Simulation of seasonal transport of microplastics and influencing factors inthe China Seas based on the ROMS model

Elucidating the mechanisms governing microplastic transport and spatial distribution in offshore waters isessential to microplastic control. However, current research on microplastic transport in the China Seas is largelyrestricted to small-scale investigations, which do not provide a comprehensive result. Therefore, in this study, weused the Regional Ocean Modeling System (ROMS) combined with the Lagrangian Transport (LTRANS v.2)model to investigate how microplastics are transported around the China Seas during different seasons and underclimatological river discharge. Our findings showed that the microplastic pathways and spatial distributionsexhibit marked seasonal variations controlled by circulation patterns in the China Seas, river discharge values,and the characteristics of the microplastic materials. Floating microplastics exhibited the longest transport distancein summer, when microplastics from the Pearl River could be transported up to 1375.8 km through theTokara and Tsushima straits. The heavy pollution areas in summer were located in the South Yellow Sea and EastChina Sea, mainly resulting from the contribution of the Yangtze River (>66%). In autumn and winter, morethan three-quarters of the microplastics beached off the south-central Chinese coast. In addition, simulating thevertical velocity of the water prolonged the time required for microplastics to reach the open ocean, therebyreducing the amount of microplastics entering the Pacific Ocean by 6% compared to the simulation without thevertical velocity of the water in summer. Microplastics with higher densities were generally transported shorterdistances. The transmission distances of PET and PS were two orders of magnitude smaller than that of PE. Thisstudy enhances knowledge of the sources and fates of offshore microplastics and provides scientific support foroffshore microplastic control.