Microplastics (MPs) have been increasingly reported in deep-sea sediments, yet their occurrence and hydrodynamic controls in trench environments, particularly those influenced by contemporary turbidity currents, remain poorly understood. Here, MPs were extracted from surface sediments collected from the Manila Trench and analyzed together with regional sedimentary dynamics. MP abundances ranged from 133 to 193 items kg-1, with fibers and fragments dominating the assemblages. High-density polymers (polyethylene terephthalate and polyvinyl chloride) were more abundant than low-density polymers (polyethylene and polypropylene), and mean MP particle size increased significantly with water depth, suggesting a potential influence of hydrodynamic sorting. Episodic turbidity currents may facilitate the transport of MPs with different densities into the deep sea. During subsequent settling, low-density MPs may remain suspended for longer and undergo further transport by deep currents, whereas high-density MPs may settle more rapidly and be preferentially retained in the sediments. These pattern suggests that canyon-trench systems may act as potential transport pathways and depositional sinks for MPs in the deep ocean.
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