Ingrid Linck Rosenhaim

• Ballast water is essential for a ship’s safe navigation and to compensate for weight changes during the load and unload of cargo. However, it is considered one of the main vectors for the transfer of aquatic organisms worldwide. These organisms can survive the voyage and discharge, reproduce, and become invasive to the host environment. With the decrease of sea ice extent in the Arctic seas, shipping has been increasing in the region, and it will keep growing. This study aims to identify areas where the discharge of ballast water represents the risk of contamination of ecosystems along the main Arctic shipping routes. For that, a series of passive tracer experiments are conducted using the regional coupled ocean-sea ice model, NAOSIM. The ballast water tracer (bw-tracer) is discharged in the model at selected ship positions. The model results show that the bw-tracer starts to accumulate at the end of spring, and its concentration increases during summer and autumn. In the west Spitsbergen sector, the bw-tracer is mainly transported by the West Spitsbergen Current and the East Greenland Current. Water recirculation between south Spitsbergen and Bear Island created an area of tracer accumulation. In the Barents Sea sector, the bw-tracer starts to accumulate south of Novaya Zemlya at the end of spring. Tracer concentration increase during summer and autumn. Particle trajectories demonstrated that organisms could be advected by the ocean surface currents to coastal ecosystems while presenting different pathways from the tracer. Tracer mixing is enhanced by the turbulent horizontal flow and vertical convection, being dependent on the mixed-layer seasonality. Eddy kinetic energy is correlated to the mixing of bw-tracer, and the displacement of particles along the trajectory pathways. Areas of tracer accumulation are indicators of high propagule pressure of non-indigenous species. That increases the chances of survival, reproduction, and establishment of invasive species.