Assessing the impact of fisheries on demersal fish assemblages of the Mauritanian continental shelf, 1987-1999, using dominance curves   总被引：3，自引：0，他引：3  

Jouffre  Didier; Inejih  Cheikh A. 《ICES Journal of Marine Science》2005,62(3):380-383

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Sedimentary record of redox-sensitive elements (U, Mn, Mo) in a transitory anoxic basin (the Thau lagoon, France)   总被引：4，自引：0，他引：4  

Franoise Elbaz-Poulichet  Jean Luc Seidel  Didier Jzquel  Edouard Metzger  Franois Prvot  Caroline Simonucci  Grard Sarazin  Eric Viollier  Henri Etcheber  Jean-Marie Jouanneau  Olivier Weber  Olivier Radakovitch 《Marine Chemistry》2005,95(3-4):271-281

In order to further document the relation between redox conditions and the sedimentary record of Mn, U and Mo in a transitory anoxic water basin, their distribution has been studied along two profiles in the Thau lagoon (France). Sediments and pore-water have been sampled at two contrasting sites located, respectively, in the shellfish-farming area and in the centre of the lagoon. In the shellfish-farming area, the particulate organic carbon (POC) data indicate a more rapid organic matter mineralisation compared to the centre of the lagoon. This results in a sharper redox gradient characterized by the appearance of H₂S in pore-water a few millimetres below the sediment–water interface. In the centre of the lagoon, H₂S appears at a depth of 35 cm.In both cores, sedimentary Mn is relatively depleted through out the whole sedimentary column and varies with the proportion of clay minerals. After an initial release into solution at the sediment–water interface in relation to Mn-oxide reductive dissolution, authigenic U is immobilized when sulphides appear. Despite the occurrence of anoxic conditions at the sediment–water interface at the site influenced by shellfish farming, the burial of U is reduced by bioturbation, which raises reducing sediments to the surface. In the centre of the lagoon, Mo profiles reflect continuous diffusion into pore water and immobilization at 15 cm probably in anoxic microenvironments. At shellfish farms, dissolved Mo undergoes removal with sulphides but contrary to U, sedimentary Mo does not appear to be strongly affected by bioturbation. The profile indicates an increase in the frequency of anoxia crises during the second half of the 20th century.  相似文献   

Airborne lidar measurements of aerosol spatial distribution and optical properties over the Atlantic Ocean during a European pollution outbreak of ACE‐2     

Cyrille Flamant  Jacques Pelon  Patrick Chazette  Vincent Trouillet  Patricia K. Quinn  Robert Frouin  Didier Bruneau  Jean François Leon  Timothy S. Bates  James Johnson  John Livingston 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):662-677

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Sediment density flow distribution on wave-influenced deltas     

Alexandre Normandeau  Jordan B. R. Eamer  Pascal Bernatchez  David Didier  Patrick Lajeunesse  Audrey Limoges  Jean-Carlos Montero-Serrano 《Sedimentology》2023,70(1):100-120

Deltas are at the transition between fluvial and marine sedimentary environments where sediment density flows are often triggered during high river discharge events, forming submarine channels and sediment waves. On wave-influenced deltas, longshore currents are particularly efficient at transporting sediment alongshore, reducing the likelihood of sediment density flows from occurring at river mouths. This study describes four deltaic sedimentary systems at different stages of their evolution on a formerly glaciated continental inner shelf of eastern Canada in order to better understand the distribution of sediment density flows on wave-influenced deltas. Three types of settings are recognized as being prone to sediment density flows: (i) in the early stages of wave-influence and on large deltas, converging longshore currents can lead to offshelf sediment transport; (ii) on wave-influenced to wave-dominated deltas, a sandy spit can re-route the river mouth and sediment density flows form where the spit intersects the delta lip; (iii) in advanced stages of wave-dominated deltas and during their demise, rocky headlands are exposed and can intersect the slope, where off-shelf sediment transport occurs. These types of sediment density flows were all characterized by debris flows or surge-type turbidity currents which have limited offshore run-out. More rarely, hyperpycnal flows form at the river mouths, especially where the river incises glaciomarine clays prone to landsliding in the river, which increases fine-grained fluvial suspended sediment concentration. Overall, these results highlight the predominance of fluvial-dominated deltas during a phase of relative sea-level fall combined with high sediment supply. However, as soon as sediment supply diminishes, wave action remobilizes sediment alongshore modifying the distribution and types of sediment density flows occurring on wave-influenced deltas.  相似文献   

Characterising groundwater and surface-water interconnections using hydrogeology,hydrochemistry and stable isotopes in the Ouémé Delta,southern Benin     

Guidah Chabi  Bio  Alassane  Abdoukarim  Kpegli  Kodjo Apelete Raoul  Lawson  Fabrice Messan Amene  Alassane Zakari  Aoulatou  Koukpohounsi  Bénito Didier  Boukari  Ousmane Touré  Vouillamoz  Jean-Michel  Yalo  Nicaise  Mama  Daouda  Boukari  Moussa 《Hydrogeology Journal》2023,31(5):1229-1243

The Mio-Pliocene aquifer of the coastal sedimentary basin of Benin is the most exploited aquifer for water supply to the urbanised region in the southern part of the country. The population explosion is putting increasing pressure on quantitative and qualitative aspects of the groundwater resources. Preventing groundwater contamination caused by surface waters requires a thorough understanding of surface-water/groundwater interactions, especially the interactions between the Mio-Pliocene aquifer and surface waters. This study aimed to investigate the interactions between groundwater and surface waters along the major rivers (Sô River and Ouémé Stream) and brooks in the Ouémé Delta. Field campaigns identified 75 springs located in the valleys which feed the rivers, and thus maintain their base flow. The piezometric results indicated, through flow direction assessment, that the Mio-Pliocene aquifer feeds Ouémé Stream and Sô River. Chemical analyses of groundwater and surface waters show similar chemical facies, and changes in the chemical composition in groundwater are also observed in the surface waters. Moreover, the isotopic signatures of surface waters are similar to those of the groundwater and springs, which led to the identification of potential groundwater discharge areas. As a result of groundwater discharge into surface waters, the fraction of groundwater in the surface water is more than 66% in the brooks, regardless of the season. In the Ouémé Stream and Sô River, the fraction of groundwater is 0–21% between June and September, while from October to March it is 47–100%.

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UVolution, a photochemistry experiment in low earth orbit: Investigation of the photostability of carbonates exposed to martian-like UV radiation conditions     

Fabien Stalport  Yuan Yong Guan  Patrice Coll  Frédérique Macari  Didier Chaput  Hervé Cottin 《Planetary and Space Science》2010,58(12):1617-1624

The detection and identification of carbonates on Mars are of prime importance to establish the evolution of its atmosphere, correlated to the history of the liquid water, or even to determine the existence of a possible ancient biological activity. Till date, no large deposits of carbonates have been found. In fact, their detection is specific to local areas and in very low amounts. The absence of such deposits is commonly attributed to the harsh environmental conditions at the surface of Mars. Additionally, the presence of UV radiation has been proposed to explain their photodecomposition and hence their absence. However, contradictory results from laboratory experiments mimicking Mars’ surface UV radiation did not resolve the behaviour of carbonates in such an environment, which is why we exposed, in low Earth orbit and in laboratory experiments, both abiotic and biotic calcium carbonates to UV radiation of wavelength above 200 nm, the same spectral distribution as the one reaching the surface of Mars. For low Earth orbit (LEO) exposure, this was done for the UVolution experiment on board the BIOPAN ESA module, which was set outside a Russian Foton automated capsule, and exposed to space conditions for 12 days in September 2007. The targeted carbonates are biominerals and abiotic samples. Our laboratory results mainly show that the exposed carbonates appear to be stable to UV radiation if directly exposed to it. The LEO experiment results tend to the same conclusion, but the integrated exposition time to Solar UV during the experiment is not sufficient to be conclusive. However, the stability of the biominerals derived from the laboratory experiment could strengthen the interest to explore deeper their potential as life records at Mars. Hence, they should be considered as primary targets for in situ analyses during future missions.  相似文献   

Holocene fire regime changes from multiple-site sedimentary charcoal analyses in the Lourdes basin (Pyrenees,France)     

Damien Rius  Boris Vannière  Didier Galop  Hervé Richard 《Quaternary Science Reviews》2011,30(13-14):1696-1709

One lake and three peat bogs from the Lourdes glacial basin (France) were used for macrocharcoal analyses and fire frequency reconstruction over the entire Holocene (11700 years). The chronology was based upon thirty-three 14C AMS dates. Comparison of the distribution of both CHarcoal Accumulation Rate (CHAR) and fire return intervals showed that charcoal accumulation significantly differs between the lake and the peat bogs, but that frequency calculation overcomes the disparity between these site types. A composite frequency was built from the four individual records to assess regional versus local variability and fire regime controls by comparisons with regional fire activity, Holocene climatic oscillations and vegetation history. The millennial variability can be depicted as follows: relatively high frequency between 8000 and 5000 cal a BP (up to 5 fires/500 yrs), relatively low frequency between 5000 and 3000 cal a BP (down to 0 fires/500 yrs), and an increase between 3000 and 500 cal a BP (up to 4 fires/500 yrs). From 8000 to 5000 cal a BP, fire frequency displays strong synchrony between sites and appears to be mostly driven by increased summer temperature characterizing the Holocene Thermal Maximum (HTM). On the contrary, during the last 3000 years fire frequency was heterogeneous between sites and most probably human-driven. However, higher frequency at the millennial scale during the mid-Holocene strongly suggests that the perception of human-driven fire regime depends on the strength of natural controls.  相似文献   

Experimental investigation of the kinetics of Ostwald ripening of quartz in silicic melts     

Hugues Cabane  Didier Laporte  Ariel Provost 《Contributions to Mineralogy and Petrology》2001,142(3):361-373

To characterise the kinetics of Ostwald ripening of quartz, we conducted four series of experiments in systems consisting of quartz, with an initial grain size of ƹ.3 to 6 µm, in equilibrium with hydrous silicic liquids. Two series were performed with a haplogranitic liquid containing 6.5 wt% H₂O at 900 °C and 1 GPa. The third series was made in the quartz-anorthite system at water saturation, 900 °C, and 1 GPa. The last series was made in the quartz-albite system at water saturation, 800 °C, and 0.2 GPa. In all series, we observed a relatively small but systematic increase of the mean grain size of quartz, % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d , with increasing run duration, t. The largest increase was in the quartz-anorthite system: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d increased by a factor of 4.3 after 326 h; the smallest increase was measured in the quartz-albite system: % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d increased by a factor of only ƹ.6 after 1,173 h. The experimental data yield very good linear fits in both ln t vs ln% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d and ln t vs % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d diagrams. The slopes in the ln t vs ln% MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8YjY-vipgYlH8Gipec8Eeeu0xXdbba9frFj % 0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9 % vr0-vr0-vqpWqaaeaabiGaciaacaqabeaabaqaamaaaOqaaiqbdsga % Kzaaraaaaa!29AA! [`(d)] \bar d diagrams, between 1/5 and 1/7, are, however, much smaller than the value of 1/3 predicted by the Lifshitz-Slyozov-Wagner theory for diffusion-controlled Ostwald ripening. A possible explanation for this discrepancy is that the diffusion-controlled regime in our experiments is only attained after a transient regime lasting from 20 h in series III to 100 h in series IV. A more straightforward explanation of the experimental results is that the rate-limiting mechanism for Ostwald ripening is quartz growth by surface nucleation not diffusion in the silicic liquid. Finally, we extrapolated our data to geological time scales to evaluate the importance of Ostwald ripening in natural quartz-bearing magmatic systems: (1) quartz cannot coarsen measurably by Ostwald ripening over reasonable time scales if the initial grain size is ƹ mm or more; and (2) Ostwald ripening may be very active at the end of nucleation events and result in the consumption of a significant proportion of crystalline nuclei.  相似文献   

Reply to the Comment By J. E. T. Channell and J. S. Stoner On 'Magnetostratigraphy of the Hettangian Langmos Section (Adnet, Austria): Evidence For Time-Delayed Phases of Magnetization'     

Yves Gallet  Didier Vandamme  Leopold Krystyn 《Geophysical Journal International》1994,119(3):1008-1008

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Dihedral angle measurements and infiltration property of SiO<Subscript>2</Subscript>-rich melts in mantle peridotite assemblages     

Jér?me?MaumusEmail author  Didier?Laporte  Pierre?Schiano 《Contributions to Mineralogy and Petrology》2004,148(1):1-12

Petrological and experimental studies demonstrated that nepheline-normative, SiO₂-rich melts can be present in the upper mantle at pressures 1.5 GPa. To evaluate the role of such melts in mantle processes and magma genesis, we carried out two types of experiments: (1) melt distribution experiments to characterize the grain-scale distribution of a small fraction of typical SiO₂-rich mantle melt (SRMM) in polycrystalline olivine (Ol) at 1,180°C, 1.2 GPa; and (2) an infiltration experiment to test the ability of SRMM to impregnate and metasomatise neighbouring non-molten mantle rocks. The median dihedral angles at Ol-Ol-SRMM contacts are equal to 50°, implying that melt should be interconnected at all melt fractions. Complications arise, however, in the investigated system because Ol–liquid interfacial energy is anisotropic, and we estimate that the connectivity threshold in the SRMM–Ol system is 0.3 vol%. Regarding the very low volume fraction of SRMM in peridotites, we conclude that these melts either occur as isolated pockets or form a network of grain edge channels with a low degree of connectivity due to a large number of dry grain edges. Even in the case where an interconnected network exists, their large viscosities should prohibit the extraction of SRMM from peridotite sources. The infiltration experiment also points to a very reduced mobility of SRMM in the upper mantle. In this experiment, a slice of synthetic dunite was immersed into a magma reservoir made of 60 wt% SRMM+40 wt% Ol, and subjected to 1,180°C-1.2 GPa for 113 h: despite this long duration, the SiO₂-rich liquid was unable to infiltrate measurably the dunite. Our experiments do not support the hypothesis that SRMM represent agents of mantle metasomatism.  相似文献