Multi-proxy indications of depositional evolution and paleo-natural disasters (flooding and fire) in the southern part of the Korean Peninsula during the Holocene

Abstract

Understanding paleoenvironmental changes and corresponding driving forces can provide valuable information for predicting and preparing for future climate change. However, under the complex climate system, the driving mechanisms behind hydroclimatic variability in terms of timescales and magnitude are still unclear, and the various ecological responses are not clear. Here, we reconstruct the history of swamp evolution and climate changes in the southern part of the Korean Peninsula during the Holocene based on multi-proxy data (palynomorphs, microscopic charcoal, diatoms, grain size, total organic carbon, C/N ratio, and δ13CTOC data). The climatic conditions in the study area gradually became cold and dry due to the weakening East Asian summer monsoon (EASM) after ca. 5400 cal yr BP, as evidenced by the shift in vegetation communities from temperate broad-leaved forests dominated by Quercus to mixed conifer and deciduous broad-leaved forests with increased cold/dry-tolerant taxa. After ca. 4700 cal yr BP, microscopic charcoal concentration to terrestrial pollen concentration values are relatively high together with a sharp decrease in palynomorph concentrations and the proportions of arboreal pollen, representing open forest with fewer plants due to frequent wildfires. In addition, the quasi-millennial frequencies of seasonal fires (dry spring) and flooding (summer rainfall) were identified in our study area during the Late Holocene, which correspond to lower sea surface temperatures of the western tropical Pacific and stronger El Niño Southern Oscillation (ENSO) activity periods. After ca. 8200 cal yr BP, the depositional environment underwent gradual backswamp expansion due to high precipitation, strengthened EASM, and relative sea-level rise during the Early to Middle Holocene. During the Late Holocene, ENSO-driven extreme hydroclimatic variability, such as frequent flooding and fire, had significant impacts on not only swamp development with large fluctuations in water level but also long-term vegetation and aquatic ecosystem dynamics.