Novel n-alkanes records reveal organic matter sources and monsoon hydroclimatic changes in Dahu Swamp in South China since the last deglaciation

The long-term evolution of complex and variable monsoon climate has not been well understood. The relatively closed Dahu Swamp in South China presents an advantageous setting for reconstruction of the paleoclimate and paleoenvironmental conditions. This study provides novel n-alkanes records to explore the accumulation of organic matter, hydroclimate changes, and driving mechanisms in the south of the East Asian monsoon region. A 16.2-kyr long n-alkanes record exhibits both unimodal and bimodal distribution patterns, with long-chain n-alkanes dominating (52.0–92.4 %), indicating that the organic matter inputs are chiefly sourced from terrestrial higher vegetation and emergent plants. With the support of previously published proxy records from the same site, the n-alkanes reveal that peat sediments are mainly developed during cold/dry conditions, which are not conducive to the growth of large aquatic plants, reduce microbial activity, and are favourable to the preservation of exogenous terrestrial organic matter. Conversely, warm/humid intervals exhibit opposite trends. The n-alkanes also document drought events, several hundred years long, which are associated with high-latitude climatic processes and low-latitude ocean-atmosphere interactions that affect the East Asian monsoon. Further periodic analysis allowed the identification of millennial (∼2200 yr) and multi-centennial cycles (∼430 yr, 520 yr, and 640 yr), illustrating the influence of solar radiation and activity on the long-term development of the East Asian monsoon. This study contributes to a deeper understanding of the dynamics related to organic matter input and hydroclimatic changes in the East Asian monsoon region, and emphasises the particular insight from the n-alkanes.