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 to be of solar origin. It may have come from a massive solar storm as a series of auroral observations are known from late 992 in Korea, Germany and Ireland.
In 2021, a scientific paper used the 993–994 carbon-14 spike as a benchmark in dendrochronology (tree-ring studies) to precisely determine that Vikings were present in L’Anse aux Meadows in Newfoundland exactly 1000 years prior, in 1021 AD.
- Miyake, F.; et al. (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.; et al. (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. PMC 4639793. PMID 26497389.
- Hayakawa, H.; et al. (2017). "Historical Auroras in the 990s: Evidence of Great Magnetic Storms : Solar Physics : Springer". Solar Physics. 292. arXiv:1612.01106. doi:10.1007/s11207-016-1039-2. S2CID 119095730.
- Kuitems, Margo; Wallace, Birgitta L.; Lindsay, Charles; Scifo, Andrea; Doeve, Petra; et al. (2021-10-20). "Evidence for European presence in the Americas in AD 1021". Nature. Retrieved 2021-10-21.