Award: OCE-1260723

The primary goals of this multi-institutional, interdisciplinary project focused on completing a multi-year experiment to study how fluid flows through the rocky basalt underlying sediments of our planet?s deep ocean crust. This study provided a framework through which we could gain a better understanding of the physical, chemical, geological and biological processes that occur within the rocky basalt of the deep subseafloor. To accomplish these goals, we used wellheads, or observatories, installed within boreholes drilled through the seafloor in the Northeast Pacific Ocean off of Vancouver Island that provided access to this environment. Our target was deep ocean crustal fluids that circulate within cracks and fissures of the basaltic rock. In previous research we injected a variety of physical and chemical tracers into the ocean crust via one borehole and, in the current project, we returned several years later in order to collect samples and data from five different boreholes. This work was the first to directly measure the hydrologic properties of the oceanic crust. Sampling deep-ocean crustal fluids has required the development of specialized equipment capable of being deployed at the seafloor in order to pump fluids from up to hundreds of meters below the surface sediment. This equipment was primarily developed through the work of earlier projects, but improved upon during its deployment in support of this project. In addition to analyzing crustal fluids for injected tracers, the recovered samples had additional benefit for understanding the microbiology and biogeochemistry of the deep subseafloor biosphere, including how subseafloor water circulation affects the cycling of organic matter. Several characteristics of the deep subseafloor environment make it a useful analog for life on other planets. Initial biogeochemical evidence and the modelling of potential metabolisms suggested that this system is energy-starved, and is likely dominated by hydrogen, methane, sulfate, iron, and nitrate cycling. Our observations also revealed that it is also a reservoir of novel microbial and viral genetic diversity that can help to inform on the evolution of key metabolic pathways such as methane cycling and sulfate reduction thought to be important to Earth?s early microbial inhabitants, and important to microorganisms inhabiting anaerobic habitats at present. This grant supported the interdisciplinary training of students and other junior scientists, and results have been distributed through scientific publications, presentations to colleagues in the sciences, and the public. Last Modified: 10/31/2017 Submitted by: Michael S Rappe