The deep sea is increasingly recognized as vulnerable to anthropogenic pressures, including marine litter, yet large geographic gaps remain in our understanding of litter distribution and ecological interactions. Submarine canyon systems can act as conduits and accumulation zones for anthropogenic material, but data from the southwestern Atlantic are scarce. Here, we present the first characterization of deep-sea marine macro-litter in the Mar del Plata Submarine Canyon (Argentina), based on 240 hours of remotely operated vehicle (ROV) video collected during 17 dives (878-3,820 m depth) aboard the R/V Falkor (too) in July-August 2025. Litter was observed during 10 dives, comprising 29 items distributed between 1,120 and 3,820 m. Plastic was the dominant material (27 items), followed by rubber (2 items). Most litter consisted of plastic sheets and bags, food wrappers, and commercial fishing-related gear, including lines, ropes, and cables. Litter was observed in multiple settings, including buried or degraded items, resting on the seabed, and trapped among rocks or drifting near the bottom. Most items were located within the canyon domain, forming localized clusters along the canyon axis and walls. Litter-fauna interactions were documented for seven items and included both sessile colonization and associations with mobile fauna, mainly on partially buried plastic items and entangled fishing-related gear. These patterns suggest that substrate stability and residence time may influence sessile colonization. The composition and distribution of debris indicate that maritime activities, particularly fisheries, are the most likely sources and further support the role of submarine canyons as accumulation zones for marine litter. This study provides critical baseline data in an understudied region and highlights the need for improved monitoring programs and management strategies for marine litter to reduce impacts in submarine canyon systems.
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