The 774–775 carbon-14 spike is an observed increase of 1.2% in the concentration of
carbon-14
Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...
isotope in
tree rings
Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed. As well as dating them, this can give data for dendroclimatology, the study of climate and atmos ...
dated to 774 or 775, which is about 20 times as high as the normal background rate of variation. It was discovered during a study of
Japanese cedar
''Cryptomeria'' (literally "hidden parts") is a Monotypic taxon, monotypic genus of Pinophyta, conifer in the cypress family (biology), family Cupressaceae, formerly belonging to the family Taxodiaceae. It includes only one species, ''Cryptomeri ...
trees, with the year of occurrence determined through
dendrochronology
Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed. As well as dating them, this can give data for dendroclimatology, the study of climate and atmos ...
.
A surge in
beryllium
Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form mi ...
isotope , detected in Antarctic ice cores, has also been associated with the 774–775 event.
It is known as the Miyake event or the Charlemagne event and it produced the largest and most rapid rise in carbon-14 ever recorded.
The event appears to have been global, with the same carbon-14 signal found in tree rings from
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
,
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
, the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
,
Finland
Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
and
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
.
The signal exhibits a sharp increase of around 1.2% followed by a slow decline (see
Figure 1
Figure 1 is a Toronto, Ontario-based online social networking service for healthcare professionals to post and comment on medical images.
Figure 1 was founded in Toronto by Dr. Joshua Landy, Richard Penner and Gregory Levey. The platform launched ...
), which is typical for an instant production of carbon-14 in the atmosphere,
indicating that the event was short in duration. The globally averaged production of
carbon-14
Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...
for this event is .
Hypotheses
Several possible causes of the event have been considered.
The "red crucifix" recorded by the ''Anglo-Saxon Chronicle'' has been variously hypothesised to have been a
supernova
A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...
or the
aurora borealis
An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of br ...
.
In China, there is only one clear reference to an aurora in the mid-770s, namely the one on 12 January 776. Instead, an anomalous "thunderstorm" was recorded for 775.
The common paradigm is that the event was caused by a
solar particle event
In solar physics, a solar particle event (SPE), also known as a solar energetic particle (SEP) event or solar radiation storm, is a solar phenomenon which occurs when particles emitted by the Sun, mostly protons, become accelerated either in the ...
(SPE), or a consequence of events as often happen, from a very strong
solar flare
A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other solar phe ...
, perhaps the strongest ever known but still within the Sun's abilities.
According to a summary of the state of knowledge on radiocarbon dating in 2020, the spike is thought to have been caused by an extreme SPE.
[
Another discussed scenario of the event origin, involving a ]gamma-ray burst
In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic explosions that have been observed in distant galaxies. They are the most energetic and luminous electromagnetic events since the Big Bang. Bursts can last from ten milli ...
, appears unlikely, because the event was also observed in isotopes and .
In 2022, a study of an extreme solar particle storm near a solar minimum 9125 years BP (7176 BCE), showed one of the largest enhancements detected in ice cores. Furthermore, the reconstruction of the / enhancement ratio suggests that this SPE event was similar or even larger than the 774/75 CE event in terms of energy (>30 MeV). The implication is the magnitude and frequency of occurrence of a potential worst-case scenario for SPE events is increased. The study also provides evidence that the 7176 BCE event occurred near a solar minimum.
Another 2022 study using the tree-ring radiocarbon record (also) concluded that Miyake events, don't appear to be caused by the solar cycle
The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfa ...
(i.e. solar flares) as thought previously and have extended durations. They occurred every ~1,000 years on average and may threaten global technologies this century.
Frequency of similar events
The event of 774 is the strongest spike over the last 11,000 years in the record of cosmogenic isotopes, but it is not unique. A similar event occurred in 993 or 994, but it was only 60% as strong; and another in . Several other events of the same kind are also suspected to have occurred during the Holocene
The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...
epoch.
From these statistics, one may expect that such strong events occur once per tens of millennia, while weaker events may occur once per millennium or even century. The event of 774 did not cause catastrophic consequences for life on Earth, 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.
As of 2017, there is "little understanding" of past variations because annual-resolution measurements are available for only a few periods (such as 774–775). In 2017, another "extraordinarily large" increase (2.0%) has been 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. Analysis is hindered by the lack of yearly radiocarbon numbers for earlier dates.
See also
* List of solar storms
Solar storms of different types are caused by disturbances on the Sun, most often from coronal mass ejections (CMEs) and solar flares from active regions, or, less often, from coronal holes. Minor to active solar storms (i.e. storming restricted t ...
* Carrington Event
The Carrington Event was the most intense geomagnetic storm in recorded history, peaking from 1 to 2 September 1859 during solar cycle 10. It created strong auroral displays that were reported globally and caused sparking and even fires in mult ...
References
External links
*
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Geomagnetic storms
Stratigraphy
Dendrology