Holocene climate controls on water isotopic variations on the northeastern Tibetan Plateau

Abstract

On the Tibetan Plateau, applications of δD and δ 18O values in paleoclimate studies tend to be complicated due to multiple processes influencing isotopic compositions in paleoclimatic archives. In this study, isotopic compositions of modern waters in the eastern Qaidam Basin on the northeastern Tibetan Plateau, and δD values of n-fatty acids (n-FA δD) from a sediment core at Hurleg Lake were systematically analyzed to infer hydroclimate controls during the Holocene. The modern water isotopic results show a major contribution of snowmelt water originating from high-elevation mountains to the north of the Qaidam Basin via river and groundwater discharge, and the importance of evaporation in affecting lake water budget in this region. n-C 26 FA δD values tend to be more negative at millennial-scale warm-dry periods during the Holocene, and vice versa, opposite to what is commonly expected. Assisted with modern water isotopic results, we infer amplified contribution of snowmelt water to the soil water around this open lake system at warm-dry periods. Meanwhile, changes in n-C 16 FA δD values at Hurleg Lake reflect the evolution of isotopic compositions of lake water, thus we use the isotopic difference between n-C 26 and n-C 16 FA (ΔD C16-C26 ) to infer hydroclimate and evaporation variations in this region. Based on our data, relatively low n-C 26 FA δD and n-C 16 FA δD values at 10-6 cal ka BP indicate large contribution of snowmelt water into the lake during the Holocene Climate Optimum. After 6 cal ka BP, changes in evaporation became the major control on lake hydrology and led to larger fluctuations of ΔD C16-C26 . Our study highlights the importance of systematic analysis on modern processes before using stable isotopes for paleoclimate reconstructions, and demonstrates that δD difference between long-chain and short-chain n-FA might be an effective way to better understand the controlling factor of hydrological variations in a climatic complex region like the Tibetan Plateau.

Paleoclimate Significance of Reconstructed Rainfall Isotope Changes in Asian Monsoon Region

“…Many factors, such as local rainfall, vegetation types, individual plant species, soil evaporation, and moisture availability, could cause different isotopic fractionation between δD p and δD wax in some environmental conditions (Sachse et al., 2012; He et al., 2016; Feng et al., 2019; C. Zhang et al., 2020). In Southwestern China, the ISM provides the majority of annual precipitation to the plants near Lugu Lake, and the amount of monsoon rainfall overwhelms soil evaporation in this humid region.…”

“…Many factors, such as local rainfall, vegetation types, individual plant species, soil evaporation, and moisture availability, could cause different isotopic fractionation between δD p and δD wax in some environmental conditions (Sachse et al, 2012;He et al, 2016;Feng et al, 2019;C. Zhang et al, 2020).…”

“…Longchain n-alkanes (e.g., C 27 , C 29 , C 31 ) are present in epicuticular leaf waxes mainly from terrestrial higher plants (Eglinton & Hamilton, 1967), which use ambient soil water and thus rainfall for lipid biosynthesis (Sachse et al, 2012). Therefore, hydrogen isotopes of long-chain n-alkanes (or leaf wax hydrogen isotopes, δD wax ) preserved in lake sediments can be used as a proxy to infer δDp (e.g., Eglinton & Eglinton, 2008;He et al, 2016;Sachse et al, 2012;C. Zhang et al, 2020).…”

Reconstruction of Climate Changes Based δ18Ocarb on the Northeastern Tibetan Plateau: A 16.1-cal kyr BP Record From Hurleg Lake

“…Hurleg Lake lies on the northeastern Tibetan Plateau, at the intersection area, which was previously affected by both the East Asian monsoon and westerly wind (Winkler and Wang, 1993;Zhao et al, 2011). Due to the particularity of its geographical location and its climatic variability and sensitivity, many studies have reconstructed the Holocene climate based on the results of lake cores derived from Hurleg Lake, including paleotemperature, paleomoisture, and paleovegetation (Zhao et al, 2007(Zhao et al, , 2011Zhao et al, 2010;Zhao et al, 2013;Fan et al, 2014;Rao et al, 2014;He et al, 2016;Song et al, 2020). However, these climatic records from Hurleg Lake mostly focused on the Holocene, while studies on the Lateglacial were limited.…”

Holocene Lake Evolution and Glacial Fluctuations Indicated by Carbonate Minerals and Their Isotopic Compositions in the Sediments of a Glacial Melt Recharge Lake on the Northwestern Tibetan Plateau

“…The δ 18 O and δ 13 C values for aragonite and calcite (if autogenous) in lacustrine sediments are controlled by the isotopic composition and temperature of the lake water (Leng and Marshall, 2004;Horton et al, 2016). Thus, calcite and aragonite and their isotopic compositions (δ 18 O and δ 13 C) in lake sediments are widely used to investigate past changes in temperature and the δ 18 O of lake water, as well as the paleoenvironmental and paleoclimatic changes (Talbot, 1990;Leng and Marshall, 2004;Henderson et al, 2010;Deocampo and Tactikos, 2010;Hren and Sheldon, 2012;Bernasconi and McKenzie, 2013;Wang et al, 2013;He et al, 2016;and references therein). These proxies may indicate the degree of closure of a lake and may contain signals of glacial meltwater linked with glacier movement.…”