Large ¹⁴ C excursion in 5480 BC indicates an abnormal sun in the mid-Holocene

Abstract

Radiocarbon content in tree rings can be an excellent proxy of the past incoming cosmic ray intensities to Earth. Although such past cosmic ray variations have been studied by measurements of14C contents in tree rings with ≥10-y time resolution for the Holocene, there are few annual14C data. There is a little understanding about annual14C variations in the past, with the exception of a few periods including the AD 774−77514C excursion where annual measurements have been performed. Here, we report the result of14C measurements using the bristlecone pine tree rings for the period from 5490 BC to 5411 BC with 1- to 2-y resolution, and a finding of an extraordinarily large14C increase (20‰) from 5481 BC to 5471 BC (the 5480 BC event). The14C increase rate of this event is much larger than that of the normal grand solar minima. We propose the possible causes of this event are an unknown phase of grand solar minimum, or a combination of successive solar proton events and a normal grand solar minimum.

More Rapid 14C Excursions in the Tree-Ring Record: A Record of Different Kind of Solar Activity at About 800 BC?

“…This effect causes a relatively flat period in apparent 14 C age, as has been noted by earlier studies and referred to as the Hallstatt period (Friedrich and Henning 1996;Grabner et al 2007;Jacobssen et al 2017). To continue our comparison with the 660 BC event (Park et al 2017), we note the rise time of that event is about 11-12 years between BC 667.5 to 659.5, similar to the increase observed in 814-804 BC and the 5480 BC event (Miyake et al 2017a). The 660 BC event of Park et al (2017) is an increase followed by a rapid decline, in contrast to the 5480 BC event and our new event presented here.…”

“…The new events reported here and by Miyake et al (2017a) and Park et al (2017) seem to associate rapid excursions of 14 C with longer-term variations caused by solar minimum-like periodicities. This is a different phenomenon from the apparently short-term and isolated Δ 14 C events at AD 774-775 and AD 993-994.…”

“…The 660 BC event also rises over a longer time (~4-11 yr) compared to the other records. At 5480 BC, a different behavior is observed (Miyake et al 2017a), but also with a rise time of approximately 10 years. Other different kinds of events at 2460 BC have already been proposed by Larsson and Larsson (2017).…”

“…Two radiocarbon ( 14 C) excursions are caused by an increase of incoming cosmic rays on a short time scale found in the Late Holocene , which are widely explained as due to extreme solar proton events (SPE). In addition, a larger event has also been reported at 5480 BC (Miyake et al 2017a), which is attributed to a special mode of a grand solar minimum, as well as another at 660 BC (Park et al 2017). Clearly, other events must exist, but could have different causes.…”

Causation of Late Quaternary Rapid-increase Radiocarbon Anomalies

“…IntCal13 results showing a steep rise of 15.3‰ D 14 C between 7440 and 7410 BP are provided in Figure 1c, but detailed 14 C assays for this period from Bristlecone Pine are also available with a 1-2 y resolution. They demonstrate a large increase (20‰) over ten years, from 7431 to 7421 BP (Miyake et al 2017). Recently, the distance of S165 was revised downward to ~.7 kpc and with an age of approximately 7500 BP; the total energy is estimated at 5 x 10 51 ergs as a Type II event (Yar-Uyaniker et al 2004).…”