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

• Authors: BÜNTGEN Ulf; WACKER Lukas; GALVAN J Diego; ARNOLD Stephanie; ARSENEAULT Dominique; BAILLIE Michael; BEER Jurg; BERNABEI Mauro; BLEICHER Niels; BOSWIJK Gretel; BRAUNING Achim; CARRER Marco; LJUNGQVIST Fredrik Charpentier; CHERUBINI Paolo; CHRISTL Marcus; CHRISTIE Duncan A.; CLARK Peter W.; COOK Edward R.; DARRIGO Rosanne; DAVI Nicole; EGGERTSSON Olafur; ESPER Jan; FOWLER Anthony M.; GEDALOF Zeev; GENNARETTI Fabio; GRIESSINGER Jussi; GRISSINO-MAYER Henri; GRUDD Hakan; GUNNARSON Bjorn E; HANTEMIROV Rashit; HERZIG Franz; HESSL Amy; HEUSSNER Karl-Uwe; JULL A. J. Timothy; KUKARSKIH Vladimir; KIRDYANOV Alexander; KOLAR Tomas; KRUSIC Paul J.; KYNCL Tomas; LARA Antonio; LEQUESNE Carlos; LINDERHOLM Hans W.; LOADER Neil J.; LUCKMAN Brian; MIYAKE Fusa; MYGLAN Vladimir S.; NICOLUSSI Kurt; OPPENHEIMER Clive; PALMER Jonathan; PANYUSHKINA Irina; PEDERSON Neil; RYBNICEK Michal; SCHWEINGRUBER Fritz H; SEIM Andrea; SIGL Michael; CHURAKOVA Olga; SPEER James H.; SYNAL Hans-Arno; TEGEL Willy; TREYDTE Kerstin; VILLALBA Ricardo; WILES Greg; WILSON Rob; WINSHIP Lawrence J.; WUNDER Jan; YANG Bao; YOUNG Giles H. F.
• Year of publication: 2018
• Type: Article in Periodical
• Magazine / Source: Nature Communications
• MU Faculty or unit: Faculty of Science
• Web: Full Text
• Doi: http://dx.doi.org/10.1038/s41467-018-06036-0
• Keywords: COSMIC-RAY EVENT; ATMOSPHERIC RADIOCARBON; AD 774-775; C-14; GRAPHITIZATION; VARIABILITY; MILLENNIUM; DYNAMICS; GRADIENT; INCREASE
• Description: 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 C-14 content in 484 individual tree rings formed in the periods 770-780 and 990-1000 CE. Distinct C-14 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 C-14 measurements are needed.