Approximately 2400-Year Cycle in the Concentration of Cosmogenic Radionuclides: Sources of Variations

Abstract

Cosmogenic isotopes, including ¹⁴C, ¹⁰Be, and ⁷Be, are produced in the Earth’s atmosphere under the effect of cosmic rays. The rate of their production is determined by several factors, such as the intensity of primary galactic cosmic rays, the level of solar activity, and the strength of the Earth’s magnetic field. Changes in the isotope concentrations and distributions receive contributions from mixing processes proceeding in the surrounding medium: the atmosphere, biosphere, and oceans. The isotopes ¹⁴C and ¹⁰Be are the most important for studying solar activity and climate. Investigation of isotope concentrations reveal that there are both long-term trends and cyclic components. As for ¹⁴C, the long-term component caused by the change in the magnetic dipole moment of the Earth with a characteristic time of about 10⁴ years is the most commonly known. It is well known that the concentrations of cosmogenic isotopes change cyclically with time. The ~2400-year cycle (Hallstatt cycle) and the ~210-year cycle (de Vries cycle) are the most famous. In the present article, we discuss the possible origin of the ~2400-year cycle.