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Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE

2018; Nature Portfolio; Volume: 9; Issue: 1 Linguagem: Inglês

10.1038/s41467-018-06036-0

2041-1723

Ulf Büntgen, Lukas Wacker, J. Diego Galván, Stephanie Arnold, Dominique Arseneault, M. G. L. Baillie, Jürg Beer, Mauro Bernabei, Niels Bleicher, Gretel Boswijk, Achim Bräuning, Marco Carrer, Fredrik Charpentier Ljungqvist, Paolo Cherubini, Marcus Christl, Duncan A. Christie, Peter W. Clark, Edward R. Cook, Rosanne D’Arrigo, Nicole Davi, Ólafur Eggertsson, Jan Esper, Anthony M. Fowler, Ze’ev Gedalof, Fabio Gennaretti, Jussi Grießinger, H. D. Grissino-Mayer, Håkan Grudd, Björn E. Gunnarson, Rashit Hantemirov, Franz Herzig, Amy E. Hessl, Karl-Uwe Heußner, A. J. T. Jull, Vladimir V. Kukarskih, Alexander V. Kirdyanov, Tomáš Kolář, Paul J. Krusic, Tomáš Kyncl, Antonio Lara, Carlos LeQuesne, Hans W. Linderholm, Neil J. Loader, Brian H. Luckman, Fusa Miyake, Vladimir S. Myglan, Kurt Nicolussi, Clive Oppenheimer, Jonathan Palmer, Irina P. Panyushkina, Neil Pederson, Michal Rybníček, Fritz Hans Schweingruber, Andrea Seim, Michael Sigl, Olga V. Churakova, James H. Speer‬, H.-A. Synal, Willy Tegel, Kerstin Treydte, Ricardo Villalba, Greg Wiles, Rob Wilson, Lawrence J. Winship, Jan Wunder, Bao Yang, Giles Young,

Climate variability and models

Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770-780 and 990-1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.