Mid-Holocene palaeohydrochemistry and palaeohydrology of Yamdrok Yumtso, southern Tibetan Plateau, reconstructed from δ¹⁸O and δ¹³C of fossil shells of the gastropod Radix auricularia

Abstract

Palaeohydrochemical and palaeohydrological changes of lakes have seldom been reconstructed from the fossil shells of the gasropod Radix auricularia, which is a new, and potentially high-resolution environnmental archive. We conducted a geochemical and stable isotope study of the shells of Radix from the exposed fluvio-lacustrine sediments near Lake Yamdrok Yumtso in the southern Tibetan Plateau. Our aims were to determine the sedimentary environment, palaeo-lake hydrochemistry and hydrological status. AMS 14C and OSL dating indicates that a lake-level stage of Yamdrok Yumtso higher than that of today occurred during ~4.7–1.2 cal. kyr BP. Results of Sr/Ca, δ13C and δ18O analysis of the fossil shells of Radix auricularia indicate that the lake-level fluctuations were mainly controlled by changes of the Indian Summer Monsoon; decreasing evaporation during the mid- to late-Holocene was also responsible. In addition, based on the geochemical relationship between Radix sp. shells and the ambient water in lakes, the values of δ18OPalaeo-water and Sr/CaPalaeo-water reconstructed using the fossil shells of Radix auricularia are −8.2‰ to −5.1‰ and 0.0012 to 0.0057, respectively. Further, based on the values of δ18Oshell, together with geomorphological evidence, we infer that Yamdrok Yumtso was a closed lake system, and we estimate its possible extent during the interval of high lake-level. In addition, we speculate that the water level of Yamdrok Yumtso at this time exceeded 4448.9 m a.s.l., but was less than 4451 m a.s.l., and that the major separation of various components of the Yamdrok Yumtso system occurred after 1.2 kyr BP.

Late-Holocene hydrological variability from the NW Himalaya and southwestern Tibetan Plateau: Paleo-salinity records from Pangong Tso

“…The δ 18 O calcite/aragonite values (VPDB) of serial samples from individual Radix shells, the calculated temperature variation (black smooth line) and salinity along the direction of shell growth during the life span of each Gastropod shell analysed from Pangong Tso. Temperatures are calculated from the δ18O calcite/aragonite of serial sampled shell and the ambient δ18O water values (from the δ18O shell and δ18O water relation given by Chen et al, 2020) of lake water using the aragonite–water isotope fractionation equation of Kim et al (2007) and the salinity quantified by using the δ18O water and salinity relation of Pangong Tso present day water. (a) - SPTG 1a.…”

“…A rapid lake-level fall is thought to be a result of an abrupt rise in evaporation and aridity. Also the chronology of the paleo-shoreline of Yamdrok Yumtso (a central TP lake) suggests that the integrated lake system with the neighbouring lakes of Gongmo Tso and Chen Co broke down into separate lake systems as the lake level fell after 1.2 ka BP (Chen et al, 2020).…”

“…The δ 18 O values of the shells of Radix sp. have earlier been used to evaluate the paleohydrological and palaeoclimatic changes over the TP (Chen et al, 2016(Chen et al, , 2017(Chen et al, , 2020Liu et al, 2009a;Taft et al, 2012aTaft et al, , 2020. The δ 18 O of the Radix species is controlled by the water isotope chemistry, thus can be used to infer the paleohydrochemistry status of the lake's ambient water (Hu et al, 2017).…”

“…The δ 18 O shell values of the hydrologically open lakes in the southern Tibetan region range from −12.1‰ to −5.9‰, and relatively lower values for the closed basins vary from −7.3‰ to −0.9‰ (Chen et al, 2020). The Radix gastropod shell can be used to quantify the ambient water oxygen isotope composition (Chen et al, 2016(Chen et al, , 2017(Chen et al, , 2020Hu et al, 2017) (Supplemental Figure 4B).…”

“…Earlier studies on freshwater gastropod shells have revealed that seasonal variations in water temperature and δ 18 O water control the oxygen isotopic signatures of the shells (Roy et al, 2019) and this relationship has been used on Radix shells to understand palaeoclimatic variations over the TP, as these shells are assumed to attain equilibrium with the lake water (Chen et al, 2016(Chen et al, , 2020Hu et al, 2017;Roy et al, 2019;Taft et al, 2012aTaft et al, , 2020. However, studies from various lakes from western China and elsewhere have discussed the factors controlling the carbonate oxygen isotopic composition and suggested that the isotopic composition is mainly controlled by authigenic carbonate minerals whether the oxygen isotope equilibrium is achieved or not (Hren and Sheldon, 2012;Li et al, 2020).…”