Abstract
ABSTRACTThe 14C peak in AD 775 (M12) has been measured and confirmed globally in several studies since it was first measured in annual tree rings by Miyake et al. (2012). However, M12 data measurements in early- and latewood are limited. This paper presents the Δ14C values in early- and latewood from AD 762–776 Zelkova serrata tree rings from Bangu-dong, Ulsan, South Korea (35°33′N, 129°20′E). The results indicate no early rise in Δ14C values in the latewood of AD 774 in this sample located at mid-latitude. A comparison of the results of this and previous studies suggests latitude dependence (Büntgen et al. 2018); that is, the early rise of Δ14C in AD 774 was not observed at mid-latitudes in South Korea but was observed at high latitudes in Finland. The half-oxidation time of 14C was estimated from a detailed analysis of a small bomb peak in AD 1962. Based on the half-oxidation time, the Δ14C rise in the latewood, but not in the earlywood, of AD 774 in Finland, and the absence of a Δ14C rise in both the early- and latewood of AD 774 in South Korea, the 14C spike was estimated to have been produced from late April to mid-June in AD 774.
Highlights
Since the discovery of the AD 775 14C peak (M12) by Miyake (Miyake et al 2012), M12 has been confirmed, and its potential causes have been investigated by several groups
It has been shown that the M12 concentrations of the cosmogenic isotope 10Be measured in Antarctic ice were too high to have been produced by a gamma ray burst (GRB) (Usoskin et al 2013)
This comparison shows that the height of the early rise in the latewood in AD 774 was dependent on latitude because the amplitude of M12 increased in accordance with an apparent increase in the latitude of the sampling site (Büntgen et al 2018)
Summary
Since the discovery of the AD 775 14C peak (M12) by Miyake (Miyake et al 2012), M12 has been confirmed, and its potential causes have been investigated by several groups. The potential causes of M12 include a solar proton event (SPE) (Melott and Thomas 2012; Thomas et al 2013; Usoskin et al 2013; Jull et al 2014; Mekhaldi et al 2015), supernova (Miyake et al 2012), gamma ray burst (GRB) (Hambaryan and Neuhäuser 2013; Pavlov et al 2013), and normal periods of low solar activity (Neuhäuser and Neuhäuser 2015). Supernovae emit high-energy particles and gamma rays. Gamma rays from supernovae and GRBs have a very short duration, which implies that a rapidly rising 14C peak may occur. The 14C peaks in AD 993/994 (Miyake et al 2013) and 660 BC (Park et al 2017) are similar to M12 and may have similar explanations
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