The Ryukyu Trench may function as a 'depocenter' for anthropogenic marine litter

While concern over anthropogenic marine litter around coastlines is increasing worldwide, information on this litter in trenches on the seafloor is very sparse. We investigated the amount of marine litter on the deep-sea bottom around the Ryukyu Islands in the Northwest Pacific, based on trawl samples. The density of litter observed in the axis of the Ryukyu Trench (7100 m) and in the basin of the Okinawa Trough ranged from 1.2 × 103 to 7.1 × 103 items km−2, or 7.5–121.4 kg km−2, which was significantly higher than that observed on the adjacent shallower continental slopes or abyssal plain (0.1 × 103 to 0.6 × 103 items km−2; 0.03–9.2 kg km−2). This suggests that trenches and troughs function as “depocenters” for anthropogenic litter because of their deeper and enclosed topographies.