Anthropogenic sources and oceanographic dynamics control the microplastic distribution in the Atlantic Ocean

This study investigated the influence of oceanographic dynamics on marine microplastic (MP) distribution and identified wastewater and greywater emissions as relevant sources. In June 2021, sub-surface water samples were continuously collected during steaming at a depth of 4 meters along five transects, spanning 1600 nautical miles from the Norwegian coast to Bear Island in the Arctic Ocean. MPs (>10 µm) were analyzed using Fourier-transform infrared imaging micro-spectroscopy, revealing concentrations ranging from 7 to 491 items m⁻³. Elevated MP levels near the Norwegian coast (max 399 items m⁻³) were linked to discharges from wastewater discharges, including greywater from ships, with polyester dominating, followed by polypropylene and acrylates/polyurethanes/varnish. The highest concentrations were observed near the remote Bear Island, likely driven by oceanographic features such as the Polar Front and mesoscale eddies, which can trap and accumulate MPs. Our results were compared to a parallel study analyzing stationary samples from the same cruise, revealeing systematically higher MP concentrations in underway samples and highlighting the importance of sampling strategies for inter-study comparisons. Overall, this study underlines the complexity of MP distribution and the combined roles of wastewater and greywater emissions, ocean current patterns, and frontal zones in understanding MP pollution in marine environments. Wastewater discharges, including ship greywater, elevate microplastic concentrations near the Norwegian coast, while oceanographic features like the Polar Front and mesoscale eddies concentrate the highest levels near the remote Bear Islands, according to sub-surface water sample analysis.