Solar superstorm of AD 774 recorded subannually by Arctic tree rings

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.

Prolonged production of 14C during the ~660 BCE solar proton event from Japanese tree rings

“…Since the phenomenon of rapid increase in CR intensity in 775 CE was solved 1-3 , 14 C analysis in annual rings has played a major role in searching for another rapid 14 C increase event 4,5 . While such events have been suggested to originate from an extreme SPE [6][7][8][9][10] , the other type with a rather long period of 14 C increase has recently been reported in German oak tree rings 11 . It is the 14 C increase in ca.…”

“…galactic cosmic rays (GCRs) modulated by a variation in the interplanetary magnetic fields due to solar activities, gamma-rays from supernova (SN) and gamma-ray burst (GRB), and an extreme SPE. Recently, O'Hare et al showed sharp increases of 10 Be and 36 Cl concentrations with high-resolution in Greenland ice cores around 2610BP (~660 BC) 12 . We name the phenomenon the "~660 BCE event" including the 14 C increase at ca.…”

“…O'Hare et al mentioned that the solar modulation of GCRs was not suitable to explain the enhancement of 10 Be, 36 Cl, and 14 C concentrations even by decreased solar activities with showing the significant large excesses against the typical amplitude of an 11-year solar cycle 12 . The increases of 14 C coincide with those of the ice core-based radionuclides, exceeding the variations of 11-year cycle in the range of 4‰ 13 .…”

“…The increases of 14 C coincide with those of the ice core-based radionuclides, exceeding the variations of 11-year cycle in the range of 4‰ 13 . Also, both SN and GRB were inappropriate for the ~660 BCE event, as the large amount of 10 Be were evidently detected in the ice cores. It is expected that undetectable amount of 10 Be atoms are produced by the gamma-ray origin 12,14 .…”

10Be Signature of the Cosmic Ray Event in the 10th Century CE in Both Hemispheres, as Confirmed by Quasi‐Annual 10Be Data From the Antarctic Dome Fuji Ice Core

“…The 775 event was identified even in the decadal 14 C data (INTCAL) and 10 Be data (Dome Fuji [DF] ice core) as a rapid change (Usoskin & Kovaltsov, 2012). The 775 and 994 events were confirmed by subsequent independent annual 14 C measurements using worldwide tree samples (Büntgen et al, 2018;Fogtmann-Schulz et al, 2017;Güttler et al, 2015;Jull et al, 2014;Miyake et al, 2012Miyake et al, , 2013Miyake et al, , 2014Park et al, 2017;Rakowski et al, 2015;Usoskin et al, 2013;Uusitalo et al, 2018). Carbon-14 is a nuclide produced by cosmic rays (CR), which are high energy particles with origins in outside the solar system (Galactic CR: GCR) or an eruption of the sun (Solar Energetic Particles).…”