Tracer applications of radiocaesium in the sea of the hebrides

Radiocaesium isotopes released at the Windscale nuclear fuel reprocessing plant in Cumbria, U.K., serve as excellent tracers of coastal currents. The radiocaesium distributions in the Hebridean Sea were monitored during the summers of 1976 and 1977 and these imply major differences in water flow through the region in these two years. In 1976 the coastal movement of Irish Sea-derived water is explained by a flow, from the North Channel, of water having source radionuclide concentrations similar to those observed in the Clyde Sea area. Advective velocities of ∼1·6 and ∼5 km day −1 are implied for northward movement through the North Channel and Hebridean Sea respectively. In 1977, however, a much more extensive ‘coastal plume’ of Irish Sea-derived water could be correlated with increased flushing through the North Channel earlier in the year. Radiocaesium distributions in the Hebridean Sea are consistent with a clockwise water flow around the southern islands of the Outer Hebrides.