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

Ulf Büntgen (1, 2, 3, 4) , Lukas Wacker (5) , J. Diego Galvan (2) , Stephanie Arnold (5) , Dominique Arseneault (6) , Michael Baillie (7) , Jürg Beer (8) , Mauro Bernabei (9) , Niels Bleicher (10) , Gretel Boswijk (11) , Achim Bräuning , Marco Carrer (12) , Fredrik Charpentier Ljungqvist (13, 14, 1) , Paolo Cherubini (2) , Marcus Christl (5) , Duncan A. Christie (15, 16) , Peter W. Clark (17) , Edward R. Cook (18) , Nicole Davi (19, 18) , Jan Esper (20) , Anthony M. Fowler (11) , Fabio Gennaretti (21) , Jussi Griessinger , Henri Grissino-Mayer (22) , Hakan Grudd (23) , Bjorn E. Gunnarson (24, 13) , Rashit Hantemirov (25) , Franz Herzig (26) , Amy Hessl (27) , Karl-Uwe Heussner (28) , A. J. Timothy Jull (29, 30, 31) , Vladimir Kukarskih (32) , Alexander Kirdyanov (1, 33, 32) , Tomáš Kolář (34) , Paul J. Krusic (24, 35, 1) , Tomáš Kyncl (4) , Antonio Lara (15, 16) , Carlos Lequesne (15) , Hans W. Linderholm (36) , Neil J. Loader (37) , Brian Luckman (38) , Fusa Miyake (39) , Vladimir S. Myglan (33) , Kurt Nicolussi (40) , Clive Oppenheimer (1) , Jonathan Palmer (41, 42) , Irina Panyushkina (43) , Neil Pederson (44) , Michal Rybníček (4) , Fritz H. Schweingruber (2) , Andrea Seim (45) , Michael Sigl (46) , Olga Churakova (sidorova) (47, 33) , James H. Speer (48) , Hans-Arno Synal (5) , Willy Tegel (45, 49) , Kerstin Treydte (2) , Ricardo Villalba (50) , Greg Wiles (51) , Rob Wilson (52, 18) , Lawrence J. Winship (53) , Jan Wunder (11, 2) , Bao Yang (54) , Giles H. F. Young (37)

1 Department of geography
2 Swiss Federal Institute for Forest, Snow and Landscape Research WSL
3 MUNI - Masaryk University [Brno]
4 CzechGlobe - Global Change Research Centre
5 Laboratory for Ion Beam Physics
6 Departement de Biologie, Chimie et Géographie
7 QUB - Queen's University [Belfast]
8 EAWAG - Swiss Federal Insitute of Aquatic Science and Technology [Dübendorf]
9 CNR - National Research Council of Italy | Consiglio Nazionale delle Ricerche
10 Office for Urbanism
11 University of Auckland [Auckland]
12 Unipd - Università degli Studi di Padova = University of Padua
13 Bolin Centre for Climate Research
14 Stockholm University
15 Universidad Austral de Chile
16 Centre for Climate and Resilience Research
17 University of Vermont [Burlington]
18 Columbia University [New York]
19 William Paterson University
20 JGU - Johannes Gutenberg - Universität Mainz = Johannes Gutenberg University
21 SILVA - SILVA
22 University of Tennessee
23 Swedish Polar Research Secretariat
24 Department of Physical Geography
25 Institute of Plant and Animal Ecology
26 Bavarian State Office for Monument Protectionent Protect
27 West Virginia University
28 DAI - German Archaeological Institute
29 Department of Geosciences [University of Arizona]
30 University of Arizona
31 Institute of Nuclear Research
32 RAS - Russian Academy of Sciences [Moscow]
33 SibFU - Siberian Federal University
34 MENDELU - Mendel University in Brno
35 NEO - Navarino Environmental Observatory
36 GU - Göteborgs Universitet = University of Gothenburg
37 Department of Geography
38 UWO - University of Western Ontario
39 Nagoya University
40 Institute of Geography
41 PANGEA Research Centre - Palaeontology, Geobiology and Earth Archives Research Centre
42 UNSW - University of New South Wales [Sydney]
43 Laboratory of Tree-Ring Research
44 Harvard Forest
45 University of Freiburg [Freiburg]
46 IPS - Institut Paul Scherrer
47 UNIGE - Université de Genève = University of Geneva
48 Indiana State University
49 Archaeological Service Kanton Thurgau
50 Glaciología y Ciencias Ambientales IANIGLA
51 College of Wooster
52 University of St Andrews [Scotland]
53 School of Natural Science
54 CAS - Chinese Academy of Sciences

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.

Mots clés: cosmic-ray event; atmospheric radiocarbon; graphitization; variability; millennium; increase; ad 774-775; c-14

Mots clés: dynamics; gradient

Domaines: Sciences du Vivant [q-bio]

Ulf Büntgen, Lukas Wacker, J. Diego Galvan, Stephanie Arnold, Dominique Arseneault, et al.. Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE. Nature Communications, 2018, pp.1-7. ⟨10.1038/s41467-018-06036-0⟩. ⟨hal-02625527⟩