[H-CG23] 混濁流:発生源から堆積物・地形形成まで

[HCG23-03] 巨大地震に伴う超深海海溝底への炭素供給：平成23年東北地方太平洋沖地震の例

*Kioka A.¹、Schwestermann T.¹、Moernaut J.¹、Ikehara K.²、Kanamatsu T.³、McHugh C.M.^4,6、Eglinton T.I.⁵、Strasser M.^1,7 (1.インスブルック大学・地質学専攻、2.産業技術総合研究所・地質調査総合センター、3.海洋研究開発機構・地震津波海域観測研究開発センター、4.ニューヨーク市立大学クイーンズ校・地球環境科学専攻、5.スイス連邦工科大学チューリッヒ校・地質学専攻、6.コロンビア大学ラモント・ドハティ地球研究所・海洋地質地球物理研究部門、7.ブレーメン大学・海洋環境科学センター)

キーワード：日本海溝、超深海帯、有機炭素、炭素循環、再堆積、2011年東北地方太平洋沖地震

The role of earthquakes on carbon cycling in deep-sea trenches along plate subduction margins is poorly constraint. The giant (Magnitude 9) Tohoku-oki earthquake in 2011 has been documented to remobilize a wide area of fine-grained surface sediment enriched in organic matter, redistributing from the slope into the deepest part of the >7 km deep Japan Trench. Yet, little is known about how and where the sediment remobilized by the 2011 earthquake had settled in the trench. In this study, we used high-resolution subbottom profilers (SBPs) acquired by Parasound and Topas systems from research cruises during 2012–2016, to image and spatially map the extensive transparent, up to ~5 m thick event-deposits. The SBP-to-core correlation and radio-nuclide dating on the youngest event deposit allowed for ground-truth of the mapped bodies to be related to the 2011 events. We quantified a total remobilized sediment volume of 0.2 km³ over the southern and central Japan Trench (36°N–39.5°N). The mapped sediment volume was then used for estimation of mass of organic carbon contained in the 2011 event deposits by measuring total organic carbon. The preliminary estimation suggests that the 2011 earthquake had triggered redistribution and eventual delivery of >1 x 10¹² g carbon to the trench by a single tectonic event. The finding sheds new light on dynamic impact of large earthquakes on carbon cycling in the deep-sea.