Miyake event

A Miyake event is an observed sharp enhancement of the production of cosmogenic isotopes by cosmic rays. It can be marked by a spike in the concentration of radioactive carbon isotope Carbon-14 in tree rings, as well as Beryllium-10 and Chlorine-36 in ice cores, which are all independently dated. At present, five significant events are known (7176 BCE, 5259 BCE, 660 BCE, 774 CE, 993 CE) for which the spike in Carbon-14 is quite remarkable, i.e. above 1% rise over a period of 2 years, and four more events (12,350BCE, 5410 BCE, 1052 CE, 1279 CE) need independent confirmation. It is not known how often Miyake events occur, but from the available data it is estimated to be every 400–2400 years.

There is strong evidence that Miyake events are caused by extreme solar particle events and they are likely related to super-flares discovered on solar-like stars. Although Miyake events are based on extreme year-to-year rises of Carbon-14 concentration, the duration of the periods over which the Carbon-14 levels increase or stay at high levels is longer than one year. However, a universal cause and origin of all the events is not yet established in science, and some of the events may be caused by other phenomena coming from outer space (such as a gamma-ray burst).

A recently reported sharp spike in Carbon-14 that occurred between 12,350 and 12,349BCE may represent the largest known Miyake event. This event was identified during a study conducted by an international team of researchers who measured radiocarbon levels in ancient trees recovered from the eroded banks of the Drouzet River, near Gap, France, in the Southern French Alps. According to the initial study the new event is roughly twice the size of the Δ increase for more recent 774CE and 993CE events, but the strength of the corresponding solar storm is not yet assessed. However, the newly discovered 12,350 BCE event has not yet been independently confirmed in wood from other regions, nor it is reliably supported by a clear corresponding spike in other isotopes (such as beryllium-10) that are usually used in combination for absolute radiometric dating.

A Miyake event occurring in modern conditions might have significant impacts on global technological infrastructure such as satellites, telecommunications, and power grids.

Discovery
The events are named after the Japanese physicist Fusa Miyake who, as a doctoral student, was the first one to identify these radiocarbon spikes and published the results with co-authors in 2012 in the journal Nature. The investigation at that time found a strong increase in the annual rings of Japanese cedars for the years 774/775. The event of 775 was independently discovered, using the low-resolution IntCal data. In 2013, Miyake and co-authors published the discovery of another similar radiocarbon spike in the years 993/994. In December 2013, Miyake received her Doctor of Science degree from Nagoya University.

Time benchmark
After a Miyake event is well-studied and confirmed, it can serve as a reference time benchmark, a "year-stamp", enabling more precise dating of historical events. Six diverse historical occurrences, from archaeological sites to natural disasters, have thus been dated to a specific year, using Miyake events as benchmarks and counting tree rings. For example, wooden houses in the Viking site at L'Anse aux Meadows in Newfoundland were dated by finding the 993 CE Miyake event and then counting tree rings, which showed that the wood is from a tree felled in 1021 CE.