Response of <italic>n</italic>-alkanes in Pliocene-Pleistocene sediments from North China to paleoclimate changes and its implications for paleovegetation evolution

Previous studies have reconstructed the paleoclimate evolution in East Asia during the Plio-Pleistocene using multiple proxies, providing a foundation for assessing the climatic and environmental significance of n-alkanes during this period. This study investigates the distribution changes of n-alkanes in XA3 sediment core (38°55.1'N, 116°4.2'E, 604.5 m depth, with a total of 126 samples) from Xiongan in North Chian Plain, focusing on their response to climatic changes and the associated vegetation type evolution during the Pliocene-Pleistocene. The XA3 age model is based on paleomagnetic dating, with a bottom age of 5.5 Ma and the Brunhes/Matuyam, the Matuyama/Gauss, and the Gauss/Gilbert boundaries are at 70.3 m, 226.2 m, and 366.5 m, respectively. The results show that the n-alkanes in the sediments have a typical bimodal distribution, indicating primary sources from microorganisms (fungi, bacteria, algae) and terrestrial plants. The terrestrial inputs consistently more, suggesting an open depositional environment, and the abundance of n-alkanes from microorganisms and aquatic plants increase significantly during warm and humid periods. Variations in the peak carbon of terrestrial n-alkanes reflect shifts in the relative contributions of herbaceous plants and trees, with distinct patterns across climatic stages: herbaceous sources dominated during the warm-dry period (4.0~5.5 Ma), while trees increased and became more prominent during the warm-humid period (2.6~4.0 Ma), and during the subsequent cold-humid period (0~2.6 Ma), trees continued to dominate, maintaining a stable ratio with herbaceous plants. Otherwise, n-alkane indicators (e. g., ACL, CPI, Paq) demonstrate strong responses to paleoclimatic changes. Principal component analysis (PCA) confirms that these climatic shifts are key drivers of n-alkane compositional evolution. This study providing a new insight into the paleoclimate-vegetation-hydrology interactions in North China.