Title

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

Authors

Liu, WG; Yang, H; Wang, HY; Yao, Y; Wang, Z; Cao, YN

Abstract

The hydrogen isotopic composition (δD) of leaf wax long-chain n-alkanes (C₂₇, C₂₉, and C₃₁) 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‰-132‰ for n-C₂₇, from -183‰-138‰for n-C₂₉, and from -189‰-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-C₂₇ to the sedimentary lipid pool than that of n-C₃₁, and (iv) n-C₂₇ 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-C₂₇ and n-C₃₁ δD values (ΔδD_C27-C31) could potentially be used to evaluate if sedimentary long-chain n-alkanes are derived from a single source; (ii) whileδD values of n-C₂₇ may be influenced by lake water hydrological changes, sedimentary n-C₃₁ is derived predominantly from terrestrial plants and thus its δD can serve as a relatively reliable indicator for terrestrial paleoclimatic and paleohydrological reconstructions.

Corresponding author

Liu Weiguo

Volume

59

Issue

7

Page

1368-1377

Pub year

July, 2016

Publication name

Science China-Earth Sciences

Details

http://link.springer.com/article/10.1007%2Fs11430-016-5263-2