[M-ZZ43] Transdisciplinary Network linking Space-Earth Environmental Science with History and Archaeology

[MZZ43-P06] Archeointensity estimated from Yayoi pottery and construction of reference curve for East Asia from -600 to 1700 CE

*Yutaka Yoshimura¹, Hyeon-Seon Ahn^2,3, Chie Kato^4,7, Yuhji Yamamoto⁵, Chisato Anai⁶, Yoshinori Tajiri^4,7, Tadahiro Hatakeyama⁸, Masao OHNO^4,7 (1.National Institute of Polar Research, 2.Korea Institute of Geoscience and Mineral Resources, 3.University of Science and Technology, 4.Faculty of Social and Cultural Studies, Kyushu University, 5.Marine Core Research Institute, Kochi University, 6.Aso Volcanological Laboratory, Kyoto University, 7.Advanced Asian Archaeological Research Center, Kyushu University, 8.Institute of Frontier Science and Technology, Okayama University of Science)

Keywords:Archeomagnetic field intensity (Archeointensity), Archeointensity reference curve, Yayoi pottery, Archeointensity dating

The reference curve of archeomagnetic field intensity (archeointensity) over the past few thousand years in Japan, as well as the reference curve of geomagnetic direction, provides essential data to understand the Earth's core dynamics. Also, the archeointensity reference curve over the past several thousand years is important because it can be used as a reference to estimate the making age of fired archeological artifacts, whose ages are unknown. Recent studies pointed out that archeointensity from previous studies in Japan before 1986 may be overestimated (Kitahara et al., 2018, 2021; Tema et al., 2023). In this study, we conducted archeointensity experiments and rock-magnetic analyses to estimate using Yayoi pottery samples of about 250 BCE to 50 CE collected at the Gokuden site in Kasuga, Fukuoka, Japan. We conducted thermomagnetic analysis for 45 pottery samples in vacuum and air atmosphere. The thermomagnetic curves in air were more reversible than those in vacuum. Based on the results, we applied the Tsunakawa-Shaw method with heating in air to 23 specimens of eight Yayoi pottery samples (one to six specimens per sample). As a result, 17 of 23 specimens from seven of eight pottery samples passed the acceptance criteria of the Tsunakawa-Shaw method. To certify the reliability of archeointensities, we set a selection criterion: (1) archeointensity obtained from three or more specimens per pottery sample, (2) standard deviation of sample-level mean is 15% or less. By the criterion, we selected the four sample-level means (36.9–46.2 µT). When the four sample-level means were arranged in chronological order, it was observed that the archeointensity was almost constant from 36.4 μT to 40.0 μT from -250 CE to -100 CE, and that the archeointensity increased to 46.2 μT in the period from 150 CE to 75CE. In addition, we constructed a reference curve of -600 CE to 1700 CE by the LOESS regression using our data and previously reported data from Japan (Kitahara et al., 2018, 2021; Tema et al., 2023) and from Republic of Korea (Hong et al., 2013). Multiple maximum (-470 CE, 340 CE, and 1150 CE) and minimum (Between -250 and -50 CE, ~ 600CE, and 1610 CE) features were observed in the reference curve. The variation of the reference curve would be a characteristic pattern of -600 CE to 1700 CE in East Asia. Using these features in the reference curve, we may be able to estimate the age of fragments of archeological artifacts of unknown age of -600 CE to 1700 CE.