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Sökning: WFRF:(De Vleeschouwer Francois)

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1.
  • de Jong, Rixt, et al. (författare)
  • Climate and Peatlands
  • 2010
  • Ingår i: Changing Climates, Earth Systems and Society. - Dordrecht : Springer Netherlands. - 9789048187157 - 9789048187164 ; , s. 85-121
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • Peatlands are an important natural archive for past climatic changes, primarily due to their sensitivity to changes in the water balance and the dating possibilities of peat sediments. In addition, peatlands are an important sink as well as potential source of greenhouse gases. The first part of this chapter discusses a range of well-established and novel proxies studied in peat cores (peat humification, macrofossils, testate amoebae, stomatal records from subfossil leaves, organic biomarkers and stable isotope ratios, aeolian sediment influx and geochemistry) that are used for climatic and environmental reconstructions, as well as recent developments in the dating of these sediments. The second part focuses on the role that peatland ecosystems may play as a source or sink of greenhouse gases. Emphasis is placed on the past and future development of peatlands in the discontinuous permafrost areas of northern Scandinavia, and the role of regenerating mined peatlands in north-western Europe as a carbon sink or source.
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2.
  • Gallego-Sala, Angela V., et al. (författare)
  • Latitudinal limits to the predicted increase of the peatland carbon sink with warming
  • 2018
  • Ingår i: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 8:10, s. 907-
  • Tidskriftsartikel (refereegranskat)abstract
    • The carbon sink potential of peatlands depends on the balance of carbon uptake by plants and microbial decomposition. The rates of both these processes will increase with warming but it remains unclear which will dominate the global peatland response. Here we examine the global relationship between peatland carbon accumulation rates during the last millennium and planetary-scale climate space. A positive relationship is found between carbon accumulation and cumulative photosynthetically active radiation during the growing season for mid- to high-latitude peatlands in both hemispheres. However, this relationship reverses at lower latitudes, suggesting that carbon accumulation is lower under the warmest climate regimes. Projections under Representative Concentration Pathway (RCP)2.6 and RCP8.5 scenarios indicate that the present-day global sink will increase slightly until around AD 2100 but decline thereafter. Peatlands will remain a carbon sink in the future, but their response to warming switches from a negative to a positive climate feedback (decreased carbon sink with warming) at the end of the twenty-first century.
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3.
  • Marquer, Laurent, et al. (författare)
  • Pollen-based reconstruction of Holocene land-cover in mountain regions : Evaluation of the Landscape Reconstruction Algorithm in the Vicdessos valley, northern Pyrenees, France
  • 2020
  • Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 228, s. 1-15
  • Forskningsöversikt (refereegranskat)abstract
    • Long-term perspectives on climate- and human-induced shifts in plant communities and tree line in mountains are often inferred from fossil pollen records. However, various factors, such as complex patterns of orographic wind fields and abundant insect-pollinated plants in higher altitudes, make pollen-based reconstruction in mountain regions difficult. Over the last decade the Landscape Reconstruction Algorithm (LRA) - a model-based approach in reconstruction of vegetation - has been successfully applied in various parts of the globe. However, evaluation of its effectiveness in mountain ranges is still limited. The present study assesses the extent to which the LRA approach helps quantify the local changes in vegetation cover at Vicdessos valley in northern French Pyrenees as a case study. In the study area well-dated sediment cores are available from eight bogs and ponds, 6-113 m in radius, located above the current tree line. We first use a simple simulation experiment to evaluate the way how pollen records from "landscape islands" (mountain tops and plateaus) would represent local vegetation and to clarify important factors affecting the LRA-based reconstruction in a mountainous region. This study then uses pollen records from these sites and vegetation and land-cover data both within a 50-km radius around the Vicdessos valley and within a 2-km radius from each site for evaluation of the REVEALS- and LOVE-based reconstruction of the regional and local plant cover, respectively, in the LRA approach. The land-cover data are complied for coniferous trees, broadleaved trees and non-forested areas from the CORINE and historical maps in three time windows: 1960-1970, 1990-2000 and 2000-2013. Major findings are as follows. (1) Accuracy of the regional vegetation estimates affects the reliability of the LRA-based reconstruction of vegetation within a 2-km radius; use of the CORINE data as input to the LOVE model improves reliability of the results over the use of the REVEALS-based estimates of regional vegetation. This implies that a systematic selection of pollen data only from sites above the tree line is problematic for estimating regional vegetation, and thus the entire LRA process. (2) Selection of the dispersal models for pollen transport (i.e. the Langrangian Stochastic Model vs. Gaussian Plume Model) does not affect significantly the LRA-based estimates at both the regional and local scales in the study area. (3) The LRA approach improves the pollen-based reconstruction of local vegetation compared to pollen percentage alone in northern Pyrenees. Although further empirical and simulation studies are necessary, our results emphasize the importance of site selection for the LRA-based reconstruction of vegetation in mountain regions. (C) 2019 Elsevier Ltd. All rights reserved.
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5.
  • Allan, Mohammed, et al. (författare)
  • High-resolution reconstruction of atmospheric deposition of trace metals and metalloids since AD 1400 recorded by ombrotrophic peat cores in Hautes-Fagnes, Belgium
  • 2013
  • Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491 .- 1873-6424. ; 178, s. 381-394
  • Tidskriftsartikel (refereegranskat)abstract
    • The objective of our study was to determine the trace metal accumulation rates in the Misten bog, Hautes-Fagnes, Belgium, and assess these in relation to established histories of atmospheric emissions from anthropogenic sources. To address these aims we analyzed trace metals and metalloids (Pb, Cu, Ni, As, Sb, Cr, Co, V, Cd and Zn), as well as Pb isotopes, using XRF, Q-ICP-MS and MC-ICP-MS, respectively in two 40-cm peat sections, spanning the last 600 yr. The temporal increase of metal fluxes from the inception of the Industrial Revolution to the present varies by a factor of 5-50, with peak values found between AD 1930 and 1990. A cluster analysis combined with Pb isotopic composition allows the identification of the main sources of Pb and by inference of the other metals, which indicates that coal consumption and metallurgical activities were the predominant sources of pollution during the last 600 years.(c) 2013 Elsevier Ltd. All rights reserved.
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6.
  • Berntsson, Annika, et al. (författare)
  • Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology, Lake Vuoksjavratje, NW Sweden
  • 2015
  • Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 44:4, s. 676-692
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we show the potential of combining multi-proxy analysis of lake sediments with catchment geomorphology to better understand palaeoenvironmental changes. Previous studies have suggested that alpine lakes in N Sweden may be highly sensitive to variations in catchment erosion and precipitation, and that this sensitivity may influence ecologically based reconstructions of past temperature changes. We analysed lake sediments covering the last 5100 years from the alpine Lake Vuoksjavratje in NW Sweden in order to identify different erosional regimes in the lake catchment, sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. The measured proxies include elemental geochemistry from XRF core scanning, grain size, sediment accumulation rates, fraction of terrestrial organic carbon and geomorphological mapping, supported by previously published chironomid and total organic carbon data. From the integrated results we identified time intervals when increased intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event occurred c. 2900 cal. a BP and is interpreted to be the result of excessive precipitation, possibly related to the climatic shift towards cooler and wetter conditions referred to as the 2.8 ka event.
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7.
  • Berntsson, Annika, 1979-, et al. (författare)
  • Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology, Lake Vuoksjávrátje, NW Sweden
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • In this paper, we highlight the importance of combining multi-proxy analysis of lake sediments with associated catchment geomorphology to better understand the late Holocene palaeoenvironmental evolution in a high latitude Alpine lake in N Sweden. Previous studies have suggested that such lakes may be highly sensitive to variations in catchment erosion and variations in precipitation, and that this sensitivity may influence ecologically-based reconstructions of past temperature changes. Here we have analysed lake sediments covering the last 5100 years from Lake Vuoksjávrátje in NW Sweden to identify different erosional regimes in the lake catchment and to identify sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. Methods that were used include XRF core scanning, grain size analysis and geomorphological mapping, supported by previously published chironomid, total organic carbon and carbon/nitrogen data. From the integrated results we identify time intervals when increased amounts/intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event in our record occurred between 3090 and 2750 cal. a BP and is interpreted to be the result of excessive precipitation in relation to the 2.8 ka event. By combining the multi-proxy analysis of a lake sediment core with a detailed catchment characterisation it is possible to reach a better understanding of the processes active within the lake catchment, the factors governing the erosional regimes and the way these are recorded in lake sediments. For future palaeoclimatological research based on lake sediments we recommend increasing the integration of catchment geomorphology, sedimentology and palaeoecology.
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8.
  • Chambers, Frank M., et al. (författare)
  • Development and refinement of proxy-climate indicators from peats
  • 2012
  • Ingår i: Quaternary International. - Oxford : Pergamon Press. - 1040-6182 .- 1873-4553. ; 268, s. 21-33
  • Tidskriftsartikel (refereegranskat)abstract
    • Peat, especially from acidic mires (bogs), is a natural archive of past environmental change. Reconstructions of past climate from bogs commenced in the 19th Century through examination of visible peat stratigraphy, and later formed the basis for a postglacial climatic scheme widely used in Northwest Europe. Nevertheless, misconceptions as to how bogs grow led to a 50-year lacuna in peat-climate study, before the concept of 'cyclic regeneration' in bogs was refuted. In recent decades, research using proxy-climate indicators from bogs has burgeoned. A range of proxies for past hydrological change has been developed, as well as use of pollen, bog oaks and pines and other data to reconstruct past temperatures. Most of this proxy-climate research has been carried out in Northern Europe, but peat-based research in parts of Asia and North America has increased, particularly during the last decade, while research has also been conducted in Australia, New Zealand and South America. This paper reviews developments in proxy-climate reconstructions from peatlands; chronicles use of a range of palaeo-proxies such as visible peat stratigraphy, plant macrofossils, peat humification, testate amoebae and non-pollen palynomorphs: and explains the use of wiggle-match radiocarbon dating and relationship to climate shifts. It details other techniques being used increasingly, such as biomarkers, stable-isotopes, inorganic geochemistry and estimation of dust flux: and points to new proxies under development. Although explicit protocols have been developed recently for research on ombrotrophic mires, it must be recognised that not all proxies and techniques have universal applicability, owing to differences in species assemblages, mire formation, topographic controls, and geochemical characteristics. (C) 2011 Elsevier Ltd and INQUA. All rights reserved.
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9.
  • De Vleeschouwer, Francois, et al. (författare)
  • Quantitative WD-XRF calibration for small ceramic samples and their source material
  • 2011
  • Ingår i: Geoarchaeology. - : Wiley. - 0883-6353 .- 1520-6548. ; 26:3, s. 440-450
  • Tidskriftsartikel (refereegranskat)abstract
    • A wavelength-dispersive X-ray fluorescence (WD-XRF) calibration is developed for small powdered samples (300 mg) with the purpose of analyzing ceramic artifacts that might be available only in limited quantity. This is compared to a conventional calibration using a larger sample mass (2 g). The comparison of elemental intensities obtained in both calibrations shows that the decrease in analyzed sample mass results in a linear decrease in measured intensity for the analyzed elements. This indicates that the small-and large-sample calibrations are comparable. Moreover, the elemental contents of four ceramic sherds and two potential clay sources fall well within the range of the certified reference materials that are the basis of the calibration curves. The advantage with the analytical method presented here is that it is rapid and requires only a small amount of sample that can easily be re-used for further analyses. This method has great potential in ceramic provenance studies. (C) 2011 Wiley Periodicals, Inc.
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10.
  • Li, Chuxian, et al. (författare)
  • Recent 210Pb, 137Cs and 241Am accumulation in an ombrotrophic peatland from Amsterdam Island (Southern Indian Ocean)
  • 2017
  • Ingår i: Journal of Environmental Radioactivity. - : Elsevier BV. - 0265-931X. ; 175-176, s. 164-169
  • Tidskriftsartikel (refereegranskat)abstract
    • Over the past 50 years, 210Pb, 137Cs and 241Am have been abundantly used in reconstructing recent sediment and peat chronologies. The study of global aerosol-climate interaction is also partially depending on our understanding of 222Rn-210Pb cycling, as radionuclides are useful aerosol tracers. However, in comparison with the Northern Hemisphere, few data are available for these radionuclides in the Southern Hemisphere, especially in the South Indian Ocean. A peat core was collected in an ombrotrophic peatland from the remote Amsterdam Island (AMS) and was analyzed for 210Pb, 137Cs and 241Am radionuclides using an underground ultra-low background gamma spectrometer. The 210Pb Constant Rate of Supply (CRS) model of peat accumulations is validated by peaks of artificial radionuclides (137Cs and 241Am) that are related to nuclear weapon tests. We compared the AMS 210Pb data with an updated 210Pb deposition database. The 210Pb flux of 98 ± 6 Bq·m−2·y−1 derived from the AMS core agrees with data from Madagascar and South Africa. The elevated flux observed at such a remote location may result from the enhanced 222Rn activity and frequent rainfall in AMS. This enhanced 222Rn activity itself may be explained by continental air masses passing over southern Africa and/or Madagascar. The 210Pb flux at AMS is higher than those derived from cores collected in coastal areas in Argentina and Chile, which are areas dominated by marine westerly winds with low 222Rn activities. We report a 137Cs inventory at AMS of 144 ± 13 Bq·m−2 (corrected to 1969). Our data thus contribute to the under-represented data coverage in the mid-latitudes of the Southern Hemisphere.
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