Speaker
Description
Cosmogenic nuclides used to detect past solar energetic particle (SEP) events are tree-ring $^{14}$C, and ice-core $^{10}$Be, and $^{36}$Cl. These nuclides serve as key proxies for reconstructing SEP events. To date, multiple extreme SEP events, including the 774 CE event, have been identified from these cosmogenic nuclide records. The magnitudes of these events are estimated to be several tens of times larger than the largest SEP events observed during the modern instrumental era, underscoring the importance of investigating their occurrence characteristics for space weather risk assessment. In recent years, substantial progress has been made in identifying extreme SEP events during the Holocene, particularly those comparable in scale to the 774 CE event. However, investigation of intermediate-size events that bridge the gap between proxy-detected extreme events and those observed in the modern era remains limited, mainly due to analytical uncertainties in cosmogenic nuclide measurements.
In this study, we focus on the 1279 CE event, one of the smallest candidate events reported from tree-ring $^{14}$C records. Although previous studies reported statistically significant increases in Δ$^{14}$C associated with this event, the annual increases were relatively small, ranging from approximately 2 to 5‰, and its origin remains under debate (Brehm et al. 2021; Miyahara et al. 2022; Scifo et al. 2024). We conducted high-precision Δ$^{14}$C measurements on tree-ring samples from Japan and the Altai region covering the period around 1279 CE. While we did not detect a statistically significant single-year increase in Δ$^{14}$C, we identified a significant multi-year increase. Our results suggest that this Δ$^{14}$C enhancement is consistent with both an extreme SEP event and variations in galactic cosmic ray flux. These findings indicate that distinguishing intermediate-size SEP events from background variations of galactic cosmic rays will be a key challenge in future studies. To address this issue, multi-proxy approaches incorporating tree-ring $^{14}$C records from multiple regions, as well as ice-core cosmogenic nuclide records, will be essential.
Co-author list:
A. J. Timothy Jull (2,3), Katsuhiko Kimura (4), Mihaly Molnár (3), Toru Moriya (5), Vladimir Myglan (6), Irina P. Panyushkina (7), Andrea Scifo (8), Mirei Takeyama (5), Fuyuki Tokanai (5), Ilya Usoskin (9,1), Lukas Wacker (10)
(1) Institute for Space‑Earth Environmental Research, Nagoya University, Nagoya 464‑8601, Japan
(2) Department of Geosciences, University of Arizona, Tucson AZ 85721, USA
(3) Isotope Climatology and Environmental Research Centre, Institute for Nuclear Research, Debrecen 4032, Hungary
(4) Fukushima University, Fukushima, Japan
(5) Yamagata University, Yamagata, Japan
(6) Siberian Federal University, Krasnoyarsk 660041, Russia
(7) Laboratory of Tree‑Ring Research, University of Arizona, Tucson AZ 85721, USA
(8) Centre for Isotope Research, University of Groningen, Groningen, The Netherlands
(9) Space Physics and Astronomy Research Unit and Sodankylä Geophysical Observatory, University of Oulu, 90014 Oulu, Finland
(10) Laboratory for Ion Beam Physics, ETH Zürich, Zürich 8093, Switzerland