Holocene vegetation and climate history at Hurleg Lake in the Qaidam Basin, northwest China

2015

Veget Hist Archaeobot

Self Cite

A dataset consisting of 70 surface pollen samples from forest, alpine meadow, alpine steppe, temperate steppe, desert steppe, shrub/semi-shrub steppe and desert sites in the Tianshan Mountains, northwestern China provides an opportunity to study the relationships between surface pollen assemblages and modern vegetation and climate in this region. Redundancy analysis (RDA), the human influence index (HII) and pollen ratios were used to facilitate analysis of the pollen data. The modern pollen assemblages are primarily composed of Picea, Artemisia, Chenopodiaceae, Poaceae, Asteraceae, Nitraria and Ephedra. The results suggest that the surface pollen assemblages of different vegetation types largely represent the modern vegetation in terms of the primary taxa and dominant types. The RDA indicates that the mean annual precipitation (MAP) and the July temperature (T July ) are the major climate variables that control the modern pollen assemblages. Picea, Artemisia, Poaceae, Cyperaceae, Fabaceae, Asteraceae, Polygonaceae and Apiaceae pollen assemblages are positively correlated with MAP and negatively correlated with T July , while the pollen ratios for certain other types, such as Chenopodiaceae, Ephedra and Nitraria, are negatively correlated with MAP and positively correlated with T July . The arboreal/non-arboreal ratios are notably high in the forest samples, indicating a sensitive response to forest vegetation. Moreover, the Artemisia/Chenopodiaceae pollen ratios are generally correlated with the vegetation type and annual precipitation change, suggesting that these factors could be useful indicators of moisture variability in arid regions. However, it is difficult to distinguish between steppe and steppe desert based on this ratio, due partly to human disturbance. The HII is significantly correlated with certain pollen taxa, including Poaceae, Plantago, Polygonaceae and Elaeagnaceae, particularly in the alpine meadow and steppe samples. Our results have implications for interpreting the available fossil pollen data in the study region and other arid and semi-arid regions.

Section: Numerical Analysismentioning

confidence: 99%

Surface pollen and its relationships with modern vegetation and climate in the Tianshan Mountains, northwestern China

Wei

2015

Veget Hist Archaeobot

Self Cite

“…The Artemisia/Chenopodiaceae (A/C) ratio has been fre-quently used to indicate humidity change in northern and western China (e.g., Liu et al, 1999;Herzschuh, 2007;Zhao et al, 2007;Zhang et al, 2010;Zhao and Li, 2013), after El-moslimany (1990) found that it is a good humidity indicator in the Middle East. Recently, Zhao et al (2012b) reviewed the reliability of the A/C ratio as humidity indicator in the arid region of China.…”

Section: Pollen Ratios Vegetation and Climatementioning

confidence: 99%

Modern pollen assemblages from surface lake sediments in northwestern China and their importance as indicators of vegetation and climate

Feng

et al. 2015

Sci. China Earth Sci.

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The modern pollen assemblages of surface lake sediments and topsoils in northwestern China were studied to understand the relationship of modern pollen data with contemporary vegetation and climate, and the differences between the pollen assemblages of surface lake sediments and topsoils. The results show that Chenopodiaceae and Artemisia are dominant elements in the pollen assemblages of northwestern China. Additionally, Ephedra, Cyperaceae, Asteraceae, Poaceae, Picea, Pinus, and Betula are also important pollen taxa. Both pollen assemblages and principal component analysis indicate that pollen data from surface lake sediments and topsoils can be used to differentiate the main vegetation types of this region (desert, steppe, meadow and forest). However, differences exist between modern pollen assemblages of the two types of sediments due to the different relevant source areas of pollen and degrees of pollen preservation. For example, the larger relevant source area of surface lake sediment results in a higher abundance of Betula in pollen assemblage from surface lake sediment, whereas the tendency to disintegrate thin-walled pollen types in topsoil leads to a higher proportion of resistant pollen, such as Asteraceae. Linear regression analysis indicates that the Artemisia/Chenopodiaceae (A/C) ratio in pollen assemblages of surface lake sediments can be used to indicate humidity changes in the study area. However, the A/C ratio in topsoils should be used carefully. Our results suggest that pollen data from surface lake sediments would be better references for interpreting the fossil pollen assemblages of lake cores or lacustrine profiles. Pollen data have been used to unravel the vegetation succession and climatic changes of the past since the pioneering work of von Post in 1916(Davis, 2000. The deciphering of fossil pollen data must be performed on the basis of the investigation of modern pollen assemblages. Numerous studies (e.g., Wright et al., 1967;Gaillard et al., 1992;Sugita, 1994;Cour et al., 1999;Davis, 2000;Shen et al., 2006;Ma et al., 2008;Zhao and Herzschuh, 2009;Herzschuh et al., 2010;Lu et al., 2011;Fall, 2012;Zheng et al., 2013;Tian et al., 2014) have been conducted to understand the relationship of modern pollen assemblages with contemporary vegetation and climate. Modern pollen assemblages are mainly collected from airborne pollen collectors (e.g., Cour et al

“…Paleoenvironmental interpretations from records of Pediastrum in lake sediments are not straight forward as previous studies are interpreted as reflecting changes in temperatures and the nutritional status of the freshwater lakes (Rull et al, 2008;Mackay et al, 2013), fluctuations in water levels (Sylvestre, 2002;Chepstow-Lusty et al, 2005;Jiang et al, 2006;Sarmaja-Korjonen et al, 2006;Zhao et al, 2007;Gosling et al, 2008;Whitney and Mayle, 2012), as well as links to levels of pH and DOC (Weckström et al, 2010). As the Pediastrum genus contains many species of diverse ecological affiliations, its abundance in sediments reflects a variety of aquatic conditions (Whitney and Mayle, 2012).…”

Section: Proxy Interpretationmentioning

confidence: 99%

“…However, it has been confirmed that Pediastrum currently prefers fresh or brackish water, and it, has not adapted to hyper-saline water conditions. Furthermore, it has been demonstrated that Pediastrum colonies increase with water depth in lakes of the northeastern Qaidam Basin (Zhao et al, 2007), and the survival depth of Pediastrum is considered to be no more than 15 m (Zheng et al, 2003;Zhang et al, 2004). Given that Pediastrum communities are found to vary among different lake habitats (Danielsen, 2010;Kaufman et al, 2010), we speculate that an increase in the salinity of the lake indicates a shrinking of the lake water body and a low lake level.…”

Section: Proxy Interpretationmentioning

confidence: 99%

“…Over the past three decades, significant research efforts have been directed toward investigating halite mineral, paleo-climate and the evolutionary history of salt lakes in the Qaidam Basin (Chen and Bowler, 1986;Zhang, 1987;Chen et al, 1990;Huang and Chen, 1990;Zhang et al, 1993Zhang et al, , 2007Zhao et al, 2007;Liu et al, 2008;Fan et al, 2010); however, the Late Pleistocene paleoclimatic variation in the eastern Qaidam Basin is still largely unclear due, in part, to limited numbers of long-sequenced paleoclimatic records. Most previous records extend only as far back as the late glacial or early Holocene Epoch (Zhao et al, 2007(Zhao et al, , 2008Liu et al, 2008), although there are a few low resolution paleoclimatic records extending back to the last glacial or the Late Pleistocene (Chen and Bowler, 1986;Chen et al, 1990;Huang and Chen, 1990;Zhang et al, 1993;Yang et al, 1995). Beyond some paleoclimatic records of sediment cores in the Qarhan Salt Lake area, the Shell Bar, located in the southeastern margin of the Qarhan Salt Lake, has been regarded as better geomorphic evidence to reflect the evolutionary history of the Qarhan paleolake .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A 94–10ka pollen record of vegetation change in Qaidam Basin, northeastern Tibetan Plateau

Wei

Fan

Palaeogeography, Palaeoclimatology, Palaeoecology

et al. 2015

Self Cite

Drill core (ISL1A) was obtained from the Qarhan Salt Lake in central eastern Qaidam Basin, northeastern Tibetan Plateau (NE TP). Fossil pollen and the lithology of the core sediment were analyzed in conjunction with AMS 14 C and 230 Th dating. The results indicated that Artemisia and Chenopodiaceae dominated the steppe/desert steppe vegetation developed around the lake between 94 and 51.2 ka, corresponding with the organic-rich silty clay deposited in the core sediments. Pediastrum continuously appeared in the core sediments between 94 and 51.2 ka, indicating freshwater to oligohaline conditions of the paleo-Qarhan Lake during the late marine isotope stage (MIS) 5, MIS 4, and early MIS 3. During the 51.2 to 32.5 ka period, Ephedra dominated shrub-desert vegetation expanded in the basin, while, Pediastrum disappeared in the core sediments. The core sediments consisted of interbedded layers of halite silt and clay-rich halite between 51.2 and 32.5 ka, signifying a shift toward drier hydrologic conditions. Thus, the paleo-Qarhan Lake experienced periods of desiccation and shallow water levels. Artemisia and Chenopodiaceae dominated steppe/desert steppe vegetation appeared again from 32.5 to 25.3 ka, with clay-rich sediments in the core, thereby suggesting an increase of runoff from the lake under relatively wetter climatic conditions. Since 25.3 ka, however, pollen concentrations declined, corresponding with the amount of halite deposited in the core sediment and, suggesting a cold, dry climatic condition during MIS2. Our findings have important implications for understanding complex regional vegetation and climatic responses to large-scale forcings in the Qaidam Basin.