Collaborative Research: Development and fabrication of a high-temperature borehole fluid sampler to characterize seawater-basalt reactions and the thermal limits of life on Earth

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Five decades of scientific ocean drilling have created more than 113-cased boreholes in the ocean. Such legacy boreholes have been drilled into a range of seafloor geologic settings and many of these boreholes are deep enough that natural geothermal gradients have warmed the boreholes to temperatures in the range (60-200 degrees C). Within this temperature range reactions pathways between seawater and basalt change, affecting how the basaltic crust ages through the dissolution of primary minerals and the precipitation of different minerals as veins, for example. This combination of dissolution and precipitation changes the characteristics of the ocean crust that ultimately affects how the crust is subducted and the potential for large destructive earthquakes. This temperature range also spans the thermal limits of microbial life, based on experiments (122 degrees C), theoretical calculations (150 degrees C), and anecdotal evidence (180 degrees C). However the scientific drilling community currently lacks the ability to collect such warm pristine borehole fluids because electronics fail at such temperatures. This project will solve this sampling problem by first testing shape memory alloys, which are metal alloys that can change their shape and length at a specific temperature that is a function of the alloy composition and fabrication process. Then a water sampling system will be developed that utilizes the properties of shape memory alloys to trigger the collection of boreholes fluids. The first deployment of the newly fabricated system will occur in July 2019 when the scientific drilling program re-enters a legacy borehole that is ~200 degrees C at the base of the hole. The broader impacts of this project will provide the scientific community with a new sampling system for collecting borehole fluids at elevated temperatures. Such a sampling system is not limited to oceanic boreholes, but could be used within the thousands of existing continental boreholes. This new high temperature fluid sampling system will allow the community to explore new directions in understanding hydrothermal processes. Hydrothermal processes and the thermal limits of life are exciting topics that engage the public. More specifically the proposed work will include the development of a hands-on module for a week-long summer day camp (ssrovcamp.org) for rising 3-5th and 6-9th grade students and students involved in the undergraduate marine education program at Santa Clara University. Combined, over 300 students were engaged in one of these two programs in 2018.The crux of this project is to design and fabricate a fluid sampling system for high temperature 60-200 degrees C borehole applications in oceanic and continental settings. The project will build on a Provisional Patent to design and fabricate standard titanium syringe-like fluid capture systems that are triggered by a novel mechanism. This mechanism will use shape memory alloys, given that such alloys change shape at a particular temperature. The sampling system will be modular in design to allow a suite of samples to be collected on a single lowering, each sampler collecting fluid at a specific temperature depending on the particular shape memory alloy that is used in that sampler. This system will be designed to be deployable from oceanic drilling vessels, continental drilling rigs, and submersibles/remotely operated vehicles (ROVs).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.