Mid- to late-Holocene paleoenvironmental changes inferred from organic geochemical proxies in Lake Tangra Yumco, Central Tibetan Plateau

Abstract

Investigations of the paleoclimate and paleoenvironmental changes in the Tibetan Plateau in recent years have led to many significant achievements. However, high-resolution lake records from the mid- to late-Holocene have not been determined for the Central Tibetan Plateau, which is in the transition zone between the Indian summer monsoon (ISM) system and the westerlies. In this study, we analyzed the distribution and compound-specific carbon isotope compositions ( δ13C) of sedimentary n-alkanes and the bulk sediment total organic matter (TOC), total nitrogen (TN), and C/N ratios to reconstruct the paleoenvironmental changes over the past 6 cal. ka BP using a 376-cm sediment core from the southern basin of Tangra Yumco, Central Tibetan Plateau. Our results indicated that clear stepwise decreases in lake productivity and lake level occurred during the mid- to late-Holocene based on decreases in δ13C values of mid-chain n-alkanes and Paq (an n-alkane-based proxy). Additionally, the variations in the TOC, TN, and C/N ratios revealed generally increased inputs of allochthonous organic matter over the past 6 cal. ka BP. When our findings at Tangra Yumco were compared with records from the Central Tibetan Plateau and adjacent regions, we found generally consistent patterns of lake environmental changes over the past 6 cal. ka BP, suggesting that the climate of the Central Tibetan Plateau was primarily influenced by the ISM system at the millennial time scale. Therefore, our results depict the evolution of the ISM over the past 6 cal. ka BP in the Central Tibetan Plateau, which corresponds to summer solar insolation and the migrations of the Intertropical Convergence Zone (ITCZ). We also propose that the climate of the North Atlantics influenced the climate of the Central Tibetan Plateau through some indirect climatic mechanisms.

Responses of sedimentary proxy indicators to lake-level fluctuations on the central Tibetan Plateau since the last deglaciation

“…The TOC and TN contents of lake sediments are linked to both climatic conditions and the lake environment (Zhao et al, 2007). The TOC content of sediments reflects lake productivity and the input of terrestrial organic matter, which are linked to climate change, within-lake processes, and watershed processes (Haberzettl et al, 2005;Mischke and Zhang, 2010;Wang et al, 2017b;Xu et al, 2006), and the TN content reflects the nutrient status of the lake watershed (Zhu et al, 2008). High TOC values in lacustrine sediments indicate a climate favoring organic productivity, typically warm periods or periods of high effective humidity (Kasper et al, 2015;Wünnemann et al, 2012;Xu et al, 2019).…”

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

“…Most of the palaeoenvironmental studies on the Tibetan Plateau have focussed on open-water lake sediments (e.g. Alivernini et al, 2018;Chen et al, 2016b;Mischke et al, 2016;Mügler et al, 2010;Wang et al, 2017;Zhu et al, 2008Zhu et al, , 2009 and the investigation of palaeo-shorelines (e.g. Chen et al, 2013;Lee et al, 2009;Liu et al, 2011;Rades et al, 2015;Shi et al, 2017).…”