Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Last glacial–interglacial vegetation and environmental dynamics in southern Siberia: Chronology, forcing and feedbacks

Elena V. Bezrukova a, Pavel E. Tarasov b,⁎, Nadia Solovieva c, Sergey K. Krivonogov d, Frank Riedel b a Institute of Geochemistry, Siberian Branch Russian Academy of Sciences, Favorsky Str. 1a, Irkutsk, 664033, Russia b Institute of Geological Sciences, Palaeontology, Free University, Malteserstr. 74-100, House D, Berlin, 12249, Germany c Department of Geography, University College London, Gower Str., London WC1E 6BT, UK d Institute of Geology and Mineralogy, Russian Academy of Sciences, Siberian Branch, Koptug ave. 3, Novosibirsk, 630090, Russia article info abstract

Article history: Radiocarbon-dated pollen and diatom records from Lake Kotokel in southern Siberia help to reconstruct the Received 15 January 2010 environmental history of the area since ~47 kyr BP. Pollen spectra composition and reconstructed biome Received in revised form 18 July 2010 scores suggest predominance of a tundra–steppe vegetation and variable woody cover (5–20%) between ~47 Accepted 21 July 2010 and 30 kyr BP, indicating generally a harsh and unstable climate during this interval, conventionally regarded Available online 25 July 2010 as the interstadial within the last glacial. The short-term climate amelioration episodes in the glacial part of the records are marked by the peaks in taiga and corresponding minima in steppe biome scores and appear Keywords: Eurasia synchronously with the hemispheric temperature and precipitation changes recorded in the Greenland ice Pollen and diatom records cores and Chinese stalagmites. Transition to full glacial environments occurred between 32 and 30 kyr BP. Quantitative vegetation reconstruction The interval at ~30–24 kyr BP was probably the driest and coldest of the whole record, as indicated by Late Pleistocene interstadials highest scores for steppe biome, woody coverage b5%, absence of diatoms and reduced size of the lake. A Last glacial maximum slight amelioration of the regional climate at ~24–22 kyr BP was followed by a shorter than the previous and Younger Dryas less pronounced deterioration phase. The late-glacial (~17–11.65 kyr BP) is marked by a gradual increase in Holocene climatic optimum tree/shrub pollen percentages and re-appearance of diatoms. After 14.7 kyr BP the climate became warmer and wetter than ever during ~47–14.7 kyr BP, resulting in the deepening of the lake and increase in the woody coverage to 20–30% ~14.5–14 kyr and ~13.3–12.8 kyr BP. These two intervals correspond to the Meiendorf and Allerød interstadials, which until now were interpreted as part of the undifferentiated Bølling/Allerød interstadial complex in the Lake Baikal region. The increase in tundra biome scores and pronounced change in the diatom composition allow (for the first time) the unambiguous identification of the Younger Dryas (YD) in the Lake Baikal region at ~12.7–11.65 kyr BP, in agreement with the formal definition and dating of the YD based on the Greenland NGRIP ice core records. The maximal spread of the taiga communities in the region is associated with a warmer and wetter climate than the present prior to ~7 kyr BP. This was followed by a wide spread of Scots pine, indicating the onset of modern environments. © 2010 Elsevier B.V. All rights reserved.

1. Introduction et al., 2009), providing important insight into the environmental dynamics in the North Pacific and North Atlantic regions. However, a Worldwide terrestrial and marine sedimentary archives demon- recent global-scale synthesis of the Holocene climatic data (Wanner et strate that the last 50-kyr interval in the Earth's history experienced a al., 2008) demonstrates a lack of palaeorecords of comparable dating number of long- and short-term climatic oscillations (Guiot et al., quality and resolution from the vast areas of Eurasia, including Siberia 1989; Vincens et al., 2005; Heusser et al., 2006; Bout-Roumazeilles et and Central Asia. The dating problem becomes even more obvious, al., 2007; Svensson et al., 2008). High-resolution and accurately dated when the pre-Holocene interval of the late Quaternary is considered pollen and sedimentary records of the late-glacial/early Holocene (Rudaya et al., 2009; Shichi et al., 2009). interval exist for several regions of Europe (Litt and Stebich, 1999; Southern Siberia – the region of Russia between ~80–120°E and Allen and Huntley, 2000; Brauer et al., 2008) and East Asia (Stebich ~50–60°N – consists of numerous sub-latitudinal mountain ranges and lakes, including Lake Baikal in the east (Fig. 1a and b). The lake sediments are one of the most promising sources of detailed palaeoenvironmental information, which provide an opportunity for ⁎ Corresponding author. Tel.: +49 30 83870280; fax: +49 30 83870745. bridging the European and Asian palaeoclimate archives and addres- E-mail addresses: [email protected] (E.V. Bezrukova), [email protected] (P.E. Tarasov), [email protected] (N. Solovieva), sing critical questions concerning Quaternary climatology, e.g. [email protected] (F. Riedel). reconstructing atmospheric circulation patterns (Williams et al.,

0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.07.020 186 E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198

Fig. 1. Simplified maps, which show: (a) northern Eurasia and the Lake Baikal region, (b) the Lake Kotokel study area, (c) location of the 47-kyr long KTK2 core (this study) and the 15-kyr long KTK1 core (Tarasov et al., 2009). The location of Lake Sihailongwan (SHL) is indicated by a black triangle.

2001), and palaeoecology, e.g. discussing local presence/absence of 2. Site setting and environments boreal trees and shrubs during the last glacial (Grichuk, 1984). Numerous publications on the Lake Baikal region (e.g. Kuzmin et Lake Kotokel (458 m a.s.l.) has an area of ~67 km2, a maximum al., 1993; Williams et al., 1997; Prokopenko et al., 2002; Shichi et al., length of ~15 km and a maximum width of ~6 km (Galaziy, 1993). In 2009 and references therein) presented coarse-resolution (millenni- the west a low-elevated mountain ridge (729 m a.s.l.) separates the al- or multi-century-scale) qualitative reconstructions of the Quater- lake from Lake Baikal (Fig. 1), and the Ulan-Burgasy Ridge (up to nary environments. Although the long cores from Lake Baikal span 2033 m a.s.l.) bounds it in the east. The average water depth is 5–6m, millions of years (Williams et al., 1997; Khursevich et al., 2005), and the maximum depth is about 15 m (Shichi et al., 2009; Tarasov et research was mainly focused on the Holocene and earlier interglacials al., 2009 and references therein). (Demske et al., 2005; Tarasov et al., 2005, 2007a; Prokopenko et al., The regional climate is continental with long winters and a well- 2007, 2010). However, little is known about glacial intervals due to pronounced summer precipitation maximum (Alpat'ev et al., 1976). the problems associated with very low pollen concentrations, poor The mean January temperature is −20 °C near the lake, but decreases organic content, low sedimentation rates and poor dating (Horiuchi et to below −26 °C with increasing elevation. The mean July temper- al., 2000; Oda et al., 2000). Until recently, even the YD cooling was not ature is 14–16 °C. The annual precipitation reaches 300–400 mm in unequivocally identified and dated in the Baikal records. This led to the coastal area and above 500 mm in the mountains (Galaziy, 1993). various hypotheses suggesting that Lake Baikal could either mask or In July and August westerly winds dominating through the year delay the effect of global change (Bezrukova et al., 2005; Demske et al., become weak, and southeastern cyclones bringing warm and wet 2005; Shichi et al., 2009). Pacific air to the region cause heavy rainfalls at the eastern branch of This study presents new pollen and diatom records from Lake Kotokel the Polar front (Bezrukova et al., 2008). The Atlantic air masses (Fig. 1c) and aims to reconstruct regional vegetation and environ- entering the region with the westerly flow may bring precipitation all mental history since ~47 kyr BP (1 kyr=1000 cal yr); to compare it with year round, but mainly during autumn and spring. Dry, cold and sunny the oxygen isotope records from the North Atlantic and North Pacific winter weather is associated with the high pressure cell centred over regions; and to discuss the underlying mechanisms of the environmental eastern Siberia (Alpat'ev et al., 1976). change in the region. Both time resolution and dating control are Modern vegetation east of Lake Baikal is a mosaic of boreal substantially improved in comparison to the earlier studies (e.g. Vipper coniferous and deciduous forests (Galaziy, 1993)andswampy and Smirnov, 1979; Bezrukova et al., 2008; Shichi et al., 2009). communities, widely distributed in the Selenga River delta and E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198 187 south of Lake Kotokel (Takahara et al., 2000; Shichi et al., 2009). applied to the upper and softer biogenic sediment (Fig. 2a) and the Forests are mainly composed of Pinus sylvestris (Scots pine), Larix 4.6 cm diameter corer was used to penetrate lower more compact sibirica (Siberian larch) and Betula (birch) trees, with some admixture layers (Shichi et al., 2009). The upper part of the core (Fig. 2a) consists of Populus tremula (aspen) and Alnus fruticosa (shrubby alder). Boreal of the soft brownish black gyttja (0–660 cm) underlined by the grey evergreen conifers, including Pinus sibirica (Siberian pine), Abies or blackish slightly laminated silty clay (660–740 cm), laminated grey sibirica (Siberian fir) and Picea obovata (Siberian spruce) grow on the silty clay (740–1010 cm) and dark-grey or grey silty clay unit (1010– Ulan-Burgasy slopes. Above 1800 m this mountain taiga vegetation is 1253 cm). replaced by open birch and larch forests and shrubby sub-alpine Eleven bulk sediment samples from the KTK2 core were submitted associations represented by Pinus pumila (shrubby pine), Alnus to Poznan Radiocarbon Laboratory. The distribution of obtained fruticosa and Betula middendorfii (shrubby birch). Alpine tundra radiocarbon ages versus composite core length (Fig. 2b, Table 1) occupies large areas north and northeast of Lake Baikal, while the demonstrates no reversals and a clear trend of increasing age with steppe is characteristic of Olkhon Island (Fig. 1) and semiarid depth. The sediment is non-calcareous, thus ensuring that a reservoir depressions along the Selenga River, where precipitation drops to effect, which usually complicates accurate dating of the Baikal cores ~160 mm/yr, (Galaziy, 1993). (Colman et al., 1996; Demske et al., 2005), is not an issue in Lake Kotokel. The KTK2 core lithology and radiocarbon dates suggest an 3. Data and methods uninterrupted accumulation of sediment between ~47 kyr BP and the present. 3.1. Core lithology and age determination The KTK2 14C AMS dates were converted to calendar dates (Table 1), which were then used to construct an age-depth model The KTK2 sediment core (52°47′N, 108°07′E; Fig. 1c) was retrieved based upon linear interpolation between the neighbouring dates from a depth of ~3.5 m in the southern part of Lake Kotokel in August (Fig. 2c). In addition, the KTK2 age model was compared with the 2005. The Livingston-type piston corer of 7.5 cm diameter was annually laminated sedimentary and high-resolution pollen records

Fig. 2. Lithology column (a), radiocarbon dates (b) and age-depth relationship (c) of the KTK2 core from Lake Kotokel. 188 E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198

Table 1 show a good correspondence (Fig. 2c), suggesting the reliability of the AMS radiocarbon dates from the KTK2 core. Radiocarbon years before present were KTK2 age model during the climatically unstable late-glacial interval. In converted to calendar years after Danzeglocke et al. (2008). particular, the onset of the Holocene interglacial conditions is well Sample depth Dated 14C age Cal. age Laboratory pronounced in both records and can be independently dated in the KTK2 (cm) material (yr BP; 68% range) (yr BP; 68% range) number core to ~11.65 kyr BP (pollen-based correlation with the LSH) and to 137–141 Brownish 3855±35 4290±80 Poz-27580 ~11.68 kyr BP (AMS dates from KTK2). black gyttja 3.2. Pollen extraction and microscopic analysis 208–212 Brownish 4575±35 5230±110 Poz-27581 black gyttja The KTK2 core material was stored in plastic liners at the Institute 289–293 Brownish 5690±35 6480±40 Poz-27582 of Geochemistry (Irkutsk) and sampled there for pollen analysis. A black total of 212 samples comprising 1 cm3 of the wet sediment were taken gyttja with a 6-cm step, yielding an average temporal resolution of 309–313 Brownish 5890±40 6720±40 Poz-27583 black 220 years. A standard procedure was used to extract pollen, including gyttja HCl and KOH treatment, heavy-liquid separation and acetolysis 501–505 Brownish 9990±50 11,470±130 Poz-27584 (Berglund and Ralska-Jasiewiczowa, 1986). Pollen and spores, black mounted in glycerin, were counted under the light microscope with gyttja – fi fi 507–511 Brownish 10,190±50 11,890±110 Poz-27593 ×400 1000 magni cation. Identi cation of the pollen and spores was black performed using regional pollen atlases and the reference pollen gyttja collection (Tarasov et al., 2007a and references therein). 685–689 Blackish 12,680±60 15,190±110 Poz-27585 All samples were rich in pollen, permitting counting up to 1800 pollen silty clay grains per slide. The KTK2 pollen diagram (Figs. 3a and 4)was 795–799 Grey silty 18,000±90 21,520±90 Poz-27586 clay constructed using the Tilia/Tilia-Graph/TGView software (Grimm, 918–922 Grey silty 21,450±110 25,480±230 Poz-27587 2004). Relative percentages for all terrestrial pollen taxa at each level clay were calculated from a terrestrial pollen sum taken as 100%. Percentages – 1036 1040 Grey silty 27,820±200 32,330±240 Poz-27589 for aquatic and cryptogam taxa were calculated in relation to the total clay 1238–1244 Grey silty 42,600±1100 46,285±1500 Poz-27637 sum of counted pollen and spores. The diagram was subdivided into local clay pollen zones (PZ), using visual inspection supported by the results of biome score calculation described in the section below. This method takes into account the ecology of pollen-producing plants (Prentice et al., from Lake Sihailongwan (SHL: Fig. 1a) and dated by both varve- 1996) and does not entirely rely upon a statistical similarity between counting and 40 calibrated AMS dates (Stebich et al., 2009). The pollen assemblages composed of numerous taxa representing ecologi- earlier studies suggested that the late-glacial–early Holocene shifts in cally different plant functional types. Pollen zones were also defined vegetation and climate in the Lake Baikal region were broadly using CONISS, which performs a stratigraphically constrained cluster synchronous to the major oscillations in the oxygen isotope records analysis useful for zonation (for technical details see Grimm, 1987). In the from China (Tarasov et al., 2007a, 2009), reflecting changes in the CONISS analysis only terrestrial pollen taxa with values of 2% or greater Northern Hemisphere (NH) temperature and East Asian monsoon and appearing in more than one sample were considered (Gervais et al., intensity (Yuan et al., 2004). For the first time a direct comparison of 2002). Results obtained with different methods are shown in Fig. 3. the high-resolution pollen records from both regions became possible. The characteristic changes in the SHL pollen/climate stratigraphy 3.3. Quantitative vegetation reconstruction (Stebich et al., 2009) were compared to the similar events in the KTK2 pollen records, and the corresponding ages of these events in the SHL The biome reconstruction method (Prentice et al., 1996) permits record were then transferred to the KTK2 record (Table 2). Both datasets the objective assignment of pollen taxa to major vegetation types/

Table 2 Complementary dates obtained via the pollen-based correlation between the pollen records from Sihailongwan Lake (Stebich et al., 2009) and Kotokel Lake, which are used in this study to refine age-depth model for the KTK2 record (Fig. 2).

Depth in the KTK2 core Inferred age Dated event in the SHL pollen record Comparable event in the KTK2 pollen record (cm) (cal yr BP) (after Stebich et al., 2009) (this study)

422.0 ~10,600 Quercus, Acer and Syringa become more common, Juglans, Tilia and High arboreal pollen values and minimal values of herbaceous Viburnum reach their empirical limit, high arboreal pollen values pollen taxa indicate the establishment of dense forest cover, indicate the establishment of dense forest cover, similar to that similar to that observed in the area today observed in the area today 506.0 ~11,650 Re-increase in thermophyllous tree pollen, and the onset of a Larix Reappearance of Abies, decrease in Artemisia reflecting the onset decline that indicate a climatic amelioration of the Holocene interglacial conditions 541.5 ~12,680 Significant declines in Fraxinus and Ulmus combined with a peak in Abrupt decrease in Picea, disappearance of Abies, increase in steppe plants and maxima in Betula and Picea highlighting a climate Artemisia reflecting a considerable reduction in woody coverage reversal III and climatic deterioration 561.5 ~13,000 Pronounced minimum in the relative frequencies of Ulmus and Short-term decrease in Picea and Abies, increase in the Fraxinus and increase in the abundance of herb pollen marks late- abundance of herb pollen reflecting prominent climatic glacial climate reversal II deterioration 591.5 ~13,650 Dynamic increase of Ulmus and Fraxinus, establishment of mixed Increase in Picea, decrease in Artemisia and in total herbs broadleaf forest 609.5 ~13,850 Ulmus minimum, the consequence of a short-term climatic reversal I Peak in Alnus fruticosa, decrease in total trees reflecting short- term climatic deterioration 651.5 ~14,400 Expansion of Ulmus and Fraxinus after the onset of the late-glacial Abrupt increase in Picea and abrupt decrease in Artemisia, climatic amelioration at ~14,450 cal yr BP appearance of Abies reflecting the late-glacial climatic amelioration E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198 189

Fig. 3. Zonation of the KTK2 pollen record (g) applied in this study using visual inspection of the pollen percentage diagram (a) and the results of biome score calculation (b) plotted against the dendrograms obtained using a stratigraphically constrained cluster analysis CONISS (c–f). biomes on the basis of the bioclimatic tolerance, ecology and comparison with the results obtained earlier for the KTK1 pollen record biogeography of pollen-producing plants. The method was success- (Tarasov et al., 2009). fully tested using extensive regional surface pollen datasets and applied to the last glacial–interglacial fossil pollen records from 3.4. Diatom analysis and pH reconstruction northern Eurasia (Edwards et al., 2000; Tarasov et al., 2000; Mokhova et al., 2009), from Lake Baikal (Tarasov et al., 2005, 2007a), and to the A total of 125 samples, sampled at 10-cm intervals, were prepared poorly-dated KTK1 record from Lake Kotokel spanning the past 15 kyr for diatom analysis using the standard hydrogen peroxide technique (Tarasov et al., 2009). In the present study all identified terrestrial (Battarbee et al., 2001). Aliquots of evaporated suspensions were pollen taxa from the KTK2 record were assigned to regional biomes embedded in Naphrax. Counting of at least 300–600 diatom valves per using the biome-taxon matrix presented in Table 3. sample along ten horizontal transects using the light microscope with A complementary approach (Williams et al., 2004), which combines phase-contrast oil immersion objectives at ×400–1000 magnification satellite-based vegetation cover dataset (DeFries et al., 1999)and was possible for most of the samples. However, diatom valves were modern surface pollen dataset from northern Eurasia (Tarasov et al., rare or not found at all in 28 samples from the glacial part of the 2007b) with the best modern analogue (BMA) approach (Guiot et al., record. Diatom concentrations (×106 valves per gram of air-dried 1989), was applied to the KTK2 pollen record in order to reconstruct sediment) and percentage diatom abundances (based on the total changes in the woody cover. The test of the method demonstrated that sum of all diatoms counted in each sample) were calculated. Diatom pollen-based modern woody cover reconstructions and original satellite nomenclature followed Krammer and Lange-Bertalot (1986–1991) measurements match well in northern Asia, providing satisfactory and AL:PE guidelines (Cameron et al., 1999). The AL:PE diatom–pH estimates of percent variance explained and root mean square error calibration dataset consists of surface-sediment diatom assemblages (RMSE) for both the total woody cover (r2 =0.77, RMSE=11.69) and from 118 lakes and contains 530 taxa. The AL:PE training set is from the broadleaved (r2 =0.66, RMSE=3.31), needle-leaved (r2 =0.79, high-altitude or high-latitude lakes in the Alps, Norway, Svalbard, RMSE=10.23) woody cover fractions at modern pollen sites (see Kola Peninsula, UK, Slovenia, Slovakia, Poland, Portugal and Spain. Tarasov et al., 2007b for the method evaluation and design). The The modern pH of Lake Kotokel water (about 7.0) fits within the robustness of the reconstruction for the past 15 kyr was ensured by AL:PE pH range (4.5–8.0) and the fossil diatom assemblages of Lake 190 E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198

Fig. 4. Simplified pollen percentage diagram of the KTK2 core (analyst E. Bezrukova). See Fig. 2a for the description of lithological units.

Kotokel are generally well represented in the AL:PE dataset. model gives slightly overestimated values. The fossil diatom assem- Therefore, the AL:PE diatom–pH model was used for pH inferences blages between 543 and 501 cm are dominated by Ellerbeckia arenaria (see Cameron et al., 1999 for the details of the AL:PE pH diatom model and E. arenaria var. teres, which are both absent from the modern performance). The reconstruction was performed using the computer dataset. Therefore, the pH inferences between 543 and 501 cm solely programme C2 ver. 1.5 (Juggins, 2007) using jack-knifed cross- rely on other fossil diatom taxa and samples between 543 and 501 cm validation. The second component in the Weighted Averaging Partial provide poor analogues for pH reconstruction. Least Squares (WAPLS) regression showed the best predictive Detrended canonical correspondence analysis (DCCA) was used to performance (Table 4) and was used for pH reconstruction. The estimate the overall species turnover measured in standard deviation modern measured lake pH varies between 6.8 and 7.3 (Kuzmin, 1988) (SD) units and to generate sample scores for axis 1, which provide an and the pH predicted by the AL:PE model is 7.8, implying that the estimate of compositional change along a temporal gradient (ter Braak, 1986). The samples' age was used as a sole environmental Table 3 variable in DCCA. In DCCA, species data were square-root trans- Terrestrial pollen taxa identified in the KTK2 record (this study) and used in the biome formed, no rare species down-weighting was applied, and nonlinear and woody cover reconstructions (after Tarasov et al., 2000, 2009). rescaling and detrending by segments were used. DCCA was carried Š Biome Taxa included out using CANOCO 4.5 (ter Braak and milauer, 2002). ZONE software (Juggins, 1991) was used to split the diatom diagram into strati- Tundra Alnus fruticosa, Betula sect. Nanae/Fruticosae, Cyperaceae, Ericales, fi Poaceae, Polemonium, Polygonum, Rumex, Salix, Saxifragaceae, graphic zones. The statistical signi cance of the stratigraphic zones Valeriana Cold deciduous Alnus, Betula sect. Albae, Ericales, Larix, Pinus sylvestris (subgen. forest Diploxylon-type), P. pumila (subgen. Haploxylon-type), Salix Table 4 – Taiga Abies sibirica, Alnus, Betula sect. Albae, Ericales, Larix, Picea Apparent and predictive (jack-knifed) statistics for the AL:PE pH diatom model applied obovata, Pinus sylvestris, P. sibirica (subgen. Haploxylon-type), to the fossil diatom data from Lake Kotokel. Ribes, Salix Performance statistics pH WAPLS, 2nd component Cool conifer Abies sibirica, Alnus, Betula sect. Albae, Ericales, Corylus, Larix, Picea forest obovata, Pinus sylvestris, P. sibirica (subgen. Haploxylon-type), r2 0.928 Ribes, Salix, Ulmus RMSE 0.203 − Steppe Apiaceae, Artemisia, Asteraceae (incl. subfam. Asteroideae and Average bias −2.299e 0.005 Cichorioideae), Brassicaceae, Caryophyllaceae, Chenopodiaceae, Maximum bias 0.384 Fabaceae, Lamiaceae, Liliaceae, Plantago, Poaceae, Polygonum, r2 (jack-knifed) 0.789 Ranunculaceae, Rosaceae, Rubiaceae, Rumex, Scrophulariaceae, RMSEP 0.349 Thalictrum, Urtica, Valeriana Jack-knifed average bias 0.011 Desert Artemisia, Boraginaceae, Chenopodiaceae, Ephedra, Polygonum Jack-knifed maximum bias 0.734 E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198 191 was then established using the programme BSTICK (Bennett, 1996). percentages reach up to 20–30% in the lower (Picea)andupper(Larix, Changes in DCCA sample scores on axis 1 were also used as an and Pinus) parts of this zone, but remain at 10%-level in the middle part. additional method of stratigraphic zone boundary identification. In The biome reconstruction shows that steppe and tundra have the the diatom percentage diagram (Fig. 6), the taxa were ordered highest scores (Fig. 5b), and scores of the taiga biome are ~5–10, in line according to their weighted average score, highlighting the diatom with the moderately low woody cover (~10%) around the lake (Fig. 5d). floristic changes. Aulacoseira granulata agg. includes A. granulata var. The vegetation was probably a mosaic of scattered trees and/or isolated angustissima, and Staurosira construens agg. includes ecologically close forest stands, shrubby and herbaceous tundra communities occupying subspecies, which have identical stratigraphic distribution in the wetter habitats and dominant cold steppe communities. KTK2 core (i.e. S. construens var. construens, S. construens var. venter PZ KTK2-7 (1000–850 cm; ~30–23 kyr BP) reveals the highest and S. construens var. binodis). Staurosirella pinnata agg. includes S. percentages of Artemisia (40–50%) and Poaceae (25–40%) and pinnata var. pinnata and S. pinnata var. lancetulla for the same reasons. extremely low percentages of boreal tree and shrub pollen. The biome reconstruction demonstrates the highest scores for steppe 4. Results and interpretations (N20) and lowest taiga scores (Fig. 5), suggesting that cold steppe vegetation absolutely predominated in the region. However, the 4.1. Pollen record and vegetation reconstruction presence of arboreal pollen, even in very low percentages, and quantitative woody cover reconstruction do not support the total The pollen diagram (Fig. 4) is subdivided into eight local pollen disappearance of cold/drought-tolerant boreal trees/shrubs from the zones (PZ) on the basis of changing pollen composition and variations vegetation. in the dominant biome scores. A brief characteristic of the pollen/ PZ KTK2-6 (850–655 cm; ~23–14.5 kyr BP) reveals the highest biome zones provided here aims to facilitate further discussion. percentages of Artemisia (up to 80%) in the lower part of this zone and PZ KTK2-8 (1253–1000 cm; ~47–30 kyr BP) demonstrates high a progressive increase in the tree/shrub pollen percentages (N40%) percentages of herbaceous and shrubby taxa, mainly Artemisia (30–50%) towards the uppermost part of this zone. The steppe remains the and Betula sect. Nanae/Fruticosae (up to 40%). Arboreal pollen dominant biome, but the tundra communities once again start to play

Fig. 5. Local pollen assemblages zones (a) and time series of individual vegetation types (biomes) dominating the study area since ~47 kyr BP (b), with qualitative characteristics of vegetation (c) and quantitative changes in woody cover percentages within a 21×21 km window (d) derived from the KTK2 pollen record following Tarasov et al. (2009). 192 E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198 a more important role. Both biome and woody cover reconstruction Regionally, small Fragilariaceae-dominated diatom assemblages oc- results point to a greater-than-present openness of the landscape curred throughout the Holocene in a small lake from the Altai around Lake Kotokel. Mountains, central Siberia (Westover et al., 2006) and in the early PZ KTK2-5 (655–540 cm; ~14.5–12.65 kyr BP) demonstrates a Holocene in a large deep-water lake from the Mongolian Altai sharp increase in arboreal taxa percentages, mainly Picea (20–50%), (Rudaya et al., 2009). Diatom assemblages suggest a turbulent and birch and alder shrubs (up to 40%). For the first time, taiga becomes turbid environment implying strong winds and a high level of erosion. the dominant biome, closely followed by tundra. Two peaks in woody These taxa are indicators of ‘disturbed’ environmental conditions, as cover percentages are reconstructed, ~14 kyr (up to 25%) and ~13 kyr they survive today in harsh arctic environments with low light BP (up to 35%), separated by an interval with lower woody coverage. penetration where other more sensitive taxa would not succeed The vegetation likely resembled the present-day boreal woodland/ (Smol, 1988). The lake level was high enough to sustain well- forest-tundra with a significant contribution of spruce, fir and larch established planktonic species at 10–20% abundance. The increase in trees and shrubs of alder, birch and willow. two small planktonic Cyclotella species in the middle of the zone at the PZ KTK2-4 (540–506 cm; ~12.65–11.65 kyr BP) reveals a sharp expense of heavily silicified Aulacoseira ambigua and small benthic decrease in arboreal taxa percentages and an increase in herbaceous Pseudostaurosira brevistriata and Opeophora martyii might imply a taxa (up to 35%). Abies pollen is not recorded in this zone and pollen of slight amelioration of climate. The 20th century climate warming was shrubby birch almost replaces shrubby alder (Fig. 4). The quantitative found to be the most plausible mechanisms underlying the replace- reconstruction shows that the tundra becomes the dominant biome ments of, for example, the larger and heavier Aulacoseira taxa and/or and suggests a decrease in the woody cover to ~15%. small benthic Fragilaria taxa by smaller planktonic Cyclotella taxa in PZ KTK2-3 (506–422 cm; ~11.65–10.6 kyr BP) reveals the domi- many arctic, subarctic and temperate lakes (Rühland et al., 2008, nance of arboreal taxa (mainly Betula — a well-known woody Winder et al., 2009). pioneer) and the return of Abies to the pollen assemblages. The DZ KTK2-6 (1069–1025 cm; ~34.6–31.5 kyr BP). In this zone biome reconstruction demonstrates equally high scores for the tundra Ophephora martyi, Staurosirella pinnata agg. and Staurosira construens and taiga biomes, suggesting a quick recovery of arboreal communi- continue to decline. Cyclotella ocellata, C. bodanica and Aulacoseira ties and boreal woodland vegetation around the lake, in line with the ambigua, which made a brief appearance in the middle of the previous reconstructed increase in the total woody cover up to 40%. zone, are replaced by planktonic Aulacoseira subarctica (max 20%) and PZ KTK2-2 (422–310 cm; ~10.6–6.8 kyr BP) demonstrates a A. islandica (max 36%). Both A. subarctica and A. islandica are heavier minimal contribution of herbaceous taxa to the pollen assemblages. and more silicified taxa compared to small and light Cyclotella and The taiga scores are noticeably higher than the scores of non-forest they require high water turbulence to maintain their position in the biomes, suggesting well-established boreal forest in the region. The water column and usually prevail during spring/autumn water total woody cover increased to above 50% and exceeded present-day turnover periods (e.g. Rühland et al., 2008; Solovieva et al., 2008). values. This implies that the lake environment might have changed either by PZ KTK2-1 (310–0cm; ~6.8–0 kyr BP) shows that Pinus is shortening the summer period of stratified water, when Cyclotella has replacing Betula as the dominant taxon. This likely reflects change in the competitive advantage, or by increasing the spring/autumn period the forest composition and the regional spread of Scots pine after of water turbulence. Both changes suggest climate cooling and the 7 kyr BP. In this zone taiga scores are noticeably higher than the scores extension of the ice-cover season. TDC remains low, fluctuating of non-forest biomes, but the woody cover decreases to its present- between 0.16 and 22.73×106 valves g− 1. DCCA sample scores day level of ~45%. increase, reaching the highest values (2.3) for the whole core. Diatoms do not occur between 31.5 and 24.2 kyr BP suggesting 4.2. Diatom record and lacustrine environments particularly harsh lake conditions. DZ KTK2-5 (880–810 cm; ~24.2–21.9 kyr BP) shows the disap- The fossil diatom assemblages of the KTK2 core from Lake Kotokel pearance of meroplanktonic and heavily silicified diatoms (Aulaco- comprise 143 diatom taxa in total. The percentage diagram (Fig. 6) seira subarctica and A. islandica), a considerable decrease in the was divided into seven diatom zones (DZ). The reconstructed pH abundance of Ophephora martyi and the almost complete dominance shows little change throughout the core, fluctuating around 8. No or of the Staurosirella pinnata agg. complex, which may survive harsh very few (1–30 valves) diatoms occurred at 1149.5, 1087.5, 1025–880, environmental conditions where other diatom taxa would not 865.5, 823.5 and 810–718 cm (Fig. 6), eliminating these samples from succeed (e.g. Smol, 1988). TDC remains low. DCCA samples scores further analyses. decrease in DZ3 to 0.71 on average. These dramatic changes in the DZ KTK2-7 (1240–1069 cm; ~46–34.6 kyr BP) is dominated by diatom assemblages might have resulted from some catchment small benthic Staurosirella pinnata agg., Staurosira construens agg., disturbance or/and a particularly cold/dry climate between 31.5 and Pseudostaurosira brevistriata and Ophephora martyi. The latter is 24.2 kyr BP, when almost no diatoms were found. As in earlier particularly abundant in the lower and upper parts of this zone. A intervals diatoms were also extremely rare or totally absent between few planktonic species, Cyclotella bodanica and Cyclotella ocellata and 810 and 718 cm (~21.9–16.9 kyr BP), indicating conditions unfavour- meroplanktonic, heavily silicified Aulacoseira ambigua, reach their able for diatom development. highest abundance in the middle of the zone and disappear in the DZ KTK2-4 (718–550 cm, ~16.9–12.7 kyr BP) follows another upper part of the zone. Total diatom concentration (TDC) reaches its disturbance episode coinciding with the LGM, during which almost no highest values (N100×106 valves g− 1) in the lower-middle part of diatoms occurred in the lake. This zone reveals the first occurrence of the zone and then quickly decreases. DCCA axis 1 sample scores planktonic Aulacoseira granulata, a heavy silicified diatom, which is slightly increase throughout the zone (Fig. 6), tracking the overall typical for plankton of large eutrophic and mesotrophic lakes and modest floristic changes in the diatom assemblages. The dominance of reservoirs (e.g. Fluin et al., 2010; Ohtaka et al., 2010). Cyclotella pioneer benthic diatom taxa (e.g. Staurosirella pinnata agg. and ocellata (max 35%) and Aulacoseira ambigua (max 34%) are two other Ophephora martyi) is typical of early stages of lake development. co-dominant planktonic species in this zone, which made a brief These taxa are commonly found in many post-glacial lakes and in late- occurrence in the middle of DZ KTK2-7. The re-occurrence of small glacial lacustrine sediments (Haworth, 1976; Smol, 1983; Solovieva Cyclotella taxa might again indicate climate amelioration and a longer and Jones, 2002; Finkelstein and Gajewski, 2008) and at present in open-water season (e.g. Rühland et al., 2008). A progressive increase many arctic and subarctic lakes with a short open-water season in the abundance of planktonic Cyclotella diatoms is accompanied by a (Smol, 1988; Lotter and Bigler, 2000; Smol and Douglas, 2007). pronounced decrease in benthic species (Fig. 6). Amphora perpusilla, E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198 193

Fig. 6. Simplified diatom percentage diagram (analyst N. Ignatova†) with diatom concentration, ALPE-reconstructed pH and DCCA axis 1 sample scores of the KTK2 core from Lake Kotokel. See Fig. 2a for a description of lithological units. All diatom taxa with an abundance N5% are shown. The taxa are sorted by their weighted averaging scores from upper left to bottom right to highlight the major changes in the diatom stratigraphy. the periphytic diatom, occurs exclusively in this zone, first reaching sediment in the Mongolian Altai (Rudaya et al., 2009). A few benthic 11% and then decreasing to 3%. Similar to DZ KTK2-7, C. ocellata Fragilariaceae (Staurosira construens agg., Pseudostaurosira brevis- abruptly disappears in the upper part of the zone replaced by A. triata, and Staurosirella pinnata agg.) are present at low abundances. ambigua, implying possible deterioration of climate and shortening of TDC values are very low, and DCCA scores decrease slightly to 0.2 on the open-water season. TDC peaks in the middle of the zone, reaching average compared to the previous zone. This short zone reflects the 156.3×106 valves g− 1. It decreases to 19.1×106 valves g− 1 towards transition from the late-glacial to the Holocene. It was likely that the end of the zone implying an abrupt decline in diatom productivity. following deglaciation catchment erosion increased, which led to This decrease is concomitant with the decrease in Cyclotella ocellata decreased water transparency and light penetration and, therefore, a and also might suggest deteriorating environmental conditions, in sharp decrease in benthic species and the dominance of the above particular, colder climate. DCCA sample scores range between 0.5 and Aulacoseira taxa. 0.7 throughout the zone. The occurrence and subsequent dominance DZ KTK2-2 (495–130 cm; ~11.6–4 kyr BP) shows continuing of planktonic eutrophic/mesotrophic Aulacoseira granulata, together dominance of Aulacoseira granulata (45–98%). Staurosira construens with relatively high abundances of Cyclotella ocellata in the middle of is another dominant taxon at some levels with abundances between 2 the zone and two peaks of A. ambigua, suggest that the nutrient status and 40%. Both Ellerbeckia arenaria var. arenaria and Ellerbeckia of the lake changed. It is likely that the changes in the catchment soils arenaria var. teres abruptly decrease down to very low numbers, and vegetation, and the possible arrival of trees facilitated the similarly to Pseudostaurosira brevistriata, Ophephora martyi and increased nutrient supply to the lake, which sustained high nutrient Staurosirella pinnata agg. TDC fluctuates frequently between demands of A. granulata. A peak in Cyclotella ocellata abundance might 13.3×106 and 136.5×106 valves g− 1. DCCA sample scores remain indicate a relatively short-lived climate amelioration episode. almost unchanged at about 0.45 on average. The diatom assemblages DZ KTK2-3 (550–495 cm; ~12.7–11.6 kyr BP) is absolutely dom- of this zone suggest mesotrophic/eutrophic environments, indicated inated by planktonic Aulacoseira granulata and large radial centric and by dominance of Aulacoseira granulata, a relatively heavy diatom with benthic Ellerbeckia arenaria var. arenaria and E. arenaria var. teres. thick siliceous frustules, which is common in the large lakes, water Aulacoseira ambigua, which prevails in the previous zone, disappears reservoirs and rivers with a relatively high nutrient content (e.g. and Cyclotella ocellata occurs at two levels at 3–4%. The prevalence of Kilham and Kilham, 1975; Margalef, 1983; Kuzmin, 1988; Gómez et two Ellerbeckia species also implies the influence of glaciogenic al., 1995; Fluin et al., 2010; Ohtaka et al., 2010). Similarly to other sediments and relatively turbid water (Hickman and Reasoner, 1994). Aulacoseira taxa from Lake Kotokel, it usually peaks during spring/ Ellerbeckia is a relatively common diatom in southeastern Siberia. It autumn water turnover periods, requiring high water turbulence to occurs, for instance, in Lake Arachlei located to the east from Kotokel maintain its position in the water column (Gómez et al., 1995). The (V. Panizzo, pers. comm.). It was also found in Hoton-Nur lake reasons behind the abrupt disappearance of Ellerbeckia are unclear. 194 E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198

Most likely it implies that the catchment erosion decreased, and suggesting an increased aridity/continentality of the regional climate nutrient supply to the lake increased and these favored development and the predominance of open herbaceous communities in the of competing diatom taxa, namely Aulacoseira granulata. landscape. The noticeable decrease in diatom concentrations followed DZ KTK2-1 (130–0 cm; ~4–0 kyr BP) differs from the previous by the virtual disappearance of diatoms from the KTK2 sediment zone by a slight decrease in Aulacoseira granulata, Staurosira (laminated grey silty clay) at ~31.5–17 kyr BP might be another construens agg. and Pseudostaurosira brevistriata, the reappearance indicator of the dry and cold climate with strongly pronounced in notable abundances of Ellerbeckia arenaria var. teres (up to 11%), seasonality. A similar dramatic reduction in diatom abundance and the total disappearance of Staurosirella pinnata agg. TDC remains occurred in Lake Baikal during periods of climate deterioration during at a similar level to DZ6, and DCCA sample scores slightly increase the MIS3 interstadial (Swann et al., 2005; Mackay, 2007). The peak in compared to the previous zone. The further reduction in benthic and cryptogam spore percentages (mainly Equisetum) recorded at ~31– periphytic diatom taxa and the thriving planktonic community imply 30 kyr BP suggests that the coastal horsetail-covered zone became a possible increase in water depth or decrease in water transparency/ closer to the KTK2 coring site than before. The highest percentages of light penetration, which affected the benthic taxa by reducing their Ranunculaceae pollen at ~30–23 kyr BP further support a shift of habitat availability. Higher values of Staurosira construens agg. meadow/wetland communities closer to the coring point, suggesting compared with other Fragilariaceae might imply warmer climate that Lake Kotokel was much smaller in size than today during this conditions (e.g. Finkelstein and Gajewski, 2008). probably the driest interval of the whole record. The reappearance of diatoms in small quantities might be a sign of 5. Discussion and conclusions a slight amelioration of the regional climate at ~24–22 kyr BP, which might have influenced the aquatic ecosystem of a small lake, but was The KTK2 pollen and diatom records span a ~47-kyr interval, not strong enough to cause visible changes in the KTK2 core lithology which includes the middle glacial interstadial conventionally attrib- and pollen assemblages/terrestrial vegetation. Both herb/grass-dom- uted to the marine isotope stage 3 (MIS3), the last glacial maximum inated pollen assemblages, the absence of aquatic macrophytes and (LGM) followed by the late-glacial climate amelioration (MIS2) and the sporadic presence of diatoms in the KTK2 records at ~22–17 kyr the Holocene interglacial (MIS1). In this section changes in the pollen BP point to a second phase of climate deterioration, conventionally and diatom assemblages are discussed in terms of the late Quaternary associated with the LGM. climate dynamics in the Lake Baikal region of southern Siberia. 5.3. The late-glacial (~17–11.65 kyr BP) 5.1. The MIS3 interstadial (~47–30 kyr BP) A gradual increase in tree/shrub pollen percentages after ~18 kyr The MIS3 interstadial was identified in the palaeorecords from NH BP and changes in the diatom and lithology records after ~17 kyr BP and conventionally dated to ~35–25 14C kyr BP (~40–30 kyr BP) indicate the late-glacial climate amelioration in the region. Particu- (Frenzel et al., 1992). The KTK2 pollen record and quantitative larly noticeable changes suggested by the KTK2 proxies and proxy- vegetation reconstruction suggest the predominance of tundra- based environmental reconstructions occurred at ~14.7–12.7 kyr BP. steppe communities with Artemisia, Poaceae and Cyperaceae and a At that time the regional climate became warmer and wetter than moderately low, but variable woody cover (5 to 20%) during ~47– during the MIS3 interval, although it did not yet reach the Holocene 30 kyr BP, reflecting generally harsh and unstable climatic conditions. levels. These changes resulted in the spread of forest vegetation Boreal tree and shrub taxa could grow continuously in the locally (increase in the woody cover percentages up to 20–30%), and a moist habitats, expanding rapidly during the intervals of interstadial- possible increase in lake level/water depth due to the melting of the like climate amelioration (e.g. ~45–42 and ~35–31 kyr BP), and mountain glaciers, thawing of the permafrost active layer and increase shrinking in their distribution areas with the onset of the cold/dry in atmospheric precipitation (Bezrukova et al., 2005). The increase in stadial-like climate (e.g. prior to ~45 and ~42–35 kyr BP). A relatively small planktonic Cyclotella ocellata also suggests climate amelioration short peak in Cyclotella ocellata, C. bodanica, and Aulacoseira ambigua (Winder et al., 2009). Recorded increases in arboreal pollen and the corresponding peak in TDC between 45 and 42 kyr BP percentages and associated peaks in taiga scores and woody cover corroborates a response of the lake system to climate amelioration. percentages indicate that trees could have quickly spread out of their Interestingly, another warm event at ~35–31 kyr BP is not as clearly glacial refugia at least twice during the late-glacial interval, reflected by the lake diatom assemblages. A distinct Picea pollen corroborating with the results obtained from the poorly-dated KTK1 maximum in the KTK2 record at ~45–43 kyr BP allows a more precise core (Tarasov et al., 2009). This study allows a more accurate dating allocation of the similar event found in the low-resolution and poorly- of the woodland intervals to ~14.5–14 kyr and 13.3–12.8 kyr BP. dated pollen record from Lake Baikal (Shichi et al., 2007). It is broadly Chronological comparison of vegetation/environmental changes synchronous with the larch woodland development in the Indigirka around Lake Kotokel with the European records (Sirocko, 2009 and Lowland, northeastern Siberia, ~45 kyr BP (Anderson and Lozhkin, references therein) puts the later phase within the Allerød interstadial 2001), the formation of the black soil in western Siberia (Frechen et (13.58/13.35–12.7/12.68 kyr BP), in line with other palaeobotanical al., 2005), and the increased diversity and abundance of testate records from northern Asia (e.g. Andreev and Tarasov, 2007), the Lake amoebae in the MIS3 interstadial sediments on the Laptev Sea coast Baikal region (e.g. Demske et al., 2005; Bezrukova et al., 2008; Shichi (Müller et al., 2009). et al., 2009) and northeastern China (Stebich et al., 2009). The earlier The KTK2 diatom record suggests relatively deep oligo-mesotrophic phase of forest development seems to be an analogue of the environments in Lake Kotokel prior to ~31.5 kyr BP, in line with the Meiendorf interstadial (14.7–14.05/13.8 kyr BP, Sirocko, 2009), pollen-based interpretation. A pronounced decrease in the diatom which until now was not distinguished in the lower-resolution pollen concentration recorded after ~42 kyr and after ~32 kyr BP likely records from the Lake Baikal region and is likely interpreted as a part indicates two major steps in climatic deterioration during the MIS3. of the undifferentiated Bølling/Allerød interstadial complex (e.g. Bezrukova et al., 2005; Demske et al., 2005; Shichi et al., 2009). 5.2. The full glacial (~30–17 kyr BP) There is no clear evidence for the short-lived Bølling event (13.67– 13.58/13.54 kyr BP, Sirocko, 2009) in the KTK2 records, probably The full glacial occurs in the KTK2 pollen record at ~30–17 kyr BP because resolution is not high enough. and is marked by an increase in herbaceous taxa percentages, the The pollen and diatom records from Lake Kotokel (e.g. decrease in highest scores for steppe and the lowest scores for taiga biome, woody cover, increase in tundra biome scores and marked changes in E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198 195 the diatom assemblages) clearly identify the YD stadial in the Lake Lozhkin, 2001; Kienast et al., 2005; Müller et al., 2009). Frenzel et al. Baikal region. The KTK2 age model allocates it within ~12.7–11.7 kyr (1992) reconstructed a colder (by 6–8 °C in winter and by 4–5°Cin BP. The YD climate reconstructions suggest lower than present summer) and drier (by 100–200 mm/yr) than present interstadial temperatures (by 2–4°С in July and by 8 °С in January) and lower climate in Siberia at ~40–30 kyr BP. Other authors (e.g. Shahgedanova, precipitation (by 100 mm/yr) around Lake Baikal (Tarasov et al., 2002 and references therein) suggested that it could have been 2007a, 2009). Very low diatom concentrations and disappearance of regionally (e.g. in western Siberia) warmer than the present. The small ‘warm’-water planktonic Cyclotella ocellata from the KTK2 palaeobotanical (Hubberten et al., 2004; Kienast et al., 2005) and isotope sediment might imply climate deterioration and shortening of the studies (Tütken, 2003; Popp et al., 2006) in the arctic parts of eastern open-water season. Predominance of Ellerbeckia arenaria var. arenaria Siberia led to the reconstruction of an extreme-continental climate, implies increased amounts of glaciogenic sediments, higher erosion characterised by low precipitation, mean annual and winter tempera- and a turbid water regime during the YD (Hickman and Reasoner, tures, but relatively high summer temperatures and/or a longer snow- 1994). Frustules of finer and thinner diatoms, for instance, small free period compared to today. The discontinuous pollen data from Fragilariaceae, might not have been well-preserved in the highly northeastern Siberia were used to infer a regional climate similar to the minerogenic sediments, whereas robust and thick Aulacoseira present at ~43.2–37.5 kyr BP, but colder/drier-than-present environ- granulata and Ellerbeckia arenaria might have a better chance to be ments prior to and after this interval (Anderson and Lozhkin, 2001). preserved in the lake sediments and therefore might be over- The KTK2 records presented here point to a drier/colder-than- represented in the fossil record. Overall, it is obvious from the KTK2 present late Pleistocene climate in the southern part of eastern Siberia records that the YD event clearly affected the regional environments. even during the interstadial episodes of climatic amelioration that are However, the YD climate remained warmer and wetter than at any visible, for example, in the taiga (maxima) and steppe (minima) time between ~47 and 17 kyr BP. biome scores (Fig. 7d). The reconstructed pattern of changes in the regional environments demonstrates that the late Pleistocene climate 5.4. The Holocene (11.65 kyr BP — present) dynamics in southern Siberia were more complex than previously thought, and resemble the temperature variations (e.g. Greenland The Holocene vegetation and climate dynamics in the region under interstadials and Heinrich events) expressed in the δ18O record from study was recently reconstructed from the KTK1 pollen record (Tarasov Greenland ice (Fig. 7a) and the East Asian Monsoon intensity signal in et al., 2009). The chronological sequence of environmental change the δ18O record from Chinese stalagmites (Fig. 7e). Minor incon- reconstructed from the KTK2 records shows great similarity with the sistencies could be explained by the lower accuracy of the KTK2 age previous study. The shift to Holocene environments appears in the model and the lower resolution of the KTK2 record in comparison to KTK2 diatom and pollen records at ~11.7–11.65 kyr BP, suggesting an the above δ18O records. Wang et al. (2001) demonstrated that the almost synchronous response of terrestrial and aquatic ecosystems to isotope records from Hulu Cave near Nanjing and from Greenland ice the global climate change. The KTK2 date agrees with the formal cores bear a remarkable resemblance, suggesting that the intensity of definition and dating of the Global Stratotype Section for the base of the the summer Pacific monsoon, which brings moisture to the eastern Holocene (~11,650 cal yr BP), derived from the Greenland NGRIP ice part of Asia, changed in accordance with North Atlantic temperatures core and selected regional records (Walker et al., 2009), suggesting a between 75 and 11 kyr BP. Evidence for climatic teleconnections synchronous onset of the Holocene interglacial across Eurasia. between Europe and Lake Baikal during MIS3 was discussed by Swann Results of pollen analysis and pollen-based biome and woody cover et al. (2005) and Mackay (2007). The Lake Kotokel records presented reconstructions from the KTK2 core correlate well with the KTK1 here link changes in the North Atlantic and North Pacific climate, results (Tarasov et al., 2009), demonstrating that a boreal woodland which are responsible for the sub-latitudinal transport of heat and spread around Lake Kotokel at ~11.65–10.5 kyr BP in response to a moisture to the central parts of Eurasia. noticeable increase in precipitation and in winter and summer Further comparison of the KTK2 records with orbitally-induced temperatures. The maximal spread of the boreal forest (taiga) insolation variations (Fig. 7b) and with the global sea level communities is associated with higher-than-present July (17–18 °C) reconstruction (Fig. 7c) suggests that the phase with the maximal and January (−19 °C) temperatures and precipitation (500–550 mm/ spread of cold steppe communities and minimal representation of yr), reconstructed at ~10.5–7 kyr BP (Tarasov et al., 2009). The pollen- woody taxa in the regional vegetation (Fig. 7d) occurred during the based reconstruction of a slight decrease in woody cover around Lake interval, when the NH summer insolation and global sea level reached Kotokel ~at 7–6.5 kyr BP likely indicates a gradual decrease in their minima, with the global ice volume consequently reaching its precipitation and temperatures towards their present-day values. A maximum. The records summarized in Fig. 7 and the KTK2 diatom noticeable increase in Pinus sylvestris pollen recorded after ~7 kyr BP record imply that the LGM in the Lake Baikal region and probably on reflects the spread of Scots pine in the Lake Baikal region (Demske et the global scale should be placed at ~25–24 kyr BP and not ~21 kyr BP, al., 2005; Bezrukova et al., 2008; Shichi et al., 2009), in line with the as conventionally used in the palaeoenvironmental studies (e.g. onset of drier and colder (similar to present) climate. The changes in Tarasov et al., 2000; Yokoyama et al., 2000; Clark et al., 2006) and in diatom assemblages support these pollen-based reconstructions. The modelling experiments (e.g. Kageyama et al., 2001). Our conclusion absolute dominance of meroplanktonic Aulacoseira granulata (maxi- based upon the Lake Kotokel data is in line with the growing body of mum ~11.6–10 kyr BP), disappearance of Ellerbeckia arenaria var. evidence from elsewhere that suggests an earlier onset of the LGM arenaria by ~11.6 kyr BP and reappearance of benthic taxa suggest (e.g. Allen and Huntley, 2000; Peltier and Fairbanks, 2006; Genty, establishment of deep- and transparent-water environments already 2008, Veres et al., 2008; Sirocko, 2009). in the early Holocene. Although this system remained rather stable The relatively high temporal resolution and reliable AMS-based throughout the Holocene, minor changes in the diatom assemblages age model of the KTK2 pollen record enable its comparison with the likely indicate gradual natural enrichment of the lake after ~7 kyr BP. reference palaeoclimatic archives representing North Atlantic (e.g. Litt and Stebich, 1999; Brauer et al., 2008; Svensson et al., 2008; Sirocko, 5.5. Factors controlling the late Quaternary environmental dynamics in 2009) and North Pacific regions (Yuan et al., 2004; Stebich et al., the Lake Baikal region 2009). This comparison suggests that the reconstructed shifts in late Pleistocene–Holocene vegetation and environments in the Lake Baikal The Lake Kotokel records contribute to the continuous debate region could have been controlled by the major factors controlling NH concerning the degree of climate amelioration and the chronological climate (Fig. 7). The correspondence between the KTK2 record and framework of the MIS3 interstadial in Siberia (e.g. Anderson and very high-resolution isotope and pollen records from far distant North 196 E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198

Fig. 7. Comparison of (a) the δ18O records from Greenland, as indicator of the Northern Hemisphere (NH) air temperature (after Svensson et al., 2008) and (e) from Chinese stalagmites (after Wang et al., 2001; Yuan et al., 2004), as indicator of the Pacific monsoon intensity, (b) the NH June and December insolation at 60°N (after Berger and Loutre, 1991), (c) global sea level (after Yokoyama et al., 2007), as indicator of the global ice volume, and (d) numerical biome scores for steppe and taiga, as palaeoclimatic indicators in the Lake Baikal region (this study), plotted along their respective time scales. The arrows refer to the Greenland Interstadials (GI1 to 12) shown in the left graph. Grey bars indicate approximate positions of the Younger Dryas (YD) and Heinrich events H1 to H5 (after Tierney et al., 2008).

Atlantic and North Pacific regions implies that southern Siberia, Prof. J.P. Smol, Dr. K. Kremenetski and Prof. A.P. Kershaw for their despite its location in the interior of the Eurasian landmass, responded thorough review, which helped to improve the manuscript. The swiftly to global change. This conclusion is a key point in the ongoing authors like to acknowledge fruitful discussions of the results debate on the synchronic/non-synchronic environmental dynamics of presented in the current study during the RFBR- and DFG-sponsored terrestrial environments within the Lake Baikal region during the last (TA-540/4) International Workshop “Bridging Eurasia” (Freie Uni- 15 kyr, based upon less accurately dated pollen records (see Demske versität Berlin, April 28–May 2 2010). The paper is dedicated to et al., 2005; Shichi et al., 2009 for discussion and references). Natalia V. Ignatova, who passed away in August 2008. Moreover, in the current absence of better-resolved and dated sequences, the KTK2 core from Lake Kotokel may serve as a regional stratotype section (Bezrukova et al., 2008), which allows one to revisit References the chronologies of the earlier published pollen/environmental Allen, J.R.M., Huntley, B., 2000. Weichselian palynological records from southern records from the Lake Baikal region and possibly reconsider some of Europe: correlation and chronology. Quat. Int. 111–125 73/74. the earlier interpretations. Alpat'ev, A.M., Arkhangel'skii, A.M., Podoplelov, N.Y., Stepanov, A.Y., 1976. Fizicheskaya geografiya SSSR (Aziatskaya chast'). Vysshaya Shkola, Moscow. Anderson, P.M., Lozhkin, A.V., 2001. The Stage 3 interstadial complex (Karginskii/ Acknowledgements middle Wisconsinan interval) of Beringia: variations in paleoenvironments and implications for paleoclimatic interpretations. Quat. Sci. Rev. 20, 93–125. This paper is a contribution to the German Research Foundation Andreev, A.A., Tarasov, P.E., 2007. Pollen records, postglacial: Northern Asia. In: (DFG) project TA-540/1. The study was also partly supported by the Elias, S.A. (Ed.), Encyclopedia of Quaternary Science, 4. Elsevier, Amsterdam, pp. 2721–2729. Russian Foundation for Basic Research (RFBR) project 09-05-00123. Battarbee, R.W., Jones, V.J., Flower, R.J., Cameron, N.G., Bennion, H., Carvalho, L., Juggins, We would like to acknowledge Prof. H. Takahara and all team S., 2001. Diatoms. In: Smol, J.P., Birks, H.J.B. (Eds.), Tracking Environmental Change members for participating in the coring campaign at Lake Kotokel in using Lake Sediments. Terrestrial, Algal, and Siliceous Indicators, 3. Kluwer Academic Publishers, Dordrecht, pp. 171–205. 2005, Prof. T. Goslar (Poznan, Poland) for the AMS dating of the KTK2 Bennett, K.D., 1996. Determination of the number of zones in a biostratigraphic samples, and Dr. E. Schalk for polishing the English. We are grateful to sequence. New Phytol. 132, 155–179. E.V. Bezrukova et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 296 (2010) 185–198 197

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