日本産樹木年輪14C年代データのIntCal13との比較と活用 [in Japanese] Comparison of 14C Ages from Japanese Tree Ring Samples with IntCal13 and Their Applications [in Japanese]
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To investigate the 14C concentration of atmospheric CO2 over the past few millennia in Japan, we measured the 14C age of annual rings from several Japanese trees with calendar dates ranging from ca. 2000 yr old to present, and we compared the tree-ring 14C age with the corresponding 14C age of IntCal13. It was revealed that the 14C age of the annual rings of Japanese trees are not consistent with IntCal13 datasets in some instances. Many cases of 14C age of tree rings are older than those of IntCal13, but younger than those of SHCal13 datasets. The average shift in Nagoya 14C age from IntCal13 datasets and one-sigma errors were obtained to be +26±36, +24±30, +16±22, +5±21, and +14±22 14C yr for the intervals AD72-382, AD589-1072, AD1413-1615, AD1617-1739, and AD1790-1860, respectively. In addition, a wood sample collected from northern end of the mainland of Japan also showed a value of +35±22 14C yr shifted older than IntCal13. We also analyzed 14C age data obtained for trees grown up in Korea, and yielded the values of +17±35 and +6±35 14C yr for the intervals AD1250-1650 and AD 1650-1850, respectively. The Japanese archipelago is situated near the boundary of the inter-tropical convergence zone in summer, and the 14C concentration of atmospheric CO2 over Japan can be influenced by air masses of the Southern Hemisphere with lower 14C concentrations during periods of higher solar activity and heightened East Asian summer monsoons. Korean Peninsula is also influenced by air masses of the Southern Hemisphere. Present results suggest that the southeast end of Eurasian Continent is located in the critical zone from where it is difficult to calibrate the 14C age of tree ring samples using existing calibration datasets. At the moment, it should be noted that calibration of the 14C dates of Japanese samples with IntCal13 induces additional systematic shifts of calibrated ages toward older ages by about 10-30 yr compared with the sample optimum calendar ages.
名古屋大学年代測定研究 (1), 108-114, 2017-03-31