Pooled versus separate measurements of tree-ring stable isotopes

Area of Science:

• Paleoclimatology
• Isotope Geochemistry
• Dendrochronology

Background:

• Tree ring isotopes (δ(13)C, δ(18)O) provide valuable palaeoclimatic and ecophysiological data.
• Isotope chronologies are often created by pooling tree rings, saving resources but limiting uncertainty assessment.

Purpose of the Study:

• To compare δ(13)C and δ(18)O chronologies from pooled versus individual tree rings.
• To assess the advantages and limitations of pooling tree rings for isotopic analysis.

Main Methods:

• Comparison of pooled and individual tree ring isotope chronologies (δ(13)C, δ(18)O).
• Analysis conducted at two Iberian Peninsula sites covering 1900-2003.
• Validation using averaged individual values (Mean) and mass-calibrated means (MassC).

Main Results:

• Pooled chronologies generally agree well with mean individual series (Mean, MassC).
• High interannual synchronicity observed, but decadal/multi-decadal δ(18)O variations showed differences.
• Pooling may obscure individual tree first-order autocorrelation and potential biases.

Conclusions:

• Pooling tree rings is a viable method for interannual isotopic analysis, showing good agreement with individual data.
• Potential loss of information regarding decadal variations and inter-tree variability exists with pooling.
• Analytical uncertainties, like sample inhomogeneity, contribute to observed differences between pooled and individual data.