How Minerals Control Hydrothermal Organic Reactivity

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Fluids circulating through the seafloor at seamounts, continental shelves, mid-ocean ridges, and elsewhere contain dissolved organic compounds that, during the course of their transit through the ocean crust, are exposed to elevated temperature-pressure environments where they are transformed into other organic molecules. These organics not only feed microbes in the deep biosphere but their reactions with minerals change them into other organic molecules. Such similar reactions and transformations that happened in the ocean crust back during the earliest days of our planet are likely to have played a major role in the formation of the essential organic components that resulted in life on Earth. This research carries out a series of high temperature and pressure experiments (200 to 350 C and 70 to 100 MPa, respectively) in which well-characterized, dissolved, isotopically-labelled, aqueous organic and chiral compounds are reacted with a variety of common seafloor hydrothermal oxide and sulfide minerals to examine the resulting changes in organic compounds and their rates of transformation. Transformations and rates of reaction will be examined both as a function of temperature and pressure as well as a function of the catalytic properties of the minerals in terms of surface area, charge distribution, and semi-conductor properties. Resulting data will be used to determine fundamental thermodynamic and kinetic parameters that can be used to make and test predictions and examine the implications of water-rock interaction and mineral catalysis as they apply to the development of organic molecules in the ocean crust. Experiments mimicking seafloor hydrothermal systems will be run as a function of pH, ionic strength, and redox state. Both hydrothermal gold bag (Dixon bomb) and static gold capsule experimental apparatuses will be used. Experiments will be designed using aqueous speciation modeling codes (e.g., SUPCRT and EQ3/6). Organic solutes, mineral reactants and products, and dissolved gases from the static and gold bag experiments will be analyzed by high precision gas chromatography and gas chromatographic mass spectrometry. X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy. Preliminary experiments have already demonstrated proof of concept in terms of experiments being successful and yielding interpretable results. Broader impacts of the research include significant integration of research and education by using the research to transform how undergraduate geochemistry, organic chemistry, and astrobiology students are taught at Arizona State University. Research will be incorporated into courses and a series of podcasts and videos on themes relating to submarine hydrothermal systems and hydrothermal organic geochemistry will be developed as part of course offerings. These will then be improved through student crowd sourcing and posted for public consumption on the Internet. Results of the project will be applicable broadly across the academic sector into the fields of chemistry and hydrology as well as geothermal and materials science. The fundamental thermodynamic parameters and rate constants to be derived will have a potentially large impact in the chemical and petroleum engineering industrial sectors.