Distribution and chronology of Pleistocene permafrost features in France: Database and first results     

Pascal Bertran  Eric Andrieux  Pierre Antoine  Sylvie Coutard  Laurent Deschodt  Philippe Gardère  Marion Hernandez  Claude Legentil  Arnaud Lenoble  Morgane Liard  Norbert Mercier  Olivier Moine  Luca Sitzia  Brigitte Van Vliet‐Lanoë 《Boreas: An International Journal of Quaternary Research》2014,43(3):699-711

Numerous periglacial features (polygons, nets, soil stripes, ice‐wedge pseudomorphs and sand‐wedge casts, involutions) have been recorded in France by examining bibliographical sources and aerial photographs. These data show that a large part of France was affected by permafrost during the Pleistocene and only the southern Aquitaine Basin and Languedoc seem to have been beyond its maximum extent. The first OSL ages obtained from the aeolian infill of wedge structures indicate that at least two phases of thermal contraction cracking occurred in southwestern France between ～25 and 36 ka. Chronostratigraphical data from loess in northern France indicate that these episodes correspond to the formation of ice‐wedge networks associated with tundra gleys. In the latter region, two additional permafrost episodes probably occurred during the Last Glacial, the older one corresponding to the end of Marine Isotope Stage (MIS) 4 around 60 ka and the more recent one to MIS 2 around 19–16 ka. Although stratigraphical data indicate that these episodes were relatively short (about one millennium), relict permafrost may have existed for longer periods in northern France.  相似文献   

First alkaline magmatism during Iberia–Newfoundland rifting     

Marion Grange  Urs Schärer  Guy Cornen  Jacques Girardeau 《地学学报》2008,20(6):494-503

The age and origin of alkaline rocks emplaced into the sediments of the rift‐related continental Lusitanian basin were investigated to constrain earliest magmatic activity occurring prior to oceanic plate formation between Iberia and Newfoundland. The U–Pb titanite ages are 146.5 ± 1.6 (2σSTERR), 145.3 ± 1.4 and 142.3 ± 1.0 Ma, and initial Pb isotopic ratios of feldspars lie at 18.418–18.978 for ²⁰⁶Pb/²⁰⁴Pb, at 15.594–15.925 for ²⁰⁷Pb/²⁰⁴Pb and at 37.105–39.216 for ²⁰⁸Pb/²⁰⁴Pb. Initial ⁸⁷Sr/⁸⁶Sr ratios measured in the same feldspar fractions lie at 0.705409–0.706462. This episode of magmatic activity lasting for at least 4.2 ± 2.6 Myr most likely marks a phase of maximum lithospheric thinning during which zones of weakness were created to allow deep magmas to reach the surface. Such zones are preferentially re‐activated Palaeozoic faults of the Iberian plate. The isotope data suggest that the dominant volume of alkaline magmas was generated by partial melting of the metasomatized subcontinental Iberian mantle.  相似文献   

The influence of climate,hydrology and permafrost on Holocene peat accumulation at 3500 m on the eastern Qinghai–Tibetan Plateau     

David J. Large  Baruch Spiro  Marion Ferrat  Michaela Shopland  Malin Kylander  Kerry Gallagher  Xiangdong Li  Chengde Shen  Goran Possnert  Gan Zhang  W. George Darling  Dominik Weiss 《Quaternary Science Reviews》2009,28(27-28):3303-3314

Peatland of the eastern Qinghai–Tibetan Plateau lies at the convergence of the East Asian and Indian monsoon systems in eastern Asia. To understand the evolution of this peatland and its potential to provide new insights into the Holocene evolution of the East Asian monsoon a 6 m peat core was collected from the undisturbed central part of a peat deposit near Hongyuan. The age-depth profile was determined using 16 ¹⁴C-AMS age dates, the peat analysed for a range of environmental variables including carbon, nitrogen and hydrogen concentration, bulk density, δ¹³C and the associated spring water analysed for hydrogen and oxygen isotopes. The age-depth profile of the recovered peat sequence covers the period from 9.6 to 0.3 kyr BP and is linear indicating that the conditions governing productivity and decay varied little over the Holocene. Using changes in carbon density, organic carbon content and its δ¹³C, cold dry periods of permafrost characterised by low density and impeded surface drainage were identified. The low δ¹⁸O and δD values of the spring water emanating around the peat deposit, down to ?13.8 and ?102‰ (VSMOW), respectively, with an inverse relationship between electrical conductivity and isotopic composition indicate precipitation under colder and drier conditions relative to the present day. In view of the current annual mean air temperature of 1 °C this suggests conditions in the past have been conducive to permafrost. Inferred periods of permafrost correspond to independently recognised cold periods in other Holocene records from across China at 8.6, 8.2–7.8, 5.6–4.2, 3.1 and 1.8–1.5 kyr BP. The transition to a cold dry climate appears to be more rapid than the subsequent recovery and cold dry periods at Hongyuan are of longer duration than equivalent cold dry periods over central and eastern China. Light–dark banding peat on a scale of 15–30 years from 9.6 to 5.5 kyr BP may indicate a strong influence of decadal oscillations possibly the Pacific Decadal Oscillation and a potential link between near simultaneous climatic changes in the northwest Pacific, ENSO, movement of the Intertropical Convergence Zone and the East Asian Monsoon.  相似文献   

REDD herrings or REDD menace: Response to Beymer-Farris and Bassett     

Neil D. Burgess  Shadrack Mwakalila  Pantaleo Munishi  Marion Pfeifer  Simon Willcock  Deo Shirima  Seki Hamidu  George B. Bulenga  Jason Rubens  Haji Machano  Rob Marchant 《Global Environmental Change》2013,23(5):1349-1354

Norwegian funded REDD+ projects in Tanzania have attracted a lot of attention, as has the wider REDD+ policy that aims to reduce deforestation and degradation and enhance carbon storage in forests of the developing countries. One of these REDD+ projects, managed by WWF Tanzania, was criticised in a scientific paper published in GEC, and consequently in the global media, for being linked to attempted evictions of communities living in the Rufiji delta mangroves by the Government of Tanzania, allegedly to make the area ‘ready for REDD’. In this response, we show how this eviction event in Rufiji mangroves has a history stretching back over 100 years, has nothing to do with REDD+ or any policy changes by government, and is not in any way linked to the work of any WWF project in Tanzania. We also outline some of the broader challenges faced by REDD+ in Tanzania.  相似文献   

Restored Eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis> L.) as a Refuge for Epifaunal Biodiversity in Mid-Western Atlantic Coastal Bays     

Jonathan S. Lefcheck  Scott R. Marion  Robert J. Orth 《Estuaries and Coasts》2017,40(1):200-212

As nearshore ecosystems are increasingly degraded by human activities, active restoration is a critical strategy in ensuring the continued provision of goods and services by coastal habitats. After being absent for nearly six decades, over 1800 ha of the foundational species eelgrass (Zostera marina L.) has been successfully re-established in the coastal bays of the mid-western Atlantic, USA, but nothing is known about the recovery of associated animal communities in this region. Here, we determine the patterns and drivers of functional recovery in epifaunal invertebrates associated with the restored eelgrass habitat from 2001 to 2013. After less than a decade, the invertebrate community in the restored bed was richer, more even, and exhibited greater variation in functional traits than a nearby reference bed. Analysis of a suite of environmental and physical variables using random forests revealed these differences were primarily due to the increasing area and density of eelgrass, a direct consequence of ongoing restoration efforts. Based on analysis of functional traits, we propose that the rapid life histories of constituent organisms may have played a key role in their successful recovery. We also speculate that diverse epifaunal communities may have contributed to the restoration success through a well-described mutualism with eelgrass. Given that restored eelgrass now make up 32 % of total seagrass cover in the mid-Atlantic coastal bays, this restoration may conserve regional biodiversity by providing new and pristine habitat, particularly given the general decline of existing eelgrass in this region.  相似文献   

Nitrile,Latex, Neoprene and Vinyl Gloves: A Primary Source of Contamination for Trace Element and Zn Isotopic Analyses in Geological and Biological Samples          下载免费PDF全文

Marion Garçon  Lucie Sauzéat  Richard W. Carlson  Steven B. Shirey  Mélanie Simon  Vincent Balter  Maud Boyet 《Geostandards and Geoanalytical Research》2017,41(3):367-380

Exogenic contamination is of primary concern for geochemical and biological clean laboratories working with sample sizes at the nanogram or even subpicogram level. Here, we determined sixty trace elements in fifteen different types of gloves from major suppliers world‐wide to evaluate whether gloves could be potential sources of contamination for routine trace element and isotope measurements. We found that all gloves contain some trace elements that can be easily mobilised in significant amounts. In weak acid at room temperature, the tested gloves released up to 17 mg of Zn, more than 1 μg of Mg, Ti, Mn, Fe, Rb, Sr, Zr, Sn, Hf and Pb and between 100 and 1000 ng of Li, Sc, V, Cr, Ni, Cu, Ga, As, Se, Y, Ag, Ba, La, Ce, Nd, Tl and Th. Vinyl gloves released lower quantities of biologically and geologically important elements, with the exception of In and Sn. Isotopic analyses indicate that all gloves share roughly the same Zn isotopic composition (average δ⁶⁶Zn = +0.10 ± 0.32‰ (2s)). A single contact between glove and labware releases an average of ~ 6 ng of Zn and hence can significantly shift δ⁶⁶Zn above the precision level when the amount of Zn determined is below 500 ng.  相似文献   

The impact of climate changes during the Holocene on vegetation in northern French Guiana     

Vincent Freycon  Marion Krencker  Robert Nasi 《Quaternary Research》2010,73(2):220-225

The impact of climatic changes that occurred during the last glacial maximum and the Holocene on vegetation changes in the Amazon Basin and the Guiana Shield are still widely debated. The aim of our study was to investigate whether major changes in vegetation (i.e. transitions between rainforests and C₄ savannas) occurred in northern French Guiana during the Holocene. We measured variations in the δ¹³C of soil organic matter at eight sites now occupied by forest or savannah. The forest sites were selected to cover two regions (forest refugia and peneplains) which are thought to have experienced different intensities of disturbance during the latest Pleistocene and the Holocene. We found that none of the forest sites underwent major disturbances during the Holocene, i.e. they were not replaced by C₄ savannahs or C₄ forest savannahs for long periods. Our results thus suggest that tropical rainforests in northern French Guiana were resilient to drier climatic conditions during the Holocene. Nevertheless, geographical and vertical variations in the ¹³C of SOM were compatible with minor changes in vegetation, variations in soil processes or in soil physical properties.  相似文献   

Non-isoprenoid macrocyclic glycerol diethers associated with authigenic carbonates     

Marion Baudrand  Vincent Grossi  Richard Pancost  Giovanni Aloisi   《Organic Geochemistry》2010,41(12):1341-1344

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Scales as a challenge for vulnerability assessment   总被引：4，自引：4，他引：0  

Alexander Fekete  Marion Damm  Jörn Birkmann 《Natural Hazards》2010,55(3):729-747

The aim of this paper is to introduce scale as a basic tool for improving the conceptual structure of vulnerability assessments. The terminology useful for vulnerability assessments and the current use of scale issues in theoretical vulnerability frameworks will be discussed briefly. Two case studies working on sub-national and on local level will demonstrate problems as well as benefits resulting from scale implications. Both assessments analyse vulnerability in context to river floods in Germany. In order to develop a spatial comparison and to integrate topics like environment and society, vulnerability assessments need to be aware of scale implications. The main point is that a scale debate on a broader spectrum than just in technical spatial terms is missing in vulnerability and risk conceptualisations so far. Vulnerability assessments and scale are highly intertwined, not only in technical application but also in conceptualisation, which needs more scientific development.  相似文献   

Understanding multiple thresholds of coupled social–ecological systems exposed to natural hazards as external shocks     

Fabrice G. Renaud  Jörn Birkmann  Marion Damm  Gilberto C. Gallopín 《Natural Hazards》2010,55(3):749-763

External suffusion, as selective erosion of fine particles through the contact with a coarser layer and moving away, is an important phenomenon in dams which may lead to their failure. To study the initiation of external suffusion, caused by water level increase upstream the dam, a series of experimental investigations were conducted on laboratory-scale model, in the hydrodynamic laboratory of école polytechnique de Montreal. On the built model, clay/moraine formed the core, sand was used as a filter and gravel performed the role of the pervious layer. Several different models (in geometry and constituent materials) were built and subjected to the water level increase upstream, which resulted in changes in the hydraulic gradient. The results showed no evidence of considerable suffusion on the clay/moraine and sand interface, while the visual and quantitative data show the presence of suffusion on the sand and gravel interface. The results of the experiments show that, when focusing on the critical hydraulic gradient that initiates the movement of the clay/moraine particles, it can be concluded that despite the differences in test conditions, the critical hydraulic gradient has approximately the same value in all cases. It was also shown that increasing the length of the filter layer or applying stair-like slopes does not have great impacts on the initiation of suffusion, whereas the gravel-size distribution has a great impact on the erosion rate.  相似文献