From the highest to the deepest: The Gaoping River–Gaoping Submarine Canyon dispersal system

Abstract

There are many different source-to-sink dispersal systems around the world, and the Gaoping River (GPR)–Gaoping Submarine Canyon (GPSC) provides an example especially as a canyon-captured system. The GPR, a small mountainous river having an average gradient of 1:150, and the GPSC, which links the river catchment to the deep-sea basin, represent two major topographic features around SW Taiwan. Together, they constitute a terrestrial-to-marine dispersal system that has an overriding impact on the source-to-sink transport of sediment in this region. The GPSC extents from the mouth of the GPR through the shelf and slope and into the northeastern Manila Trench, a distance of about 260km. It is a major conduit for the transport of terrestrial sediment and carbon to the South China Sea and the landward transport of particles of marine and biological origin.In the GPSC the dominant mode of suspended-sediment transport is tidal oscillations and the net direction is up-canyon. In contrast, sediment transport associated with episodic gravity-driven events is down-canyon. The steady sedimentation of the tidal regime results in hemipelagic mud across the canyon floor, whereas the gravity-driven (hyperpycnal) regime causes turbidite erosion and deposition along the canyon thalweg.Typhoon-induced river floods often lead to hyperpycnal plumes at the river mouth, which directly and indirectly ignite hyperpycnal turbidity currents in the canyon forming an effective agent for transporting large amounts of terrestrial organic material (modern and fossil carbon) to the South China Sea basin. Therefore, the GPR–GPSC represents a source-to-sink system in which terrestrial sediment in a mountainous catchment is promptly removed and transported to the deep sea by episodic gravity flows. This is also a pathway by which modern terrestrial organic carbon is quickly and effectively delivered to the deep sea.