EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Detection of solar proton events by using radiocarbon in tree-rings

Nicolas Brehm1, Marcus Christl1, Hans-Arno Synal1, Raimund Muscheler2, Florian Adolphi3, Alex Bayliss4, Timothy Knowles5, Emanuelle Casanova6, Kurt Nicolussi7, and Lukas Wacker1
Nicolas Brehm et al.
  • 1ETH Zürich, Physics, IPA, Switzerland (
  • 2Climate and Environmental Physics, Physics Institute & Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 3Department of Geology, Lund University , Lund, Sweden
  • 4Historic England, Cannon Bridge House, London, UK
  • 5BRAMS, University of Bristol, Bristol, UK
  • 6School of Chemistry, University of BristoBristol, UK
  • 7Institute of Geography, University of Innsbruck, Innsbruck, Austria

Our Sun erratically expels large amounts of energetic particles into the interplanetary space and towards Earth, which can be observed as so-called solar proton events (SPE). A strong SPE might cause major damage to satellites and could even disrupt transformers at the ground1. This rises the questions how often strong SPEs occur. Since direct observations of SPEs are limited to the last decades, cosmogenic radionuclides can be used to detect such events further back in time. The production rate of cosmogenic nuclides, such as radiocarbon, is primarily dependent on the incoming flux of highly energetic galactic cosmic rays (GCR). Under normal conditions, the Sun’s magnetic field carried by the (low energy) solar protons shields us from (high energy) GCRs, resulting in a lower production of cosmogenic radionuclides when the Sun is active. During a SPE, however, the sudden and drastic increase of high the energy solar protons themselves may lead to an elevated production of cosmogenic radionuclides on Earth. Only recently, such sharp increases in cosmogenic nuclide production occurring within less than one year have been detected in several radionuclide records (10Be, 36Cl, 14C) from ice core and tree ring records, and have been attributed to SPEs2,3.

Until now, only three SPE could confidently be detected in cosmogenic radionuclide records1,4,5. The reason for this is a general lack of accurately dated and annually resolved radionuclide records and/or the strong dampening of the production signal e.g. by the carbon cycle. To find and identify such events we measured radiocarbon in tree ring records at annual resolution with accelerator mass spectrometry (AMS). In this new, accurately dated and annually resolved 14C record spanning the past about 1000 yr we found several new candidates for SPEs. Their timing and amplitude in terms of cosmogenic nuclide production was characterized by using a global carbon cycle box model. Once unambiguously identified such spiked production increases recorded in the absolutely dated tree ring record have a great potential to be used as a global tool to synchronize other not well dated (climate) records with cosmogenic radionuclides (e.g. 10Be, 36Cl).

1              Schrijver, C. J. et al. (2012) Estimating the frequency of extremely energetic solar events, based on solar, stellar, lunar, and terrestrial records. Journal of Geophysical Research: Space Physics 117

2              Miyake, F., Masuda, K. & Nakamura, T. (2013) Another rapid event in the carbon-14 content of tree rings. Nature communications 4, 1748

3              Mekhaldi, F. et al. (2015) Multiradionuclide evidence for the solar origin of the cosmic-ray events of ᴀᴅ 774/5 and 993/4. Nature Communications 6, 8611

4              Miyake, F., Nagaya, K., Masuda, K. & Nakamura, T. A (2012) signature of cosmic-ray increase in AD 774-775 from tree rings in Japan. Nature 486, 240-242

5              O'Hare, P. et al. (2019) Multiradionuclide evidence for an extreme solar proton event around 2,610 B.P. ( approximately 660 BC). Proc Natl Acad Sci U S A 116, 5961-5966

How to cite: Brehm, N., Christl, M., Synal, H.-A., Muscheler, R., Adolphi, F., Bayliss, A., Knowles, T., Casanova, E., Nicolussi, K., and Wacker, L.: Detection of solar proton events by using radiocarbon in tree-rings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17774,, 2020

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