Holocene vegetation and climate dynamics in the ... - AGU Publications

Holocene vegetation and climate dynamics in the Altai Mountains and surrounding areas Xiaozhong Huang1, Wei Peng1, Natalia Rudaya2,3,4, Eric C. Grimm5, Xuemei Chen1,6, Xianyong Cao7,3, Jun Zhang1, Xiaoduo Pan6,7, Sisi Liu1, Chunzhu Chen1,8, Fahu Chen1,7 1

Key Laboratory of Western China’s Environmental System (Ministry of Education); College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, Gansu, 730000, China.

2

Kazan State University, Ul. Kremlyovskaya 18, Kazan, 420000, Russia.

3

Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Department of Periglacial Research, Potsdam, Germany.

4

Institute of Earth and Environmental Science, University of Potsdam, Karl-Liebknecht-Str. 24-25, Potsdam-Golm, 14476, Germany.

5

Department of Earth Sciences, University of Minnesota, Minneapolis, MN, 55455, USA.

6

Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, Gansu, 730000, China.

7

Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, 100101, China.

8

School of Geographic Science, Nantong University, Nantong, Jiangsu, 226019, China.

Corresponding Author: Xiaozhong Huang, ([email protected])

Key Points: 

A new pollen data set from a large deep lake was used to interpret the regional vegetation and climate of the southern slope of Altai.



We found vegetation had different long-term responses to climate change in and around the Altai Mountains.



Different vegetation dynamics and their impact on geophysical processes should be incorporated into coupled vegetation-climate models.

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1029/2018GL078028 © 2018 American Geophysical Union. All rights reserved.

Abstract A comprehensive understanding of the regional vegetation responses to long-term climate change will help to forecast earth system dynamics. Based on a new well-dated pollen dataset from Kanas Lake and a review on the published pollen records in and around the Altai Mountains, the regional vegetation dynamics and forcing mechanisms are discussed. In the Altai Mountains, the forest optimum occurred during 10-7 ka for the upper forest zone and the tree line decline and/or ecological shifts were caused by climatic cooling from around 7 ka. In the lower forest zone, the forest reached an optimum in the middle Holocene, and then increased openness of the forest, possibly caused by both climate cooling and human activities, took place in the late Holocene. In the lower basins or plains around the Altai Mountains, the development of proto-grassland or forest benefited from increasing humidity in the middle to late Holocene.

© 2018 American Geophysical Union. All rights reserved.

1 Introduction Vegetation plays a critical role in the Earth system through its effects on surface albedo (Mykleby et al., 2017), atmospheric aerosol (Jin & Wang, 2018) and greenhouse gas composition and the global carbon cycle (Piao et al., 2009). As a result, vegetation and ecosystems are sensitive to climate change. For this reason, investigating past changes in Holocene vegetation patterns at various spatial scales can be used for developing analogues of future vegetation composition and response to changing climate dynamics under the current global warming scenario (Blyakharchuk et al., 2007; Feurdean et al., 2017; Hopcroft et al., 2017; Zhao et al., 2017). Many studies have focused on Holocene vegetation change in central Asia and its implications for the evolution of humidity over a large area (An et al., 2012; Chen et al., 2016a; Huang et al., 2015; Huang et al., 2009; Liu et al., 2008; Sun et al., 1994; Tarasov et al., 2000; Tarasov et al., 1997). However, most of the lake sites are in basins at lower altitudes which are relatively dry and fed by rivers originating from the surrounding mountains. Many of the sites do not have reliable records for the early Holocene because the lakes shrank or disappeared completely, resulting in possible hiatuses in the sedimentary record, such as Lake Bosten (Huang et al., 2009) and Lake Wulungu (Liu et al., 2008). In arid central Asia, the mountainous areas provide most of the water resources for the low-lying oases, wetlands and lakes, and therefore it is important to understand the past vegetation and climate dynamics of these higher elevation areas. In the large area of the Altai Mountains and the surrounding region, the numerous lakes are important archives of Holocene climate and vegetation history (Fig. 1). The pollen record from Hoton-Nur (2080 m, site 10) (Rudaya et al., 2009) shows a different pattern of vegetation evolution that recorded in Achit Nuur (1444±5 m, site 12) (Sun et al., 2013) in western Mongolia. A quantitative reconstruction of annual precipitation of Bayan-Nur (site 13) area


(Tian et al., 2014) is also quite different from that reconstructed from Hoton Nur. Based on the previous studies, it appears that the Altai Mountains lie along a climatic boundary in central Asia with the patterns of vegetation and climate evolution depending on site location (Rudaya et al., 2009; Wang & Feng, 2013). Therefore, Lake Kanas (site 9 in Fig. 1) is a potentially important site for exploring regional vegetation and climate evolution during the Holocene.

2 Physical Geography, Samples and Methods Kanas Lake (1365 m a.s.l.) is 25-km long and ~2-km wide, and the average depth of the basin is 97 m (Feng & Ren, 1990; Wu et al., 2014). It was formed by the damming of a valley by an end moraine that formed during the last glaciation (Xu et al., 2009), and the lake center is relatively flat. The coring site was in the southeastern bay, in a water depth of 19.85 m; the site is far from the inflowing river in the northern part of the basin and the sedimentary environment is apparently stable. The Kanas Lake area has an annual precipitation of around 400-700 mm with a relatively high proportion as winter snowfall. Aridity increases eastwards of the Altai Mountains, because of the major influence of the Mongolian anticyclone. The mountain area has a long cold winter (October through May) and a short cool summer (June to August). To the south of the Altai Mountains, there is the arid Gurbantonggut Desert in the Zunggar Basin where the precipitation is less than 200 mm per year (Zhuang et al., 2012). The vegetation of the Kanas drainage is characterized by a series of altitudinal zones: 1) 3000-3500 m (= m a.s.l.), tundra vegetation; 2) 2300-3000 m, sub-alpine and alpine meadow; 3) 1300-2300 m, forest; 4) 500-1300 m, desert and desert steppe (Xinjiang Comprehensive Survey Team & Institute of Botany, 1978). Also see major plant compositions in the auxiliary material (Text S1) and map of vegetation of the Kanas Lake area in Fig. S1 (Hou, 2001). A sediment core KNS11-B (244 cm) (48˚43′23″N, 87˚01′22″E) (Fig. S1) was obtained from a water depth of 19.85 m in Kanas Lake using a piston corer. The bathymetry of the


sampling site is uniform. The core was frozen and transported to Lanzhou University and then sliced into 1-cm intervals. Grain-size distributions were measured using a Malvern MS 2000 laser grain-size analyzer following sample preparation using standard procedures (Peng et al., 2005). Pollen analysis was conducted at a 2-cm interval (a total of 123 samples). Samples of volume ~1 cm3 were prepared by treatment with 10% HCl and concentrated HF to remove carbonates and siliceous material, respectively (Fægri & Iversen, 1989). A Lycopodium tablet was added to each sample to estimate pollen concentrations. A pollen sum of >300 (average 378) terrestrial pollen grains was counted for all the samples. Pollen identification is based on the Pollen Flora of China (Wang et al., 1995) supplemented by modern regional pollen reference collections. Pollen assemblage zones were defined by stratigraphically constrained cluster analysis (CONISS) (Grimm, 1987), including all pollen taxa with percentages of at least 1% in one sample.

3 Chronology and Pollen Data Nine samples of terrestrial plant macrofossils (Fig. S2) were used for AMS

14

C dating

(Table S1) and one sample from bulk organic material. The samples were prepared and dated by Beta Analytic in the USA. An age model for the upper 201 cm was constructed using Bacon version 2.2. (Blaauw & Christen, 2011) and the IntCal13 calibration curve (Reimer et al., 2013) (Fig. S3). Based on this age model, the sedimentation rate for the upper 5 cm of core KNS11B (0.05 cm/yr) is comparable to that calculated on the basis of a 210Pb chronology of a core from the lake center (0.052 cm/yr) (Feng & Ren, 1990) as well as a sedimentation rate of 0.029-0.07 cm/yr on the basis of new 210Pb data for the uppermost 2.5 cm (Fig. S4). A detailed discussion of the age model is provided in supplementary Text S2. 24 major pollen taxa were identified including trees such as Abies, Pinus, Betula, Picea, Larix and Juniperus, and herb taxa with a high pollen productivity, such as Cyperaceae,


Poaceae, Artemisia and Amaranthaceae (= Chenopodiaceae). Five pollen zones were identified using CONISS (Fig. 2) and pollen assemblages were described in supplementary file in detail (Text S3). Surface pollen samples from arid central Asia (Cao et al., 2014) and western Siberia (Bordon et al., 2009) were used for quantitative reconstruction (Cao et al., 2017), and more details are listed in Text S4. A surface sample distribution map is shown in Figure S5 and the Pann passed the significance test (Fig. S6).

4 Discussion Based on our field investigations and vegetation description (Xinjiang Comprehensive Survey Team & Institute of Botany, 1978), there is a distinct pattern of the spatial distribution of the main plant species in the taiga forest of the Altai Mountains. Betula mainly grows in the valleys at the lower part of Picea and Larix forest; and Ephedra is one of the main taxa in desert and desert-steppe areas distributing in the lower Gobi desert basins (Huang et al., 2009; Li et al., 2017). Juniperus shrub is distributed within a wide elevation range from several hundred meters to >2000 m, which means that this shrub is not sensitive to temperature and is mainly growing on open sunny slopes with dry conditions. For example, Juniperus is widely distributed in the eastern Altai Mountains (See Fig. S7 photo d, near to eastern Gobi Altai area) where there is ~200 mm less precipitation, while it is rare in the Kanas Lake area (Fig. S7 a,b,c). Therefore, it is classified as a drought-tolerant species based on modern ecology (McDowell et al., 2015). In addition, Larix is regarded as one of the most frost-tolerant species (Blyakharchuk & Chernova, 2013). Field observations indicate that there is more Larix at higher elevations and it is distributed at higher altitudes than Picea (Fig. S7). In summary, the distribution of temperature-sensitive tree and shrub species from warm to cold is: Betula > Picea > Larix, and the most drought tolerant shrub species are Ephedra followed by Juniperus. Therefore, in Kanas Lake area, Betula can be regarded as an indicator of a warm climate with


high humidity and Larix of a cold climate, while Ephedra and Juniperus are indicators of a dry climate. With regard to herb taxa, a lot of Artemisia spp., Poaceae and some Chenopodiaceae grow within the grassy areas of open forest. Thus, an increased herb pollen content reflects an extension of grassland within the forest, and the sum of herb pollen taxa represents the degree of openness of the forest around the lake (Sugita et al., 1999), which may be related to both climatic conditions in the Holocene and anthropogenic grazing activity in the historical period (Huang et al., 2017b). The evolution of vegetation in the Kanas Lake area can be divided into five stages. Stage 1 (13.4-13 ka) - Steppe-dominated with sparse trees covering the pollen zone 1 (Fig. 2). This stage comprises the Late Glacial. The vegetation of the Kanas catchment was steppe, dominated by Poaceae, Artemisia, and Amaranthaceae, possibly with shrub such as Rosaceae (e.g., Spirae alpine, Rosa albertii) and Juniperus, with Picea. The low representation of tree pollen types indicates a cold and relatively dry climate recorded in ice core (Vinther et al., 2009) (Fig. 3 a). Stage 2 (13-11.7 ka) Steppe-dominated with less trees compared to Stage 1. This stage corresponds to the Younger Dryas stadial. It is notable that the sedimentary shift from coarse to fine sediments at around 11.7 ka (180 cm, Fig. S3) matches with the boundary between pollen zone 2 and 3. The changes in vegetation occur in phase with no leads or lags with environmental change. Stage 3 (11.7-8.5 ka) - The increased tree pollen percentages compared to Stage 2, especially Picea and Abies, indicate the rapid development of a somewhat open forest, growing with Juniperus and Ephedra. Stage 4 (8.5-4 ka) - The vegetation around the lake was dominated by forest with some grassland, as indicated by the highest tree and shrub pollen frequencies, especially Betula and


Salix, within the entire sequence (Zone 4 in Fig. 2). After ~7 ka, the decreasing frequencies of trees and shrubs indicate forest recession. Based on modern plant distributions, the high tree (e.g., Betula) and shrub pollen frequencies suggest a warmer and more humid climate than during the previous stage. Stage 5 (4-0 ka) - Tree pollen frequencies decreased continuously and herb pollen frequencies increased, indicated a progressive opening of the forest (Pollen zone 5 in Fig. 2). The decreased Betula representation indicates climatic cooling, while the disappearance of Juniperus and Ephedra may indicate an increase in humidity. It is also notable that the boundary between pollen subzones 5a and 5b at 1.4 ka which is ~500 years prior to the main shift in grain size at ~0.9 ka (Fig. S3). The two transitions appear to be unrelated and could reflect independent processes such as changing precipitation.

The site locations discussed here are shown in Fig. 1. A pollen record from the Narenxia peat section (1760 m a.s.l., site 8), about 8 km west of Kanas Lake, indicates that the pollen concentration was very low before 9.5 ka and the local vegetation was dominated by wetland and steppe species. After 9.5 ka, it became a Cyperaceae-dominated peatland with some Pinus and Picea, especially after 3.2 ka, indicating the close proximity of taiga forest (Feng et al., 2017). In the southwestern Tuva Republic, Lake Grusha (2413 m a.s.l.) and Lake Akkol (2204 m a.s.l.) (site 6, 7) are located in the modern shrub land-tundra belt. Holocene pollen data from Lake Grusha indicate that the regional tree line of the forested zone was ascending from 11-10 ka, but the upper tree line descended from around 7 ka and 6-4.8 ka respectively (Blyakharchuk et al., 2007). In the western Mongolian Altai Mountains, Lake Hoton-Nur (2083 m a.s.l., site 10), located at an elevation below the present upper limit of the Larix forest (Photo S1), documents the development of taiga forest at ~10 ka, while the regional forest became unstable from 7 ka and retreated from around 4.7 ka (Rudaya et al., 2009). As


Larix pollen is an under-represented pollen type, the lower tree &shrub pollen in the middle to late Holocene could have been contributed to by the ecological transition from Picea to Larix dominated and/or decreased forest coverage. In view of the fact that there was no obvious increase of Larix pollen during this period, a decline in forest most likely took place. At lower elevations in western Mongolia, Achit Nuur (1444 m a.s.l., site 12) recorded an increasing trend of tree pollen types and a corresponding humidity increase after about 6.5 ka (Sun et al., 2013). The pollen data from the southern Siberian Lowland (60~120 m a.s.l., site 1, 2) indicated that the taiga forest developed after around 7 ka and that the early Holocene climate was warm and dry (Blyakharchuk, 2003). Similarly, a pollen record from the Ozerki wetland (210 m a.s.l., site 11) indicated that the early Holocene vegetation was steppe and that it changed to Betula-dominated open woodland, later with more Pinus, in the middle and late Holocene, respectively (Tarasov et al., 1997). A pollen record from Wulungu Lake (480 m a.s.l., site 14) in the central Zunggar Basin, indicated that the lake level was much lower in the early Holocene than in the middle to late Holocene (Liu et al., 2008). The changes in tree and shrub pollen frequencies indicate that forest evolution in the Altai Mountains generally followed changing summer insolation at middle to higher latitudes in the Northern Hemisphere (Fig. 3 c). This suggests that the forest in the high mountains was more sensitive to temperature than to precipitation (Fig. 1). In addition, at the upper tree line, the extremely cold winters and heavy snowfall will cause significant physical damage to trees, especially to younger trees, while the lower temperatures will also reduce the organic matter and nutrient content of the soils (Mayor et al., 2017). The pollen record from Kanas Lake indicates that forest development occurred at the beginning of the Holocene, earlier than at the other sites in the high mountains. Kanas Lake is located at a much lower elevation than the other three lakes, and the forest would have taken less time to reach the vicinity of the lake


from glacial refuge areas (Birks, 2015). In the middle Holocene, summer insolation decreased and glacial advances occurred at many high mountainous areas of the Northern Hemisphere, including the Altai Mountains (Agatova et al., 2012a; Chernykh et al., 2013; Clague et al., 2009; Herren et al., 2013). A colder climate (likely cold winter) prevailed during the middle Holocene (Huang et al., 2015; Thompson et al., 1997), which would have damaged the forest and depressed vegetation productivity from around 7 ka, especially at higher elevations in the Altai Mountains (Blyakharchuk et al., 2007; Rudaya & Li, 2013; Rudaya et al., 2009). Since Kanas Lake is located in the lower valley and close to the warmer and drier desert area to the south, this cooling could have increased the effective humidity and therefore the maximum in the representation of trees and shrubs occurred at ~7 ka and then subsequently decreased with continued cooling (Marcott et al., 2013) (Fig. 3 b). On the other hand, Larix, the most frost-tolerant tree (Blyakharchuk & Chernova, 2013), increased after about 7 ka indicating that the cooling was ecologically significant (Fig. 2). In the Baikal area, a record from Lake Kotokel shows that thermophilous Ulmus was replaced by humidity-tolerant Pinus after 7.3 ka, reflecting the same climatic cooling and ecological change (Tarasov et al., 2009). In the wet Ulagan high-mountains, the tree pollen content of three lakes (with elevations between 1985 and 2150 m a.s.l., site 3, 4, 5) indicates that the forest was relatively stable since around 9-10 ka; while, a cooling climate was reflected by decreased percentages of Abies and Picea by about 7.5 ka (Blyakharchuk et al., 2004). During the late Holocene, the forest in the Kanas Lake area became increasingly open compared to the middle Holocene, which is indicated by the greater representation of herb pollen types such as Artemisia (Fig. 2). The quantitatively reconstructed Pann suggested that the annual precipitation did not decrease significantly in the late Holocene (Fig. 3 h). The forest recession was caused by occasional cold climatic events from around 4 ka and by heavy winter


snowfall, as indicated by a simulated increase in regional winter precipitation (Chen et al., 2016b) and glacial advances (Agatova et al., 2012a; Agatova et al., 2012b; Chernykh et al., 2013; Lehmkuhl, 2012; Zhao et al., 2013). On the other hand, in the lower basins or plains, the higher A/C ratio indicated that the regional climate became more humid (Blyakharchuk et al., 2004; Liu et al., 2008), which is also supported by the disappearance of drought-tolerant species of Juniperus and Ephedra in the Kanas Lake pollen record (Fig. 2 and Fig. 3 g). Clearly, in the late Holocene, it is increasingly difficult to disentangle the impacts of human activity and climate on vegetation (Miehe et al., 2007). Especially after about 1.4 ka, the increase in Artemisia pollen may indicate that the regional vegetation zonation moved upwards because of the warmer climate of the Middle Ages (Ge et al., 2003; Schluetz & Lehmkuhl, 2007), and/or increased human impacts on the vegetation of the area. As recorded in the Chinese historical book “Bei Shu”, the Turks moved to the Altai Mountains in the middle 6th century from the Daxing’anling Mountains in northeastern China (Rui, 1994). They mainly practiced nomadic pastoralism which may have had a destructive effect on the forest and increased the area of grassland. In addition, Artemisia pollen is one of the main indicators of human impacts on steppe vegetation (Li et al., 2008). After the Turks, the region was occupied by the Mongols until the present day who practice the same pastoral lifestyle. The synthesized regional humidity was generally increasing during the Holocene especially after 7-8 ka in northern Xinjiang (Fig. 3 i) (Wang & Feng, 2013) and the core area of ACA (Chen et al., 2016a). After ~7-8 ka, a more negative Arctic Oscillation (AO) (Fig. 3 c) (Rimbu et al., 2003) and North Atlantic Oscillation (NAO) would have caused lower temperatures and higher regional precipitation in ACA (Chen et al., 2016b). This pattern is also supported by the pollen record from Kanas Lake, where the highest percentages of Juniperus and Ephedra, and lower reconstructed Pann occur in the early Holocene (Fig. 3 g, h). The lower reconstructed precipitation values during ca. 10.5-8.5 ka were most likely contributed to by: (i)


relatively lower pollen % values of trees & shrubs; (ii) higher representation of Juniperus and Ephedra (Ephedra’s optima Pann is13 mm); and (iii) the reduced representation of Betula, which has an optima Pann of 625 mm. On the other hand, with the decreasing summer insolation (Fig. 3 d), a large-scale decrease in mean annual temperature in the Northern Hemisphere occurred from around 7 ka (Marcott et al., 2013) (Fig. 3 b), and neo-glaciations commenced in the western Mongolian Altai Mountains (Agatova et al., 2012a; Herren et al., 2013) and on the northern and central Tibetan Plateau (Thompson et al., 2005), also indicating a cooling climate and more precipitation in winter. The cooling climate may have resulted in intensified eolian activity (Qiang et al., 2014). Both the enlargement of the glaciers/snow cover and enhanced eolian activity may have resulted in further cooling of the climate due to higher albedo and higher atmospheric dust content. This could have had two primary effects: (i) enhanced cloud nucleation resulting in diminished insolation; and/or (ii) dust fertilization of the oceans resulting in enhanced planktonic productivity which then may have led to the sequestration of atmospheric CO2 and thus lowered global temperatures (Martin, 1990). This cooling also resulted in an ecological transformation of a large part of arid central Asia (Herzschuh et al., 2006; Huang et al., 2015; Tarasov et al., 2009). Coupled vegetation-climate models would benefit from higher (1-10 km) resolution spatial data showing how vegetation dynamics vary under different geomorphological and climatic regimes. Such improvements may facilitate clarification of which vegetated areas contribute the most global temperature change through feedback effects like albedo. Based on the pollen-based vegetation dynamics in and around the Altai Mountains, it is clear that the vegetation and climate dynamics in the high mountains were different from those in the lower basins. This pattern is in accord with recent observations and climate model simulation results of intensified warming and accelerated dryland expansion under global warming (Huang et al., 2017a; Huang et al., 2016). This has important implications for the


future evolution of the vegetation of the Altai Mountains and surrounding areas under the influence of ongoing climate change: the early Holocene vegetation under a warmer climate is a potential reference plant community for a warmer future. An increasing number of records have shown that the accelerated tree mortality in semi-arid areas is connected to a warmer and drier climate (McDowell & Allen, 2015; McDowell et al., 2015).

5 Conclusion Pollen data from a sediment core from Kanas Lake in the southern Altai Mountains have been used to reconstruct the regional vegetation history and climate during the Holocene. The results show that the southern taiga forest responded rapidly to climatic warming following the cold Younger Dryas event. This response was faster than that which was recorded in the high mountains. In the early Holocene, there was low forest cover as evidenced by relatively low tree and shrub pollen frequencies and high representation of drought-tolerant species compared to the middle Holocene. It was proposed that the warmer climate in the early Holocene could have resulted in widespread aridification of semi-arid areas, but conversely forest expanded in the high mountains in central Asia because of relatively low temperatures. The climatic cooling in the middle Holocene caused significant vegetation change at a wide spatial scale: 1) the forest composition changed with tree line decline in the mountains; and 2) vegetation coverage increased in the arid area and steppe transitioned into forest on the semi-humid plains. The reconstructed early Holocene climate of the Altai Mountains and surrounding areas matches the current global warming trend observed that ‘dry areas became drier’ and ‘wet areas became wetter’. The changing northern hemisphere insolation was the dominant driver of climate change. The analytical evidence presented reveals differential sensitivity and response of vegetation dynamics in the mountains compared with the lower basins/plains. This emphasizes the need to further examine local-scale processes contributing to vegetation composition and


response. Future studies could assess how geomorphic and local climatic factors affect vegetation response and provide important data that can be incorporated into vegetation-climate models to more accurately simulate the impact of vegetation dynamics on global-scale geophysical processes and associated feedbacks.

Acknowledgments: This study was funded by the National Key Research and Development Program of China (grant no. 2017YFA0603403) and the National Natural Science Foundation of China (grant no. 41571182). The work of Natalia Rudaya was funded by the Alexander von Humboldt Foundation (Ref 3.3-RUS-1151158-HFST-E); Russian Government Program of Competitive Growth of Kazan Federal University; and the Russian Foundation for Basic Research (RFBR), Grant No. 16-55-44065. We thank Prof. Yan Zhao for providing the 210Pb data and Dr. Huiwen Zhang for her help with fieldwork. Dr. Chris Oldknow has helped to edit the revised manuscript. We also would like to thank the two anonymous reviewers and Editor Valerie Trouet for their constructive comments. The pollen data of this study will be made available in the Neotoma Paleoecology Database after publication.


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Figure 1 (a) and (b): Geomorphology of central Asia (a) and location of Kanas Lake (1365 m, Site 9 in map b) and location of the sites cited in the text (map b, c, d). Sites 1 and 2: Kirek Lake (90 m) and Zhukovskoe Mire (80 m) (Blyakharchuk, 2003); Sites 3, 4, and 5: Lake Uzunkol (1985 m), Lake Kendegelukol (2050 m), and Lake Tashkol (2150 m) (Blyakharchuk et al., 2004); Sites 6 and 7: Lake Grusha (2413 m) and Lake Akkol (2204 m) (Blyakharchuk et al., 2007); Site 8: Narenxia peat section (1760 m) (Feng et al., 2017); Site 9: Kanas Lake (1365 m) (this study); Site 10: Lake Hoton (2083 m) (Rudaya et al., 2009); Site 11: Ozekri swamp (210 m) (Tarasov, et al., 1997); Site 12: Achit Nuur (1444 m) (Sun et al., 2013); Site 13: Lake Bayan Nuur (930 m) (Tian et al., 2014); Site 14: Lake Wulungu (478 m) (Liu et al., 2008). (c): mean annual temperature and (d): mean monthly precipitation distribution in the Altai Mountains and surrounding area (the climate parameters are average values of 1980-2010, and the gridded


climate dataset is from Climatic Research Unit, https://crudata.uea.ac.uk/cru/data/hrg/; Dataset DOI: http://doi.org/10/gcmcz3).


Figure 2 Pollen diagram for core KNS11B (shaded areas are five times exaggeration)


Figure 3 Comparison of the records from Kanas Lake: the tree and shrub pollen content (f), the sum of Juniperus and Ephedra (g) and quantitative annual precipitation reconstruction based


on transfer function (h) with other records: (a) NGRIP oxygen isotope record (Vinther et al., 2009); (b) temperature anomalies of Northern Hemisphere 30-90º N (Marcott et al., 2013); (c) variations in the Arctic Oscillation (normalized standard deviation scale) after (Rimbu et al., 2003); (d) insolation record for 65º in the Northern Hemisphere; (e) tree and shrub pollen content at Hoton Nur (Rudaya et al., 2009); (i) lake level variations of Wulungu Lake (Liu et al., 2008); (j) Holocene moisture evolution of the northern Xinjiang region (Wang & Feng, 2013). The grey band indicates the Younger Dryas stadial whilst the grey lines at ~7 ka and ~4 ka indicate delimit the timings of temperature decrease and/or the significant ecological shifts discussed in the text.
