Researcher Database

Masanobu Yamamoto
Faculty of Environmental Earth Science Earth System Science Biogeosystem Science

Researcher Profile and Settings


  • Faculty of Environmental Earth Science Earth System Science Biogeosystem Science

Job Title

  • Professor


  • 1995 Ph.D (Science) Nagoya University(Nagoya University)


Research funding number

  • 60332475

J-Global ID

Research Interests

  • Paleoclimatology   古海洋学   有機地球化学   Organic Geochemistry Paleoceanography   

Research Areas

  • Natural sciences / Biogeoscience
  • Natural sciences / Space and planetary science
  • Natural sciences / Solid earth science
  • Natural sciences / Solid earth science

Academic & Professional Experience

  • 2019/11 - Today Hokkaido University Faculty of Environmental Earth Science Professor
  • 2006/04 - 2019/10 - 大学院地球環境科学研究院 准教授
  • 2000 - 2006 大学院地球環境科学研究科 助教授
  • 2000 - 2006 Associate Professor
  • 2006 - Associate Professor,Faculty of Environmental Earth Science
  • 1996 - 2000 Tohoku University Graduate School of Science
  • 1996 - 2000 Associate Professor
  • 1995 - 2000 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 - 2000 Chief Researcher
  • 1988 - 1995 工業技術院地質調査所燃料部石炭課 研究員
  • 1988 - 1995 Researcher,Geological Survey of Japan


  •        - 1988  Tohoku University
  •        - 1988  Tohoku University  Graduate School, Division of Natural Science
  •        - 1986  Tohoku University  Faculty of Science
  •        - 1986  Tohoku University  Faculty of Science

Association Memberships

  • 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   

Research Activities

Published Papers

  • 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 0584-8547 2018/08/01 [Refereed][Not invited]
    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 1040-6182 2018/07/20 [Refereed][Not invited]
    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) 1440-1738 2018/05/01 [Refereed][Not invited]
    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 1432-072X 2018/03/01 [Refereed][Not invited]
    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 0262-821X 2018/01/05 [Refereed][Not invited]
    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 1040-6182 2018 [Refereed][Not invited]
    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 0079-6611 2017/12 [Refereed][Not invited]
    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 1040-6182 2017/11 [Refereed][Not invited]
    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 1040-6182 2017/09 [Refereed][Not invited]
    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 1040-6182 2017/09 [Refereed][Not invited]
    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 1814-9324 2017/09 [Refereed][Not invited]
    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 1866-3508 2017/09 [Refereed][Not invited]
    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 0921-8181 2017/07 [Refereed][Not invited]
    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 0289-0003 2017/06 [Refereed][Not invited]
    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.
  • M. Yamamoto
    Journal of Geological Society of Japan 124 3 - 16 2017/01/01 [Refereed][Not invited]
  • 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 1873-9652 2016/12 [Refereed][Not invited]
    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 0959-6836 2016/11 [Refereed][Not invited]
    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 0016-7037 2016/10 [Refereed][Not invited]
    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 0959-6836 2016/10 [Refereed][Not invited]
    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 0278-4343 2016/08 [Refereed][Not invited]
    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 0967-0645 2016/03 [Refereed][Not invited]
    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 1040-6182 2016/03 [Refereed][Not invited]
    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 1367-9120 2016/03 [Refereed][Not invited]
    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.
  • Yaeko Igarashi, Masanobu Yamamoto, Atsushi Noda, Ken Ikehara, Hajime Katayama
    MARINE GEOLOGY 368 58 - 65 0025-3227 2015/10 [Refereed][Not invited]
    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 0304-4203 2014/10 [Refereed][Not invited]
    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 1040-6182 2014/10 [Refereed][Not invited]
    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 0146-6380 2014/08 [Refereed][Not invited]
    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 1040-6182 2014/05 [Refereed][Not invited]
    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 0916-8370 2014/02 [Refereed][Not invited]
    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.
  • Masanobu Yamamoto, Fukashi Ohira, Fujio Kumon
    GEOCHEMICAL JOURNAL 48 (2) 207 - 217 0016-7002 2014 [Refereed][Not invited]
    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 [Refereed][Not invited]
  • Gang Li, Hisao Ando, Hitoshi Hasegawa, Masanobu Yamamoto, Takashi Hasegawa, Tohru Ohta, Noriko Hasebe, Niiden Ichinnorov
    ALCHERINGA 38 (3) 305 - 316 0311-5518 2014 [Refereed][Not invited]
    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 1525-2027 2013/12 [Refereed][Not invited]
    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 0031-0182 2013/09 [Refereed][Not invited]
    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 1367-9120 2013/06/05 [Refereed][Not invited]
    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 1367-9120 2013/06/05 [Refereed][Not invited]
    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 1367-9120 2013/06 [Refereed][Not invited]
    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 1814-9324 2013 [Refereed][Not invited]
    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 0146-6380 2012/12 [Refereed][Not invited]
    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 0916-8370 2012/12 [Refereed][Not invited]
    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 0267-8179 2012/12 [Refereed][Not invited]
    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 0267-8179 2012/12 [Refereed][Not invited]
    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 0036-8075 2012/09 [Refereed][Not invited]
    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.
  • Yaeko Igarashi, Masanobu Yamamoto, Ken Ikehara
    JOURNAL OF ASIAN EARTH SCIENCES 40 (6) 1102 - 1110 1367-9120 2011/04 [Refereed][Not invited]
    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 1367-9120 2011/04 [Refereed][Not invited]
    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.
  • Sze Ling Ho, Masanobu Yamamoto, Gesine Mollenhauer, Masao Minagawa
    ORGANIC GEOCHEMISTRY 42 (1) 94 - 99 0146-6380 2011/01 [Refereed][Not invited]
    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 0094-8276 2011/01 [Refereed][Not invited]
    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 0277-3791 2010/10 [Refereed][Not invited]
    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.
  • Saki Harii, Masanobu Yamamoto, Ove Hoegh-Guldberg
    MARINE BIOLOGY 157 (6) 1215 - 1224 0025-3162 2010/06 [Refereed][Not invited]
    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
    Bulletin of the Geological Survey of Japan 61 325 - 336 1346-4272 2010 [Refereed][Not invited]
    &nbsp;&nbsp;&nbsp;&nbsp;We obtained a continuous 45 m-long core from the Miocene sedimentary sequence and basement Cretaceous granite at Kanamaru, northeast Japan. The Miocene sequence intercalates with a uranium-rich seam (U = 25-100 ppm; Th = 23-42 ppm). We analyzed the kerogen and biomarkers in the core to characterize the organic matter.<br>&nbsp;&nbsp;&nbsp;&nbsp;Visual kerogen analysis indicated that coaly and woody kerogen is abundant in relatively organic-rich samples, while amorphous kerogen is abundant in organic-lean samples. Pyrolysis gas chromatography-mass spectrometry demonstrated that the organic matter in pyrolysates comprises mainly alkyl-aromatic hydrocarbons (alkyl-benzenes, alkyl-indenes, alkyl-naphthalenes, etc.) and n-alkanes. Acyclic isoprenoid alkanes (mainly pristane), n-alkenes, and n-fatty acids were detected as minor components. Most of these compounds are characteristic of the typeIII kerogen that derived from terrestrial higher plants. These results suggest that amorphous kerogen originated from terrestrial higher plants, and we speculate that they were heavily degraded by oxidation and lost their woody texture.<br>&nbsp;&nbsp;&nbsp;&nbsp;Thermal alteration index (TAI) of <i>Pinus</i> pollen was about 2.6, and Tmax values of Rock-Eval pyrolysis range from 441 &deg;C to 444 &deg;C, which indicate that the thermal maturation of the coaly shale reached the stage of early catagenesis. This maturity was also suggested by high abundance of diagenetically generated isomers of hopanes in pyrolysates.<br>&nbsp;&nbsp;&nbsp;&nbsp;In the sediment sequence, a peak of uranium and uranium/thorium ratio is ca. 2 m shallower than the peak of organic carbon content, but it corresponds to a lithological boundary. This inconsistency suggests that organic matter was not involved in concentrating uranium. Uranium was possibly concentrated from groundwater at the lithological boundaries between different redox levels during the period of high groundwater level.
  • Masanobu Yamamoto
    JOURNAL OF QUATERNARY SCIENCE 24 (8) 836 - 847 0267-8179 2009/12 [Refereed][Not invited]
    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 0916-8370 2009/12 [Refereed][Not invited]
    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.
  • Amo Miki, Hagino Kyoko, Suzuki Noriyuki, Horiguchi Takeo, Yamamoto Masanobu
    Researches in organic geochemistry 25 (0) 91 - 94 1344-9915 2009/11/30 [Refereed][Not invited]
  • Yamamoto Masanobu
    Fossils. 0 (86) 45 - 58 2009/10/16 [Refereed][Not invited]
    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 0031-0182 2009/09/15 [Refereed][Not invited]
    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 0921-8181 2009/07 [Refereed][Not invited]
    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 0091-7613 2009/07 [Refereed][Not invited]
    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.
  • YAMAMOTO Masanobu, IGARASHI Yaeko, OBA Tadamichi
    The Quaternary research 48 (3) 195 - 206 2009/06/01 [Refereed][Not invited]
  • 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 1525-2027 2009/03 [Refereed][Not invited]
    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.
  • Kumon Fujio, Yamamoto Masanobu, Nagahashi Yoshitaka, Aoike Kan
    The Journal of the Geological Society of Japan 115 (7) 301 - 310 0016-7630 2009 [Refereed][Invited]
    We reviewed the results of previous studies on paleoclimate and paleoenvironment in and around the Japanese Islands during the Last Interglacial period. Sediment cores recovered from deep-sea settings around the Japanese Islands provide valuable information in understanding the ocean paleoenvironment and age framework since marine isotope stage 6. Analyses of pollen, diatoms, and total organic carbon in lake sediments have contributed to clarifying the land climate in detail, in combination with age constraints provided by tephra marker beds. Great progress has been made in tephra stratigra...
  • Yamamoto Masanobu
    The Journal of the Geological Society of Japan 115 (7) 325 - 332 0016-7630 2009 [Refereed][Not invited]
    This study presents a new perspective of North Pacific paleoceanography over the last two glacial cycles, based on assessments of U37K’-derived paleotemperature records from IMAGES Core MD01-2421 off central Japan and Ocean Drilling Program (ODP) Sites 1014 and 1016 off California. The temperature differences between ODP Sites 1014 and 1016 (ΔSSTNEP=SSTODP1014-SSTODP1016) reflect the intensity of the California Current. Comparison of ΔSSTNEP and SST derived from Core MD01-2421 reveals anti-phase variations: high ΔSSTNEP (weakening of the California Current) corresponds to low SST at the Jap...
  • 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
    Yamamoto Masanobu
    化石 86 44 - 57 2009 [Refereed][Not invited]
  • 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 [Refereed][Not invited]
  • Tomoya Shintani, Masanobu Yamamoto, Min-Te Chen
    TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES 19 (4) 341 - 346 1017-0839 2008/08 [Refereed][Not invited]
    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 1017-0839 2008/08 [Refereed][Not invited]
    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.
  • Masanobu Yamamoto, Tatsufumi Okino, Saiko Sugisaki, Tatsuhiko Sakamoto
    ORGANIC GEOCHEMISTRY 39 (6) 754 - 763 0146-6380 2008 [Refereed][Not invited]
    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 0967-0637 2007/09 [Refereed][Not invited]
    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 0025-3227 2007/03 [Refereed][Not invited]
  • Masanobu Yamamato, Masumi Yamamuro, Yuichiro Tanaka
    QUATERNARY SCIENCE REVIEWS 26 (3-4) 405 - 414 0277-3791 2007/02 [Refereed][Not invited]
    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.
  • Harii, S, Nadaoka, K, Yamamoto, M, Iwao, K
    Marine Ecological Progress Series 346 89 - 96 1616-1599 2007 [Refereed][Not invited]
  • Mark Pagani, Nikolai Pedentchouk, Matthew Huber, Appy Sluijs, Stefan Schouten, Henk Brinkhuis, Jaap S. Sinninghe Damste, Gerald R. Dickens
    NATURE 442 (7103) 671 - 675 0028-0836 2006/08 [Refereed][Not invited]
    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 0921-8181 2006/08 [Refereed][Not invited]
    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 0921-8181 2006/08 [Refereed][Not invited]
    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 0028-0836 2006/06 [Refereed][Not invited]
    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 0028-0836 2006/06 [Refereed][Not invited]
    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 0028-0836 2006/06 [Refereed][Not invited]
    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 0304-4203 2006/02 [Refereed][Not invited]
    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 0146-6380 2006 [Refereed][Not invited]
    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 0031-0182 2005/12 [Refereed][Not invited]
    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 0025-3227 2005/08 [Refereed][Not invited]
    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 0009-2541 2005/05 [Refereed][Not invited]
    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.
  • S Nagao, T Usui, M Yamamoto, M Minagawa, T Iwatsuki, A Noda
    CHEMICAL GEOLOGY 218 (1-2) 63 - 72 0009-2541 2005/05 [Refereed][Not invited]
    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 Delta(14)C and delta(13)C 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 Delta(14)C value, ON 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 delta(13)C 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 Delta(14)C and delta(13)C 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. (c) 2005 Elsevier B.V All rights reserved.
  • M Yamamoto, R Suemune, T Oba
    GEOPHYSICAL RESEARCH LETTERS 32 (5) L05609  0094-8276 2005/03 [Refereed][Not invited]
    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.
  • Lipid compositions of a diatom Chaetoceros pseudocurvisetus in three different life forms
    Yamamoto Masanobu, Kuwata Akira, Maruyama Akihiko, Higashihara Takanori
    Researches in organic geochemistry 20 7 - 13 2005 [Refereed][Not invited]
    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 ...
  • M Yamamoto, T Oba, J Shimamune, T Ueshima
    GEOPHYSICAL RESEARCH LETTERS 31 (16) L16311  0094-8276 2004/08 [Refereed][Not invited]
    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 [Refereed][Not invited]
  • 第三紀海成珪質堆積岩中のホパン酸-おもなホパン酸と28-ノルホパン酸のGC/MSによる解析-
    Researches in Organic Geochemistry 19 31 - 38 1344-9915 2004 [Refereed][Not invited]
  • YAMAMOTO Masanobu, IRINO Tomohisa, OBA Tadamichi, MURAYAMA Masafumi, IKEHARA Minoru, KODAMA Kazuto, KAWAHATA Hodaka
    Journal of the Japanese Association for Petroleum Technology 67 (6) 590 - 593 2002/11/01 [Refereed][Not invited]
  • S Harii, H Kayanne, H Takigawa, T Hayashibara, M Yamamoto
    MARINE BIOLOGY 141 (1) 39 - 46 0025-3162 2002/07 [Refereed][Not invited]
    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 0016-7002 2001 [Refereed][Not invited]
    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.
  • YAMAMOTO Masanobu, TAGUCHI Kazuo
    Journal of the Japanese Association for Petroleum Technology 65 (5) 469 - 476 0370-9868 2000/09/01 [Refereed][Not invited]
  • Yamamoto Masanobu
    Researches in organic geochemistry 15 (0) 27 - 31 1344-9915 2000/06 [Refereed][Not invited]
    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...
  • M Yamamoto, Y Shiraiwa, Inouye, I
    ORGANIC GEOCHEMISTRY 31 (9) 799 - 811 0146-6380 2000 [Refereed][Not invited]
    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 [Refereed][Not invited]
  • 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 [Refereed][Not invited]
  • 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 0916-8958 2000 [Refereed][Not invited]
  • YAMAMOTO Masanobu
    地球化学 33 (3) 191 - 204 1999/08/25 [Refereed][Not invited]
    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 1344-9915 1999/06/30 [Refereed][Not invited]
    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 1999/06 [Refereed][Not invited]
  • 山本 正伸
    地質調査所月報 50 (5) 329 - 359 1999/06 [Refereed][Not invited]
  • Masanobu Yamamoto, Bat-erdene Delegiin, Ulziikhishig Pureyiin
    Bulletin Geological Survey of Japan 49 (6) 257 - 274 1998/06 [Refereed][Not invited]
  • YAMAMOTO Masanobu, BAT-ERDENE Delegiin, ULZIIKHISHIG Pureyiin, WATANABE Yoshio, TAKEDA Nobuyori, KAJIWARA Yoshiteru, NAKAJIMA Terumasa
    Journal of the Japanese Association for Petroleum Technology 63 (3) 239 - 250 1998/05 [Refereed][Not invited]
  • YAMAMOTO Masanobu, SUZUKI Yuichiro, ENOMOTO Minoru, KAJIWARA Yoshiteru, TAKEDA Nobuyori
    Journal of the Japanese Association for Petroleum Technology 63 (2) 158 - 164 1998/03 [Refereed][Not invited]
  • 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 0883-8305 1997/12 [Refereed][Not invited]
    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 1997/02 [Refereed][Not invited]
  • Molecular palaeontology of the earliest Danian at Geulhemmerberg (the Netherlands)
    M Yamamoto, K Ficken, M Baas, HJ Bosch, JW deLeeuw
    GEOLOGIE EN MIJNBOUW 75 (2-3) 255 - 267 0016-7746 1996 [Refereed][Not invited]
    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.
  • WATANABE Yoshio, YAMAMOTO Masanobu, WATANABE Mahito
    Journal of the Japanese Association for Petroleum Technology 60 (1) 15 - 26 0370-9868 1995/01 [Refereed][Not invited]
  • YAMAMOTO Masanobu, WATANABE Yoshio
    Journal of the Japanese Association for Petroleum Technology 60 (1) 27 - 38 0370-9868 1995/01 [Refereed][Not invited]
    MICROCHEMICAL JOURNAL 50 (3) 281 - 288 0026-265X 1994/12 [Refereed][Not invited]
    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 1994/09 [Refereed][Not invited]
  • 山本 正伸, 渡部 芳夫, 渡辺 真人
    地質調査所月報 45 (8) 527 - 530 1994/09 [Refereed][Not invited]
    QUATERNARY SCIENCE REVIEWS 13 (5-7) 641 - 645 0277-3791 1994 [Refereed][Not invited]
    Bulletin of the Geological Survey of Japan 44 (11) 685 - 691 1993/11 [Refereed][Not invited]
    ORGANIC GEOCHEMISTRY 19 (4-6) 389 - 402 0146-6380 1992/12 [Refereed][Not invited]
    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.
    CHEMICAL GEOLOGY 93 (1-2) 193 - 206 0009-2541 1991/11 [Refereed][Not invited]
    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.
  • Yamamoto M, Taguchi K, Sasaki K
    Researches in organic geochemistry 7 (0) 55 - 57 1344-9915 1990/04 [Refereed][Not invited]

Books etc

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


  • ボルネオでの泥炭コアリング
    山本正伸  PALEO  5-  1  -13  2017/04/01  [Not refereed][Not invited]
  • 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  NEWS  9-  4  -1  2016/04/01  [Not refereed][Not invited]
  • 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  2015/04  [Not refereed][Not invited]
    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.
  • 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  2013/04/01  [Not refereed][Not invited]
  • Min-Te Chen, Masanobu Yamamoto, Youbin Sun, Chris Turney  JOURNAL OF QUATERNARY SCIENCE  27-  (9)  865  -865  2012/12  [Refereed][Not invited]
  • Latent 1,500-year climate oscillation in the Holocene,
    Yamamoto, M  PAGES news, 20, 2, 66-67.  20-  66  -67  2012/12  [Refereed][Invited]
  • 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  2008/04/01  [Refereed][Invited]
  • 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  2007/04/01  [Not refereed][Not invited]
  • 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  2007/04/01  [Not refereed][Not invited]
  • 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  2007/04/01  [Not refereed][Not invited]
  • 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  2006/04/01  [Not refereed][Not invited]
  • Abe, C, Yamamoto, M, Irino, T  Proceeding of the Ocean Drilling Program  202-  1  -14  2006  [Refereed][Not invited]
  • 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  2005/04/01  [Not refereed][Not invited]
  • 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  2005/04/01  [Not refereed][Not invited]
  • 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  2005/04/01  [Not refereed][Invited]
  • 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  2004/04/01  [Not refereed][Not invited]
  • 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  2004/04/01  [Not refereed][Not invited]
  • 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  2004/04/01  [Not refereed][Not invited]
  • 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  [Refereed][Not invited]
  • 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  2003/04/01  [Not refereed][Not invited]
  • 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  2003/04/01  [Not refereed][Not invited]
  • 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  2003/04/01  [Not refereed][Not invited]
  • Nonthermal factors affecting production and unsaturation of alkenones in Emillania huxleyi and Gephyrocapsa oceanica
    JM Sorrosa, M Yamamoto, Y Shiraiwa  ADVANCED RESEARCH ON PLANT LIPIDS  133  -136  2003  [Not refereed][Not invited]
  • 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  [Not refereed][Not invited]
  • 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  2002/04/01  [Not refereed][Not invited]
  • 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  2001/04/01  [Not refereed][Not invited]
  • 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  2001/04/01  [Not refereed][Not invited]
  • Introduction: Geochemical cycles and global changes
    Tsunogai, S, Montani, S, Obata, H, Ono, T, Watanabe, Y, Yamamoto, M  Journal of Oceanography  370-  647  -650  2001/04/01  [Not refereed][Invited]
  • 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  2001/04/01  [Not refereed][Invited]
  • 山本 正伸  海洋  32-  (9)  618  -622  2000/09  [Not refereed][Invited]
  • 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  2000/04/01  [Not refereed][Not invited]
  • 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  1997/04/01  [Not refereed][Invited]
  • 地球環境の変遷と石油天然ガス根源岩の形成.
    渡部芳夫, 山本正伸  地質ニュース  497-  7  -16  1995/06/01  [Not refereed][Invited]
  • 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  1995/04/01  [Not refereed][Not invited]
  • バイオマーカーと古環境
    山本正伸  Science & Technonews Tsukuba  46-  38  -40  1995/04/01  [Not refereed][Invited]
  • 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  1995/04/01  [Not refereed][Not invited]
  • 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  1995/04/01  [Not refereed][Invited]
  • Nkajima Terumasa, Watanabe Yoshio, Harayama Satoru, Yamamoto Masanobu  Journal of the Geological Society of Japan  99-  (5)  ix  -x  1993/05/15  [Refereed][Not invited]
  • 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  1993/04/01  [Not refereed][Not invited]
  • 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  1993/04/01  [Not refereed][Not invited]
  • 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  1992/04/01  [Not refereed][Not invited]
  • 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  1992/04/01  [Not refereed][Not invited]
  • 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  1990/04/01  [Not refereed][Not invited]
  • 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  1986/03/01  [Not refereed][Invited]

Awards & Honors

  • 2019/09 Geologiocal Society of Japan Paper Award
     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: YAMAMOTO Masanobu
  • 2016/07 日本有機地球化学会 2016年度有機地球化学賞(学術賞)受賞
    受賞者: 山本 正伸
  • 2015/11 地球環境史学会 2014年度地球環境史学会貢献賞
    受賞者: 山本 正伸
  • 1999/02 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
  • 1997/07 有機地球化学研究会 研究奨励賞(田口賞)受賞
    受賞者: 山本 正伸

Research Grants & Projects

  • 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
    Date (from‐to) : 2019/06 -2024/03 
    Author : 山本 正伸
  • 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])
    Date (from‐to) : 2017/04 -2020/03 
    Author : 山本正伸
  • 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
    Date (from‐to) : 2018/04 -2020/03 
    Author : 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
    Date (from‐to) : 2017/10 -2020 
    Author : 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
    Date (from‐to) : 2016/04 -2019/03 
    Author : 山本正伸
  • ベンガル湾Exp.353古環境復元(掘削航海番号:Exp. 353 種別 [JR])
    Date (from‐to) : 2015/04 -2018/03 
    Author : 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
    Date (from‐to) : 2015/04 -2018/03 
    Author : 山本正伸
  • 南大洋と北極海の完新世水温変動の高時間解像度復元
    Date (from‐to) : 2013/04 -2016/03 
    Author : 山本正伸
  • 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
    Date (from‐to) : 2013/04 -2015/03 
    Author : 山本正伸
  • 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
    Date (from‐to) : 2010/04 -2013/03 
    Author : 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
    Date (from‐to) : 2007/04 -2012/03 
    Author : 山本正伸
  • 氷河期の熱帯温度の研究
    Date (from‐to) : 2006/04 -2008/03 
    Author : 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
    Date (from‐to) : 2006/04 -2008/03 
    Author : 山本正伸
  • 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
    Date (from‐to) : 2004/04 -2007/03 
    Author : 山本正伸
  • Paleoceanography of the Arctic Ocean
    Date (from‐to) : 2004
  • Paleoceanography of the tropical Pacific
    Date (from‐to) : 2001
  • Paleoceanography of the North Pacific
    Date (from‐to) : 1995
  • 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」
    Author : 山本正伸

Educational Activities

Teaching Experience

  • Inter-Graduate School Classes(Educational Program):Antarctic Science
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : 極域、南極、北極、海氷、氷床、大気、海洋、気候システム、生態系、南極観測、南極条約
  • Fundamental Lecture in Paleoclimatology and Paleoceanography
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 古環境,古気候,古海洋,地球温暖化 Paleoenvironment, Paleoclimatology, Paleoceanography, Global warming
  • Advanced Course in Paleoceanography and Biomarker Geochemistry
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 有機地球化学 Organic geochemistry
  • Advanced course in Paleoclimatology
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 有機地球化学 Organic geochemistry
  • Advanced Course in Environmental Analytical Chemistry
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : 化学分析、データ解析 Chemical analysis, Data analysis
  • Arts and Science Courses in English 2
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 国際本部
    キーワード : Polar regions, the Antarctic, the Arctic, sea ice, ice sheet, atmosphere, ocean, climate system, ecosystem, Antarctic expeditions, Antarctic treaty
  • Laboratory Work in Earth and Planetary Sciences II
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 堆積物,堆積岩,堆積環境,水圏環境,古海洋,古気候,気象,天気図,統計解析,地震,地震波,震源
  • Environmental geoscience
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 気候変化、炭素循環、古環境、氷期・間氷期、人類環境、生物圏

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