Departmental Bulletin Paper Influence of dam reservoir on deep marine sedimentological environment : An example of the Kumano Trough, central Japan

Shirai, Masaaki  ,  Omura, Akiko

(51)  , pp.119 - 126 , 2016 , Department of Geography, Tokyo Metropolitan University
Sedimentation rate (mass accumulation rate; MAR) of surface hemipelagic sediments in the Kumano Trough, a forearc basin approximately 2000 m deep off the eastern Kii Peninsula, central Japan, was estimated from excess Pb-210 radioactivity profile and dry bulk density of the core sample. The estimated excess Pb-210 radioactivity profile was subdivided into three segments. The top segment was inferred to be affected by biological mixing in the surface mixing layer (SML). In contrast, a difference between segment-2 and segment-3 would reflect decease in MAR. With a simple model, the influence of the biological mixing and boundary age between segment-2 and segment-3 were estimated. The relationship between decreasing age of hemipelagic sediment MAR in the Kumano Trough (1950s) and dam construction age (1950s–1960s) was reasonable. Additionally, the relationship was supported by similarity in sediment grain size of dam reservoir and hemipelagic environment. Consequently, the construction of dams probably influences the deep marine hemipelagic environment of the forearc basin 2000 m below sea level.

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