Tracing the sources of floating plastic in Romanian waters under changing regional pressures through backtracking modeling

This study presents an integrated assessment of floating marine macro litter (FMML) distribution and transport in the western Black Sea, based on visual observations conducted during a research cruise in July 2024. Eight transects were surveyed along the Romanian coast, revealing a marked contrast between coastal and offshore FMML densities. While nearshore stations showed relatively low concentrations, offshore transects beyond the Northwestern Shelf (NWS) exhibited densities exceeding 9000 items/km², primarily due to the presence of elongated white plastic strips. Lagrangian backtracking simulations using the LOCATE model identified distinct origin pathways: coastal FMML was linked to riverine systems such as the Danube, Dniester, and Dnieper-Bug, whereas offshore litter appeared to originate near the Crimean Peninsula. Persistent mesoscale cyclonic activity, revealed through analysis of the Q parameter, was found to create convergence zones that facilitate debris accumulation, with one particularly stable gyre located near 32°E and 44°N. These findings suggest the influence of both natural circulation and conflict-driven inputs on FMML distribution. The combined use of observational surveys, transport modeling, and circulation patterns offers a replicable framework for marine litter monitoring and supports science-based management strategies under evolving environmental and geopolitical conditions.