Tree-rings reveal two strong solar proton events in 7176 and 5259 BCE
2 Organic Geochemistry Unit - OGU (Bristol, United Kingdom)
3 University of Bristol [Bristol]
4 BioArch - BioArchéologie, Interactions Sociétés Environnements
5 Alfred Wegener Institute [Potsdam]
6 Skane University Hospital [Lund]
7 Georg-August-University of Goettingen = Georg-August-Universität Göttingen
8 Historic England
9 Institute of Geography
10 Universität Bremen [Deutschland] = University of Bremen [Germany] = Université de Brême [Allemagne]
11 UNIBE - Universität Bern = University of Bern = Université de Berne
12 University of Arizona
13 LTRR - Laboratory of Tree-Ring Research [University of Arizona]
14 Swiss Federal Institute for Forest, Snow and Landscape Research WSL
15 Laboratory of Dendrochronology, Institute of Plant and Animal Ecology, Ural Branch of Russian Academy of Sciences
16 SGO - Sodankyla Geophysical Observatory, University of Oulu
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Résumé
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 14 C, 10 Be and 36 Cl have been found. Analyzing annual 14 C concentrations in tree-rings from Switzerland, Germany, Ireland, Russia, and the USA we discovered two spikes in atmospheric 14 C occurring in 7176 and 5259 BCE. The ~2% increases of atmospheric 14 C recorded for both events exceed all previously known 14 C 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.