Microplastics affect marine snow formation and sinking to the ocean's interior

Microplastics (MPs) are ubiquitous in the ocean and increasingly found embedded within marine snow (MS), organic-rich particle aggregates that play a central role in vertical carbon and MP flux. This study combined laboratory and onboard incubations to investigate how MPs influence the formation and sinking behavior of MS aggregates. Our data indicated that MPs significantly enhanced MS aggregation in both settings, likely by providing hydrophobic interfaces that promote entanglement and adhesion with organic matter. The polymer density and morphology of MPs further modulated aggregate sinking dynamics and structure. Dense polyethylene terephthalate (PET) pellets formed fast-sinking aggregates, whereas buoyant polyethylene (PE) and fibrous PET formed looser, slower-sinking structures. These differences often resulted in sinking rates lower than theoretical predictions, especially for larger and more irregular aggregates. Our findings suggest that MP incorporation into MS can enhance aggregate production, alter settling rates, and facilitate MP entry into food webs, with potential consequences for carbon transport and marine ecosystems.