δ¹³C records of Japanese cedars from Yakushima Island and past atmospheric CO₂

抄録

δ¹³C records of annual growth rings of two Japanese cedars (Cryptomeria japonica) from Yakushima Island, southern Japan are presented for the past 200 years. Some portions of the short-term fluctuations in the δ¹³C records from the Japanese cedars are correlated with the variabilities of the ring-thickness index. Regressions between the ring-thickness indices and δ¹³C values were used to “correct” the δ¹³C records for local climate and environmental effects. These corrected δ¹³C records from the two Japanese cedars show a steady downward trend with time, but with pronounced short-term fluctuations superimposed on the trend. The overall δ¹³C fall from 1870 to the present is between 1.2–1.4‰, consistent with the δ¹³C records of atmospheric CO₂ estimated from ice-core bubbles, which show a fall of 1.14 ± 0.15‰ from 1740 to the present (Friedli et al., 1986). The δ¹³C fall seems to be related to the increase in the concentration of atmospheric CO₂ as a result of fossil fuel burning and deforestation. The corrected δ¹³C records show small increases at 1900 and 1950, which can not be explained satisfactorily at present.