Dissolved and particulate metals (Fe, Zn, Cu, Cd, Pb) in two habitats from an active hydrothermal field on the EPR at 13°N

Le texte intégral est accessible via Archimer: http://archimer.ifremer.fr/doc/2008/publication-3830.pdfInternational audienceThe distribution of Fe, Cu, Zn, Pb, Cd between the dissolved ( 2 μm) fractions was measured after in-situ filtration in two hydrothermal habitats. The total metal concentration ranges exhibit a clear enrichment compared with the seawater concentration, accounting for the hydrothermal input for all the metals considered. Iron is the predominant metal (5-50 μM) followed by Zn and Cu. Cd and Pb are present at the nM level. At the scale studied, the behavior of temperature, pH and dissolved iron is semi-conservative whereas the other dissolved and particulate metals are characterized by non-conservative patterns. The metal enrichment of the > 2 μm fraction results from the settlement and accumulation of particulate matter close to the organisms, acting as a secondary metal source. The enrichment observed in the dissolved fraction can be related to the dissolution or oxidation of particles (mainly polymetallic sulfide) or to the presence of small particles and large colloids not retained on the 2 μm frit. SEM observations indicate that the bulk particulate observed is characteristic of crystalline particles settling rapidly from the high temperature smoker (sphalerite, wurtzite and pyrite), amorphous structures and eroded particles formed in the external zone of the chimney. Precipitation of Zn, Cu, Cd and Pb with Fe as wurtzite, sphalerite and pyrite is the main process taking place within the area studied and is semi-quantitative. The distribution of the dominant observed fauna has been related to the gradient resulting from the dilution process, with the alvinellids worms colonizing the hotter and more variable part of the mixing zone, but also to the metallic load of the mixing zone. Dissolved and particulate metal concentrations are therefore necessary abiotic factors to be studied in a multiparametric approach to understand the faunal distribution in hydrothermal ecosystems

Optimisation de l’identification et du dénombrement du microphytoplancton avec le système couplé de numérisation et d’analyse d’images FlowCAM – Zoo/PhytoImage (système innovant). Action 9 – Livrable 3. Evolution du matériel de numérisation : prototype FastCAM et perspectives. Rapport final, février 2016

This deliverable contains all development work of the FastCAM, new tool for fast imaging of the phytoplankton, which took place in 2015. It consists of: One report of the FastCAM and its comparison with the FlowCAM presentation: The FlowCAM enables the digitalization of a sample of phytoplankton with X10 and X 4 magnifications. The first allows a better morphological description and therefore a higher taxonomic resolution but with a longer scan time (16 X). Thus, for routine analyses, only scanning at 4 X is possible. A considerable gain would be able to do an acquisition to the magnification 10 X with a time of analysis more short, comparable to 4 X. A fast flow imaging system has therefore developed in this sense. He was called FastCAM. The system is based on the use of a high resolution (2 Megapixels) and high‐speed camera allowing the acquisition to 340 FPS. In this way, it allows to scan 10 mL of sample with a X 10 magnification within 15 min. Comparison of the images with those obtained with the FlowCAM clearly shows a gain to the use of the FastCAM. The outlook now is the establishment of a set of learning for a coupling with Zoo/Phytoimage and the industrial transfer of the system. A slide show presentation of the system showed during a project meeting (on the 4th of November 2015).Ce livrable contient l’ensemble des travaux de développement du FastCAM, nouvel outil de numérisation rapide du phytoplancton, ayant eu lieu en 2015. Il est constitué de deux documents : Un rapport de présentation du FastCAM et de sa comparaison avec le FlowCAM. Le FlowCAM permet la numérisation d’un échantillon de phytoplancton avec des grandissements X10 et X4. Le premier permet une meilleure description morphologique et donc une meilleure résolution taxonomique mais avec un temps d'acquisition environ 16X plus long. Ainsi, pour des analyses en routine, seule une numérisation au X4 est possible. Un gain considérable serait de pouvoir réaliser une acquisition au grandissement 10X avec un temps d'analyse plus court, comparable au 4X. Un système d’imagerie rapide en flux a donc été développé en ce sens. Il a été nommé FastCAM. Le système repose sur l’utilisation d’une caméra rapide haute résolution (2 Megapixels) permettant l’acquisition à 340 images/s. Grâce à cela, il permet de numériser 10 mL d’échantillon avec un grandissement X10 en moins de 15 min. La comparaison des images à celles obtenues avec le FlowCAM en un temps équivalent au X4 montre clairement un gain à l’utilisation du FastCAM. Les perspectives maintenant sont la constitution d’un set d’apprentissage pour un couplage avec le logiciel Zoo/Phytoimage. Un diaporama de présentation du système, présenté lors d’une réunion de projet (4 novembre 2015

Direct and fast detection of Alexandrium minutum algae by using high frequency microbalance

In this paper, a simple detection of a toxic algae, Alexandrium minutum, was developed using highly sensitive quartz crystal microbalance. In terms of performance, compared with other conventional analytical tools, the main interest of our immunosensor is based on a fast and direct detection of these living cells. This system requires the use of one monoclonal antibody directed against the surface antigen of A. minutum. We demonstrate that the whole living and motile algae are caught and detected. The high specificity of the biosensor is also demonstrated by testing several other dinoflagellate species. The frequency shift is correlated to the A. minutum cells concentration. This simple system is potentially promising for environmental monitoring purposes

Monoclonal antibody against the surface of Alexandrium minutum used in a whole-cell ELISA

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Probing acoustics of liquid foams by optical diffusive wave spectroscopy

Sound propagation through liquid foams, which are dispersions of gas bubbles in a continuous liquid phase, is not well known yet. To characterize foam acoustics at the local scale, we have studied the effect of an external acoustic wave on bubble displacements inside an aqueous foam. We quantify these displacements by using a technique based on optical diffusive wave spectroscopy, that we specially developped to resolve tiny deformations in materials. Bubble displacements induce a modulation on the photon correlation curve. Measurements for various sound frequencies and amplitudes are interpreted using a light diffusion model. It allows us to unravel a nontrivial acoustic displacement profile inside the foam; in particular, we find that the acoustic wave creates a localized shear in the vicinity of the solid walls holding the foam, as a consequence of inertial contributions. This study of how bubbles "dance" inside a foam as a response to sound turns out to provide new insights on foam acoustics and sound transmission into a foam, foam deformation at high frequencies, and analysis of light scattering data in samples undergoing nonhomogeneous deformations

Shaving foam: A complex system for acoustic wave propagation

While liquid foams have applications in an increasing number of industrial areas (food, cosmetic or petroleum industry), it remains difficult to non-invasively probe their structure and/or composition. Since the propagation of acoustic waves is very sensitive to parameters such that the liquid fraction, the bubble size distribution, or even the nature of the liquid phase, acoustic spectroscopy could be a very powerful tool to determine the structure and/or composition of liquid foams. In this context, we present an investigation of the acoustic properties of a useful and common foam, often considered as a model system: shaving foam. Phase velocity and attenuation of acoustic waves in a commercial shaving foam (Gillette) were measured over a broad frequency range (0.5 to 600 kHz), using four different experimental setups: an impedance tube (0.5-6 kHz), an acousto-optic setup based on Diffusive Wave Spectroscopy (0.4-10 kHz), and two transmission setups with narrow-band (40 kHz) and broad-band (60-600 kHz) transducers. We present the results and discuss the advantages and shortcomings of each setup in terms of a potential spectroscopy technique

PROPAGATION OF ACOUSTIC WAVES IN A FOAM - PART I: EXPERIMENTS

International audienceWe present an experimental investigation of the acoustic properties of liquid foams. Velocity and attenuation of sound were measured in different foam samples, with a systematic study of the role of parameters such as the frequency, the liquid volume fraction, the bubble size, the nature of the gas, and the nature of the surfactants. Three experimental setups were used to cover a frequency range spanning three orders of magnitude (500 Hz to 600 kHz): an impedance tube [Pierre, 2013a], a pair of narrow-band 40 kHz transducers [Ben Salem, 2013], and a pair of broadband transducers [Pierre, 2013b]. Two main regimes of propagation were identified, with a limit at approximately fR=5 kHz.mm, where f is the frequency and R the average bubble size. At low frequencies (or for small bubbles), the velocity was found to follow the so called mixture law, i.e. depending only on the liquid volume fraction, with no clear influence neither on the bubble size, nor on the type of surfactant. A noticeable exception were Gillette foam samples, in which the velocity was higher than expected. The attenuation, on the other hand, was found to depend mainly on the nature of the gas and the bubble size. Three sources of attenuation were identified: thermal losses due to heat exchange during bubble oscillations, local viscous losses, and viscous losses along the wall of the tube (Kirchhoff losses). The latter term could be related to a macroscopic viscosity of the foam, whose order of magnitude and dependence on R were in good agreement with previous measurements at lower frequencies [Costa, 2013].In the second regime, at high frequencies (or for large bubbles), the propagation of acoustic waves was dispersive, with a peak of attenuation and a velocity reaching values substantially higher than in the previous regime. The frequency of the maximum of attenuation was close to the Minnaert resonance of the individual bubbles of the foams, suggesting that foams might behave acoustically like (very concentrated) bubbly liquids

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