Holocene transition from climate-driven to human-dominated wetland dynamics in Sinchang-dong, South Korea.

In this study, we reconstruct the Holocene environmental history of the Sinchang-dong wetland, a key archaeological site in South Korea, using a multi-proxy approach integrating diatom and phytolith assemblages with quantitative archaeological demographic data. A Bayesian age-depth model (ca. 9.0-1.0 ka) reveals contrasting ecosystem responses to the 8.2 ka and 4.2 ka climatic events and intensified human activity. Both events are marked by diatom-poor intervals and elevated chrysophyte/diatom ratios, indicating phases of hydro-ecological instability. Responses differed between the two intervals: the 8.2 ka event was followed by a more prolonged recovery, whereas the 4.2 ka event was followed by more rapid reorganization of the wetland system. A statistically significant regime shift at ca. 2.3 ka, identified using Sequential t-test Analysis of Regime Shifts (STARS), marks a transition from a climate-driven lacustrine system to an anthropogenically dominated agricultural landscape. This shift coincides with increased Oryza sativa phytoliths, adoption of iron farming tools, and regional demographic expansion. After ca. 2.3 ka, human activity surpassed climate as the dominant driver of wetland dynamics, illustrating the transition of small East Asian wetlands from climate-sensitive to human-dominated systems.