RADSOCARBQN AGES OF ANNUAL RINGS FROM JAPANESE WOOD: EVIDENT AGE OFFSET BASED ON INTCAL09

摘要

To investigate the radiocarbon concentration of atmospheric CO_2 over the past few millennia in Japan, we measured the ~(14)C age of annual rings from 3 Japanese trees with calendar dates ranging from -2000 yr old to present, and we compared the tree-ring ~(14)C age with the corresponding ~(14)C age from IntCal09. In some instances, the ~(14)C ages of the annual rings of Japanese trees are not consistent with the IntCal09 data sets. Often, the ~(14)C ages of tree rings are older than those from IntCal09, but younger than those from the SHCal04 data sets. The average shifts in the Nagoya ~(14)C age from IntCal09 data sets and 1 cj errors were determined to be +26 ±36, +24 ± 30, +16 ± 22, +5 ± 21, and +14 ± 22 ~(14)C yr for the intervals AD 72-382, 589-1072, 1413-1615, 1617-1739, and 1790-1860, respectively. The Japanese Archipelago is situated near the boundary of the Intertropical Convergence Zone in summer, and the ~(14)C concentration of atmospheric CO_2 over Japan can be influenced by air masses of the Southern Hemisphere with lower ~(14)C concentrations during periods of higher solar activity and heightened East Asian summer monsoons. Our results suggest that the Japanese Archipelago is located in a critical zone where it is difficult to calibrate the ~(14)C age of tree-ring samples using existing calibration data sets. It should be noted that calibration of the ~(14)C dates of Japanese samples with IntCal09 may induce additional systematic shifts of calibrated ages toward older ages by about 30 yr compared with the sample optimum calendar ages.