Increase of radiocarbon concentration in tree rings from Kujawy (SE Poland) around AD 774–775

Abstract

Evidence of a rapid increase in atmospheric radiocarbon (14C) content in AD 774–775 was presented by Miyake et al. (2012), who observed an increase of about 12‰ in the 14C content in annual tree rings from Japanese cedar. Usoskin et al. (2013) report a similar 14C spike in German oak, and attribute it to exceptional solar activity. If this phenomenon is global in character, such rapid changes in 14C concentration may affect the accuracy of calibrated dates, as the existing calibration curve is composed mainly of decadal samples. Single-year samples of dendro-chronologically dated tree rings of deciduous oak (Quercus robur) from Kujawy, a village near Krakow (SE Poland), spanning the years AD 765–796, were collected and their 14C content was measured using the AMS system in the Leibniz Laboratory. The results clearly show a rapid increase of 9.2±2.1‰ in the 14C concentration in tree rings between AD 774 and AD 775, with maximum Δ14C=4.1±2.3‰ noted in AD 776.