Baltic Amber Migrations as a Model of Microplastics Behavior in the Sea Coastal Zone

The problem of microplastic pollution is of increasing concern. Behaviour of microplastic particles (0.5 mm < L < 5mm in the largest dimension) in marine environment is difficult to predict, and no field observations are available up to now. Baltic amber (succinite), with its density of about 1.05-1.09 g/cm3, fits the range of densities of slightly negatively buoyant plastics: polyamide, polystyrene, acrylic, etc. Baltic citizens have observed amber migrations for centuries, and the collected information may shed some light onto general features of microplastic particles behaviour. Events of “amber washing-out” at the sea shore of the Sambian peninsula (Kaliningrad oblast, Russia) typically take place in autumn-winter time. Experience of divers indicates that amber is washed out from the depths as deep as 15 m. Massive presence in amber-containing debris of the red algae Furcellaria lumbricalis, dominating in the sea at depths of 6-15 m, proves this fact. From oceanographic viewpoint, important for the “amber washing-out” are: strong and long-lasting storm, phase of wind decrease or direction change, developed long surface waves, shore exposure to wind. Analysis of characteristic wave lengths after long storms, dimensions of their surf zone, and changes in underwater bottom profile is carried out. Conclusion is that slightly negatively buoyant microplastic particles should migrate for a long time between beaches and underwater slopes until they are broken into small enough pieces that can be transported by currents to deeper area and deposited out of reach of stormy waves.