Investigations into flushing of pollutants in the Irish Sea

We applied the three-dimensional general ocean and coastal circulation model to the Irish Sea in order to determine water renewal time scales in the region. The model forcing functions comprised of tides, meteorological forcing, including wind stress and calculations of heat fluxes, river discharges and temperature fluxes at the open lateral boundaries. The calibrated barotropic and baroclinic model accurately reflects temperature fields and water circulation in the Irish Sea, including such important features as the Western Irish Sea Gyre, a cyclonic density-driven circulation developing in the western Irish Sea during spring and summer each year. We carried out several simulations to investigate the importance of various forcing functions upon flushing of the Irish Sea. The net flow through the Irish Sea is highly variable throughout the year due to the joint action of wind and density gradients; the net flow is northwards and the yearly average flow equals c.2.50 km ³/d. The barotropic and baroclinic model predicted average residence times of the Irish Sea region of 386 and 444 days in the cases of passive tracer transport simulations commencing in June and December, respectively. We showed the slackening effects of baroclinic circulation on water renewal in the region, as the results obtained from the model forced only with tides indicate c.27% decrease in the predicted value of the average residence time. Interestingly, there is no substantial difference in the estimates of average residence times of surface layer and the entire water column. The obtained results indicate strong spatial and temporal variability in flushing rates indicating that careful management approach is required.