UDC 551.89

N. A. Rudaya ¹, P. E. Tarasov ², N. I. Dorofeyuk ³, I. A. Kalugin ⁴, A. A. Andreev ⁵, B. Dikman ⁵, A.V. Darin ⁴

¹ Institute of Archeology and Ethnography SB RAS 17 Akademika Lavrentieva Ave., Novosibirsk, 630090, Russia

E-mail: nrudaya@yandex.ru

² Free University, Geological Institute, Department of Paleontology

Free University of Berlin, Institute of Geological Sciences, Palaeontology Department

Malteserstr, 74 - 100, Building D, Berlin, 12249, Germany

³ Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences

33 Leninsky Ave., Moscow, 119071, Russia

⁴ Joint Institute of Geology, Geophysics and Mineralogy SB RAS

3 Akademika Koptyuga Ave., Novosibirsk, 630090, Russia

⁵ A. Wegener Institute for Polar and Marine Research

Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam

Telegrafenberg, A43, Potsdam, 14473, Germany

DYNAMICS OF THE NATURAL ENVIRONMENT OF THE MONGOLIAN ALTAI IN THE HOLOCENE*

The article is devoted to studying the dynamics of the natural environment of the Mongolian Altai in the Holocene. The data of spore-pollen and diatom analyses of samples from the bottom sediment column of Vysokogorny lake served as the material for reconstructions. Khoton-Nur, located on the eastern macroslope of the Mongolian Altai. The results obtained made it possible to reconstruct the period of cold dry climate and the development of cryophytic steppe associations in the late Pleistocene - early Holocene (11500 - 10700 BP); in the Middle Holocene (9300 - 6500 BP) - the existence of the warmest and most humid conditions that caused the expansion of forest vegetation; after 6500 BP-an increase in climate continentality, a decrease in the number of forests and the development of tundra and steppe communities. The last 3000 years are characterized by the disappearance of forests and the spread of steppes, which may be due not only to climatic factors, but also to increased anthropogenic influence.

Introduction

The Mongolian Altai, located in the center of the Euro-Asian continent, is a watershed between the rivers of the Arctic Ocean basin and the drainless basin of Central Asia and is characterized by a sharply continental climate, a special type of high-altitude zone with forest belt loss, the development of tundra and cryophytic steppes in the highlands, as well as the identity and mosaic of vegetation cover. The Mongolian Altai is a habitat for many rare and endemic animal and animal species.

* The research was carried out with the financial support of the Russian Foundation for Basic Research (projects N 08 - 05 - 00773, 06 - 05 - 64931), The Presidium of the Siberian Branch of the Russian Academy of Sciences (project No. 108), as well as the German Academic Exchange Foundation (DAAD, No. 325, A / 05 / 00162), the INTAS Foundation (N 06 - 1000014 - 5781), the German Research Community (DFG, 436RUS17 / 17 / 06). The authors are grateful to V. Yankovskaya (Institute of Botany, Brno) for their help in identifying non-pollinated palynomorphs, and to A. Ebel (Tomsk State University). for advice on the current distribution of vegetation, L. Nazarova (Institute of Polar and Marine Research, Potsdam) for assistance in identifying the remains of Chironomidae, and N. Tserendash (Institute of Geology and Mineral Resources of the Russian Academy of Sciences, Ulaanbaatar) for organizing field work.

plants. The main economically viable natural resources (forests, productive pastures, water reserves) are concentrated in high-altitude areas, which have always attracted the attention of the nomadic population of Central Asia. Despite the fact that currently the anthropogenic load in the Mongolian Altai is estimated as "moderate" [Ecosystems..., 2005], there is a tendency to desertification and land degradation [Vegetation dynamics..., 1999; Ecosystems..., 2005].

An integral picture of changes in the natural environment is provided by paleobiological and geochemical data obtained from the bottom sediments of lakes. In the deep-water parts of water bodies, precipitation accumulates over time, which is removed from the catchment area and contains the remains of animals and plants that lived in the catchment area, as well as organisms that lived in the lake (Davydova, 1985; Battarbee, 1986; Battarbee et al., 2001).

The greatest amount of work on the palynological study of bottom sediments of Mongolian lakes was carried out by the paleobotanical team of the joint Soviet-Mongolian integrated expedition in the 80s of the last century (Vipper et al., 1978, 1981; Dorofeyuk and Tarasov, 2000; Vegetation dynamics..., 1999; Tarasov, Dorofeyuk and Metel'tseva, 2000). The latest deposits of reference sections in Mongolia were studied by E. M. Malaeva (1989) using palynological methods. In the last decade, only a few works have been published on reconstructing the climate and vegetation of Mongolia based on data obtained from bottom sediments of the Ubsu-Nur Lakes in the Great Lakes Basin (Grunert, Lehmkuhl, Walther, 2000) and Telman and Hubsugul Lakes in Central Mongolia (Peck et al., 2002; Fowell et al., 2003). Prokopenko et al., 2007].

The Holocene dynamics of the natural environment and climate of Central Asia have been most fully studied in China (Winkler and Wang, 1993; Rhodes et al., 1996; Herzschuh et al., 2004, 2005, 2006; Wunnemann, Mischke, Chen, 2006; etc.). A number of studies are devoted to changes in the natural environment during the Holocene and Late Pleistocene in Northern and Central Kazakhstan [Tarasov, Jolly, Kaplan 1997; Kremenetski, Tarasov, and Cherkinsky, 1997], the Russian Altai and Tuva [Blyakharchuk et al., 2004, 2007, 2008; Schlutz and Lehmkuhl, 2007]. The latter are supplemented by the results of analysis of diatom residues (Westover et al., 2006) and chironomids (Ilyashuk B., Ilyashuk E., 2007).

This paper is devoted to the study of lacustrine deposits of Lake Baikal. Khoton-Nur Lake, located on the eastern macroslope of the Mongolian Altai in Northwestern Mongolia (Fig. 1). For the first time, a column of bottom sediments from an isolated bay of this lake was studied by spore-pollen and diatom methods in 1980. At the same time, several radiocarbon dates were obtained [Tarasov et al., 1996; Vegetation dynamics..., 1999]. The analysis of the column (Khoton-1) was carried out with low time resolution and, although it revealed a general trend of Holocene changes in the biota and climate in the region, it is insufficient for detailed paleogeographic reconstructions (Tarasov, Dorofeyuk, Metel'tseva, 2000). This article presents the results of spore-pollen and diatom analyses of the sediment column from the deep-water part of the lake (Khoton-2), conducted with high time resolution. Their interpretation made it possible to draw up a map of the development of the natural environment and climate of the Mongolian Altai in the Holocene and compare it with paleogeographic reconstructions in neighboring regions.

Natural conditions of the research area

Khoton-Nur Lake (48°40' N, 88°18' E, 2,083 m above sea level) is located in the intermountain tectonic zone of the southern part of Kazakhstan.

1. Study area (A) and drilling points Khoton-1, Khoton-2 (B).

2. Modern vegetation of the northern part of the Mongolian Altai.

1 - lichen and moss-lichen tundras (Cetraria, Cladonia, Alectoria, Aulacomnium, Polytrichum); 2 - high - altitude kobresia and sedge forests (Kobresia myosuroides, K. smirnovii, Carex stenocarpa, C. rupestris); 3 - larch forests (Larix sibirica); 4-cryophytic steppes (Festuca lenensis, Oxytropis oligantha, Potentilla nivea); 5 - mixed grass and grass steppes (Festuca lenensis, Poa attenuata, Koeleria macrantha); 6 - dry mixed grass and grass steppes (Festuca lenensis, Agropyron cristatum, Potentilla sericed); 7-desolate steppes (Stipa glareosa, Anabasis brevifolia); 8 - Pinus sibirica.

1). Its area is 50.1 ^km2, its length is about 21.5 km, its greatest width is 4.0 km; its average depth is 26.6 m, and its maximum depth is about 58 m (Tarasov et al., 1994). The lake is an oligotrophic type; its waters are characterized by a mineralization of about 0.500 mg / l, pH = 7.5, and belong to the sodium bicarbonate group (Sevastyanov et al., 1994).

The main supply of the lake is provided by the Karatyr and Ak-Su rivers, as well as other small rivers flowing down from the slopes of the Mongolian Altai. The system of lakes Khoton-Nur and Khurgan-Nur, connected by a wide channel, is the source of the Khovd River, which drains the entire Mongolian Altai. Education of oz. Khoton-Nur is associated with damming of the surface runoff of the Karatyr and Ak-Su Rivers by terminal moraines of the last Late Pleistocene glaciation (Khilko and Kurushin, 1982).

Mongolian Altai is located in the North Gobi climatic province with a sharply continental climate characterized by low precipitation, constant and strong winds, and large amplitudes of seasonal and daily temperatures. In general, the study area is characterized by a long harsh winter (the average annual temperature in January is -24... -25°C) and short cool (the average temperature in July is about 12-15°C) and moderately humid summers. The average annual precipitation in the lake basin is 250-300 mm per year (National Atlas..., 1990).

Khoton-Nur Lake is located in the high mountain belt of the Mongolian Altai. 2) is mainly represented by dry mountain steppes (with Agropyron cristatum, Artemisia frigida, Arenaria meyeri, Potentilla sericea, Astragalus brevifolia). On the slopes in the northern part of the lake, cryophytic small-grained grass and mixed-grass steppes (with Festuca lenensis, Poa attenuata, Arenaria meyeri, Oxytropis oligantha, Androsace chamaejasme) are common in combination with sedimentary sedge (Carex stenocarpa, C. rupestris) and cobresia (Kobresia myosuroides, K. smirnovii) [Volkova, 1994].

The dominant tree species in the vicinity of the lake is Siberian larch (Larix sibirica). It forms pure larch forests with undergrowth of round-leaved birch (Betula rotundifolia), glaucous willow (Salix glauca) and moss-grassy cover of Festuca altaica, Carex orbicularis, Hedysarum neglectum, and Aulacomnium turgidum in the upper reaches of the Ak-Su River. Larch trees with an admixture of Siberian spruce (Picea obovata) grow on mountain slopes in the southwestern part of the lake and along river valleys. The Siberian pine (Pinus sibirica), which forms the forest boundary in the Russian Altai and Sayan Mountains, is found only 50 km north of the lake, in the Ak-Su River valley (Grubov, 1982; National Atlas..., 1990). Lichen, moss, and yernik tundras appear in the highlands (above 3000 m) (Volkova, 1994).

Compared to China, Kazakhstan, and the Russian Altai, the Mongolian Altai is sparsely populated. Only 18 thousand people live in the Bayan-Ulga aimag (on the territory of which the lake is located). [National Atlas..., 1990]. The population leads a nomadic lifestyle, mainly engaged in animal husbandry. Despite the sparsely populated territory, the anthropogenic load in the river valleys and along the coast of Lake Baikal is very high. Khoton-Nur is assessed as moderate and high, mainly due to excessive grazing of pastures [Ecosystems..., 2005].

Materials and methods

In 2004, in the south-eastern part of the lake's water area. Khoton-Nur (48°37 '18.1" N, 88°20 ' 45 " E) a well was drilled at a depth of 35 m and a column of bottom sediments was obtained.

1, B). The sediments are divided into two bundles - the lower one (257 - 205 cm) and the upper one (205 - 0 cm), separated by a cavity, probably at the site of an ice lens. A sharp boundary between the packs suggests a break in sedimentation. In general, the sediments are fairly uniform and are represented by banded clay siltstones with an admixture of organic matter (3 - 4%), underlain by gray-blue clay at a depth of approx. Granulometric analysis showed that the average particle diameter varies over the intervals: 257-190 cm-10-20 microns, 190-50 cm-20-30 microns, 50-0 cm-15-20 microns. Under the microscope, particles of quartz, feldspar, light and brownish mica can be distinguished. The composition of rocks varies between depths of 185 and 150 cm, which is reflected in a slight increase in the content of Fe2O3, _TiO2, and MgO, and a decrease in - SiO2, and a _decrease in magnetism.

The low content of organic matter in the sediment column was a serious problem for radiocarbon dating. Ten samples with insignificant organic residues were sent to the radiocarbon laboratory of the University of Kiel (Germany). The material of six of them was insufficient for AMS dating. Analysis of two samples showed an age of more than 53 thousand years, i.e. beyond the capabilities of the radiocarbon method. Based on the material from a depth of 236.5-237.0 cm, a date of 32450 ± 380 BP was obtained (Table 1). It can be assumed that the lower member of gray-blue clay accumulated in the late Pleistocene to the last glacial maximum, or this date is also ancient. Thus, a single date of 9130 ± 40 BP obtained from a depth of 174.5 - 175.0 cm seems adequate. To verify its reliability and construct a depth-time model for the Khoton-2 column, we used the results of dating the Khoton-1 column (Table 1). 2) from a small bay in the north-eastern part of the lake from a depth of 4.8 m (see Fig. The location of the sampling site close to the shore in a semi-enclosed organic-rich bay with stable sedimentation conditions allowed us to obtain a sequence of six ^14C dates in the range of 9070-2950 BP [Vegetationdynamics..., 1999; Tarasov, Dorofeyuk, Metel'tseva, 2000]. These dates were calibrated [CalPal...], and an age model for the Haughton-1 column was constructed based on them. Comparison of the Haughton-1 and -2 spore-pollen spectra showed a coincidence of 13 events in changes in the content of 21 taxa. Based on the correlation of these events using the calibrated dates of the Haughton-1 column, an age model for Haughton-2 was constructed (without the lower part of the column). It is a regression line with a second-degree polynomial approximation (Figure 3).

One hundred samples (1-2 g of dry matter each) with an interval of 2.5 cm were processed for spore-pollen analysis using a standard technique [Faegri, Iversen, 1989]. Pollen grains and spores were counted using a light microscope with x400 magnification. Lycopodium spore tablets were used to calculate their concentration. Taxonomic affiliation was determined by the following factors:

Table 1. Dates obtained from fine organic remains of the Khoton-2 sediment column

Table 2. Dates obtained from the overlap of the Khoton-1 sediment column (Tarasov, Dorofeyuk, Metel'tseva, 2000)

Calibrated date, thousand liters

Figure 3. Model of change in the age of bottom sediments

Khoton-2 with a depth of. Palynological events that similarly manifest themselves in the spore-pollen spectra from the Khoton-1 and Khoton-2 columns: 1 - peak pollen content of herbaceous taxa (Tr), especially wormwood; 2 - decrease in the pollen content of Tr (especially wormwood) and a slight increase in the pollen content of tree taxa (Dr); 3-peak pollen content 4-peak of Tr pollen content (especially wormwood) and a decrease in the share of Dr pollen; 5 - peak of ephedra pollen content, a decrease in the concentration of Tr pollen (especially wormwood); 6-peak of Siberian spruce pollen content; 7-beginning of an increase in the concentration of wormwood and haze pollen, a decrease in the share of Siberian spruce pollen; 8 - peak of Siberian spruce pollen content; 9-peak of Siberian larch pollen content; 10-beginning of increase in Tr pollen concentration; 11-peak of Dr pollen content; 12 - increase in Siberian spruce pollen content; 13-date obtained by the AMS method for the Haughton-2 column - 10304 ± 56 cal. l. n. 14 - decrease in the content of Siberian spruce pollen.

atlases [Kupriyanova and Alyoshina, 1972, 1978; Reille, 1992, 1995, 1998]. A total of 54 pollen and spore types were identified, which is 2.5 times more than in the Khoton-1 column (Tarasov, Dorofeyuk, Metel'tseva, 2000). Spore-pollen analysis revealed good preservation and a relatively high concentration of pollen and spores in the upper part of the column (0 - 205 cm) - up to 500 grains per sample, while in the lower part it is very low-often less than 100 grains per sample, which is insufficient for statistical analysis (Faegri and Iversen, 1989). Therefore, only for the upper part of the column, percentages in the spectra of all pollen taxa were calculated (the total sum was taken as 100%), with the exception of spores, coniferous stomata, and other non-pollen palynomorphs.

Samples prepared for spore-pollen analysis were also used to count stomata of coniferous and other non-pollen palynomorphs (NPPs). The stomata found in the Haughton-2 column belong to the genera Picea and Larix (defined by [Trautmann, 1953; Sweeney, 2004]). Non-pollen palynomorphs are represented by chlamydospores of the endomycorrhizal fungus Glomus, the remains of sporopollenin cells of colonial green algae (Botryococcus braunii, Pediastrum cf. boryanum), eggs of tardigrades (Macrobiotus hibernicus and M. hufelandi), and remains of Chironomidae jaws (Cladotanytarsus and Mesocricotopus), which were identified using published descriptions, images, and photographs (Jankovska, 1991; Van Geel, 2001; Komarek and Jankovska, 2001).

58 samples were selected for diatom analysis with an interval of approx. 5 cm. The samples were subjected to technical processing by the method of disintegration in hydrogen peroxide, in which the shells of diatoms were cleaned of organic matter [Diatoms..., 1974; Battarbee, 1986]. Subsequently, permanent preparations were prepared from the treated samples in Naphrax medium. Identification of diatoms was performed using a light microscope using oil immersion, giving a magnification of at least x750, and an eyepiece with a scale ruler. Counting of diatomaceous algae leaves was carried out in a horizontal row in the middle part of the cover glass up to 500-600 pcs. To calculate the concentration (total and individual species) in 1 g of dry sediment, we used the quantitative data processing technique and formula proposed by N. N. Davydova [1985]. The total amount of algae detected in the preparation was taken as 100%, and the relative share of each species and, accordingly, its role in the diatom complex was determined: < 1% - single, 1 - 5% - common, 5 - 10% - subdominants, > 10% - dominants.

Diatoms were divided into planktonic, benthic, and fouling species (periphyton) based on their association with certain biotopes. Freshwater and brackish-water (mesohalobic) algae were distinguished in relation to the salinity of water. The first ones are halophobic (they live in waters with a salt content of up to 0.2% o), indifferent (0.2 - 0.3%o) and halophilic (0.4 - 0.5% o). Mesohalobic diatoms prefer water with a salt content of > 0.5% O. In relation to the active reaction of the medium, algae are divided into acidophilic (waters with pH < 7), circum-neutral (pH ≈ 7), alkaliphilic (pH ≥ 7), and alkalibiont (pH > 7). According to the main types of the lake's diatom flora range, the Arctic-Alpine, boreal, and cosmopolitan geographical groups were distinguished.

The spore-pollen and diatom diagrams were constructed using the TILIA-TILIAGRAPH software (Grimm, 1991). The division into palynozones and diatom zones was carried out using the CONISS program (Grimm, 1987).

Results of spore-pollen analysis

The spore-pollen diagram shows five palynozones (PS) (Fig. 4).

Fig. 4. Spore-pollen diagram for Lake Baikal deposits. Khoton-Nur (Khoton-2), a - presence of Picea stomata; b - presence of Larix stomata.

PZ 5 (257-205 cm; up to 1800 grains/^cm3; the upper limit is dated to ca. 11500 BP*). Due to the low pollen concentration, the percentage of taxa was not calculated. Pollen of herbaceous plants (Chenopodiaceae, Artemisia, Cyperaceae) and the desert-semidesert shrub Ephedra is most common. Single grains of Picea obovata, Pinus sibirica, and Larix sibirica were recorded.

PH 4 (205-175 cm; up to 21,000 grains/cm ³; ∼11,500-10700 bp). Herbaceous taxa (up to 85%) dominate here, including Chenopodiaceae and Artemisia. A characteristic feature of the zone is a significant content of Ephedra pollen (up to 15%). Among tree taxa, the most abundant pollen is Picea obovata. Pollen of Pinus sibirica and Larix sibirica is found.

PZ 3 (175.0-97.5 cm; up to 25,000 grains/^cm3; ∼10700-7900 bp). It is characterized by a sharp increase in the pollen content of woody plants (up to 75%) and a decrease in the pollen content of herbaceous plants. The share of Picea obovata pollen reaches 70%. The abundance of pollen from Pinus sibirica, Larix sibirica, and Betula sect is also increasing. Nanae. The pollen content of Chenopodiaceae and Artemisia is significantly reduced.

PZ 2 (97.5-40.0 cm; up to 20,000 grains/^cm3; ∼7900-4900 bp). A distinctive feature of the zone is the sharp changes in the ratio of pollen of woody and herbaceous plants, especially in the pollen content of Picea obovata (varies from 10 to 75%). The share of Pinus sibirica pollen increases, while Abies sibirica reaches its maximum (4%). Among herbaceous taxa, Artemisia, Chenopodiaceae, Poaceae, and Cyperaceae pollen dominates.

PZ 1 (40-0 cm; up to 6320 grains/^cm3; ∼4900-0 bp). A general reduction in the amount of tree pollen is noteworthy (due to a decrease in the content of Picea obovata pollen to 10 - 40%). At the same time, the share of Pinus sibirica pollen increases slightly. The pollen content of herbaceous taxa increases to 60-70%. Artemisia, Chenopodiaceae, Poaceae, and Cyperaceae pollen continues to dominate.

Results of analysis of non-pollinated palynomorphs

One of the notable features of the Khoton-2 spectrum is the presence of larch and spruce stomata in all but one of the FCS (Fig. 4). Despite their small number (no more than five in the sample), they are quite common in FCS 3 and 2 and sporadically in FCS 4 and 1. Among other SPS, they predominate in the FCS of the same species. Remains of Botryococcus braunii, which appear as early as BP 5 and are constantly present in BP 3 and 1. B. braunii is a widespread alga that lives in water bodies from the Arctic to tropical latitudes and prefers oligotrophic conditions (Tyson, 1995; Smittenberg et al., 2005). PZ 1-4 also contains remnants of Pediastrum cf. boryanum. Eggs of Macrobiotus (M. hibernicus and M. hufelandi) and jaws of Cladotanytarsus and Mesocricotopus (Chironomidae, Diptera) appear in sediments younger than 9000-9450 years (BP 3). Isolated Glomus chlamydospores were found in zones 2 and 1.

Diatom analysis results

Diatom flora of bottom sediments of Lake Baikal. Khoton-Nur includes 295 taxa from 67 genera. The previously published composition of diatoms of thanatocenoses of the lake (Dorofeyuk and Tsetsegmaa, 2002) was supplemented with 90 taxa, which were first identified in the sediments of its deep-water part. 13 of them are new to the Mongolian algal flora: Cyclotella operculata var. unipunctata, Amphora dusenii, Brachysira brebissonii, Caloneis tenuis, Cavinula jarnefeltii, C. lacustris, Cymbella behrei, Diploneis clomblitensis, Eunotia polydentula, Gomphonema abbreviatum, Luticola crf. undulata, Navicula farta, Stauroneis sibirica. Centric diatoms are represented by 21 taxa, of which the genera Cyclotella (10) and Aulacoseira (5) are the most diverse. Among pennate diatoms, the genera Gomphonema (15 taxa), Cymbella and Navicula (12 species each), and Eunotia (11) are distinguished by the largest number of species.

The dominant diatom complex (DC) of the Haughton-2 column is dominated by centric planktonic species: Aulacoseira distans f. distans, A. italica var. italica + var. tenuissima, Cyclotella bodanica var. bodanica, C. ocellata, Ellerbeckia arenaria var. teres, Stephanodiscus minutulus. At different stages of the lake's development, it includes pennate subdominants: Achnanthidium minutissimum var. minutissimum, Campylodiscus noricus var. noricus, Cymbella delicatula, Martyana martyi, Navicula farta, Pseudostaurosira brevistriata, Staurosira construens f. construens, Staurosirella pinnata var. pinnata.

The ecological and geographical structure of the DC is shown in Fig. 5, and the dynamics is shown in the diagram (Fig. 6).Five diatom zones (DIZ) are distinguished.

DZ 5 (257-205 cm; the upper boundary of the zone dates from about 11500 BP). The dominant assemblage is represented by the planktonic Cyclotella ocellata, characteristic of the littoral plankton of oligotrophic, relatively shallow reservoirs; C. bodanica , a stenothermic species inhabiting the pelagial of deep lakes; and Staurosirella pinnata, a fouling species often found in the plankton of reservoirs. There are three phases of DC development in the zone. In phase 5c (257-250 cm; 9.2 - 13.1 million stv/g; 31-48 taxa), C. ocellata is the absolute dominant. In phase 5b (250-235 cm; 3.1 -

* Hereafter, all dates are calibrated.

5. Ecological and geographical groups of diatoms for Lake Baikal deposits. Khoton-Nur (Khoton-2). A - according to the availability of biotopes: 1-planktonic, 2 - fouling, 3-benthic; B-relative to water salinity: 4-indifferent, 5-halophobic, 6-halophilic, 7-mesohalobic, 8-species with unclear ecology; C-relative to active water reaction: 9-indifferent, 10-acidophilic, 11-alkaliphilic, 12 - alkalibiont, 13 - species with unclear ecology; D - by main types of range: 14 - arctoalpine, 15 - boreal, 16 - cosmopolitan, 17 - other.

Fig. 6. Diagram of changes in the species composition of diatoms for Lake Baikal deposits. Khoton-Nur (Khoton-2).

7.5 million stv / g; 32-40 taxa), C. bodanica takes the first position, followed by S. pinnata, and C. ocellata takes the third place. At a depth of 235 cm, the leading position in the recreation center belongs to S. pinnata. Phase 5a (235-250 cm; 4.5 - 22 million stv/g; 58 taxa) is again dominated by C. ocellata, and C. bodanica and S. pinnata alternately occupy the second and third positions.

DZ 4 (205-175 cm; ∼11500-10700 bp; 69 Ma) stv/g at a depth of 185 cm and 9 million stv / g in the upper part of the DZ; 39-58 taxa). It is characterized by instability of all DC characteristics. The dominant group of diatoms is characterized by the greatest variability. The dominant species in most samples is S. pinnata, the co-dominant species is C. bodanica. Occupied by

At the first position on the lower boundary of the zone, C. ocellata gradually becomes a co-dominant, and then completely falls out of the dominant group. A characteristic feature of the DC of this zone is the introduction of the planktonic species Aulacoseira italica, which is widespread in continental mesotrophic and eutrophic reservoirs,into the dominants. Starting from DZ 4, there is a slight but noticeable increase in the acidophilic group of algae (see Fig. 4), associated with an increase in the content of A. distans residues, which becomes a subdominant.

DZ 3 (175-70 cm; ∼10700-6600 BP). Two phases are distinguished here. In phase 3b (175.0 - 130.5 cm; ∼10700 - 9150 bp; 60-81 Ma/g), the dominant complex is dominated by the pelagic species C. bodanica, the co-dominant of which is S. pinnata. In phase 3a (130.5-70.0 cm; ∼6600-9150 bp; 28-70 million stv/g), C dominates. ocellata, shifting C. bodanica to the position of co-dominant. Only in samples from a depth of 75-80 cm does the latter again occupy a leading position.

DZ 2 (70-50 cm; ∼6600-5500 bp; 69-91 million stv. / y). It is characterized by the predominance of the planktonic species Aulacoseira italica var. italica and its ecological form A. italica var. tenuissima, which inhabits relatively shallow mesotrophic and eutrophic lakes [Diatoms..., 1992]. C. ocellata and C. bodanica are co-dominant in this zone.

DZ 1 (50-0 cm; ∼5500-0 bp; 23-73 Ma stv. / d). The dominant complex is dominated by the planktonic species Aulacoseira distans. The dominant group also includes A. italica, C. ocellata, and C. bodanica. A distinctive feature of the zone is an increase in the content of acidophilic algae leaves up to 62% (at a depth of 5 cm), which indicates a significant acidification of the lake waters (see Fig.

Interpretation of results

Climate of the Mongolian Altai in the Holocene. The lower part of the Khoton-2 sediment column can be attributed to the end of the Pleistocene epoch (ca. 11500 BC). The end of the Pleistocene and the beginning of the Holocene in the Mongolian Altai were characterized by a continental cold and dry climate. Continentality became even stronger (the climate became drier, but not warmer) between ∼11500 and ∼10700 AD. Its weakening, accompanied by the development of forest vegetation, began after ∼10700 AD and lasted throughout the Middle Holocene. The wettest climatic conditions were recorded between 9300 and 6500 years ago. Approximately 8000 years ago, a slight cold snap was recorded. Aridity and continentality gradually began to increase after ~6500 AD. This trend has continued to the present day.

History of the development of the lake. Khoton-Nur in the Holocene.

The results of the analysis of diatoms and partially NPS can be used to reconstruct the history of Lake Baikal development. Khoton-Nur. In the early Holocene (∼11500 BC), the lake level was the highest and the water was the coldest for the entire reconstructed period. The transition from the cold and oligotrophic stage to the shallower and mesotrophic one occurred in the 11500 - ca. 10700 BP interval. The diatom complex of the transition to the Middle Holocene period can be characterized as typical of deep-water oligotrophic and cold high-mountain lakes (excluding a short drop in the lake level between ∼10000 and ∼9800 BP). The high level of the lake and oligotrophic conditions persisted until ~6600 BP, and then the level began to gradually decrease and was the lowest, apparently, in the interval 6600-5500 BP. The appearance, and then the constant presence in the deposits of Khoton-2 of the remains of the jaws of chironomids (inhabitants of the deep-water zone) later than 9000 BP indicate that that, despite the progressive decrease in the level, the lake remained quite deep.

The late Holocene diatom complex corresponds to the cold phase of the lake's development. At the same time, significant acidification of water was observed, which may be due to leaching of the main cations from the soils of catchment areas. This process can be caused by climate change, disruption of the catchment regime as a result of fires and wind erosion, strong anthropogenic impact, and transformation of the catchment's soil and vegetation cover (Battarbee et al., 2001). A significant reduction in coniferous forest areas and the sedimentation of most of the catchment area in the late Holocene led to the leaching of the main cations of the humus horizons of soils and their removal into the lake.

Vegetation history of the Mongolian Altai in the Holocene. At the end of the Pleistocene - beginning of the Holocene, cryophytic steppes and cryoxerophytic groups dominated by sedges and cobresies were developed in the highlands of the Mongolian Altai, while dry mixed grass and grass steppes with elements of desolate ones were developed in the middle belts. In the early Holocene (∼11500 - ca. 10700 BP), the composition of the vegetation cover did not change significantly, although an increase in the proportion of ephedra pollen in the spore-pollen spectra may indicate a wider distribution of desert-steppe communities at this time.

Since about 10700 BC, tundra communities with dwarf birch began to replace cryophytic steppes and sedge cryoxerophytic groups in the highlands of the Mongolian Altai. At the same time, in the vicinity of the lake. Khoton-Nur began to spread woody vegetation (mainly forests with Sibir spruce).-

and Siberian larch). One of the reliable proofs of the existence of the forest is the presence of coniferous stomata in the bottom sediments of the lake. They indicate the local growth of conifers (regardless of the level of pollen concentration of these trees in the spectra). [Sweeney, 2004] within a 20 m radius of the sample collection site [Parshall, 1999]. This circumstance is extremely important for reconstructing the existence of larch forests in the vicinity of the lake, because despite the fact that Siberian larch is the most widespread coniferous species in the Mongolian Altai (Volkova, 1994; Vegetation dynamics..., 1999), its pollen is usually not numerous in the Paleo spectra and has poor preservation (Pisaric et al., 2001], which significantly reduces the value of paleogeographic constructions.

The period of maximum development of the dark coniferous taiga in the Mongolian Altai is reconstructed between 9300 and 6500 years ago. Around 8000 years AGO, glacial tundras began to spread more widely in the highlands. The reduction of forest-occupied areas in parallel with the spread of desert-steppe and steppe communities occurred approximately between 6500 and 5000 BC. Later, about 5000 AD, this process continued. Tundra, steppe and desert-steppe elements began to play a significant role in the composition of the vegetation cover.

The period from 3000 BC to the present is characterized by the progressive disappearance of forests and widespread distribution of grass steppes, cryoxerophytic communities dominated by sedge and cobresia, high-mountain tundras with dwarf birch and willow, as well as desert-steppe communities with sagebrush and haze. Coniferous forests apparently remained only on the western macroslope of the Mongolian Altai and along the river valleys.

Changes in the composition of spores, pollen, and NPP obtained from the Khoton-2 bottom sediment column do not indicate any significant human impact on the natural environment in the region. Eggs of tardigrades (genus Macrobiotus) that are constantly present in the spectra after ~ 8000 BP indicate the existence of uncontaminated ecotopes (Jankovska, 1991). Chlamydospores of the fungus genus Glomus, which are an indicator of soil erosion in the lake basin, including as a result of human activity [Van Geel et al., 2003], occur exceptionally rarely in the sediment column. Only diatom analysis shows a sharp increase in the concentration of planktonic acidophilic alga Aulacoseira distans in the range of 2900-approx. 1200 bp. Aulacoseira species require an increased silica content in water, while not being competitive, so their widespread distribution is usually confined to periods with low concentrations of other diatoms [Wolfe et al., 2000]. The existence of such conditions may be associated with a cooling climate or increased anthropogenic load (Battarbee et al., 2001). The transition to nomadic cattle breeding was almost completely completed among the tribes inhabiting the Mongolian Altai between 3000 and about 2000 AD (Novgorodova, 1989; Jacobson, 2001). The first millennium BC was characterized by population growth in Mongolia (Novgorodova, 1989). Thus, the increased anthropogenic load could be one of the reasons for changes in the natural environment in the lake basin. Khoton-Nur.

Discussion of the results

The arid and cold climate that led to the development of cryophytic steppes in the Mongolian Altai in the early Holocene is also being reconstructed in neighboring regions. Dry and desolate steppes at the end of the Pleistocene were common in intermountain basins in Northwestern Mongolia (Lake Baikal). Achit-Nur); even in the basins and highlands of Khangai and Khentei (Central Mongolia), forest and tundra communities were replaced by dry steppes during this period (Vegetation dynamics..., 1999).

North of the Mongolian Altai, the cold and dry climate at the beginning of the Holocene was reconstructed for the Russian Altai and Tuva (Blyakharchuk et al., 2004, 2007, 2008; Westover et al., 2006; Ilyashuk B., Ilyashuk E., 2007). In the south-eastern part of the Russian Altai and Tuva, alpine meadows shrank and sagebrush steppes with ephedra in combination with glacial tundra expanded. The central part of the Russian Altai, which is now covered with forest, was completely occupied by treeless tundra, which was in direct contact with the highlands. In Northern Kazakhstan, the end of the Pleistocene and the beginning of the Holocene were characterized by the spread of sagebrush-haze communities and birch spikes (Tarasov, Jolly, and Kaplan, 1997).

The period of maximum climate humidity and expansion of forest vegetation (9300-approx. 6500 BP) is also recorded in regional schemes of natural environment development in Central Mongolia. Even in the present-day zone of desolate steppes in the northwestern regions, forest areas with Siberian larch and Siberian pine were developed in the Middle Holocene (Dorofeyuk and Tarasov, 2000; Vegetation dynamics..., 1999).

In the Russian Altai, the forest belt was formed between 9,000 and ~ 6,000 years ago. Steppe communities remained only in intermountain basins and on the slopes of the southern exposure (Blyakharchuk et al., 2004). Maximum development of dark coniferous taiga up to-

Around 7500-6500 BP, Siberian spruce and Siberian fir completely disappeared, and the vegetation cover of the territory was dominated by forests dominated by Siberian pine and Siberian larch. Tuva also recorded the development of coniferous forests with Siberian pine, scots pine, Siberian larch, Siberian fir, and Siberian spruce in the Early and Middle Holocene (Blyakharchuk et al., 2008). In Northern Kazakhstan, the climate in the Middle Holocene also tended to warm and moisten : steppe communities grew in combination with birch forests (8600-about 8000 BP), and scots pine appeared in the vicinity of the Irtysh River about 7300 BP (Kremenetski, Tarasov, and Cherkinsky, 1997; Tarasov, Jolly, and Kaplan, 1997)..

In Northwestern China, the transition from dry continental to more humid conditions in the Middle Holocene was also reconstructed (Rhodes et al., 1996; Wunnemann et al., 2006). In the Dzungarian Gobi (Manas Lake, Xinjiang), the warmest and wettest climate was 8300-6800 BP, when desert vegetation gave way to sagebrush steppes (Rhodes et al., 1996). In Inner Mongolia, the Middle Holocene was characterized by humidification of the climate and the spread of woody vegetation between 9200 and 6500 BP (Jiang et al., 2006). A cold snap was recorded here after 8000 AD. We noted a synchronous event for the Mongolian Altai. In the most arid region of Central Asia, the Tibetan Plateau, humidification and a decrease in climate continentality, dated to 10800-4400 BP, were manifested in the development of temperate steppes and subalpine shrubs (Herzschuh et al., 2006).

The continental climate in the Mongolian Altai began to increase around 6000-4900 AD. The area occupied by forest vegetation was reduced due to the development of dry steppes. Similar events took place in the Russian Altai and Tuva after 6500 AD.The climate became colder and more continental. The Russian Altai was covered with forests of Siberian pine, and cryophytic mixed grass and sagebrush steppes were developed in the intermountain basins [Blyakharchuk et al., 2004, 2007, 2008; Ilyashuk B., Ilyashuk E., 2007].

In Northwestern China (the Dzungarian Gobi), climate aridization began between 6800 and 5100 BP (Rhodes et al., 1996). On the territory of Inner Mongolia, the tendency to increase the continental climate, accompanied by a significant reduction in the range of deciduous species and the development of coniferous forests, was manifested between 6500 and 5100 BP (Jiang et al., 2006).

Over the past 3,000 years, the Mongolian Altai has continued to experience climate continentalization and forest decline. At the same time, the remains of coniferous wood found in a small basin of the Gobi Altai (Bayan-Sayr, 45°34'20" N; 96°54'36" E) and dated to 5000 - 3000 BP (Dinesman, Kiseleva, Knyazev, 1989) indicate that the coniferous forest areas are located in the southern part of the Altai territory. forests in the late Holocene existed in suitable ecotopes much further south than their present distribution. The latest dates obtained from these materials for fir and spruce are 3829 ± 159 and 4229 ± 330 BP, respectively. Larch wood remains found in the Gobi Altai (Uert-Am, 45°37 ' 48 "N, 96°49' 48 " E) are dated to 2171 ± 119 L. N. The absence of this breed here at present may be due to increased economic activity.

Cooling and decreasing humidity of the climate in the south-east of the Russian Altai and in Tuva have been recorded for the last 4,000 years. Cold winters have led to the development of permafrost, the spread of high-altitude tundra and cryophytic steppes. Over the last 3000 years, the reduction in the area of forest vegetation in Tuva may have been due to increased pasture load [Blyakharchuk et al., 2004, 2007, 2008]. In Inner Mongolia, the late Holocene (after 2600 BP) was also characterized by an increase in climate aridity and the development of steppe communities (Jiang et al., 2006).

Thus, reconstruction of the natural environment of the Mongolian Altai in the Holocene based on the results of spore-pollen and diatom analyses of Lake Baikal sediments. Khoton-Nur is in good agreement with the regional patterns of vegetation and climate change in Northwestern and Central Mongolia, the mountains of Southern Siberia, and Northern and Northwestern China. Increased pasture load, tree felling, and natural forest decline due to changing climatic conditions may have caused significant changes in the natural environment of the Mongolian Altai in the late Holocene.

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The article was submitted to the Editorial Board on 04.05.08.

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