Identification potential sources of marine debris based on backward trajectory modelling in Tidung Island

Marine debris poses an increasing threat to the coastal ecosystems of the Seribu Islands, particularly Tidung Island, where hydrodynamic influences on debris transport remain poorly understood. This study simulated the movement and seasonal origin of floating debris using backward modeling integrated with validated hydrodynamic and Lagrangian modules in OpenFlows FLOOD. The model, forced by tidal, wind, and bathymetric data, showed strong agreement with the field observations, with correlation coefficients of 0.84–0.94, and RMSE values of 0.069–0.097 across tidal elevation and currents. Simulations under contrasting monsoon conditions revealed current velocities of 0.10–0.28 m/s during the west monsoon and 0.03–0.24 m/s during the east monsoon, producing southwestward flow in the west season and weaker northwestward circulation in the east. Backward analysis showed that during the western monsoon, offshore debris from the northern Java Sea was advected southward and accumulated near Tidung Island, whereas during the east monsoon, debris mainly originated from local activities and remained confined due to weak circulation. These findings highlight the dual role of Tidung Island as both a receiver of offshore debris and a trap for local waste, underscoring the need for stronger community management and integrated policy actions to reduce marine debris.