SOUTH-AMERICAN TREE-RINGS SHOW DECLINING DELTA-C-13 TREND

A composite, 290-year tree-ring deltaC-13 chronology was developed from a site in Chile where 5 Fitroya cupressoides (alerce) trees were sampled, 2 increment cores per tree, and the holocellulose component was analyzed in 5-year ring groups. This chronology shows a decreasing deltaC-13 trend of approximately 1.2 parts per thousand, primarily since the turn of this century. This deltaC-13 decline is similar to that of major tree-ring studies in the Northern Hemisphere, but it is the only major Southern Hemisphere study which clearly exhibits such a deltaC-13 trend. This is the first evidence for any interhemispheric reproducibility of tree-ring deltaC-13 chronologies, and furthermore, the Fitzroya deltaC-13 trend conforms well to that of deltaC-13 of atmospheric CO2 determined from ice cores and direct measurements. This correspondence suggests the alerce deltaC-13 trend has not been substantially influenced by systematic changes in environmental factors such light, relative humidity and soil moisture or by changing atmospheric CO2 concentration, all of which are, in theory, capable of altering C(i)/C(a) ratios and obscuring the atmospheric deltaC-13 record contained in the tree rings.