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排序方式: 共有234条查询结果,搜索用时 31 毫秒
61.
Antonio Pusceddu Silvia Bianchelli Miquel Canals Anna Sanchez-Vidal Xavier Durrieu De Madron Serge Heussner Vasilios Lykousis Henko de Stigter Fabio Trincardi Roberto Danovaro 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(3):441-457
We describe the quantitative and compositional (phytopigment, protein, carbohydrate and lipid) patterns of sedimentary organic matter along bathymetric gradients in seven submarine canyons and adjacent open slopes located at four European regions: one along the NE Atlantic and three along the Mediterranean continental margins. The investigated areas are distributed along a putative longitudinal gradient of decreasing primary production from the Portuguese (northeastern Atlantic Ocean), to the Catalan (western Mediterranean Sea), Southern Adriatic (central Mediterranean Sea) and Southern Cretan (eastern Mediterranean Sea) margins. Sediment concentrations of organic matter differed significantly between the Portuguese margin and the Mediterranean regions and also from one study area to the other within the Mediterranean Sea. Differences in quantity and composition of sediment organic matter between canyons and open slopes were limited and significant only in the eutrophic Portuguese margin, where the differences were as large as those observed between regions (i.e. at the mesoscale). These results suggest that the overall trophic status of deep margin sediments is controlled mostly by the primary productivity of the overlying waters rather than by the local topography. Moreover, we also report that the quantity and nutritional quality of sediment organic matter in canyons and adjacent open slopes do not show any consistent depth-related pattern. Only the Nazaré and Cascais canyons in the Portuguese margin, at depths deeper than 500 m, displayed a significant accumulation of labile organic matter. The results of our study underline the need of further investigations of deep margins through sampling strategies accounting for adequate temporal and spatial scales of variability. 相似文献
62.
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64.
AMS radiocarbon cross-dating of plant debris and marine shells trapped in a lake basin on Mount St. Hilaire (Québec, Canada) provides a direct assessment of a reservoir effect totaling ca. 1800 14C years during the early stage of Champlain Sea. Pollen-based extrapolation of bottommost ages on terrestrial plant macrofossils in sediments of this lake, and of another lake nearby support an estimate of 11,100 ± 100 14C yr B.P. for marine invasion in the Central St. Lawrence River Lowlands. Results indicate a 400–1000 years younger regional chronology of ice retreat, now congruent with the one inferred from the New England varve chronology. This is a summary of a longer paper to be published in French. 相似文献
65.
Large-eddy Simulation of the Dispersion of Solid Particles in a Turbulent Boundary Layer 总被引:2,自引:2,他引:2
Ivana Vinkovic Cesar Aguirre Michel Ayrault Serge Simoëns 《Boundary-Layer Meteorology》2006,121(2):283-311
A large-eddy simulation (LES) with the dynamic Smagorinsky-Germano subgrid-scale (SGS) model is used to study the dispersion of solid particles in a turbulent boundary layer. Solid particles are tracked in a Lagrangian way. The instantaneous velocity of the surrounding fluid is considered to have a large-scale part (directly computed by the LES) and a small-scale part. The SGS velocity of the surrounding fluid is given by a three-dimensional Langevin model written in terms of SGS statistics at a mesh level. An appropriate Lagrangian correlation time scale is considered in order to include the influences of gravity and inertia of the solid particle. Inter-particle collisions and the influence of particles on the mean flow are also taken into account. The results of the LES are compared with the wind-tunnel experiments of Nalpanis et al. (1993 J Fluid Mech 251: 661–685) and of Tanière et al. (1997 Exp in Fluids 23:463–471) on sand particles in saltation and in modified saltation, respectively. 相似文献
66.
Serge Y. Maestrini Brigitte R. Berland Martine Bréret Christian Béchemin Roberto Poletti Attilio Rinaldi 《Estuaries and Coasts》1997,20(2):416-429
From April 1993 to March 1994, 135 samples were collected at two sites in the coastal Adriatic Sea, both near (14.5 km) and far (63 km) from the Po River delta. The nutrient(s) limiting algal growth potential (AGP) were estimated by bioassay usingNitzshia closterium (local isolate) andThalassiosira pseudonama (strain 3-H). Estimates were also made by comparing the nutrient molar ratios, ΣN:P and ΣN:Si (whereΣN=NO3 ?+NO2 ?+NH4 ++urea), to the Redfield Ratio (16∶1, 1∶1). According to the bioassay results, phosphorus was the sole nutrient limiting AGP in 2% of the samples and was the most limiting nutrient in 69% of the samples; nitrogen was sole limiting nutrient in 18% of the samples. In 11% of samples, nitrogen and phosphorus were equally co-limiting. Omission of phosphorus from spike enrichments allowed, on average, only a 1.6-fold increase in biomass over that in the unenriched controls. Similar omission of nitrogen allowed a 4-fold increase, while silicon, iron, and micronutrients resulted in 14-fold, 18-fold, and >20-fold increases, respectively. In most of the samples, ΣN:P was much greater than 16, indicating a marked phosphorus deficiency, while ΣN:Si values suggested that silicon was the third most limiting nutrient in 35% of samples. In water collected for from the Po delta, the yield ofN. closterium was not limited by any nutrients other than the three major ones: P, N and Si. In these same waters,T. pseudonana was also potentially limited by iron and, to a lesser extent, by vitamins. The role of iron varied. In samples collected near the Po delta, iron acted as the third most limiting nutrient forN. closterium in June and September; it appeared 29 times out of 78 on the list of potentially limiting nutrients forT. pseudonana, including 5 times as the most limiting. Altogether, comparison with published results suggests that the roles of iron and silicon in AGP limitation have increased during the past three decades, and could become even more important if eutrophication in the Adriatic Sea continues to increase. 相似文献
67.
Petrology and U/Pb geochronology of the Telohat migmatites,Aleksod, Central Hoggar,Algeria 总被引:6,自引:0,他引:6
Pierre Barbey Jean-Michel Bertrand Serge Angoua Danielle Dautel 《Contributions to Mineralogy and Petrology》1989,101(2):207-219
The Aleksod region is composed of metasedimentary rocks and large areas of biotite and hornblende-bearing migmatites. Anatexis
associated with the main deformation stages, occurred under high pressure and temperature conditions estimated at 13±2 Kbar
and 750±50° C. The bulk mineralogical composition of the Telohat migmatites shows that their protolith was granodioritic.
Internal structures of zircons and U-Pb data suggest a polyphased evolution, with a 2131±12 Ma age for the protolith and a
609±17 Ma age for the Pan-African tectono-metamorphic evolution, thus precluding any Kibaran event in the Aleksod area. Leucosomes
are richer in Sr and display lower Rb, Zr, Nb, Y, Th, U and REE contents than melanosomes wherein accessory phases are stored.
Eu contents are also lower in the leucosomes but in lesser proportion than the other rare earth's, leading to a significant
positive anomaly. Petrogenetic modelling accounting for accessory mineral phases clearly shows that the trace element contents
of leucosomes and melanosomes follow a distribution law consistent neither with equilibrium nor fractional melting. Their
trace element patterns are best explained by the model of disequilibrium melting, with mixing of a few residual phases. The
present results and previous Sr isotopic data as well raise the question of disequilibrium melting in anatexis of crustal
material
CRPG Contribution no 782 相似文献
68.
Didier Miallier Laurent Michon Jacques Évin Thierry Pilleyre Serge Sanzelle Gérard Vernet 《Comptes Rendus Geoscience》2004,336(15):1345-1353
On the basis of radiocarbon ages obtained on wood burned by base surges and tephrochronological observations, it has been possible to assess that the Puy Chopine, aged ca 9700 yr is older by a few centuries than both the Vasset and Kilian volcanoes. The last two have nearly the same age, ca 9300–9400 yr. Layers of trachytic tephra, most probably originated from Kilian or Vasset, can be observed overlapping those from the Pariou. This last volcano had been previously thought to be the younger of the area on the basis of the observation of trachytic tephra beneath its own tephra. However, new observations allow us to assume that those trachytes originated from the acid phase of the Pariou itself. Therefore, it can be assessed that the four volcanoes erupted according to the following sequence: Chopine/Pariou/?Vasset?/Kilian; the chronological situation of Vasset lies on poor arguments and it should be confirmed. To cite this article: D. Miallier et al., C. R. Geoscience 336 (2004). 相似文献
69.
Christian Coulon M'hamed Megartsi Serge Fourcade Ren C. Maury Herv Bellon Amina Louni-Hacini Joseph Cotten Alain Coutelle Daniel Hermitte 《Lithos》2002,62(3-4):87-110
During the Neogene, a magmatic change from calc-alkaline to alkaline types occurred in all the regions surrounding the western Mediterranean. This change has been studied in Oranie (western Algeria). In this area, potassic to shoshonitic calc-alkaline andesites (with La/Nb ratios in the range 4–6) were mainly erupted between 12 and 9 Ma. They were followed (between 10 and 7 Ma) by basalts displaying geochemical features which are transitional between calc-alkaline and alkaline lavas (La/Nb=1–1.7). After a ca. 3-Ma quiescence period, volcanic activity resumed, with the eruption of OIB-type alkaline basalts (La/Nb=0.5–0.6), from 4 to 0.8 Ma. A combined geochemical approach, using incompatible elements and Sr, Nd and O isotopes, allows us to conclude that the transitional basalts derived from the melting of a heterogeneous mantle source, at the boundary between lithosphere and asthenosphere. We propose that melting of a previously subduction-modified lithospheric mantle occurred between 12 and 10 Ma, in response to the upwelling of hot asthenosphere flowing up into an opening gap above a detached sinking slab. As a result, calc-alkaline magmas were formed. From 10 to 7 Ma, the transitional basalts were generated through melting of the boundary mantle zone between the lithosphere and the upwelling asthenosphere. During that stage, the contribution of the lithospheric source was still predominant. Then, as sinking of the oceanic slab progressed, the increasing uprise of the asthenosphere led to the formation and emplacement (from 4 to 0.8 Ma) of typical within-plate alkaline basalts derived from a plume-modified asthenospheric mantle. 相似文献
70.
Jean-François Royer Daniel Cariolle Fabrice Chauvin Michel Déqué Hervé Douville Rong-Ming Hu Serge Planton Annie Rascol Jean-Louis Ricard David Salas Y Melia Florence Sevault Pascal Simon Samuel Somot Sophie Tyteca Laurent Terray Sophie Valcke 《Comptes Rendus Geoscience》2002,334(3):147-154
Two climate simulations of 150 years, performed with a coupled ocean/sea-ice/atmosphere model including stratospheric ozone, respectively with and without heterogeneous chemistry, simulate the tropospheric warming associated with an increase of the greenhouse effect of carbon dioxide and other trace gases since 1950 and their impact on sea–ice extent, as well as the stratospheric cooling and its impact on ozone concentration. The scenario with heterogeneous chemistry reproduces the formation of the ozone hole over the South Pole from the 1970s and its deepening until the present time, and shows that the ozone hole should progressively fill during the coming decades. To cite this article: J.-F. Royer et al., C. R. Geoscience 334 (2002) 147–154. 相似文献