||The complex interplay between tectonic and climate activities shapes the Earth’s surface and produces large amounts of sediments conveying from land to the sea. Therefore, more than 20 billion tons of sediments is exported to the ocean each year. There is approximately 70% of the global fluvial sediment discharge from the orogens in southern Asia and high-standing islands fringing the Pacific and Indian Oceans. The contribution by small mountainous rivers (SMR) to the world ocean’s sediment budget in this region, although significant, has often been underestimated. Therefore, the research in the sediment dynamics is necessary for evaluating the sediment budget from SMR to the basin.|
The Gaoping River (GPR) has high sediment yield whose ranking is the 12th in the world and connects to the head of the Gaoping Submarine Canyon (GPSC) just 1 km apart. Moreover, the GPSC cuts through the Gaoping shelf and slope and merges into the Manila Trench which eventually links to the South China Sea. Therefore, this dispersal system is an ideal play for studying the dynamics of the source-to sink (S2S) processes.
This dissertation presents field investigations in the GPR estuary, hypopycnal plume area, and GPSC. Because of the complexity of the GPR-GPSC dispersal system, multidiscipline and different approaches were adopt in the different region in the system. In the estuary and the plume area, both temporal and spatial schemes were conducted to measure the hydrodynamic, hydrographic, water samples, and sediment samples. In the GPSC, three sediment trap moorings with CTD, OBS, and ADCP were deployed during the dry, flood season, and after the typhoon, respectively.
In the estuary, the interaction between river flow and tidal oscillation produces two layered circulation which flows downstream in the top-core layer and upstream in the near bed layer. A dynamic sediment barrier was found in the lower reach of the estuary. Except extreme floods, river effluents spread over the coast seawater through the hypopycnal processes. Most effluent sediments transport along the coastal jet and deposit in the coastal or near-shore ocean. In the GPSC, canyons, major sediment transport and rapid sediment deposition occur in the benthic nepheloid layer (BNL). Sediments in the hyperpycnal plume are trapped in the head region of the submarine canyon during the normal condition and flow down the canyon conduit to the deep basin during extreme floods. We also captured the warm water and suspended sediment carried by passing turbidity currents that originated in the adjacent GPR.