Holocene vegetation and climate of the Alashan Plateau, NW China, reconstructed from pollen data

Transcription

1 Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) Holocene vegetation and climate of the Alashan Plateau, NW China, reconstructed from pollen data Ulrike Herzschuh a, *, Pavel Tarasov b, Bernd Wünnemann c, Kai Hartmann c a Institute of Geological Sciences, Branch Palaeontology, Freie Universität Berlin, Malteserstrasse , Berlin, Germany b Alfred-Wegener-Institute for Polar and Marine Research, Telegrafenberg A43, Potsdam, Germany c Institute of Geographic Sciences, Branch Physical Geography, Freie Universität Berlin, Malteserstrasse , Berlin, Germany Received 5 November 2003; received in revised form 12 March 2004; accepted 6 April 2004 Abstract A set of 55 recent pollen spectra from the Alashan Plateau and the Qilian Mountains (Qilianshan), northwestern China has been analyzed. The established relationships between the pollen spectra and modern vegetation and precipitation patterns of the studied area have been applied to 65 fossil pollen spectra from a 825 cm long sediment record collected in the topographic depression formerly occupied by Eastern Juyan palaeolake (41.89jN; jE; 892 m a.s.l.). Several qualitative approaches (e.g. indicator plant species; Artemisia/Chenopodiaceae and Ephedra fragilis-type s.l./ephedra distachya-type pollen ratios) and quantitative methods of vegetation and climate reconstruction have been tested with the surface pollen and then applied to the Eastern Juyan pollen record. Fossil pollen data reveal pronounced environmental changes in the studied area of the Alashan Plateau between ca. 10,700 and 1700 cal. yr B.P. Desert taxa, as Chenopodiaceae, Nitraria, Calligonum, Reaumuria were abundant in the vegetation cover around the study site through the whole record. Pollen spectra dated to ca. 10, cal. yr B.P. are characterised by highest values of Chenopodiaceae, E. fragilis-type and other desert indicating taxa, suggesting rather dry climate. Most favourable conditions are reconstructed between 5400 and 3900 cal. year B.P. on the basis of relative increase in abundance of Artemisia pollen. A return to dry conditions occurred at about 3900 cal. yr B.P. The lake finally desiccated after 1700 cal. yr B.P. Reconstructed dry climate oscillations between 5900 and 5400 and 3100 cal. yr B.P. correlate well with similar events found in the published records from northern and western China and central Mongolia. However, Eastern Juyan record does not show the early Holocene humidity maximum, as suggested by the sedimentary data from monsoon-influenced areas of China. D 2004 Elsevier B.V. All rights reserved. Keywords: Holocene vegetation and climate; Recent and fossil pollen spectra; China; Alashan Gobi; Eastern Juyan palaeolake 1. Introduction * Corresponding author. Department of Geological Science, Branch Palaeontology, Freie Universität Berlin, Malteserstrasse , Berlin, Germany. Tel.: ; fax: address: herzschu@hotmail.com (U. Herzschuh). The main difficulties in applying pollen spectra for palaeoecological and palaeoclimatic reconstruction arise from their interpretation. The most common problems frequently discussed in palynological studies (e.g. Moore et al., 1991; Prentice, 1985; Pardoe, 2001) can be summarised as follows: (a) complicated processes which influence composition of an individual pollen spectrum (e.g. pollen transport, re-deposition, pollen source area); (b) unequal representation of different plant taxa in pollen spectra; and (c) difficulties in identification of pollen and /$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi: /j.palaeo

2 2 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 1 17 spores at high taxonomic (e.g. species or genus) level. In arid environments the number of identified pollen taxa is limited and good climate indicator taxa are rare. These make an objective climate reconstruction very difficult. Different pollen ratios have been set up to extract semi-quantitative palaeoclimatic information from the pollen records collected in the arid regions. The well known Artemisia/Chenopodiaceae ratio (A/C) was suggested by El-Moslimany (1990) in the Middle East to distinguish shifts from steppe-like vegetation to desert-like environments and to reconstruct changes in moisture conditions. The same approach was later applied to the pollen spectra from central Asia (Liu et al., 1999; Cour et al., 1999; Van Campo, 1996). Prentice et al. (1996) suggested an objective way to assign fossil pollen spectra to one of the major vegetation types ( biomes ) through an attribution of terrestrial pollen taxa to a limited number of ecologically and climatically defined groups of plants ( plant functional types ). Pollen-based vegetation reconstruction use the same biome classification scheme as climate-based BIOME1 vegetation model (Prentice et al., 1992), facilitating data-model comparison procedure. Being tested with the extensive surface pollen data sets from the Near East, central Asia (Tarasov et al., 1998a; 1998b) and China (Yu et al., 1998) the method of biomization demonstrated a capability to distinguish steppe and desert biomes with high accuracy, which is important for the interpretation of pollen spectra from the arid regions. Since the works of Overpeck et al. (1985) and Guiot (1990) the best modern analogues (BMA) method is considered to be a powerful approach to extract quantitative climatic information from pollen data. Recently the BMA method has been applied to the late Quaternary pollen records from northern (Andreev et al., 2003) and eastern Asia (Nakagawa et al., 2002, 2003), suggesting its high potential for temperature and precipitation reconstructions. The Holocene climate and vegetation history of the arid zone in central Asia is still poorly investigated and the number of high-resolution records is limited. The earlier works (e.g. Lister et al., 1991; Rhodes et al., 1996; Zhou et al., 2001; An et al., 2000) brought up contradictory ideas about Holocene climate evolution and the driving forces causing reconstructed changes. Different time periods are suggested for the Holocene climatic optimum in the northern part of China. An et al. (2000) reconstruct the most favourable (wettest) conditions in this area in the early Holocene (between and 7000 cal. yr B.P.) and explain it by the gradual retreat and weakening of summer monsoon activity in China during the Holocene from NW to SE in response to the orbital forcing. Zhou et al. (2001, 2002) suggest that the maximum monsoon activity in the study region occurred during the mid-holocene (ca cal. yr B.P.). The aims this paper are to present the first pollen record from the Alashan Plateau covering the major part of the Holocene ( cal. yr B.P.); to test different qualitative and quantitative approaches suggested for the vegetation and climate reconstruction in the arid environments, against a representative set of surface modern pollen spectra from the region; and to apply the reconstruction methods to the detailed and adequately dated pollen record from Eastern Juyan palaeolake. 2. Study area The study area lies between the Tibetan Plateau and the Gobi Desert and includes the Chinese part of the Alashan Gobi with elevations of m a.s.l. and the northern macro-slope of the Qilian Mountains, which exceed 6000 m (Fig. 1). The area is situated outside the direct influence of the Asian summer monsoon and Westerlies and the present-day climate is extremely dry and continental. Annual precipitation values do not exceed 40 mm in some parts of the Alashan Plateau (Meteorological Bureau, Gansu Province, 1982). The eastern part of Qilian Mountains receives up to 480 mm precipitation per year (Fig. 1; Domrös and Peng, 1988). Most of the precipitation falls in summer. The Eastern Juyan palaeolake formerly occupied a depression situated at the outer edge of a large inland delta of the Hei River (Fig. 1), and separated from the river by a small ridge striking along the meridian. Detailed geomorphological investigations using remote sensing techniques (Wünnemann and Hartmann, 2002; Hartmann, 2003) helped to identify in the

3 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) Fig. 1. Study area of the Qilian Mountains and the Alashan Plateau in northwestern China. Black dots indicate locations of the pollen surface sample sites and the coring site is shown by an arrow. Numbers indicate annual sum of precipitation in mm (Meteorological Bureau, Gansu Province, 1982). depression several well preserved Holocene shorelines indicating lake level changes. Hartmann (2003) suggested that the lake level fluctuations of Eastern Juyan palaeolake were mainly controlled by the atmospheric precipitation and water supply from the nearby Gobi Altai, which makes this site a very promising object for palaeoclimatic studies. The early and middle Holocene history of the human occupation of the region is poorly known. During the Han Dynasty (202 BC 220 AD) agricultural settlements occurred in the Hexi (Gansu) Corridor in the places suitable for irrigation and along the rivers (Chen et al., 1999). However, until the Tang Dynasty ( AD) the area was sparsely populated. No traces of human activities, which influenced the hydrological regime of the palaeolake have been found in the Eastern Juyan depression so far. Modern vegetation of the Alashan Plateau and the foothills of the Qilian Mountains is dominated by semi-desert and desert plant communities, mainly consisting of shrubs and dwarf shrubs. Kürschner (in press) used a phytosociological (or Braun-Blanquet) approach (Mueller-Dombois and Ellenberg, 1974) to classify the present-day vegetation in the region into five zonal (1 5) and four azonal (6 9) community types described as follows.

4 4 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) Shrub semi-deserts and montane dwarf-shrub communities (1) Sympegma regelii Kalidium cuspidatum community grows at the foothills of the Qilian Mountains; (2) Asterothamnus centrali-asiaticus Gymnocarpos przewalskii Arnebia fimbriata community occupies large sandy-gravelly sayrs ( m) of the eastern part of the Beishan north of Jinta Semi-desert and desert communities (3) Calligonum mongolicum Haloxylon ammodendron community dominates on sands, sandy-gravelly sayrs, small dunes and areas where aeolian sands are mixed with alluvial deposits; (4) Nitraia sphaerocarpa Artemisia tschernieviana community is widely distributed on the stony soils, rock and gravel deserts, sandy gravelly alluvial plains and terraces of the Alashan Plateau; (5) Ammopiptanthus mongolica community is restricted to sandy-gravelly sayrs and run-off gullies. Other taxa commonly presented in the communities 2 5 are Reaumuria soogorica, Zygophyllum xanthoxylon and Ephedra przewalskii Riparian forests, woodland and shrubbery (6) Sophora alopecuroides Populus euphratica community is typical for the Hei River banks and former river beds; (7) Tamarix ramosissima community dominates the Hei River oases. The ruderal invaders, e.g. Lycium ruthenicum, Peganum harmala and Sophora alopecuroides are also common Halophytic community and marshes (8) Halerpestes cymbalaria Crypsis aculeata community is found on moist inundated sandy-clayey river sites along the Hei River; (9) Phragmites australis community is typical in the salty desert depressions with a high ground water table. The vegetation patterns of the Qilian Mountains are described (Chen et al., 1994; Wang et al., 2002) as follows. Below 2600 m a natural temperate steppe with Achnatherum splendens and Stipa species exists but is only fragmentary due to intensive agriculture. Remnants of the former forest belt consisting of Picea wilsoni, P. crassifolia, Pinus tabulaeformis and Betula platyphylla are poorly preserved between 3200 and 2600 m. Scrubs (mainly Potentilla fructicosa and Caragana jubata) are common between 3800 and 3200 m. Above 3800 m an alpine Kobresia-meadow gradually turns into a subnival vegetation and bare rock. 3. Material and methods 3.1. Sampling and dating methods A total of 55 pollen surface samples have been collected from moss cushion or soil surface (Table 1). Each sample consists of at least five sub-samples following Adam and Mehringer (1975). Vegetation observed at each sampling site has been described in the field (Table 1). Detailed vegetation descriptions are given in Herzschuh et al. (2003) and Kürschner (in press). The 825 cm long sedimentary record (41.89jN; jE; 892 m a.s.l.) consisting of lacustrine and aeolian sediment layers (Fig. 2) was obtained by digging (upper 400 cm) and coring with the use of a Livingstone corer (Wright, 1980). Five AMS datings on bulk organic material performed in the radiocarbon laboratory of Kiel University were used to construct age-depth model (Hartmann et al., 2003). Our model is based on the assumption, that at the coring site the sedimentation rate was stable during the lacustrine phases. A Sedimentation rate of 0.72 mm/year estimated in the lacustrine layer between the AMS-dated levels at 253 and 414 cm was applied to determine the age of the other lacustrine units (Fig. 2). The interpolation method was used to estimate the ages of the reconstructed pollen events Pollen analysis Pollen samples were processed in the laboratory following Faegri and Iversen (1989). In addition to the usual treatment heavy liquid separation has been applied to the surface pollen samples. In total 55 recent and 65 fossil pollen samples have been microscopically analysed. At least 400 pollen grains have been counted in each sample, except for a few fossil samples with extremely low pollen concentration ( < 5000 grains/cm 3 ).

5 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) Table 1 Location, observed vegetation type (classification of nos.1 19 after Hou, 2001 and nos after Kürschner, in press), modern biomes simulated from climate data and reconstructed from surface pollen data; A/C and Ef/Ed ratios calculated for each recent pollen spectrum from the Alashan Plateau and Qilian Mountains No. Latitude Longitude Elevation Observed vegetation Biome reconstruction from A/C Ef/Ed jn je (m a.s.l.) Climate data Pollen data alpine sparse tundra steppe vegetation tundra steppe Kobresia spp. steppe steppe Meadow steppe steppe tundra steppe Potentilla steppe steppe fructicosa steppe steppe scrub steppe steppe steppe steppe steppe steppe steppe steppe tundra steppe steppe steppe steppe steppe Picea crassifolia steppe steppe forest patch steppe steppe Betula platyphylla steppe steppe forest patch steppe steppe Stipa bungeana steppe steppe steppe Sympegma regelii- semi-desert desert Kalidium cuspidatum desert desert community desert desert Asterothamnus desert desert centrali-asiaticus desert desert Gymnocarpus desert desert przewalskii desert desert community desert desert desert desert Calligonum desert desert mongolicum desert desert Haloxylon desert desert ammodendron desert desert community desert desert desert desert desert desert desert desert Nitraria desert desert sphaerocarpa desert desert Artemisia desert desert tschernieviana desert desert community desert desert desert desert (continued on next page)

6 6 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 1 17 Table 1 (continued) No. Latitude Longitude Elevation Observed vegetation Biome reconstruction from A/C Ef/Ed jn je (m a.s.l.) Climate data pollen data desert desert desert desert Ammopiptanthus mongol. com. desert desert Sophora desert desert alopecuroides Populus. Euphratica community desert oasis Tamarix ramosissima desert oasis community desert oasis desert oasis desert oasis Halerpestes cymbalaria desert desert Crypsis aculeata desert oasis community desert oasis Phragmites australis community desert desert Our pollen identification is based on the published pollen keys (Moore et al., 1991; Wang et al., 1995; Wan andwei,1999;zhangandzhou,1998)andonanextensive type-slide collection of more than 600 plant species from the study region. Ephedra species are attributed to the E. distachya-type and Ephedra fragilis-type s. l. (Welten, 1957;Lang,1994)onthebasisofthetypeslidesandregional publications(wangetal.,1995). The total sum of arboreal and non-arboreal taxa identified in each pollen spectrum is taken as 100% for the calculation of the pollen percentages. The local pollen zone boundaries in the Eastern Juyan pollen diagram were defined by visual inspection Interpretation methods Traditional interpretation of pollen records is usually based on the presence and abundance of the indicator taxa and on the various pollen ratios. In Europe taxa indicators are successfully used for the vegetation and climate reconstruction (e.g. Birks and Birks, 1980). However, the use of this approach in the arid regions is limited by the poor pollen identification and the lack of good indicator species. In the present study we spent much effort in order to refine the identification of the indicator pollen taxa. The following desert indicating pollen taxa suggested by the modern vegetation studies in the region (Kürschner, in press) have been indentified: Nitraria (mainly N. sphaerocarpa and N. tangutorum); Calligonum (mainly C. mongolicum) and Reaumuria (R. soongorica). The A/C ratio (El-Moslimany, 1990) has been applied to the pollen spectra from arid regions, particularly in central Asia (e.g. Van Campo, 1996; Demske and Mischke, 2003) in order to distinguish steppe from desert and to reconstruct changes in the local precipitation. The main assumption of this approach is that higher Chenopodiaceae percentages in the pollen spectra point to a greater participation of desert plants in the vegetation and to a more pronounced aridity, while steppe-like less arid environments are characterised by a high content of Artemisia pollen. Yu et al. (1998) and Cour et al. (1999) reported that Chinese desert areas yield A/C values below 0.5. Artemisia and Chenopodiaceae are very abundant in the study region both in the vegetation cover and in the recent pollen spectra, providing a possibility to test potential of the A/C ratio for the reconstruction of palaeoenvironments. Ephedra is another taxon which traditionally used to distinguish steppe and desert pollen spectra. By pollen

7 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) Fig. 2. Lithology and radiocarbon chronology of the Eastern Juyan palaeolake record (41.89jN; jE; 892 m a.s.l.). analysis at least two pollen types can be distinguished: E. distachya-type (Ed) and E. fragilis-type (Ef) s.l. (Welten, 1957). Prentice et al. (1996) attributed Ephedra to the desert biome on the basis of the regional geobotanical studies and the fact that Ephedra species are abundant under the arid conditions, when a (ratio of actual to potential evapotranspiration) is below 0.2. Tarasov et al. (1998b) found that among the Ephedra species, E. fragilis-type s.l. is often distinguished in the pollen spectra from arid climates with mean temperature of the warmest month above 22 jc. In the study region the following Ephedra species have been described (Liu, 1985): E. przewalskii, E. intermedia, E. rhyditosperma, E. sinica, E. equisetina, E. media. Among them E. przewalskii is the only species belonging to the E. fragilis-type s.l. This species is thought to be a characteristic of desert vegetation, while the others mainly grow in the semi-desert. High values of E. fragilis-type s.l. in the Ef /Ed ratio are supposed to indicate comparatively dry conditions. Fowell et al. (2003) suggested an aridity pollen index to distinguish dry steppe from moist meadow steppe and forest steppe vegetation in north-central Mongolia. They assumed that Artemisia and Chenopodiaceae characterise dry environments, whereas Cyperaceae and Poaceae are more abundant under comparatively moist conditions. This assumption matches the results of vegetation analysis by Hilbig (1995), who reported a decrease in species number and abundance of Poaceae in the vegetation with increasing aridity. The vegetation analyses from the Alashan Plateau (Kürschner, in press) demonstrate that Poaceae and Cyperaceae species in extreme arid climate conditions are more abundant in the azonal vegetation communities. Thus, the calculation of the proposed aridity index for the fossil pollen spectra from the Alashan Plateau likely not provide information about zonal vegetation. Changes in arboreal pollen percentages and arboreal/non-arboreal pollen ratio are often used for the palaeoclimatic interpretation of the pollen records from the forest-steppe and steppe environments, where increase in AP likely corresponds to the onset of wetter conditions. Tarasov et al. (1998a) tested this statement with extensive surface pollen data set from northern Eurasia. Surface pollen spectra collected in the extra-arid environments (e.g. Karakum desert of western Turkmenistan) experience relatively high percentages of long-distant transported tree pollen, mainly of Betula and Pinus. This feature is a consequence of the sparse or no vegetation cover at the sampling sites and very low pollen production of the local plants. Following Tarasov et al. (1998a) we assume that AP/NAP pollen ratio is not an appropriate method to infer moisture signal from the Eastern Juyan pollen record. Qualitative interpretation of the pollen records can be checked with a quantitative method of pollen-based biome reconstruction (Prentice et al., 1996). The method is based on the objective assignment of pollen taxa to plant functional types (PFT) and to main vegetation types (biomes) on the basis of the known ecology and biogeography of modern plants. The

8 8 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 1 17 Table 2 Assignments of pollen taxa to PFTs used in the biomization procedure Code Plant functional type Pollen taxa included aa arctic/alpine shrub Betula, Gentiana, Polygonum aviculare-type, Polygonum bistorta-type, Rumex, Salix, Saxifragaceae bec boreal evergreen conifer Picea sf steppe forb/shrub Apiaceae, Asteroidae (Asteraceae), Chichorioidae (Asteraceae), Brassicaceae, Caryophyllaceae, Hippophaë, Fabaceae, Lamiaceae, Liliaceae, Papaveraceae, Plantaginaceae, Plumbaginaceae, Polygonum aviculare-type, Polygonum bistorta-type, Rumex, Ranunculaceae, Ranuculus-type, Caltha, Thalictrum, Potentilla, Rosaceae, Cannabis sf/ df steppe/desert forb/shrub Artemisia, Chenopodiaceae, bs boreal summergreen Betula, Populus, Salix trees/shrubs ts temperate summergreen Betula, Salix trees/shrubs s sedge Cyperaceae op oasis+ riparian trees/shrubs Elaeagnus, Populus, Lycium, Cannabis, Peganum cdf cold desert forb/shrub Ephedra distachya-type wdf warm desert forb/shrub Ephedra fragilis-type h heath Ericales ec eurythermic conifer Pinus Diploxylon-type cbc cold boreal conifer Pinus Haploxylon-type btc boreal-temperate crops Cerealia g grass Poaceae df desert forb/ shrub Athraphaxis, Calligonum, Nitraria, Reaumuria, Tamaricaceae, Tribulus, Zygophyllum wte2 warm temperate Tamarix sclerophyll shrub ts1 cool temperate summergreen trees Ulmus All identified terrestrial pollen taxa are used in the biome scores calculation. However taxa which abundance is less 0.5% (Acer, Alnus, Boraginaceae, Sambucus, Juniperus, Fagus, Quercus, Tsuga, Aconitum, Koenigia, Galium, Rubiaceae, Urtica) do not influence the results of biomization and thus are not shown in the table. equation to calculate the affinity scores for all pollen samples was published by Prentice et al. (1996): A ik ¼ X j d ij qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi fmax½0; ðp jk h j ÞŠg; where A ik is the affinity of pollen sample k for biome i; summation is over all taxa j; d ij is the entry in the biome versus taxon matrix for biome i and taxon j; p jk are the pollen percentages, and h j is the universal threshold pollen percentage of 0.5% suggested for minimisation of possible noise mainly due to longdistant transport or re-deposition of exotic pollen grains (Prentice et al., 1996). The biome with the highest score or, when several biomes have the same score, the one defined by a smaller number of taxa was then assigned to the given pollen spectrum. Pollen taxa from the former Soviet Union and Mongolia were assigned to the regional PFTs and to biomes by Tarasov et al. (1998a,b, 2000a,b) and data from China were first presented in Yu et al. (1998). Both studies use very similar assumptions. However the taxa-pft-biome matrix used in the biomization procedure by Tarasov et al. (1998a,b, 2000a,b) contains more taxa found in our records from the Alashan Plateau and the Qilian Mountains, and has been accepted as a basis for the present study. Oasis vegetation is an important vegetation type in the desert areas Africa and Asia, including the northern part of China (Zohary, 1973; Kürschner, in press). Under the natural conditions oases are mainly characterized by riparian trees and shrubs, grasses and mesophylous plants, which makes the vegetation different from the surrounding desert vegetation. In our surface pollen data set «oasis spectra» are repre- Table 3 Assigments of PFTs to biomes Biome Code Plant functional types Tundra TUND aa, bs, s, h, g Cold decidous forest CLDE aa, bs, h, ec, cbc Taiga TAIG aa, bs, h, bec, ec, cbc Cold mixed forest CLMX aa, bs, h, ec, ts1 Cool conifer forest COCO aa, bs, h, bec, ec, cbc, ts1 Temperate decidous forest TEDE ts, aa, bs, h, ec, ts1 Cool mixed forest COMX aa, bs, h, bec, ec, cbc, ts1 Desert DESE sf/df, cdf, wdf, df Oasis OASI sf/df, op, btc, g, wte2, ts1 Steppe STEP sf/df, sf, g, wte2

9 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) Fig. 3. Pollen percentage diagram of modern pollen samples from the Alashan Plateau and the Qilian mountains.

10 10 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 1 17 sented by 10 samples (No in Table 1). The earlier works dealing with the reconstruction of natural zonal vegetation from Mongolian and Chinese pollen data did not reconstruct oasis vegetation. In the present study we included a new biome called oasis that enables us to reconstruct the extension of this vegetation type in the study area. The final assignment of pollen taxa from the region to the main vegetation types discussed in the present study is shown in Tables 2 and 3. The sum of 61 terrestrial pollen taxa identified in the surface and fossil pollen records has been taken as 100%. Among them 12 taxa do not exceed abundance of 0.5%. The biomization method has been first tested with 55 surface pollen spectra and then applied to the fossil pollen spectra. The best modern analogue (BMA) method (Guiot, 1990) uses chord distances to determine the similarity between each analyzed pollen spectrum and each spectrum in the reference pollen data set of 55 modern pollen spectra (Table 1 and Fig. 3). Minimum, maximum and mean values of annual precipitation were reconstructed from the eight best modern analogues determined for each fossil sample. All identified terrestrial pollen taxa (excluding aquatic pollen and spores) were used in the reconstruction. Fossil pollen spectra from the Eastern Juyan core are well represented in the assemblages from the reference data set: all fossil taxa (above 0.5%) occur in the modern pollen samples. Modern precipitation values ( P ann ) for each of the modern pollen sampling sites were calculated from an updated version of the climate database of Leemans and Cramer (1991) with precise topography (W. Cramer, personal communication, 2001). PPPBase software (Guiot and Goeury, 1996) facilitated the calculations. 4. Results and interpretation 4.1. Modern pollen spectra Pollen spectra from semi-desert and desert communities (the Alashan Plateau and the foothills of the Qilian Mountains) mainly consist of Chenopodiaceae, Artemisia, Ephedra fragilis-type s.l., Nitraria, Calligonum and Reaumuria (Fig. 3). All taxa are abundant in the vegetation at and around sampling sites. Pollen spectra from the Chenopodiaceae-rich communities and the Calligonum mongolicum Haloxylon ammodendron community show high values of Chenopodiaceae pollen, while Artemisia and Ephedra fragilistype s.l. pollen are abundant in the spectra from Nitraria sphaerocarpa Artemisia tschernieviana community and Asterothamnus centrali-asiaticus Gymnocarpus przewalskii community. The pollen of Nitraria, Calligonum and Reaumuria in the modern pollen spectra are mainly produced by N. sphaerocarpa, C. mongolicum and R. soongorica-typical desert taxa growing in the area. Pollen spectra from oasis vegetation communities (Fig. 3) contain as expected high values of Populus (riparian woodland) and other riparian trees/ shrubs (mainly Tamarix). Some ruderal taxa (e.g. Lycium, Peganum) (Fig. 3) are common in the pollen spectra from the oasis sites. Besides the mentioned indicator-taxa other desert elements (e.g. Artemisia and Chenopodiaceae) reach high abundances in the oasis pollen spectra. Within the surface samples from the Alashan Plateau percentages of Poaceae and Cyperaceae pollen are comparatively high in the oasis spectra. The pollen sample collected from the Stipa bungeana-dominated steppe association contains high percentages of Poaceae pollen and pollen of various steppe and alpine herbs and shrubs (e.g. Brassicaceae and Apiaceae). Highest percentages of Betula, Pinus and Picea pollen are observed in the modern spectra from the forest steppe localities (Fig. 3) in the Qilian Mountains. In the spectra from the mountain shrublands Rosaceae pollen (mainly Potentilla) are abundant and spectra from the alpine meadows show high frequencies for Cyperaceae (Fig. 3). The content of the modern pollen spectra from forest-steppe, steppe and alpine localities in the Qilian Mountains is dominated by Pinus, Picea, Betula, Rosaceae and Cyperaceae pollen, and differs substantially from the desert and oasis spectra of the Alashan Plateau. However, Artemisia pollen reach high frequencies in the spectra from both regions. Results of the pollen analysis (Fig. 3) demonstrate that the modern spectra reflect well observed vegetation at the surface pollen sampling sites (Table 1), suggesting that regional pollen data can be used for the reconstruction of the vegetation. Qualitative vegetation descriptions and interpretations of the modern pollen spectra are very close to the results of the

11 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) quantitative pollen-based biome reconstruction (Table 1). Modern biomes were simulated from the modern climate data (Leemans and Cramer, 1991) using BIOME1 vegetation model (Prentice et al., 1992). The results agree with the results of pollen-based biome reconstruction and with observed vegetation at most of the sampling sites (Table 1). The fact that the model simulates desert at all oasis sites is reasonable, because of the intrazonal character of the oasis vegetation and climatic conditions similar to the surrounding desert. The A/C and Ef/Ed pollen ratios were calculated for each analysed surface spectrum (Table 1). Obtained values were directly compared with the local vegetation and precipitation sums at the sampling sites in order to evaluate significance of the selected ratios for the palaeoenvironmental interpretation of the fossil pollen spectra from the region. The correlation (r) between precipitation and Ef/Ed and A/C values is rather weak: 0.34 and 0.39, respectively, preventing us from using the ratios for the quantitative climate reconstruction. However, modern spectra from desert sites in 67% of cases (one sigma) have A/C ratios below 1 and Ef/Ed ratios above 10, while the spectra from the sites with more favourable climate (e.g. forest-steppe, steppe and alpine meadows) in 67% of cases have A/C ratios above 2.3 and Ef/Ed ratios below 5. These results suggest that both ratios can be applied to the Eastern Juyan fossil pollen record as a qualitative indicators of the past vegetation and moisture conditions Fossil pollen spectra The pollen diagram for Eastern Juyan pollen record was zoned by visual inspection (Fig. 4) into three local pollen zones (PZ). The basal pollen zone (PZ 1: cm) is notable for its generally very low pollen concentration. Its spectra are characterised by highest percentages of Chenopodiaceae, Ephedra fragilis-type s.l., Nitraria, Calligonum and Reaumuria, suggesting arid desert environments around the coring site. The upper part of PZ 1 experiences relatively high values of Betula and Pinus pollen. Taking into account very low pollen concentration and highest percentages of desert-indicator taxa we interpret such increase in AP as a consequence of the low pollen production of the local plants due to pronounced aridity, and not as an evidence of the climate amelioration and occurrence of trees close to the coring site. In the pollen zone 2 (PZ 2: cm) Artemisia pollen percentages increase and percentages of desert taxa (Chenopodiaceae, Ephedra fragilis-type s.l., Nitraria, Calligonum and Reaumuria) decrease in comparison to PZ 1, suggesting amelioration of the climate. The uppermost pollen zone (PZ 3: cm) is characterized by increase of Chenopodiaceae, Nitraria, Calligonum and Reaumuria pollen percentages. Thus pollen spectra become similar to these of PZ 1. However, low values of E. fragilis-type s.l. and slightly higher pollen concentration suggest that conditions likely were less arid then during formation of PZ 1. Results of the biome reconstruction (Fig. 5) support qualitative interpretation of the pollen diagram (Fig. 4). Taxa attributed to the desert were better represented in the vegetation during the first half of the Holocene (ca. 10, cal. yr B.P.). Calculated numerical scores of desert biome exceed 16 and scores of steppe biome vary between 13 and 15. The mid-holocene interval (ca cal. yr B.P.) is characterized by co-dominance of desert and steppe taxa in the vegetation, which might be interpreted as occurrence of semi-desert environments. The scores of both desert and steppe biomes vary between 14 and 16. Desert taxa expanded again ca cal. yr B.P. The scores of desert biome are distinctly higher than the scores of steppe biome at that time. However, the distances between the score values are smaller than during the first half of the Holocene, suggesting slightly wetter climate conditions during the late Holocene. The scores of oasis biome in the fossil pollen spectra vary between 13 and 15, but never exceed values of steppe and desert. This would suggest that distribution of the intrazonal vegetation associations around the lake was rather stable and that changes in the biome scores inferred from Eastern Juyan record primarily reflect regional changes in the vegetation, caused by the climate change. Qualitative palaeoclimatic interpretation of the fossil pollen spectra can be extended by using indicator species and pollen ratios (Fig. 5). Relatively high frequencies of the desert indicator species (Nitraria, Calligonum, Reaumuria) and the values of A/C>3 and Ef/Ed < 3 suggest that the area around the study site experienced rather dry climate conditions during for-

12 12 Fig. 4. Pollen percentage diagram of the Eastern Juyan palaeolake record (41.89jN; jE; 892 m a.s.l.). Magnification by 10 is used to emphasize the changes in the percentages of the less abundant taxa. U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 1 17

13 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) Fig. 5. Climate and vegetation reconstruction of the Eastern Juyan palaeo-lake record (41.89jN; jE; 892 m a.s.l.). mation of the PZ 1 (ca cal. yr B.P.) and PZ 3 (ca cal. yr B.P.). Wetter conditions likely occurred ca cal. yr B.P. Outside this interval phases with relatively wetter conditions are reconstructed: around 9100, ca , ca , ca cal. yr B.P. and around 1700 cal. yr B.P. (Fig. 5). Quantitative precipitation reconstruction using the BMA method suggests generally dry conditions with P ann between 50 and 100 mm during the first half of Holocene (Fig. 5). The reconstruction reveals four wetter oscillations. However, each of them is represented by only one pollen sample, consisting with the unstable climate and hydrological regime of the palaeolake at that time. The reconstructed values of P ann for the middle Holocene phase ( cal. yr B.P.) are mostly between 80 and 180 mm/year, except for a dry phase occurred ca cal. yr B.P. Despite larger uncertainties precipitation values suggested by the BMA reconstruction are distinctly higher during the wetter phases, than during the dry phases of the early and late Holocene. 5. Discussion and conclusion The pollen data from Eastern Juyan palaeolake is the first Holocene pollen record with reasonably good resolution and dating control from the vast desert areas of northern China and southern Mongolia. The previously reported records from this region either represent a short time interval (Mischke et al., 2002) or have poor resolution (Wünnemann et al., 1998). In the section below, we compare our results with the other available records from the study region and from adjacent areas. Changes in the water level of Eastern Juyan palaeolake have been inferred from sedimentological and geochemical data of the same core (Hartmann, 2003). Results of this reconstruction suggest that during the early Holocene the water regime in the lake was very unstable. At that time lacustrine sedimentation at the cored site was several times interrupted by short-term dry phases, characterised by the accumulation of aeolian sand (Fig. 2). A long phase with relatively stable water conditions and lacustrine sedimentation is

14 14 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 1 17 reconstructed from ca to 3200 cal. yr B.P. After that time the water regime became again less stable, as suggested by the presence of aeolian interbeds in the upper part of the sediment core. These reconstruction results fit well to our interpretation of the fossil pollen records, suggesting that changes in the lake level were more or less synchronous to the reconstructed changes in vegetation around the lake. Consequently, climate can be suggested as the most probable cause for the reconstructed changes in both the lacustrine and terrestrial environments. Palaeonvironmental reconstructions derived from the Eastern Juyan records (Hartmann, 2003, this study) suggest that dry conditions with desert vegetation and low lake levels prevailed in the area during the first half of the Holocene (ca cal. yr B.P.). These results are in a broad agreement with the early Holocene dry phase reconstructed from pollen, diatom and lithology records from northern-central Mongolia (e.g. Gunin et al., 1999; Tarasov et al., 2000a,b). By contrast, several reconstructions based on sedimentary data from adjacent regions of northern China point towards much wetter conditions during the early Holocene. The length and occurrence of the humid phase vary significantly from site to site e.g cal. yr B.P. Tengger desert (Wünnemann et al., 1998); cal. yr B.P. Ordos Plateau (Chen et al., 2003); cal. yr B.P. Qinghai Lake (Lister et al., 1991). The Dunde Ice core pollen record collected in the Qilian Mountains several hundred kilometres south-west of the Eastern Juyan site suggest favourable climate condition between and 4800 cal. yr B.P. (Liu et al., 1998), but it has a poor time resolution during this period. Inconsistency in the appearance of the humid phase can partly be explained by poor sample resolution and an inadequate dating quality of different records. However, such a simple explanation can not solve the problem of asynchronous climatic changes in the whole region. The dry phase between 5900 and 5400 cal. yr B.P., is suggested in our record by high Calligonum frequencies, low A/C ratios and high desert biome scores. Similar event has been reconstructed from lithology and ostracod records at another site on the Alashan Plateau (Mischke et al., 2002) and in the Tengger desert (Zhang et al., 2000). At the same time very dry conditions were reconstructed from the sedimentary records collected from the lakes from Ordos Plateau (Chen et al., 2003), Zunggar Basin (Rhodes et al., 1996), south-west Tibet (Gasse et al., 1996), Bosten Lake, Tarim Basin (Wünnemann et al., 2003), Terkhiin-Tsagan-Nur and Telmen Lake, central Mongolia (Tarasov et al., 1996; Fowell et al., 2003), Hubsugul Lake, northern Mongolia and Aral Sea (Tarasov et al., 1996). The dry episode reconstructed at large area of central Asia between ca and 5400 cal. yr B.P. might represent a supra-regional climate signal. The most humid phase, suggested by lacustrine sedimentation, reconstructed high annual precipitation values and the expansion of semi-desert or dry steppe vegetation around Eastern Juyan Lake, is dated to ca cal. yr B.P. This corresponds well with the reconstruction of high levels of the terminal palaeolake in the Hei River basin (Wünnemann et al., 1998; Mischke et al., 2002). The occurrence of wetter climate, suggested by the reconstruction of high lake levels and relatively dense vegetation cover, is also reported for the Tengger Desert (Zhang et al., 2000; Yu et al., 2001). Eastern Juyan records suggest that climate became drier and less stable after 3900 cal. yr B.P than during the mid-holocene wet interval. A short-term dry episode occurred between 3200 and 3000 cal. yr B.P. It is characterised by sand accumulation, decreased annual precipitation (less than 100 mm/year) and expansion of typical desert plants, as indicated by high desert plant pollen frequencies and high desert biome scores. The dry phase was followed by a comparatively wet period. These rapid climate fluctuations are in phase with reported lake level changes from the Alashan Plateau (Wünnemann et al., 1998; Mischke et al., 2002) and with the climatic implications derived from the Dunde Ice core oxygen isotope record (Yao and Thompson, 1992). Disappearance of the lake after ca cal. yr B.P. indicates increased aridity of the regional climate towards present-day conditions. Pollen and sedimentary records from Telmen Lake (48j50VN, 97j20VE, 1789 m) in Central Mongolia (Fowell et al., 2003) suggest that in the lake basin the interval cal. yr B.P. was characterised by relatively moist conditions. The wet phase was interrupted by the arid excursion dated to about 2000 cal.

15 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) yr BP. Furthermore, the arid interval is reconstructed between ca and 1200 cal. yr BP, consistent with our records. Furthermore, the radiocarbon date from the peat layer deposited in the eastern part of the Aral Sea points to a very deep regression of the lake around the 4th 5th century AD (Tarasov et al., 1996), suggesting that climate change towards aridity was not only a local feature reconstructed at the Alashan Plateau. Our records from the Eastern Juyan palaeolake suggest that during the Holocene most favourable conditions occurred after ca cal. yr B.P. and not during the first half of the Holocene, as reconstructed at several sites from adjacent areas of Northwest China. On the other hand, very dry early Holocene and wet mid-holocene conditions have been derived from sedimentary records located in central and northern Mongolia (Tarasov et al., 1996; Fowell et al., 2003), consistent with our results. The fact that the Holocene records from the Alashan Plateau reveal more similarity with the records from the Middle Asia and Mongolia than with the areas located more to the south needs more careful investigation. Until today environmental changes in China were mainly explained by the climate changes associated with the south and south-east Asian monsoon circulation (e.g. Winkler and Wang, 1993; An et al., 2000). Zhang et al. (2003) presented a 2326-year tree-ring record from Northwest China and pointed out possible relationships between the North Atlantic and climate variability on the north-eastern Qinghai Tibetan Plateau. This study together with our paper suggests that other mechanisms, which are capable of explaining climate and environmental changes in the northern part of central Asia should be sought with the help of the climate modelling. The results of the environmental reconstructions from the Eastern Juyan pollen records suggest that relatively small changes in precipitation might cause drastic changes in the local environments (e.g. appearance and desiccation of the lake; spread and retreat of desert plant communities). Recently, the Chinese government has paid much attention to the problem of desertification. However, the environmental changes in the deserts of northern China and the underlying mechanisms of these changes are still poorly understood. The lack of data is a major impediment to our efforts in increasing spatial resolution of palaeoenvironmental reconstructions for this remote, but climatically sensitive region. Acknowledgements The research project was supported by Deutsche Forschungsgemeinschaft (DFG). U. Herzschuh is grateful to Deutscher Akademischer Austauschdienst and Studienstiftung des Deutschen Volkes for Graduate Fellowships. The work of P. Tarasov is supported by the Alexander von Humboldt Foundation. We would like to thank H. Kürschner for supporting the surface sample studies, Jin Ming for the assistance in the field, F. Gasse for the critical comments and K.E. Barber for language correction and helpful remarks, which made substantial improvement of the final text. The complete pollen data can be obtained from the corresponding author upon request. References Adam, D.P., Mehringer, P.J., Modern pollen surface samples an analysis of subsamples. Journal Research, USA Geological Survey 3, An, Z., Porter, S.C., Kutzbach, J.E., Wu, X., Wang, S., Liu, X., Li, X., Zhou, W., Asynchronous Holocene optimum of the East Asian monsoon. Quaternary Science Reviews 19, Andreev, A.A., Tarasov, P.E., Siegert, C., Ebel, T., Klimanov, V.A., Melles, M., Bobrov, A., Dereviagin, A.Y., Lubinski, D., Hubberten, H.-W., Late Pleistocene vegetation and climate on the northern Taymyr Peninsula, Arctic Russia. Boreas 32, Birks, H.J.B., Birks, H.H., Quaternary Palaeoecology. Edward Arnold, London. Chen, G., Peng, M., Huang, R., Lu, X., Vegetation characteristics and its distribution of Qilian Mountain Region. Acta Botanica Sinica 36, Chen, F., Shi, Q., Wang, J., Environmental change documented by sedimentation of Lake Yiema in arid China since the Late Glaciation. Journal of Paleolimnology 22, Chen, C.-T.A., Lan, H.-C., Lou, J.-Y., Chen, Y.-C., The dry Holocene Megathermal in Inner Mongolia. Palaeogeography, Palaeoclimatology, Palaeoecology 193, Cour, P., Zheng, Z., Duzer, D., Calleja, M., Yao, Z., Vegetational and climatic significance of modern pollen rain in northwestern Tibet. Review of Palaeobotany and Palynology 104, Demske, D., Mischke, S., Palynological investigation of a

16 16 U. Herzschuh et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 211 (2004) 1 17 Holocene profile section from the Palaeo-Gaxun-Nur-Basin. Chinese Science Bulletin 48, Domrös, M., Peng, G., The climate of China Springer. Berlin. El-Moslimany, A.P., Ecological significance of common nonarboreal pollen: examples from drylands of the Middle East. Review of Palaeobotany and Palynology 64, Faegri, K., Iversen, J., Textbook of Pollen Analysis, 4th ed. Wiley, Chichester. Fowell, S.J.B., Hansen, C.S., Peck, J.A., Khosbayar, P., Ganbold, E., Mid to late Holocene climate evolution of the Lake Telmen Basin, North Central Mongolia, based on palynological data. Quaternary Research 59, Gasse, F., Fontes, J.C., Van Campo, E., Wei, K., Holocene environmental changes in Bangong Co basin (Western Tibet) 4. Discussion and conclusions. Palaeogeography, Palaeoclimatology, Palaeoecology 120, Guiot, J., Methodology of the last climatic cycle reconstruction from pollen data. Palaeogeography, Palaeoclimatology, Palaeoecology 80, Guiot, J., Goeury, C., PPPBASE, a software for statistical analysis of paleoecological and paleoclimatological data. Dendrochronologia 14, Gunin, P.D., Vostokova, E.A., Dorofeyuk, N.I., Tarasov, P.E., Black, C.C. (Eds.), Vegetation dynamics of Mongolia. Geobotany, vol. 26. Kluwer Academic Publishing, Dordrecht. 238 pp. Hartmann, K., Spätpleistozäne und Holozäne Morphodynamik im nördlichen Gaxun Nur Becken, Innere Mongolei, NW China, unter besonderer Berücksichtigung des Juanze-Paläosees. Unpublished PhD Theses. Hartmann, K., Wuennemann, B., Röper, H.-P., Herzschuh, U., The Holocene evolution of Juyan Lake, Inner Mongolia, China. Berliner Paläobiologische Abhandlungen 2, Herzschuh, U., Kürschner, H., Ma, Y., The surface pollen and relative pollen production of the desert vegetation of the Alashan Plateau, western Inner Mongolia. Chinese Science Bulletin 48, Hilbig, W., The Vegetation of Mongolia. SPB Academic Publishing, Amsterdam. Hou, H. (Ed.), Vegetation atlas of China. Science Press China, Beijing. Kürschner, H., Phytosociological studies in the Alashan Gobi a contribution to the flora and vegetation of Inner Mongolia (NW China). Phytocoenologia (in press). Lang, G., Quartäre Vegetationsgeschichte Europas. Fischer, Jena. Leemans, R., Cramer, W.P., The IIASA database for mean monthly values of temperature, precipitation and cloudiness of a global terrestrial grid. Research Report. International Institute for Applied Systems Analyses, Laxenburg, Austria. RR-91-18, November Lister, G.S., Kelts, K., Zao, C., Yu, J., Niessen, F., Lake Qinghai, China: closed-basin lake levels and the oxygen isotope record for ostracoda since the latest Pleistocene. Palaeogeography, Palaeoclimatology, Palaeoecology 84, Liu, Y. (Ed.), Flora in Desertis Reipublicae Populorum Sinarum: Tomus 1. Science Press, Beijing. Liu, K., Yao, Z., Thompson, L.G., A pollen record of Holocene climatic changes from the Dunde ice cap, Qinghai-Tibetan Plateau. Geology 26, Liu, H., Cui, H., Pott, R., Speier, M., The surface pollen of the woodland-steppe ecotone in southeastern Inner Mongolia, China. Review of Palaeobotany and Palynology 105, Meteorological Bureau, Gansu Province, Climate Data from Gansu Province (in chin.). Mischke, S., Fuchs, D., Riedel, F., Schudack, M.E., Mid to Late Holocene palaeoenvironment of Lake Eastern Juyanze (north-western China) based on ostracods and stable isotopes. Geobios 35, Moore, P.D., Webb, J.A., Collinson, M.E., Pollen Analysis, 2nd ed. Blackwell, Oxford. Mueller-Dombois, D.H., Ellenberg, H., Aims and Methods of Vegetation Ecology. Wiley, New York. Nakagawa, T., Tarasov, P., Kotoba, N., Gotanda, K., Yasuda, Y., Quantitative pollen-based climate reconstruction in Japan: application to surface and late Quaternary spectra. Quaternary Science Reviews 21, Nakagawa, T., Kitagawa, H., Yasuda, Y., Tarasov, P.E., Kotoba, N., Gotanda, K., Sawai, Y., Asynchronous climate changes in the North Atlantic and Japan during the Last Termination. Science 299 (5607), Overpeck, J.T., Webb, T., Prentice, I.C., Quantitative interpretation of fossil pollen spectra: dissimilarity coefficients and the method of modern analogs. Quaternary Research 23, Pardoe, H.S., The representation of taxa in surface pollen spectra on alpine and sub-alpine glacier forelands in southern Norway. Review of Palaeobotany and Palynology 117, Prentice, I.C., Pollen representation, source area and basin size: toward a unified theory of pollen analysis. Grana 23, Prentice, I., Cramer, W., Harrison, S.P., Leemans, R., Monserud, R.A., Solomon, A.M., A global biome model based on plant physiology and dominance, soil properties and climate. Journal of Biogeography 19, Prentice, I.C., Guiot, J., Huntley, B., Jolly, D., Cheddadi, R., Reconstructing biomes from palaecological data: a general method and its application to European pollen data at 0 and 6 ka. Climate Dynamics 12, Rhodes, T.E., Gasse, F., Lin, R., Fontes, J.-C., Wei, K., Bertrand, P., Gibert, E., Mélières, F., Tucholka, P., Wang, Z., Cheng, Z., A Late Pleistocene-Holocene lacustrine record from Lake Manas, Zunggar (northern Xinjiang, western China). Palaeogeography, Palaeoclimatology, Palaeoecology 120, Tarasov, P.E., Pushenko, M., Harrison, S.P., Saarse, L., Andreev, A.A., Aleshinskaya, Z.V., Davydova, N.N., Dorofeyuk, N.I., Efremov, Y.V., Elina, G.A., Elovicheva, Y.K., Filimonova, L.V., Gunova, V.S., Khomutova, V.I., Kvavadze, E.V., Neustreuva, I.Yu., Pisareva, V.V., Sevastyanov, D.V., Shelekhova, T.S., Subetto, D.A., Uspenskaya, O.N., Zernitskaya, V.P., Lake status records from the former Soviet Union and Mongolia: Documentation of the Second Version of the Database. NOAA Paleoclimatology Publications Series Report, Boulder, CO, vol. 5, 224 pp.