Diving into the deep: unveiling small microplastics in Norwegian coastal sediment cores

High concentrations of microplastics (MPs) have been documented in the deep-sea surface sediments of the Arctic Ocean, yet studies on the high-resolution vertical distribution of MPs in sediment from European waters to the Arctic are scarce. The European-wide project FACTS (Fluxes and Fate of Microplastics in Northern European Waters), funded by JPI Oceans, aimed to address the vertical transport of MPs in this study area. This study examines MPs in five sediment cores collected from the Norwegian Coastal Current (NCC), encompassing the water-sediment interface and sediment layers up to 19 cm depth. Advanced analytical methods for MP identification down to 11 μm in size were combined with radiometric dating and lithology observations. Our findings reveal the widespread presence of MPs across sediment cores, spanning layers predating the mass production and introduction of plastics. MP concentrations exhibit significant variation across the sediment cores with the smallest size class (11 μm) predominating most sediment layers. A total of 18 different polymer types were identified across all the sediment layers, with correlations between polymer diversity and depth showing high variability between stations. Our results suggest that differences in seafloor topography and the impact of anthropogenic activities (e.g. fishing) lead to varying environmental conditions at the sampling sites, influencing the vertical distribution of MPs. This calls into question the reliability of using environmental parameters to predict MP accumulation zones and MPs in sediment cores as indicators of the Anthropocene.