Microplastics have become a major marine pollutant, even reaching remote locations such as the Arctic. To date, the relative contributions of microplastics originating from riverine and oceanic sources in the Arctic Ocean are relatively unknown. This study focuses on modeling the pathways and relative contributions of microplastics from several oceanic and riverine sources into the Arctic Ocean. To our knowledge, this is the first such a comprehensive investigation of microplastics in the Arctic Ocean. It aims to provide a baseline for guiding future observational studies of marine microplastic pollution, which in turn, should help constraining models to better understand and interpret its origins and extent in the Arctic Ocean.

We use the Regional Arctic System Model (RASM) with multiple passive tracers, representing marine microplastics originating from different sources (the Barents Sea, North Pacific, Eurasian and North American rivers), to investigate their pathways and relative contributions in the central Arctic Ocean from a 40-year (1979 to 2021) RASM hindcast simulation. The majority of microplastics are buoyant, hence they are transported in the ocean by surface currents, which are strongly influenced by near-surface winds. Given that passive tracers introduced in RASM follow water masses, including their mixing and transformation, we diagnose the modeled pathways of buoyant microplastics only at the surface layer, while their relative contributions are quantified based on tracer concentrations over the upper 50 m depth range of RASM. In this presentation, model results are summarized to address the following three hypotheses: (i) the anticyclonic Beaufort Gyre in the western Arctic acts as the northernmost convergence zone for the accumulation of microplastics, (ii) the majority of microplastics in the Arctic Ocean originate from the lower latitude oceans, and are advected northward with the surface currents, and (iii) the relative contribution of microplastics from the Eurasian rivers is larger than that from the North American rivers draining into the Arctic.