THE ROLE OF EXOPOLYMERIC SUBSTANCES IN METAL CYCLING AND DIAGENESIS IN ESTUARINE SEDIMENTS – IMPLICATIONS FOR FOSSIL AND MODERN ESTUARIES

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THE ROLE OF EXOPOLYMERIC SUBSTANCES IN METAL CYCLING AND DIAGENESIS IN ESTUARINE SEDIMENTS – IMPLICATIONS FOR FOSSIL AND MODERN ESTUARIES

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Job description

Offer DescriptionThe objectives of the postdoctoral project will be:(i) to characterize the relationships between exopolymeric susbtances (EPS), microbial activity and community, and the distribution of metals and minerals in sediments from two estuaries with contrasting climates: the Gironde estuary (southwestern France), and the Guadiana estuary (border of Portugal and Spain). These analyses will be carried out on sediment cores (
5m deep);(ii) cultivate benthic diatoms, the main producers of EPS, to extract and characterize EPS under different conditions (salinity, sediment substrate, metal concentration). In this way, EPS produced in culture and those present in sediment will be compared;(iii) analyze interactions between EPS and certain metals present in estuarine waters, to understand the role of EPS in the precipitation or dissolution of these metals during estuarine sediment diagenesis(sediment to sedimentary rock transition);(iv) use EPS for diagenesis experimentsunder controlled pressure and temperature conditions, where organic and mineral diagenetic transformations will be monitored.More broadly, these results will be used to understand how metals are incorporated into sediments during diagenesis, and how interactions betweensediments and estuarine microbial communities have evolved over geological time. The results obtained on modern estuaries will be compared with ancient sedimentary formations (e.g., Upper Cretaceous and Permian sandstones). This work will be integrated into EXODIA’s Task 1 “Relationships between microbial activity, exopolymeric substances, metals and water in modern estuaries” and Task 2 of the EXODIA project “Cultivation, selection and identification of key microorganisms in the EPS and metal cycle”. Strong interaction will be expected between the postdoctoral resarcher and the PhD student in charge of cultures under oxic and anoxic conditions in Task 2 (CBMN and ICMCB laboratories, Bordeaux).Sediments will be recovered by coring (
5 meters deep) in the shallow intertidal and subtidal zones of the Gironde and Guadiana estuaries (Figure 1A-B-C). The sediments will then be analyzed by various methods (XRD, XRF, laser granulometry). Pore water geochemistry will be analyzed by ICP-OES, ICP-MS and electrochemistry (microelectrodes; Figure 1F). Microbial activity will be measured by various colorimetric assays and microcalorimetry. The various EPS fractions (colloidal and bound) will be extracted from the sediment and analyzed by colorimetric assays (proteins, polysaccharides, acidity; Figure 1D), titrations, and FTIR and Raman spectroscopies. EPS will be produced in diatom culturessubjected to different growth conditions (sedimentary substrate, salinity; Figure 1E). Their composition will be compared with EPS extracted from the sediment, and EPS produced in cultures of bacteria or archaea (produced by the EXODIA Task 2 PhD student). The affinity of these EPS for various metals (Ca, Mg, Mn, Fe, Cd, Zn, Cu, etc.) will be measured by titration, electrochemistry and calorimetry. Finally, sediments from the Gironde will also be placed in sapphire high-pressure/high-temperature (HP/HT) reactors for several months to simulate diagenetic processes comparable to those encountered during sediment burial in a sedimentary basin. The experimental set-up will incorporate pH, temperature and pressure probes, but above all biochemical probes using UV-Vis and Raman spectroscopy (i.e. measurements of gases and EPS modifications). Mineralogy and metals will be characterized ex situ at key stages of the experiment. Finally, the distribution of metals in the EPS could be analyzed by XRF (Figure 1G) and X-ray spectroscopy at the Synchrotron Soleil (Paris-Saclay), under reserve of the acceptance of our application for beamline time.

The postdoctoral fellow will be part of a friendly and multidisciplinary team, and will work with national (IC2MP Poitiers, GEOPS, Paris-Saclay) and international (University of Connecticut, USA, University of Basel, Switzerland) partners in order to learn about the different approaches and techniques used. He/she will present his/her work at national and international conferences but will also be encouraged to present it to the public via various events and media (Fête de la Science, The Conversation, etc.). He/she will also publish his/her results in top-level international scientific journals.Where to apply E-mailraphael.bourillot@bordeaux-inp.frRequirementsResearch Field Environmental science » Earth science Education Level PhD or equivalentResearch Field Geosciences » Geology Education Level PhD or equivalentSkills/QualificationsPhD in Geosciences, Earth Sciences, Environmental Sciences or Biogeochemistry. Skills in geomicrobiology, sedimentology, biogeochemistry and/or diagenesis are expected. Knowledge ofenvironmental microbiology would be an interesting complement. Use of GIS softwares (e.g. ArcGIS) and coding in R or Python for data analysis and statistics would also be a plus.In terms of interpersonal skills, we expect the researcher to demonstrate an aptitude for field and laboratory work, teamwork and communication. A degree of autonomy is expected, particularly inlaboratory work, data processing and writing scientific publications. Good organizational skills will be required to coordinate field missions and analyses. Scientific curiosity and motivation for the subject are essential.Languages ENGLISH Level ExcellentResearch Field Geosciences » GeologyAdditional InformationSelection processTo apply, send a CV, cover letter and the contact details of two referees to no later than the evening of December 13, 2024. Selected candidates will be invited to an interview with committee members from the EXODIA project.Work Location(s)Number of offers available 1 Company/Institute UMR EPOC Country France City Pessac Postal Code 33600 Street 1 Allee Daguin GeofieldContact CityPessac WebsiteStreet1, avenue du Dr Schweitzer Postal Code33607 E-Mailraphael.bourillot@bordeaux-inp.frSTATUS: EXPIREDShare this page

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Location

Pessac, Gironde

Job date

Sun, 10 Nov 2024 07:59:12 GMT

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