[A-OS19] Physical Oceanography (General)

[AOS19-06] Medium-term oceanic transport of microplastics in and around the South China Sea analyzed with climatological and synoptic models

*Kosei Matsushita¹, Yusuke Uchiyama¹, Naru Takaura¹, Taichi Kosako² (1.Kobe University, 2.Port and Airport Research Institute)

Keywords:Microplastics, the South China Sea, Particle tracking model, monsoons, mesoscale eddies, El Niño

Lagrangian particle tracking experiments were conducted to evaluate the transport of microplastics (MPs) derived from the four major rivers, i.e., Pearl , Han (China), Mekong (Vietnam), Pasig (Philippines) rivers, that have been known to discharge a huge amount of plastic wastes into the South China Sea (SCS). We carried out two types of the experiments: 1) 2D tracking of MP particles placed at surface to represent positively buoyant (light) MPs, and 2) 3D tracking of neutrally buoyant MP particles that are passively transported by ambient flow, using the pre-computed 3D current velocity field by the HYCOM-ROMS downscaling model at a lateral resolution of 5 km for the SCS. We released more than 1 x 10⁵ particles continuously for the four-year period from 2012 to 2015 into the synoptic model and for one year into the climatological model. The MP particles are discharged at the mouths of the four major MP-source rivers located in the SCS. The comparative synoptic and climatological experiment enables us to analyze the seasonal and inter-annual variability of the river-derived MP transport. The seasonally varying monsoons in the SCS are found to provoke strong seasonal variability in the river-derived MP transport. We found that mesoscale eddies generated along the east coast of the Philippines promote westward transport and accumulation of the MPs from Pasig river. The comparative experiments also allow extracting medium-term climatological variability in the MP transport in the El Niño years (2014-2015).