Drift of buoyant objects in the Baltic sea – model data analysis

Marine debris and pollution of the sea is well recognized problem. Knowledge of the potential destination and time of arrival for buoyant or nearly buoyant contaminants as, for example, microplastics, is necessary for effective policy planning.

This work analyzes characteristics of buoyant objects in the Baltic Sea using simulations of Lagrangian particle movement. Simulations are based on current and wind model data. Initially particles are regularly distributed (spaced 5 km) over the Baltic Sea and a new simulation and particle release is started every day over a period of 10 years – years 2008-2017. It is assumed that upon reaching the coast particle gets washed out on the coast.

The aim of this work was to acquire following 3 drift characteristics for possible buoyant object movement in the Baltic Sea:

1. How many days does it take from different regions of the Sea to reach the coast, what regions (clusters) can be identified that share similar behavior for different seasons;
2. Which coastal regions are most at risk – which regions get particles washed out the most;
3. What are main pathways for the particles – which sea regions affect which coastal regions the most.

As the distributions of floating time and location are non-normal then the methods of Symbolic Data Analysis (SDA) were used. To be more exact, statistics from each sea point or coastal segment was described by empirical distribution function (histogram) and differences/similarities were calculated using squared Wasserstein distance. The simulations cover multiple seasons – therefore the difference between seasons is also examined for each of 3 drift characteristics.

Part of the research is supported from the Latvian Academy of Sciences, project lzp-2018/1-0162 DRIMO - DRIft MOdelling for pollution reduction and safety in the Baltic Sea, 2018 - 2021.