Research

Below, the 3 main economic and societal issues addressed by VOLTAIRE are recalled to provide context for the scientific achievements of the Labex.

1. MINERAL AND ENERGY RESOURCES

The first scientific target for the VOLTAIRE LABEX concerns deep and hot aqueous or magmatic fluids. It echoes a major socioeconomic issue, that of mineral and energy resources, which are one of the major points of interest of the new national agency ANCRE9. This issue is one of the main economic challenges that our societies must face due to the tensions that develop on the raw material market, and even the shortages that have been announced for some of them, the increase in the global population (9 billion estimated by 2050) and the economic growth of emerging countries (Brazil, India, and China). The LABEX is positioned on major scientific problems that can help meet this economic challenge. This will be made possible by a formal partnership of researchers from ISTO and the BRGM, experts in lithosphere deformation, deep fluids and their implications in mineral and energy resource concentrations.

One of the questions that interest VOLTAIRE is the process for localizing deformation at different scales and the role of fluids in this distribution of deformation (Burov et al., 2001). Indeed, geofluids are one of the major agents in lithospheric deformation at different time scales, from the short-time seismic scale to the long-term geological scale. Fluids (aqueous or silicate liquids) play a fundamental role in tectonic processes since they affect the strength of rocks. Conversely, geodynamics allow or hinder the migration of fluids, by opening or closing conduits, on the seismic scale or that of the formation of a crustal detachment or a mountain chain (Sibson, 1983; Famin et al., 2005b; Gratier et Gueydan, 2005; Handy et al., 2007). Generally, the effects of feedback between fluid and deformation, whether positive or negative, and although they are widely accepted, currently remain very poorly defined and quantified.

Although several teams in France and worldwide are studying these interactions between fluids and the deep dynamics of the lithosphere, VOLTAIRE is equipped to develop cutting-edge research in this field thanks to the cooperation between experimentalists and field geologists at different scales. This association does not exist anywhere else in France at this level in the field of petrology and experimental deformation (Paterson press, experimentation and analysis of geological fluids) or in the use of these field observations to resolve geodynamic questions (mountain chain genesis, continental accretion, dynamics
of extension and subduction, etc…).

Fluids, whether they are aqueous or magmatic, are also essential vectors for the chemical elements at the origin of concentration processes. Although mineral deposits and energy resources are clearly distinguished by their specific metallogeny, we can nevertheless consider that each results from the combination of three groups of natural processes: (1) pre-concentration, (2) transport, concentration and (3) deposition or trapping. Fluids are the main (thermal and chemical) transfer agents for hydrothermal/geothermal systems, a particular example of which is provided by the small hydrogen producer systems of the oceanic ridges (Charlou et al., 2002). Hydrothermal systems are traditionally studied following two approaches, most often carried out disjointly.

The role of fluids as chemical agent, which is generally grasped by combining the approaches of characterization (both natural fluids and paleo-fluids), experimentation (study of fluid/rock interactions, solubility measurements) and thermodynamic modeling. The new methods for measuring concentrations of metals in hydrothermal paleo-systems (Gama et al., 2001; Ulrich et al., 1999), the experimental determination, of the speciation of major/trace elements, notably metal ones, in hightemperature and high-pressure fluids (Pokrovski et al., 2009), the calibration of thermodynamic codes for fluid-mineral equilibriums (Oelkers et al., 2009) are tools that allow better understanding the mechanisms of metal concentration and the deposition of mineralizations.

The role of fluids from the physical point of view is most often approached by field observation, experimentation and hydrodynamic modeling. These approaches, necessarily onmultiple scales, essentially aim to understand the mechanisms of fluid circulation, mainly in relation to the evolution of permeabilities (Famin et al., 2004; Coumou et al., 2009; Eldursi et al., 2009; Sizaret et al., 2009), deformation and fracturation (Sibson, 1996, 2007) constraining fluid flows and establishing thermomechanical assessments of hydrothermal circulations (Garibaldi et al., 2010). This is a potential tool for the definition of preferential trapping zones for mineralizations or metallotects (Chauvet et al., 2006).

VOLTAIRE seeks to combine these two approaches in as integrated a way as possible, relying on nationally-recognized know-how in several fields: experimentation (Jego et al., 2010), characterization of solid and fluid phases (Gama et al., 2001) and digital modeling (Eldursi et al., 2009). The pre-magmatic concentrations component exploits the leading European position held by ISTO around activities of experimental simulation of magmatic processes (Scaillet et al., 2008; Gaillard et al., 2008), which could be considerably enhanced via the PLANEX équipement d’excellence. Note that the study of hydrothermal systems can apply i) to the field of geomimetic processes such as hydrothermal synthesis of minerals (Mottet et al., 1992), cleanup and leaching under hydrothermal conditions and ore processing (the Bayer process for alumina production, the INCO hydrometallurgical process for processing of New Caledonia ore) and ii) that of high-enthalpy geothermal energy, i.e., deep aquifers. This last topic is at the heart of the second economic and societal issue discussed below.

Mineral resources linked to sedimentary basins will be approached from two major angles i) that of deep fluid circulation in the more superficial series, joining hydrogeology issues and ii) that of organomineralization processes linked to the genetic relationship between organic sedimentary material and metals (Disnar and Sureau, 1990; Nakahsima et al. 1999; Piqué et al. 2009). The scientific questions posed on surface mineralizer fluids also concern the second socioeconomic issue discussed below.

Furthermore, it is no longer possible today to conduct the work of exploring and prospecting for new resources, whether mineral or energy, without considering environmental, economic and regulatory constraints (Jebrak and Marcoux, 2008). Thus, it is necessary to evaluate the economic relevance of the exploitation of available and exploitable resources that have not yet been exploited (see A. Coumoul, J.M. Eberlé, C. Hocquard, in the BRGM econotes, http://www.brgm.fr/AgendaNews/econotes.jsp). Cost-benefit analysis will be a preferred tool, alongside the contributions of industrial economics. The driving role of technical progress and innovation in this field will be a key element for consideration.

Finally, the development of the materials recycling sector, which is probably a (short to medium-term) solution to the risk of exhausting finite resources (De Beir et al. (2007), De Beir et al. (2010), Fodha and Magris (2010)), will be considered so as to quantify the role of eco-industries in global resource trends. National and/or community public policies seeking to support these eco-industries must be evaluated beforehand, from the angle of sustainable development as well as the angle of competition. LEO already has experience in this field and a capacity for expertise that allows planning longer-term avenues for research, respectively pertaining to the economic analysis of geological resources (I) and, on the other hand, to the evaluation of the contribution of geotechnology with regard to global change (II). Among the latter, geological storage of waste makes up part of the team’s fields of excellence (Fall and Fodha (2009), Ayong Le Kama and Fodha (2010), Ayong Le Kama, et al. (2010)).

 2: SUSTAINABLE MANAGEMENT OF SURFACE ENVIRONMENTS

The second scientific challenge for VOLTAIRE concerns the study of natural fluids of surface environments, whose complexity and reactivity are increased due to the intervention of living things and the interface with the atmosphere. This scientific issue responds to a major societal question: sustainable management and economic exploitation of surface environments. Since aquifer recharge is conducted through these environments and the unsaturated subjacent area, this transfer constitutes a key step in the definition of the chemical and biological composition of the water tables.

Preserving the available quantity and chemical quality of the water contained in aquifer reservoirs at reasonable depths is therefore a part of this issue. Altogether, this is a strategic sector where public authorities and regulatory bodies need to standardize and rationalize the exploitation of these resources while guaranteeing their accessibility and their quality on the basis of expertise as well as scientific and technical advances. Although closely linked, two principal components can be distinguished: on the one hand, the issue linked to the study of transfer-reagents in aquifers in the wider sense, and, on the other hand, the issue concerning the contribution of living or post mortem organic material to the chemistry of
the fluids/gases produced at continental interfaces.

1) In the matter of transfer-reactant in especially unsaturated supergene environments, the usual approaches by characteristic curves and average functions of the environment are currently updated by more mechanistic considerations, which explicitly integrate the living component into the reasoning frame. Thus, the links between microbial communities and biogeochemical cycles are studied both from thephenomenological point of view (e.g. Holloway et al., 2009; Drenovsky et al., 2010) and by coupled modeling approaches (e.g. Or et al., 2007; André et al., 2010) including studies on physicochemical descriptors of microbial catalysis (e.g. Jin and Bethke, 2002; Heimann et al., 2010). Simultaneously, more “conventional” research continues to feed community progress in: 1/ colloidal transport, which also includes nanoparticles (e.g. Lecoanet et al., 2004), 2/ the significance of hysteresis effects in biophysicochemical transport and retention (e.g. Hilfer, 2006; Pettenati et al., 2008), as well as the effects of cavitation on so-called “inkbottle” systems (e.g. Or and Tuller, 2002; Gawin and Sanavia, 2010). 3/ hydrophobicity expression mechanisms, notably involving interface tension, in conjunction with the permeability to water and air of unsaturated media (e.g. Shokri et al., 2008; Bachmann and McHale, 2009; Leroy et al., 2010), 4/ the description of porous three-dimensional networks, analytically and digitally, and the relationship of this structure with the biophysicochemical properties of unsaturated environments (e.g. Or and Ghezzehei, 2007; Lehmann and Or, 2009), 5/ thermokinetic modeling of supergene alteration, including the respective effects of mobile and immobile water (e.g. Richards and Kump, 2003; Mercury et al., 2003; Lassin et al., 2005; Rijniers et al., 2005; Pettenati et al., 2008).

The use of deep aquifer zones as an alternative energy reserve or as a strategy for managing CO2 waste (specifically in saline aquifers) requires more knowledge of these complex environments. They are the chemical consequences of capillary equilibriums which are the cores of the project target, with: 1/ capillary stabilization/destabilization notably gas hydrates at oceanic bottoms (e.g. Henry et al., 1999), 2/ setting up and validating multiphase chemical-transport models at the scale of depleted and/or polluted aquifers, target of the geological storage of CO2 (e.g. Pruess and Garcia, 2002; Mahadevan et al., 2006; Doughty, 2007; André et al., 2007, 2010; Leroy et al., 2010).

Another focal point of this project that interests the international community is the physicochemistry of natural systems, with the very large problem of three-dimensional imaging of pore topology, a field already mentioned (microtomography, microscanning, etc.) and also all the laboratory measurements intended to quantify the properties of natural materials, soaked with different types of solutions: geomechanical behavior, possibly associated with thermal or chemical effects (e.g. Coussy, 2006; Scherer, 2008), elution curves (e.g. Kwon et al., 2009), permeability, hydraulic conductivity and diffusion (e.g. Abrams and Loague, 2000; Gray and Schrefler, 2007), kinetics of drying and associated processes, including mechanisms for plugging or boring natural conduits (e.g. Shahidzadeh-Bonn et al., 2008, Thullner and Baveye, 2008).

In all, VOLTAIRE will study aquifers from the angle of the vadose zone-saturated zone continuum. The project aims to contribute to quantitative modeling of the movement of water bodies and water-rock interactions (chemistry-transport coupling) as well as the associated thermal and mechanical effects. We are looking to develop coupled THMC (thermal hydrological-mechanical and chemical) models by direct extension of models concerning deep geofluids.

2) Furthermore, the surface environment is the location for recycling organic matter (OM), mainly under the effect of microorganisms; this is a major element of the functioning of ecosystems and thus the global C and nutrient (N, P) cycles. Geomicrobiology and biogeochemistry of natural microbial systems are currently key disciplines to respond to environmental issues such as management of aquatic, mineral and energy resources, as well as biodiversity. In this area, an essential scientific problem concerns the role of the “microorganism-organic substrate” loop, which plays a major, but nevertheless currently very poorly understood, role regarding several fundamental processes or mechanisms such as:

i) the fluxes of greenhouse gases of biogenic origin (GGs10 and VOCs11) and the biogeochemical cycles of the associated elements (e.g. C, N) (Gogo et al., submitted). In fact, there are currently still major uncertainties and unknowns regarding the physical and biogeochemical processes of carbon, nitrogen, sulfur and halogen cycles at the level of terrestrial ecosystems (IPCC 2007c) and they remain yet to be studied in order to understand the mechanisms of these emissions and the response of ecosystems (in terms of emissions) notably wetlands and agricultural land (Galloway et al. 2008, Del Grosso et al. 2009) in the face of these disruptions. The fluxes of gas emissions measured will be integrated into conceptual and digital models for the overall functioning of these hydro-ecosystems marked by varying degrees of anthropization: from open environments, such as cultivated land, to reducing environments, such as lakes, peatlands and mangroves.

ii) the biogeochemical processes at the origin of transformations and fluxes of metal contaminants and organic pollutants (Marchand et al., 2006, 2008, 2010; Naylor et al., 2006; Negimet al., 2010). The approach will be based on both laboratory and field experimentation at different scales (from cm3 to m3) in static and dynamic systems.

iii) the role of biofilms in bio-organic mineralization processes and the impact of microorganisms on metal pollutants (Gautret et al., 2006; Malam Issa, Défarge et al., 2009) with, in particular, the role of the interactions of microorganisms with surface minerals and/or processes at interfaces (speciation/precipitation/dissolution);

iv) the impact of the functioning of microbial communities in the deep subsoil, and notably the role of these communities on the state of subterranean ground water subject to various kinds of pollution (diffuse, concentrated or periodic), the understanding of which role is essential for the reduction of industrial risks and to control costs in the field of subsoil exploitation.

In order to answer these different questions, VOLTAIRE will combine the complementary skills of experts from the BRGM, ISTO and INRA. ISTO’s organic geochemists are specialized in the study of the dynamics of complex organic residues resulting from the degradation of biomass and the functioning of natural environment vectors (Laggoun-Défarge et al., 2008; Lallier-Vergès et al., 2008; Défarge, Gautret et al., 2009; Jacob et al., 2007). The BRGM Ecotechnologies Unit is at the cutting edge of topics centered on the characterization of the bacterial processes that are involved in the transfer and transformation of substances in the subsoil and on the use of bacterial strains or populations to develop bioremediation processes and mineral exploitation (Joubert et al., 2007; Battaglia et al., 2008; Quemeneur et al., 2008; Challan-Belval et al., 2009; Spoalore et al., 2010). Finally, the Soil Science Laboratory of Orléans INRA specializes in the study of the physicochemical properties and hydraulic and biologic functioning of soil (Garrido et al., 2002), notably with regard to the formation of molecular nitrogen compounds (Hénault et al., 2005; Gabrielle et al., 2006).

The flux of gas emissions measured will be integrated into conceptual and digital models for the overall functioning of these hydro-ecosystems marked by varying degrees of anthropization: from open environments like cultivated land to hydromorphic reducing environments. Experimental studies on demonstrators, mesocosms, phytotrons and lysimeters will complement field studies in an original way by a powerful analysis of the microbiogeochemical mechanisms. Permanently-instrumented OSUC and INRA sites installed in different ecosystems will provide the necessary monitoring of the evolution over time of
these environments under anthropogenic and climatic stress. Since all of these experimental plans require the development of new sensors, an R&D effort will be undertaken in partnership with companies in the sector to advance the analysis of biophysicochemical parameters in the vadose zone. The miniaturization of electronic components will continue in the next decade. Current sectors may be improved to develop new and improved microcomponents, such as microprobes or microelectromechanical systems (MEMS). This trend has consequences on microelectronic design (Y. Kebbati, M. Boujrharhe, 2010). Developments in electronics are a field of excellence for the LPC2E, often generating patents12.

 3: MONITORING THE ATMOSPHERIC ENVIRONMENT

In addition to the studies conducted on the subsoil and soil, notably on mechanisms of gas production and transfer into the atmosphere, VOLTAIRE is dedicated to the study of VOC emissions into the troposphere and their chemical transformation with a study of the environmental impact (pollution, climate) and feedback on these emissions in the face of anthropogenic disruptions and global change.

Significant changes of the chemical composition of the atmosphere have been observed for several decades (IPCC 2007a), primarily linked to human activity. They concern greenhouse gases, aerosol contents and primary and secondary pollutants of the lower atmosphere. Although major progress has been made in the understanding of the mechanisms of formation, transport and elimination of chemical species, which control the chemical composition of the reactive atmospheric system, great uncertainties remain in the understanding and impact of a large number of chemical systems, notably linked to the role of the continental biosphere. In fact, continental biospheres considerably influence the chemical composition of the atmosphere and remain the primary source of greenhouse gas and VOC emission (Atkinson and Arey, 2003) with strong feedback on these emissions in the face of climate or direct anthropogenic disruption in the case of wetlands (peatlands) and cultivated land (IPCC 2007b).

The emission of very reactive species can notably play a key role in the control of hydroxyl radical concentrations and therefore on the oxidizing capacity of the atmosphere and the formation of ozone (greenhouse gas) and certain gaseous pollutants. The atmospheric transformations of chemical species coming from the biosphere can also lead to the formation of polyfunctional organic compounds (whose atmospheric fate remains unknown) and on secondary organic aerosols (SOAs) that have an impact on ecosystems and health (Kanakidou et al., 2005; Hallquist et al., 2009).

Areas of volcanic activity can also generate emissions of volatile compounds (halogens and sulfurs) that can affect the chemistry of the atmosphere and the climate (Brobrowski et al., 2003). The impact of these emissions was neglected in modeling studies until the past few years. The chemical mechanisms and transport of halogenated compounds in the plumes of emissions are currently very poorly characterized. Experimental simulations, measurements of species at craters outlets and in plumes as well as a validation of processes by appropriate atmospheric modeling will be conducted by VOLTAIRE in order to
better understand the impact of these emissions on tropospheric chemistry and on climate.

Thanks to the complementarity of approaches combining field experience, experimental simulations, laboratory studies and modeling, VOLTAIRE has the ability to answer these scientific questions. ICARE and the LPC2E have resources and skills available for fast and sensitive measurement of VOC concentrations and reactive species (by chemical ionization mass spectrometry) and greenhouses gases (by SPIRIT13; Guimbaud et al., submitted). The INRA laboratory specializes in methods for measuring the flux at different scales, and ISTO specializes in the organic and mineral analysis of soil and sediments, as well as in the experimental simulation of volcanic outgassing ((Burgisser and Scaillet, 2007, Pichavant et al., submitted). The BRGM is an expert in the measurement of isotope ratios in gas phase and condensed carbon species and its skills will be a major asset for the analysis of samples taken in soil or air.

Volatile compounds and their transformation products can reach the stratosphere and affect its physicochemical properties. Their possible transport into and their fate in the upper troposphere – lower stratosphere (UTLS14) and in the stratosphere are a major issue, notably for stratospheric ozone, the greenhouse effect and global change. Our research units have an experimental culture (on board balloons and satellites) and powerful modeling for the study of the physicochemical processes of the UTLS and the stratosphere. In the past few years, we have quantified the contribution of very short-lived (VSLS) chlorinated compounds in the total stratospheric budget (WMO 2010 coming soon, according to Mébarki et al., 2010), whose importance on the mechanisms of ozone destruction are known, at a key moment when it begins its ascent. As for stratospheric water vapor, a chemical species playing an essential role on the radiation budget and on the chemistry of the stratospheric ozone, our recent balloon observations (Berthet et al., to be submitted) have questioned, like the modeling work of Fueglistaler and Haynes (2005), the increasing trend (1% per year) over the past 30 years, resulting from surveys by American hygrometers (Oltmans and Hofmann, 1995; Oltmans et al., 2000). Another major discovery has been the demonstration (at all latitudes and seasons) of very large quantities of solid aerosols in the stratosphere, attributed to the presence of soot and meteorite dust (Renard et al., 2010). VOLTAIRE will take these particles into account in the interpretation of the various types of observations and in the models. Simultaneously, the scientific community has proven the difficulty of determining the liquid sulfate aerosol load of the stratosphere, primarily resulting from the sulfur emitted by volcanic eruptions, and essential in the chemistry of ozone (SPARC Report, 2006).

The real stratospheric quantities of liquid sulfate aerosols must be integrated into the models, as well as the associated sulfur budget; the still-uncertain origin of the soot detected must be determined (Fulcheri et al., 2002, Bourrat, 2004). Other questions remain in suspense, such as the impact of biomass burning on the intertropical UTLS (an active region from the climatic point of view) and so-called high-energy events, propagating above tropical storms, on the chemistry of stratospheric ozone. These questions will be the subject of intensive studies at the LPC2E, which is responsible for the TARANIS satellite and COBRAT balloon projects dedicated to the observation of these phenomena, in strong synergy with VOLTAIRE. The more general, but major, question of the impact of climate change on the stratosphere, and retroactively, of the stratosphere on the climate, notably through the scientific problems described above, remains to be elucidated (Baldwin et al., 2007). Finally, it is important to specify that in the case of a major eruption in the coming years (the last being Mount Pinatubo in 1991), we will be well-armed in terms of the panoply of observations and possibilities for studies of the effects generated on the stratosphere.

All these studies need to be supported by powerful tools for modeling the dynamics (at local and global scales) and the chemistry involved in these processes. A major asset to meet these scientific challenges resides in the technological skill of the LPC2E in the measurement of trace elements and aerosols in stratospheric balloons combined with modeling (Berthet et al., 2006; Huret et al., 2006).

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