Regional offsets of 14-C concentration from standard calibration datasets in northern hemisphere have been frequently argued based on the some systematic difference found in samples from different regions. In order to avoid biasing in dating, it is important to investigate local effect in 14-C concentration for individual region, although INTCAL datasets could generally be used as radiocarbon calibration curve. In this study, we investigated a local radiocarbon calibration curve using Japanese wood samples. The period from 9c BC to 2c BC is our current target, because it corresponds to a period of transition from the Jomon to the Yayoi culture in Japan, and its absolute age has been vigorously discussed in Japanese archaeology. The wood sample used in this study was a bogwood of Japanese cypress found at Iida, Nagano Prefecture. It included tree-rings of 685BC to 193BC which was dendro-chronologically dated. The sample was cut into 5 years tree-ring specimens. Alpha-celluloses were extracted by AAA treatments, and bleaching with chlorine, and assayed into graphite targets. AMS measurements were performed at Nagoya University. We will repeat measurements four times with the same samples. The first AMS measurements for all tree-ring samples have been finished by now. The data shows that, for the most part, the 14-C concentration agrees well with INTCAL04 calibration curve within the statistical errors of AMS measurement. However, we found a significant disagreement of about 50 14-C years peaking at around 370 BC, where the calibration curve have steep declining slope. The feature found in Japanese wood samples from 400 BC to 300 BC is much smoother than the INTCAL04 calibration curve. We believe the effect to be a regional effect. The possible cause of this difference will be discussed. This work was supported by a Grant-in Aid for Creative Scientific Research of the Japan Society for the Promotion of Science (No.16GS0118).
See more of Poster Session I
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)