Plastics from Surface to Seabed: Vertical Distribution of (Micro)plastic Particles in the North Pacific Ocean

In this study, the vertical distribution of microplastic items across the water column and deep-sea sediments in the North Pacific Ocean, at depths exceeding 5 km, was investigated, covering two previously detected hotspots of surface-floating plastic items, the North Pacific Subtropical Gyre and the World Heritage Site Papaha̅naumokua̅kea Marine National Monument, and a less polluted open ocean site between them. Concentrations ranged from 8 to 2600 items m^-3 in the water column and 1100 to 3200 items kg^-1 in sediments, with distinct distribution patterns between stations. Our results demonstrate that microplastics are ubiquitously distributed vertically throughout the study sites in the North Pacific Ocean. The similar polymer composition across the samples, dominated by polyethylene and polypropylene, suggests that the plastic items originate from surface fallout, indicating vertical transport as a crucial dispersion pathway. The high abundance of small plastics at the analytical size detection limit of 11 μm is particularly concerning and underscores the necessity to analyze even smaller particles. This study substantially contributes to narrowing critical knowledge gaps regarding distribution and transport pathways of marine plastics in the North Pacific Ocean and provides crucial information for environmental management and policy actions.