Roger was fortunate to be an invited speaker at the 2025 SSRL/LCLS User Meeting held at SSRL in Menlo Park, CA, Sep 21-26. In his talk (above), he presented exciting micro-X-Ray Fluorescence maps of different sulfur species in cryosectioned eelgrass roots and rhizomes. The results point to at least two different defense mechanisms that these enigmatic plants use to counteract the nighttime threat of a potent phytotoxin, hydrogen sulfide. Roger and coauthor Jocelyn Richardson are writing up their preliminary study for submission to New Phytologist. Next steps are likely to include studies of seagrasses grown in controlled laboratory settings, to isolate different pathways of sulfur transformations in the organisms.
In May-June 2025, Roger traveled to the Cariboo Plateau (BC, Canada) to join in with some fun fieldwork with Sasha Wilson, Jonathan Spence (U Alberta), Maija Raudsepp (Macewan U), Ian Power, and Jamie Burnett (Trent U).
The Lakes on the Plateau have interesting chemistry such as very high alkalinity and salinity, lots of unusual carbonate minerals like magnesite, and some may be analogs for aqueous environments on early Earth and Mars.
Stay tuned for some geochemical data from the lake sediments!
Roger and colleagues have had two companion papers come out this Thanksgiving Day in Science Magazine. The collective message is that marine sedimentary pyrite sulfur isotopes (canonically a proxy for ocean oxidation state) are dominantly controlled by local environmental conditions (e.g., sedimentation rate, porosity, permeability, organic matter abundance, reactive iron abundance). This much was already suspected based on some decades-old papers and, since 2017, a body of work by Virgil Pasquier and others. What is new here is that methods have been developed to attribute mechanism to the local controls on pyrite sulfur isotopes.
Roger and colleagues at Washington University in St. Louis developed a method to isolate individual pyrite grains from sediment samples and measure their sulfur isotope ratios by Secondary Ion Mass Spectrometry. This method allows the extraction of information about metabolism (i.e., the magnitude of isotopic fractionation associated with microbial sulfate reduction) and ‘system openness’ (the degree of Rayleigh distillation of sulfate in sediment pore waters) from individual sediment samples. Ultimately, the latter factor was found to almost exclusively control variations in bulk pyrite sulfur isotopes between glacials and interglacials in a Pleistocene core from the Mediterranean.
Itay Halevy wrote the companion paper, which describes a state-of-the-art numerical model simulating pyrite formation in marine sediments. The model is applied to all published marine pyrite sulfur isotope ratios from modern sediments, and the sedimentary record. Itay argues that almost all bulk pyrite sulfur isotope data likely dominantly reflect changes in system openness (which can also be a function of parameters likely bottom water O2 and sulfate concentrations, in addition to the aforementioned local sedimentary parameters). The paper is a treasure trove of information and arguably one of the most important advances in the sulfur isotope world since the turn of the millennium.
See Roger’s paper here, and Itay’s paper here. See write-up of the papers (by Talia Ogliore at Washington University in St. Louis) here.
Roger has published a paper from his postdoctoral work at the University of Chicago, with coauthors Clara Blättler (PI), Tara Kalia (talented U Chicago undergrad), Jocelyn Richardson (SSRL), Olivier Gros (Universite des Antilles), and Juan Lopez-Garriga (University of Puerto Rico). The paper, included in the November issue of Geology, is titled “Inorganic sulfate–based signatures of chemosymbiosis in modern infaunal lucinids“, and is a bit of a thematic departure from Roger’s previous work. See explainer thread below:
We argue that most sulfate in modern lucinid shells is derived from pore water sulfide. This sulfate bears a clear signature of chemosymbiosis, and we suggest that carbonate-associated sulfate could be a useful proxy for chemosymbiosis in various fossils.
The Bryant Lab is delighted to welcome Emily Apel to the group – she will be conducting her PhD research developing paleoproxies for seawater pH, and investigating carbon and sulfur cycle response to environmental perturbations using geochemistry and modeling.
The Bryant Lab is delighted to welcome its first official member, Isabelle Rein. Isabelle comes to us fresh off a masters at Washington State University, where she focused on halogen geochemistry as a tracer of fluid flow in metamorphic rocks. At Purdue, she will be combining field work, geochemistry and modeling to investigate biogeochemical cycling and ecosystem dynamics during the early Triassic and late Ediacaran.
7/19/23 – Roger attended the Life & Planet conference at the Geological Society of London. The conference was dedicated to the memory of James Lovelock, the legendary scientist of Gaia hypothesis and microwave oven invention fame. Roger presented a talk on sulfur isotopes in 2 billion year old sedimentary rocks from Fennoscandia.
Post-talk discussion with some friendly UCL researchers.
7/15/23 – Roger attended the Goldschmidt conference in Lyon, France. He presented an invited talk on diagenesis and geochemical proxy development in Eocene carbonates from Florida and the Bahamas.
01/03/2023 – Dr. Bryant has arrived at Purdue University to take up a position of Assistant Professor in the Department of Earth, Atmospheric, and Planetary Sciences.
Lab renovations are set to begin soon. Stay tuned for more updates.
The Bryant Lab 