South American tree rings show declining delta13C trend

Abstract

A composite, 290-year tree-ring δ¹³C 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 δ¹³C trend of approximately 1.2‰, primarily since the turn of this century. This δ¹³C 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 δ¹³C trend. This is the first evidence for any interhemispheric reproducibility of tree-ring δ¹³C chronologies, and furthermore, the Fitzroya δ¹³C trend conforms well to that of δ¹³C of atmospheric CO2 determined from ice cores and direct measurements. This correspondence suggests the alerce δ¹³C 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 Ci/Ca ratios and obscuring the atmospheric δ¹³C record contained in the tree rings. DOI: 10.1034/j.1600-0889.1994.t01-1-00007.x