Variations of streambed vertical hydraulic conductivity before and after a flood season   总被引：1，自引：0，他引：1  

Guangdong Wu  Longcang Shu  Chengpeng Lu  Xunhong Chen  Xiao Zhang  Emmanuel K. Appiah-Adjei  Jingsi Zhu 《Hydrogeology Journal》2015,23(7):1603-1615

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‘I hate sand … it gets everywhere’—Phanerozoic sedimentary recycling from NW Africa     

James Lovell-Kennedy  Emmanuel Roquette  Stefan Schröder  Jonathan Redfern 《Basin Research》2023,35(1):187-213

Over 10,000 published detrital zircon ages have been reprocessed (applying a +10% normal and reverse concordance range) and analysed to understand the evolution of the detrital zircon record of north-west Africa during the Phanerozoic. Using dissimilarity and clustering analysis, shifts in detrital zircon populations allow interpretation of the evolution of source regions and source to sink systems throughout the Phanerozoic within the West Gondwana superfan. Previous thermochronology and field studies conducted across north-west Africa indicate significant and sustained shifts in source regions in Meso-Cenozoic times which are not recorded in the detrital zircon geochronology record. This discrepancy is most notable for Mesozoic to modern source to sink studies focused on the evolution of the Atlasic rift and opening of the Atlantic and Tethyan Oceans to the west and north respectively. Our results indicate a high degree of similarity between samples from Cambrian times onwards due to successive phases of sediment recycling. This highlights the need to integrate detrital zircon analysis with other techniques to provide confident reconstruction of sediment routing systems across Morocco. This systematic review also reveals the ubiquitous occurrence of Mesoproterozoic zircons within Moroccan sediment. No basement of this age is known from north-west Africa—often described as the ‘Mesoproterozoic Gap’, which was thought to be a diagnostic feature of sediment derived from the West African Craton. However, zircons of this age form 7% of all analysed zircons and are present in sediments from at least 700 Ma. The presence of this population is interpreted as strongly diagnostic of provenance from either the Amazonian Craton or the Eastern Gondwana Orogen within Central Africa. Their presence in the Moroccan detrital record from the Neoproterozoic onwards raises questions about the position of the West African Craton in the Proterozoic, and for the spatial extent of Mesoproterozoic orogeny within north Africa.  相似文献   

Interannual variability of the South Pacific Convergence Zone and implications for tropical cyclone genesis   总被引：3，自引：1，他引：2  

Emmanuel M. Vincent  Matthieu Lengaigne  Christophe E. Menkes  Nicolas C. Jourdain  Patrick Marchesiello  Gurvan Madec 《Climate Dynamics》2011,36(9-10):1881-1896

The interannual variability of the South Pacific Convergence Zone (SPCZ) and its influence on tropical cyclone (TC) genesis in the South Pacific are investigated using observations and ERA40 reanalysis over the 1979?C2002 period. In austral summer, the SPCZ displays four typical structures at interannual timescales. The first three are characterized by a diagonal orientation of the SPCZ and account for 85% of the summer seasons. One is close to climatology and the other two exhibit a 3° northward or southward departure from the SPCZ climatological position. In contrast, the fourth one, that only encompasses three austral summer seasons (the extreme 1982/1983 and 1997/1998 El Ni?o events and the moderate 1991/1992 El Ni?o event), displays very peculiar behaviour where the SPCZ largely departs from its climatological position and is zonally oriented. Variability of the western/central Pacific equatorial sea surface temperature (SST) is shown to modulate moisture transport south of the equator, thereby strongly constraining the location of the SPCZ. The SPCZ location is also shown to strongly modulate the atmospheric circulation variability in the South Pacific with specific patterns for each class. However, independently of its wide year-to-year excursions, the SPCZ is always collocated with the zero relative vorticity at low levels while the maximum vorticity axis lies 6° to the south of the SPCZ position. This coherent atmospheric organisation in the SPCZ region is shown to constrain tropical cyclogenesis to occur preferentially within 10° south of the SPCZ location as this region combines all the large-scale atmospheric conditions that favour the breeding of TCs. This analysis also reveals that cyclogenesis in the central Pacific (in the vicinity of French Polynesia) only occurs when the SPCZ displays a zonal orientation while this observation was previously attributed to El Ni?o years in general. Different characteristics of El Ni?o Southern Oscillation (ENSO)-related Pacific equatorial warming are shown to impact differently on the SPCZ position, suggesting that for regional scales, such as the South Pacific, the SPCZ classification is more appropriate than a simple ENSO index to characterize TC interannual variability. These findings suggest that forecasting the strength of El Ni?o through SST variations in the eastern Pacific may not be sufficient to accurately predict cyclogenesis in the South Pacific, especially east of the dateline.  相似文献   

Study of the spatial and historical distribution of sediment inorganic contamination in the Toulon bay (France)   总被引：4，自引：0，他引：4  

Tessier E  Garnier C  Mullot JU  Lenoble V  Arnaud M  Raynaud M  Mounier S 《Marine pollution bulletin》2011,62(10):2075-2086

This study presents trace elements levels in surface and deep sediments of the Toulon bay (SE France) subjected to anthropogenic inputs (navy base, harbors, etc.). The studied elements (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) are defined as priority contaminants in aquatic systems. Fifty-five points scattered on the entire bay were sampled, allowing the determination of contaminants distribution with a high resolution. Several approaches were used to assess the degree of contamination and the potential toxicity of the Toulon bay sediments: comparison to the French legislation, surface-weighted average metal concentrations, enrichment factors (EF), geoaccumulation indices (Igeo), trace element stock calculation and comparison to sediment quality guidelines. A principal component analysis was performed to reveal common behavior of the studied contaminants. Results demonstrated the very high contamination of the small bay, especially in Hg (EF up to 1500), Cu, Pb and Zn, with export to the large bay further governed by hydrodynamics.  相似文献   

Eddy resolving modelling of the Gulf of Lions and Catalan Sea   总被引：1，自引：1，他引：0  

Pierre Garreau  Valérie Garnier  Amandine Schaeffer 《Ocean Dynamics》2011,61(7):991-1003

The generation process of strong long-lived eddies flowing southwestwards along the Catalan slope was revealed through numerical modelling and in situ observations. Careful analyses of a particular event in autumn 2007 demonstrated a link between a “LATEX” eddy, which remained in the southwestern corner of the Gulf of Lions and a “CATALAN” eddy, which moved along the Catalan Shelf, since the death of the former gave birth to the latter. The origin of such eddies was found to be an accumulation of potential energy in the southwestern corner of the Gulf of Lions: under the influence of the negative wind stress curl associated with the Tramontane, a warm and less dense water body can be isolated and fed by a coastal current carrying warm water from the Catalan Sea. In summer, this structure can grow and intensify to generate a strong anticyclonic eddy. After a long period of Tramontane, a burst of southeasterlies and northerlies appeared to detach the “LATEX” eddy, which flowed out of the Gulf of Lions, migrating along the Catalan continental slope and continued into the Balearic Sea as the “CATALAN” eddy.  相似文献   

Public perception of flood hazard and flood risk in Iceland: a case study in a watershed prone to ice-jam floods   总被引：1，自引：1，他引：0  

Emmanuel Pagneux  Guðrún Gísladóttir  Salvör Jónsdóttir 《Natural Hazards》2011,58(1):269-287

Understanding and improving the public perception has become an important element in the management of flood risk worldwide. In Iceland, studying perception of flood hazard and flood risk is, however, in its early stages. This paper presents a case study on the public perception of flood hazard and flood risk in an Icelandic town prone to ice-jam floods. Awareness of the population regarding historical inundations, self estimation of flood risk and worry is considered. The factual knowledge of the residents is deconstructed in flood hazard parameters accessible to the lay population: number of events, dates, genesis and boundaries. The performance of the respondents is rated for each parameter and the influence of several predictors evaluated. The research shows three significant patterns: there is poor awareness and little worry about historical inundations in the area; experience of the past flooding events in town is the most effective source of knowledge; awareness, risk estimation and worry are not correlated.  相似文献   

Temporal evolution of weathered cataclastic material in gravitational faults of the La Clapiere deep-seated landslide by mechanical approach     

Thomas Lebourg  Hernandez Mickael  Jomard Herv��  El Bedoui Bedoui Samyr  Bois Thomas  Zerathe Swann  Tric Emmanuel  Vidal Maurin Jr 《Landslides》2011,8(2):241-252

After a few years of research, the observation and the analysis of the deep-seated landslides suggest that these are mainly controlled by tectonic structures, which play a dominant role in the deformation of massif slopes. The La Clapière deep-seated landslide (Argentera Mercantour massif) is embedded in a deep-seated gravitational slope deformation affecting the entire slope, and characterized by specific landforms (trenches, scarps??). Onsite, the tangential displacement direction of the trenches and the scarps are controlled by the tectonic structures. The reactivation of the inherited fault in gravitational faults create a gouge material exposed to an additional mechanical and chemical weathering as well as an increased of leaching. The displacement of these reactivated faults gets increasingly important around the area of the La Clapière landslide and this since 3.6?ka BP. In this study, mechanical analysis and grain size distributions were performed and these data were analysed according to their proximity the La Clapiere landslide and times of initiation of the landslide by ¹⁰Be dating. Triaxial test results show that the effective cohesion decreases and the effective angle of internal friction increases from the unweathered area to the weathered area. The whole distribution of the grain size indicates that the further the shear zone is open or developed, the further the residual material loses its finest particles. This paper suggests that the mechanical evolution along the reactivated fault is influenced by the leaching processes. For the first time, we can extract from these data temporal behaviour of the two main mechanical parameters (cohesion and angle of internal friction) from the beginning of the La Clapiere landslide initiation (3.6 ka BP) to now.  相似文献   

Deciphering the weathering processes using environmental mineralogy and geochemistry: Towards an integrated model of laterite and podzol genesis in the Upper Amazon Basin     

Emmanuel Fritsch  Etienne Balan  Nadia Régina Do Nascimento  Thierry Allard  Marion Bardy  Guilherme Bueno  Sylvie Derenne  Adolpho José Melfi  Georges Calas 《Comptes Rendus Geoscience》2011,343(2-3):188-198

This article reports major results from collaborative research between France and Brazil on soil and water systems, carried out in the Upper Amazon Basin. It reveals the weathering processes acting in the partly inundated, low elevation plateaus of the Basin, mostly covered by evergreen forest. Our findings are based on geochemical data and mineral spectroscopy that probe the crystal chemistry of Fe and Al in mineral phases (mainly kaolinite, Al- and Fe-(hydr)oxides) of tropical soils (laterites). These techniques reveal crystal alterations in mineral populations of different ages and changes of metal speciation associated with mineral or organic phases. These results provide an integrated model of soil formation and changes (from laterites to podzols) in distinct hydrological compartments of the Amazon landscapes and under altered water regimes.  相似文献   

The geometry of the Archean, Paleo- and Neoproterozoic tectonics in the Southwest Cameroon     

Sbastien Owona  Joseph Mvondo Ondoa  Lothar Ratschbacher  Simon Pierre Mbola Ndzana  Flix M. Tchoua  Georges Emmanuel Ekodeck 《Comptes Rendus Geoscience》2011,343(4):312-322

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Whiting-related sediment export along the Middle Miocene carbonate ramp of Great Bahama Bank     

Mélanie Turpin  Laurent Emmanuel  John J. G. Reijmer  Maurice Renard 《International Journal of Earth Sciences》2011,100(8):1875-1893

Modern aragonite needles are present all along the modern leeward margin of Great Bahama Bank (ODP Leg 166), while Middle Miocene sediments contain needles only in more distal areas (Sites 1006 and 1007). In contrast to the rimmed, flat-topped platform topography during the Plio-Pleistocene, the Miocene Great Bahama Bank morphology is a carbonate ramp profile. This might imply a different location and precipitation type for Miocene aragonite needles. In this study, aragonite needles in Miocene sediments were isolated using a granulometric separation method. Furthermore, the isolation of the various carbonate components enables the identification of primary versus diagenetic components. The Miocene aragonite needles are concentrated in the finest granulometric sediment fractions (<12 μm). The fraction-specific geochemical analyses (δ¹³C, δ¹⁸O and Sr elemental abundance) represent useful tools to assess the possible sources of the aragonite mud. The geochemical variation of the fractions, rich in pristine aragonite needles, and the characteristics of the needle morphology point to whiting phenomena as the main sediment source and algal fragmentation as a minor component. Both components indicate shallow-water environments as the main sediment source area. Ramp-top-related fine-grained particles now present at distal sites were likely exported as suspended material similar to present-day transport mechanisms. The scarcity of needles at proximal sites is probably linked to hydrodynamic processes but dissolution and recrystallization processes cannot be excluded. The granulometric separation approach applied here enables a better characterization of the finest carbonate particles representing an important step towards the discrimination between primary and diagenetic fine-grained components.  相似文献