A rapid cosmic-ray increase in BC 3372-3371 from ancient buried tree rings in China

TL;DR

This study identifies a rapid increase in $^{14}$C in ancient Chinese tree rings around BC 3372-3371, suggesting a significant cosmic-ray event likely caused by a large solar proton event.

Contribution

It provides the first high-resolution $^{14}$C data from ancient tree rings for BC 3388-3358, revealing a previously undocumented rapid $^{14}$C increase.

Findings

Detected a ~9‰ $^{14}$C increase in BC 3372-3371

Suggests the event was caused by a large solar proton event

Enhances understanding of cosmic-ray event frequency in ancient times

Abstract

Cosmic rays interact with the Earth's atmosphere to produce $^{14}$C, which can be absorbed by trees. Therefore, rapid increases of $^{14}$C in tree rings can be used to probe previous cosmic-ray events. By this method, three $^{14}$C rapidly increasing events have been found. Plausible causes of these events include large solar proton events, supernovae or short gamma-ray bursts. However, due to the lack of measurements of $^{14}$C by year, the occurrence frequency of such $^{14}$C rapidly increasing events is poorly known. In addition, rapid increases may be hidden in the IntCal13 data with five-year resolution. Here we report the result of $^{14}$C measurements using an ancient buried tree during the period between BC 3388 and 3358. We find a rapid increase of about 9\textperthousand~ in the $^{14}$C content from BC 3372 to BC 3371. We suggest that this event could originate from a large solar proton event.