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

Radiocarbon in tree-rings reveals the solar 11-yr cycle over the last millennium

Lukas Wacker1, Nicolas Brehm1, Alex Bayliss2, Marcus Christl1, Hans-Arno Synal1, Florian Adolphi3,4, Jürg Beer5, Bernd Kromer6, Raimund Muscheler3, Sami K. Solanki7,8, Ilya Usoskin9, Niels Bleicher10, Silvia Bollhalder1, and Cathy Tyres2
Lukas Wacker et al.
  • 1ETH Zurich, Ion Beam Physics, Physic, Zürich, Switzerland (
  • 2Historic England, London, UK
  • 3Department of Geology, Lund University, Lund, Sweden
  • 4Climate and Environmental Physics, Physics Institute & Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 5Eawag, Dübendorf, Switzerland
  • 6Heidelberg University, Institute of Environmental Physics, Heidelberg, Germany
  • 7Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
  • 8School of Space Research, Kyung Hee University, Yongin, Gyeonggi-Do, Republic of Korea
  • 9Space Physics and Astronomy unit and Sodankylä Geophysical Observatory, University of Oulu, Finland
  • 10Underwater archaeology and Dendroarchaeology, Office for Urbanism, Zurich

The influence of solar variability on the Earth’s climate is a major subject of interest for understanding past and predicting future climate changes. While the observational record of solar activity (e.g. sunspots) covers only the last about 400 yr, cosmogenic nuclides stored in tree rings (14C) or ice cores (10Be, 36Cl) are used as proxies for solar activity and allow solar reconstructions reaching much further back in time 1-3. Major drawbacks of cosmogenic nuclide based solar reconstructions are the presence of weather-induced noise (e.g. 10Be in ice cores) or the low temporal resolution of long precisely dated records (14C in tree rings). Here, we present a continuous, annually resolved 14C record from precisely dated tree rings covering the past about 1’000 yr (969-1933 AD) comprising almost 1’300 highest-precision 14C measurements. The annually resolved 14C record adds significantly to the radiocarbon calibration curve4, which has hitherto been based mainly on decay counting measurements. A multi box carbon cycle model is used to extract annual 14C production changes from the tree ring data. The resulting high-resolution record of 14C production is then used to reconstruct the solar modulation parameter over the last millennium. The comparison of solar modulation with global temperature provides evidence that low solar activity could have caused the temperature reduction during the Little Ice Age. The 14C record further reveals for the first time the presence of the eleven-year solar cycle over the past 1’000 yr. The amplitude of this so called Schwabe cycle is found to correlate with the general level of the solar modulation with high amplitudes during periods of strong solar modulation and vice versa.


1 Bard, E., Raisbeck, G., Yiou, F. & Jouzel, J. (2000) Solar irradiance during the last 1200 years based on cosmogenic nuclides. Tellus Series B-Chemical and Physical Meteorology 52, 985-992.

2 Muscheler, R. et al. (2007) Solar activity during the last 1000 yr inferred from radionuclide records. Quaternary Science Reviews 26, 82-97.

3 Usoskin, I.G. (2017) A history of solar activity over millennia, Living Rev. Sol. Phys. 14, 3.

4 Reimer, P. J. et al. (2013) Intcal13 and Marine13 Radiocarbon Age Calibration Curves 0-50,000 Years Cal Bp. Radiocarbon 55, 1869-1887.

How to cite: Wacker, L., Brehm, N., Bayliss, A., Christl, M., Synal, H.-A., Adolphi, F., Beer, J., Kromer, B., Muscheler, R., Solanki, S. K., Usoskin, I., Bleicher, N., Bollhalder, S., and Tyres, C.: Radiocarbon in tree-rings reveals the solar 11-yr cycle over the last millennium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11118,, 2020

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