AbstractA key factor in understanding both the environmental impact of a leak from a CCS system and how to design appropriate monitoring tools is an understanding of the dispersal of a CO2 plume in seawater. The natural, tidally driven dynamics of regions such as the CCS targeted North Sea make this highly non-trivial. In the work described here we have adapted a fine scale model of marine hydrodynamics to include CO2 relevant processes and simulated a range of hypothetical leak scenarios whilst also testing the impact of tidal variability and model configuration.