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 isotope 10
Be, 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 the 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.

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 has been variously hypothesised to have been a supernova[9] or the aurora borealis.[2][10]

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]

The most widely accepted theory is that the event was caused by a solar particle event (SPE) from a very strong solar flare, perhaps the strongest known.[2][7][14][15][16][3] Another proposed origin, involving a gamma-ray burst,[8][17] is regarded as unlikely, because the event was also observed in isotopes 10
Be and 36
Cl.[16]

Frequency of similar events
The AD 774/75 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 several other events of the same kind (Miyake events) have occurred during the Holocene epoch.[14] The 993–994 carbon-14 spike was about 60% as strong;[18] another event occurred in c. 660 BCE.[19][20] In 2023 the strongest yet discovered event was reported, which occurred in 12,350-12,349 BC.[21]

The event of 774 did not have any significant consequences for life on Earth,[22][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.[23]

14
C variations are poorly understood, because annual-resolution measurements are available for only a few periods (such as 774–775).[24] In a 2017 study, a 14
C increase of (2.0%) was 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.[24]

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. 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.
  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. Owano, Nancy (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. 294 (4): 42. arXiv:1903.03075. Bibcode:2019SoPh..294...42H. doi:10.1007/s11207-019-1424-8. S2CID 118718677.
  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. 55 (6): 1537–45. 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. arXiv:1903.06806. 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): 1504. arXiv:1406.7306. doi:10.1088/1674-4527/15/9/007. S2CID 124499827.
  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. S2CID 56189671.
  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. S2CID 14253803.
  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)". 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.
  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. S2CID 202565732.
  21. Edouard Bard; et al. (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. doi:10.1098/rsta.2022.0206.
  22. Sukhodolov, Timofei; et al. (March 28, 2017). "Atmospheric impacts of the strongest known solar particle storm of 775 AD". Scientific Reports. 7 (1): 45257. Bibcode:2017NatSR...745257S. doi:10.1038/srep45257. ISSN 2045-2322. PMC 5368659. PMID 28349934.
  23. 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.
  24. 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): 881–4. Bibcode:2017PNAS..114..881M. doi:10.1073/pnas.1613144114. PMC 5293056. PMID 28100493.
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