Université Paris-Saclay and Université Paris-Cité

The PhD project will be organized between two laboratories in Paris and its region (LISA http://www.lisa.u-pec.fr/fr) and GEOPS (https://www.geops.universite-paris-saclay.fr). The GEOPS laboratory is recognized for Earth Science research. A specific team (more than 15 permanent scientists and technical staff in 2025 and 5-10 PhD students) is working on the evolution of the Critical Zone, this thin layer located at the surface of the Earth which supports the main physiochemical interactions in terrestrial ecosystems (e.g., soils, rivers, forests). The LISA laboratory is internationally recognized for its research on atmospheric deposition, especially on the mineral dust cycle. In this field, the research activities are mainly focused on quantifying dust emissions, transport, and deposition to assess their radiative and biogeochemical impacts. To reach this objective, the scientists from this theme (14 permanent scientists, technical staff, and 5 PhD students in 2025) perform intensive (ground-based and airborne) and long-term field laboratory experiments coupled with numerical simulations.

Homepage: https://www.universite-paris-saclay.fr

We are looking for a motivated student for a PhD project to determine the flux of atmospheric deposition reaching the Amazon basin and to assess its importance for the functioning of the Amazon rainforest.

Scientific Context
The Amazon rainforest is one of the main carbon sinks on Earth, sequestering 0.42-0.65 PgC annually through photosynthesis [1]. In a context of rapid disturbances induced by climate change, the importance of the Amazon as a carbon sink is highly debated due to the uncertainty about the response of ecosystems to these disturbances [2]. In this region, where the Amazon rainforest grows on highly altered soils, biological productivity, and therefore photosynthesis, is limited by the availability of nutrients in the soil (e.g., phosphorus, potassium, metals) [3,4]. Atmospheric inputs (rain or dry particle deposition) have been put forward for several decades as sources of these nutrients, essential for the persistence of the Amazon ecosystem [5]. The importance of atmospheric deposition is also questioned on a geological time scale, since these deposits, although significant, are often overlooked or forgotten in calculations involving physical erosion or chemical alteration fluxes on a continental scale [6].

The atmospheric particles making up these inputs are chemically diverse (sea salts, anthropogenic particles, soot associated with biomass fires and desert dust). This chemical diversity leads to a diversity of available nutrients [7, 8]. In South America, the main period of atmospheric input occurs between December and April, due to massive outbreaks of Saharan dust. However, for some aerosols, such as soot from biomass fires, inputs from Central Africa are not only restricted to this period. In order to constrain the real effect of atmospheric deposition at the scale of the Amazon basin, it is therefore necessary on the one hand, to obtain a fine physicochemical characterization of these particles, and on the other hand, to quantify and/or model the deposition fluxes.

PhD project

This thesis project is part of the ANR ATMO-GEO project (Evaluating the role of ATMOspheric deposition on Amazonian GEOchemical balance) funded over four years (2025-2028, P.I. D. Guinoiseau). This project brings together geochemists, chemists and atmospheric physicists, forming a high-level international consortium (Université Paris-Saclay, LISA, Université Paris-Cité, University of Miami, Max Planck Institute of Chemistry, Mainz, Germany, University of São Paulo, ATMO-Guyane). The aim of this thesis is to quantify atmospheric deposition at the scale of the Amazon basin, based on ambitious sampling at two observatories: the ATMO coastal site in Cayenne, French Guiana, and the Amazon Tall Tower Observatory (ATTO), a 300 m-high tower located in a remote place 150 km northeast of Manaus, Brazil. Their strategic positioning (on the trajectory of dominant winds on the annual scale) will enable us to quantify the effect of air mass continentalization on deposition flux reduction. Two distinct types of sampling will be carried out at the two observatories:
-the measurement of total deposition, which will be carried out over at least one full year with the help of our Guianese, German and Brazilian partners. This will give us direct access to total deposition, 90-100% of which is dominated by wet deposition [9, 10].
-collection of wet deposition on the scale of a rainfall event over short periods (one month) but repeated annually, in order to determine the partitioning of chemical elements between soluble and insoluble phases (the latter being collected on a filter).

In both cases, sample preparation, which requires ultra-clean conditions, will be carried out in a clean room at GEOPS and LISA laboratories, prior to chemical composition measurement by spectrometry or chromatography. Particles collected on filters during rainy periods will be characterized by X-ray fluorescence or after acid digestion. A few isotopic analyses (Sr-Nd-Pb) may be carried out on selected samples to characterize the sources of aerosols collected in these deposits.

The PhD student will be responsible for:
-the coordination of sampling of the total deposition over a one year campaign (end 2025-end 2026) and on two observatories in South America (ATMO Cayenne, French Guiana and ATTO, 150 km northeast of Manaus, Brazil) using the method developed by Heimburger et al. (2012) [11].
-the chemical characterization of rainfall (soluble vs. insoluble fractions) at event scale over one-month periods at both observatories.
-the determination of the chemical composition of the deposition and elemental partitioning within rainfall events.
-the interpretation of the data, estimating the contribution of dry and wet deposition to the main nutrients fluxes.
-the comparison of the results obtained on the physiochemistry of the deposition with the characterization of aerosols carried out as part of another thesis in the ATMO-GEO project (e.g. scavenging ratio).

Data interpretation work will be carried out in close collaboration with the ANR project’s modeling team. The data acquired will be used to feed and constrain the GEOS-Chem model, developed by C. Pöhlker’s group (MPIC, Mainz, Germany), in order to better constrain nutrient deposition fluxes at the scale of the Amazon Basin.

Profile and skills

Technical skills:

-The candidate will have a sound knowledge of atmospheric sciences (particularly atmospheric chemistry).
-The candidate should have good analytical chemistry skills (of laboratory experiments and spectrometric measurements).
-Initial experience in water geochemistry and statistical processing would be an asset.
-Experience and interest in field campaigns will be highly appreciated.

Language :
Level of English required: Intermediate: You can speak the language comprehensibly, coherently and confidently on familiar everyday topics. The candidate will be working in an international team (ANR ATMO-GEO https://anr.fr/Projet-ANR-24-CE01-1243) where English will be the common language.

Supervision and scientific interactions

-Main supervision: Pr. Karine Desboeufs (LISA, U-Paris-Cité), et Dr. Damien Guinoiseau (GEOPS, U. Paris-Saclay)

-Scientific interactions: -Dr. Charlotte Skonieczny, Pr. Cécile Quantin, Léa Collignon – Université Paris-Saclay. -Pr. Benoît Laurent – LISA, UPC-UPEC, France
-Dr. Stephen J.G Galer & Dr. Christopher Pöhlker – Max Planck Institute of Chemistry, Mainz. -Dr. Cassandra Gaston – University of Miami, Miami.
-Pr. Paulo Artaxo & Pr. Luis Machado– Universidade de São Paulo, São Paulo. -Kathy Panechou – Observatoire ATMO Guyane, Cayenne.

GEOPS and LISA laboratories

The PhD project will be organized between two laboratories in Paris and its region (LISA http://www.lisa.u-pec.fr/fr) and GEOPS (https://www.geops.universite-paris-saclay.fr). The GEOPS laboratory is recognized for Earth Science research. A specific team (more than 15 permanent scientists and technical staff in 2025 and 5-10 PhD students) is working on the evolution of the Critical Zone, this thin layer located at the surface of the Earth which supports the main physiochemical interactions in terrestrial ecosystems (e.g., soils, rivers, forests). The LISA laboratory is internationally recognized for its research on atmospheric deposition, especially on the mineral dust cycle. In this field, the research activities are mainly focused on quantifying dust emissions, transport, and deposition to assess their radiative and biogeochemical impacts. To reach this objective, the scientists from this theme (14 permanent scientists, technical staff, and 5 PhD students in 2025) perform intensive (ground-based and airborne) and long-term field laboratory experiments coupled with numerical simulations.

Objectives for promoting the doctoral student’s research work

-Publication of A-rank scientific articles
-Participation in national (Réunion des Sciences de la Terre, Staubtag meeting) and international (Goldschmidt, AGU) conferences.
-Dissemination of results to local populations (French Guiana, Amazonas State in Brazil). Presentation of the scientific outreaches to the annual ATTO workshop in Manaus, Brazil (taking place in October every year).
-Open access publications in line with agreements already signed between French universities (Couperin) or the Max Planck Society (DEAL) and major publishers.

References

[1] Pan, Y. et al. A Large and Persistent Carbon Sink in the World’s Forests. Science 333, (2011).
[2] Brienen, R. J. W. et al. Long-term decline of the Amazon carbon sink. Nature 519, (2015).
[3] Gaillardet, J. et al. Chemical and physical denudation in the Amazon River Basin. Chemical Geology 142, (1997).
[4] Cunha, H. F. V. et al. Direct evidence for phosphorus limitation on Amazon forest productivity. Nature 608, (2022).
[5] Ellsworth, D. S. et al. Convergence in phosphorus constraints to photosynthesis in forests around the world. Nature Communications 13, (2022).
[6] -Reichholf, J.H.,. Is Saharan Dust a Major Source of Nutrients for the Amazonian Rain Forest? Studies on Neotropical Fauna and Environment 21, 251-255. 1986)
[7] Wittmann, H. et al. Sediment production and delivery in the Amazon River basin quantified by in situ–produced cosmogenic nuclides and recent river loads. Bulletin 123, (2011).
[8] Barkley, A. E. et al. African biomass burning is a substantial source of phosphorus deposition to the Amazon, Tropical Atlantic Ocean, and Southern Ocean. Proceedings of the National Academy of Sciences 116, (2019).
[9] Prospero, J. M. et al. Characterizing and Quantifying African Dust Transport and Deposition to South America: Implications for the Phosphorus Budget in the Amazon Basin. Global Biogeochemical Cycles 34, (2020).
[10] Wang, X. et al. The export of African mineral dust across the Atlantic and its impact over the Amazon Basin. Atmos. Chem. Phys. 23, (2023).
[11] Heimburger, A. et al Direct measurements of atmospheric iron, cobalt, and aluminum-derived dust deposition at Kerguelen Islands. Global Biogeochemical Cycles 26, (2012)

To apply, please contact Karine Desboeufs (karine.desboeufs@lisa.ipsl.fr) and Damien Guinoiseau (damien.guinoiseau@universite-paris-saclay.fr) who can provide more detailed information on the application submission. Applicants may already provide the following documents in English (or French) language, possibly compiled into a single PDF file, to karine.desboeufs@lisa.ipsl.fr and damien.guinoiseau@universite-paris-saclay.fr :

Cover letter explaining your motivation to do this PhD
A CV
Contact information or recommandations of two references
Copies of your Master degrees with transcripts

Application deadline is fixed to the 15th of June 2025. The anticipated start date is October 1, 2025.