Hydrogen isotope records of long-chain alkanes from the monsoon boundary zone over the last 2400 years in North China

• Published in: Journal of hydrology (Amsterdam) 2024-04, Vol.633, p.131008, Article 131008
• Main Authors: Guo, Xin, Li, Wenbao, Shi, Xiaohong, Liu, Tingxi, Shi, Yujiao
• Format: Article
• Language: English
• Subjects: Biomarker; EASM precipitation; Lake Dali; Late Holocene; δDwax
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2024.131008

•The δDwax-C31 value can be used as a proxy for the regional precipitation in the monsoon boundary zone (MBZ).•Over the past 2400 years, precipitation in the MBZ has been decreasing.•Decreased temperature caused anomalous negative δDwax-C31 in MBZ from 1800 to 1600 cal.a BP.•Multi-proxy approach can reconstruct ancient climate and environmental conditions. The East Asian Summer Monsoon (EASM) plays a key role in the climate dynamics of East Asia, affecting the livelihood of millions of people by contributing to agriculture and water resources. The monsoon boundary zone (MBZ) is particularly sensitive to shifts in climate patterns. However, the complexity of water vapor sources in the region makes it difficult to understand precipitation processes. To address this issue, the records of lipid biomarker abundances and leaf wax stable hydrogen isotope composition of C31–alkanes (δDwax-C31) from a 238 cm sediment core extracted in Lake Dali, located at the northern edge of the EASM, were sampled and examined by 2 cm per sample. Based on analyses of the biogenic molecular indicators(biomarkers), precipitation isotopes, and other indicators of the evolution of the climate environment, we have reconstructed precipitation change history over the past 2400 years. The results show the decrease in alkanes concentrations, along with high A.I. values in Lake Dali sediments indicate an arid trend over the past 2400 years, which have led to a decrease in basin productivity and the development of grasslands. The low temperatures greatly limit the growth of C4 vegetation in this cold region, so the long-chain alkanes in the lake sediments is mainly derived from the leaf wax lipids of C3 vegetation in the grassland. The increase of Paq and the reduction of ACL indicate that the decrease of grass vegetation inputs in the basin and the outbreak of aquatic vegetation. Notably, aquatic vegetation outbreaks may be due to reduced precipitation leading to shrinking lakes and increased nutrients in the lakes. By comparing with the biogenic indicators of Lake Dali and other regional records, the δDwax-C31 value can be used as a proxy for the regional precipitation, with a gradual decrease from about −240 ‰ to about −190 ‰, which indicates a general decreasing trend in the precipitation in the last 2400 years. Specifically, in exception of some significant fluctuations on the centennial to millennial scale, δDwax-C31 value decrease by about 40 ‰ between 1800 and 1600 cal.a BP over a p