Core Program

Integrated Marine Geological and Biological Investigations of the Suruga Trough and related regions

The Suruga-Nankai Trough regions represent complex geomorphological features related to plate tectonics and active volcano-sedimentary-erosional processes occurring on the seafloor around island arcs such as Japan (Fig.1).
In this project, we propose that those sedimentary topographies are formed by submarine turbidity currents mainly triggered by fluvial hyperpycnal (high-density) flood water along the plate subduction boundary. Such flood-induced turbidity currents are not only responsible for sedimentation and erosion but also provide nutrients and organic matter from terrestrial to deep-marine environments. Turbidity currents charged by abundant terrestrial-human products therefore would have a very large impact on the ecology of marine organisms, carbon burial, and dispersal of anthropogenic materials.
We have chosen the Fuji River-Suruga Trough region as a model field to test our models. Our goal is to verify the flood-induced turbidity currents that occur in this region and is to prove that the event enhances marine production, heavy marine snow-fall and the creation of a hot ecological events. We plan to detect the events of turbidity current using newly developed detection apparatus and current-profiling buoy-system. This project aims to observe the entire flow process from river flood to deep-sea turbidity current transformation. We have been working together with other organizations (Waseda University, MaOI Institute at Shizuoka, AIST and JAMSTEC) to analyze the ecological parameters including environmental DNA-based genetic information of both microbes and higher organisms living there, together with flow simulation model. Integrating the above lines of studies, we will be able to merge for the first time, geological processes, ecological dynamics, and environmental impacts of turbidity current activities active within these regions where the human activities and deep-sea environments are so closely connected.

Figure 1. Geomorphology of the Suruga and Eastern Trough region. The upper left figure shows plate tectonics around Japan. The Nankai-Suruga Trough is a part of the subduction boundary of the Philippine Sea Plate under the Eurasia Plate. To the east of Suruga Trough, the strong compression tectonics-dominated area where the Izu-Ogasawara Island arc collides against the Honshu arc is called the Izu-Collision Zone. The main geomorphological map is produced by ELSAMAP cartography of Kokusai Kogyo Co., Ltd., which enhances the steepness of the slope by reddish coloring. Fan-delta (marine steep-slope fan developed in front of the delta) of the Fuji River, Suruga Trough, Nankai Deep-sea Channel, Tenryu Submarine Canyon, and Shionomisaki Submarine Canyon are shown from Taira, A. & JAMSTEC (2020).