[M-IS17] Ocean Plastics, an earth science perspective

[MIS17-04] Numerical analysis on marine microplastic transport in Hiroshima Bay

*Yusuke Uchiyama¹, Motoki Ubara¹, Taichi Kosako², Shoma Hikino³ (1.Graduate School of Engineering, Kobe University, 2.Port and Airport Research Institute, 3.Kyoto Prefectural Chutan Regional Promotion Bureau)

Keywords:microplastics, Lagrangian transport and dispersal, Regional Ocean Modeling System (ROMS)

A detailed numerical analysis on the oceanic transport of marine microplastics (MPs) in a semi-enclosed estuary, viz., Hiroshima Bay, was performed using a high-resolution 3-D Seto Inland Sea circulation model coupled with a Lagrange particle tracking model. The MP transport in Hiroshima Bay is characterized by southward transport along the west coast of the bay, discharge at the bay mouth east of Suo-Oshima Island, and stagnation in the multi-island inner bay area. These transport patterns are well explained by the counterclockwise estuarine circulation and the intensification and degeneracy of the surface mixed layer affected by baroclinic instability, which are seasonally varied by river discharge and surface cooling. The sink-source relationship of MP was further discussed through a comparison of the results of field surveys and the modeled destination strength that reflects geographical collectivity of MP particles.