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   

Hydrothermally enhanced magnetization at the center of the Haughton impact structure?          下载免费PDF全文

W. Zylberman  Y. Quesnel  P. Rochette  G. R. Osinski  C. Marion  J. Gattacceca 《Meteoritics & planetary science》2017,52(10):2147-2165

Haughton is a ~24 Myr old midsize (apparent diameter 23 km) complex impact structure located on Devon Island in Nunavut, Canada. The center of the structure shows a negative gravity anomaly of ?12 mGal coupled to a localized positive magnetic field anomaly of ~900 nT. A field expedition in 2013 led to the acquisition of new ground magnetic field mapping and electrical resistivity data sets, as well as the first subsurface drill cores down to 13 m depth at the top of the magnetic field anomaly. Petrography, rock magnetic, and petrophysical measurements were performed on the cores and revealed two different types of clast‐rich polymict impactites: (1) a white hydrothermally altered impact melt rock, not previously observed at Haughton, and (2) a gray impact melt rock with no macroscopic sign of alteration. In the altered core, gypsum is present in macroscopic veins and in the form of intergranular selenite associated with colored and zoned carbonate clasts. This altered core has a natural remanent magnetization (NRM) four to five times higher than materials from the other core but the same magnetic susceptibility. Their magnetization is still higher than the surrounding crater‐fill impact melt rocks. X‐ray fluorescence data indicate a similar proportion of iron‐rich phases in both cores and an enrichment in silicates within the altered core. In addition, alternating‐field demagnetization results show that one main process remagnetized the rocks. These results support the hypothesis that intense and possibly localized post‐impact hydrothermal alteration enhanced the magnetization of the clast‐rich impact melt rocks by crystallization of magnetite within the center of the Haughton impact structure. Subsequent erosion was followed by in situ concentration in the subsurface leading to large magnetic gradient on surface.  相似文献   

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   

Microscale investigations of microbial communities in coastal surficial sediments   总被引：3，自引：0，他引：3  

Marion Köster  Rainer Wardenga  & Maja Blume 《Marine Ecology》2008,29(1):89-105

The upper millimeters of sediments are considered major locations of microbial colonization and activity. The goal of our study was to investigate variations of microbial communities in the uppermost sediment layers of the coastal Baltic Sea with emphasis on the complex interplay between microbiology and physico‐chemical sediment properties. We selected a high‐resolution methodological approach that combined the cryolanding sampling technique (spatial resolution of 250 μm) with microsensor‐, spectrophotometric and microscopic analyses. While the oxygen penetration depths in dark conditions ranged from 1.4 mm to 2.6 mm during the study period, this zone expanded by about 1 mm in light and could be divided into three micro‐horizons: (i) an upper zone with a high net O₂ production, (ii) an intermediate zone with increased O₂ consumption on account of light‐stimulated respiration and (iii) a lower zone with lower O₂ consumption. Time‐series experiments revealed a rapid response of the benthic microbial community to altered light intensities. In May and July, the net O₂ budget in the porewater of sediments was positive within 35 and 22 min after illumination, respectively, whereas in June O₂ production exceeded O₂ consumption after 112 min. The thickness of the O₂ production and O₂ consumption micro‐zones decreased from May to July coinciding with an increase in temperature. In May, sites of enhanced O₂ consumption were closely associated with subsurface maxima of microbial numbers and enzymatic activities indicating a tight coupling between photoautotrophic and heterotrophic processes between 1‐ and 2‐mm depth. In June and July, the microbial abundance and enzymatic activity hardly varied with depth. Spatial and temporal microheterogeneity of microbial distribution and activity in O₂ gradients was seen as a reflection of the complex interplay between microbiology and physico‐chemical sediment properties.  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   

Whose sustainability? Top–down participation and emergent rules in marine protected area management in Indonesia     

Marion Glaser  Wasistini Baitoningsih  Sebastian C.A. Ferse  Muhammad Neil  Rio Deswandi 《Marine Policy》2010

A review of a major community-based marine protected area programme (CB-MPA) in an Indonesian island archipelago is the point of departure for this article. Despite a well-designed institutional structure to facilitate local participation, local knowledge about the CB-MPA is found to be low and resource access and influence on decision-making in the programme is negligible for the majority of islanders. At the same time, most of those who know about the programme consider it as pertaining to the public authority only. These findings stand in contrast to evidence on non-formal ways of protecting and managing marine areas in the same geographical area but outside the formal MPA institutional framework. In particular, the article identifies a number of emergent rules-in-use in marine management, which operate parallel to legally established MPAs. It is argued that emergent forms of marine area protection such as non-formal self-organising island exclusion zones (IEZ) offer as yet mostly unused potentials for formal MPA development, particularly in those coastal and marine areas without traditional forms of marine and coastal management.  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   

Seasonal changes in blood cells of Arctic char (Salvelinus alpinus L.) from a high mountain lake     

Rudolf Hofer  Marion Stoll  Nikolaus Romani  Franz Koch  Holmer Sordyl 《Aquatic Sciences - Research Across Boundaries》2000,62(4):308-319

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Cathodoluminescence microanalysis of silica and amorphized quartz     

Marion A. Stevens-Kalceff 《Mineralogy and Petrology》2013,107(3):455-469

Cathodoluminescence (CL) techniques are used to investigate the defect structures of pure synthetic silicon dioxide (SiO₂) polymorphs. Pure, synthetic Types I, II, III and IV amorphous SiO₂ polymorphs, pure, synthetic crystal α-SiO₂ and pure, synthetic amorphized crystal α-SiO₂ have been investigated and their characteristic defects have been determined and compared. The CL emission from pure SiO₂ polymorphs is generally related to local point defects in the tetrahedrally coordinated SiO₂ host lattice. A range of CL emissions associated with non bridging oxygen defects, oxygen deficient defects and the radiative recombination of self trapped excitons are observed from both the pure synthetic crystal and amorphous SiO₂ polymorphs. In addition CL emissions associated with residual concentrations of Aluminium impurities are also observed from α-SiO₂ (quartz) and Type I and II a-SiO₂ (fused quartz). Localised amorphous micro-volumes may exist within natural α-SiO₂ due to the presence of a high concentration of pre-existing or induced defects. Amorphization of α-SiO₂ diminishes the difference between the defect structures and associated CL from α-SiO₂ and a-SiO₂. Thus CL investigation of the defect structure of a-SiO₂ polymorphs provides useful insight into the microstructure of amorphized α-SiO₂.  相似文献