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Last Updated :2024/07/25

研究者情報

マスター

アカウント（マスター）

  • 氏名

    山本　正伸(ヤマモト　マサノブ), ヤマモト　マサノブ

所属（マスター）

  • 地球環境科学研究院　地球圏科学部門　環境変動解析学分野

所属（マスター）

  • 地球環境科学研究院　地球圏科学部門　環境変動解析学分野

独自項目

syllabus

  • 2021, 大学院共通授業科目（教育プログラム）：南極学, Inter-Graduate School Classes(Educational Program):Antarctic Science, 修士課程, 大学院共通科目, Polar regions, the Antarctic, the Arctic, sea ice, ice sheet, atmosphere, ocean, climate system, ecosystem, Antarctic expeditions, Antarctic treaty
  • 2021, 大学院共通授業科目（一般科目）：複合領域, Inter-Graduate School Classes(General Subject):Inter-Disciplinary Sciences, 修士課程, 大学院共通科目, 北極域、地球環境、温暖化、気候変動、炭素循環、水循環、人間活動、永久凍土、北極域航路、国際政治、持続的開発 Arctic, Global environment, Global warming, Climate change, Ecosystems, Human activity, Permafrost, Northern Sea Route, Global politics, Sustainable development
  • 2021, 北極域総論, Introduction to Circumpolar North, 修士課程, 環境科学院, 北極域、地球環境、温暖化、気候変動、炭素循環、水循環、人間活動、永久凍土、北極域航路、国際政治、持続的開発 Arctic, Global environment, Global warming, Climate change, Ecosystems, Human activity, Permafrost, Northern Sea Route, Global politics, Sustainable development
  • 2021, 古気候学特論, Advanced Course in Paleoclimatology, 修士課程, 環境科学院, 古気候，古海洋，地球温暖化 Paleoclimatology, Paleoceanography, Global warming
  • 2021, 古環境学基礎論, Fundamental Course in Paleoenvironmental Science, 修士課程, 環境科学院, 古環境，古気候，古海洋，地球温暖化 Paleoenvironment, Paleoclimatology, Paleoceanography, Global warming
  • 2021, 地球惑星科学実験Ⅱ, Laboratory Work in Earth and Planetary Sciences II, 学士課程, 理学部, 堆積物，堆積環境，水圏環境，化石，古海洋，古気候，気象，天気図，統計解析，地震，地震学，地震波，震源解析
  • 2021, 地球惑星科学特別講義, Special Lectures on Earth and Planetary Sciences, 学士課程, 理学部, 海洋プランクトン，微化石，古環境復元
  • 2021, 地球環境学, Environmental geoscience, 学士課程, 理学部, 気候変化、炭素循環、古環境、氷期・間氷期、人類環境、生物圏
  • 2021, 一般教育演習(ﾌﾚｯｼｭﾏﾝｾﾐﾅｰ), Freshman Seminar, 学士課程, 全学教育, 北極域、地球環境、温暖化、気候変動、炭素循環、水循環、人間活動、永久凍土、北極域航路、国際政治
  • 2021, 科学・技術の世界, The World of Science and Technology, 学士課程, 全学教育, 地球環境，気候，古気候，炭素循環，有機物，CO2, 海洋，大気，陸地，植生

researchmap

プロフィール情報

学位

  • 博士（理学）（名古屋大学）

プロフィール情報

  • 姓

    山本, ヤマモト

  • 名

    正伸, マサノブ

  • ID各種

    200901029068310187

対象リソース

業績リスト

研究キーワード

  • 古気候学   古海洋学   有機地球化学   Organic Geochemistry Paleoceanography   

研究分野

  • 自然科学一般 / 地球生命科学
  • 自然科学一般 / 宇宙惑星科学
  • 自然科学一般 / 固体地球科学

経歴

  • 2019年11月 - 現在 北海道大学 大学院地球環境科学研究院 教授
  • 2006年04月 - 2019年10月 - 大学院地球環境科学研究院 准教授
  • 2000年 - 2006年 大学院地球環境科学研究科 助教授
  • 2000年 - 2006年 Associate Professor
  • 2006年 - Associate Professor,Faculty of Environmental Earth Science
  • 1996年 - 2000年 東北大学大学院理学研究科(連携講座） 助教授
  • 1996年 - 2000年 Associate Professor
  • 1995年 - 2000年 工業技術院地質調査所燃料資源部燃料鉱床課 主任研究員
  • 1995年 - 2000年 Chief Researcher
  • 1988年 - 1995年 工業技術院地質調査所燃料部石炭課 研究員
  • 1988年 - 1995年 Researcher,Geological Survey of Japan

学歴

  •         - 1988年   東北大学   理学研究科   博士課程前期地学専攻終了
  •         - 1988年   東北大学
  •         - 1986年   東北大学   理学部   地学科地学第二
  •         - 1986年   東北大学

委員歴

  • 2022年05月 - 現在   日本地球惑星科学連合   Progress in Earth and Planetary Sciences編集委員
  • 2022年04月 - 現在   地球環境史学会   会長
  • 2018年 - 現在   石油技術協会   理事   石油技術協会
  • 2017年 - 現在   有機地球化学会   理事   有機地球化学会
  • 2014年04月 - 現在   日本地球掘削科学コンソーシアム   理事機関代表
  • 2021年04月 - 2023年03月   日本地質学会北海道支部   支部長
  • 2011年 - 2019年   日本海洋学会   JO編集委員   日本海洋学会
  • 2014年 - 2018年   日本地球掘削科学コンソーシアム   部会幹事   日本地球掘削科学コンソーシアム
  • 2014年 - 2017年   International Ocean Drilling Program   Scientific Evaluation Panel委員   International Ocean Drilling Program
  • 2003年 - 2017年   有機地球化学会   運営委員   有機地球化学会
  • 2017年   地球環境史学会   各賞選考委員長   地球環境史学会
  • 2014年 - 2016年   地球環境史学会   副会長   地球環境史学会
  • 2013年 - 2014年   European Geoscience Union   Guest editor   European Geoscience Union
  • 2013年 - 2014年   北極環境コンソーシアム   長期構想報告書執筆者   北極環境コンソーシアム
  • 2013年 - 2014年   地球環境史学会   会誌編集院長   地球環境史学会
  • 2006年 - 2014年   International Ocean Drilling Program   Curatorial Advisory Board委員   International Ocean Drilling Program
  • 2010年 - 2013年   地質学会   代議員   地質学会
  • 2011年 - 2012年   Quaternary Research Association   Guest editor   Quaternary Research Association
  • 2010年 - 2012年   地質学会   北海道支部幹事庶務   地質学会
  • 2012年   地球環境史学会   評議員   地球環境史学会
  • 2009年 - 2011年   日本地球掘削科学コンソーシアム   IODP部会執行部員   日本地球掘削科学コンソーシアム
  • 2010年 - 2010年   International Ocean Drilling Program   Science Steering and Evaluation Panel委員   International Ocean Drilling Program
  • 2001年 - 2008年   日本地球化学会   地球化学講座編集委員   日本地球化学会
  • 2004年 - 2007年   有機地球化学会   ROG編集委員長   有機地球化学会
  • 2001年 - 2007年   地質学会   地質学雑誌編集委員   地質学会
  • 2003年 - 2006年   International Ocean Drilling Program   Scientific Technology Panel委員   International Ocean Drilling Program
  • 1996年 - 2005年   有機地球化学会   事務局   有機地球化学会
  • 2003年   有機地球化学会   マニュアル作成委員長   有機地球化学会
  • 2000年   石油技術協会   会誌編集委員   石油技術協会

受賞

  • 2019年09月 日本地質学会 地質学会論文賞
     Hitoshi Hasegawa, Hisao Ando, Noriko Hasebe, Niiden Ichinnorov, Tohru Ohta, Takashi Hasegawa, Masanobu Yamamoto, Gang Li, Bat‐Orshikh Erdenetsogt, Ulrich Heimhofer, Takayuki Murata, Hironori Shinya, G. Enerel, G. Oyunjargal, O. Munkhtsetseg, Noriyuki Suzu 
    受賞者: 山本 正伸
  • 2016年07月 日本有機地球化学会 2016年度有機地球化学賞（学術賞）受賞
     バイオマーカーによる古海洋環境の復元に関する研究 
    受賞者: 山本 正伸
  • 2015年11月 地球環境史学会 2014年度地球環境史学会貢献賞
     後期第四紀の北太平洋亜熱帯循環変動に関する研究 
    受賞者: 山本 正伸
  • 1999年02月 地質調査所 地質調査所月報賞
     Yamamoto, M., Bat-erdene, D., Ulziikhishig, P., Watanabe, Y., Imai, N., Kajiwara, Y., Takeda, N., Nakajima, T. (1998) Organic geochemistry and palynology of Lower Cretaceous Zuunbayan oil shales, Mongolia, Bull. Geol. Surv. Japan, 49, 6, 257-274. 
    受賞者: 山本 正伸
  • 1997年07月 有機地球化学研究会 研究奨励賞（田口賞）受賞
     アザーレン組成に基づく石油移動の有機地球化学的研究 
    受賞者: 山本 正伸

論文

  • Wakana Harigai, Aya Saito, Chika Zemmoto, Shigenori Karasawa, Touta Yokoi, Atsushi J. Nagano, Hitoshi Suzuki, Masanobu Yamamoto
    BMC Ecology and Evolution 23 1 2023年08月07日 
    Abstract Background Phylogeographical approaches explain the genetic diversity of local organisms in the context of their geological and geographic environments. Thus, genetic diversity can be a proxy for geological history. Here we propose a genus of woodland isopod, Ligidium, as a marker of geological history in relation to orogeny and the Quaternary glacial cycle. Results Mitochondrial analysis of 721 individuals from 97 sites across Japan revealed phylogenetic divergence between the northeastern and southwestern Japan arcs. It also showed repeated population expansions in northeastern Japan in response to Quaternary glacial and interglacial cycles. Genome-wide analysis of 83 selected individuals revealed multiple genetic nuclear clusters. The genomic groupings were consistent with the local geographic distribution, indicating that the Ligidium phylogeny reflects its regional history. Conclusion Ligidium DNA sequence analysis can provide insight into the geological, geographical, and paleoenvironmental history of the studied region.
  • Mutsumi Iizuka, Osamu Seki, David J. Wilson, Yusuke Suganuma, Keiji Horikawa, Tina van de Flierdt, Minoru Ikehara, Takuya Itaki, Tomohisa Irino, Masanobu Yamamoto, Motohiro Hirabayashi, Hiroyuki Matsuzaki, Saiko Sugisaki
    Nature Communications 14 1 2023年04月18日 
    Abstract The Last Interglacial (LIG: 130,000–115,000 years ago) was a period of warmer global mean temperatures and higher and more variable sea levels than the Holocene (11,700–0 years ago). Therefore, a better understanding of Antarctic ice-sheet dynamics during this interval would provide valuable insights for projecting sea-level change in future warming scenarios. Here we present a high-resolution record constraining ice-sheet changes in the Wilkes Subglacial Basin (WSB) of East Antarctica during the LIG, based on analysis of sediment provenance and an ice melt proxy in a marine sediment core retrieved from the Wilkes Land margin. Our sedimentary records, together with existing ice-core records, reveal dynamic fluctuations of the ice sheet in the WSB, with thinning, melting, and potentially retreat leading to ice loss during both early and late stages of the LIG. We suggest that such changes along the East Antarctic Ice Sheet margin may have contributed to fluctuating global sea levels during the LIG.
  • Michinobu Kuwae, Bruce P Finney, Zhiyuan Shi, Aya Sakaguchi, Narumi Tsugeki, Takayuki Omori, Tetsuro Agusa, Yoshiaki Suzuki, Yusuke Yokoyama, Hirofumi Hinata, Yoshio Hatada, Jun Inoue, Kazumi Matsuoka, Misaki Shimada, Hikaru Takahara, Shin Takahashi, Daisuke Ueno, Atsuko Amano, Jun Tsutsumi, Masanobu Yamamoto, Keiji Takemura, Keitaro Yamada, Ken Ikehara, Tsuyoshi Haraguchi, Stephen Tims, Michaela Froehlich, Leslie Keith Fifield, Takahiro Aze, Kimikazu Sasa, Tsutomu Takahashi, Masumi Matsumura, Yukinori Tani, Peter R Leavitt, Hideyuki Doi, Tomohisa Irino, Kazuyoshi Moriya, Akira Hayashida, Kotaro Hirose, Hidekazu Suzuki, Yoshiki Saito
    The Anthropocene Review 205301962211350 - 205301962211350 2022年12月19日 
    For assessment of the potential of the Beppu Bay sediments as a Global Boundaries Stratotype Section and Point (GSSP) candidate for the Anthropocene, we have integrated datasets of 99 proxies. The datasets for the sequences date back 100 years for most proxy records and 1300 years for several records. The cumulative number of occurrences of the anthropogenic fingerprint reveal unprecedented increases above the base of the 1953 flood layer at 64.6 cm (1953 CE), which coincides with an initial increase in global fallout of 239Pu+240Pu. The onset of the proliferation of anthropogenic fingerprints was followed by diverse human-associated events, including a rapid increase in percent modern 14C in anchovy scales, changes in nitrogen and carbon cycling as recorded by anchovy δ15N and δ13C, elevated pollution of heavy metals, increased depositions of novel materials (spheroidal carbonaceous particles, microplastics, polychlorinated biphenyls), the occurrence of hypoxia (Re/Mo ratio) and eutrophication (biogenic opal, TOC, TN, diatoms, chlorophyll a), unprecedented microplankton community changes (compositions of carotenoids, diatoms, dinoflagellates), abnormally high spring air temperatures as inferred from diatom fossils, and lithological changes. These lines of evidence indicate that the base of the 1953 layer is the best GSSP level candidate in the stratigraphy at this site.
  • Hitoshi Hasegawa, Nagayoshi Katsuta, Yasushi Muraki, Ulrich Heimhofer, Niiden Ichinnorov, Hirofumi Asahi, Hisao Ando, Koshi Yamamoto, Masafumi Murayama, Tohru Ohta, Masanobu Yamamoto, Masayuki Ikeda, Kohki Ishikawa, Ryusei Kuma, Takashi Hasegawa, Noriko Hasebe, Shoji Nishimoto, Koichi Yamaguchi, Fumio Abe, Ryuji Tada, Takeshi Nakagawa
    Scientific Reports 12 1 2022年12月19日 
    Abstract Understanding climate variability and stability under extremely warm ‘greenhouse’ conditions in the past is essential for future climate predictions. However, information on millennial-scale (and shorter) climate variability during such periods is scarce, owing to a lack of suitable high-resolution, deep-time archives. Here we present a continuous record of decadal- to orbital-scale continental climate variability from annually laminated lacustrine deposits formed during the late Early Cretaceous (123–120 Ma: late Barremian–early Aptian) in southeastern Mongolia. Inter-annual changes in lake algal productivity for a 1091-year interval reveal a pronounced solar influence on decadal- to centennial-scale climatic variations (including the ~ 11-year Schwabe cycle). Decadally-resolved Ca/Ti ratios (proxy for evaporation/precipitation changes) for a ~ 355-kyr long interval further indicate millennial-scale (~ 1000–2000-yr) extreme drought events in inner-continental areas of mid-latitude palaeo-Asia during the Cretaceous. Millennial-scale oscillations in Ca/Ti ratio show distinct amplitude modulation (AM) induced by the precession, obliquity and short eccentricity cycles. Similar millennial-scale AM by Milankovitch cycle band was also previously observed in the abrupt climatic oscillations (known as Dansgaard–Oeschger events) in the ‘intermediate glacial’ state of the late Pleistocene, and in their potential analogues in the Jurassic ‘greenhouse’. Our findings indicate that external solar activity forcing was effective on decadal–centennial timescales, whilst the millennial-scale variations were likely amplified by internal process such as changes in deep-water formation strength, even during the Cretaceous ‘greenhouse’ period.
  • Masanobu Yamamoto, Fangxian Wang, Tomohisa Irino, Kazuyoshi Yamada, Tsuyoshi Haraguchi, Hideto Nakamura, Katsuya Gotanda, Hitoshi Yonenobu, Christian Leipe, Xuan-Yu Chen, Pavel E. Tarasov
    QUATERNARY INTERNATIONAL 623 8 - 18 2022年06月 
    Rebun is a small island located northwest of Hokkaido Island where hunter-fisher-gatherer cultural traditions continued until the 19th century CE. In this study, we quantified polycyclic aromatic hydrocarbons (PAHs), pentacyclic triterpene methyl ethers (PTMEs), n-fatty acids, and glycerol dialkyl glycerol tetraethers (GDGTs) in sediments from Lake Kushu in northern Rebun Island to reconstruct changes in limnology, the local environment and local to regional fire activities during the past 17,000 years (i.e., 17 ka). The PAH concentration increased from 11 to 10 cal ka BP. PAH and PTME compositions indicate that this change was associated with an increase of fire activity at proximal locations (i.e., the vicinity of Lake Kushu) and a change in the composition of grasses growing around the lake. A peak in PAH concentrations at 6.6-6.0 cal ka BP likely indicates intensive fire activity on Rebun Island. The PAH composition after 6 cal ka BP mainly reflected the combustion of conifers near the lake. The GDGTs, n-fatty acids, perylene, and PTME concentrations were higher around 10 cal ka BP and after 6 cal ka BP compared to the remaining periods, suggesting better preservation of those compounds under lake conditions marked by lower oxygen concentrations.
  • Yudai Segawa, Masanobu Yamamoto, Michinobu Kuwae, Kazuyoshi Moriya, Hitoshi Suzuki, Koji Suzuki
    Journal of Geophysical Research: Biogeosciences 127 6 2022年05月27日
  • Masanobu Yamamoto, Steven C. Clemens, Osamu Seki, Yuko Tsuchiya, Yongsong Huang, Ryouta O'ishi, Ayako Abe-Ouchi
    NATURE GEOSCIENCE 15 4 307 - + 2022年04月 [査読有り]
     
    Atmospheric CO2 and polar ice volume have been strongly coupled over the past 805,000 years. However, the prior extent of coupling, during times of lower-amplitude ice-volume variability, is unknown because continuous high-resolution CO2 records are lacking. We reconstructed the past 1,460,000 years of atmospheric CO2 (similar to 1,700year sample resolution) by taking advantage of the unique relationship between CO2 concentration and leaf-wax delta C-13 resulting from changes in the extent of C-3 and C-4 vegetation in East India. Notably, reconstructed interglacial CO2 concentrations were lower before the transition to large volume variability during the mid-Pleistocene Transition (900,000 years ago). Prior to the mid-Pleistocene Transition, CO2 exhibited a secular trend similar to that of deep-ocean carbon isotopes. At orbital time scales, phase analysis indicates that the CO2 lead relative to ice volume changed to a lag during the mid-Pleistocene Transition. Combined, these findings suggest that deep-ocean circulation controlled the long-term CO2 trend, and that interaction between CO2, continental ice and deep-ocean circulation was reorganized during the mid-Pleistocene Transition, involving a decrease in carbon storage in the deep Pacific.
  • Masanobu Yamamoto, Osamu Seki
    GEOPHYSICAL RESEARCH LETTERS 49 5 2022年03月 [査読有り]
     
    In Hokkaido, northern Japan, densely populated societies of hunter-fisher-gatherer cultures persisted over the Holocene until the 19th century. We used the cellulose delta O-18 values of Sphagnum and vascular plants in peat cores from Rishiri Island to understand paleoclimate changes in Hokkaido over the past 4,400 years and discuss the impacts of climate changes on the development of the cultures. The cellulose delta O-18 values showed multi-centennial and millennial variations, reflecting the intensity of the Tsushima Warm Current and the summer position of the westerly jet. The marine hunter-fisher cultures responded to changes in the strength of Tsushima Warm Current and coastal primary production. In contrast, the inland cultures responded to changes in the latitudinal position of the summer westerlies. This implies that human societies of different lifestyles responded differently to climate changes.
  • Kenta Suzuki, Masanobu Yamamoto, Brad E. Rosenheim, Takayuki Omori, Leonid Polyak
    Quaternary Geochronology 66 2021年10月 
    Sediments up to about 50 ka old can be dated by radiocarbon (14C), and typically biogenic carbonate minerals formed by organisms like foraminifera or mollusks are the primary choice for dating. However, carbonate-poor environments, typical for polar seas, limit the possibilities for 14C dating to bulk organic matter (OM), which is typically biased by the old carbon. In this study, ramped pyrolysis-oxidation (RPO) 14C dating of bulk OM was applied to two Arctic Ocean sediment cores with independent age constraints from prior studies in order to assess its applicability in this environment. Application of RPO to Arctic sediment samples yielded a series of progressively older ages with increasing pyrolysis temperatures and with sediment depth, similar to previous applications in Antarctica. The difference between the independently dated carbonate ages and the RPO-derived ages was proportional to the gradient of 14C ages of the released carbon vs. the pyrolysis temperature. Using this empirical relationship, we propose a new method to estimate sediment age based on RPO 14C data. Ages derived by this method in our data set show offsets from the independent age controls mostly under ~700 years. These results are much closer to the actual ages than the bulk OM data. This simple method may have a broad application to sediments with biogenic carbonate deficiency whereby dating is reliant on bulk OM.
  • Masanobu Yamamoto, Takafumi Kikuchi, Hiromichi Sakurai, Ryoma Hayashi, Osamu Seki, Takayuki Omori, Abdullah Sulaiman, Hasrizal Shaari, Mohd Zulhilmy Abdullah, Lulie Melling
    Geophysical Research Letters 48 18 2021年09月28日 [査読有り][通常論文]
     
    The forcing of multicentennial climate variability in the Western Pacific Warm Pool (WPWP) region is not fully understood. Here, we generated 6-kyr-long continuous charcoal records from five peatlands in Borneo. Every several hundred years, peaks of charcoal influx were identified in the composite record, indicating that the peatlands repeatedly experienced dry conditions and wildfires. Major fire events were identified at similar to 5.4, 4.7, 4.4, 3.7, 3.2, 2.7, 2.4, 2.2, 1.7, 1.1, 0.6, and 0.3 ka. Most of these coincided with the maxima of Borneo speleothem delta O-18 and occurred in the high solar activity periods following the solar minima. This suggests that the higher solar activity decreased rainfall, increasing dryness and wildfire frequency. This result challenges the hypothesis that high solar activity intensifies atmospheric convection in the WPWP area.
  • Hiromichi Sakurai, Masanobu Yamamoto, Osamu Seki, Takayuki Omori, Tomonori Sato
    Geochemistry, Geophysics, Geosystems 22 9 2021年09月28日 [査読有り][通常論文]
     
    The cellulose delta O-18 of plant tissues in peat is a potential climate proxy. However, understanding what is driving the shifts in delta O-18 of cellulose is required for its application. Here, we analyzed the delta O-18 values of Sphagnum and vascular plant cellulose, as well as the delta O-18 and delta D values of pore water, in a 4-m-long peat core from the Bekanbeushi ombrotrophic bog to understand paleoclimatic changes in northern Japan over the past 2,000 years. The cellulose delta O-18 values of Sphagnum were lower than those of vascular plant tissues, although both draw water from the same layer. Whereas the cellulose delta O-18 values of Sphagnum more directly reflect those of precipitation, those of vascular plants become enriched through transpiration. Thus, the difference between vascular plants and Sphagnum (Delta delta O-18(vp-sp)) is a potential proxy for relative humidity. Cellulose delta O-18 of Sphagnum revealed centennial variations with maxima around 800, 1300, and 1500 CE and minima around 500, 1000, 1700, and 1900 CE. The Delta delta O-18(vp-sp) was inversely correlated with Sphagnum cellulose delta O-18, indicating that the axis of summer westerlies was more frequently located to the north and the climate was moist in the former periods, whereas the axis of summer westerlies was generally located to the south and the climate was dry in the latter periods. These results suggest a warm and moist climate during the former periods due to frequent rainy summers driven by strong East Asian summer monsoon activity, and the opposite conditions in the latter periods.
  • Sher-Rine Kong, Masanobu Yamamoto, Hasrizal Shaari, Ryoma Hayashi, Osamu Seki, Norhayati Mohd Tahir, Muhammad Fais Fadzil, Abdullah Sulaiman
    PLOS ONE 16 9 e0256853 - e0256853 2021年09月08日 [査読有り][通常論文]
     
    The reconstruction of fire history is essential to understand the palaeoclimate and human history. Polycyclic aromatic hydrocarbons (PAHs) have been extensively used as a fire marker. In this work, the distribution of PAHs in Borneo peat archives was investigated to understand how PAHs reflect the palaeo-fire activity. In total, 52 peat samples were analysed from a Borneo peat core for the PAH analysis. Pyrogenic PAHs consist of 2–7 aromatic rings, some of which have methyl and ethyl groups. The results reveal that the concentration of pyrogenic PAHs fluctuated with the core depth. Compared to low-molecular-weight (LMW) PAHs, the high-molecular-weight (HMW) PAHs had a more similar depth variation to the charcoal abundance. This finding also suggests that the HMW PAHs were mainly formed at a local fire near the study area, while the LMW PAHs could be transported from remote locations.
  • Haijun Yuan, Fanfan Meng, Masanobu Yamamoto, Xingqi Liu, Hailiang Dong, Ji Shen, Huaqun Yin, Jianjun Wang
    ECOLOGICAL INDICATORS 126 2021年07月 [査読有り][通常論文]
     
    Understanding the relationship between historical vegetation and bacteria is critical for disentangling spatiotemporal variations in microbial communities. However, the utility of historical vegetation as indicated by the reconstruction proxies like n-alkanes to explain microbial succession has been understudied, especially regarding aquatic microbes living under contrasting climates. Here, we studied bacterial and n-alkane succession in sediment cores from Kusai Lake and Lugu Lake under contrasting climates, that is, the drier and colder climates and the warmer and wetter conditions, respectively, and further explored how bacterial communities are affected by historical vegetation. In both lakes, the Shannon diversity of bacteria and n-alkanes consistently and significantly (P < 0.05) decreased towards deep-depth sediments, and their compositional dissimilarity Bray-Curtis increased with depth changes, with slopes of 0.00048 and 0.00027 in Kusai and Lugu lakes, respectively. Furthermore, there was strong synchrony between bacteria and historical vegetation, which was underpinned by similar ecological processes such as environmental selection (e.g., climatic perturbations). Compared to Lugu Lake, however, both the Shannon diversity and compositions of bacteria or n-alkanes changed faster in Kusai Lake, which was influenced by abiotic factors such as the sediment Na and loss-on-ignition. Except for abiotic variables, we found that bacterial diversity and composition were also affected by n-alkane attributes such as the C27/C31, carbon preference index, Shannon diversity and composition in both lakes. In particular, n-alkane attributes generally exerted stronger effects on bacterial characteristics than abiotic variables. For example, nalkane attributes showed strong direct effects on bacterial community composition, with path coefficients of 0.485 and 0.976 (P < 0.001) in Kusai and Lugu lakes, respectively, while abiotic variables had no direct effect. Thus, our findings provide new evidence that historical vegetation could substantially explain variations in bacterial communities across temporal scales.
  • Masanobu Yamamoto, Fangxian Wang, Tomohisa Irino, Kenta Suzuki, Kazuyoshi Yamada, Tsuyoshi Haraguchi, Katsuya Gotanda, Hitoshi Yonenobu, Xuan-Yu Chen, Pavel Tarasov
    FRONTIERS IN EARTH SCIENCE 9 2021年06月 [査読有り][招待有り]
     
    The summer climate of northern Japan since the last glacial period has likely been determined by atmospheric and oceanic dynamics, such as changes in the North Pacific High, the position of the westerlies, the Kuroshio Current, the Tsushima Warm Current (TWC), and the East Asian summer monsoon. However, it is unclear which factor has been most important. In this study, we analyzed leaf wax delta C-13 and delta D and glycerol dialkyl glycerol tetraethers (GDGTs) in sediments from Lake Kushu, Rebun Island, northern Japan, and discuss changes in climate over the past 17,000 years. The GDGT-based temperature, the averaged chain length, delta C-13 and delta D of long-chain n-fatty acids indicated that the climate was cold during the Oldest Dryas period similar to 16 ka and warm in the early Middle Holocene from similar to 9 to 6 ka. This climate change is consistent with the sea surface temperature in the Kuroshio-Oyashio transition, but inconsistent with changes in the TWC in the Sea of Japan. The results imply that the summer climate of northern Japan was controlled mainly by changes in the development of the North Pacific High via changes in the position of the westerly jet and East Asian summer monsoon rainfall, whereas the influence of the TWC was limited over a millennial timescale.
  • Steven C. Clemens, Masanobu Yamamoto, Kaustubh Thirumalai, Liviu Giosan, Julie N. Richey, Katrina Nilsson-Kerr, Yair Rosenthal, Pallavi Anand, Sarah M. McGrath
    Science Advances 7 23 2021年06月 [査読有り][通常論文]
     
    South Asian precipitation amount and extreme variability are predicted to increase due to thermodynamic effects of increased 21st-century greenhouse gases, accompanied by an increased supply of moisture from the southern hemisphere Indian Ocean. We reconstructed South Asian summer monsoon precipitation and runoff into the Bay of Bengal to assess the extent to which these factors also operated in the Pleistocene, a time of large-scale natural changes in carbon dioxide and ice volume. South Asian precipitation and runoff are strongly coherent with, and lag, atmospheric carbon dioxide changes at Earth's orbital eccentricity, obliquity, and precession bands and are closely tied to cross-equatorial wind strength at the precession band. We find that the projected monsoon response to ongoing, rapid high-latitude ice melt and rising carbon dioxide levels is fully consistent with dynamics of the past 0.9 million years.
  • Sarah M. McGrath, Steven C. Clemens, Yongsong Huang, Masanobu Yamamoto
    Geophysical Research Letters 48 4 2021年02月28日 [査読有り][通常論文]
     
    Orbital-scale Indian Summer Monsoon variability is often interpreted as a direct response to northern hemisphere summer insolation. Here we present a continuous (0-640 kyr) orbital scale precipitation isotope (delta D-precip) record using leaf wax delta D from the core monsoon zone of India. The delta D-precip record is quantitatively coherent with, and delta D-precip minima in phase with, greenhouses gas maxima, and ice volume minima across all orbital bands. The delta D-precip record is also coherent and in phase with the two existing orbital-scale Indian speleothem delta O-18 records, demonstrating a consistent regional response among independent proxies. These findings preclude interpretation of Indian precipitation isotope records as a direct response to northern hemisphere summer insolation. Rather, they dominantly reflect changes in moisture source and transport paths associated with changes in greenhouse gases and ice volume. The orbital-scale precipitation isotope responses of the Indian and East Asian monsoon systems are uncoupled and are driven by different forcings.
  • Wakana Harigai, Aya Saito, Hitoshi Suzuki, Masanobu Yamamoto
    ZOOLOGICAL SCIENCE 37 5 417 - 428 2020年10月 [査読有り][通常論文]
     
    The genetic diversity of the genus Ligidium in Hokkaido and Niigata, northern Japan, was investigated by analyzing the cytochrome c oxidase subunit 1 (CO1) region in the mitochondrial DNA (mtDNA). The genetic diversity in Hokkaido was much lower than that in Niigata. Nine different operational taxonomic units (OTUs) were identified. Only a single OTU, most likely Ligidium japonicum, was found in Hokkaido, whereas all nine OTUs were found in Niigata. Using the mtDNA evolutionary rate determined for the marine invertebrate Haptosquilla pulchella (Miers, 1880), population expansion for OTU1 in Hokkaido was estimated to have occurred at 12,600 years BP, suggesting that Ligidium underwent a bottleneck due to glacial cooling, and the population then expanded after postglacial warming. Assuming that the expansion of the OTU1 population occurred at 9600 years BP, when the sea surface temperature rose offshore of Tokachi in the Northwestern Pacific, the evolutionary rate (mu) of the mtDNA CO1 region in Ligidium is calculated as: 0.087 (95% confidence intervals: min: 0.042- max: 0.12) (substitutions/site/million years). The presence of a haplotype common to Hokkaido and Niigata implies that the haplotype migrated across the Tsugaru Strait. Considering that geological evidence indicates that the Tsugaru Strait was continuously present even during the last glacial maximum when the sea level was at its lowest, accidental transport by human beings or animals might have been critical to the migration of Ligidium.
  • Kenta Suzuki, Masanobu Yamamoto, Osamu Seki
    Geological Magazine 157 6 979 - 988 2020年06月 [査読有り][通常論文]
     
    Vegetation changes in the Indus River basin within the past 10.8 million years were investigated based on the analysis of n-fatty acids and their carbon isotopes in sediments from IODP Site U1457 in the Laxmi Basin of the Arabian Sea. The delta C-13 of long-chain n-C-32 fatty acid shifted from -34 to -22 parts per thousand from 10 to 6.3 Ma, while the delta C-13 of mid-chain n-C-24 fatty acid was nearly constant at around -23 to -22 parts per thousand over the same period. This large difference in the delta C-13 values suggests that the mid-chain fatty acids reflect the contribution of aquatic vascular C-3 plants. Before 6.3 Ma, the average chain length of n-fatty acids and the delta C-13 values of long-chain fatty acids were negatively correlated, suggesting that the delta C-13 values reflected the relative abundance of terrestrial C-3 versus aquatic C-3 plants in the Indus River basin and western India. After 5.8 Ma, the average chain length was variable, but the delta C-13 values remained nearly the same, suggesting that the delta C-13 values reflected heavier delta C-13 values of both aquatic C-3 and C-4 plants. A three-end-member model calculation suggests that terrestrial C-3 plants were replaced by C-4 plants in the Indus River basin and western India from 9.7 or 8.2 to 6.3 Ma. Aridification in those areas during the late Miocene period may have driven the replacement of terrestrial C-3 plants by C-4 plants. An episodic increase in the abundance of terrestrial plants around 8 Ma is attributed to elevated precipitation by regionally enhanced moisture transport.
  • Dukki Han, Young Jin Joe, Jong-Sik Ryu, Tatsuya Unno, Gibaek Kim, Masanobu Yamamoto, Kihong Park, Hor-Gil Hur, Ji-Hoon Lee, Seung-Il Nam
    Spectrochimica Acta - Part B Atomic Spectroscopy 146 84 - 92 2018年08月01日 [査読有り][通常論文]
     
    Physical and geochemical investigations coupled with laser-induced breakdown spectroscopy (LIBS) were performed on three surface sediment cores (ARA02B/01A, ARA02B/02, and ARA02B/03A) recovered from the western Arctic Ocean (Chukchi Sea) during the IBRV ARAON 2011 expedition. The LIBS technique was applied to conduct elemental analysis of the Arctic sediments and compare the results to those obtained using an X-ray fluorescence (XRF) core scanner and inductively coupled plasma (ICP) system. The LIBS technique showed an elemental composition similar to that using XRF and ICP in each sediment core. Qualitative and semi-quantitative LIBS analyses provide distinguishable patterns between sediment cores, similar to those observed in the ICP analysis. In particular, the elemental pattern of LIBS responded to the color change of the sediment cores. Dark brown layers in the upper parts of the cores were indicated by the color indices and showed elevated Mn/Al ratios, suggesting the influence of regional variation in terrestrial input since the deglacial period. In this study, grain size distribution and contents of detrital dolomite and organic carbon as well as elemental composition (LIBS) were considered to determine sediment provenance and sedimentation environments during the Holocene. Furthermore, the present study showed that the LIBS technique may be used as an applicable method to unravel regional variations in sedimentary composition in the Arctic Ocean.
  • Ziye Li, Min-Te Chen, Da-Cheng Lin, Houjie Wang, Xuefa Shi, Shengfa Liu, Yusuke Yokoyama, Masanobu Yamamoto, Chuan-Chou Shen, Horng-Sheng Mii, Rainer Arief Troa, Rina Zuraida, Eko Triarso, Marfasran Hendrizan
    Quaternary International 482 1 - 12 2018年07月20日 [査読有り][通常論文]
     
    The Indo-Pacific warm pool (IPWP) is an area hosting key tropical climate processes such as the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). The tropical climate processes, via various feedback mechanisms, control the surface ocean climate in the Indian Ocean and its surrounding continents on annual to inter-annual timescales. However, little has been known about how the tropical processes are effective forcing climate mechanism over longer timescales. Here we presented a reconstruction of the spatiotemporal pattern of sea surface temperature (SST) with inferred hydroclimate changes since the early Holocene (∼11ka), using proxies of planktonic foraminifer shell Mg/Ca, organic biomarker (TEX86), foraminifer oxygen isotopes, and a terrigenous BIT index measured from a 220 cm long Core BS24 (2.724041°N, 97.010943°E, 1015 m water depth) which was taken offshore of northwest Sumatra in the eastern Indian Ocean. With an age model of 13 AMS 14C dating by the uses of planktonic foraminiferal shells from the core, the TEX86 H temperatures of BS24 show as summer-weighted, and reflect integrated thermal effects from the surface to thermocline water, while the Mg/Ca temperature of BS24 better reflects mean annual SST. Our results, along with a regional synthesis of published SST records from the IPWP, suggest that the IPWP has migrated eastwardly since the mid-Holocene (∼5ka). In phase with this eastward migration, the IPWP SSTs have decreased, but the upwelling in the eastern Indian Ocean appears to have been a persistent feature since the mid-Holocene. Our Empirical Orthogonal Function (EOF) analysis on the compiled IPWP SST records indicates two dominant modes of spatio-temporal variability of surface hydrographes in the IPWP that are attributed to a combined effect of orbital and solar forcing, with expressions analogous to the Indian ocean basin-wide mode (IOBM) and the Indian Ocean dipole model (IOD).
  • Hitoshi Hasegawa, Hisao Ando, Noriko Hasebe, Niiden Ichinnorov, Tohru Ohta, Takashi Hasegawa, Masanobu Yamamoto, Gang Li, Bat-Orshikh Erdenetsogt, Ulrich Heimhofer, Takayuki Murata, Hironori Shinya, G. Enerel, G. Oyunjargal, O. Munkhtsetseg, Noriyuki Suzuki, Tomohisa Irino, Koshi Yamamoto
    Island Arc 27 3 2018年05月01日 [査読有り][通常論文]
     
    Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer-scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro-laminae and calculated sedimentation rate, the micro-lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo-Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.
  • Takafumi Kataoka, Koji Suzuki, Tomohisa Irino, Masanobu Yamamoto, Seigo Higashi, Hongbin Liu
    Archives of Microbiology 200 2 329 - 342 2018年03月01日 [査読有り][通常論文]
     
    Microbial nitrification is a key process in the nitrogen cycle in the continental shelf ecosystems. The genotype compositions and abundance of the ammonia monooxygenase gene, amoA, derived from ammonia-oxidizing archaea (AOA) and bacteria (AOB) in two size fractions (2–10 and 0.2–2 µm), were investigated in the East China Sea (ECS) in May 2008 using PCR-denaturing gradient gel electrophoresis (DGGE) and quantitative PCR (qPCR). Four sites were selected across the continental shelf edge: continental shelf water (CSW), Kuroshio branch water (KBW), transition between CSW and KBW (TCSKB) and coastal KBW (CKBW). The gene copy numbers of AOA-amoA were higher than those of AOB-amoA in ECS. The relative abundance of amoA to the total 16S rRNA gene level reached approximately 15% in KBW and CKBW for the free-living fraction of AOA, whereas the level was less than 0.01% throughout ECS for the AOB. A cluster analysis of the AOA-amoA-DGGE band pattern showed distinct genotype compositions in CSW in both the size fractions and in the surface of the TCSKB and KBW. Sequences of the DGGE bands were assigned to two clades. One of the clades exclusively consisted of sequences derived from the 2–10-µm fraction. This study revealed that AOA-amoA abundance dominated over AOB-amoA throughout the ECS, whereas the genotype composition of AOA-amoA were distributed heterogeneously across the water masses. Additionally, this is the first report showing the distribution of AOA-amoA genotypes characteristic to particle-associated AOA in the offshore of the East China Sea.
  • Paul N. Pearson, IODP Expedition 363 Shipboard Scientific Party, Ivano W. Aiello, Tali L. Babila, Germain Bayon, Luc Beaufort, Samantha C. Bova, Jong-Hwa Chun, Haowen Dang, Anna Joy Drury, Tom Dunkley Jones, Patrícia P.B. Eichler, Fernando Allan Gil Salazar, Kelly Gibson, Robert G. Hatfield, Ann E. Holbourn, Daniel L. Johnson, Denise K. Kulhanek, Yuho Kumagai, Tiegang Li, Braddock K. Linsley, Niklas Meinicke, Gregory S. Mountain, Bradley N. Opdyke, Christopher R. Poole, Christina Ravelo, Yair Rosenthal, Takuya Sagawa, Anaïs Schmitt, Jennifer B. Wurtzel, Jian Xu, Masanobu Yamamoto, Yi Ge Zhang
    Journal of Micropalaeontology 37 1 97 - 104 2018年01月05日 [査読有り][通常論文]
     
    Agglutinated foraminifera are marine protists that show apparently complex behaviour in constructing their shells, involving selecting suitable sedimentary grains from their environment, manipulating them in three dimensions, and cementing them precisely into position. Here we illustrate a striking and previously undescribed example of complex organisation in fragments of a tube-like foraminifer (questionably assigned to Rhabdammina) from 1466m water depth on the northwest Australian margin. The tube is constructed from well-cemented siliciclastic grains which form a matrix into which hundreds of planktonic foraminifer shells are regularly spaced in apparently helical bands. These shells are of a single species, Turborotalita clarkei, which has been selected to the exclusion of all other bioclasts. The majority of shells are set horizontally in the matrix with the umbilical side upward. This mode of construction, as is the case with other agglutinated tests, seems to require either an extraordinarily selective trial-and-error process at the site of cementation or an active sensory and decision-making system within the cell.
  • Xudong Wu, Xingqi Liu, Jianjun Wang, Masanobu Yamamoto
    Quaternary International 487 33 - 42 2018年 [査読有り][通常論文]
     
    We report 1900-year long records of alknone concentration, C38/C37 ratio, and U37 k, U37 k’ and a newly-developed alkenone unsaturation index U37 k’’-based temperatures in a sediment core retrieved from Kusai Lake in the northern Qinghai-Tibetan Plateau. The predominance of C37 and C38 alkenones with minor presence of C39 and C40 alkenones, and the absence of C38 methyl alkenones are indicative of alkneones produced by Isochrysis, which is consistent with the results of sedimentary haptophyte DNA analyses. The interval from 400 to 1200 AD is characterized by higher alkenone concentrations and C38/C37 ratios than the other intervals, which can be attributed to the predominant production of Isochrysis during the entire phytoplankton blooms. With the assistance of information on gene abundance, we attributed this phenomenon to drastic ecological changes in Kusai Lake around 1200 AD in response to climatic changes from warm and wet to cold and dry conditions, and resultant decreased riverine inflow but increased nutrient concentration. The U37 k’’-based temperatures with U37 k’’ substituting U37 k’ in a equation concluded based on studies on lakes from high latitude areas in Germany are the most reliable reconstructed summer surface water temperatures for Kusai Lake since they are close to the current summer monthly mean temperature of Wudaoliang Meteorological Station, approximately 50 km to the south of Kusai Lake, and exhibit variations that are generally in accordance with those of the 51-year moving average summer temperatures reconstructed from thicknesses of varve light layers in Kusai Lake sediments. Besides, variations showed by this U37 k’’-based summer surface water temperatures are also generally consistent with those showed by reconstructed temperatures in China.
  • Michinobu Kuwae, Masanobu Yamamoto, Takuya Sagawa, Ken Ikehara, Tomohisa Irino, Keiji Takemura, Hidetaka Takeoka, Takashige Sugimoto
    PROGRESS IN OCEANOGRAPHY 159 86 - 98 2017年12月 [査読有り][通常論文]
     
    Paleorecords of pelagic fish abundance could better define the nature of fishery productivity dynamics and help understand responses of pelagic fish stocks to long-term climate changes. We report a high-resolution record of sardine and anchovy scale deposition rates (SDRs) from Beppu Bay, Southwest Japan, showing multidecadal and centennial variability in the abundance of Japanese sardine and Japanese anchovy during the last 2850 years. Variations in the sardine SDR showed periodicities at similar to 50, similar to 100, and similar to 300 yr, while variations in the anchovy SDR showed periodicities at similar to 30 and similar to 260 yr. Comparisons between and correlation analyses of the time series of the sardine and anchovy SDRs demonstrate that there is not a consistent out-of-phase relationship during the last 2850 years. This indicates that the multidecadal alternations in the sardine and anchovy populations commonly seen in the 20th century did not necessarily occur during earlier periods. The Japanese sardine SDR record shows a long-term decreasing trend in the amplitudes of the multidecadal to centennial fluctuations. This decreasing trend may have resulted from an increasing trend in the winter sea surface temperature in the western North Pacific. The multicentennial variability in sardine abundance during the last millennium is consistent with the variabilities in the abnormal snow index in East Asia and the American tree ring-based Pacific Decadal Oscillation index, suggesting a basin-wide or regional climate-marine ecosystem linkage.
  • Da-Cheng Lin, Min-Te Chen, Masanobu Yamamoto, Yusuke Yokoyama
    QUATERNARY INTERNATIONAL 459 1 - 16 2017年11月 [査読有り][通常論文]
     
    Millennial-scale climate variability was persistent feature for Greenland ice core and North Atlantic marine records during the Marine Isotope Stage (MIS) 3. Studying high quality climatic archives outside of the Greenland and North Atlantic with precise constraint of absolute dating and high resolution sampling is a prerequisite to understand how the millennial-scale changes well expressed in North Hemisphere (NH) high latitudes had been propagated out to the other regions. Here, we generated the surface and subsurface hydrography (U-37(k') and TEX86H temperatures) and terrestrial material input (n-alkanes) records with precise AMS C-14 dated control for the 45 ka from a core (MD972146) retrieved from the northern South China Sea (SCS). Then, we compared our records to the oxygen isotope record from a Greenland NGRIP ice core, and the mean grain size record from a loess sequence at Gulang, China. We found that the millennial-scale oscillations of hydrolography and terrestrial material inputs records during the time since the last deglaciation and of similar to 33-45 ka share similar patterns in timing and amplitude of the NH high latitude climate. However, we found that a non-NH pattern of millennial-scale oscillations for the late MIS 3, similar to 20-33 ka of our hydrography and terrestrial material inputs records. Our studies imply that the changes of obliquity also may be important in determining the timing and amplitude of millennial-scale East Asian Monsoon (EAM) variability expressed in the northern SCS hydrography and terrestrial material inputs. (c) 2017 Elsevier Ltd and INQUA. All rights reserved.
  • Masanobu Yamamoto, Yasuto Yamamoto, Keiji Takemura
    QUATERNARY INTERNATIONAL 452 129 - 136 2017年09月 [査読有り][通常論文]
     
    We investigated glycerol dialkyl glycerol tetraethers (GDGTs) in sediments taken from a 97 m long borehole core in the estuary of the Ohno River, Kyushu, Japan. Our aim was to understand the influence of estuary-produced branched GDGTs on MBT'/CBT indices and the terrestrial contribution on TEX86 in estuary sediments by comparing with soils in its drainage basin and offshore marine sediments. In borehole sediments covering the last 8000 years, TEX86 and MBT'/CBT records are inconsistent with other paleoclimate records from western and central Japan, implying that the application of TEX86 and MBT'/CBT as paleotemperature proxies to this sample set was unsuccessful. The isoprenoid GDGT compositions of the study site were closer to those of the surface soils in the Ohno River drainage area rather than those in Beppu Bay sediments. TEX86 reflects a mixing ratio of estuary and soil GDGTs. In contrast to isoprenoid GDGTs, the branched GDGT compositions were closer to those of Beppu Bay sediments rather than those of surface soils, implying that the branched GDGTs were mainly of estuary origin. Variation in BIT shows a consistent pattern with that of water depth reconstructed from a molluskan fossil record. The input of terrestrial labile organic matter could contribute to the production of branched GDGTs. In turn, the BIT indirectly reflects the contribution of terrestrial organic matter. (C) 2016 Elsevier Ltd and INQUA. All rights reserved.
  • Keitaro Yamada, Keiji Takemura, Michinobu Kuwae, Masanobu Yamamoto, Tohru Danhara
    QUATERNARY INTERNATIONAL 452 33 - 42 2017年09月 [査読有り][通常論文]
     
    In this study, we revised eruptive ages, especially the Aso and Yufu volcanoes, central Kyushu, by analyzing a sediment core of southwestern Beppu Bay, southwest Japan, where undisturbed sediments are continuously deposited in a dysoxic basin. We identified two ash-fall layers in the sequence covering the last ca. 3000 years by using the refractive index of volcanic glasses and other parameters. These layers were likely correlated with N2 ash of the Aso volcano and Yufu-dake 1 ash (Yf1) of the Yufu volcano on the basis of the refractive indices of volcanic glasses, heavy mineral compositions, special distribution, and facies. According to high precision age models, the eruptive ages (68.2% probability range) of these tephras were 1470-1490 and 2010-2100 cal yr BP, respectively, and concordant with reported ages of previous research. These precise ages of tephras improve linking or dating in the various environments, and contribute to investigation of environmental changes or sedimentary process from source to sink. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.
  • Masanobu Yamamoto, Seung-Il Nam, Leonid Polyak, Daisuke Kobayashi, Kenta Suzuki, Tomohisa Irino, Koji Shimada
    CLIMATE OF THE PAST 13 9 1111 - 1127 2017年09月 [査読有り][通常論文]
     
    The Beaufort Gyre (BG) and the Bering Strait inflow (BSI) are important elements of the Arctic Ocean circulation system and major controls on the distribution of Arctic sea ice. We report records of the quartz / feldspar and chlorite / illite ratios in three sediment cores from the northern Chukchi Sea, providing insights into the long-term dynamics of the BG circulation and the BSI during the Holocene. The quartz / feldspar ratio, interpreted as a proxy of the BG strength, gradually decreased during the Holocene, suggesting a long-term decline in the BG strength, consistent with an orbitally controlled decrease in summer insolation. We propose that the BG rotation weakened as a result of the increasing stability of sea-ice cover at the margins of the Canada Basin, driven by decreasing insolation. Millennial to multi-centennial variability in the quartz / feldspar ratio (the BG circulation) is consistent with fluctuations in solar irradiance, suggesting that solar activity affected the BG strength on these timescales. The BSI approximation by the chlorite / illite record, despite a considerable geographic variability, consistently shows intensified flow from the Bering Sea to the Arctic during the middle Holocene, which is attributed primarily to the effect of higher atmospheric pressure over the Aleutian Basin. The intensified BSI was associated with decrease in sea-ice concentrations and increase in marine production, as indicated by biomarker concentrations, suggesting a major influence of the BSI on sea-ice and biological conditions in the Chukchi Sea. Multi-century to millennial fluctuations, presumably controlled by solar activity, were also identified in a proxy-based BSI record characterized by the highest age resolution.
  • Maria Fernanda Sanchez Goni, Stephanie Desprat, Anne-Laure Daniau, Frank C. Bassinot, Josue M. Polanco-Martinez, Sandy P. Harrison, Judy R. M. Allen, R. Scott Anderson, Hermann Behling, Raymonde Bonnefille, Francesc Burjachs, Jose S. Carrion, Rachid Cheddadi, James S. Clark, Nathalie Combourieu-Nebout, Colin. J. Courtney Mustaphi, Georg H. Debusk, Lydie M. Dupont, Jemma M. Finch, William J. Fletcher, Marco Giardini, Catalina Gonzalez, William D. Gosling, Laurie D. Grigg, Eric C. Grimm, Ryoma Hayashi, Karin Helmens, Linda E. Heusser, Trevor Hill, Geoffrey Hope, Brian Huntley, Yaeko Igarashi, Tomohisa Irino, Bonnie Jacobs, Gonzalo Jimenez-Moreno, Sayuri Kawai, A. Peter Kershaw, Fujio Kumon, Ian T. Lawson, Marie-Pierre Ledru, Anne-Marie Lezine, Ping Mei Liew, Donatella Magri, Robert Marchant, Vasiliki Margari, Francis E. Mayle, G. Merna McKenzie, Patrick Moss, Stefanie Mueller, Ulrich C. Mueller, Filipa Naughton, Rewi M. Newnham, Tadamichi Oba, Ramon Perez-Obiol, Roberta Pini, Cesare Ravazzi, Katy H. Roucoux, Stephen M. Rucina, Louis Scott, Hikaru Takahara, Polichronis C. Tzedakis, Dunia H. Urrego, Bas van Geel, B. Guido Valencia, Marcus J. Vandergoes, Annie Vincens, Cathy L. Whitlock, Debra A. Willard, Masanobu Yamamoto
    EARTH SYSTEM SCIENCE DATA 9 2 679 - 695 2017年09月 [査読有り][通常論文]
     
    Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard-Oeschger (D-O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D-O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73-15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (C-14, U-234/Th-230, optically stimulated luminescence (OSL), Ar-40/Ar-39-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft Access (TM) at https://doi. org/10.1594/PANGAEA. 870867.
  • Sunghan Kim, Boo-Keun Khim, Ken Ikehara, Takuya Itaki, Akihiko Shibahara, Masanobu Yamamoto
    GLOBAL AND PLANETARY CHANGE 154 33 - 43 2017年07月 [査読有り][通常論文]
     
    Changes in water column conditions in the northwestern Pacific during the last 23 ka were reconstructed using geochemical and isotope proxies and redox elemental compositions along with published data (alkenone sea surface temperature (SST) and benthic foraminiferal fauna) at core GH02-1030. Surface water primary productivity in terms of biogenic opal and TOC contents, which mainly represented export production of diatom, was closely related to alkenone (spring-summer) SST and the development of spring-summer mixed layer depth. The different variation patterns of nitrate and silicic acid utilization, estimated by bulk delta N-15 and delta Si-30(diatom) values, respectively, are most likely due to the water column denitrification influence on bulk delta N-15. Dysoxic bottom water conditions occurred during the Bemptysetlling-Alleremptysetd (BA) and the Pre-Boreal (PB), which was evident by laminated sediments, abundant dysoxic benthic foraminifers, and increased redox elemental compositions. Although surface water productivity increased during the BA and PB, dysoxic bottom water conditions were caused by a combination of enhanced surface water productivity and reduced ventilation of North Pacific Intermediate Water (NPIW) in response to meltwater input from the high latitude areas. Based on records of core GH02-1030 and other cores in the northwestern Pacific, the Okhotsk Sea, and the Bering Sea, which are all proximal to the modern NPIW source region, dissolved oxygen concentrations of bottom water were more depleted during the BA than PB. Such difference was attributed to more sluggish NPIW ventilation due to more meltwater input during the BA than the PB. The opening or closure of the Bering Strait is critical to the direction of meltwater transport to the northwestern Pacific.
  • Kaori Hanazaki, Morihiko Tomozawa, Yutaro Suzuki, Gohta Kinoshita, Masanobu Yamamoto, Tomohisa Irino, Hitoshi Suzuki
    ZOOLOGICAL SCIENCE 34 3 201 - 210 2017年06月 [査読有り][通常論文]
     
    Reliable estimates of evolutionary rates of mitochondrial DNA might allow us to build realistic evolutionary scenarios covering broad time scales based on phylogenetic inferences. In the present study, we sought to obtain estimates of evolutionary rates in murine rodents using calibrations against historical biogeographic events. We first assumed that land-bridge-like structures that appeared intermittently at glacial maxima with 100,000-year intervals shaped the divergence patterns of cytochrome b (Cytb) sequences (1140 bp) of the larger Japanese wood mouse Apodemus speciosus. The comparison of sequences from peripheral remote islands that are separated from one another by deep straits allowed us to estimate mitochondrial DNA evolutionary rates (substitutions/site/million years) to be 0.027 to 0.036, with presumed calibrations from 140,000, 250,000, 350,000, and 440,000 years ago. Second, we addressed rapid expansion events inferred from analyses of the Cytb sequences of the lesser Japanese wood mouse A. argenteus. We detected five expansion signals in the dataset and established three categories based on the expansion parameter tau values: 3.9, 5.6-5.7, and 7.8-8.1. Considering that the climate became warmer 15,000, 53,000, and 115,000 years ago after preceding periods of rapid cooling, we calculated evolutionary rates to be 0.114, 0.047, and 0.031, respectively. This preliminary concept of the evolutionary rates on a time scale from 15,000 to 440,000 years ago for the wood mouse should be refined and tested in other species of murine rodents, including mice and rats.
  • 山本正伸
    地質学雑誌 124 3 - 16 2017年01月01日 [査読有り][通常論文]
  • Daisuke Kobayashi, Masanobu Yamamoto, Tomohisa Irino, Seung-Il Nam, Yu-Hyeon Park, Naomi Harada, Kana Nagashima, Kazuhisa Chikita, Sei-Ichi Saitoh
    POLAR SCIENCE 10 4 519 - 531 2016年12月 [査読有り][通常論文]
     
    This paper describes the distribution of detrital minerals and sediment color in the surface sediments of the western Arctic Ocean and the northern Bering Sea and investigates the relationship between mineral composition and sediment provenance. This relationship was used to determine the provenance of western Arctic Ocean sediments deposited during the last glacial period. Sediment color is governed by water depth, diagenesis, and mineral composition. An a*-b* diagram was used to trace color change during diagenesis in the Arctic Ocean sediments. The mineral composition of surface sediments is governed by grain size and provenance. The feldspar/quartz ratio of the sediments studied was higher on the Siberian side than on the North American side of the western Arctic Ocean. The (chlorite broken vertical bar kaolinite)/illite and chlorite/illite ratios were high in the Bering Sea but decrease northwards in the Chukchi Sea. Thus, these ratios are useful for provenance studies in the Chukchi Sea area as indices of the Beaufort Gyre circulation and the Bering Strait inflow. The sediments deposited during the last glacial period have a lower feldspar/quartz ratio and a higher dolomite intensity than Holocene sediments on the Chukchi Plateau, suggesting a greater contribution of North American grains during the last glacial period. (C) 2016 Elsevier B.V. and NIPR. All rights reserved.
  • Leonid Polyak, Simon T. Belt, Patricia Cabedo-Sanz, Masanobu Yamamoto, Yu-Hyeon Park
    HOLOCENE 26 11 1810 - 1821 2016年11月 [査読有り][通常論文]
     
    Two sediment cores from the Chukchi Sea margin were investigated for the Arctic sea-ice biomarker IP25, along with marine and terrestrial sterols and glycerol dialkyl glycerol tetraethers (GDGTs). This is the first paleoclimatic application of IP25 in the Chukchi-Alaskan region of the Arctic, which is key for understanding Arctic-Pacific interactions and is experiencing rapid sea-ice retreat under present warming. Sea-ice and related circulation conditions were characterized in this study with a multicentury resolution for the long-term Holocene record to multidecadal for the last several centuries. Sea ice was found to be present during the entire record but with considerable spatial and temporal variability. After very low deglacial IP25 values, possibly related to permanent sea ice and/or an iceberg-dominated environment, cores from the upper slope and shelf show IP25 maxima, interpreted as representing a relative proximity to the sea-ice margin, in the early (ca. 8-9ka) and middle (ca. 5-6ka) Holocene, respectively. Along with isoprenoid GDGT distribution, this asynchronicity in sea-ice history probably reflects oceanographic evolution of the Chukchi margin affected by the Beaufort Gyre circulation and Pacific water inflow via Bering Strait. Data for the last several centuries, with elevated values of brassicasterol and terrestrial sterols covarying with dinosterol and IP25, are interpreted in terms of long-distance import by currents combined with diagenetic transformations. We infer that high-amplitude variability in the late Little Ice Age', starting in the late 18th century, is related to the intensity of the Alaskan Coastal Current. This interval is preceded by three centuries of presumably diminished Alaskan Coastal Current but overall increased Bering Strait Inflow resulting in reduced sea-ice cover according to dinocyst-based data.
  • Masanobu Yamamoto, Akifumi Shimamoto, Tatsuo Fukuhara, Yuichiro Tanaka
    GEOCHIMICA ET COSMOCHIMICA ACTA 191 239 - 254 2016年10月 [査読有り][通常論文]
     
    Branched glycerol dialkyl glycerol tetraethers (branched GDGTs) are commonly found in distal marine sediments. However, their presence in the water column, source and delivery process are not fully understood. In this study, we examined seasonal and depth variation in the flux of branched GDGTs in sinking particles and underlying sediment at 39 degrees N, 147 degrees E in the mid-latitude NW Pacific from November 1997 to August 1999. Branched GDGTs showed synchronous variation in their sinking flux at different depths, and the variation was similar to that of lithogenic material of eolian dust origin. Their degrees of cyclization and methylation were nearly constant and bear some resemblance to those of alkaline soils. This suggests that westerly winds transport branched GDGTs to the study site via the atmosphere from continental Asia. The sinking flux of branched GDGTs was higher in 1999 than in 1998, presumably reflecting changes in the migration path of Asian dust in response to the El Nino-Southern Oscillation. Synchronous variation in branched GDGT concentrations at different depths implies rapid vertical transport of branched GDGTs to deep water with a sinking velocity exceeding 260 m d(-1). The sinking flux of the branched GDGTs decreased with increasing depth, but the rate of decrease was much smaller than those of other compounds. The preservation efficiency of branched GDGTs was 3.5-6.4% of surface inputs at the water-sediment interface, which is much higher than those of isoprenoid GDGTs (1.0-1.3%) and other compounds. The branched and isoprenoid tetraether (BIT) index values were extremely low (i.e. < 0.0015) in comparison with any other studies so far. The BIT values in the surface sediment were five times higher than those in sinking particles, which is attributed to the preferential preservation of branched GDGTs in oxic environments. (C) 2016 Elsevier Ltd. All rights reserved.
  • Stefanie Mueller, Mareike Schmidt, Annette Kossler, Christian Leipe, Tomohisa Irino, Masanobu Yamamoto, Hitoshi Yonenobu, Tomasz Goslar, Hirofumi Kato, Mayke Wagner, Andrzej W. Weber, Pavel E. Tarasov
    HOLOCENE 26 10 1646 - 1660 2016年10月 [査読有り][通常論文]
     
    Rebun Island with Hamanaka and Funadomari among the 43 documented archaeological sites and the environmental archive stored in the Lake Kushu sediment proves to be one of the key areas to study the interplay between ecology, climate and human activities. This paper focuses on the potential of palaeobotanical records from Rebun Island for improving the chronological control and understanding of late Quaternary climate changes and habitation environments of northern hunter-gatherers in the Hokkaido Region of Japan. A set of 57 radiocarbon dates of the RK12 core (Lake Kushu) demonstrates that it represents a continuous environmental archive covering the last c. 17,000years. The RK12 pollen record reflects distinct vegetation changes associated with the onset of the lateglacial warming about 15,000 cal. yr BP and the cold climate reversal after c. 13,000 cal. yr BP. The onset of the current Holocene interglacial after c. 11,700 cal. yr BP is marked by a major spread of trees. The middle Holocene (c. 8000-4000 cal. yr BP) is characterized by a major spread of deciduous oak in the vegetation cover reflecting a temperature increase. A decline of oak and spread of fir and pine is recorded at c. 2000 cal. yr BP. After c. 1100 cal. yr BP, arboreal pollen percentages decrease, possibly linked to intensified usage of wood during the Okhotsk and Ainu culture periods. The results of diatom analysis suggest marshy or deltaic environments at the RK12 coring site prior to c. 10,500 cal. yr BP and a brackish lagoon between c. 10,500 and 7000 cal. yr BP. A freshwater lake developed after 6500 cal. yr BP, likely reflecting sea level stabilization and formation of the sand bar separating the Kushu depression from the sea. Plant macrofossil analysis shows use of various wild plants and also domesticated barley during the Okhotsk and Ainu periods.
  • Suk-Hee Yoon, Jung-Hyun Kim, Hi-Il Yi, Masanobu Yamamoto, Jong-Ku Gal, Sujin Kang, Kyung-Hoon Shin
    CONTINENTAL SHELF RESEARCH 125 114 - 126 2016年08月 [査読有り][通常論文]
     
    We investigated the source, composition and reactivity of sedimentary organic carbon (OC) in a river dominated continental marginal sea, the eastern Yellow Sea. A multi-proxy approach was applied to 9 riverbank sediments and 69 marine surface sediments, combining bulk and molecular organic parameters. The riverbank sediments (n=9) have on average low C/N ratio (4.8 +/- 0.5) and enriched delta C-13(Toc) values (-21.5 +/- 0.6%) while the BIT index is on average 0.27. The sedimentary OC in the marine surface sediments appears to have a predominantly marine origin (on average C/N ratio=7.0 +/- 0.6 and delta C-13(TOC)=-21.9 +/- 0.5%, n=69) with minor contribution of continental (i.e. soil- and lake/river-derived) OC (on average BIT index=0.00 +/- 0.01, n=69). However, the Delta C-14 values were depleted (on average - 227 +/- 53%, n=8). Accordingly, our results highlight that fossil OC, potentially derived from erosion of sedimentary bedrocks in the catchment areas and/or human activities is being contributed to the sedimentary OC pool in the eastern Yellow Sea. More work is needed to better constrain the source, composition, and age of the organic material supplied to the eastern Yellow Sea, given the lack of biogeochemical data from the Korean rivers. (C) 2016 Elsevier Ltd. All rights reserved.
  • Masanobu Yamamoto, Daisuke Kobayashi
    DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 125 177 - 183 2016年03月 [査読有り][通常論文]
     
    This paper presents records of TEX86L- and U-37(K)-derived sea-surface temperatures (SSTs) from Ocean Drilling Program Site 882 in the subarctic North Pacific over the last 5.8 million years. The TEX86L-derived SST record shows a cooling trend from 17 degrees C at 3.6 Ma to 8 degrees C at 2.3 Ma. This cooling preceded the onset of extensive Northern Hemisphere glaciation (NHG) at 2.7 Ma, coinciding with the intensification of the East Asian winter monsoon, surface cooling in the North Atlantic, and the gradual development of NHG. The results of this study suggest that the reorganization of atmospheric circulations in the northern high latitudes from 3.6 to 2.3 Ma was associated with the early-stage development of the ice sheets and sea ice in the arctic and subarctic regions, inducing the cooling of the North Atlantic and the subarctic North Pacific and the intensification of the East Asian winter monsoon. (C) 2015 Elsevier Ltd. All rights reserved.
  • Yasuto Yamamoto, Taku Ajioka, Masanobu Yamamoto
    QUATERNARY INTERNATIONAL 397 380 - 391 2016年03月 [査読有り][通常論文]
     
    We investigated branched and isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) in surface soils and a paleosol sequence to understand the effects of environmental and postdepositional factors on branched GDGT composition in different soil types and to reconstruct the past changes in the mean annual air temperature (MAAT) in southwestern Japan during the last 15 ka. The estimated MAAT was overestimated by 6 degrees C and 2 degrees C when the global and regional soil calibrations were applied, respectively. Additionally, the estimated MAAT increased downward by a maximum of 4 degrees C in the upper 30 cm of the soil sequence. This is likely to reflect the addition of newly produced branched GDGTs in subsurface soils. The estimated MAATs in a paleosol sequence are thus similar to 10 degrees C and similar to 6 degrees C higher than those expected when the global and regional soil calibrations were applied, respectively, but the variation agrees with the Holocene variation in the MAAT estimated by the pollen assemblage. This indicates that the MBT'/CBT-derived MAAT is biased, but the variation reflects the past changes in MAAT. (C) 2014 Elsevier Ltd and INQUA. All rights reserved.
  • Keitaro Yamada, Keiji Takemura, Michinobu Kuwae, Ken Ikehara, Masanobu Yamamoto
    JOURNAL OF ASIAN EARTH SCIENCES 117 13 - 22 2016年03月 [査読有り][通常論文]
     
    Strike-slip basins are one of the most important accumulation spaces for sediment of terrigenous, biogenic, and volcanic origins, and generally include large amount of event deposits. Although these event deposits are important basin filling process, research on this topic, particularly the effects of event deposits, is insufficient. In this study, we discuss sedimentation features based on grain composition and other properties for ca. 3000 year periods in Beppu Bay, which is strike-slip basin located at the western end of an arc-bisecting dextral fault known as Median Tectonic Line (MTL) associated with the northwestward subduction of the Philippine Sea Plate. This sediment is composed of hemipelagic clay and coarser event layers of turbidites referred to as types A, B, and C; ash layers referred to as type D; and other referred to as type E. The turbidite event layers, which accounted for 92% of the total major event layer, with >1 cm thickness, consist of particles related to volcanism, including hydrothermal activity. The events control the regional filling rate and transportation of coarse and heavy volcaniclastic materials. In particular, type A, which accounted for 73% of the total major event layer thickness, is likely induced by earthquakes related to the MTL, according to its age. As a result, the basin filling processes are controlled mainly by tectonics related to the subduction of the Philippine Sea Plate. (C) 2015 Elsevier Ltd. All rights reserved.
  • Takeshi Fujii, Masanobu Yamamoto, Ryo Nakano, Takuya Nirazawa, Yu Rong, Shuang-Lin Dong, Yukio Ishikawa
    JOURNAL OF INSECT PHYSIOLOGY 82 109 - 113 2015年11月 
    The majority of moth species utilize compounds derived from de novo synthesized fatty acids as their sex pheromones (type I). In contrast, species belonging to two recently diverged moth families, Arctiidae and Geometridae, utilize alkenes and their epoxides, which are derived from dietary essential fatty acids (EFAs), as their sex pheromones (type II). In the latter species, EFAs are considered to be converted into alkenes, often after chain elongation, in specialized cells called oenocytes. These alkenes are transported through the hemolymph to the pheromone gland, from which they are secreted with or without further modifications. We confirmed that the appearance of EFA-derived alkenes in the hemolymph was closely associated with the completion of pheromone gland formation in an arctiid moth Eilema japonica. Analyses of the hemolymph of several moth species utilizing type-I sex pheromones demonstrated the occurrence of (ZZZ)-3,6,9-tricosatriene (T23), a typical type-II component, in the hemolymph of a noctuid Mamestra brassicae and two crambids Ostrinia furnacalis and Ostrinia scapulalis. Our results demonstrated that moths utilizing type-I pheromones have the ability to synthesize type-II sex pheromones, and suggested that recently diverged groups of moths may have secondarily exploited EFA-derived alkenes as sex pheromones. (C) 2015 Elsevier Ltd. All rights reserved.
  • Yaeko Igarashi, Masanobu Yamamoto, Atsushi Noda, Ken Ikehara, Hajime Katayama
    MARINE GEOLOGY 368 58 - 65 2015年10月 [査読有り][通常論文]
     
    Hokkaido Island in northern japan is located in a cool temperate to boreal climate zone influenced by summer monsoons and typhoons during summer-autumn, while its eastern area is influenced by the subarctic Oyashio Current. Palynomorph (pollen and spores) distribution was investigated in surface sediments from the shelf and slope (40-2300 m water depth) in the offshore area of Tokachi Plain, central-eastern Hokkaido Island. The objective of this study was to examine the source, transportation, and deposition of palynomorphs in marine environments. The majority of palynomorphs were transported from the Tokachi coastal plain by both strong local winds from the mountain areas during the spring-summer and the floods caused by heavy monsoon and typhoon rainfall. Approximately 10% of all palynomorphs were transported from both southwest and west areas by the wind. Palynomorph transportation by the Oyashio Current could not be discriminated because the same vegetation is present in Hokkaido and the islands in upper streams of the Oyashio Current. The total grain abundance was dependent on water depth. High concentrations were observed at depths of 700-1500 m, which is a region associated with high levels of fine silt and clay, suggesting that the transportation and deposition of palynomorphs are controlled by their grain sizes. This study supported a strong correlation between the distribution of sediments and the concentration of palynomorphs. (C) 2015 Elsevier B.V. All rights reserved.
  • Yu-Hyeon Park, Masanobu Yamamoto, Seung-Il Nam, Tomohiro Irina, Leonid Polyak, Naomi Harada, Kana Nagashima, Boo-Keun Khim, Kazuhisa Chikita, Sei-Ichi Saitoh
    MARINE CHEMISTRY 165 10 - 24 2014年10月 [査読有り][通常論文]
     
    Isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGTs) and grain size distribution were investigated in surface sediments from the western Arctic Ocean including the Chukchi Sea and the adjacent northern Bering Sea to understand their source and transportation in the Arctic region and test environmental proxies derived from the GDGT composition. Coarse sediments such as sand and silty sand are distributed in the Yukon and Mackenzie River estuaries, the northern Bering Sea near Bering Strait, and some areas of the outer shelf of the Bering Sea. In the Chukchi Sea, silt, grading from sandy to clayey silt, predominates and becomes finer northward towards the deep Arctic Ocean Isoprenoid GDGTs are abundant on the outer shelf and slope of the Chukchi Sea and the upper slope of the Bering Sea. The higher abundances are attributed to a combination of higher prodnction of marine Archaea (Thaumarchaeota) at the shelf edge, redeposition of GDGT-carrying fine particles, and better preservation of GDGTs at sites with higher sedimentation rates. The TEX86 - and TEX86L-derived temperatures are not consistent with sea surface temperatures in the study area, with unrealistically high TEX86 - and TEX86L-derived temperatures in samples north of 73 degrees N probably biased by factors other than temperature. Branched GDGTs are abundant on the Chukchi shelf and in the Yukon and Mackenzie River estuaries. At the shelf edge of the Chukchi Sea, both branched and isoprenoid GDGTs are abundant, indicating common concentration processes such as sediment redeposition and efficient preservation at sites with high sedimentation rates. Sediments from the western Arctic Ocean north of 75 degrees N, the Yukon and Mackenzie River estuaries, and the Yukon River have higher cyclization ratio of branched tetraethers (CBT) than sediments from the Chukchi and Bering Seas, suggesting two different sources of branched GDGTs inferred as soil and marine bacteria. (C) 2014 Elsevier B.V. All rights reserved.
  • Fukashi Ohira, Masanobu Yamamoto, Keiji Takemura, Akira Hayashida
    QUATERNARY INTERNATIONAL 349 59 - 67 2014年10月 [査読有り][通常論文]
     
    To understand the responses of terrestrial vegetation in central Japan to global climate changes, we generated a record of lignin composition from core BIW08-B in Lake Biwa, central Japan, during the last 147,000 years by TMAHepyrolysiseGC/MS. Lignin abundance was intermittently elevated and associated with a high ratio of cinnamyl (C) to vanillyl (V) phenols (C/V ratio) of lignin, suggesting episodic inflows of herbaceous plant-derived organic matter into Lake Biwa. The largest inflow occurred during the last deglaciation. Variation in the ratio of syringyl (S) to vanillyl (V) phenols (S/V ratio), which is a contribution index of angiosperms against gymnosperms, showed a precession-like cycle, was consistent with a pollen record from Lake Biwa, and showed a pattern similar to the S/V record from an offshore marine site in the northwestern Pacific. The variation reflected the regional replacement of cool-temperate deciduous broadleaf forests, subalpine conifer forests, and Japanese cedar forests in central Japan caused by the repetition of warmer, dry and cooler, wet climates on a precession cycle. (c) 2013 Elsevier Ltd and INQUA. All rights reserved.
  • Taku Ajioka, Masanobu Yamamoto, Jun Murase
    ORGANIC GEOCHEMISTRY 73 70 - 82 2014年08月 [査読有り][通常論文]
     
    We investigated glycerol dialkyl glycerol tetraether (GDGT) distributions in soils and river/lake sediments in the Lake Biwa basin of central Japan, in order to understand their source and fate in a terrigenous environment. GDGTs in 16 soil profiles exhibited significant depth variation at each site. Branched (br) GDGTs were generally most abundant in the surface litter layer (O layer) and decreased with depth, while the maximum concentration of crenarcheol appeared in the upper soil layer (A layer), above the maximum concentration of the other isoprenoid (iso) GDGTs. The finding is consistent with different microbial communities contributing to the GDGT pools of the subsurface soil sequences. The relationship between methylation index of br tetraethers/cyclization ratio of br tetraethers (MBT0/CBT) and pH/mean annual air temperature (MAAT) for Lake Biwa basin soils was consistent with that found in global soil samples. The GDGT distributions in surface sediments from the lake differed from those in soils and river sediments in the watershed, suggesting that the GDGTs were produced in the lake water rather than supplied from the land. The CBT for lake sediments from different water depths corresponded to water pH values. We thus infer that the CBT for lake sediments may serve as proxy for lake water pH and can be applied to paleoenvironmental reconstruction. (C) 2014 Elsevier Ltd. All rights reserved.
  • Da-Cheng Lin, Min-Te Chen, Masanobu Yamamoto, Yusuke Yokoyama
    QUATERNARY INTERNATIONAL 333 207 - 215 2014年05月 [査読有り][通常論文]
     
    Millennial-scale climate changes are well-expressed in Greenland ice core and North Atlantic marine records. The timing and the amplitude of the millennial-scale changes outside Greenland and the North Atlantic are poorly known, mainly due to the lack of high quality climatic archives with precise constraints of numerical dating. Here, we report a new, high-resolution AMS C-14 dated alkenone sea surface temperature (SST) record of the last 45,000 years from a marine sediment core (MD972146) retrieved from the northern South China Sea (SCS). The SST record shows millennial-scale oscillations during the intervals of since the Last Glacial Maximum (LGM, similar to 21,000 BP) to the present, and similar to 34-45 ka, that are nearly in-phase with those from the Northern Hemisphere (NH). SST oscillations during similar to 21-34 ka do not match well with the NH patterns, implying that a dominance of "non-NH" mechanisms may have governed the SST changes outside the NH high latitudes during the particular time interval. The "non-NH" climatic pattern during similar to 21-34 ka has been only reported from a SST record from the Okinawa Trough sediments (MD012404) and a grain size record from Chinese loess sequences (Gulang), but not from the other SCS records which had been investigated using lower resolution sampling and age dating. (C) 2014 Elsevier Ltd and INQUA. All rights reserved.
  • Hasrizal Bin Shaari, Masanobu Yamamoto, Tomohisa Irino, Tadamichi Oba
    JOURNAL OF OCEANOGRAPHY 70 1 25 - 34 2014年02月 [査読有り][通常論文]
     
    Isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) and alkenones were analyzed in sediment samples retrieved from Ocean Drilling Program Site 1241 covering the last 150000 years to understand the hydrological evolution of the eastern Pacific warm pool (EPWP). GDGT and alkenone concentrations showed higher values in marine isotope stage (MIS)-2 and MIS-6, which suggests the enhancement of primary production at glacial maxima. - and -derived temperature depicted different temperature evolutions. -derived temperature was marked by small variation during the glacial-interglacial cycles, whereas -derived temperature showed pronounced glacial-interglacial variation that was similar to Mg/Ca-derived temperature records from nearby cores in the EPWP. Given that enhanced primary production during glacial maxima suggests nutricline shoaling, unchanged over glacial-interglacial cycles can be interpreted as the shift of alkenone production depth. seems not to be influenced by glacial-interglacial changes in nutricline depths, recording an integrated temperature in surface and thermocline water. The shallow nutricline in the EPWP during glacial maxima most likely reflected the intense formation of Antarctic intermediate water.
  • T. Ajioka, M. Yamamoto, K. Takemura, A. Hayashida, H. Kitagawa
    CLIMATE OF THE PAST 10 5 1843 - 1855 2014年 [査読有り][通常論文]
     
    We generated a 280 000 yr record of water pH and temperature in Lake Biwa, central Japan, by analysing the methylation index (MBT') and cyclisation ratio (CBT) of branched tetraethers in sediments from piston and bore-hole cores. Our aim was to understand the responses of precipitation and air temperature in central Japan to the East Asian monsoon variability on orbital timescales. Because the water pH in Lake Biwa is determined by phosphorus and alkali cation inputs, the record of water pH should indicate the changes in precipitation and temperature in central Japan. Comparison with a pollen assemblage in a Lake Biwa core suggests that lake water pH was determined by summer temperature in the low-eccentricity period before 55 ka, while it was determined by summer precipitation in the high-eccentricity period after 55 ka. From 130 to 55 ka, the variation in lake pH (summer precipitation) lagged behind that in summer temperature by several thousand years. This perspective is consistent with the conclusions of previous studies (Igarashi and Oba, 2006; Yamamoto, 2009), in that the temperature variation preceded the precipitation variation in central Japan.
  • Masanobu Yamamoto, Fukashi Ohira, Fujio Kumon
    GEOCHEMICAL JOURNAL 48 2 207 - 217 2014年 [査読有り][通常論文]
     
    We generated a record of lignin and fatty acid compositions from the TK-2004 core in Takano Basin, central Japan, during 39-162 ka by TMAH-thermochemolysis-GC/MS. We tested lignin and fatty acid compositions in the sediments of a small lake (1.88 km(2) watershed) as a paleovegetation proxy to understand the responses of terrestrial vegetation in central Japan to global climate change. Variation in terrestrial organic carbon contents estimated by C/N and Sigma 8 was parallel to the total organic content (TOC) variation, suggesting that the inflow of terrestrial organic matter was a major factor determining the TOC. The ratio of mid-chain C-20-C-24 n-fatty acids to short-chain C-14-C-18 n-fatty acids (MFA/SFA ratio) and the ratio of cinnamyl to vanillyl phenols (C/V ratio) of lignin gradually increased from mid-MIS 6 to early MIS 3. The increase in both parameters suggested increase in the contribution of submerged and floating plants as the flats were expanded in the lake margin. The ratio of syringyl to vanillyl phenols (S/V ratio) corresponded to the pollen vegetation index. This correspondence indicated that the S/V ratio reflected the relative abundance of angiosperms to gymnosperms in the Takano Basin. The consistency of the S/V ratio at the site of core TKN-2004 and the other two locations suggests that the S/V ratio in a small basin is a robust proxy for terrestrial vegetation on a regional scale.
  • Ajioka, T, Yamamoto, M, Takemura, K, Hayashida, A, Kitagawa, H
    Climate of the Past 9 2777 - 2788 2014年 [査読有り][通常論文]
  • Gang Li, Hisao Ando, Hitoshi Hasegawa, Masanobu Yamamoto, Takashi Hasegawa, Tohru Ohta, Noriko Hasebe, Niiden Ichinnorov
    ALCHERINGA 38 3 305 - 316 2014年 [査読有り][通常論文]
     
    Two spinicaudatan species, Triglypta eedemtensis Li sp. nov. and Dundgobiestheria mandalgobiensis Li gen. et sp. nov., are described on the basis of scanning electron microscopy (SEM) imaging of newly collected specimens from paper-thin laminated black shale of the Eedemt Formation exposed at the Eedemt locality in the Khootiin Khotgor coal mine region of Dundgobi Province in southeast Mongolia. Triglypta eedemtensis is ornamented mainly with puncta and a punctate fine reticulum; radial lirae occur only on two or three growth bands near the venter. The small spinicaudatan Triglypta is a common component of the Middle Jurassic Euestheria ziliujingensis fauna and Sinokontikia fauna, and is a typical taxon in the Middle Jurassic lacustrine sequences of northern Hebei and the Junggar and Turpan basins of the Xinjiang Autonomous District of China; however, it does not occur in stratigraphically higher units elsewhere. Therefore, the age of the Eedemt Formation should be considered Middle Jurassic rather than Early Cretaceous. The Eedemt Formation is much older than the Early Cretaceous Shinekhudag Formation in the Shine Khudag area of southeast Mongolia.
  • Stefan Schouten, Ellen C. Hopmans, Antoni Rosell-Mele, Ann Pearson, Pierre Adam, Thorsten Bauersachs, Edouard Bard, Stefano M. Bernasconi, Thomas S. Bianchi, Jochen J. Brocks, Laura Truxal Carlson, Isla S. Castaneda, Sylvie Derenne, Ayca Dogrul Selver, Koushik Dutta, Timothy Eglinton, Celine Fosse, Valier Galy, Kliti Grice, Kai-Uwe Hinrichs, Yongsong Huang, Arnaud Huguet, Carme Huguet, Sarah Hurley, Anitra Ingalls, Guodong Jia, Brendan Keely, Chris Knappy, Miyuki Kondo, Srinath Krishnan, Sara Lincoln, Julius Lipp, Kai Mangelsdorf, Alfredo Martinez-Garcia, Guillemette Menot, Anchelique Mets, Gesine Mollenhauer, Naohiko Ohkouchi, Jort Ossebaar, Mark Pagani, Richard D. Pancost, Emma J. Pearson, Francien Peterse, Gert-Jan Reichart, Philippe Schaeffer, Gaby Schmitt, Lorenz Schwark, Sunita R. Shah, Richard W. Smith, Rienk H. Smittenberg, Roger E. Summons, Yoshinori Takano, Helen M. Talbot, Kyle W. R. Taylor, Rafael Tarozo, Masao Uchida, Bart E. van Dongen, Benjamin A. S. Van Mooy, Jinxiang Wang, Courtney Warren, Johan W. H. Weijers, Josef P. Werne, Martijn Woltering, Shucheng Xie, Masanobu Yamamoto, Huan Yang, Chuanlun L. Zhang, Yige Zhang, Meixun Zhao, Jaap S. Sinninghe Damste
    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 14 12 5263 - 5285 2013年12月 [査読有り][通常論文]
     
    Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility +/- 3-4 degrees C when translated to temperature) but a large spread in BIT measurements (reproducibility +/- 0.41 on a scale of 0-1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0 degrees C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the true (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.
  • Hasrizal bin Shaari, Masanobu Yamamoto, Tomohisa Irino
    PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY 386 8 - 15 2013年09月 [査読有り][通常論文]
     
    TEX86H- and U-37'(K)-derived paleotemperatures, and isoprenoid glycerol dialkyl glycerol tetraether (GDGT), and alkenone concentrations were examined for ODP Site 1239 in the eastern equatorial Pacific (EEP) for the last 430 kyr. We propose that the difference between TE86H- and U-37'(K)-derived temperatures (Delta T) and the abundance ratio of GDGTs to alkenones (GDGT/alkenone ratio) are potential upwelling indices which show consistent results with other upwelling indices. The Delta T and GDGT/alkenone ratio were maximal during the last five deglaciations, suggesting intensified upwelling. The intensification of upwelling in the EEP coincided with those at the Peru margin and in the Southern Ocean. This coincidence suggests that the reorganization of the Southern Hemisphere atmospheric circulation induced the intensification of the subtropical high-pressure cell, causing stronger southeast trade winds along the west coast of South America and the southern westerlies over the Southern Ocean, enhancing upwelling in both regions. (C) 2013 Elsevier B.V. All rights reserved.
  • Masanobu Yamamoto, Midori Kishizaki, Tadamichi Oba, Hodaka Kawahata
    Journal of Asian Earth Sciences 69 86 - 92 2013年06月05日 [査読有り][通常論文]
     
    We generated a 42,000-year record of TEX86 (TEX86L and TEX86H) from core MD98-2195 to better understand changes in the hydrology of the East China Sea (ECS) in the last glacial period. The TEX86-derived temperature showed an intense cooling in the last glacial period, whereas U37K-derived spring sea surface temperature (SST) and foraminiferal Mg/Ca-derived summer SST showed a much smaller-scale cooling. The difference between the TEX86- and Mg/Ca-derived temperatures was around 14°C from 19 to 16ka and abruptly decreased to around 5°C from 16 to 13ka. This suggests a strong winter cooling of the surface water during the last glacial period. TEX86-, U37K'-, and Mg/Ca-derived temperatures were lowest at 18-17ka, implying that the formation of cold water was maximized during that period. These results show that the cold water mass developed in the northern Okinawa Trough during the last glacial and the Kuroshio branch did not fully enter the northern margin of the Okinawa Trough. © 2012 Elsevier Ltd.
  • Michinobu Kuwae, Masanobu Yamamoto, Ken Ikehara, Tomohisa Irino, Keiji Takemura, Takuya Sagawa, Tatsuhiko Sakamoto, Minoru Ikehara, Hidetaka Takeoka
    Journal of Asian Earth Sciences 69 133 - 148 2013年06月05日 [査読有り][通常論文]
     
    We analyzed the lithology, magnetic susceptibility, bulk density, and X-ray radiographs of 14 sediment cores (1-9m long) from Beppu Bay in the western Seto Inland Sea, Japan, to establish the late Holocene stratigraphy in the deepest part of the bay and to develop an age-depth model for the sediments there. The cores contained 18 thick (major event) high-density layers (16 turbidites and two volcanic ash > 1cm thick), and both lithological observations and density variations in the hemipelagic mud that is dominant in the cores revealed a further 55 thin (minor event) high-density layers (< 1cm thick). Analyses of color properties and opal and sand contents of the hemipelagic mud defined nine lithological units. After stratigraphic correlation of the event layers among cores, we projected 14C dates onto a single composite core. Forty-two AMS 14C dates from bivalve mollusk shells were used to construct a wiggle-matching-based age-depth model for the late Holocene sequence and to determine the local reservoir effect (ΔR). The age-depth model showed a sedimentation rate of 0.23-0.30cm/yr for a 7.8m-long composite core and an age of ∼2800calyr BP at the base. Wiggle-matching provided ΔR values of 115-155yr for late Holocene bivalve samples from Beppu Bay, which is consistent with previous estimates reported from coastal areas near the Kuroshio Front. Comparison of wiggle-matching-derived ages of thick turbidites with the ages of historical earthquakes showed differences within ±25yr. Our study demonstrated that wiggle matching with optimal fitting based on either the weighted least-squares or maximum likelihood method can minimize the effect of scatter of age data due to reworking and burrowing of bivalves and thus improve the accuracy of age-depth models. © 2012 Elsevier Ltd.
  • Da-Cheng Lin, Min-Te Chen, Masanobu Yamamoto, Yusuke Yokoyama
    JOURNAL OF ASIAN EARTH SCIENCES 69 93 - 101 2013年06月 [査読有り][通常論文]
     
    High sedimentation rate (SR) cores retrieved from the South China Sea (SCS) form the basis for studying the marine components of millennial-scale Asian monsoon (AM) variability and for comparison with the AM reconstructions from cave records on land (e.g. Dongge and Hulu). However, carefully correlating the SCS sedimentary records to the cave records that are precisely dated by U/Th methods with resolution of decadal-scale, has not been completed: Such a correlation is essential when comparing AM influences expressed over land and sea, but requires a construction of marine AMS C-14 age models that are precise enough to be compared to the cave U/Th age models. For the purpose of establishing such a correlation, this study presents new data from intensive AMS C-14 dated marine cores retrieved from the northern SCS (MD972146, MD972148). The discrepancy of marine and cave delta O-18 record for the interval of similar to 18-30 ka might be due to the change of marine C-14 reservoir age in SCS surface water during the glacial period, and to the change in interhemispheric dominance of the AM systems. With the new AMS C-14 dating on MD972146 and MD972148, we examined the millennial-scale records of planktonic foraminifer delta O-18 and carbonate contents of MD972146, MD97248, and SONNE 17940-2 and compared those records with Dongge-Hulu delta O-18 record of the past 30 ka. Our results show that in the intervals corresponding to the high-latitude Northern Hemisphere (NH) Younger Dryas (YD) and Heinrich I event (HI), the AMS C-14 dated millennial-scale oscillations show relatively heavy delta O-18 and low carbonate contents, but H2 and H3 are in the opposite direction. Our results indicate the complexity for the marine cores which were used in interpreting the millennial-scale AM variability. (c) 2012 Elsevier Ltd. All rights reserved.
  • M. Yamamoto, H. Sai, M. -T. Chen, M. Zhao
    CLIMATE OF THE PAST 9 6 2777 - 2788 2013年 [査読有り][通常論文]
     
    The response of the East Asian winter monsoon variability to orbital forcing is still unclear, and hypotheses are controversial. We present a 150 000 yr record of sea surface temperature difference (Delta SST) between the South China Sea and other Western Pacific Warm Pool regions as a proxy for the intensity of the Asian winter monsoon, because the winter cooling of the South China Sea is caused by the cooling of surface water at the northern margin and the southward advection of cooled water due to winter monsoon winds. The Delta SST showed dominant precession cycles during the past 150 000 yr. The Delta SST varies at precessional band and supports the hypothesis that monsoon is regulated by insolation changes at low-latitudes (Kutzbach, 1981), but contradicts previous suggestions based on marine and loess records that eccentricity controls variability on glacial-interglacial timescales. Maximum winter monsoon intensity corresponds to the May perihelion at precessional band, which is not fully consistent with the Kutzbach model of maximum winter monsoon at the June perihelion. Variation in the East Asian winter monsoon was anti-phased with the Indian summer monsoon, suggesting a linkage of dynamics between these two monsoon systems on an orbital timescale.
  • Masanobu Yamamoto, Akifumi Shimamoto, Tatsuo Fukuhara, Yuichiro Tanaka, Joji Ishizaka
    ORGANIC GEOCHEMISTRY 53 52 - 62 2012年12月 [査読有り][通常論文]
     
    Seasonal and depth variation in the flux of glycerol dialkyl glycerol tetraethers (GDGTs) and TEX86 (TEX86H and TEX86L) values in sinking particles was examined by conducting a 21 month time-series sediment trap experiment at a mooring station (WCT-2, 39 degrees N, 147 degrees E) in the mid-latitude NW Pacific. The aim was to understand the sinking process of GDGTs in the water column and the preservation of the TEX86 signal in the water column and sediment surface. In the shallow trap, the sinking flux of GDGTs showed maxima from May 1998 to February 1999. The maximal peaks in sinking flux corresponded to peaks in the sinking flux of organic carbon, opal and lithogenic material. GDGT concentration in the total fine fraction and the caldarchaeol/crenarchaeol ratio at three depths (ca. 1300-4800 m) varied synchronously, implying rapid vertical transport of GDGTs to deeper water with a sinking velocity >260 m day(-1) below ca. 1300 m. The changes in TEX86-based temperature were different from those in contemporary sea surface temperature (SST). The former was lower than the SST from May to December and corresponded to the temperature at the thermocline, whereas it was higher than the SST from December to May. The annual average sinking flux of the GDGTs decreased with depth. The GDGT half-depth, the depth range over which half of the GDGT is lost, was calculated to be 3108-3349 m, implying that GDGTs were well preserved during sinking. The flux-weighted average TEX86-based temperature was constant with depth and corresponded roughly to mean annual SST. The findings support a previous hypothesis that the GDGTs produced in surface water are preferentially delivered to the deeper water column via grazing and repackaging in larger particles. The constant TEX86 at different depths indicates that it was not affected by degradation in the water column. The preservation efficiency of GDGTs was 1.0-1.3% at the water-sediment interface. Despite significant GDGT degradation, there was a small difference in TEX86 values between sinking particles and surface sediment. (C) 2012 Elsevier Ltd. All rights reserved.
  • Takahiro Nakanishi, Masanobu Yamamoto, Tomohisa Irino, Ryuji Tada
    JOURNAL OF OCEANOGRAPHY 68 6 959 - 970 2012年12月 [査読有り][通常論文]
     
    We investigated the spatial distribution of glycerol dialkyl glycerol tetraethers (GDGTs), alkenones, and polyunsaturated fatty acids in particulate organic matter collected at four sites along a depth transect from the continental shelf to the Okinawa Trough in the East China Sea during the spring bloom in 2008. The maximum alkenone concentration appeared in the top 25 m at all sites and the values were consistent with in situ water temperatures in the depth interval, suggesting that the alkenones were produced mainly in surface water. At the slope and shelf sites, GDGTs in the water column showed a concentration maximum at 74-99 m depth, and the agreed with in situ water temperatures, suggesting the in situ production of GDGTs in the depth interval. The low-salinity surface water above 20 m depth was characterized by low GDGT concentrations and low -based temperatures, suggesting either the production of GDGTs in winter season or the lateral advection of GDGTs by an eastward current. At the slope and Okinawa Trough sites, TEX86-based temperatures were nearly constant in the water column deeper than 300 m and corresponded to temperatures at the surface and near-surface waters rather than in situ temperatures. This observation is consistent with a hypothesis that Thaumarchaeota cells produced in surface waters are delivered to deeper water and also indicates that the residence time of suspended GDGTs in the deep-water column is large enough to mix the GDGTs produced in different seasons.
  • Takahiro Nakanishi, Masanobu Yamamoto, Ryuji Tada, Hirokuni Oda
    JOURNAL OF QUATERNARY SCIENCE 27 9 956 - 963 2012年12月 [査読有り][通常論文]
     
    The East China Sea (ECS) responds to changes in the strength of the Kuroshio and East Asian monsoon activity. Multidecadal resolution records of the palaeotemperature indices TEX86H and U-37(K ') from core KY07-04 PC-1 show that the hydrology of the ECS responded to variability in the East Asian winter monsoon. Unlike Mg/Ca-derived sea surface temperatures, which show neither warming nor cooling trends during the Holocene, the TEX86H record showed a general warming trend at a rate of 0.2 degrees C ka-1. This warming was attributable to shrinkage of the Yellow Sea Central Cold Water and/or weaker winter cooling of the surface water. The TEX86H record indicated a centennial-scale variability with an similar to 1 degrees C amplitude superimposed on the warming trend that reflected changes in the East Asian winter monsoon and/or the Kuroshio. Temperature minima appeared at ca. 3.0, 4.7, 6.2, 7.9 and 9.0 ka, and spectral analysis of the last 7 ka revealed significant peaks with periodicities of approximately 210, 250, and 440 years that were close to those observed in solar radiation. The reconstructed winter monsoon variability is consistent with Chinese documentary records for the last two millennia. Copyright (c) 2012 John Wiley & Sons, Ltd.
  • Liang-Jian Shiau, Min-Te Chen, Chih-An Huh, Masanobu Yamamoto, Yusuke Yokoyama
    JOURNAL OF QUATERNARY SCIENCE 27 9 911 - 920 2012年12月 [査読有り][通常論文]
     
    The Australian summer monsoon (ASM) is primarily a synoptic feature determined by the differential thermal response to solar insolation between the Australian continent and the western Pacific warm pool (WPWP) in austral summer. Little is known about the process involved in driving long-term ASM variability. Here we present a 180 ka record of terrestrial fluxes into offshore southeastern Papua New Guinea (PNG), a prevailing monsoon area in the WPWP. Terrestrial fluxes were estimated by a 230Th-normalized method, indicating higher terrestrial inputs into the ocean during glacial stages. We argue that the higher terrestrial fluxes are mainly fluvial, which in turn are linked to stronger ASM precipitation on land, though the increased terrestrial flux could possibly also be due to the lowstand or glacial erosion of mountain glaciers. Cross-spectral analysis indicates that the ASM precipitation maxima are controlled by local summer insolation maxima, WPWP sea-surface temperature minima and East Asian winter monsoon (EAWM) maxima in precession frequency bands (21 ka-1). This result suggests that the 21 ka components of the ASM in the past 180 ka are not only insolation driven but also a dynamic component strengthened by cross-hemispheric pressure gradient resulted from the precession maxima forcing. Copyright (c) 2012 John Wiley & Sons, Ltd.
  • Mitchell Lyle, Linda Heusser, Christina Ravelo, Masanobu Yamamoto, John Barron, Noah S. Diffenbaugh, Timothy Herbert, Dyke Andreasen
    SCIENCE 337 6102 1629 - 1633 2012年09月 [査読有り][通常論文]
     
    The water cycle in the western United States changed dramatically over glacial cycles. In the past 20,000 years, higher precipitation caused desert lakes to form which have since dried out. Higher glacial precipitation has been hypothesized to result from a southward shift of Pacific winter storm tracks. We compared Pacific Ocean data to lake levels from the interior west and found that Great Basin lake high stands are older than coastal wet periods at the same latitude. Westerly storms were not the source of high precipitation. Instead, air masses from the tropical Pacific were transported northward, bringing more precipitation into the Great Basin when coastal California was still dry. The changing climate during the deglaciation altered precipitation source regions and strongly affected the regional water cycle.
  • 野間 恵理子, 入野 智久, Shaari Hasrizal, 山本 正伸
    日本地質学会学術大会講演要旨 2012 214 - 214 一般社団法人 日本地質学会 2012年
  • Yaeko Igarashi, Masanobu Yamamoto, Ken Ikehara
    JOURNAL OF ASIAN EARTH SCIENCES 40 6 1102 - 1110 2011年04月 [査読有り][通常論文]
     
    Vegetation and climate since the LGM in eastern Hokkaido were investigated based on a pollen record from marine core GH02-1030 from off Tokachi in the northwestern Pacific. We also examined pollen spectra in surface samples from Sakhalin to compare and understand the climatic conditions of Hokkaido during the last glacial period. Vegetation in the Tokachi region in the LGM (22-17 ka) was an open boreal forest dominated by Picea and Larix. During the last deglaciation (17-10 ka), vegetation was characterized by abundant Betula. In the Kenbuchi Basin, central Hokkaido, a remarkable increase of Lath and Pinus occurred in the LGM and the last deglaciation, which was assigned as the "Kenbuchi Stadial." Comparison of climatic data between the core GH02-1030 and that of Kenbuchi Basin demonstrates that variations in temperature and precipitation were larger in inland Hokkaido than in the maritime area of the Pacific coast. During the LGM in the Tokachi region, the August mean temperature was about 5 degrees C lower, and annual precipitation was about 40% lower than today. In the Kenbuchi Basin, central Hokkaido, the August mean temperature was about 8 degrees C lower, and annual precipitation was half that of today. During the last deglaciation, August mean temperatures were about 3 degrees C lower, and annual precipitation was about 30% lower than today in the Tokachi region. In the Kenbuchi Basin, August mean temperatures were about 5-8 degrees C lower, and annual precipitation was about 40-60% lower than today. Cold ocean water and a strengthened summer monsoon after 15 ka may have resulted in the formation of advection fogs, reduced summer temperatures, and a decrease in the seasonal temperature difference in the Tokachi district, which established favorable maritime conditions for Betula forests. (C) 2010 Elsevier Ltd. All rights reserved.
  • Tomoya Shintani, Masanobu Yamamoto, Min-Te Chen
    JOURNAL OF ASIAN EARTH SCIENCES 40 6 1221 - 1229 2011年04月 [査読有り][通常論文]
     
    We have generated a record of TEX86 (TEX86H)-derived sea surface temperatures (SSTs) over the last 28 ka for core MD97-2146 from the northern South China Sea (SCS). The TEX86H-derived temperature of a core-top sample corresponds to the SSTs in warmer seasons. The SST record shows a drop during the Oldest Dryas period, an abrupt rise at the onset of the Bolling-Allered period, a plateau across the Younger Dryas period, and an abrupt rise at the beginning of the Holocene. The glacial-interglacial contrast in TEX86H-derived temperature is almost the same as that in foraminiferal Mg/Ca ratio-derived temperature, but it is larger than those in U-37(K') and transfer function-derived temperatures. Possible interpretations are: (1) the seasonal shift of glycerol dialkyl glycerol tetraether (GDGT) production, (2) the overestimation of temperature change by TEX86H, and (3) the underestimation of temperature change by U-37(K'), and transfer function approaches. The similar variation in TEX86H-derived temperature at the study site and Chinese stalagmite 8180 during the last deglaciation suggests that changes in TEX86H-derived temperature in this period reflected atmospheric and oceanic reorganization on a millennial timescale. The long-chain n-alkanes are mainly of higher plant origin before similar to 14 ka and a mixture of higher plant and lithic origins after 14 ka; the abundance ratio of long-chain to short-chain n-fatty acids decreases at similar to 15 ka, suggesting a drastic change in sediment sources at similar to 14-15 ka. We attribute the higher content of fresh higher plant n-alkanes and long-chain n-fatty acids before similar to 14-15 ka to enhanced aeolian transportation and/or arid environments. Increased precipitation likely due to intensified summer monsoon after similar to 14-15 ka enhanced the erosion of sedimentary rocks and increased the contribution of lithic n-alkanes. (C) 2010 Elsevier Ltd. All rights reserved.
  • 小林 大祐, 山本 正伸
    日本地球化学会年会要旨集 58 23 - 23 日本地球化学会 2011年 
    本研究では、北太平洋亜寒帯域に位置するOcean Drilling Program Site 882の海底堆積物コアから採取された試料から、北太平洋亜寒帯域の過去580万年間の水温を復元した．水温の復元はTEX86古水温推定法(Shouten et al., 2002)を用いて行った．TEX86古水温は過去580万年間で-1℃から12℃の水温の変動を示した．TEX86古水温は100万年スケールの長周期変動に10万年スケールの短周期変動が重複したような変動を示した．
  • 長谷川 精, 安藤 寿男, 長谷川 卓, 太田 亨, 山本 正伸, 長谷部 徳子, Li Gang, Ichinnorov Niiden
    日本地球化学会年会要旨集 58 22 - 22 日本地球化学会 2011年 
    本研究はモンゴルのアプチアン期湖成層（シネフダグ層）を対象に，OAE1a時の陸域環境変動の解明を試みている．シネフダグ湖成層は，頁岩とドロマイトのリズミカルな互層（数10cm，数m，10~20 mサイクル）からなる．本研究では，その堆積メカニズムを解明するため，堆積相解析，鉱物組成分析，有機地球化学分析を行った．C/N比およびロックエバル分析の結果，シネフダグ湖成層の有機物は主に湖内の藻類に由来することが示唆された．またドロマイト層準では藻類やバクテリアが卓越するのに対し，頁岩層準では藻類に加えて湖岸からの高等植物起源有機物の流入も寄与していたことが示唆された．これらの結果と堆積相解析から，シネフダグ湖成層に見られる頁岩とドロマイトのリズミカルな互層（数千年，数万年，数10万年サイクルに相当）は，地球軌道要素の変動に起因した湖水位の変動，すなわち湿潤－乾燥といった気候変動に対応している可能性が示唆された．
  • 味岡 拓, 山本 正伸, 竹村 恵二, 林田 明
    日本地球化学会年会要旨集 58 11 - 11 日本地球化学会 2011年 
    琵琶湖集水域土壌および琵琶湖堆積物コア(BIW07-6)中の分枝GDGTを分析した．琵琶湖集水域土壌から得られたMBT/CBTと土壌pH/年平均気温(MAAT)との関係は全球土壌データセットから得られた関係と異なっており，琵琶湖集水域土壌には温度応答の異なるバクテリアが生息する可能性や季節性の影響が考えられる．また，土壌と表層堆積物中の分枝GDGT組成は明らかに異なっており，琵琶湖内で分枝GDGTが生産されていることを強く示唆している．琵琶湖表層水および底層での分枝GDGTの生成が考えられるが，CBT-pHは底層での生成を支持していた．BIW07-6から復元されたMBT/CBT温度は花粉記録と調和的であり，分枝GDGT組成の古温度プロキシとしての有効性が示された．
  • 入野 智久, 山本 正伸
    日本地球化学会年会要旨集 58 110 - 110 日本地球化学会 2011年 
    新生代における山地の隆起と気候変動の関係を検討するために、ペルー沖ODP Site 1237コアの鉱物・化学組成を検討する。特に堆積物コアに含まれる中央アンデス起源と思われる火山灰の寄与と砕屑物および海洋炭酸塩組成の分析を通して、この地域の長い時間スケールの火山活動と気候・海洋変動との間の関係を解析することを目的とした。コアは前期漸新世までおよんでおり、4 Maまでは95%以上が炭酸塩の軟泥である。砕屑鉱物組成が検討できた2.5 Ma以降では、火山活動の活発化に遅れて乾燥化が起こることが示唆された。
  • ビンシャリ ハスリザル, 山本 正伸, 入野 智久
    日本地球化学会年会要旨集 58 144 - 144 日本地球化学会 2011年 
    ODPサイト1237, 1239, 1241の堆積物に含まれるグリセロール・ジアルキル・グリセロール・テトラエーテルを分析することにより過去１５万年間のTEX86古水温変動を求め，水温の緯度勾配の変化を検討した．
  • 山本 康人, 味岡 拓, 山本 正伸, 竹村 恵二
    日本地球化学会年会要旨集 58 10 - 10 日本地球化学会 2011年 
    ブランチ型グリセロール・ジアルキル・グリセロール・テトラエーテル(ブランチGDGT )の組成に基づくMBT/CBT指標は、近年過去の気温を復元する手法として提唱された。 本研究では、このブランチGDGTを用いて、大分県大野川の河口で採取したボーリングコアと大野川上流の久住山山腹の露頭土壌から、過去10000年間の古気温復元を行った。
  • 山本 正伸, 中西 貴大, 岸崎 翠, 入野 智久, 多田 隆治, 小田 啓邦
    日本地球化学会年会要旨集 58 142 - 142 日本地球化学会 2011年 
    北部南シナ海の沖縄トラフ北部男女海盆から採取されたMD98-2195コア，KY07-04 PC-1コア，KY07-04 PL-1コアのTEX86水温変動に基づき，過去４万年間の冬季モンスーン変動を議論した．
  • Park Yu-Hyeon, 山本 正伸, Polyak Leonid
    日本地球化学会年会要旨集 58 111 - 111 日本地球化学会 2011年 
    The Arctic Ocean plays an important role in global climate changes by positive feedbacks involving changes in sea-ice coverage, thermohaline circulation, and boreal vegetation (Miller et al., 2010). The Pacific sector of in the Arctic Ocean is sensitive to global climate changes and the sea ice coverage responds to changes in temperature and the inflow of extent of input of the Pacific water. The Alaska margin in the western Arctic receives considerable amount of sediments from the Yukon River and smaller rivers in northern Alaska (Ortiz et al., 2009).We investigated molecular distributions of branched and isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) as terrestrial and marine biomarkers, respectively, to explore possibilities of paleo-temperature estimation and to estimate GDGT-based temperature, the contribution of soil organic matter and the soil pH. We discuss whether GDGT composition in marine sediment reflect sea surface temperature (SST) and mean annual air temperatures (MAAT) and, the changes in the provenance of terrestrial OM in Chukchi- Alaska margin sediments since the early Holocene. The SST and MAAT estimated using a global calibration equation proposed by Kim et al. (2010) and Weijers et al. (2008), respectively, in the core-top sediments show much higher values than modern annual temperature measured by instruments in northern Alaska. The reconstructed temperature must be biased toward a warmer direction. The each global calibration by Kim et al. (2010) and Weijers et al. (2008) does not fully cover polar region and the temperature estimate was done by extrapolation. We thus need future effort to create a calibration equation based on the data set in polar region to improve temperature estimates. The changing patterns of paleo-temperatures in both cores show a similar variation. The TEX86L-derived SST indicates that it was cooler in the middle Holocene than in the early and late Holocene. Both cores show a warming in air temperature and an increase in soil pH over the past 10 ka. BIT value shows a decreasing pattern on both cores over the past 10 ka. In particular, parameters from 9.5 to 7 ka show significant variation. The climatic oscillation from 9.5 to 7 ka is consistent with rapid climate changes observed globally and an area near northern Alaska margin (Brachfeld et al., 2009). These trends suggest that 1) the warming in northern Alaska began since 10 ka, 2) the contribution of marine OM became larger 3) changes in soil pH may have reflected changes in the provenance of soil.
  • Hisao Ando, Hitoshi Hasegawa, Takashi Hasegawa, Toru Ohta, Masanobu Yamamoto, Noriko Hasebe, Gang Li, Niiden Ichinnorovu
    地質学雑誌 117 11 XI - XII The Geological Society of Japan 2011年 [査読有り][通常論文]
  • Sze Ling Ho, Masanobu Yamamoto, Gesine Mollenhauer, Masao Minagawa
    ORGANIC GEOCHEMISTRY 42 1 94 - 99 2011年01月 [査読有り][通常論文]
     
    TEX86L and TEX86H are organic palaeothermometers based on the lipids of Group 1 Crenarchaeota, recently proposed as a modified version of the original TEX86 index, but with significantly improved geographical coverage. Since few data from the global core top calibration are from the Pacific, this study was carried out to assess whether the global core top calibration is regionally biased or not. The result of principal components analysis of the fractional abundance of GDGTs, an analysis of variance (ANOVA) and the comparison of the residuals of TEX86H derived sea surface temperature (SST) estimates of the Pacific subset with that of the global data set suggest that the Pacific subset has a similar TEX86H-SST relationship with the global data set. However, the regression line through the Pacific data and an ANOVA on the residuals of TEX86L derived SST estimates suggest otherwise. The contradictory findings are likely to stem from the large scatter in the Pacific TEX86L values in the mid temperature range. While regionality does not seem to exert a strong bias on TEX86L and TEX86H calibration, it appears that there is a strong need to resolve the large scatter in the global data set, especially in the mid and high latitudes, in order to improve the calibration for a better SST estimation. (C) 2010 Elsevier Ltd. All rights reserved.
  • Liang-Jian Shiau, Min-Te Chen, Steven C. Clemens, Chih-An Huh, Masanobu Yamamoto, Yusuke Yokoyama
    GEOPHYSICAL RESEARCH LETTERS 38 8 1 - 6 2011年01月 [査読有り][通常論文]
     
    Abrupt climate changes such as Dansgaard-Oeschger (D-O) cycles and Heinrich events (HEs) are prevalent during the last glacial cycle and widely documented in Northern Hemisphere (NH) high latitudes. However, in tropical regions and the Southern Hemisphere (SH) far fewer records exist, especially in the western Pacific warm pool (WPWP) area. Here, we present a 50k archive of U-37(k') sea surface temperature (SST), planktic foraminifera oxygen isotopes, and terrestrial input indicators including branched and isoprenoid tetraether (BIT) biomarkers, Th-232 activity, and non-biogenic sediment components recorded in core MD052928 from the WPWP (near southern Papua New Guinea, PNG). The planktic foraminifer oxygen isotopes in the core show millennial-scale changes indicating fresher seawater during the NH cold periods (i.e., Heinrich Events, HEs) and suggesting hydrological changes that are most likely linked to the strength of the boreal winter Asian-Australian monsoon (AAM). Our observations are corroborated by evidence from the same core that indicates increased terrestrial input caused by higher precipitation on land and more river runoff from southern PNG during the cold periods. Consistent with other nearby hydrological records from land, our study indicates persistent millennial-scale hydrological changes within the past 50k in the western tropical Pacific and Southeast Asia. The timing of the millennial-scale changes appears to have been determined by the latitudinal displacement of the Intertropical Convergence Zone (ITCZ) that reflects a history of heat transport from the tropics and WPWP. Citation: Shiau, L.-J., M.-T. Chen, S.C. Clemens, C.-A. Huh, M. Yamamoto, and Y. Yokoyama (2011), Warm pool hydrological and terrestrial variability near southern Papua New Guinea over the past 50k, Geophys. Res. Lett., 38, L00F01, doi: 10.1029/2010GL045309.
  • Hikaru Takahara, Yaeko Igarashi, Ryoma Hayashi, Fujio Kumon, Ping-Mei Liew, Masanobu Yamamoto, Sayuri Kawai, Tadamichi Oba, Tomohisa Irino
    QUATERNARY SCIENCE REVIEWS 29 21-22 2900 - 2917 2010年10月 [査読有り][通常論文]
     
    High-resolution pollen records from Taiwan, Japan and Sakhalin document regional vegetation changes during Dansgaard-Oeschger (D-O) cycles during the last glacial. During the period from the cold phase (GS 18/19) to warm phase (D-O 19), the biome shift from temperate conifer forest to cold/cool conifer forest in Japan and from subtropical forest to temperate deciduous/conifer forest in Taiwan. The vegetation in D-O 17, cool mixed forest in central Japan, temperate deciduous broadleaf forest in western Japan and subtropical forest in Taiwan, indicates warm condition but not wet in all area. These vegetation changes lead to biome shift from MIS (Marine Isotope Stage) 4 to MIS 3. The abundance of Cryptomeria japonica and Fagus crenata in D-O 12 and D-O 8 indicates wet conditions brought by the strong summer monsoon through the Islands and high snowfall brought by the inflow of the Tsushima Warm Current into the Sea of Japan. The registration of other D-O warming events in MIS 3, although reflected by shifts in the abundance of key species, is not sufficient to produce changes in biomes. Development of cold deciduous forest in HS (Heinrich events) 1 in Sakhalin, Hokkaido and central Japan was conspicuous and was much larger than that in YD. Vegetation response in YD was small scale and within the same biome in the East Asian Islands. In D-O 1 at the termination of the last glacial, the same taxa that developed in the early Holocene, cold evergreen needleleaf trees in northern region, temperate deciduous broadleaf trees in central and western Japan, and warm-temperate evergreen trees in Taiwan, increased. (C) 2009 Elsevier Ltd. All rights reserved.
  • Kashiwaya K, Ochiai S, Sumino G, Tsukamoto T, Szyniszewska A, Yamamoto M, Sakaguchi A, Hasebe N, Sakai H, Watanabe T, Kawai T
    Quaternary International 219 1-2 178 - 187 2010年06月 [査読有り][通常論文]
     
    A provisional age model is proposed for HDP-04 sedimentary records from Lake Hovsgol on the Mongolian Plateau of a middle-latitude zone during the Brunhes epoch. The model is established on the basis of two procedures; first age model (linear age model) with some dates (C-14, (238)U-(234)U-(230)Th and paleomagnetic events) and a second age model with auto-orbital tuning for the first age model. The age model suggests that the MIS-1 to MIS-7 interval is included in the upper part and the MIS-11 to MIS-19 is included in the lower part, in addition to the missing part of about 100 ky. The glacial interglacial cycle is most clearly presented by aridity (water level change): three Milankovitch parameters (precession, obliquity and eccentricity) are detected in most datasets. Grain size is, occasionally, large in glacial intervals and small in interglacial ones in the upper part (above the hiatus), possibly related to material mobility with water level change (change in erosion area) and wind availability. A deep depression (cold stage comparable to glacial periods), corresponded to an insolation minimum, is detected at about the MIS-5d in records, indicating that this region is highly sensitive to solar insolation. Another depression found during the MIS-11 interval also corresponded to a small insolation minimum, showing that the interval was not a simple prolonged interglacial period. (C) 2010 Elsevier Ltd and INQUA. All rights reserved.
  • Saki Harii, Masanobu Yamamoto, Ove Hoegh-Guldberg
    MARINE BIOLOGY 157 6 1215 - 1224 2010年06月 [査読有り][通常論文]
     
    The long-distance dispersal of larvae provides important linkages between populations of reef-building corals and is a critical part of coral biology. Some coral planulae have symbiotic dinoflagellates (Symbiodinium spp.) that probably provide energy in addition to the lipids provisioned within the egg. However, our understanding of the influence of symbionts on the energy metabolism and survivorship of planulae remains limited. This study examines the relative roles of symbiotic dinoflagellate photosynthesis and stored lipid content in the survivorship of the developing stages of the corals Pocillopora damicornis and Montipora digitata. We found that survivorship decreased under dark conditions (i.e. no photosynthetic activity) for P. damicornis and M. digitata at 31 and 22 days after release/spawning, respectively. The lipid content of P. damicornis and M. digitata planulae showed a significant decrease, at a higher rate, under dark conditions, when compared with light conditions. When converted to energy equivalents, the available energy provided by the depletion of lipids could account for 41.9 and 84.7% of larval metabolism for P. damicornis (by day 31) and 38.4 and 90.1% for M. digitata (by day 21) under light and dark conditions, respectively. This finding indicates that not all energy requirements of the larvae are met by lipids: energy is also sourced from the photosynthetic activities of the symbiotic dinoflagellates within these larvae, especially under light conditions. In addition, the amounts of three main lipid classes (wax esters, triglycerides, and phospholipids) decreased throughout the experiment in the planulae of both species, with the wax ester content decreasing more rapidly under dark conditions than under light conditions. The observations that the planulae of both species derive considerable amounts of energy from wax esters, and that symbiotic dinoflagellates enable larvae to use their stores at lower rates, suggested that symbiotic dinoflagellates have the potential to extend larval life under light conditions.
  • 山本 正伸, 関 陽児, 内藤 一樹
    地質調査研究報告 61 9 325 - 336 National Institute of Advanced Industrial Science and Technology, Geological Survey of Japan 2010年 [査読有り][通常論文]
     
    新潟県・山形県県境金丸ウラン鉱床地区において掘削採取された中新統釜杭層コア試料についてケロジェンとバイオマーカーの分析を行い，ウラン濃集層(U=25−100 ppm; Th=23−42 ppm) に含まれる有機物の特徴を明らかにした．<br> ビジュアルケロジェン分析により，有機炭素量の高い試料では，木質ケロジェンが多く，有機炭素量が低い試料では，無定型ケロジェンが多いことが示された．熱分解ガスクロマトグラフ質量分析により，熱分解物は主にアルキル芳香族炭化水素（アルキルベンゼン，アルキルインデン，アルキルナフタレンなど）とn- アルカンからなり，鎖状イソプレノイドアルカン，n- アルケン，n- 脂肪酸を微量伴うことが示された．これらの多くは，陸上高等植物に由来するIII型ケロジェンに特徴的な化合物である．これらの結果から，本分析試料中の無定型ケロジェンは，木質ケロジェンと同様に，陸上高等植物起源であり，強く酸化分解を被り，材の形状を失い，無定型化したものであると考えられる．<br> 炭質頁岩中のマツ花粉の色度（TAI）は約2.6であった．またロックエバル分析によるTmax値は441 &deg;C−444 &deg;Cであった．これらから，試料の熟成度が初期カタジェネシス期段階に達したことが示された．また，熱分解生成物中に，ホパンの異性体のうち，続成作用により生成する異性体が多いことからも，カタジェネシス期段階の熟成度が指示される．<br> 掘削井において，ウラン濃度とウラン／トリウム比のピークは岩相境界に対応しているが，有機炭素量ピークよりも2メートル浅い．この有機炭素ピークとウラン濃度ピークが一致しないことから，有機物がウラン濃集には関与していないことが示唆される．地下水位が高かった時代に，岩相境界において酸化還元電位の勾配が生じ，そこでウランが濃縮した可能性が考えられる．
  • Masanobu Yamamoto
    JOURNAL OF QUATERNARY SCIENCE 24 8 836 - 847 2009年12月 [査読有り][通常論文]
     
    We present a palaeoceanographic perspective of the North Pacific during the last two glacial cycles based on U-37(K')-derived palaeotemperature records of IMAGES Core MD01-2421 off the coast of central Japan and cores from the Ocean Drilling Program (ODP) Sites 1014 and 1016 off the coast of California. The sea surface temperature (SST) differences between ODP Sites 1014 and 1016 (Delta SSTnortheastern (Pacific (NEP)) = SSTODP1014 - SSTODP1016) indicate the intensity of the California Current. Comparison of Delta SSTNEP and the SST from Core MD01-2421 revealed anti-phase variation; high Delta SSTNEP (indicating weakening of the California Current) corresponded to low SST at the Japan margin (indicating the southward displacement of the north-western Pacific subarctic boundary and weakening of the Kuroshio Extension), and vice versa. This finding suggests that the intensity of the North Pacific subtropical gyre circulation has varied in response to precessional forcing and that this response has been linked with changes in tropical ocean-atmosphere interactions. In the precessional cycle, the SST variation derived from Core MD01-2421 lags ca. 2.5-4 ka behind the variations shown by Hulu and Sanbao stalagmite delta O-18 records and by the pollen temperature index from Core MD01-2421, suggesting out-of-phase variations of the North Pacific subtropical gyre circulation and the East Asian summer monsoon. These findings indicate that the behaviour of interactions between tropical ocean-atmosphere dynamics and the East Asian summer monsoon may have varied in response to the precessional cycle. Copyright (C) 2009 John Wiley & Sons, Ltd.
  • Masaki Inagaki, Masanobu Yamamoto, Yaeko Igarashi, Ken Ikehara
    JOURNAL OF OCEANOGRAPHY 65 6 847 - 858 2009年12月 [査読有り][通常論文]
     
    We investigated marine and terrestrial environmental changes at the northern Japan margin in the northwestern Pacific during the last 23,000 years by analyzing biomarkers (alkenones, long-chain n-alkanes, long-chain n-fatty acids, and lignin-derived materials) in Core GH02-1030. The U-37(K') derived temperature in the last glacial maximum (LGM) centered at 21 ka was similar to 10 degrees C, which was 2 degrees C lower than the core-top temperature (similar to 12 degrees C). This small temperature drop does not agree with pollen evidence of a large air temperature drop (more than VC) in the Tokachi area. This disagreement might be attributed to a bias of U-37(K')-derived temperature within 2.5 degrees C by a seasonal shift in alkenone production. The U-37(K')-derived temperature was significantly low during the last deglaciation. Because this cooling was significant in the Kuroshio-Oyashio transition zone, the temperature drops are attributable to the southward displacement of the Kuroshio-Oyashio boundary. Abundant lignin-derived materials, long-chain n-alkanes and long-chain n-fatty acids indicate a higher contribution of terrigenous organic matter from 17 to 12 ka. This phenomenon might have resulted from an enhanced coastal erosion of terrestrial soils due to marine transgression and/or an efficient inflow of higher plant debris to river waters from 17 to 12 ka.
  • 天羽 美紀, 萩野 恭子, 鈴木 徳行, 堀口 健雄, 山本 正伸
    Researches in organic geochemistry 25 0 91 - 94 日本有機地球化学会 2009年11月30日 [査読有り][通常論文]
  • 山本 正伸
    化石 0 86 45 - 58 日本古生物学会 2009年10月16日 [査読有り][通常論文]
     
    We present a palaeoceanographic perspective of the North Pacific during the last two glacial cycles based on U^<K'>_<37>-derived palaeotemperature records from Japan and California margins. At the Japan margin, the sea surface temperature (SST) in the Kuroshio-Oyashio transition has varied in response to precessional cycle. At the California margin, SST has varied in response to ice volume changes, but the SST difference between inshore and offshore sites (ΔSST_<northeastern Pacific (NEP)>=SST_<ODP1014>-SST_<ODP1016>) has responded to precessional cycle. Comparison of ΔSST_<NEP> and the SST...
  • Kazuho Fujine, Ryuji Tada, Masanobu Yamamoto
    Palaeogeography, Palaeoclimatology, Palaeoecology 280 3-4 350 - 360 2009年09月15日 [査読有り][通常論文]
     
    Paleo-sea-surface temperatures in the northeastern- and southeastern-parts of the Japan Sea were reconstructed for the last 160 kyr using alkenone temperatures (UK′37-temperatures). UK′37-temperatures at two sites show distinct glacial-interglacial changes during the last 160 kyr except for the interval corresponding to middle MIS 3 to MIS 2. On orbital-timescales, UK′37-temperature tends to be high during MIS 5e, MIS 5c, and MIS 5a, which coincides with the intervals of stronger East Asian summer monsoon activity. The amplitude of temperature fluctuations in the Japan Sea is significantly higher than those in the neighboring seas. We suggest that the SST variation was amplified by the increasing source water (Kuroshio water) temperature and the changes in the volume transport of the Tsushima Warm Current (TWC) and/or the north-south oscillation of the sub-polar front position within the Japan Sea. Millennial-scale temperature fluctuations in the Japan Sea show that the temperature at the northern site was higher than that at the southern site during warmer periods of MIS 5, which is called "temperature reversal." By analogy with modern oceanography, the temperature reversal could reflect the enhanced volume transport of the TWC and the spatial relationship between the studied site and the branches of the TWC, which is an essential factor in north-south temperature reversal around the eastern Japan Sea. Temperature drops were found at 114 ka, 111 ka, 93 ka, 87 ka, and 77 ka in MIS 5. Those events were associated with an increase in organic carbon and alkenone contents and can be correlated with the abundance peaks of ice-rafted debris (IRD) at Site GH05-1208 in the northern Japan Sea, suggesting that the surface water was cooled by enhanced mixing and consequent upwelling in a stronger winter monsoon regime. © 2009 Elsevier B.V. All rights reserved.
  • Masanobu Yamamoto, Leonid Polyak
    GLOBAL AND PLANETARY CHANGE 68 1-2 30 - 37 2009年07月 [査読有り][通常論文]
     
    Hydrocarbons and glycerol dialkyl glycerol tetraethers (GDGTs) were analyzed in Late Pleistocene sediments of Core HLY0503-08JPC collected at the Mendeleev Ridge during the Healy-Oden Trans Arctic Expedition 2005 (HOTRAX'05) to investigate environmental changes in the western Arctic Ocean during the last full glacial cycle, ca. 130 kyr. Variations in long-chain n-alkane and GDGT concentrations correspond to alternated color banding, brown (interglacial/interstadial) and grayish (glacial/stadial) layers. Grayish layers are characterized by abundant higher-plant n-alkanes and branched GDGTs, implying larger contribution of terrestrial plant and soil organic matter (OM) in glacial environments, possibly due to the deposition of fine-grained products of glacial erosion in the Amerasian basin. Lithic n-alkanes derived from mature OM show pronounced peaks, which can be classified into six types presumably indicative of various sediment sources. Some peaks are correlated to events of iceberg discharge and freshwater outbursts from proglacial lakes of the Eurasian and, possibly, Laurentide ice sheets, suggesting that other peaks may correspond to similar events. (C) 2009 Elsevier B.V. All rights reserved.
  • Dai Isono, Masanobu Yamamoto, Tomohisa Irino, Tadamichi Oba, Masafumi Murayama, Toshio Nakamura, Hodaka Kawahata
    GEOLOGY 37 7 591 - 594 2009年07月 [査読有り][通常論文]
     
    Suborbital climate variability during the last glacial period is suggested to have involved a 1500-year pacing cycle, but the expression and spatial distribution of the similar to 1500-year oscillation during interglacials remains unclear. We generated a multidecade resolution record of alkenone sea surface temperature (SST) in the northwestern Pacific off central Japan during the Holocene. The SST record showed centennial and millennial variability with an amplitude of similar to 1 degrees C throughout the entire Holocene. Spectral analysis for SST variation revealed a statistically significant peak with 1470-year periodicity. The SST variation partly correlated with the variations of ice-rafted hematite-stained grain content in North Atlantic sediments. These findings indicate that the mean latitude of the Kuroshio Extension has varied on a 1500-year cycle, and suggest that a climatic link exists between the North Pacific gyre system and the high-latitude North Atlantic thermohaline circulation. The regular pacing at 1500-year intervals seen throughout both the Holocene and the last glacial period suggests that the oscillation was a response to external forcing.
  • 山本 正伸, 五十嵐 八枝子, 大場 忠道
    第四紀研究 = The Quaternary research 48 3 195 - 206 2009年06月01日 [査読有り][通常論文]
  • Stefan Schouten, Ellen C. Hopmans, Jaap van der Meer, Anchelique Mets, Edouard Bard, Thomas S. Bianchi, Aaron Diefendorf, Marina Escala, Katharine H. Freeman, Yoshihiro Furukawa, Carme Huguet, Anitra Ingalls, Guillemette Menot-Combes, Alexandra J. Nederbragt, Masahiro Oba, Ann Pearson, Emma J. Pearson, Antoni Rosell-Mele, Philippe Schaeffer, Sunita R. Shah, Timothy M. Shanahan, Richard W. Smith, Rienk Smittenberg, Helen M. Talbot, Masao Uchida, Benjamin A. S. Van Mooy, Masanobu Yamamoto, Zhaohui Zhang, Jaap S. Sinninghe Damste
    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 10 2009年03月 [査読有り][通常論文]
     
    Recently, two new proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) were proposed, i.e., the TEX86 proxy for sea surface temperature reconstructions and the BIT index for reconstructing soil organic matter input to the ocean. In this study, fifteen laboratories participated in a round robin study of two sediment extracts with a range of TEX86 and BIT values to test the analytical reproducibility and repeatability in analyzing these proxies. For TEX86 the repeatability, indicating intralaboratory variation, was 0.028 and 0.017 for the two sediment extracts or +/- 1-2 degrees C when translated to temperature. The reproducibility, indicating among-laboratory variation, of TEX86 measurements was substantially higher, i.e., 0.050 and 0.067 or +/- 3-4 degrees C when translated to temperature. The latter values are higher than those obtained in round robin studies of Mg/Ca and U-37(k') paleothermometers, suggesting the need to primarily improve compatibility between labs. The repeatability of BIT measurements for the sediment with substantial amounts of soil organic matter input was relatively small, 0.029, but reproducibility was large, 0.410. This large variance could not be attributed to specific equipment used or a particular data treatment. We suggest that this may be caused by the large difference in the molecular weight in the GDGTs used in the BIT index, i.e., crenarchaeol versus the branched GDGTs. Potentially, this difference gives rise to variable responses in the different mass spectrometers used. Calibration using authentic standards is needed to establish compatibility between labs performing BIT measurements.
  • 公文 富士夫, 山本 正伸, 長橋 良隆, 青池 寛
    地質学雑誌 115 7 301 - 310 日本地質学会 2009年 [査読有り][招待有り]
     
    更新世後期の最終間氷期を中心に，日本列島陸域および周辺海域の古気候・古環境変動について研究の現状を紹介し，今後の課題を提起した．海洋域では海底コアの多面的な解析が，海洋環境と古気候変動の解明に大きく貢献している．陸域の研究では，長期間に及ぶ連続堆積物を用いた花粉分析や珪藻分析，有機炭素分析によって高精度の古気候復元が試みられている．海域と陸域を繋ぐ鍵として広域テフラの有用性は高く，琵琶湖堆積物や高野層に挟まれた指標テフラは古気候を時間・空間的に結合させて復元する鍵となる．特に指標テフラ密度の高い9〜10万年前の日本列島とその周辺は，有望な研究対象である．このように，テフラを介して海域と陸域の古気候・古環境情報を比較・統合して，高時間分解能で総合的な古気候復元を行うことは，日本列島の地域性を明らかにするとともに，汎世界的な気候変動のシステムを理解する上でも必要な貢献となる．
  • 山本 正伸
    地質学雑誌 115 7 325 - 332 The Geological Society of Japan 2009年 [査読有り][通常論文]
     
    過去2回の氷期サイクルにおける北太平洋中緯度域の古海洋環境変動を理解するために，茨城県鹿島沖MD01-2421コアとOcean Drilling Program 1014地点と1016地点の古水温解析から得られた知見を総合した．鹿島沖古水温は2.3万年の歳差運動周期に対応して変動し，氷床拡大期に高水温，縮小期に低水温を示した．カリフォルニア沖の1014地点と1016地点の古水温差（ΔSSTNEP）はカリフォルニア海流の強度を反映する．このΔSSTNEPは鹿島沖古水温と逆位相で変動しており，鹿島沖の水温が低いとき（黒潮続流・親潮境界の南下，黒潮続流の弱化），ΔSSTNEPは大きい（カリフォルニア海流の弱化）．これらのことから，北太平洋亜熱帯循環強度が歳差運動に応答して変動していることが示唆された．
  • 古水温変動からみた北太平洋の軌道強制力に対する応答
    山本正伸
    化石 86 44 - 57 2009年 [査読有り][通常論文]
  • 現生ハプト藻Emiliania huxleyi培養試料中の長鎖アルケンのGC/MS解析
    天羽美紀, 萩野恭子, 鈴木徳行, 堀口健雄, 山本正伸
    Researches in Organic Geochemistry 25 91 - 94 2009年 [査読有り][通常論文]
  • Tomoya Shintani, Masanobu Yamamoto, Min-Te Chen
    TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES 19 4 341 - 346 2008年08月 [査読有り][通常論文]
     
    We have generated a record of alkenone sea surface temperatures (SSTs) during the last 28000 years from Core MD97-2146 for the northern South China Sea (SCS). The SST record showed a typical pattern for change in the northern SCS SST. The SST during the LGM was similar to 25 degrees C, this decreased to similar to 24 degrees C to 17 ka, increased to similar to 25.5 degrees C to 14.5 ka, decreased again to similar to 24.5 degrees C to 11.8 ka, increased gradually to similar to 27 degrees C to 6 ka, and then increased more gradually to reach similar to 27.5 degrees C at present. The SST difference (Delta SSTNSCS = SSTMD97-2146 - SSTMD97-2141) between Cores MD97-2146 (the northern SCS; this study) and MD97-2141 (the Sulu Sea; Rosenthal et al. 2003) was used to characterize the SST changes in the northern SCS relative to changes in the adjacent WTP region. The Delta SSTNSCS decreased from 21 to 11.8 ka and increased after 11.8 ka, indicating slower warming of the northern SCS during the last deglaciation than that of the adjacent western tropical Pacific region. We infer that the slow warming of the northern SCS was principally a result of stronger winter monsoon during the last deglaciation and early Holocene. In addition, the cool water inflow through the Taiwan Strait after 13 ka and the warm water inflow through the Sunda Shelf after 11 ka could influence the SST in the northern SCS.
  • Liang-Jian Shiau, Pai-Sen Yu, Kuo-Yen Wei, Masanobu Yamamoto, Teh-Quei Lee, Ein-Fen Yu, Tien-Hsi Fang, Min-Te Chen
    TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES 19 4 363 - 376 2008年08月 [査読有り][通常論文]
     
    Variations in sea surface temperature (SST), productivity, and biogenic components such as total organic carbon (TOC), carbonate, and opal contents measured from IMAGES (International Marine Global Changes Study) core MD972142 provide information about long-term paleoceanographic changes during the past similar to 870000 years in the southeastern South China Sea (SCS). MD972142 U-37(k)-SSTs varied from 25 to 29 degrees C, paralleling the glacial to interglacial changes. MD972142 biogenic components show relatively high carbonate and opal, and low TOC contents in interglacial stages, and low carbonate and opal and high TOC contents in glacial stages, and these variations appear to be sensitive to regional terrestrial sediment input and productivity. Our analysis indicates that the MD972142 carbonate record is primarily controlled by terrestrial sediment inputs that are associated with sea level fluctuations during past glacial-interglacial stages. The TOC record reflects past glacial-interglacial changes in both monsoon-induced productivity and terrestrial organic matter input in the SCS. The TOC record exhibits several short-term peaks that are associated with lower U-37(k)-SSTs (especially in MIS 2 - 4, 10, 12), perhaps implying a much strengthened winter monsoon. The opal record shows relatively high content in most interglacial stages, which appears to be linked to increased summer monsoon upwelling or increased siliceous sediment input by more precipitation and river runoff during warm climate conditions. The TOC and opal contents both show long-term increasing trends since the mid-Brunhes, most noticeably from similar to 330 kya. The long-term trends observed in this study are most likely attributable to changes in SCS hydrography, productivity, and/or preservation in response to the increased strength of the East Asian monsoon system on possibly tectonic timescales.
  • 大庭 雅寛, 海保 邦夫, 掛川 武, 山本 正伸, 坂田 将, 古川 善博, 佐藤 誠悟
    日本地球化学会年会要旨集 55 21 - 21 日本地球化学会 2008年 
    古細菌由来のエーテル脂質を存在状態別に分析する手法を用いて、現世や地質時代の様々な試料について有機地球化学的研究を行った。1.暁新世/始新世の地球温暖化事変期（PETM）の堆積物中に含まれるテトラエーテル脂質を分析し、その濃度からTEX86を算出し、当時の海洋表層温度を推定した。その結果、PETM最初期に寒冷化を挟む２回の温暖化事変が起きたことが判明した。2.水曜海山の人口熱水孔から採取された沈殿物中のエーテル脂質を分析した結果、メタン菌に特徴的なエーテル脂質を検出した。他のバイオマーカー分析や鉱物分析などの結果も合わせて考察した結果、人工熱水孔内における微生物活動は多様性に富み、非常に活発であったことが判明した。
  • 市川 記央, 山本 正伸, 沖野 龍文, 加 三千宣, 杉本 隆成, 武岡 英隆
    日本地球化学会年会要旨集 55 413 - 413 日本地球化学会 2008年 
    地球環境の将来予測において，歴史時代の気温，降水量の変化を復元することが急務である。本研究では，別府湾から採取した海底コアに含まれるテトラエーテル脂質（GDGT）を分析することにより，過去1500年間の別府湾の水温の変動を復元した。復元した結果、西暦500年頃から1040年頃にかけては14～16℃前後の低い値を推移し、1050年頃から1400年頃の間では17℃前後の高温になり、1300年頃から2005年までは13℃～17℃まで範囲で激しく変動した。
  • 中西 貴大, 山本 正伸, 沖野 龍文, 入野 智久, 小田 啓邦, 横山 祐典, 松崎 浩之, 多田 隆治
    日本地球化学会年会要旨集 55 414 - 414 日本地球化学会 2008年 
    KY07-04航海により採取されたピストンコアPC-1とマルチプルコアPL-1を使用して、東シナ海北部の過去5000年間の表層水温を、バイオマーカー指標であるアルケノンに基づくUK37'とGDGT指標であるTEX86を用いて、40年から80年間隔と時間的解像度を高めて水温変動を復元した。アルケノン水温は過去5000年間に渡って23.5℃から24℃とほぼ一定の値を示した。一方、TEX86水温はアルケノン水温とは異なり、20.4℃から24.8℃の間で激しく変動した。両者の水温変動に違いが見られる理由として、それぞれの物質をつくる生物の生息時期や深度の違いが挙げられるが、GDGTをつくるクレンアーキオータの生息深度は不明である。これを解決する手段として、本年５月に行われたKT08-10航海にてコアサイト付近の表層から中層の海水を採取し、ろ過後脂質を抽出し、GDGTを分析した。発表では、海水より求めたTEX86水温の結果も合わせて報告する。
  • 山本 正伸, ポリアク レオニド
    日本地球化学会年会要旨集 55 420 - 420 日本地球化学会 2008年 
    将来の気候変化を予測する上で，気候変動における北極域の役割を解明することが急務である．過去の北極海の環境を復元することは北極域の役割を解明するためのひとつの手段であるが，北極海堆積物は一般に貧化石であり，微古生物学的手法による古環境研究に制約が多い．そこで，近年バイオマーカーを用いた古環境復元が期待されている．本研究では，HOTRAX'05（Healy-Oden Trans Arctic Expedition 2005）においてメンデレーフ海嶺から採取されたHLY0503-08JPCコアの後期第四紀堆積物のn-アルカンとテトラエーテル脂質（GDGT）を分析し，過去13万年間の北極海への陸起源有機物の流れ込みを復元した．長鎖n-アルカンとGDGTの濃度は堆積物の色調の変化（灰色層と褐色層の互層）に対応して周期的に変動する．氷期および亜氷期に堆積した灰色層は高等植物起源n-アルカン（高CPI）と分枝GDGTに富み，陸上植物と土壌有機物の寄与が大きい．これらの化合物は大陸氷床による陸上土壌の浸食によりもたらされたと考えられる．BIT指標は灰色層よりも褐色層で低く，間氷期および亜間氷期では北極海でのクレンアーキオータの生産が高まったことが示唆された．熟成有機物起源ｎ-アルカン（低CPI）はスパイクピーク状に高濃度を示し，過去13万年間の層準内で16本のピークが認められた．いくつかの高濃度ピークはユーラシア氷床崩壊と淡水流出のタイミングと一致しており，アイスダム湖の崩壊にともなう基盤岩の浸食により，熟成有機物がもたらされたと考えられる．この熟成有機物ピークは，北極域における氷床の崩壊史を復元する手がかりになりうる．
  • Masanobu Yamamoto, Tatsufumi Okino, Saiko Sugisaki, Tatsuhiko Sakamoto
    ORGANIC GEOCHEMISTRY 39 6 754 - 763 2008年 [査読有り][通常論文]
     
    Biomarkers in Late Pleistocene sediments collected from the Integrated Ocean Drilling Program (IODP)-Arctic Coring Expedition (ACEX) Hole M0004C (central Arctic Ocean) were investigated. The major biomarkers are long chain n-alkanes, n-fatty acids and n-alkan-1-ols, indicating fresh organic matter (OM) derived predominantly from higher plants. The dominance of terrestrial biomarkers is attributed to severe OM degradation caused by slow sedimentation in oxygen-rich benthic water and/or low primary production due to permanent sea ice coverage. Hopanes, representing thermally altered OM, tend to be abundant in samples with abundant ice rafted debris (IRD). An OM-rich dark grey layer deposited during marine isotope stage (MI5) 6 contains a significant amount of branched glycerol dialkyl glycerol tetraethers (branched GDGTs), suggesting ice erosion of organic-rich continental soil followed by transportation to the central Arctic by drifting ice. The labile-refractory index (i.e., the abundance ratio of long chain n-alkan-1-ols to the sum of long chain n-alkanes and long chain n-alkan-1-ols) decreases above the dark grey layer, indicating that the OM became more refractory. This change suggests that coverage of the source region by OM-rich soil decreased because of extensive glacial erosion during MIS-6. (C) 2008 Elsevier Ltd. All rights reserved.
  • Masanobu Yamamoto, Akifumi Shimamoto, Tatsuo Fukuhara, Hiroshi Naraoka, Yuichiro Tanaka, Akira Nishimura
    DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 54 9 1571 - 1592 2007年09月 [査読有り][通常論文]
     
    Seasonal and depth variations in alkenone flux and molecular and isotopic composition of sinking particles were examined using a 21 -month time-series sediment trap experiment at a mooring station WCT-2 (39 degrees N, 147 degrees E) in the midlatitude NW Pacific to assess the influences of seasonality, production depth, and degradation in the water column on the alkenone unsaturation index U(37)(K). Analysis of the underlying sediments was also conducted to evaluate the effects of alkenone degradation at the water-sediment interface on U(37)(K). Alkenone sinking flux and U(37)(K)-based temperature showed strong seasonal variability. Alkenone fluxes were higher from spring to fall than they were from fall to spring. During periods of high alkenone flux, the U(37)(K)-based temperatures were lower than the contemporary sea-surface temperatures (SSTs), suggesting alkenone production in a well-developed thermocline (shallower than 30 m). During low alkenone flux periods, the U(37)(K) -based temperatures were nearly constant and were higher than the contemporary SSTs. The nearly constant carbon isotopic ratios Of C37:2 and C38:2 alkenones suggest that alkenones produced in early fall were suspended in the surface water until sinking. The alkenone sinking flux decreased exponentially with increasing depth. The decreasing trend was enhanced during the periods of high alkenone flux, suggesting that fresh and labile particles sank from spring to fall, while old and stable particles sank from fall to spring. The 037, -based temperature usually increased with increasing depth. The preservation efficiency of alkenones was similar to 2.7-5.2% at the water-sediment interface. Despite the significant degradation of the alkenones, there was little difference in U(37)(K), levels between sinking particles and the surface sediment. (C) 2007 Elsevier Ltd. All rights reserved.
  • V. K. Banakar, T. Oba, A. R. Chodankar, T. Kuramoto, M. Yamamoto, M. Minagawa
    MARINE GEOLOGY 238 1-4 115 - 117 2007年03月 [査読有り][通常論文]
  • Masanobu Yamamoto, Masumi Yamamuro, Yuichiro Tanaka
    QUATERNARY SCIENCE REVIEWS 26 3-4 405 - 414 2007年02月 [査読有り][通常論文]
     
    Alkenone sea surface temperature (SST) records were generated from the Ocean Drilling Program's (ODP) Sites 1014 and 1016 to examine the response of the California Current System to global climate change during the last 136ka. The temperature differences between these sites (Delta SSTNEP = SSTODP10144-SSTODP1016) reflected the intensity of the California Current and varied between 0.4 and 6.1 degrees C. A high ASSTNEP (weaker California Current) was found for late marine isotope stage (MIS) 2 and early MIS 5e, while a low ASSTNEP (stronger California Current) was detected for mid-MIS 5e and MIS 1. Spectral analysis indicated that this variation pattern dominated 23- (precession) and 30-ka periods. Comparison of the Delta SSTNEP and SST based on data from core MD01-2421 at the Japan margin revealed anti-phase variation; the high ASSTNEP (weakening of the California Current) corresponded to the low SST at the Japan margin (the southward displacement of the NW Pacific subarctic boundary), and vice versa. This variation was synchronous with a model prediction of the tropical El Nino-Southern Oscillation behavior. These findings suggest that the intensity of the North Pacific High varied in response to precessional forcing, and also that the response has been linked with the changes of tropical ocean-atmosphere interactions. (c) 2007 Elsevier Ltd. All rights reserved.
  • Saki Harii, Kazuo Nadaoka, Masanobu Yamamoto, Kenji Iwao
    MARINE ECOLOGY PROGRESS SERIES 346 89 - 96 2007年 [査読有り][通常論文]
     
    Stored lipids in marine planktonic larvae play an important role in buoyancy and as an energy source and thus are a key to understanding the dispersal and settlement potential of larvae. However, little is known about lipid content and composition in different coral species or their temporal changes during larval dispersal. We examined the lipid content and composition of eggs and planula larvae of Acropora tenuis, a reef-building coral, and their temporal changes over the course of larval dispersal and settlement. The total content and composition of lipids in newly released planulae of the brooding corals A. brueggemanni, Pocillopora damicornis and Heliopora coerulea were also examined for comparison. A. tenuis eggs were positively buoyant; lipids accounted for 85% of their dry weight, but decreased to 50% of their dry weight within 30 d after spawning. Wax esters were a major component of lipids in the eggs; they decreased appreciably by 5 d after spawning and decreased thereafter. In contrast, the phospholipid content remained almost constant. The period of rapid decrease in wax esters occurred before settlement, suggesting that A. tenuis planulae consume mainly wax ester lipids as an energy source during the planktonic phase. In contrast, the lipid content of H. coerulea planulae, which have a shorter dispersal period, was lower (41% of dry weight) than that found in 5-d-old planulae of A. tenuis and newly released planulae of A. brueggemanni and P damicornis (> 58% of dry weight). Triacylglycerols in lipids were detected in P. damicornis and H. coerulea planulae, which settle quickly after release, but not in A. tenuis or A. brueggemanni, suggesting that triacylglycerols are used for rapid energy. These findings suggest that lipids are used for buoyancy and as an
  • Mark Pagani, Nikolai Pedentchouk, Matthew Huber, Appy Sluijs, Stefan Schouten, Henk Brinkhuis, Jaap S Sinninghe, Damsté, Gerald, R. Dickens, Jan Backman, Steve Clemens, Thomas Cronin, Frédérique Eynaud, Jérôme Gattacceca, Martin Jakobsson, Ric Jordan, Michael Kaminski, John King, Nalân Koc, Nahysa C. Martinez, Jens Matthiessen, David McInroy, Theodore C. Moore, Kathryn Moran, Matthew O'Regan, Jonaotaro Onodera, Heiko Pälike, Brice Rea, Domenico Rio, Tatsuhiko Sakamoto, David C. Smith, Ruediger Stein, Kristen E, K, St. John, Itsuki Suto, Noritoshi Suzuki, Kozo Takahashi, Mahito Watanabe, Masanobu Yamamoto
    Nature 443 598  2006年10月 [査読有り][通常論文]
  • Mark Pagani, Nikolai Pedentchouk, Matthew Huber, Appy Sluijs, Stefan Schouten, Henk Brinkhuis, Jaap S. Sinninghe Damste, Gerald R. Dickens
    NATURE 442 7103 671 - 675 2006年08月 [査読有り][通常論文]
     
    The Palaeocene/ Eocene thermal maximum represents a period of rapid, extreme global warming similar to 55 million years ago, superimposed on an already warm world(1-3). This warming is associated with a severe shoaling of the ocean calcite compensation depth(4) and a > 2.5 per mil negative carbon isotope excursion in marine and soil carbonates(1-4). Together these observations indicate a massive release of C-13- depleted carbon(4) and greenhouse- gas-induced warming. Recently, sediments were recovered from the central Arctic Ocean(5), providing the first opportunity to evaluate the environmental response at the North Pole at this time. Here we present stable hydrogen and carbon isotope measurements of terrestrial- plant- and aquatic- derived n- alkanes that record changes in hydrology, including surface water salinity and precipitation, and the global carbon cycle. Hydrogen isotope records are interpreted as documenting decreased rainout during moisture transport from lower latitudes and increased moisture delivery to the Arctic at the onset of the Palaeocene/ Eocene thermal maximum, consistent with predictions of poleward storm track migrations during global warming(6). The terrestrial- plant carbon isotope excursion ( about -4.5 to -6 per mil) is substantially larger than those of marine carbonates. Previously, this offset was explained by the physiological response of plants to increases in surface humidity(2). But this mechanism is not an effective explanation in this wet Arctic setting, leading us to hypothesize that the true magnitude of the excursion - and associated carbon input was greater than originally surmised. Greater carbon release and strong hydrological cycle feedbacks may help explain the maintenance of this unprecedented warmth.
  • Toshinori Ueshima, Masanobu Yamamoto, Tomohisa Irino, Tadamichi Oba, Masao Minagawa, Hisashi Narita, Masafumi Murayama
    GLOBAL AND PLANETARY CHANGE 53 1-2 21 - 28 2006年08月 [査読有り][通常論文]
     
    We have generated an oceanic primary production record from Core MD01-2421, off central Japan, in the western North Pacific, for the last 145,000 years, in order to examine how the Aleutian Low has responded to orbital-scale climate change. The variation of total organic carbon (TOC) was pronounced with a 41-ky periodicity. High TOC corresponds to a high angle of the Earth's obliquity. The variation of TOC was delayed behind the variation of obliquity by similar to 1 ky and preceded the variation of delta O-18 of benthic foraminifera Uvigerina by similar to 6 ky. The TOC varied inversely with Polar Circulation Index (Mayewski, P.A., Meeker, L.D., Twickler, M.S., Whitlow, S., Yang, Q., Lyons, B., Prentice, M., 1997. Major features and forcing of high-latitude northern hemisphere atmospheric circulation using a 110,000-year-long glaciochemical series. J. Geophys. Res. 102 (C 12), 26345-26366.). Since the primary production in the Kuroshio-Oyashio mixed zone is related to the intensity of the winter Aleutian Low, these correspondences imply that the intensity of the winter Aleutian Low has responded to the obliquity forcing by the atmospheric reorganization in the northern high latitudes. The winter Aleutian Low was stronger when the obliquity was large, implying that the lower insolation in winter presumably increased the temperature contrast between the land and the ocean, deepening the winter Aleutian Low. (C) 2006 Elsevier B.V. All rights reserved.
  • Tadamichi Oba, Tomohisa Irino, Masanobu Yamamoto, Masafumi Murayama, Akira Takamura, Kaori Aoki
    GLOBAL AND PLANETARY CHANGE 53 1-2 5 - 20 2006年08月 [査読有り][通常論文]
     
    Very large sea surface temperature (SST) fluctuations are expected in the northwest Pacific Ocean between glacial and interglacial periods due to possible latitudinal migrations of the steep SST front between the Oyashio and Kuroshio Currents. To reconstruct the SST changes for the past 144,000 years, we conducted high-resolution oxygen and carbon isotope analysis of both benthic and planktonic foraminifera from an IMAGES core off central Japan. Using a newly developed method [Oba, T., Murayama, M., 2004. Sea surface temperature and salinity changes in the northwest Pacific since the last glacial maximum. J. Quat. Sci. 19(4), 335-346] for the reconstruction of the SST, we have found very large (similar to 20 degrees C) SST fluctuations, with minimum SSTs of 3-4 degrees C during Marine Isotope Stage (MIS) 2 and the MIS 6/5e transition, and with peak SSTs of 22-23 degrees C during early MIS 1 and the MIS 5a/4, 5c/5b and 5c/5d transitions. The SSTs varied in parallel with changing carbon isotope differences between Globorotalia inflata and Globigerina bulloides, which suggests that the SST changes were primarily caused by the latitudinal displacements of the Kuroshio-Oyashio Currents. We have also found that northward shifts of the Kuroshio Current lagged up to several thousand years at these transitions. Strong correlation between the SST shifts and orbital forcing indicates that the latitudinal displacements of the Kuroshio-Oyashio Currents were influenced by summer insolation at 65 degrees N associated with ENSO-like climatic variability in the tropical Pacific. (C) 2006 Elsevier B.V. All rights reserved.
  • H Brinkhuis, S Schouten, ME Collinson, A Sluijs, JSS Damste, GR Dickens, M Huber, TM Cronin, J Onodera, K Takahashi, JP Bujak, R Stein, J van der Burgh, JS Eldrett, IC Harding, AF Lotter, F Sangiorgi, HVV Cittert, JW de Leeuw, J Matthiessen, J Backman, K Moran
    NATURE 441 7093 606 - 609 2006年06月 [査読有り][通常論文]
     
    It has been suggested, on the basis of modern hydrology and fully coupled palaeoclimate simulations, that the warm greenhouse conditions(1) that characterized the early Palaeogene period (55-45 Myr ago) probably induced an intensified hydrological cycle(2) with precipitation exceeding evaporation at high latitudes(3). Little field evidence, however, has been available to constrain oceanic conditions in the Arctic during this period. Here we analyse Palaeogene sediments obtained during the Arctic Coring Expedition, showing that large quantities of the free-floating fern Azolla grew and reproduced in the Arctic Ocean by the onset of the middle Eocene epoch (similar to 50 Myr ago). The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an similar to 800,000-year interval. The abundant remains of Azolla that characterize basal middle Eocene marine deposits of all Nordic seas(4-7) probably represent transported assemblages resulting from freshwater spills from the Arctic Ocean that reached as far south as the North Sea(8). The termination of the Azolla phase in the Arctic coincides with a local sea surface temperature rise from similar to 10 degrees C to 13 degrees C, pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans. We suggest that onset and termination of the Azolla phase depended on the degree of oceanic exchange between Arctic Ocean and adjacent seas.
  • A Sluijs, S Schouten, M Pagani, M Woltering, H Brinkhuis, JSS Damste, GR Dickens, M Huber, GJ Reichart, R Stein, J Matthiessen, LJ Lourens, N Pedentchouk, J Backman, K Moran
    NATURE 441 7093 610 - 613 2006年06月 [査読有り][通常論文]
     
    The Palaeocene/Eocene thermal maximum, similar to 55 million years ago, was a brief period of widespread, extreme climatic warming(1-3), that was associated with massive atmospheric greenhouse gas input(4). Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition(5). We show that sea surface temperatures near the North Pole increased from similar to 18 degrees C to over 23 degrees C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations(6), but the absolute polar temperatures that we derive before, during and after the event are more than 10 degrees C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms - perhaps polar stratospheric clouds(7) or hurricane-induced ocean mixing(8) - to amplify early Palaeogene polar temperatures.
  • Kathryn Moran, Jan Backman, Henk Brinkhuis, Steven C. Clemens, Thomas Cronin, Gerald R. Dickens, Frederique Eynaud, Jerome Gattacceca, Martin Jakobsson, Richard W. Jordan, Michael Kaminski, John King, Nalan Koc, Alexey Krylov, Nahysa Martinez, Jens Matthiessen, David McInroy, Theodore C. Moore, Jonaotaro Onodera, Matthew O'Regan, Heiko Palike, Brice Rea, Domenico Rio, Tatsuhiko Sakamoto, David C. Smith, Ruediger Stein, Kristen St John, Itsuki Suto, Noritoshi Suzuki, Kozo Takahashi, Mahito Watanabe, Masanobu Yamamoto, John Farrell, Martin Frank, Peter Kubik, Wilfried Jokat, Yngve Kristoffersen
    NATURE 441 7093 601 - 605 2006年06月 [査読有り][通常論文]
     
    The history of the Arctic Ocean during the Cenozoic era ( 0 - 65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm 'greenhouse' world, during the late Palaeocene and early Eocene epochs, to a colder 'icehouse' world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent similar to 14 Myr, we find sedimentation rates of 1 - 2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (similar to 3.2 Myr ago) and East Antarctic ice (similar to 14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (similar to 45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at,49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (similar to 55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.
  • T Usui, S Nagao, M Yamamoto, K Suzuki, Kudo, I, S Montani, A Noda, M Minagawa
    MARINE CHEMISTRY 98 2-4 241 - 259 2006年02月 [査読有り][通常論文]
     
    Organic carbon (C) and total nitrogen (N) contents and corresponding isotope ratios were determined in surficial sediment (0-3 cm) at 94 stations ranging from 21 to 1995 m water depth off Tokachi, Hokkaido, Japan, to elucidate the distribution and source of sedimentary organic matter. Suspended particulate organic matter (POM) in the seawater and suspended POM and sediment in the Tokachi River were also examined. delta C-13, delta N-15 and C/N ratios of the samples in the Tokachi River suggest that the spring snowmelt is an important process for the transport of terrestrial organic matter to the coastal waters. delta C-13 values of suspended POM in the Surface seawater were higher in May and November than in August, while delta N-15 values of the POM were higher in May and August than in November. These changes are attributed to seasonal changes in phytoplankton growth rate and nitrate availability. delta C-13 and delta N-15 values in the sediments off Tokachi were lowest near the Tokachi River mouth, and increased offshore to constant values that persisted from 134 to 1995 m water depth. The spatial variation in C/N ratios in the sediment mirrored those of delta C-13 and delta N-15. Comparison of delta C-13, delta N-15 and C/N ratios in the sediments off Tokachi with those in the Tokachi River and seawater indicates that about half of the organic matter in the sediment was of terrestrial origin near the Tokachi River mouth, and the sedimentary organic matter from 134 to 1995 in water depth was of marine origin. The organic C content in the sediment was high near the Tokachi River mouth, and also around 1000 m water depth. The C content was significantly correlated with silt plus clay content, with different regression lines for those stations shallower and deeper than 134 m, owing to several stations of higher C content with the elevated C/N ratio on the inner shelf. These results suggest that transport and deposition of organic-rich fine sediment particles by hydrodynamic processes were major factors controlling C content off Tokachi. In addition, the supply of a fraction of terrestrial organic matter with high C/N probably also affected C content on the inner shelf. (c) 2005 Elsevier B.V. All rights reserved.
  • Kazuho Fujine, Masanobu Yamamoto, Ryuji Tada, Yoshiki Kido
    ORGANIC GEOCHEMISTRY 37 9 1074 - 1084 2006年 [査読有り][通常論文]
     
    The novel alkenoate, ethyl tetratriacontadienoate (C34:2EE), has been found in late Quaternary sediments of the Japan Sea by using gas chromatography-mass spectrometry (GC-MS). It accompanied hexatriacontadien-3-one (C36:2EK) previously found in Black Sea sediments. A linear relationship between C36:2EK and C34:2EE concentrations points to both compounds being derived from the same source, most likely a specific haptophyte. The relative abundance of C34:2EE in total alkenones and alkenoates was significantly higher during the Last Glacial Maximum when the delta O-18 in planktonic foraminifera was anomalously light, strongly suggesting that C34:2EE is associated with low salinity environments. As samples with abundant C34:2EE also possessed anomalously high U-37(K') values, low salinity may have an ecological or physiological influence on both the unsaturation and carbon chain length of alkenones and alkenoates. (c) 2006 Elsevier Ltd. All rights reserved.
  • M Yamamoto, Y Ichikawa, Y Igarashi, T Oba
    PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY 229 3 179 - 186 2005年12月 [査読有り][通常論文]
     
    In order to understand the responses of terrestrial vegetation in central Japan to global climate changes, we have generated the record of lignin composition from Core MD01-2421 off central Japan in the NW Pacific during the last 145,000 years by tetramethylammonium hydroxide (TMAH)-pyrolysis-gas chromatography-mass spectrometry (GUMS). The relative abundance of lignin was significantly low in early MIS-1 and MIS-5e and higher in MIS-5c to early MIS-4. This reflects glacial-interglacial changes in sea level and riverine runoff. The ratio of syringyl (S)- to vanillyl (V)-phenols (S/V ratio), which is a contribution index of angiosperms against gymnosperms, was lower in MIS-2, MIS-4 and MIS-6, reflecting the glacial-interglacial variation of air temperature. The ratio of cinnamyl (C)- to vanillyl (V)-phenols (C/V ratio), which indicates the contribution of grasses, was higher in late MIS-2, early-mid MIS-3 and MIS-6. The periods of higher C/V ratio correspond to the periods of lower sea surface temperatures (SSTs), suggesting a dry and cold climate in late MIS-2, mid-MIS-3 and MIS-6. (c) 2005 Elsevier B.V All rights reserved.
  • VK Banakar, T Oba, AR Chodankar, T Kuramoto, M Yamamoto, M Minagawa
    MARINE GEOLOGY 219 2-3 99 - 108 2005年08月 [査読有り][通常論文]
     
    Sea surface salinity reconstruction for the Holocene and the Last Glacial Maximum (LGM) suggests that the LGM-Eastern Arabian Sea was more saline (by similar to 1.5 psu) than the Holocene due to weakened freshwater flux to the region, and intensified winter monsoons. Time-series of sedimentary organic-carbon (Cars), Ealkenone and delta(13)C(org) for the last 100 kyr, together, indicate increased glacial productivity. Significantly reduced sedimentary-delta(15)N during the LGM indicates, however, diminished water column denitrification in spite of increased productivity. The distinct decoupling of denitrification from productivity during the LGM can be explained by vigorous ventilation of the thermocline as a result of simultaneously intensified formation of high-salinity water and deep-winter mixing in northern-Arabian Sea related to the extreme cold climate. The closely comparable time-series delta(15)N records across the Arabian Sea suggest basin-wide homogenisation of the isotopic signal. This probably resulted from combined monsoon-dependent surface water mixing, due to changes in the relative strength of reversing surface circulations, and intermediate water mixing, due to changes in north-south salinity gradient. (c) 2005 Elsevier B.V. All rights reserved.
  • M Yamamoto, H Naraoka, R Ishiwatari, S Ogihara
    CHEMICAL GEOLOGY 218 1-2 117 - 133 2005年05月 [査読有り][通常論文]
     
    A series of C(29)-C(31) 28-norhopanoic acids occur in Neogene marine sediments of the Onnagawa, Funakawa and Tentokuji Formations, northeastern Japan, and in the Monterey Formation of California, USA. The 28-norhopanoic acids exist mainly as free acids but are partly bound to kerogen and the polar fraction of the solvent extract via an ester bond. The (13) C depletions of C(29) and C(31) 28-norhopanoic acids compared with those Of C(30) and C(32) regular hopanoic acids indicate that these 28-demethylated and regular hopanoic acids are derived from different precursor organisms. The Upper Onnagawa Formation contains abundant 28-norhopanoic acids and is characterized by the occurrence of Calyptogena sp. (Bivalvia), which lives in a specific chemoautrophic ecosystem that utilizes chemical substrates from hydrothermal vents or cold seeps. The depletion of 28-norhopanoic acids in (13)C compared with kerogen suggests that the 28-norhopanoic acids have been derived from bacteria that utilized (13)C-depleted CO(2) as their carbon source. (c) 2005 Elsevier B.V. All rights reserved.
  • Seiya Nagao, Toshihiro Usui, Masanobu Yamamoto, Masao Minagawa, Teruki Iwatsuki, Atsushi Noda
    Chemical Geology 218 1-2 63 - 72 2005年05月 [査読有り][通常論文]
     
    Accelerator mass spectrometry was used to measure radiocarbons of riverine suspended particles and sediments from the estuary, continental shelf and slope off the coast of Tokachi River in Japan. The spatial distribution of Δ14C and δ13C values of sedimentary organic matter was divided into those of (1) estuary, (2) continental shelf, and (3) continental slope. For shelf sediments, respective maxima can be seen for Δ14C value, C/N ratio and organic carbon content at a station near the river mouth. The mean grain size of surface sediments also exhibits a similar trend. The δ13C values show a minimum near the river mouth. The shelf composition does not appear to be a simple mixture of terrestrial and marine origin. From the above data, it is considered that the spatial distribution of Δ14C and δ13C values may reflect variations in dispersion and deposition processes together with the size fractionation of riverine suspended particles, the resuspension of sediments, and differences in the contribution of marine organic matter. ? 2005 Elsevier B.V. All rights reserved.
  • M Yamamoto, R Suemune, T Oba
    GEOPHYSICAL RESEARCH LETTERS 32 5 L05609  2005年03月 [査読有り][通常論文]
     
    We have generated a high-resolution record of alkenone sea surface temperature (SST) between 10-24 ka from Core MD01-2421 off central Japan, in the northwestern Pacific. The cooling by 5 degrees C from 21 ka to 12.8 ka implies the equatorward shift of the subarctic boundary in the northwestern Pacific by similar to 2.8 degrees in latitude. This shift was a result of the stronger summer Okhotsk High. The Okhotsk High was likely enhanced by the combined effects of El Nino-like conditions in the tropical Pacific and the heating of the land surface of northeastern Siberia.
  • 山本 正伸, 桑田 晃, 丸山 明彦, 東原 孝規
    Researches in Organic Geochemistry 20 7 - 13 日本有機地球化学会 2005年 [査読有り][通常論文]
     
    Lipids were analyzed for three different life forms of a marine planktonic diatom,Chaetoceros pseudocurvisetus, cultured in different nutrient media, in order to examine the influence of nutrient deficiency to the variation of the lipid distribution.
    TLC-FID and GC-MS analyses show large differences in lipid composition between the vegetative cell (VC) cultured in a nitrate-rich medium and the resting spore (RS) and resting cell (RC) cultured in nitrate-poor media. TLC-FID profiles of total lipids showed that triacylglycerols are abundant in the VC, whilst free fatty acids and sterols are abundant in the RS and RC. The VC shows lack of n-alkanes, unsaturated fatty acids and sterols. In contrast, the RS and RC show a broad n-alkane distribution maximizing at C17 with no odd/even carbon number preference, the presence of a C21 polyunsaturated alkene, phytadienes, unsaturated fatty acids and Δ5-sterols. A C30 sterol is specifically detected in the RS, while pristane in the RC.
    These results indicate that the distribution of lipids from C. pseudocurvisetus is strongly affected by nutrient condition. This finding suggests the possibility of the use of lipids to indicate paleonutrient conditions of sea surface water, and also provides a new insight to explain lipid distributions in field samples investigated before.
  • M Yamamoto, T Oba, J Shimamune, T Ueshima
    GEOPHYSICAL RESEARCH LETTERS 31 16 L16311  2004年08月 [査読有り][通常論文]
     
    The late Quaternary records of alkenone sea surface temperature (SST) in the Japan and California margins showed orbital-scale anti-phase SST variations between the two margins. This east-west seesaw-like change agreed well with the long-term El Nino-Southern Oscillation (ENSO) behavior predicted by the Zebiak-Cane ENSO model [Clement et al., 1999] as regards both the timing and frequency during 0-60 ka and 120-145 ka, and is attributed to the precession-controlled change in tropical ENSO behavior. This anti-phase SST change was not clearly demonstrated during 60-120 ka. This finding suggests that the influence of tropical climatic dynamics on the mid-latitude North Pacific varied in response to glacial-interglacial cycles.
  • Have the tropical Pacific ocean-atmosphere interactions behaved as a driver of centurial- to orbital-scale climate changes?" "
    Yamamoto, M
    Global Environmental Change in the Ocean and on Land (eds. Shiyomi, M., et al.), Terrapub (2004). 265 - 278 2004年 [査読有り][通常論文]
  • 山本 正伸
    Researches in Organic Geochemistry 19 31 - 38 有機地球化学会 2004年 [査読有り][通常論文]
  • 山本 正伸, 入野 智久, 大場 忠道, 村山 雅史, 池原 実, 小玉 一人, 川幡 穂高
    石油技術協会誌 67 6 590 - 593 石油技術協会 2002年11月01日 [査読有り][通常論文]
  • S Harii, H Kayanne, H Takigawa, T Hayashibara, M Yamamoto
    MARINE BIOLOGY 141 1 39 - 46 2002年07月 [査読有り][通常論文]
     
    Larval dispersal and recruitment are important in determining adult coral distribution; however, few studies have been made of coral larval dispersal. This study examined the larval behavior, survivorship competency periods and settlement of two brooding corals, Heliopora coerulea and Pocillopora damicornis, in relation to different potential larval dispersal patterns. We also examined the lipid content of H. coerulea as a means of flotation and a source of energy. Planulae of H. coerulea were on average 3.7 mm in length, lacked zooxanthellae, and were mostly benthic, probably because of restricted movement and low lipid content (54% by dry weight). Planulae of P. damicornis were on average 1.0 mm in length, had zooxanthellae and swam actively. The competency period of H. coerulea was shorter (30 days) than that of P. damicornis (100 days). Forty percent of H. coerulea planulae crawled onto the substrata within I h of release, and 47% settled within 6 h. By contrast, fewer than 10% of P. damicornis planulae crawled onto the substrata within the first hour and 25% settled within 6 h of release. The planulae of H. coerulea may have a narrower dispersal range than those of P. damicornis, settling and recruiting near parent colonies. Thus, brooding corals exhibit variations in larval dispersal patterns, which are characterized by their position in the water column and competency periods.
  • M Yamamoto, H Kayanne, M Yamamuro
    GEOCHEMICAL JOURNAL 35 6 385 - 401 2001年 [査読有り][通常論文]
     
    We have applied organic carbon and total nitrogen analyses, Rock-Eval pyrolysis, and gas chromatography-mass spectrometric lipid analysis with in situ methylation with tetramethylammonium hydroxide (TMAH-pyrolysis-GC/MS) to characterize the organic matter in recent lagoonal sediments from the Great Barrier Reef (GBR). On a pyrogram, GBR sediments showed the unique feature that S-1 and S-3 values were anomalously high. The high S-1 value presumably reflects a higher proportion of hydrolyzed lipids, and the high S-3 value is due to the degradation of carbonate minerals in a low temperature range. Associated with a CaCO3 increase towards the offshore area, the organic carbon/total nitrogen ratio (C/N ratio) decreased, S-1 and S-2 values increased, and total fatty acid and phytol concentrations increased. These changes have negative correlations with the branched/total fatty acid ratio, implying that the changes reflect the degree of eubacterial activity. The higher preservations of lipids and lignin phenols in CaCO3-rich sediments are attributable to their higher preservation effect resulting from an impermeable carbonate matrix. The anteiso/iso-fatty acid ratio has a significant negative correlation with the total fatty acid concentration and a positive correlation with the branched/total fatty acid ratio, indicating that the ratios are closely related to the degree of eubacterial degradation of organic matter.
  • 山本 正伸, 田口 一雄
    石油技術協会誌 65 5 469 - 476 The Japanese Association for Petroleum Technology 2000年09月01日 [査読有り][通常論文]
     
    秋田県矢島地域の新第三系女川層•船川層ビチュメンと猿倉原油の窒素官能基を非水滴定法により強塩基性窒素(ピリジン態窒素),弱塩基性窒素(主にアミド態窒素),非塩基性窒素(ピロール態窒素と非反応性窒素)に分けて定量した。一次生産性が高かったと考えられる層準で,高い強塩基性窒素量が認められた。この含有量が古一次生産力に関連している可能性が考えられる。また,強塩基性窒素の全窒素に対する割合はビチュメンよりも原油のほうが高い。この違いの原因として,熟成度の違いと石油移動に伴う分別の両者の可能性が考えられた
  • Yamamoto Masanobu
    Researches in organic geochemistry 15 0 27 - 31 日本有機地球化学会 2000年06月 [査読有り][通常論文]
     
    A newly developed method was employed for separately extracting carbonate- and noncarbonate-assciated lipids. The sample examined was a lime mud from the inner Great Barrier Reef. Unsaturated n-fatty acids and phytol were enriched in the carbonate fraction, indicating that the carbonate-associated organic matter was derived primarily from marine algae. In contrast, saturated n-fatty acids, n-heptadecane, labdane and C_<25:1> highly branched isoprenoid alkene were enriched in the noncarbonate fraction, indicating that the source of the noncarbonate-associated organic matter includes higher p...
  • 珪藻の生物地球化学とその古海洋学的応用
    山本正伸, 渡辺真人, 三田直樹, 東原直規, 丸山明彦, 山室真澄, 田中裕一郎
    地調月報 51 205 - 216 2000年05月 [査読有り][通常論文]
  • M Yamamoto, Y Shiraiwa, Inouye, I
    ORGANIC GEOCHEMISTRY 31 9 799 - 811 2000年 [査読有り][通常論文]
     
    The physiological responses of alkenone unsaturation indices to changes in growth status of E. huxleyi and G. oceanica strains isolated from a water sample of the NW Pacific were examined using an isothermal batch culture system. In both E. huxleyi and G. oceanica the unsaturation index U-37(K') changed during the growth period, but the effects of this change were different. This suggests that genotypic variation rather than the adaptation of the strains to the geographical environment of the sampling location is a major factor iri determining the physiological responses to U-37(K'). Changes of U-37(K') were associated with those of the unsaturation indices of C-38 and C-39 alkenones, the abundance ratios of lower to higher homologues of alkenones, the abundance ratios of saturated to polyunsaturated n-fatty acids, the abundance ratio of ethyl alkenoate to alkenones, and sterol contents. These associations might be attributable to the physiological response of lipids for maintaining their fluidity. The degree of unsaturation both in alkenones and n-fatty acids increased at day 8, possibly due to nutrient depletion. The ethyl alkenoate/total alkenone and ethyl alkenoate/C-37 alkenone ratios increased abruptly at day 8 in both strains. These ratios should be useful in clarifying the relationship between the marine environment and its corresponding growth phase of batch culture. E. huxleyi and G. oceanica can be effectively distinguished using the U-37(K')-U-38Et(K) diagram. (C) 2000 Elsevier Science Ltd. All rights reserved.
  • Source characterization of carbonate- and noncarbonate-associated lipids in a coral reef sediment.
    Researches in Organic Geochemistry 15 13 - 17 2000年 [査読有り][通常論文]
  • Late Quaternary records of organic carbon, calcium carbonate and biomarkers from Site 1016 off Point Conception, California margin.
    ODP Scientific Results 167 183 - 194 2000年 [査読有り][通常論文]
  • 山室 真澄, 田中 至, 山本 正伸, 有信 哲哉
    水環境学会誌 23 3 168 - 172 Japan Society on Water Environment 2000年 [査読有り][通常論文]
     
    Bioaccumulation of di-2-ethylhexyl phtalate (DEHP) and di-n-butyl phtalate (DBP) by a wintering diving duck, Aythya fuligula, was studied by a conventional analysis modified to minimize contamination. The 0.061 μg · g-1 for DEHP and the 0.041 μg · g-1 for DBP were detected in a blank sample throughout whole procedure. Added DEHP and DBP were recovered at 105.2% and 106.3%, respectively. Trophic level of A. fuligula was examined using carbon and nitrogen stable isotope ratios. Nitrogen stable isotope ratios suggested that organic component of the liver of A. fuligula was changed with its food bivalve, Corbicula japonica, by 70 days after duck's arrival. Mean concentrations of DEHP and DBP on basis of fat in the livers of ducks and the flesh of C. japonica were 332μg · g-1 and 7.51μg · g-1 for DEHP, and 12.1μg · g-1 and 6.88μg · g-1 for DBP, respectively. Concentrations of DEHP in the livers of ducks increased towards the middle of December 1994, and decreased afterwards, suggesting that both bioaccumulation and decomposition of DEHP occurred in the liver of ducks. Increase of DEHP concentrations towards the middle of December 1994 was attributed to the backflow of saline water from urbanized area, because carbon isotope ratios and the concentrations of DEHP in the liver of ducks showed positive correlation.
  • 山本 正伸
    地球化学 33 3 191 - 204 日本地球化学会 1999年08月25日 [査読有り][通常論文]
     
    Alkenone paleothermometry has been used for generating late Quaternary records of sea surface temperature from deep-sea core sediments. This paper summarizes its principles, applications, problems and future. A critical problem comes from culture experiments of Emiliania huxleyi and Gephyrocapsa oceanica. The results indicate large variations in the U^<K'>_<37>-temperature relationship among different species or strains. Even single strains show variations in U^<K'>_<37> in different growth phases and culture conditions. These suggest that some physiological or environmental factor, in addi...
  • Yamamoto Masanobu
    Researches in organic geochemistry 14 0 1 - 2 日本有機地球化学会 1999年06月30日 [査読有り][通常論文]
     
    Petroleum migration is one of the key processes for the formation of oil fields. To understand the process, it is necessary to find the tools to assess the direction and distance of petroleum migration (secondary migration) and the degree of the fractionation of oil compositions during the migration. Recently nitrogen compounds became a useful tool to indicate the degree of the fractionation. This tool was proposed, and was first applied to the Sarukawa Oil Field, Japan, by Yamamoto (1992).
  • 山本 正伸, 渡部 芳夫, 渡辺 真人
    地質調査所月報 50 5 361 - 376 経済産業省産業技術総合研究所地質調査所 1999年06月 [査読有り][通常論文]
  • 山本 正伸
    地質調査所月報 50 5 329 - 359 経済産業省産業技術総合研究所地質調査所 1999年06月 [査読有り][通常論文]
  • 山本 正伸, Bat-erdene Delegiin, Ulziikhishig Pureyiin
    地質調査所月報 49 6 257 - 274 経済産業省産業技術総合研究所地質調査所 1998年06月 [査読有り][通常論文]
  • 山本 正伸, バッテルデン デレギン, オルツィヒシ プレイン, 渡部 芳夫, 武田 信從, 梶原 義照, 中嶋 輝充
    石油技術協会誌 63 3 239 - 250 The Japanese Association for Petroleum Technology 1998年05月 [査読有り][通常論文]
     
    Elemental analyses, Fischer assay pyrolysis, Rock-Eval pyrolysis and biomarker analyses were conducted for twenty-six lacustrine oil shales from the Lower Cretaceous Dsunbayan Group, Mongolia.
    The Dsunbayan oil shales show large variations of organic carbon content (1.7-21.3wt%) and oil yield (0.3-11.8 wt%). A Rock-Eval pyrolysis shows that immature Type I kerogen dominates in these samples. Biomarker compositions show that major source organisms of the Dsunbayan oil shale were an autotrophic prokaryote such as a cyanobacterium, nonmarine algae, terrestrial higher plants, heterotrophic bacteria and bacterivorous ciliates.
    Good correlations exist among organic carbon content, oil yield, bitumen content and n-heptadecane anomaly {2×n-C17/(n-C16+n-C18)n-alkane ratio}. The samples with high n-heptadecane anomaly are rich in β-carotane, which suggests that the degree of bottom water anoxia controlled organic carbon content and oil yield, and was related to the contribution of an autotrophic prokaryote which sourced dominant n-heptadecane.
    High C/S ratio and little sulfur compound in the Dsunbayan oil shales indicate that they were deposited in a freshwater environment. The tropical-subtropical climate promoted thermal stratification and bottom water anoxia in the freshwater lakes. The degree of development of bottom-water anoxia was likely controlled by nutrient supply from the surrounding area.
  • 山本 正伸, 鈴木 祐一郎, 榎本 稔, 梶原 義照, 武田 信從
    石油技術協会誌 63 2 158 - 164 The Japanese Association for Petroleum Technology 1998年03月 [査読有り][通常論文]
     
    A thermogravimetric analysis (TGA) and a Rock-Eval pyrolysis (RE) were applied to estimating the shale oil content (oil yield) in 26 oil shales from the Dsunbayan Group, Mongolia.
    The weight loss during 211-505°C (WL2-WL1) by TGA and the generation potential (S1+S2) of RE are well correlated with the Fischer assay (FA) oil yield, with the following formulae, respectively.
    WL2-WL1 (wt%)=0.720×{FA oil yield (wt%)}+2.55
    S1+S2 (mg/g)=12.4×{FA oil yield (wt%)}-1.49
    The oil yields estimated from TGA weight loss and RE generation potential both have small deviations (mostly within 1wt%) from the FA values. These estimations can be effectively applied as easy and inexpensive methods to estimate oil yields of large number of oil shale samples.
  • 山本 正伸, 山室 真澄, 田中 裕一郎, 多田 隆治, Ingrid L. Hendy, James P. Kennett
    日本地質学会学術大会講演要旨 1998 136 - 136 一般社団法人 日本地質学会 1998年
  • AC Ravelo, M Lyle, Koizumi, I, JP Caulet, E Fornaciari, A Hayashida, F Heider, J Hood, S Hovan, T Janecek, A Janik, R Stax, M Yamamoto
    PALEOCEANOGRAPHY 12 6 729 - 741 1997年12月 [査読有り][通常論文]
     
    Recent modeling studies call on increased ocean heat transport to explain high-latitude warming observed for intervals throughout the middle Pliocene. Possible vehicles for ocean heat transport are the poleward arms of the subtropical gyres. Sites from the California margin (Ocean Drilling Program Leg 167) provide monitors of wind field within the eastern arm of the gyre which may be an indication of basin-wide subtropical gyral strength. At most sites (water depths from 1106 to 4212 m) CaCO3 mass accumulation rate (MAR) was highest in the middle Pliocene (3.5-2.0 Ma). This high CaCO3 MAR ''event'' is attributed primarily to higher CaCO3 production due to higher offshore upwelling associated with the zone of the greatest wind stress curl. Thus, in the middle Pliocene, there was enhanced wind stress curl along the California margin, and possibly enhanced North Pacific sub-tropical gyral circulation and meridional ocean heat advection.
  • 山本 正伸, 山室 真澄, 茅根 創
    地質調査所月報 48 2 79 - 92 経済産業省産業技術総合研究所地質調査所 1997年02月 [査読有り][通常論文]
  • M Yamamoto, K Ficken, M Baas, HJ Bosch, JW deLeeuw
    GEOLOGIE EN MIJNBOUW 75 2-3 255 - 267 1996年 [査読有り][通常論文]
     
    Organic compound distributions in extracts of three selected clay samples from the lowermost Danian section at Geulhemmerberg were analysed in order to enhance the understanding of the depositional environment immediately after the Cretaceous/Tertiary (K/T) boundary. A highly dominant C-40:2 ethyl ketone is identified. This compound is probably derived from specific, highly abundant non-coccolithophorid Prymnesiophyte algae which may already have been present in late Maastrichtian times. Fatty acids as well as their randomly oxidized hydroxy- and keto counterparts are also abundant. These compounds probably indicate bacterially transformed biochemicals of terrestrial origin, although they are probably not derived from the Bryophyte moss spores abundantly present in these sediments. Their distributions are, however, strikingly similar to those of fatty acids in Antarctic soils. omega(16)-, omega(17)-, and omega(22)-keto- and hydroxy fatty acids with highly specific distribution patterns and a clear even over odd carbon number preference are thought to be of marine origin. The biochemical relationships between these compounds and the C-40:2 ethyl ketone suggest that they may originate from the same algae. This presence of highly functionalized organic compounds demonstrates the extreme immaturity and excellent preservation of the unique Geulhemmerberg K/T boundary sediments.
  • 渡部 芳夫, 山本 正伸, 渡辺 真人
    石油技術協会誌 60 1 15 - 26 The Japanese Association for Petroleum Technology 1995年01月 [査読有り][通常論文]
     
    In order to assess the hydrocarbon potential of the Middle Miocene (10-12Ma) Onnagawa diatomaceous sediments, outcrop samples from seven sites in the Aomori and Akita Prefectures were examined for the distribution of their major and minor elements. Three factors optimal for the good source rock generation, i. e., supply of biogenous materials, small dilution effect by terrigenous detrius, and anoxic bottom water condition, were extracted by multivariate statistical analyses. Spatial distributions of these factors indicate source facies developed in the central deep part of the basin, which was kept stagnant by restricted circulation of sea water. During 10 to 9Ma, paleoceanic condition changed drastically due to the initiation of localized upwelling.
  • YAMAMOTO Masanobu, WATANABE Yoshio
    石油技術協会誌 60 1 27 - 38 The Japanese Association for Petroleum Technology 1995年01月 [査読有り][通常論文]
     
    秋田県矢島地域に分布する中期中新世から鮮新世にかけての堆積物 (女川層, 船川層, 天徳寺層) 中に含まれる有機化合物の分析を行った. 古海洋環境解析にあたっては, 高等植物指標としてC27/C21ノルマルアルカン比, C28/C16ノルマルアルカノイック酸比, C22オメガヒドロキシノルマルアルカノイック酸/C16ノルマルアルカノイック酸比を, 珪藻指標としてはC25高分岐イソプレノイドアルカン/C21ノルマルアルカン比を, 渦鞭毛藻指標としてダイノステラン/4-デスメチルステラン比を, バクテリア指標としてはホパン/ステラン比を用いた.
    C27/C21ノルマルアルカン比, C28/C16ノルマルアルカノイック酸比, C22オメガヒドロキシノルマルアルカノイック酸/C16ノルマルアルカノイック酸比は船川層で急激に増加している. これは砕屑物の流入の増加に伴う陸上高等植物起源有機物の流入の増加を反映している. 珪藻指標のC25高分岐イソプレノイドアルカン/C21ノルマルアルカン比は女川層で高く, 船川層•天徳寺層で低い. 渦鞭毛藻指標のダイノステラン/4-デスメチルステラン比は女川層下部と天徳寺層で高く, 女川層中上部と船川層で低い. 女川層を通してのC25高分岐イソプレノイドアルカン/C21ノルマルアルカン比とダイノステラン/4-デスメチルステラン比の相反する挙動は女川層沈積時の表層水のシリカ栄養塩濃度に対応しているものと解釈される.天徳寺層に見られる高いダイノステラン/4-デスメチルステラン比は沿岸生の渦鞭毛藻の増加に対応しているように見える. 船川層におけるホパン/ステラン比の増加は恐らく底層水の酸化に起因する好気性バクテリアの活動度の増加を反映している.
  • N IMAI, M YAMAMOTO
    MICROCHEMICAL JOURNAL 50 3 281 - 288 1994年12月 [査読有り][通常論文]
     
    Distributions of elements in laminated dolomite and zircon crystal were obtained by laser ablation inductively coupled plasma mass spectrometry. The variation of signal intensity was normalized by an internal standard method using the sum of the signals of Ca and Mg which was assumed to be constant in every position for the dolomite sample and using Zr signal for the zircon sample. The concentrations of elements change correspondingly across the laminated structure of dolomite. U and Th show a zoned distribution in the zircon crystal. (C) 1994 Academic Press, Inc.
  • 渡部 芳夫, 山本 正伸, 今井 登
    地質調査所月報 45 8 509 - 525 経済産業省産業技術総合研究所地質調査所 1994年09月 [査読有り][通常論文]
  • 山本 正伸, 渡部 芳夫, 渡辺 真人
    地質調査所月報 45 8 527 - 530 経済産業省産業技術総合研究所地質調査所 1994年09月 [査読有り][通常論文]
  • N IMAI, K SHIMOKAWA, M YAMAMOTO
    QUATERNARY SCIENCE REVIEWS 13 5-7 641 - 645 1994年 [査読有り][通常論文]
  • 山本 正伸
    地質調査所月報 44 11 685 - 691 経済産業省産業技術総合研究所地質調査所 1993年11月 [査読有り][通常論文]
  • M YAMAMOTO
    ORGANIC GEOCHEMISTRY 19 4-6 389 - 402 1992年12月 [査読有り][通常論文]
     
    A comparative study of alkylbenzoquinolines in crude oils and rock extracts (bitumens) from Japan and Sumatra shows that the ratios of nitrogen-masked isomers (NMIs) to nitrogen-exposed isomers (NEIs), and the ratio of higher homologs to lower homologs is higher in crude oils than in corresponding bitumens. Also, a regular increase in the ratios of NMIs to NEIs with increasing migration distance is observed for a series of crude oils from the Sarukawa Oil Field, northeastern Japan. These results are attributed to the preferential migration of NMIs caused by their weak adsorption on clay minerals and/or their low solubility in interstitial water, and the selective removal of lower homologs caused by their irreversible adsorption onto clays during oil migration, which are regarded as geochromatographic phenomena. It is suggested that those ratios can be used to estimate the degree of fractionation of oils during primary and secondary migration.
  • M YAMAMOTO, K TAGUCHI, K SASAKI
    CHEMICAL GEOLOGY 93 1-2 193 - 206 1991年11月 [査読有り][通常論文]
     
    Basic nitrogen compounds in bitumen and crude oils were analyzed by acid extraction, column liquid chromatography and gas chromatography-mass spectrometry. Various kinds of azaarenes and azadibenzothiophenes are found in both bitumens and crude oils, except cyclic amides which are found only in bitumens. It is suggested that basic nitrogen heterocycles found in the bitumens from non-marine sediments are generated mostly from the high M.W. geo-polymers during the later stage of diagenesis, based on the variation of their amounts with increasing maturity. The difference in the ratio of 2-ring to 3-ring azaarenes found between marine and non-marine sediments seems to reflect the influence of the depositional environments. A large difference in the distribution of C1-C4 alkyl homologues and isomers of azaphenanthrenes between bitumens and crude oils is observed. The isomers with nitrogen atoms masked by the side chains are found in both bitumens and crude oils, while the isomers with exposed nitrogen atoms are seen only in bitumens. These differences are attributed to the preferential migration of higher homologues and nitrogen-masked isomers caused by their weak adsorption on clay minerals during primary migration of oils.
  • 山本 正伸, 田口 一雄, 佐々木 清隆
    Researches in organic geochemistry 7 0 55 - 57 日本有機地球化学会 1990年04月 [査読有り][通常論文]

MISC

  • 山本正伸, 清家弘治, POLYAK L., GEMERY L., JOE Y.J., 内田翔馬, 小林稔, 小野寺丈尚太郎, 村山雅史, 岩井雅夫, 山本裕二, JORDAN R., 山田桂, 堀川恵司, 朝日博史, 安藤卓人, 鈴木健太, 加三千宣, 永淵修, DAVID L., DAVID L., SZAREK R., 菅沼悠介, 大森貴之 日本地球化学会年会要旨集(Web) 70th 2023年
  • 梶田 展人, 関 宰, 山本 正伸, 大河内 直彦, 岡田 誠, 羽田 裕貴, 菅沼 悠介 日本地球化学会第69回年会講演要旨集 2022年11月
  • 安藤寿男, 長谷川精, 長谷部徳子, ICHINNOROV N, 太田亨, 長谷川卓, 山本正伸, LI G, ERDENETSOGT B‐O, HEIMHOFER U 日本古生物学会年会講演予稿集 2018 26 2018年06月22日 [査読無し][通常論文]
  • 長谷川精, 安藤寿男, 勝田長貴, 村木綏, ICHINNOROV N, 村山雅史, 山本鋼志, 太田亨, 長谷川卓, 山本正伸, 長谷部徳子, HEIMHOFER U 日本堆積学会大会プログラム・講演要旨 2018 21‐22 2018年03月25日 [査読無し][通常論文]
  • 長谷川精, 安藤寿男, 勝田長貴, 村木綏, ICHINNOROV Niiden, 村山雅史, 山本鋼志, 太田亨, 長谷川卓, 山本正伸, 長谷部徳子, HEIMHOFER Ulrich, 池田昌之, 西本昌司, 山口浩一, 阿部文雄, 多田隆治 日本地球惑星科学連合大会予稿集(Web) 2018 ROMBUNNO.MIS10‐01 (WEB ONLY) 2018年 [査読無し][通常論文]
  • 櫻井弘道, 山本正伸, 関宰, 大森貴之, 佐藤友徳 日本地球惑星科学連合大会予稿集(Web) 2018 ROMBUNNO.MIS01‐P06 (WEB ONLY) 2018年 [査読無し][通常論文]
  • ボルネオでの泥炭コアリング
    山本正伸 PALEO 5 1 -13 2017年04月01日 [査読無し][通常論文]
  • 櫻井弘道, 山本正伸, 関宰, 大森貴之 日本地球惑星科学連合大会予稿集(Web) 2017 ROMBUNNO.MIS23‐P12 (WEB ONLY) 2017年 [査読無し][通常論文]
  • 山本正伸, 菊池隼史, 櫻井弘道, 林竜馬, 関宰, 大森貴之, SULAIMAN Abdullah, BIN SHAARI Hasrizal, MELLING Lurie 日本地球惑星科学連合大会予稿集(Web) 2017 ROMBUNNO.MIS06‐06 (WEB ONLY) 2017年 [査読無し][通常論文]
  • Exp. 353 Indian Monsoon Rainfall (2014/11/29〜2015/1/29、JR)インド夏季モンスーンの復元
    臼井洋一, 浦本豪一郎, 山本正伸, 安藤卓人 J-DESC 9 4 -1 2016年04月01日 [査読無し][通常論文]
  • 山本正伸, 臼井洋一, 浦本豪一郎, 安藤卓人, CLEMENS Steven, WOLFGANG Kuhnt, LEVAY Leah 日本地球惑星科学連合大会予稿集(Web) 2016 ROMBUNNO.MIS16‐P01 (WEB ONLY) 2016年 [査読無し][通常論文]
  • Steven C. Clemens, Wolfgang Kuhnt, Leah J. LeVay, Pallavi Anand, Takuto Ando, Milos Bartol, Clara T. Bolton, Xuan Ding, Karen Gariboldi, Liviu Giosan, Edmund C. Hathorne, Yongsong Huang, Priyank Jaiswal, Sunghan Kim, John B. Kirkpatrick, Kate Littler, Gianluca Marino, Philippe Martinez, Dinesh Naik, Aditya Peketi, Stephen C. Phillips, Marci M. Robinson, Oscar E. Romero, Netramani Sagar, Katie B. Taladay, Samuel N. Taylor, Kaustubh Thirumalai, Goichiro Uramoto, Yoichi Usui, Jiasheng Wang, Masanobu Yamamoto, Liping Zhou Integrated Ocean Drilling Program: Preliminary Reports (353) 1 -46 2015年04月 [査読無し][通常論文]
     
    International Ocean Discovery Program (IODP) Expedition 353 (29 November 2014-29 January 2015) drilled six sites in the Bay of Bengal, recovering 4280 m of sediments during 32.9 days of on-site drilling. Recovery averaged 97%, including coring with the advanced piston corer, half-length advanced piston corer, and extended core barrel systems. The primary objective of Expedition 353 is to reconstruct changes in Indian monsoon circulation since the Miocene at tectonic to centennial timescales. Analysis of the sediment sections recovered will improve our understanding of how monsoonal climates respond to changes in forcing external to the Earth's climate system (i.e., insolation) and changes in forcing internal to the Earth's climate system, including changes in continental ice volume, greenhouse gases, sea level, and the ocean-atmosphere exchange of energy and moisture. All of these mechanisms play critical roles in current and future climate change in monsoonal regions. The primary signal targeted is the exceptionally low salinity surface waters that result, in roughly equal measure, from both direct summer monsoon precipitation to the Bay of Bengal and runoff from the numerous large river basins that drain into the Bay of Bengal. Changes in rainfall and surface ocean salinity are captured and preserved in a number of chemical, physical, isotopic, and biological components of sediments deposited in the Bay of Bengal. Expedition 353 sites are strategically located in key regions where these signals are the strongest and best preserved. Salinity changes at IODP Sites U1445 and U1446 (northeast Indian margin) result from direct precipitation as well as runoff from the Ganges-Brahmaputra river complex and the many river basins of peninsular India. Salinity changes at IODP Sites U1447 and U1448 (Andaman Sea) result from direct precipitation and runoff from the Irrawaddy and Sal-ween river basins. IODP Site U1443 (Ninetyeast Ridge) is an open-ocean site with a modern surface water salinity very near the global mean but is documented to have recorded changes in monsoonal circulation over orbital to tectonic timescales. This site serves as an anchor for establishing the extent to which the north to south (19°N to 5°N) salinity gradient changes over time.
  • 池原実, 関宰, 井尻暁, 佐藤暢, 山本正伸, 大河内直彦, 岡崎裕典, 松崎琢也 日本地球惑星科学連合大会予稿集(Web) 2015 ROMBUNNO.MIS21‐P01 (WEB ONLY) 2015年 [査読無し][通常論文]
  • Ando H., Hasegawa H., Ohta T., Hasegawa T., Yamamoto M., Hasebe N., Murata T., shinya H., Li G., Ichinnorov N., Erdenetsogt B., Heimhofer U. Science reports of Niigata University. (Geology) 29 14 -15 2014年10月 
    The 2nd International Symposium on Earth History of Asia 31 October – 3 November, Niigata, Japan
  • 入野 智久, 中井 淑恵, 山本 正伸, 宮崎 雄三, 河村 公隆, 山田 和芳, 米延 仁志 日本地球化学会年会要旨集 61 (0) 287 -287 2014年 [査読無し][通常論文]
     
    遠距離輸送されるバイオマス燃焼起源物質の定量を目指して，堆積物中の極細粒元素状炭素（EC）量評価のために，Thermal optical transmittance法の応用を検討した．スクロース，フミン酸，フルボ酸，フラーレンのEC・有機炭素（OC）分析を行った結果，O2雰囲気，550℃-700℃に耐えるOCも存在することが分かったので，700℃-850℃で検出されるフラクションのみをECとして定義した．この方法で，礼文島・久種湖の湖底堆積物コアから選んだ試料を，2μmを境に粗粒および細粒に分画し，それぞれの粒度画分についてEC・OC分析を行った．その結果，粗粒・細粒画分中のEC・OC変動が異なる事が分かり、粗粒ECはローカルな，細粒ECはローカル，遠方両方のバイオマス燃焼起源である可能性が示唆された．ECの細粒/粗粒比変動は大陸規模でのバイオマス燃焼変動を反映する可能性がある．
  • 後期更新世のグレートベースン湖の形成は熱帯由来の降雨が原因：太平洋および米国西部の水循環
    山本正伸 サイエンス誌に載った日本人研究者2012 45 -45 2013年04月01日 [査読無し][通常論文]
  • Min-Te Chen, Masanobu Yamamoto, Youbin Sun, Chris Turney JOURNAL OF QUATERNARY SCIENCE 27 (9) 865 -865 2012年12月 [査読有り][通常論文]
  • Latent 1,500-year climate oscillation in the Holocene,
    Yamamoto, M PAGES news, 20, 2, 66-67. 20 66 -67 2012年12月 [査読有り][招待有り]
  • Shimada Misaki, Takahara Hikaru, Kuwae Michinobu, Yamamoto Masanobu, Ikehara Ken, Irino Tomohisa, Takemura Keiji, Sagawa Takuya, Sakamoto Tatsuhiko, Ikehara Minoru, Takeoka Hidetaka 日本花粉学会会誌 58 212 -213 2012年08月23日
  • Hayashi Ryoma, Takahara Hikaru, Igarashi Yaeko, Kumon Fujio, Liew Ping-Mei, Yamamoto Masanobu, Kawai Sayuri, Oba Tadamichi, Irino Tomohisa, Shichi Koji 日本花粉学会会誌 58 81 -82 2012年08月23日
  • Sze Ling Ho, Masanobu Yamamoto, Gesine Mollenhauer, Masao Minagawa ORGANIC GEOCHEMISTRY 46 55 -55 2012年05月 [査読無し][通常論文]
  • 川村泰士, 長谷部徳子, 安藤寿男, 長谷川精, 長谷川卓, 太田亨, 山本正伸 フィッション・トラックニュースレター (24) 73 -74 2011年10月30日 [査読無し][通常論文]
  • 片岡剛文, 入野智久, 山本正伸, 鈴木光次, 東正剛 日本海洋学会大会講演要旨集 2009 185 2009年03月23日 [査読無し][通常論文]
  • S. L. Ho, M. Nuita, M. Yamamoto, M. Minagawa, T. Sagawa, K. Horikawa, M. Murayama, Y. Kato GEOCHIMICA ET COSMOCHIMICA ACTA 72 (12) A382 -A382 2008年07月 [査読無し][通常論文]
  • East-west seesaw of sea surface temperature variation in the mid-latitude North Pacific during the last two glacial cycles
    Yamamoto, M, Oba, T PAGES news 20 66 -67 2008年04月01日 [査読有り][招待有り]
  • 公文 富士夫, 山本 正伸, 長橋 良隆, 青池 寛 日本地質学会学術大会講演要旨 114 34 -34 2007年09月01日
  • 山本 正伸 日本地質学会学術大会講演要旨 114 35 -35 2007年09月01日
  • International Antarctic Institute project in Hokkaido University.
    Hondoh, T, Sugiyama, S. Aoki, S, Yamamoto, M, Sueyoshi, T, Nihashi, S, Kimura, H Proceedings of the International Symposium Asian Collaboration in IPY2007-2008, in Tokyo, March 2007, published by National Institute of Polar Research, 93 -99 2007年04月01日 [査読無し][通常論文]
  • 十勝沖海底コア・GH02-1030の花粉群による北海道東部地域21,000年間の古植生復元
    五十嵐八枝子, 山本正伸, 池原研 平成18年度研究概要報告書．地質調査総合センター速報，産業技術総合研究所地質調査総合センター 39 165 -171 2007年04月01日 [査読無し][通常論文]
  • GH02航海で採取された十勝沖表層堆積物中の花粉・胞群
    五十嵐八枝子, 山本正伸, 野田篤 平成18年度研究概要報告書．地質調査総合センター速報，産業技術総合研究所地質調査総合センター 39 150 -164 2007年04月01日 [査読無し][通常論文]
  • 鹿島沖海底コアに見いだされたスーピー層（ハイドレート層）とその近傍層準のバイオマーカー組成
    山本正伸 「海洋炭素循環とメタンハイドレート水中に吸収された炭酸ガスの分解」に関する研究開発専門委員会報告書.．，日本学術振興会 204 -208 2006年04月01日 [査読無し][通常論文]
  • Chikara Abe, Masanobu Yamamoto, Toshihisa Irino Proceedings of the Ocean Drilling Program: Scientific Results 202 1 -14 2006年02月 [査読有り][通常論文]
  • 伊澤祐輔, 山本正伸, 関宰, 河村公隆, CHEN M‐T 日本地球化学会年会講演要旨集 53rd (0) 168 -146 2006年 [査読無し][通常論文]
     
    西部熱帯太平洋は地球上において重要な熱と水蒸気の貯蔵庫であり、気候変動や水循環の研究する上で重要な場所である。そこで、本研究は南シナ海南部で掘削されたMD972151コア中の脂肪酸の分析を行い、過去15万年間の分布を明らかにした。陸上高等植物起源である長鎖脂肪酸(C24,26,28)濃度は完新世よりも最終氷期最寒期(LGM)において高かった。この変動は海水準の変化が陸起源物質の流入に大きな影響を与えることを示唆した。また、LGMにおける長鎖脂肪酸の水素同位体比は海洋生物起源である短鎖脂肪酸(C16,18)よりも重い値を示した。
  • 山本 正伸, 磯野 大, 入野 智久, 村山 雅史, 中村 俊夫, 川幡 穂高 日本地質学会学術大会講演要旨 2006 (0) 31 -31 2006年 [査読無し][通常論文]
  • GH02-1030コアのリグニンフェノール及び脂肪酸．
    稲垣正樹, 山本正伸, 池原研 千島孤−東北日本孤会合部の海洋地質学的研究．平成16年度研究概要報告書−根室沖・日高沖海域−．地質調査総合センター速報 33 188 -192 2005年04月01日 [査読無し][通常論文]
  • GH02-1030コアのアルケノン古水温変動
    稲垣正樹, 山本正伸, 池原研 千島孤−東北日本孤会合部の海洋地質学的研究．平成16年度研究概要報告書−根室沖・日高沖海域−．地質調査総合センター速報 33 185 -187 2005年04月01日 [査読無し][通常論文]
  • IODP Expedition 302, Arctic Coring Expedition (ACEX): A first look at the Cenozoic Paleoceanography of the central Arctic Ocean.
    Backman, J, Moran, K, McInroy, D, the IODP Expeditio, Scientists Scientific Drilling 1 12 -17 2005年04月01日 [査読無し][招待有り]
  • GH02航海で採取された十勝沖表層堆積物のリグニンフェノール組成．千島孤−東北日本孤会合部の海洋地質学的研究
    市川豊, 山本正伸 平成15年度研究概要報告書−釧路沖・日高沖海域−．地質調査総合センター速報 30 186 -196 2004年04月01日 [査読無し][通常論文]
  • GH02-1030コアのリグニンフェノール組成（予報）
    稲垣正樹, 山本正伸 千島孤−東北日本孤会合部の海洋地質学的研究．平成15年度研究概要報告書−釧路沖・日高沖海域−．地質調査総合センター速報 30 180 -185 2004年04月01日 [査読無し][通常論文]
  • GH02航海で採取された十勝川表層堆積物の有機炭素・全窒素の安定同位体比とC/N比（予報）．
    碓井敏宏, 山本正伸, 南川雅男 千島孤−東北日本孤会合部の海洋地質学的研究．平成15年度研究概要報告書−釧路沖・日高沖海域−．地質調査総合センター速報 30 170 -179 2004年04月01日 [査読無し][通常論文]
  • Data Report: Organic carbon, and alkenone sea-surface temperature from Sites 1175, 1176, and 1178, Nankai Trough
    Yamamoto, M Proceedings of Ocean Drilling Program, Scientific Results 190 (196) 1 -10 2004年 [査読有り][通常論文]
  • 造礁サンゴ幼生２種の分散に関わる定着期間および脂質特性
    波利井佐紀, 灘岡和夫, 山本正伸, 茅根創, 林原毅, 岩尾研二 2004年日本ベントス学会・プランクトン学会合同大会講演要旨集 63 2004年 [査読無し][通常論文]
  • T Ueshima, M Yamamoto, T Oba, T Kuramoto, M Minagawa, T Irino GEOCHIMICA ET COSMOCHIMICA ACTA 67 (18) A502 -A502 2003年09月 [査読無し][通常論文]
  • M Yamamoto, J Shimamune, T Ueshima, T Oba GEOCHIMICA ET COSMOCHIMICA ACTA 67 (18) A552 -A552 2003年09月 [査読無し][通常論文]
  • Y Ichikawa, M Yamamoto, T Oba GEOCHIMICA ET COSMOCHIMICA ACTA 67 (18) A164 -A164 2003年09月 [査読無し][通常論文]
  • 十勝沖コア試料中における微生物群集構造の PCR-DGGE法による解析．
    鈴木聡, 片岡悠子, 山本正伸 地質調査総合センター「千島孤−東北日本孤会合部の海洋地質学的研究 十勝沖海域」平成１４年度研究概要報告書 184 -191 2003年04月01日 [査読無し][通常論文]
  • GH02航海で採取された十勝沖海底コアGH02-1023およびGH02-1030の有機炭素量．
    山本正伸 地質調査総合センター「千島孤−東北日本孤会合部の海洋地質学的研究 十勝沖海域」平成１４年度研究概要報告書 177 -183 2003年04月01日 [査読無し][通常論文]
  • GH02航海で採取された十勝沖表層堆積物の有機炭素量．
    山本正伸, 市川豊 地質調査総合センター「千島孤−東北日本孤会合部の海洋地質学的研究 十勝沖海域」平成１４年度研究概要報告書 170 -176 2003年04月01日 [査読無し][通常論文]
  • JM Sorrosa, M Yamamoto, Y Shiraiwa ADVANCED RESEARCH ON PLANT LIPIDS 133 -136 2003年 [査読無し][通常論文]
  • Data Report: Alkenone compounds and major ellement composition in late Quaternary hemipelagic sediments from ODP Site 1151 off Sanriku, northern Japan.
    Fujine, K, Yamamoto, M, Tada, R Proceedings of the Ocean Drilling Program, Scientific Results 186 1 -12 2003年 [査読無し][通常論文]
  • 西部北太平洋北緯39 度東経147度地点におけるアルケノンフラックスの評価 NH99試料について￥
    山本正伸, 嶋本晶文, 福原達雄, 田中裕一郎, 西村昭 地質調査総合センター速報「海洋中の堆積物形成過程に関する研究」産業技術総合研究所． 64 -71 2002年04月01日 [査読無し][通常論文]
  • 西部北太平洋沈降粒子中のアルケノン炭素同位体組成の季節変動（予報）．
    山本正伸, 奈良岡浩 地質調査総合センター速報「海洋中の堆積物形成過程に関する研究平成１２年度研究概要報告」 112 -121 2001年04月01日 [査読無し][通常論文]
  • 西部北太平洋２地点における水柱と堆積物表層におけるアルケノンフラックスの評価（予報）
    山本正伸, 嶋本晶文, 福原達雄, 田中裕一郎, 西村昭 地質調査総合センター速報「海洋中の堆積物形成過程に関する研究平成１２年度研究概要報告」 90 -111 2001年04月01日 [査読無し][通常論文]
  • Introduction: Geochemical cycles and global changes
    Tsunogai, S, Montani, S, Obata, H, Ono, T, Watanabe, Y, Yamamoto, M Journal of Oceanography 370 647 -650 2001年04月01日 [査読無し][招待有り]
  • 沈み込み帯における有機物の輸送過程
    山本正伸 月刊地球号外 32 96 -100 2001年04月01日 [査読無し][招待有り]
  • 山本 正伸 海洋 32 (9) 618 -622 2000年09月 [査読無し][招待有り]
  • アルケノンによる石灰質成分のフラックス算出の試み
    山本正伸 地質調査所速報「海洋中の堆積物形成過程に関する研究」平成１１年度研究概要報告 85 -89 2000年04月01日 [査読無し][通常論文]
  • Leg167：カリフォルニア縁辺海の湧昇史と古海洋学
    Lyle, M, 小泉格, 林田明, 丸山俊明, 多田隆治, 山本正伸 ODPニュースレター 14 19 1997年04月01日 [査読無し][招待有り]
  • 渡部芳夫, 山本正伸 地質ニュース 497 7 -16 1995年06月01日 [査読無し][招待有り]
  • オマーンにみる原生代・石油根源岩のラミナ構造
    山本正伸, 鈴木祐一郎, 今井登, 梶間幹雄 地質ニュース 487 口絵 1995年04月01日 [査読無し][通常論文]
  • バイオマーカーと古環境
    山本正伸 Science & Technonews Tsukuba 46 38 -40 1995年04月01日 [査読無し][招待有り]
  • パラオ諸島サンゴ礁における有機物の堆積過程とその起源
    山本正伸, 山室真澄, 茅根創 月刊海洋 27 (9) 567 -572 1995年04月01日 [査読無し][通常論文]
  • 古海洋環境の復元：分子地球化学的アプローチの現状と課題
    山本正伸 地質ニュース 495 15 -24 1995年04月01日 [査読無し][招待有り]
  • 中嶋 輝充, 渡部 芳夫, 原山 智, 山本 正伸 地質學雜誌 99 (5) ix -x 1993年05月15日 [査読有り][通常論文]
  • 東北日本女川堆積盆の堆積環境．
    渡部芳夫, 山本正伸, 今井登 「資源評価のための三次元モデリング手法に関する研究」最終年度報告書．地質調査所 15 -36 1993年04月01日 [査読無し][通常論文]
  • 東北日本中新統女川層珪藻質岩の有機分子組成と古海洋環境．
    山本正伸, 渡部芳夫 「資源評価のための三次元モデリング手法に関する研究」最終年度報告書．地質調査所 101 -129 1993年04月01日 [査読無し][通常論文]
  • 地球環境の変遷と炭化水素根源岩の形成
    渡部芳夫, 山本正伸 「炭化水素鉱床の成因と同ポテンシャルの予測技術に関する研究動向」平成３年度工業技術院特別研究推進費調査報告書 32 -49 1992年04月01日 [査読無し][通常論文]
  • 使える探査技術”石油移動指標”の開発の現状と課題所．
    山本正伸 「炭化水素鉱床の成因と同ポテンシャルの予測技術に関する研究動向」平成３年度工業技術院特別研究推進費調査報告書 1992年04月01日 [査読無し][通常論文]
  • 山本 正伸 地球科學 46 (1) 85 -85 1992年01月25日
  • 秋田県能代・鷹巣地域の女川層（岩谷層）珪質岩類のバイオマーカー組成
    山本正伸 「資源評価のための三次元モデリング手法に関する研究」第一次中間報告書．地質調査所 42 -54 1990年04月01日 [査読無し][通常論文]
  • 青森県鯵ヶ沢町中村川地域の地質と大童寺層泥質岩中の有機物 −特に，C25にピークを持つノルマルアルカン分布パターンについて
    佐々木清隆, 山本正伸 田口一雄教授退官記念論文集「石油鉱床学の諸問題」 223 -239 1986年03月01日 [査読無し][招待有り]

書籍等出版物

  • 北極環境研究の長期構想
    北極環境コンソーシアム編 
    北極環境コンソーシアム 2014年
  • 地球と宇宙の化学事典
    日本地球化学会編 
    朝倉書店 2012年
  • 地球温暖化の科学
    北海道大学大学院環境科学院編 
    北海道大学出版会 2007年
  • 有機地球化学
    石渡良志, 山本正伸編 
    培風館 2004年

担当経験のある科目（授業）

  • 自然科学実験（空中写真および水分析）北海道大学
  • 地球惑星科学実験（スメアスライド観察）北海道大学理学部
  • 地球環境学北海道大学理学部
  • 地球環境と北極域の科学北海道大学
  • 古気候を解明する北海道大学
  • 南極学特論北海道大学大学院共通
  • 古環境学基礎論北海道大学大学院環境科学院
  • 有機地球化学特論北海道大学大学院環境科学院
  • 古気候学特論北海道大学大学院環境科学院

所属学協会

  • 有機地球化学研究会運営委員   日本有機地球化学会（運営委員   日本有機地球化学会   日本地質学会（会誌編集委員）   日本地球化学会（地球化学講座編集委員）   石油技術協会（会誌編集委員）   会誌編集委員）   石油技術協会編集委員   米国地球物理学連合   日本海洋学会   欧州有機地球化学協会   石油技術協会   有機地球化学会   日本地質学会   Geological Society of JapanGeocehmical Society of JapanJapanese Association of Petroleum Geology and TechnologyJapanese Assocaition of Organic GeochemistsOceanographic Society of JapanAmerican Geophysical UnionEuropean Association of Organic Geochemists   

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2020年04月 -2025年03月 
    代表者 : 関 宰, 山本 正伸, 菅沼 悠介, 池原 実
     
    南極氷床が温暖化に対して敏感であることが明らかになり、温暖化の進行による海面上昇に対する危機感が高まっている。最新のIPCC特別報告書では将来の海面上昇予測が大幅に上方修正され、最も温暖化が進行するシナリオによれば300年後に海面が数メートル上昇するという。この上方修正は南極氷床融解量の見積もりの変更によるものであり、現在「温暖化が進行した場合にどの段階でどのような速度で南極氷床融解が進行しうるのか？」が海面上昇予測における核心的な問いになっている。氷床の応答時間は長く、その特性の本質的な理解にはより温暖な気候状態における長期間の氷床変動を調べる必要があり、今後の予測に関しては不確かさが非常に大きい。本研究では、国際深海科学掘削計画（IODP）において西南極ロス海で昨年掘削された最新の海底堆積物コアを用い、現在より全球平均気温が+1℃から+5℃（海面が+5から+40mまで上昇）温暖であった時代における南極氷床の融解過程を100年スケールの解像度で復元し、+5℃まで温暖化が進行する過程における南極氷床融解の特性を明らかにする。 中期鮮新世温暖期（約330-300万年前）および中期中新世気候最適期（約1600万年前前後の数万年間）を対象とする。最新の地球化学的手法を駆使し、海水温や南極氷床の変動の復元および氷床の融解地域の特定を行い、氷床の大規模かつ不可逆的な融解イベントが起こっていたのかどうか、もし起こっていたとしたらどの地域でどのように進行するのか、またそれを導く要因の解明を行う。
  • 過去600万年間にわたる大気中二酸化炭素濃度と気候の相互作用の解明
    日本学術振興会：科学研究費補助金基盤研究（S）
    研究期間 : 2019年06月 -2024年03月 
    代表者 : 山本 正伸
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2018年04月 -2023年03月 
    代表者 : 高橋 啓一, 百原 新, 渡辺 勝敏, 田畑 諒一, 里口 保文, 山川 千代美, 山本 正伸, 三浦 収, 林 竜馬, 大槻 達郎, 仲谷 英夫
     
    【古地理班】地質学的観点から琵琶湖の地史研究を行ったほか，琵琶湖南湖東岸で行われたボーリング試料の堆積年代の再検討を行い，その成果を報告した（里口編，2021）． 【植生史・古気候班】琵琶湖地域での水辺の古植生の特徴を捉えるため，同時代の他の地域での比較研究を進めた．10月および11月に八王子市北浅川河床の調査を行い，10点の樹幹化石を確認し，試料を採取した．また，この場所から以前産出した樹幹化石（国立科学博物館蔵）の同定を行い，メタセコイア属であることを明らかにした． 【陸上大型動物班】琵琶湖地域から発見されている脊椎動物化石の意義を検討するために，後期更新世の化石について再検討した．例えば，ナウマンゾウでは，300か所の地点を再検討し，初出の時期がMIS 10の時代（約36～34万年前）であったとするのが妥当であるという結論に達した．また、オオツノジカの産出時代については，確かな年代を示すものは，MIS 6の時代（約13万年前）以降であり，こうした時代に淡水性の生物も日本列島に渡来した可能性を指摘した．また，マイクロウェアの研究においては，ミエゾウの化石資料からレプリカを収集した．さらに，ナウマンゾウ化石を用いてマイクロウェアの定量的な解析を行う方法を検討し，報告した（山田，2021）． 【水棲生物班】琵琶湖及び周辺地域の魚類や貝類の進化史を描き出すために，引き続き様々な分子遺伝解析を行った．魚類においては，琵琶湖のカマツカの表現型多様性パターンに関する形態比較，食性解析，集団遺伝解析から，本種における食性に関係した集団内の適応的な機能形態的多様性の拡大を明らかにし，報告した（Endo and Watanabe, 2020）．貝類については，西日本のカワニナに見られるmtDNAが琵琶湖起源であることを明らかにし，報告した（Miura et al., 2020）.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2019年04月 -2022年03月 
    代表者 : 長谷川 精, 石村 豊穂, 山本 正伸, 太田 亨, 勝田 長貴, 村山 雅史, 山田 圭太郎
     
    モンゴルの白亜系年縞湖成層を対象に超高時間分解能な解析（季節レベル～数十年解像度）を行い，約1億年前の気候変動を詳細に解読した。年縞ラミナを対象に蛍光顕微鏡解析と微小領域同位体比分析を行った結果，太陽活動（11年周期や125年周期）を反映した夏季藻類生産量と降水量の変動が明らかになった。またXRFコアスキャナーを用いて約35万年区間を解析した結果，蒸発/降水量変動の指標であるCa/Tiが，千年スケールおよび地球軌道要素変動で大きく振幅変調したことが明らかになった。この千年スケール変動は高緯度深層水の沈み込み強弱を伴っていた可能性が示唆され，「温室期」の気候安定性を理解する上でも重要である。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2019年04月 -2022年03月 
    代表者 : 守屋 和佳, 長谷川 卓, 山本 正伸, 石村 豊穂
     
    本研究では，地球温暖化時代の極相期の一つである白亜紀中期セノマニアン期からチューロニアン期(CTB;約9千4百万年前)に生じた海洋無酸素事変を対象として，平均古水温の緯度勾配と，古水温の季節変動幅との時系列変動を明らかにする．平均古海水温の算出に加え，海水温の季節変動幅の算出から，炭素循環擾乱イベントに対する海水温の動的応答の解析を行うことで，温室時代の気候フィードバックがどのような順序で，どのような時間スケールで生じたのかを明らかにする．2020年度は，早稲田大学現有の連続フロー型安定同位体比質量分析計を用いて，堆積物中の有機炭素および全窒素安定同位体比分析を行った．堆積物全岩試料を乾燥させ，均質に粉末化した後に脱灰し，これらを安定同位体比分析に使用した．黒色頁岩が産出する層準では，堆積物中の有機炭素含有量が20wt%を超える層準が確認され，CTBに生じた海洋無酸素事変の層準を確認した．また，海洋無酸素事変が発生した層準よりも下位の層準でも有機炭素含有量の増加を検出した．この層準は大規模な海洋無酸素事変の前駆的現象である可能性があり，今後詳細な検討を行う．有機炭素同位体比は黒色頁岩が産出する層準よりも有意に下位の層準から増加し始め，黒色頁岩層準で最大に達した．また，炭素同位体比の変化に同調して，堆積物中の炭素／窒素含有量比も大きく変化することから，海洋無酸素事変に並行して堆積物に供給される炭素の給源組成に変化が起きていたことが推測される．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2018年04月 -2022年03月 
    代表者 : 佐川 拓也, 松崎 賢史, 山本 正伸, 久保田 好美
     
    全海洋で最も温暖な西部熱帯太平洋域における過去の鉛直水温構造の変化と全球的な気候変動の関係を理解するために、国際深海科学掘削計画で採取した堆積物コアに含まれる浮遊性有孔虫３種の殻の化学分析を行った。過去４００万年間にわたる表層から亜表層にかけた鉛直水温記録を復元することで表層暖水塊の厚さの変化を推定した。その結果、熱帯太平洋の暖水塊厚さの変化は熱帯－極域の温度勾配の変化と連動してることが明らかになった。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2017年04月 -2021年03月 
    代表者 : 関 宰, 池原 実, 堀川 恵司, 山本 正伸, 菅沼 悠介
     
    産業革命前よりも全球気温が+1℃高い最終間氷期は、海水準が+6-9m高かったと推定されている。最終間氷期の南極氷床の動態をより深く理解することは、将来の温暖化シナリオにおける海水準の変化を予測する上で重要な知見を提供する。本研究では、東南極付近で採取された海底堆積物コア（GC1407）のネオジム同位体比やベリリウムの分析などを行い、最終間氷期のウィルクス氷床（WBIS）の氷床変動を復元した。その結果、LIG期間中のWBISの後退の時期とその大きさを調べた。その結果、最終間氷期の前半だけでなく、後半にも著しいWBISの後退が起こっていたことを初めて示した。
  • 西部赤道太平洋Exp.363古環境復元（掘削航海番号：Exp. 363 種別 [JR]）
    国立研究開発法人海洋研究開発機構：IODP乗船後研究委託業務
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 山本正伸
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2016年04月 -2020年03月 
    代表者 : 守屋 和佳, 山本 正伸, 石村 豊穂
     
    本研究では，統合国際深海掘削計画第342次航海により，カナダニューファンドランド沖から採取された，始新世／漸新世境界の堆積物を用いて研究を実施した．堆積物から抽出された浮遊性有孔虫化石の酸素同位体比，おなじく堆積物から抽出された有機分子のTEX86解析から，始新世／漸新世境界における平均的海水温，海水温の季節変動幅，および氷床量の時系列変動を明らかにした．
  • 長鎖脂肪酸の同位体比を用いた完新世長江下流域の乾湿および植生変動の復元
    文部科学省：新学術領域研究（研究領域提案型）公募研究
    研究期間 : 2018年04月 -2020年03月 
    代表者 : 山本 正伸
  • アジアモンスーンの長期的変動に関する共同研究
    日本学術振興会：頭脳循環を加速する戦略的国際研究ネットワーク推進プログラム
    研究期間 : 2017年10月 -2020年 
    代表者 : 山本正伸
  • 別府湾柱状堆積物の解析にもとづく過去8000年間の太平洋十年規模変動の復元
    日本学術振興会：科学研究費補助金基盤研究（A）
    研究期間 : 2016年04月 -2019年03月 
    代表者 : 山本正伸
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 長谷川 卓, 堀川 恵司, 山本 正伸, 守屋 和佳, 神谷 隆宏, 森下 知晃, 後藤 晶子
     
    カナダ国ブリティッシュコロンビア州バンクーバー島近傍の小島であるホーンビー島の海蝕台に露出する上部白亜系カンパニアン階－マーストリヒチアン階の地質調査を行い，得られた地質試料の酸素および炭素同位体比分析を行った． 最も重要な成果は，長径約２ｍの炭酸塩コンクリ―ションがメタン冷湧水性炭酸塩であることを同定したこと，そしてその酸素同位体比から，カンパニアン期後期には東太平洋の水深約200ｍの海底に約8℃という，深層水に匹敵する低温の水が存在したことが明らかになったことである．このことは，この場所に深層からの湧昇流が存在したことを示唆し，北東太平洋の古海洋を考察する上で非常に重要である．
  • ベンガル湾Exp.353古環境復元（掘削航海番号：Exp. 353 種別 [JR]）
    国立研究開発法人海洋研究開発機構：IODP乗船後研究委託業務
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 山本正伸
  • ボルネオ島泥炭掘削：過去4000年間の熱帯大気対流活動の復元
    日本学術振興会：科学研究費補助金基盤研究（B）海外学術
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 山本正伸
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2014年06月 -2018年03月 
    代表者 : 長谷川 卓, 木元 克典, 堀川 恵司, 山本 正伸, 守屋 和佳, 岡 顕, 後藤 晶子, 外山 浩太郎
     
    世界各地の8つの始新世の深海掘削コアを用いて遠洋性バライト及び炭酸塩付随硫酸(CAS)を抽出し，その硫黄同位体比(d34S)を測定した．遠洋性バライトは極めてまれで，当時のNADWをトレースする素材にはならなかった．50Maのd34S急上昇イベントはバライトとCASのどちらにも検出されなかった．海水のd34Sは51-41Maの期間に漸進的に上昇した．バライトとCASの両方を検出した試料における両者の比較からCASが過去の海水のd34Sプロキシとして機能することが解った．世界海水のd34Sは51-47Maには均質だが，45-40Maは南北傾斜を見せる．北極海アウトフロー水が影響した可能性がある．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2013年04月 -2016年03月 
    代表者 : 安藤 寿男, 長谷川 精, 太田 亨, 山本 正伸, 長谷部 徳子, 長谷川 卓
     
    モンゴル南東部の白亜紀前期のシネフダグ層の湖成泥岩層を対象に，露頭とボーリング掘削による連続コアから，精密サイクル層序を確立した．凝灰岩中のジルコンのFT，U/Pb年代からその堆積年代は123-119Ma（アプチアン前期）と判定した．泥岩層の年縞の各種解析から，約2，10，40万年というミランコビッチ周期の地球軌道要素変動に起因した湖水位変動に加えて，太陽活動周期（約11年，約88年，約400年）に類似した周期の気候変動が記録されていることが判明した．
  • 南大洋と北極海の完新世水温変動の高時間解像度復元
    日本学術振興会：科学研究費補助金基盤研究（B）
    研究期間 : 2013年04月 -2016年03月 
    代表者 : 山本正伸
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2013年04月 -2015年03月 
    代表者 : 山下 洋平, 山本 正伸
     
    海洋細菌由来の難分解性溶存有機物が海洋に普遍的に存在する事は広く知られている。一方、近年、海洋には古細菌が普遍的に存在し、その存在数は海洋細菌と同等である事が明らかとなった。すなわち、海洋細菌と同様に古細菌由来の難分解性成分が海洋溶存有機物中に普遍的に存在する可能性がある。しかし、古細菌由来の溶存有機物は検出されていない。 本申請研究では、海洋溶存有機物から古細菌特有の細胞膜構成脂質であるグリセロール・ジアルキル・グリセロール・テトラエーテル（GDGTs）を検出する事を目的とした。その結果、西部北太平洋および太平洋側北極海の表層から深層における溶存有機物画分からGDGTsが検出された。
  • 堆積物中セルロース酸素同位体比分析による古気候復元
    日本学術振興会：科学研究費補助金萌芽研究
    研究期間 : 2013年04月 -2015年03月 
    代表者 : 山本正伸
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2010年04月 -2014年03月 
    代表者 : 加 三千宣, 山本 正伸, 中村 有吾, 竹村 恵二, 守屋 和佳, 谷 幸則
     
    地球温暖化に伴って、数十年スケールで大変動する太平洋のイワシ資源は、今後どのような変動を示すのか。中世温暖期におけるイワシ存在量の数十年スケール変動の振幅変化とそのメカニズムの解明を試みた。マイワシには過去1000年間において300年スケールの変動が見つかり、中世温暖期とそれにつづく小氷期という汎地球規模の気候変動に対して応答しないことがわかった。一方で、マイワシ存在量の300年スケール変動の背後には太平洋とその東西陸域を含む空間規模を持つ気候変動と関連している可能性が示唆された。日本マイワシ資源変動の環境要因として、北西太平洋の餌環境が重要である可能性が示唆された。
  • 別府湾海底コアの解析にもとづく10年スケール気候変動・レジームシフトの歴史的変遷の解明
    三井物産環境基金：研究助成
    研究期間 : 2010年04月 -2013年03月 
    代表者 : 山本正伸
  • バイオマーカー水素同位体比を用いた過去１５万年間の熱帯太平洋大気対流活動の復元
    日本学術振興会：科学研究費補助金基盤研究（A）
    研究期間 : 2007年04月 -2012年03月 
    代表者 : 山本正伸
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2009年 -2011年 
    代表者 : 安藤 寿男, 長谷川 卓, 太田 亨, 山本 正伸, 長谷部 徳子, 高橋 正道, 長谷川 精
     
    モンゴル南東部の白亜紀中期(シネフダグ層)とジュラ紀中期(エーデムト層)の湖成層を対象に,(1)炭素同位体比,カイエビ化石,凝灰岩のF-T年代などに基づく年代層序の構築と,(2)岩相変化(頁岩・ドロマイト互層)から復元した湖水位変動の周期解析,鉱物・主要元素組成による化学風化度変動,有機化学指標(TEX_<86>)による湖水温復元などに基づく古環境変動復元を行い,モンゴル湖成層には,白亜紀中期温室期に頻発した海洋無酸素事変期(OAE1a～1b)の,地球軌道要素を反映した降水量および古気温変動が記録されている.
  • 氷河期の熱帯温度の研究
    財団法人交流協会：共同研究事業
    研究期間 : 2006年04月 -2008年03月 
    代表者 : 山本正伸
  • TEX86指標を用いた過去６００万年間の北半球水温緯度勾配の復元
    日本学術振興会：科学研究費補助金萌芽研究
    研究期間 : 2006年04月 -2008年03月 
    代表者 : 山本正伸
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2006年 -2008年 
    代表者 : 長尾 誠也, 山本 正伸, 入野 智久, 藤嶽 暢英, 荒巻 能史
     
    石狩川河川水の懸濁態有機物の放射性炭素のδΔ14C値は年間を通じて大きな変動を示し、雪融けと降雨時には古い有機物が移動していることが明らかとなった。その変動幅は下流域<中流域<河口域<上流域の順であり、河川に供給される懸濁態の有機物は、河川流域環境や水の供給経路等の特徴と関連して変動することが考えられる。これらの結果から、沿岸域への影響評価には、雪融けと降雨時の粒子の供給量と供給機構の重要性が示唆された。
  • 陸起源有機分子を用いた融氷期東アジア水循環の高時間解像度復元
    日本学術振興会：科学研究費補助金基盤研究（B）
    研究期間 : 2004年04月 -2007年03月 
    代表者 : 山本正伸
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2003年 -2005年 
    代表者 : 長尾 誠也, 山本 正伸, 藤嶽 暢英, 入野 智久, 児玉 宏樹
     
    本研究の目的は。重要ではあるがデータの蓄積に乏しく、季節や地域によりその変動幅が大きく、沿岸域での炭素の吸収と放出量の見積もりを行う上で不確定要素の1つと考えられている河川から海洋への有機体炭素の移行量と移行動態を検討するものである。そのために、寒冷、温帯、および熱帯域の河川を対象に、河川流域の特性、植生、気候による土壌での有機物の分解と生成機構・時間スケールと河川により供給される有機物の特性、移行量との関係を難分解性有機物である腐植物質に着目して調べた。 泥炭地を有する十勝川、湿原を流れる別寒辺牛川、褐色森林土の久慈川、スコットランド、ウクライナ、インドネシアの河川水中の溶存腐植物質を非イオン性の多孔質樹脂XAD-8を用いた分離法により分離生成し、いくつかの特性について分析を行った。また、河川水中の有機物の起源と移行動態推定のために、放射性炭素(Δ^<14>C)および炭素安定同位体比(δ^<13>C)を測定し、両者を組み合わせた新しいトレーサー手法を検討した。その結果、放射性炭素(Δ^<14>C)は-214〜+180‰の範囲で変動し、土壌での溶存腐植物質の滞留時間が流域環境により大きく異なることが考えられる。 上記の検討と平行して、連続高速遠心機により河川水20〜100Lから懸濁粒子を分離し、放射性炭素および炭素安定同位体比を測定した。その結果、久慈川では年間を通してΔ^<14>Cは-19〜-94‰、炭素同位体比(δ^<13>C)は-24.0〜-31.1‰の範囲で変動し、石狩川ではΔ^<14>Cは-103〜-364‰、δ^<13>Cは-25.9〜-34.2‰、十勝川ではΔ^<14>Cは-111〜-286‰、δ^<13>Cは-25.0〜-31.6‰であった。これらの結果は、流域の環境条件および雪解けや降雨による河川流量の変動等がこれら炭素同位体比の変動を支配している可能性が考えられる。 以上の結果から、放射性炭素および炭素安定同位対比を組み合わせる新しいトレーサー手法は、河川の流域環境の違いを反映し、移行動態および起源推定のために活用できることが示唆された。また、現時点では、大部分の地域では核実験以前に陸域に蓄積された有機物が河川を通じて移行していることが明らかとなった。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2004年 -2004年 
    代表者 : 多田 隆治, 鬼頭 昭雄, 酒井 治孝, 福澤 仁之, 横山 祐典, 山本 正伸
     
    本企画研究では、 1)6月25日-27日に上海,同斉大学で開催された第2回IGCP-476国際シンポジウム・ワークショップと、引き続き6月28日-7月1日に行なわれた揚子江上流巡検・現地討論会に、IGCP-476国内委員会の主要メンバー10名を含む12名を参加させ、IODP,ICDP,IMAGESを活用したヒマラヤ・チベットの隆起と東アジア-北西太平洋域における気候・海洋変動の連動性に関する研究発表および研究計画の提案を行った。更に中国内陸部共同調査や東シナ海共同調査等の実現へ向けての打ち合わせを行なった。また、各国からの提案を基に、更に計画相互の連携や国際共同研究の可能性を探った。 2)IGCP-476が目指す科学目標を広く世間に知らせるために、地質学会第111回年会(於:千葉大)において、9月20日にシンポジウム「ヒマラヤ-チベットの隆起とアジアモンスーンの進化、変動」を開催し、4件の講演を行なった。その結果は、地質学雑誌特集号に発表される予定である。 3)本企画研究の年度前半の活動を通じて、気候モデルコミュニティーと古気候コミュニティー、テクトニクス研究コミュニティーの間の相互理解を更に深める事が重要であるとの認識に至った。そこで、各コミュニティー間の相互理解を進め、次のステップの戦略を考える目的で、12月23日-24日に、九州大学国際研究交流プラザにおいてIGCP-476国内ワークショップ「アジア・モンスーンの進化、変動理解のための統合的研究戦略」を開催し、22名の講演者、41名の参加者を集めた。そして、そこで、IGCP-476の基に結集した研究者コミュニティーの輪を、今後どの様に広げ、どの様な研究テーマに向かって、どの様な戦略で、研究活動を推進して行くべきかについて、議論を行なった。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2003年 -2004年 
    代表者 : 多田 隆治, 山本 正伸, 横山 祐典, 板木 拓也
     
    本研究では、日本海から採取された複数のコアを用いて、特に最終氷期から後氷期にかけての日本海海洋環境の高時間解像度復元を行ない、同じコアからモンスーン強度変動の指標(風成塵粒度)を取り出して海洋環境指標と比較する事により、アジアモンスーンの変動に応答して日本海の表層および深層環境がどのように変化したかを立体的に明らかにする事を目的として研究を行なった。 海洋表層水環境の指標としては、浮遊性有孔虫の酸素同位体比、アルケノン水温、浮遊性有孔虫の^<14>C年代、珪藻群集組成、有機物含有量などを用い、表層水温、塩分、起源、生物生産性などを推定した。深層水の指標としては、平行葉理保存度、有機炭素/硫黄比、炭酸塩鉱物含有量、底生有孔虫の酸素同位体比などを利用し、深層水の溶存酸素濃度、循環速度、CCDなどを復元した。更に、モンスーン強度の指標としては、風成塵の粒度、フラックス、石英のESR信号強度、鉱物組成などを用い、偏西風の強さ、黄砂の供給源、後背地の乾燥度などを推定した。 こうした結果を基に、表層水環境、深層水環境、アジアモンスーン変動の位相関係を調べ、夏季モンスーンフロントが黄河、揚子江集水域に達した時期に栄養塩に富み、塩分が低い黄海・東シナ海沿岸水域が拡大して日本海に流入し、日本海の生物生産性を上げると共に弱い密度成層を引き起こして深層水循環を低下させ、深層水の還元化を招いたとするTada et al.(1999)の仮説を検証し、それが基本的に正しい事を示した。また、夏季モンスーン変動に伴い、黄海、東シナ海沿岸水の日本海への流入量が増加した時に、日本海の水温分布、表層における生物生産性、深層水循環はどう変化したか、そうした変化はどのくらいの時間で起こったのか、をより具体的に明らかにした。更に、規模は小さいが、同様の周期や変動様式を持った変動が、後氷期にも存在した可能性も示した。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2001年 -2003年 
    代表者 : 南川 雅男, 入野 智久, 長尾 誠也, 山本 正伸, 松井 章, 西本 豊弘
     
    先史人類が生活した痕跡を遺跡から検出することを目的に、土壌や骨に含まれる有機分子と炭素窒素同位体の分析方法を検討し、その指標の有効性について研究した。特に農耕や家畜の飼育などに焦点をあて、そのような生業活動の後に土壌や遺物に残留したはずの特徴ある化学物質を脂質化合物から同定し、人類活動の判別方法として妥当性を試験した。可能性のあるマーカーとしてステロイド成分、脂肪酸、などの脂質について検討した。農耕栽培によって撹乱を受けた土壌を、自然植生の土壌と区別するものとして土壌有機物の^<13>C、^<15>N濃度の変化が有効であることを見いだした。C4植物の栽培による^<13>C濃度の増加は現代のトウモロコシ栽培地と同様であった。また家畜や人類の排泄物からの動物性脂質由来の有機分子は畑作における施肥のマーカーとして検出できるかどうかを江戸時代の埋没遺跡(上福島中町遺跡)の人家跡と畑跡の土壌で検討した。ヒトの胆汁に含まれるデオキシコール酸が肥だめ跡や、施肥をしたと思われる畑土壌から検出された。現在飼育されている家畜糞から作られる堆肥についても研究し、ステロール、脂肪酸、胆汁酸の構成成分の分析を行った。反芻動物とそれ以外、鳥類などの種類の違いにより、分子組成の異なる結果が得られた。これらの分析手段を縄文前期の美々遺跡の土壌に応用したところ、自然植生の土壌と異なり、何らかの人為攪乱の可能性が示唆された。この方法による栽培や施肥の同定を検証する方法として、有機バイオマーカの利用法が有効であることを明らかにした。家畜化によりイノシシの食性が変化することを、約7千年前から2千年前までの琉球や韓国出土骨の分析により検証した。その結果琉球列島で出土した弥生相当期以前のイノシシには、現地産の野生イノシシとは異なる食性の個体が多数含まれており、その一部は朝鮮半島とのつながりを示す結果であることを明らかにした。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2001年 -2003年 
    代表者 : 大場 忠道, 山本 正伸, 長尾 誠也, 岡田 尚武, 成田 尚史, 入野 智久, 村山 雅史, 的場 保望, 本山 功
     
    本研究は、日本列島東岸の鹿島沖の水深2,200mから採取されたIMAGES海底コア(MD01-2421、長さ45.6m)を、班員のそれぞれの専門を生かして過去2回の氷期・間氷期を含む14万年間について、気候変化に伴う黒潮と親潮の消長、それによる海洋表層の水温・塩分の変化、生物生産量や海底環境の変化、供給された陸源物質の量的・質的変化などを総合的に解析し、氷床コアや陸上コアに見られる環境変化と結び付けられる程度に、当海域の海洋環境変化を高分解能で復元することを目的として研究が行われた。その結果、過去の全球的な気候変化に応じて黒潮と親潮の南北移動が起こっており,最終氷期やその前の氷期には、現在の釧路沖あるいは根室沖と同様な親潮が鹿島沖まで南下していた。その結果,有孔虫の酸素同位体比やMg/Caから推定される表層水温は現在よりも12〜13℃低下していた。しかし、アルケノンによる古水温推定や微化石による水塊移動とはそれぞれ微妙に異なっている。また、アルケノンによる古水温には2.3万年の歳差運動周期が認められる。酸素同位体比からの古水温や放散虫の群集組成には、グリーンランド氷床コアのDansgaard-Oeschgerサイクルが認められ、それは海流系の南北移動で引き起こされた。花粉分析の結果は、過去14万年間に寒冷・乾燥気候(亜高山帯針葉樹林)〜温暖気候(温〜冷温帯広葉樹林)〜冷涼・多雨気候(スギ・コウヤマキ優占林)の変動サイクルが4回繰り返し生じたことが明らかになった。その時期は、MIS 6〜5e、5d〜5b前半、5b後半〜4前半、3後半〜1であったが、海洋環境の変遷よりも2〜3千年早く起こっている。また、花粉分析から湿潤と考えられる時期に砕屑物質の供給量が増加している。さらに、オパール量は氷期に少なくその原因として海氷の発達や表層塩分の低下などが考えられる.また、底生有孔虫群集から氷期には北大西洋深層水の形成が弱く,その結果も鹿島沖における氷期の生物生産量の低下に関連していた可能性がある。
  • IGCP-581 第二回シンポジウム「アジアの河川システムの発達：テクトニクスと気候」
    日本地球掘削科学コンソーシアム：会員提案型活動経費
    代表者 : 山本正伸

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