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Radiocesium (137Cs) released in the Fukushima Dai-ichi Nuclear Power Plant accident is still cycling in the forest ecosystem. We examined the mobility of 137Cs in the external parts—leaves/needles, branches, and bark—of the two major tree species in Fukushima, Japanese cedar (Cryptomeria japonica) and konara oak (Quercus serrata). This variable mobility will likely lead to spatial heterogeneity of 137Cs and difficulty in predicting its dynamics for decades. We conducted leaching experiments on these samples by using ultrapure water and ammonium acetate. In Japanese cedar, the 137Cs percentage leached from current-year needles was 26–45% (ultrapure water) and 27–60% (ammonium acetate)—similar to those from old needles and branches. In konara oak, the 137Cs percentage leached from leaves was 47–72% (ultrapure water) and 70–100% (ammonium acetate)—comparable to those from current-year and old branches. Relatively poor 137Cs mobility was observed in the outer bark of Japanese cedar and in organic layer samples from both species. Comparison of the results from corresponding parts revealed greater 137Cs mobility in konara oak than in Japanese cedar. We suggest that more active cycling of 137Cs occurs in konara oak. [ABSTRACT FROM AUTHOR]

The spring Arctic Oscillation (AO) significantly affects the subsequent summer rainfall in the East Asian summer monsoon (EASM) region, and analysis of meteorological data indicates this teleconnection strength varied on interdecadal timescales during the late 20th century. Tree‐ring records may be able to extend the relatively short observational record, but the extent to which these proxy reconstructions correspond to AO variability has yet to be explored in this region. Therefore, we present new tree‐ring cellulose oxygen isotope (δ18O) records from northeastern Japan (Akita, northern limit of EASM), spanning a.d. 1950 to 2003 which overlaps with the instrumental record. Tree‐ring δ18O is used for reconstructing the past hydroclimate variability and allows us to consider whether tree‐ring δ18O has the potential to clarify the longer‐term interdecadal changes in the spring AO‐EASM relationship. Measurements and analyses show that our tree‐ring δ18O data sets have a significant negative correlation with May‐June‐July relative humidity, and the tree‐ring δ18O in northeastern Japan also significantly correlates with the summer EASM index. Temporal comparisons between our record and observed monthly AO index indicate that reconstructed following early summer relative humidity significantly correlates to the previous March‐April‐May AO. This linkage changes on interdecadal timescales, and the linkage is relatively strong during early 1970s through early 1990s. Similar results are also obtained using a separate tree‐ring δ18O record from a separate location about 200 km to the southeast, suggesting that tree‐ring cellulose δ18O in northeastern Japan is indeed useful for better understanding the long‐term teleconnection between the spring AO and EASM. Key Points: New tree‐ring cellulose oxygen isotope chronologies in northeastern Japan are reportedTree‐ring oxygen isotope record significantly correlates to the Spring Arctic OscillationTree‐ring cellulose oxygen isotope in northeastern Japan can be applied to better understand the long‐term spring AO‐EASM relationship [ABSTRACT FROM AUTHOR]