Download or read book Holocene Paleo Environmental Reconstruction in Central Tibetan Plateau Inferred from a Lacustrine Sediment Record written by Man-Ching Cheung and published by Open Dissertation Press. This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Holocene Paleo-environmental Reconstruction in Central Tibetan Plateau Inferred From a Lacustrine Sediment Record" by Man-ching, Cheung, 張敏青, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Previous studies on reconstructing the paleoclimate on the Tibetan Plateauare commonly based on a single proxy, and have thus limited the usage of their results. Therefore this study was designed firstly to evaluate the applicability of organic carbon isotopes from modern plants in the Tibetan Plateau as a paleo-environmental proxy, and secondly to apply palynology, organic geochemistry and biomarkers to the reconstructions ofpaleo-environmental history of central Tibet. The new, comprehensive records reveal the history of regional precipitation, temperature and vegetation change in responding to Holocene climatic changesin the region. Organic carbon isotope (δ13C) and lipid n-alkanes were measured from plant samples collected from various altitudes and environments across the study area. The δ13C results indicate the importance of availability of water to C3/C4 herbs distribution in this alpine region. The molecular distributions of trees, shrubs, herbs and submergent macrophytes show distinctive features in a number of indices. These indices are considered to be useful for paleo-environmental reconstructions. A 5.8m-long peat core, which were dated back to 95,000 yr BP was obtained from a river valley at an altitude of 4300 m above sea level. The pollen data from the core reveals a sparse herbaceous vegetation in the catchment area during early Holocene, suggesting non-favourable conditions for vegetation growth. The environment became wetter during the early mid-Holocene around 8100-7000 cal. yr BP, and since then a sedge-dominated wetland habitat was developed. This vegetation changed little until about 1100 cal. yr BP; from which an increase of drought-tolerant herbs was indicated by the pollen data, implying a slightly drier condition of the latter part of late Holocene. The pollen record suggests that the optimum precipitation in central Tibet occurred later and lasted longer than that in the East Asian Monsoon region. Finally, bulk sample carbon geochemistry(TOC, δ13C) as well as the biomarkers analysis on n-alkanes and GDGTs as paleo-limnology and paleo-temperature indicators respectively were applied to the core. Before 1500 cal. yr BP, the wetland was dominated by both vascular herbs as suggested by the δ13Cdata and aquatic floating/submerged macrophytes as indicated by mid-chain n-alkanes. The relative proportion of the two sources of organic matter input varied slightly, and vascular herbs increased in two episodes(5400 -4700 and 2800 -2300 cal. yr BP) indicated by the increase of long-chain n-alkanes (>n-C25). Considering of the soil water content variation by the ratios of iGDGTs to bGDGTs, the change between the two plant communities could to be caused by different lake status. GDGTs paleo-temperature reconstruction indicates a warm period from 6700 to 6000 cal. yr BP, which is believed to be the warmest and highly humid in central Tibetan region. Then the temperature decreased towards the late Holocene, consistent with other paleo climate records across the Plateau region, i.e. largely controlled by change of solar insolation. Along the decreasing trend, a warm episode at about 1200 yr BP that inferred from MAAT was suggested corresponding with the North Hemisphere Medieval Warming. DOI: 10.5353/th_b5270537 Subjects: Paleoecology - Tibet, Plateau of Paleoecology - Holocene

Download or read book Holocene Paleo environmental Reconstruction in Central Tibetan Plateau Inferred from a Lacustrine Sediment Record written by 張敏青 and published by . This book was released on 2014 with total page 181 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Late Glacial to Holocene Climate and Vegetation Changes on the Tibetan Plateau Inferred from Fossil Pollen Records in Lacustrine Sediments written by Yongbo Wang and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The past climate in central Asia, and especially on the Tibetan Plateau (TP), is of great importance for an understanding of global climate processes and for predicting the future climate. As a major influence on the climate in this region, the Asian Summer Monsoon (ASM) and its evolutionary history are of vital importance for accurate predictions. However, neither the evolutionary pattern of the summer monsoon nor the driving mechanisms behind it are yet clearly understood. For this research, I first synthesized previously published Late Glacial to Holocene climatic records from monsoonal central Asia in order to extract the general climate signals and the associated summer monsoon intensities. New climate and vegetation sequences were then established using improved quantitative methods, focusing on fossil pollen records recovered from Tibetan lakes and also incorporating new modern datasets. The pollen-vegetation and vegetation-climate relationships on the TP were also evaluated in order to achieve a better understanding of fossil pollen records. The synthesis of previously published moisture-related palaeoclimate records in monsoonal central Asia revealed generally different temporal patterns for the two monsoonal subsystems, i.e. the Indian Summer Monsoon (ISM) and East Asian Summer Monsoon (EASM). The ISM appears to have experienced maximum wet conditions during the early Holocene, while many records from the area affected by the EASM indicate relatively dry conditions at that time, particularly in north-central China where the maximum moisture levels occurred during the middle Holocene. A detailed consideration of possible driving factors affecting the summer monsoon, including summer solar insolation and sea surface temperatures, revealed that the ISM was primarily driven by variations in northern hemisphere solar insolation, and that the EASM may have been constrained by the ISM resulting in asynchronous patterns of evolution for these two subsystems. This hypothesis is further supported by modern monsoon indices estimated using the NCEP/NCAR Reanalysis data from the last 50 years, which indicate a significant negative correlation between the two summer monsoon subsystems. By analogy with the early Holocene, intensification of the ISM during coming decades could lead to increased aridification elsewhere as a result of the asynchronous nature of the monsoon subsystems, as can already be observed in the meteorological data from the last 15 years. A quantitative climate reconstruction using fossil pollen records was achieved through analysis of sediment core recovered from Lake Donggi Cona (in the north-eastern part of the TP) which has been dated back to the Last Glacial Maximum (LGM). A new data-set of modern pollen collected from large lakes in arid to semi-arid regions of central Asia is also presented herein. The concept of "pollen source area" was introduced to modern climate calibration based on pollen from large lakes, and was applied to the fossil pollen sequence from Lake Donggi Cona. Extremely dry conditions were found to have dominated the LGM, and a subsequent gradually increasing trend in moisture during the Late Glacial period was terminated by an abrupt reversion to a dry phase that lasted for about 1000 years and coincided with the first Heinrich Event of the northern Atlantic region. Subsequent periods corresponding to the warm Bølling-Allerød period and the Younger Dryas cold event were followed by moist conditions during the early Holocene, with annual precipitation of up to about 400 mm. A slightly drier trend after 9 cal ka BP was then followed by a second wet phase during the middle Holocene that lasted until 4.5 cal ka BP. Relatively steady conditions with only slight fluctuations then dominated the late Holocene, resulting in the present climatic conditions. In order to investigate the relationship between vegetation and climate, temporal variations in the possible driving factors for vegetation change on the northern TP were examined using a high resolution late Holocene pollen record from Lake Kusai. Moving-window Redundancy Analyses (RDAs) were used to evaluate the correlations between pollen assemblages and individual sedimentary proxies. These analyses have revealed frequent fluctuations in the relative abundances of alpine steppe and alpine desert components, and in particular a decrease in the total vegetation cover at around 1500 cal a BP. The climate was found to have had an important influence on vegetation changes when conditions were relatively wet and stable. However, after the 1500 cal a BP threshold in vegetation cover was crossed the vegetation appears to have been affected more by extreme events such as dust storms or fluvial erosion than by the general climatic trends. In addition, pollen spectra over the last 600 years have been revealed by Procrustes analysis to be significantly different from those recovered from older samples, which is attributed to an increased human impact that resulted in unprecedented changes to the composition of the vegetation. Theoretical models that have been developed and widely applied to the European area (i.e. the Extended R-Value (ERV) model and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model) have been applied to the high alpine TP ecosystems in order to investigate the pollen-vegetation relationships, as well as for quantitative reconstructions of vegetation abundance. The modern pollen-vegetation relationships for four common pollen species on the TP have been investigated using Poaceae as the reference taxa. The ERV Submodel 2 yielded relatively high PPEs for the steppe and desert taxa (Artemisia Chenopodiaceae), and low PPEs for the Cyperaceae that are characteristic of the alpine Kobresia meadows. The plant abundances on the central and north-eastern TP were quantified by applying these PPEs to four post-Late Glacial fossil pollen sequences. The reconstructed vegetation assemblages for the four pollen sequences always yielded smaller compositional species turnovers than suggested by the pollen spectra, indicating that the strength of the previously-reported vegetation changes may therefore have been overestimated. In summary, the key findings of this thesis are that (a) the two ASM subsystems show asynchronous patterns during both the Holocene and modern time periods, (b) fossil pollen records from large lakes reflect regional signals for which the pollen source areas need to be taken into account, (c) climate is not always the main driver for vegetation change, and (d) previously reported vegetation changes on the TP may have been overestimated because they ignored inter-species variations in pollen productivity

Download or read book The Identification and Use of Palaearctic Chironomidae Larvae in Palaeoecology written by Stephen J. Brooks and published by . This book was released on 2007 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Lake Records of Environmental and Climate Change on the Tibetan Plateau written by Zhang Chengjun and published by Frontiers Media SA. This book was released on 2022-11-07 with total page 269 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Late Quaternary Hydrological Paleoenvironmental and Geomorphological Processes in the Tibetan Plateau and Its Adjacent Areas written by Xiangjun Liu and published by Frontiers Media SA. This book was released on 2022-02-23 with total page 263 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Holocene Climate Changes in the Asia Pacific Region written by Liangcheng Tan and published by Frontiers Media SA. This book was released on 2021-03-08 with total page 206 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Terrestrial Impacts of the Holocene Asian Monsoon written by Anoop Ambili and published by Frontiers Media SA. This book was released on 2022-09-16 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Climates Landscapes and Civilizations written by Liviu Giosan and published by John Wiley & Sons. This book was released on 2013-05-09 with total page 574 pages. Available in PDF, EPUB and Kindle. Book excerpt: Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 198. Climates, Landscapes, and Civilizations brings together a collection of studies on the history of complex interrelationships between humans and their environment by integrating Earth science with archeology and anthropology. At a time when climate change, overpopulation, and scarcity of resources are increasingly affecting our ways of life, the lessons of the past provide multiple reference frames that are valuable for informing our future decisions and action plans. Volume highlights include discussions of multiple connotations of the Anthropocene, landscapes as a link between climate and humans, synoptic approaches to explore large-scale cultural patterns, regional studies for contextualizing cultural complexity, and environmental determinism and social theory. Straddling the fields of Earth sciences, anthropology, and archaeology and presenting research from across several continents, Climates, Landscapes, and Civilizations will appeal to a wide readership among scientists, scholars, and the public at large.

Download or read book Tectonic and Climatic Evolution of the Central northern Tibetan Plateau written by Lin Li and published by . This book was released on 2016 with total page 227 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The uplift history of the Tibetan Plateau serves as key evidence for understanding the dynamic models that build the Plateau and its influence on Cenozoic climate change of East Asia. This dissertation contributes to our knowledge for the growth history of the central and northern Tibetan Plateau through sedimentary analysis of basin sequences, and stable isotope analysis of carbonate rocks and modern surface waters. Field work in the Hoh Xil basin of central Tibet, including facies analysis, paleocurrent reconstruction, detrital zircon provenance analysis, and stable isotope analysis, suggests that a unified Hoh Xil basin, including both the east and west sub-basins, experienced a transition from pre-India-Asia collision foreland basin to post-collision hinterland basin setting at around 50 Ma. The Qiangtang terrane, serving as the main source for sediments deposited in the Hoh Xil basin, experienced significant topographic growth during the Cretaceous time. Far field deformation in the Hoh Xil basin was initiated shortly after India-Asia collision; contractional deformation and concomitant filling of the Hoh Xil hinterland basin provides clues for outward and upward growth of the Tibetan Plateau during Cenozoic time. Work in the western Qaidam basin provides new lithostratigraphy and carbonate stable isotope data that records early-middle Miocene topographic growth of the northern Tibetan Plateau. A hydrological change from restricted sub-basin to open marginal basin around 20 Ma was probably caused by late Oligocene-early Miocene tectonic activity around the Qaidam basinches A major topographic growth in the northern Tibetan Plateau is inferred around 15 Ma based on a negative shift in oxygen isotopic values, sedimentary facies changes from marginal lacustrine to fluvial, and an increase in sedimentation rate. A 13-12 Ma aridification event that was observed over a large area of the northern Plateau was likely caused by continued topographic growth to a critical point to block moisture from entering the northern Tibetan Plateau. To understand the caveats of stable isotope-based paleoaltimetry in the central and northern Tibetan Plateau, a comprehensive data set of 1,315 river water samples (450 newly collected) was compiled. With this large data set, a consistently assumed, but not well-documented prerequisite is demonstrated that river waters are a good substitute for isotopic studies of precipitation on the high Tibetan Plateau on the mean annual scale. The spatial variations of [delta]18O/[delta]D and d-excess values in the plateau margins can be modeled as a Rayleigh distillation process, on which stable isotope-based paleoaltimetry is based. On the contrary, the isotopic values of meteoric waters in the interior of the plateau are controlled by the combined effects of mixing of different moisture sources, contribution of recycled moisture from local surface water evaporation, and sub-cloud evaporation. A Rayleigh distillation model modified by sub-cloud evaporation is provided to simulate the isotopic variations in the western Plateau. This new understanding indicates that stable isotope-based paleoaltimetry is most reliable in the southern margins of the Plateau, and increasingly unreliable toward the northern Plateau. In addition, the contour maps of modern isotopic variations of meteoric waters across the whole Tibetan Plateau also provide validation criteria for isotopic simulations using general circulation models"--Pages v-vi.

Download or read book Annually Laminated Lake Sediments written by Wojciech Tylmann and published by MDPI. This book was released on 2020-04-28 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: The collection of papers presented in this book illustrates the recent progress made in varved sediment research and highlights the large variety of methodological approaches and research directions applied. The contributions cover monitoring of modern sediment fluxes using sediment traps; geochronological and sedimentological analyses of annually laminated lacustrine sediments or varves; and multiproxy investigations, including geochemical and biological proxies as well as spatiotemporal analyses based on multicore studies supported by satellite images and X-ray computed tomography (CT). The scientific issues discuss the influences of hydrological and climatological phenomena on short-term changes in sediment flux, the relationships between biogeochemical (limnological) processes in the water column and the formation of varves, the preservation of environmental signals in varved sediments, and possibilities of synchronizing varved records with other high-resolution environmental archives such as tree rings.

Download or read book Micro XRF Studies of Sediment Cores written by Ian W. Croudace and published by Springer. This book was released on 2015-07-21 with total page 668 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume presents papers on the use of micro-XRF core scanners in palaeoenvironmental research. It contains a broad ranging view of instrument capability and points to future developments that will help contribute to higher precision elemental data and faster core analysis. Readers will find a diverse range of research by leading experts that have used micro-XRF core scanners in a wide range of scientific applications. The book includes specific application papers reporting on the use of XRF core scanners in a variety of marine, lacustrine, and pollution studies. In addition, coverage also examines practical aspects of core scanner usage, data optimisation and data calibration and interpretation. In a little over a decade, micro-XRF sediment core scanners have made a substantive contribution to palaeoenvironmental research. Their impact is based on their ability to rapidly, non-destructively and automatically scan sediment cores. Not only do they rapidly provide important proxy data without damaging samples, but they can obtain environmental data at decadal, annual and even sub-annual scales. This volume will help both experienced and new users of these non-destructive core scanners take full advantage of one of the most powerful geochemical screening tools in the environmental scientist's toolbox.

Download or read book Holocene Paleo environmental Variability Reconstructed from a Lake Sediment Record from Southeast Greenland written by Gregory Andrew De Wet and published by . This book was released on 2013 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Paleoclimate Investigation and Interpretation of Lacustrine Sediment from Lake Telmen and Lake Ugiy Mongolia written by Paul Joseph McDonald and published by . This book was released on 2008 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Mongolia, located in Central Asia, experiences the most continental climate on Earth. Although detailed paleoclimate data are abundant for selected areas throughout Asia, datasets from within Mongolia are relatively scarce and demonstrate significant spatial and temporal variability. In older paleoclimatic reconstructions Mongolian climate was thought to be controlled by the East Asian monsoon system in a similar manner to China to the south. However in recent decades, additional paleoclimate records throughout central Asia have indicated a climate asynchronous with China, dominated by the Westerlies rather than the East Asian monsoon. The objective of this thesis study is to supplement existing paleoclimate proxy records in order to better understand Holocene climate variability in Mongolia and to assess the role of the Westerlies in producing that variability. This study produces new bulk-carbonate isotopic and mineralogic records for north-central Mongolia from a 7,110 year Lake Telmen and a 5,100 year Lake Ugiy sediment core. Lake Telmen is a saline (4 g/l), closed-basin lake, ideal for amplifying hydrologic variability into large sedimentological responses and is thus well-suited for paleoclimate study. The relatively heavy [delta]18O carbonate stable isotopes (averaging -0.5 [zero/zero zero]) and abundant ankerite, quartz and phillipsite minerals suggest an arid climate dominated prior to approximately 4,500 yr B.P. Since 4,500 yr B.P., the Lake Telmen sediment data suggests an increase in humidity evidenced by lighter [delta]18O values (averaging -1.2 [zero/zero zero]) with a corresponding mineralogical shift to abundant monohydrocalcite and calcite. These new records are in agreement with previous Lake Telmen paleoclimate interpretations based upon pollen, diatoms and lithology, suggesting the East Asian monsoon does not control the Holocene climate in the Telmen region. The Lake Ugiy sediment core mineralogy supports this interpretation, revealing abundant terrigenous minerals, a shallow lake, and more arid conditions prior to approximately 4,000 yr. B.P.A more humid climate since 4,000 yr B.P. is based on lacustrine mud with calcite and Mg calcite inferred to represent deeper water conditions. Brief arid intervals occur during the otherwise humid late Holocene as inferred from heavy isotope values and ankerite, quartz and phillipsite abundance in Lake Telmen, and abundant Mg calcite in Lake Ugiy at about 1,300-1,600, 2,000-2,200 and 2,800-3,100 yr B.P. The records from this thesis study support published interpretations that suggest central Asian Holocene climate is dominated by the Westerlies and is asynchronous with Chinese climate dominated by the East Asian monsoon. A North Atlantic high pressure system associated with cold sea surface temperature (SST) redirected the Westerly track causing the movement of dry air into Mongolia during the early Holocene. However, during the early Holocene increased boreal summer insolation produced a stronger East Asian summer monsoon system and increased moisture in China. By the late Holocene the disappearance of the Laurentide ice sheet allowed for increased North Atlantic SST and the development of a low pressure system. The more zonal Westerlies now carried warm moist air across Europe and into Mongolia thereby increasing the moisture balance in the late Holocene. During the late Holocene, North Atlantic SST periodically cooled due to ice rafting. The cold North Atlantic and altered atmospheric pressure gradient may have diverted the path of the Westerlies so that cold dry air flowed into Mongolia. These cold episodes are known as Bond cycles and included events dated at 1,400 and 2,800 yr B.P. These Bond cycles are similar in age to brief arid events within Mongolia and suggest hemispheric teleconnnection and a possible role for North Atlantic SST to influence Mongolian climate."--Abstract.

Download or read book Freshwater Benthic Diatoms of Central Europe written by Horst Lange-Bertalot and published by . This book was released on 2003 with total page 942 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Holocene Climate Change and Environment written by Navnith Kumaran and published by Elsevier. This book was released on 2021-09-24 with total page 693 pages. Available in PDF, EPUB and Kindle. Book excerpt: Holocene Climate Change and Environment presents detailed, diverse case studies from a range of environmental and geological regions on the Indian subcontinent which occupies the central part of the monsoon domain. This book examines Holocene events at different time intervals based on a new, high-resolution, multi-proxy records (pollen, spores, NPP, diatoms, grain size characteristics, total organic carbon, carbon/nitrogen ratio, stable isotopes) and other physical tools from all regions of India. It also covers new facilities in chronological study and luminescence dating, which have added a new dimension toward understanding the Holocene glacial retreats evolution of coastal landforms, landscape dynamics and human evolution. Each chapter is presented with a unified structure for ease of access and application, including an introduction, geographic details, field work and sampling techniques, methods, results and discussion. This detailed examination of such an important region provides key insights in climate modeling and global prediction systems. Provides data and research from environmentally and geologically diverse regions across the Indian subcontinent Presents an integrated and interdisciplinary approach, including considerations of human impacts Features detailed case studies that include methods and data, allowing for applications related to research and global modeling

Download or read book Paleoenvironmental Reconstruction Using Laminated Sediments Containing Authigenic Carbonate Minerals written by Chad Andrew Wittkop and published by . This book was released on 2004 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt: