Many recent studies have indicated the abundance of anthropogenic polymers with a long period of degradation across the World Ocean – from the Arctic to the Antarctic – located everywhere from the surface to the bottom. Small plastic particles – microplastics – are the most environmentally hazardous type because of their harmful impact on marine biota. However, there is currently significant uncertainty regarding their physical properties, which may vary in time due to the particles’ biofouling or degradation, and their pathways in the sea. In order to fill this knowledge gap, our team is conducting a research project aimed at investigation of physical characteristics and dynamical properties of microplastic particles gathered in the water column and bottom deposits of the Baltic Sea. This project, entitled MicroplAstics Research in the BaLtic marine Environment (MARBLE), is funded by the Russian Science Foundation, project # 15-17- 10020. The research team is based on the Laboratory for Marine Physics LAMP of the Atlantic Branch atlantic.ocean.ru of P.P.Shirshov Institute of Oceanology www.ocean.ru of Russian Academy of Sciences www.ras.ru.