USING RADIUM ISOTOPES TO STUDY COASTAL MIXING PROCESSES

Naturally occurring radium isotopes are produced by thorium decay in the sediments. In the coastal ocean, the activities of radium isotopes change by decay and coastal transport processes. Short-lived radium isotopes (²²³Ra, ²²⁴Ra) have been used in the coastal ocean to calculate offshore coastal mixing rate (Moore, 2000). But in Moore’s method, advection was not considered in setting up the mass-balance equation, which makes it not suitable for coastal environments where advection is significant. As an attempt to study coastal transport processes, including eddy diffusion and advection, using radium isotopes as tracers, in this study an inverse method is applied to solve for an average advection velocity and eddy diffusivity from offshore radium distributions. Radium data of the South Atlantic Bight from previous studies (Moore, 2000; Moore, 2007) are used as the input data to test the method. Our results are consistent with meteorological data in this area and this method will be a useful tool in using radium as a tracer to study coastal transport processes in relatively hydrological complex coastal regions.

References:

Moore, W. S. (2000) Determining coastal mixing rates using radium isotopes. Cont. Shelf Res. 20, 1993-2007.

Moore, W. S. (2007) Seasonal distribution and flux of radium isotopes on the southeastern U.S. continental shelf. J. Geophys. Res. 112, C10013, doi: 10.1029/2007JC004199.