Changes in solar activity during the wolf minimum-new insights from a high-resolution 14c record based on danish oak

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We present a new biennial record of radiocarbon (14C) measured in Danish oak. The new record covers the years 1251-1378 CE, thereby spanning the Grand Solar Minimum known as the Wolf Minimum. Two oak samples from every other year were measured at the AMS facility at Aarhus University (Denmark), resulting in an average precision of 1.4‰ for the record. Spectral analysis of the new record revealed two peaks at 27 and 9.1 years, which could indicate the Hale cycle was lengthened and the Schwabe cycle shortened during the Wolf Minimum, but it is also possible that the amplitude of the Schwabe cycle was too small to be accurately identified with the acquired precision of this record. The record was bandpass filtered to investigate the variability of the amplitude in different bands, which showed a dampening of the amplitude during the second half of the Wolf Minimum in bands centered on the Schwabe and the Hale cycle, respectively. A reconstruction of the solar modulation function, Φ, also showed a periodicity of ca. 9 years, and indicated that the Wolf Minimum was preceeded by one cycle of decreased solar activity.

OriginalsprogEngelsk
TidsskriftRadiocarbon
Vol/bind63
Nummer1
Sider (fra-til)91-104
Antal sider14
ISSN0033-8222
DOI
StatusUdgivet - feb. 2021

Bibliografisk note

Funding Information:
We would like to acknowledge financial support from the Villum Foundation (VKR023114 and VKR010116). Funding for the Stellar Astrophysics Centre is provided by the Danish National Research Foundation (Grant Agreement DNRF106). We thank the staff at AARAMS for help with the laboratory work. We would also like to thank Raimund Muscheler for help with the carbon box model.

Publisher Copyright:
© 2020 by the Arizona Board of Regents on behalf of the University of Arizona.

Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

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