Multiradionuclide evidence for the solar origin of the cosmic-ray events of ᴀᴅ 774/5 and 993/4.
The origin of two large peaks in the atmospheric radiocarbon ((14)C) concentration at AD 774/5 and 993/4 is still debated. There is consensus, however, that these features can only be explained by an increase in the atmospheric (14)C production rate due to an extraterrestrial event. Here we provide evidence that these peaks were most likely produced by extreme solar events, based on several new annually resolved (10)Be measurements from both Arctic and Antarctic ice cores. Using ice core (36)Cl data in pair with (10)Be, we further show that these solar events were characterized by a very hard energy spectrum with high fluxes of solar protons with energy above 100 MeV. These results imply that the larger of the two events (AD 774/5) was at least five times stronger than any instrumentally recorded solar event. Our findings highlight the importance of studying the possibility of severe solar energetic particle events.
Department of Geology-Quaternary Sciences, Lund University, 22362 Lund, Sweden.
Florian
http://orcid.org/0000-0001-8323-2955
F
Mekhaldi
Department of Geology-Quaternary Sciences, Lund University, 22362 Lund, Sweden.
Raimund
R
Muscheler
Department of Geology-Quaternary Sciences, Lund University, 22362 Lund, Sweden.
Florian
http://orcid.org/0000-0003-0014-8753
F
Adolphi
Department of Geology, United Arab Emirates University, 17551 Al Ain, UAE.|Department of Earth Sciences, Uppsala University, 75236 Uppsala, Sweden.
Ala
A
Aldahan
Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
Jürg
J
Beer
Division of Hydrologic Sciences, Desert Research Institute, Reno, Nevada 89512, USA.
Joseph R
JR
McConnell
Tandem Laboratory, Uppsala University, 75120 Uppsala, Sweden.
Göran
G
Possnert
Division of Hydrologic Sciences, Desert Research Institute, Reno, Nevada 89512, USA.|Laboratory for Radiochemistry and Environmental Chemistry, Paul Scherrer Institut, 5232 Villigen, Switzerland.
Michael
M
Sigl
Center for Ice and Climate, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark.
Anders
http://orcid.org/0000-0002-4364-6085
A
Svensson
Laboratory of Ion Beam Physics, ETH Zürich, 8093 Zürich, Switzerland.
Hans-Arno
HA
Synal
Space Sciences Laboratory, University of California, Berkeley, California 94720, USA.
Kees C
KC
Welten
PRIME Laboratory, Purdue University, West Lafayette, Indiana 47907, USA.
Thomas E
TE
Woodruff