• Erosion and accumulation periods show minimum and maximum activity concentrations. • Marine erosion agents influence the temporal variability of activity concentration. • Minerals containing Ra and K are transported during erosion and accumulation periods. • 226Ra, 228Ra and 40K seems to be suitable tracers for beach sediment dynamics. The aim of this study is to analyse the role of natural radionuclides 226Ra, 228Ra, 40K and unsupported 210Pb (210Pb ex), as erosion and accumulation process tracers. For this purpose, a complex system, including both the characteristic dynamics of a closed beach and those associated with a beach open to wave action, was studied. A 3-year study of monthly variation of 226Ra, 228Ra, 40K and 210Pb ex was carried out at Las Canteras beach, on the Island of Gran Canaria (Spain), covering several erosion and accumulation periods. A correlation analysis, ANOVA test and Tukey's Honestly Significant Difference (HSD) Test proved that the marine erosion and accumulation agents influenced the activity concentration values found for the different radionuclides. Moreover, the geochemical analysis of samples from maximum and minimum activity concentration values showed that the natural radionuclides studied could be suitable tracers for studying beach sediment dynamics in erosion and accumulation periods. [ABSTRACT FROM AUTHOR]