Tree-ring δ¹⁸O reveals thaw-buffered warming in northernmost permafrost regions of China

Permafrost is widespread in the northernmost part of China where it constitutes a major global carbon reservoir and plays a critical role in the stability of this cold-region's ecosystems. Accelerating warming in recent decades has heightened ecological and hydrological vulnerabilities, emphasizing the need for a deeper understanding of climate variability and its governing mechanisms. In this study, we analyze tree-ring oxygen isotope (δ¹⁸O) records from two dominant tree species, sampled across multiple sites within the permafrost zone. Our results identify summer maximum temperature and relative humidity as the primary climatic factors influencing δ¹⁸O fractionation. The δ¹⁸O records demonstrate high sensitivity and temporal stability in response to growing-season climate variability, indicating strong potential for reconstructing past regional temperature and moisture conditions. The δ¹⁸O series reveals a predominantly cold and wet climate from the 1900s to the mid-1950s, followed by a pronounced shift toward warmer and drier conditions beginning in the late 1950s. Notably, the rate of warming in this region has been considerably lower than the Northern Hemisphere average, likely due to the latent heat buffering associated with permafrost thaw. Furthermore, variations in regional atmospheric moisture are primarily modulated by large-scale circulation systems, including the East Asian Summer Monsoon (EASM), El Niño–Southern Oscillation (ENSO), and North Atlantic Oscillation (NAO). Collectively, these findings advance our understanding of climate dynamics in permafrost-affected regions and provide valuable insights for predicting future climate change, enhancing ecosystem resilience, and informing the conservation of forests and permafrost in cold environments.