The past 5000 years history of solar modulation of cosmic radiation from 10 Be and 14 C studies

Abstract

¹⁰ Be is produced in a similar way as ¹⁴ C by the interaction of cosmic radiation with the nuclei in the atmosphere. Assuming that the ¹⁰ Be and ¹⁴ C variation are proportional and considering the different behaviour in the Earth system, the ¹⁰ Be concentrations in ice cores can be compared with the ¹⁴ C variations in tree rings. A high correlation is found for the short-term variations ( ¹⁴ C-Suess-wiggles). They reflect with a high probability production rate variations. More problematic is the interpretation of the long-term trends of ¹⁴ C and ¹⁰ Be. Several explanations are discussed. The reconstructed CO ₂ concentrations in ice cores indicate a rather constant value (280 ± 10 p.p.m. by volume) during the past few millenia. Measurements on the ice core from Byrd Station, Antarctica, during the period 9000 to 6000 years BP indicate a decrease that might be explained by the extraction of CO ₂ from the atmosphere-ocean system to build the terrestrial biomass pool during the climatic optimum.