青海湖及柴达木盆地湖泊正构烷烃碳、氢同位素地球化学意义

The compound-specific carbon and hydrogen isotope compositions (δ13C and δD) of leaf wax n-alkanes have been used to address a wide range of research questions in paleoclimate and paleoenvironment studies, and have made a series of encouraging results. However, with the development of scientific studies and the requirement of quantitive paleoclimate reconstructions, the sources, differences in isotope compositions, and geochemical mechanisms of leaf wax n-alkanes in lakes have receieved more attention. During the past several years, we have found that there are large amounts of aquatic plants in Lake Qinghai (in particular at the lake bottom) and the n-alkane δ13C values for some submerged plants are quite similar to that of terrestrial C4 plants. Therefore, whether or not the submerged plants may affect the isotope compositions of sedimentary long-chain n-alkanes merit attention. In this study, we will systematically investigate the distribution and isotope compositions of n-alkanes derived from terrestrial plants, aquatic plants, and surface sediments for plateau lakes, focused on lakes in the Lake Qinghai region and the Qaidam Basin. Our aim is to explore the environmental controls on the n-alkane δ13C and δD values in lake sediments. Our results will provide further insight into the mechanisms controlling the sedimentary n-alkane δ13C and δD values, which is useful for the proper application of compound-specific δ13C and δD of sedimentary n-alkanes as an indicators in paleoclimate and paleoenvironment studies.

湖泊沉积物中源于植物叶蜡正构烷烃组分的稳定碳氢同位素已被广泛应用于古环境重建，在过去全球变化领域已取得一系列突出的研究成果。然而，伴随着研究程度的深入和定量化重建古环境的需要，对湖泊叶蜡正构烷烃的来源、同位素组成变化和地球化学机制的研究受到更多的关注。我们在过去几年的研究中发现，在青海湖（尤其是湖底）存在大量的水生植物，其中一些沉水植物的正构烷烃碳同位素与陆地C4植物的正构烷烃碳同位素很相似。因此，水生植物是否会对湖泊沉积物长链正构烷烃同位素产生影响值得关注。本研究拟以我国青藏高原北部青海湖和柴达木盆地不同类型湖泊为重点，进一步详细调查高原湖泊现代水生植物、沉积物和陆地植物正构烷烃分布和碳、氢同位素的组成，揭示湖泊沉积物中正构烷烃碳、氢同位素的控制因素，为利用湖泊沉积记录中的叶蜡正构烷烃的碳、氢同位素组成重建湖泊环境变化提供可信的地球化学机制。

湖泊沉积物中源于植物叶蜡组分的稳定碳氢同位素已被广泛应用于古环境重建。然而，伴随着研究程度的深入和定量化重建古环境的需要，湖泊叶蜡正构烷烃的来源、同位素组成变化和地球化学机制的研究受到更多的关注。本研究以我国青藏高原北部青海湖和柴达木盆地不同类型湖泊为重点，详细调查了高原湖泊现代水生植物、沉积物和陆地植物正构烷烃和脂肪酸分布和碳、氢同位素的组成，结合青海湖岩芯样品正构烷烃的碳氢同位素变化，我们发现：（1）湖泊中大量生长的水生植物对湖泊沉积物的长链正构烷烃和长链脂肪酸存在较大贡献，这些水生植物正构烷烃和脂肪酸的氢同位素组成受湖水氢同位素、植物光合作用方式和表面包裹碳酸盐等影响；（2）湖泊水生植物正构烷烃和脂肪酸的氢同位素分馏值变化均较小；（3）青海湖全新世以来的正构烷烃单体碳氢同位素变化表明青海湖在早全新世时期降水量较大，但沉水植物大量生长，湖水位较低；（4）现代陆地植物的氢同位素结果表明在全球范围内，陆地单子叶和双子叶植物叶蜡氢同位素存在差异。本研究结果揭示了湖泊沉积物中叶蜡碳、氢同位素的控制因素，为利用湖泊沉积记录中的叶蜡碳、氢同位素组成重建湖泊环境变化提供了可信的地球化学机制认识。