[P-EM17] Space Weather and Space Climate

[PEM17-13] ¹⁴C during the ~660 BCE solar proton event from Japanese tree rings

★Invited Papers

*Hirohisa Sakurai¹, Fusa Miyake², Fuyuki Tokanai¹, Kazuho Horiuchi³, Hiroko Miyahara⁴, Kimiaki Masuda², Motonari Ooyama⁵, Minoru Sakamoto⁶, Takumi Mitsutani⁷, Toru Moriya¹ (1.Faculty of Science, Yamagata University, 2.ISEE, Nagoya University,, 3.Hirosaki University, 4.Graduate School of Science and Technology, Hirosaki University, 5.Botanical Gardens, Tohoku University, 6.National Museum of Japanese History, 7.National Institutes for Cultural Heritage, Nara National Research Institute for Cultural Properties)

Keywords:14C, ~660 BCE event, SPE

Annual rings record the intensity of cosmic rays that had entered into the Earth’s atmosphere. Several rapid ¹⁴C increases in the past, such as the 775 CE and 994CE ¹⁴C spikes, have been reported to originate from extreme solar proton events (SPEs). Another rapid ¹⁴C increase, also known as the ca. 660 BCE event in German oak tree rings as well as increases of ¹⁰Be and ³⁶Cl in ice cores, was presumed similar to the 775 CE event; however, as the ¹⁴C increase of approximately 10‰ in 660 BCE had taken a rather longer rise time of 3–4 years as compared to that of the 775 CE event, the occurrence could not be simply associated to an extreme SPE. In this study, to elucidate the rapid increase in ¹⁴C concentrations in tree rings around 660 BCE, we have precisely measured the ¹⁴C concentrations of earlywoods and latewoods inside the annual rings of Japanese cedar for the period 669–633 BCE. Based on the feature of ¹⁴C production rate calculated from the fine measured profile of the ¹⁴C concentrations using an 11-Box model of carbon cycle, we found that the ¹⁴C rapid increase occurred within 665–663.5 BCE, and that duration of ¹⁴C production describing the event is distributed from one month to 3.4 years. The possibility of occurrence of consecutive SPEs over up to three years is offered.