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Open Access Publications from the University of California

A deconvolution of the tree ring based delta 13 C record


We assumed that the tree-ring-based 13C/12C record constructed by Freyer and Belacy (1983) to be representative of the fossil fuel and forest-soil induced 13C/12C change for atmospheric CO2. Through the use of a modification of the Oeschger et al. ocean model, we have computed the contribution of the combustion of coal, oil, and natural gas to this observed 13C/12C change. A large residual remains when the tree-ring-based record is corrected for the contribution of fossil fuel CO2. A deconvolution was performed on this residual to determine the time history and magnitude of the forest-soil reservoir changes over the past 150 years. Several important conclusions were reached. (1) The magnitude of the integrated CO2 input from these sources was about 1.6 times that from fossil fuels. (2) The forest-soil contribution reached a broad maximum centered at about 1900. (3) Over the 2 decade period covered by the Mauna Loa atmospheric CO2content record, the input from forests and soils was about 30% that from fossil fuels. (4) The 13C/12C trend over the last 20 years was dominated by the input of fossil fuel CO2. (5) The forest-soil release did not contribute significantly to the secular increase in atmospheric CO2 observed over the last 20 years. (6) The pre-1850 atmospheric  values must have been in the range 245 to 270×10−6atmospheres.

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