Gouffre de la Sambuy is an alpine cave, located in the French northern Western Alps, in the Bauge... more Gouffre de la Sambuy is an alpine cave, located in the French northern Western Alps, in the Bauges massif. This subalpine massif is included in the "delphinohelvetic" domain of the external Alps, drifted over the foreland (jurassian and molassic domains). Bauges massif presents with these folded structures a medium altitude (< 2 500 m asl) and mountainous relief built with only sedimentary rocks. To the east of the massif, the Sambuy summit is 2198 m asl, the main entrance of the cave (SB9) is open at 1 820 m asl. The average of temperature in this area is 1.6°C. The precipitations are over 2 100 mm/year. The cave is approximately 900 m development and 120m depth. The final part of the cave is on the top of the Hauterivian marls. During speleogenesis studies on 2012, speleologists have founded bacterial mats and gypsum in the marly parts of the cave. Upper, in the middle part, the Barremian limestone wall of a 25 m shaft was covered by unusual fine and white deposits looking like lichen. To understand these ecosystems, climate aerologic measurements like air temperature, pressure, and wind speed were realized during each visit in winter, spring and summer. Due to the difficulties to access to the cave with no possibilities to get electrical power, no monitoring was realized for the climate parameters. In spring, the wall deposits have been sampled with swab and store in sterile tube for laboratory molecular analysis. DNA was extracted, PCR amplifications and cloning-sequencing were performed targeting bacterial 16SrRNA and eukaryotic 18SrRNA genes. For the bacterial community, we identified 29 different OTUs and the richness estimator (Schao) showed a global richness of 65 OTUs. The bacterial community was mainly composed by Proteobacteria, Acidobacteria, Actinobacteria, Nitrospirae and an important part of uncultured bacteria. Some of these bacterial taxa are known to be involved in nitrogen cycling. For the eukaryotic community, 32 OTUs were identified from our clones library, and the Schao index showed a global richness of 86 OTUs. Rhizaria (with mostly Cercozoa, genus Cermononas) was a dominant group, followed by Fungi (mostly Dikaria). Some Alveolata belonging to Ciliophora were also detected, as well as an important part of uncultured fungi and others. Additional sequencing analyses should be performed to depict in depth the taxonomic composition in these microbial mats. Our preliminary results showed that these microbial mats comprised a rather high diversity of prokaryotic and eukaryotic taxa, which physiological/biochemical characteristics and biotic interactions have still to be described.
EGU General Assembly Conference Abstracts, May 1, 2014
In this study, we propose to use soils water-extracted organic matter (OM) as a database of fluor... more In this study, we propose to use soils water-extracted organic matter (OM) as a database of fluorescence signal, to interpret quantitatively the the fluorescence of speleothems OM. Due to its efficiency to described dissolved organic matter (DOM) characteritics, fluorescence has been used to determined DOM signatures in natural systems, water circulations, OM transfer from soils, OM evolution in soils or recently, DOM changes in engineered treatment systems. Fluorescence has also been used in speleothems studies, mainly as a growth indicator. Only few studies interpret it as an environmental proxy. Speleothem fluorescence can be used as an environmental proxy, to record the past soil evolutions. Qualitative changes of OM are easily measured. However, it's today complicated to quantify the fluorescence signal of speleothems due to the analytical method generally used. That's why we propose to interpret quantitatively the fluorescence signal of speleothems, using soil fluorescence as a database of fluorescence signal.
In this study, we propose a framework to interpret quantitatively the fluorescence of speleothems... more In this study, we propose a framework to interpret quantitatively the fluorescence of speleothems organic matter (OM) by the way of a bank of water-extracted organic matter. Due to its efficiency to described dissolved organic matter (DOM) characteritics, fluorescence has been used to determined DOM signatures in natural systems, water circulations, OM transfer from soils, OM evolution in soils or recently, DOM changes in engineered treatment systems. Fluorescence has also been used in speleothems studies, mainly as a growth indicator. Only few studies interpret it as an environmental proxy. Indeed, the fluorescence of OM provides information on the type of organic molecules trapped in speleothems and their evolutions. But the most direct information given by fluorescence is the variation of OM quantities. Actually, increase of fluorescence intensity is generally related to an increase in OM quantity but may also be induced by calcite optical effect or qualitative change of OM. However, analytical technics used in water environments cannot be used for speleothem samples. In this study we propose to give a frame to interpret quantitatively the fluorescence signal of speleothems. 3 different samples of stalagmites from french northern Prealps were used. To allow the quantification of the fluorescence signal, we need to measure the fluorescence and the quantity of organic matter on the same sample. OM of speleothems was extracted by an acid digestion method and analysed with a spectrofluorimeter. However, it was not possible to quantify directly the OM, as the extract solvant was a high-concentrated acid. To solve this problem, a calibration using soil extracts was realised. Soils were chosen in order to represent the diversity of OM present in the environment above the caves. Attention was focused on soil and vegetation types, and landuse. Organic material was water extracted from soils and its fluorescence was also measured. Total organic carbon was performed on the same samples. This allow to compare the two fluorescence signals. A range of OM concentrations can be then attributed to the speleothem signal. Fluorescence measurements were also realised on solid samples, using the MUESLI (Muesli Uses Emission Fluorescence for Line scanning and Imaging). Comparison with the two fluorescence signals, will evaluate the adaptability of the concentrations range for solid measurements, generally used. This method offers the possibility to associate a fluorescence signal on solid speleothem, with a non-destructive method, to an environmental range of organic carbon quantities
Moonmilk is a peculiar type of karst deposit, which is a porous, plastic deposit constituted by n... more Moonmilk is a peculiar type of karst deposit, which is a porous, plastic deposit constituted by needle-fiber of calcite and more than 80% of water. Abiotic and biotic environment parameters are involved to explain moonmilk development [1-3]. Thus moonmilk deposits, which can be dated [1], could be potentially used to retrieve past environmental conditions [4]. Furthermore, walls coated by moonmilk were widely used by prehistoric Man for parietal representation (Chauvet cave for instance). Finally, because of their porosity, moonmilk deposits constitute a potential natural recorder of contaminant flow through karst systems. These three goals (environment proxy, conservation, natural traps to present flows) need to improve our knowledge of the link between the entrance fluxes of water coming from the cover soil and the role of moonmilk toward this water in order to better sort the influence of biotic and abiotic parameters in growth. The studied cave (Les Elaphes, Massif des Bauges, France, 1400 m) has the particularity to present 3 kinds of moonmilk containing more or less clay: pure white moonmilk (WM), brownish moonmilk (BM) and clayey moonmilk (CM) assumed to be more or less directly connected to soils sources. Each sample was analyzed with a large range of tools (XRD, oriented XRD for clay, SEM, grading, FTIR). A complete description of the organic matter (OM) entrapped in moonmilk and also contained in the soils above was done thanks to fluorescence spectroscopy measurement. Specific OM and pollutants, more particularly PAHs (Polycyclic Aromatic Hydrocarbons, contaminant produced by human activity since several centuries) could be transported with the flux as function of season or period of time. Estimation of the PAHs content was realized in the various fractions of moonmilk (in free water, adsorbed on clay and OM, entrapped in calcite matrix) and then compared to content in soil and streaming water in order to understand the flow of contaminant. In parallel, we analyzed (through DNA PCR based methods) the bacterial community structure in the 3 different moonmilk deposits. We used both molecular fingerprinting (DGGE), and cloning-sequencing (on 16S), to compare the structure of Eubacteria and Archae in these 3 samples. The objective was not to quantify the relative importance of the various bacterial phylotypes in the moonmilk formation but, rather, to provide first knowledge regarding the identity of the main bacterial groups in these samples, and the similarity (or not) in the bacterial composition from these 3 kinds of moonmilk.
Reaction between dissolved water and sulphide was experimentally investigated in soda-lime-silica... more Reaction between dissolved water and sulphide was experimentally investigated in soda-lime-silicate (NCS) and sodium trisilicate (NS3) melts at temperatures from 1000 to 1200°C and pressures of 100 or 200 MPa in internally heated gas pressure vessels. Diffusion couple experiments were conducted at water-undersaturated conditions with one half of the couple being doped with sulphide (added as FeS or Na 2 S; 1500-2000 ppm S by weight) and the other with H 2 O ($3.0 wt.%). Additionally, two experiments were performed using a dry NCS glass cylinder and a free H 2 O fluid. Here, the melt was water-saturated at least at the melt/fluid interface. Profiling by electron microprobe (sulphur) and infrared microscopy (H 2 O) demonstrate that H 2 O diffusion in the melts is faster by 1.5-2.3 orders of magnitude than sulphur diffusion and, hence, H 2 O can be considered as a rapidly diffusing oxidant while sulphur is quasi immobile in these experiments. In Raman spectra a band at 2576 cm À1 appears in the sulphide-H 2 O transition zone which is attributed to fundamental S-H stretching vibrations. Formation of new IR absorption bands at 5025 cm À1 (on expense of the combination band of molecular H 2 O at 5225 cm À1) and at 3400 cm À1 was observed at the front of the in-diffusing water in the sulphide bearing melt. The appearance and intensity of these two IR bands is correlated with systematic changes in S K-edge XANES spectra. A pre-edge excitation at 2466.5 eV grows with increasing H 2 O concentration while the sulphide peak at 2474.0 eV decreases in intensity relative to the peak at 2477.0 eV and the feature at 2472.3 eV becomes more pronounced (all energies are relative to the sulphate excitation, calibrated to 2482.5 eV). The observations by Raman, IR and XANES spectroscopy indicate a well coordinated S 2À-H 2 O complex which was probably formed in the glasses during cooling at the glass transition. No oxidation of sulphide was observed in any of the diffusion couple experiments. On the contrary, XANES spectra from experiments conducted with a free H 2 O fluid show complete transformation of sulphide to sulphate near the melt surface and coexistence of sulphate and sulphide in the center of the melt. This can be explained by a lower H 2 O activity in the diffusion couple experiments or by the need of a sink for hydrogen (e.g., a fluid which can dissolve high concentration of hydrogen) to promote oxidation of sulphide by H 2 O via the reaction S 2À + 4H 2 O = SO 4 2À + 4H 2. Sulphite could not be detected in any of the XANES spectra implying that this species, if it exists in the melt, it is a subordinate or transient species only.
HAL (Le Centre pour la Communication Scientifique Directe), Sep 29, 2014
ABSTRACT Stalagmites are well established as accurate archives for paleoclimate and paleoenvironm... more ABSTRACT Stalagmites are well established as accurate archives for paleoclimate and paleoenvironmental records, with inorganic proxies being widely used. Organic proxies are a growing field, providing access to information stored in a separate carbon pool, and relating to microbial activity, vegetation cover, and temperature. However, the key factors controlling these proxies are not yet well defined. δ13C analysis of speleothem calcite (effectively the dissolved CO2 pool) is a routinely used technique, but the controls are not as well defined as for δ18O, with the proxy record potentially affected by vegetation change, soil conditions or microbial activity. Parallel measurement of δ13C of the preserved organic matter has been suggested as a method of resolving this signal, with an inverse relationship between the two records previously being suggested as a proxy for microbial control. However, this technique is in its infancy in speleothems, and requires testing in a greater range of contexts. This study uses a multi-proxy approach, combining δ13C analysis of calcite and the preserved organic matter, with a highly novel laser fluorescence technique to investigate climatic and land-use driven environmental variations during the Holocene period. Four stalagmites were sampled in the same room of the Garde-Cavale karst system (1300m a.s.l.), in the Bauges massif, in the northern Prealps. These samples cover the last 12 ka. δ13C analysis of soluble acid bulk organic matter was performed via LC-IRMS at La Trobe University and the University of Orléans. δ13C of the calcite was performed at University of Melbourne, Australia. Organic matter fluorescence was measured at the University of Savoie, France. This fluorescence technique provides a high resolution record (100 µm step along the growth axis), and is a non-destructive method. The three proxies show different trends during the Holocene period, although major environmental events are marked by changes in all records. Further work is needed to establish whether the differences in the proxy records are due to differing environmental controls, or whether there are methodological factors affecting the record. In particular, the organic δ13C proxy is currently under further investigation to test for sensitivity to fluctuations in instrumental parameters and matrix effects. However, in the long term, this multi-proxy approach, combining organic and inorganic techniques has great promise in resolving our understanding of environmental variations.
Contributions to Mineralogy and Petrology, Jul 22, 2008
High-resolution manganese K-edge X-ray absorption near edge structure spectra were collected on a... more High-resolution manganese K-edge X-ray absorption near edge structure spectra were collected on a set of 40 Mn-bearing minerals. The pre-edge feature information (position, area) was investigated to extract as much as possible quantitative valence and symmetry information for manganese in various ''test'' and ''unknown'' minerals and glasses. The samples present a range of manganese symmetry environments (tetrahedral, square planar, octahedral, and cubic) and valences (II to VII). The extraction of the pre-edge information is based on a previous multiple scattering and multiplet calculations for model compounds. Using the method described in this study, a robust estimation of the manganese valence could be obtained from the pre-edge region at 5% accuracy level. This method applied to 20 ''test'' compounds (such as hausmannite and rancieite) and to 15 ''unknown'' compounds (such as axinite and birnessite) provides a quantitative estimate of the average valence of manganese in complex minerals and silicate glasses. Keywords Manganese Á Valence Á Symmetry Á Mineral Á Glass Á XANES pre-edge Communicated by J. Hoefs.
La recherche de la matiere organique (MO) est regulierement utilisee dans une problematique visan... more La recherche de la matiere organique (MO) est regulierement utilisee dans une problematique visant a decrire la dynamique actuelle et l'evolution passee de l'environnement. Cette matiere organique provient directement de l'environnement, par la degradation des vegetaux ou par les sols. Cette MO se trouve naturellement piegee dans une matrice de carbonate de calcium, ou plus precisement de calcite (dans les sols, dans les speleothemes, dans les lacs, les oceans). Cependant, les mecanismes d'insertion et les types d'interactions sont peu etudies dans ces matrices naturelles. L'investigation plus specifiquement des matieres humiques dans la calcite vise donc a connaitre les conditions de partitionnement de cette matiere a differents stades de son transfert (interactions sol/eau, eau/solide puis eau/calcite). Differents mecanismes de piegeage de la MO dans la matrice de calcite peuvent etre impliques au cours de la croissance cristalline de la calcite et en fonction du type de MO. Plusieurs facteurs specifiques lies aux echantillons naturels (defauts cristallins, variation chimique, changement de densite ...) sont limitant pour permettre de differencier ces differents mecanismes par une approche globale. Pour s'affranchir de ces limites, une methodologie basee sur la caracterisation d'echantillons analogues synthetiques est donc proposee. Des echantillons de calcite sont alors synthetises dans des conditions controlees pour y introduire des acides humiques standards et naturels a differentes concentrations. Des extraits de sols provenant du plateau des Coulmes (Vercors) sont utilises comme MO naturelles et rajoutes dans la solution calcifiante afin de les pieger lors de la croissance cristalline de la calcite. Selon la nature des sols, differents comportements peuvent etre observes vis-a-vis de leur influence sur la morphologie de la calcite. Afin d'identifier le type d'interaction entre la matrice et l'acide humique, les echantillons sont analyses a differentes echelles d'un point de vue morphologique et structural (microscope optique, microscope electronique a balayage (MEB), microscopie FTIR, diffraction des rayons X (DRX), spectroscopie d'absorption X (XANES). D'autres methodes semi quantitatives (UV-vis, colorimetrie, spectroscopie de fluorescence) sont utilisees pour renseigner sur le fractionnement et l'evolution moleculaire des MO lors de l'inclusion dans la matrice. D'un point de vue quantitatif, la combinaison de ces techniques permet d'identifier une incorporation de MO proportionnelle a la concentration initiale en solution. En ce qui concerne les mecanismes d'insertion, une rigidification de la structure de la MO est mise en evidence, comme par exemple la formation de colloides ou par adsorption avec formation de liaisons hydrogene a la surface de la calcite. Les mesures synchrotron permettent de suivre la localisation et l'evolution de l'environnement chimique du soufre contenu dans la MO lors de son insertion, mettant en evidence une adsorption de surface ainsi qu'un partitionnement. Aucune modification structurale n'a ete observee dans la matrice de calcite. L'insertion de MO ne semble pas perturber la cristallisation ni induire de defauts structuraux significatifs. Des experiences complementaires de desorption des MO apres insertion permettent de demontrer la stabilite de la structure atomique de la MO et revelent une structure en couche.
ABSTRACT Organic matter (OM) entrapped in calcite is regularly used for environmental studies; ho... more ABSTRACT Organic matter (OM) entrapped in calcite is regularly used for environmental studies; however, insertion mechanisms and types of interaction remain poorly understood. The present study used a new methodology to investigate interactions between OM and the calcite matrix during crystallization processes with humic acid (HA) entrapment. A multimethod approach confirmed that HA is both adsorbed onto the calcite surface and incorporated into the calcite lattice during crystallization. Our results also confirm the log-linear correlation between fluorescence intensity and calcite matrix HA concentration. Fourier transform infrared spectroscopy showed that HA in colloidal conformation is adsorbed onto the calcite surface as a result of the structure of the OH stretching band. We also developed a new method based on synchrotron analysis that uses sulfur as a tracer element for entrapped HA and that localizes the OM electrostatically adsorbed onto the calcite surface. Changes in the sulfur environment, determined using X-ray absorption near-edge structure spectroscopy, indicated more complex insertion mechanisms than simple adsorption of HA during calcite crystallization. Desorption experiments revealed the stability of the OM atomic structure and its layered nature. These results allowed us to draw up a general model of OM insertion in calcite.
Gouffre de la Sambuy is an alpine cave, located in the French northern Western Alps, in the Bauge... more Gouffre de la Sambuy is an alpine cave, located in the French northern Western Alps, in the Bauges massif. This subalpine massif is included in the "delphinohelvetic" domain of the external Alps, drifted over the foreland (jurassian and molassic domains). Bauges massif presents with these folded structures a medium altitude (< 2 500 m asl) and mountainous relief built with only sedimentary rocks. To the east of the massif, the Sambuy summit is 2198 m asl, the main entrance of the cave (SB9) is open at 1 820 m asl. The average of temperature in this area is 1.6°C. The precipitations are over 2 100 mm/year. The cave is approximately 900 m development and 120m depth. The final part of the cave is on the top of the Hauterivian marls. During speleogenesis studies on 2012, speleologists have founded bacterial mats and gypsum in the marly parts of the cave. Upper, in the middle part, the Barremian limestone wall of a 25 m shaft was covered by unusual fine and white deposits looking like lichen. To understand these ecosystems, climate aerologic measurements like air temperature, pressure, and wind speed were realized during each visit in winter, spring and summer. Due to the difficulties to access to the cave with no possibilities to get electrical power, no monitoring was realized for the climate parameters. In spring, the wall deposits have been sampled with swab and store in sterile tube for laboratory molecular analysis. DNA was extracted, PCR amplifications and cloning-sequencing were performed targeting bacterial 16SrRNA and eukaryotic 18SrRNA genes. For the bacterial community, we identified 29 different OTUs and the richness estimator (Schao) showed a global richness of 65 OTUs. The bacterial community was mainly composed by Proteobacteria, Acidobacteria, Actinobacteria, Nitrospirae and an important part of uncultured bacteria. Some of these bacterial taxa are known to be involved in nitrogen cycling. For the eukaryotic community, 32 OTUs were identified from our clones library, and the Schao index showed a global richness of 86 OTUs. Rhizaria (with mostly Cercozoa, genus Cermononas) was a dominant group, followed by Fungi (mostly Dikaria). Some Alveolata belonging to Ciliophora were also detected, as well as an important part of uncultured fungi and others. Additional sequencing analyses should be performed to depict in depth the taxonomic composition in these microbial mats. Our preliminary results showed that these microbial mats comprised a rather high diversity of prokaryotic and eukaryotic taxa, which physiological/biochemical characteristics and biotic interactions have still to be described.
EGU General Assembly Conference Abstracts, May 1, 2014
In this study, we propose to use soils water-extracted organic matter (OM) as a database of fluor... more In this study, we propose to use soils water-extracted organic matter (OM) as a database of fluorescence signal, to interpret quantitatively the the fluorescence of speleothems OM. Due to its efficiency to described dissolved organic matter (DOM) characteritics, fluorescence has been used to determined DOM signatures in natural systems, water circulations, OM transfer from soils, OM evolution in soils or recently, DOM changes in engineered treatment systems. Fluorescence has also been used in speleothems studies, mainly as a growth indicator. Only few studies interpret it as an environmental proxy. Speleothem fluorescence can be used as an environmental proxy, to record the past soil evolutions. Qualitative changes of OM are easily measured. However, it's today complicated to quantify the fluorescence signal of speleothems due to the analytical method generally used. That's why we propose to interpret quantitatively the fluorescence signal of speleothems, using soil fluorescence as a database of fluorescence signal.
In this study, we propose a framework to interpret quantitatively the fluorescence of speleothems... more In this study, we propose a framework to interpret quantitatively the fluorescence of speleothems organic matter (OM) by the way of a bank of water-extracted organic matter. Due to its efficiency to described dissolved organic matter (DOM) characteritics, fluorescence has been used to determined DOM signatures in natural systems, water circulations, OM transfer from soils, OM evolution in soils or recently, DOM changes in engineered treatment systems. Fluorescence has also been used in speleothems studies, mainly as a growth indicator. Only few studies interpret it as an environmental proxy. Indeed, the fluorescence of OM provides information on the type of organic molecules trapped in speleothems and their evolutions. But the most direct information given by fluorescence is the variation of OM quantities. Actually, increase of fluorescence intensity is generally related to an increase in OM quantity but may also be induced by calcite optical effect or qualitative change of OM. However, analytical technics used in water environments cannot be used for speleothem samples. In this study we propose to give a frame to interpret quantitatively the fluorescence signal of speleothems. 3 different samples of stalagmites from french northern Prealps were used. To allow the quantification of the fluorescence signal, we need to measure the fluorescence and the quantity of organic matter on the same sample. OM of speleothems was extracted by an acid digestion method and analysed with a spectrofluorimeter. However, it was not possible to quantify directly the OM, as the extract solvant was a high-concentrated acid. To solve this problem, a calibration using soil extracts was realised. Soils were chosen in order to represent the diversity of OM present in the environment above the caves. Attention was focused on soil and vegetation types, and landuse. Organic material was water extracted from soils and its fluorescence was also measured. Total organic carbon was performed on the same samples. This allow to compare the two fluorescence signals. A range of OM concentrations can be then attributed to the speleothem signal. Fluorescence measurements were also realised on solid samples, using the MUESLI (Muesli Uses Emission Fluorescence for Line scanning and Imaging). Comparison with the two fluorescence signals, will evaluate the adaptability of the concentrations range for solid measurements, generally used. This method offers the possibility to associate a fluorescence signal on solid speleothem, with a non-destructive method, to an environmental range of organic carbon quantities
Moonmilk is a peculiar type of karst deposit, which is a porous, plastic deposit constituted by n... more Moonmilk is a peculiar type of karst deposit, which is a porous, plastic deposit constituted by needle-fiber of calcite and more than 80% of water. Abiotic and biotic environment parameters are involved to explain moonmilk development [1-3]. Thus moonmilk deposits, which can be dated [1], could be potentially used to retrieve past environmental conditions [4]. Furthermore, walls coated by moonmilk were widely used by prehistoric Man for parietal representation (Chauvet cave for instance). Finally, because of their porosity, moonmilk deposits constitute a potential natural recorder of contaminant flow through karst systems. These three goals (environment proxy, conservation, natural traps to present flows) need to improve our knowledge of the link between the entrance fluxes of water coming from the cover soil and the role of moonmilk toward this water in order to better sort the influence of biotic and abiotic parameters in growth. The studied cave (Les Elaphes, Massif des Bauges, France, 1400 m) has the particularity to present 3 kinds of moonmilk containing more or less clay: pure white moonmilk (WM), brownish moonmilk (BM) and clayey moonmilk (CM) assumed to be more or less directly connected to soils sources. Each sample was analyzed with a large range of tools (XRD, oriented XRD for clay, SEM, grading, FTIR). A complete description of the organic matter (OM) entrapped in moonmilk and also contained in the soils above was done thanks to fluorescence spectroscopy measurement. Specific OM and pollutants, more particularly PAHs (Polycyclic Aromatic Hydrocarbons, contaminant produced by human activity since several centuries) could be transported with the flux as function of season or period of time. Estimation of the PAHs content was realized in the various fractions of moonmilk (in free water, adsorbed on clay and OM, entrapped in calcite matrix) and then compared to content in soil and streaming water in order to understand the flow of contaminant. In parallel, we analyzed (through DNA PCR based methods) the bacterial community structure in the 3 different moonmilk deposits. We used both molecular fingerprinting (DGGE), and cloning-sequencing (on 16S), to compare the structure of Eubacteria and Archae in these 3 samples. The objective was not to quantify the relative importance of the various bacterial phylotypes in the moonmilk formation but, rather, to provide first knowledge regarding the identity of the main bacterial groups in these samples, and the similarity (or not) in the bacterial composition from these 3 kinds of moonmilk.
Reaction between dissolved water and sulphide was experimentally investigated in soda-lime-silica... more Reaction between dissolved water and sulphide was experimentally investigated in soda-lime-silicate (NCS) and sodium trisilicate (NS3) melts at temperatures from 1000 to 1200°C and pressures of 100 or 200 MPa in internally heated gas pressure vessels. Diffusion couple experiments were conducted at water-undersaturated conditions with one half of the couple being doped with sulphide (added as FeS or Na 2 S; 1500-2000 ppm S by weight) and the other with H 2 O ($3.0 wt.%). Additionally, two experiments were performed using a dry NCS glass cylinder and a free H 2 O fluid. Here, the melt was water-saturated at least at the melt/fluid interface. Profiling by electron microprobe (sulphur) and infrared microscopy (H 2 O) demonstrate that H 2 O diffusion in the melts is faster by 1.5-2.3 orders of magnitude than sulphur diffusion and, hence, H 2 O can be considered as a rapidly diffusing oxidant while sulphur is quasi immobile in these experiments. In Raman spectra a band at 2576 cm À1 appears in the sulphide-H 2 O transition zone which is attributed to fundamental S-H stretching vibrations. Formation of new IR absorption bands at 5025 cm À1 (on expense of the combination band of molecular H 2 O at 5225 cm À1) and at 3400 cm À1 was observed at the front of the in-diffusing water in the sulphide bearing melt. The appearance and intensity of these two IR bands is correlated with systematic changes in S K-edge XANES spectra. A pre-edge excitation at 2466.5 eV grows with increasing H 2 O concentration while the sulphide peak at 2474.0 eV decreases in intensity relative to the peak at 2477.0 eV and the feature at 2472.3 eV becomes more pronounced (all energies are relative to the sulphate excitation, calibrated to 2482.5 eV). The observations by Raman, IR and XANES spectroscopy indicate a well coordinated S 2À-H 2 O complex which was probably formed in the glasses during cooling at the glass transition. No oxidation of sulphide was observed in any of the diffusion couple experiments. On the contrary, XANES spectra from experiments conducted with a free H 2 O fluid show complete transformation of sulphide to sulphate near the melt surface and coexistence of sulphate and sulphide in the center of the melt. This can be explained by a lower H 2 O activity in the diffusion couple experiments or by the need of a sink for hydrogen (e.g., a fluid which can dissolve high concentration of hydrogen) to promote oxidation of sulphide by H 2 O via the reaction S 2À + 4H 2 O = SO 4 2À + 4H 2. Sulphite could not be detected in any of the XANES spectra implying that this species, if it exists in the melt, it is a subordinate or transient species only.
HAL (Le Centre pour la Communication Scientifique Directe), Sep 29, 2014
ABSTRACT Stalagmites are well established as accurate archives for paleoclimate and paleoenvironm... more ABSTRACT Stalagmites are well established as accurate archives for paleoclimate and paleoenvironmental records, with inorganic proxies being widely used. Organic proxies are a growing field, providing access to information stored in a separate carbon pool, and relating to microbial activity, vegetation cover, and temperature. However, the key factors controlling these proxies are not yet well defined. δ13C analysis of speleothem calcite (effectively the dissolved CO2 pool) is a routinely used technique, but the controls are not as well defined as for δ18O, with the proxy record potentially affected by vegetation change, soil conditions or microbial activity. Parallel measurement of δ13C of the preserved organic matter has been suggested as a method of resolving this signal, with an inverse relationship between the two records previously being suggested as a proxy for microbial control. However, this technique is in its infancy in speleothems, and requires testing in a greater range of contexts. This study uses a multi-proxy approach, combining δ13C analysis of calcite and the preserved organic matter, with a highly novel laser fluorescence technique to investigate climatic and land-use driven environmental variations during the Holocene period. Four stalagmites were sampled in the same room of the Garde-Cavale karst system (1300m a.s.l.), in the Bauges massif, in the northern Prealps. These samples cover the last 12 ka. δ13C analysis of soluble acid bulk organic matter was performed via LC-IRMS at La Trobe University and the University of Orléans. δ13C of the calcite was performed at University of Melbourne, Australia. Organic matter fluorescence was measured at the University of Savoie, France. This fluorescence technique provides a high resolution record (100 µm step along the growth axis), and is a non-destructive method. The three proxies show different trends during the Holocene period, although major environmental events are marked by changes in all records. Further work is needed to establish whether the differences in the proxy records are due to differing environmental controls, or whether there are methodological factors affecting the record. In particular, the organic δ13C proxy is currently under further investigation to test for sensitivity to fluctuations in instrumental parameters and matrix effects. However, in the long term, this multi-proxy approach, combining organic and inorganic techniques has great promise in resolving our understanding of environmental variations.
Contributions to Mineralogy and Petrology, Jul 22, 2008
High-resolution manganese K-edge X-ray absorption near edge structure spectra were collected on a... more High-resolution manganese K-edge X-ray absorption near edge structure spectra were collected on a set of 40 Mn-bearing minerals. The pre-edge feature information (position, area) was investigated to extract as much as possible quantitative valence and symmetry information for manganese in various ''test'' and ''unknown'' minerals and glasses. The samples present a range of manganese symmetry environments (tetrahedral, square planar, octahedral, and cubic) and valences (II to VII). The extraction of the pre-edge information is based on a previous multiple scattering and multiplet calculations for model compounds. Using the method described in this study, a robust estimation of the manganese valence could be obtained from the pre-edge region at 5% accuracy level. This method applied to 20 ''test'' compounds (such as hausmannite and rancieite) and to 15 ''unknown'' compounds (such as axinite and birnessite) provides a quantitative estimate of the average valence of manganese in complex minerals and silicate glasses. Keywords Manganese Á Valence Á Symmetry Á Mineral Á Glass Á XANES pre-edge Communicated by J. Hoefs.
La recherche de la matiere organique (MO) est regulierement utilisee dans une problematique visan... more La recherche de la matiere organique (MO) est regulierement utilisee dans une problematique visant a decrire la dynamique actuelle et l'evolution passee de l'environnement. Cette matiere organique provient directement de l'environnement, par la degradation des vegetaux ou par les sols. Cette MO se trouve naturellement piegee dans une matrice de carbonate de calcium, ou plus precisement de calcite (dans les sols, dans les speleothemes, dans les lacs, les oceans). Cependant, les mecanismes d'insertion et les types d'interactions sont peu etudies dans ces matrices naturelles. L'investigation plus specifiquement des matieres humiques dans la calcite vise donc a connaitre les conditions de partitionnement de cette matiere a differents stades de son transfert (interactions sol/eau, eau/solide puis eau/calcite). Differents mecanismes de piegeage de la MO dans la matrice de calcite peuvent etre impliques au cours de la croissance cristalline de la calcite et en fonction du type de MO. Plusieurs facteurs specifiques lies aux echantillons naturels (defauts cristallins, variation chimique, changement de densite ...) sont limitant pour permettre de differencier ces differents mecanismes par une approche globale. Pour s'affranchir de ces limites, une methodologie basee sur la caracterisation d'echantillons analogues synthetiques est donc proposee. Des echantillons de calcite sont alors synthetises dans des conditions controlees pour y introduire des acides humiques standards et naturels a differentes concentrations. Des extraits de sols provenant du plateau des Coulmes (Vercors) sont utilises comme MO naturelles et rajoutes dans la solution calcifiante afin de les pieger lors de la croissance cristalline de la calcite. Selon la nature des sols, differents comportements peuvent etre observes vis-a-vis de leur influence sur la morphologie de la calcite. Afin d'identifier le type d'interaction entre la matrice et l'acide humique, les echantillons sont analyses a differentes echelles d'un point de vue morphologique et structural (microscope optique, microscope electronique a balayage (MEB), microscopie FTIR, diffraction des rayons X (DRX), spectroscopie d'absorption X (XANES). D'autres methodes semi quantitatives (UV-vis, colorimetrie, spectroscopie de fluorescence) sont utilisees pour renseigner sur le fractionnement et l'evolution moleculaire des MO lors de l'inclusion dans la matrice. D'un point de vue quantitatif, la combinaison de ces techniques permet d'identifier une incorporation de MO proportionnelle a la concentration initiale en solution. En ce qui concerne les mecanismes d'insertion, une rigidification de la structure de la MO est mise en evidence, comme par exemple la formation de colloides ou par adsorption avec formation de liaisons hydrogene a la surface de la calcite. Les mesures synchrotron permettent de suivre la localisation et l'evolution de l'environnement chimique du soufre contenu dans la MO lors de son insertion, mettant en evidence une adsorption de surface ainsi qu'un partitionnement. Aucune modification structurale n'a ete observee dans la matrice de calcite. L'insertion de MO ne semble pas perturber la cristallisation ni induire de defauts structuraux significatifs. Des experiences complementaires de desorption des MO apres insertion permettent de demontrer la stabilite de la structure atomique de la MO et revelent une structure en couche.
ABSTRACT Organic matter (OM) entrapped in calcite is regularly used for environmental studies; ho... more ABSTRACT Organic matter (OM) entrapped in calcite is regularly used for environmental studies; however, insertion mechanisms and types of interaction remain poorly understood. The present study used a new methodology to investigate interactions between OM and the calcite matrix during crystallization processes with humic acid (HA) entrapment. A multimethod approach confirmed that HA is both adsorbed onto the calcite surface and incorporated into the calcite lattice during crystallization. Our results also confirm the log-linear correlation between fluorescence intensity and calcite matrix HA concentration. Fourier transform infrared spectroscopy showed that HA in colloidal conformation is adsorbed onto the calcite surface as a result of the structure of the OH stretching band. We also developed a new method based on synchrotron analysis that uses sulfur as a tracer element for entrapped HA and that localizes the OM electrostatically adsorbed onto the calcite surface. Changes in the sulfur environment, determined using X-ray absorption near-edge structure spectroscopy, indicated more complex insertion mechanisms than simple adsorption of HA during calcite crystallization. Desorption experiments revealed the stability of the OM atomic structure and its layered nature. These results allowed us to draw up a general model of OM insertion in calcite.
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