Radioactive species in sea water

Radioactive species, in the dissolved state in sea water, can serve to define rates and directions of water movement. The requirements for such applications are that tracer species be soluble, chemically conservative, of half-life compatible with the process timescale under study and have non-uniform inputs. Boundary and point source inputs generate concentration gradients induced by the known-rate kinetics of radioactive decay. Advection-diffusion and box-model treatments are widely used in data interpretation and examples of a range of applications, based on 14C, 222Rn, 228Ra and fallout nuclides, are presented. Reactive nuclides such as 228Th and 210Pb can, on the other hand, be used to trace the fate of many heavy metals introduced into the marine environment. The release of waste from the nuclear industry provides a very convenient source of tracers for coastal waters. This application is illustrated by several studies of Windscale-derived radio-caesium in Scottish waters. (author)