Publication: Multi-centennial fluctuations of radionuclide production rates are modulated by the Earth's magnetic field
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2018-06-29
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Nature Publishing Group
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Abstract
The production of cosmogenic isotopes offers a unique way to reconstruct solar activity during the Holocene. It is influenced by both the solar and Earth magnetic fields and thus their combined effect needs to be disentangled to infer past solar irradiance. Nowadays, it is assumed that the long-term variations of cosmogenic production are modulated by the geomagnetic field and that the solar field dominates over shorter wavelengths. In this process, the effects of the non-dipolar terms of the geomagnetic field are considered negligible. Here we analyse these assumptions and demonstrate that, for a constant solar modulation potential, the geomagnetic field exerts a strong modulation of multi-centennial to millennial wavelengths (periods of 800 and 2200 yr). Moreover, we demonstrate that the non-dipole terms derived from the harmonic degree 3 and above produce maximum differences of 7% in the global average radiocarbon production rate. The results are supported by the identification, for the first time, of a robust coherence between the production rates independently estimated from geomagnetic reconstructions and that inferred from natural archives. This implies the need to review past solar forcing reconstructions, with important implications both for the assessment of solar-climate relationships as well as for the present and future generation of paleoclimate models.
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© 2018 The Author(s)
F.J.P.C. is funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 659901. F.J.P.C. and J.F.G.R. acknowledge the Marie Sklodowska-Curie project CLIMAGNET. M.G.P acknowledges the Ramon y Cajal Program. The authors are grateful to the Spanish research projects CGL2017-87015-P/CGL2015-63888-R of the Spanish Ministry of Economy and Competitiveness. We are also grateful to the Editor and two anonymous reviewers for their constructive comments.