Dissolved trace metals in the Western Mediterranean Sea: total concentration and fraction isolated by C18 Sep-Pak technique     

Yi-Yong Yoon  Jean-Marie Martin  Marie Helen Cott 《Marine Chemistry》1999,66(3-4)

An investigation of trace metal distributions in the Western Mediterranean Sea was carried out during the RRS Discovery cruise (July 1993) in which a transect from the Strait of Gibraltar to the Strait of Sicily was conducted. Organically complexed dissolved trace metals and their total concentrations were measured to investigate the end-members and to predict the environmental capacity of the Mediterranean for potential toxic metals. The distribution of trace metals can be accounted for by the mixing of several end-members and by some atmospheric inputs to the surface water. For Pb and Fe, the effects of the atmospheric inputs are more pronounced than for the other metals. Due to the rapid exchange of water masses, the Western Mediterranean may have the ability to assimilate the increased external inputs for some trace metals such as Cu, Cd, Ni and Zn. But the external inputs for Pb and Fe exceed the removal capacity of the Western Mediterranean and these elements may accumulate in the water column of the western basin. The C18 Sep-Pak technique and direct determination by DPASV were used to determine the amount of trace metal–organic complexes. The C18 Sep-Pak column isolates only a small fraction of trace metals except for Cu. The maximum hydrophobic fractions for the studied trace metals, except for Cd and Pb, which are not detectable, were found in the subsurface layer at all stations. This maximum may well be linked to picoplankton activity and the picoplankton, prochlorophytes may have an important role in the speciation of dissolved Cu as well as Synechococcus. These organic ligands for Cu were produced at the maximum of biological activity in the Western Mediterranean basin and seem to be accumulated at halocline level by Mediterranean hydrodynamic characteristics. However, direct determination by DPASV showed that the major part of Cu, Cd and Pb, complexed by organic materials, was not isolated by C18 Sep-Pak technique.  相似文献   

Surface chemistry and structural properties of mackinawite prepared by reaction of sulfide ions with metallic iron     

Martine Mullet  Sophie BoursiquotMustapha Abdelmoula  Jean-Marie GéninJean-Jacques Ehrhardt 《Geochimica et cosmochimica acta》2002,66(5):829-836

Tetragonal FeS_1−x mackinawite, has been synthesized by reacting metallic iron with a sodium sulfide solution and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), transmission Mössbauer spectroscopy (TMS) and X-ray photoelectron spectroscopy (XPS). Based on XRD and TEM analyses, synthetic mackinawite exhibits crystallization and is identical to the natural mineral. Unit cell parameters derived from XRD data are a = b = 0.3670 nm and c = 0.5049 nm. The bulk Fe:S ratio derived from the quantitative dispersive energy analysis is practically 1. XPS analyses, however, showed that mackinawite surface is composed of both Fe(II) and Fe(III) species bound to monosulfide. Accordingly, monosulfide is the dominant S species observed at the surface with lesser amount of polysulfides and elemental sulfur. TMS analysis revealed the presence of both Fe(II) and Fe(III) in the mackinawite structure, thus supporting the XPS analysis. We propose that the iron monosulfide phase synthesized by reacting metallic iron and dissolved sulfide is composed of Fe(II) and S(-II) atoms with the presence of a weathered thin layer covering the bulk material that consists of both Fe(II) and Fe(III) bound to S(-II) atoms and in a less extent of polysulfide and elemental sulfur.  相似文献   

Geochemical characteristics of an intracontinental shoshonitic association: the example of the Damavand volcano,IranCaractéristiques géochimiques d'une association shoshonitique intracontinentale : exemple du Damavand,Iran     

Hossein Mehdizadeh  Jean-Michel Liotard  Jean-Marie Dautria 《Comptes Rendus Geoscience》2002,334(2):111-117

Lavas of the Quaternary Damavand volcano (Central Alborz, Northern Iran) have been analysed for major and trace elements. The shoshonitic character of this magmatic series is definitively confirmed and most samples correspond to banakites. The Nb, Ta and Ti negative anomalies observed in all lavas suggest that they derive from of a sub-continental lithosphere metasomatised in a subduction setting. Their variable trace element enrichments are explained both by mineral fractionation and by crustal contamination in a shallow magmatic chamber. To cite this article: H. Mehdizadeh et al., C. R. Geoscience 334 (2002) 111–117.  相似文献   

Analyse d'Image pour l'Évaluation de l'Exposition de la Côte à l'Action des Vagues     

Élizabeth L. Simms  Alvin E. Simms  & Jean-Marie M. Dubois 《Geografiska Annaler: Series A, Physical Geography》1997,79(3):167-176

A method of analysis was developed to estimate wind-induced wave heights in the coastal zone. The analysis is based on a digital bathymetry model in raster format. The model uses wind characteristics such as direction, velocity, and fetch. In addition, underwater terrain slope magnitude and orientation, and water depth are used in the computation of the model to estimate wave heights. Two analyses are shown, taking into account waves built from short fetch wind and indefinite fetch wind. The analysis was applied to Hare Bay in northern Newfoundland. First, we take into account a northerly wind of 6.9 ms⁻¹ where the fetch is 19 km or less. The estimated wave heights vary between 0 and 0.5 m. With the second application, we considered an indefinite ESE fetch wind of 17.8 ms⁻¹. In this case, the wave heights resulting from the application of the model vary between 0 and 11.8 m. We compared the modelling results based on ESE wind and the wave energy derived through visual analysis. Relationships were identified between the wave height classes and the wave energy categories.  相似文献   

Découverte d''une frayère de poissons téléosteens dans des diatomites messiniennes du Djebel Murdjadjo (environs d''Oran, Algérie)     

Jean Gaudant  Jean-Paul Saint-Martin  Mostefa Bessedik  Bouhameur Mansour  Pierre Moissette  Jean-Marie Rouchy 《Journal of African Earth Sciences》1997,24(4):511-529

A new locality of Messinian fossil fish has been found in the diatomite outcropping in the surroundings of the former “Ferme Giraud”, in the Murdjadjo Massif (near Oran, Algeria). It has yielded an oligospecific fish fauna, including five species indicative of a littoral marine environment that may have occurred in a gulf bottom. This was probably linked to a brackish lagoon, as indicated by the diatom flora.  相似文献   

Release of cadmium in the Danube estuary: contribution of physical and chemical processes as determined by an experimental approach     

Garnier JM  Guieu C 《Marine environmental research》2003,55(1):5-25

The behavior of dissolved cadmium (Cd) in the Danube estuary was investigated through field sampling and mixing experiments using Danube River water and Black Sea water. The experiments were performed by mixing these two end-member waters in various proportions, with the addition of stable or radioactive Cd to the freshwater Danube end-member prior to the mixing. The release of Cd that resulted in maximum concentrations under field conditions was well simulated by mixing experiments. The experimental results were modeled assuming that the release of Cd was the sum of the contribution of physical effects resulting from dilution effects and the contribution of chemical effects resulting from dissolved Cd-complex formation (and isotopic exchange when concerned). In the absence of dissolved Cd-complexing ligands, the release of Cd due to the dilution of the particulate phase during mixing could explain part of the maximum concentrations observed in field conditions. Kinetic effects were established by comparing the theoretical and measured contribution of chemical effects resulting from dissolved Cd-complex formation. The non-equilibrium state observed during the mixing experiment suggested the presence of particulate labile Cd that was not easily mobilized. All these features supported the hypothesis that Cd released in estuaries is controlled both by the dilution of the particulate phase and by kinetic competitive complexation between particulate ligands (covering a large spectrum of nature and strength) and dissolved ligands.  相似文献   

Geometry and structure of the Vitiaz Trench Lineament (SW Pacific)     

Bernard Pelletier  Jean-Marie Auzende 《Marine Geophysical Researches》1996,18(2-4):305-335

Swath bathymetric, sonar imagery and seismic reflection data collected during the SOPACMAPS cruise Leg 3 over segments of the Vitiaz Trench Lineament and adjacent areas provide new insights on the geometry and the stuctural evolution of this seismically inactive lineament. The Vitiaz Trench Lineament, although largely unknown, is one of the most important tectonic feature in the SW Pacific because it separates the Cretaceous crust of the Pacific Plate to the north from the Cenozoic lithosphere of the North Fiji and Lau Basins to the south. The lineament is considered to be the convergent plate boundary between the Pacific and Australian Plates during midde to late Tertiary time when the Vitiaz Arc was a continuous east-facing are from the Tonga to the Solomon Islands before the development of the North Fiji and Lau Basins. Progressive reversal and cessation of subduction from west to east in the Late Miocene-Lower Plioene have been also proposed. However, precise structures and age of initiation and cessation of deformation along the Vitiaz Trench Lineament are unknown.The lineament consists of the Vitiaz Trench and three discontinuous and elongated troughs (Alexa, Rotuma and Horne Troughs) which connect the Vitiaz Trench to the northern end of the Tonga Trench. Our survey of the Alexa and Rotuma Troughs reveals that the lineament is composed of a series of WNW-ESE and ENE-WSW trending segments in front of large volcanic massifs belonging to the Melanesian Border Plateau, a WNW trending volcanic belt of seamounts and ridges on Pacific crust. The Plateau and Pacific plate lying immediately north of the lineament have been affected by intense normal faulting, collapse, and volcanism as evidenced by a series of tilted blocks, grabens, horsts and ridges trending N 120° to N100° and N60°–70°. This tectonism includes several normal faulting episodes, the latest being very recent and possibly still active. The trend of the fault scarps and volcanic ridges parallels the different segments of the Vitiaz Trench Lineament, suggesting that tectonics and volcanism are related to crustal motion along the lineament.Although the superficial observed features are mainly extensional, they are interpreted as the result of shortening along the Vitiaz Trench Lineament. The fabric north of the lineament would result from subduction-induced normal faulting on the outer wall of the trench and the zig-zag geometry of the Vitiaz Trench Lineament might be due to collision of large volcanic edifices of the Melanesian Border Plateau with the trench, provoking trench segmentation along left-lateral ENE-WSW trending transform zones. The newly acquired bathymetric and seismic data suggest that crustal motion (tectonism associated with volcanism) continued up to recent times along the Vitiaz Trench Lineament and was active during the development of the North Fiji Basin.  相似文献   

Compressive tectonism along the eastern margin of Malaita Island (Solomon Islands)     

Jean-Marie Auzende  Loren Kroenke  J. -Y. Collot  Y. Lafoy  Bernard Pelletier 《Marine Geophysical Researches》1996,18(2-4):289-304

New bathymetric and geophysical data were collected in the region east of the island of Malaita during the SOPACMAPS II cruise of the French research vessel L'ATALANTE. This region, part of the Malaita Anticlinorium was interpreted as a piece of oceanic crust from the Ontong Java Plateau obducted over the old Solomon Islands arc during collision between the Pacific and Australian plates. It has been generally accepted that convergent motion between the Australia and Pacific plates since the Late Miocene was absorbed exclusively along the San Cristobal trench, southwest of the Solomon Islands Arc.Bathymetry, imagery, and geophysical data (magnetism, gravity, seismic) acquired during the SOPACMAPS II survey allow us to classify the successive parallel ridges mapped within the region as being recent volcanic, oceanic crust, or deformed sedimentary ridges.Seismic profiling provides evidence of successive compressive events along the Malaita margin caused by the relative motion between the Solomon Islands and the Pacific plate. The main phase of convergence probably occurred during Oligocene-early Miocene time, but some relative motion between the two domains are still being absorbed along the East Malaita boundary. The existence of active faulting in the sedimentary cover throughout the region and the present-day deformation of the outer sedimentary ridge is a good illustration of this phenomenon.  相似文献   

Comparison of free-surface and rigid-lid finite element models of barotropic instabilities     

Laurent White  Jean-Marie Beckers  Eric Deleersnijder  Vincent Legat 《Ocean Dynamics》2006,56(2):86-103

The main goal of this work is to appraise the finite element method in the way it represents barotropic instabilities. To that end, three different formulations are employed. The free-surface formulation solves the primitive shallow-water equations and is of predominant use for ocean modeling. The vorticity–stream function and velocity–pressure formulations resort to the rigid-lid approximation and are presented because theoretical results are based on the same approximation. The growth rates for all three formulations are compared for hyperbolic tangent and piecewise linear shear flows. Structured and unstructured meshes are utilized. The investigation is also extended to time scales that allow for instability meanders to unfold, permitting the formation of eddies. We find that all three finite element formulations accurately represent barotropic instablities. In particular, convergence of growth rates toward theoretical ones is observed in all cases. It is also shown that the use of unstructured meshes allows for decreasing the computational cost while achieving greater accuracy. Overall, we find that the finite element method for free-surface models is effective at representing barotropic instabilities when it is combined with an appropriate advection scheme and, most importantly, adapted meshes.  相似文献   

Discovery of a double impact crater in Libya: the astrobleme of Arkenu     

Philippe Paillou  Ake Rosenqvist  Jean-Marie Malezieux  Bruno Reynard  Tom Farr  Essam Heggy 《Comptes Rendus Geoscience》2003,335(15):1059-1069

Using orbital imaging radar, we detected a double circular structure, located in the southeastern part of the Libyan Desert, which is partially hidden under sandy sediments. Fieldwork confirmed it to be an unknown double impact crater, each crater having a diameter of about 10 km, younger than 140 Ma. Sampling on the site enabled the observation of quantities of shatter cone structures and impact breccias containing planar fractures. To cite this article: P. Paillou et al., C. R. Geoscience 335 (2003).  相似文献