Radiocarbon concentration around 774/775 CE in sub-annual tree rings from Kujawy near Kraków

The rapid radiocarbon (Δ 14 C) increase in 774/775 CE (M12) provides a key benchmark for extreme cosmogenic production events. We present sub-annual (earlywood/latewood) Δ 14 C measurements from oak sample KU89 ( Quercus robur ) collected near Kujawy, SE Poland (771–778 CE). The KU89 sub-annual record shows a pronounced rise of 21.4 ± 2.4‰ between LW1 774 CE and EW 777 CE (Δ 14 C from −19.0 ± 1.7‰ to 2.4 ± 1.7‰), indicating rapid incorporation of newly produced 14 C. Adopting the Park et al. (2020) framework and a tropospheric half-oxidation time (HOT) of 3.8 months (within a range from 2.3 to 6.7 months), we numerically estimate the M12 production onset in mid 774 CE (late April–mid June), consistent with prior sub-annual studies from Finland and Korea. Applying the same approach to the 665/664 BCE and 993/994 CE Miyake events yield plausible onset windows (from late January up to end of April 663 BCE and from middle July 993 CE to middle February 994 CE, respectively). While the combination of high-resolution tree-ring data and HOT-informed modeling improves temporal constraints on cosmogenic 14 C production, uncertainties remain (HOT variability, tree physiology, baseline selection, and model assumptions). We recommend increased intra-ring sampling, multi-site replication across latitudes, and coupled atmospheric–carbon-cycle modeling to further refine timing and transport characteristics of Miyake events.