This research develops a Hele-Shaw type apparatus made of infrared transparent germanium glass, to allow, for the first time, a window into subsurface Earth environments that permits direct observation of complex hydrothermal and hyperbaric processes in the laboratory. The reactor will enable controlled, non-invasive, real-time visualization of hydrologic and potentially biogeochemical processes applied to a subsurface system at temporal and spatial scales inaccessible in nature. An innovative combination of scientific approaches using forward and inverse hydrodynamic modeling facilitate the design and interpretation of geochemical experimental results using the apparatus. Justification for this effort is based on rapidly growing evidence of prolific microbial populations thriving in "extreme conditions" in Earth surface and subsurface environments and the importance of microbial mediation of geochemical processes. In hydrothermal systems, microscale catalysis of mineral precipitation and dissolution and the creation of biofilms play a crucial role in the development of fluid flow patterns, thereby affecting the spatial and temporal evolution and occurrence of thermophilic microbial populations. Fundamental questions addressed with the apparatus include: (1) how the subsurface biosphere affects the geochemistry and fluid dynamics of porous flow systems and (2) how geochemical heterogeneity in subsurface environments affects microbial populations. Broader impacts of the work include support of two early career PIs both of whom are from groups under-represented in the sciences and one of whom is a faculty member at a primarily undergraduate institution. The device also has strong possibilities for educational purposes and public outreach through its ability to do video imaging of real time changes in the distribution of microbes, biofilms, and temperature in the reactor.
