Accurate Determination of exp 13 C/ exp 12 C in CO sub 2 of past Atmospheres from exp 13 C/ exp 12 C in Tree Rings by Removal of Climatic Interferences. Final Technical Progress Report

摘要

Analysis of delta exp 13 C in tree rings offers the potential for reconstructing changes in delta exp 13 C of atmospheric CO sub 2 , which combined with exp 14 C trends will be important in evaluating the past and present role of the biosphere as a net carbon dioxide source or sink. One problem with such tree-ring delta exp 13 C records is that in addition to changes in atmospheric delta exp 13 C, climatic factors may influence the isotopic composition of the rings. This study examines delta exp 13 C in cellulose of five-year intervals of juniper tree rings. The sampling sites were near weather stations for which climate data are readily available. delta exp 13 C vs winter climate relationships were derived from those sites not under the influence of local pollution sources. These relationships facilitated development of a delta exp 13 C record from which climate effects have been factored out. The resulting 1930-1979 delta exp 13 C reconstruction shows a pronounced delta exp 13 C decrease from 1930 to 1960 and then a post-1960 flattening of the curve. We interpret this trend as representing an increasing role of biospheric CO sub 2 sinks relative to sources, although other interpretations may be possible within the limits of precision of data analysis. Research with this technique is continuing with pinyon pine and dendroclimatological reconstructions to verify these results and to develop a climate-free delta exp 13 C chronology back to pre-industrial time. (ERA citation 07:062017)