Regional Differences in Carbon-14 Data of the 993 CE Cosmic Ray Event

Abstract

Cosmogenic nuclides such as 14C from tree rings and 10Be and 36Cl from ice cores are excellent proxies for the past extremely large solar energetic particle (SEP) events, which are dozens of times larger than the largest SEP event in the history of observation. So far, several rapid 14C increases have been discovered, which are considered to have originated from extreme SEP events (or set of successive SEP events) from verifications using multiple cosmogenic nuclide analyses in natural archives. Although these events are characterized by a rapid increase in cosmogenic nuclide concentrations, 14C data recorded worldwide do not always show similar variations, especially during the 993 CE event, where a rapid increase was recorded in either 992–993 CE or 993–994 CE in several records. We present new 14C data of the Japanese cedar sample for the 993 CE event. Although the latest data show no significant increase in 1 year, an overall increase pattern is consistent with the previously reported 14C data of the Japanese cedar, which supports that a significant 14C increase occurred from 993 to 994 CE in the Japanese sample. Given the dominant 14C production in high latitudes by SEPs, the difference in timing of increase may be a transport effect in the atmosphere. Moreover, the difference in the timing of the 14C increase can cause a 1-year age-determination error using the 993 CE radiocarbon spike. Compared with the 14C data between tree samples from high latitude and midlatitude, including Japan, high-latitude data can capture 14C changes originating from SEP events more quickly and clearly and may be more suitable for a SEP event exploration in the past.

Modelling cosmic radiation events in the tree-ring radiocarbon record

“…A similar late rise is found in Japanese cedar for the 993 CE event by Miyake et al [114], who interpret this as being affected by global atmospheric circulation patterns in different latitudinal Radiocarbon Zones, and an oceanic versus continental distinction. By contrast, in the ensemble of tree rings over 774 CE, prolonged and sharp rises are seen across these categories: there are trees showing both phenomenologies from Zones 0-2, continental or oceanic regions, different growth speeds and altitudes.…”

“…We exclude the Japanese cedar from Miyake et al. [114], as it shows a delayed rise compared to the other 993 CE datasets, and for the purposes of the present work, we await a consensus on how to interpret this.…”

“…We apply this code to an analysis of all publicly available 14 C data for the six events previously identified in the literature, gathering the COSMIC network data from many sites across both hemispheres for 774 CE and 993 CE from Büntgen et al [23]; additional data, including early and late wood data, for 774 CE from Uusitalo et al [112], and Danish oak over 993 CE from Fogtmann-Schulz et al [64]; English oak over 993 CE from Rakowski et al [113]; the discovery data for 7176 BCE and 5259 BCE from Brehm et al [16]; earl tree-rings over 660 BCE from Park et al [15], and early and late wood over 660 BCE from Sakurai et al [24]; and data from the decades leading up to 5410 BCE from Miyake et al [25]. We exclude the Japanese cedar from Miyake et al [114], as it shows a delayed rise compared to the other 993 CE datasets, and for the purposes of the present work, we await a consensus on how to interpret this. Before examining the modelled outputs in detail, some general observations should be made about the reliability and sensitivity of the underlying data.…”

Transient Offset in 14C After the Carrington Event Recorded by Polar Tree Rings

“…Such observations cannot be understood assuming that atmospheric 14 C transport occurs solely through mid‐latitudes, unless production occurred near ground levels at high latitudes. In fact, considering the 993 CE event, it is puzzling why there is no increase at all in the mean values of the low latitude zone (NH2) for the year 993 CE, as opposed to the more northern locations of NH1 and particularly of NH0 (Figure 4d of Miyake et al., 2022). All the above indicate fast high‐latitude transport of stratospheric air to troposphere consistent with Liang et al.…”

“…A fast rise of 14 C level in high-latitude trees in Finnish Lapland (Uusitalo et al, 2018) and Yamal (Jull et al, 2014) has been observed in 774 CE. Furthermore, an early elevated signal in high-latitude trees has been observed in 993 CE (Miyake et al, 2022). Such observations cannot be understood assuming that atmospheric 14 C transport occurs solely through mid-latitudes, unless production occurred near ground levels at high latitudes.…”