Holocene lake-level fluctuations of Selin Co on the central Tibetan plateau: Regulated by monsoonal precipitation or meltwater?

https://doi.org/10.1016/j.quascirev.2021.106919Get rights and content

Highlights

  • Holocene lake-level history of Selin Co built using K-feldspar luminescence dating method.

  • The lake level experienced highstand between at 10–7 ka but a striking decline afterward.

  • Monsoonal rainfall might not be unique factor driving Holocene lake evolution.

  • Glacial meltwater highlighted as key influence on lake-levels.

Abstract

Over the Tibetan Plateau (TP), lakes as paleoenvironmental archives have been the most extensively investigated for their sensitivities to climate change on different timescales. Well-preserved shoreline and terrace remains surrounding these lakes provide critical geomorphological and sedimentary evidence that can be used to infer past lake levels over geological timescales. These features can offer an analogue for understanding how future lake-levels respond to global warming. In this study, we investigated a series of water level-related depositional profiles around the Selin Co basin from the central TP, by dating 28 samples using K-feldspar luminescence techniques. Combining the obtained chronological data with sedimentological, stratigraphic evidence and differential GPS survey observations, the Holocene history of lake-level fluctuations in Selin Co was inferred. The results show a stable highstand between 10 ka and 7 ka but a striking subsequent lake-level decline. This pattern appears to follow the solar insolation-forced changes in the intensity of the Indian summer monsoon (ISM), particularly during the early Holocene. However, such gradual weakening of ISM intensity after the early Holocene may not interpret the dramatically rapid shrinking of Selin Co, implying other components are largely underrecognized driving factors accounting for the effective moisture of lakes in the early Holocene. Here, we argue that the increased meltwater input from glaciers and permafrost, together with increased precipitation, might have resulted in the high lake level at 10–7 ka, as the high summer temperature during the early Holocene induced massive melting water flow into the lake. By 7 ka, the abrupt lake-level drop is likely related to the decreased meltwater owing to decreasing regional temperatures documented from glacier landforms, ice cores and lacustrine sediments. Therefore, we highlight that meltwater from glaciers and permafrost poured into lakes on the central TP, particularly during warm periods on the millennial timescales, might also dominate the Holocene high lake levels.

Introduction

The Tibetan Plateau (TP), known as the “Water Tower of Asia” or “the Third Pole”, is highly relevant to global climate change and Asian monsoon systems (i.e., East Asian summer monsoon (EASM) and Indian summer monsoon (ISM)) due to the fact that: (1) it harbours the largest concentration of glaciers outside polar latitudes; (2) its runoff and meltwater provide over 1 billion people with water for their own livelihoods and agriculture (Krause et al., 2010; Song et al., 2013; Jonell et al., 2020; Wei et al., 2020, Fig. 1). The Asian monsoon can be understood as being principally a product of seasonal temperature differences between the Indian and Pacific Oceans and the Asian continent. These differences drive wind and weather systems in a strongly seasonal fashion that characterizes the climate throughout South and East Asia (i.e., Indian summer monsoon and East Asian summer monsoon) (Webster et al., 1998). Today, there are 1055 lakes (>1 km2 area) that occupy a cumulative area of 41,831 km2 distributed across the TP(Ma et al., 2011). These lakes represent important indicators of water resource availability under climate change (Liu et al., 2018; Zhang et al., 2013). Based on remote-sensing investigations, most lakes in the inner TP have experienced significant expansion in area and rapid rises in water levels since the 1970s (Lei et al., 2014; Meng et al., 2012; Song et al., 2014; Wan et al., 2014; Zhang et al., 2019). Selin Co, the largest lake in Tibet, expanded from 1617 km2 during the mid-1970s to 2341 km2 during the 2010s, and its level rose by ∼12 m (Meng et al., 2012; Zhang et al., 2011; Shi et al., 2017). Because of the obvious increase in air temperature during the past decades (∼0.3 °C/decade) (Guo and Wang, 2012; Yang et al., 2014), many glaciers in the inner TP have significantly retreated since the 1970s, causing increasing meltwater flow into lake basins (Bolch et al., 2010; Yao et al., 2012). Subsequently, glacial meltwater became a dominant factor over decadal timescales, and it triggered the expansion of several large lakes in the interior TP, including Nam Co, Selin Co and Linggo Co (Zhu et al., 2010; Meng et al., 2012; Lei et al., 2012). Furthermore, a recent study using laser elevation measurements reported that glacier meltwater contributed ∼25% to the lake water balance in the inner TP between 2003 and 2009 (Zhang et al., 2017b). In fact, glacier-fed lakes at approximately 33° N north of the plateau exhibited more rapid level increases than non-glacier-fed lakes after 2000, reflecting the fact that the presence of glacier meltwater supply augments lake expansion (Song et al., 2014). However, the majority of research outcomes suggested that increased precipitation, rather than glacial meltwater has caused most lake expansions during recent decades (Yang et al., 2014, Zhang et al., 2017b). This was attributed to increased transport of moisture from the western and southwestern TP by the westerlies and the Indian summer monsoon, respectively (Benn and Owen, 1998; Tian et al., 2007).

It should be noted that over millennial time-scales, meltwater from glaciers may have also poured into lakes on the plateau, particularly during the Holocene warm periods. Yet the relative contribution of meltwater to Holocene high lake-level events remains unclear. Based on their calculation of the changes in ratio of lake area to total basin area for a large number of lakes over the TP, Hudson and Quade (2013) proposed that the glacial meltwater had a very limited impact on the regional lake expansions during the early Holocene. In contrast, for non-glacier-fed lakes, the lack of glacial meltwater input during the early Holocene could have resulted in relatively lower lake levels because temperature-induced evaporation could outweigh the increased monsoonal precipitation (Jin et al., 2016). Therefore, more records with robust chronologies and hydrological implications in this region are needed to trace the effects of meltwater on lake level fluctuations. These explorations should be helpful in understanding and interpreting many expanding lakes in the context of the rapid temperature rise and changing precipitation patterns that are occurring today on the TP (Cheng et al., 2020).

In this study, we investigated a set of abandoned shorelines and outcrops of the Selin Co basin on the central TP. Previous studies of paleo-shorelines around this lake suggested that Selin Co has experienced dramatic fluctuations in lake levels and environmental variations throughout the Holocene (Shi et al., 2015, 2017; Li et al., 2009; Xue et al., 2010). However, the timing of and the factors influencing lake-level expansion and decline over millennial time scales are still controversial (e.g., Shi et al., 2015; 2017; Xue et al., 2010). Here, we mainly focus on the southern portion of the Selin Co basin, where steep slopes are extensive and a unique staircase of paleo-shoreline is well preserved. Using luminescence and radiocarbon techniques together with detailed field stratigraphic descriptions and sedimentological analysis, we first constrain the timing of past lake water-level changes and then provide insight on the different factors influencing lake level fluctuations in the Selin Co basin, particularly during the early to middle Holocene.

Section snippets

Study area

Selin Co (30°03′ N-33°40′ N, 87°39′ E−92°26′ E, Fig. 2a) is the largest endorheic lake on the central TP. It has a water area of ∼2341 km2 (data obtained in 2010) and a maximum water depth of ∼59 m (Zhang et al., 2011; Meng et al., 2012; Gyawali et al., 2019). The elevations of its basin drainage range from 4532 m to 6406 m above sea level (a.s.l.), and the modern water level of Selin Co is approximately 4542 m a.s.l. (Guo et al., 2016) (Fig. 2b). In the same catchment, another lake, called

Sampling sites

Five paleo-lacustrine sections and six beaches from two areas (Block 1 and Block 2, Fig. 3a), were investigated in 2017. We measured the elevations of all of the studied sections using a high-precision differential global positioning system (dGPS). In the southeastern Lake Cuoe (Block 1), three sites (CE1, CE2, and CE3) can be feasibly identified from natural exposure caused by river cutting; these sites were excavated to allow collection of samples for luminescence dating and sedimentological

Chronology

To confirm the suitability of the applied pIRIR protocol, we first tested the effects of different elevated temperatures on De. A total of 18 aliquots of a representative sample (NL-1467) were prepared and measured under different temperatures (130, 150, 170, 190, 225 and 290 °C) prior to IR stimulation at 50 °C. The results show no obvious trend in the pIRIR De values regardless of the preheat temperature used before IR50 measurement except at 290 °C (Fig. 5a). Therefore, we chose pIRIR

Conclusions

This study applied the luminescence dating method to a series of well-preserved paleoshorelines and paleolacustrine outcrops around the Selin Co basin on the central Tibetan Plateau to reveal the history of lake level fluctuations during the past ∼10 ka. Our results showed that the lake underwent a prominent highstand during the early Holocene (∼10–7 ka), a rapid regression at approximately 7–6 ka and a lowstand status that was sustained until ∼2.4 ka. This pattern does not follow the gradually

Author contribution

Yandong Hou: Visualization, Software, Investigation, Data curation, writing original draft, Writing – review & editing; Hao Long: Funding acquisition, Writing – review & editing; Formal analysis, Investigation, Visualization, Data curation, Project administration; Ji Shen: Supervision, Writing – review & editing; Lei Gao: Writing – review & editing, Data curation, Software;

Declaration of competing interest

The authors declare that there is no conflict of interest.

Acknowledgments

This research was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (No. XDB40010200), the Second Tibetan Plateau Scientific Expedition and Research Program (No. 2019QZKK0202), the Program of Global Change and Mitigation (grant No. 2016YFA0600502), the National Natural Science Foundation of China (No. 41977381, 41807417), Youth Innovation Promotion Association CAS (grant No. 2015251) and Natural Science Foundation of the Jiangsu Province for the Young Research

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