774–775 carbon-14 spike

The 774–775 carbon-14 spike is an observed increase of around 1.2% in the concentration of the radioactive carbon-14 isotope in tree rings dated to 774 or 775 CE, which is about 20 times higher than the normal year-to-year variation of radiocarbon in the atmosphere. It was discovered during a study of Japanese cedar tree-rings, with the year of occurrence determined through dendrochronology.[1] A surge in beryllium-10 (10Be), detected in Antarctic ice cores, has also been associated with the 774–775 event.[2] The 774–775 CE carbon-14 spike is one of several Miyake events 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 carbon-14 spike around 774. Colored dots are measurements in Japanese (M12) and German (oak) trees; black lines are 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, which is consistent with 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 (1.3 ± 0.2) × 108 atoms/cm2.[2][7][8]

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[9] or the aurora borealis.[2][10]

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]

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

As established by Ilya G. Usoskin and colleagues,[14] the current scientific paradigm[15] is that the event was caused by a solar particle event (SPE) from a very strong solar flare, perhaps the strongest known.[16] Another proposed origin, involving a gamma-ray burst,[8][17] is regarded as unlikely, because the event was also observed in isotopes 10Be and 36Cl.[16][clarification needed]

Frequency of similar events

The AD 774/75 event in view of 10Be, 14C, and 36Cl

The event of 774 is the strongest spike over the last 11,000 years in the record of cosmogenic isotopes,[18] but several other events of the same kind (Miyake events) have occurred during the Holocene epoch.[18] The 993–994 carbon-14 spike was about 60% as strong;[19] another event occurred in c. 660 BCE.[20][21] In 2023 the strongest event yet discovered was reported, which occurred in 12,350-12,349 BC.[22]

The event of 774 had no significant consequences for life on Earth,[23][24] 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.[25]

14C variations are poorly understood, because annual-resolution measurements are available for only a few periods (such as 774–775).[26] In a 2017 study, a 14C 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.[26]

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): 240–2. Bibcode:2012Natur.486..240M. doi:10.1038/nature11123. PMID 22699615. S2CID 4368820.
  2. ^ a b c d e f 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. S2CID 55137950.
  3. ^ Reimer, Paula; et al. (August 2020). "The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0–55 cal kBP)". Radiocarbon. 62 (4): 725–757. Bibcode:2020Radcb..62..725R. doi:10.1017/RDC.2020.41. hdl:1893/30981. S2CID 216215614.
  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. S2CID 19045243.
  6. ^ Güttler, D.; Beer, J.; Bleicher, N. (2013). "The 774/775 AD event in the southern hemisphere". ETH-Zurich: Laboratory of Ion Beam Physics: Annual Report 2013. LIBRUM. p. 33. ISBN 9783952403846. OCLC 887695262.
  7. ^ Melott, A.L.; Thomas, B.C. (2012). "Causes of an AD 774-775 14C increase". Nature. 491 (7426): E1–E2. arXiv:1212.0490. Bibcode:2012Natur.491E...1M. doi:10.1038/nature11695. PMID 23192153. S2CID 205231715.
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  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): 1504. arXiv:1406.7306. doi:10.1088/1674-4527/15/9/007. S2CID 124499827.
  14. ^ Usoskin, I.G.; Kromer, B.; Ludlow, F.; Beer, J.; Friedrich, M.; Kovaltsov, G.A.; Solanki, S.K.; Wacker, L. (2013). "The AD775 cosmic event revisited: the Sun is to blame". Astronomy and Astrophysics Letters. 552: L3. arXiv:1302.6897. doi:10.1051/0004-6361/201321080.
  15. ^ Usoskin, I.G.; Miyake, F.; Baroni, M.; et al. (2023). "Extreme Solar Events: Setting up a Paradigm". Space Science Reviews. 219 (8): 73. doi:10.1007/s11214-023-01018-1. hdl:20.500.11850/641517.
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  20. ^ O'Hare, Paschal; et al. (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. 116 (13): 5961–6. Bibcode:2019PNAS..116.5961O. doi:10.1073/pnas.1815725116. PMC 6442557. PMID 30858311.
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