Sampling epifauna, a necessity for a better assessment of benthic ecosystem functioning: an example of the epibenthic aggregated species Ophiothrix fragilis from the Bay of Seine     

Lozach S  Dauvin JC  Méar Y  Murat A  Davoult D  Migné A 《Marine pollution bulletin》2011,62(12):2753-2760

Sampling the sea bottom surface remains difficult because of the surface hydraulic shock due to water flowing through the gear (i.e., the bow wave effect) and the loss of epifauna organisms due to the gear’s closing mechanism. Slow-moving mobile epifauna, such as the ophiuroid Ophiothrix fragilis, form high-density patches in the English Channel, not only on pebbles like in the Dover Strait or offshore Brittany but also on gravel in the Bay of Seine (>5000 ind m⁻²). Such populations form high biomasses and control the water transfer from the water column to the sediment. Estimating their real density and biomass is essential for the assessment of benthic ecosystem functioning using trophic web modelling. In this paper, we present and discuss the patch patterns and sampling efficiency of the different methods for collecting in the dense beds of O. fragilis in the Bay of Seine. The large Hamon grab (0.25 m⁻²) highly under-estimated the ophiuroid density, while the Smith McIntyre appeared adequate among the tested sampling grabs. Nowadays, diving sampling, underwater photography and videos with remote operated vehicle appear to be the recommended alternatives to estimate the real density of such dense slow-moving mobile epifauna.  相似文献   

A new methodology for computing ionic profiles and disjoining pressure in swelling porous media     

Aline C. Rocha  Marcio A. Murad  Christian Moyne  Saulo P. Oliveira  Tien D. Le 《Computational Geosciences》2016,20(5):975-996

A new two-scale computational model is proposed to construct the constitutive law of the swelling pressure which appears in the modified form of the macroscopic effective stress principle for expansive clays saturated by an aqueous electrolyte solution containing multivalent ionic species. The microscopic non-local nanoscale model is constructed based on a coupled Poisson-Fredholm integral equation arising from the thermodynamics of inhomogeneous fluids in nanopores (Density Functional Theory), which governs the local electric double layer potential profile coupled with the ion-particle correlation function in an electrolytic solution of finite size ions. The local problem is discretized by invoking the eigenvalue expansion of the convolution kernel in conjunction with the Galerkin method for the Gauss-Poisson equation. The discretization of the Fredholm equation is accomplished by a collocation scheme employing eigenfunction basis. Numerical simulations of the local ionic profiles in rectangular cell geometries are obtained showing considerable discrepancies with those computed with Poisson-Boltzmann based models for point charges, particularly for divalent ions in calcium montmorillonite. The constitutive law for the disjoining pressure is reconstructed numerically by invoking the contact theorem within a post-processing approach. The resultant computational model is capable of capturing ranges of particle attraction characterized by negative values of the disjoining pressure overlooked by the classical electric double layer theory. Such results provide further insight in the role the swelling pressure plays in the modified macroscopic effective stress principle for expansive porous media.  相似文献   

Cold seep communities in the deep eastern Mediterranean Sea: composition, symbiosis and spatial distribution on mud volcanoes   总被引：2，自引：0，他引：2  

Karine Olu-Le Roy  Myriam Sibuet  Aline Fiala-Mdioni  Serge Gofas  Carmen Salas  Andr Mariotti  Jean-Paul Foucher  John Woodside 《Deep Sea Research Part I: Oceanographic Research Papers》2004,51(12):1915-1936

Two mud volcano fields were explored during the French–Dutch MEDINAUT cruise (1998) with the submersible NAUTILE, one south of Crete along the Mediteranean Ridge at about 2000 m depth (Olimpi mud field) and the other south of Turkey between 1700 and 2000 m depth (Anaximander mud field) where high methane concentrations were measured. Chemosynthetic communities were observed and sampled on six mud volcanoes and along a fault scarp. The communities were dominated by bivalves of particularly small size, belonging to families commonly found at seeps (Mytilidae, Vesicomyidae, Thyasiridae) and to Lucinidae mostly encountered in littoral sulfide-rich sediments and at the shallowest seeps. Siboglinid polychaetes including a large vestimentiferan Lamellibrachia sp. were also associated. At least four bivalve species and one siboglinid are associated with symbiotic chemoautotrophic bacteria, as evidenced by Transmission Electronic Microscopy and isotopic ratio measurements. Among the bivalves, a mytilid harbors both methanotrophic and sulfide-oxidizing bacteria. Video spatial analysis of the community distribution on three volcanoes shows that dense bivalve shell accumulations (mainly lucinids) spread over large areas, from 10% to 38% of the explored areas (2500–15000 m²) on the different volcanoes. Lamellibrachia sp. had different spatial distribution and variable density in the two mud volcano fields, apparently related with higher methane fluxes in the Anaximander volcanoes and maybe with the instability due to brines in the Olimpi area. The abundance and richness of the observed chemosynthetic fauna and the size of some of the species contrast with the poverty of the deep eastern Mediterranean. The presence of a specialized fauna, with some mollusk genera and species shared with other reduced environments of the Mediterranean, but not dominated by the large bivalves usually found at seeps, is discussed.  相似文献   

The Effect of Salinity and Temperature Gradients on the Distribution of Littoral Microalgae in Experimental Solar Ponds, Dead Sea Area, Israel     

Inka  Dor Aline  Ehruch 《Marine Ecology》1987,8(2):193-205

Abstract. Several species of cyanobacteria, diatoms and one euglenid alga populated the littoral zone of hypersaline solar ponds investigated over a period of three years. The composition of the microalgae community changed with salinity and temperature. In the shallow marginal zone the diatoms predominated in winter and spring, at salinities of 30–72 g-1^-1 and at temperatures not exceeding 30o°C, whereas in summer, cyanobacteria were the most abundant. In the deeper zone, at higher salinities and temperatures, cyanobacteria predominated throughout the year. The depth limit of algal growth was 60-80cm, where salinity and temperature exceeded 211 g-1^-1 and 48°C.
The most euryhaline and eurythermal among cyanobacteria were Aphanolhece halophytica F remy and Phormidium hypolimneticum C ampbell , among diatoms Nitzschia sp. aff. N. rostellata H ustedt , Amphora coffeaeformis (A gardh ) K utzing , and Navicula massadaea E hrlich .  相似文献   

Assessing the limits of the Modified Gaussian Model for remote spectroscopic studies of pyroxenes on Mars     

Lisa C. Kanner  John F. Mustard  Aline Gendrin 《Icarus》2007,187(2):442-456

We investigate the ability to refine pyroxene composition and modal abundance from laboratory and remotely acquired spectra. Laboratory data including the martian meteorites, Shergotty, Zagami, MIL03346, and ALH84001 as well as additional pyroxene-rich spectra obtained from the OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité) spectrometer for Mars are characterized using the Modified Gaussian Model (MGM), a spectral deconvolution method developed by Sunshine et al. [Sunshine, J.M., Pieters, C.M., Pratt, S., 1990. J. Geophys. Res. 95, 6955-6966]. We develop two sensitivity tests to assess the extent to which the MGM can consistently predict (1) pyroxene composition and (2) modal abundance for a compositionally diverse suite of pyroxene spectra. Results of the sensitivity tests indicate that the MGM can be appropriately applied to remote spectroscopic measurements of extraterrestrial surfaces and can estimate pyroxene composition and relative abundance within a derived uncertainty. Deconvolved band positions for laboratory spectra of the meteorites Shergotty and Zagami are determined within ±17 nm while remotely acquired OMEGA spectra are defined within ±50 nm. These results suggest that absolute compositions can be uniquely derived from laboratory pyroxene-rich spectra and non-uniquely derived from the remote measurements of OMEGA at this time. While relative pyroxene chemistries are not assessed from OMEGA measurements at this time, relative pyroxene abundances are estimated using a normalized band strength ratio between the low-calcium (LCP) and high-calcium (HCP) endmember components and are constrained to ±10%. The fraction of LCP in a two-pyroxene mixture is the derived value from the normalized band strength ratio, LCP/(LCP + HCP). This calculation for relative abundance is robust in the presence of up to 10-15% olivine. Deconvolution results from the OMEGA spectra indicate that the ancient terrain in the Syrtis Major region is uniquely enriched in LCP (59±10% LCP) relative to HCP while the volcanics of Syrtis Major are uniquely enriched in HCP (39±10% LCP).  相似文献   

Settlement Analysis of Açu Dam,Brazil     

de Souza  Andriele Nascimento  da Silva  Aline Ribeiro  Santos  Olavo F.  de Freitas Neto  Osvaldo 《Geotechnical and Geological Engineering》2022,40(3):1565-1583

Geotechnical and Geological Engineering - The Armando Ribeiro Gonçalves Dam, popularly known as The Açu Dam, is an important geotechnical construction in Rio Grande do Norte state,...  相似文献   

Metal loading effect on rare earth element binding to humic acid: Experimental and modelling evidence   总被引：1，自引：0，他引：1  

Rémi Marsac  Mélanie Davranche  Gérard Gruau  Aline Dia 《Geochimica et cosmochimica acta》2010,74(6):1749-5637

The effect of metal loading on the binding of rare earth elements (REE) to humic acid (HA) was studied by combining ultrafiltration and Inductively Coupled Plasma Mass Spectrometry techniques. REE-HA complexation experiments were performed at pH 3 for REE/C molar ratios ranging from ca 4 × 10⁻⁴ to 2.7 × 10⁻². Results show that the relative amount of REE bound to HA strongly increases with decreasing REE/C. A middle-REE (MREE) downward concavity is shown by patterns at high metal loading, whereas patterns at low metal loading display a regular increase from La to Lu. Humic Ion Model VI modelling are close to the experimental data variations, provided that (i) the ΔLK₂ parameter (i.e. the Model VI parameter taken into account the presence of strong but low density binding sites) is allowed to increase regularly from La to Lu (from 1.1 to 2.1) and (ii) the published log K_MA values (i.e. the REE-HA binding constants specific to Model VI) are slightly modified, in particular with respect to heavy REE. Modelling approach provided evidence that patterns with varying REE/C likely arises because REE binding to HA occurs through two types of binding sites in different density: (i) a few strong sites that preferentially complex the heavy REE and thus control the atterns at low REE/C; (ii) a larger amount of weaker binding sites that preferentially complex the middle-REE and thus control the pattern at high REE/C. Hence, metal loading exerts a major effect on HA-mediated REE binding, which could explain the diversity of published conditional constants for REE binding with HA. A literature survey suggests that the few strong sites activated at low REE/C could be multidentate carboxylic sites, or perhaps N-, or P-functional groups. Finally, an examination of the literature field data proposed that the described loading effect could account for much of the variation in REE patterns observed in natural organic-rich waters (DOC > 5 mg L⁻¹ and 4 ? pH ? 7).  相似文献   

Hydrosedimentary records and Holocene environmental dynamics in the Yamé Valley (Mali,Sudano-Sahelian West Africa)     

Yann Le Drézen  Laurent Lespez  Michel Rasse  Aline Garnier  Sylvie Coutard  Eric Huysecom  Aziz Ballouche 《Comptes Rendus Geoscience》2010,342(3):244-252

Research conducted in the Yamé Valley (Dogon Country, Mali) provides valuable information about the river systems and their Holocene evolution in Sudano-Sahelian West Africa. Past research in the region has relied primarily on marine and lacustrine records. The new results confirm correlation between palaeoclimatic fluctuations recorded in both the river system and in tropical African lakes. They offer a new continental milestone for understanding of the environmental repercussions of Holocene monsoon oscillations. These studies demonstrate the value of river systems as a palaeoenvironmental record and the role of palaeoclimatic and anthropogenic factors in the Holocene dynamics of Sudano-Sahelian hydrosystems.  相似文献   

Origin and evolution of fluids from mud volcanoes in the Barbados accretionary complex     

Arnaud Godon  Nathalie Jendrzejewski  Aline Dia  Jacques Boulègue 《Geochimica et cosmochimica acta》2004,68(9):2153-2165

A large collection of fluids (54 interstitial fluids and four expelled fluids) were sampled at the Manon site, at the outer edge of the Barbados accretionary complex. These warm fluids (up to 20°C) are expelled by sub-marine (5000 mbsl) mud volcanoes consisting of diapirs (unchanneled flow) and diatremes (channeled).Chlorine stable isotope ratios of these fluids were measured by IRMS with a reproducibility of ± 0.05‰ (1σ) versus SMOC (Standard Mean Ocean Chloride).A large range of δ³⁷Cl between −5.3‰ and +0.1‰ is observed. Data from each volcanic structure describe a mixing between seawater and a low-δ³⁷Cl fluid. The whole set of data is interpreted as the result of a mixing between two deep components and seawater. The two deep fluids are chemically distinct (e.g., in Ca, Mg, K, Li, Sr and Br contents and Br/Cl ratio). They display low and significantly different ⁸⁷Sr/⁸⁶Sr ratios (0.707790 and 0.707892, respectively) and δ³⁷Cl values (−4.51 and −5.24‰, respectively).Physicochemical processes such as mineralogical transformation, diffusion, compaction or ion filtration are known to fractionate chlorine stable isotopes and can produce fluids with negative δ³⁷Cl values. Ion filtration due to sediment compaction appears to be the more likely process to explain the negative δ³⁷Cl values observed at the Manon site. A model for the generation of these signatures is proposed where a residual negative δ³⁷Cl fluid reservoir is created at the bottom of the prism or the sediment pile. Further compaction/fracturing and/or dewatering of the slab may flush out these fluids and focus them towards the décollement zone. Mixing between the fluids and ultimately with seawater and water released during gas hydrate destabilizations may explain the data set within the individual cores and between the different structures.  相似文献   

Isostasy of aseismic tectonic units in the South Atlantic Ocean and geodynamic implications     

Aline Bulot  M. Diament  M.G. Kogan  J. Dubois 《Earth and Planetary Science Letters》1984,70(2):346-354

Mechanical isostasy of the lithosphere in the South Atlantic Ocean was studied using information on gravity anomalies and bathymetry with additional constraints imposed by the altimetric geoid. The isostatic responses (admittances) over the Walvis Ridge, Rio Grande Rise and Trindade Seamount Chain were computed using a three-dimensional algorithm. The eastern Walvis Ridge and the Rio Grande Rise have the same response, which is well explained by an Airy model of isostasy. The other features are regionally supported. A variation in the thickness of the elastic plate was found along the western Walvis Ridge. A high value of the elastic plate thickness (20 km) was found under the Trindade Chain. Geodynamic implications are discussed in the light of these results.  相似文献