Abstract
Abstract. Deep (>1 km depth) scientific boreholes are unique assets that can be used to address a variety of microbiological, hydrologic, and biogeochemical hypotheses. Few of these deep boreholes exist in oceanic crust. One of them, Deep Sea Drilling Project Hole 504B, reaches ∼190 ∘C at its base. We designed, fabricated, and laboratory-tested the Multi-Temperature Fluid Sampler (MTFS), a non-gas-tight, titanium syringe-style fluid sampler for borehole applications that is tolerant of such high temperatures. Each of the 12 MTFS units collects a single 1 L sample at a predetermined temperature, which is defined by the trigger design and a shape memory alloy (SMA). SMAs have the innate ability to be deformed and only return to their initial shapes when their activation temperatures are reached, thereby triggering a sampler at a predetermined temperature. Three SMA-based trigger mechanisms, which do not rely on electronics, were tested. Triggers were released at temperatures spanning from 80 to 181 ∘C. The MTFS was set for deployment on International Ocean Discovery Program Expedition 385T, but hole conditions precluded its use. The sampler is ready for use in deep oceanic or continental scientific boreholes with minimal training for operational success.
Highlights
The current and future direction of scientific ocean drilling depends on technological advances to achieve a wide range of scientific objectives
Objectives related to microbial life in the subseafloor and a dynamic Earth represent two of the four current themes that guide scientific ocean drilling within the International Ocean Discovery Program (IODP; IODP Science Plan for 2013–2023)
Because of (a) the uniqueness of these warm, deep boreholes; (b) the aspiration to characterize the thermal limits of life within the crust; (c) the desire to elucidate water– rock reactions and crustal alteration in a natural setting; and (d) the lack of a fluid sampler that is inexpensive, easy to operate, and affords a versatile array of experimental possibilities, we developed the Multi-Temperature Fluid Sampler (MTFS)
Summary
The current and future direction of scientific ocean drilling depends on technological advances to achieve a wide range of scientific objectives. Objectives related to microbial life in the subseafloor and a dynamic Earth represent two of the four current themes that guide scientific ocean drilling within the International Ocean Discovery Program (IODP; IODP Science Plan for 2013–2023) While advances in these areas have been achieved using traditional coring and sample analyses, nontraditional means of instrumenting boreholes and direct sampling of legacy boreholes continue to transform our knowledge of these themes (D’Hondt et al, 2019; Orcutt et al, 2011; Smith et al, 2011; Neria et al, 2016; Wheat et al, 2020). Scientific ocean drilling during the past 5 decades has resulted in more than 100 cased boreholes, many of which are suitable for reentry and further discovery (Edwards et al, 2012) Such boreholes tap a range of thermal, hydrologic, physical, and crustal conditions, providing the underpinnings for a range of potential experiments to elucidate crustal and microbial evolution and function as well as the impact of both on ocean processes. It incorporates a mechanical trigger that utilizes the thermal-response properties of a shape memory alloy (SMA), which is a precise mixture of metals that allows the alloy to be physically modified at room temperature and to return to its original shape at an activation temperature that depends on the composition of the alloy, the geometry of the SMA material, and the design of the trigger mechanism
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