these modelisation Ra e LI dans le modèle océanique NEMO PISCES (M/F)

Job Description

Thesis Subject

Trace elements and their isotopes are essential to the functioning of the oceans and, more broadly, the Earth system. Some act as contaminants (e.g., Hg, Cd, Li), while others serve as micronutrients (e.g., Fe, Zn, Ni). They also function as tracers of physical, biological, or chemical processes (e.g., Ra, Th, Pa), and others provide insight into past environmental conditions (e.g., δ¹⁸O, Nd, Pa, Th). Against this backdrop, the international GEOTRACES program—"International Study of the Marine Biogeochemical Cycles of Trace Elements and Their Isotopes"—was established; more than 150 oceanographic cruises, coordinated by 35 countries, have been conducted across the globe's ocean basins, yielding an extraordinary volume of data that is now available. Numerical modeling offers a unique tool for leveraging these observations and gaining a better understanding of the mechanisms controlling the distribution of these tracers in the ocean—such as transport, biogeochemistry, internal cycling, and sources and sinks.
In this thesis, we propose to explicitly simulate the cycles of radium (Ra) and lithium (Li)—and their isotopes—using the NEMO global dynamic coupled model linked to the PISCES marine biogeochemistry model. Several radium isotopes are present in the ocean, with half-lives ranging from a few days (224Ra and 223Ra) and a few years (228Ra: 5.75 years) to several hundred years (226Ra: 1,600 years). These isotopes enter the ocean primarily via rivers, marine sediments (continental margins and the ocean floor), hydrothermal activity, and submarine groundwater discharge. Consequently, these tracers make it possible to constrain exchanges at the continent-ocean or deep-sediment-ocean interfaces. We will compare simulation results with GEOTRACES data, specifically data from the GEOVIDE expedition in the North Atlantic Ocean (ANR GEOMOBS project). Lithium has a very long residence time in the ocean (several million years). With the energy transition and battery production, global consumption is set to increase nearly a thousandfold in the coming decades; as this component is currently rarely recycled, a significant portion will end up in the oceans. This tracer will be studied within the framework of the PREVENT project (https://prevent.lsce.ipsl.fr), which investigates the dispersal of this tracer in the ocean and its uptake into the food web (fish). In a collaborative setting, the PhD candidate will also contribute to modeling work on other tracers (Fe, Pa, Th, Nd) included in the ANR GEOMOBS project. The doctoral candidate will benefit from high-quality supervision in modeling (LSCE, IPSL) as well as recognized expertise in trace element and isotope cycles across several laboratories (LSCE, LEGOS, LOV). They will participate in international conferences and author scientific publications.

Your Work Environment

The LSCE is a joint research unit (CEA/CNRS/UVSQ) located on the Saclay Plateau. It comprises teams engaged in experimental and modeling activities within the fields of climate and environmental sciences. The proposed PhD project will be carried out within the LSCE's Climate Modeling team.

Constraints and risks

none

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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