Séminaire de Virgil Pasquier
Université Lausanne
Lieu : ENS, Amphi L
Date : 23/06/2025
Heure : 14h – 15h
Microbial and environmental controls on the S-isotopic composition of pyrite in modern marine sediments (and sedimentary rocks)

Résumé :
Reconstructions of past environmental conditions and biological activity are often based on stable isotope proxies whose interpretations are inherently non-unique. This is particularly true of the sulfur (δ34SPYR-Δ33SPYR) isotopic composition of sedimentary pyrite, which is used to reconstruct ocean-atmosphere oxidation state and track the evolution of several microbial metabolic pathways.
My use and approach of sulfur, i.e., bulk and in-situ, present a novel microanalytical approach to deconvolve the multiple signals that influence pyrite isotopes, yielding both the unambiguous determination of biological fractionations and novel information about depositional conditions.
Over the last few years, I apply this approach to recent glacial-interglacial sediments, which feature among the largest observed S isotopic variability across these environmental transitions. Despite profound environmental changes, the biological fractionation (εmic) remained essentially invariant throughout this interval and the observed isotopic range in δ34SPYR-Δ33SPYR were instead driven by climate-induced variations in the depositional environment.