Glacial fluctuations over the last 3500 years reconstructed from a lake sediment record in the northern Tibetan Plateau

Journal Pre-proof Glacial fluctuations over the last 3500 years reconstructed from a lake sediment record in the northern Tibetan Plateau

Tianlong Yan, Jianhua He, Zongli Wang, Can Zhang, Xiaoping Feng, Xiaoshuang Sun, Chengcheng Leng, Cheng Zhao PII:

S0031-0182(19)30830-2

DOI:

https://doi.org/10.1016/j.palaeo.2020.109597

Reference:

PALAEO 109597

To appear in:

Palaeogeography, Palaeoclimatology, Palaeoecology

Received date:

14 September 2019

Revised date:

7 January 2020

Accepted date:

7 January 2020

Please cite this article as: T. Yan, J. He, Z. Wang, et al., Glacial fluctuations over the last 3500 years reconstructed from a lake sediment record in the northern Tibetan Plateau, Palaeogeography, Palaeoclimatology, Palaeoecology (2018), https://doi.org/10.1016/ j.palaeo.2020.109597

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© 2018 Published by Elsevier.

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Glacial fluctuations over the last 3,500 years reconstructed from a lake sediment record in the northern Tibetan Plateau

Tianlong Yana,b,c, Jianhua Hec, Zongli Wangc,*, Can Zhanga, Xiaoping Fenga,b,

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Xiaoshuang Suna,b, Chengcheng Leng a,b, Cheng Zhaoa,*

State Key Laboratory of Lake Science and Environment, Nanjing Institute of

Key Laboratory of Western China‟s Environmental Systems, Ministry of Education,

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c

University of Chinese Academy of Sciences, Beijing 100049, China

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b

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Geography and Limnology, Chinese Academy of Science, Nanjing 210008, China

China

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*Corresponding Author

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School of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000,

E-mail address:

*Zongli Wang: [email protected]; *Cheng Zhao: [email protected]

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Abstract Reconstructing glacial fluctuations can provide insights into glacial variations in response to climate change and can help predict future glacial changes in the context of global warming. Here, we use an ~2-yr-resolution record of inert elements derived from a sediment core from Tian‟E Lake in the northern Tibetan Plateau, together with

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proxies for magnetic susceptibility and n-alkanes, to reconstruct fluctuations of the Qiyi Glacier over the last 3,500 years. Eight major glacial advances can be identified

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at 1450-1250 BC, 1100-800 BC, 250-100 BC and 200-300 AD, 600-700 AD,

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1250-1350 AD, 1600-1750 AD, and 1850-1950 AD. These glacial advances coincided

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with cold intervals, such as the Neoglaciation and the Little Ice Age, suggesting often

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mentioned temperature controls on glacial-mass variations in the past. Moreover, due

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to the wet-cold climate combinations in the Westerlies-dominated areas, these intervals can also be correlated with wet conditions, as revealed by previously

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reported carbonate contents, total organic carbon levels and Artemisia/Amaranthaceae ratios from the same lake. These results indicate that humid environments can also contribute to glacial advances in the northern Tibetan Plateau. Our study reveals a series of high-magnitude multi-decadal to multi-centennial-scale glacial fluctuations during the late Holocene and suggests that wet conditions can also facilitate glacial advances in the Westerlies-dominated regions such as the northern Tibetan Plateau.

Keywords: Qilian Mountain; Tian‟E Lake; Qiyi Glacier; climate change; global warming 2

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1. Introduction Current global warming has induced rapid glacial melting in polar regions and in low-latitude high-elevation mountain areas (Thompson et al., 2006; Chen et al., 2013). In particular, glacial melting on the Tibetan Plateau, the third pole of the world, is of

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great significance for the water resources, environment, ecosystem, and economic development in populous Southeast Asia (Xu et al., 2009; Yang et al., 2014). However,

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recent studies have suggested that the glacial variations on the Tibetan Plateau show

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spatially varying characteristics due to the complex climate conditions on the highest

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plateau in the world. For example, glaciers in the Himalayas have been observed to

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shrink under the current global warming conditions, while glaciers in the eastern

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Pamir Mountains have been observed to expanding duo to increases in regional precipitation (Yao et al., 2012). Therefore, it is necessary to evaluate glacial dynamics

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over long time scales, which certainly can aid the predictions of future changes for high-elevation glaciers on the Tibetan Plateau. Indeed, the climate of the Tibetan Plateau is complex; in particular, the northern Tibetan Plateau is influenced by the interplay of the Asian summer monsoon and the Westerlies circulations (An et al., 2012; Chen et al., 2016). At the same time, the glaciers in the northern Tibetan Plateau have had a profound impact on the Hexi Corridor, also known as “the granary”, in western China. Thus, it is crucial to assess the response of glaciers to climate changes in this climate-sensitive and economically important area. Qiyi Glacier is one of the large glaciers in the northern Tibetan Plateau. Changes 3

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of Qiyi Glacier over the past 60 years have been studied through the collection of data by instruments (Wang et al., 2010; Wang et al., 2011; Wang et al., 2014), but the glacier‟s fluctuations on longer decadal- to multi-centennial timescales are still not well documented. Although geological surveys on glacial moraines can provide some valuable information regarding past glacial changes, such surveys cannot provide high

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resolution and continuous records (Karlén, 1981). Instead, lake sediments located downstream from glaciers can provide continuous and high-resolution information of

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glacial fluctuations. In this study, we use a multi-proxy record from a lake located

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downstream of the Qiyi Glacier in the northern Tibetan Plateau to reconstruct glacial

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fluctuations and to infer the influences of climate on the decadal- to centennial-scale

2. Study area

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glacial variations in this climate-sensitive region.

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Qiyi Glacier (39°14′13″ N, 97°45′20″ E, 4,310-5,145 m a.s.l.) is located in the Qilian Mountains on the northern Tibetan Plateau (Fig. 1). It had an area of 2.7 km2 and a length of 3.7 km in 2005 (Wang et al., 2010). This area is under the influence of the Westerlies, but is close to the modern limit of the East Asian Summer Monsoon circulations. Instrumental data from the Jiuquan Meteorological Station, ~72 km northeast of Qiyi Glacier, show that the mean annual temperature and precipitation were 7.6℃ and 90 mm, respectively, from 1951-2018. Over the past 50 years, the glacier's equilibrium line has risen by approximately 230 m (Wang et al., 2010), which was likely caused by recent warming. 4

Journal Pre-proof Tian‟E Lake (39°14′20″ N, 97°55′26″ E, 3,012 m a.s.l.) is located ~8 km downstream of the northeastern flank of the Qiyi Glacier. Tian‟E Lake is a small, closed freshwater lake with a surface area of 0.12 km2. The mean depth of the lake is approximately 12 m and its maximum depth is 14.2 m. The lake is mainly recharged by groundwater, with some visible groundwater seeping out as springs on the west

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side. The lake is adjacent to the Jingtieshan Iron Mine. According to regional survey data, the Fe contents are high and are closely related to the iron ore body (Zhou et al.,

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1999). Vegetation cover in the catchment basin is limited except for some swamplands

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on the west side of the lake where the groundwater seeps out. The plants around the

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lake are mainly reeds. Forests around the lake catchment are now absent but existed

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from 1530-1420 BC, with the highest tree pollen frequencies (mean 13.1% Picea)

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occurring during the last 3,500 years (Zhang et al., 2018). The vegetation currently

cristatum.

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consists mainly of Achnatherum splendens, Leymus chinensis, and Agropyron

3. Materials and methods

A 7.9-m-long sediment core (TEB) was retrieved in the winter of 2015 at the lake centre and was recovered through the frozen lake surface with a UWITEC piston corer. The core was split into two halves and was refrigerated at 4℃ prior to analysis. The age model of the top 6.21 m of core TEB is based on accelerator mass spectrometry (AMS) 14C dating of nine terrestrial plant fragments that were dated at Peking University, China (Yan et al., 2018; Zhang et al., 2018). All radiocarbon dates 5

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were calibrated to calendar years using the calibration of Calib 6.01 (Reimer et al., 2004) reported as “BC/AD”. After being covered with Ultralene film (4 um), the archival half of the core was imaged and analysed by an Avaatech Core Scanner at the Key Laboratory of Western China‟s Environmental Systems, Ministry of Education (MOE), Lanzhou University,

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China. The elements Al, Si, K, S, Ca, Ti and Fe were scanned at 1 mA, 10 s and a tube voltage of 10 kV; Rb, Sr and Zr were scanned at 2 mA, 20 s, 30 kV (Yan et al., 2018).

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All elements were measured at intervals of 2 mm, and the units are represented as

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counts per second (cps).

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The working half of the core was sampled at continuous 1 cm intervals. Each

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subsample was analysed for magnetic susceptibility. Approximately 1 g of the

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freeze-dried subsample was packed into 10 cm3 plastic boxes. The low-frequency magnetic susceptibility (χlf) was measured at 470 Hz using a Bartington MS2B sensor

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at the MOE Key Laboratory of Western China‟s Environmental Systems, Lanzhou University, China. The measurements were repeated at least 3 times to test their reproducibility.

We also selected and analysed 16 subsamples to determine n-alkane distributions. Approximately 5-7 g of the freeze-dried samples were extracted 4 times using an ultrasonic shaker with organic solvents (dichloromethane: methanol=9:1, v/v), ensuring complete extraction of organic matter from samples. After drying with N2 gas, the extracted total lipids were hydrolysed using 6% KOH in a methyl alcohol solution for 12 h. The supernatant was then obtained after adding NaCl and n-hexane, 6

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which was followed by centrifuging. Finally, the neutral lipids containing n-alkanes were further extracted using silica gel column chromatography with n-hexane (Zhang et al., 2019; Wu et al., 2020). The n-alkanes were measured using an Agilent 7890 Gas Chromatography system at the State Key Laboratory of Lake Science and Environment in Nanjing Institute of Geography and Limnology using Gas

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Chromatography procedures as previously reported (Zhang et al., 2019). The parameters associated with plant types, including average chain lengths

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(ACL) and proportions of aquatic (Paq) were calculated from the measured n-alkane

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data. The formulas for ACL and Paq are referenced in (Poynter and Eglinton, 1990;

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Ficken et al., 2000):

(1)

Paq= (C23+C25) / (C23+C25+C29+C31)

(2)

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ACL= (17×C17+19×C19+21×C21+ … +33×C33) / (C17+C19+C21+… +C33)

4. Results

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where Ci is the abundance of the ith n-alkane.

The age model shows that the upper 6.21 m of core TEB covers the past ~3,500 years with an average accumulation rate of ~0.18 cm/yr (Table 1, Fig. 2A, Yan et al., 2018; Zhang et al., 2018). The 9 elements with relatively high abundance obtained by XRF analyses are listed in Figure 2, and the most abundant elements are Ca and Fe. Sr and Ca show positive correlations with each other (Fig. 2B), with high values from 1450-800 BC, a gradual decrease between 800 BC and 1250 AD, and an increasing trend since 1250 AD. In contrast, inert elements, including Rb, Ti, Cu, Pb, and Fe, 7

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exhibit anti-phase relations with them (Fig. 2C-F). For the last 3,500 years, the inert elements were found to display quite low values for the period of 1450-800 BC before showing an increase to higher values in 800 BC-1250 AD and a decrease with high-magnitude fluctuations between 1250-1950 AD. Inert elements exhibited their lowest values during the period of 1600-1750 AD. Overall, the inert elements show eight multi-decadal- to centennial-scale low-value periods. The magnetic

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susceptibility values, with a mean of 15.9×10-8 m3 kg-1, exhibit changes consistent

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with inert elements but with less variability (Fig. 2G). ACL, with an average value of

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25.94, shows a pattern consistent with inert elements and magnetic susceptibility

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except for the relatively high values observed from 200-300 AD. By contrast, Paq

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5. Discussion

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shows an opposite relationship with ACL, with an average value of 0.33 (Fig. 2H).

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5.1 Multi-proxy records of glacial fluctuations from Tian’E Lake Inert elements, including Rb, Ti, Cu, Pb and Fe, exhibit conservative geochemical behaviour (Chen et al., 2004; Shen et al., 2010; Liu et al., 2014; Li et al., 2020). In paleolimnological studies, they are usually used to reflect the strength of erosional forces in lake catchments, with higher contents indicating stronger erosion of mineral materials resulting from increased regional precipitation (Shen et al., 2013; Zhang et al., 2017; Peng et al., 2019). Similarly, magnetic susceptibility values are derived from magnetic minerals and are a useful proxy for reflecting the degree of mineral erosion (Maher et al., 2003; Sartori et al., 2005). Magnetic susceptibility has

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also been widely used as an indicator of soil erosion and higher values reflect stronger soil erosion in paleolimnological studies (Dearing et al., 2008; Oldfield, 2013; Zhang et al., 2019). When studying glacial fluctuations using lake sediments, both inert element abundances and magnetic susceptibility levels in lakes close to glaciers have been used as indicators of catchment erosion caused by glacial activities. Previous

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studies have shown that higher inert elements abundances and higher magnetic susceptibility values in lake sediments can be the indicators of glacial advances

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caused by glacier-induced soil erosion (Zhang et al., 2009; Liu et al., 2014; Huang et

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al., 2016). However, the increased levels of inert elements and magnetic susceptibility

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values contained in lake sediments can also be ascribed to larger weathering source

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areas resulting from glacial retreat. Glacial retreat can expose more weathering source

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areas, which can effectively promote the addition of erosional and magnetic minerals to the lake. Although no previous studies have revealed this type of mechanism, we

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believe this is likely the case for Tian‟E Lake based on the following two lines of evidence. (1) The altitude of the equilibrium line of the Qiyi Glacier (Wang et al., 2010), the Fe contents and the magnetic susceptibility levels (with coarser resolution) in the core TEB at Tian‟E Lake show consistent changes during the period 1958-2008 AD (Fig. 3A,B), with the lowest equilibrium line (glacial advance) corresponding to the lowest Fe contents; however, there are some uncertainties in the chronology at the top of the core. (2) The intervals of low inert elements levels and magnetic susceptibility values, during the cold Neoglaciation and the Little Ice Age, were consistent with the appearance of glacial moraines (Yang et al., 2006), which were thought to be formed 9

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during glacial advances. There are no correlations between the inert elements (or magnetic susceptibility) and the observed regional precipitation or with melt-water runoff from Qiyi Glacier between 1958 and 2008 AD (Fig. 3A,C,D); thus it is likely that weathered source areas associated with glacial fluctuations, rather than precipitation induced, play a more important role in controlling the input of erosional

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materials into the lake. Advances of the Qiyi Glacier can cover many of the weathering source areas and reduce the amount of inert elements (and the magnetic

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susceptibility levels) entering the lake (Fig. 4). In contrast, glacial retreat can expose

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the weathering sources and promote the entry into the lake of these elements and

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promote higher magnetic susceptibility values. Therefore, we use inert elements

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concentrations and magnetic susceptibility values in the lake sediment as indicators for

versa.

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glacial fluctuations, with low contents corresponding to glacial advances and vice

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It must be noted that in addition to changes of glacial fluctuations, vegetation cover can also have some impact on the input of material into lakes. High vegetation coverage, especially terrestrial plants, can prevent materials in the catchment from entering lakes. The proxy of n-alkanes is used to estimate whether plant coverage plays a critical role. ACL can reflects the relative contributions of terrestrial plants versus aquatic organisms, with higher ACL indicating more terrestrially sourced organic matter (Poynter and Eglinton, 1990). In contrast, Paq reflects the proportion of aquatic plants and higher values indicate greater aquatic contributions (Ficken et al., 2000). During the periods with low inert elements contents and low magnetic susceptibility 10

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values, which are associated with glacial advances, the low ACL and high Paq values indicate less terrestrially sourced organic matter and more aquatically sourced materials (Fig. 2). Therefore, it is less likely that the terrestrial plant coverage can affect the input of mineral materials and further testifies the importance of glacial changes for the element concentrations in the sediments of Tian‟E Lake.

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5.2 Qiyi Glacier fluctuations over the last 3,500 year

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Eight distinct glacial advances can be identified based on the proxies of inert

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elements and magnetic susceptibility over the last 3,500 year (Fig. 2). They are

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1450-1250 BC, 1100-800 BC, 250-100 BC and 200-300 AD, 600-700 AD, 1250-1350

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AD, 1600-1750 AD, and 1850-1950 AD.

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During the Neoglaciation period (1450-800 BC), the glacier exhibited notable advances as suggested by the significantly low values of inert elements and magnetic

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susceptibility. This glacial advance is supported by previous studies that were based on the analysis of glacial moraines (Yang et al., 2006). This research showed that the equilibrium line declined to 4,000 m and that the glacier advanced 2 km during the Neoglaciation, which was 300 m lower than the modern glacial terminus. Within this time interval, there were three large glacial retreats, centred at 1330 BC, 1200 BC and 930 BC. The magnitude of the glacial variability was large, indicating unstable conditions. Following this period, the Qiyi Glacier abruptly retreated, as indicated by the increase in inert elements and magnetic susceptibility. For the time interval between 900-1250 AD, corresponding to the Medieval 11

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Warm Period (Hughes and Diaz, 1994; Broecker, 2001), the glacier retreated remarkably, resulting in a larger weathering source area as revealed by generally high contents of inert elements and magnetic susceptibility values. After 1250 AD, the Qiyi Glacier showed advances as revealed by low inert element contents and magnetic susceptibility values. This period corresponds well

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with the beginning of the Little Ice Age (Grove, 2001). The Little Ice Age consisted of three events with glacial advances (Fig. 2F). A previous study also reported three

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glacial advances that were indicated by glacial moraines in the Little Ice Age (Yang et

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al., 2006), although there are differences in the time durations and scales. The period of

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1600-1750 AD was characterized by extremely low inert element levels and magnetic

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susceptibility values, indicating that the weathering source area was smaller, caused by

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extensive glacial advances. This period is commonly called the maximum of the Little Ice Age (Yao et al., 1996). The last glacial advance during the Little Ice Age occurred

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between 1850 AD and 1950 AD. The amplitude of the glacial changes increased markedly during the Little Ice Age, especially during 1600-1750 AD, suggesting an unstable environment, similar to the Neoglaciation, and a period with cold and unstable conditions, than the Medieval Warm Period. After 1950 AD, the relatively high inert element contents and magnetic susceptibility levels suggest that the weathering sources expanded and that the glacier retreated again during the current warm period.

5.3 Controlling factors for glacial fluctuations 12

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Previous studies have suggested that glacial retreats, including those of the Qiyi Glacier, are controlled by temperature in the context of recent global warming (Kaser et al., 2004; Wang et al., 2010; Wang et al., 2011; Wang et al., 2017). Earlier in time, glacial changes were also correlated with temperature variations during the late Holocene in the western and southeastern Tibetan Plateau (Liu et al., 2014; Huang et

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al., 2016). It seems that temperature is the main controlling factor for glacial changes, although the contribution from precipitation has occasionally been mentioned (Yao et

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al., 2012; Wang et al., 2017). In fact, both cold temperatures and increased moisture

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conditions can promote glacial advances, but it is not clear which is the main factor

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because glacial responses differ dramatically in various areas of the Tibetan Plateau

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and its surroundings (Yao et al., 2012). Here, we use the representative element Fe,

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which can accurately reflect the activity of the Qiyi Glacier in the northern Tibetan Plateau, to compare the precipitation and spatial temperature changes over the last

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3,500 years (Fig. 5; Yan et al., 2018; Zhang et al., 2018; Thompson et al., 1997; Yang et al., 2002; Kobashi et al., 2013). Comparisons of temperature show that Fe-based glacial advances correlate with the low temperatures in stages 1-5 as recorded by the oxygen isotopes in the Guliya Ice Core (Fig. 5B; Thompson et al., 1997), which is also located in the northern Tibetan Plateau. Moreover, comparisons with multi-proxy reconstructed Chinese temperatures show that glacial advances generally correspond to low temperatures in stages 1-5 (Fig. 5C; Yang et al., 2002). This was especially true during stage 2 (1600-1750 AD), which was the coldest period and is called the maximum of the 13

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Little Ice Age; the lowest temperatures correspond to rapid glacial advances during the past 1,000 years. Moreover, the glacial advances clearly coincide with low modelled northern hemisphere temperatures in stages 1-8 (Fig. 5D; Kobashi et al., 2013). In general, Fe-based glacial advances correlate with the temperature records from the northern Tibetan Plateau, China and the Northern Hemisphere during this

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cold period, indicating that glaciers are sensitive to temperatures in the northern Tibetan Plateau.

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Changes in moisture conditions around Tian‟E Lake have been reconstructed in

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previous research using total organic carbon, carbonate contents and Artemisia and

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Amaranthaceae ratios from the same core, for which higher contents of these proxies

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reflect wetter environments and vice versa (Zhang et al., 2018; Yan et al., 2018). There

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is a significant negative correlation between Fe and the precipitation proxies (Fig. 5E-F).The eight glacial advances correspond to eight wet intervals, suggesting that the

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glacial fluctuations were facilitated by regional moist conditions as well, such as the humid conditions during the Neoglaciation and the Little Ice Age. Much attention has been paid to understanding the processes and possible mechanisms of climatic and environmental changes in the northern Tibetan Plateau at decadal to millennial time scales (Qiang et al. 2005; Zhao et al., 2009, 2013; Zhang et al., 2010; He et al., 2013; Chen et al., 2016). Previous studies have concluded that the northern Tibetan Plateau was characterized by an arid Medieval Warm Period and a wet Little Ice Age that was influenced by the Westerlies (Qiang et al. 2005; Chen et al., 2009; He et al., 2013). The cold-dry and warm-wet assemblages recorded at Tian‟E 14

Journal Pre-proof Lake using different proxies further confirm the point that Tian‟E Lake and the Qiyi Glacier were mainly influenced by the Westerlies over last 3,500 years. Moist conditions could contribute to glacial advances in Westerlies-dominated regions in addition to temperature, as has often been documented in previous studies. These wet periods with glacial advances can be correlated with cold intervals such as the

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Neoglaciation and the Little Ice Age, due to the wet-cold climate combination in Westerlies-dominated areas. Wet conditions with low temperatures combined to push

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the glaciers forward.

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6. Conclusions

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Based on the advantageous geographical position between Tian‟E Lake and the Qiyi Glacier and the robust age results from core TEB, we used inert elements

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combined with proxies for magnetic susceptibility and n-alkanes, to reconstruct

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high-resolution glacial fluctuations over the last 3,500 years. We find eight major glacial advances at 1450-1250 BC, 1100-800 BC, 250-100 BC and 200-300 AD, 600-700 AD, 1250-1350 AD, 1600-1750 AD, and 1850-1950 AD. Glacial fluctuations were supported by nearby glacial moraines during the Neoglaciation and the Little Ice Age. After comparisons with broader regional paleoclimate reconstructions, we show that glacial fluctuations are not only sensitive to temperature changes in the northern Tibetan Plateau but also can be promoted by regional moisture conditions in the Westerlies-dominated regions. Our study reveals a series of high-magnitude multi-decadal to multi-centennial-scale glacial fluctuations during the late Holocene and suggests that wetter environments could also facilitate glacial advances in the Westerlies-dominated regions such as the northern Tibetan Plateau. 15

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Acknowledgements We sincerely thank two anonymous reviewers for their constructive comments and suggestions. We also thank Qiang Wang (Lanzhou University) for taking part in the experiments using XRF; Hong Chen (Lanzhou University) for the magnetic

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susceptibility measurements; and Zhenting Wang (Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences) for field assistance.

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This work is supported by the Strategic Priority Research Program of Chinese

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Academy of Sciences (#XDA2009000004), the Program of Global Change and

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Mitigation (#2016YFA0600502), the Natural Science Foundation of China (Grants

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No. 41877293), the Natural Science Foundation of China (Grants No. 41571182), and

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the Open Foundation of the MOE Key Laboratory of Western China‟s Environmental

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Figure captions Fig. 1. Location and settings. (A) Map showing the location of the study site - Qiyi Glacier and Tian‟E Lake (red dot) on Qilian Mountain, northern Tibetan Plateau, (B) picture of Tian‟E Lake catchment. The springs are indicated by lines on the west side of the lake, (C) picture showing the relationship of the locations of Tian‟E Lake and

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the Qiyi Glacier, (D) bathymetry of Tian‟E Lake. The red dot indicates the location of core TEB. (For interpretation of the references to colour in this figure legend, the

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reader is referred to the Web version of this article.)

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Fig. 2. Stratigraphic changes of various proxies for glacial fluctuations in core TEB

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from Tian‟E Lake. (A) Age-depth model (Zhang et al., 2018; Yan et al., 2018), (B)

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elements Ca and Sr, (C) elements Rb and Ti, (D) elements Cu and Zn, (E) elements Pb and K, (F) element Fe, (G) magnetic susceptibility, (H) average chain length and

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relative proportion of aquatic. The eight glacial advance stages are highlighted with blue shading. The time ranges of Neoglaciation, Medieval Warm Period and Little Ice Age are divided by black dashed lines. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3. Comparison of the proxies with instrumental data. (A) Element Fe and magnetic susceptibility, (B) the altitude of the equilibrium line of the Qiyi Glacier (Wang et al., 2010). The grey line represents the initial values and the black line represents the 10-point running mean. (C) the precipitation at the Jiuquan 24

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Meteorological Station, (D) the meltwater from Qiyi Glacier (Song et al., 2010). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4. The glacier-lake conceptual model showing glacial fluctuations. The inert

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elements uncovered by the glacier are indicated by solid red dots. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web

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version of this article.).

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Fig. 5. Comparisons of Fe-based glacial fluctuations with temperature reconstructions.

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(A) Element Fe in Tian‟E Lake (this study), (B) δ18O values recorded by the Guliya ice core (the grey line represents the initial values and the black line represents the

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20-point running mean, Thompson et al., 1997), (C) reconstructed temperatures for China over the last 2,000 years (Yang et al., 2002), (D) reconstructed temperatures for

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the Northern Hemisphere using a climate model in a Greenland ice core (Kobashi et al., 2013), (E) carbonate and total organic carbon contents in Tian‟E Lake (Zhang et al., 2018; Yan et al., 2018), (F) values of the Artemisia/Amaranthaceae ratios (Zhang et al., 2018). The eight glacial-advance stages (numbers 1-8) are highlighted with blue shading. The time ranges of Neoglaciation, Medieval Warm Period and Little Ice Age are divided by black dashed lines. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

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Table caption

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Table 1. The results of AMS 14C dating of core TEB.

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Sample No.

Depth (m)

Material

δ13C (‰)

TE1-1-003

0.01

plant residues

-37.33±0.23

Modern

-64±80

TE1-1-023

0.26

plant residues

-35.23±0.23

125±25

137±25

TE1-1-047

0.56

plant residues

-32.89±0.23

250±45

213±45

TE1-2-026

1.66

plant residues

-29.53±0.24

305±25

367±25

TE1-2-085

2.4

plant residues

-26.21±0.23

615±25

603±25

TE2-2-003

4.07

plant residues

-25.97±0.24

1170±40

1093±40

TE2-2-103

5.27

plant residues

-27.51±0.23

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Table 1 14

2065±40

2033±40

TE3-1-044

5.85

plant residues

-25.47±0.23

2985±30

3160±30

TE3-1-079

6.21

plant residues

-23.56±0.24

3255±35

3484±35

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Calendar age (cal. yr BP, 1 σ)

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☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

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1. Continuous high-resolution glacial fluctuations inferred from lacustrine sediments 2. Large multi-decadal-scale glacial fluctuations existed during the late Holocene

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3. Wetter conditions could also facilitate glacial advances in the Westerlies regions

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