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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2018-237
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2018-237
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 18 Jun 2018

Submitted as: research article | 18 Jun 2018

Review status
This discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The revised manuscript was not accepted.

Impact of the 2011 off the Pacific coast of Tohoku earthquake on a deep-sea benthic ecosystem: evidence from living and dead benthic foraminifera on the landward slope of the Japan Trench

Akira Tsujimoto1, Ritsuo Nomura1, Hidetaka Nomaki2, Kazuno Arai3, Mutsuo Inoue4, and Katsunori Fujikura2 Akira Tsujimoto et al.
  • 1Faculty of Education, Shimane University, 1060 Nishikawatsucho, Matsue, Shimane 690-8504, Japan
  • 2Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
  • 3Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, Kochi 783-8502, Japan
  • 4Low Level Radioactivity Laboratory, Kanazawa University, Wake, Nomi, Ishikawa 923-1224, Japan

Abstract. We examined the impact of the earthquake and tsunami following the 2011 off the Pacific coast of Tohoku earthquake on the deep-sea benthic ecosystems based on radionuclide and benthic foraminiferal analysis of core sediments, collected from 3200 and 3600 m water depths 5 and 17 months after the earthquake. Radionuclide analysis of the excess 210Pb, 134Cs, and 137Cs indicated that some of the analyzed sediment core recorded deposits before the earthquake, event deposits just after the earthquake, and deposits after the Fukushima Daiichi Nuclear Power Plant accident, which caused the release of a large amount of radioactive material 4 days after the earthquake. Uvigerina senticosa, Chilostomella oolina, and Elphidium batialis were the dominant species in the study area prior to the earthquake. In core 4W-2012, the original or pre-earthquake assemblage layer was covered by 5-cm-thick event deposits following the earthquake that contained a high diversity allochthonous foraminiferal assemblage. Following the episodic deposition, foraminiferal density drastically decreased and many species disappeared, resulting in a decrease in species diversity. Above 10 cm depth in the sediment, living specimens of opportunistic and competitive species gradually increased toward the sediment surface and became dominant in the top 1 cm of the core. Thus, the episodic deposition resulting from the earthquake caused a drastic decrease in the original benthic foraminifera and colonization of opportunistic species with a low diversity within 17 months. Although there were differences in vertical change in the radionuclides and benthic foraminifera between sites, faunal change may have already occurred 5 months after the earthquake.

Akira Tsujimoto et al.
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Interactive discussion
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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Akira Tsujimoto et al.
Akira Tsujimoto et al.
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Short summary
We examined the impact of the earthquake and tsunami following the 2011 off the Pacific coast of Tohoku earthquake on the deep-sea benthic ecosystems. The episodic deposition of sediments resulting from the earthquake caused a drastic decrease in the original benthic foraminifera and colonization of opportunistic species with a low diversity within 17 months.
We examined the impact of the earthquake and tsunami following the 2011 off the Pacific coast of...
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