Pooled versus separate measurements of tree-ring stable isotopes |
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Authors: | Dorado Liñán Isabel Gutiérrez Emilia Helle Gerhard Heinrich Ingo Andreu-Hayles Laia Planells Octavi Leuenberger Markus Bürger Carmen Schleser Gerhard |
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Affiliation: | a Universitat de Barcelona, Departament d'Ecologia, Diagonal 645, 08028, Barcelona, Spainb German Centre for Geosciences, Climate Dynamics and Landscape Evolution, Dendro Laboratory, Telegrafenberg, 14473, Potsdam, Germanyc Tree-Ring Laboratory, Lamont-Doherty Earth Observatory of Columbia University, Palisades NY, USAd Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerlande Oeschger Centre of Climate Change Research, University of Bern, Zähringerstrasse 25, 3012 Bern, Switzerland |
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Abstract: | δ13C and δ18O of tree rings contain time integrated information about the environmental conditions weighted by seasonal growth dynamics and are well established as sources of palaeoclimatic and ecophysiological data. Annually resolved isotope chronologies are frequently produced by pooling dated growth rings from several trees prior to the isotopic analyses. This procedure has the advantage of saving time and resources, but precludes from defining the isotopic error or statistical uncertainty related to the inter-tree variability. Up to now only a few studies have compared isotope series from pooled tree rings with isotopic measurements from individual trees. We tested whether or not the δ13C and the δ18O chronologies derived from pooled and from individual tree rings display significant differences at two locations from the Iberian Peninsula to assess advantages and constraints of both methodologies. The comparisons along the period 1900-2003 reveal a good agreement between pooled chronologies and the two mean master series which were created by averaging raw individual values (Mean) or by generating a mass calibrated mean (MassC). In most of the cases, pooled chronologies show high synchronicity with averaged individual samples at interannual scale but some differences also show up especially when comparing δ18O decadal to multi-decadal variations. Moreover, differences in the first order autocorrelation among individuals may be obscured by pooling strategies. The lack of replication of pooled chronologies prevents detection of a bias due to a higher mass contribution of one sample but uncertainties associated with the analytical process itself, as sample inhomogeneity, seems to account for the observed differences. |
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Keywords: | Dendrochronology Tree rings Stable isotopes Pooling Carbon-13 Oxygen-18 |
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