Excursions in the ¹⁴C record at A.D. 774–775 in tree rings from Russia and America

Abstract

The calibration of radiocarbon dates by means of a master calibration curve has been invaluable to Earth, environmental and archeological sciences, but the fundamental reason for calibration is that atmospheric radiocarbon content varies because of changes in upper atmosphere production and global carbon cycling. Improved instrumentation has contributed to high-resolution (interannual) radiocarbon activity measurements, which have revealed sudden and anomalous activity shifts previously not observed at the common resolution of 5-10 years of most of the calibration scale. One such spike has been recently reported from tree rings from Japan and then again in Europe at A.D. 774-775, for which we report here our efforts to both replicate its existence and determine its spatial extent using tree rings from larch at high latitude (northern Siberia) and bristlecone pine from lower latitude (the White Mountains of California). Our results confirm an abrupt~15‰ 14 C activity increase from A.D. 774 to 776, the size and now the hemispheric extent of which suggest that an extraterrestrial influence on radiocarbon production is most likely responsible.

Relationship between solar activity and Δ14C peaks in AD 775, AD 994, and 660 BC

“…The strongest peak of Δ 14 C, corresponding to the event of AD 775 (called henceforth M12), and another peak in AD 993/4 were measured by Miyake (Miyake et al 2012(Miyake et al , 2013) using 14 C in annually resolved Japanese cedar tree-ring sequences, and M12 has been confirmed by several studies (Usoskin et al 2013;Jull et al 2014;Güttler et al 2015;Rakowski et al 2015;Büntgen et al 2016) including three that showed peaks with slightly different starting times. Data from high-latitude Siberian and Altai (Jull et al 2014;Büntgen et al 2016) record the AD 775 peak but show a Δ 14 C rise beginning one year earlier, and Δ 14 C data in New Zealand kauri (Güttler et al 2015) indicate a peak delayed by half a year.…”

“…The Carrington Event of 1859 involved major magnetic storms on August 28-29 and September 2-3, with auroras visible at geomagnetic latitudes as low as 25°and 18°, respectively (Green and Boardsen 2006), suggesting that two closely spaced CMEs interacted strongly with the geomagnetic field. As noted by Jull et al (2014), there is no evidence for this event in the annual 14 C record, which at first sight appears to Solar Activity and Δ 14 C Peaks 1153 https://www.cambridge.org/core/terms. https://doi.org/10.1017/RDC.2017.59 challenge the hypothesis outlined above, but we have no information on the intensity, spectrum, and duration of the SEP event and the conditions for efficient particle acceleration leading to a very hard energy spectrum may not have been met (Li et al 2006).…”

“…Recently, superflares from Sun-like stars were observed with a thousand times the energy release of the largest flares on our Sun, although the life stage at which Sun-like stars make superflares and differences between the Sun and Sun-like stars are still under debate (Maehara et al 2012(Maehara et al , 2015. This is a popular theory (Miyake et al 2012;Usoskin et al 2013;Jull et al 2014;Mekhaldi et al 2015) but a potential problem is that it requires a SEP fluence at least five times larger than for any event recorded in the era of ground-based or satellite observations (Mekhaldi et al 2015). Therefore, we consider the fact that large SEP events are often also associated with large geomagnetic storms (Li et al 2006), which can have the effect of enlarging the area of the atmosphere that is irradiated by solar energetic particles (Leske et al 2001).…”

“…Data from high-latitude Siberian and Altai (Jull et al 2014;Büntgen et al 2016) record the AD 775 peak but show a Δ 14 C rise beginning one year earlier, and Δ 14 C data in New Zealand kauri (Güttler et al 2015) indicate a peak delayed by half a year.…”

“…Gamma rays from supernova and gamma ray bursts have a very short duration time, implying that a short 14 C peak could occur, but M12 concentrations of the cosmogenic isotope 10 Be measured in Antarctic ice are much too high to have been produced by a GRB (Usoskin et al 2013). Since no evidence exists for any Δ 14 C increase due to an historical SEP event (Jull et al 2014), any solar phenomenon associated with the M12 peak must have been extremely intense and/or was a much more prolific producer of 14 C than those in the instrumental record. However, comparison of M12 10 Be and 36 Cl data from polar ice cores (Mekhaldi et al 2015) show a larger percentage increase over the long term background for 36 Cl than 10 Be.…”