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Feng QIN 《中国科学:地球科学(英文版)》2021,(3):425-439
Modern pollen analysis is the basis for revealing the palaeovegetation and palaeoclimate changes from fossil pollen spectra. Many studies pertaining to the modern pollen assemblages on the Tibetan Plateau have been conducted, but little attention has been paid to pollen assemblages of surface lake sediments. In this study, modern pollen assemblages of surface lake sediments from 34 lakes in the steppe and desert zones of the Tibetan Plateau are investigated and results indicate that the two vegetation zones are dominated by non-arboreal pollen taxa and show distinctive characteristics. The pollen assemblages from the desert zone contain substantially high relative abundance of Chenopodiaceae while those from the steppe zone are dominated by Cyperaceae. Pollen ratios show great potential in terms of separating different vegetation zones and to indicate climate changes on the Tibetan Plateau. The Artemisia/Chenopodiaceae ratio and arboreal/non-arboreal pollen ratio could be used as proxies for winter precipitation. Artemisia/Cyperaceae ratio and the sum of relative abundance of xerophilous elements increase with enhanced warming and aridity. When considering the vegetation coverage around the lakes, hierarchical cluster analysis suggests that the studied sites can be divided into four clusters: meadow, steppe, desert-steppe, and desert. The pollen-based vegetation classification models are established using a random forest algorithm. The random forest model can effectively separate the modern pollen assemblages of the steppe zone from those of the desert zone on the Tibetan Plateau. The model for distinguishing the four vegetation clusters shows a weaker but still valid classifying power. It is expected that the random forest model can provide a powerful tool to reconstruct the palaeovegetation succession on the Tibetan Plateau when more pollen data from surface lake sediments are included. 相似文献
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SHANG Xue LI XiaoQiang AN ZhiSheng JI Ming & ZHANG HongBin State Key Lab of Loess & Quaternary Geology Institute of Earth Environment Chinese Academy of Sciences Xi’an China Graduate University of Chinese Academy of Sciences Beijing 《中国科学D辑(英文版)》2009,52(10):1510-1519
Lake Qinghai is the largest inland brackish lake in China and lies within the NE Tibetan Plateau. Our study shows that pollen assemblages in each vegetation belt are significantly correlated with the vegetation types of this area. Among the herbaceous and shrubby pollen assemblages, Artemisia is over-represented, while Poaceae, Cyperaceae and Polygonaceae are under-represented. Artemisia/ Chenopodiaceae (A/C) ratios with the regional vegetation characteristic can be used as a proper index to reconstruct the... 相似文献
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Northeast China is an essential area for studying the strength of East Asian Summer Monsoon(EASM), due to its northernmost location in EASM domain. However, the lack of sufficient modern pollen data in this region hinders an effective interpretation of fossil pollen records and quantitative vegetation/climate reconstructions. Here, 44 surface pollen samples from forest, steppe, and meadow were used to explore pollen-vegetation-climate relationships. Cluster analysis, species indicator analysis, and principal components analysis, were used to identify the discontinuous and continuous trends in pollen dataset. In addition, correlation analysis and boosted regression trees were used to investigate primary explanatory variables, while coinertia analysis and redundancy analysis to examine pollen-vegetation and pollen-climate correlations respectively. Our results show that:(1) vegetation can be well represented by surface pollen assemblages, i.e. forest is characterized by a high proportion of tree pollen(70%) dominated by Betula(40%) along with Alnus, Larix, and Pinus, whereas Steppe by herb pollen(80%),dominated by Artemisia, Chenopodiaceae;(2) significant correlations exist between pollen assemblages and mean annual temperature and then mean annual precipitation;(3) pollen ratios of Artemisia/Chenopodiaceae and arboreal/non-arboreal can respectively be used as good indicators of humidity and temperature in Northeast China. 相似文献
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XU QingHai LI YueCong YANG XiaoLan & ZHENG ZhenHua College of Resource Environment Hebei Normal University Shijiazhuang China Institute of Geology Geophysics Chinese Academy of Sciences Beijing China Hebei Institute of Geography Science Shijiazhuang China 《中国科学D辑(英文版)》2007,50(4):582-599
205 surface pollen samples from different communities in Northern China were analyzed to understand the quantitative relationship between pollen and its original vegetation. Pollen analysis and vegetation investigation show that the pollen assemblages differ a lot in different vegetation regions. Arboreal pollen account for more than 30% in temperate broad-deciduous forests region. In temperate steppe regions, herb pollen percentages are more than 90%, where Artemisia and Chenopodiaceae are domi- nant pollen types with Artemisia percentages more than 30%. In temperate desert, Chenopodiaceae pollen percentages are more than Artemisia, where ferns are rare. Cyperaceae pollen percentages are more than 20% in sub-alpine or cold meadows. The relations between pollen percentages and vegeta- tion cover indicate that most arboreal pollen shows a close relationship with parent plant covers, most shrubby pollen types have more or less correlations, but most herbs do not show clear correlations. For arboreal pollen types, Picea pollen shows the closest correlation with spruce trees coverage, then is Quercus and Carpinus. Betula, Larix and Juglans have also high correlation coefficients with their plants coverage, but Betula pollen is of overrepresented pollen type and more than 40% in birch forest, while Larix and Juglans pollen is underrepresented and pollen percentages are more than 10% in Larix or Juglans pure forests. Pinus is of overrepresented pollen type, and pollen percentages have some relations with plants cover. Pine forest might present when Pinus pollen percentages are more than 30%. The relations between Ulmus and Populus pollen percentages and vegetation cover are not close, where they are mixed with other arbors, they cannot be recorded easily, but if their pollen percentages are more than 1%, Ulmus or Populus trees should exist. For shrubby pollen types, the correlation be- tween Vitex pollen percentages and vegetation cover is the highest, then is Corylus, Tamariaceae and Nitraria, and their pollen percentages are less than 1% where original plant are absent. Caragana and Spiraea pollen percentages have some relations with vegetation cover. The relations between pollen percentages and vegetation cover are not clear for Rosaceae and Saxifragaceae. For herb pollen types, Cyperaceae pollen has the closest correlation with vegetation cover, where pollen percentages are more than 20% when Cyperaceae are constructive or dominant species in vegetation, and pollen per- centages are less than 5% where Cyperaceae are not constructive or dominant species (cover less than 30%). Artemisia and Chenopodiaceae pollen percentages mainly have close relations with ecological regions. The relations between pollen percentages and cover are not clear for Gramineae, Legumi- nosae and Compositae. 相似文献
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Quan Li 《中国科学:地球科学(英文版)》2018,61(3):270-284
Pollen diversity offers abundant clues into the floristic diversity and history of vegetation change. Few palynological studies investigated modern pollen diversity or the past floristic diversity on the Tibetan Plateau (TP). Based on modern pollen assemblages from 37 topsoils and 63 surface lake sediments in the Nam Co catchment on the central TP, this study quantitatively explored spatial distribution of modern pollen diversity using Shannon-Wiener index (H) and palynological richness (E(T n ), n=600). Pollen diversity indices showed spatial variability among vegetation types, reflecting the differences in terrestrial floristic diversity in the lake catchment. Their values were high in the southeastern region of the lake catchment which is covered by alpine steppe, while values were low for alpine meadow and marsh meadow. The pollen diversity in lacustrine pollen assemblage could be an effective proxy to document past floristic diversity. The past floristic diversity in the lake catchment, recovered from a fossil pollen record of NMLC-1, showed a long-term change of ascending overlaid by several rapid diversity changes during the last 8400 years due to the downward shift of altitudinal vegetation belt driven by a general climatic cooling. The results imply that under the environmental challenge of climate warming and vegetation degradation, alpine vegetation restoration in the Nam Co catchment and the central TP should pay attention to altitudinal vegetation belt and zonal vegetation of alpine steppe, and use the long-term change of floristic diversity as a historical analogue. 相似文献
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XU QingHai CAO XianYong TIAN Fang ZHANG ShengRui LI YueCong LI ManYue LI Jie LIU YaoLiang LIANG Jian 《中国科学:地球科学(英文版)》2014,57(6):1254-1266
The Relative Pollen Productivities(RPPs)of common steppe species are estimated using Extended R-value(ERV)model based on pollen analysis and vegetation survey of 30 surface soil samples from typical steppe area of northern China.Artemisia,Chenopodiaceae,Poaceae,Cyperaceae,and Asteraceae are the dominant pollen types in pollen assemblages,reflecting the typical steppe communities well.The five dominant pollen types and six common types(Thalictrum,Iridaceae,Potentilla,Ephedra,Brassicaceae,and Ulmus)have strong wind transport abilities;the estimated Relevant Source Area of Pollen(RSAP)is ca.1000 m when the sediment basin radius is set at 0.5 m.Ulmus,Artemisia,Brassicaceae,Chenopodiaceae,and Thalictrum have relative high RPPs;Poaceae,Cyperaceae,Potentilla,and Ephedra pollen have moderate RPPs;Asteraceae and Iridaceae have low RPPs.The reliability test of RPPs revealed that most of the RPPs are reliable in past vegetation reconstruction.However,the RPPs of Asteraceae and Iridaceae are obviously underestimated,and those of Poaceae,Chenopodiaceae,and Ephedra are either slightly underestimated or slightly overestimated,suggesting that those RPPs should be considered with caution.These RPPs were applied to estimating plant abundances for two fossil pollen spectra(from the Lake Bayanchagan and Lake Haoluku)covering the Holocene in typical steppe area,using the"Regional Estimates of Vegetation Abundance from Large Sites"(REVEALS)model.The RPPs-based vegetation reconstruction revealed that meadow-steppe dominated by Poaceae,Cyperaceae,and Artemisia plants flourished in this area before 6500–5600 cal yr BP,and then was replaced by present typical steppe. 相似文献
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Airborne pollen is indicative of vegetation and climatic conditions. This study investigates airborne pollen trapping in the Betula microphylla-dominated wetland of Ebinur Lake in Northwestern China from September 2012 to August 2015 using Pearson correlation analysis and the Hybrid Single-particle Lagrangian Integrated Trajectory model. Higher temperatures and moderate precipitation during the flowering period facilitated an increase in birch pollen with more exotic spruce pollen carried from the Tianshan Mountains by airflows, leading to the highest arbor pollen concentrations from September 2012 to August2013. Peak pollen concentrations from September 2013 to August 2014 were possibly due to an increase in herbaceous pollen resulting from higher temperatures, lower precipitation and more exotic pollen from the desert of southwest Ebinur Lake and Central Asia in summer and autumn. Between September 2014 and August 2015, unfavorable climate conditions in summer and autumn decreased the pollen dispersal of xerophytes such as Artemisia and Chenopodiaceae, with little pollen transported from the Kazakh hilly area in late summer, resulting in the lowest pollen concentrations. Climatic parameters and air mass movements both greatly affected the atmospheric pollen concentration. The results provide information concerning the dispersion and distribution of birch pollen, paleoenvironmental reconstruction and wetland conservation. 相似文献
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地下水补给型湖泊表层沉积物矿物组成及其形成机制——以巴丹吉林沙漠湖泊群为例 总被引：1，自引：0，他引：1
盐湖中的矿物沉积记录着丰富的环境气候变化信息,是古环境研究的重要对象.在无地表径流补给的盐湖中,其矿物组成及沉积特征与有地表径流补给的湖泊相比是否有一定的特殊性,是值得探讨的问题.采集巴丹吉林沙漠33个不同矿化度地下水补给型湖泊的表层沉积物和10个地表风积砂样品,通过X衍射的方法,分析样品的矿物组成.结果显示:湖泊表层沉积物主要为石英、长石、辉石、云母等碎屑矿物,部分湖泊含有少量的碳酸盐和氯化物盐类矿物.湖泊沉积物的矿物组成与湖水矿化度的关系较为密切,淡水湖仅分布碎屑矿物,微咸水湖含有碎屑矿物和碳酸盐类矿物,盐湖含有碎屑矿物、碳酸盐类矿物和氯化物.风积砂样品中主要为碎屑矿物,占总矿物含量的90%,对湖泊沉积物的矿物组成影响较大,但对湖泊沉积物中的盐类矿物没有贡献,表明湖泊表层沉积物中盐类矿物主要是自生作用形成的.虽然本地区湖泊边缘的沉积物中盐类矿物种类相对较少并且含量较低,但其盐类矿物组成与分布能够响应湖水矿化度的变化,其环境指示意义与有径流补给的盐湖相同,可以指示其湖水的盐度.因此,可以从巴丹吉林沙漠地下水补给型湖泊沉积的盐类矿物中提取相应的古环境信息,用于恢复古气候和古环境的研究. 相似文献
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HUANG Fei Kealhofer Lisa XIONG Shangfa & HUANG Fengbao . Nanjing Institute of Geology Paleontology Chinese Academy of Sciences Nanjing China . Anthropology Sociology Department Santa Clara University CA USA . Institute of Geology Geophysics Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2005,48(7)
~~Holocene grassland vegetation, climate and human impact in central eastern Inner Mongolia1.Ye,D.Z.,Chou,J.E,Liu,J.Y.et al.,Causes of sand-stormy weather in northern China and control measures,Acta Geographica Sinica(in Chinese),2000,55(5):513-520.
2.Qiu,X.E,Zeng,Y.,Miao,Q.L.,Temporal spatial distribution as well as tracks and source areas of sand dust storms in China,Acta Geographica Sinica(in Chinese),2001,56(3):316-322.
3.Cui,H.T,Kong,Z.C,Preliminary analysis on the cli… 相似文献
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M. van Hardenbroek O. Heiri M. F. Wilhelm A. F. Lotter 《Aquatic Sciences - Research Across Boundaries》2011,73(2):247-259
The distribution of benthic invertebrates and their subfossil remains was examined within the basin of De Waay, a dimictic,
eutrophic lake in the Netherlands. We focused on Chironomidae, but also report the abundances of 11 invertebrate groups that
potentially produce chitinous remains that are preserved in the fossil record, although their remains could only be identified
at a coarser taxonomic resolution. Most living invertebrates sampled in different seasons were constrained to the littoral
zone, with the exception of a few taxa (Ceratopogonidae, Chaoborus flavicans, and Chironomus) that are adapted to low oxygen conditions in the seasonally anoxic profundal zone. In contrast, assemblages of invertebrate
remains in lake surface sediments were similar in the entire lake basin, suggesting that considerable numbers of invertebrate
remains are transported and redeposited off-shore in Lake De Waay, due to its steep bathymetry. These results indicate that
a single sediment sample obtained from the centre of this lake contains subfossil invertebrate remains originating from the
entire lake basin. In Lake De Waay, the majority of taxa found in the living assemblages were identified as remains in lake
surface sediments, at least for the Chironomidae that could be identified at a similar taxonomic level in living and subfossil
assemblages. Of the total 44 chironomid taxa found in Lake De Waay, 35 taxa occurred in the living assemblages and 34 taxa
occurred in the subfossil assemblages. Thirty chironomid taxa occurred both as living and subfossil specimens, and on average
these 30 taxa represent 94% of the specimens encountered in a sediment sample. Five rare chironomid taxa present as living
larvae were not detected in the subfossil assemblages. Conversely, eight rare and four common chironomid taxa were found in
subfossil remains, but not in living assemblages. Our results indicate that subfossil assemblages in surface sediment samples
provide spatially integrated and representative samples of the living assemblage. However, a combined approach examining both
the living benthic invertebrate fauna and invertebrate remains in lake surface sediments will potentially give a more complete
and detailed overview of benthic invertebrates in a lake ecosystem than an approach based exclusively on one of these groups. 相似文献
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Lake sediments are valuable natural archives to reconstruct paleoclimate and paleoenvironmental changes which consist of inorganic and organic sediment compounds of allochthonous origin from the catchment and of autochthonous production in the lake. However, for robust paleo-reconstructions it is important to develop a better understanding about sedimentation processes, the origin of inorganic and organic sediment compounds and their distribution within the lake. In this context, modern process studies provide important insights, although environmental and anthropological changes can affect the spatial distribution of sediment compounds through time. Therefore, in this study the spatial distribution of grain size and geochemical proxies in 52 surface sediment samples from Lake Khar Nuur, a small high-altitude lake in the Mongolian Altai with a small and anthropogenically used hydrological catchment, is investigated. The results show a distinct sediment focussing in the two deep basins of the lake, which therefore act as accumulation zones. In those accumulation zones, total organic carbon (TOC), total nitrogen (N) and their isotopic composition (δ13CTOC, δ15N) as well as n-alkanes indicate that organic sediment compounds are a mixture of both allochthonous and autochthonous origin. While the recent catchment vegetation consists of grasses/herbs and the shrub Betula nana (L.) with distinct differences in their n-alkane homologue patterns, those differences are not reflected in the sediment surface samples which rather indicates that grass-derived n-alkanes become preferentially incorporated in the lake. Extensive anthropogenic activity such as grazing and housing in the southern part of the catchment causes soil erosion which is well reflected by high TOC, N and sulphur (S) contents and 15N depleted δ15N values at the central southern shore, i.e. increased allochthonous sediment input by anthropogenically-induced soil erosion. Overall, the surface sediments of Lake Khar Nuur origin from allochthonous and autochthonous sources and are focussed in the accumulation zones of the lake, while their distribution is both environmentally and anthropogenically driven. 相似文献
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Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China 总被引：15，自引：0，他引：15
J. A. Holmes 《中国科学D辑(英文版)》2006,49(12):1280-1290
Short sediment cores retrieved from Bosten Lake, the largest inland freshwater lake in China, were used to explore humidity and precipitation variations in arid central Asia during the past millennium. The chronology of the cores was established using 137Cs, 210Pb and AMS 14C dating re- sults. Multi-proxy high-resolution analysis, including pollen ratios of Artemisia and Chenopodiaceae (A/C), carbonate content and grain size, indicates that the climate during the past millennium can be divided into three stages: a dry climate between 1000―1500 AD, a humid climate during the Little Ice Age (LIA) (c. 1500―1900 AD), and a warm dry period after 1900 AD. On centennial timescales, the climate change in northwestern China during the past 1000 years is characterized by oscillations between warm-dry and cold-humid climate conditions. All the proxies changed significantly and indi- cate increased precipitation during the LIA, including increased pollen A/C ratios and pollen concen- trations, decreased carbonate content and increased grain size. The humid period during the LIA re- corded by the Bosten Lake sediments is representative of arid central Asia and is supported by nu- merous records from other sites. During the LIA, the water runoff into the Keriya River and Tarim River in the Tarim Basin increased, while the ice accumulation in the Guliya ice core increased. Additionally, the lake levels of the Aral and Caspian Sea also rose, while tree-ring analysis indicates that precipita- tion increased. We hypothesize that both the lower temperature within China and the negative anomalies of North Atlantic Oscillation (NAO) during this period may have contributed to the humid climate within this area during LIA. 相似文献
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Ge Yu Xiangjun Sun Boqiang Qin Changqing Song Haiyu Li I. C. Prentice P. S. Harrison 《中国科学D辑(英文版)》1998,41(2):130-136
Biomization provides an important way to assign pollen taxa to biomes and to simulate palaeo-vegetation patterns, so that
pollen data can be mapped to reconstruct biogeography and climate. The authors have tested the applicability of this procedure
to assign modern pollen surface samples from China to biomes. The procedure successfully delineated the major vegetation types
of China. When the same procedure was applied to 6 ka B. P. fossil pollen samples, the reconstructions showed that the forest
zones were systematically shifted northwards ca. 300–500 km beyond their present northern limits in eastern China; the area
of desert and steppe vegetation was reduced compared to the present in northwestern China; the area of tundra was reduced
largely on the Tibetan Plateau. This research is a contribution to the project of BIOME 6000 in Pacific-Asian regions.
Project supported by the Funding for Returned Students from the Overseas of the State Education Commission of China, the Postdoctoral
Station, and State Pilot Laboratory of Coast & Island Development of Nanjing University, Financial support has also been provided
by European Community (EV5V-CT95-0075) and by the Swedish Natural Science Research Council (G-AA/GU 09334-321). 相似文献