774–775 carbon-14 spike

The 774–775 carbon-14 spike is an observed increase of 1.2% in the concentration of carbon-14 isotope in tree rings dated to 774 or 775, which is about 20 times as high as the normal background rate of variation. It was discovered during a study of Japanese cedar trees, with the year of occurrence determined through dendrochronology.[1] A surge in beryllium isotope 10
Be, detected in Antarctic ice cores, has also been associated with the 774–775 event.[2] It is known as the Miyake event or the Charlemagne event and it produced the largest and most rapid rise in carbon-14 ever recorded.[3][4]

The event appears to have been global, with the same carbon-14 signal found in tree rings from Germany, Russia, the United States, Finland and New Zealand.[2][5][6]

The time profile of the carbon-14 spike around 774. The colored dots represent the measurements in Japanese (M12) and German (Oak) trees, while the black lines represent the modeled profile corresponding to the instant production of carbon-14.[2]

The signal exhibits a sharp increase of around 1.2% followed by a slow decline (see Figure 1), which is typical for an instant production of carbon-14 in the atmosphere,[2] indicating that the event was short in duration. The globally averaged production of carbon-14 for this event is calculated as Q = 1.3×108 ± 0.2×108 atoms/cm2.[2][7][8]

Hypotheses

Several possible causes of the event have been considered.

Annus Domini (the year of the Lord) 774. This year the Northumbrians banished their king, Alred, from York at Easter-tide; and chose Ethelred, the son of Mull, for their lord, who reigned four winters. This year also appeared in the heavens a red crucifix, after sunset; the Mercians and the men of Kent fought at Otford; and wonderful serpents were seen in the land of the South-Saxons.

— Anglo-Saxon Chronicle[9]

The "red crucifix" recorded by the Anglo-Saxon Chronicle was thought to have been a supernova.[9] However, since no supernova remnant has been found for this year, it is interpreted as an aurora borealis.[2][10]

In China, there is only one clear reference to an aurora in the mid-770s, namely the one on 12 January 776.[11][12] Instead, an anomalous "thunderstorm" was recorded for 775.[13]

The common paradigm is that the event was caused by a solar particle event (SPE), or a consequence of events as often happen, from a very strong solar flare, perhaps the strongest ever known but still within the Sun's abilities.[2][7][14][15][16] According to a summary of the state of knowledge on radiocarbon dating in 2020, the spike is thought to have been caused by an extreme solar proton event.[3] Another discussed scenario of the event origin, involving a gamma-ray burst,[8][17] appears unlikely, since the event was also observed in isotopes 10
Be and 36
Cl.[16]

Frequency of similar events
The AD 774/5 event in view of 10
Be, 14
C and 36
Cl

The event of 774 is the strongest spike over the last 11,000 years in the record of cosmogenic isotopes,[14] but it is not unique. A similar event occurred in 993 or 994, but it was only 60% as strong[18] as well as another event of c. 660 BCE.[19][20] Several other events of the same kind are also suspected to have occurred during the Holocene epoch.[14]

From these statistics, one may expect that such strong events occur once per tens of millennia, while weaker events may occur once per millennium or even century. The event of 774 did not cause catastrophic consequences for life on Earth,[21][15] but had it happened in modern times, it might have produced catastrophic damage to modern technology, particularly to communication and space-borne navigation systems. In addition, a solar flare capable of producing the observed isotopic effect would pose considerable risk to astronauts.[22]

As of 2017, there is "little understanding"[23] of 14
C past variations because annual-resolution measurements are only available for a few periods (such as 774–775). In 2017, another "extraordinarily large" 14
C increase (2.0%) has been associated with a 5480 BCE 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.[23]

In 2019, evidence of another "enormous solar storm" in around 660 BCE was published, comparable with the 774–775 and 993 events[24] and likely relevant with the auroral records in Assyrian records.[25] One of the conclusions of the work is that an exclusive reliance on 14
C records may lead to underestimation of the number of possibly catastrophic events. High-resolution measurements are needed for 14
C, 10
Be and 36
Cl.

See also

References
  1. Miyake, F.; Nagaya, K.; Masuda, K.; Nakamura, T. (2012). "A signature of cosmic-ray increase in AD 774–775 from tree rings in Japan". Nature. 486 (7402): 240–242. Bibcode:2012Natur.486..240M. doi:10.1038/nature11123. PMID 22699615.
  2. Usoskin, I. G.; et al. (2013). "The AD775 cosmic event revisited: The Sun is to blame". Astronomy & Astrophysics. 552 (1): L3. arXiv:1302.6897. Bibcode:2013A&A...552L...3U. doi:10.1051/0004-6361/201321080.
  3. Reimer, Paula; et al. (August 2020). "THE INTCAL20 NORTHERN HEMISPHERE RADIOCARBON AGE CALIBRATION CURVE (0–55 CAL kBP)". Radiocarbon.
  4. University of Kansas (November 30, 2012). "Researcher points to Sun as likely source of eighth-century 'Charlemagne event'".
  5. Jull, A.J.T.; Panyushkina, I.P.; Lange, T.E.; et al. (2014). "Excursions in the 14C record at AD 774–775 in tree rings from Russia and America". Geophys. Res. Lett. 41 (8): 3004–3010. Bibcode:2014GeoRL..41.3004J. doi:10.1002/2014GL059874. hdl:10150/628657.
  6. Güttler, D.; Beer, J.; Bleicher, N. (2013). "The 774/775 AD event in the southern hemisphere". Annual Report of the Laboratory of Ion Beam Physics. ETH-Zurich.
  7. Melott, A.L.; Thomas, B.C. (2012). "Causes of an AD 774-775 C increase". Nature. 491 (7426): E1–E2. arXiv:1212.0490. Bibcode:2012Natur.491E...1M. doi:10.1038/nature11695. PMID 23192153.
  8. Pavlov, A.K.; Blinov, A.V.; Konstantinov, A.N.; et al. (2013). "AD 775 pulse of cosmogenic radionuclides production as imprint of a Galactic gamma-ray burst". Mon. Not. R. Astron. Soc. 435 (4): 2878–2884. arXiv:1308.1272. Bibcode:2013MNRAS.435.2878P. doi:10.1093/mnras/stt1468.
  9. Nancy Owano (2012-06-30). "Red Crucifix sighting in 774 may have been supernova". Phys.org.
  10. Hayakawa, H. (2019). "The Celestial Sign in the Anglo-Saxon Chronicle in the 770s: Insights on Contemporary Solar Activity". Solar Physics. Springer. 294 (4): 42. arXiv:1903.03075. Bibcode:2019SoPh..294...42H. doi:10.1007/s11207-019-1424-8.
  11. Stephenson, F. R. (2015). "Astronomical evidence relating to the observed 14C increases in A.D. 774–5 and 993–4 as determined from tree rings". Advances in Space Research. Elsevier. 55 (6): 1537–1545. Bibcode:2015AdSpR..55.1537S. doi:10.1016/j.asr.2014.12.014.
  12. Stephenson, F. R. (2019). "Do the Chinese Astronomical Records Dated AD 776 January 12/13 Describe an Auroral Display or a Lunar Halo? A Critical Re-examination" (PDF). Solar Physics. 294 (4): 36. Bibcode:2019SoPh..294...36S. doi:10.1007/s11207-019-1425-7.
  13. Ya-Ting Chai & Yuan-Chuan Zou (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. 15 (9).
  14. Usoskin, I.G.; Kovaltsov, G.A. (2012). "Occurrence of Extreme Solar Particle Events: Assessment from Historical Proxy Data". Astrophys. J. 757 (1): 92. arXiv:1207.5932. Bibcode:2012ApJ...757...92U. doi:10.1088/0004-637X/757/1/92.
  15. Thomas, B. C.; Melott, A. L.; Arkenberg, K. R.; Snyder, B. R. (2013). "Terrestrial effects of possible astrophysical sources of an AD 774–775 increase in 14C production". Geophysical Research Letters. 40 (6): 1237. arXiv:1302.1501. Bibcode:2013GeoRL..40.1237T. doi:10.1002/grl.50222.
  16. Mekhaldi; et al. (2015). "Multiradionuclide evidence for the solar origin of the cosmic-ray events of ᴀᴅ 774/5 and 993/4". Nature Communications. 6: 8611. Bibcode:2015NatCo...6.8611M. doi:10.1038/ncomms9611. PMC 4639793. PMID 26497389.
  17. Hambaryan, V. V.; Neuhauser, R. (2013). "A Galactic short gamma-ray burst as cause for the 14C peak in AD 774/5". Monthly Notices of the Royal Astronomical Society. 430 (1): 32–36. arXiv:1211.2584. Bibcode:2013MNRAS.430...32H. doi:10.1093/mnras/sts378.
  18. Miyake, F.; Masuda, K.; Nakamura, T. (2013). "Another rapid event in the carbon-14 content of tree rings". Nature Communications. 4: 1748. Bibcode:2013NatCo...4.1748M. doi:10.1038/ncomms2783. PMID 23612289.
  19. O'Hare, Paschal; et al. (2019). "Multiradionuclide evidence for an extreme solar proton event around 2,610 B.P. (∼660 BC)". Proc. Natl. Acad. Sci. U.S.A. 116 (13): 5961–5966. Bibcode:2019PNAS..116.5961O. doi:10.1073/pnas.1815725116. PMC 6442557. PMID 30858311.
  20. Hayakawa, Hisashi; Mitsuma, Yasuyuki; Ebihara, Yusuke; Miyake, Fusa (2019). "The Earliest Candidates of Auroral Observations in Assyrian Astrological Reports: Insights on Solar Activity around 660 BCE". The Astrophysical Journal. 884 (1): L18. arXiv:1909.05498. Bibcode:2019ApJ...884L..18H. doi:10.3847/2041-8213/ab42e4.
  21. Sukhodolov, Timofei; et al. (March 28, 2017). "Atmospheric impacts of the strongest known solar particle storm of 775 AD". Scientific Reports. Springer Nature. 7 (1): 45257. Bibcode:2017NatSR...745257S. doi:10.1038/srep45257. ISSN 2045-2322. PMC 5368659. PMID 28349934.
  22. Townsend, L. W.; Porter, J. A.; deWet, W. C; Smith, W. J.; McGirl, N. A.; Heilbronn, L. H.; Moussa, H. M. (2016-06-01). "Extreme solar event of AD775: Potential radiation exposure to crews in deep space". Acta Astronautica. Special Section: Selected Papers from the International Workshop on Satellite Constellations and Formation Flying 2015. 123: 116–120. Bibcode:2016AcAau.123..116T. doi:10.1016/j.actaastro.2016.03.002.
  23. Miyake, F.; Jull, A. J.; Panyushkina, I. P.; Wacker, L.; Salzer, M.; Baisan, C. H.; Lange, T.; Cruz, R.; Masuda, K.; Nakamura, T. (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. 114 (5): 881–884. Bibcode:2017PNAS..114..881M. doi:10.1073/pnas.1613144114. PMC 5293056. PMID 28100493.
  24. O'Hare, Paschal; et al. (2019). "Multiradionuclide evidence for an extreme solar proton event around 2,610 B.P. (∼660 BC)". Proc. Natl. Acad. Sci. U.S.A. 116 (13): 5961–5966. Bibcode:2019PNAS..116.5961O. doi:10.1073/pnas.1815725116. PMC 6442557. PMID 30858311.
  25. Hayakawa, Hisashi; et al. (2019). "The Earliest Candidates of Auroral Observations in Assyrian Astrological Reports: Insights on Solar Activity around 660 BCE". Astrophysical Journal Letters. 884: L18. Bibcode:2019ApJ...884L..18H. doi:10.3847/2041-8213/ab42e4. hdl:2241/00157962.
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