Organic matter source traced by n-alkane records derived from lacustrine sediments from Daping swamp in the western Nanling Mountains (South China) and its response to climatic variability since the last deglacial

Abstract

Previous multi-proxy records have revealed the advantages of well-preserved and long-scale geological archives from the lake sediments of Daping swamp in the western Nanling Mountains in South China. However, the exact organic matter (OM) sources in the sediments and their response to climatic variability still remain unclear. In this study, we present a 15.3-kyr n-alkane record extracted from lacustrine sediments in this swamp to explore the OM sources and the relationship between OM input and climatic changes. The results indicated that the n-alkane composition in sediments was dominated by long-chain n-alkanes (C27-C31), implying that the OM mainly originated from the terrestrial higher plants and emergent aquatic plants. The n-alkane data further verified that changes in OM sources were related to the surface erosion-transportation-deposition processes controlled by climatic changes. Lake level change, which was also regulated by climate conditions, played an important role in impacting OM accumulation; warmer and wetter conditions would result in rising lake levels that favored more aquatic OM and less terrestrial OM input, and vice versa. Variability of the Asian summer monsoon intensity regulated by the dynamic variations in low-latitude processes (e.g., solar insolation, intertropical convergence zone, and El Niño/Southern Oscillation), as well as high-latitude processes (e.g., meltwater input in the North Atlantic), was closely related to the OM accumulation in sediments.