Award: OCE-1634025

Seawater flows though the basaltic crust in the ocean just like groundwater flows through permeable formations on continental crust. Millions of wells have been drilled into these permeable aquifers on continental crust. Most wells are used to extract water for drinking or irrigation. Wells also have been used to pump wastes fluids into the crust and aid in the extraction of oil and natural gas. To assess the permeability and properties of these crustal reservoirs many tracer tests have been conducted in which a tracer (chemical or dye) is pumped into one hole and monitored in others. On the basis of the when the tracer arrives, one can characterize the aquifer. However, prior to this experiment, only one hole-to-hole experiment has ever been conducted in the oceanic crust, even though the upper permeable basalt that underlies an impermeable sediment is one of the largest crustal water reservoirs on Earth. This project represents the second hole-to-hole experiment in the oceanic crust. What makes this experiment novel is that it was fully conducted by a remotely operated vehicle (ROV) and it utilized a legacy borehole, one that was drilled and cased into the basaltic crust, but left for future potential work. We deployed a tracer (dissolved cesium) in the legacy borehole and monitored a nearby borehole to detect when the tracer arrived. The tracer arrived within 11 days. This provides constraints for the hydrologic parameters of the oceanic aquifer and means that future expeditions could inject nutrients or potential metabolites to assess reaction pathways and kinetics of reactions within the basaltic crust. The ocean crustal reservoir is home to one of the largest biomes on Earth and one that appears to be slow growing, yet is sustainable for millions of years or potentially much longer. Much of the project focused on the development of technology to conduct the proposed work and the month-long expedition. These technological developments will make future experiments possible and were incorporated into several hands-on activities for the Seafloor Science and Remotely Operated Vehicle (SSROV) summer camp. The summer camp is a week-long camp for two levels, 3-5th and 6-9th grades. In 2018, 197 campers and 20 high school and college students participated in the camp. Last Modified: 10/05/2018 Submitted by: C. Geoffrey Wheat