Dissipation length in stable layers     

J. F. Louis  A. Weill  D. Vidal-Madjar 《Boundary-Layer Meteorology》1983,25(3):229-243

An attempt is made, for an anticyclonic stable situation in the atmospheric boundary layer during November 1978, to estimate the dissipation length. The turbulent dissipation and the turbulent kinetic energy, as measured on a 100 m high mast, exhibit large variability, due to the sporadic turbulent structure of the stable layer, and associated variability of the Richardson number. A comparison with different parameterizations of the turbulent dissipation rate allows a validation of these parameterizations.  相似文献   

Structure of heavy metal sorbed birnessite. Part III: Results from powder and polarized extended X-ray absorption fine structure spectroscopy     

Alain ManceauBruno Lanson  Victor A. Drits 《Geochimica et cosmochimica acta》2002,66(15):2639-2663

The local structures of divalent Zn, Cu, and Pb sorbed on the phyllomanganate birnessite (Bi) have been studied by powder and polarized extended X-ray absorption fine structure (EXAFS) spectroscopy. Metal-sorbed birnessites (MeBi) were prepared at different surface coverages by equilibrating at pH 4 a Na-exchanged buserite (NaBu) suspension with the desired aqueous metal. Me/Mn atomic ratios were varied from 0.2% to 12.8% in ZnBi and 0.1 to 5.8% in PbBi. The ratio was equal to 15.6% in CuBi. All cations sorbed in interlayers on well-defined crystallographic sites, without evidence for sorption on layer edges or surface precipitation. Zn sorbed on the face of vacant layer octahedral sites (□), and shared three layer oxygens (O_layer) with three-layer Mn atoms (Mn_layer), thereby forming a tridentate corner-sharing (TC) interlayer complex (Zn-3O_layer-□-3Mn_layer). ^TCZn complexes replace interlayer Mn²⁺ (Mn_inter²⁺) and protons. ^TCZn and ^TCMn_inter³⁺ together balance the layer charge deficit originating from Mn_layer⁴⁺ vacancies, which amounts to 0.67 charge per total Mn according to the structural formula of hexagonal birnessite (HBi) at pH 4. At low surface coverage, zinc is tetrahedrally coordinated to three O_layer and one water molecule (^[IV]TC complex: (H₂O)-^[IV]Zn-3O_layer). At high loading, zinc is predominantly octahedrally coordinated to three O_layer and to three interlayer water molecules (^[VI]TC complex: 3(H₂O)-^[VI]Zn-3O_layer), as in chalcophanite (^[VI]ZnMn₃⁴⁺O₇·3H₂O). Sorbed Zn induces the translation of octahedral layers from −a/3 to +a/3, and this new stacking mode allows strong H bonds to form between the ^[IV]Zn complex on one side of the interlayer and oxygen atoms of the next Mn layer (O_next): O_next…(H₂O)-^[IV]Zn-3O_layer. Empirical bond valence calculations show that O_layer and O_next are strongly undersaturated, and that ^[IV]Zn provides better local charge compensation than ^[VI]Zn. The strong undersaturation of O_layer and O_next results not only from Mn_layer⁴⁺ vacancies, but also from Mn³⁺ for Mn⁴⁺ layer substitutions amounting to 0.11 charge per total Mn in HBi. As a consequence, ^[IV]Zn,Mn_layer³⁺, and Mn_next³⁺ form three-dimensional (3D) domains, which coexist with chalcophanite-like particles detected by electron diffraction. Cu²⁺ forms a Jahn-Teller distorted ^[VI]TC interlayer complex formed of two oxygen atoms and two water molecules in the equatorial plane, and one oxygen and one water molecule in the axial direction. Sorbed Pb²⁺ is not oxidized to Pb⁴⁺ and forms predominantly ^[VI]TC interlayer complexes. EXAFS spectroscopy is also consistent with the formation of tridentate edge-sharing (^[VI]TE) interlayer complexes (Pb-3O_layer-3Mn), as in quenselite (Pb²⁺Mn³⁺O₂OH). Although metal cations mainly sorb to vacant sites in birnessite, similar to Zn in chalcophanite, EXAFS spectra of MeBi systematically have a noticeably reduced amplitude. This higher short-range structural disorder of interlayer Me species primarily originates from the presence of Mn_layer³⁺, which is responsible for the formation of less abundant interlayer complexes, such as ^[IV]Zn TC in ZnBi and ^[VI]Pb TE in PbBi.  相似文献   

Analyse multirésolution croisée de pluies et débits de sources karstiquesMultiresolution cross-analysis of rainfall rates and karstic spring runoffs     

David Labat  Rachid Ababou  Alain Mangin 《Comptes Rendus Geoscience》2002,334(8):551-556

In order to quantify the quality of the rainfall/discharge relationship across time-scales, we propose the use of both orthogonal wavelet multiresolution analysis and cross-correlation analysis. By using the two techniques together, it is possible to show, scale-by-scale, the influence of the input to the system (rainfall) on the response (discharge) of the aquifer and also to relate these results to the internal structure of the aquifer and to the degree of organisation of the karst drainage. An application of this method to three Pyrenean karsts is also shown. To cite this article: D. Labat et al., C. R. Geoscience 334 (2002) 551–556.  相似文献   

Signification des ferruginisations des formations néoprotérozoı̈ques du Nord-Burkina Faso (Afrique de l'Ouest)Meaning of ironstones in the sedimentary Neoproterozoic formations of the northern Burkina Faso (western Africa)     

Alain Blot 《Comptes Rendus Geoscience》2002,334(12):909-915

There are many small ferruginous outcrops of different facies, often breccia-like, in the Neoproterozoic sedimentary formations in northern Burkina. These outcrops are made up of goethite and quartz, and are often along with high grades of various elements. It could be a question of gossans. Their large distribution in this part of the Taoudéni Basin offers it prospects as a province geochemically rich in Cu, Pb, Zn, Mo, As, Cd, Co... This basin would be a geochemical bin for ancient formations, which would have been evacuated before the Neoproterozoic. The ironstones would be the mark of further concentrations. To cite this article: A. Blot, C. R. Geoscience 334 (2002) 909–915.  相似文献   

Preliminary results on a high east–west gradient in the macrozoobenthic community structure of the macrotidal Mont Saint-Michel bay     

Sbastien Thorin  Alain Radureau  Eric Feunteun  Jean-Claude Lefeuvre 《Continental Shelf Research》2001,21(18-19)

Environmental conditions in terms of river inputs, salt marsh development, shellfish cultures, hydrodynamics and sediment characteristics are very different from the western and the eastern part of the Mont Saint-Michel bay. A large scale study on the spatial structure of the intertidal macrozoobenthic community was then performed at the bay scale in order to determinate how these various conditions may modify the community composition and species density. In terms of density, the community was globally dominated by suspension/deposit filter-feeding bivalves, as well as amphipods in the eastern high levels of the intertidal zone. Several biocoenotic assemblage of the Macoma balthica community were described and large differences in the species composition and density were observed between the eastern and the western sectors of the bay. Total density for all species and recruitment were much higher in the eastern sector than in the west. We discussed about these east–west variations in terms of hydrodynamics, sedimentation processes and trophic conditions. Indeed, the large salt marsh extension and river inputs, as well as the lack of shellfish cultures in the east, may favour high food availability for benthic invertebrates of the area whereas the low river inputs and salt marsh development, the high sedimentation process and the intensification of mussel and oyster cultures in the west may create less favourable environments.  相似文献   

Dissolved organic carbon, nitrogen and phosphorus in the N-E Atlantic and the N-W Mediterranean with particular reference to non-refractory fractions and degradation     

Alain Aminot  Roger Krouel 《Deep Sea Research Part I: Oceanographic Research Papers》2004,51(12):933

Dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) measured in deep profiles in the N-E Atlantic and in the N-W Mediterranean in the period 1984–2002 are described. After accurate validation, they show close agreement with those previously published.Classic profiles were obtained, with concentrations decreasing in deep waters. In the Mediterranean and in the Atlantic comparable concentrations were found in the 1500–2000 m waters, 44–46 μmol l⁻¹ DOC, 2.6–2.8 μmol l⁻¹ DON and 0.02–0.03 μmol l⁻¹ DOP. In the surface layers, DOC concentrations were higher, but DON and DOP concentrations lower, in the Mediterranean than in the Atlantic, leading to higher element ratios in the Mediterranean. In autumn, values were, respectively, DOC:DON 17 vs. 14, DOC:DOP 950 vs. 500 and DON:DOP 55 vs. 35. The data suggest an increase in DOC and DON in the North Atlantic Central Water over 15 years, which may be linked to the North Atlantic climatic oscillations.Refractory DOM found in the 1500–2000 m layer exhibited C:N:P ratios of 1570:100:1. The labile+semi-labile (=non-refractory) DOM (nrDOM) pool was computed as DOM in excess of the refractory pool. Its contribution to total DOM above the thermocline in the open sea amounted to 25–35% of DOC, 30–35% of DON, and 60–80% of DOP. Element ratios of the nrDOM varied among stations and were lower than those of refractory DOM, except for C:N in the Mediterranean: nrDOC:nrDON 10–19, nrDOC:nrDOP 160–530 and nrDON:nrDOP 15–38. The specific stoichiometry of DOM in the Mediterranean led us to postulate that overconsumption of carbon is probably a main process in that oligotrophic sea.By coupling non-refractory DOM stoichiometry and relationships between the main DOM elements in the water column, the relative mineralization of C, N and P from DOM was studied. Below the thermocline, the preferential removal of phosphorus with regard to carbon from the semi-labile DOM can be confirmed, but not the preferential removal of nitrogen. In the ocean surface layers, processes depend on the oceanic area and can differ from deep waters, so preferential carbon removal seems more frequent. Bacterial growth efficiency data indicate that bacteria are directly responsible for mineralization of a high proportion of DON and DOP in the deep water.  相似文献   

Narrowband acoustic identification of monospecific fish shoals     

Scalabrin  Carla; Diner  Noel; Weill  Alain; Hillion  Alain; Mouchot  Marie-Catherine 《ICES Journal of Marine Science》1996,53(2):181-188

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Partitioning of transition metals between diopside and coexisting silicate liquids. I. Nickel,cobalt and manganese     

David J. Lindstrom  Daniel F. Weill 《Geochimica et cosmochimica acta》1978,42(6):817-831

Distribution coefficients have been experimentally determined for the partitioning of nickel, cobalt and manganese between calcium-rich clinopyroxenes and coexisting silicate liquids. Temperatures ranged from 1110–1360°C and oxygen fugacities in the furnaces were controlled by gas mixtures at one atmosphere total pressure. Bulk compositions used include synthetic compositions in the system albite-anorthite-diopside and a natural basalt. Charges were doped with a few percent transition metal oxides and analyzed by electron microprobe. Measured clinopyroxene/liquid distribution coefficients range from 1.5–14 for Ni, 0.5–2.0 for Co and 0.3–1.2 for Mn. Diopside/liquid distribution coefficients for nickel are shown to be independent of Ni content over a range of from 3 ppm to 3 wt.% Ni in the liquid and to increase with decreasing temperature. From analyses of pyroxenes grown from experimental charges differing only in the amounts of transition metals present, nickel and cobalt are shown to occupy the M1 site of diopside while manganese occupies both M1 and M2.Ordinary weight ratio distribution coefficients are strongly dependent on liquid composition as well as temperature. For example, experiments on synthetic Ab-An-Di compositions give clinopyroxene/liquid distribution coefficients higher by about a factor of five than those from experiments at the same temperature on a natural basalt. For Ni and Co, which occupy only the M1 site of clinopyroxene, an equilibrium constant can be defined in terms of activities of components in the liquid and solid phases. Activities of components in the solid are approximated by their mole fractions. An activity/concentration model based on the viscosity model of BOTTINGA and WEILL (1972) is used for the liquid. This model approximates the activity of silica as its mole fraction among the network-forming components SiO₂, TiO₂, KAlO₂, NaAlO₂ and Ca_0.5AlO₂.Activities of network modifiers such as CaO are approximated as their mole fractions among the network-modifying components CaO, MgO, FeO, FeO_1.5, etc. When these estimated activities are used in the expression for the equilibrium constant, the effects of compositional differences on trace element distribution coefficients can be understood and the results of experiments on synthetic and natural compositions reconciled.  相似文献   

Natural speciation of Ni, Zn, Ba, and As in ferromanganese coatings on quartz using X-ray fluorescence, absorption, and diffraction     

Alain Manceau  Martine Lanson  Nicolas Geoffroy 《Geochimica et cosmochimica acta》2007,71(1):95-128

The mineralogy of natural ferromanganese coatings on quartz grains and the crystal chemistry of associated trace elements Ni, Zn, Ba, and As were characterized by X-ray microfluorescence, X-ray diffraction, and EXAFS spectroscopy. Fe is speciated as ferrihydrite and Mn as vernadite. The two oxides form alternating Fe- and Mn-rich layers that are irregularly distributed and not always continuous. Unlike naturally abundant Fe-vernadite, in which Fe and Mn are mixed at the nanoscale, the ferrihydrite and vernadite are physically segregated and the trace elements clearly partitioned at the microscopic scale. Vernadite consists of two populations of interstratified one-water layer (7 Å phyllomanganate) and two-water layer (10 Å phyllomanganate) crystallites. In one population, 7 Å layers dominate, and in the other 10 Å layers dominate. The three trace metals Ni, Zn, and Ba are associated with vernadite and the metalloid As with ferrihydrite. In vernadite, nickel is both substituted isomorphically for Mn in the manganese layer and sorbed at vacant Mn layer sites in the interlayer. The partitioning of Ni is pH-dependent, with a strong preference for the first site at circumneutral pH and for the second at acidic pH. Thus, the site occupancy of Ni in vernadite may be an indicator of marine vs. continental origin, and in the latter, of the acidity of streams, lakes, or soil pore waters in which the vernadite formed. Zinc is sorbed only in the interlayer at vacant Mn layer sites. It is fully tetrahedral at a Zn/Mn molar ratio of 0.0138, and partly octahedral at a Zn/Mn ratio of 0.1036 consistent with experimental studies showing that the ^VIZn/^IVZn ratio increases with Zn loading. Barium is sorbed in a slightly offset position above empty tetrahedral cavities in the interlayer. Arsenic tetrahedra are retained at the ferrihydrite surface by a bidentate-binuclear attachment to two adjacent iron octahedra, as commonly observed. Trace elements in ferromanganese precipitates are partitioned at a few, well-defined, crystallographic sites that have some elemental specificity, and thus selectivity. The relative diversity of sorption sites contrasts with the simplicity of the layer structure of vernadite, in which charge deficit arises only from Mn⁴⁺ vacancies (i.e., no Mn³⁺ for Mn⁴⁺ substitution). Therefore, sorption mechanisms primarily depend on physical and chemical properties of the sorbate and competition with other ions in solution, such as protons at low pH for Ni sorption.  相似文献   

Magnetostratigraphic dating of an intensification of glacial activity in the southern Italian Alps during Marine Isotope Stage 22     

Giovanni Muttoni  Cesare Ravazzi  Marzia Breda  Carlo Laj  Alain Mazaud 《Quaternary Research》2007,67(1):161-173

We applied magnetostratigraphy and mammal biostratigraphy to date climate-sensitive pollen cycles and lithostratigraphic units of the Pliocene-Pleistocene Leffe sedimentary succession from the Southern Alps, Italy. The Leffe section was correlated to additional sections (Casnigo, Fornaci di Ranica, and Pianengo) to construct a stratigraphic network along a common fluviatile system (the Serio River) sourced in the Southern Alps and flowing southward into the Po River Basin. We obtained a coherent scenario of climate variability for the last ∼ 2 Myr. At Leffe, lacustrine deposition commenced during the Olduvai Normal Subchron (1.94-1.78 Ma) and lasted up to a chronologic level compatible with Marine Isotope Stage (MIS) 22 (0.87 Ma). Pollen analysis revealed that climate varied cyclically from warm-temperate to cool during this time interval, but never as cold as during glacial intervals. At around MIS 22, climate cooled globally. Gravels, attributed to high-energy braided river systems fed locally by alluvial fans, prograded from the Serio River catchment area over the Leffe Basin and toward the Po Plain in response to a generalized event of vegetation withdrawal and enhanced physical erosion. At this time, Alpine valley glaciers reached their first maximum southward expansion with glacier fronts located at only ∼ 5 km upstream from Leffe.  相似文献