Description du sujet de thèse

Despite decades of research and the study of hundreds of ice cores, what is commonly referred to as the chemistry of ice cores has provided very little information about the chemical processes in the atmosphere in the past. This is because the concentration and elemental isotopic composition of the compounds targeted in the ice do not differentiate between source, transformation in the atmosphere, or sink effects, while assuming that they have not been influenced by post-depositional effects (even though they often have). With the Orbitrap-iso, it is now possible to quantitatively and qualitatively increase the number of isotopic proxies to a level where specific information related to the transformation of compounds in the atmosphere becomes accessible.
The aim of this thesis is to document the isotopic composition of sulfate and nitrate at different spatial and temporal scales in ice cores, including isotopically poly-substituted compositions that have never been measured before. Ice cores from high latitudes will be particularly interesting for their insight into the past oxidation capacity of the atmosphere, as they allow the study of long-term processes related to major climate transitions. Each ice core presents its scientific interest due to its location and the timescale it covers. These ice cores from high latitudes come from various international projects (EPICA, Vostok, EGRIP, etc.) and cover several glacial-interglacial transitions that need to be studied with this analytical tool.
The central hypothesis of the study is that the isotopologue ratios of nitrate and sulfate found in the ice are characteristic of the oxidation mechanisms that produced them. Since this mechanistic information about their formation is inaccessible through concentration measurements and elemental isotopic ratios, it is necessary to develop new isotopic tools based on poly-substituted molecules while documenting the natural variability observed in polar ice cores over target periods of climatic interest (glacial-interglacial transitions and the industrial revolution).
Thanks to DOC-PAST, we have the opportunity to open a new disciplinary field to address one of the fundamental questions of paleoclimate that remains unresolved: the link between atmospheric chemistry and climate.
Tasks to be undertaken:
Task 1: Cut and prepare ice core samples in a cold room.
Task 2: Analyze samples on the PANDA ice core analysis platform to extract basic concentration profiles.
Task 3: Acquire the knowledge to execute and process samples for the new Orbitrap isotope analyzer.
Task 4: Document the isotopologues of sulfate and nitrate during glacial/interglacial and preindustrial/industrial transitions in EPICA/Vostok and EGRIP ice cores using the Orbitrap isotope analyzer.
Task 5: High-resolution analysis in ice cores of specific selected events (volcanic, forest fires, industrial revolution) and establish natural variability for each ice core.
Task 6: Interpret, present, and publish the obtained data.

Applicant should have a good understanding of analytical chemistry, with basic knowledge in environmental chemistry dealing with trace species. Knowledge of at least one of the following techniques: IRMS, GC or LC, optical spectroscopy is an advantage. Basic knowledge in physical chemistry of the atmosphere and ice cores or closely related disciplines will be preferable but not necessary. The very oriented laboratory and fieldwork of this thesis requires a candidate motivated and skillful with manual work. It is expected that the candidate will be organized, autonomous, master a programming language for data analysis (preferentially Python) and show a spirit of initiative. Work in cold conditions (cold room and/or sampling work in Antarctica) is a characteristic of this position.

Contexte de travail

The Institute of Environmental Geosciences (IGE) is a public research laboratory under the supervision of CNRS/INSU, IRD, Grenoble Alpes University (UGA), INRAE and Grenoble-INP.
It brings together about 330 people including 190 permanent members (researchers, teacher-researchers, engineers) and about 140 PhD students, post-doctoral fellows and staff on fixed-term contracts. The laboratory also welcomes each year several dozen interns and scientific visitors. The laboratory is located on three sites on the Grenoble University Campus (Glagiologie, OSUG-B/Maison Climat Planète, and INRAE Grenoble Saint Martin d'Hères).
The IGE is one of the main laboratories of the Observatoire des Sciences de l'Univers de Grenoble (OSUG) which is a federative structure of INSU.

The doctoral student will work in the ICE3 team of the IGE and will be placed under the responsibility of Joël Savarino, research director and Nicolas Caillon, research engineer.

As part of the ERC Doc-Past, the PhD student will analyse the isotopic composition of nitrate and sulphate in several ice cores drilled in polar regions (Antarctica, Greenland) with the aim of connecting the chemical evolution of the atmosphere with the climate

Contraintes et risques

Work in cold rooms
Work in extreme environments (altitude, polar zones)
Handling of chemical products

Informations complémentaires

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