University of Oulu

Brehm, N., Christl, M., Knowles, T.D.J. et al. Tree-rings reveal two strong solar proton events in 7176 and 5259 BCE. Nat Commun 13, 1196 (2022).

Tree-rings reveal two strong solar proton events in 7176 and 5259 BCE

Saved in:
Author: Brehm, Nicolas1; Christl, Marcus1; Knowles, Timothy D. J.2;
Organizations: 1Laboratory of Ion Beam Physics, ETHZ, Otto-Stern Weg 5 HPK, 8093, Zurich, Switzerland
2Bristol Radiocarbon Accelerator Mass Spectrometry Facility, Bristol University, Bristol, BS81TS, UK
3Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, 27568, Bremerhaven, Germany
4Department of Geology – Quaternary Sciences, Lund University, 22362, Lund, Sweden
5British Antarctic Survey, Ice Dynamics and Paleoclimate, Cambridge, CB3 0ET, UK
6Albrecht von Haller Institute for Plant Sciences, Department of Palynology and Climate Dynamics, Georg-August-University, Wilhelm-Weber-Str. 2a, 37073, Göttingen, Germany
7Historic England, Cannon Bridge House, 25 Dowgate Hill, London, EC4R 2YA, UK
8Department of Geography, Universität Innsbruck, Innrain 52, 6020, Innsbruck, Austria
9Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012, Bern, Switzerland
10University of Arizona, the Laboratory for Tree-Ring Research, 1215 E. Lowell Street, Tucson, AZ, 85721-0045, USA
11Swiss Federal Research Institute WSL, Zürcherstrasse 111, 8903, Birmensdorf, Switzerland
12Laboratory of Dendrochronology, Institute of Plant and Animal Ecology, Ural Branch of Russian Academy of Sciences, 8 Marta Street, 202, Ekaterinburg, 620144, Russia
13Laboratory of Natural Science Methods in Humanities, Ural Federal University, 19 Mira Street, Ekaterinburg, 620002, Russia
14School of Natural and Built Environment, The Queen’s University, Belfast, BT7 1NN, UK
15Sodankylä Geophysical Observatory and Space Physics and Astronomy Research Unit, University of Oulu, Oulu, FIN-90014, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.5 MB)
Persistent link:
Language: English
Published: Springer Nature, 2022
Publish Date: 2022-05-17


The Sun sporadically produces eruptive events leading to intense fluxes of solar energetic particles (SEPs) that dramatically disrupt the near-Earth radiation environment. Such events have been directly studied for the last decades but little is known about the occurrence and magnitude of rare, extreme SEP events. Presently, a few events that produced measurable signals in cosmogenic radionuclides such as ¹⁴C, ¹⁰Be and ³⁶Cl have been found. Analyzing annual ¹⁴C concentrations in tree-rings from Switzerland, Germany, Ireland, Russia, and the USA we discovered two spikes in atmospheric ¹⁴C occurring in 7176 and 5259 BCE. The ~2% increases of atmospheric ¹⁴C recorded for both events exceed all previously known ¹⁴C peaks but after correction for the geomagnetic field, they are comparable to the largest event of this type discovered so far at 775 CE. These strong events serve as accurate time markers for the synchronization with floating tree-ring and ice core records and provide critical information on the previous occurrence of extreme solar events which may threaten modern infrastructure.

see all

Series: Nature communications
ISSN: 2041-1723
ISSN-E: 2041-1723
ISSN-L: 2041-1723
Volume: 13
Article number: 1196
DOI: 10.1038/s41467-022-28804-9
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: The Laboratory of Ion Beam Physics is partially funded by its consortium partners PSI, EAWAG, and EMPA. N.B. is funded by the Swiss National Science Foundation (SNSF grant #SNF 197137). The establishment of the BRAMS Facility was jointly funded by the NERC, BBSRC and the University of Bristol and the measurements in this work were partly funded by an ERC Proof of Concept grant awarded to R.P.E. and financing E.C. postdoctoral contract (LipDat H2020 ERC-2018-PoC/812917). We thank Bisserka Gaydarska for sub-sampling the inter-laboratory replicates from M49, M234, Q2729 and Q2750, Cathy Tyers for reviewing the dating of the Irish and German samples, and Alexander Land for assistance in dating sample M49. P.F. received funding from the SNF Sinergia project CALDERA (no. 183571). R.H. is funded by Russian Science Foundation (grant # 21-14-00330). I.U. acknowledges the support from the Academy of Finland (grant 321882 ESPERA). C.L.P.’s and M.W.S.’s work on bristlecone pine was funded by the M.H. Wiener Foundation (ICCP Project). K.N. acknowledges the support provided by the Austrian Science Fund FWF (grant I-1183-N19).
Academy of Finland Grant Number: 321882
Detailed Information: 321882 (Academy of Finland Funding decision)
Copyright information: © The Author(s) 2022. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit