University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Graduate School Professional Papers 2018 Photochemical Cycling of Reactive Oxygen Species in Hydrothermal Systems: Impacts on Biosignature Preservation Megan A. Mave Let us know how access to this document benefits ouy . Follow this and additional works at: https://scholarworks.umt.edu/etd Part of the Geochemistry Commons Recommended Citation Mave, Megan A., "Photochemical Cycling of Reactive Oxygen Species in Hydrothermal Systems: Impacts on Biosignature Preservation" (2018). Graduate Student Theses, Dissertations, & Professional Papers. 11275. https://scholarworks.umt.edu/etd/11275 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. PHOTOCHEMICAL CYCLING OF REACTIVE OXYGEN SPECIES IN HYDROTHERMAL SYSTEMS: IMPACTS ON BIOSIGNATURE PRESERVATION By MEGAN ALANA MAVE B.S. Earth Sciences, The Ohio State University, Columbus, OH, 2016 Thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Geosciences The University of Montana Missoula, MT June 2018 Approved by: Scott Whittenburg, Dean of The Graduate School Graduate School Dr. Nancy W. Hinman, Committee Chair Department of Geosciences Dr. W. Payton Gardner, Committee Co-Chair Department of Geosciences Dr. Scott R. Miller, Committee Co-Chair Department of Biological Sciences i Mave, Megan, M.S., Spring 2018 Geosciences Photochemical Cycling of Reactive Oxygen Species in Hydrothermal Systems: Impacts on Biosignature Preservation Committee Chair: Nancy W. Hinman Life originated on early Earth, despite harsh, highly reducing conditions. Life may have also emerged on early Mars, when conditions on the two planets were similar (i.e. before atmosphere loss and desiccation). NASA’s 2020 Mars rover mission aims to identify biosignatures (i.e. evidence of life) in early Martian deposits. Potential exploration sites include extinct hydrothermal springs, due to their high habitability and preservation potential. This study aims to better understand biosignature preservation in hydrothermal systems analogous to those on early Mars (i.e. reducing and Fe-rich). Reactive oxygen species (ROS) are highly reactive molecules formed primarily by photochemical reactions. ROS are widespread, shape aquatic redox chemistry, and control biogeochemical cycles with redox-sensitive elements (Fe, S, O, and C). Of interest to this study, ROS can oxidize Fe2+ to Fe3+, which can adsorb or bind to negatively charged cell membranes. Rapid Fe3+-binding (i.e. entombment) can preserve complex organic molecules, or biomarkers. Recent studies have found that entombment by Fe3+, specifically, is key in biomarker preservation. In reducing systems, ROS are the primary oxidants and, thereby, determine Fe- oxidation rates and preservation potential. ROS formation is typically controlled by photo- reactions with dissolved organic carbon. However, Fe redox reactions more likely control ROS formation in these Fe-rich systems. Field and laboratory experiments were conducted at YSNP in relevant water compositions to better understand controls on ROS cycling. In-situ H2O2 cycles observed in these hydrothermal waters were comparable to other higher-temperature systems. Reactions with reduced metals from hydrothermal source waters were responsible for constant, “baseline” ROS production. Reaction rates varied based on particle size (particulate or soluble matter) and water composition. Fe speciation (photochemical reactivity), concentration, and solubility further determined ROS formation and decay rates. Specifically, photochemically active metal species enhanced both ROS formation and decay rates, depending on incident UV irradiance, and rates increased along with Fe concentration and solubility (i.e. acidic conditions). Low O2 conditions slowed H2O2 decay, allowing H2O2 to - accumulate. Hydrothermal reactants appear to produce more H2O2 per O2 molecule compared to other water compositions. Findings can improve our understanding of ROS as they relate to Fe entombment and biomarker formation. ii ACKNOWLEDGMENTS I would like to express my gratitude to everyone who made this project possible. Foremost, I would like to thank my advisor, Nancy Hinman, for your expertise and guidance. Thank you for safely shepherding us across Yellowstone’s active geyser fields, while sharing your wealth of geologic and historic park knowledge. Thanks also go to my lab partner, Laura Stevens, for sharing your enthusiasm for astrobiology and delicious homemade treats. Thanks to my other committee members, Payton Gardner and Scott Miller, for your time and feedback throughout this process. I appreciate the Eagle Scouts of America and everyone else who agreed to wake up at 4am and help collect the data that made this project possible. Thanks to the NASA Astrobiology Institute, the SETI Institute, Sigma Xi Grant-in-Aid of Research, and the University of Montana for your financial support of my research and education. I would also like to thank the Yellowstone Center for Resources and the U.S. Park Service for allowing us to collect samples for this research. Thank you to my parents, for being inspiring role models and pushing me, while whole-heartedly supporting me in all of my endeavors. Finally, I’d like to thank my partner, Andrew Sabula, for his patience and friendship. Thank you for getting me out of the office and making me laugh when I needed it most. iii LIST OF TABLES Table 1: Hot Spring Water Composition ....................................................................................... 15 Table 2: Elk Geyser Sampling Schedule, 2017 ............................................................................. 17 Table 3: Sample Collection and Storage ....................................................................................... 18 Table 4: Analytical Methods Summary ......................................................................................... 18 Table 5: ICP Limits of Detection (mg/L) ...................................................................................... 21 Table 6: IC Limits of Detection (mg/L) ........................................................................................ 22 Table 7: Field Observations at Elk Geyser .................................................................................... 22 Table 8: Elk Geyser Field Study Summary ................................................................................... 26 Table 9: UV and H2O2 Field Study Comparison ........................................................................... 26 Table 10: Particulate Matter Field Study Summary (Whirlpak Bag Experiments) ....................... 30 Table 11: Particulate Matter Field Study, Estimated Formation Rates ......................................... 30 Table 12: Fe-added Field Study (Fisherbrand Tube Experiments) ............................................... 31 Table 13: Particulate Matter Formation Study (Laboratory) ......................................................... 32 Table 14: Particulate Matter Field and Lab Study Result Comparison ......................................... 32 Table 15: Particulate Matter Dark Decay Lab Study .................................................................... 33 Table 16: Fe-added Formation Lab Study ..................................................................................... 34 Table 17: Fe-complexation Lab Study .......................................................................................... 35 Table 18: Catalase Lab Study ........................................................................................................ 36 Table 19: Superoxide Dismutase (SOD) Lab Study ...................................................................... 36 Table 20: Stirring Lab Study ......................................................................................................... 37 Table 21: 4 hour Formation Rate Laboratory Study Summary ..................................................... 38 Table 22: Relative H2O2 Formation and Decay Rates in Particulate Matter Study ....................... 42 Table 23: Equilibrium Constants of Fe and Inorganic Complexant Species at STP ..................... 47 Table 24: Fe complexation Result Summary ................................................................................ 48 Table 25: PHREEQ Modeling Summary ...................................................................................... 49 Table 26: Superoxide Pathway Description .................................................................................. 51 Table 27: SOD Summary .............................................................................................................. 52 iv LIST OF FIGURES Figure 1: Idealized Fe Entombment Schematic ............................................................................... 4 Figure 2: Simplified hydrogen peroxide formation and decay pathways ........................................ 8 Figure 3: Hydrogen peroxide vertical profile measured in Sharpes Bay, Ontario Canada ........... 10 Figure 4: Regional map of Yellowstone National Park ................................................................. 12 Figure