Beschreibung:
<jats:title>Summary</jats:title><jats:p>
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<jats:list-item><jats:p>For accurate interpretation of oxygen isotopes in tree rings (δ<jats:sup>18</jats:sup>O), it is necessary to disentangle the mechanisms underlying the variations in the tree's internal water cycle and to understand the transfer of source versus leaf water δ<jats:sup>18</jats:sup>O to phloem sugars and stem wood.</jats:p></jats:list-item>
<jats:list-item><jats:p>We studied the seasonal transfer of oxygen isotopes from precipitation and soil water through the xylem, needles and phloem to the tree rings of <jats:italic>Larix decidua</jats:italic> at two alpine sites in the Lötschental (Switzerland). Weekly resolved δ<jats:sup>18</jats:sup>O records of precipitation, soil water, xylem and needle water, phloem organic matter and tree rings were developed.</jats:p></jats:list-item>
<jats:list-item><jats:p>Week‐to‐week variations in needle‐water <jats:sup>18</jats:sup>O enrichment were strongly controlled by weather conditions during the growing season. These short‐term variations were, however, not significantly fingerprinted in tree‐ring δ<jats:sup>18</jats:sup>O. Instead, seasonal trends in tree‐ring δ<jats:sup>18</jats:sup>O predominantly mirrored trends in the source water, including recent precipitation and soil water pools. Modelling results support these findings: seasonal tree‐ring δ<jats:sup>18</jats:sup>O variations are captured best when the week‐to‐week variations of the leaf water signal are suppressed.</jats:p></jats:list-item>
<jats:list-item><jats:p>Our results suggest that climate signals in tree‐ring δ<jats:sup>18</jats:sup>O variations should be strongest at temperate sites with humid conditions and precipitation maxima during the growing season.</jats:p></jats:list-item>
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