Speaker
Description
Annual-resolution ¹⁴C records from tree rings have become powerful proxies for detecting extreme solar behaviour, including short-lived cosmic-ray enhancements related to solar energetic particle (SEP) events and variations in solar magnetic activity. A recent study compiling an annually resolved ¹⁴C record from 1–970 CE, based on five new and three existing tree-ring series measured at the Curt-Engelhorn-Center Archaeometry (Germany) and the Centre for Isotope Research at the University of Groningen, demonstrated the potential of such datasets. Using statistical carbon-cycle modelling, adaptive decomposition of solar cycles, and probabilistic detection of rapid ¹⁴C increases, the work
identified four intervals of reduced solar activity, two periods of weakening and subsequent strengthening of the eleven-year solar cycle, and four candidate particle events in 14, 553, 675, and 954 CE.
Building on this approach, we present several newly measured, high-precision annual ¹⁴C datasets derived from tree-ring samples processed independently in multiple laboratories and originating from different geographic regions. The records cover a key interval in the late Middle Holocene, shortly after the Mid-Holocene Optimum. Despite differences in site conditions, tree species, and laboratory procedures, all datasets show a synchronous and abrupt radiocarbon increase within a narrow time window. The consistency and magnitude of this signal suggest a large-scale atmospheric forcing rather than local environmental or analytical effects, indicating a possible solar origin.
To evaluate the significance of this excursion, we compared the new records with available ¹⁴C datasets, including both annually resolved and lower-resolution archives. The results indicate that the observed increase is rare within the Holocene background variability and comparable to other short-lived radiocarbon anomalies. We further investigated potential production mechanisms using the open-source carbon box model ticktack to reconstruct atmospheric ¹⁴C production. Two scenarios were tested: (1) a one-year production pulse representing an impulsive SEP-type event, and (2) a multi-year production increase reflecting enhanced cosmic-ray flux due to reduced solar magnetic
shielding. Preliminary simulations show that both scenarios can reproduce the amplitude and temporal structure of the observed signal within model uncertainties.
Future work will apply a fully three-dimensional carbon transport model to better resolve atmospheric mixing and regional offsets, enabling discrimination between competing production scenarios. These results provide new constraints on short-term solar variability during the late Middle Holocene and contribute to understanding extreme solar behaviour in the pre-instrumental era.
Co-author list:
Bao Yang (2), Fusa Miyake (3), Irina Panyushkina (4), Jente Joosten (1), Vivian Kroon (1), Håkan Grudd (5), David Brown (6), Ronny Friedrich (7), Michael Dee (1)
(1) Centre for Isotope Research, University of Groningen, Groningen, Netherlands
(2) School of Geography and Ocean Science, Nanjing University, Nanjing, People’s Republic of China
(3) Institute for Space‑Earth Environmental Research, Nagoya University, Nagoya, Japan
(4) Laboratory of Tree‑Ring Research, University of Arizona, Tucson, USA
(5) Swedish Polar Research Secretariat, Abisko Scientific Research Station, Abisko, Sweden
(6) School of Natural and Built Environment, The Queen’s University Belfast, Belfast, UK
(7) Curt‑Engelhorn‑Center for Archaeometry (CEZA), Mannheim, Germany