Deep strong currents and sediment transport in the Northwestern Mediterranean Sea     

Claude Millot  André Monaco 《Geo-Marine Letters》1984,4(1):13-17

The Petit Rhône Canyon (Gulf of Lions) is incised by a narrow meandering thalweg. Two current meters were moored near the bottom, one in the channel and the other on the levee. None of the measured currents is associated with the sediment transport peculiar to deep-sea fan building. This transport is mainly influenced by relatively high speeds (1 h means up to 48 cm/s; 1 day means > 30 cm/s) measured in diverse directions.  相似文献   

Changes in the northern Gulf of St. Lawrence ecosystem estimated by inverse modelling: Evidence of a fishery-induced regime shift?   总被引：1，自引：0，他引：1  

Claude Savenkoff  Martin Castonguay  Denis Chabot  Mike O. Hammill  Hugo Bourdages  Lyne Morissette   《Estuarine, Coastal and Shelf Science》2007,73(3-4):711-724

Mass-balance models have been constructed using inverse methodology for the northern Gulf of St. Lawrence for the mid-1980s, the mid-1990s, and the early 2000s to describe ecosystem structure, trophic group interactions, and the effects of fishing and predation on the ecosystem for each time period. Our analyses indicate that the ecosystem structure shifted dramatically from one previously dominated by demersal (cod, redfish) and small-bodied forage (e.g., capelin, mackerel, herring, shrimp) species to one now dominated by small-bodied forage species. Overfishing removed a functional group in the late 1980s, large piscivorous fish (primarily cod and redfish), which has not recovered 14 years after the cessation of heavy fishing. This has left only marine mammals as top predators during the mid-1990s, and marine mammals and small Greenland halibut during the early 2000s. Predation by marine mammals on fish increased from the mid-1980s to the early 2000s while predation by large fish on fish decreased. Capelin and shrimp, the main prey in each period, showed an increase in biomass over the three periods. A switch in the main predators of capelin from cod to marine mammals occurred, while Greenland halibut progressively replaced cod as shrimp predators. Overfishing influenced community structure directly through preferential removal of larger-bodied fishes and indirectly through predation release because larger-bodied fishes exerted top-down control upon other community species or competed with other species for the same prey. Our modelling estimates showed that a change in predation structure or flows at the top of the trophic system led to changes in predation at all lower trophic levels in the northern Gulf of St. Lawrence. These changes represent a case of fishery-induced regime shift.  相似文献   

Gills of hydrothermal vent annelids: Structure, ultrastructure and functional implications in two alvinellid species     

Claude Jouin  Franoise Gaill 《Progress in Oceanography》1990,24(1-4)

The anatomy, fine structure, diffusion distances and respiratory surface areas of the gills of two species of the polychaete family Alvinellidae have been investigated. Each gill consists of a stem on which are inserted two opposite rows of respiratory elements: flat sickle-shaped lamellae in Alvinella pompejana and cylindrical filaments in Paralvinella grasslei. Both lamellae and filaments have a ciliated mucous epidermis, a central layer of supporting and muscle cells and are devoid of coelomic cavity. Each respiratory element possesses one afferent and one efferent marginal vessel, united to each other distally, and connected proximally to separate longitudinal vessels running in the stem. Superficial parallel blood spaces connect the marginal vessels across the lamella or filament. Deeper, between the basal laminae of the epidermis and that of the central cell layer, a blood sinus is also present. The marginal vessels and the superficial blood spaces actually are intraepidermal extensions of this deep blood sinus. The diffusion distances are very small owing to the intraepidermal position of the respiratory blood spaces. The specific gill surface areas in A. pompejana and P. grasslei are the largest known today in polychaetes, respectively 12 and 47 cm² per g wet weight. The distinctive features of the gills are possibly related to a low oxygen content of the ambient seawater. Numerous crystalline granules scattered in the gill epidermis suggest that this epithelium has a detoxifying function.  相似文献   

Compressibility and permeability of sand–kaolin mixtures. Experiments versus non‐linear homogenization schemes     

Claude Boutin  Grzegorz Kacprzak  Doanh Thiep 《国际地质力学数值与分析法杂志》2011,35(1):21-52

This study deals with the behaviour of mixtures of sand and saturated kaolin paste considered as composite materials made of permeable and deformable (with non‐linear behaviour) matrix (the kaolin paste) with rigid and impervious inclusions (the sand grains). Oedometric and permeability tests highlight the key role of the state of the clay paste, and show the existence of a threshold of sand grain concentration above which a structuring effect influences both compressibility and permeability. At the light of these experiments two homogenization schemes (with simplifying assumptions to make the problem manageable) are considered to model these two parameters. Qualitative and quantitative comparisons with experimental data point out their respective domain of interest and limitations: a tangent homogenization scheme is shown to be sufficient to describe the macroscopic properties for dilute sand concentration; above the concentration threshold, the structuring effect is captured by the new homogenization scheme developed in this paper. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Measure of the exponential splitting of the homoclinic tangle in four-dimensional symplectic mappings     

Elena Lega  Massimiliano Guzzo  Claude Froeschlé 《Celestial Mechanics and Dynamical Astronomy》2009,104(1-2):191-204

Using four-dimensional symplectic maps as a model problem, we numerically compute the unstable manifolds of the hyperbolic manifolds of the phase space related to the single resonances. We measure an exponential dependence of the size of the lobes of these manifolds through many orders of magnitude of the perturbing parameter. This is an indirect numerical verification of the exponential decay of the normal form, as predicted by the Nekhoroshev theorem. The variation of the size of the lobes turns out to be correlated to the diffusion coefficient.  相似文献   

A numerical study of the hyperbolic manifolds in a priori unstable systems. A comparison with Melnikov approximations     

Elena Lega  Massimiliano Guzzo  Claude Froeschlé 《Celestial Mechanics and Dynamical Astronomy》2010,107(1-2):115-127

Using numerical methods we study the hyperbolic manifolds in a model of a priori unstable dynamical system. We compare the numerically computed manifolds with their analytic expression obtained with the Melnikov approximation. We find that, at small values of the perturbing parameter, the topology of the numerically computed stable and unstable manifolds is the same as in their Melnikov approximation. Increasing the value of the perturbing parameter, we find that the stable and unstable manifolds have a peculiar topological transition. We find that this transition occurs near those values of the perturbing parameter for which the error terms of Melnikov approximations have a sharp increment. The transition value is also correlated with a change in the behaviour of dynamical quantities, such as the largest Lyapunov exponent and the diffusion coefficient.  相似文献   

Local and remote impacts of a tropical Atlantic salinity anomaly   总被引：1，自引：1，他引：0  

Juliette Mignot  Claude Frankignoul 《Climate Dynamics》2010,35(7-8):1133-1147

The climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical Atlantic are investigated in a coupled ocean–atmosphere general circulation model. Locally, the salinity increase leads to a rapid deepening and cooling of the surface mixed layer. This induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current. A remote atmospheric response to the tropical Atlantic perturbation is detected in the North Atlantic sector after ten years. It has the form of a robust wave-like tropospheric perturbation seemingly excited by the weakening of atmospheric deep convection over the Amazonian basin. Meanwhile, the salt anomaly is carried northward by the mean oceanic circulation. It is traced up to the convection sites and then on its return path at depth towards lower latitudes. Consistent with the density increase, deep convection is enhanced after the arrival of the salt anomaly and the Atlantic meridional overturning circulation (AMOC) intensifies about 20 years after the beginning of the perturbation. The adjustment of the tropical Atlantic to the AMOC intensification then modifies its initial response to the freshwater forcing, leading to a weaker cooling in the northern tropical Atlantic than in the southern tropical Atlantic, a slight northward shift of the tropical Atlantic precipitation pattern and an intensification of the North Brazil current. On the other hand, no significant anomalous precipitations are found in the Pacific. The initial remote atmospheric response is also modulated, by an NAO-like response to the AMOC intensification.  相似文献   

Rivières & rivaux. Les frontières de l'eau,par Vazken Andréassian et Jean Margat     

Claude Cosandey 《水文科学杂志》2013,58(8)

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⁸⁷Rb-⁸⁷Sr age of fragments and soils from the lunar sea of fertility     

Jean Louis Birck  Claude J Allegre 《Geochimica et cosmochimica acta》1973,37(9):2025-2031

The Luna 16 materials were dated by the Rb-Sr method.An internal isochron age of 3.4 ± 0.2 has been determined for a 6 mg fragment.The Luna 16 total soil is poorer in radiogenic Sr than any other analyzed soil from the Moon. Apollo 14 and 15 soils have also been studied; all of them fall nearly on a 4.65 b.y. isochron with the ADOR initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio.A comparison of the integrated $\text{Rb}\text{Sr}$ of the basalt source region and the $\text{Rb}\text{Sr}$ of the rocks suggests that these basaltic fragments have been generated with only minor $\text{Rb}\text{Sr}$ fractionation.The existence of an old Rb-rich subcrust which contaminated the basalts is also in agreement with the present results.  相似文献   

Etude de la thermoluminescence de la meteorite Saint Severin     

Georges Valladas  Claude Lalou 《Earth and Planetary Science Letters》1973,18(1):168-171

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