Holocene provenance variations and palaeofloods response to ENSO-driven monsoon precipitation in the subalpine peatland in southern China

Abstract

There have been few investigation of the provenance of sediments and hydrological response to past climatic change in the subalpine peatland in southern China. The source of sediments and regional climatic variations during the Holocene have been deduced from Rare Earth Elements (REEs), SrNd isotopic data and grain size end-member modeling analysis (EMMA) derived from peat sediments from the southwestern mountainous region of Hunan Province, China. From the distinctive SrNd isotopes patterns, LREEs enrichment, and the Eu anomaly observed in these sediments, it can be concluded that local weathering residues have been the primary sedimentary source throughout the Holocene. Based on the method of EMMA, four distinct end members were identified. EM2, signifying weathering products of moderate particle size, is sensitive to climate variations. This sensitivity makes it an effective marker to track the historical evolution of the East Asian summer monsoon (EASM) intensity. The results suggest that the prevalence of the relatively weak EASM during the interval 11,600–9000 cal yr BP, followed by an overall weakening trend during the past 9000 years. EM3 + EM4, the coarsest component in the peat sediments, indicate strong runoff typically caused by the extreme weather events. Notably, the occurrence of relatively high EM3 + EM4 component during the interval 5400–4500 cal yr BP and 3500–2600 cal yr BP is consistent with the previous reported palaeoflood events in the Yangtze River basin. We suggest that the regional flood patterns are predominantly controlled by the East Asian monsoon system, which in turn, is driven by ENSO activities. For a comprehensive understanding of regional flood patterns, it is imperative to extend research into high-altitude areas.