Spatial pattern of current-driven hits to the nearshore from a major marine fairway in the Gulf of Finland

The spatial pattern of hits to the nearshore by tracers originating in a major fairway in the Gulf of Finland and transported by surface currents is analysed based on Lagrangian trajectories of water parcels reconstructed using the TRACMASS model from three-dimensional velocity fields by the Rossby Centre circulation model RCO for 1987-1996. The probabilities for a hit to different parts of the nearshore and the ability of different sections of the fairway to serve as starting points of tracers (equivalently, certain type of nearshore pollution) have extensive seasonal variability. The potential of the fairway to impact the nearshore in this manner is roughly inversely proportional to its distance from the nearest coast. A short section of the fairway to the south of Vyborg and a segment to the west of Tallinn are the most probable starting points of tracers. The most frequently hit nearshore areas are short fragments between Hanko and Helsinki, the north-eastern coast of the gulf to the south of Vyborg, and longer segments from Tallinn to Hiiumaa on the southern coast of the gulf.