Alashan Plateau Research Articles

Paleo-Atmospheric Precipitation Recharged to Groundwater in Middle-Latitude Deserts of Northern China

It is a difficult and hot issue in the hydrological studies of arid areas to choose suitable methods to evaluate the recharge of atmospheric precipitation to groundwater and its response to climate change in desert areas. This study reviews the theories and problems of vadose (unsaturated)-zone tracing methods selected by predecessors in hydrological studies and takes the deserts in middle latitudes of northern China as an example to extract decadal, centennial, and millennian information of atmospheric precipitation to groundwater recharge on a regional scale since the late Holocene. The fluctuations of atmospheric precipitation and chronological sequences of desert unsaturated zone were estimated by using the chlorine mass balance (CMB) theory. It indicates that the Badain Jaran Desert in the central Alashan Plateau and the surrounding Gobi deserts have experienced fluctuations of groundwater recharge on a centennial scale during the late Holocene period from about 700 to 2000 years ago. Multiple CMB profile records can identify four periods of relative wetness (1330–1430, 1500–1620, 1700–1780, and 1950–1990) and three periods of relative drought (1430–1500, 1620–1700, and 1900–1950) over the past millennium. These records are consistent with other paleoclimatic records in the northern margin of the Qinghai-Tibet Plateau, and relatively correspond to those in the eastern part of China. This indicates that groundwater recharge in the Alashan Plateau broadly reflects the degree of climatic variability in northwest China over the centennial scale and may be affected by the changes in the intensity of the East Asian summer monsoon. The estimated average recharge rate of precipitation in the Alashan Plateau in the last millennium is about 1.3~2.6 mm/a, which brings new geological evidence for understanding the source of groundwater recharge in the region but is quite different from other environmental records. It should be noted that there are uncertainties in the CMB records of the vadose zone profiles, mainly due to the assumption of atmospheric Cl input in the CMB estimation and the selection of the homogeneous vadose profile (piston flow). This study suggests that this uncertainty and its error should be extensively tested in the future by comparing deterministic data (such as regional reference stations) with large-scale random atmospheric Cl input backgrounds.

Desertification and Related Climate Change in the Alashan Plateau since the Last 40 ka of the Last Glacial Period

Clues of climate change on the Alashan Plateau since the last glacial period (40 ka) are important for revealing the mechanism of desertification of middle-latitude deserts in the Northern Hemisphere (NH). Studies are still rare for the understanding of the specific relationship of climate changes between the Alashan Plateau and the global. Based on a systematic and comparative analysis of the existing research in China and the international academic community, this paper reviews the environmental evolution history of the Alashan Plateau since the last glacial period from the records of paleo-environment and geomorphological characteristics in different deserts of the plateau (e.g., Badanjilin, Tenggeli, and Wulanbuhe). From about 40 ka to the end of the last glacial maximum, the climate on the plateau was wetter than it is today, and to the end of the Pleistocene, the climate was generally dry and the aeolian activities were enhanced. However, the climate was arid during the whole last glacial period in the Wulanbuhe Desert, evidently different from the overall pattern of the plateau. The Tenggeli Desert was characterized by an arid climate in the early Holocene. The most controversial events for the Alashan Plateau are the drought events in the middle Holocene in the Badanjilin Desert. The role and impact of the westerlies and the East Asian Summer Monsoon (EASM) systems on the climate change of the desert and even the whole plateau is a vexed question that brings different views in different periods. There is still a lack of definite evidence representing the events of global environmental change that occurred on the plateau during the discussed period. The distinctive morphology of dune mountains and the distribution of sand dunes are mutually indicative of the direction and energy of wind systems on the plateau. It is suggested that appropriate wind energy is the significant key to the desertification in these middle-latitude deserts on the plateau. From a global-scale review of climate change, the desertification of the modern-scale sandy desert landscapes on the Alashan Plateau is generally related to the global glacial period and the cold and dry climate during the past 40 ka.

Insights into the age and genesis of the clay dunes in the Suhongtu Basin, Alashan Plateau, China

Clay dunes are characterized by high content of silt and clay and they are both a unique aeolian landform and an important paleoenvironmental archive attesting to changing climatic and hydrological conditions. Although clay dunes have been identified on several continents, they have attracted relatively little research attention. Numerous clay dunes are developed in the Suhongtu (SHT) Basin, Alashan Plateau, China. However, their genesis, age, and process of evolution are unknown. In this study we measured the grain size of various clay dune samples using dynamic image analysis (DIA) and laser diffraction analysis (LDA). Comparison of the results obtained by the two methods revealed significant differences between them: the grain size of clay dune samples obtained by DIA have a unimodal distribution (with a mode at ~200–400 μm), and the grain-size composition is dominated by medium sand; while the results obtained using LDA show a bimodal distribution (with modes at ~4 and 200–400 μm), and the grain-size composition consists mainly of clay and silt. This indicates that the clay dunes in the SHT Basin are formed by wind transport and accumulation in the form of the mixing of sand-sized aggregates of clay-silt with quartz sand grains. The morphology, mobility, and sedimentary structures of the clay dunes in the SHT Basin differ substantially from those of the well-studied clay dunes in Australia and North America, which can be mainly attributed to the relatively low clay content, abundant sand source and extremely arid conditions. During field investigations we studied seven stratigraphic sections, comprising multiple aeolian clay dune and lacustrine units, with age control provided by optically stimulated luminescence (OSL) and AMS 14C dating. Lacustrine sediments in the basal parts of sections yielded OSL age between 7.84 ± 0.71 ka and 6.33 ± 0.84 ka, suggesting that the SHT Basin was occupied by a lake during 7.8–6.3 ka when the precipitation was relatively high and the climate was humid. The oldest clay dune deposit, with an AMS 14C age of 1.27 cal kyr B.P, probably represents the onset of the modern clay dune landscape in the SHT Basin. Most of the clay dune deposits yielded OSL ages between 0.50 ± 0.04 ka and 0.18 ± 0.05 ka, indicating aeolian reactivation in the past ~500 years.

Arid–humid variations in the summer climate and their influence mechanism in Asian monsoon margin of Northwest China during 1960–2010: A case study in the Alashan Plateau

AbstractIn the Asian monsoon margin of Northwest China, the impact factors for variations in the aridity and humidity of the summer climate are complex and unclear. In this study, we selected the Alashan Plateau, located in the mid‐latitude arid zone and the Asian monsoon margin of Northwest China, as the study area. Changes in the aridity indexK(a proxy for the arid–humid variations in the summer climate of the Alashan Plateau) were calculated for the period 1960–2010 using meteorological data. Relationships among the aridity indexK, changes in the intensity of atmospheric circulations, and local precipitation and evaporation in summer are discussed. The results indicated that the arid–humid variations in the summer climate in different regions of Alashan Plateau exhibit significant spatial differences. The summer climate became more humid during 1960–1968 and 1988–1995 and arid in 1996–2010 with different trends, but exhibited asynchronous changes during other periods. Hence, the arid–humid variations in the summer climate exhibited significant spatial differences in the Alashan Plateau. These variations were mainly affected by East Asian summer monsoon in the eastern Alashan Plateau, local precipitation and evaporation in the central and northwestern Alashan Plateau, and atmospheric circulations and evaporation in the southwestern Alashan Plateau. The increase in the monsoon precipitation is not the only factor that affected arid–humid variations in the summer climate over the entire Alashan Plateau, therefore, other non‐circulation factors, such as local precipitation and evaporation, should also be considered. The study provides new evidence on how to understand the mechanisms driving global and regional climate change.

Mammal inventory in the Mongolian Gobi, with the southeasternmost documented record of the Snow Leopard, Panthera uncia (Schreber, 1775), in the country

Studies on mammal diversity and distribution are an important source to develop conservation and management strategies. The area located in southern Mongolia, encompassing the Alashan Plateau Semi-Desert and the Eastern Gobi Desert-Steppe ecoregions, is considered strategic for the conservation of threatened species. We surveyed the non-volant mammals in the Small Gobi-A Strictly Protected Area (SPA) and its surroundings, by using camera trapping, live trapping, and occasional sightings. We recorded 18 mammal species belonging to 9 families and 6 orders. Among them, 4 are globally threatened or near-threatened, 2 are included in the CITES Appendix I, and 2 are listed in the Appendix II. Moreover, we provide the southeasternmost record for the Snow Leopard (Panthera uncia) in Mongolia, supported by photographic evidence. Our study highlights the importance of this protected area to preserve rare, threatened, and elusive species.

Origin and morphology of barchan and linear clay dunes in the Shuhongtu Basin, Alashan Plateau, China

Clay dunes are characterized by a relatively high content of silt and clay and are typically developed on the lee side margin of closed-basins in arid and semi-arid areas. Although they are widely distributed aeolian landforms on Earth, little is known about their development and distribution in Asia. Our field investigations have identified for the first time the occurrence of clay dunes in the Alashan Plateau, north China. The clay dunes occur in three isolated lowland areas of the Suhongtu (SHT) Basin and their morphologies (barchans, hooked barchans, asymmetrical barchans, and linear or seif dunes) differ substantially from those of the well-studied clay dunes in Australia, Africa and North America. These differences could be mainly attributed to the asymmetrical bimodal wind regime, prolonged drought and sediment physical properties, which indicate that dunes of any type can be formed in sand, silt or clay. Based on the known evolution of the SHT paleo-lake basin and regional climate change, we infer that the landscape of modern clay dunes in the desert of the Alashan Plateau does not predate MIS 5, and probably formed during the late Holocene. Analyses of grain-size distributions and the contents of trace and rare earth elements, combined with geomorphological characteristics, indicate that the source sediments of the clay dunes are mainly local Cretaceous-Tertiary and Quaternary red fluvial-lacustrine mudstone and sediments, while the ultimate source is the weathered and denuded products of granitoids of the East Altay Mountains. Comparison of the morphology and alignment of the clay dunes with the prevailing wind pattern tends to support Tsoar's (1984) model of the transition in dune shape from barchans to seif or linear dunes. During 2003–2013, the seif or linear dunes of the SHT Basin migrated laterally and elongated northeastward at rates of about 2–4 m/yr and 16–20 m/yr, respectively.

Radiocarbon dating of aquatic gastropod shells and its significance in reconstructing Quaternary environmental changes in the Alashan Plateau of northwestern China

Using landform evolution and lake sediment records to reconstruct Quaternary environmental changes requires reliable chronology. However, there is an ongoing debate regarding the fossil shells of aquatic gastropods in carbonate rock area to be used for radiocarbon dating. The focus of this debate is whether living gastropods incorporate the dead carbon, which would affect the accuracy of the dating results. Living aquatic gastropods were selected from habitats on carbonate terrain in arid region. In this study, 64 shell samples from living gastropods, including Cipangopaludina chinensis, Gyraulus convexiusculus, and Radix auricularia, collected from the Alashan Plateau of northwestern China, were dated by accelerator mass spectrometry (AMS) 14C dating. The results revealed that only five samples (~8%) from the same site contained no dead carbon. The other 59 samples (~92%) contained dead carbon in various amounts: ~59% samples contained 0–10% dead carbon, and ~33% samples contained more than 10% dead carbon. Of the samples, 56 were Radix auricularia and their 14C ages varied from present to 3253 cal yr BP. Two of the samples were Gyraulus convexiusculus samples dated at 379 and 290 cal yr BP which are highly consistent with 14C ages of Radix auricularia samples from the same site. The other six Cipangopaludina chinensis samples were dated at 407–863 cal yr BP. Thus, most of living aquatic gastropods from habitats on carbonate terrain contained dead carbon. The amount of dead carbon in the gastropod shells was nonselective among the three species. Radiocarbon dating of aquatic gastropod shells may not be useful for studying processes that occurred over multi-millennial timescales at different localities in areas of carbonate rock. It is difficult to establish high-resolution chronologies using 14C ages of gastropod shells in arid regions with carbonate rocks unless the limestone effect has been corrected.

Assessing the impact of desertification dynamics on regional ecosystem service value in North China from 1981 to 2010

Deserts and desertified land form an important ecosystem that supports the inhabitants of dry land areas, and desertification dynamics have a significant impact on the regional Ecosystem Service Value (ESV). In this paper, the desertification dynamics in North China from 1981 to 2010 and their impact on the regional ESV were analyzed by decomposing the processes of desertification. The results showed that the area and structure of deserts and desertified land had greatly changed, and the area of land that experienced desertification reversion was higher than expansion. Desertification reversion was the key process that promoted an increase in the total ESV of the whole research region; the increment of the ESV can be attributed to the reversal from deserts and desertified land to non-desertified lands reached 90.13 billion yuan. Desertification expansion from undegraded grassland to deserts and desertified land was the dominant process that produced a decreased in the regional ESV. Horqin grassland, Hetao plain, and Wumeng Qianshan and Tumote plain had a higher sensitivity than other sub-regions, and Alashan plateau had the lowest sensitivity among all of the sub-regions. To enhance economic development and the ecological services supply, “win–win” measures should be used for sub-regions with different sensitivities.

Holocene climate change inferred from grain‐size analysis in the eastern Alashan Plateau, Inner Mongolia, Northern China

A grain‐size analysis in Tonggunao sedimentary profile indicated that 6 arid and 6 wet episodes have been detected in the Holocene, reflecting millennium‐scale climate change. The study area is located in the eastern Alashan Plateau, with the Helan Mountains to the east and the Tengger Desert to the west. It has a vulnerable natural ecology that is sensitive to environmental and climatic changes. The rapid climatic changes revealed by the analysis may be representative of the global climate‐change pattern during the Holocene.

Circadian patterns of plasma leptin, insulin and glucose concentration in the toad-headed lizard Phrynocephalus versicolor

To understand the circadian rhythms of the glucose metabolism and related hormones in desert reptiles, we studied the daily changes in plasma leptin, insulin, and glucose in the toad-headed lizard, Phrynocephalus versicolor, in the semi-desert of the Alashan Plateau. Blood samples were obtained from groups of 20 lizards (about equal sex ratio for each group) at 4-h intervals throughout a 24-h period. Leptin, insulin, and glucose levels were determined using ELISA, RIA, and the glucose oxidase method, respectively. Ambient temperature and humidity were also measured when the blood samples were taken. We found that: (1) there was a significant difference in plasma leptin concentrations at different times of day; (2) no significant circadian rhythm could be measured for plasma insulin and glucose; (3) ambient temperature, humidity, and body condition had no significant effect on plasma leptin, insulin, and glucose levels; and (4) there were significant correlations between plasma glucose concentrations and leptin concentrations 8 h later, and between insulin concentrations and leptin concentration 8–12 h later. These results suggested that the secretions of leptin and insulin played an important role in glucose metabolism in reptiles in an arid environment.

Lead isotopes combined with a sequential extraction procedure for source apportionment in the dry deposition of Asian dust and non-Asian dust

Lead isotopic compositions were determined in leachates that were generated using sequential extractions of dry deposition samples of Asian dust (AD) and non-Asian dust (NAD) and Chinese desert soils, and used to apportion Pb sources. Results showed significant differences in 206Pb/207Pb and 206Pb/204Pb isotopic compositions in non-residual fractions between the dry deposition samples and the Chinese desert soils while 206Pb/207Pb and 206Pb/204Pb isotopic compositions in residual fraction of the dry deposition of AD and NAD were similar to the mean 206Pb/207Pb and 206Pb/204Pb in residual fraction of the Alashan Plateau soil. These results indicate that the geogenic materials of the dry deposition of AD and NAD were largely influenced by the Alashan Plateau soil, while the secondary sources of the dry deposition were different from those of the Chinese desert soils. In particular, the lead isotopic compositions in non-residual fractions of the dry deposition were homogenous, which implies that the non-residual four fractions (F1 to F4) shared the primary anthropogenic origin. 206Pb/207Pb values and the predominant wind directions in the study area suggested that airborne particulates of heavily industrialized Chinese cities were one of the main Pb sources. Source apportionment calculations showed that the average proportion of anthropogenic Pb in the dry deposition of AD and NAD was 87% and 95% respectively in total Pb extraction, 92% and 97% in non-residual fractions, 15% and 49% in residual fraction. Approximately 81% and 80% of the anthropogenic Pb was contributed by coal combustion in China in the dry deposition of AD and NAD respectively while the remainder was derived from industrial Pb contamination. The research result proposes that sequential extractions with Pb isotope analysis are a useful tool for the discrimination of anthropogenic and geogenic origins in highly contaminated AD and NAD.

Indication of millennial-scale moisture changes by the temporal distribution of Holocene calcareous root tubes in the deserts of the Alashan Plateau, Northwest China

Calcareous root tubes or rhizoliths have a strong potential for paleoenvironmental studies, especially in reconstructing paleoenvironmental conditions and paleovegetation. Previous studies suggested that the effectivity of the moisture level affects the formation of calcareous root tubes in the deserts of the Alashan Plateau, Northwest China. However, it remains unclear whether the temporal distribution of calcareous root tubes can be used to reconstruct paleo-effective moisture in this area. In this study, based on conventional 14C dating results of 34 Holocene calcareous root tube samples collected from the Badain Jaran Desert, the Tengger Desert and the Ulan Buh Desert in the Alashan Plateau of northwestern China, millennial-scale changes in paleo-effective moisture during the Holocene in this area were reconstructed. The frequency of the 14C dating results demonstrates that ~62% of the Holocene samples were dated to 7–5cal kyr BP, and ~38% of the Holocene samples were dated to 4–2cal kyr BP, indicating an arid period during the early Holocene (before 8.0cal kyr BP), a humid period during the mid-Holocene (8.0–5.0cal kyr BP) and a humid to arid period during the late Holocene (after 5.0cal kyr BP). The reconstruction results were consistent with other previous reconstruction results from lake sediments and aeolian sand–lacustrine sequences, which indicated that temporal distribution of calcareous root tubes can reflect millennial-scale changes in paleo-effective moisture in this area. However, a single sample could indicate local environmental changes that may differ from the overall desert environmental changes. Hence, the relatively humid environmental record obtained from the presence of calcareous root tubes is a local signal or a regional signal that should be noted.

Formation and environmental significance of late Quaternary calcareous root tubes in the deserts of the Alashan Plateau, northwest China

Calcareous root tubes are widely distributed across the Badain Jaran Desert and the Tengger Desert of the Alashan Plateau in northwest China. However, the reliability of their 14C dating results and their environmental significance remain unclear. In this study, the conventional 14C ages of 31 calcareous root tube samples and one aquatic mollusc shell sample, which were all collected from the Badain Jaran Desert and the Tengger Desert, were measured. The results reveal that nine of the 14 calcareous root tube samples from the Badain Jaran Desert were from Marine Isotope Stage (MIS) 3, while two samples were from MIS 2. The other three samples were dated to the mid-Holocene, one of which is consistent with the aquatic mollusc shell sample collected from the shoreline of Zhunzhahanjilin Lake in the Badain Jaran Desert. Moreover, the 17 calcareous root tube samples from the Tengger Desert were all dated to the mid- and late-Holocene, most of which were from the mid-Holocene. The results demonstrate that calcareous root tubes can be used as 14C dating materials and that the accuracy of their 14C dating depends on the time scale. The dating results were reliable at the millennial scale. However, the reliability of the ages from MIS 3a is lower than that of the Holocene ages, though the ages were reliable in tens of thousands years. Based on the statistical analysis, the overwhelming majority of calcareous root tubes collected from the deserts of the Alashan Plateau were formed during MIS 3a and the mid-Holocene. The concentrated emergence of calcareous root tubes in phases implies that they were formed during periods of relatively humid environments in desert areas, arid regions. Moreover, the results indicate that the effectivity of the moisture level probably affects the formation of calcareous root tubes, and the presence of calcareous root tubes indicates the occurrence of periods of relatively humid environments in the study area.

A New Species ofMongolotmethisfrom the Gobi Region of Mongolia (Orthoptera: Pamphagidae)

Abstract A new species of grasshopper (Orthoptera: Pamphagidae, subfamily Thrinchinae) from the western edge of the Alashan plateau semi-desert in Southern Mongolia is described. The morphological characters of Mongolotmethis michidi new species and some characters of Mongolotmethis gobiensis, the most closely related species, are described.

LANDSAT IMAGES REVEAL TRENDS IN THE AEOLIAN DESERTIFICATION IN A SOURCE AREA FOR SAND AND DUST STORMS IN CHINA'S ALASHAN PLATEAU (1975–2007)

ABSTRACTThe development and reversal of aeolian desertification have been widely recognised as the dominant causes of changes in the source areas of dust storms. The Alashan Plateau, which is near China's Hexi Corridor, is one of the major dust storm source regions in northern China. To investigate the relationship between climatic and anthropogenic factors and the development of aeolian desertification, we reconstructed the temporal and spatial evolution of aeolian desertification and the underlying processes from 1975 to 2007 using Landsat images and analysed the driving forces. The results show that aeolian desertified land in the study area covered 32 847·79 km2 in 2007, amounting to 11·3 per cent of the total area, with an initial period of desertification expansion from 1975 to 2000 and a reversal of desertification from 2000 to 2007. On the basis of the analysis of effects of climate changes and human activities in the region, aeolian desertification was principally driven by human activities in this area; climatic variations had little effect on the area of severe desertification. Copyright © 2011 John Wiley & Sons, Ltd.

Isotopic evidences for provenance of East Asian Dust

We have systematically collected samples in the possible source regions (the deserts and sandy lands of North China, northeastern past of the Tibetan Plateau, Chinese Loess Plateau and southern part of Mongolia) of the East Asian dust. Based on Nd–Sr isotopic ranges, the source regions can be divided into four isotopic regions: Region A1: the Gurbantunggut Desert in Junggar basin and Hunlun Buir sandy land in northeastern China; Region A2: the Hunshandake sandy land, Horqin sandy land and southern part of Mongolia; Region B: the Taklimakan Desert in Tarim basin, northeastern past of the Tibetan Plateau, Chinese Loess Plateau, Badain Jaran Desert and Tengger Desert in Alashan Plateau; Region C: the Hobq Desert and Mu Us Desert in the Ordos Plateau. Through comparison of Nd–Sr isotopes, it can be inferred that the sediments of the north-central Pacific and dust particles in the Greenland ice cores are mainly derived from Region B. Dusts of East Asian dust storm are derived mostly from Region B also, and less from Region A2. The materials of dust storm at Beijing area in April 2006, originated largely from the Hobq Desert and Mu Us Desert in the Ordos Plateau. The floating dust at Beijing area in April 2006, is the mixing of dust of distant deserts and local dust at Beijing area. Loess of the Chinese Loess Plateau may largely originate from Region B.

Partitioned Bayesian analyses, dispersal–vicariance analysis, and the biogeography of Chinese toad-headed lizards (Agamidae: Phrynocephalus): A re-evaluation

The toad-headed lizards of genus Phrynocephalus are distributed from northwestern China to Turkey and are one of the major components of the central Asian desert fauna. To date, published morphological and molecular phylogenetic hypotheses of Phrynocephalus are only partially congruent, and the relationships within the genus are still far from clear. We re-analyzed published mitochondrial gene sequence data (12S, 16S, cyt b, ND4-tRNALeu) by employing partition-specific modeling in a combined DNA analysis to clarify existing gaps in the phylogeny of Chinese Phrynocephalus. Using this phylogenetic framework, we inferred the genus’ historical biogeography by using weighted ancestral-area analysis and dispersal–vicariance analysis in combination with a Bayesian relaxed molecular-clock approach and paleogeographical data. The partitioned Bayesian analyses support the monophyly of Phrynocephalus and its sister-group relationship with Laudakia. An earlier finding demonstrating the monophyly of the viviparous group is corroborated. However, our hypothesis of internal relationships of the oviparous group differs from a previous hypothesis as our results do not support monophyly of the oviparous taxa. Instead, the viviparous taxa form a clade with many oviparous taxa exclusive of P. helioscopus and P. mystaceus. Our results also suggest that: (1) P. putjatia is a valid species, comprising populations from Guide, Qinghai Province and Tianzhu, Gansu Province; (2) P. hongyuanensis is not a valid species, synonymized instead with P. vlangalii; (3) P. zetangensis is not a valid species and should be included in P. theobaldi; (4) the population occurring in Kuytun, Xinjiang Uygur Autonomous Region is recognized as P. guttatus instead of P. versicolor; and (5) the Lanzhou population of P. frontalis is part of P. przewalskii. Congruent with previous hypotheses, the uplift of the Tibetan Plateau played a fundamental role in the diversification of Phrynocephalus. An evolutionary scenario combining aspects of vicariance and dispersal is necessary to explain the distribution of Phrynocephalus. Bayesian divergence-time estimation suggests that Phrynocephalus originated at the Middle–Late Miocene boundary (15.16–10.4Ma), and diversified from Late Miocene to Pleistocene from a center of origin in Central Asia, Tarim Basin, and Junggar Basin temperate desert, followed by several rapid speciation events in a relatively short time. The proposed biogeographic scenarios also indicate that the Tarim Basin desert may be the secondary diversification center, followed by Junggar Basin temperate desert and Alashan Plateau temperate desert. In the viviparous group, the allopatric speciation of P. theobaldi and P. vlangalii may have been caused by the uplifting of Tanggula Mountain Ranges. In addition, the results of this study make an important contribution to understanding the uplift of the Tibetan Plateau and Tian Shan Mountains and the biogeography of the entire region.

Desert plant pollen production and a 160-year record of vegetation and climate change on the Alashan Plateau, NW China

Recent and subfossil pollen spectra from the Alashan Plateau are presented in order to provide information on desert plant representation and on recent changes in vegetation and climate in this remote area in northern China. The desert vegetation composition is faithfully represented by the surface pollen spectra. The comparison of the desert plant species to the related pollen taxa yielded the following sequence from over-representation to under-representation: Chenopodiaceae, Artemisia, Ephedra fragilis-type s.l., Reaumuria, Nitraria and Calligonum. A 72 cm long sediment record from a small hydrologically-closed inter-dune lake (SE Badan Jilin Sand Sea, southern Alashan Plateau) covering the past ∼160 years (dated by137Cs) was analysed palynologically. Intervals of denser Artemisia coverage on the sand dunes around the lake, indicating wetter climate, occurred from the mid-1850s to the mid-1870s, during the first two decades of the 20th century and from the late 1930s to the beginning of the 1960s.

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

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 (41.89°N; 101.85°E; 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. 10,700–5400 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.

A mid-Holocene drought interval as evidenced by lake desiccation in the Alashan Plateau, Inner Mongolia, China

The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorphologic and lithological evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates strong lake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summer monsoon margin, is also presented. These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levels in the mid-Holocene around 5000–7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associated with the present Asian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south Inner Mongolian Plateau. The period was also probably colder, at least in the high Asian plateaus and mountains.