研究者データベース

大木 淳之(オオキ アツシ)
水産科学研究院 海洋生物資源科学部門 海洋環境科学分野
准教授

基本情報

所属

  • 水産科学研究院 海洋生物資源科学部門 海洋環境科学分野

職名

  • 准教授

学位

  • 博士(理学)(東京大学)

ホームページURL

J-Global ID

プロフィール

  • 1973年埼玉県出身。
    海洋環境を調べる研究をしている。実習船や研究船で野外観測し、実験室にて分析する仕事である。北海道大学水産学部では、海洋生物科学科の教員として主に化学系の授業を受け持っている。
    現在の主な研究テーマは、海洋植物が放出する有機ハロゲンガスの分布に関する研究である。とくに最近は、有機ヨウ素ガスの動態に着目している。地球表層で動的なヨウ素の大部分は海水中に無機ヨウ素として存在していて、それを海洋植物が取り込み有機化している。その有機ヨウ素の一部は揮発性を有していて、大気中に揮散する。大気中の有機ヨウ素は光分解して無機化し、いずれは雨となり川に流れて海に戻る。地球表層のヨウ素循環を駆動しているのが海洋植物なのである(と推測される)。私(と共同研究者たち)は北海道周辺を中心に、北極海~赤道域~南極海まで観測を行ってきた。海洋植物や有機物に関連するので、それらと共に動く栄養塩の動態も同時に調べている。
    2006年頃までは、大気中の黄砂粒子の動態や海水への溶け具合、大気中粒子の水溶性イオン成分に挙動に関する研究を行っていた。とくに、粒子の粒径分布の特徴を解析するのが好きである。最近は、大気中粒子の仕事はしていないが、海水の仕事がもう少し落ち着いたら、水産学部の実習船を使って、大気観測も継続的に行いたい。


    2019年度より、北海道大学の「バランスドオーシャン事業」(https://repun-app.fish.hokudai.ac.jp/)に携わっている。海の分野のオンライン教材を集積して、北大の学生や一般に提供するものである。その提案書を書いたり、アイデアを出したり、自らオンライン教材を作ったり、他の教員に教材つくりをお願いしたりしている。これまでは、ウエブとか、オンラインとか、苦手意識(面倒くさい?)があったが、否応なく、そういう世界に入ってしまった。最近は、ビデオ撮影、動画教材化、などに使う小道具を集めて、スタッフと一緒に制作に頭悩ます日々を送っている。

    趣味は、「山登り」と言いたいところだが、最近はほとんど山に行っていない。去年、海での仕事の合間をみて、海釣りをはじめた。何時間も釣り糸を垂らしても、まだ一匹も釣れていない。魚釣れない記録がどれだけ続くやら。
    最近は、函館にてゴーヤ栽培と椎茸栽培を趣味にしている。初夏(7月)の函館は涼しく、北海道の中でもゴーヤ栽培に不向きである。ポットで発芽させ、6月中は毎晩家の中に入れ、7月はビニールハウスで育て、8月にようやく収穫できる。2016年は毎日2本収穫するのを楽しみにしている。2020年には、毎日6本、3か月間、ゴーヤを収穫した。大学内で、同僚教員にゴーヤを配るのに忙しい。(一度でも、「ゴーヤ美味しい」と口を滑らせると、毎週のようにゴーヤが届けられるようになるので要注意)

    当研究室では、海の研究をしたい学生を募集しています。研究室HPを見てください。
    北大水産学部HPからリンクしています。

研究キーワード

  • 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   

研究分野

  • 環境・農学 / 環境動態解析

職歴

  • 2011年04月 - 現在 北海道大学 水産科学研究科(研究院) 准教授
  • 2006年09月 - 2011年03月 国立環境研究所 NIESポスドクフェロー
  • 2006年04月 - 2006年09月 北海道区水産研究所 支援研究員
  • 2003年04月 - 2006年03月 北海道大学地球環境科学研究科 学振PD

学歴

  • 2000年04月 - 2003年03月   東京大学   理学系研究科   地球惑星科学専攻博士課程
  • 1997年04月 - 1999年03月   東京理科大学   理学研究科   物理学専攻修士課程
  • 1993年04月 - 1997年03月   東京理科大学   理学部   物理学科

所属学協会

  • 日本分析化学会   日本地球化学会   日本海洋学会   

研究活動情報

論文

  • Daiki NOMURA, Pat WONGPAN, Takenobu TOYOTA, Tomonori TANIKAWA, Yusuke KAWAGUCHI, Takashi ONO, Tomomi ISHINO, Manami TOZAWA, Tetsuya P. TAMURA, Itsuka S. YABE, Eun Yae SON, Frederic VIVIER, Antonio LOURENCO, Marion LEBRUN, Yuichi NOSAKA, Toru HIRAWAKE, Atsushi OOKI, Shigeru AOKI, Brent ELSE, Francois FRIPIAT, Jun INOUE, Martin VANCOPPENOLLE
    Bulletin of Glaciological Research 38 0 1 - 12 2020年 [査読有り][通常論文]
  • Response of Arctic biodiversity and ecosystem to environmental change: Findings from the ArCS project
    Hirawake T., Uchida M., Abe H., Alabia I.D., Hoshino T., Masumoto S., Mori A., Nishioka J., Nishizawa B, Ooki A., Takahashi A., Tanabe Y., Tojo M., Tsuji M., Ueno T., Waga H., Watanabe Y., Yamaguchi A., Yamashita Y.
    Polar Science in press 2020年 [査読有り][通常論文]
  • 氷河と海氷の融解減少が北極海表層の物質循環過程に与える影響
    野村大樹, 漢那直也, 大木淳之
    地球化学 2020年01月 [査読有り][通常論文]
  • 北極域における臭素および有機硫黄化合物の生物地球化学
    亀山宗彦, 大木淳之, 野村大樹
    地球化学 2020年01月 [査読有り][通常論文]
  • 「北極域の地球化学」特集序文
    大木淳之, 亀山宗彦
    地球化学 53 2020年01月 [査読有り][通常論文]
  • 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 2019年12月 [査読有り][通常論文]
  • Youhei Yamashita, Yuki Yagi, Hiromichi Ueno, Atsushi Ooki, Toru Hirawake
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 124 11 7545 - 7556 2019年11月 [査読有り][通常論文]
     
    Pacific water is an important nutrient source for sustaining biological production in the Chukchi Sea, western Arctic Ocean, which is one of the productive regions in the world. Therefore, to understand the impacts of future environmental changes on biological production in the sea, it is crucial to understand the origins, modification processes, and spatiotemporal variations of the water masses from the Bering Sea with changes in nutrient concentrations. To improve water mass analysis in the shelf regions of the Bering and Chukchi Seas, we observed levels of humic-like fluorescent organic matter (FOMH) by using an in situ fluorometer directly connected to a temperature-salinity sensor during a cruise in the early summer of 2013 and evaluated the potential of FOMH as a third parameter of water mass analysis. The levels of FOMH were different among specific water masses in the region, and FOMH seemed to behave semiconservatively in the shelf regions of the Bering and Chukchi Seas during the early summer of 2013. The distributional pattern of FOMH implies that FOMH estimated by the in situ fluorometer has the potential to (1) separate warm water into riverine-affected Alaskan Coastal Water and historically photobleached summer Bering Basin Water; (2) distinguish the Anadyr Water, which has low FOMH levels and high nutrient concentrations, from the Bering Shelf Water; and (3) determine different formation/modification processes of dense shelf water that contains high nutrient concentrations.
  • Hideyoshi Yamaoka, Tetsuya Takatsu, Kota Suzuki, Naoto Kobayashi, Atsushi Ooki, Mitsuhiro Nakaya
    Fisheries Science 2019年09月 [査読有り][通常論文]
  • Abe, Hiroto, Sampei, Makoto, Hirawake, Toru, Waga, Hisatomo, Nishino, Shigeto, Ooki, Atsushi
    FRONTIERS IN MARINE SCIENCE 6 2019年03月 [査読有り][通常論文]
     
    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.
  • Takafumi Kataoka, Atsushi Ooki, Daiki Nomura
    Microbes and Environments 34 2 215 - 218 2019年 [査読有り][通常論文]
  • Ryohei Sasayama, Nanako Hioki, Yuichiroh Morita, Yutaka Isoda, Keiri Imai, Atsushi Ooki, Kenshi Kuma
    Journal of Oceanography 74 4 1 - 13 2018年02月16日 [査読有り][通常論文]
     
    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.
  • Yuichiroh Morita, Kei Yamagata, Atsuki Oota, Atsushi Ooki, Yutaka Isoda, Kenshi Kuma
    GEOCHIMICA ET COSMOCHIMICA ACTA 215 33 - 50 2017年10月 [査読有り][通常論文]
     
    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.
  • 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 2017年06月 [査読有り][通常論文]
     
    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).
  • 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 2016年10月 [査読有り][通常論文]
     
    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.
  • Kazuki Tanaka, Nobuyuki Takesue, Jun Nishioka, Yoshiko Kondo, Atsushi Ooki, Kenshi Kuma, Toru Hirawake, Youhei Yamashita
    SCIENTIFIC REPORTS 6 2016年09月 [査読有り][通常論文]
     
    The spatial distribution of dissolved organic carbon (DOC) concentrations and the optical properties of dissolved organic matter (DOM) determined by ultraviolet-visible absorbance and fluorescence spectroscopy were measured in surface waters of the southern Chukchi Sea, western Arctic Ocean, during the early summer of 2013. Neither the DOC concentration nor the optical parameters of the DOM correlated with salinity. Principal component analysis using the DOM optical parameters clearly separated the DOM sources. A significant linear relationship was evident between the DOC and the principal component score for specific water masses, indicating that a high DOC level was related to a terrigenous source, whereas a low DOC level was related to a marine source. Relationships between the DOC and the principal component scores of the surface waters of the southern Chukchi Sea implied that the major factor controlling the distribution of DOC concentrations was the mixing of plural water masses rather than local production and degradation.
  • A. Ooki, S. Kawasaki, K. Kuma, S. Nishino, T. Kikuchi
    BIOGEOSCIENCES 13 1 133 - 145 2016年 [査読有り][通常論文]
     
    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.
  • 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 2015年12月 [査読有り][通常論文]
     
    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. Ooki, S. Kawasaki, K. Kuma, S. Nishino, T. Kikuchi
    Biogeosciences Discussions 12 14 11245 - 11278 2015年07月17日 [査読有り][通常論文]
     
    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. VOIs are believed to play a role in ozone destruction in the troposphere and lower stratosphere. 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+ (correlate coefficient R = 0.93) and between CH3I and NH4+ (R = 0.77), suggesting production of these VOIs increased with 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- - 16PO43-) simultaneously occurred in this water, suggesting production of the three VOIs in the sediment or the bottom layer water over the shelf, probably in association with 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 though the subsurface CDW and the surface ACW.
  • Atsushi Ooki, Daiki Nomura, Shigeto Nishino, Takashi Kikuchi, Yoko Yokouchi
    JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 120 6 4108 - 4128 2015年06月 [査読有り][通常論文]
     
    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.
  • 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 2014年10月 [査読有り][通常論文]
     
    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.
  • 大木淳之
    分析化学 62 12 1071 - 1078 2013年 [査読有り][通常論文]
     
    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.
  • Daiki Nomura, Atsushi Ooki, Daisuke Simizu, Mitsuo Fukuchi
    ANTARCTIC SCIENCE 23 6 623 - 628 2011年12月 [査読有り][通常論文]
     
    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.
  • Atsushi Ooki, Yoko Yokouchi
    MARINE CHEMISTRY 124 1-4 119 - 124 2011年03月 [査読有り][通常論文]
     
    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.
  • Yoko Yokouchi, Takuya Saito, Atsushi Ooki, Hitoshi Mukai
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 116 2011年03月 [査読有り][通常論文]
     
    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.
  • Y. Morino, T. Ohara, Y. Yokouchi, A. Ooki
    Journal of Geophysical Research Atmospheres 116 2 2010JD014762  2011年 [査読有り][通常論文]
     
    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.
  • Atsushi Ooki, Yoko Yokouchi
    GEOCHEMICAL JOURNAL 45 6 E1 - E7 2011年 [査読有り][通常論文]
     
    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.
  • 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 2010年10月 [査読有り][通常論文]
     
    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.
  • 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 118 156 - 170 2010年02月28日 [査読無し][通常論文]
     
    Biogenic trace gases, especially halomethanes, which are important with respect to atmospheric chemistry, are released from the ocean and carry halogens to the troposphere and stratosphere. The concentrations of 10 halocarbons and isoprene in seawater were measured during the spring of 2007 in the western North Pacific Ocean (37-43° 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.
  • 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 2010年 [査読有り][通常論文]
     
    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.
  • Sohiko Kameyama, Hiroshi Tanimoto, Satoshi Inomata, Urumu Tsunogai, Atsushi Ooki, Yoko Yokouchi, Shigenobu Takeda, Hajime Obata, Mitsuo Uematsu
    ANALYTICAL CHEMISTRY 81 21 9021 - 9026 2009年11月 [査読有り][通常論文]
     
    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.
  • Atsushi Ooki, Jun Nishioka, Tsuneo Ono, Shinichiro Noriki
    JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 114 2009年02月 [査読有り][通常論文]
     
    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%.
  • Atsushi Ooki, Yoko Yokouchi
    ENVIRONMENTAL SCIENCE & TECHNOLOGY 42 15 5706 - 5711 2008年08月 [査読有り][通常論文]
     
    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.
  • Atsushi Ooki, Mitsuo Uematsu, Shinichiro Noriki
    ATMOSPHERIC ENVIRONMENT 41 1 81 - 91 2007年01月 [査読有り][通常論文]
     
    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.
  • Atsushi Ooki, Mitsuo Uematsu
    Journal of Geophysical Research D: Atmospheres 110 3 1 - 13 2005年02月16日 [査読有り][通常論文]
     
    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.
  • 永尾一平, 宇山悠紀子, 大木淳之, 植松光夫
    Journal of Aerosol Research 19 2 122 - 127 2004年 [査読有り][通常論文]
  • A Ooki, K Miura, M Uematsu
    JOURNAL OF OCEANOGRAPHY 59 6 799 - 807 2003年12月 [査読有り][通常論文]
     
    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.
  • 大木 淳之
    地球化学 37 3 日本地球化学会 2003年08月 [査読無し][通常論文]
  • SASAKAWA M, OOKI A
    J Geophys Res 108 D3 AAC13.1-AAC13.9  2003年02月 [査読有り][通常論文]
  • A Ooki, M Uematsu, K Miura, S Nakae
    ATMOSPHERIC ENVIRONMENT 36 27 4367 - 4374 2002年09月 [査読有り][通常論文]
     
    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.
  • K Aranami, S Watanabe, S Tsunogai, A Ohki, K Miura, H Kojima
    JOURNAL OF ATMOSPHERIC CHEMISTRY 41 1 49 - 66 2002年01月 [査読有り][通常論文]
     
    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.

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