Proposed thesis topics in 2024

1- The role of ice on the formation of martian valley networks

Thousands of valley networks incise the Martian southern hemispheric highlands, and stand as a reflect of an ancient past characterized by active hydrology and surface liquid water. After a peak of valley network formation around ~3.8 Byr ago (Gya), surface water presence and active hydrology steadily decreased in activity throughout Mars’ history, until reaching Mars’ present state of a desertic, global cryosphere. Whereas surface liquid water activity is a robust interpretation of the conditions on early Mars (4-3.5 Gya), the role of ice in the formation of these valleys is much less understood. Indeed, the surface conditions at the time of valley network formation and generally throughout Mars’ history have fluctuated between subfreezing and melting, suggesting that ice may have played a significant – yet largely overlooked – role in valley network formation. Such a role likely included permafrost and ground ice melt, snowmelt, and glacial melt, with potential geographic variations such as those related to latitude distribution and elevation.
The objective of this project is to characterize the role of ice on the formation of valley networks on Mars, spanning both ancient valleys (>3.5 Gya) to comparatively much younger valleys (~100 Mya) through geomorphological observations of Martian valleys complimented with terrestrial analogue observations. This objective can be broken down into three: (1) Characterization of distinctive morphologies associated with permafrost and ground ice melt, to snowmelt, and to glacial melt leading to channel and valley development, (2) mapping martian valleys located in a focus study region on the north – northeast of Hellas basin, a known region of ice accumulation on Mars, (3) identifying the presence/absence of distinctive landforms and morphologies related to permafrost, snow, and glacial ice melt within the valley networks, noting their distribution and age dates to put the findings in the larger perspective of Mars’ long-term climate change.

> Contacts : Anna Grau Galofre (LPG) & Nicolas Mangold (LPG)

> Submit an application before May 13 on the 3MG doctoral school website

2- Impact of gas and ions filled ices on the structure and evolution of large ocean worlds

Exploration of Jupiter’s and Saturn’s system by space missions (Galileo, Cassini-Huygens) revealed that some of their icy moons possess a salt water ocean under their cold icy surface. Observations of various sulfate and chlorinated salts on the surface of Europa  and Ganymede as well as in the eruptive plume of Enceladus suggest an oceanic origin and put some constraints on the possible oceanic composition.  For the largest moons (Ganymede, Callisto and Titan), due to high pressure reached in their deep interior, the existence of high pressure ice phases capable of incorporating into their lattice large amounts of salt compounds, called salt-filled ices, may strongly affect the  chemical differentiation processes leading to the formation of subsurface oceans.  Similarly to the case of salty ices, light gas compounds, such as H2, CH4 and N2, may also be incorporated in filled-ice structures, and thus could be stored in the deep interior and sporadically released during the interior evolution. These icy moons likely formed from a complex mixture of ices, organics and silicate minerals, which subsequently evolves as their interior progressively warm up and chemically differentiate.  Beyond large ice moons,  similar processes may affect the thermo-chemical structure and evolution of water-rich exoplanets and their atmosphere composition.  Storage and transport of salt and light gas compounds by filled-ice phases may have a major impact on the chemical evolution and hence the habitability of these ocean worlds.  

The present PhD project is part of the ANR project “EXOTIC-ICES” (2024-2028), involving three laboratories in France (IMPMC, LPG, IPGP), dedicated to the characterization of the exotic properties of gas and ions filled ices under extreme conditions and their implications for water-rich planetary interiors. In this context, the goal of the PhD work is to determine under which planetary contexts, salt and gas filled-ice phases may exist and to characterize their impacts on the internal structure, dynamics and chemical evolution of large icy moons and extrasolar water-rich planets. This modeling work will rely on the experimental data and ab initio calculations provided by the project partners (IMPMC & IPGP in Paris) regarding  the stability and properties of filled-ice phases.  Using thermal convection codes and 1D parameterized models, we will quantify how much H2 and CH4 may be released by water-rock interactions and thermal degradation of organic compounds, stored in filled-ice phases and  subsequently transported through the hydrosphere to the surface. These models will be used to predict the release rate of H2/CH4 through time and its impact on the atmosphere evolution of Titan and water-rich exoplanets, such as Trappist-1 planets.  Salt-ice-water interactions will also be modeled throughout the evolution of these ice-rich interiors from accretion to present,  and will be used to predict the partitioning of salt compounds between the ocean and the high-pressure ice mantle. Using the model results, synthetic density and electric conductivity profiles considering different salt contents and distributions  will be constructed and will be used to predict the magnetic and gravimetric signatures of salt partitioning between the ocean and the high-pressure ice layer in preparation of the ESA  Juice mission.  

> Contacts : Gabriel Tobie (LPG), Gaël Choblet (LPG), Livia Bove (IMPMC)

> Apply from April 1 to May 26 on the CNRS job portal :

3- Characteristics of quaternary fault activities in the Armorican Massif using geomorphology and geophysical techniques

Context: France is situated far from plate tectonic boundaries and considered now a stable continental region with a very low strain rate, especially in the north west. However, the recent Mw4.9 2019 Le Teil and 2023 La Laigne earthquakes highlighted that active faults are not all clearly identified and should be better characterized. The Armorican Massif is cross-cut by several inherited faults and shear zones, which formed during the Cadomian and Hercynian orogens, the opening of Mezo-Cenozoic basins and several compressional phases over the Cenozoic. The historical and instrumental seismicity present a moderate activity, trending SE-NW, in agreement with the direction of main regional shear zones and faults. Besides these observations, identifying active faults (i.e., active over quaternary, then the last 2 Ma) and what drives the deformation, remains a difficult task. 

Objectives: this project proposes to analyze major faults of the Armorican Massif using high resolution data available since few years. Guided by the recent seismicity locations, and based on satellite images and topographic data, the PhD. candidate will first map precisely the fine structure of faults and analyze their interactions with the morphology and quaternary deposits. Then, sites of interests will be investigated during field work campaigns, where geological and geophysical tools will be deployed to characterize the fault structures at depth, and their links with the observed surface scarps. The goal will be to detect and localize possible discontinuities at depth in the quaternary deposits, identify their lithology and quantify their thickness. Finally, the PhD. candidate will perform paleo-seismological trenching to look for deformation in the quaternary deposits.

Environments and collaborations: the LPG (Nantes facility), through the OSUNA, is now in charge of the observation and characterization of seismic activities along faults and shear zones in the NW part of France, and involved in the development of new techniques to acquire high resolution topography (LiDAR). The PhD. candidate will benefit from the expertise of seismologists and geomorphologists in the lab, and regional collaborations in geomorphology and geophysics (Géosciences Rennes and Université Gustave Eiffel) in the frame of current projects (QASArm, ALEP, SALLE), funded by the observatory (OSUNA). Finally, the French action FACT (ACTive Faults) launched in 2019 through the research infrastructure Résif/Epos-France gather national experts in seismo-tectonics, collaborating each other to better understand active faults in France.

Required profile

The PhD. candidate will be a graduate student in Earth sciences and will need to use the common tools to study active faults (GIS, electric, seismic and radar geophysics). A good knowledge of basic notions in field work geology, geomorphology, tectonic and geophysics is required. A strong ability to work as a team is also required.

> Contacts : Eric Beucler (LPG, Osuna) & Clément Perrin (LPG, Osuna)

> Submit an application before May 13 on the 3MG doctoral school website

4- What influence do intense rainfall events have on the speciation of remobilized metals and their fate ?

Population growth, the energy transition and rising living standards are resulting in an exponential increase in the quantities of metals extracted, while technological developments are leading to a diversification of the metals needed for industrial development, causing an unprecedented increase in metal discharges into the environment. Metals are considered as toxic (e.g. Cd) or as trace elements (e.g. Cu), but increasing their concentrations beyond certain thresholds degrades the quality of ecosystems and threatens human and animal health (“One Health” concept) in contaminated areas.
Climate models predict that the frequency, intensity and number of short-term extreme precipitation events, as well as the variability of floods, will increase as the global climate evolves. This state of affairs no longer makes it possible to accurately constrain the fate and source-sink balance of metals in the Critical Zone (CZ), and consequently the continent’s overall contributions to the oceans. In the CZ, soils are metal sinks, particularly wetlands. Their hydrological cycle (high water/low water) favors the formation of chemical gradients and biogeochemical processes controlling the metal cycle. Extreme floods are characterized by water levels and flows well above the oscillatory levels observed over time. The source-sink balance of metals in wetlands is then unbalanced, increasing metals exported within very short timescales (“flash pollution”) and in partially known physico-chemical forms, possibly toxic and in quantities and concentrations that need to be estimated.

Objectives :

– Characterization of material exported from wetlands during extreme rainfall events. Hypothesis: The colloidal fraction is mainly responsible for the export of metals from wetlands.

– Influence of organic matter origin and Fe speciation on metal remobilization
Hypothesis: Fe speciation and the physicochemical characteristics of OM control the aggregate’s ability to transport metals and transform their speciation, mainly through microbial-induced electron transfer.

– Metal distribution, speciation and isotopic composition Hypothesis: Metal remobilization is mainly controlled by the redox process during precipitation and flooding.

Methodology :

– The thesis topic will include field experiments with several sampling campaigns and in situ and laboratory characterization of samples and laboratory experiments to mimic observed conditions to work under controlled conditions and identify metal remobilization processes.

– The basic tools of geochemistry and mineralogy will be combined with isotope geochemistry, molecular speciation (spectroscopic techniques) and microbiology.

> Contacts : Gildas Ratié (LPG) & Yann Morizet (LPG)

> Submit an application before May 13 on the 3MG doctoral school website

5- Measurements of the physico-chemical properties of alumino/boro/silicate glasses and glass-ceramics for the immobilization of pollutants from nuclear energy

France’s energy independence is based on the use of nuclear power. While this source of energy has the advantage of being continuous, it has the disadvantage of producing radioactive waste that is hazardous to people and needs to be incorporated into immobilization matrices that remain stable over geological time in the natural environment. In the nuclear energy cycle, the management of final waste is an essential step. Some radioisotopes (36Cl, 77Se, 129I) are highly volatile, so there are no suitable solutions for their immobilization. Our knowledge of magmatic systems under extreme conditions in Earth Sciences and inorganic chemistry in Materials Sciences has enabled us to develop a protocol for immobilizing these elements in matrices (glasses and glass-ceramics) synthesized under high-pressure conditions.
Validation of these particular matrices for storage in natural environments involves three prerequisites: 1) high incorporation of these radio-elements, 2) good chemical durability and 3) high mechanical strength. While much progress has been made in recent years in optimizing the incorporation of volatile nuclear waste and the associated chemical durability, little is known about the study of its mechanical strength. The link between the three aspects also remains to be established.

Meeting these objectives requires a multi-scale experimental approach: from atomic-scale studies to macroscopic properties. This is followed by a modeling phase to target the appropriate matrix compositions for the long-term immobilization of these radioisotopes.
The aim of this thesis is to study changes in the physico-chemical properties of glasses and glass-ceramics doped with volatile pollutants (i.e. Cl, Se and I) synthesized under high-pressure conditions. The three main objectives of this thesis are to evaluate 1) the mechanical strength properties, 2) the chemical durability of the matrices produced and 3) to establish the link between the first two.
This thesis will be based on an experimental approach to the synthesis of glassy materials under extreme conditions, and of glass-ceramics in a more advanced stage. The materials thus produced will be studied in three stages: 1) characterization of atomic structures, 2) study of the mechanical strength of the synthesized materials, and 3) modeling of physical properties as a function of atomic-scale structure. The first two will be carried out jointly (2/3) and the third at the end of the first two (1/3).
The laboratories involved are LPG and IMN. In addition, we will be working closely with the Subatech laboratory, which has in-depth knowledge of the immobilization of nuclear waste.

> Contacts : Yann Morizet (LPG), Dimitri Deneele (IMN) & Mickaël Paris

> Submit an application before May 13 on the 3MG doctoral school website

6- Sulfur incorporation in foraminiferal shells to unlock past ocean carbonate chemistry

The chemical composition of the foraminiferal shell reflects the composition of seawater which varies depending on the physicochemical parameters of the environment. The cosmopolitan distribution of foraminifera, their great preservation potential and their abundance in the oceanic archives make these organisms the ideal candidate for reconstructing the past climate of deep times. Currently, the development and application of biogeochemical proxies aims to determine the evolution of the past carbon cycle, which is essential for understanding past and future climate responsiveness to atmospheric CO2 emissions.

The objective of this thesis will be to develop and calibrate a new geochemical tool to reconstruct the carbonate system in the past. We propose to develop (calibrate, validate and apply) a proxy based on the incorporation of sulfur into the shells of foraminifera, as a new indicator of the concentration of carbonate ions [CO32-]. The S/Ca values ​​of foraminifera are assumed to change with [CO32-] due to the substitution of SO42- with CO32- in the crystal lattice. Thus, the SO4/ CO3 ratio in seawater can be reconstructed by the S/Ca ratio of foraminifera by ICP-MS measurements. Calibrations under controlled conditions are necessary on various species of foraminifera. To address the challenges of applying the S/Ca proxy as a [CO32-] proxy, we will use a suite of techniques to study sulfur incorporation into foraminiferal calcite (µXRF, NanoSims, ICP-MS), and we will perform controlled CO2 experiments in the laboratory and apply the calibrations on foraminifera from geological samples.

> Contacts : Emmanuelle Geslin (LPG), Inge van Dijk (LPG) & Christine Bartas (LPG)

> Submit an application before May 13 on the VAAME doctoral school website

Published on April 2nd, 2024