Solar superstorm of AD 774 recorded subannually by Arctic tree rings.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 30154404.
- Also identified by DOI 10.1038/s41467-018-05883-1 and PMC identifier 6113262.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Recently, a rapid increase in radiocarbon (<sup>14</sup>C) 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 <sup>14</sup>C 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 <sup>14</sup>C poleward increase, in accord with the solar origin of the event. Furthermore, both annual <sup>14</sup>C data and carbon cycle modelling, and separate earlywood and latewood <sup>14</sup>C measurements, confine the photosynthetic carbon fixation to around the midsummer.