Observed increase concentration of carbon-14 in tree rings dated 774 or 775
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 several
Miyake events and it produced the largest and most rapid rise in carbon-14 ever recorded.[3][4]
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.
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 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 event yet discovered 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]
^
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.
ISBN9783952403846.
OCLC887695262.
^
ab
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.
^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.
^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.
S2CID124499827.
^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.