Variation of ¹⁴C in Japanese Tree Rings Related to the Fukushima Nuclear Accident

Abstract

Radiocarbon (14C) analysis was performed on Japanese cedar (Cryptomeria japonica) tree rings from Koriyama, Fukushima prefecture. Our primary aim was to detect any 14C release from the Fukushima Dai-ichi nuclear power plant accident on 11 March 2011. We also completed and assessed the 14C level in Japanese tree rings for the period of 1990–2014 because of the lack of environmental 14C results in the Japanese island that time. For this reason, we used a trajectory model to investigate the air mass forward and backward trajectories at the area of the power plant and sampling site. The modeling data show that the air masses mainly moved to the Pacific Ocean, both during March 2011 and during the growing season (March–September). During the period 1990–2014 there was no significant 14C excess in any of the samples, but there was a detectable Suess effect in almost every tree ring sample. The average fossil contribution was 0.83 ± 0.01% and the calculated anthropogenic component ratio, the 14C excess varied between +0.5 and –1.6%. The Δ14C value decreased from 150.0‰ to 9.5‰ from 1990–2014, which follows the decline of the 14C bomb peak, in addition to any detectable Suess effect.

Impact of the Fukushima Accident on 3H and 14C Environmental Levels: A Review of Ten Years of Investigation

“…The northern negative Δ 14 C values (−40‰), which were under the influence of the Oyashio intrusion described in the previous paragraph, changed to the positive values (68‰) in the south. This trend, together with the uniform mixing of radiocarbon in the surface mixed layers (the depth of 100–200 m), was in good agreement with the previous results [ 92 , 93 ]. The anthropogenic (bomb-produced) 14 C water column inventories at 35–40°N, which would be noticeably increased in the case of the significant impact of the FDNPP accident, were actually lower.…”