Radionuclides as ocean tracers
Marine Analytical Chemistry
School of Science / Centre for Marine Ecosystems Research
Radionuclides, both from natural and anthropogenic origin, are powerful ocean tracers that provide key information on fluxes, pathways and time scales of marine processes. Their added value compared to hydrographic parameters (e.g., temperature and salinity) relies either on their known rates of radioactive decay and production or on their time-variable releases from sources. Both aspects introduce a temporal dimension that allows quantifying rates or time scales of marine processes. Their wide range of half-lives and historical inputs, together with their physicochemical characteristics allow tracing a broad spectrum of marine processes. This chapter aims at providing an overview of the application of radionuclides as tracers of ocean processes. The chapter is structured in four sections: The first part reviews the main principles of radioactivity and the origin of radionuclides. The second section introduces the key aspects that allow using radionuclides as ocean tracers, followed by (third section) three real and contemporary instructive examples that cover different marine processes and require radionuclides with specific properties: i) thorium-234/uranium-238 (234Th/238U) pair to quantify the biological pump, ii) radium (Ra) isotopes to estimate the magnitude of submarine groundwater discharge, and iii) iodine-129 (129I) to investigate the large-scale ocean circulation. Finally, this chapter provides a summary of the different methods and techniques used to measure radionuclides in seawater.