@article{d03736de03404d49baf936634b44ddf6,
title = "Multiradionuclide evidence for the solar origin of the cosmic-ray events of 774/5 and 993/4",
abstract = "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.",
author = "Florian Mekhaldi and Raimund Muscheler and Florian Adolphi and Ala Aldahan and J{\"u}rg Beer and McConnell, {Joseph R.} and G{\"o}ran Possnert and Michael Sigl and Anders Svensson and Synal, {Hans Arno} and Welten, {Kees C.} and Woodruff, {Thomas E.}",
note = "Funding Information: We thank Anna Sturevik Storm for her help with the chemical preparation of the NGRIP samples for 10Be measurements. This work was supported by the Swedish Research Council (grant DNR2013-8421 to R.M.). This work was also supported by the U.S. National Science Foundation (NSF) Polar Programs grants including 0839093 and 1142166 to J.R.M. for development of the Antarctic ice-core records and 0909541 and 1204176 to J.R.M. for development of the Arctic ice core records; K.C.W. was funded by NSF grants 0636964 and 0839137; T.W. was funded by NSF grants 0839042 and 0636815. The authors appreciate support of the WAIS Divide Science Coordination Office for collection and distribution of the WAIS Divide ice core; Ice Drilling and Design and Operations for drilling; the National Ice Core Laboratory for curating the core; Raytheon Polar Services for logistics support in Antarctica; and the 109th New York Air National Guard for airlift in Antarctica. NorthGRIP and NEEM are directed and organized by the Center of Ice and Climate at the Niels Bohr Institute and U.S. NSF. It is supported by funding agencies and institutions in Belgium (FNRS-CFB and FWO), Canada (NRCan/GSC), China (CAS), Denmark (SNF, FIST), France (IFRTP, IPEV, CNRS/INSU, CEA and ANR), Germany (AWI), Iceland (RannIs), Japan (MEXT, NIPR), Korea (KOPRI), The Netherlands (NWO/ALW), Sweden (VR, SPRS), Switzerland (SNF), United Kingdom (NERC), and the USA (U.S. NSF Polar Programs). Publisher Copyright: {\textcopyright} 2015 Macmillan Publishers Limited. All rights reserved.",
year = "2015",
month = oct,
day = "26",
doi = "10.1038/ncomms9611",
language = "English",
volume = "6",
journal = "Nature Communications",
issn = "2041-1723",
publisher = "Nature Publishing Group",
}