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PROPOSITION of THESIS-Avignon University-FRANCE PhD CONTRACT 2018-2021 Targeted call (please check the corresponding case): ministerial PhD contract ED 536 □ ministerial PhD contract ED 537 □ PhD contract FR Agorantic ------------------------------------------------------------------------------------------------------------------------ PhD supervisor: Christophe EMBLANCH (UMR EMMAH, Université d’Avignon et de Pays de Vaucluse, France) Co-supervisors : Florent BARBECOT (GEOTOP, UQAM, Canada), Marina GILLON (UMR EMMAH, Université d’Avignon et des Pays de Vaucluse, France), Elisabeth GIBERT-BRUNET (UMR GEOPS, Université Paris Sud/Paris Saclay, France) Contact: Name : GILLON Surname : Marina Mail : [email protected] Phone: +33 490144467 French title: Compréhension des fractionnements isotopiques hors équilibre lors de la formation des carbonates et leur dépendance avec les facteurs environnementaux, en vue de reconstitutions d’évolution des conditions hydriques sur la période récente (centaines d’années) English title: Understanding of non-equilibrium isotopic fractionations during carbonate formation and their dependence on environmental factors, in order to reconstructing changes in water conditions over the recent period (hundreds of years) 13 18 Key-words: non-equilibrium isotopic fractionation, C, O, dissolved carbon, carbonates, CO2, hydrosystems Co tutorship : Yes - Country: Canada Candidate profile: The candidate must have a master’s degree (or equivalent) in Earth Sciences or a related discipline with essential hydrochemistry-isotopy knowledge. He/she must demonstrate autonomy and a real ability to work in a team as part of a multidisciplinary project. He/She will have to develop a mathematical approach. He/She will also have to go to the study sites to acquire new data and he/she will have to develop laboratory experiments. Required skills: hydrochemistry-isotopy, numeric development; appreciated skills: Field work and laboratory work. Detailed presentation of subject: Contract / Parternship: ministerial PhD contract ED536 Field/ Topic: Hydrochemistry - Isotopy – isotopic fractionation – carbonate precipitation Objectives: This thesis aims to decipher the mechanisms of non-equilibrium isotopic fractionation during degassing of CO2 and during the precipitation of carbonates and their dependence on environmental factors such as temperature or hydrological conditions. This fine understanding should enable the exploitation of carbonate deposits as recorders of water conditions for reconstructions of evolution of environmental changes - anthropogenic and / or climatic - over the recent period (hundred years), period during which they have very strongly impacted the hydrosystems. Context and challenges: The management of water resources is based on the knowledge and recording of the behavior of hydrosystems subjected to climate change, to major changes in land use and to increasing pumping. At the level of emergence of the aquifer, underground cavities, carbonate deposits are of great interest since their chemical and isotopic compositions "record" the variations of environmental factors of the environment in which they precipitate, in connection with the evolution of flow regime and environmental forcings to which hydrosystems are subject (Gonfiantini et al, 1968, Matsuoka et al, 2001, Andrews, 2006, Brasier et al, 2010). These archives record very variable answers. However, at the present time, they have not been associated with quantitative modeling of hydrosystem responses to external forcings (eg de Marsily, 2008). Indeed, the kinetics of precipitation of these carbonates are high and the isotopic fractionations of the calco-carbonic system are not properly constrained. It is therefore not possible to propose a quantitative analysis of these signals to establish their dependence with the hydrological parameters (flow, morphology and height of water in the precipitation zone, etc.), biological (possible algal development), or geochemical (water chemistry, isotopic compositions of water, dissolved carbon and CO2) as well as the processes involved between the different phases (degassing rate, precipitation rate). Recent work (Fleurent et al, 2015) has confirmed the need to take into account the isotopic desequilibrium during the formation of carbonates and have demonstrated a real dependence of isotopic water-carbonate fractionation with the rate of precipitation of carbonates. Some authors have approached these kinetic fractionations for 18O from ion by ion crystal growth model (Watkins et al., 2014) or by surface kinetics models (dePaolo, 2011). Other authors have focused on the isotopic fractionation of 13C during degassing (Deirmendjian and Abril, 2018). However, the variability and dependence of isotopic fractionation factors on environmental parameters such as the rate of CO2 diffusion during degassing or microbiological activity, are still poorly understood. However, their understanding is essential for a fine interpretation of the chemical and isotopic recordings made by the carbonates and thus to go back to the environmental conditions which prevailed at the time of their deposits. Method: Many data were acquired during L. Fleurent's thesis (2015) both in the laboratory and in the natural environment (source de l’Ours, Massif-Central, France). These data will be the basis for a mathematical development that aims to identify the processes that make it possible to explain non-equilibrium isotopic fractionations and to put them in the form of equations. Preliminary work has already begun and shows the need to take into account the diffusion of isotopologues of the calco-carbonic system during degassing and precipitation. The variability of the calibration parameters and variability of non-equilibrium isotopic fractionations introduced into the equations must be able to be connected to real physical parameters (temperature, chemistry, thickness of the water film). New field sampling campaigns and new laboratory experiments are planned to further constrain the different parameters at which isotopic fractionations are sensitive. We propose to investigate the impact of biological films on these kinetic fractionations by comparison of samples from a source where algal development is proven (source de l’Ours, France) with flows in the gallery of the LSBB site (Rustrel, France) where the biological activity is probably absent. In addition, for the latter site, precipitation is localized (eliminating the migration problem of the water flow), the temperature is constant, only the flow regime and the water chemistry force the isotopic recording. In addition, the PhD student will carry out original experiments of carbonate precipitation under controlled conditions on pilots set up at GEOTOP (UQAM, Canada). These experiments will identify the kinetic processes controlling the isotopic equilibrium for variable chemistries - PCO2 – and variable saturations. Thanks to the association of isotope analyzer with the experimental systems entirely dedicated to this project, a continuous recording of isotopic signatures could be possible for a fine understanding of all the processes affecting the calco- carbonic system. All these results will be integrated into numerical models describing the behavior of the isotopologues of the calco-carbonic system. The purpose of this approach is to be able to obtain equations allowing, from current observations of hydrosystems and isotopic recordings in carbonate deposits, a reconstruction of the variations of water and temperature conditions for the recent period. References: Andrews J.E., 2006. Palaeoclimatic records from stable isotopes in riverine tufas: Synthesis and review. Earth-Science Reviews, 75, 85-104. Deirmendjian L., Abril G., 2018, Carbon dioxide degassing at the groundwater-stream- atmosphere interface: isotopic equilibration and hydrological mass balance in a sandy watershed, Journal of Hydrology, 558, 129–143. de Marsily G., 2008. Eau, changements climatiques, alimentation et évolution démographique. Revue des sciences de l'eau, Journal of Water Science, 21, 111-128. DePaolo D. J., 2011, Surface kinetic model for isotopic and trace element fractionation during precipitation of calcite from aqueous solutions, Geochimica et Cosmochimica Acta, 75, 139- 1056. Fleurent L., 2015. Mécanismes d’enregistrement géochimique liés à des processus cinétiques au moment de la précipitation des travertins, thèse de doctorat en cotutelle Université Paris Sud/ Paris-Saclay et UQAM (Montréal, Canada), 343 p. Gonfiantini R., Panichi C., Tongiorgi E., 1968. Isotopic disequilibrium in travertine deposition. Earth and Planetary Science Letters, 5, 55-58. Matsuoka J., Kano A., Oba T., Watanabe T., Sakai S., Seto K., 2001. Seasonal variation of stable isotopic compositions recorded in a laminated tufa, SW Japan. Earth and Planetary Science Letters, 192, 31-44. Watkins J.M., Hunt J.D., Ryerson F.J., DePaolo D.J., 2014, The influence of temperature, pH and growth rate on the 18O composition of inorganically precipitated calcite, Earth and Planetary Science letters, 404,332-343 .

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