PhD thesis (M/F) on Modeling Amazonian paleoclimates and their link to global scale changes

Job Description

Thesis Subject

The Amazon Basin and its rainforest play a central role in the global water and carbon cycles. Climate change and land-use changes in the Amazon could trigger a self-sustaining dieback process of the rainforest, whose extent and biodiversity depend on precipitation. Climate models project a decrease in Amazonian precipitation by the end of the century, which could be further amplified by a slowdown in the Atlantic Meridional Overturning Circulation (AMOC). This PhD is part of the French-Brazilian project AMACLIM (https://www.lsce.ipsl.fr/anr-fapesp-amaclim/), which aims to better describe and understand the joint evolution of Amazonian climate and vegetation using paleoclimate records from the last glacial-interglacial cycles and global climate models.
Paleoclimate reconstructions allow us to describe natural hydroclimatic changes in the Amazon under different forcings. Existing records reveal past variations in Amazonian hydroclimate at orbital and millennial timescales over the last 50,000 years. However, many questions remain, particularly regarding the causes of these past climate changes: the impact of climate system forcings (solar insolation, variations in atmospheric greenhouse gas composition), the role of atmospheric circulation (Intertropical Convergence Zone, South American monsoon system), and the role of abrupt changes in the AMOC. The role of the possible feedbacks from South American vegetation, particularly in the Amazon, in the region's climate dynamics also remains to be determined. This vegetation feedback may also be sensitive to changes in dust input from the Sahara, which is itself modulated by atmospheric circulation changes and surface conditions in West Africa.
This PhD aims to improve our understanding of climate variations in the Amazon Basin by modeling several contrasting paleoclimatic episodes. The following types of simulations will be conducted and analysed:
- Realistic simulations of the climate during the Last Interglacial (approximately 127,000 years ago) and the Last Glacial Maximum (approximately 20,000 years ago), as part of the Paleoclimate Modelling Intercomparison Project (PMIP, https://pmip.lsce.ipsl.fr/– Kageyama et al., 2017), as well as episodes of significant AMOC variations during Marine Isotope Stage 3 (MIS3), following the work already carried out by Ji-Woong Yang. Extensions to the seldom simulated MIS6 could also be considered, following the AMACLIM team advice. These simulations will incorporate known forcings for each of these climates (solar insolation, atmospheric greenhouse gas concentrations, and the presence of additional Northern Hemisphere ice sheets for the Last Glacial Maximum). Their realism can be evaluated using existing and newly acquired records from the AMACLIM project. Particular attention will be paid to accounting for climate variability and the uncertainties of both model and data approaches in these comparisons between climate reconstructions and model results.
- Sensitivity simulations to test the impact of a single forcing or feedback for each of the forementioned climatic episodes. The role of vegetation phenology and changes in vegetation cover in relation to changes in precipitation and tropical atmospheric circulation will be examined in particular. The question will be to determine the extent to which vegetation changes amplify or mitigate precipitation changes linked to large-scale mechanisms.
- The possibility of examining the response and feedback of aerosols, particularly Saharan dust, for these different climates and abrupt climate changes linked to AMOC variations remains open for the later stages of the PhD.
During this PhD, the student will acquire highly valued skills in climate modeling, climate simulation analysis, and will contribute to expand the knowledge on the factors driving climate and vegetation changes in the Amazon Basin, in connection with major changes in the planet's energy balance, as well as atmospheric and oceanic circulations.

Candidate Profile
We are looking for a student with the following profile:
- Master's degree in meteorology, climatology, oceanography or other fields of the geosciences.
- Ideally, experience in analyzing large datasets (e.g., using Python).
- Strong interest in research and modeling approaches.
- Ability to work in a team at LSCE, IPSL, and within the AMACLIM project.
- Synthesis skills (literature review, analysis of model results and comparison to reconstructions) and ability to share results through oral and written presentations.
Applicants are requested to contact the two scientific supervisors below by email, attaching their CV and a cover letter. Selection will be made after an oral interview with the scientific supervisors.

Your Work Environment

The PhD thesis will take place at Laboratoire des Sciences du Climat et de l'Environnement (LSCE), a joint research unit (UMR 8212) of Commissariat à l'Énergie Atomique et aux Énergies Alternatives (CEA), Centre National de la Recherche Scientifique (CNRS) and Université de Versailles Saint-Quentin en Yvelines (UVSQ), located on the CEA's Orme des Merisiers site at the heart of the Paris-Saclay University campus. It is part of the Institut Pierre-Simon Laplace (IPSL). LSCE, which brings together over 350 researchers, PhD students, engineers, technicians and administrative staff, studies past, present and future mechanisms in the evolution of the Earth's climate and external environment, using observations and modeling exercises.
The PhD thesis is funded by the French-Brazilian (ANR-FAPESP) AMACLIM project, which aims to use interglacial and millennial-scale climate changes of the last 220,000 years as natural experiments to provide the first integrated understanding of atmosphere-land-ocean interactions that control natural changes in Amazon climate and vegetation under different climatic forcings of the past two glacial cycles. This project provides a dynamic working environment between about twenty scientists and seven PhD students in France and in Brazil. Close links are expected with another PhD thesis of paleoclimate modelling based in Brazil.
The PhD thesis is also part of an active French-Brazilian collaboration in paleoclimatology, focusing on both modeling and the reconstruction of paleoclimates in tropical South America (e.g., joint oceanographic cruise AMARYLLIS-AMAGAS II, International Research Project SARAVA, CAPES-COFECUB project), from which the student will directly benefit.
Research stays at the University of São Paulo (USP) or the State University of Rio de Janeiro (UERJ) in Brazil are expected for up to a few months during every year of the PhD thesis.

Constraints and risks

No particular risk

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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