InCEES Professor, Department of Earth & Planetary Sciences; McDonnell Center for the Space Sciences
Interim Director, International Center for Energy, Environment & Sustainability (InCEES)
Director, Environmental Studies Program
I lead the Stable Isotope Biogeochemistry Group, where our work focuses on using geochemical analyses (predominantly those of the stable isotopes of sulfur as well as carbon, oxygen, and nitrogen) to understand biogeochemical cycling in the modern and the ancient. In our research we make use of both gas-source isotope ratio mass spectrometers (IRMS) and secondary ion mass spectrometry (SIMS), including our new Cameca ims 7f/geo instrument installed in Dec 2013. To see curriculum vitae, Click here.
Stable Isotope Biogeochemistry involves the use of the stable isotopic compositions of elements that make up minerals and organic matter to understand and/or reconstruct biological activity. Typically, carbon (δ13C), nitrogen (δ15N) or sulfur (δ34S – or, more recently, Δ33S/Δ36S) isotopes are analyzed, with the results linked to the activity of certain metabolic pathways and the presence of specific phylogenies. In the modern, stable isotope biogeochemistry is used to understand biological cycling within microbially-dominated environments (e.g., microbial mats, or marine sediments), reconstruct larger-scale ecosystem dynamics and food webs, and trace the development of human agriculture (e.g., the spread of maize domestication). On a global-scale, these isotopes provide the best estimate for global biological productivity as well as the burial of both reduced carbon (organic matter) and sulfur (pyrite), which are the two dominant factors that regulate atmospheric oxygen levels (pO2). Isotope studies of carbon and sulfur throughout Earth history provide one of the most powerful tools for reconstructing environmental change throughout Earth history, particularly the accumulations of oxygen in the ocean-atmosphere system during the Paleoproterozoic (~2.2-2.5 billion years ago) and the late Neoproterozoic (~635 – 541 million years ago) and the evolutionary radiations and mass extinctions of taxa throughout the Phanerozoic.