Secular variations in carbon-14 and their geophysical implications

Abstract

Cosmic ray production of the radioactive carbon isotope C-14, which is the basis for the radiocarbon dating method, has not remained constant over time. The result is that radiocarbon dates show significant deviations from the true age. The identification of the causes and magnitudes of these deviations has created a new too that is contributing to the investigation of different geophysical: phenomena. Variations in the activity of the Sun produce fluctuations of the C-14 level in the atmosphere and biosphere, with resulting distortions in radiocarbon dates of up to 200 years. The detailed record of these fluctuations over the past 12 000 years provides a valuable data set for assessing the effect of changes in solar activity on global climate. The modulation of the cosmic ray flux by the magnetic dipole field of the Earth causes more significant longer-term changes in the production rate of C-14. Once the C-14 levels in the environment back to 50 000 years ago have been established with sufficient precision, they will become an important indicator of changes in the geomagnetic moment and facilitate the identification of local non-dipole effects that occur at various places on Earth.