Terrestrial effects of possible astrophysical sources of an AD 774‐775 increase in ¹⁴C production

Abstract

We examine possible sources of a substantial increase in tree ring 14C measurements for the years AD 774‐775. Contrary to claims regarding a coronal mass ejection (CME), the required CME energy is not several orders of magnitude greater than known solar events. We consider solar proton events (SPEs) with three different fluences and two different spectra. The data may be explained by an event with fluence about one order of magnitude beyond the October 1989 SPE. Two hard spectrum cases considered here result in moderate ozone depletion, so no mass extinction is implied, though we do predict increases in erythema and damage to plants from enhanced solar UV. We are able to rule out an event with a very soft spectrum that causes severe ozone depletion and subsequent biological impacts. Nitrate enhancements are consistent with their apparent absence in ice core data. The modern technological implications of such an event may be extreme, and considering recent confirmation of superflares on solar‐type stars, this issue merits attention.

A history of solar activity over millennia

“…This event is confirmed by annual 14 C data from a German oak tree , Russian and American tree samples (Jull et al 2014), New Zealand trees (Güttler et al 2013), etc., and corals from the Chinese Sea (Liu et al 2014) According to model simulations, the production of 14 C appears in agreement with that of 10 Be Melott and Thomas 2012;Pavlov et al 2013). Although some exotic scenarios were proposed for the event: an unidentified nearby supernova ); a gamma-ray burst (Hambaryan and Neuhäuser 2013;Pavlov et al 2013); or even a cometary impact on Earth (Liu et al 2014), it is generally accepted now that it was a signature of a (probably, consequence of) extreme SEP event Eichler and Mordecai 2012;Usoskin et al 2013;Melott and Thomas 2012;Thomas et al 2013;Cliver et al 2014). A detailed analysis performed by Mekhaldi et al (2015) not only confirmed its solar origin but also made it possible to assess, based on data from different cosmogenic isotopes, the reconstructed integral spectrum as shown in Fig.…”

Supernovae and Single-Year Anomalies in the Atmospheric Radiocarbon Record

“…$ Furthermore,$ it$ has$ since$ been$ established$ that$ the$ anomalies$ were$ globally$ synchronous$ and$ approximately$ uniform$ in$ magnitude.$ The$ 775$ CE$ spike$ has$ already$ been$ uncovered$in$dendrochronological$archives$from$Germany$ (Usoskin$et#al.$2013),$ the$ USA$ and$ Russia$ (Jull$ et# al.$ 2014),$ and$ New$ Zealand$ (Güttler$ et# al.$ 2015).$ Henceforth,$ these$ singlePyear$ spikes$ in$ 14 C$ concentration$ will$ be$ referred$ to$ as$ Miyake#Events.$$ $ In$addition$to$their$unprecedented$abruptness$and$scale,$Miyake$Events$are$also$ unique$because$they$represent$significant$increases$in$ 14 C.$A$myriad$of$geological$ and$ oceanographic$ processes$ can$ drive$ depletions,$ but$ no$ terrestrial$ process$ -$ prior$ to$ the$ nuclear$ age$-$could$be$responsible$for$such$sharp$enrichments.$On$ this$ basis,$ as$ well$ as$ their$ global$ impact,$ it$ was$ deduced$ that$ the$ spikes$ must$ have$ been$ the$ result$ of$ intense$ pulses$ of$ radiation$ from$ space.$ At$ first,$ the$ sun$ was$ not$ considered$ a$ likely$ cause,$ as$ it$ was$ not$ thought$ capable$ of$ emitting$ radiation$ of$ the$ required$ energy,$ so$ supernovae$ and$ other$ γPray$ sources$ were$ preferred$ (Miyake$ et# al.$ 2012;$ Pavlov$ et# al.$ 2013;$ Hambaryan$ $ &$ Neühauser$ 2013).$However,$the$consensus$now$is$that$intense$Solar$Energetic$Particle$(SEP)$ events$ were$ indeed$ responsible$ (Melott$ &$ Thomas$ 2012;$ Thomas$ et# al.$ 2013;$ Usoskin$et#al.$2013;$Güttler$et#al.$2015;$Mekhaldi$et#al.$2015).$SEPs$either$arise$ because$ of$ extreme$ solar$ flares$ or$ Interplanetary$ Coronal$ Mass$ Ejections$ (ICMEs).$ A$ supernova$ origin$ has$ now$ effectively$ been$ discounted,$ on$ two$ main$ grounds.$ Firstly,$ no$ historical$ observations$ exist$ for$ supernovae$ around$ 775$ or$ 994$ CE;$ although,$ the$ expected$ galactic$ SN$ rate$ of$~$ 1$ -$ 2$ per$ century$ does$ suggest$that$many$past$events$have$gone$undetected$ (Tammann$et#al.$1994).$As$ is$ shown$ in$ Table$ 1,$ only$ a$ handful$ of$ observations$ do$ exist,$ and$ none$ of$ them$ pertain$ to$ the$ night$ sky$ of$ the$ Southern$ Hemisphere.$ $ Secondly,$ no$ Galactic$ supernova$remnant$can$be$attributed$to$an$event$at$either$of$these$dates.$$ The$aim$of$this$study$is$to$establish$categorically$whether$any$historical$SNe$can$ be$detected$in$the$past$atmospheric$ 14 C$record.$$ * Methods* We$ combined$ new$ and$ existing$ 14 C$ measurements$ on$ annual$ treePrings$ that$ traversed$the$following$historical$astronomical$records.$ Figure$1.$If$anything,$a$levelling$or$gradual$decrease$in$atmospheric$ 14 C$levels$can$ be$discerned$in$the$data$for$the$ten$years$following$each$historical$observation.$It$ is$ important$ to$ emphasise$ that$ the$ observation$ dates$ of$ the$ supernovae$ in$ the$ second$ millennium$ CE$ are$ exactly$ known,$ although$ the$ evidence$ pertaining$ to$ the$ earlier$ events$ is$ more$ equivocal.$ Thus,$ any$ rise$ in$ 14 C,$ which$ predates# the$ historical$observation,$as$can$be$seen$in$the$profile$relating$to$SN1054,$cannot$be$ causally$ linked$ with$ the$ stellar$ explosi...…”

The Economic Impact of Space Weather: Where Do We Stand?

“…(56,83) Alternative proxies, Carbon-14 (in tree rings) and Beryllium-10 (in polar ice cores), are of current interest, (84,85) strongly suggesting an intense global atmospheric radiation event occurred around AD775 (86)(87)(88)(89) due to the Sun. (87,(90)(91)(92) Geomagnetic storm statistics are more complex because likelihood depends on both the solar wind driver (typically, but not exclusively, a CME) and the magnetospheric response. The probability of a Carrington-like event occurring in the next decade is estimated to be 12% (55) (50% in the next 50 years).…”