774–775 carbon-14 spike

Hypotheses

Several possible causes of the event have been considered.

The Anglo-Saxon Chronicle recorded "a red crucifix, after sunset", which has been variously hypothesised to have been a supernova or the aurora borealis.

In China, there is only one clear reference to an aurora in the mid-770s, on 12 January 776. However, an anomalous "thunderstorm" was recorded for 775.

As established by Ilya G. Usoskin and colleagues,{{cite journal | author-link=Ilya G. Usoskin |first2=F. |last2= Miyake |display-authors=etal Another proposed origin, involving a gamma-ray burst, is regarded as unlikely, because the event was also observed in isotopes Be and Cl – a gamma-ray burst would not have produced significant Be, and cosmogenic radionuclides are concentrated near the poles, suggesting a flux of charged particles.

Frequency of similar events

The event of 774 is the strongest spike over the last 11,000 years in the record of cosmogenic isotopes, but several other events of the same kind (Miyake events) have occurred during the Holocene epoch. The 993–994 carbon-14 spike was about 60% as strong; another event occurred in . In 2023 the strongest event yet discovered was reported, which occurred in 12,350-12,349 BC.

The event of 774 had no significant consequences for life on Earth, but had it happened in modern times, it might have produced catastrophic damage to modern technology, particularly to communication and space-borne navigation systems. Also, a solar flare able to produce the observed isotopic effect, would pose considerable risk to astronauts.

C variations are poorly understood, because annual-resolution measurements are available for only a few periods (such as 774–775). In a 2017 study, a C increase of (2.0%) was associated with a 5480 BC event, but it is not associated with a solar event because of its long duration, but rather to an unusually fast grand minimum of solar activity.

References

References

1. Reimer, Paula. (August 2020). "The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0–55 cal kBP)". Radiocarbon.
2. University of Kansas. (November 30, 2012). "Researcher points to Sun as likely source of eighth-century 'Charlemagne event'".
3. (2019). "The Celestial Sign in the Anglo-Saxon Chronicle in the 770s: Insights on Contemporary Solar Activity". Solar Physics.
4. Owano, Nancy. (2012-06-30). "Red Crucifix sighting in 774 may have been supernova".
5. (2015). "Astronomical evidence relating to the observed {{sup". Advances in Space Research.
6. (2019). "Do the Chinese Astronomical Records Dated AD 776 January 12/13 Describe an Auroral Display or a Lunar Halo? A Critical Re-examination". Solar Physics.
7. Ya-Ting Chai. (2015). "Searching for events in Chinese ancient records to explain the increase in ¹⁴C from 774–775 CE and 993–994 AD". Research in Astronomy and Astrophysics.
8. Mekhaldi. (2015). "Multiradionuclide evidence for the solar origin of the cosmic-ray events of ᴀᴅ 774/5 and 993/4". Nature Communications.
9. O'Hare, Paschal. (2019). "Multiradionuclide evidence for an extreme solar proton event around 2,610 B.P. (~660 BC)". Proceedings of the National Academy of Sciences of the United States of America.
10. (2019). "The Earliest Candidates of Auroral Observations in Assyrian Astrological Reports: Insights on Solar Activity around 660 BCE". The Astrophysical Journal.
11. (Oct 9, 2023). "A radiocarbon spike at 14 300 cal yr BP in subfossil trees provides the impulse response function of the global carbon cycle during the Late Glacial". Philosophical Transactions of the Royal Society A.
12. (March 28, 2017). "Atmospheric impacts of the strongest known solar particle storm of 775 AD". Scientific Reports.
13. (2016-06-01). "Extreme solar event of AD775: Potential radiation exposure to crews in deep space". Acta Astronautica.
14. (2017). "Large ¹⁴C excursion in 5480 BC indicates an abnormal sun in the mid-Holocene". Proceedings of the National Academy of Sciences of the United States of America.