Diel variation of benthic respiration in a coral reef sediment (Reunion Island,Indian Ocean)     

Jacques Clavier  Laurent Chauvaud  Pascale Cuet  Clémentine Esbelin  Patrick Frouin  Dorothée Taddei  Gérard Thouzeau 《Estuarine, Coastal and Shelf Science》2008

Oxygen and total dissolved inorganic carbon (DIC) fluxes at the water–sediment interface were measured using benthic chambers to assess the short-term variations of community respiration (CR) in the back reef sediments of Reunion Island (Indian Ocean). Benthic CR had a daily cycle of minimal (6:00 AM) and maximal values (6:00 PM), showing increases of oxygen and DIC fluxes of 2.8- and 3.8-fold, respectively. Average CR values were observed at midday and midnight. The evolution of fluxes was positively related to oxygen concentration in ambient water, but not to temperature changes. In the study area, high daytime primary production augments the amount of energy available for community metabolism and increases benthic respiration. The benthic communities are therefore subjected to short-term variable environmental conditions with oxygen supersaturation during the day, and moderately hypoxic conditions at the end of the night.  相似文献   

Fraile Detection of Solar $$-Modes by Fossat et al.     

Hannah Schunker  Jesper Schou  Patrick Gaulme  Laurent Gizon 《Solar physics》2018,293(6):95

The internal gravity modes of the Sun are notoriously difficult to detect, and the claimed detection of gravity modes presented by Fossat et al. (Astron. Astrophys.604, A40, 2017) is thus very exciting. Given the importance of these modes for understanding solar structure and dynamics, the results must be robust. While Fossat et al. described their method and parameter choices in detail, the sensitivity of their results to several parameters was not presented. Therefore, we test the sensitivity of the results to a selection of the parameters. The most concerning result is that the detection vanishes when we adjust the start time of the 16.5-year velocity time-series by a few hours. We conclude that this reported detection of gravity modes is extremely fragile and should be treated with utmost caution.  相似文献   

Improvements on Fresnel arrays for high contrast imaging     

Roux Wilhem  Koechlin Laurent 《Experimental Astronomy》2018,45(1):21-40

The Fresnel Diffractive Array Imager (FDAI) is based on a new optical concept for space telescopes, developed at Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse, France. For the visible and near-infrared it has already proven its performances in resolution and dynamic range. We propose it now for astrophysical applications in the ultraviolet with apertures from 6 to 30 meters, aimed at imaging in UV faint astrophysical sources close to bright ones, as well as other applications requiring high dynamic range. Of course the project needs first a probatory mission at small aperture to validate the concept in space. In collaboration with institutes in Spain and Russia, we will propose to board a small prototype of Fresnel imager on the International Space Station (ISS), with a program combining technical tests and astrophysical targets. The spectral domain should contain the Lyman-α line (λ =?121 nm). As part of its preparation, we improve the Fresnel array design for a better Point Spread Function in UV, presently on a small laboratory prototype working at 260 nm. Moreover, we plan to validate a new optical design and chromatic correction adapted to UV. In this article we present the results of numerical propagations showing the improvement in dynamic range obtained by combining and adapting three methods : central obturation, optimization of the bars mesh holding the Fresnel rings, and orthogonal apodization. We briefly present the proposed astrophysical program of a probatory mission with such UV optics.  相似文献   

Why chromatic imaging matters     

Joel Sanchez-Bermudez  Florentin Millour  Fabien Baron  Roy van Boekel  Laurent Bourgès  Gilles Duvert  Paulo J. V. Garcia  Nuno Gomes  Karl-Heinz Hofmann  Thomas Henning  Jacob W. Isbell  Bruno Lopez  Alexis Matter  J-Uwe Pott  Dieter Schertl  Eric Thiébaut  Gerd Weigelt  John Young 《Experimental Astronomy》2018,46(3):457-473

During the last two decades, the first generation of beam combiners at the Very Large Telescope Interferometer has proved the importance of optical interferometry for high-angular resolution astrophysical studies in the near- and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u ? v coverage per pointing increases significantly, providing an opportunity to use reconstructed images as powerful scientific tools. Therefore, interferometric imaging is already a key feature of the new generation of VLTI instruments, as well as for other interferometric facilities like CHARA and JWST. It is thus imperative to account for the current image reconstruction capabilities and their expected evolutions in the coming years. Here, we present a general overview of the current situation of optical interferometric image reconstruction with a focus on new wavelength-dependent information, highlighting its main advantages and limitations. As an Appendix we include several cookbooks describing the usage and installation of several state-of-the art image reconstruction packages. To illustrate the current capabilities of the software available to the community, we recovered chromatic images, from simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we aim at showing the importance of selecting good regularization functions and their impact on the reconstruction.  相似文献   

Calderas,landslides and paleo-canyons on Piton de la Fournaise volcano (La Réunion Island,Indian Ocean)     

Olivier Merle  Philippe Mairine  Laurent Michon  Patrick Bachèlery  Magali Smietana 《Journal of Volcanology and Geothermal Research》2010,189(1-2):131-142

Based upon a re-interpretation of previous data and a new field campaign, a structural evolution is proposed for the early history of Piton de la Fournaise volcano from 500,000 to 50,000 years. Conceptually, it is shown that the formation of a caldera in which lava flows are contained inside the caldera depression, gives time for erosion to excavate deep canyons on the external slopes of the volcano, for example, the Rivière des Remparts, the Rivière Langevin and the Rivière de l'Est canyons on Piton de la Fournaise volcano. These canyons are infilled when lavas, filling the caldera and overflowing its rim, are able again to flow on the external slopes of the volcano. In the past, this excavating/infilling process has occurred twice following the formation of the Rivière des Remparts and Morne Langevin calderas. The formation of the third caldera, the Plaine des Sables caldera, was followed by the excavation of the current canyons. In addition to this process, two large landslides have been documented in the field. The first, which happened about 300,000 years ago, is apparently the first episode of the break up of Piton de la Fournaise volcano, predating the formation of the four large calderas. The second landslide, which occurred 150,000 years ago and is considered to be less extensive, has carried away the entire southern flank of the Rivière des Remparts caldera.  相似文献   

Geochemical comparison between minettes and kersantites from the Western European Hercynian orogen: trace element and PbSrNd isotope constraints on their origin     

Laurent Turpin  Danielle Velde  Guy Pinte   《Earth and Planetary Science Letters》1988,87(1-2)

Trace element and isotopic characteristics of late Carboniferous to early Permian minettes and kersantites have been determined. These lamprophyres have been sampled throughout the Western European Hercynian orogen, from Brittany to the west to Schwarzwald to the east. In spite of sharp petrological differences reflected by mineralogy and major element geochemistry, minettes and kersantites exhibit close identity with respect to trace element and isotopic features. These features comprise enrichment in incompatible elements, highCs/Rb and lowCe/Pb ratios, Ta and Ti relative depletion, high abundance in transition elements and highNi/Mg ratios. Pb isotope ratios are undistinguishable from those measured on Hercynian continental crust. Initial¹⁴³Nd/¹⁴⁴Nd ratios are between0.5120 (ε_i −5) and0.5122 (ε_i −1) for minettes and kersantites whereas initial⁸⁷Sr/⁸⁶Sr ratios vary between 0.7055–0.710 for minettes and 0.707–0.708 for kersantites. No simple mixing relations are visible on RbSr and SmNd isochron diagrams. The exceptional homogeneity of these geochemical characteristics along a 1000 km traverse does not allow for an hypothesis of enrichment through upper level assimilation and thus leads to propose that these rocks originated through melting of a mantle enriched by recycling of crustal material.  相似文献   

Paleo-stress orientations from calcite twins in the North Pyrenean foreland, determined by the Etchecopar inverse method   总被引：1，自引：0，他引：1  

C. Tourneret  P. Laurent 《Tectonophysics》1990,180(2-4):287-302

During the last decade, it has been shown that accurate analyses of calcite twinning in thin section may allow computation of the paleo-deviatoric stress tensor associated with this deformation. Following from the work of Larroque and Laurent (1988), and Lacombe et al. (1989), this is a new application of the Etchecopar inverse method. Weakly deformed limestones from about 150 to 200 km north of the Pyrenean chain (South France) were studied. The Etchecopar inverse method, which can be used on a microcomputer, is comparable to the method of analysis of striated fault planes proposed by Etchecopar et al. in 1981, as it determines the principal stress orientations and the stress ellipsoid shape ratio φ = (σ₂ − σ₃)/(σ₁ − σ₃). The Etchecopar method using calcite twins has been selected for this study because it is suitable for the determination of polyphase deformation in coarse-grained limestones (Lacombe et al. 1989).

Ten samples of oolitic limestones, cemented with sparry calcite, from the Bajocian (170 Ma) and the Oligocene (30 Ma) were studied. For each of them, only one or two stress tensors were determined: the first is characterized by a principal compressive stress axis σ₁ which is horizontal and approximately N-S. Local departures from this orientation have been observed and are interpreted as local stress perturbations. For the second, which was defined in the Oligocene, but occurred only locally in the Jurassic limestones, the position of σ₁ is nearly vertical; the direction of extension σ₃ is either NE-SW or undefined into the horizontal plane (σ₂ = σ₃); this radial extension is interpreted as the result of two or more superposed extensive deformation phases with vertical σ₁. The N-S compression was never found in the Oligocene limestones, and from its orientation, it is assumed to correspond to the Pyrenean deformation. These results are compared to the more complex deformation pattern obtained from classical microtectonical studies (Arthaud and Choukroune, 1972; Bonijoly and Blès, 1983; Granier and Blès, 1988; Blès et al., 1989). Only the major tectonic events are recorded by calcite twinning. Finally, the suitability of calcite twin analyses for the determination of complex polyphase deformation is discussed.  相似文献   

The stratospheric version of LMDz: dynamical climatologies, arctic oscillation, and impact on the surface climate     

François Lott  Laurent Fairhead  Frederic Hourdin  Phu Levan 《Climate Dynamics》2005,25(7-8):851-868

A climatology of the stratosphere is determined from a 20-year integration with the stratospheric version of the Atmospheric General Circulation Model LMDz. The model has an upper boundary at near 65 km, uses a Doppler spread non-orographic gravity waves drag parameterization and a subgrid-scale orography parameterization. It also has a Rayleigh damping layer for resolved waves only (not the zonal mean flow) over the top 5 km. This paper describes the basic features of the model and some aspects of its radiative-dynamical climatology. Standard first order diagnostics are presented but some emphasis is given to the model’s ability to reproduce the low frequency variability of the stratosphere in the winter northern hemisphere. In this model, the stratospheric variability is dominated at each altitudes by patterns which have some similarities with the arctic oscillation (AO). For those patterns, the signal sometimes descends from the stratosphere to the troposphere. In an experiment where the parameterized orographic gravity waves that reach the stratosphere are exaggerated, the model stratosphere in the NH presents much less variability. Although the stratospheric variability is still dominated by patterns that resemble to the AO, the downward influence of the stratosphere along these patterns is near entirely lost. In the same time, the persistence of the surface AO decreases, which is consistent with the picture that this persistence is linked to the descent of the AO signal from the stratosphere to the troposphere. A comparison between the stratospheric version of the model, and its routinely used tropospheric version is also done. It shows that the introduction of the stratosphere in a model that already has a realistic AO persistence can lead to overestimate the actual influence of the stratospheric dynamics onto the surface AO. Although this result is certainly model dependent, it suggests that the introduction of the stratosphere in a GCM also call for a new adjustment of the model parameters that affect the tropospheric variability.  相似文献   

Impact of meteorological data resolution on the forecasted ozone concentrations during the ESCOMPTE IOP2a and IOP2b     

Laurent Menut  Isabelle Coll  Sylvie Cautenet 《Atmospheric Research》2005,74(1-4):139-159

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The junction of Fensch and Moselle rivers,France; mineralogy and composition of river materials     

Emmanuelle Montarges-Pelletier  Laurent Jeanneau  Pierre Faure  Isabelle Bihannic  Odile Barres  Bruno S. Lartiges 《Environmental Geology》2007,53(1):85-102

The Moselle river flows in the north-east of France, from Vosges Mountains to neighboring countries Luxembourg and Germany. One of its tributaries, the Fensch river, drains a highly industrialized watershed, strongly impacted by mining, smelting and surfacing activities. The objective of this work, part of a general research program on Moselle watershed (Zone Atelier Moselle) was to assess the impact of the polluted Fensch river on the global quality of the Moselle river. For that purpose, water, sediments and suspended particulate matter were sampled in both rivers, upstream and downstream the junction. Four main sampling campaigns were carried out, in winter during a flood event and in spring at low water level. On a first step, mineralogical analyses (XRD and FTIR) and chemical analyses (ICP-MS, ICP-AES), were performed on sediments, suspended particulate matters and filtered waters. Major and trace elements concentrations were obtained on two different granulometric fractions (0–2 mm and 0–50 μm) revealing the enrichment in heavy metals of fine particles. From one collecting campaign to another, seasonal variations could be evidenced on suspended matter composition even though major minerals (calcite, quartz and kaolinite) were always present. Furthermore, spatial variations were evidenced for Fensch and Moselle downstream sediments. Thus, very fine-grained sediments, poorly crystallized, displaying at the same time higher metal concentrations and higher organic matter content than in Fensch river material, were collected downstream, in a low hydrodynamic conditions zone, assumed as a preferential sedimentary zone or even as a placer. Strong correlations could be revealed between iron content and contaminant concentrations, confirming the origin of polluted material.  相似文献