Missions

Triple Oxygen Isotope Composition of Water and Biogenic Silica, Relative Humidity, Vegetation, and Evapotranspiration over the Last 3000 Years in Intertropical Africa: A Tanzanian Case Study
Continental atmospheric relative humidity is a key parameter of the water cycle, as it largely controls evapotranspiration, which accounts for over half of annual global precipitation. It also governs plant stomatal opening, thereby affecting photosynthesis and terrestrial ecosystem growth. In turn, ecosystem dynamics influence evapotranspiration and atmospheric water vapor. These climate–vegetation feedbacks are recognized but remain poorly quantified and insufficiently integrated into climate models, which contributes to uncertainties in predictions of precipitation and atmospheric humidity—particularly in intertropical regions. Yet such projections are crucial for anticipating how ecosystems and societies will adapt to climate change.
We are seeking a postdoctoral researcher to work on producing quantitative records of atmospheric relative humidity over the past 3000 years in intertropical Africa. Concurrent changes in vegetation will also be explored. This will help determine whether climatic and vegetation changes occurred simultaneously or sequentially, and will provide insights into their causal relationships.
To this end, peat cores have been collected in Tanzania, in the volcanic Rungwe Massif north of Lake Nyasa (formerly Lake Malawi). These records are expected to span the last 3000 years.

Activités

Main Activities:
• Establish the chronology of the record using a combination of ¹⁴C and ²¹⁰Pb dating
• Extract phytoliths and analyze their triple oxygen isotope composition
• Use the 17O-excess of phytoliths—a recently calibrated quantitative proxy for atmospheric relative humidity, developed through collaborative projects led by CEREGE
• Compare isotopic data with similar records under study in West Africa
• Extract and analyze charcoal using FTIR to identify fire types (natural vs. anthropogenic) that may have triggered or accelerated vegetation changes
In parallel:
• Analyze the triple oxygen isotope composition (δ¹⁸O and 17O-excess) of regional precipitation, using ongoing monitoring since 2024
• Assess interannual stability of precipitation 17O-excess, essential for accurately constraining phytolith-derived relative humidity proxies
• Determine the potential contribution of evaporation from Lake Nyasa—the world's 9th largest lake—to monthly regional rainfall
• Collaborate with climate modellers
This project builds on new analytical developments to trace present and past water cycles at the soil–plant–atmosphere and open-water–atmosphere interfaces

Compétences

We are looking for a motivated and creative candidate with a PhD in Earth sciences, hydrology, or paleoclimatology, and expertise in stable oxygen isotope geochemistry. Prior experience with triple oxygen isotope systems (mass-dependent fractionation) would be highly valued. Excellent command of English and strong teamwork skills are essential. The position also involves significant participation in sample preparation and laser spectrometry measurements.

Contexte de travail

The recruited researcher will be based at CEREGE, a highly interdisciplinary Earth sciences laboratory, as part of the CLIMAT team and especially the PANISS laboratory group. They will also work closely with partners in the ANR-funded PAST-17 project, which involves several French and international laboratories, including Tanzanian institutions.

Contraintes et risques

A field mission in Tanzania is planned.