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doi:10.2204/iodp.proc.332.105.2011

Methods

The general design of the SmartPlug deployed during Expedition 319 remained little changed for Expedition 332 given the robust design and ease of handling. Structurally, both “plugs” included a hollow-bore 3.5 inch EU 8rd box-end threaded coupling at the upper end, which mates with the lower end of the Baker Hughes packer, and an outer O-ring sealed structural shell that is designed to withstand the loads encountered during hole reentry operations (Figs. F2A, F3) (see also “SmartPlug/GeniusPlug” in the “Methods” chapter [Expedition 332 Scientists, 2011]). Housed inside are a high-precision pressure period counter with a 12.8 MHz real-time clock (RTC-PPC system, resolving ~10 ppb of full-scale pressure, or ~0.7 Pa), a 24-bit/channel analog to digital converter and data logger (designed and built by Bennest Enterprises, Ltd., Minerva Technologies, Ltd., and the Pacific Geoscience Centre, Geological Survey of Canada), two pressure sensors (Model 8B7000-2-I; Paroscientific, Inc., USA), and an independent miniature temperature logger (MTL) (Antares, Germany). Four independent temperature readings are made: (1) with the MTL, (2) with a platinum thermometer mounted on the primary data logger end cap, and (3) with each of the two pressure sensors. The inside of the structural shell is exposed to water in the cased borehole above through the internal open bore of the casing packer seal. One of the pressure sensors is connected to this volume to provide a hydrostatic reference, and the second sensor is connected to the sealed, screened borehole interval via hydraulic tubing that passes through the bottom end of the structural shell. RS-422 communications with the main instrument for setting recording parameters and downloading data are conducted via a multisegment Seacon AWQ connector on the logger pressure case. Communications with the MTL are conducted with a special Antares interface and WinTemp software. The instrument frame is shock-mounted within the structural shell, and the pressure sensors are mounted with secondary shock pads within the frame (Fig. F2B). Structural components are constructed with 4140 alloy steel, and pressure sensor housings and hydraulic tubing are constructed from 316 stainless steel.

The extension unit for the GeniusPlug configuration is made of the same material and includes a bulkhead to hydraulically separate the SmartPlug body from the OsmoSampler and FLOCS (Figs. F2B, F4, F5). The OsmoSamplers will provide a time series of pore fluid geochemical data from the screened interval in order to asses any fluid flow or geochemical transients (e.g., Solomon et al., 2009). The FLOCS experiment is designed for in situ cultivation of microbial populations and to evaluate turnover rates and carry out DNA sequencing on populations of microbes on the different substrates included in the chambers. Because these observatory components were added to the bottom end of the SmartPlug configuration, only borehole fluid entering through the casing screens enters the lower portion of the instrument where the intakes for the OsmoSampler and FLOCS are located. These two experiments are constrained in a 7.15 inch high and 6.3 inch diameter space. The OsmoSampler has two 2ML1 ALZET membranes attached to the housing with two-part epoxy (Hysol ES1902). The ends of the distilled water and saturated salt (noniodized table salt, NaCl) reservoirs are sealed with a single O-ring and held in place with a setscrew. This configuration will pump 73 mL/y at 20°C. The pump is attached to 150 m of small-bore Teflon tubing that holds 170 mL (1.19 mm inside diameter and 2.0 mm outside diameter). The tubing was filled with 10% HCl for 5 days before it was rinsed with 18.2 MΩ water. Thus, this sampler can be deployed at 20°C for 2 y and maintain a continuous record for longer if the borehole temperature is cooler than 20°C.

The FLOCS experiment is attached to two pumps, each identical to the ones described above for the OsmoSampler (Figs. F2B, F4). Both pumps are attached via a T-connection to double the pump rate (146 mL/y at 20°C). These pumps are attached to 150 m of small-bore Teflon tubing that holds 170 mL and were prepared as above. At 20°C these pumps will fill the sample coil in ~14 months. The pumps will continue to work because of the amount of excess salt in the pump but will only preserve the last 14 months of fluid within the sample coil. The loss of the early portion of the record was deemed acceptable because the FLOCS is filled with about 50 mL of sterile seawater that must pass through the coils before borehole fluids are collected within the coils. As this sterile seawater enters the distilled water portion of the pump, it will decrease the pump rate but only minimally, even for a 2 y deployment. The inlet was attached to a syringe with 18.2 MΩ water until just before deployment.

The FLOCS experiment consists of a single unit that has four chambers. All of the parts were sterilized and materials packed with sterile tools in a hood. The chamber closest to the inlet contained two grids with autoclaved rock chips (1–2 mm thick and 5 mm × 5 mm) mounted on them facing out. These two grids were separated by autoclaved glass wool and 5 mm borosilicate glass beads. Rock chips were attached to the plastic grids using “5 min epoxy.” One grid has basalt glass in the bottom portion (AT11-20-4055-B6) and basalt above it (J2-246-R2). The other grid has basalt in the bottom portion (J2-244-R4) and olivine above it. Above the grids are three chambers filled with barite, olivine, and NanTroSEIZE Expedition 316 sediment, respectively. The latter was a clayey mud recovered at Site C0004, comprising material from a depth equivalent to the depth interval near the megasplay fault zone in Hole C0010A some 3 km away from Site C0004 (see Tobin et al., 2009; Saffer, McNeill, Byrne, Araki, Toczko, Eguchi, Takahashi, and the Expedition 319 Scientists, 2010). These materials were crushed from bulk rocks, sieved to <250 µm, and autoclaved. Teflon mesh screens were placed inside the cassette caps to prevent rock fragments from escaping the cassette. At sea, the FLOCS was filled with ~50 mL of sterile seawater. Additional seawater was added to remove air bubbles. During this process, some of the sediment from the end capsule escaped. The inlet was attached to a syringe with sterile seawater until just before deployment.

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