Experimental Investigations of Peridotite-H2O-CO2 Interactions under Hydrothermal Conditions: A Study of Carbon Sequestration and Abiotic Synthesis of Organic Compounds

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The reaction of some rocks found on Earth's surface with carbon dioxide (CO2) dissolved in surface and subsurface waters can result in mineral reactions that remove CO2 from the fluid. This, in turn, removes CO2 from the atmosphere in a process called carbon sequestration. Under the right conditions, the same reactions can cause the formation of organic compounds in a process called abiotic synthesis which results in the formation of organic compounds from inorganic chemical species. If we better understand processes of carbon sequestration involving natural rock systems, we may be able to devise efficient and effective means for reducing atmospheric CO2 by locking atmospheric carbon up in minerals. A better understanding of how organic compounds form from inorganic materials and interactions with minerals will help us better understand how microbes that live deep in Earth's subsurface are able to survive and thrive in environments where they are isolated from conventional sources of the organic material. This research provides fundamental experimental data and thermodynamic parameters that improve our understanding of how rocks (i.e. peridotites) that are common on the seafloor and also that occur in some places on land react with CO2-charged aqueous fluids to precipitate the mineral serpentine (i.e. a process called serpentinization) and minerals containing carbon (i.e., carbonates). Experiments will also examine how the same reactions reduce carbon from CO2 to form hydrocarbons that can serve as food for microbes living deep inside the Earth in rocks and sediments. Broader impacts of the work include broadening participation of groups under-represented in the sciences by engaging Puerto Rican undergraduates in research and bringing them to the Woods Hole Oceanographic Institution as Woods Hole Summer Student Fellows. Students will remain in residence for 10 to 12 weeks and participate in the experimental work. The effort also includes close interaction between a faculty member at the University of Puerto Rico, Mayaguez and researchers at Woods Hole Oceanographic Institution in Massachusetts. Additional impacts include training of a female PhD student and interaction between the scientists and high school students at the Falmouth Academy near Woods Hole MA. The interaction with the Academy will include lectures and visits to the experimental lab at Woods Hole so students can see, first hand, what it is like to do science and what tools and approaches scientists use.To achieve research goals, laboratory experiments will be run in Dixon bombs at temperatures from 200 to 300 C, 35 MPa, and water-to-rock ratios found in natural seafloor hydrothermal systems. Each experiment will last for several months and involve the reaction of peridotite (lherzolite) and minerals (olivine) with CO2-charged fluids. Experiments have been designed to cause the formation and growth of serpentine and carbonate minerals from starting materials. Changes in fluid composition will be monitored over the duration of the experiments, as will the compositional changes in system solids. Special attention will be paid to the formation of carbonate minerals of various types and the abiotic synthesis of organic compounds in particular CO2, H2, HCOOH, CO, CH3OH, and CH4. Run reactants and products will be characterized and examined by petrographic and spectroscopic techniques. Using these resulting data, correlations will be made between mineral replacement reactions and fluid chemical changes. Additionally, changes in fluid chemistry will be used to determine stable and metastable heterogeneous phase equilibria, reaction pathways, and kinetic rates of both serpentinization and mineral carbonation reactions. Reaction path models will be used for the system Mg-Si-Fe-Al-Ca-Na-K-O-H-C both to help design the experiments and analyze results using thermodynamic and kinetic constraints.