Marine plastic pollution has become a major global environmental challenge, yet existing ocean plastic models often oversimplify the transport and transformation of plastics, limiting their capability to simulate long-term environmental fate and project future changes under different emission and climate scenarios. Here we present an integrated ocean plastic cycling framework developed within the Parallel Ocean Program (POP2) of the Community Earth System Model (CESM).
The model explicitly simulates the transport and fate of marine plastics under a unified mass-conserving framework. It incorporates polymer-specific density, particle size distributions, dynamic biofouling, calcium carbonate ballast, vertical buoyancy transitions, surface transport, beaching, sedimentation and resuspension, biological ingestion, and sea-ice trapping, enabling plastic exchanges among the ocean surface, three-dimensional ocean interior, beaches, marine sediments, and sea ice.
A key innovation of the framework is the explicit coupling of polymer properties with dynamic surface coating processes. Rather than prescribing fixed sinking velocities or empirical surface drift, the model allows the effective density of individual plastic particles to evolve through biofilm growth and mineral ballast, leading to realistic transitions among multiple environmental compartments. A second innovation is the separation of active and permanently buried reservoirs for both beaches and marine sediments, enabling independent diagnosis of beaching, resuspension, weathering, and long-term burial, instead of treating coastal deposition as an irreversible sink.
Model performance is evaluated against available global observations of marine plastics across multiple environmental compartments. Built upon the CESM Earth system modeling framework, the model provides a scalable platform for coupling marine plastics with atmospheric, terrestrial, and cryospheric processes. This work lays the foundation for a fully coupled Earth system model of plastics, providing new opportunities to quantify the global plastic cycle and assess the impacts of future plastic emissions and climate change on the environmental fate of plastics.

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