Holocene hydroclimatic reorganization and prehistoric settlement response in the East Asian summer monsoon transition zone

Abstract. Holocene hydroclimatic changes in the East Asian monsoon region were spatially heterogeneous, but their timing and driving mechanisms within the monsoon transition zone remain insufficiently constrained. Here, we present a multi-proxy biomarker record from Nansi Lake, eastern China, to reconstruct Holocene hydroclimatic variability in this sensitive monsoon transition belt. The record indicates relatively dry conditions during the early Holocene, a pronounced humid interval during the middle Holocene, and generally drier but more variable conditions during the late Holocene. This pattern is broadly consistent with the middle-Holocene moisture maximum recorded in northern China, but contrasts with central-sector records characterized by wetter early and late Holocene conditions and drier mid-Holocene. Beyond this latitudinal contrast, proxy records across the monsoon transition zone reveal a longitudinal hydroclimatic gradient, with peak Holocene humidity generally delayed from west to east. This eastward delay may have been modulated by changes in El Niño activity and regional topographic effects on monsoon moisture transport. Furthermore, comparison with archaeological site distributions suggests that this hydroclimatic reorganization was accompanied by an eastward shift in prehistoric settlement density within the transition zone. These findings highlight the spatial complexity of Holocene hydroclimatic change in monsoon transition regions and provide a long-term perspective on landscape–human interactions under changing moisture regimes.