The tree-ring δ¹⁸O network over Northeast China captures regional climate variability: coherence, gradients, and site-dependent controls

Northeast China is highly sensitive to ongoing climate change, yet tree-ring oxygen isotope (δ¹⁸O) studies remain limited, constraining regional-scale understanding of isotope fractionation and the relative roles of temperature and moisture (i.e., “temperature” versus “amount” effects). Here we develope eight tree-ring δ¹⁸O series from multiple tree species across Northeast China and integrate these records with instrumental observations and gridded climate datesets to evaluate spatial structure, climatic sensitivity, and dominant controls on the δ¹⁸O variability. The tree-ring δ¹⁸O exhibits a pronounced latitudinal gradient, with lower values north of 50°N and higher values to the south. Interannual δ¹⁸O variability is significantly coherent over distances up to ∼850 km, indicating a robust regionally shared climate signal. While temperature explains most δ¹⁸O variability at the majority of sites, several locations show stronger sensitivity to moisture-related variables, revealing substantial spatial heterogeneity in fractionation mechanisms across contrasting environments. Moreover, spatial correlation patterns between the δ¹⁸O and CRU gridded climate fields reinforce the proxy's capacity to capture regional-scale climate variability. By providing the first systematic regional synthesis of the tree-ring δ¹⁸O across Northeast China, this study advances mechanistic understanding of isotope fractionation in a climatically complex transition zone and offers practical guidance for selecting optimal sites and species for future isotope-based climate reconstructions, as well as for related physiological and ecological applications.