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Heterogeneous seafloor deposition of heavy microplastics in the North Pacific estimated over 65 years
Summary
Using a massive computer simulation tracking over 577 million particles, this study modeled where heavy (dense) microplastics sink to the seafloor in the North Pacific over 65 years. The results showed that 22% of heavy microplastics traveled more than 100 kilometers from where they entered the ocean before settling, carried by powerful currents like the Kuroshio. Deposition patterns were highly uneven — creating distinct hotspots on the seafloor — and have accelerated sharply since the 2000s. This research highlights how the ocean floor is becoming an increasingly significant long-term reservoir for plastic pollution.
Marine plastic pollution has been a public concern for many decades; however, transport processes of heavy microplastics to the seafloor have long been overlooked given the difficulties in sampling and modeling. The distribution of heavy microplastic deposition on the seafloor in the North Pacific for 65 years since 1951, was estimated using a particle tracking model with 577,143,840 particles. The model revealed that 22 % of heavy microplastics were deposited over 100 km offshore from their release locations. Strong currents, including the Kuroshio Current and Equatorial Counter Current, advected the heavy microplastics offshore; however, the behaviors of different-sized microplastics with different sinking velocities made the seafloor deposition heterogeneous. The seafloor was separated into six (three) clusters based on the origins (composition of sinking velocity categories) of the deposited microplastics. Deposited microplastics showed a rapid increase since the 2000s even for the open ocean far from emission sources.