title: Pooled versus separate measurements of tree-ring stable isotopes.
abstract: δ(13)C and δ(18)O 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 δ(13)C and the δ(18)O 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 δ(18)O 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.
authors.affiliation: Universitat de Barcelona, Departament d'Ecologia, Diagonal 645, 08028, Barcelona, Spain. isabel@gfz-potsdam.de
authors.forename: Isabel
authors.initials: I
authors.lastname: Dorado Liñán
authors.forename: Emilia
authors.initials: E
authors.lastname: Gutiérrez
authors.forename: Gerhard
authors.initials: G
authors.lastname: Helle
authors.forename: Ingo
authors.initials: I
authors.lastname: Heinrich
authors.forename: Laia
authors.initials: L
authors.lastname: Andreu-Hayles
authors.forename: Octavi
authors.initials: O
authors.lastname: Planells
authors.forename: Markus
authors.initials: M
authors.lastname: Leuenberger
authors.forename: Carmen
authors.initials: C
authors.lastname: Bürger
authors.forename: Gerhard
authors.initials: G
authors.lastname: Schleser
mesh_terms: D002244:Carbon / Q000032:analysis*; D002247:Carbon Isotopes / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods*; D010100:Oxygen / Q000032:analysis*; D010103:Oxygen Isotopes / Q000032:analysis; D012621:Seasons; D014197:Trees / Q000737:chemistry* / Q000254:growth & development; D014934:Wood / Q000737:chemistry* / Q000254:growth & development
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D002244:Carbon; D010100:Oxygen