Declining trend in the C-13/C-12 ratio of atmospheric carbon dioxide from tree rings of South African Widdringtonia cedarbergensis

Stable carbon isotope chronologies using tree ring wood cellulose have proved useful for developing hypotheses on climate and environment change. However, within both the Southern Hemisphere and Africa there has been very little tree-ring-based isotope research. Here we report the first high-resolution (annual) C-13/C-12 chronology for both Africa and the Southern Hemisphere. The 77-yr stable carbon isotope chronology was developed from six Widdringtonia cedarbergensis trees from a site in the Cedarberg Mountains, Western Cape Province, South Africa. The results indicate that C-13/C-12 ratios are not different from 1900 to 1949. After 1949, however, values become significantly more negative to 1977. The isotopic record from the pooled trees at the Die Bos site does not correlate with rainfall. This correlation is not significant even when the Widdringtonia stable carbon isotope record is detrended for the anthropogenic CO2 contribution. The Widdringtonia record does, however, correlate significantly with atmospheric C-13/C-12 CO2 Values derived from ice core data, tree ring C-13/C-12 chronologies from the Northern Hemisphere, and recent Southern Hemisphere records. (C) 1999 Universityof Washington.