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.
