Astronomy:993–994 carbon-14 spike
The 993–994 carbon-14 spike was a rapid increase in carbon-14 content from tree rings, and followed the 774–775 carbon-14 spike. This event is also confirmed by a sharp increase of beryllium-10 and hence considered as solar-origin.  It may have come from a massive solar storm as a series of auroral observations are known to be observed in late 992. 
- Miyake, F. (2013). "Another rapid event in the carbon-14 content of tree rings : Nature Communications : Nature Publishing Group". Nature Communications 4: 1748. doi:10.1038/ncomms2783. PMID 23612289.
- Mekhaldi, F. (2015). "Multiradionuclide evidence for the solar origin of the cosmic-ray events of ᴀᴅ 774/5 and 993/4 : Nature Communications : Nature Publishing Group". Nature Communications 6: 8611. doi:10.1038/ncomms9611. PMID 26497389.
- Hayakawa, H. (2017). "Historical Auroras in the 990s: Evidence of Great Magnetic Storms : Solar Physics : Springer". Solar Physics 292. doi:10.1007/s11207-016-1039-2.
Original source: https://en.wikipedia.org/wiki/ 993–994 carbon-14 spike. Read more