Solar superstorm of AD 774 recorded subannually by Arctic tree rings

J. Uusitalo (), L. Arppe, T. Hackman, S. Helama, G. Kovaltsov, K. Mielikäinen, H. Mäkinen, P. Nöjd, V. Palonen, I. Usoskin and M. Oinonen
Additional contact information
J. Uusitalo: University of Helsinki
L. Arppe: University of Helsinki
T. Hackman: University of Helsinki
S. Helama: Natural Resources Institute Finland
G. Kovaltsov: Ioffe Physical-Technical Institute
K. Mielikäinen: Natural Resources Institute Finland
H. Mäkinen: Natural Resources Institute Finland
P. Nöjd: Natural Resources Institute Finland
V. Palonen: University of Helsinki
I. Usoskin: University of Oulu
M. Oinonen: University of Helsinki

Nature Communications, 2018, vol. 9, issue 1, 1-8

Abstract: Abstract Recently, a rapid increase in radiocarbon (14C) was observed in Japanese tree rings at AD 774/775. Various explanations for the anomaly have been offered, such as a supernova, a γ-ray burst, a cometary impact, or an exceptionally large Solar Particle Event (SPE). However, evidence of the origin and exact timing of the event remains incomplete. In particular, a key issue of latitudinal dependence of the 14C intensity has not been addressed yet. Here, we show that the event was most likely caused by the Sun and occurred during the spring of AD 774. Particularly, the event intensities from various locations show a strong correlation with the latitude, demonstrating a particle-induced 14C poleward increase, in accord with the solar origin of the event. Furthermore, both annual 14C data and carbon cycle modelling, and separate earlywood and latewood 14C measurements, confine the photosynthetic carbon fixation to around the midsummer.

Date: 2018
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DOI: 10.1038/s41467-018-05883-1

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