Seasonal temperature dynamics since the last deglaciation revealed by pollen records from northeastern China

Understanding the seasonal expression of temperature signals preserved in terrestrial proxies remains a key challenge in paleoclimatology. Here, we present a high-resolution pollen record from the Greater Khingan Mountains, northeastern China, spanning the last 15.2 kyr, to investigate seasonal temperature evolution since the last deglaciation. Principal component analysis (PCA) of pollen assemblages identifies two distinct climate-related signals. PCA Axis 1 primarily reflects winter temperature variability, with higher values indicating colder winter conditions and stronger influence of the East Asian winter monsoon (EAWM), whereas PCA Axis 2 represents growing-season temperature variability associated with changes in the East Asian summer monsoon (EASM). The reconstructed seasonal temperature records reveal contrasting trajectories since the last deglaciation. Growing-season temperatures increased rapidly during the early Holocene, coinciding with maximum EASM intensity, whereas winter temperatures continued to rise into the middle Holocene. This seasonal contrast resulted in a delayed ecological optimum in the Greater Khingan Mountains. The Holocene Optimum (HO) inferred from vegetation development occurred between ∼6 and 3 ka BP, when temperate forest elements reached their maximum expansion under relatively favorable annual thermal conditions, despite the weakening of summer monsoon intensity after the early Holocene. These results demonstrate that pollen assemblages can preserve separable seasonal climate signals and highlight the importance of winter temperature evolution in regulating vegetation responses at mid-high latitudes.