WAVES AND BEACH: COMPARING POTENTIAL MECHANICAL FRAGMENTATION OF PLASTIC LITTER AT OCEAN COAST ACROSS LATITUDES

Abstract

Mechanical fragmentation of plastic litter in the surf zone is one of the key but least controlled processes of secondary microplastics (MPs) generation in the ocean. This study presents a quantitative assessment of the mechanical fragmentation potential along the coasts of the Pacific and Atlantic Oceans (from 54 °N to 54 °S), based on an analysis of significant wave height data (database sail.ocean.ru, 1963–2022) and beach sediments of various types (coarse sand, granules, fine and coarse pebbles). The maximum fragmentation potential is reached in January on the eastern Pacific coast at latitudes 34–54 °N, under the combination of wave heights ≥3 m and pebble-boulder beaches. In summer, the potential decreases approximately threefold even on coarse-clastic shores. Sandy beaches in all studied areas yield 1–2 orders of magnitude lower MPs output. The hemispheric asymmetry index shows a shift in dominance: for example, in January, the Northern Hemisphere dominates on the western Atlantic coast (0.31), while in July, the Southern Hemisphere dominates (−0.43). MPs concentrations on sandy beaches reported in the literature are explained by the accumulation of externally supplied particles rather than by local generation. The identified “hot spots” of mechanical fragmentation can serve as a basis for predicting pollution risks in coastal zones.