Spatial synchrony in δ18O time-series from a tree-ring network are driven by synchronous hydroclimate variability in the transitional zone of the Asian summer monsoon

Owing to the increased need to assess global forest behavior under changing climatic conditions within a longterm context, spatial coherence in tree-ring records is of widespread interest. Spatial networks of tree growth have been widely discussed from regional to global scales, but few studies have reported stable oxygen isotopes in networks of tree rings (delta O-18(tree)), thus impeding a comprehensive hydroclimatic interpretation of delta O-18(tree) records over large spatial scales, i.e., isoscapes. In this study, a network of four annually resolved delta O-18(tree) chronologies (1805-2016) was developed for Southwest China, the transitional zone of the Asian summer monsoon, to test spatial coherence in delta O-18(tree) variations and to explore the climatic factors driving synchrony at different spatial scales. The quantitative analyses show that the four chronologies exhibit consistent annual variations, with the first principal component (PC1) accounting for 70% of the total variance, which uniformly respond to local relative humidity (RH) and precipitation delta O-18 during the monsoon season. This confirms the spatial coherence in delta O-18(tree) records. Furthermore, significant inter-site correlations of local RH and precipitation delta O-18 are also detected, revealing that it is the regionally homogeneous year-to-year variations in the hydroclimate that should be responsible for spatial coherence. For a larger spatial perspective, spatial correlation analyses reveal that the most prominent correlations between delta O-18(tree) and hydroclimate fields occur in the Indochina Peninsula, in which delta O-18(tree) changes are synchronized with those in Southwest China and the synchrony temporally varies with the Indian summer monsoon (ISM) intensity, indicating that coherent delta O-18(tree) variations are linked to ISM-related moisture transport. In addition, delta O-18(tree) records have shown strong in-phase relationships with the natural variabilities of the ISM and El Nino-Southern Oscillation (ENSO) across interannual and interdecadal timescales over the last 150 years, suggesting that spatial coherence in delta O-18(tree) records can be utilized to reflect the long-term history of large-scale atmospheric circulation.

Automated summary

This study developed a network of four annually resolved tree-ring records in Southwest China, demonstrating spatial coherence and a strong relationship with local humidity and precipitation, as well as synchronization with the Indian summer monsoon. The records also showed in-phase relationships with the Indian summer monsoon and El Nino-Southern Oscillation over the past 150 years, reflecting the long-term history of large-scale atmospheric circulation.