Speaker
Description
Rapid increases in atmospheric radiocarbon ($^{14}$C), known as Miyake events, have been identified across multiple time periods, with Solar Proton Events (SPEs) considered the most probable cause. Among these, the ~660 BC event stands out due to its apparently prolonged rise time compared to other confirmed events such as AD 774–775 and AD 993–994, prompting hypotheses ranging from double SPEs to encounters with interstellar gas clouds. In this study, we present new annual and subannual $^{14}$C measurements from Scots pine (Pinus sylvestris) tree rings from Finnish Lapland (66.8°N), covering the periods 680–650 BC and 670–655 BC, respectively.
Our results reveal that the $^{14}$C signal begins rising in the latewood of 665 BC, reaching near-full intensity by 664 BC, with a peak around 662–661 BC at an amplitude of approximately 15‰. This timing aligns closely with independent high-latitude measurements from Yamal, Russia, but precedes the rise observed at lower-latitude sites in Germany, Japan, and the Altai region. The earlier and more pronounced signal at high latitudes mirrors patterns documented for the AD 774 and AD 993 events, pointing to a consistent mechanism involving either direct tropospheric $^{14}$C production at polar latitudes or a rapid component of stratosphere-to-troposphere air mass transfer in polar regions.
Carbon cycle box model simulations reproduce the observed peak shape well. Importantly, the model yields nearly identical fits for scenarios involving either a single or double SPE, indicating that the box model approach alone cannot resolve whether one or multiple production events caused the ~660 BC anomaly. Qualitative comparison of the high-latitude peak shapes of the ~660 BC and AD 774 events reveals striking similarity, which argues against the need for multiple SPEs or more exotic causes, and instead supports a scenario where the observed peak shape arises from the interplay of initial $^{14}$C production and atmospheric transport processes. These findings underscore the necessity of developing latitude-resolved, dynamic carbon cycle models capable of capturing the rapid polar transfer of stratospheric CO$_2$ into the troposphere and its subsequent dilution into lower-latitude air masses.
Based on: Park J, Uusitalo J, Hong W, Park G, Sung K, Hackman T, Helama S, Mäkinen H, Nöjd P and Oinonen M (2026). Early 14C i
ncrease in high-latitude trees at 665–664 BC. Radiocarbon, in press. doi:10.1017/RDC.2026.10195
Co-authors:
Junghun Park (1), Wan Hong (1), Gyujun Park (1), Kilho Sung (3), Thomas Hackman (4), Samuli Helama (5), Harri Mäkinen (6), Pekka Nöjd (6), Markku Oinonen (2)
(1) Korea Institute of Geoscience and Mineral Resources, Geoanalysis Center, Republic of Korea
(2) Finnish Museum of Natural History, University of Helsinki, Helsinki, Finland
(3) GNS Science, Gracefield, Lower Hutt, New Zealand
(4) Department of Physics, University of Helsinki, Helsinki, Finland
(5) Natural Resources Institute Finland, Rovaniemi, Finland
(6) Natural Resources Institute Finland, Helsinki, Finland