One year measurements of aerosol optical properties over an urban coastal site: Effect on local direct radiative forcing     

Auromeet Saha  Marc Mallet  Jean Claude Roger  Philippe Dubuisson  Jacques Piazzola  Serge Despiau 《Atmospheric Research》2008,90(2-4):195-ICNAA07

We present results of direct aerosol radiative forcing over a French Mediterranean coastal zone based on one year of continuous observations of aerosol optical properties during 2005–2006. Monthly-mean aerosol optical depth at 440 nm ranged between 0.1 and 0.34, with high Angstrom coefficient (α > 1.2). The single scattering albedo (at 525 nm) estimated at the surface ranged between 0.7 and 0.8, indicating significant absorption. The presence of aerosols over the Mediterranean zone during summer decreases the shortwave radiation reaching the surface by as much as 26 ± 3.9 W m^− 2, and increases the top of the atmosphere reflected radiation by as much as 5.2 ± 1.0 W m^− 2. The shortwave atmospheric absorption translates to an atmospheric heating of 2.5 to 4.6 K day^− 1. Concerted efforts are needed for investigating the possible impact of the increase in heating rate on the maintenance of heat-waves frequently occurring over this coastal region during summer time.  相似文献   

Fluidization Process in Submarine Landslides: Physical and Numerical Considerations     

Sueng Won Jeong  Jacques Locat  Serge Leroueil  Jean-Loup Robert 《Marine Georesources & Geotechnology》2013,31(2):190-207

Fluidization processes in submarine landslides were studied by physical and numerical means. To examine soil-water interactions in the fluidization process, the computer axial tomography (CAT)-scan imaging techniques and laboratory vanes were utilized with a focus on the transition from failure to post-failure. Based on the results that were obtained from the scanning images and laboratory vane tests after the process of water infiltration into the soil sample, it appears that a gradual decrease in shear strength is unavoidable with increasing water content in a shear zone. From the numerical results, which were based on the dam-break problem using the transport equation coupled with the Navier-Stokes equation, if the slide is assumed to be initially unstable, a possible transition of fluidization processes that are dependent upon a change in density occurs. The density of the mud decreases with time during the flow at the interface between mud and water. The upper part of the mud pushes the lower part of the mud and then induces a rotation of mud that moves substantial distances. These results emphasize the importance of the soil-water interaction, the need for sediment rheology and the influence of the water circulation on the motion of the landslide.  相似文献   

The West African monsoon onset in 2006: sensitivity to surface albedo, orography, SST and synoptic scale dry-air intrusions using WRF     

Emmanouil Flaounas  Serge Janicot  Sophie Bastin  Rémy Roca 《Climate Dynamics》2012,38(3-4):685-708

In order to test the sensitivity of the transitional phase of the 2006 West African monsoon (WAM) onset to different mechanisms, weather research and forecasting (WRF) model simulations have been carried out addressing the role of the Saharan heat low (SHL) and its sensitivity to the albedo field and to the northern Africa orography, and the role of the sea surface temperature (SST) in the eastern tropical Atlantic and Mediterranean. Lowering albedo over the desert region induces a northward location of the inter-tropical convergence zone (ITCZ), while removing mountains in North Africa reduces rainfall over West Africa. Shifting SST forward by 15?days leads to a northward location of the ITCZ before the WAM onset. However none of these factors modifies the timing of the WAM onset in 2006. The transitional phase of the 2006 WAM onset has been examined in more detail. The enhancement of SHL intensity, combined with the development of the oceanic cold tongue in the Guinea gulf, leads to low-level moisture flux divergence in the ITCZ reducing rainfall and increasing low-level humidity over the Sahel. However, weakening of convection can be clearly attributed to dry-air intrusions in mid-levels, originating from the subtropical westerly jet and associated with Rossby wave pattern over North Africa. Sensitivity tests on the synoptic scale forcing outside of the WRF model domain confirm the dominating role of large-scale dynamics to control the transitional phase of the WAM onset and its timing. However it is shown that the regional factors can modulate this larger scale forcing.  相似文献   

Contemporaneous multi-scale structures in the Montagne des Mémises (Préalpes du Chablais, Haute-Savoie, France)     

Anne Guyomard  Jean-Yves Josnin  Jean-Claude Hippolyte  Serge Fudral 《Swiss Journal of Geoscience》2009,102(1):3-14

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Impact of tectonic erosion by subduction processes on intensity of arc volcanism     

Serge E.  Lallemand 《Island Arc》1996,5(1):16-24

Abstract According to new estimates, more than 2 km³ of terrestrial material is transported every year with the subducting lithospheric plates to depths greater than 20-30 km. A comparable amount of subducted material is partly restored to the nearby margins through underplating, diapirism or forearc volcanism; partly rejuvenated through arc and back-arc magmatism; and the rest is recycled into the deep mantle. This study emphasizes the connection between the consumption of some arcs and the intensity of arc volcanism. In many cases (Japan, Peru, Izu-Bonin, Guatemala), interruption in tectonic erosion of the margin is followed by a hiatus of arc volcanism. The delay between the presumed cause (i.e. absence of subducted arc-type crust) and the response (i.e. lack of explosive volcanism) corresponds to the time required for the subducting slab to reach the melting depth (i.e. 2-4 million years). Alternately, intense tectonic erosion of the margin is followed by paroxysms of arc volcanism. Crustal contamination of volcanic rocks may be caused directly by magma sources which may contain arc material derived from the subcrustal erosion of the margin.  相似文献   

Trace elements behavior in granite genesis: A case study The calc-alkaline plutonic association from the Querigut complex (Pyrénées,France)     

Serge Fourcade  Claude J. Allegre 《Contributions to Mineralogy and Petrology》1981,76(2):177-195

The different granitoids of the zoned Querigut complex (Hercynian Pyrenees) are associated with a series of basic to intermediate rocks ranging from hornblende-bearing peridotites to quartz-diorites. The whole complex appears as a calc-alkaline plutonic suite typical of orogenic zones. The distribution of lanthanides and other trace elements amongst coexisting minerals indicate they are essentially held by accessory phases, particularly in granitoids. This restricts the use of those elements in the calculation of petrogenetic models for acidic plutonic rocks. Magmatic differentiation, mainly by hornblende + plagioclase fractionation, can produce the basic series. This differentiation cannot directly produce the different granitoids, which require a preponderant contribution of crustal melts. The sequence of different granitoids can be explained either by an heterogeneity in the source region, or by magmatic differentiation. The most plausible interpretation of the whole complex calls for the emplacement of a mantle-derived magma into a wet, anatectic continental crust, with interactions between basic rocks and the soproduced acidic melts.  相似文献   

Eutrophication and some European waters of restricted exchange   总被引：1，自引：0，他引：1  

Paul Tett  Linda Gilpin  Harald Svendsen  Carina P. Erlandsson  Ulf Larsson  Susanne Kratzer  Eric Fouilland  Carol Janzen  Jae-Young Lee  Christian Grenz  Alice Newton  Joo Gomes Ferreira  Teresa Fernandes  Serge Scory 《Continental Shelf Research》2003,23(17-19):1635

Regions of Restricted Exchange (RREs) are an important feature of the European coastline. They are historically preferred sites for human settlement and aquaculture and their ecosystems, and consequent human use, may be at risk from eutrophication. The OAERRE project (EVK3-CT1999-0002) concerns ‘Oceanographic Applications to Eutrophication in Regions of Restricted Exchange’. It began in July 2000, and studies six sites. Four of these sites are fjords: Kongsfjorden (west coast of Spitzbergen); Gullmaren (Skagerrak coast of Sweden); Himmerfjärden (Baltic coast of Sweden); and the Firth of Clyde (west coast of Scotland). Two are bays sheltered by sand bars: Golfe de Fos (French Mediterranean); and Ria Formosa (Portuguese Algarve). Together they exemplify a range of hydrographic and enrichment conditions. The project aims to understand the physical, biogeochemical and biological processes, and their interactions, that determine the trophic status of these coastal marine RRE through the development of simple screening models to define, predict and assess eutrophication. This paper introduces the sites and describes the component parts of a basic screening model and its application to each site using historical data. The model forms the starting point for the OAERRE project and views an RRE as a well-mixed box, exchanging with the sea at a daily rate E determined by physical processes, and converting nutrient to phytoplankton chlorophyll at a fixed yield q. It thus uses nutrient levels to estimate maximum biomass; these preliminary results are discussed in relation to objective criteria used to assess trophic status. The influence of factors such as grazing and vertical mixing on key parameters in the screening model are further studied using simulations of a complex ‘research’ model for the Firth of Clyde. The future development of screening models in general and within OAERRE in particular is discussed. In addition, the paper looks ahead with a broad discussion of progress in the scientific understanding of eutrophication and the legal and socio-economic issues that need to be taken into account in managing the trophic status of RREs.  相似文献   

Evolution of sand banks     

Serge Berné 《Comptes Rendus Geoscience》2002,334(10):731-732

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Dating multistage paleofluid percolations: A K-Ar and O/O study of fracture illites from altered Hercynian plutonites at the basement/cover interface (Poitou High, France)     

Michel Cathelineau  Serge Fourcade  Stephane Buschaert  Davy Rousset  Alain Meunier  Marc Javoy 《Geochimica et cosmochimica acta》2004,68(11):2529-2542

Isotopic age determination of fluid events in basement fractures is of prime importance for the reconstruction of paleo-hydraulic regimes. However, material from fracture or wall-rock is not generally easily dated. In the case of fractures filled by minerals such as phyllosilicates, it can be expected that subsequent fluid circulation may cause partial alteration or recrystallization of the previous phyllosilicates, disturbing the isotope signature. Using a specific methodology, including the extraction process without contamination of the finest (<0.2 μm) authigenic fractions, identification of clay fractions by X-ray diffraction (XRD), scanning electron microscopy, and electron microprobe, analysis of stable isotope composition (D/H, δ¹⁸O) and K-Ar dating, fluid event ages can be estimated. This methodology was applied to the northwestern margin of the French Massif Central, where basinal brines have interacted with the sedimentary cover (infra-Toarcian formations) and the fractured Hercynian crystalline basement. During periods of unknown age, precipitates from brines sealed most basement fractures as carbonates, and a recrystallization of early Hercynian phengite (+chlorite) into illite and illite/smectite minerals occurred in the earlier fractures.XRD patterns show that the clay fraction is dominated by illite and ordered mixed-layer minerals having a relatively high amount of illite (I-S R3). In the shallowest samples beneath the paleo-surface, a late assemblage is identified as a mixture of I-S minerals, a part of them being characterized by significant amounts of swelling layers (I-S R0).The δD values of the clay fractions are fairly constant around −50 ± 10‰, but δ¹⁸O values of the same clay fractions display a wide range from 8‰ to 18‰ (SMOW). The study of the size fractions between 2 and 0.2 μm reveals a correlation between K-Ar ages and δ¹⁸O values, which cannot be related to a change in the relative amounts of clay minerals. Deep fractures (at depths of 570 and 923 m) are characterized by δ¹⁸O values around 10.3 ± 0.4‰ SMOW and old ages ranging from 253 to 272 Ma. The finest fractions (<0.2 μm) of clays located at shallow level (<300 m) beneath the paleo-surface yield the highest δ¹⁸O values (15.7-18.2‰) and the youngest K-Ar dates (188 to 198 Ma). These dates are likely to record the extensional episode and thermal anomaly related to the rifting of central Atlantic Ocean (c. 190 Ma). The other important thermal/extensional episode which affected the Aquitaine Basin, namely the opening of the Gascogne gulf at c. 120 Ma, is not detected by the K-Ar method on the clay fractions. We believe that resetting of clay-type K-Ar ages linked to recrystallization was favoured in the upper part of the basement where the ancient (Hercynian) clay minerals were destabilized by subaerial low-temperature alteration during Permo-Triassic times.From a methodologic point of view, the analytical characterization of several size fractions of clays from reactivated fractures, using both stable isotope geochemistry and K-Ar isotope geochemistry, can be considered as a powerful tool for dating fluid events when no suitable material for conventional methods is available.  相似文献   

La plate-forme carbonatée oxfordienne de Lorraine : arguments pour une ouverture vers la mer Germanique     

Cédric Carpentier  Bernard Lathuilière  Serge Ferry 《Comptes Rendus Geoscience》2004,336(1):59-66

The study of sedimentary facies in the quarry of Dompcevrin (Middle Oxfordian) located northwestward of St-Mihiel (Meuse department) provides evidences of high-energy depositional conditions. The occurrence of beaches associated with hurricane coral breccias containing megaclasts is characteristic of platform edge environments. The open sea was located northeastward, in the direction of Germany, as it is indicated by the direction of progradation of beaches. It is concluded that the Oxfordian carbonate platform of Lorraine was opened to the northeast toward the Germanic Sea during the Middle Oxfordian. To cite this article: C. Carpentier et al., C. R. Geoscience 336 (2004).  相似文献