Nicolas BIENVILLE

PhD student

I am currently pursuing a PhD at the Laboratory of Climate and Environmental Sciences at Université Paris-Saclay (south of Paris) under the supervision of Amaelle LANDAIS in the GLACCIOS team.

My research focuses on understanding the link between biosphere and climate and specifically understanding the archiving of its atmospheric signal in Ice Caps.
keywords: oxygen, isotopes, fractionation, ice cores, paleoclimate

E-mail : nicolas.bienville@lsce.ipsl.fr
Website : https://www.linkedin.com/in/nicolasbienville

Research

Earth atmospheric dioxygen is mainly produced by biosphere photosynthesis, and biosphere respiration is also one of the main consumers of this gas. The evolution of atmospheric O₂ is thus linked to global biosphere productivity.

In ice cores we extract air from bubbles to study the composition of the past atmosphere. However, as O₂ concentration in air bubbles is affected by close off processes, it is difficult to reconstruct its variations in the past atmosphere from ice core analyses. In turn, the isotopic composition of O₂ (δ¹⁸O and δ¹⁷O), is also influenced by biological processes and is less influenced by close-off processes so that this tracer should provide useful information on the past biosphere activity.

Quantitative interpretation of the isotopic composition of O₂in the past relies on robust estimate of oxygen fractionation coefficients associated with the relevant biological processes: photosynthesis and respiration. In the past decades, some determinations of these biological fractionation coefficients were performed in uncontrolled large-scale environments or at the scale of the micro-organisms in conditions very different from the natural environment. There are thus inconsistencies in previous determinations of the O₂ fractionation coefficients limiting the interpretation of δ¹⁸O and δ¹⁷O of O₂.

In order to come up with coherent estimates of oxygen fractionation coefficients during biological processes, we developed closed biological chambers as a biosphere replica, with controlled environment parameters (light, temperature, CO₂ concentration), which were used in combination with a newly designed optical spectrometer for continuous measurements of O₂ concentration and of its isotopic composition.