[M-IS33] 2011年巨大地震・津波以後の東北沖海洋科学

[MIS33-P07] 2011年東北地方太平洋沖地震後の上部漸深海帯底生生物群集

*野牧 秀隆¹、望月 智弘²、北橋 倫³、布浦 拓郎¹、新井 和乃⁴、豊福 高志¹、菅 寿美¹、脇田 昌英¹、田中 源吾⁵、滋野 修一¹、田角 栄二¹、藤倉 克則¹、渡邉 修一¹ (1.海洋研究開発機構、2.東京工業大学、3.東京大学、4.埼玉大学、5.熊本大学)

キーワード：メイオベントス, 底生微生物, 2011年東北地方太平洋沖地震, 堆積物

We examined the effects of mass sedimentation events caused by the 2011 off the Pacific coast of Tohoku earthquake on abundances and vertical distributions of prokaryotes and metazoan meiofauna in sediments, using sediment cores collected from eight bathyal stations off Tohoku 1 and 2.5 years after the M9.0 earthquake. Event deposits of 1 to 7 cm thick were observed at the topmost part of the sediment cores at all sampling stations. At some stations, prokaryotic cell abundances were lower in the surface event-deposit layers compared to those in deeper sediments. These variations were explained by environmental parameters such as a sorting factor and mean grain size, suggesting that turbidite sedimentation affected prokaryotic cell abundances. Nematodes had anomalously higher subsurface abundances at the stations where subsurface peak prokaryotic cell numbers were observed. Although there are no corresponding data before the earthquake from the same sites, it is likely that the subsurface peaks in prokaryotic cell numbers and meiofaunal density resulted from the sedimentation events. The effects of sedimentation events on the organisms were observed 2.5 years after the earthquake, indicating that episodic sedimentation events on scales of several centimeters have a large effect on small organisms inhabiting sediments.