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

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.     

Improvements on Fresnel arrays for high contrast imaging

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.     

Petroleum accumulation and leakage in a deeply buried carbonate reservoir,Níspero field (Mexico)

The filling history of the Níspero deeply buried Lower Cretaceous carbonate reservoir (below 4000 m) from the south part of Gulf of Mexico was studied using a combination of data from petrography, stable isotopes and fluid inclusions and compared with a one-dimensional burial model to derive timing.     

Characteristics of developing waves as a function of atmospheric conditions,water properties,fetch and duration

For any specific wind speed, waves grow in period, height and length as a function of the wind duration and fetch until maximum values are reached, at which point the waves are considered to be fully developed. Although equations and nomograms exist to predict the parameters of developing waves for shorter fetch or duration conditions at different wind speeds, these either do not incorporate important variables such as the air and water temperature, or do not consider the combined effect of fetch and duration. Here, the wind conditions required for a fully developed sea are calculated from maximum wave heights as determined from the wind speed, together with a published growth law based on the friction velocity. This allows the parameters of developing waves to be estimated for any combination of wind velocity, fetch and duration, while also taking account of atmospheric conditions and water properties.     

Formula for predicting bedload transport rate in oscillatory sheet flows

The method of Wang [Wang, Y.-H., 2007. Formula for predicting bedload transport rate in oscillatory sheet flow. Coastal Engineering 54, 594–601] to predict the wave friction factor is discussed. At the threshold of sediment entrainment the proposed equation produces a wide scatter of data points when plotted against an equation based on the Shields parameter. It is shown that a better correlation coefficient can be obtained by calculating the critical wave friction factor directly from the wave period, as well as the sediment and water properties.     

Record of enhanced late Pliocene tectono‐volcanic activity in the Lesser Antilles forearc basin: Insights into the long‐term behaviour of the Lesser Antilles subduction zone

In this study, we investigate the Lesser Antilles forearc basin, focusing on the late Pliocene to Pleistocene sedimentary archives in order to track the occurrence of extreme events triggered by enhanced subduction‐related tectono‐volcanic activity. We identify late Piacenzian deposits covering a major regional erosional surface, displaying sedimentary dykes and large marine boulders embedded in a mixed continental–marine matrix, characteristic of tsunamites. We interpret this episode of platform emersion and the successive cataclysmic deposits as resulting from enhanced tectonic activity at the interface of the subduction zone, synchronous with the initiation of the Lesser Antilles volcanic arc. We then discuss the implications in terms of the mechanical behaviour of the Lesser Antilles subduction zone.     

Multisite surface reaction versus transport control during the hydrolysis of a complex oxide

Dissolution experiments of a tholeiite basalt glass carried out at different pH and T (up to 300°C) using a rotatingdisc apparatus show that, depending on pH and T, dissolution can be controlled by one of the following steps: (1) surface reaction; (2) transport of reactants in solution; and (3) mixed reaction. The activation energies of these different processes were found to be 60, 9 and 15–50 kJ mol⁻¹, respectively. Taking account of these results, it appears likely that surface reactions are not rate limiting for the hydrolysis of most crystalline silicate minerals in hydrothermal and metamorphic processes, and that caution should be exercised when predicting rate of reactions at high temperatures solely on the basis of activation energies measured at low temperatures.

Comparison of experimental and theoretical potentiometric titrations of the basalt glass and its constituent oxides indicates that the adsorption of H⁺ and OH⁻ ions at the basalt surface is metal cation specific and that the net adsorption can be predicted from the sole knowledge of the acidity constants of the network-forming constituent oxides. We found that in the acidic pH region dissolution is promoted by the adsorption of H⁺ on al and Fe surface sites while in the basic region, dissolution is promoted by the adsorption of OH⁻ on Si sites. The combination of the two distinct types of surface sites, Al and Fe on the one hand, and Si on the other hand, results in a dissolution rate minimum at a pH-value between the pH_zpc of the two groups of oxide components. Linear regressions with a slope n=3.8 are observed both in acid and alkaline solutions in logarithmic plots of the rate of dissolution vs. the surface charge. The value of n, which represents the number of protonation or hydroxylation steps prior to metal detachment, has been found equal to the mean valence of the network-forming metals.

Combining concepts of surface coordination chemistry with transition state theory afforded characterisation of the activated complexes involved in basalt dissolution processes. From the values obtained for the thermodynamic properties of activation for basalt dissolution it is assumed that the activated complexes formed during the H₂O-promoted dissolution of the basalt glass are more tightly bonded than those formed during H⁺- or OH⁻-promoted dissolution.     

Gravimetry on the Erimo Seamount, Japan

A gravimetric survey on the sea-bottom was performed on the Erimo Seamount by the French submersible “Nautile”. It took place during the second phase of the Kaiko French-Japanese Program. The reference station was established on the Erimo submarine observatory at a depth of 3942 m and from this point the survey of four stations was carried out. The obtained accuracy of the gravity field measurements was about 0.1 mGal.

A three-dimensional model of the seamount and its surroundings was constrained by the free-air anomaly values from the sea surface and from the sea bottom and by the perfect Seabeam topography survey of the whole area. The model which fitted the observed values best, allowed us to identify a low-density layer of coral limestones and volcaniclastics capping the seamount and to define the geometry of the interface between basalts and coral rocks.     

Les courbes flux chimique-debit et le fonctionnement des aquiferes karstiques

When integrating both chemical content and discharge, the chemical flux is a choice parameter, as much for the study of water transit as for weathering budgets.

In a karst system, the flux allows the identification of: (a) the main aquifer of the system that supplies the spring to the point of complete drying-up; (b) the “piston-effect” of seepage upon highly mineralized waters contained in karst channels; (c) the qualitative passage from a regime of water decline to one of water depletion; (d) several outlets belonging (or not) to the same karst system; (e) the homogeneity in the capability of mixing the system, and thus, a contrario, the importance of its karstification; (f) the heterogeneity of seepage and of reserves.

Abstract

Intégrant à la fois la concentration chimique et le débit qui la véhicule, le flux chimique est un paramètre de choix autant pour l'étude des transits d'eau que pour celle des bilans de l'altération.

Dans le système karstique, le flux permet d'identifier: (a) l'aquifère principal du système, capable d'alimenter la source jusqu'au tarissement total; (b) le phénomène d' “effet-piston” de l'infiltration sur les eaux minéralisées présentes dans les drains; (c) le passage qualitatif de la décrue au tarissement au cours d'une récession; (d) l'appartenance ou non de plusieurs exutoires au même système karstique; (e) l'homogénétité et les qualités de bon mélangeur du système et donc, à contrario, l'importance de sak arstification; (f) l'hétérogénéité de l'infiltration ou celle des réserves.