Pathways of suspended particles transport in the bottom layer of the southern Baltic Sea depending on the wind forcing (Numerical Simulation)

A random-walk model for a nonuniform diffusivity media coupled with an ocean circulation model has been applied to describe the pathways of suspended particles transport in the bottom boundary layer (BBL) of the southern Baltic Sea. The circulation model is based on the Princeton Ocean Model, in which the vertical grid size is logarithmically refined towards the bottom in order to resolve the BBL. Fields of the flow velocity and eddy diffusivities simulated by the POM, along with the settling velocity of the suspended particles, are used as an input for the random-walk model. A number of numerical experiments were performed to study the pathways of suspended particles in the southern Baltic BBL depending on the wind conditions. In particular, the suspended particles introduced into the BBL in the center of the Bornholm Basin at westerly and southerly winds are found to be trapped in the basin provided that the particles’ settling velocity is equal or greater than 2 m/day. The trapping phenomenon is explained by the combined effect of the Ekman transport convergence in the BBL due to the cyclonic gyre and the gravitational settling of the particles.