Climatic information recorded in stable carbon isotopes in tree rings of Cryptomeria fortunei, Tianmu Mountain, China

The Cryptomeria fortunei (CF) tree-ring δ13Cp series, which was collected from the West Tianmu Mountain forestland (30°20′ N, 119°26′ E), located in the north-west of Zhejiang Province, China, belonging to the northern margin of the mid-subtropical region of Eastern China, were determined based on cross-dated tree-ring age. There was a significant decline in the δ13Cp series occurring from 1685 to 1985, more especially from 1835 to 1985 in response to increasing atmospheric CO2 concentrations and decreasing atmospheric δ13Ca. To reduce the noise and enhance the climatic signals, we compared the polynomial function with the correction method developed by McCarroll and Loader (2004) to remove the low-frequency variation in the raw tree ring δ13Cp series (defined as the δ13Cpoly series, δ13Ccor series, respectively), and found the most suited correction method was the correction method developed by McCarroll and Loader (2004) in our study area. High-frequency correlation analysis between the δ13Ccor series and many meteorological parameters recorded by Xian Rending weather station revealed that the current August–September mean maximum temperature and previous year mean minimum and mean maximum temperature (P < 0.005) most strongly influenced tree ring δ13Cp discrimination from 1956 to 1985, and the strongest temperature signal captured was the current August–September mean maximum temperature (r = 0.54, P < 0.005). Mainly on this basis, the varied history of current August–September mean maximum temperatures in the West Tianmu Mountain area were reconstructed from 1685 to 1985. The reconstructed maximum temperatures revealed a slight warming trend and showed close correlation with the climatic fluctuations of the Little Ice Age cold period before 1900 as well as the 20th century warm period after 1900. It also better corresponded with some climate events recorded in historical records. Spectrum analysis showed that in the reconstructed series there was quasi-periodicity of 66.7 yr, 21.1 yr, 3.2 yr, 2.3 yr and 2.0 yr. These cycles coincided with the “torque effect” variation of planets and the geocentric convergence, and changes in solar activity and irradiance, as well as the “Quasi-biennial oscillation” (QBO). This indicated that the δ13Cp chronology of tree rings in West Tianmu Mountain showed a good record of the sun's activities, the change in the sun radiation and ENSO events.