L- 1) were highest in the present study. However, the peaks of CH3Br, CH2ClI, and CH2I2 were observed in the Tsugaru warm current region, where concentrations of chlorophyll a were not as high (maximum: 0.65 μg 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 CH2I2 (r2 = 0.69 and r2 = 0.71, respectively) and with CH2ClI (r2 = 0.87 and r2 = 0.77, respectively). These results suggest that some species of prasinophytes might contribute to CH2I2 and CH2ClI production. For other compounds, there was no peak in the vertical profile in seawater. In the depth profiles, the peak of CH2ClI was observed above the peak of CH2I2; these profiles suggest that a photochemical reaction could yield CH2ClI from CH2I2 in seawater. The mean mixing ratio and range of CH3Cl, CH3Br, and CH2ClI in the air were measured as 548 (524-609), 12.1 (8.6-19.0), and 0.27 (0.03-0.90) pptv, respectively. CH2I2 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 °C to 19 °C). The highest mixing ratio of CH2ClI in air was also observed near the station at which the highest concentration of CH2ClI was observed in seawater; the sea-to-air fluxes of CH2ClI and CH2I2 were 3.8 and 1.6 nmol m- 2 day- 1, respectively. These results suggest that the production of CH2ClI and CH2I2 in seawater is an important source of organic iodine compounds in the remote atmosphere. © 2009 Elsevier B.V. All rights reserved.
• Methyl halides in surface seawater and marine boundary layer of the northwest Pacific

  Atsushi Ooki, Atsushi Tsuda, Sohiko Kameyama, Shigenobu Takeda, Sachihiko Itoh, Toshio Suga, Hirofumi Tazoe, Ayako Okubo, Yoko Yokouchi

  Journal of Geophysical Research: Oceans 115 (10) 2169-9291 2010 [Refereed][Not invited]
   

  The partial pressures of methyl halides (CH3X X = Cl, Br, or I) and of CHClF2 (HCFC-22), which are all volatile organic compounds (VOCs), were measured in the air of the marine boundary layer (pVOC air) and in surface seawater (pVOCwater) during a cruise from the subarctic to subtropical regions of the northwest Pacific in summer of 2008. In the northern transition water (TWN) with high biological activity, high levels of the three CH3Xs in surface seawater were frequently observed, probably owing to their enhanced production by phytoplankton. Supersaturation of CH3Br was only present in TW N water, with a saturation anomaly (SCH3Br) of 0.95 [SCH3X = (pCH3Xwater - pCH3X air)/pCH3Xair]. The highest saturation anomalies for CH3Cl (SCH3Cl = 1.6) and CH3I (SCH3I = 91) were found in the southern subtropical water (ST S) with low biological production south of the subtropical front. We found that the molar concentrations of CH3Cl (CCH3Cl) and CH3I (CCH3I) sharply increased with increasing sea surface temperature (SST) in the subtropical waters. The maximum CCH3Cl (144 pmol l-1) was present in STS water at SST = 30°C and is 1.5 times the value extrapolated from the previously reported relationship between CCH3Cl and SST. Photochemical production might have contributed to the production of CH3Cl and CH3I in ST S water. Copyright 2010 by the American Geophysical Union.
• Equilibrator Inlet-Proton Transfer Reaction-Mass Spectrometry (EI-PTR-MS) for Sensitive, High-Resolution Measurement of Dimethyl Sulfide Dissolved in Seawater

  Sohiko Kameyama, Hiroshi Tanimoto, Satoshi Inomata, Urumu Tsunogai, Atsushi Ooki, Yoko Yokouchi, Shigenobu Takeda, Hajime Obata, Mitsuo Uematsu

  ANALYTICAL CHEMISTRY 81 (21) 9021 - 9026 0003-2700 2009/11 [Refereed][Not invited]
   

  We developed an equilibrator inlet-proton transfer reaction-mass spectrometry (EI-PTR-MS) method for fast detection of dimethyl sulfide (DAIS) dissolved in seawater. Dissolved DMS extracted by bubbling pure nitrogen through the sample was continuously directed to the PTR-MS instrument. The equilibration of DMS between seawater and the carrier gas, and the response time of the system, were evaluated in the laboratory. DMS reached equilibrium with an overall response time of 1 min. The detection limit (50 pmol L-1 at 5 s integration) was sufficient for detection of DMS concentrations in the open ocean. The EI-PTR-MS instrument was deployed during a research cruise in the western North Pacific Ocean. Comparison of the EI-PTR-MS results with results obtained by means of membrane tube equilibrator-gas chromatography/mass spectrometry agreed reasonably well on average (R-2 = 0.99). EI-PTR-MS captured temporal variations of dissolved DMS concentrations, including elevated peaks associated with patches of high biogenic activity. These results demonstrate that the EI-PTR-MS technique was effective for highly time-resolved measurements of DMS in the open ocean. Further measurements will improve our understanding of the biogeochemical mechanisms of the production, consumption, and distribution of DMS on the ocean surface and, hence, the air-sea flux of DMS, which is a climatically important species.
• Size dependence of iron solubility of Asian mineral dust particles

  Atsushi Ooki, Jun Nishioka, Tsuneo Ono, Shinichiro Noriki

  JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 114 2169-897X 2009/02 [Refereed][Not invited]
   

  Asian mineral dust was sampled at Hokkaido, northern Japan, in spring 2004 and 2006. Iron solubility of the bulk aerosol, the size-segregated aerosol (0.45 < D < 11 mu m), the snow containing a lot of mineral dust, and a simulated Asian dust standard (CJ-2) were measured by an iron dissolution experiment using a newly developed continuous leaching method. The iron solubility of the bulk aerosol samples was 1.2-2.2%. Within the 1.1 < D < 11 mu m size range, iron solubility (0.52-8.2%) was higher in the smaller fractions of the size-segregated aerosol samples. We considered that the preferential removal of larger mineral dust particles from the air by snow resulted in the low iron solubility of the snow samples. Iron solubility of mineral dust was relatively lower in the 4.7 < D < 11 mu m fraction of the size-segregated aerosol samples (0.52%), in the snow samples (0.20-0.57%), and in the CJ-2 standard (0.33%), which are dominated by large size particles (D > 4.7 mu m). We suggest that an iron solubility of around 0.4% is typical for Asian mineral dust of large particles transported to Hokkaido. In the high-nutrient low-chlorophyll region of the western subarctic North Pacific near the Asian continent, where the mineral dust deposition is dominated by large particles, the iron solubility of the mineral dust entering the ocean is around 0.4%.
• Measurements of brominated halocarbons in the mixed water region of NW-Pacific

  Ooki Atsushi, Yokouchi Yoko

  Abstracts of Annual Meeting of the Geochemical Society of Japan 日本地球化学会 56 325 - 325 2009 

  2008～2009年（冬、春、夏）に北西太平洋の親潮-黒潮混合域で大気と海水中の臭素系ハロカーボン分圧の測定を行った。１月に北海道沿岸で海水中のブロモホルム分圧が上昇したのは大型藻類に由来すると考えられる。春季ブルーム時期の５月は外洋域で海水中の分圧が比較的高く、これは植物プランクトンに由来すると考えられる。また、５月は海水に比べて大気中のブロモホルム分圧の方が高かった。表面海水中のブロモホルム分圧の高い海洋上を大気が長距離輸送された結果と考えられる。
• Development of a silicone membrane tube equilibrator for measuring partial pressures of volatile organic compounds in natural water

  Atsushi Ooki, Yoko Yokouchi

  ENVIRONMENTAL SCIENCE & TECHNOLOGY 42 (15) 5706 - 5711 0013-936X 2008/08 [Refereed][Not invited]
   

  Methods for determining volatile organic compounds (VOCs) in water and air are required so that the VOCs' fluxes in water environments can be estimated. We developed a silicone membrane tube equilibrator for collecting gas-phase samples containing VOCs at equilibrium with natural water. The equilibrator consists of six silicone tubes housed in a polyvinyl chloride pipe. Equilibrated air samples collected from the equilibrator were analyzed with an automated preconcentration gas chromatography-mass spectrometry system for hourly measurements of VOC partial pressures. The partial pressures of all the target VOCs reached equilibrium within 1 h in the equilibrator. The system was used to determine VOC partial pressures in Lake Kasumigaura, a shallow eutrophic lake with a high concentration of suspended particulate matter (SPM). Compressed air was used daily to remove SPM deposited on the inner wall of the equilibrator and to maintain the equilibrium conditions for more than a week without the need to shut the system down. CH(2)Br(2), CHCl(3), CHBrCl(2), CH(2)BrCl, C(2)H(5)l, C(2)Cl(4), CH(3)l and CH(3)Br in the lake were supersaturated with respect to the air, whereas CH(3)Cl was undersaturated. CHCl(3) had the highest flux (6.2 nmol m(-2) hr(-1)) during the observation period.
• Characteristics of halogenated volatile organic compounds in the sub-arctic western North Pacific

  Ooki Atsushi, Yokouchi Yoko

  Abstracts of Annual Meeting of the Geochemical Society of Japan 日本地球化学会 55 313 - 313 2008 

  大気中の揮発性有機化合物（VOC）は主要な反応性微量気体であり、様々な大気化学反応にかかわっている。大気中で長寿命（＞0.5年）と短寿命（＜0.5年）のハロカーボンは成層圏と対流圏（及び下部成層圏）のオゾンを破壊することがいわれている。短寿命ハロカーボンの多くは海洋の大型藻類や植物プランクトンが主要起源であること、長寿命ハロカーボンのうち塩化メチルと臭化メチルについては陸上や海洋の生物が生成・消滅過程に関与していることが考えられている。本研究では、西部北太平洋亜寒帯におけるハロカーボンの動態とフラックスの特徴を明らかにするため、大気と表面海水中のハロカーボン分圧を連続測定した。表層海水中のハロカーボンを４グループに分け、それらの動態を特徴付けることができた。
• Size-resolved sulfate and ammonium measurements in marine boundary layer over the North and South Pacific

  Atsushi Ooki, Mitsuo Uematsu, Shinichiro Noriki

  ATMOSPHERIC ENVIRONMENT 41 (1) 81 - 91 1352-2310 2007/01 [Refereed][Not invited]
   

  Marine background levels of non-sea-salt- (nss-) SO(4)(2-) (5.0-9.7 neq m(-3)), NH(4)(+) (2.1-4.4 neq m(-3)) and elemental carbon (EC) (40-80 ngC m(-3)) in aerosol samples were measured over the equatorial and South Pacific during a cruise by the R/V Hakuho-maru from November 2001 to March 2002. High concentrations of nss-SO(4)(2-) (47-94 neq m-(3)), NH(4)(+) (35-94 neq m(-3)) and EC (130-460 ngC m(-3)) were found in the western North Pacific near the coast of the Asian continent under the influence of the Asian winter monsoon. Particle size distributions of ionic components showed that the equivalent concentrations of nss-SO(4)(2-) were balanced with those of NH(4)(+) in the size range of 0.06 < D < 0.22 mu m, whereas the concentration ratios of NH(4)(+) to nss-SO(4)(2-) in the size range of D > 0.22 mu m were decreased with increase in particle size. We estimated the source contributions of those aerosol components in the marine background air over the equatorial and South Pacific. Biomass burning accounted for the large fraction (80-98% in weight) of EC and the minor fraction (2-4% in weight) of nss-SO(4)(2-). Marine biogenic source accounted for several tens percents of NH(4)(+) and nss-SO(4)(2-). In the accumulation mode, 70% of particle number existed in the size range of 0.1 < D < 0.2 mu m. In the size rage of 0.06 < D < 0.22 mu m, the dominant aerosol component of (NH(4))(2)SO(4) would be mainly derived from the marine biogenic sources. (c) 2006 Elsevier Ltd. All rights reserved.
• Chemical interactions between mineral dust particles and acid gases during Asian dust events

  Atsushi Ooki, Mitsuo Uematsu

  Journal of Geophysical Research D: Atmospheres 110 (3) 1 - 13 0148-0227 2005/02/16 [Refereed][Not invited]
   

  Acid gas reactions during the passage from the source regions to the western North Pacific modify the chemical characteristics of Asian mineral dust particles as they pass through heavily industrial regions. We conducted aerosol samplings to investigate the interaction of mineral dust particles with acid gases in the western North Pacific region during the high-dust season. The concentration peaks of NO3 - and mineral dust particles were in the coarse mode range (D > 1.25 μm) in all aerosol samples, while non-sea-salt-(nss)-SO42- had an apparent peak in the coarse mode range only in an Asian dust event that experienced rain. Nitrate was the dominant acid substance associated with the mineral dust particles rather than nss-S)42-. In the urban air of Tokyo we also conducted an in situ experiment to react ambient acid gases with mineral dust particle loaded on a filter. The in situ experiment indicated that HNO3 had reacted with mineral dust particles much more efficiently than SO2 had. HNO3 (+NO2) and HCI accounted for large fractions (48% and 40%) of acid gases that reacted with mineral dust particles, while SO2 accounted for a small fraction (12%). The high adsorption of HNO3 on mineral dust particles would change their surface properties from hydrophobic to hygroscopic and form an efficient mechanism to remove nitrogen compounds to the ocean surface layer. Copyright 2005 by the American Geophysical Union.
• Chemical Compositions of Marine Aerosols Measured during ACE-Asia Cruise of R/V Mirai

  NAGAO Ippei, UYAMA Yukiko, OHKI Atsushi, UEMATSU Mitsuo

  Earozoru Kenkyu 日本エアロゾル学会 19 (2) 122 - 127 0912-2834 2004 [Refereed][Not invited]
   

  In order to study the chemical composition of marine aerosol and an impact caused by the primary production in spring season, aerosol sampling and measurement of dimethylsulfide (DMS) concentration were carried out on board of R/V Mirai during MR01-K02 cruise from May 14 to 28 2001.
  Based on the relationship between in-situ seawater DMS concentration and chlorophyll-a (CHL-a) estimated from satellite, amount of DMS emitted from the sea surface is estimated along the way of air parcel.
  MSA concentration observed on May 25 and 27 was about 2∼3 times higher than the average MSA concentration of this cruise. This enhancement is supposed to be due to a large amount of DMS supplied from high CHL-a area during an air parcel transport.
  Besides, nss-Ca²⁺ concentration between May 18 and 20 was about 3∼4 times higher than the average concentration of this cruise. Trajectory analysis and other approaches such as analysis of physical properties of aerosols in this period showed that Kosa particles were observed in the atmospheric marine boundary layer.
  An influence of Kosa particles on the marine production and succeeding sulfur emission should be explored.
• The increase of biogenic sulfate aerosol and particle number in marine atmosphere over the northwestern North Pacific

  A Ooki, K Miura, M Uematsu

  JOURNAL OF OCEANOGRAPHY 59 (6) 799 - 807 0916-8370 2003/12 [Refereed][Not invited]
   

  During a cruise aboard the R/V Hakuho-maru in the northwestern North Pacific in the summer of 1998 the particle number concentrations and the major ionic components of size fractionated aerosols were measured to investigate the aerosol produced by marine biological activity. Continuous low concentrations of nitrate (<1.8 nmol m(-3)), similar to the marine air background level, were found over the northwestern North Pacific (40-45degreesN) and the Sea of Okhotsk (44-45'N). Over the Sea of Okhotsk, a high concentration of chlorophyll-a (5.4 mg m(-3)) in seawater was observed, and atmospheric concentrations of non sea-salt (nss-)sulfate (44 nmol m(-3)), methane sulfonic acid (MSA) (1.8 nmol m(-3)) and particle number in the size range of 0.1 < D < 0.5 mum (199 cm(-3)) were found to be 9, 7, and 2 times, respectively, higher than those in the background marine air. The increase in particle number concentrations mainly in the size range of 0.2 < D < 0.3 mum was likely caused by the increase of biogenic sulfate over the high productive region of the Sea of Okhotsk. In humid air conditions (R.H. > 96%), the increased biogenic sulfate that condensed the large amount of water vapor would not have sufficient solute mass to activate as cloud condensation nuclei (CNN) and would remain as aerosol particles in the marine air with frequent sea-fogs over the high productive region. Biogenic sulfate originating from dimethyl sulfide (DMS) would gradually grow into the CCN size and continuously supply a great number of CCN to the marine air in the northwestern North Pacific.
• Chemical characteristics of atmospheric aerosols over the western North Pacific region(Abstract of doctoral thesis)

  Ooki Atsushi

  地球化学 日本地球化学会 37 (3) 155 - 155 0386-4073 2003/08 [Not refereed][Not invited]
  
• Aerosol size distribution during sea fog and its scavenge process of chemical substances over the northwestern North Pacific.

  SASAKAWA M, OOKI A

  J Geophys Res 108 (D3) AAC13.1-AAC13.9  0148-0227 2003/02 [Refereed][Not invited]
  
• Sources of sodium in atmospheric fine particles

  A Ooki, M Uematsu, K Miura, S Nakae

  ATMOSPHERIC ENVIRONMENT 36 (27) 4367 - 4374 1352-2310 2002/09 [Refereed][Not invited]
   

  Concentrations of size fractionated particulate sodium and potassium were measured in both marine and urban air. Marine air sampling was conducted during a cruise on R/V Hakuho-maru in the northwestern North Pacific in the summer of 1998. Urban air sampling was performed in the central part of Tokyo in 1997 and 1998. The fine sodium concentration (D < 1.1 mum) in "Urban" air (180 ng m(-3)) was 3 times higher than that in "Marine" air (56 ng m(-3)). In the urban air samples, the size distributions of sodium and potassium showed bimodal peaks in the fine particle range (D < 1.1 mum) and in the coarse particle range (D > 1.1 mum). The existence of anthropogenic sodium in the fine particle range was detected in the urban air. The K/Na weight ratios in the fine particle range of the urban air (1.8-2.7) was 50-75 times higher than that in seawater (0.036). Potassium in the urban air is thought to be derived largely from anthropogenic sources. In the urban air samples, a high correlation between fine sodium and fine potassium concentrations suggests that they have the same anthropogenic source. Reevaluating the K/Na ratios in marine air to be relatively higher than that in seawater, we can estimate that several percents of anthropogenic sodium can be transported from land to remote marine air. (C) 2002 Elsevier Science Ltd. All rights reserved.
• Chemical assessment of oceanic and terrestrial sulfur in the marine boundary layer over the northern North Pacific during summer

  K Aranami, S Watanabe, S Tsunogai, A Ohki, K Miura, H Kojima

  JOURNAL OF ATMOSPHERIC CHEMISTRY 41 (1) 49 - 66 0167-7764 2002/01 [Refereed][Not invited]
   

  Dimethylsulfide (DMS) in surface seawater and the air, methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO42-) in aerosol, and radon-222 (Rn-222) were measured in the northern North Pacific, including the Bering Sea, during summer (13 July - 6 September 1997). The mean atmospheric DMS concentrations in the eastern region (21.0 +/- 5.8 nmole/m(3) (mean +/- S.D.), n = 30) and Bering Sea (19.9 +/- 9.8 nmole/m(3), n = 10) were higher than that in the western region (11.1 +/- 6.4 nmole/m(3), n = 31) (p<0.05), although these regions did not significantly differ in the mean DMS concentration in surface seawater. Mean sea-to-air DMS flux in the eastern region (21.0 +/- 10.4 mu mole/m(2)/day, n = 19) was larger than those in the western region (11.3 +/- 16.9 mu mole /m(2)/day, n = 22) and Bering Sea (11.2 +/- 7.8 mu mole/m(2)/day, n = 7) (p < 0.05). This suggests that the longitudinal difference in atmospheric DMS was produced by that in DMS flux owing to wind speed, while the possible causes of the higher DMS concentrations in the Bering Sea include (1) later DMS oxidation rates, (2) lower heights of the marine boundary layer, and (3) more inactive convection. The mean MSA concentrations in the eastern region (1.18 +/- 0.84 nmole/m(3), n = 35) and Bering Sea (1.17 +/- 0.87 nmole/m(3), n = 13) were higher than that in the western region (0.49 +/- 0.25 nmole/m(3), n = 28) (p < 0.05). Thus the distribution of MSA was similar to that of DMS, while the nss-SO42- concentrations were higher near the continent. This suggests that nss-SO42- concentrations were regionally influenced by anthropogenic sulfur input, because the distribution of nss-SO42- was similar to that of Rn-222 used as a tracer of continental air masses.

MISC

• 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
• 酸素安定同位体比を用いたベーリング海北部アナディール湾における高密度陸棚水形成の評価

  野村大樹, 野村大樹, 野村大樹, 阿部泰人, 平譯享, 平譯享, 大木淳之, 大木淳之, 山下洋平, 村山愛子, 小野数也, 西岡純, 西岡純  日本海洋学会大会講演要旨集  2020-  2020
• 局所的に強いベーリング海峡通過流が引き起こす海底堆積有機物の巻き上げ

  阿部泰人, 三瓶真, 平譯享, 和賀久朋, 西野茂人, 大木淳之  日本海洋学会大会講演要旨集  2018-  133  2018/09  [Not refereed][Not invited]
  
• Enrichment of marine bacteria with adding a halocarbon, Bromoform (CHBr₃)

  KATAOKA Takafumi, OOKI Atsushi, NOMURA Daiki  日本微生物生態学会大会(Web)  32nd-  215 (WEB ONLY)  2018  [Not refereed][Not invited]
  
• 光分解性有機ヨウ素ガスの鉛直分布

  立松俊和, 大木淳之, 野村大樹, 平譯享, 田中雄大, 田中雄大, 安田一郎  日本海洋学会大会講演要旨集  2017-  183  2017/09  [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

  Kentaro Matsumoto, Daichi Arima, Kohei Matsuno, Yasuhiro Yamasaki, Hiroji Onishi, Atsushi Ooki, Toru Hirawake, Atsushi Yamaguchi, Ichiro Imai  北海道大学水産科学研究彙報  66-  (1)  29  -38  2016/03  [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.
• 西部北太平洋155°E線に沿った春季植物プランクトン群集の水平および鉛直分布

  松本健太郎, 有馬大地, 松野孝平, 山崎康裕, 大木淳之, 平譯享, 山口篤, 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  2015-  167  2015/09/03  [Not refereed][Not invited]
  
• 北極海の淡水流入に伴う鉄の供給と植物プランクトンの応答

  武居信行, 大木淳之, 平譯享, 西岡純  日本海洋学会大会講演要旨集  2014-  140  2014/09/01  [Not refereed][Not invited]
  
• インド洋における海洋大気エアロゾル中微量金属の化学的特徴と分布

  森本大介, 成田祥, 古谷浩志, 大木淳之, 植松光夫  日本海洋学会大会講演要旨集  2013-  135  2013/03/11  [Not refereed][Not invited]
  
• 2C1116 Measurements of non-methane hydrocarbons at Fukue-Island and analyses of photochemical impacts on hydrocarbon ratios(1 Space-5 East Asia,General Presentations)

  YOKOUCHI Yoko, TAKAMI Akinori, OOKI Atsushi, NOZOE Susumu, SADANAGA Yasuhiro, BANDOW Hiroshi, OHARA Toshimasa  大気環境学会年会講演要旨集  0-  (50)  424  -424  2009/08/20  [Not refereed][Not invited]
  
• 西部北太平洋春季ブルームにおける海水中の微量ガスの分布特性

  木村匡恵, 栗原路子, 岩本洋子, 成田祥, 大木淳之, ウン ヨンジュン, 津田敦, 鈴木光次, 谷幸則, 横内陽子, 植松光夫, 橋本伸哉  日本海洋学会大会講演要旨集  2008-  2008
• Temporal variation of atmospheric trace components over the northwestern North Pacific during a Kosa event

  M Sasakawa, A Ooki, T Ui, M Uematsu  GEOCHIMICA ET COSMOCHIMICA ACTA  67-  (18)  A412  -A412  2003/09  [Not refereed][Not invited]
  
• 海洋生物生産によるエアロソルの生成と雲核形成への影響 (総特集 海洋生物生産の加速と海洋大気)

  大木 淳之, 三浦 和彦, 植松 光夫  海洋  34-  (3)  227  -231  2002/03
• 海塩粒子の変質の地理的分布

  早野 輝朗, 宇井 剛史, 原 壮史, 三浦 和彦, 中江 茂, 児島 紘, 植松 光夫, 大木 淳之, 和田 誠, 猪原 哲, 横内 陽子  大気電気研究  58-  85  -86  2001/03/15
• Physical Properties of Marine Aerosols Measured on the R/V Mirai During ACE-Asia

  Kazuhiko Miura, Ryo Ashikawa, Takahito Inaba, Hiroshi Kojima, Mitsuo Uematsu, Atsushi Ooki, Itsushi Uno, Nobuo Sugimoto  AGU 2001 Fall Meeting, EOS, Transactions  82-  (47)  59  2001  [Not refereed][Not invited]
  
• 北太平洋・ベーリング海上で捕集したエアロゾル

  三浦 和彦, 近藤 辰也, 原 壮史, 大木 淳之, 小野 卓男, 中江 茂, 児島 紘  大気電気研究  (55)  47  -48  1999/09/15
• 都市大気エアロゾルの粒径別化学組成成分

  隠岐 嘉重, 大木 淳之, 山崎 泰典, 中江 茂, 三浦 和彦  大気電気研究  (54)  54  -54  1999/03/15
• 東京都心における大気安定度と汚染物質濃度との関係

  西村 俊次, 松田 和秀, 秋生 淳一, 大木 淳之, 中江 茂, 三浦 和彦  大気電気研究  (52)  116  -116  1998/04/10
• 船観測によるエアロゾル化学組成分析と特徴

  大木 淳之, 松田 和秀, 中江 茂, 三浦 和彦, 児島 紘, 秋生 淳一  大気電気研究  (52)  117  -118  1998/04/10
• 2A1130 Concentrations of Sox and Noy in the marine atmosphere

  Ooki A., Matsuda K., Nakae S., Miura K.  大気環境学会年会講演要旨集  (39)  325  -325  1998
• Study on Aerosol Particles over the Subarctic North Pacific Ocean and the Bering Sea

  K. Miura, A. Ohki, T. Ono, S. Nakae, H. Kojima  Prel. Rep. of the Hakuho Maru Cruise KH-97-2  88  -91  1998  [Not refereed][Not invited]
  
• 西部北太平洋における大気中酸性物質濃度について白鳳丸KH95-2, KH96-3研究航海の結果

  松田 和秀, 秋生 淳一, 大木 淳之, 中江 茂, 三浦 和彦  大会講演予講集  71-  279  -279  1997/05
• 東京湾岸から沿岸における大気エアロゾル成分の特徴

  大木 淳之, 松田 和秀, 秋生 淳一, 小田切 さやか, 市川 正明, 安 賢一, 山田 哲也, 中江 茂, 三浦 和彦  大気電気研究  (50)  51  -51  1997/04/10

Presentations

• 南極海の海氷上部における高濃度ブロモホルムと大気への放出  [Not invited]

  野村大樹, 大木淳之, DIECKMANN G. S, DAMM E, MEINERS K, 田村岳史

  日本海洋学会大会講演要旨集  2013/08
• 噴火湾の底層貧酸素状態緩和に寄与する中層湾外水の流入  [Not invited]

  大西広二, 田中聖二, 大木淳之, 久万健志

  日本海洋学会大会講演要旨集  2013/08
• 冷却トラップを用いた大気及び海水中の有機ガス測定法の開発と応用  [Not invited]

  大木淳之, 川崎修歩, 久万建志

  分析化学討論会講演要旨集  2013/05
• インド洋における海洋大気エアロゾル中微量金属の化学的特徴と分布  [Not invited]

  森本大介, 成田祥, 古谷浩志, 大木淳之, 植松光夫

  日本海洋学会大会講演要旨集  2013/03
• 遠投式採水器を用いた噴火湾における揮発性溶存有機臭素の観測  [Not invited]

  三輪一爾, 大木淳之, 久万健志, 川崎修歩, 大西広二

  日本海洋学会大会講演要旨集  2013/03
• 噴火湾海盆域底層における栄養塩と鉄の挙動とその起源  [Not invited]

  日置菜々子, 久万健志, 大木淳之, 大西広二

  日本海洋学会大会講演要旨集  2013/03
• 南大洋から北極海における揮発性有機ヨウ素化合物の分布と生成過程  [Not invited]

  大木淳之, 川崎修歩, 久万健志, 横内陽子

  日本地球化学会年会講演要旨集  2013
• 南大洋とインド洋における海水中ブロモホルムの測定―新たな化学トレーサーとしての有用性について―  [Not invited]

  大木淳之, 野村大樹, 飯田高大, 横内陽子

  日本海洋学会大会講演要旨集  2012/03
• 北西太平洋と南北インド洋における表面海水中イソプレン濃度の測定  [Not invited]

  大木淳之, 横内陽子, 児玉武稔, 古谷研, 武田重信, 津田敦

  日本海洋学会大会講演要旨集  2011/03
• Bromoform concentration in slush layer in Antarctic fast ice  [Not invited]

  NOMURA DAIKI, OOKI ATSUSHI, FUKUCHI MITSUO

  極域科学・宙空圏・気水圏・生物・地学シンポジウム講演予稿集(CD-ROM)  2010

Association Memberships

• THE JAPAN SOCIETY FOR ANALYTICAL CHEMISTRY   GEOCHEMICAL SOCIETY OF JAPAN   THE OCEANOGRAPHIC SOCIETY OF JAPAN   

Works

• 北極の海 the Arctic Ocean

  上野洋路, 大木淳之 LASBOS Moodle 2021/04 - Today 

  LASBOS Moodleにて北極関係のコースを集約、説明を加えて発信する内容
• LASBOS SDGs top

  大木淳之, バランスドオーシャンスタッフ LASBOS Moodle 2021/04 - Today 

  LASBOS Moodleのコース群からSDGsに関連する情報を集約、発信する内容
• General Mapping Tools (GMT)- Forum and Index

  大木淳之 LASBOS Moodle 2021/04 - Today 

  GMT演習コース
• 植物プランクトンによるイソプレン生成に関する研究

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋化学研究紹介コース
• 海洋のヨウ素循環の概要

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋化学研究紹介コース
• 噴火湾における物質循環研究

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋化学研究紹介コース
• 気液平衡器による海水中の有機ガスモニタリング手法

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋化学研究紹介コース
• 海岸の水を釣り竿で採取（MIWAサンプラー）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋化学の研究紹介コース
• 電気化学（ダニエル電池）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－酸化還元コース
• 酸化還元反応（呼吸形式の順番）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－酸化還元コース
• 酸化還元反応（標準電極電位）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－酸化還元コース
• 呼吸反応（酸化還元反応）の前後におけるエネルギー差

  大木淳之 LASBOS Moodle 2021/04 - Today
• 化学平衡から反応が進むとき（水酸化マンガンが溶解する条件）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－化学平衡コース
• 化学平衡から反応が進むとき

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－化学平衡コース
• 化学平衡の基本式（水酸化マンガンの沈殿条件）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－化学平衡コース
• 化学平衡の基本式（水の解離平衡）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－化学平衡コース
• 化学平衡の基本式（塩化ナトリウムの溶解平衡濃度）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－化学平衡コース
• 化学平衡の条件式を導く

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－化学平衡コース
• 物質が持つエネルギーの内訳（化学反応前後の変化）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学ー物理化学コース
• 物質が持つエネルギーの内訳（エントロピーと内部エネルギー）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－物理化学コース
• 物質が持つエネルギーの内訳（エントロピーと熱力学関数）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－物理化学コース
• 物質が持つエネルギーの内訳（エントロピー増大の法則）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－物理化学コース
• 物質が持つエネルギーの内訳（エントロピー）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－物理化学コース
• 物質が持つエネルギー（エンタルピー）の内訳（概要）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－物理化学コース
• 物質が持つエネルギーの内訳（はじめに）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－物理化学コース
• 自分スケールで計測の定量評価

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－濃度定量コース
• ブランク（空試料）測定

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－濃度定量コース
• 検出下限（限界）と定量下限（概要）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－濃度定量コース
• 検量線の例題（１－３）低濃度の扱い

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－濃度定量コース
• 検量線の例題（１－２）高濃度の扱い

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－濃度定量コース
• 検量線の例題（１－１）基本問題

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－濃度定量コース
• 標準試料の濃度計算（検量線法）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－濃度定量コース
• 有効数字を含む加減・乗除の計算（簡易ルール）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－精度管理コース
• 有効数字（はじめに）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学ー精度管理コース
• 感度アップの方法（ガス成分の濃縮）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－手法コース
• ガスクロマトグラフィー

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－手法コース
• イオンクロマトグラフィー

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－手法コース
• クロマトグラフィー（イオン交換樹脂）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－手法コース
• 溶存酸素の測定法（ウインクラー法）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－手法コース
• ピペットの使い方（正しく使うコツ）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学－手法コース
• 精密電子天秤を使って標準試料を調整

  大木淳之 LASBOS Moodle 2021/04 - Today 

  分析化学ー手法コース
• 海洋堆積物観測の紹介

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋堆積物での硫酸呼吸による硫化水素発生

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 呼吸反応で得られるエネルギー

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 化学反応で得られるエネルギー

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 堆積物中の化学反応（概要）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海底堆積物と生物かく乱

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋の堆積物の化学（はじめに）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• リン酸（P)と酸素消費量（AOU）のXYプロット

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 全海洋のNとPのXYプロット

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋の窒素とリン比率（N/P =16）の不思議

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋基礎生産のモデル計算（解析課題）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 基礎生産と有機物分解による、C、N、P、Oの移動

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 鉄制限－鉄未制限時のSi取り込み比率（研究紹介）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 太平洋側北極海（チャクチ海）での硝酸不足

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 基礎生産を制限する栄養塩成分（海域による特徴）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 栄養塩の全球分布（ケイ酸の相違）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 栄養塩の全球分布

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 珪藻による珪酸塩の消費と生物生産

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海の基礎生産を制限する要因（表層への栄養塩供給）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海の栄養成分とは何か

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 溶存酸素の全球分布

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• みかけの酸素消費量（AOU）の鉛直分布

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• みかけの酸素消費量（AOU）の概要

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 正味の酸素消費量

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋の酸素（概要）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 地球の酸素

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 全炭酸とアルカリ度のXYプロット

  大木淳之 LASBOS Moodle 2021/04 - Today
• 太平洋におけるアルカリ度と全炭酸の鉛直断面図

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋の炭酸カルシウム粒子の飽和深度

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋のアルカリ度と炭酸カルシウム粒子の溶解

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 炭酸カルシウム粒子の形成と二酸化炭素の飽和濃度

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海水のpHを計算

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 雨水のpHを計算

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 水に溶ける炭酸系成分の濃度や成分比を計算

  大木淳之 LASBOS Moode 2021/04 - Today 

  海洋学－海洋化学コース
• 海水中の炭酸系成分と水の平衡状態の反応式

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋の二酸化炭素の鉛直分布

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 地球の気候変化と炭素収支の歴史

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋のハロカーボン

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学ー海洋化学コース
• エアロゾル形成と成長、雲凝結核

  大木淳之 LASBOS Moodle 2021/04 - Today
• CLAW仮説の終焉とSOLAS研究へ

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 有機硫黄ガスとCLAW仮説

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋の有機ガス（概要と補足）

  大木淳之 2021/04 - Today
• 有機物の組成

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 溶存有機炭素の14C年代推定

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 放射性炭素同位体による年代推定法

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学ー海洋化学コース
• 難分解性の有機物

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋の溶存有機炭素の全球分布

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 有機炭素の測定

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 課題：海洋の粒子沈降を計算

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• セジメントトラップ観測

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• マリンスノー（TEPが正体？）とウナギ仔魚の摂餌

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋での有機物粒子の沈降（説）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 粒子の沈降速度

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋の有機物のサイズ分類

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋の有機物（はじめに）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学ー海洋化学コース
• 課題（深層循環は永遠なのか？）

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 水塊区分

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 表層混合層

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 北太平洋の中層水

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学ー海洋化学コース
• 深層循環の駆動とベルトコンベヤーモデル

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コース
• 海洋の塩分

  大木淳之 LASBOS Moodle 2021/04 - Today 

  海洋学－海洋化学コースの教材
• 酸化還元反応（半反応式の作り方―呼吸反応）

  大木淳之 LASBOS Moodle 2021/04 

  分析化学－化学平衡コース
• 粒子状と溶存態の有機物

  大木淳之 LASBOS Moodle 2021/04 

  海洋学ー海洋化学コース
• 春季ブルームと表層混合層

  大木淳之 2021/04 

  海洋学－海洋化学コース

Research Projects

• 海の暗い所で珪藻が栄養塩を消費する事実－生存戦略の仮説を提唱－

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2022/06 -2025/03 

  Author : 大木 淳之, 野坂 裕一, 亀山 宗彦, 野村 大樹

   

  北海道噴火湾で珪藻が大増殖する春先に、有光層の直下（無光層）にて、海水中の栄養塩が減る現象が捉えられた。北海道噴火湾の珪藻ブルーム時に採取した海水に栄養塩を添加したところ、暗所でも栄養塩が急速に消費されることがわかった。有光層で栄養不足に陥った珪藻が無光層に沈降して、無光層に豊富にある栄養塩を吸収することが考えられた。珪藻ブルームで見られるタラシオシラ・ノルデンスキオルディの無菌培養株を培地で増殖させ、培地中の栄養塩が枯渇したのを確認してから、栄養塩（硝酸イオン、リン酸イオン、ケイ酸）を添加、暗所に移す暗所培養実験を行った。すると、暗所に置いてから３日ほどで、硝酸イオン、リン酸イオン、ケイ酸が枯渇した。暗所にて、珪藻が栄養塩を吸収することが確認された。同様の実験にて、過剰量の栄養塩を添加したところ、硝酸イオンとリン酸イオンの暗所での取り込みは数日で終わった。しかし、ケイ酸については暗所での培養期間中（１１日間）、取り込みが続いた。暗所で栄養塩を吸収させた後、再び明所に置いて増殖する能力があるかを確かめた。１１日間暗所に置いた後では、増殖を確認することができなかった。暗所に置いた時点で、栄養塩枯渇のため死滅しつつあった可能性、暗所で吸収した栄養塩では再増殖に使えない可能性が考えられた。珪藻が浮力を保つ方法として、透明細胞外重合粒子（TEP）を放出することを想定している。自然海水中および培養海水中のTEP濃度を測定する手法を確立した。
• 海氷表面に見られる有機臭素ガスの高濃度現象―低温化学反応チャンバー実験による検証

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2020/04 -2023/03 

  Author : 野村 大樹, 薮下 彰啓, 山下 洋平, 大木 淳之

   

  高緯度海域に分布する海氷は、地球規模の気候変動を制御する要因として大きな役割を担っている。従来、海氷は、物質循環の観点において大気と海洋間の「障壁」として認識されてきた。しかし、実際、海氷表面では、結氷による濃縮効果によって溶存物質が高濃度化し、大気に対して放出源になることが予想される。ただ、極域の厳しい環境での観測の難しさにより、海氷表面での「低温化学」に関する反応機構の解明に至っていない。本研究では、自然界で起こる結氷現象を室内でのチャンバー実験で再現し、有機臭素ガス、特にブロモホルムに関して、海氷表面での化学反応機構・大気への放出過程を明らかにすることが目的である。本課題は、極域大気中オゾン濃度の急激な減少を招く有機臭素ガスの発生源が特定されていないことから設定した。本研究で提唱する海氷表面でのブロモホルム生成は、有機臭素ガスの大気への新たな発生源の提案となり、長年謎とされてきた大気中オゾン消失現象の原因解明に一石を投じることとなる。しかし、これまでの応募者らによる観測事実と低温環境での化学反応の新たな知見により、反応仮説を提唱するに至ったが、反応機構は検証されていない。そこで本年度は、チャンバー実験を実施し、本研究の解明に向けてのデータの採取を行った。具体的には、購入したチャンバーを利用した化学反応実験、また、室内での結氷および積雪を再現し、ブロモホルム生成に関する室内実験を実施した。また、これまでの観測データの解析を実施した。これらの解析を実施することにより、当初の目的に向けて順調に研究が進んでいる状況にある。
• Iodine cycle in coastal environment- chemical speciation affected by decomposition of organic matter decomposition-

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

  Date (from‐to) : 2016/04 -2021/03 

  Author : Ooki Atsushi

   

  We have found the increase of iodoethane concentrations in the bottom water of the Funka Bay, Hokkaido, Japan, 1 month after the spring diatom bloom. We made a hypothesis that volatile organic compounds are produced from ocean sediment, and carried out ocean sediment observation in the Funka Bay and Bering and Chukchi Seas. From the repetitive observation in the Funka Bay, we found drastic increase of iodoethane in the surface of the sediment on sea floor during the spring diatom bloom. And we carried out dark incubation using diatom aggregate collected by plankton net during the bloom. The incubation experiment results showed that the diatom aggregate produced iodoethane 3 days after the start of the experiment. Another incubation using sterile diatom culture also showed the same results.
• Structure of surface mixed layer analyzed by temporal change of vertical distribution of photodegradable organic iodine gases

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

  Date (from‐to) : 2016/04 -2018/03 

  Author : 大木 淳之

   

  H28年度に実施した海洋観測にて、北太平洋亜寒帯循環域で海洋表面から水深300mの海水を鉛直的に採取し光分解性を有する有機ガス濃度を測定した。さらに、分光放射照度と鉛直拡散係数の測定を行った。H29年度には、光分解性を有する有機ヨウ素ガス種（ジヨードメタンとクロロヨードメタン）の鉛直プロファイルを再現するモデル（光分解と光生成、鉛直輸送、微生物による正味の生成を考慮）を構築した。ジヨードメタンのモデル結果では、微生物による生成に対して、表層混合層内での光分解が卓越するため、混合層内の濃度がモデル開始から数時間内にゼロに収束してしまった。混合層内でのジヨードメタンの濃度を実測値に保つには、日中のみ、ジヨードメタンの光分解を補償するだけの未知の生成過程が存在しなくてはならない。つまり、ジヨードメタンが光分解すると同時に、その減少分を補うだけ光生成していることが示唆された。H29年度の研究では、ジヨードメタンの光生成過程を調べる実験も行ったが、その実験的証拠を得るには至らなかった。そこで、ジヨードメタンの濃度を保つメカニズムは不明のままとして、その濃度が定常状態に保たれていることを仮定し、クロロヨードメタンの鉛直分布モデルを構築した。クロロヨードメタンモデルにおいては、ジヨードメタンの光分解に起因するクロロヨードメタンの光生成の項を加えた（過去の知見を引用）。クロロヨードメタンの光生成項を加えないと、ジヨードメタンと同様に表層での光分解が卓越して表層水中の濃度が速やかにゼロに収束してしまったが、光生成項を加えると実際の濃度をよく再現するモデル結果が得られた。クロロヨードメタンの鉛直プロファイルは、光生成と光分解、鉛直混合により決まることが明らかとなった。これにより、クロロヨードメタンの濃度、光生成と光分解を得れば、鉛直混合を読み解く道筋をつけることができた。
• 海氷融解による生態系の変化が物質循環に与える影響ー豪州砕氷船による国際南極観測ー

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2015/04 -2018/03 

  Author : 飯田 高大, 田村 岳史, 茂木 正人, 大木 淳之, 野村 大樹

   

  本研究では、南極海の氷縁域において、海洋生態系と化学物質循環を総合的に観測するプロジェクトを立ち上げ、豪州が代表の砕氷船を用いた国際共同観測に参画する。近年、南極の季節海氷域における生態系変動が化学物質循環のパターンを変え、地球環境変化に大きな影響を及ぼす可能性が指摘されている。しかし、南極域へのアクセスは気象・海況条件が厳しいため現地観測データは乏しく、その影響を評価するにはほど遠い。そこで、地球温暖化の影響が顕著に表れつつある季節海氷域に特化して、海氷融解の物理環境変化がもたらす植物・動物プランクトン群集の変動を解析し、生態系変動により引き起こされる化学物質循環の変化を明らかにし、全球規模での環境応答を予測する。本年度（平成27年度）は、これまで我々が海氷観測のプラットフォーム及び観測サイトとして利用してきた巡視船そうやとサロマ湖において、以下の予備的調査観測を実施した。また、海洋生態系における海氷の役割を解明する目的で、東京海洋大学海鷹丸を用いて南極海季節海氷域において海洋観測を実施した。 1. 巡視船そうや航海観測: オホーツク海の海氷監視にあたる巡視船そうやに乗船し、外洋域の海氷を採取した。海氷中の化学成分、植物及び動物プランクトンの種類同定用サンプルを採取した。現在、分析・解析を実施している。 2. サロマ湖現地観測: 南極海の海氷上での海氷採取作業等を想定し、掘削機器の動作試験と取扱法の習熟、海氷サンプルの採取を行った。オーストリアから訪問した共同研究者とともに本観測を実施した。 3. 南極海での海洋観測：東京海洋大学海鷹丸で、平成28年1月に南極海の南緯60度から65度、東経110度付近において海洋観測を実施した。観測項目は各種ネットによるプランクトン・魚類の採集、海氷の採取、水温・塩分である。現在、分析・解析を実施している。
• Spatila-temporal distribution of monohalomethane in the N Pacific

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

  Date (from‐to) : 2012/04 -2016/03 

  Author : Ooki Atsushi

   

  Monohalomethanes (chloromethane, bromomethane, and iodomethane) are the dominant organic halogen compounds in the atmosphere. Ocean is an important source of monohalomethane. Spatial-temporal distributions of monohalomethane were measured in the NW Pacific and estern Arctic Ocean. Over the continental shelf of the Chukchi Sea in the Arctic Ocean, the concentration maxima of 3 monohalomethanes were found in the bottom layer water, in which bottom sediment, denitrification would occur owing to a large amount of settling organic particle. In the Funka-Bay, Hokkaido, Japan, concentration maxima of bromomethane and chloromethane were found in the subsurface layer in June when decompositions of organic material proceed. Phytoplankton culture experiment showed that productions of monohalomethane were found in the senescence stage after the exponential growth. It is considered that monohalomethane production in seawater is associated with cell senescence and degradation of organic matter.
• High concentration of brominated halocarbons in the mixed water region of the northwest Pacific

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

  Date (from‐to) : 2010 -2011 

  Author : OOKI Atsushi, YOKOUCHI Yoko

   

  High concentrations of brominated halocarbons(CH_3Br, CH_2Br_2, CHBr_3) were found in the mixed water region of the northwest Pacific(42-44°N, 145-160°E). Obvious concentration maximum of the halocarbons were found in the subsurface layer of the southern mixed water(30°N), while the uniform vertical distributions were found in the subarctic water(45°N) from surface to subsurface layer. The horizontal-vertical distribution of brominated halocarbons would be determined from mixed layer formation process, air-sea gas exchange, and phytoplankton production of halocarbons.
• A study on the production and emission of marine-derived volatile halocarbons

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

  Date (from‐to) : 2006 -2010 

  Author : YOKOUCHI Yoko, HASHIMOTO Shinya, ITOH Nobuya, OOKI Atsushi

   

  We conducted systematic measurements of marine-derived halocarbons in the air and in the ocean. Full picture of methyl halides distribution in north-west Pacific and Indian Ocean was obtained from the shipboard measurements. We also found that the strains of cryptophytes and cyanobacteria produced halocarobons during decline phase, and that the in vivo biogenic emission of methyl iodide from marine microalgae was dependent on S-adenosyl-L-methionine (SAM) halide ion/thiol methyl transferase (HTMT) reaction.
• 大気中人為起源物質による鉱物粒子の変質過程と海洋環境へ与える影響に関する研究

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2003 -2005 

  Author : 大木 淳之

   

  大気から地表面へ沈着する鉱物粒子の粒径分布と粒径別鉱物粒子の鉄溶出率を測定した。大気エアロゾルを海水に抽出して鉄溶出率を測定する手法を確立し、人為起源エアロゾルの鉄溶出率を測定した。 1.粒径別鉱物粒子の鉄溶出率 2001年3月11日に大規模な黄砂現象を北海道札幌市で観測した。大気境界層上部に位置する手稲山頂で積雪中の黄砂粒子を集めた。黄砂粒子を沈降法で1