Stephen P. Obrochta

写真a

Affiliation

Graduate School of International Resource Sciences  Department of Earth Resource Science 

Homepage URL

http://www.gipc.akita-u.ac.jp/~geoinformatics/index_e.html

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Research Interests 【 display / non-display 】

  • paleoenvironmental reconstruction

  • paleoclimatology

  • Paleoceanography

  • stratigraphy

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Graduating School 【 display / non-display 】

  • 　
    -
    1997.12

    Eckerd College   Department of Marine Science   Carbonate sedimentology and petrology   Graduated

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Graduate School 【 display / non-display 】

  • 　
    -
    2008.12

    Duke University  Earth and Ocean Science Department  Doctor's Course  Completed

  • 　
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    2004.07

    University of South Florida  Geological Oceanography  Master's Course  Completed

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Degree 【 display / non-display 】

  • Duke University -  Doctor of Philosophy

  • University of South Florida -  Master of Science

  • Eckerd College -  Bachelor of Science

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Campus Career 【 display / non-display 】

  • 2020.11
    -
    Now

    Akita University   Graduate School of International Resource Sciences   Department of Earth Resource Science   Professor  

  • 2014.12
    -
    2020.10

    Akita University   Abolished organization   Dept. of Earth Resource Science   Associate Professor  

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External Career 【 display / non-display 】

  • 2014.10
    -
    2014.12

    University of Tokyo Atmosphere Ocean Research Institute   Department of Ocean Floor Geoscience   JSPS Postdoctoral Foreign Researcher (Pathways)  

  • 2010.11
    -
    2014.09

    University of Tokyo Atmosphere Ocean Research Institute   Department of Ocean Floor Geoscience   Postdoctoral Researcher  

  • 2010.04
    -
    2010.11

    University of Tokyo Atmosphere Ocean Research Institute   Department of Ocean Floor Geoscience   JSPS Postdoctoral Foreign Researcher  

  • 2008.11
    -
    2010.03

    University of Tokyo Ocean Research Institute   Department of Ocean Floor Geoscience   JSPS Postdoctoral Foreign Researcher  

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Research Career 【 display / non-display 】

  • Integrated Drilling Program Expedition 347, Baltic Sea Paleoclimate

    (not selected)  

    Periods of research：

    2014.01
    -
    Now

    Classification of research form：International Collaboration

  • Paleo-tsunami and earthquake records of ruptures along the Nankai Trough, offshore South-Central Japan

    (not selected)  

    Periods of research：

    2014.09
    -
    Now

    Classification of research form：International Collaboration

  • Replacement of Neanderthals by Modern Humans

    (not selected)  

    Periods of research：

    2010.12
    -
    Now

    Classification of research form：Collaboration within Japan

  • Tropical Indo-Pacific paleoceanography and paleoclimatology

    (not selected)  

    Periods of research：

    2014.02
    -
    Now

    Classification of research form：Collaboration within Japan

  • Indonesian Archipelago and Timor Sea Sea Level and Paleoceanography

    (not selected)  

    Periods of research：

    2011.01
    -
    Now

    Classification of research form：International Collaboration

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Thesis for a degree 【 display / non-display 】

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Research Achievements 【 display / non-display 】

    ◆Original paper【 display / non-display 】

  • A new model of Holocene reef initiation and growth in response to sea-level rise on the Southern Great Barrier Reef

    Sanborn, K.L., Webster, J.M., Webb, G.E., Braga, J.C., Humblet, M., Nothdurft, L., Patterson, M.A., Dechnik, B., Warner, S., Graham, T., Murphy, R.J., Yokoyama, Y., Obrochta, S.P., Zhao, J.-X., Salas-Saavedra, M.

    Sedimentary Geology   397   2020.03  [Refereed]

    Research paper (journal)   International Co-author

    The fossil record provides valuable data for improving our understanding of both past and future reef resilience and vulnerability to environmental change. The spatial and temporal pattern of the initiation of the Holocene Great Barrier Reef presents a case study of reef response to rapid sea-level rise. Past studies have been limited by the lack of well-dated and closely spaced reef core transects and have not closely examined the composition of the reef-building communities through time. This study presents 80 new high precision U-Th and 5 radiocarbon ages from twelve new cores located along three transects across different geomorphic and hydrodynamic settings of One Tree Reef, southern Great Barrier Reef, to document three distinct stages of Holocene reef development in unprecedented detail. Temporal constraints on changing paleoecological assemblages of coral, coralline algae and associated biota revealed three distinct phases of reef development, consisting of: 1)a fast, shallow and clear-water reef initiation from 8.2 until 8 ka; 2)a shift to slower, deeper and more turbid-water reef growth from 8 to 7 ka; and 3)a return to shallow and rapid branching coral growth in clear-water conditions as the reef "catches up" to sea-level. A minimum lag prior to reef initiation of 700 years was identified, which differs in length depending on reef environment and Pleistocene substrate height. In this new model, reef growth initiated on the topographically lower leeward margin and patch reef, prior to the start of windward margin development, contrary to the traditional reef growth model. While there was a shift to conditions less favorable for reef growth at 8 ka, this did not prevent the slow accretion of more sediment-tolerant coral communities. The majority of the reef reached sea level by similar to 6 ka. This new conceptual model of Holocene reef growth provides new constraints on changes in paleoenvironment that controlled reef community composition and growth trajectories through sea-level rise following inundation. (C) 2019 Elsevier B.V. All rights reserved.

    DOI

  • Tsunami deposits refine great earthquake rupture extent and recurrence over the past 1300 years along the Nankai and Tokai fault segments of the Nankai Trough, Japan

    Osamu Fujiwara, Akira Aoshima, Toshiaki Irizuki, Eisuke Ono, Stephen P. Obrochta, Yoshikazu Sampei, Yoshiki Sato, Ayumi Takahashi

    Quaternary Science Reviews   227   2020.01  [Refereed]

    Research paper (journal)   Domestic Co-author

    © 2019 Elsevier Ltd Study of prehistoric to medieval-age tsunami deposits along a riverbank site near the eastern Nankai Trough, central Japan, show that, not only did Tokai earthquakes occur with a higher frequency than previously thought, but that contemporaneous ruptures of the Tokai and Nankai fault segments were also more common. The site revealed a ∼1-km long coast-normal cross section of the strand plain and exposed four sandy tsunami deposits, each of which indicates inundation over 2 km inland of the coast. Radiocarbon dating of previously studied and newly discovered deposits in the region indicates a shorter recurrence time for Tokai earthquakes and clarifies their linkage with Nankai earthquakes. We attribute the younger two tsunami deposits to the 1498 and 1096 CE Tokai earthquakes. The older two deposits confirm the occurrence of the Tokai earthquakes in 887 CE and in the latest 7th century. These events are not reliably recorded in historical documents in the Tokai region but were noted in the Nankai area. The 887 CE earthquake likely represents a full-length rupture of the Tokai and Nankai segments, as was the case for the 1707 CE earthquake. Integrated with the previous studies, these new results show that nine Tokai earthquakes occurred over the last 1300 years, the oldest in the latest 7th century, and in 887, 1096, 1361, 1498, 1614, 1707, 1854 and 1944 CE. Recalculated recurrence intervals range from 90 to 265 years. Except for the 1498 Meio Tokai earthquake, the Tokai earthquakes occurred simultaneously with Nankai earthquakes.

    DOI

  • Organic carbon accumulation and productivity over the past 130 years in Lake Kawaguchi (central Japan) reconstructed using organic geochemical proxies

    Yamamoto, S., Hubert-Ferrari, A., Lamair, L., Miyata, Y., Ochiai, S., Nagao, S., Miyauchi, N., Yoshida, K., Fujiwara, O., Yokoyama, Y., Heyvaert, V.M.A., De Batist, M., Boes, E., Brückner, H., De Rycker, K., Garrett, E., Miyairi, Y., Nakamura, A., Obrochta, S., Riedesel, S., Shishikura, M., Walstra, J., The QuakeRecNankai Team

    Journal of Paleolimnology     2020  [Refereed]

    Research paper (journal)   Domestic Co-author

    DOI

  • A Rapid, Deterministic Age-Depth Modeling Routine for Geological Sequences With Inherent Depth Uncertainty

    Lougheed, B.C, Obrochta, S, P

    Paleoceanography and Paleoclimatology ( Paleoceanography and Paleoclimatology )  34 ( 1 ) 122 - 133   2019.01  [Refereed]

    Research paper (journal)   International Co-author

    DOI

  • High precision radiocarbon dating of Lake Motosu sediments clarifies the ages of Mt. Fuji eruptions

    Stephen Obrochta, Fujiwara Osamu, Yokoyama Yusuke, Miayiri Yosuke

    Isotope News   763   22 - 25   2019.06

    Research paper (journal)   Domestic Co-author

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    ◆International conference proceedings【 display / non-display 】

  • Segmentation of Coring Images Using Fully Convolutional Neural Networks

    Szilard Fazekas, Stephen P. Obrochta, Tatsuhiko Sato and Akihiro Yamamura

    Proceedings ICITEE 2017     1 - 5   2017.11  [Refereed]

    Research paper (international conference proceedings)   Domestic Co-author

    DOI

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    ◆Other【 display / non-display 】

  • Mt. Fuji Holocene eruption history reconstructed from coring survey in Lake Motosu, Fuji Five Lakes

    藤原 治, Obrochta Stephen, 横山 祐典, 宮入 陽介, 常松 佳恵

    GSJ地質ニュース = GSJ chishitsu news ( 産業技術総合研究所地質調査総合センター )  8 ( 3 ) 66 - 69   2019.03

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Grant-in-Aid for Scientific Research 【 display / non-display 】

  • Environmental reconstruction during the formation time of the Great Barrier Reef

    Grant-in-Aid for Scientific Research(B)

    Project Year： 2024.04  -  2027.03 

  • Timing and magnitude of the Scandinavian Ice Sheet contribution to post-glacial sea level rise

    Grant-in-Aid for JSPS Fellows

    Project Year： 2023.12  -  2025.10 

  • Untangling the Holocene Temperature Conundrum using coral skeletons

    Fund for the Promotion of Joint International Research

    Project Year： 2023.09  -  2028.03 

  • A study on Longterm Environmental changes and Wethering

    Grant-in-Aid for Scientific Research(A)

    Project Year： 2020.04  -  2023.03  Investigator(s): Yusuke Yokoyama, Naohiko Ohkochi, Stephen Obrochta

  • Grant-in-Aid for Scientific Research(S)

    Project Year： 2017.04  -  2022.03 

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Presentations 【 display / non-display 】

  • Mt. Fuji Holocene eruption history reconstructed: eruptions and environmental change

    スティーブン オブラクタ

    UTokyo/ANU Exchange in Tokyo  (東京大学駒場キャンパス)  2019.01  -  2019.01 

  • A rapid, deterministic age-depth modelling routine for geological sequences with inherent depth uncertainty

    Stephen P. Obrochta and Bryan C. Lougheed

    American Geophysical Union Fall Meeting 2018  (Washington DC, USA)  2018.12  -  2018.12 

  • Towards reconstructing environmental conditions related to Australian Great Barrier Reef initiation

    Stephen Obrochta, Wataru Miwa, Kotaro Shirai Yusuke Yokoyama, Yosuke Miyairi, Jody Webster, Al Hine

    2019年度日本地球惑星科学連合大会  (千葉県、幕張メッセ)  2019.06  -  2019.06 

  • An 8,000-year climate record from Lake Motosu, Japan: Implications for the East Asian Monsoon

    Sarah McDonald, Jonathon Tyler, Stephen Obrochta, Yusuke Yokoyama, Yosuke, Kosuke Ota

    2019年度日本地球惑星科学連合大会  (千葉県、幕張メッセ)  2019.06  -  2019.06 

  • An age-depth modeling method for improved treatment of uncertainty

    Stephen Obrochta, Bryan C Lougheed, Raimund Muscheler, Yusuke Yokoyama, Yosuke Miyairi

    2018年度日本地球惑星科学連合大会  (千葉県、幕張メッセ)  2018.05  -  2018.05 

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