Advancing annually resolved oxygen isotope dendrochronology to overcome wood-dating limitations in the Euro-Atlantic region.

Stable oxygen isotope dendrochronology has emerged as a ground-breaking technique for dating historic timbers when conventional tree-ring-width dendrochronology falls short. In the Euro-Atlantic region, thousands of timbers in historic buildings and archaeological sites from the Late Medieval and Early modern periods contain few tree rings or exhibit complacent growth (i.e., minimal year-to-year variation), making them undatable with conventional ring-width dendrochronology. Here, we present a 300-year-long annually-resolved δ18O reference chronology for the Eastern Netherlands-Northwest Germany region (TWR δ18O), covering the period 1300-1600 CE. We explore its correlations with other European δ18O chronologies, and its potential for dating short and complacent tree-ring series. We found that the TWR δ18O chronology exhibits strong coherence with independent δ18O records from Belgium and the UK, and weaker correlations with French and more continental chronologies. Our results demonstrate that δ18O dendrochronology can successfully date single timbers with as few as 30 rings when a local reference δ18O chronology is available. In the absence of such data, combining δ18O series from 3-5 coeval samples and extending the temporal coverage improves dating success through correlations with regional chronologies. These findings provide guidance for sampling strategies and the development of δ18O chronologies in the Euro-Atlantic region. The dating of currently undatable samples and their integration into dendrochronological repositories will enable a more accurate reconstruction and interpretation of past construction activities, timber trade, and forest management practices, ultimately transforming our understanding of post-medieval timber use and environmental history.