Submersible observations of Equatorial Atlantic mantle: The St. Paul Fracture Zone region     

Hekinian  R.  Juteau  T.  Gràcia  E.  Sichler  B.  Sichel  S.  Udintsev  G.  Apprioual  R.  Ligi  M. 《Marine Geophysical Researches》2000,21(6):529-560

The St. Paul F.Z. is a large structural domain made up of multiple transform faults interrupted by several Intra-Transform Ridge (ITR) spreading segments. Two regions were studied in details by submersible: (1) The ITR short (<20 km in length) segment near 0° 37N–25° 27W and 1° N–27° 42W and (2) The St. Peter and St. Paul's Rocks (SPPR) massif located at 29° 25W (¡3700 m depth). (1) The short ITR segments consist of a magma starved rift valley with recent volcanic activities at 4700 m depth. A geological profile made along the rift valley wall showed localized volcanics (basalts and dykes) which are believed to overlay and intrude the ultramafics. The geological setting and the high ultramafic/volcanic ratio suggest an extremely low magmatic supply and crustal-mantle uplift during lithospheric stretching and denudation. (2) The St. Peter and St. Paul's Rocks (SPPR) massif consists of a sigmoidal ridge within the active transform zone. The SPPR is divided into two different geological domains called the North and the South Ridges. The North Ridge consists of strongly tectonized fault scarps composed of banded and mylonitized peridotite, sporadic gabbros (3900–2500 m) and metabasalts (2700–1700 m). The South Ridge is less tectonized with undeformed, serpentinized spinel lherzolite (2000–1400 m) and basalts. Extensional motion and denudation accompanied by diapirism affected the South Ridge within a transform domain. Instead, the North Ridge was formed during an important strike-slip and faulting motion resulting in the uplifted portion of the St. Paul F.Z. transverse ridge. There is a regional compositional variation of the volcanics where E-MORBs and alkali basalts are produced on the SPPR massif and are comparable to the adjacent northern segments of the Mid-Atlantic Ridge. On the other hand, N and T- MORBs collected from the eastern part of the St. Paul F.Z. (25° 27W IRT) are similar to the volcanics from the southern segments of the MAR. The peridotites exposed in these provinces (SPPR and ITR) are similar in their REE and trace element distribution. Different degrees (3–15%) of partial melting of a mixed composite mantle consisting of spinel and amphibole bearing lherzolite veined with 5–40% clinopyroxenite gave rise to the observed MORBs and alkali basalts.  相似文献   

Total oxyradical scavenging capacity and cell membrane stability of haemocytes of the Arctic scallop,Chlamys islandicus,following benzo(a)pyrene exposure     

Camus L  Jones MB  Børseth JF  Grøsvik BE  Regoli F  Depledge MH 《Marine environmental research》2002,54(3-5):425-430

Industrial activities, notably oil and gas industries, are expanding in the Arctic. Most of the biomarkers were developed using temperate organisms living at temperatures above 10 degrees C. Little is known about the biomarker responses of organisms living between -1.88 and 5 degrees C. Therefore, assessment of the toxicity of chemicals to cold-water adapted species is required. In this study, the Arctic scallop, Chlamys islandicus, was selected as a key species for bio-monitoring because of wide distribution in Arctic waters and its commercial value. Test animals, stored in seawater at 2 degrees C, were injected with benzo(a)pyrene (diluted in cod liver oil 5 mg ml(-1)) in the adductor muscle every 24 h for four days giving a final dose of 0, 74 and 90.6 mg kg(-1) wet weight for control, low and high dose, respectively. The biomarkers used were total oxyradical scavenging capacity (TOSC) in the digestive gland and cell membrane stability of haemocytes. TOSC values were significantly reduced (ca. 30%) in exposed groups (P < 0.05), indicating a depletion in oxyradical molecular scavengers. The antioxidant defences appeared to be overwhelmed by the reactive oxygen species as the plasma membranes of haemocytes were destabilised (P < 0.05) probably due to lipid peroxidation. These data indicate that reactive oxygen species (ROS) were produced by Arctic scallops via the metabolisation of benzo(a)pyrene at 2 degrees C.  相似文献   

Failure and size effect for notched and unnotched concrete beams     

D. Grégoire  L.B.  Rojas‐Solano  G. Pijaudier‐Cabot 《国际地质力学数值与分析法杂志》2013,37(10):1434-1452

Modelling failure in geomaterials, concrete or other quasi‐brittle materials and proper accounting for size effect, geometry and boundary effects are still pending issues. Regularised failure models are capable of describing size effect on specimens with a specific geometry, but extrapolations to other geometries are rare, mostly because experimental data presenting size effect for different geometries and for the same material are lacking. Three‐point bending fracture tests of geometrically similar notched and unnotched specimens are presented. The experimental results are compared with numerical simulations performed with an integral‐type non‐local model. Comparisons illustrate the shortcomings of this classical formulation, which fails to describe size effect over the investigated range of geometries and sizes. Finally, experimental results are also compared with the universal size effect law. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Dynamics of snow ablation in a small Alpine catchment observed by repeated terrestrial laser scans     

Luca Egli  Tobias Jonas  Thomas Grünewald  Michael Schirmer  Paolo Burlando 《水文研究》2012,26(10):1574-1585

The spatio‐temporal distribution of snow in a catchment during ablation reflects changes in the total amount of snow water equivalent and is thus a key parameter for the estimation of melt water run‐off. This study explores possible rules behind the spatial variability of snow depth during the ablation season in a small Alpine catchment with complex topography. The snow depth observations are based on more than 160 000 terrestrial laser scanner data points with a spatial resolution of 1 m, which were obtained from 11 scanning campaigns of two consecutive ablation seasons. The analysis suggests that for estimating cumulative snow melt dynamics from the catchment investigated, assessing the initial snow distribution prior to the melt season is more important than addressing spatial differences in the melt behaviour. Snow volume and snow‐covered area could be predicted well using a conceptual melt model assuming spatially uniform melt rates. However, accurate results were only obtained if the model was initialized with a pre‐melt snow distribution that reflected measured mean and standard deviation. Using stratified melt rates on the other hand did not improve the model results. At least for sites with similar meteorological and topographical conditions, the model approach presented here comprises an efficient way to estimate snow depletion dynamics, especially if persistent snow accumulation pattern between years facilitate the characterization of the initial snow distribution prior to the melt. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The Hospitalet gneiss dome (Pyrenees) revisited: lateral flow during Variscan transpression in the middle crust     

Yoann Denle  Philippe Olivier  Grard Gleizes  Pierre Barbey 《地学学报》2007,19(6):445-453

A new structural and kinematic study of the Hospitalet dome (Pyrenees) is presented. This dome corresponds to the eastern half of an EW‐trending antiformal structure made of an orthogneissic core intruded by granitoids, partly covered by Upper Proterozoic to Lower Ordovician metapelites. Its Variscan evolution can be split into four stages: (i) development of a strong high temperature pervasive deformation associated with subhorizontal foliations and lineations, and with non‐coaxial top‐to‐the‐east kinematics; (ii) formation of a south‐verging overturned megafold; (iii) emplacement of calc‐alkaline granitoids; and (iv) formation of mylonitic bands on the southern border of the dome, with reverse dextral kinematics. The flat lying pervasive high‐T deformation is interpreted as a large lateral flow developed in a dextral transpressive regime inducing an important uncoupling between the middle and upper crusts. The next stages happened in a progressive deformation in the same transpressive regime.  相似文献   

Permian granites in the Pyrenees: the Aya pluton (Basque Country)     

Yoann Denèle  Jean‐Louis Paquette  Philippe Olivier  Pierre Barbey 《地学学报》2012,24(2):105-113

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Performance comparison of two biotic indices measuring the ecological status of water bodies in the Southern Baltic and Gulf of Lions   总被引：1，自引：1，他引：0  

Fleischer D  Grémare A  Labrune C  Rumohr H  Berghe EV  Zettler ML 《Marine pollution bulletin》2007,54(10):1598-1606

Two biotic indices, ATZI Marine Biotic Index (AMBI) and Benthic Quality Index (BQI) have been recently introduced within the EC Water Framework Directive to assess the quality of marine habitats: both are based on sensitivity/tolerance classification and quantitative information on the composition of soft-bottom macrofauna. Their performance, especially with regard to sampling effort was assessed based on two data sets collected in Southern Baltic and one from the Gulf of Lions Mediterranean. AMBI was not affected by sampling effort but BQI was. Two modifications were proposed for BQI (i.e., BQI) (1) the removal of the scaling term (i.e., BQI(W)), and (2) the replacement of the scaling term by different scaling term (i.e., BQI(ES)). Both modified BQIs were largely independent of sampling effort. Variability was slightly lower for BQI(W) than for BQI(ES). BQI was highly correlated with BQI(W) and with BQI(ES) both in the Southern Baltic and in the Gulf of Lions. However, the proportions of stations, which were not attributed the same ecological quality status (EcoQ) when using BQI and its two modified forms were always high. Differences in ecological classification were mostly due to the scales used to infer EcoQ. Based on this study we recommend to use BQI(ES) in future studies because it apparently constitutes the best compromise in (1) being independent of sampling effort, (2) limiting the variability in computation in relation with sampling effort, (3) being correlated with BQI and corresponding EcoQ.  相似文献   

Nutrient dynamics at the sediment-water interface in a Mediterranean lagoon (Thau, France): influence of biodeposition by shellfish farming activities   总被引：2，自引：0，他引：2  

Mesnage V  Ogier S  Bally G  Disnar JR  Lottier N  Dedieu K  Rabouille C  Copard Y 《Marine environmental research》2007,63(3):257-277

The Thau Lagoon, a French Mediterranean shallow lagoon, is a site where extensive shellfish farming occurs. The aim of the present work is to evaluate the role of this activity on nutrient exchange at the sediment-water interface in relation to organic matter (OM) sedimentation and degradation. Two stations inside (C5) and outside (C4) of the shellfish farming areas were sampled at three seasons. Porewater chemistry surveys and calculated diffusive fluxes were used to evaluate the trophic status of the Thau lagoon. Quantitative (Particulate Organic Carbon) as well as qualitative OM (Hydrogen Index, Carbohydrates) analyses were performed on sediments to assess OM characteristics. Results emphasized that surficial sediments at C5 are always more enriched in OM. Porewater nutrient concentrations are 10-20 times higher at C5 than at C4. In June 2003, the porewater profiles exhibit a sharp gradient at the bottom waters, indicating a hypereutrophic status, leading to an anoxic crisis.  相似文献   

Effects of industrial outfalls on tropical macrobenthic sediment communities in Reunion Island (Southwest Indian Ocean)     

Bigot L  Conand C  Amouroux JM  Frouin P  Bruggemann H  Grémare A 《Marine pollution bulletin》2006,52(8):865-880

Temporal changes in the composition of soft bottom macrobenthic assemblages at Reunion Island (Southwest Indian Ocean) were studied in the context of a long-term environmental monitoring programme studying the impacts of effluents of industrial sugar cane refineries that are transferred to shallow and deep coastal environments by different pathways: surface discharge and deep underground injection. Seven stations (between 20 and 160 m depth) were surveyed between 1994 and 2003 on the industrial zone. One additional station was surveyed on a reference site. Spatio-temporal changes in the composition of macrobenthic communities were assessed using several diversity indices, ABC curves, MDS and associated ANOSIM tests and biotic indices. Among the 171 taxa recorded, polychaetes were dominant (89 species), followed by crustaceans and molluscs. The analysis of spatial changes in the composition of macrobenthos showed the existence of distinct benthic communities along the depth gradient. Temporal changes in macrobenthos composition were most prominent at the shallowest station. They mainly corresponded to the decline of several initially dominant taxa and the increase of the Eunicid polychaete Diopatra cuprea. This station further showed increasing macrofaunal abundance, biomass and sediment organic content over time, concomitant with decreasing sediment grain sizes. In deeper environments, temporal changes were much smaller. Macrofaunal abundance and species richness increased progressively, suggesting a moderate impact on benthic ecosystems resulting from slight enrichments due to effluents rich in organic matter. Our results highlight an original response to disturbance pattern involving opportunistic Eunicidae species (D. cuprea) not previously described. Moreover, they allow for the comparison of the impact on macrofauna caused by industrial effluents exported by two distinct and different pathways in a tropical coastal high-energy marine environment.  相似文献   

North American transect of stable hydrogen and oxygen isotopes in water beetles from a museum collection     

Maarten van Hardenbroek  Darren R. Gr?cke  Peter E. Sauer  Scott A. Elias 《Journal of Paleolimnology》2012,48(2):461-470

Museum collections contain a wealth of insect remains originating from a wide geographic range, which can be used to investigate their utility as a proxy for environmental isotope ratios. Chitinous remains of insects such as beetles (Coleoptera) are chemically stable and their stable isotope composition is strongly related to that of environmental water in the period of cuticle formation. We present a dataset of chitin ??D and ??¹⁸O in two genera of water beetles from a museum collection containing 40 locations for Helophorus (water scavenging beetles) and 48 locations for Hydroporus (predaceous diving beetles) that were selected from latitudes 27?C82°N in North America. Only two genera were used to minimize inter-sample variation caused by species-specific differences in metabolic effects, feeding strategy, habitat, and life cycle. The isotopic composition of water beetle exoskeletons had a strong latitudinal trend (North?CSouth) from ?160 to +65??? for ??D and from 7 to 34??? for ??¹⁸O, paralleling gradients of isotopes in precipitation. Strong relationships were observed between isotopic composition of beetles and modelled July precipitation (0.71?<?R ²?<?0.82, p?<?0.001). The relationship between ??D and ??¹⁸O in the beetle samples had a systematic offset from the global meteoric water line, which was likely caused by metabolic effects during chitin formation. The offset between ??D values in beetles and in modelled precipitation was 33??? larger, on average, for Hydroporus compared with Helophorus, suggesting fractionation of hydrogen isotopes during passage through the food chain. This trophic level effect was not observed for stable oxygen isotopes. Furthermore, the observed deviations between isotopic composition of water beetles and modelled precipitation at collection sites were not constant and indicated local hydrological deviations from modelled precipitation. The largest deviations were observed for sites in the Southern US and the Arctic that are highly evaporative and at sites in the Rocky Mountains and Coastal Mountains that were fed by snow melt. Our results indicated that the isotopic composition of water beetles from a museum collection was systematically related to ??D and ??¹⁸O values of precipitation at the collection site.  相似文献