HR: 0830h
AN: B11C-0702    [PDF]
TI: Evidence that Earlywood-Latewood Size and Isotope Differences Can Influence Long-term Tree-Ring $\delta^{13}$C Trends
AU: * Li, Z
EM: zli@utk.edu
AF: Department of Earth and Planetary Sciences, University of Tennessee, 306 G&G Building, Knoxville, TN 37996 United States
AU: Leavitt, S W
EM: sleavitt@ltrr.arizona.edu
AF: Laboratory of Tree-Ring Research, University of Arizona, 105 W. Stadium, Bldg. #58, Tucson, AZ 85721 United States
AU: Mora, C I
EM: cmora@utk.edu
AF: Department of Earth and Planetary Sciences, University of Tennessee, 306 G&G Building, Knoxville, TN 37996 United States
AU: Liu, R
EM: rongmoliu@llqg.ac.cn
AF: State Lab of Loess and Quaternary Geology, Chinese Academy of Sciences, No.23 Xi'ying Road, Xi'an, 710054 China
AB: Inter-annual $\delta^{13}$C analysis of alpha-cellulose was performed on two Chinese pine trees ({\it P. tabulaeformis} Carr.) for the period of 1896 to 1990A.D. Seasonal $\delta^{13}$C analysis was conducted on the outer 13 annual rings of one of the trees. The inter-annual data exhibit a long-term decline greater than 2%$_{0}$. This decline is much larger than the actual atmospheric $\delta^{13}$C decrease caused by industrialization since A.D.1850, although results are consistent with the previous studies of other tree rings from the Northern Hemisphere that claim to have recorded the anthropogenic trend of atmospheric $\delta^{13}$C. Here we present evidence that the long-term trend of $^{13}$C/$^{12}$C in tree rings could also result from ecophysiological effects superimposed on the anthropogenic trend. These effects are associated with the decreasing/increasing productivity of earlywood or latewood associated with the changing growth history of the tree. Theoretical calculations show that the long-term trend of $^{13}$C/$^{12}$C in tree rings caused by ecophysiological effects can be enhanced or reduced depending on the seasonal $\delta^{13}$C pattern, which indicate that a 2%$_{0}$ difference between earlywood and latewood could produce a 1.5%$_{0}$ long-term change in $\delta^{13}$C during 100-year period by this ecophysiological effect alone. This amplitude is nearly equivalent to the -1.35%$_{0}$ decline in atmospheric $\delta^{13}$C since pre-industralization. Based on the seasonal $\delta^{13}$C data, we removed the long-term ecophysiological effects on $\delta^{13}$C from one of these trees (HL02). The corrected data are in agreement with the observed size and timing of the $\delta^{13}$C decline in atmospheric CO$_{2}$. This study suggests that the long-term tree-ring $\delta^{13}$C data used to infer the anthropogenic impact on atmospheric $^{13}$C/$^{12}$C trend might be improved by correcting for possible ecophysiological effects if latewood and earlywood widths are measured. We argue that previous tree-ring calculations of the transfer of biospheric carbon to the atmosphere from fossil-fuel combustion in the Northern Hemisphere could be overestimated, and perhaps Southern Hemisphere studies finding no decline in $delta^{13}$C can also be re-examined in light of these findings.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting