Late Glacial to Holocene environments in the present-day coldest region of the Northern Hemisphere inferred from a pollen record of Lake Billyakh , Verkhoyansk Mts , NE Siberia

Late Glacial to Holocene environments in the present-day coldest region of the Northern Hemisphere inferred from a pollen record of Lake Billyakh, Verkhoyansk Mts, NE Siberia S. Müller, P. E. Tarasov, A. A. Andreev, and B. Diekmann Freie Universität Berlin, Geological Sciences, Palaeontology Section, Berlin, Germany Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Germany Received: 24 September 2008 – Accepted: 1 October 2008 – Published: 26 November 2008 Correspondence to: S. Müller (stefanie.mueller@awi.de) Published by Copernicus Publications on behalf of the European Geosciences Union.


Introduction
Global and regional climate models predict noticeable 21st century climate warming, which is expected to be most pronounced in high latitudes of the Northern Hemisphere (ACIA, 2004).In particular, predicted winter warming is expected to exceed the global annual average, causing great reduction of sea-ice cover and significant degradation of permafrost (French and Williams, 2007).All these changes will most certainly destabilize fragile Arctic vegetation and environments and might in turn influence global atmospheric circulation and climate.The International Council for Science (ICSU, 2004) agreed to establish the International Polar Year (IPY) in 2007-2008 in order to "start a new era in polar science; to intensify interdisciplinary research programs focussing on the Arctic and the Antarctic regions and to understand better the strong links these regions have with the rest of the globe".
The investigation presented in this paper is part of the IPY project 106 "Lake Records of Late Quaternary Climate Variability in northeastern Siberia" and the German Research Foundation project "Late Quaternary environmental history of interstadial and interglacial periods in the Arctic reconstructed from bioindicators in permafrost sequences in NE Siberia".Both projects focus on generating high-resolution S. Müller et al.: Late Glacial to Holocene environments in NE Siberia  -Martínez, 1996-Martínez, -2004)).
vegetation and climate proxy records from the lacustrine sediments along a north-south transect from Yakutia (Sakha) Republic of Russia -the region of Eurasia, which is known for its climate extremes, with the Verkhoyansk Mountain Range being the coldest area in the Northern Hemisphere (Shahgedanova et al., 2002).The coastal and mountain areas are dominated by tundra vegetation, whereas cold deciduous forest and taiga vegetation are widespread in central and southern Yakutia, where mean July temperatures reach 15-19 • C (Alpat 'ev et al., 1976).Because of its relatively dry continental climate, this part of Siberia did not experience extensive Late Pleistocene glaciation (Stauch, 2006;Popp et al., 2007;Stauch et al., 2007) in contrast to other arctic regions, including northern parts of western Siberia, Europe and North America which were covered by large ice sheets.
Since the second half of the last century peat and lake sediments from the region have been studied by means of pollen analysis, and results were used to reconstruct past vegetation and climate conditions of the Late Quaternary (e.g.Khotinsky, 1977;Velichko et al., 1997).However, detailed reconstructions of the vegetation and climate history were limited by the shortage of reliable radiocarbon data.During the last decade, strengthening of international co-operation in the Arctic facilitated access to several highresolution and adequately dated pollen records from north-eastern Eurasia covering the Late Pleistocene and Holocene periods (e.g.Andreev and Klimanov, 1989;Peterson, 1993;Texier et al., 1997).These records were then used for quantitative vegetation reconstruction in the global vegetation mapping BIOME6000 project (e.g.Tarasov et al., 1998;Prentice et al., 2000).Despite a general progress in the environmental studies of northeastern Eurasia, the Verkhoyansk Mountain area is still poorly investigated.
This paper fills the gap in the earlier pollen studies of the region and presents a high resolution pollen record from Lake Billyakh, located in the central part of the Verkhoyansk Mountain region (Fig. 1).The record spans the last 15 kyr (1 kyr=1000 cal.yr) as suggested by the age model, which is based on seven radiocarbon dates.Both qualitative interpretation of the pollen data and quantitative pollen-based biome reconstruction are used to interpret changes in regional vegetation and climate during the Late Glacial-Holocene time interval.We then discuss these results together with the published results of earlier palaeoenvironmental studies from northeastern Eurasia.

Regional setting
The Verkhoyansk Mountain Range (2389 m a.s.l.) is one of the most prominent mountain chains of northeastern Eurasia.It extends along 128 • E longitude east of the Lena River for 900 km from the Laptev Sea coast to about 64 • N. The southern latitudinal section extends north of the Aldan River (Lena's right tributary) for 350 km between 128 • and 136 • E (Alpat 'ev et al., 1976;Shahgedanova et al., 2002).
Lake Billyakh (65 • 17 N, 126 • 47 E; altitude 340 m) is situated in the central part of the Verkhoyansk Mountains (Fig. 1a), occupying a longitudinal depression between the Tekir-Khaya Ridge and the Muosutchanskiy Ridge (Fig. 1b).The lake extends for about 11 km from north to south and for about 3 km from west to east.It has an average water depth of 8 m and a maximum depth of about 25 m.The lake is fed by direct precipitation and by several small creeks and streams flowing from the surrounding mountain slopes (Fig. 1b).An outflow stream flows from the southern part of the lake towards the Lena River.
The region is characterised by the world's most extreme continental climate.Verkhoyansk (67 • 33 N, 133 • 33 E; 137 m a.s.l.) is known as the Northern Hemisphere's Pole of Cold.There the instrumentally measured minimum and maximum temperatures reached −67.8 • C and 39 • C, respectively.The mean values for January and July temperatures are −48.6 • C and 13.9 • C and annual precipitation reaches 181 mm (Rivas-Martínez, 1996-2004;Fig. 1c).The very cold and long winters together with short summers cause the large thickness of continuously frozen ground reaching 400-900 m (Gavrilova, 1993).

Coring and lithology
Sediment coring with an UWITEC piston corer system was performed at one site in the central profundal basin of the lake and at three other sites located near the northern shore (Diekmann et al., 2007;Fig. 1b).A total of 35 m of sediment were recovered from the four sites and transported to Germany for further analyses.
The 660 cm long core PG1756 described in the present study was recovered from a small subbasin about 800 m off the northern shore, from 7.9 m water depth.The core consists of homogenous dark greenish grey sandy silt (0-145 cm), homogenous dark greenish grey clayey silt (145-374 cm), finely stratified dark greenish grey sandy silt (374-429 cm), greyish silt (429-450 cm) and basal dark greyish sand below 450 cm (Fig. 2a).

Pollen analysis
The core material stored at AWI (Potsdam) was sampled there for pollen analysis.Samples were taken as 1 cm slices every 5 cm, yielding an average temporal resolution of 190 years.Further chemical treatment of the samples and pollen analysis were performed in the pollen laboratory at FU Berlin.Pollen extraction from the samples consisting of 1.5 g sediment was performed according to standard procedures, including 7-µm ultrasonic fine-sieving, HF treatment and acetolysis (Faegri et al., 1989;Cwynar et al., 1979).One tablet of Lycopodium marker spores was added to each sample for calculating total pollen and spore concentrations (Stockmarr, 1971).Water-free glycerol was used for sample storage and preparation of the microscopic slides.Pollen and spores were identified at magnifications of 400× and 1000×, with the aid of published keys (Kupriyanova et al., 1972(Kupriyanova et al., , 1978;;Bobrov et al., 1983;Reille, 1992Reille, , 1995Reille, , 1998;;Beug, 2004) and a modern pollen reference collection at FU Berlin.
Preservation of pollen and spores was very good, and corroded grains were found mainly in the lower part of the core below 419 cm, in sediments with a higher sand content.Bisaccate pollen of Pinus and Picea were frequently broken.The pollen and spore content of the samples was sufficiently high to allow counting of a minimum of 500 terrestrial pollen grains per sample.In total, 71 pollen and spore taxa were identified in the PG1756 core.In this study pollen of Pinus was separated into two morphological types, e.g.P .subgen.Diploxylon and P .subgen.Haploxylon.In the study area these two pollen types are produced by P. sylvestris (tree pine) and P. pumila (shrub pine), respectively.Betula pollen was also divided into two morphological types: B. sect.Nanae (shrub birch) and B. sect.Albae (tree birch).The contribution of re-deposited pollen and spores was unimportant, suggesting non-disturbed pollen assemblages.
Calculated pollen percentages refer to the total sum of terrestrial pollen, which does not include pollen of aquatic plants, spores of pteridophytes and mosses, algae and redeposited pollen and spore grains.For these taxa, percentages were calculated using the total terrestrial pollen sum plus the sum of palynomorphs in the respective group.The Tilia/Tilia-Graph/TGView software (Grimm, 1993(Grimm, , 2004) ) was used for calculating pollen percentages and for drawing the pollen percentage diagram.The local pollen zones in the diagram were divided using CONISS (Grimm, 2004) and numbered from the top to the bottom of the core to allow future comparison with longer pollen sequences from Lake Billyakh.

Quantitative technique for vegetation reconstruction and palaeoclimatic interpretation
Pollen-based vegetation reconstruction was performed using the quantitative method of biome reconstruction first described by Prentice et al. (1996) and adapted for reconstruction of northern Eurasian vegetation types (biomes) by Tarasov et al. (1998).The approach allows the objective assignment of pollen taxa to plant functional types (PFTs) and to biomes on the basis of the modern ecology, bioclimatic tolerance and geographical distribution of pollen producing plants.The biome reconstruction method was successfully tested using an extensive surface pollen data set from northern Eurasia and applied to mid-Holocene and Last Glacial Maximum (LGM) pollen data (Tarasov et al., 1999a(Tarasov et al., , 1999b)).
The results of biome reconstruction proved to be useful for the objective interpretation of the Late Quaternary vegetation and climate dynamics at global, regional and local scales and for data-model comparison (Texier et al., 1997;Prentice et al., 1996;Prentice et al., 2000;Tarasov et al., 2005).
In this study all identified terrestrial pollen taxa were initially used for the construction of the biome-PFT-taxon matrix.Among them only 28 taxa, which exceed the universal threshold of 0.5% suggested by Prentice et al. (1996) and used by Tarasov et al. (1998), influenced biome Table 1.Terrestrial pollen taxa identified in the core PG1756 from Lake Billyakh and their attribution to the vegetation types/biomes characteristic for northern Asia.Taxa whose percentages in the pollen spectra do not exceed 0.5% (threshold suggested by Prentice et al., 1996) and do not influence results of biome reconstruction are indicated with an asterisk.

Biome
Terrestrial pollen taxa  reconstruction as shown in Table 1.Square root transformation was applied to the pollen percentage values to diminish the influence of the most abundant pollen taxa and enhance the influence of minor taxa.Details of the method, including the equation used to calculate biome scores and discussion of the taxa attribution to the PFTs and to biomes are provided in Tarasov et al. (1998).

Age-depth model
Plant material from 7 samples was radiocarbon dated at the Leibniz Laboratory for Radiometric Dating in Kiel.The age model for the PG1756 core takes into account 7 radiocarbon dates, spanning the time interval between 13 and 1 kyr BP (Table 2).Radiocarbon years were converted to calendar years using the CalPal program available online (Danzeglocke et al., 2008).A reasonable time-depth relationship arises from a fit with a polynomial function (Fig. 2b), which then was applied for age calculation of the pollen zone boundaries and their discussion in terms of temporal changes of vegetation and climate.One date (8356±124 yr BP, 244 cm depth) seemed to be slightly older than suggested by the other dates and did not fit in with our age-depth model.The calculation was repeated without this date.However, exclusion of the date from the analysis did not influence the age model.Using the equation in Fig. 2b the bottom of the analysed core can be dated to about 15 kyr BP.

Pollen analysis
Complete results of the pollen analysis are provided in Appendix A. The simplified pollen percentage diagram is shown in Fig. 3 and the main results of the pollen analysis are  incorporated in the following chapter 4 for further interpretation and discussion.

Interpretation and discussion
Our results suggest distinct vegetation and environmental changes around Lake Billyakh since 15 kyr BP related to Late Quaternary regional climate and environmental dynamics.The environmental reconstruction (Fig. 4c) is based on the qualitative interpretation of the pollen record (Figs. 3  and 4a) with quantitative results of the biome reconstruction (Fig. 4b).

Late Glacial
The pollen assemblages prior to 13.5 kyr BP (PAZ VIII; 455-428 cm, 15-13.5 kyr BP) are characterised by lowest pollen concentrations through the whole record, increasing from 1900 grains/g in the lower part to 7200 grains/g in the upper part of this zone.The pollen assemblages are dominated by herbaceous taxa (89-99%), with the highest proportion of sedge (40-57%) and grass pollen (24-29%) in the whole record, suggesting a wide spread of herbaceous tundra communities (Prentice et al., 1996;Tarasov et al., 1998)  Asteraceae subfam.Cichorioideae and some other taxa attributed to the steppe biome can successfully grow in the mountain steppe and meadow communities and on the dry slopes of southern exposition (Walter, 1974).A wide spread of the dry environments is suggested by the high percentages of Selaginella rupestris spores (20-40%).This species of spike-moss usually occurs in dry and cold rocky places with disturbed or thin soil cover.Permanent presence of arctic and alpine shrubs and dwarf shrubs represented by Betula sect.Nanae, Duschekia fruticosa and Salix (0.5-10%) in the pollen spectra supports the interpretation of local occurrence of shrub tundra patches in the regional vegetation.The presence of Larix (0.5-2%) in the pollen spectra moreover points to the growth of larch around the lake already during the early Late Glacial about 15 kyr ago.This conclusion is based on the consideration that larch pollen is usually strongly underrepresented in the pollen diagrams and poorly transported far from the pollen-producing tree (Tarasov et al., 1998;Pisaric et al., 2001).
Results of the biome reconstruction demonstrate almost equally high scores for the tundra and steppe biomes and low scores for the cold deciduous forest biome, suggesting the reconstruction of generally open tundra-steppe vegetation between 15 and 13.5 kyr BP.Grichuk (1984) pointed out that such plant communities were typical for the periglacial steppe or "tundra-steppe" vegetation of the LGM, which was widely distributed in northern Eurasia.Predominance of herbaceous steppe-like vegetation prior to 13.7 kyr BP is suggested by the pollen record from Levinson-Lessing Lake (74 • 28 N; 98 • 38 E) in the northeastern Taymyr Peninsula (Andreev and Tarasov, 2007;Table 3).At that time dwarf shrub tundra had limited coverage and survived only in the locally wet habitats.Similar vegetation cover is reconstructed from the Lake Dolgoe (71 • 52 N, 127 • 04 E) pollen record in the lower Lena River before 14.5 kyr BP (Pisaric et al., 2001).According to the Biome 4 vegetation model, dominance of herbaceous vegetation in the Arctic can be explained by the extremely continental climate with low precipitation and severe winter conditions (Kaplan, 2001).
The model also suggests that in such environments, snow thickness of less than 15 cm during the winter would result in disappearance of perennial shrubs from the tundra vegetation.
During the second half of the Late Glacial (13.4-11.3kyr) both pollen assemblages composition and the dominant biome scores (Fig. 4b) suggest a distinct two-step change in the vegetation and environment of the study area, which roughly corresponds to the Bølling-Allerød Interstadial and the Younger Dryas Stadial.PAZ VII (427-387 cm, 13.4-11.3kyr BP) is characterised by a noticeable increase in pollen concentrations from 13 500 to 72 700 grains/g.Recorded increases in Betula sect.Nanae (26-52%) and Duschekia fruticosa (up to 29% at 114 cm) pollen percentages indicate that birch-and alder-dominated shrub tundra communities started to play a greater role in the study area between 13.4 and 12.5 kyr BP.A great reduction of the drought tolerant vegetation communities is also suggested by a significantly lower content of the rock spike moss spores (3-10%).Biome reconstruction shows a pronounced decrease in steppe biome scores and highest scores for the tundra biome, suggesting replacement of the former tundra-steppe vegetation by the herb and shrub tundra communities.Such change in the vegetation would imply a quick shift to wetter environments caused by increased precipitation and/or melting of permafrost due to summer warming and decreasing winter temperature during the Bølling-Allerød Interstadial (Grichuk, 1984).A dramatic increase in shrub birch and willow pollen associated with a significant decrease in herbaceous pollen taxa occurs in the pollen record from Levinson-Lessing Lake after 13.7 kyr BP (Andreev and Tarasov, 2007), and establishment of shrub birch tundra between 14.5 and 13 kyr BP is reconstructed from the Dolgoe Lake pollen record (Pisaric et al., 2001) in response to the climate amelioration during the Allerød interval.Reviewing climate changes in East Europe and Siberia at the Late Glacial-Holocene transition, Velichko et al. (2002) provided a quantitative reconstruction of the Allerød climate anomalies at two sites from central Yakutia.The pollen-based reconstructions suggest that mean January temperatures were 1.5-3 • C, mean July temperature were 1 • C and annual precipitation was 25-60 mm below the present-day values.

Younger Dryas Stadial
After 12.5 kyr BP both the pollen spectra composition and the steppe biome score demonstrate a short-term strengthening of the herbaceous vegetation communities compared to the shrub tundra vegetation, suggesting a decrease in available moisture and possibly a decrease in winter temperatures.This episode of climate deterioration deduced from the Lake Billyakh record is dated to 12.4-11.3kyr BP, thus falling well within the age limits of the Younger Dryas Stadial known for its generally colder and dryer climate, particularly in the North Atlantic sector.Velichko et al. (2002) (Fradkina et al., 2005;Pisaric et al., 2001;Andreev and Tarasov, 2007).However, the Lake Chabada (61 • 59 N; 129 • 22 E, 290 m a.s.l.) pollen record from central Yakutia demonstrates a locally quick spread of boreal forest soon after 12 kyr BP (Tarasov et al., 2007).Location of the lake on the ancient erosion-accumulative plain of the Lena River, which provides locally favourable conditions for arboreal vegetation, may explain this difference in low scores of the forest biome in the Lake Billyakh record during the Early Holocene.The already mentioned under-representation of larch -the dominant taxon in the regional cold deciduous forest -in the pollen records from larger lakes is another possible explanation.The fact that more or less constant amounts of Larix pollen (0.5-4%) occur throughout the whole record provides support for such interpretation.
The Early Holocene (11-8 kyr BP) thermal maximum in the Arctic is explained by a combined effect of higher-thanpresent Northern Hemisphere summer insolation and much lower-than-present sea level (Lozhkin and Anderson, 2006).The substantial warming at the Late Glacial-Holocene transition is recorded in various arctic regions of the Northern Hemisphere (e.g.MacDonald et al., 2000a;Andreev et al., 2004;Kaufman et al., 2004;Kaplan and Wolfe, 2006), including Smorodinovoye Lake (64 • 46 N; 141 • 06 E; 798 m a.s.l.) east of the Verkhoyansk Mountains (Anderson et al., 2002) as well as at sites from central Yakutia west of the Verkhoyansk Range (Velichko et al., 1997).However, the latter study suggests that both January and July temperatures and annual precipitation were lower than today by 1 • C, 0.5 • C and 25 mm/yr, respectively.Summer temperatures at least 4 • C warmer than present are reconstructed at the Bol'shoy Lyakhovsky Island (Andreev et al., 2009) in the East Siberian Sea, suggesting that warming was more pronounced in northern Yakutia than in central and southern Yakutia.This corroborates the inference of an initial spread of boreal forest across northern Asia after 11.5 kyr BP, the advance towards the current Arctic coastline between 10 and 8 kyr BP, and its retreat to its present position after 4.5 kyr BP (MacDonald et al., 2000a).

Middle Holocene
The pollen spectra of PAZ IV (302-242 cm, 7.3-5 kyr BP) and PAZ III (241-129 cm, 5-1.8 kyr BP) are characterised by relatively high (80 200-104 100 grains/g) and moderately high (40 200-87 000 grains/g) pollen concentrations and closely resemble modern surface pollen spectra from the study area, suggesting that vegetation around Lake Billyakh became similar to modern vegetation already in the Middle Holocene after 7 kyr BP.Biome reconstruction demonstrates an increase in the forest biome scores, suggesting that cold deciduous and taiga forests strengthened their positions in the region.Our pollen record shows a fourfold increase in Pinus subgen.Diploxylon percentages (12-34%), reflecting the spread of Pinus sylvestris in the region after 7 kyr BP.This feature is in good agreement with other study results carried out in northeastern Siberia (Andreev et al., 1997(Andreev et al., , 2002;;MacDonald et al., 2000a;Pisaric et al., 2001;Andreev and Tarasov, 2007).MacDonald et al. (2000b) pointed out that lower-than-present winter insolation and associated cold and dry winter conditions might have caused desiccation and root damage of Pinus sylvestris, restricting its earlier spread in northern Eurasia.In turn, warmer-than-present mid-Holocene summers in conjunction with an orbitally-induced increase in winter insolation and sea-level rise caused further degradation of permafrost and promoted the spread of Scots pine and in a broader regional context, spruce and Siberian pine taiga forest (Andreev and Tarasov, 2007).The appearance of wind transported Abies in PAZ IV and III of our record is consistent with the mid-Holocene amelioration of the regional climate, since fir is one of the most sensitive Siberian trees to winter temperature and moisture availability (Tarasov et al., 2007).The Smorodinovoye Lake pollen record (Anderson et al., 2002) indicates that mid-Holocene climatic changes in the upper Indigirka basin resemble those in the Lake Billyakh area.Both records suggest that maximum postglacial warming occurred after 7 kyr BP, thus a few thousand years later than in the northern and northeastern records of the arctic region.Actually, this timing of maximum warming is more consistent with postglacial climate development in central and northern Europe (e.g.Davis et al., 2003), suggesting strong climate teleconnections to Europe via the westerly wind system.

Late Holocene
The Late Holocene pollen spectra from Lake Billyakh are characterised by a decrease in pollen concentrations to 22 300 grains/g in PAZ II (128-50 cm, 1.8-0.5 kyr BP) and to 15 300 grains/g in PAZ I (49-0 cm, 0.5-0 kyr BP).The spectra show a progressive increase in the amount of herbaceous (11-29%) pollen during the last 2 kyr.This trend is accompanied by a distinct minimum in the Pinus subgen.Diploxylon (11%) pollen percentages about two to three hundred years ago.The later change might be associated with intensified human activities (e.g. the migration and spread of semi-nomadic Yakuts into the Middle Lena region since early medieval time) and/or with climate deterioration during the "Neoglacial" and particularly during the Little Ice Age.Popp et al. (2006) inferred a cold signal from stableisotope composition of ground ice younger than 1 kyr BP in the Verkhoyansk Mountains Foreland.However, the question of human-environmental interactions in the region during the past millennia needs further investigation.

Conclusions
In the recent study we present first detailed and well dated pollen record from the Verkhoyansk Mountains, the coldest region of Eurasia and Northern Hemisphere.The pollen record is then interpreted in terms of Late Glacial and Holocene vegetation and climate dynamics.Our reconstruction demonstrates substantial changes in the regional vegetation during the past 15 kyr.Major changes in the pollen assemblages and vegetation can be associated with well recognised large-scale palaeoclimatic events, the Allerød warming and Younger Dryas cooling, the onset of the Holocene and Middle Holocene thermal optimum.
The most severe cold and dry conditions are documented in the oldest part of our record, between 15-13.5 kyr BP when the landscape was mainly covered by mosaic herbaceous (tundra and steppe) and rock spike moss vegetation.During 13.4-12.5kyr BP the region experienced climate amelioration and spread of shrub tundra communities associated with the Bølling-Allerød Interstadial, followed (12.4-11.3kyr BP) by a return to the relatively cold-dry conditions associated with the Younger Dryas Stadial.The Younger Dryas climate, however, was less severe than conditions before 13.5 kyr BP, as suggested by higher percentages of tree and shrub pollen.Climate amelioration associated with the onset of the Holocene is dated to 11.2 kyr BP.Subsequently, steppe elements played a minor role in the vegetation cover, shrub tundra communities became dominant and boreal woods started to play a greater role in the vegetation cover.Both species richness and spatial extent of the forests reached their maximum between 7 and 2 kyr BP.
Another important aspect of the Lake Billyakh pollen record is that it demonstrates the uninterrupted growth of larch in the study area during the past 15 kyr, as indicated by the persistence of Larix pollen in the whole record.This conclusion confirms an earlier hypothesis of Grichuk (1984), who postulated the existence of many scattered refugia where boreal shrubs and trees could survive periods of harsh glacial climate and quickly spread with the onset of warmer conditions.We suggest that small populations of larch in the Verkhoyansk foreland and in the nearby Lena River valley had locally sufficient water supplies and high enough summer temperatures for growth and reproduction during the Late Glacial.To verify the presence of larch around Lake Billyakh during the LGM we intend to perform a detailed pollen analysis of the 9 m long PG1755 sediment core, which covers the time interval since 50 kyr BP until today.S. Müller et al.: Late Glacial to Holocene environments in NE Siberia age-depth model discussed in the text.All raised palynological data are available in the PANGAEA data information system (see doi:10.1594/PANGAEA.708170).

Fig. 4 .
Fig. 4. Local pollen zones and pollen assemblage characteristics of the PG1756 core (A); time series of individual vegetation types (biomes) dominating in the study area since 15 kyr BP (B); summary of the reconstructed changes in vegetation and climate around Lake Billyakh (C).

Table 3 .
Summary of major vegetation changes and climate trends reported for the sites mentioned in the discussion.