Modelling the transport of microplastic pollution across the Antarctic Circumpolar Current

Microplastic pollution is a ubiquitous marine environmental contaminant that is found in all the world’s oceans. The Southern Ocean is not exempt from microplastic pollution, with numerous studies reporting microplastics to be present in the region, including south of the Antarctic Circumpolar Current (ACC). However, the challenges involved in collecting data on microplastic pollution in the Southern Ocean mean there are large areas of the Southern Ocean where microplastic pollution levels are largely unknown. In addition, the processes and resulting transport pathways that move microplastic pollution across the ACC into the highly sensitive Antarctic marine ecosystem are not yet well understood.To tackle these knowledge gaps, we use a modelling approach to simulate the transport pathways of microplastic in the Southern Ocean, with a specific focus on cross-ACC transport. Specifically, we use the Lagrangian particle tracking framework OceanParcels, forced with ocean velocity fields from a Southern Ocean configuration of NEMO-LIM3 with 1/12॰ horizontal resolution. This model set up, which includes the effect of Stokes drift and sub-grid scale diffusion alongside underlying ocean currents, has allowed us to identify key regions where surface microplastic pollution may cross the ACC and potential hotspots of microplastic accumulation along the Antarctic coastline. We describe seasonal and inter-annual variability in microplastic transport through analysis of 22 years of model output, and suggest potential drivers of this variability. The results of our study will inform future field research into microplastic pollution in the Southern Ocean.