Manned submersible dives in the northwest South China Sea encountered substantial amounts of plastic litter accumulated at the base of scours along the floor of a submarine canyon, which may associate with the depositional behaviors of turbidity currents. In this study, we conduct numerical simulations using field-scale bathymetry to investigate the relationship between the canyon floor morphology, flow processes, and the locations and sizes of the plastic litter piles. The consistent deposition pattern caused by the numerical turbidity currents with different input parameters indicate that morphology of the canyon may exert a dominant influence on turbidite deposition. This is attributed to a significant reduction in shear velocity as simulated turbidity currents flowing through the scours on the canyon floor. Spatial correspondence between deposits of turbidity currents and plastic litter accumulation suggests that suspended sediments and plastic may undergo simultaneous dynamic processes during the transportation of turbidity currents.
The issue of marine plastic litter has attracted wide attention, particularly in terms of its transportation mechanisms and locations of accumulation on the ocean floor. Turbidity currents are subaqueous sediment-gravity flows that can transport large amounts of sediment, nutrients and pollutants into the deep sea, yet there is sparse research on the dynamics of plastic litter transport under the control of turbidity currents, and its accumulation in the deep sea. Here, we present a series of numerical simulations of turbidity currents in a submarine canyon with various input parameters, when combined with observational data on topography and plastic litter distribution, confirm that turbidity currents constitute a plausible mechanism for the transport of plastic litter and for its accumulation in response to changes in flow associated with scours. In addition, we find that the concavity of the scours is also necessary for plastic litter accumulation, since it induces significant fluctuations in the shear velocity and the corresponding depositional process.
Numerical simulations were applied to investigate turbidity currents as a cause for plastic litter accumulations in a submarine canyon The simulated turbidite deposits and observed plastic litter accumulations exhibit a strong spatial correspondence The morphology of the canyon floor may exert dominant influence on the plastic litter accumulations in submarine canyons