Evolution of particle size and concentration in the Rhône river mixing zone: : influence of salt flocculation     

Antoine Thill  Stphane Moustier  Jean-Marie Garnier  Claude Estournel  Jean-Jacques Naudin  Jean-Yves Bottero 《Continental Shelf Research》2001,21(18-19)

The salt induced flocculation phenomenon is often proposed as a major mechanism influencing the deposition of the suspended matter near the mouth of major rivers. However, depending on the particular mixing conditions between fresh water and marine water and on suspended solids (SS) reactivity, salt induced aggregation may be a minor factor controlling fast deposition of SS. This work combines field studies and laboratory experiments in order to assess the importance of salt induced flocculation in the case of the saltwedge estuary of the Rhône river. Sampling of the mixing zone has been performed in contrasted hydrodynamic conditions from a low water discharge period (500 m³ s⁻¹) to a small flood event (2400 m³ s⁻¹) for particle counting and salinity measurements. Through laboratory experiments, it is shown that the Rhône river particulate matter has a poor average reactivity regarding salt induced flocculation. Considering the hydrodynamics of the estuary, we show that the evolution of the concentration of larger particles (>5 μm) can be explained by settling and dilution. In contrast, the smallest measured fraction (2–5 μm) shows a more complex behavior and settling processes alone cannot explain the observed particle concentrations during the field studies. Four hypotheses are discussed for explaining the 2–5 μm particle concentration evolutions.  相似文献   

Estimation de la porosité dans un matériau argileuxPorosity assessments in a clay material     

Xavier Guillot  Muzahim Al-Mukhtar  Faiza Bergaya  Jean-Marie Fleureau 《Comptes Rendus Geoscience》2002,334(2):105-109

Porosity measurements on a clay material, carried out through various microscopic techniques, show a significant difference with the total porosity macroscopically estimated. Analyses have allowed to assign this difference, whose importance is linked to the hydromechanical stresses sustained by the material, to microporous spaces lower than 2 nm and to closed pore volumes, not accessible by the used techniques. Besides, the role of the drying methods of samples, which do not allow the removal of a part of the water, is highlighted. Its elimination would lead to irreversible microtextural modifications, prejudicial to the understanding of the macroscopic behaviour of the material. To cite this article: X. Guillot et al., C. R. Geoscience 334 (2002) 105–109.  相似文献   

Accretion disc outbursts: a new version of an old model   总被引：1，自引：0，他引：1  

Jean-Marie Hameury  Kristen Menou  Guillaume Dubus  Jean-Pierre Lasota  & Jean-Marc Huré 《Monthly notices of the Royal Astronomical Society》1998,298(4):1048-1060

We have developed 1D time-dependent numerical models of accretion discs, using an adaptive grid technique and an implicit numerical scheme, in which the disc size is allowed to vary with time. The code fully resolves the cooling and heating fronts propagating in the disc. We show that models in which the radius of the outer edge of the disc is fixed produce incorrect results, from which probably incorrect conclusions about the viscosity law have been inferred. In particular we show that outside-in outbursts are possible when a standard bimodal behaviour of the Shakura–Sunyaev viscosity parameter α is used. We also discuss to what extent insufficient grid resolution has limited the predictive power of previous models. We find that the global properties (magnitudes, etc.) of transient discs can be addressed by codes using a high, but reasonable, number of fixed grid points. However, the study of the detailed physical properties of the transition fronts generally requires resolutions which are out of reach of fixed grid codes. It appears that most time-dependent models of accretion discs published in the literature have been limited by resolution effects, improper outer boundary conditions, or both.  相似文献   

Influence of spatial scales of observation on temporal change in diversity and trophic structure of fine-sand communities from the English Channel and the southern North Sea   总被引：2，自引：0，他引：2  

Ghertsos  Konstantinos; Luczak  Christophe; Dewarumez  Jean-Marie; Dauvin  Jean-Claude 《ICES Journal of Marine Science》2000,57(5):1481-1487

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Surface reactivity of the Rhône suspended matter and relation with trace element sorption     

Jean-Marie Gamier  Jean-Marie Martin  Jean-Marie Mouchel  Alain J. Thomas 《Marine Chemistry》1991,36(1-4)

The reactivity of the Rhône estuarine suspended matter is investigated through three operational parameters: the heat of immersion in water (HI), the ammonium saturation index (ASI) and the specific surface area (SSA). The two former parameters are highly correlated for samples collected both in surface river water and in its plume water and in a deeper nepheloid layer. Using both ASI and HI theoretical contributions of each main individual suspended matter component, it is shown that actual and calculated HI values are in agreement, whereas measured ASI values are significantly lower than those calculated. Surface normalization of these reactive properties is discussed on the basis of the SSA measured by the (BET) N2 adsorption. This evaluation, on freeze-dried suspended matter, appears to underestimate the actual particulate reactive surface area in the natural environment; indeed, it is shown that the ammonium ion surfacial density obtained from ASI and SSA data is unrealistically high.To verify that HI and ASI may be considered as criteria for the surface potential reactivity of particles, it has been attempted to relate these parameters and the extent of sorption of radioactive tracer, which is either discharged in the Rhone river or introduced in a batch experiment. Relationships between both ASI and HI and the content of ⁵⁴Mn, ⁶⁰Co, ⁶⁵Zn, ¹⁰⁹Cd and ¹³⁷Cs, which are established for some of them, suggest that HI and ASI are useful indicators of particulate affinity for certain metals.  相似文献   

How geographic distance and depth drive ecological variability and isolation of demersal fish communities in an archipelago system (Cape Verde, Eastern Atlantic Ocean)     

Anibal Medina  Jean-Claude Brêthes  Jean-Marie Sévigny  & Bruno Zakardjian 《Marine Ecology》2007,28(3):404-417

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Mapping the Miocene Farallon Ridge jump on the Pacific plate: a seismic line of weakness     

Emile A. Okal  Jean-Marie Bergeal 《Earth and Planetary Science Letters》1983,63(1):113-122

Bathymetric and magnetic data are used to obtain estimates, on the Pacific and Nazca plates, of the boundaries separating lithosphere generated at the old Farallon Ridge from the more recent one created at the present-day East Pacific Rise. An excellent correlation is found with the sites of known teleseismically recorded intraplate seismicity, suggesting that these boundaries, which are lines of age discontinuity in the plate, must be zones of weakness of the lithospheric plate. In particular, the so-called Region C, identified by Okal et al. as a major site of seismic release, sits on a small piece of Farallon plate, in the immediate vicinity of the northern extension of the fossil Roggeveen Rise, cut across by the East Pacific Rise during the ridge jump.  相似文献   

⁴⁰Ar/³⁹Ar ages for the alkaline volcanism and the basement of Gorringe Bank,North Atlantic ocean     

Gilbert Féraud  Janine Gastaud  Jean-Marie Auzende  Jean-Louis Olivet  Guy Cornen 《Earth and Planetary Science Letters》1982,57(1):211-226

Gorringe Bank is situated on the Europe-Africa plate boundary at the eastern end of the Azores-Gibraltar fracture zone. It has two summits, Gettysburg Bank to the Southwest and Ormonde Bank to the northeast.We applied the⁴⁰Ar/³⁹Ar stepwise heating method to date six samples of the alkaline volcanic rocks, two gabbros from the Ormonde Bank and a dolerite from the Gettysburg Bank. The results that the alkaline volcanism lasted probably for less than 6 Ma(66-60 Ma).Although the nature of this volcanism precludes any subduction feature during its setting, the alkaline volcanism of Ormonde is probably linked to Upper Cretaceous/Eocene compressive tectonic events.The basement rocks of Gorringe Bank reveal distrubed⁴⁰Ar/³⁹Ar age spectra. One plagioclase and one biotite from a gabbro give evidence for a thermic event whose age is tentatively estimated at about 75 Ma, and related to a variation in the direction of the relative movement between Europe and Africa. The more probable age given by a plagioclase of another gabbro and by a dolerite (110 Ma) corresponds to tilting northeastward of the Gorringe massif.  相似文献   

Analyses of insoluble residues of altered organic matter by C CP/MAS nuclear magnetic resonance     

Patrick Landais  Marc Monthioux  Jean-Marie Dereppe  Claudette Moreaux 《Organic Geochemistry》1988,13(4-6)

Alteration phenomena affecting organic matter during diagenesis frequently lead to the formation of residues almost insoluble. Data from ¹³C CP/MAS nuclear magnetic resonance analyses (NMR) of these residues have been compared to those obtained by other techniques such as elemental analysis, infrared spectroscopy, Rock-Eval pyrolysis or gas chromatography. Three examples of alteration phenomena have been chosen: the artificial and natural oxidation of coals, the biodegradation of oils and solid bitumens, and the radiolytic degradation of organic matter. NMR results and those obtained by other techniques converge on similar general conclusions. Additional information can be extracted from ¹³C NMR data: e.g. definition of the phenol/carbonyl ratio, transformation of the aromatic network and aromatic ring substitution. These comparisons are good evidence for the reliability of non-destructive analysis of the insoluble fraction of altered organic material by ¹³C CP/MAS NMR.  相似文献   

Reconstruction and analysis of long-term satellite-derived sea surface temperature for the South China Sea     

Hong-Ngu T. Huynh  Aida Alvera-Azcárate  Alexander Barth  Jean-Marie Beckers 《Journal of Oceanography》2016,72(5):707-726

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