Award: OCE-1260180

This project was part of a collaborative package of grants to investigators from six institutions: the Universities of Alaska, California at Santa Cruz, California at Santa Barbara, Hawaii, Miami (this project), and Southern California. The overall goal of the collaborative program was to conclude a 2004-2014 phase of hydrogeological and microbiological experiments conducted in six sealed subseafloor borehole observatories called "CORKs" that had been installed in 2004 and 2010 by the Integrated Ocean Drilling Program in sediment-covered young oceanic crust on the eastern flank of the Juan de Fuca Ridge. This location is known for significant off-axis hydrothermal circulation of warm (~65°C) formation fluids in the permeable oceanic basement beneath the less permeable sediment cover. The CORKs included downhole sensor strings, as well as instrumentation installed above seafloor to access subseafloor fluids and pressure signals via wellhead valves, all designed to elucidate the physical, chemical, and microbiological effects of and controls on the active circulation of formation fluids at the location. The set of experiments included a ground-breaking hole-to-hole tracer hydrologic test – the first ever conducted in the oceanic crust – to resolve the actual direction of the extensive flow of formation fluids. The overall collaborative program supported a 2014 research cruise using the manned research submersible DSRV Alvin to recover downhole sensor strings and data and samples from the wellhead instrumentation. Aspects supported by this particular project included download of formation pressure data from recorders on the wellheads and recovery of long-term temperature loggers installed on the downhole sensor strings. Pressure data were successfully recovered from all of the CORK installations. Downhole sensor strings with autonomous formation temperature loggers were recovered from three of the installations, and the long-term temperature records provided important constraints for the interpretation of the ground-breaking hole-to-hole tracer hydrologic experiment. The results of that experiment were published recently in peer-reviewed scientific literature (Neira et al., 2016, Earth and Planetary Science Letters, v. 450, pp. 355-365). These results confirmed a hypothesis of dominant formation fluid flow direction from south to north, consistent with permeability provided by tectonic fabric that is aligned generally parallel to the Juan de Fuca seafloor spreading center to the west. The results also indicate that the high formation permeability may be confined to a relatively low proportion of basement void/pore space that is inter-connected (termed "effective porosity"). Thus, the project has fulfilled the most important aspects of the intellectual merit as originally proposed. In addition, this project has also fulfilled important aspects of the broader impact as originally proposed, both in terms of support of graduate education and in providing a permanent archive of the data from the project. The first author of the tracer experiment paper mentioned above was at the time a graduate student at University of California at Santa Barbara. In addition, the project has supported analyses of tidal signals in the pressure data by a graduate student of Hispanic descent at the University of Miami who is expected to earn his doctorate by summer of 2018. Finally, the pressure and temperature data from this specific project are now posted on the internet for open public access via the IEDA Marine Geoscience Data System, at http://www.marine-geo.org. Last Modified: 02/13/2017 Submitted by: Keir Becker