(M/F) Impact of reconstructed climatic and environmental changes in the tropical Pacific zone, using the geochemistry of marine carbonate archives (corals and foraminifera), on associated microbial communities

Job Description

Thesis Subject

Coral reefs ecosystems in the South Pacific, which are biodiversity hotspots, are heavily threatened by climate warming, extreme events, pollution, and urbanization. Their resilience depends in part on their microbiomes, which are essential to their health. Thus, this research project aims to understand how current and past global and local changes influence the evolution of these microbial communities. By studying the links between past environmental and climatic variations reconstructed at high resolution over the last century from the geochemical signature of marine biogenic carbonates (foraminifera and corals), and the parallel co-evolution of microbial biodiversity, determined from the same samples, the objective is to better assess the resilience of these fragile ecosystems and anticipate their future evolution.
The PhD student (F/M) will carry out both the identification of benthic foraminifera species from sediment cores collected from selected sites in New Caledonia (anthropized, mining watersheds, pristine...) and at least one other Pacific island (Palau, Nauru, PNG or Fiji), as well as the preparation and geochemical analyses of the shells. In parallel, coral cores will be collected near the sediment cores, and high-resolution geochemical signatures over time will be determined. The elemental and isotopic signatures such as Mg/Ca, B/Ca, Sr/Ca, Ni/Ca, Cr/Ca, δ11B, δ18O, δ34S will be calibrated using measured environmental data (T°C, pH, salinity, metal concentration), before being applied to reconstruct global and local climatic and environmental disturbances recorded over time within these environments, and their correlations with microbial biodiversity variations reconstructed from the same samples.
We anticipate close links between the evolution of microbial communities and environmental changes, whether gradual (global warming) or sudden, such as ENSO effects, cyclones, the intensification of human activities, and associated disturbances (e.g., mining). On this basis, predictive models using artificial intelligence tools will be developed to anticipate future trends in microbial biodiversity based on past and current environmental data.
This PhD project offers interdisciplinary training, based on supervision and collaborations involving geochemists, microbiologists, data science specialists, local communities, and decision-makers to understand the past, monitor the present, and anticipate the future of Pacific island environments' reefs. Understanding this issue constitutes a major scientific challenge: it will allow for a more robust assessment of the resilience of island coral ecosystems to global pressures, and the design of conservation and sustainable management strategies based on quantitative and predictive foundations. This project is intended to be subsequently deployed across other Pacific island territories.


The PhD student (M/F) will have the following missions:
1. Sampling of sediment cores, coral cores, and seawater from contrasting sites in New Caledonia and South Pacific islands.
2. Washing, picking, and identification of foraminifera shells collected along the retrieved sediment cores.
3. Preparation and geochemical analysis of foraminifera shells and nearby collected coral cores.
4. Processing of data from geochemical analyses and production of high-resolution paleo-environmental reconstructions over the last century.
5. Assistance in integrating microbial data acquired by another PhD student from the same samples with the geochemical data to identify resilience biomarkers and model future trajectories of reef microbiomes

Your Work Environment

UMR LOCEAN 7159 (Laboratory of Oceanography and Climate: Experiments and Numerical Approaches) conducts studies on physical and biogeochemical ocean processes and their role in climate, in interaction with marine ecosystems. Its teams, widely recognized at the international level, address a broad range of time and space scales for a better understanding of ocean dynamics and variations within the climate system, as well as its present, past, and future evolution. Dependent on four head institutions – SU, CNRS, IRD, and MNHN –, the laboratory is a major component of the Fédération de Recherche en sciences de l'environnement (IPSL).
Since 2014, research in New Caledonia has been structured around CRESICA (Consortium for Research, Higher Education, and Innovation in New Caledonia). This consortium brings together nine institutions (BRGM, CHT, Cirad, CNRS, IAC, Ifremer, IPNC, IRD, UNC) and its mission is to: foster interdisciplinary research, coordinate actors around strategic projects for the region, train young researchers in connection with the École Doctorale du Pacifique, disseminate results to society, and optimize resources by pooling equipment and means. Thus, the PhD student will have privileged access to essential local infrastructures, notably: (LA) ICPMS, ICP-OES, on the IRD site (UAR IMAGO) LAMA (Laboratory of Mineral and Environmental Analyses), and the Plateforme du vivant (Living Platform for microbiology and genomics).
The PhD student (F/M) will thus benefit from multidisciplinary supervision and a rich scientific environment, with state-of-the-art infrastructure and a local, regional, and international network, allowing them to develop varied skills in a tropical and island context, with major scientific and societal stakes.

Constraints and risks

• Laboratory work, clean lab (chemistry/geochemistry)
• Travel to sites/fieldwork

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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