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151.
The effects of fortnightly, semidiurnal, and quaterdiurnal lunar tidal cycles on suspended particle concentrations in the tidal freshwater zone of the Seine macrotidal estuary were studied during periods of medium to low freshwater flow. Long-term records of turbidity show semidiurnal and spring-neap erosion-sedimentation cycles. During spring tide, the rise in low tide levels in the upper estuary leads to storage of water in the upper estuary. This increases residence time of water and suspended particulate matter (SPM). During spring tide periods, significant tidal pumping, measured by flux calculations, prevents SPM transit to the middle estuary which is characterized by the turbidity maximum zone. On a long-term basis, this tidal pumping allows marine particles to move upstream for several tens of kilometers into the upper estuary. At the end of the spring tide period, when the concentrations of suspended particulate matter are at their peak values and the low-tide level drops, the transport of suspended particulate matter to the middle estuary reaches its highest point. This period of maximum turbidity is of short duration because a significant amount of the SPM settles during neap tide. The particles, which settle under these conditions, are trapped in the upper estuary and cannot be moved to the zone of maximum turbidity until the next spring tide. From the upper estuary to the zone of maximum turbidity, particulate transport is generated by pulses at the start of the spring-neap tide transition period.  相似文献   
152.
This work is part of an attempt to quantify the relationship between the permeability tensor (K) and the micro-structure of natural porous media. A brief account is first provided of popular theories used to relate the micro-structure toK. Reasons for the lack of predictive power and restricted generality of current models are discussed. An alternative is an empirically based implicit model whereinK is expressed as a consequence of a few pore-types arising from the dynamics of depositional processes. The analytical form of that implicit model arises from evidence of universal association between pore-type and throat size in sandstones and carbonates. An explicit model, relying on the local change of scale technique is then addressed. That explicit model allows, from knowledge of the three-dimensional micro-geometry to calculateK explicitly without having recourse to any constitutive assumptions. The predictive and general character of the explicit model is underlined. The relevance of the change of scale technique is recalled to be contingent on the availability of rock-like three-dimensional synthetic media. A random stationary ergodic process is developed, that allows us to generate three-dimensional synthetic media from a two-dimensional autocorrelation functionr( x , y ) and associated probability density function measured on a single binary image. The focus of this work is to ensure the rock-like character of those synthetic media. This is done first through a direct approach:n two-dimensional synthetic media, derived from single set ( ,r( x , y )) yieldn permeability tensorsK i-1,n i (calculated by the local change of scale) of the same order. This is a necessary condition to ensure thatr( x , y ) and carry all structural information relevant toK. The limits of this direct approach, in terms of required Central Process Unit time and Memory is underlined, raising the need for an alternative. This is done by comparing the pore-type content of a sandstone sample andn synthetic media derived fromr( x , y ) and measured on that sandstone-sample. Achievement of a good match ensures that the synthetic media comprise the fundamental structural level of all natural sandstones, that is a domainal structure of well-packed clusters of grains bounded by loose-packed pores.  相似文献   
153.
We provide petrographic, major and trace element data for over 30 spinel peridotite xenoliths from the Tokinsky Stanovik (Tok) volcanic field on the Aldan shield to characterize the lithospheric mantle beneath the south-eastern margin of the Siberian craton, which formed in the Mesoproterozoic. High equilibration temperatures (870–1,010°C) of the xenoliths and the absence of garnet-bearing peridotites indicate a much thinner lithosphere than in the central craton. Most common among the xenoliths are clinopyroxene-poor lherzolites and harzburgites with Al2O3 and CaO contents nearly as low as in refractory xenoliths from kimberlite pipes (Mir, Udachnaya) in the central and northern Siberian craton. By contrast, the Tok peridotites have higher FeO, lower Mg-numbers and lower modal orthopyroxene and are apparently formed by shallow partial melting (3 GPa). Nearly all Tok xenoliths yield petrographic and chemical evidence for metasomatism: accessory phlogopite, amphibole, phosphates, feldspar and Ti-rich oxides, very high Na2O (2–3.1%) in clinopyroxene, LREE enrichments in whole-rocks.Electronic Supplementary Material Supplementary material is available for this article at  相似文献   
154.
The current formulations of the Fe–Ti oxide thermobarometer (titanomagnetite–ilmenitess) fail to reproduce experimental results, in particular at the high temperatures that are relevant for basaltic assemblages. With the aim of improving the experimental basis of the calibration in the Fe–Ti–O system, we have synthesised assemblages of titanomagnetite–ilmenitess (Tmt–Ilmss), ilmenitess–pseudobrookitess (Ilmss–Psbss) and single-phase samples under a wide range of fO2 (fixed with CO/CO2 mixtures or by solid oxygen buffers) in sub-solidus conditions (1,000–1,300°C) at 1 bar. Runs lasted 24 h at 1,300°C and up to 240 h at 1,000°C and were terminated by quenching in water. All run products are polycrystalline, roughly equigranular aggregates, with grain sizes of 10–50 m. They were examined and analysed with the SEM and EMP. Tmt compositions are broadly in accordance with the current models at moderate fO2, but significantly richer in Ti at low fO2 and high T, due to cationic vacancies. Ilmss compositions depart from the predicted values practically at all fO2 and T conditions, which is related to unsatisfactory thermodynamic models for the rhombohedral oxide. For Ilmss–Psbss assemblages the best agreement between our data and current calculations is at 1,000°C and moderately high fO2. Otherwise, experimental and calculated data strongly disagree. The experimental data set on the three Fe–Ti oxide solid solutions presented here is intended to support new versions of both the titanomagnetite–ilmenitess thermo-oxybarometer and the ilmenitess–pseudobrookitess oxybarometer.  相似文献   
155.
The southern termination of the left-lateral ‘Moyenne Durance’ Fault (FMD) consists in several segments, some being connected to WSW-trending south-verging reverse faults. To the south, the Aix fault is reactivated in a post-Oligocene strike-slip movement showing that these two faults might belong to the same system. This system seems to transfer, in turn, slip to the east-trending, south-verging Trévaresse reverse fault, allowing southward propagation of the Alpine deformation front in western Provence. Fault kinematics analysis shows lateral stress field change between the two faults. Strike-slip stress state is characterized by an average N150°E trending σ1 near the FMD termination, whilst strike-slip and reverse faulting stress states show north-trending σ1 to the south. To cite this article: P. Guignard et al., C. R. Geoscience 337 (2005).  相似文献   
156.
157.
Preliminary results about the stability of an intermediate water current   总被引:1,自引:0,他引:1  
Experiments were run on a 14 m diameter rotating platform to study the stability conditions for a constant volume flow rate current of intermediate water. The flow was introduced in a two-layer system initially at rest in solid body rotation, along the sidewall of the tank, and allowed freely to evolve. A sink collected the intermediate water and thus ensured that the free surface height was constant. Thus the upstream conditions were the rotation rate, the volume flow rate, the density and the initial width of the intermediate current, which was in geostrophic equilibrium when it left the source; i.e. its thickness along the wall at the source was fixed by this condition. The relevant parameters appear to be the Ekman and the Burger numbers. The data collected from the experiments are very consistent, and it appears that there were five typical flow regimes: (1) a stable current along the whole basin; (2) a series of cyclonic vortices attached to the outer edge of the current, with an upstream stable current; (3) a large cyclonic vortex attached to an anticyclonic instability; (4) dipoles shed from the current into the interior fluid; and (5) generation of lenses of intermediate water, similar to meddies. This last result shows that no topographical effect is required to generate such long-lived lenses, which then drift slowly upstream as the dipoles do.  相似文献   
158.
Furadan is a carbamate pesticide used widely to combat agricultural pests. However little information is available about the toxicity of furadan in aquatic macroinvertebrates. The in vivo effects of furadan were evaluated in mussels, Perna perna, and oysters, Crassostrea rhizophorae. Glutathione S-transferase (GST), catalase (CAT) and cholinesterase (ChE) activities were measured in the gills of both species exposed to furadan (100 microg/l) for 96 h. No changes were observed in GST activity in the exposed groups. CAT activity was higher (9%) in the oysters exposed to furadan. ChE activity was inhibited by 64 and 35%, respectively, in C. rhizophorae and P. perna exposed to furadan, suggesting that the former is more susceptible to the toxic effects of furadan.  相似文献   
159.
Abstract. In the field, feeding activity of the algivorous Blennius sanguinolentus increased remarkably from morning to late afternoon. Swimming is evenly distributed; other behaviour does not fall into regular daily patterns. No association was found, save in extreme values, between the distribution of any activity and environmental factors measured simultaneously. We suggest that the feeding cycle is an adaptation to the metabolic properties of green algae, the staple diet of B. sanguinolentus. Activity distributions following predictable short-term fluctuations in food quality are expected to be found in other animals.  相似文献   
160.
β-dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) concentrations were recorded from September 1999 to September 2000 in two geographically close ecosystems, differently affected by eutrophication: the Little Bay of Toulon and the Niel Bay (N.W. Mediterranean Sea, France). Little Bay had higher nutrient levels ([NO3]max. = 30.3 μM; [PO43−]max. = 0.46 μM) and higher chlorophyll a concentrations ([chl a]mean = 2.4 μg/L) compared to Niel Bay ([NO3]max. = 19.7 μM; [PO43−]max. = 0.17 μM; [chl a]mean = 0.4 μg/L). In the two sites, we measured dissolved (DMSPd < 0.2 μm) and particulate DMSP (DMSPp > 0.2 μm) concentrations. The DMSPp was particularly analysed in the 0.2–5, 5–90 and > 90 μm fractions. In the eutrophicated Little Bay, DMSPd concentrations showed a clear seasonality with high values from January to March (124–148 nM). The temporal profile of the DMSPp concentrations was similar, peaking in February–March (38–59 nM). In the less eutrophic Niel Bay, DMSPp concentrations were much lower (6–9 nM in March–April), whereas DMSPd concentrations were relatively high (110–92 nM in February–March). DMS concentrations were elevated from the end of the winter to the spring in Little Bay, ranging from 3 nM in October to 134 nM in March. In the less eutrophic Niel Bay, lower DMS levels were observed, generally not exceeding 20 nM. Each particulate fraction (0.2–5; 5–90; > 90 μm) contained less DMSP in Niel Bay than in Little Bay. At both sites, the 5–90 μm fraction made up most of the DMSPp. This 5–90 μm fraction consisted of microphytoplankton, principally Dinophyceae and Bacillariophyceae. The 5–90 μm biomass calculated from cell biovolumes, was more abundant in Little Bay where the bloom at the end of the winter (165 μg/L in March) occurred at the same time as the DMSP peaks. The estimated DMSPp to biomass ratio for the 5–90 μm fraction was always higher in Little Bay than in Niel Bay. This suggests that the high DMSP levels recorded in Little Bay were not only due to a large Dinophyceae presence in this ecosystem. Indeed, the peak of DMSPp to biomass ratio obtained from cell biovolumes (0.23 nmol/μg in March) was consistent with the proliferation of Alexandrium minutum. This Dinophyceae species may account for between 50% (2894 cells/L) and 63% (4914 cells/L) of the total phytoplankton abundance in the Little Bay of Toulon.  相似文献   
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