基本情報

所属

• 低温科学研究所　水・物質循環部門

職名

• 准教授

学位

• 博士（地球環境科学）（北海道大学）

ホームページURL

http://kaken.nii.ac.jp/d/r/30374648.ja.html

J-Global ID

• 201301081975666990

研究キーワード

• 大気エアロゾル   セルロース   同位体測定   環境動態解析   環境変動   完新世   エアロゾル   吸湿特性   水圏化学   太平洋   有機物トレーサー   鮮新世温暖期   降水   泥炭   化学組成   データ・モデル統合   酸素同位体   東・南アジア   大気圏   気候変動   海洋ゲートウェイ   雲凝結核   

研究分野

• 自然科学一般 / 地球生命科学
• 環境・農学 / 環境動態解析
• 自然科学一般 / 固体地球科学
• 自然科学一般 / 宇宙惑星科学

担当教育組織

•  修士課程　環境科学院
•  博士課程　環境科学院

職歴

• 2012年 - 2015年 北海道大学 低温科学研究所 准教授

研究活動情報

論文

• Multiple episodes of ice loss from the Wilkes Subglacial Basin during the Last Interglacial

  Mutsumi Iizuka, Osamu Seki, David J. Wilson, Yusuke Suganuma, Keiji Horikawa, Tina van de Flierdt, Minoru Ikehara, Takuya Itaki, Tomohisa Irino, Masanobu Yamamoto, Motohiro Hirabayashi, Hiroyuki Matsuzaki, Saiko Sugisaki

  Nature Communications 14 1 2023年04月18日 

  Abstract The Last Interglacial (LIG: 130,000–115,000 years ago) was a period of warmer global mean temperatures and higher and more variable sea levels than the Holocene (11,700–0 years ago). Therefore, a better understanding of Antarctic ice-sheet dynamics during this interval would provide valuable insights for projecting sea-level change in future warming scenarios. Here we present a high-resolution record constraining ice-sheet changes in the Wilkes Subglacial Basin (WSB) of East Antarctica during the LIG, based on analysis of sediment provenance and an ice melt proxy in a marine sediment core retrieved from the Wilkes Land margin. Our sedimentary records, together with existing ice-core records, reveal dynamic fluctuations of the ice sheet in the WSB, with thinning, melting, and potentially retreat leading to ice loss during both early and late stages of the LIG. We suggest that such changes along the East Antarctic Ice Sheet margin may have contributed to fluctuating global sea levels during the LIG.
• Influence of Earlier Snowmelt on the Seedling Growth of Six Subboreal Tree Species in the Spring

  Erica Marumo, Miki U. Ueda, Osamu Seki, Kentaro Takagi, Kobayashi Makoto

  Forests 14 3 600 - 600 2023年03月17日 

  Climate warming is advancing snowmelt timing in the spring at high latitudes. To predict tree growth in subboreal forests under warmer climates based on mechanistic understanding, it is important to assess how advancing snowmelt influences tree growth in the spring via ecophysiological changes in subboreal forests. In this study, we conducted a field manipulation experiment of snowmelt timing and investigated the response of tree growth, leaf functional traits, and bud-burst phenology in the spring for the seedlings of six dominant tree species in subboreal forests. We found that the spring growth of only one species (Kalopanax septemlobus) out of six species responded positively to advancing snowmelt. Among the leaf functional traits (leaf mass per area, leaf nitrogen content, leaf δ13C value, leaf dry matter content, and leaf area) and bud-burst phenology, only the increase in leaf area was linked to the enhanced shoot growth of K. septemlobus. The significant change in K. septemlobus might be associated with its ecological characteristics to prefer regeneration in canopy gaps. These results indicate that advancing snowmelt under warmer winters can be beneficial for tree species that can plastically develop leaf area in Japanese subboreal forests.
• Antiphased dust deposition and productivity in the Antarctic Zone over 1.5 million years

  Michael E. Weber, Ian Bailey, Sidney R. Hemming, Yasmina M. Martos, Brendan T. Reilly, Thomas A. Ronge, Stefanie Brachfeld, Trevor Williams, Maureen Raymo, Simon T. Belt, Lukas Smik, Hendrik Vogel, Victoria L. Peck, Linda Armbrecht, Alix Cage, Fabricio G. Cardillo, Zhiheng Du, Gerson Fauth, Christopher J. Fogwill, Marga Garcia, Marlo Garnsworthy, Anna Glüder, Michelle Guitard, Marcus Gutjahr, Iván Hernández-Almeida, Frida S. Hoem, Ji-Hwan Hwang, Mutsumi Iizuka, Yuji Kato, Bridget Kenlee, Suzanne OConnell, Lara F. Pérez, Osamu Seki, Lee Stevens, Lisa Tauxe, Shubham Tripathi, Jonathan Warnock, Xufeng Zheng

  Nature Communications 13 1 2022年12月 

  Abstract The Southern Ocean paleoceanography provides key insights into how iron fertilization and oceanic productivity developed through Pleistocene ice-ages and their role in influencing the carbon cycle. We report a high-resolution record of dust deposition and ocean productivity for the Antarctic Zone, close to the main dust source, Patagonia. Our deep-ocean records cover the last 1.5 Ma, thus doubling that from Antarctic ice-cores. We find a 5 to 15-fold increase in dust deposition during glacials and a 2 to 5-fold increase in biogenic silica deposition, reflecting higher ocean productivity during interglacials. This antiphasing persisted throughout the last 25 glacial cycles. Dust deposition became more pronounced across the Mid-Pleistocene Transition (MPT) in the Southern Hemisphere, with an abrupt shift suggesting more severe glaciations since ~0.9 Ma. Productivity was intermediate pre-MPT, lowest during the MPT and highest since 0.4 Ma. Generally, glacials experienced extended sea-ice cover, reduced bottom-water export and Weddell Gyre dynamics, which helped lower atmospheric CO₂ levels.
• Ancient marine sediment DNA reveals diatom transition in Antarctica

  Linda Armbrecht, Michael E. Weber, Maureen E. Raymo, Victoria L. Peck, Trevor Williams, Jonathan Warnock, Yuji Kato, Iván Hernández-Almeida, Frida Hoem, Brendan Reilly, Sidney Hemming, Ian Bailey, Yasmina M. Martos, Marcus Gutjahr, Vincent Percuoco, Claire Allen, Stefanie Brachfeld, Fabricio G. Cardillo, Zhiheng Du, Gerson Fauth, Chris Fogwill, Marga Garcia, Anna Glüder, Michelle Guitard, Ji-Hwan Hwang, Mutsumi Iizuka, Bridget Kenlee, Suzanne O’Connell, Lara F. Pérez, Thomas A. Ronge, Osamu Seki, Lisa Tauxe, Shubham Tripathi, Xufeng Zheng

  Nature Communications 13 1 2022年10月02日 

  Abstract Antarctica is one of the most vulnerable regions to climate change on Earth and studying the past and present responses of this polar marine ecosystem to environmental change is a matter of urgency. Sedimentary ancient DNA (sedaDNA) analysis can provide such insights into past ecosystem-wide changes. Here we present authenticated (through extensive contamination control and sedaDNA damage analysis) metagenomic marine eukaryote sedaDNA from the Scotia Sea region acquired during IODP Expedition 382. We also provide a marine eukaryote sedaDNA record of ~1 Mio. years and diatom and chlorophyte sedaDNA dating back to ~540 ka (using taxonomic marker genes SSU, LSU, psbO). We find evidence of warm phases being associated with high relative diatom abundance, and a marked transition from diatoms comprising <10% of all eukaryotes prior to ~14.5 ka, to ~50% after this time, i.e., following Meltwater Pulse 1A, alongside a composition change from sea-ice to open-ocean species. Our study demonstrates that sedaDNA tools can be expanded to hundreds of thousands of years, opening the pathway to the study of ecosystem-wide marine shifts and paleo-productivity phases throughout multiple glacial-interglacial cycles.
• Latitudinal variance in the drivers and pacing of warmth during mid‐Pleistocene MIS 31 in the Antarctic Zone of the Southern Ocean

  Jonathan P. Warnock, Brendan T. Reilly, Maureen E. Raymo, Michael E. Weber, Victoria Peck, Trevor Williams, Linda Armbrecht, Ian Bailey, Stephanie Brachfeld, Zhiheng Du, Gerson Fauth, Marga M. García, Anna Glüder, Michelle Guitard, Marcus Gutjahr, Sidney Hemming, Iván Hernández‐Almeida, Freida S. Hoem, Ji‐Hwan Hwang, Mutsumi Iizuka, Yuji Kato, Bridget Lee, Yasmina M. Martos, Suzanne O’Connell, Lara F. Pérez, Thomas A. Ronge, Osamu Seki, Lisa Tauxe, Shubham Tripathi, Xufeng Zheng, Joseph Stoner, Reed P. Scherer

  Paleoceanography and Paleoclimatology 37 8 2022年08月05日
• Early snowmelt by an extreme warming event affects understory more than overstory trees in Japanese temperate forests

  Kobayashi Makoto, Pamela H. Templer, Ayumi Katayama, Osamu Seki, Kentaro Takagi

  ECOSPHERE 13 7 2022年07月 

  The occurrence of extreme warm events and early snowmelt is predicted to increase in high-latitude ecosystems, even during periods of time when there is no coincident reduction in total precipitation. However, because extreme events like these occur unpredictably, little is known about how advancing snowmelt by a single extreme warm event, without a reduction in precipitation amount, influences overstory trees and understory vegetation simultaneously in an ecosystem. We conducted a warming experiment (four 20 x 20 m plots) in temperate forests of Japan to determine the effects of earlier snowmelt on both understory dwarf bamboo plants and overstory birch trees. Our experimental treatment advanced snowmelt by about 10 days and increased soil temperatures that were associated with increased rates of soil nitrogen (N) mineralization and nitrification. Furthermore, these changes led to lower C:N ratios of leaves together with the greater growth of understory bamboo vegetation, with no changes in leaf C:N or growth rates of overstory birch trees. Together, our results demonstrate that advancing snowmelt by an extreme warm event in temperate forests is likely to affect N cycling and will benefit understory vegetation without a commensurate change in overstory vegetation, likely due to the increase in available soil N. These results also demonstrate that with the projected increase in the frequency of extreme warm events and advanced snowmelt, understory vegetation is likely to benefit more than overstory trees in Japanese temperate forests with heavy snow.
• Episodes of Early Pleistocene West Antarctic Ice Sheet Retreat Recorded by Iceberg Alley Sediments

  Ian Bailey, Sidney Hemming, Brendan T. Reilly, Gavyn Rollinson, Trevor Williams, Michael E. Weber, Maureen E. Raymo, Victoria L. Peck, Thomas A. Ronge, Stefanie Brachfeld, Suzanne O'Connell, Lisa Tauxe, Jonathan P. Warnock, Linda Armbrecht, Fabricio G. Cardillo, Zhiheng Du, Gerson Fauth, Marga Garcia, Anna Glueder, Michelle Guitard, Marcus Gutjahr, Iván Hernández‐Almeida, Frida S. Hoem, Ji‐Hwan Hwang, Mutsumi Iizuka, Yuji Kato, Bridget Kenlee, Yasmina M. Martos, Lara F. Pérez, Osamu Seki, Shubham Tripathi, Xufeng Zheng

  Paleoceanography and Paleoclimatology 37 7 2022年07月
• Dust correlation and oxygen isotope stratigraphy in the Southern Ocean over the last 450 kyrs: An Indian sector perspective

  Hiroki Matsui, Minoru Ikehara, Yusuke Suganuma, Osamu Seki, Ikumi Oyabu, Kenji Kawamura

  Quaternary Science Reviews 286 2022年06月15日 

  The chronology of Southern Ocean (SO) marine sediment cores forms the basis of understanding the SO paleoceanography, with significant implications for global climate. Because tuning of the oxygen isotope (δ18O) record of a marine sediment core to a δ18O stack (δ18O stratigraphy) is difficult in the SO because of a general paucity of calcareous foraminifera, tuning of the dust proxy signal of a marine sediment core to the dust record of an ice core (dust correlation) is a promising way to construct an age–depth model. However, the reliability of dust correlation has not been established, especially beyond the last ∼300 kyrs, and such work has been performed more in the Atlantic and Pacific sectors of the SO than in the Indian sector. Here we present a new dust correlation using the rock magnetic record, together with continuous δ18O stratigraphy, for a marine sediment core in the Indian sector of the SO over the last ∼410 kyrs. The δ18O stratigraphy is consistent with the dust correlation within their chronological uncertainties, supporting the reliability of the latter chronology for glacial–interglacial timescales. However, the dust correlation often produces older ages than the δ18O stratigraphy by up to 3 kyrs (410–126 ka and 84–50 ka). We additionally compiled, based on dust correlation, available dust proxy records in the circum-Antarctic SO for the last 450 kyrs to discuss variations in the dust proxy record within the Indian sector and between all three sectors. For the Indian sector, there is a marked difference in dust proxy signals for Marine Isotope Stage (MIS) 6 between two cores that have markedly different latitudinal positions relative to the oceanic fronts. Increased biogenic magnetite production by iron fertilization in the Subantarctic Zone during MIS 6 may partly explain the difference between the two cores. For the circum-Antarctic SO, moving correlation coefficients were computed between the marine sediment-core dust proxy signals and the dust flux of an Antarctic ice core. Strong correlation was recognized for intervals of high dust flux in the ice core, except for MIS 6. Although minor, the slightly lower correlation in the Indian sector than in the other sectors indicates a contribution from local dust source and volcanic materials and thus suggests the necessity for caution when performing dust correlation in the Indian sector of the SO.
• Increased interglacial atmospheric CO2 levels followed the mid-Pleistocene Transition

  Masanobu Yamamoto, Steven C. Clemens, Osamu Seki, Yuko Tsuchiya, Yongsong Huang, Ryouta O’ishi, Ayako Abe-Ouchi

  Nature Geoscience 15 4 307 - 313 2022年04月 

  Atmospheric CO2 and polar ice volume have been strongly coupled over the past 805,000 years. However, the prior extent of coupling, during times of lower-amplitude ice-volume variability, is unknown because continuous high-resolution CO2 records are lacking. We reconstructed the past 1,460,000 years of atmospheric CO2 (similar to 1,700year sample resolution) by taking advantage of the unique relationship between CO2 concentration and leaf-wax delta C-13 resulting from changes in the extent of C-3 and C-4 vegetation in East India. Notably, reconstructed interglacial CO2 concentrations were lower before the transition to large volume variability during the mid-Pleistocene Transition (900,000 years ago). Prior to the mid-Pleistocene Transition, CO2 exhibited a secular trend similar to that of deep-ocean carbon isotopes. At orbital time scales, phase analysis indicates that the CO2 lead relative to ice volume changed to a lag during the mid-Pleistocene Transition. Combined, these findings suggest that deep-ocean circulation controlled the long-term CO2 trend, and that interaction between CO2, continental ice and deep-ocean circulation was reorganized during the mid-Pleistocene Transition, involving a decrease in carbon storage in the deep Pacific.
• Impact of Climate Change on Hunter-Fisher-Gatherer Cultures in Northern Japan Over the Past 4,400 Years

  Masanobu Yamamoto, Osamu Seki

  GEOPHYSICAL RESEARCH LETTERS 49 5 2022年03月 

  In Hokkaido, northern Japan, densely populated societies of hunter-fisher-gatherer cultures persisted over the Holocene until the 19th century. We used the cellulose delta O-18 values of Sphagnum and vascular plants in peat cores from Rishiri Island to understand paleoclimate changes in Hokkaido over the past 4,400 years and discuss the impacts of climate changes on the development of the cultures. The cellulose delta O-18 values showed multi-centennial and millennial variations, reflecting the intensity of the Tsushima Warm Current and the summer position of the westerly jet. The marine hunter-fisher cultures responded to changes in the strength of Tsushima Warm Current and coastal primary production. In contrast, the inland cultures responded to changes in the latitudinal position of the summer westerlies. This implies that human societies of different lifestyles responded differently to climate changes.
• Sensitivity of the West Antarctic Ice Sheet to +2 °C (SWAIS 2C)

  Molly O. Patterson, Richard H. Levy, Denise K. Kulhanek, Tina van de Flierdt, Huw Horgan, Gavin B. Dunbar, Timothy R. Naish, Jeanine Ash, Alex Pyne, Darcy Mandeno, Paul Winberry, David M. Harwood, Fabio Florindo, Francisco J. Jimenez-Espejo, Andreas Läufer, Kyu-Cheul Yoo, Osamu Seki, Paolo Stocchi, Johann P. Klages, Jae Il Lee, Florence Colleoni, Yusuke Suganuma, Edward Gasson, Christian Ohneiser, José-Abel Flores, David Try, Rachel Kirkman, Daleen Koch

  Scientific Drilling 30 101 - 112 2022年02月25日 

  Abstract. The West Antarctic Ice Sheet (WAIS) presently holds enough ice to raise global sea level by 4.3 m if completely melted. The unknown response of the WAIS to future warming remains a significant challenge for numerical models in quantifying predictions of future sea level rise. Sea level rise is one of the clearest planet-wide signals of human-induced climate change. The Sensitivity of the West Antarctic Ice Sheet to a Warming of 2 ∘C (SWAIS 2C) Project aims to understand past and current drivers and thresholds of WAIS dynamics to improve projections of the rate and size of ice sheet changes under a range of elevated greenhouse gas levels in the atmosphere as well as the associated average global temperature scenarios to and beyond the +2 ∘C target of the Paris Climate Agreement. Despite efforts through previous land and ship-based drilling on and along the Antarctic margin, unequivocal evidence of major WAIS retreat or collapse and its causes has remained elusive. To evaluate and plan for the interdisciplinary scientific opportunities and engineering challenges that an International Continental Drilling Program (ICDP) project along the Siple coast near the grounding zone of the WAIS could offer (Fig. 1), researchers, engineers, and logistics providers representing 10 countries held a virtual workshop in October 2020. This international partnership comprised of geologists, glaciologists, oceanographers, geophysicists, microbiologists, climate and ice sheet modelers, and engineers outlined specific research objectives and logistical challenges associated with the recovery of Neogene and Quaternary geological records from the West Antarctic interior adjacent to the Kamb Ice Stream and at Crary Ice Rise. New geophysical surveys at these locations have identified drilling targets in which new drilling technologies will allow for the recovery of up to 200 m of sediments beneath the ice sheet. Sub-ice-shelf records have so far proven difficult to obtain but are critical to better constrain marine ice sheet sensitivity to past and future increases in global mean surface temperature up to 2 ∘C above pre-industrial levels. Thus, the scientific and technological advances developed through this program will enable us to test whether WAIS collapsed during past intervals of warmth and determine its sensitivity to a +2 ∘C global warming threshold (UNFCCC, 2015).
• Assessment of long-chain n-alkanes as a paleoclimate proxy in the Bering Sea sediments

  Osamu Seki, Yusuke Okazaki, Naomi Harada

  Progress in Oceanography 198 102687 - 102687 2021年11月
• The significance of pyrogenic polycyclic aromatic hydrocarbons in Borneo peat core for the reconstruction of fire history

  Sher-Rine Kong, Masanobu Yamamoto, Hasrizal Shaari, Ryoma Hayashi, Osamu Seki, Norhayati Mohd Tahir, Muhammad Fais Fadzil, Abdullah Sulaiman

  PLOS ONE 16 9 e0256853 - e0256853 2021年09月08日 [査読有り][通常論文]
   

  The reconstruction of fire history is essential to understand the palaeoclimate and human history. Polycyclic aromatic hydrocarbons (PAHs) have been extensively used as a fire marker. In this work, the distribution of PAHs in Borneo peat archives was investigated to understand how PAHs reflect the palaeo-fire activity. In total, 52 peat samples were analysed from a Borneo peat core for the PAH analysis. Pyrogenic PAHs consist of 2–7 aromatic rings, some of which have methyl and ethyl groups. The results reveal that the concentration of pyrogenic PAHs fluctuated with the core depth. Compared to low-molecular-weight (LMW) PAHs, the high-molecular-weight (HMW) PAHs had a more similar depth variation to the charcoal abundance. This finding also suggests that the HMW PAHs were mainly formed at a local fire near the study area, while the LMW PAHs could be transported from remote locations.
• Cellulose Oxygen Isotopes of Sphagnum and Vascular Plants in a Peat Core Reveal Climate Change in Northern Japan Over the Past 2,000 Years

  Hiromichi Sakurai, Masanobu Yamamoto, Osamu Seki, Takayuki Omori, Tomonori Sato

  GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 22 9 2021年09月 

  The cellulose delta O-18 of plant tissues in peat is a potential climate proxy. However, understanding what is driving the shifts in delta O-18 of cellulose is required for its application. Here, we analyzed the delta O-18 values of Sphagnum and vascular plant cellulose, as well as the delta O-18 and delta D values of pore water, in a 4-m-long peat core from the Bekanbeushi ombrotrophic bog to understand paleoclimatic changes in northern Japan over the past 2,000 years. The cellulose delta O-18 values of Sphagnum were lower than those of vascular plant tissues, although both draw water from the same layer. Whereas the cellulose delta O-18 values of Sphagnum more directly reflect those of precipitation, those of vascular plants become enriched through transpiration. Thus, the difference between vascular plants and Sphagnum (Delta delta O-18(vp-sp)) is a potential proxy for relative humidity. Cellulose delta O-18 of Sphagnum revealed centennial variations with maxima around 800, 1300, and 1500 CE and minima around 500, 1000, 1700, and 1900 CE. The Delta delta O-18(vp-sp) was inversely correlated with Sphagnum cellulose delta O-18, indicating that the axis of summer westerlies was more frequently located to the north and the climate was moist in the former periods, whereas the axis of summer westerlies was generally located to the south and the climate was dry in the latter periods. These results suggest a warm and moist climate during the former periods due to frequent rainy summers driven by strong East Asian summer monsoon activity, and the opposite conditions in the latter periods.
• Tropical Western Pacific Hydrology During the Last 6,000 Years Based on Wildfire Charcoal Records From Borneo

  Masanobu Yamamoto, Takafumi Kikuchi, Hiromichi Sakurai, Ryoma Hayashi, Osamu Seki, Takayuki Omori, Abdullah Sulaiman, Hasrizal Shaari, Mohd Zulhilmy Abdullah, Lulie Melling

  GEOPHYSICAL RESEARCH LETTERS 48 18 2021年09月 

  The forcing of multicentennial climate variability in the Western Pacific Warm Pool (WPWP) region is not fully understood. Here, we generated 6-kyr-long continuous charcoal records from five peatlands in Borneo. Every several hundred years, peaks of charcoal influx were identified in the composite record, indicating that the peatlands repeatedly experienced dry conditions and wildfires. Major fire events were identified at similar to 5.4, 4.7, 4.4, 3.7, 3.2, 2.7, 2.4, 2.2, 1.7, 1.1, 0.6, and 0.3 ka. Most of these coincided with the maxima of Borneo speleothem delta O-18 and occurred in the high solar activity periods following the solar minima. This suggests that the higher solar activity decreased rainfall, increasing dryness and wildfire frequency. This result challenges the hypothesis that high solar activity intensifies atmospheric convection in the WPWP area.
• Investigation of Adequate Calibration Methods for X-ray Fluorescence Core Scanning Element Count Data: A Case Study of a Marine Sediment Piston Core from the Gulf of Alaska

  Md Nurunnabi Mondal, Keiji Horikawa, Osamu Seki, Katsuya Nejigaki, Hideki Minami, Masafumi Murayama, Yusuke Okazaki

  JOURNAL OF MARINE SCIENCE AND ENGINEERING 9 5 2021年05月 

  X-ray fluorescence (XRF) core scanner elemental count data are useful for high-resolution paleoceanographic studies. However, because several factors, such as changes in physical core properties, significantly affect element count intensities, the appropriate calibration of the count data is required. Besides, the existing approaches for calibration were not widely employed and require rigorous testing based on sediment variety. In this study, we analyzed high-resolution element intensity (cps) using a wet muddy marine sediment piston core that was collected from the northeast Gulf of Alaska and tested several approaches with ratio and log-ratio methods, and the reliability was evaluated by comparison with the concentrations that were measured by WD-XRF and an elemental analyzer. The results show that the lighter elements (Ti and K) exhibited a significantly weak relationship between raw counts measured by ITRAX and concentrations that were measured by the WD-XRF, indicating that some factors artificially influence ITRAX intensity data. The Cl intensity that is expressed as the water content in marine sediment increased significantly in the upper 202 cm by 42% and the top 25 cm by 73% as compared to the down-core (below 202 cm), which deviates the X-ray scattering and element-counts. The calibration of raw data through coherent/incoherent X-ray scattering ratio (CIR) and additive- and centered-log ratio reduces the offsets. The calibration by CIR performed best for Sr, Fe, Mn, Ti, Ca, K, and Br (0.56 < R-2 < 0.91), and the correlation with concentration significantly increased for Ti and K of 100% and 56%, respectively. Therefore, the study suggests that the correction of raw counts through CIR is an effective approach for wet marine sediment when core physical properties have greater variability.
• New Magnetostratigraphic Insights From Iceberg Alley on the Rhythms of Antarctic Climate During the Plio-Pleistocene

  Brendan T. Reilly, Lisa Tauxe, Stefanie Brachfeld, Maureen Raymo, Ian Bailey, Sidney Hemming, Michael E. Weber, Trevor Williams, Marga Garcia, Michelle Guitard, Yasmina M. Martos, Lara F. Perez, Xufeng Zheng, Linda Armbrecht, Fabricio G. Cardillo, Zhiheng Du, Gerson Fauth, Anna Glueder, Marcus Gutjahr, Ivan Hernandez-Almeida, Frida S. Hoem, Ji-Hwan Hwang, Mutsumi Iizuka, Yuji Kato, Bridget Kenlee, Suzanne O'Connell, Victoria Peck, Thomas A. Ronge, Osamu Seki, Shubham Tripathi, Jonathan Warnock

  PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY 36 2 2021年02月 

  International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea's Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well-resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic delta O-18 records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire similar to 3.3 Myr record does not match the amplitude modulation of benthic delta O-18 records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic delta O-18 at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic delta O-18 during intervals between similar to 3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession-paced variations not captured in benthic delta O-18 during the 41-kyr world.
• 東南極リュツォホルム湾海底堆積物から復元した最終氷期以降の氷床後退過程

  菅沼 悠介, 羽田 裕貴, 板木 拓也, 石輪 健樹, 藤井 昌和, 加藤 悠爾, 大森 貴之, 天野 敦子, 岩井 雅夫, 西田 尚央, 草原 和弥, 平野 大輔, 関 宰, 香月 興太, 川又 基人, 松井 浩紀, 奥野 淳一, 池原 実, 三浦 英樹

  日本地質学会学術大会講演要旨 2021 101  一般社団法人 日本地質学会 2021年 

  近年，衛星観測などによって南極氷床の融解や流出の加速が相次いで報告され，近い将来の急激な海水準上昇が社会的に強く懸念されている．最近の気候・氷床モデルシミュレーションによると，近年融解が加速している西南極氷床のみならず，西南極氷床より1桁大きな体積をもつ東南極氷床の一部も温暖化に敏感であることが指摘されている．しかし，南極氷床の質量収支は，氷床表面での涵養と消耗のみでなく，氷床沿岸でおきる棚氷の底面融解や氷床からの分離も含むため，そのメカニズムの理解と定量的な観測は容易ではなく，気候変動予測精度向上における課題となっている．一方，南極大陸やその周辺の海底堆積物は採取が困難であり，また断片的ではあるとはいえ，過去の南極氷床変動を復元するために極めて貴重な情報を提供する．こういった情報を集積・解析することで過去の気候変動に対する南極氷床の応答の復元できれば，南極氷床融解メカニズムの理解だけでなく，その知見を将来の気候変動の予測に利用することもできる．そこで我々は，砕氷船しらせによって東南極リュツォホルム湾から新たに採取された海底堆積物試料と，既存レガシーコアを解析・分析し，最終氷期における最大氷床拡大域と完新世におきた急激な東南極氷床融解過程の復元と，そのメカニズムについての考察を進めている．現状では海底堆積物の年代制約に課題があるものの，当該地域における氷床融解過程とそのメカニズムについて得られた新たな知見について報告する．
• Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat

  Kate E. Ashley, Robert McKay, Johan Etourneau, Francisco J. Jimenez-Espejo, Alan Condron, Anna Albot, Xavier Crosta, Christina Riesselman, Osamu Seki, Guillaume Mass, Nicholas R. Golledge, Edward Gasson, Daniel P. Lowry, Nicholas E. Barrand, Katelyn Johnson, Nancy Bertler, Carlota Escutia, Robert Dunbar, James A. Bendle

  CLIMATE OF THE PAST 17 1 1 - 19 2021年01月 

  Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large-cavity ice shelves is not included in current Earth System models and may be a driver of this phenomena. We examine a Holocene sediment core off East Antarctica that records the Neoglacial transition, the last major baseline shift of Antarctic sea ice, and part of a late-Holocene global cooling trend. We provide a multiproxy record of Holocene glacial meltwater input, sediment transport, and sea-ice variability. Our record, supported by high-resolution ocean modelling, shows that a rapid Antarctic sea-ice increase during the mid-Holocene (similar to 4.5 ka) occurred against a backdrop of increasing glacial meltwater input and gradual climate warming. We suggest that mid-Holocene ice shelf cavity expansion led to cooling of surface waters and sea-ice growth that slowed basal ice shelf melting. Incorporating this feedback mechanism into global climate models will be important for future projections of Antarctic changes.
• New insights into Holocene hydrology and temperature from lipid biomarkers in western Mediterranean alpine wetlands

  Jaime L. Toney, Antonio Garcia-Alix, Gonzalo Jimenez-Moreno, R. Scott Anderson, Heiko Moossen, Osamu Seki

  QUATERNARY SCIENCE REVIEWS 240 2020年07月 

  Alpine regions of the Mediterranean realm are among the most climatically sensitive areas in the world. Thus, alpine wetlands from the southern Iberian Peninsula, in the westernmost part of the Mediterranean region, are highly sensitive sensors of environmental changes. Difficulties have surfaced in separating controls by temperature and/or precipitation in previous paleoenvironmental studies from alpine environments in this area. We present a Holocene biomarker record (n-alkanes and long-chain diols) from a high elevation lake, Laguna de Rio Seco (LdRS), in the south of the Iberian Peninsula, which contributes to the identification of these forcing mechanisms. The hydrological history of the area, primarily water availability and evapotranspiration, is reconstructed by means of the n-alkane record, including the indices of average chain length, portion aquatic, and carbon preference index, as well as hydrogen isotopes (delta D) of aquatic (delta D-aq) and terrestrial (delta D-wax) n-alkanes. Temperatures are also estimated using the algae derived long-chain diols. We interpret delta D-aq and delta D-wax fluctuations as showing changes in the source and amount of precipitation throughout the LdRS record. An Atlantic precipitation source appears to have predominated during the early-middle Holocene, but an occasional Mediterranean influence with an isotopic enrichment in precipitation is detected in the middle-late Holocene that is likely related to the setting of the current atmospheric pattern in southeastern Iberia under the joint control of the North Atlantic Oscillation (NAO) and the Western Mediterranean dynamics, such as the Western Mediterranean Oscillation (WeMO). Our new record from LdRS is consistent with a generalized trend of a humid early-middle Holocene with low temperature variability, evolving towards an arid middle-late Holocene with abrupt temperature changes. In addition to these long-term trends during the last similar to 10,500 years, two phases of climate instability, evidenced by abrupt depletions in delta D-aq, have been identified at the end of these periods, one between similar to 6500 and 5500 cal yr BP and another in the last similar to 500 years. These episodes would represent strengthened winter cold conditions that favoured the persistence of snowpack and frozen soil in the catchment, causing reduced terrestrial plant growth and low lake evaporation. According to the long-chain diol record, temperatures during these phases were relatively low, but experienced abrupt increases at the end of each period. (C) 2020 Elsevier Ltd. All rights reserved.
• Late Miocene changes in C-3, C-4 and aquatic plant vegetation in the Indus River basin: evidence from leaf wax delta C-13 from Indus Fan sediments

  Kenta Suzuki, Masanobu Yamamoto, Osamu Seki

  GEOLOGICAL MAGAZINE 157 6 979 - 988 2020年06月 

  Vegetation changes in the Indus River basin within the past 10.8 million years were investigated based on the analysis of n-fatty acids and their carbon isotopes in sediments from IODP Site U1457 in the Laxmi Basin of the Arabian Sea. The delta C-13 of long-chain n-C-32 fatty acid shifted from -34 to -22 parts per thousand from 10 to 6.3 Ma, while the delta C-13 of mid-chain n-C-24 fatty acid was nearly constant at around -23 to -22 parts per thousand over the same period. This large difference in the delta C-13 values suggests that the mid-chain fatty acids reflect the contribution of aquatic vascular C-3 plants. Before 6.3 Ma, the average chain length of n-fatty acids and the delta C-13 values of long-chain fatty acids were negatively correlated, suggesting that the delta C-13 values reflected the relative abundance of terrestrial C-3 versus aquatic C-3 plants in the Indus River basin and western India. After 5.8 Ma, the average chain length was variable, but the delta C-13 values remained nearly the same, suggesting that the delta C-13 values reflected heavier delta C-13 values of both aquatic C-3 and C-4 plants. A three-end-member model calculation suggests that terrestrial C-3 plants were replaced by C-4 plants in the Indus River basin and western India from 9.7 or 8.2 to 6.3 Ma. Aridification in those areas during the late Miocene period may have driven the replacement of terrestrial C-3 plants by C-4 plants. An episodic increase in the abundance of terrestrial plants around 8 Ma is attributed to elevated precipitation by regionally enhanced moisture transport.
• Dust deposition tracks late-Holocene shifts in monsoon activity and the increasing role of human disturbance in the Puna-Altiplano, northwest Argentina

  James Hooper, Samuel K. Marx, Jan-Hendrik May, Liliana C. Lupo, Julio J. Kulemeyer, Elizabeth de los A. Pereira, Osamu Seki, Henk Heijnis, David Child, Patricia Gadd, Atun Zawadzki

  HOLOCENE 30 4 519 - 536 2020年04月 

  The Puna-Altiplano plateau represents a regionally significant dust source, which is critically located at the nexus between the tropical and sub-polar synoptic systems that dominate the South American climate. Dust emissions in this region would therefore be expected to be sensitive to changes in these systems, in particular the strength and position of the South American Summer Monsoon (SASM). Here, we present a late-Holocene multi-proxy study where changes in dust flux, reconstructed from a high-altitude peat mire, are examined in light of climate variability and human impacts. Results show that for most the 4300 cal. yr BP record, dust flux sensitively tracked changes in SASM activity. Prior to 2600 cal. yr BP relatively high dust flux implies dry conditions prevailed across the Puna-Altiplao in association with reduced SASM activity. The chemistry of dust deposited at this time matched the large endorheic basins on the Puna, which host ephemeral lakes and terminal fans, indicating these were actively supplying dust to the airstream. After 2600 cal. yr BP, SASM activity increased while dust flux decreased and the dust chemistry changed, collectively implying the shutting down of the Puna-Altiplano as a significant dust source. Dust flux increased after 1000 cal. yr BP during the 'Medieval Warm Period', associated with a return to drier conditions and reactivation of dust sources across the endorheic basins of the Puna. Natural variability in dust flux was dwarfed, however, by the very significant increase in flux after 400 cal. yr BP following Spanish Colonisation and associated changing landuse practices. This finding attests to the globally significant role of humans on dust emissions.
• Ice core records of levoglucosan and dehydroabietic and vanillic acids from Aurora Peak in Alaska since the 1660s: a proxy signal of biomass-burning activities in the North Pacific Rim

  Ambarish Pokhrel, Kimitaka Kawamura, Bhagawati Kunwar, Kaori Ono, Akane Tsushima, Osamu Seki, Sumio Matoba, Takayuki Shiraiwa

  Atmospheric Chemistry and Physics 20 1 597 - 612 2020年01月17日 

  Abstract. A 180 m long (343 years) ice core was drilled in the saddle of Aurora Peak in Alaska (63.52∘ N, 146.54∘ W; elevation: 2825 m) and studied for biomass-burning tracers. Concentrations of levoglucosan and dehydroabietic and vanillic acids exhibit multidecadal variability, with higher spikes in 1678, 1692, 1695, 1716, 1750, 1764, 1756, 1834, 1898, 1913, 1966 and 2005 CE. Historical trends of these compounds showed enhanced biomass-burning activities in the deciduous broadleaf forests, boreal conifer forests, and/or tundra woodland and mountain ecosystems before the 1830s and after the Great Pacific Climate Shift (GPCS). The gradually elevated level of dehydroabietic acid after the GPCS is similar to p-hydroxybenzoic acid (p-HBA) from the Svalbard ice core, suggesting common climate variability in the Northern Hemisphere. The periodic cycle of levoglucosan, which seemed to be associated with the Pacific Decadal Oscillation (PDO), may be more involved with the long-range atmospheric transport than other species. These compounds showed significant correlations with global lower-tropospheric temperature anomalies (GLTTAs). The relations of the biomass-burning tracers with the PDO and GLTTA in this study suggest that their emission, frequency and deposition are controlled by the climate-driven forces. In addition, historical trends of dehydroabietic and vanillic acids (burning products of resin and lignin, respectively) from our ice core demonstrate the Northern Hemispheric connections to the common source regions as suggested from other ice core studies from Svalbard, Akademii Nauk and Tunu Greenland in the Northern Hemisphere.
• Perspectives on a Seamless Marine-lake Sediment Coring Study in East Antarctica

  Yusuke Suganuma, Takeshige Ishiwa, Moto Kawamata, Jun'chi Okuno, Kota Katsuki, Takuya Itaki, Osamu Seki, Heitaro Kaneda, Hiroki Matsui, Yuki Haneda, Masakazu Fujii, Daisuke Hirano

  JOURNAL OF GEOGRAPHY-CHIGAKU ZASSHI 129 5 591 - 610 2020年 

  The Antarctic Ice Sheet (AIS) is one of the largest potential contributors to future sea-level changes. Recently, an acceleration of AIS volume loss through basal melting and iceberg calving has been reported based on several studies using satellite observations, including radar altimetry, interferometer, and gravity measurements. A recent model that couples ice sheet and climate dynamics and incorporates hydrofracturing mechanism of buttressing ice shelves predicts a higher sea-level rise scenario for the next 500 years. However, the calibration and reproducibility of the sea-level rise projection from these models relies on geological sea-level reconstructions of past warm intervals. This suggests that a highly reliable reconstruction of the past AIS is essential for evaluating its stability and anticipating its contribution to future sea-level rise. In particular, a relative sea-level reconstruction in East Antarctica is the key to solving the problems and refining future projections. The current understanding of sea-level change along the East Antarctic margin is reviewed, including Glacial Isostatic Adjustment (GIA) effects, and a new strategy is proposed to address this topic based on seamless sediment coring from marine to lake in the East Antarctic margin. This project will provide essential data on AIS change since the last interglacial period.
• Sources of atmospheric black carbon and related carbonaceous components at Rishiri Island, Japan: The roles of Siberian wildfires and of crop residue burning in China

  Chunmao Zhu, Yugo Kanaya, Hisayuki Yoshikawa-Inoue, Tomohisa Irino, Osamu Seki, Yasunori Tohjima

  ENVIRONMENTAL POLLUTION 247 55 - 63 2019年04月 

  A field study was conducted to clarify sources of atmospheric black carbon and related carbonaceous components at Rishiri Island, Japan. We quantified equivalent black carbon (eBC) particle mass and the absorption Angstrom exponent (AAE), atmospheric CO and CH4, in addition to levoglucosan in total suspended particles, a typical tracer of biomass burning. Sixteen high eBC events were identified attributable to either anthropogenic sources or biomass burning in Siberia/China. These events were often accompanied by increases of co-emitted gases such as CH4 and CO. Specifically, we observed pollution events with elevated eBC, AAE, levoglucosan, and CH4-CO slope in late July 2014, which were attributed to forest fires in Siberia by reference to the FLEXPART model footprint and fire hotspots. In autumn, drastic increases of eBC, AAE, and levoglucosan were observed, accompanied by an eBC-CO slope of >15 ng m(-3)/ppb, resulting from long-range transport of emissions from extensive burning of crop residue on the Northeast China Plain. Other than the sources of fossil fuel combustion in China and forest fires in Siberia, we report for the first time that pollution events in northern Japan are caused by crop residue burning in China. This study elucidated valuable information that will improve understanding of the effects of biomass burning in East Asia on atmospheric carbonaceous components. (C) 2019 Elsevier Ltd. All rights reserved.
• Assessment for paleoclimatic utility of biomass burning tracers in SE-Dome ice core, Greenland

  Parvin F, Seki O, Fujita K, Iizuka Y, Matoba S, Ando T, Sawada K

  Atmospheric Environment 196 86 - 94 2019年01月 [査読有り][通常論文]
   

  We provide continuous records of biomass burning molecular tracers (levoglucosan and dehydroabietic acid) in a Greenland ice core collected from the Southeastern Dome (the SE-Dome ice core) over the past several decades to assess the paleoclimatic utility of these tracers in Greenland ice cores. An air mass backward-trajectory analysis indicates that eastern Canada is likely the primary source region of the biomass burning tracers. Comparisons of levoglucosan and dehydroabietic acid data in the SE-Dome ice core and area burned (vegetation fire) events in Canada suggests that the biomass burning tracers in the ice core document most of the pronounced biomass burning events in eastern Canada over the past several decades, confirming that analyses of biomass burning molecular tracers in Greenland ice cores are useful to reconstruct the frequency of significant biomass burning events in a local region. However, our study also highlights that the wind pattern when the biomass burning occurs is decisive for the registration of a biomass burning event in an ice core even though long-term changes in the wind regime associated with decadal-scale climate oscillations do not significantly influence the transport and deposition of biomass burning tracers on the Greenland ice sheet.
• Genomic identification of the long-chain alkenone producer in freshwater Lake Toyoni, Japan: implications for temperature reconstructions

  Julien Plancq, Jill L McColl, James A Bendle, Osamu Seki, Jillian M Couto, Andrew C Henderson, Yohei Yamashita, Kimitaka Kawamura, Jaime L Toney

  Org. Geochem. 125 189 - 195 2018年11月 [査読有り][通常論文]
   

  Identifying the lacustrine haptophyte species that produce long-chain alkenones (LCAs) is essential prior to down-core temperature reconstructions. Here, we investigated the identity of LCA-producing species from Lake Toyoni, Japan using 18S ribosomal DNA (rDNA) and organic geochemical analyses. The rDNA analyses identified eighteen operational taxonomic units (OTUs) of which only one fell within the haptophyte phylotype. This haptophyte belongs to the Group I phylotype, as supported by the LCA distribution found in surface and down-core sediments, and is closely related to a haptophyte found in Lake BrayaSo (Greenland). The inferred temperature using the Greenland calibration is very close to the Lake Toyoni surface temperature recorded during the spring/early summer season, when the LCA-producing haptophyte is likely to bloom. We therefore suggest that the temperature calibration from the Lake BrayaSo, Greenland is a suitable calibration for down-core temperature reconstructions at Lake Toyoni. (C) 2018 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license.
• Novel alkenone-producing strains of genus Isochrysis (Haptophyta) isolated from Canadian saline lakes show temperature sensitivity of alkenones and alkenoates

  Hiroya Araie, Hideto Nakamura, Jaime L. Toney, Heather A. Haig, Julien Plancq, Takashi Shiratori, Peter R. Leavitt, Osamu Seki, Ken-ichiro Ishida, Ken Sawada, Iwane Suzuki, Yoshihiro Shiraiwa

  Organic Geochemistry 121 89 - 103 2018年07月01日 [査読有り][通常論文]
   

  Alkenone-producing species have been recently found in diverse lacustrine environments, albeit with taxonomic information derived indirectly from environmental genomic techniques. In this study, we isolated alkenone-producing algal species from Canadian saline lakes and established unialgal cultures of individual strains to identify their taxonomical and molecular biological characteristics. Water and sediments collected from the lakes were first enriched in artificial seawater medium over a range of salinities (5–40 g/L) to cultivate taxa in vitro. Unialgal cultures of seven haptophyte strains were isolated and categorized in the Isochrysis clade using SSU and LSU rRNA gene analysis. The alkenone distributions within isolated strains were determined to be novel compared with other previously reported alkenone-producing haptophytes. While all strains produced the typical C37 and C38 range of isomers, one strain isolated from Canadian salt lakes also produced novel C41 and C42 alkenones that are temperature sensitive. In addition, we showed that all alkenone unsaturation indices (e.g., U37 K and U37 K′) are temperature-dependent in culture experiments, and that alkenoate indices (e.g., U37 A, U38 A, RIA38 and A37/A38) provide alternative options for temperature calibration based on these new lacustrine algal strains. Importantly, these indices show temperature dependence in culture experiments at temperatures below 10 °C, where traditional alkenone proxies were not as sensitive. We hypothesize that this suite of calibrations may be used for reconstructions of past water temperature in a broad range of lakes in the Canadian prairies.
• Mid- to- late Holocene hydroclimatic changes on the Chinese Loess Plateau: evidence from n-alkanes from the sediments of Tianchi Lake

  Huiling Sun, James Bendle, Osamu Seki, Aifeng Zhou

  Journal of Paleolimnology 60 4 1 - 13 2018年06月25日 [査読有り][通常論文]
   

  We have reconstructed the history of mid-late Holocene paleohydrological changes in the Chinese Loess Plateau using n-alkane data from a sediment core in Tianchi Lake. We used Paq (the proportion of aquatic macrophytes to the total plant community) to reflect changes in lake water level, with a higher abundance of submerged macrophytes indicating a lower water level and vice versa. The Paq-based hydrological reconstruction agrees with various other lines of evidence, including ACL (average chain length), CPI (carbon preference index), C/N ratio and the n-alkane molecular distribution of the sediments in Tianchi Lake. The results reveal that the lake water level was relatively high during 5.7–3.2 ka BP, and decreased gradually thereafter. Our paleohydrological reconstruction is consistent with existing paleoclimate reconstructions from the Loess Plateau, which suggest a humid mid-Holocene, but is asynchronous with paleoclimatic records from central China which indicate an arid mid-Holocene. Overall, our results confirm that the intensity of the rainfall delivered by the EASM (East Asian summer monsoon) is an important factor in affecting paleohydrological changes in the region and can be considered as further evidence for the development of a spatially asynchronous “northern China drought and southern China flood” precipitation pattern during the Holocene.
• A 60 Year Record of Atmospheric Aerosol Depositions Preserved in a High-Accumulation Dome Ice Core, Southeast Greenland

  Yoshinori Iizuka, Ryu Uemura, Koji Fujita, Shohei Hattori, Osamu Seki, Chihiro Miyamoto, Toshitaka Suzuki, Naohiro Yoshida, Hideaki Motoyama, Sumito Matoba

  Journal of Geophysical Research: Atmospheres 123 1 574 - 589 2018年01月16日 [査読有り][通常論文]
   

  ©2017. American Geophysical Union. All Rights Reserved. The Southeastern Greenland Dome (SE-Dome) has both a high elevation and a high accumulation rate (1.01 m we yr−1), which are suitable properties for reconstructing past environmental changes with a high time resolution. For this study, we measured the major ion fluxes in a 90 m ice core drilled from the SE-Dome region in 2015 and present the records of annual ion fluxes from 1957 to 2014. From 1970 to 2010, the trend of nonsea-salt (nss) SO42− flux decreases, whereas that for NH4+ increases, tracking well with the anthropogenic SOx and NH3 emissions mainly from North America. The result suggests that these fluxes reflect histories of the anthropogenic SOx and NH3 emissions. In contrast, the decadal trend of NO3− flux differs from the decreasing trend of anthropogenic NOx emissions. Although the cause of this discrepancy remains unclear, it may be related to changes in particle formation processes and chemical scavenging rates caused by an increase in sea salt and dust and/or a decrease in nssSO42−. We also find a high average NO3− flux (1.13 mmol m−2 yr−1) in the ice core, which suggests a negligible effect from postdepositional NO3− loss. Thus, the SE-Dome region is an excellent location for reconstructing nitrate fluxes. Over a decadal time scale, our NO3− flux record is similar to those from other ice cores in Greenland high-elevation sites, suggesting that NO3− concentration records from these ice cores are reliable.
• Changes in Sea Surface and Intermediate Water Temperature over the Late Pleistocene in the Northwest Pacific

  Matsuzaki Kenji Marc Raymond, Kubota Yoshimi, Okazaki Yusuke, Seki Osamu, Itaki Takuya, Ikehara Minoru

  日本地質学会学術大会講演要旨 2018 0 316 - 316 一般社団法人 日本地質学会 2018年
• Historical Trends of Biogenic SOA Tracers in an Ice Core from Kamchatka Peninsula

  Pingqing Fu, Kimitaka Kawamura, Osamu Seki, Yusuke Izawa, Takayuki Shiraiwa, Kirsti Ashworth

  ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS 3 10 351 - 358 2016年10月 [査読有り][通常論文]
   

  Biogenic secondary organic aerosol (SOA) is ubiquitous in the Earth's atmosphere, influencing climate and air quality. However, the historical trend of biogenic SOA is not well known. Here, we report for the first time the major isoprene- and monoterpene-derived SOA tracers preserved in an ice core from the Kamchatka Peninsula. Significant variations are recorded during the past 300 years with lower concentrations in the early-to-middle 19th century and higher concentrations in the preindustrial period and the present day. We discovered that isoprene SOA tracers were more abundant in the preindustrial period than the present day, while monoterpene SOA tracers stay almost unchanged. The causes of the observed variability are complex, depending on atmospheric circulation, changes in emissions, and other factors such as tropospheric oxidative capacity. Our data presents an unprecedented opportunity to shed light on the formation, evolution, and fate of atmospheric aerosols and to constrain the uncertainties associated with modeling their atmospheric concentrations.
• Ice core records of monoterpene- and isoprene-SOA tracers from Aurora Peak in Alaska since 1660s: Implication for climate change variability in the North Pacific Rim

  Ambarish Pokhrel, Kimitaka Kawamura, Kaori Ono, Osamu Seki, Pingqing Fu, Sumio Matoba, Takayuki Shiraiwa

  ATMOSPHERIC ENVIRONMENT 130 105 - 112 2016年04月 [査読有り][通常論文]
   

  Monoterpene and isoprene secondary organic aerosol (SOA) tracers are reported for the first time in an Alaskan ice core to better understand the biological source strength before and after the industrial revolution in the Northern Hemisphere. We found significantly high concentrations of monoterpene- and isoprene-SOA tracers (e.g., pinic, pinonic, and 2-methylglyceric acids, 2-methylthreitol and 2-methylerythritol) in the ice core, which show historical trends with good correlation to each other since 1660s. They show positive correlations with sugar compounds (e.g., mannitol, fructose, glucose, inositol and sucrose), and anti-correlations with alpha-dicarbonyls (glyoxal and methylglyoxal) and fatty acids (e.g., C-18:1) in the same ice core. These results suggest similar sources and transport pathways for monoterpene- and isoprene-SOA tracers. In addition, we found that concentrations of C-5-alkene triols (e.g., 3-methyl-2,3,4-trihydroxy-1-butene, cis-2-methyl 1,3,4-trihydroxy-1-butene and trans-2-methyl-1,3,4-trihydroxy-1-butene) in the ice core have increased after the Great Pacific Climate Shift (late 1970s). They show positive correlations with a-dicarbonyls and fatty acids (e.g., C-18:1) in the ice core, suggesting that enhanced oceanic emissions of biogenic organic compounds through the marine boundary layer are recorded in the ice core from Alaska. Photochemical oxidation process for these monoterpene- and isoprene-/sesquiterpene-SOA tracers are suggested to be linked with the periodicity of multi-decadal climate oscillations and retreat of sea ice in the Northern Hemisphere. (C) 2015 Elsevier Ltd. All rights reserved.
• Ice-core records of biomass burning

  Mauro Rubino, Antonio D’Onofrio, Osamu Seki, James A. Bendle

  Anthropocene Review 3 2 140 - 162 2016年 [査読有り][通常論文]
   

  We review the approaches for estimating biomass burning from ice-cores and consider the challenges and assumptions in their application. In particular, we consider the potential of biomarker proxies for biomass burning, hitherto not widely applied to glacial ice archives. We also review the available records of biomass burning in ice-cores and consider how variations in fire regimes have been related to atmospheric and land-use changes. Finally, we suggest that future developments in ice-core science should aim to combine multiple biomarkers with other records (black carbon, charcoal) and models to discern the types of material being burnt (C3 versus C4 plants, angiosperms, gymnosperms, peat fires, etc.) and to improve constraints on source areas of biomass burning. An ultimate goal is to compare the biomass burning record from ice-cores with hindcasts from models to project how future climate change will influence biomass burning and, inversely, how fire will affect climate.
• North Atlantic Holocene climate evolution recorded by high-resolution terrestrial and marine biomarker records

  Heiko Moossen, James Bendle, Osamu Seki, Ursula Quillmann, Kimitaka Kawamura

  QUATERNARY SCIENCE REVIEWS 129 111 - 127 2015年12月 [査読有り][通常論文]
   

  Holocene climatic change is driven by a plethora of forcing mechanisms acting on different time scales, including: insolation, internal ocean (e.g. Atlantic Meridional Overturning Circulation; AMOC) and atmospheric (e.g. North Atlantic Oscillation; NAO) variability. However, it is unclear how these driving mechanisms interact with each other. Here we present five, biomarker based, paleoclimate records (air-, sea surface temperature and precipitation), from a fjordic sediment core, revealing North Atlantic terrestrial and marine climate in unprecedented detail. The Early Holocene (10.7-7.8 kyrs BP) is characterised by relatively high air temperatures while SSTs are dampened by melt water events, and relatively low precipitation. The Middle Holocene (7.8-3.2 kyrs BP) is characterised by peak SSTs, declining air temperatures and high precipitation. A pronounced marine thermal maximum occurs between similar to 7 -5.5 kyrs BP, 3000 years after the terrestrial thermal maximum, driven by melt water cessation and an accelerating AMOC. The neoglacial cooling, between 5.8 and 3.2 kyrs BP leads into the late Holocene. We demonstrate that an observed modern link between Icelandic precipitation variability during different NAO phases, may have existed from similar to 7.5 kyrs BP. A simultaneous decoupling of both air, and sea surface temperature records from declining insolation at similar to 3.2 kyrs BP may indicate a threshold, after which internal feedback mechanisms, namely the NAO evolved to be the primary drivers of Icelandic climate on centennial time-scales. (C) 2015 Elsevier Ltd. All rights reserved.
• Carbonaceous aerosol tracers in ice-cores record multi-decadal climate oscillations

  Osamu Seki, Kimitaka Kawamura, James A. P. Bendle, Yusuke Izawa, Ikuko Suzuki, Takayuki Shiraiwa, Yoshiyuki Fujii

  SCIENTIFIC REPORTS 5 14450  2015年09月 [査読有り][通常論文]
   

  Carbonaceous aerosols influence the climate via direct and indirect effects on radiative balance. However, the factors controlling the emissions, transport and role of carbonaceous aerosols in the climate system are highly uncertain. Here we investigate organic tracers in ice cores from Greenland and Kamchatka and find that, throughout the period covered by the records (1550 to 2000 CE), the concentrations and composition of biomass burning-, soil bacterial-and plant wax-tracers correspond to Arctic and regional temperatures as well as the warm season Arctic Oscillation (AO) over multi-decadal time-scales. Specifically, order of magnitude decreases (increases) in abundances of ice-core organic tracers, likely representing significant decreases (increases) in the atmospheric loading of carbonaceous aerosols, occur during colder (warmer) phases in the high latitudinal Northern Hemisphere. This raises questions about causality and possible carbonaceous aerosol feedback mechanisms. Our work opens new avenues for ice core research. Translating concentrations of organic tracers (mu g/kg-ice or TOC) from ice-cores, into estimates of the atmospheric loading of carbonaceous aerosols (mu g/m(3)) combined with new model constraints on the strength and sign of climate forcing by carbonaceous aerosols should be a priority for future research.
• Pliocene cooling enhanced by flow of low-salinity Bering Sea water to the Arctic Ocean

  Keiji Horikawa, Ellen E. Martin, Chandranath Basak, Jonaotaro Onodera, Osamu Seki, Tatsuhiko Sakamoto, Minoru Ikehara, Saburo Sakai, Kimitaka Kawamura

  NATURE COMMUNICATIONS 6 7587  2015年06月 [査読有り][通常論文]
   

  Warming of high northern latitudes in the Pliocene (5.33-2.58 Myr ago) has been linked to the closure of the Central American Seaway and intensification of North Atlantic Deep Water. Subsequent cooling in the late Pliocene may be related to the effects of freshwater input from the Arctic Ocean via the Bering Strait, disrupting North Atlantic Deep Water formation and enhancing sea ice formation. However, the timing of Arctic freshening has not been defined. Here we present neodymium and lead isotope records of detrital sediment from the Bering Sea for the past 4.3 million years. Isotopic data suggest the presence of Alaskan glaciers as far back as 4.2 Myr ago, while diatom and C-37:4 alkenone records show a long-term trend towards colder and fresher water in the Bering Sea beginning with the M2 glaciation (3.3 Myr ago). We argue that the introduction of low-salinity Bering Sea water to the Arctic Ocean by 3.3 Myr ago preconditioned the climate system for global cooling.
• Spatial distributions of dicarboxylic acids, ω-oxoacids, pyruvic acid and α-dicarbonyls in the remote marine aerosols over the North Pacific

  Mozammal Hoque, Mozammal Hoque, Kimitaka Kawamura, Osamu Seki, Naoki Hoshi

  Marine Chemistry 172 1 - 11 2015年05月 [査読有り][通常論文]
   

  © 2015 Elsevier B.V. To better understand the sources and atmospheric processing of organic aerosols in the remote marine atmosphere, aerosol (TSP) samples were collected over the North Pacific (13°14'N-53°37'N and 140°46'E-179°54'W) in May-July, 2010 during a cruise of T/V Oshoro Maru, and studied for dicarboxylic acids (C2-C11), ω-oxoacids, pyruvic acid and α-dicarbonyls as well as organic and elemental carbon, water-soluble organic carbon and total nitrogen. Over the North Pacific, diacids are most abundant followed by ω-oxoacids and α-dicarbonyls. Although the molecular compositions of diacids are generally characterized by the predominance of oxalic (C2) acid, we found a predominance of succinic (C4) acid in four samples, which were collected in the central northern North Pacific. We consider that photochemical degradation of unsaturated fatty acids emitted from the ocean surface is the main source of C4 over the central northern North Pacific, where Chlorophyll-a maximized during the cruise. Moreover, seven samples collected in the central northern North and western North Pacific shows predominance of malonic (C3) acid over C4, suggesting the photochemical degradation of C4 to C3. Spatial distributions of diacids, ω-oxoacids and α-dicarbonyls together with total carbon and water soluble total nitrogen contents showed higher abundances in the coastal western North Pacific followed by the central northern North and subtropical Pacific, signifying that continental aerosols are transported long distances to the remote marine atmosphere.
• Ice core profiles of saturated fatty acids (C-12:0-C-30:0) and oleic acid (C-18:1) from southern Alaska since 1734 AD: A link to climate change in the Northern Hemisphere

  Ambarish Pokhrel, Kimitaka Kawamura, Osamu Seki, Sumio Matoba, Takayuki Shiraiwa

  ATMOSPHERIC ENVIRONMENT 100 202 - 209 2015年01月 [査読無し][通常論文]
   

  An ice core drilled at Aurora Peak in southeast Alaska was analyzed for homologous series of straight chain fatty acids (C-12:0-C-30:0) including unsaturated fatty acid (oleic acid) using gas chromatography (GC/FID) and GC/mass spectrometry (GC/MS). Molecular distributions of fatty acids are characterized by even carbon number predominance with a peak at palmitic acid (C-16:0, av. 20.3 +/- SD. 29.8 ng/g-ice) followed by oleic acid (C-18:1, 19.6 +/- 38.6 ng/g-ice) and myristic acid (C-14:0, 15.3 +/- 21.9 ng/g-ice). The historical trends of short-chain fatty acids, together with correlation analysis with inorganic ions and organic tracers suggest that short-chain fatty acids (except for C-12:0 and C-15:0) were mainly derived from sea surface micro layers through bubble bursting mechanism and transported over the glacier through the atmosphere. This atmospheric transport process is suggested to be linked with Kamchatka ice core SD record from Northeast Asia and Greenland Temperature Anomaly (GTA). In contrast, long-chain fatty acids (C-20.0-C-30:0) are originated from terrestrial higher plants, soil organic matter and dusts, which are also linked with GTA. Hence, this study suggests that Alaskan fatty acids are strongly influenced by Pacific Decadal Oscillation/North Pacific Gyre Oscillation and/or extra tropical North Pacific surface climate and Arctic oscillation. We also found that decadal scale variability of C-18:1/C-18:0 ratios in the Aurora Peak ice core correlate with the Kamchatka ice core SD, which reflects climate oscillations in the North Pacific. This study suggests that photochemical aging of organic aerosols could be controlled by climate periodicity. (C) 2014 Elsevier Ltd. All rights reserved.
• Lignin phenols and BIT index distributions in the Amur River and the Sea of Okhotsk: Implications for the source and transport of particulate terrestrial organic matter to the ocean

  O. Seki, Y. Mikami, S. Nagao, J. A. Bendle, T. Nakatsuka, V. I. Kim, V. P. Shesterkin, A. N. Makinov, M. Fukushima, H. M. Moossen, S. Schouten

  PROGRESS IN OCEANOGRAPHY 126 146 - 154 2014年08月 [査読無し][通常論文]
   

  Delta and coastal regions play a key role in the global carbon cycle as the main repository of inputs of terrestrial organic matter, delivered by rivers to marine sediments. The Amur River system is one of the largest in Asia and supplies organic matter to the Sea of Okhotsk and the North Pacific Ocean. We measured lignin phenols (a proxy for terrestrial plant derived organic matter) and the branched and isoprenoidal tetraether (BIT) index (a proxy for riverborne soil organic matter), in soils and river bed sediments from the Amur River basin and surface sediments from the Sea of Okhotsk, to study the source, transport, and deposition of fluvial particulate organic matter to the ocean. Concentrations of lignin phenols are relatively high in sediments from the shallow continental shelf compared to that of the deep offshore basin. For the first time we report a spatial distribution of the BIT index which shows a similar pattern to that of lignin phenol concentrations, with relatively high values in the coastal sites. The highest values of both lignin concentrations and BIT values are observed in a site proximal to mouth of Amur River. These results indicate that terrestrial organic matter deposited in the Sea of Okhotsk mostly originates from soil organic matter supplied from Amur River. Spatial distributions of lignin phenols/TOC (LP/TOC) and the BIT index in the Sea of Okhotsk and comparison with S/V (a contribution index of angiosperm vs. gymnosperms) and C/V ratios (indicative of the relative contribution of non-woody tissue vs. woody tissue), between the Amur River basin and Okhotsk Sea samples, suggest that Amur River fluvial organic matter is supplied and deposited to the northwestern continental shelf. Furthermore, S/V values from our Amur River and Okhotsk Sea continental shelf sediment samples are consistent with the reported S/V ratio (0.32) of particulate organic matter in the North Pacific Intermediate Water (NPIW) layer (750 m depth). Hence, our study supports previous studies from the NW Pacific Ocean, which suggest inputs of terrestrial organic matter from the Amur River via the Sea of Okhotsk, as a major source of particulate organic matter to the North Pacific Ocean. (C) 2014 Elsevier Ltd. All rights reserved.
• Holocene sea surface temperature and sea ice extent in the Okhotsk and Bering Seas

  Naomi Harada, Kota Katsuki, Mitsuhiro Nakagawa, Akiko Matsumoto, Osamu Seki, Jason A. Addison, Bruce P. Finney, Miyako Sato

  PROGRESS IN OCEANOGRAPHY 126 242 - 253 2014年08月 [査読無し][通常論文]
   

  Accurate prediction of future climate requires an understanding of the mechanisms of the Holocene climate; however, the driving forces, mechanisms, and processes of climate change in the Holocene associated with different time scales remain unclear. We investigated the drivers of Holocene sea surface temperature (SST) and sea ice extent in the North Pacific Ocean, and the Okhotsk and Bering Seas, as inferred from sediment core records, by using the alkenone unsaturation index as a biomarker of SST and abundances of sea ice-related diatoms (F. cylindrus and F. oceanica) as an indicator of sea ice extent to explore controlling mechanisms in the high-latitude Pacific. Temporal changes in alkenone content suggest that alkenone production was relatively high during the middle Holocene in the Okhotsk Sea and the western North Pacific, but highest in the late Holocene in the eastern Bering Sea and the eastern North Pacific. The Holocene variations of alkenone-SSTs at sites near Kamchatka in the Northwest Pacific, as well as in the western and eastern regions of the Bering Sea, and in the eastern North Pacific track the changes of Holocene summer insolation at 50 degrees N, but at other sites in the western North Pacific, in the southern Okhotsk Sea, and the eastern Bering Sea they do not. In addition to insolation, other atmosphere and ocean climate drivers, such as sea ice distribution and changes in the position and activity of the Aleutian Low, may have systematically influenced the timing and magnitude of warming and cooling during the Holocene within the subarctic North Pacific. Periods of high sea ice extent in both the Okhotsk and Bering Seas may correspond to some periods of frequent or strong winter-spring dust storms in the Mongolian Gobi Desert, particularly one centered at similar to 4-3 thousand years before present (kyr BP). Variation in storm activity in the Mongolian Gobi Desert region may reflect changes in the strength and positions of the Aleutian Low and Siberian High. We suggest that periods of eastward displacement or increased intensity of the Aleutian Low correspond with times of increased extent of sea ice in the western Okhotsk Sea and eastern Bering Sea. (C) 2014 Elsevier Ltd. All rights reserved.
• Assessment and calibration of TEX86 paleothermometry in the Sea of Okhotsk and sub-polar North Pacific region: Implications for paleoceanography

  Osamu Seki, James A. Bendle, Naomi Harada, Madoka Kobayashi, Ken Sawada, Heiko Moossen, Gordon N. Inglis, Seiya Nagao, Tatsuhiko Sakamoto

  PROGRESS IN OCEANOGRAPHY 126 254 - 266 2014年08月 [査読無し][通常論文]
   

  We measured TEX86 indices in surface sediments and sediment cores from marginal seas and open ocean sites in the North Pacific to test the accuracy of TEX86 paleothermometry in the region. Application of the global core top TEX86L and TEX86H, calibrations in the Sea of Okhotsk and northern North Pacific sub-polar region results in over- and under-estimations of TEX86 derived SSTs in surface sediments in deep-ocean and coastal areas, respectively. Further challenges apparent in applying TEX86L and TEX86H in late Quaternary sediment cores from the Okhotsk Sea (MR06-04 PC7) and northwestern Pacific (MR00-K03 PC1) are unrealistically warm Holocene mean annual reconstructed temperatures (TEX86L) and excessively cold Glacial temperatures (TEX1,16), compared with other high-latitude records and climate models. Application of a calibration based on a sub-set of deep (<1000 m) core-top sites appears to improve temperature reconstructions in the Holocene, but still yields underestimation of SSTs (mean annual = -5 degrees C for TEX86H) in the Glacial period in the Okhotsk Sea core MR06-04 PC7. However, a regional comparison of Okhotsk Sea and sub-polar surface sediment TEX86L values with observational sea-water temperatures at different seasons and water depths reveals that an optimized positive correlation is obtained with summer sub-surface temperatures (August, 20 m depth). The unique hydrographic setting of the Okhotsk Sea region likely exerts a strong control on the ecology of GDGT producers (assumed to be primarily be marine Thaumarchaeota), resulting in highly season and depth specific export production and a distinct regional gradient in surface sediment TEX86 values. When our new regional TEX86L calibration is applied to the sediment cores, TEX86L, and alkenone U-37(K') temperature estimates overlap in the Holocene and TEX86L produces plausible LGM to Holocene temperature reconstructions. Our study provides a region specific calibration and confirms the importance of acquiring local calibration equations, to optimize TEX86 paleothermometry for specific regions and ocean basins. (C) 2014 Elsevier Ltd. All rights reserved.
• バイオマーカーを用いた古気候研究

  関宰

  地球化学 48 2 67 - 79 The Geochemical Society of Japan 2014年06月25日 [査読無し][通常論文]
   

  Organic geochemical proxies have been extensively applied to geochemical study and reconstruction of past environmental conditions. Biomarkers are preserved in a wide variety of archives such as ice core, peat bog, lacustrine and marine sediments and thus can reconstruct various aspects of environmental conditions including the land, ocean and atmosphere. The fundamentals of this approach are the compositions, abundances and compound-specific isotopic compositions of organic molecules that are preserved in archives. For instance, UK´37 and TEX86 indices register upper water column temperature in the ocean while molecular distribution and stable carbon and hydrogen isotopic compositions of leaf wax lipids can be used to reconstruct terrestrial vegetation and climate such as temperature and hydrology in a past. In this paper, I present the applications of biomarkers in paleoclimate study based on results of my work.
• Paleoclimate variability in central Taiwan during the past 30Kyrs reflected by pollen, δ13CTOC, and n-alkane-δD records in a peat sequence from Toushe Basin

  Hong Chun Li, Ping Mei Liew, Osamu Seki, Tz Shing Kuo, Kimitaka Kawamura, Liang Chi Wang, Teh Quei Lee

  Journal of Asian Earth Sciences 69 166 - 176 2013年06月05日 [査読無し][通常論文]
   

  A total of 233 samples from the upper 16m of the Toushe peat core retrieved in central Taiwan were measured for TOC and δ13CTOC values. From these samples, 17 selected samples with large δ13CTOC fluctuations were analyzed for n-alkane and δD of the C27 and C29 n-alkanes. Combining with the detailed high-resolution pollen and geochemical records, this study reveals more detailed climatic variations in terms of temperature and precipitation as well as abrupt climatic events during the past 30Kyrs. Before the Last Glacial Maximum (LGM), climate was cold and damp with predominantly woodland vegetation in Toushe Basin, and turned to cold and dry after 25Kyr BP. Climatic conditions there were the worst during LGM over the past 30Kyrs, especially around 23 and 18Kyr BP when the woodland was diminished and C4 grass was dominated. Although short durations of relatively wet conditions could be found at 17, 16 and 14Kyr BP, cold and dry climates were prevailing during 29.5-28, 24-22, 17-15 and 13-11.5Kyr BP, corresponding to Heinrich (H) Events 3, 2, 1, and Younger Dryas (YD), respectively. During the early Holocene, dry climate occurred at ∼11, ∼10, 9.7-9.2 and ∼8Kyr BP; whereas wet condition appeared at 10.3, 9.8, 9-7.5Kyr BP. In the middle Holocene, climate kept warm and moderate wet in the first half period, but many dry events existed in the second half following a cold and dry event at 6Kyr BP. After a sharply warm peak at 5.2Kyr BP, the climate in Toushe turned to cold quickly, and tree/shrub vegetation disappeared completely with the replacement of C3 grasses. In the late Holocene, climate was relatively wetter with predominant C3 grasses in the basin. Our climatic interpretations based on the peat records agree well with the Greenland ice core and Chinese speleothem records on millennium time scales during the last glacial period. Dry climates corresponding to weakening of the East Asian Summer Monsoon (EASM) during the Heinrich events and Younger Dryas in central Taiwan and eastern China demonstrate the climatic forcing on such long time scales in concert with regional monsoon climate. However, the discrepancies exist between our peat record and the Dongge/Hulu stalagmite record on: (1) the age of H2; (2) climate intensities of LGM and H1; and (3) wetness condition during Holocene. These observations call for further study on high-resolution climatic changes especially on moisture budget in the East Asian monsoonal region. © 2012 Elsevier Ltd.
• Influence of aerosol source regions and transport pathway on δD of terrestrial biomarkers in atmospheric aerosols from the East China Sea

  Shinya Yamamoto, Kimitaka Kawamura, Osamu Seki, Tadashi Kariya, Tadashi Kariya, Meehye Lee

  Geochimica et Cosmochimica Acta 106 164 - 176 2013年04月 [査読無し][通常論文]
   

  We measured stable hydrogen isotope ratios (δD) of terrestrial biomarkers (n-alkanes and n-fatty acids) in atmospheric total suspended particles collected at Jeju Island in the East China Sea, from April 2001 to March 2002, to better understand the influence of long-range atmospheric transport on their seasonal variations. The δD values of the C27, C29 and C31 n-alkanes (δDALK) show a significant negative correlation with the CPI values of n-alkanes (r2=0.26, p<0.01), suggesting that the δDALK variations are partly attributed to a superimposed contribution from fossil fuel hydrocarbons. Seasonal variations in the concentrations of the C22-C28 even-carbon numbered n-fatty acids revealed relatively high concentrations in spring, autumn and winter seasons, in which the air masses are transported from northeast Asia. In contrast, the concentrations are low in summer when the air masses are transported from Southeast Asia and the Pacific. Relatively high C26/FA and low C24/FA ratios in spring, autumn and winter samples suggest that the C26 n-fatty acids are more abundantly transported from the Asian continent during these seasons. Seasonal variations in the δ D of the C22-C26 even-carbon numbered n-fatty acids exhibit significant enrichment with D (by ~40‰) in May and June to August samples, whereas the δ D of the C28 n-fatty acids gradually decrease during summer. The magnitude of the δ D offsets (~45‰) between the C28 n-fatty acid and the other homologues are much larger than those observed in East Asia spanning 18 ° N-50 ° N latitude (ca. 30‰), suggesting that the decoupling is likely attributed to the mixing of distinct source vegetation with different δ D ratios. Comparison of the weighted-mean δ D values of n-fatty acids (δ D FA) between air mass source categories revealed relatively low values (~-170‰) in samples with trajectories from the northeastern part of the Asian continent, supporting that the δ D analyses may be a powerful tool in deciphering the source regions of terrestrial biomarkers in atmospheric aerosols from the Asian continent. The results of this study provides important implications for paleoclimate studies that the δ D variations of long-range transported terrestrial biomarkers in remote ocean sediments may have recorded past changes in source strengths of the biomarkers and therefore have a potential to reconstruct paleo-wind patterns and transport of terrestrial carbon over the Pacific. © 2013 Elsevier Ltd.
• n-Alkanes in Fresh Snow in Hokkaido, Japan: Implications for Ice Core Studies

  Paula Sankelo, Kimitaka Kawamura, Osamu Seki, Hideaki Shibata, James Bendle

  ARCTIC ANTARCTIC AND ALPINE RESEARCH 45 1 119 - 131 2013年02月 [査読無し][通常論文]
   

  Plant waxes (e.g. long-chain n-alkanes) in ice cores are a promising paleovegetation proxy. However, much work needs to be done to assess how n-alkanes are transported from source areas to, and incorporated into, glacial archives. In this paper we present analyses of n-alkanes in seasonal snow and assess the information on source vegetation. n-Alkanes with carbon numbers C-18 to C-43 were extracted from snow samples collected at two sites in Hokkaido, northern Japan, during winter 2009-2010. Molecular distributions revealed that the majority of the n-alkanes originated from higher vegetation (ca. 65%), rather than anthropogenic sources. The distribution characteristics confirmed that the n-alkane signal had a wide regional origin, rather than a local source. We determined stable carbon and hydrogen isotopic compositions for the C-27 n-alkane. The delta C-13 of the C-27 (-28.2 to -33.0 parts per thousand) was more representative of C3 than C4 vegetation, while the delta D of the C-27 ( -169.9 to -223.1 parts per thousand) indicated growth latitudes more northerly than Hokkaido. The nalkanes in the snow preserve information about the source vegetation type (photosynthetic group, growth site), confirming that if deposited with seasonal snows that firnify to form glacial ice, they have potential to record broad, regional vegetation changes over time.
• Assessment of hydrogen isotopic compositions of n-fatty acids as paleoclimate proxies in Lake Biwa sediments

  Osamu Seki, Kimitaka Kawamura, Ryoshi Ishiwatari

  JOURNAL OF QUATERNARY SCIENCE 27 9 884 - 890 2012年12月 [査読有り][通常論文]
   

  Compound specific hydrogen isotopic compositions (dD) of free and bound forms of n-fatty acids (FA) were measured throughout a 200?m sediment core taken from Lake Biwa to assess application of biomarker dD values to paleoclimate study in this central Japan lake. The results of our study suggest that the sources of the C16 n-FA in the two forms are different, whereas both free and bound C28 n-FA originate from terrestrial plants. The dD of combined (free plus bound) C28 n-FA in the 200?m sediment core shows a large variability, with relatively low and high values during the glacial and interglacial periods, respectively. Based on comparison of our record with other marine and lacustrine paleoclimate data, we found that the sedimentary record of C28 n-FA dD likely reflects the temperature-induced change in dD of summer precipitation. This finding suggests that dD values of C28 n-FA could be used as a proxy for summer paleotemperatures in the sediments of Lake Biwa and other lakes. Copyright (c) 2012 John Wiley & Sons, Ltd.
• Paleoceanographic changes in the Eastern Equatorial Pacific over the last 10 Myr

  Osamu Seki, Daniela N. Schmidt, Stefan Schouten, Ellen C. Hopmans, Jaap S. Sinninghe Damste, Richard D. Pancost

  PALEOCEANOGRAPHY 27 2012年09月 [査読無し][通常論文]
   

  To examine the Late Neogene evolution of tropical Pacific oceanography, we determined multiple geochemical proxy records for temperature (U-37(K)' and TEX86H indices) and primary productivity (algal biomarkers and diol indices) in sediments recovered at ODP Site 1241 in the East Equatorial Pacific (EEP) spanning a record of the last 10 Myr. The TEX86H temperatures are lower than those recorded by U-37(K)' indices, exhibiting large fluctuations and suggesting strong warming during the Mid Pliocene Warm Period (MPWP; 4.5-3.2 Ma) and significantly colder temperature during the Late Miocene cooling period (7-5 Ma) and after the Middle Pliocene Warm Period (MPWP). Such variations could reflect changes in the EEP thermocline temperatures, but we suggest that they instead reflect changes in the depth of export production of glycerol dialkyl glycerol tetraether lipids in response to changes in the upper ocean structure. A combination of temperature records, inferred to represent different and likely varying depths in the water column, as well as algal biomarker records for export production and ecosystem structure, suggest that both productivity and inference upwelling were reduced in the EEP during warmer periods, such as the MPWP and prior to 7 Ma. In contrast, stronger upwelling conditions and associated increased productivity likely prevailed from 7 to 5 Ma and for the past 3 Myr, both corresponding to globally cool intervals. A further increase in EEP productivity occurred at ca 1.8 Ma, coincident with the development of the E-W Pacific SST gradient. These results confirm previous work that protracted El Nino-like conditions prevailed during warmer intervals of the Pliocene before ultimately descending into the current climate state.
• Sea surface temperature changes in the Okhotsk Sea and adjacent North Pacific during the last glacial maximum and deglaciation

  Naomi Harada, Miyako Sato, Osamu Seki, Axel Timmermann, Heiko Moossen, James Bendle, Yuriko Nakamura, Katsunori Kimoto, Yusuke Okazaki, Kana Nagashima, Sergey A. Gorbarenko, Akira Ijiri, Takeshi Nakatsuka, Laurie Menviel, Megumi O. Chikamoto, Ayako Abe-Ouchi, Stefan Schouten

  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 61-64 93 - 105 2012年02月 [査読有り][通常論文]
   

  We estimated sea surface temperatures (SSTs) in the western Okhotsk Sea during the last glacial maximum (LGM) and the last glacial termination from measurements of the alkenone unsaturation index (U-37(K')), the Tetra Ether indeX of tetraethers consisting of 86 carbon atoms (TEX86), and TEX86L in piston core sediments, which reveal the climate response of this region to different types of forcings. TEX86L is a modification of TEX86 proposed for high-latitude ocean regions. The TEX86L-derived temperatures were not different from the alkenone-derived temperatures from the same and nearby sediment samples. During the LGM, alkenone-derived temperatures in the Okhotsk Sea were relatively warm. These and similarly warm alkenone-derived temperatures found at many other sites in the western North Pacific may reflect a shift in the season of biomarker production from early summer and autumn to mid-summer during the LGM as a result of the expansion of the season of sea-ice cover. Empirical orthogonal function (EOF) analysis of alkenone-derived temperatures at 14 sites from the North Pacific suggested substantial cooling between 20 and 14 cal kyr BP during the deglaciation at 11 of the sites (including 4 sites in the Okhotsk Sea). This dominant EOF mode suggests either an overall seasonal bias in alkenone-derived temperatures or potential shifts in the Haptophyseae production season. The second EOF mode of variability indicated a deglacial warming trend punctuated by millennial-scale cold events, associated with reorganizations of the Atlantic Meridional Overturning Circulation. The SST pattern corresponding to this EOF mode is indicative of millennial-scale meridional shifts of the axis of the westerly jet, which may have affected heat transport across the Kuroshio. Reconstructed temperature changes, in particular in the Okhotsk Sea, provide insight into the conditions that modulated the ventilation history of intermediate waters in the North Pacific. (C) 2012 Elsevier Ltd. All rights reserved.
• Assessment for paleoclimatic utility of terrestrial biomarker records in the Okhotsk Sea sediments

  Osamu Seki, Naomi Harada, Miyako Sato, Kimitaka Kawamura, Akira Ijiri, Takeshi Nakatsuka

  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 61-64 85 - 92 2012年02月 [査読無し][通常論文]
   

  We measured terrestrial plant biomarker (long-chain n-alkanes) in the sediment cores taken from the Sea of Okhotsk to examine paleoclimatic utility of long-chain n-alkanes in marine sediments. This study demonstrates that sedimentary record of n-alkane in the sea has a high potential to provide important complementary paleo-climate/paleo-environmental information. Molecular distributions of long-chain n-alkanes in marine sediments show a typical signature of terrestrial plant wax derived n-alkanes with strong odd carbon number predominance from the last glacial to the present, suggesting a source of long-chain n-alkanes in the Okhotsk Sea sediments has been terrestrial higher plants throughout the time. The down core profiles of concentrations of C25-C35 n-alkanes in XP07-C9 collected from the northwestern site revealed three events of enhanced terrestrial organic matter input during the last deglaciation. The two pronounced events correspond to Melt Water Pulse (MWP) events 1A (14.5-12.5 ka) and 1B (11-6.5 ka). These events possibly linked to increases in river discharge and erosion of submerged continental shelf due to drastic rise in sea level. Down core profiles of molecular distributions of n-alkanes in the Okhotsk Sea sediments significantly vary over the last 25 kyr, and are similar to that of a peat core sequence in the East Russia and essentially consistent with pollen data from marine and peat core sequences. (C) 2011 Elsevier Ltd. All rights reserved.
• 北海道沙流川における河川水中懸濁粒子と河口域海底堆積物の鉱物・主要元素組成

  入野 智久, 山下 洋平, 関 宰, 池原 研, 長尾 誠也

  日本地質学会学術大会講演要旨 2012 220 - 220 一般社団法人 日本地質学会 2012年
• 分子レベル安定炭素・水素同位体比の古気候研究への適用

  関宰

  Res Org Geochem 27 13 - 21 2011年09月30日 [査読無し][通常論文]
  
• 分子レベル安定炭素・水素同位体比の古気候研究への適用(<特集>有機化合物の安定同位体比を用いた有機地球化学的研究の発展とその応用(Part II))

  関 宰

  Researches in organic geochemistry 27 13 - 21 日本有機地球化学会 2011年09月30日 [査読無し][通常論文]
   

  Biomarkers have increasingly become common tools in the reconstruction of past environmental conditions. Molecular analyses of terrestrial biomarker lipids extracted from ocean, lake and bog sediments have been used for reconstructions of paleovegetation and associated paleoclimate histories. Stable carbon and hydrogen isotopic compositions of certain biomarkers provide powerful paleoclimate information. Stable carbon isotopic composition of C_<37> alkenone, which is specific biomarker of certain haptophyte algae, have been used to reconstruct concentration of atmospheric carbon dioxide in ...
• Plant-wax hydrogen isotopic evidence for postglacial variations in delivery of precipitation in the monsoon domain of China

  Osamu Seki, Philip A. Meyers, Shinya Yamamoto, Kimitaka Kawamura, Takeshi Nakatsuka, Weijian Zhou, Yanhong Zheng

  GEOLOGY 39 9 875 - 878 2011年09月 [査読無し][通常論文]
   

  The Asian monsoon is a key component of the Earth's climate system that directly affects the livelihood of 60% of the world population. Reliable reconstruction of changes in monsoon precipitation during the Holocene is required to better understand the present climate conditions and to predict future climate processes in the Asian monsoon domain. Reconstruction of changes in Holocene monsoon precipitation has been done in various regions of this domain using a variety of paleoclimate proxies. However, different proxies have yielded different paleoclimate records of long-term monsoon rainfall variability. We apply compound-specific stable hydrogen isotope compositions of the plant wax n-alkanes isolated from the Hongyuan peat sequence in eastern Tibet to reevaluate the regional carbonate oxygen isotopic and lake-level records. The D/H ratios of the n-alkanes resolve the apparent discrepancy among the different paleoclimate proxies. Our result indicates that lake-level fluctuation is a reliable recorder of changes in the amount of summer monsoonal precipitation while long-term isotope records largely reflect large-scale changes in the source of water vapor rather than a local precipitation signal. Combining lake-level, biomarker, and carbonate isotopic records, we conclude that the early Holocene monsoon precipitation in southwest China has been greatly influenced by the Indian monsoon.
• Long-range atmospheric transport of terrestrial biomarkers by the Asian winter monsoon: Evidence from fresh snow from Sapporo, northern Japan

  Shinya Yamamoto, Kimitaka Kawamura, Osamu Seki

  ATMOSPHERIC ENVIRONMENT 45 21 3553 - 3560 2011年07月 [査読有り][通常論文]
   

  Molecular distributions of terrestrial biomarkers were investigated in fresh snow samples from Sapporo, northern Japan, to better understand the long-range atmospheric transport of terrestrial organic matter by the Asian winter monsoon. Stable carbon (delta(13)C) and hydrogen (delta D) isotope ratios of C(22)-C(28) n-alkanoic acids were also measured to decipher their source regions. The snow samples are found to contain higher plant-derived n-alkanes, n-alkanols and n-alkanoic acids as major components. Relative abundances of these three biomarker classes suggest that they are likely derived from higher plants in the Asian continent. The C(27)/C(31) ratios of terrestrial n-alkanes in the snow samples range from 1.3 to 5.5, being similar to those of the plants growing in the latitudes >40 degrees N of East Asia. The delta(13)C values of the n-alkanoic acids in the snow samples (-33.4 to -27.6 parts per thousand) are similar to those of typical C(3) gymnosperm from Sapporo (-34.9 to -29.3 parts per thousand). However, the SD values of the n-alkanoic acids (-208 to -148 parts per thousand) are found to be significantly depleted with deuterium (by similar to 72 parts per thousand) than those of plant leaves from Sapporo. Such depletion can be most likely interpreted by the long-range atmospheric transport of the n-alkanoic acids from vegetation in the latitudes further north of Sapporo because the SD values of terrestrial higher plants tend to decrease northward in East Asia reflecting the SD of precipitation. Together with the results of backward trajectory analyses, this study suggests that the terrestrial biomarkers in the Sapporo snow samples are likely transported from Siberia, Russian Far East and northeast China to northern Japan by the Asian winter monsoon. (C) 2011 Elsevier Ltd. All rights reserved.
• Quality assessment of umbilical cord blood units at the time of transplantation

  Yoshinori Kudo, Masayoshi Minegishi, Osamu Seki, Hiroyuki Takahashi, Akira Suzuki, Ayuko Narita, Yuko Sato, Machiko Abe, Natsuko Ishioka, Hideo Harigae, Shigeru Tsuchiya

  INTERNATIONAL JOURNAL OF HEMATOLOGY 93 5 645 - 651 2011年05月 

  Total nucleated cell (TNC) count, CD34(+) cell count, colony-forming unit-granulocyte-macrophage (CFU-GM) content, and cell viability impact the outcome of umbilical cord blood (UCB) transplantation. Assessments of unit quality have usually been provided by cord blood banks (CBBs), but it is unclear whether pre-freezing tests or pre-transplant release tests performed by CBBs are reproducible. The aim of this study was to compare the UCB characteristics analyzed at the site of infusion of the UCB with those provided by CBBs. Samples were taken from 54 UCB units for assessment of post-thaw characteristics. TNC counts and CD34(+) cell contents measured at our hospital before infusion showed good correlations with values assessed in pre-freezing tests (r = 0.900 and 0.943, respectively) and pre-transplant release tests (r = 0.829 and 0.930, respectively). Our data reveal that the TNC counts and CD34(+) cell contents determined by pre-freezing and pre-transplant release tests, which are the most important UCB unit selection criteria, accurately reflected the quality of infused UCB units. However, CFU-GM content was poorly correlated (r = 0.560 and 0.606). Correlation of post-thaw cell viabilities measured before infusion and during the pre-transplant release tests was also poor (r = 0.308). We suggest that the TNC count and CD34(+) cell content estimated before cryopreservation and in pre-transplant release tests provided by CBBs are reproducible and can assist the transplant physicians in selection of appropriate UCB units.
• 北西太平洋表層堆積物中の陸上植物テルペノイドバイオマーカーの起源と輸送過程

  小林 まどか, 沢田 健, 関 宰

  日本地球化学会年会要旨集 58 25 - 25 日本地球化学会 2011年 

  陸上高等植物に由来するテルペノイド(HPT)は、植物の分類によって異なる構造を持つことが知られており、陸源物質の海洋への輸送の供給源や後背地を特定するための有用なバイオマーカーになり得ると考えられる。本研究では、レテン、カダレン、フリーデリンという3種類のHPTに着目して、北西太平洋の表層堆積物中での化合物分布を調べ、それぞれの化合物の起源と輸送過程について考察した。
  分析の結果、レテンの分布からは後背地の植生の影響以外に、化石燃料を含む都市大気による影響がみられた。フリーデリンは北西太平洋日本沖で特に多く、陸から遠く離れた外洋域のコアからは総じて微量しか検出されなかったことから、主に河川経由で輸送されていると考えられる。一方でカダレンについては地域・海域による傾向はあまり見られなかったが、これはカダレンが主に大気経由で広範囲に輸送されていることを示唆している。
• 過去１５万年間の琵琶湖堆積物コア中の植物起源脂肪酸の水素同位体比記録

  関 宰, 河村 公隆, 石渡 良志

  日本地球化学会年会要旨集 58 12 - 12 日本地球化学会 2011年 

  本研究はバイマーカーの水素同位体比の古環境研究への適用を目的として、琵琶湖堆積物コア中の植物起源脂肪酸の水素同位体比を測定した。復元された過去１５万年間の脂肪酸の水素同位体比は～４０パーミルもの変動を示し、その変動パターンは中国の鍾乳石の酸素同位体比と類似しており、北緯３０度における夏の日射量の変動に同調していることが示された。このことから 脂肪酸の水素同位体比は中国の鍾乳石の酸素同位体比と同様に、地球の歳差運動の周期による夏期の日射量変動に応答したシグナルを反映していると考えられ、陸域の古気候トレーサーとして有用であることが示唆された。
• Environmental influences over the last 16ka on compound-specific δ13C variations of leaf wax n-alkanes in the Hani peat deposit from northeast China

  Shinya Yamamoto, Kimitaka Kawamura, Osamu Seki, Philip A. Meyers, Philip A. Meyers, Yanhong Zheng, Weijian Zhou

  Chemical Geology 277 3-4 261 - 268 Elsevier B.V. 2010年10月 [査読無し][通常論文]
   

  Compound-specific carbon isotope ratios (δ13C) of leaf wax n-alkanes (C21-C33 odd carbon numbered n-alkanes) were measured in the Hani peat sequence from northeast China. These data were compared with lipid biomarker compositions to assess changes in local vegetation and paleoclimate for the last 16ka. The δ13C values of n-alkanes range between -36.6 and -30.7%, showing that the compounds originate from C3 plants. Much larger variations (~5.4%) in the n-alkane δ13C values than those of atmospheric CO2 during the last 16ka (< 0.5%) indicate that the isotopic values were affected by environmental factors in addition to the postglacial δ13C variations in the atmospheric reservoir. The stratigraphic records of δ13C reveal decoupled fluctuations among the individual n-alkanes, particularly between 15.5 and 11.4ka. Synchronous excursions in the δ13C offsets among individual n-alkanes (δδ13C) and lipid biomarker paleoplant proxies (Paq, and C23/C31 and C27/C31) from 14.9 to 13.2ka and 12.7 to 11.6ka suggest that vegetational changes are the most likely causes for the decoupled δ13C variations. Parallel fluctuations of the δ13C values of terrestrial higher plant-derived C29 and C31 n-alkanes and the n-alkane average chain-length (ACL) from 11 to 6ka indicate that the δ13C variations responded to net evaporation changes. Negative shifts in the n-alkane δ13C values coinciding with the ACL decreases at 10.5-9.3ka and 8.1ka indicate the short-term onset and fluctuations of the summer monsoon strength in eastern China during the early Holocene. © 2010 Elsevier B.V.
• Paleoenvironmental significance of compound-specific δ13C variations in n-alkanes in the Hongyuan peat sequence from southwest China over the last 13 ka

  Shinya Yamamoto, Kimitaka Kawamura, Osamu Seki, Philip A. Meyers, Philip A. Meyers, Yanhong Zheng, Weijian Zhou

  Organic Geochemistry 41 5 491 - 497 Elsevier 2010年05月 [査読無し][通常論文]
   

  Compound-specific 13C/12C ratios of the C23, C25, C27, C29 and C31 n-alkanes in the Hongyuan peat sequence from southwest China were measured to decipher paleoenvironmental information recorded in the δ13C variations over the last 13 ka. The δ13C values of the n-alkanes range between -35.4‰ and -30.5‰, falling within the range of those from modern C3 peat-forming vegetation. However, the vertical trends do not match with those of the δ13C value for the C3 peat-forming plant cellulose. Such a discrepancy between the δ13C profiles implies that the n-alkane δ13C values are unlikely to reflect signals from emerged aquatic plants in the bog. Because submerged/floating aquatic plants are major contributors of mid-chain (C23 and C25) n-alkanes in the sequence, the decoupling between the C23 and C25 n-alkanes and the peat cellulose likely reflects the situation that these mid-chain homologues primarily record the isotopic signals of submerged/floating aquatic plants. The stratigraphic profile of δ13C values of submerged/floating aquatic plant n-alkanes (C23 and C25) reveals two prominent positive excursions (0.8-2.4‰) during the early to middle Holocene. The excursions coincide with peat accumulation maxima and stronger Indian monsoon activity in southwest China, indicating that the δ13C variations in submerged/floating aquatic plants are closely related to changes in bog primary productivity controlled by the Asian monsoon activity. © 2010 Elsevier Ltd. All rights reserved.
• Carbon isotopes and lignin composition of POC in a small river in Bekanbeushi Moor, northern Japan

  Seiya Nagao, Takafumi Aramaki, Osamu Seki, Masao Uchida, Yasuyuki Shibata

  NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 268 7-8 1098 - 1101 2010年04月 [査読無し][通常論文]
   

  Carbon isotope and lignin phenol compositions were investigated to assess particulate organic carbon (POC) in a small river from the Bekanbeushi Moor in the eastern part of Hokkaido, Japan. Suspended solids were collected 5 times at a fixed station during July 2004-April 2008. The delta C-13 values of the riverine POC are almost constant: -29.1 parts per thousand, to -28.7 parts per thousand. In contrast, the POC shows wide variations in Delta C-14 values from -103 parts per thousand during the snowmelt event to +9 +/- 16.7. during summer and winter. The cinnamyl over vanillyl phenol (C/V) ratios indicate a predominance of nonwoody materials and no seasonal variation, suggesting that the wetland river transports older POC from the riverbank during the spring snowmelt. The river also transports newly produced and stored soil organic matter as riverine POC from the low moor in times of low flow conditions. (C) 2009 Elsevier B.V. All rights reserved.
• Alkenone and boron-based Pliocene pCO(2) records

  Osamu Seki, Gavin L. Foster, Daniela N. Schmidt, Andreas Mackensen, Kimitaka Kawamura, Richard D. Pancost

  EARTH AND PLANETARY SCIENCE LETTERS 292 1-2 201 - 211 2010年03月 [査読無し][通常論文]
   

  The Pliocene period is the most recent time when the Earth was globally significantly (similar to 3 degrees C) warmer than today. However, the existing pCO(2) data for the Pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo-pCO(2). This disagreement, coupled with the general low temporal resolution of the published records, does not allow a robust assessment of the role of declining pCO(2) in the intensification of the Northern Hemisphere Glaciation (INHG) and a direct comparison to other proxy records are lacking. For the first time, we use a combination of foraminiferal (delta B-11) and organic biomarker (alkenone-derived carbon isotopes) proxies to determine the concentration of atmospheric CO2 over the past 5 Ma. Both proxy records show that during the warm Pliocene pCO(2) was between 330 and 400 ppm, i.e. similar to today. The decrease to values similar to pre-industrial times (275-285 ppm) occurred between 3.2 Ma and 2.8 Ma - coincident with the INHG and affirming the link between global climate, the cryosphere and pCO(2). (c) 2010 Elsevier B.V. All rights reserved.
• A compound-specific n-alkane δ13C and δD approach for assessing source and delivery processes of terrestrial organic matter within a forested watershed in northern Japan

  Osamu Seki, Takeshi Nakatsuka, Hideaki Shibata, Kimitaka Kawamura

  Geochimica et Cosmochimica Acta 74 2 599 - 613 Elsevier Ltd. 2010年01月 [査読無し][通常論文]
   

  We measured molecular distributions and compound-specific hydrogen (δD) and stable carbon isotopic ratios (δ13C) of mid- and long-chain n-alkanes in forest soils, wetland peats and lake sediments within the Dorokawa watershed, Hokkaido, Japan, to better understand sources and processes associate with delivery of terrestrial organic matter into the lake sediments. δ13C values of odd carbon numbered C23-C33 n-alkanes ranged from -37.2‰ to -31.5‰, while δD values of these alkanes showed a large degree of variability that ranged from -244‰ to -180‰. Molecular distributions in combination with stable carbon isotopic compositions indicate a large contribution of C3 trees as the main source of n-alkanes in forested soils whereas n-alkanes in wetland soil are exclusively derived from marsh grass and/or moss. We found that the n-alkane δD values are much higher in forest soils than wetland peat. The higher δD values in forest samples could be explained by the enrichment of deuterium in leaf and soil waters due to increased evapotranspiration in the forest or differences in physiology of source plants between wetland and forest. A δ13C vs. δD diagram of n-alkanes among forest, wetland and lake samples showed that C25-C31 n-alkanes deposited in lake sediments are mainly derived from tree leaves due to the preferential transport of the forest soil organic matter over the wetland or an increased contribution of atmospheric input of tree leaf wax in the offshore sites. This study demonstrates that compound-specific δD analysis provides a useful approach for better understanding source and transport of terrestrial biomarkers in a C3 plant-dominated catchment. © 2009 Elsevier Ltd. All rights reserved.
• Large changes in seasonal sea ice distribution and productivity in the Sea of Okhotsk during the deglaciations

  Osamu Seki, Tatsuhiko Sakamoto, Saburo Sakai, Stefan Schouten, Ellen C. Hopmans, Jaap S. Sinninghe Damste, Richard D. Pancost

  GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 10 2009年10月 [査読有り][通常論文]
   

  Changes in the surface environment of the central Sea of Okhotsk were reconstructed using TEX86 paleothermometry, facilitated by the BIT index, in order to investigate paleoenvironmental changes during the glacial-interglacial cycles. The core top TEX86-derived temperature is the same as the present-day summer sea surface temperature (SST), suggesting that TEX86 records seasonal rather than annually averaged SSTs in this region. The TEX86 record reveals similar to 3 degrees C lower summer SST during glacial maxima than during interglacial periods and significant warming during the deglaciations (15-10 ka and 136-130 ka). This is consistent with previous inferences of more expanded and persistent seasonal sea ice during the glacial periods than the present-day and its substantial retreat during the deglaciation. Timing of the deglacial warming also coincided with a distinct increase in coccolithophorid productivity, suggesting a causal relationship between sea surface warming and coccolithophorid blooms during the deglaciations. The relationship could reflect an increase in the supply of fresh and warm water from the Amur River during deglaciation, which significantly impacted hydrology by facilitating sea surface stratification, which in turn promoted production of coccolithophids.
• Hydrogen isotopic ratios of plant wax n-alkanes in a peat bog deposited in northeast China during the last 16 kyr

  Osamu Seki, Philip A. Meyers, Kimitaka Kawamura, Yanhong Zheng, Weijian Zhou

  ORGANIC GEOCHEMISTRY 40 6 671 - 677 2009年06月 [査読無し][通常論文]
   

  Based on paleoclimatic reconstructions using various proxies, the Holocene Climate Optimum (10.5-6 ka) has been characterized as a warmer and wetter period in most of East Asia. The summer monsoons associated with the East Asian Monsoon evidently intensified and extended further inland from the Pacific Ocean, a source region of moisture. A notable exception to this general pattern exists in northeast China, where less wet conditions are recorded. We determined molecular compositions of individual plant wax hydrocarbons and their hydrogen isotope compositions (delta D values) in a radiocarbon-dated peat core recovered from the Hani marsh in Jilin Province (China) and confirmed that the temperature-dependent effective precipitation in northeast China decreased during the Holocene Climate Optimum. A combination Of P(aq), an indicator of the relative contribution of aquatic to terrestrial plants, and the difference in delta D between low (C(23), C(25) and C(27)) and high molecular weight (C(31)) n-alkanes in the Hani peat bog indicates a dramatic change in vegetation from the deglaciation to the Holocene. No significant differences were observed between the delta D values of low and high molecular weight n-alkanes with relatively high delta D values and low P(aq) during the early Holocene, indicating that all n-alkanes were produced by evapotranspiration-sensitive terrestrial plants during that time. However, lower delta D values of mid-chain n-alkanes (C(23), C(25) and C(27)) relative to the long chain n-alkane (C(31)), together with higher P(aq) values during the deglaciation (14-11 ka), suggest an increase in the contribution of aquatic plants and a higher water level during the period. The study demonstrates that northeast China was under a markedly wetter climate condition during the late deglaciation. For the 16 kyr record in the Hani peat sequence, we infer that moisture delivery by the East Asian Monsoon was relatively invariable in northeast China, but increased evaporation during the warmer Holocene Climate Optimum reduced the effective precipitation, defined by the balance between precipitation and evaporation. (C) 2009 Elsevier Ltd. Ail rights reserved.
• Time-series sediment trap record of alkenones from the western Sea of Okhotsk

  Osamu Seki, Takeshi Nakatsuka, Kimitaka Kawamura, Sei-Ichi Saitoh, Masaaki Wakatsuchi

  MARINE CHEMISTRY 104 3-4 253 - 265 2007年03月 [査読有り][通常論文]
   

  C-37-C-39 alkenones were measured in time-series sediment trap samples collected from August 1998 to June 2000 at two depths in the seasonal sea ice region of the western Sea of Okhotsk, off Sakhalin, in order to investigate alkenone production and water-column processes in the region. Measurable export fluxes of alkenones are ranged from < 0. 1 to 5.8 mu g/m(2) /day and clearly showed that the alkenone production was restricted to autumn. In 1998, maximum export flux of alkenones occurred in September when surface water column was well stratified with low nutrients in the surface mixing layer. In the next year, the maximum flux is observed in October. Comparison between alkenone temperature and satellite based sea surface temperature (SST) shows that the estimated alkenone temperatures in August 1998 were found to be similar to 10 degrees C lower than the temporal satellite SST, suggesting that alkenones are produced in surface to subsurface thermocline layers during the period. Annual mean flux of alkenones is lower in the lower traps than that of the upper traps, suggesting rapid degradation of alkenones in water column, but the U-K (37)' value is not significantly altered. This study indicates that U-K (37)' values preserved in the surface sediments off Sakhalin reflect the seasonal temperature signal of near surface water, rather than annual mean surface temperature. (C) 2007 Elsevier B.V. All rights reserved.
• Cycladophora davisiana (Radiolaria) in the Okhotsk Sea: A key for reconstructing glacial ocean conditions

  Yusuke Okazaki, Osamu Seki, Takeshi Nakatsuka, Tatsuhiko Sakamoto, Minoru Ikehara, Kozo Takahashi

  JOURNAL OF OCEANOGRAPHY 62 5 639 - 648 2006年10月 [査読有り][通常論文]
   

  Cycladophora davisiana, a radiolarian species dwelling at mesopelagic depths, is known as a representative glacial fauna due to its unique distribution during glacial periods. In the present ocean, abundant production of C. davisiana is only observed in the Okhotsk Sea, indicating an adaptation of C. davisiana for seasonal sea-ice covered conditions. We found pronounced abundant production of C. davisiana during the early to middle Holocene in the Okhotsk Sea, suggesting more favorable conditions for C. davisiana than the present Okhotsk Sea. In order to clarify the reason, oceanographic conditions during the Holocene were reconstructed based on biomarkers, lithogenic grains including ice-rafted debris (IRD), biogenic opal, and total organic carbon (TOC) in two sediment cores from the Okhotsk Sea. These indicators suggest that the pronounced C. davisiana production may be attributed to: 1) a supply to mesopelagic depths under intensified stratification of fine organic particles derived from coccolithophorids, bacteria, and detrital materials; and 2) cold, well-ventilated intermediate water formation.
• Fluxes, source and transport of organic matter in the western Sea of Okhotsk: Stable carbon isotopic ratios of n-alkanes and total organic carbon

  O Seki, C Yoshikawa, T Nakatsuka, K Kawamura, M Wakatsuchi

  DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 53 2 253 - 270 2006年02月 [査読無し][通常論文]
   

  Settling particles and surface sediments collected from the western region of the Sea of Okhotsk were analyzed for total organic carbon (TOC), long-chain n-alkanes and their stable carbon isotope ratio (delta C-13) to investigate sources and transport of total and terrestrial organic matter in the western region of the sea. The delta C-13 measurements of TOC in timeseries sediment traps indicate lateral transport of resuspended organic matter from the northwestern continental shelf to the area off Sakhalin via the dense shelf water (DSW) flow at intermediate depth. The n-alkanes in the surface sediments showed strong odd carbon number predominance with relatively lighter delta C-13 values (from -33%. to -30%.). They fall within the typical values of C3-angiosperins, which is the main vegetation in east Russia, including the Amur River basin. On the other hand, the molecular distributions and delta C-13 values of n-alkanes in the settling particles clearly showed two different sources: terrestrial plant and petroleum in the Sea of Okhotsk. We reconstructed seasonal change in the fluxes of terrestrial n-alkanes in settling particles using the mixing model proposed by Lichtfouse and Eglinton [1995. C-13 and C-14 evidence of a soil by fossil fuel and reconstruction of the composition of the pollutant. Organic Geochemistry 23, 969-973]. Results of the terrestrial n-alkane fluxes indicate that there are two transport pathways of terrestrial plant n-alkanes to sediments off Sakhalin, the Sea of Okhotsk. One is lateral transport of resuspended particles with lithogenic material from the northwestern continental shelf by the DSW flow. Another is the vertical transport of terrestrial plant n-alkanes, which is independent of transport of lithogenic material. The latter may include dry/wet deposition of aerosol particles derived from terrestrial higher plants possibly associated with forest fires in Siberia. (c) 2005 Elsevier Ltd. All rights reserved.
• Decreased surface salinity in the Sea of Okhotsk during the last glacial period estimated from alkenones

  O Seki, K Kawamura, T Sakamoto, M Ikehara, T Nakatsuka, M Wakatsuchi

  GEOPHYSICAL RESEARCH LETTERS 32 8 1 - 4 2005年04月 [査読無し][通常論文]
   

  Studies of sediment cores from the Sea of Okhotsk, which is characterized by seasonal sea ice, have shown a large variability of sea ice indicators during the glacial-interglacial cycles. In this study, we apply the relative abundance of the C-37: 4 alkenone to total C-37 alkenones (% C-37: 4) as a molecular indicator of salinity and water masses to further investigate surface oceanographic condition in the Sea of Okhotsk in the glacial period. We found a large fluctuation of % C-37: 4 ( 4 - 35%) with higher values ( 20 similar to 35%) during the last glacial period and lower values (< 8%) during warm periods, suggesting a decreased surface salinity in the glacial period. The variation of % C-37: 4 was found to be consistent with the ice rafted debris (IRD) in the sediment core ( correlation coefficient (r(2)) between % C-37: 4 and IRD: 0.72). This suggests that the duration of seasonal sea ice was longer in the glacial period than today. The lowered surface salinity in the glacial might also have been seriously affected by the close-off of the shallow Soya Strait, which currently transports massive volumes of saline water from the Sea of Japan to the Sea of Okhotsk.
• Decreased surface salinity in the Sea of Okhotsk during the last glacial period estimated from alkenones

  O Seki, K Kawamura, T Sakamoto, M Ikehara, T Nakatsuka, M Wakatsuchi

  GEOPHYSICAL RESEARCH LETTERS 32 8 L08710.1-L08710.4  2005年04月 [査読無し][通常論文]
   

  Studies of sediment cores from the Sea of Okhotsk, which is characterized by seasonal sea ice, have shown a large variability of sea ice indicators during the glacial-interglacial cycles. In this study, we apply the relative abundance of the C-37: 4 alkenone to total C-37 alkenones (% C-37: 4) as a molecular indicator of salinity and water masses to further investigate surface oceanographic condition in the Sea of Okhotsk in the glacial period. We found a large fluctuation of % C-37: 4 ( 4 - 35%) with higher values ( 20 similar to 35%) during the last glacial period and lower values (< 8%) during warm periods, suggesting a decreased surface salinity in the glacial period. The variation of % C-37: 4 was found to be consistent with the ice rafted debris (IRD) in the sediment core ( correlation coefficient (r(2)) between % C-37: 4 and IRD: 0.72). This suggests that the duration of seasonal sea ice was longer in the glacial period than today. The lowered surface salinity in the glacial might also have been seriously affected by the close-off of the shallow Soya Strait, which currently transports massive volumes of saline water from the Sea of Japan to the Sea of Okhotsk.
• Reconstruction of paleoproductivity in the Sea of Okhotsk over the last 30 kyr

  O Seki, M Ikehara, K Kawamura, T Nakatsuka, K Ohnishi, M Wakatsuchi, H Narita, T Sakamoto

  PALEOCEANOGRAPHY 19 1 2004年03月 [査読無し][通常論文]
   

  Marine-and terrestrial-derived biomarkers (alkenones, brassicasterol, dinosterol, and long-chain n-alkanes), as well as carbonate, biogenic opal, and ice-rafted debris (IRD), were measured in two sediment cores in the Sea of Okhotsk, which is located in the northwestern Pacific rim and characterized by high primary productivity. Down-core profiles of phytoplankton markers suggest that primary productivity abruptly increased during the global Meltwater Pulse events 1A (about 14 ka) and 1B (about 11 ka) and stayed high in the Holocene. Spatial and temporal distributions of the phytoplankton productivity were found to be consistent with changes in the reconstructed sea ice distribution on the basis of the IRD. This demonstrates that the progress and retreat of sea ice regulated primary productivity in the Sea of Okhotsk with minimum productivity during the glacial period. The mass accumulation rates of alkenones, CaCO3, and biogenic opal indicate that the dominant phytoplankton species during deglaciation was the coccolithophorid, Emiliania huxleyi, which was replaced by diatoms in the late Holocene. Such a phytoplankton succession was probably caused by an increase in silicate supply to the euphotic layer, possibly associated with a change in surface hydrography and/or linked to enhanced upwelling of North Pacific Deep Water.
• Variation of alkenone sea surface temperature in the Sea of Okhotsk over the last 85 kyrs

  O Seki, K Kawamura, M Ikehara, T Nakatsuka, T Oba

  ORGANIC GEOCHEMISTRY 35 3 347 - 354 2004年 [査読無し][通常論文]
   

  Sea-surface temperatures (SSTs) in the Sea of Okhotsk were reconstructed based on alkenone unsaturation indices in two sediment cores. Alkenone-SSTs were found to range from 3 to 9 C over the last 85 kyr with higher SST values in warm periods: Holocene and the oxygen isotope stage (OIS) 5a. In the last glacial periods (OIS 4 and 3), average alkenone SST was estimated to be 4 C, which was 4 C lower than the Holocene on average. However, alkenone SSTs around the last glacial maximum (LGM) are as high as those of the Holocene. The variation patterns of U-37(K') in the Okhotsk Sea were found to be similar to those reported in the Sea of Japan [Org. Chem. 32 (2001) 57] over the last 30 kyr, although the SSTs were lower in the Sea of Okhotsk. The higher U-37(K') values around the LGM may be a rather common phenomenon in semi-closed marginal seas such as the Japan Sea and the Okhotsk Sea, which are both adjacent to the northwestern Pacific. Such an anomaly in the LGM may have been caused by either a seasonal shift of coccolith blooming or a contribution from a different strain or species that produces alkenones. (C) 2003 Elsevier Ltd. All rights reserved.
• Sediment core profiles of long-chain n-alkanes in the Sea of Okhotsk: Enhanced transport of terrestrial organic matter from the last deglaciation to the early Holocene

  O. Seki, O. Seki, K. Kawamura, T. Nakatsuka, K. Ohnishi, M. Ikehara, M. Wakatsuchi

  Geophysical Research Letters 30 1 - 1 2003年01月01日 [査読無し][通常論文]
   

  Terrestrial plant-derived n-alkanes (C25-C35) were measured in three piston cores (PC1, PC2 and PC4) in the Sea of Okhotsk covering the last 30 kyrs. Down core profiles of the n-alkane concentrations and mass accumulation rates (MAR) were characterized by deglacial maxima. In particular, cores PC2 and PC4, which were collected from the central and western Sea of Okhotsk, respectively, show a two-step increase around the Meltwater Pulse events (MWP) 1A (14.5-13.5 kyr BP) and 1B (about 10 kyr BP). This finding was interpreted by the outflow of terrestrial organic matter from the submerged land shelf to the Sea of Okhotsk through the East Sakhalin Current. This study demonstrated that the sea level rise forced by global warming in the deglaciation period may have caused the enhanced transport of terrestrial organic matter in marginal seas.
• Millennial climate oscillations in NE Pacific surface waters over the last 82 kyr: New evidence from alkenones

  Osamu Seki, Ryoshi Ishiwatari, Kohei Matsumoto

  Geophysical Research Letters 29 59 - 1 2002年12月01日 [査読無し][通常論文]
   

  A climate instability in the last glacial, corresponding to Dansgaard-Oeschger (D-O) events, has been already recognized in the California margin in northeast Pacific. Detailed sea surface temperature (SST) changes in this region, however, have not been so far well elucidated. Here we report estimates of alkenone-derived SSTs with the DO-time scale from ODP Hole 1017E, off Point Conception, over the last 80 kyr. Our results show that alkenone SSTs clearly record D-O and Heinrich Events. We also found that alkenone-SSTs during 82-58 ka and 18-15 ka were considerably higher, and those in 15-12 ka were lower than those derived from δ18O of planktonic foraminifera. These results appear to reflect fluctuations of water masses.
• Variations in organic carbon isotopic composition in sediments at site 1017 during the last 25 K.Y.

  R. Ishiwatari, K. Matsumoto, O. Seki, S. Yamamoto

  Proceedings of the Ocean Drilling Program: Scientific Results 167 273 - 276 2000年01月01日 [査読無し][通常論文]
   

  A high-resolution analysis of Hole 1017E revealed that total organic carbon (TOC) concentrations (24.8 ± 2.9 mg/g) and δ13C of TOC (-21.3 ± 0.2‰) in Holocene sections are higher than those in glacial sediments (14.2 ± 4.8 mg/g and -22.1‰ ± 0.1‰, respectively). The 306- to 280-cm section has high total sulfur concentrations, which may correspond to anoxia Event 1 (1 of the warm interstadials of GISP2) in the Santa Barbara Basin.

講演・口頭発表等

• 網走湖堆積物中有機物分析による過去300年間の環境変化  [通常講演]

  栄田直樹, 山本修一, 関宰, 瀬戸浩二

  日本地球化学会年会講演要旨集 2014年
• カリフォルニア沖における融氷期のメタン放出イベント  [通常講演]

  中國正寿, 関宰, 山本修一

  日本地球化学会年会講演要旨集 2014年
• アイスコア解析から明らかになった十年規模の気候変動に対する炭素質エアロゾルのインパクト  [通常講演]

  関宰, 河村公隆, 藤井理行, BENDLE James

  日本地球化学会年会講演要旨集 2014年
• 古気候・古環境分野からの提案  [通常講演]

  原田尚美, 大河内直彦, 南雅代, 関宰, 岡崎裕典

  日本地球化学会年会講演要旨集 2014年
• ベーリング海低塩分水の北極海への流入による鮮新世の寒冷化  [通常講演]

  堀川恵司, MARTIN E, 小野寺丈尚太郎, 関宰, 坂本竜彦, 池原実, 坂井三郎, 河村公隆

  日本地球化学会年会講演要旨集 2014年
• Role of Arctic and Antarctic regions in late Neogene climate evolutions  [通常講演]

  SEKI Osamu, ONODERA Jonaotaro, OKA Akira, IKEHARA Minoru

  極域科学シンポジウム講演予稿集(CD-ROM) 2014年
• 更新世初期のベーリング海峡閉鎖が長期的な気候変動に与えたインパクト  [通常講演]

  関宰, 小野寺丈尚太郎, 池原実, 岡崎裕典, 河村公隆, 高橋孝三

  日本海洋学会大会講演要旨集 2013年08月
• 完新世におけるオホーツク海およびベーリング海の表層水温と海氷の変化  [通常講演]

  原田尚美, 香月興太, 中川光弘, 松本亜希子, 関宰, 佐藤都, 長島佳菜

  日本海洋学会大会講演要旨集 2013年08月
• 北海道河川の懸濁粒子・堆積物のバイオマーカー分析による陸上植物由来有機物の輸送・堆積過程の検討  [通常講演]

  沢田健, 澤井健之, 関宰

  堆積学研究 2012年12月
• 北海道沙流川における河川水中懸濁粒子と河口域海底堆積物の鉱物・主要元素組成  [通常講演]

  入野智久, 山下洋平, 関宰, 池原研, 長尾誠也

  日本地質学会学術大会講演要旨 2012年09月
• 過去500万年間のベーリング海気候変動―海氷出現と寒冷化―IODP Expedition323掘削成果  [通常講演]

  高橋孝三, 岩崎晋弥, 兼松芳幸, 小野寺丈尚太郎, 岡崎裕典, 須藤斎, 朝日博史, 池上隆仁, 坂本竜彦, 池原実, 関宰, 堀川恵司, 岡田誠, 井尻暁, RAVELO A.C, ZARIKIAN ALVAREZ C

  日本海洋学会大会講演要旨集 2012年09月
• 北海道河川の懸濁粒子・堆積物のバイオマーカー分析による陸上植物由来有機物の輸送・堆積過程の検討  [通常講演]

  沢田健, 澤井健之, 関宰

  日本堆積学会大会プログラム・講演要旨 2012年06月
• グリーンランドアイスコアの過去450年間の土壌ダストの記録  [通常講演]

  関宰, 河村公隆, BENDLE James, 藤井理行

  日本地球化学会年会講演要旨集 2012年 

  本研究では有機分子の土壌ダストトレーサーである高分子ジカルボン酸と起源トレーサーである陸上高等植物由来の高分子脂肪酸の分子組成と安定炭素同位体比をグリーンランドアイスコア（Site-J）に適用し、過去450年間の土壌有機エアロゾルの沈積量とその起源の変動を復元した。Site-Jの高分子ジカルボン酸の濃度や高分子脂肪酸の平均炭素鎖(ACL)は過去450年間においてアイスコア中のベリリウム10（10Be）から復元した太陽放射量の変動と同調した数十年規模の変動を示し、有機物トレーサーから土壌ダストと太陽活動の関連を支持する結果がはじめて得られた。さらに脂肪酸ACLや安定炭素同位体比から太陽活動の変化に伴い土壌有機エアロゾルの起源が変化していたことが新たに示唆された。
• カリフォルニア沖堆積物におけるホパン組成の変動と古環境  [通常講演]

  中國正寿, 関宰, 山本修一, 石渡良志

  日本地球化学会年会講演要旨集 2012年 

  カリフォルニア沖堆積物コア(ODP Leg 167， Hole 1017E)における炭化水素化合物の分析を行った。検出された主要な化合物は、アルカン、高分枝炭化水素(HBI)、ホパン類などであった。なかでもホパン類の組成は、現世堆積物で見いだされる組成と異なり、続成変化の進んだ熟成した組成を示した。これら熟成したホパン類の深度分布は、急激な気温上昇が起こった約1万5千年前に高い濃度を示した。この時代は、最終氷期に大規模化したカリフォルニア地域の高山氷河(タイオガ氷河)が融解した時代と一致する。したがって、これらホパン類の増加は、融解水がカリフォルニアの海岸線域に存在する石油生成帯を含むモントレー層を浸食した結果、増加したことを示唆している。
• 北西部北太平洋及びオホーツク海における最終氷期最寒期及び融氷期の表層水温変動  [通常講演]

  原田尚美, 関宰, 木元克典, 岡崎裕典, 長島佳菜, 井尻暁, 中塚武

  日本第四紀学会講演要旨集 2011年08月
• 過去15万年間の琵琶湖堆積物コア中の植物起源脂肪酸の水素同位体比記録  [通常講演]

  関宰, 河村公隆, 石渡良志

  日本地球化学会年会講演要旨集 2011年 

  本研究はバイマーカーの水素同位体比の古環境研究への適用を目的として、琵琶湖堆積物コア中の植物起源脂肪酸の水素同位体比を測定した。復元された過去１５万年間の脂肪酸の水素同位体比は～４０パーミルもの変動を示し、その変動パターンは中国の鍾乳石の酸素同位体比と類似しており、北緯３０度における夏の日射量の変動に同調していることが示された。このことから 脂肪酸の水素同位体比は中国の鍾乳石の酸素同位体比と同様に、地球の歳差運動の周期による夏期の日射量変動に応答したシグナルを反映していると考えられ、陸域の古気候トレーサーとして有用であることが示唆された。
• 北西太平洋表層堆積物中の陸上植物テルペノイドバイオマーカーの起源と輸送過程  [通常講演]

  小林まどか, 沢田健, 関宰

  日本地球化学会年会講演要旨集 2011年 

  陸上高等植物に由来するテルペノイド(HPT)は、植物の分類によって異なる構造を持つことが知られており、陸源物質の海洋への輸送の供給源や後背地を特定するための有用なバイオマーカーになり得ると考えられる。本研究では、レテン、カダレン、フリーデリンという3種類のHPTに着目して、北西太平洋の表層堆積物中での化合物分布を調べ、それぞれの化合物の起源と輸送過程について考察した。
  分析の結果、レテンの分布からは後背地の植生の影響以外に、化石燃料を含む都市大気による影響がみられた。フリーデリンは北西太平洋日本沖で特に多く、陸から遠く離れた外洋域のコアからは総じて微量しか検出されなかったことから、主に河川経由で輸送されていると考えられる。一方でカダレンについては地域・海域による傾向はあまり見られなかったが、これはカダレンが主に大気経由で広範囲に輸送されていることを示唆している。

その他活動・業績

• 南大洋における風成塵-磁気相関と酸素同位体層序のクロスチェック

  MATSUI Hiroki, IKEHARA Minoru, SUGANUMA Yusuke, SUGANUMA Yusuke, SEKI Osamu, OKUNO Jun’ichi, OKUNO Jun’ichi, OYABU Ikumi, KAWAMURA Kenji, KAWAMURA Kenji 日本地球惑星科学連合大会予稿集(Web) 2020 2020年
• 最終間氷期の南極氷床崩壊と海水準上昇

  関宰 低温科学 76 135‐144 2018年03月07日 [査読無し][通常論文]
  
• IODP Exp.374速報:新生代後期におけるロス海西南極氷床変動史

  杉崎彩子, 関宰, 石野沙季, MCKAY Rob, DE SANTIS Laura, KULHANEK Denise K 日本地球惑星科学連合大会予稿集(Web) 2018 ROMBUNNO.MIS08‐08 (WEB ONLY) 2018年 [査読無し][通常論文]
  
• 中央海嶺における海底マグマ活動の盛衰は全球気候変動に影響するか?―精密な年齢付き海底地形観測による制約へ向けて―

  藤井昌和, 藤井昌和, 喜岡新, 山崎俊嗣, 沖野郷子, 田村千織, 関宰, 野木義史, 野木義史, 奥野淳一, 奥野淳一, 石輪健樹, 大藪幾美 日本地球惑星科学連合大会予稿集(Web) 2018 ROMBUNNO.MIS06‐01 (WEB ONLY) 2018年 [査読無し][通常論文]
  
• CO2濃度に支配される最終氷期の北半球高緯度植生変遷

  関宰, 原田尚美, 五十嵐八枝子 日本地球惑星科学連合大会予稿集(Web) 2018 ROMBUNNO.MIS10‐29 (WEB ONLY) 2018年 [査読無し][通常論文]
  
• 南極アイスコア等による古環境復元~2017年度の活動~

  川村賢二, 川村賢二, 川村賢二, 植村立, 本山秀明, 本山秀明, 飯塚芳徳, 堀内一穂, 青木周司, 東久美子, 東久美子, 藤田秀二, 藤田秀二, 関宰, 平林幹啓, 中澤文男, 中澤文男, 大藪幾美, 大野浩, 津滝俊, 阿部彩子 日本地球惑星科学連合大会予稿集(Web) 2018 ROMBUNNO.MIS06‐P12 (WEB ONLY) 2018年 [査読無し][通常論文]
  
• 別寒辺牛湿原泥炭コアのミズゴケセルロース酸素同位体比を用いた過去2000年間の古気候復元

  櫻井弘道, 山本正伸, 関宰, 大森貴之, 佐藤友徳 日本地球惑星科学連合大会予稿集(Web) 2018 ROMBUNNO.MIS01‐P06 (WEB ONLY) 2018年 [査読無し][通常論文]
  
• 北海道沙流川における洪水時懸濁物鉱物組成の制御要因

  入野智久, 中田聡史, 池原研, 山下洋平, 関宰, 長尾誠也 日本地質学会学術大会講演要旨 124th 36 2017年09月10日 [査読無し][通常論文]
  
• 放射性炭素による汽水域での懸濁態有機物の動態研究

  長尾誠也, 鈴木智代, 落合伸也, 関宰 日本海洋学会大会講演要旨集 2017 81 2017年09月 [査読無し][通常論文]
  
• 白鳳丸KH17‐3次航海におけるアラスカ湾でのコア試料採泥と今後の展開

  堀川恵司, 村山雅史, 関宰 日本第四紀学会講演要旨集 47 86 2017年08月26日 [査読無し][通常論文]
  
• 融雪時期の操作が樹木の葉形質におよぼす影響は個体サイズによって異なるか?

  丸毛絵梨香, 高木健太郎, 関宰, 小林真 日本生態学会大会講演要旨(Web) 64th ROMBUNNO.P1‐R‐464 (WEB ONLY) 2017年 [査読無し][通常論文]
  
• 大雪山地域の高層湿原泥炭の鉱物組成に基づく完新世における黄砂供給量の変動

  入野智久, 平井啓介, 関宰, HOOPER James, MARX Samuel K 日本地球惑星科学連合大会予稿集(Web) 2017 ROMBUNNO.MIS23‐P13 (WEB ONLY) 2017年 [査読無し][通常論文]
  
• 最終間氷期の突然かつ急激な南極氷床崩壊イベントの検証とメカニズムの解明に向けて

  関宰 日本地球惑星科学連合大会予稿集(Web) 2017 ROMBUNNO.MIS10‐07 (WEB ONLY) 2017年 [査読無し][通常論文]
  
• 南極氷床と気候の変動及び相互作用に関する研究展望

  川村賢二, 川村賢二, 川村賢二, 杉山慎, 植村立, 本山秀明, 本山秀明, 澤柿教伸, 飯塚芳徳, 堀内一穂, 青木周司, 東久美子, 東久美子, 藤田秀二, 藤田秀二, 関宰, 平林幹啓, 大藪幾美 日本地球惑星科学連合大会予稿集(Web) 2017 ROMBUNNO.MIS10‐12 (WEB ONLY) 2017年 [査読無し][通常論文]
  
• ボルネオ泥炭中微粒炭量からみた過去6000年間の西部熱帯太平洋乾湿変動

  山本正伸, 菊池隼史, 櫻井弘道, 林竜馬, 関宰, 大森貴之, SULAIMAN Abdullah, BIN SHAARI Hasrizal, MELLING Lurie 日本地球惑星科学連合大会予稿集(Web) 2017 ROMBUNNO.MIS06‐06 (WEB ONLY) 2017年 [査読無し][通常論文]
  
• 別寒辺牛湿原泥炭コアのミズゴケセルロース酸素同位体比を用いた過去2000年間の古気候復元

  櫻井弘道, 山本正伸, 関宰, 大森貴之 日本地球惑星科学連合大会予稿集(Web) 2017 ROMBUNNO.MIS23‐P12 (WEB ONLY) 2017年 [査読無し][通常論文]
  
• ロシア船を用いた親潮源流域の観測研究―航海の概要と親潮上流の栄養物質分布―

  西岡純, 安田一郎, 小野数也, 中村知裕, 鈴木光次, 渡辺豊, 山下洋平, 平譯享, LIU Hongbin, 藤尾伸三, 柳本大吾, 田中雄大, 原田尚美, 関宰, 岡崎裕典, 長尾誠也, 井上睦夫, 小畑元, 田副博文, 小川浩史, 宗林留美, 三寺史夫, 江淵直人, 若土正暁, VOLKOV Y.N 日本海洋学会大会講演要旨集 2016 107 2016年08月 [査読無し][通常論文]
  
• 日本周辺に存在する「陸海結合システム」の理解に向けて

  西岡純, 三寺史夫, 白岩孝行, 関宰, 中村知裕, 的場澄人, 江淵直人 低温科学 74 175 -180 2016年03月31日 [査読無し][通常論文]
   

  日本は，オホーツク海，日本海，東シナ海といった「縁辺海」と「北太平洋」に面しており，太平洋からみると縁辺海と大洋を隔てる列島の一部である．さらにベーリング海を含めたこれら北太平洋の縁辺海は，自然科学的視点からみても，人間活動の場として見ても多くの共通性と特異性を持ち合わせている．これらのすべての縁辺海には，大河川や，規模は小さいが数多くの中・小河川が流れ込むことで，陸域の影響が大きく現れる．これら河川を通じて陸からの物質を受け取り，縁辺海内部で起こる様々な物理的プロセスと生物的・化学的反応を介して物質循環が活発に起こっている場所である．これらの各縁辺海は，陸域の影響を大洋に伝える間の緩衝作用も担うと同時に，大洋の影響も強く受け，物質的にも暖流（黒潮）や寒流（親潮）で結ばれている．縁辺海の自然科学的な機能を明らかにすることは，東シナ海，日本海，オホーツク海を経由して，北太平洋へと至る，長大な物質循環システムを理解することに繋がる．本稿では，環オホーツク域の「陸海結合システム」という概念に焦点を当て，環オホーツク域で進めてきた研究で残されている課題と，日本の周辺領域も含めたさらに大きなスケールで陸海結合システムをとらえるための研究展開について記す．Linkage between land and ocean is one of important issue for understanding earth system, and marginal seas are a key place for this linkage. The South China Sea, the East China Sea, the Japan Sea, the Sea of Okhotsk and the Bering Sea are marginal seas located on the north/west rim of the Pacific Ocean. These marginal seas received strong influence from the land via large and small scale river discharge, which include human influence. The marginal seashave high productivity and active biogeochemical cycles relative to those in oceanic regions, which are controlled by individual local processes, such as fresh water discharge, interior current systems, tidal mixing, local upwelling, continental shelves interactions, sea ice production/melting, and flows through straits. Further, recent studies indicated that some of the marginal seas strongly influence to the Pacific Ocean on physical and biogeochemicalprocesses. Therefore, clarifying roles of the marginal seas for linkage between land and oceanic region is one of the major remaining issue for understanding whole Pacific Ocean. In this paper, we discuss remaining issue to understand not only pan-Okhotsk biogeochemical system but also the role of Pacific marginal seas in linking adjacent land with ocean.
• 北太平洋亜寒帯の融氷期生物生産増大イベントの原因

  関宰 低温科学 74 143 -151 2016年03月31日 [査読無し][通常論文]
   

  高緯度縁辺海を含む北太平洋亜寒帯域は生物生産が高いことで知られているが，オホーツク海やベーリング海東部を除く大部分は高栄養塩低クロロフィル（HNLC）海域と呼ばれ，鉄の供給不足により生物生産が制限されている海域でもある．近年の研究から高緯度縁辺海の大陸棚起源の鉄が北太平洋亜寒帯域における生物生産の鍵を握っている可能性が示唆された．一方，古海洋の研究からこの海域では気候変動に伴い海洋循環や生物生産が劇的に変動したことが明らかにされている．本稿では最終氷期から現在にいたるこの海域の生物生産の変遷を解説し，高緯度縁辺海から外洋への物質供給システムが外洋の生物生産に与えた影響について議論する．The subpolar North Pacific region is one of the highest productive area in the ocean. This region is alsocharacterized by high nutrient low chlorophyll (HNLC) region where iron is a key micronutrient that limits primaryproduction in the ocean. Recent studies suggest that iron supply from the continental shelf in the Sea of Okhotskpotentially plays a substantial role in sustaining primary production in the subarctic North Pacific. On the other hand,paleoceanographic studies revealed that productivity has been dramatically changed in this region associated with theglacial-interglacial cycle. In this paper, I review changes in productivity in this region from the last glacial maximumperiod to the present and discuss a potential impact of iron transport from subpolar marginal sea to the subarcticNorth Pacific on the deglacial productivity spike
• 新生代後期(過去約1000万年間)の長期的な全球寒冷化における南大洋の役割

  関宰, 堀川恵司, 小野寺丈尚太朗, 岡崎裕典, 阿部彩子 日本海洋学会大会講演要旨集 2016 127 2016年03月 [査読無し][通常論文]
  
• グリーンランド南東ドームにおける浅層掘削計画 -掘削報告と初期コア解析-

  飯塚芳徳, 的場澄人, 大藪幾美, 山崎哲秀, 門田萌, 新堀邦夫, 青木輝夫, 斉藤健, 宮本淳, 古川崚仁, 藤田秀二, 堀彰, 山口悟, 大野浩, 鈴木利孝, 植村立, 関宰, 本山秀明 雪氷研究大会講演要旨集(Web) 2015 190(J‐STAGE) 2015年 [査読無し][通常論文]
  
• グリーンランド南東ドームにおける浅層掘削計画-掘削報告と初期コア解析-

  飯塚 芳徳, 的場 澄人, 大藪 幾美, 山崎 哲秀, 門田 萌, 新堀 邦夫, 青木 輝夫, 斉藤 健, 宮本 淳, 古川 崚仁, 藤田 秀二, 堀 彰, 山口 悟, 大野 浩, 鈴木 利孝, 植村 立, 関 宰, 本山 秀明 雪氷研究大会講演要旨集 2015 190 2015年
• 南極周極流・ウェッデルジャイアと海氷移流のダイナミクスの解明を目指して

  池原実, 関宰, 井尻暁, 佐藤暢, 山本正伸, 大河内直彦, 岡崎裕典, 松崎琢也 日本地球惑星科学連合大会予稿集(Web) 2015 ROMBUNNO.MIS21‐P01 (WEB ONLY) 2015年 [査読無し][通常論文]
  
• ベーリング海低塩分水の北極海への流入による鮮新世の寒冷化

  堀川恵司, MARTIN E, 小野寺丈尚太郎, 関宰, 坂本竜彦, 池原実, 坂井三郎, 河村公隆 日本地球化学会年会講演要旨集 61st 198 2014年 [査読無し][通常論文]
  
• 古気候・古環境分野からの提案

  原田尚美, 大河内直彦, 南雅代, 関宰, 岡崎裕典 日本地球化学会年会講演要旨集 61st 139 2014年 [査読無し][通常論文]
  
• アイスコア解析から明らかになった十年規模の気候変動に対する炭素質エアロゾルのインパクト

  関宰, 河村公隆, 藤井理行, BENDLE James 日本地球化学会年会講演要旨集 61st 203 2014年 [査読無し][通常論文]
  
• カリフォルニア沖における融氷期のメタン放出イベント

  中國正寿, 関宰, 山本修一 日本地球化学会年会講演要旨集 61st 309 2014年 [査読無し][通常論文]
  
• 網走湖堆積物中有機物分析による過去300年間の環境変化

  栄田直樹, 山本修一, 関宰, 瀬戸浩二 日本地球化学会年会講演要旨集 61st 303 2014年 [査読無し][通常論文]
  
• 完新世におけるオホーツク海およびベーリング海の表層水温と海氷の変化

  原田尚美, 香月興太, 中川光弘, 松本亜希子, 関宰, 佐藤都, 長島佳菜 日本海洋学会大会講演要旨集 2013 78 2013年08月30日 [査読無し][通常論文]
  
• 更新世初期のベーリング海峡閉鎖が長期的な気候変動に与えたインパクト

  関宰, 小野寺丈尚太郎, 池原実, 岡崎裕典, 河村公隆, 高橋孝三 日本海洋学会大会講演要旨集 2013 84 2013年08月30日 [査読無し][通常論文]
  
• 分子レベル安定同位体分析の古環境復元への応用

  関 宰 ぶんせき (448) 214 -215 2012年04月05日 [査読無し][通常論文]
  
• 大陸と外洋を結ぶ溶存鉄:アムール川とオホーツク海・親潮 河川・汽水域における溶存鉄の挙動

  長尾誠也, 寺島元基, 関宰, 川東正幸, 児玉宏樹, KIM Vladimir I, SHESTERKIN Vladimir P, LEVSHINA Svetlana I, MAKHINOV Alexei N 海洋と生物 34 (1) 42 -48 2012年02月15日 [査読無し][通常論文]
  
• 立山・室堂平の積雪層中の陸上植物バイオマーカー組成とその安定水素同位体比

  山本真也, 中村進之介, 関宰, 河村公隆 日本地球化学会年会講演要旨集 58th (0) 381 -360 2011年 [査読無し][通常論文]
   

  本研究では，偏西風によりアジア大陸から輸送される陸起源有機物の起源域・輸送過程を明らかにすることを目的に、立山に2010年冬から2011年春にかけて堆積した積雪層中の陸上植物バイオマーカーの分子組成とその安定水素同位体比の測定を行った。立山の積雪試料中には、典型的な陸上植物バイオマーカーである炭素優位性を示すC25-C36ノルマルアルカン、C22-C28の脂肪族アルコール、C22-C28脂肪酸が主要な化合物として含まれており、その濃度は黄砂を含む層準で増加する（~8.4μg/l）傾向にあった。一方、C22-C28脂肪酸のδD値（平均–143‰）は、同時期の札幌降雪中のC22-C28脂肪酸に比べ最大65‰高く、その起源域の違いが示唆された。比較の為に、中国のレス堆積物中のC22–C28脂肪酸のδD値を測定したところ、–143‰と立山の降雪試料に近い値が得られ、中国内陸部のレス堆積物が、自由対流圏を介して北西太平洋域へ運搬される陸上植物バイオマーカーの主要な供給源となっていることが示唆された。
• C‐14を用いた別寒辺牛湿原における粒子態有機物の移行挙動研究

  長尾誠也, 関宰, 荒巻能史 日本原子力研究開発機構JAEA-Conf 34 -38 2010年03月 [査読無し][通常論文]
  
• Carbon istopes of POC in a small river in Bekanbeushi moor, northern Japan

  Nagao S., Aramaki T., Seki O., Uchida M., Shibata Y. 年報 金沢大学環日本海域環境研究センター = K-INET Kanazawa University 20 (2008) 71 -71 2010年01月29日 

  [研究報告]
• ガスクロマトグラフ/熱分解/同位体質量分析計による分子レベル水素同位体比の分析と地球化学研究への応用

  関宰 日本分析化学会年会講演要旨集 58th 448 2009年09月10日 [査読無し][通常論文]
  
• pCO(2) and climate; Evidence from boron based proxies of pH and pCO(2)

  Gavin L. Foster, Osamu Seki, Richard D. Pancost, Daniela N. Schimdt GEOCHIMICA ET COSMOCHIMICA ACTA 73 (13) A391 -A391 2009年06月 [査読無し][通常論文]
  
• 過去1.3万年間におけるチベット泥炭コアのn‐アルカンの水素同位体比の変動

  関宰, MEYERS Philip A, 河村公隆, 中塚武, ZHENG Yanhong, ZHOU Weijian 日本地球化学会年会講演要旨集 56th (0) 40 -36 2009年 [査読無し][通常論文]
   

  バイオマーカーの水素同位体比は水循環に関する情報を保持していると考えられ、過去の気候（降水量や気温、相対湿度等）を復元する手法として近年注目を集めている。同位体比から過去の水循環を復元する他の手法としては、年輪や泥炭中のセルロースの水素・酸素同位体比や鍾乳石の酸素同位体比などが挙げられる。年輪や鍾乳石といった古気候記録媒体は比較的年代を正確に決めることが出き、高時間分解能の解析が可能な点で優れている。しかしながら、それらに記録された同位体比は有効降水量だけでなく、過去における水蒸気の起源の変化によっても影響されるため、同位体記録が主にどの変動を反映しているかを識別することが困難という問題点も抱えている。本研究では中国の泥炭コア中の水生植物と陸上植物由来n-アルカンの水素同位体比の分析から、過去の相対湿度変動の復元を試みた。
• バイオマーカーを用いた古気候変遷と物質循環に関する地球化学的研究

  関宰 日本地球化学会年会講演要旨集 56th (0) 244 -235 2009年 [査読無し][通常論文]
  
• 石狩川における粒子態有機物の特徴と移行挙動

  三上昌人, 長尾誠也, 関宰, 三上裕, 福嶋正巳 資源・素材学会北海道支部春季講演会講演要旨集 2009 27 -28 2009年 [査読無し][通常論文]
  
• オホーツク海の最終氷期から完新世にかけての表層水温の変動 (総特集 北半球高緯度海域における気候変動研究--近未来温暖化影響予測に向けた最新の知見)

  関 宰 月刊地球 30 (3) 150 -156 2008年05月 [査読無し][通常論文]
  
• 北半球高緯度海域における気候変動研究―近未来温暖化影響予測に向けた最新の知見―オホーツク海の最終氷期から完新世にかけての表層水温の変動

  関宰 月刊地球 30 (3) 150 -156 2008年05月01日 [査読無し][通常論文]
  
• 海底堆積物コアに記録された長時間スケールのオホーツク海の古海洋環境の変動

  坂本竜彦, 原田尚美, 井尻暁, 飯島耕一, 関宰 日本海洋学会大会講演要旨集 2008 95 2008年03月14日 [査読無し][通常論文]
  
• アルケノン安定炭素同位体比による中新世後期および鮮新世の大気CO2濃度変動の復元

  関 宰, ダニエル シュミト, 河村 公隆, パンコスト リチャード 日本地球化学会年会要旨集 55 (0) 425 -425 2008年 [査読無し][通常論文]
   

  地球の気候は鮮新世中期以前（約300万年以前）では現在よりも氷床量が少なく温暖で海水準が高い"温室"状態であったと考えられている。その後の地球の寒冷化を導いた要因としてはテクトニクス変動による熱と水蒸気の輸送の変化が有力視されてきたが、他の有力な仮説として、大気CO2濃度の減少も提案されている。いくつかの気候モデルはCO2減少説を支持しているが、北半球の氷床が劇的に成長していった鮮新世における大気CO2濃度の連続的な復元データが報告されていないのが現状である。そこで我々はカリブ海堆積物コア中のアルケノンと浮遊性有孔虫の安定炭素同位体比の分析を行い中新世後期から鮮新世にかけての大気CO2濃度変動の詳細な復元を試みた。
• オホーツク海表層堆積物における有機物の起源推定

  三上裕, 関宰, 長尾誠也, 福島正巳, 荒巻能史, 内田昌男, 柴田康行, 南秀樹, 加藤義久, 坂本竜彦, 中塚武 日本地球化学会年会講演要旨集 55th (0) 411 -379 2008年 [査読無し][通常論文]
   

  海洋の有機物の約90%は大陸棚堆積物に沈着しているため，大陸棚は二酸化炭素の吸収や保存の場として炭素循環において重要な役割を担っている。しかし，陸と海洋の物質が複雑に混合し，化学・物理過程も複雑に作用するため，有機物の起源や堆積過程など不透明な部分が多い。 オホーツク海は北太平洋西部に位置する縁辺海であり，全面積のおよそ40%は大陸棚が占める。北西部にはアムール川が流れ込み，多量の陸起源物質が大陸棚に供給される一方で，生物生産も活発である。また，大陸棚上の物質を外洋へ輸送する東サハリン海流や高密度陸棚水の存在が報告されている。本研究では，オホーツク海表層堆積物中の全有機炭素含量(TOC)，炭素同位体比(δ13C，Δ14C)およびリグニンフェノール総量(Λ)を測定し．オホーツク海表層堆積物における各項目の空間分布を示し，有機炭素の起源および堆積過程を検討した。
• アルケノン安定炭素同位体比による中新世後期および鮮新世の大気CO₂濃度変動の復元

  関宰, SCHMIDT D. N, 河村公隆, PANCOST R. D 日本地球化学会年会講演要旨集 55th 460 2008年 [査読無し][通常論文]
  
• バイオマーカー分析に基づく過去１０００万年間における東赤道太平洋とカリブ海の気候変動

  関 宰, シュミット ダニエラ, ショウテン ステファン, ホプマン エレン, 河村 公隆, パンコスト リチャード 日本地球化学会年会要旨集 54 (0) 151 -151 2007年 [査読無し][通常論文]
   

  鮮新世における気候変動の鍵となるイベントは北半球の氷河化である。パナマ地峡の形成とそれに伴うグローバルな海洋循環の再編成がその要因として有力であると考えられているが、パナマ海峡の閉鎖の正確なタイミングはいまだ良くわかっておらず、海峡の閉鎖がもたらす気候インパクトはいまだ不明瞭である。また、もう一つの仮説として、北太平洋高緯度域表層の成層化による大気CO2濃度の減少が提唱されているが、大気CO2濃度と北半球の氷床発達の関連も十分に研究されていないのが現状である。我々は鮮新世初期から中期の気候状態および後期に起こった北半球の氷河化の要因を明らかにすることを目的として、東赤道太平洋(ODP1241)およびカリブ海(ODP999/1000)の堆積物コア中のバイオマーカーの定量、同位体分析から過去の水温、生物生産、大気CO2濃度の復元等を行った。講演ではこれら最新のデータを発表する。
• 鮮新世における気候状態と北半球の氷床発達の要因の研究

  関宰, SCHMIDT Daniela N, SCHOUTEN Stefan, HOPMANS Ellen C, 河村公隆, PANCOST Richard D 日本地球化学会年会講演要旨集 54th 159 2007年 [査読無し][通常論文]
  
• 南シナ海南部海底堆積物中の脂肪酸による過去15万年間の環境変動

  伊澤祐輔, 山本正伸, 関宰, 河村公隆, CHEN M‐T 日本地球化学会年会講演要旨集 53rd (0) 168 -146 2006年 [査読無し][通常論文]
   

  西部熱帯太平洋は地球上において重要な熱と水蒸気の貯蔵庫であり、気候変動や水循環の研究する上で重要な場所である。そこで、本研究は南シナ海南部で掘削されたMD972151コア中の脂肪酸の分析を行い、過去15万年間の分布を明らかにした。陸上高等植物起源である長鎖脂肪酸(C24,26,28)濃度は完新世よりも最終氷期最寒期(LGM)において高かった。この変動は海水準の変化が陸起源物質の流入に大きな影響を与えることを示唆した。また、LGMにおける長鎖脂肪酸の水素同位体比は海洋生物起源である短鎖脂肪酸(C16,18)よりも重い値を示した。
• オホーツク海におけるバクテリアと放散虫中層種の関係:氷期海洋中層環境復元の手がかり

  岡崎裕典, 関宰, 中塚武, 高橋孝三, 池原実 日本海洋学会大会講演要旨集 2005 83 2005年 [査読無し][通常論文]
  
• 北海道泥川流域の森林、湿原、湖試料におけるn-アルカンの水素同位体比

  関 宰, 中塚 武, 柴田 英昭, 河村 公隆 日本地球化学会年会要旨集 51 (0) 106 -106 2004年 [査読無し][通常論文]
   

  植物の水素同位体比は主に利用する水の同位体比と湿度によっておおむね決まると考えられており、植物の水素同位体比は水循環に関した情報を保持していると考えられている。しかしながら地球化学分野における研究例は少なく、地球化学的トレーサーとしての性能は未知数である。北海道の雨龍研究林の泥川流域において森林・湿原と湿度の異なる環境においてそれぞれ土壌のサンプリングを行い陸上植物バイオマーカーのn-アルカンの水素同位体比を測定した。アルカンの水素同位体比は最大70パーミルの差がみられ、湿原のサンプルは森林のそれよりも一貫して低い値を示した。これは湿度環境の違いを反映したものと思われる。泥川河口の堆積物のアルカンの水素同位体比は森林と湿原の中間の値を示し、両サイトからの有機物の寄与を示唆する。この研究により有機物の水素同位体比測定は河川の有機物の起源推定に有用であることが示唆された。
• オホーツク海セジメントトラップ中のバイオマーカー組成

  関宰, 吉川知里, 河村公隆, 中塚武, 若土正暁 日本海洋学会大会講演要旨集 2002 325 2002年03月27日 [査読無し][通常論文]
  
• バイオマーカーを用いたオホーツク海における過去3万年の環境変動の解析

  関宰, 河村公隆, 中塚武, 池原実 日本地球化学会年会講演要旨集 2001 249 2001年10月18日 [査読無し][通常論文]
  
• 最終氷期‐間氷期サイクルにおけるカリフォルニア沖のアルケノン表面海水温度の変動

  関宰, 松本公平, 石渡良志 日本地球化学会年会講演要旨集 1999 199 1999年09月29日 [査読無し][通常論文]
  
• カリフォルニア沖堆積物の過去4万年におけるステロールの変動 ODP Leg167 Hole1017Eの解析 V

  松本公平, 関宰, 石渡良志 日本地球化学会年会講演要旨集 1999 272 1999年09月29日 [査読無し][通常論文]
  
• カリフォルニア沖堆積物の過去約4万年におけるアルケノン,表面海水温度の変動

  関宰, 松本公平, 吉川博康, 石渡良志 日本地球化学会年会講演要旨集 1998 64 1998年10月 [査読無し][通常論文]
  
• カリフォルニア沖堆積物の過去4万年におけるステロールの変動 ODP Leg167 Hole1017Eの解析 III

  松本公平, 関宰, 吉川博康, 石渡良志 日本地球化学会年会講演要旨集 1998 174 1998年10月 [査読無し][通常論文]
  
• カリフォルニア堆積物(ODP Leg167,Site1017)中の陸起源有機物 熱分解メチル化法による解析 2

  吉川博康, 山本修一, 松本公平, 関宰, 石渡良志 日本地球化学会年会講演要旨集 1998 65 1998年10月 [査読無し][通常論文]
  

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