14C AGE MEASUREMENTS OF SINGLE-YEAR TREE RINGS OF OLD WOOD SAMPLES 22,000 14C YEARS BP

Radiocarbon ages of single-year tree rings were measured for Kaminoyama wood samples using accelerator mass spectrometry (AMS) in 2 Japanese facilities, MALT and JAEA, in order to investigate the periodic variation of C-14 concentrations relating to the 11-yr solar cycle near 26,000 yr BP. Eight sequential measurements of C-14 ages were carried out for a set of 13 alternate single-year tree rings covering 26 yr. Averages of the 5 data sets in MALT and 3 data sets in JAEA were 22,146 +/- 50 and 22,407 +/- 58 C-14 yr BP, respectively, indicating an offset of 260 +/- 77 C-14 yr. Multiple sequential measurements are advantageous for evaluating offsets. The standard deviation of the residuals of C-14 ages from the averages in each data set was 118 C-14 yr, in contrast to that of 234 C-14 yr for the combined data sets due to an elimination effect in the offsets. The profiles of weighted mean values for the residuals of C-14 ages showed similar enhancements with a width of similar to 12 yr for measurements in the 2 facilities. This indicates the reproducibility of the multiple sequential measurements. In the profile for the combined 8 data sets, the C-14 enhancement was 73 +/- 36 C-14 yr from the average.