Grant: Discovery Grants Program - Individual

Our program focuses on the cycle of quantitatively important forms of organic matter (OM) in aquatic environments. The central theme of this program is to study the sources, fate and reaction histories of complex organic mixtures by designing novel bulk, molecular and isotopic analytical methods addressing pressing needs in biogeochemistry. During the last DG cycle, we studied the interactions between reactive iron oxides and sedimentary OM and the role played by these interactions on carbon preservation in sediments. We also carried out seed experiments and projects in preparation for this renewal and the next DG cycle. These include the development and application of a method for the measurement of the ?13C value of dissolved OM in seawater, designing compound-specific stable isotope analysis (CSIA) methods for measuring the ?13C and ?2H values of methane to decipher its sources and assess OM degradation pathways in anoxic sediments, as well as for measuring the same stable isotopes in organic biomarkers to better understand OM cycling in sediments. The research proposed here focuses on the St. Lawrence Estuary and Gulf (SLEG) and will answer some of the burning questions that were raised by our previous work. It represents a shift in scope and methods as we have now developed a series of machine learning approaches that help us getting the most out of the sometimes limited number of available samples and measured parameters. We also move away from iron oxides and launch an in-depth study on the role of iron sulfides (FeS) in the preservation of sedimentary OM. This includes the development of advanced wet chemical, electrochemical (potentiometry) and synchrotron X-ray methods for quantifying and characterizing OM protected through its association with FeS. Also new, we will use molecular modeling and single molecule atomic force microscopy to better understand the interactions between organic compounds and the surface of FeS nanoparticles. A second new initiative is the development of a comprehensive biomarkers and CSIA toolbox specifically adapted to the SLEG. The performance of biomarkers proxies will be evaluated, and machine learning approaches including bulk, spectroscopic, molecular and isotopic proxy data will be developed to make their interpretation much more robust. These complementary methods and tools will then be combined to predict the impact of a further decrease in bottom waters dissolved O2 concentrations as the SLEG bottom waters are slowly but surely progressing from the current hypoxic conditions to anoxic ones in the near future. Mechanistically understanding the dynamics of shielded OM at the redox interface represents one of the greatest analytical frontiers remaining in biogeochemistry. Developing new analytical strategies is a fundamental prerequisite for obtaining a mechanistic understanding of OM preservation in aquatic systems. Our work on OM interactions with Fe sulfides, in particular, will prove very promising.