Influence of aquatic plants on the hydrogen isotope composition of sedimentary long-chain n-alkanes in the Lake Qinghai region, Qinghai-Tibet Plateau

• Published in: Science China. Earth sciences Vol. 59; no. 7; pp. 1368 - 1377
• Main Authors: Liu, WeiGuo, Yang, Hong, Wang, HuanYe, Yao, Yuan, Wang, Zheng, Cao, YunNing
• Format: Journal Article
• Language: English
• Published: Beijing Science China Press 01-07-2016; Springer Nature B.V
• Subjects: Aquatic plants; Arid zones; Earth and Environmental Science; Earth Sciences; Freshwater; Geochemistry; Hydrogen; Isotopes; Lakes; Research Paper; Rivers; Sediments; Semiarid lands; Terrestrial environments; 同位素组成; 水生植物; 湖泊沉积物; 烷烃同系物; 西藏高原; 长链正构烷烃; 陆地植物; 青海湖地区; Qinghai Lake; Asia, Qinghai-Tibet Plateau; China, People's Rep. Qinghai Prov., Qinghai L; Hydrogen isotope; Long-chain n-alkanes; Paleohydrology proxy; Lake Qinghai; Aquatic plants
• ISSN: 1674-7313; 1869-1897
• DOI: 10.1007/s11430-016-5263-2

The hydrogen isotopic composition（δD） of leaf wax long-chain n-alkanes（C_27, C_29, and C_31） from lacustrine sediments has been widely applied to reconstruct terrestrial paleoclimatic and paleohydrological changes. However, few studies have addressed whether the aquatic-derived n-alkanes can affect the δD values of lake sedimentary long-chain n-alkanes, which are usually regarded as a recorder of the terrestrial hydrological signals. Here we systematically investigated δD values of long-chain n-alkanes from modern aquatic plants, both near-shore and off-shore surface sediments, surrounding terrestrial plant litters, as well as river water and lake water in Lake Qinghai and its satellite lakes on the northeastern Qinghai-Tibet Plateau. Our data showed that（i） δD values of long-chain n-alkanes from aquatic plants varied from-184‰ to-132‰ for n-C_27, from-183‰ to-138‰ for n-C_29, and from-189‰ to-130‰ for n-C31, respectively, with no significant differences among the three n-alkanes homologues;（ii） δD values of long-chain n-alkanes from aquatic plants were generally more positive than those from surrounding terrestrial plants, possibly because that they recorded the D-enrichment of lake water in this semi-arid region;（iii） δD values of long-chain n-alkanes from surface sediments showed significant differences among the three n-alkanes homologues, due to the larger aquatic input of n-C_27 to the sedimentary lipid pool than that of n-C_31, and（iv） n-C_27 δD values of near-shore aquatic plants and near-shore sediments are more negative than those from off-shore as a result of lower δD values of near-shore lake water. Our findings indicate that in this region（i） the offset between sedimentary n-C_27 and n-C_31 δD values（ΔδDC_27-C_31） could potentially be used to evaluate if sedimentary long-chain n-alkanes are derived from a single source;（ii） while δD values of n-C_27 may be influenced by lake water hydrological changes, sedimentary n-C_31 is derived predominantly from terrestrial plants and thus its δD can serve as a relatively reliable indicator for terrestrial paleoclimatic and paleohydrological reconstructions.