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Materials and methods

Construction of Expedition 336 CORK observatories

CORK assembly during Expedition 336 followed the basic plans used during previous expeditions (Fisher et al., 2011). For a more detailed outline of each observatory deployed during Expedition 336, see the operations for this expedition (Expedition 336 Scientists, 2012). In general, the lowermost portion of the CORK installation consisted of coated and perforated 6¾ inch outside diameter (OD) steel drill collars, which were coated on the outside and inside with Xylan (polytetrafluoroethylene [PTFE] fluoropolymer). During installation, tool marks on the exterior of the drill collars were covered with a coat of freshly prepared Alocit 28 epoxy paint (Fig. F1). Perforated steel pipe (5½ inch diameter) was connected to the drill collars and was the location of the miniscreens and OsmoSampler instruments (described in Edwards et al., 2012). This section of perforated casing was precoated with either Tuboscope TK-34XT on the inside and outside or TK-34XT on the inside with Amerlock epoxy paint (white) on the outside. Tool marks were coated with Alocit 28 epoxy paint. Slotted (vertical slots of 0.020 inches width × 2.75 inches length, 5% open area) and unslotted 4½ inch OD fiberglass casing was made of an aromatic amine curing formulation. A similar aromatic amine–cured fiberglass from STAR FiberGlassSystems was previously tested for carbon and nitrogen leaching characteristics (Orcutt et al., 2010). Combination swellable and inflatable rubber packers were used to isolate hydrologic zones of interest. The combination packer swellable material was Freecap/​Xtracap that had also been examined previously for carbon and nitrogen leaching (Orcutt et al., 2010). Any exposed steel below the packer element (combo packer mandrel, landing seat, etc.) was coated with Amerlock epoxy paint during deployment in the moonpool on the R/V JOIDES Resolution. On the exterior of the casing, plastic-coated umbilical lines were held in place with Nylon 11 Smartbands and either plastic (acetal polyoxymethylene) centralizers (for fiberglass casing) or Xylan-coated steel centralizers (for coated steel casing). Steel-to-steel connections were lubricated and sealed with Loctite 30561 thread sealant with PTFE. Fiberglass-to-steel connections were lubricated and sealed with APT 3 thread sealant. Fiberglass-to-fiberglass connections were lubricated and sealed with TF-15 grease (a black reprocessed PTFE fluorocarbon resin with molybdenum disulfide).

Leaching experiments

To examine the carbon and nitrogen release from the alternative borehole observatory materials used or considered during Expedition 336, samples of the materials were incubated in sterile seawater (Sigma S9148) for a period of up to 1 month at various temperatures. The temperatures used (4°C, room temperature [20–22°C], and/or 60°C) were chosen to approximate the range that borehole observatories would experience at either the Juan de Fuca Ridge flank (warmer) or North Pond (cooler) locations. The materials that were tested include the following:

  • Tuboscope Coat TK-2 (liquid phenolic-based coating, TAM International, Houston, Texas, USA)
  • Tuboscope Coat TK-34XT (modified epoxy-phenolic liquid coating, TAM International)
  • Tuboscope Coat TK-69 (epoxy-modified phenolic liquid coating, TAM International)
  • Tuboscope Coat TK-805 (phenolic Novolac [powder] coating, TAM International)
  • Amerlock 400 epoxy paint (Ameron International)
  • Alocit 28 epoxy paint (15 standard grey RAL7004 and hardener, A&E Systems)
  • Xylan coat (a PTFE fluoropolymer, Whitford)
  • Aliphatic-cured epoxy fiberglass (STAR FiberGlassSystems, San Antonio, Texas, USA)
  • Anhydride-cured epoxy fiberglass (STAR FiberGlassSystems)
  • Aromatic amine–cured epoxy fiberglass (STAR FiberGlassSystems)
  • Standard inflatable rubber packer polymer (TAM International)
  • Freecap FSC-11 swellable packer polymer (TAM International)
  • Bestolife 60% lead-base dope (60% pure metallic lead in a petroleum grease mixture with nonmetal additives; Bestolife Corporation, Dallas, Texas, USA)
  • Bestolife ZN 50 dope (50% zinc in a petroleum grease mixture; Bestolife Corporation)
  • Bestolife Eco-Sil dope (silicone and titanium oxide mixture; Bestolife Corporation)
  • APT 3 thread sealant (APT Sealant, Wichita, Kansas, USA)
  • Loctite 30561 thread sealant with PTFE (Teflon, Loctite Corporation)
  • Dow Corning Compound 111 valve lubricant and sealant (a polydimethlysiloxane, Dow Corning Corporation)
  • TF-15 grease (a black reprocessed PTFE fluorocarbon resin with molybdenum disulfide, Jet-Lube of Canada Ltd.)

Leaching experiments for the TAM International Tuboscope-coated steel products and packer materials were conducted in acid-washed and baked (450°C, to remove organics) 60 mL glass I-Chem vials with Teflon-lined screw caps (Fig. F2). Prior to incubation, samples were washed in dilute detergent and rinsed thoroughly with deionized water, followed by rinsing in 100% ethanol and air-drying. Coated steel samples were incubated in 35 mL of sterile seawater, which covered the lower 3½ inches of the piece and avoided the end that had an internal threaded hole into the steel. Strips of the packer material were cut (1¼ cm wide × 10 cm long) to fit into the incubation vessels (Fig. F2B). Samples were briefly cleaned as described above, with the exception of the Freecap FSC-11 packer material, which immediately soaked up any liquid upon contact. Materials were incubated at temperature for 1 h and then transferred with sterile tools to a fresh vial prepared at the appropriate temperature. This procedure was repeated after 1 day, 1 week, and 1 month of incubation.

Leaching experiments with the Amerlock 400 epoxy paint were conducted in two different ways. In the first instance, steel coupons (60 cm2 surface area) were coated with Amerlock applied by the vendor with heating. The coated coupons were rinsed as described above, then incubated in 50 mL of sterile seawater in large-mouth glass jars (acid-washed and baked) sealed with a plastic lid (care was taken to avoid contact of the seawater with the lid) (Fig. F3). These samples were also incubated for periods of 1 h, 1 day, 1 week, and 1 month as described above. Leaching tests with the Xylan coating were performed in a similar manner. In the second instance, fresh Amerlock epoxy paint (roughly 500 µL or 0.2 g material) was injected into the base of 8 mL glass vials (acid-washed and baked) with plastic screw cap lids and allowed to harden overnight (Fig. F2C). Subsequently, 5 mL of sterile seawater was added to the vial for the incubation for 1 day and 1 month time periods. Leaching experiments with the Alocit 28 epoxy paint, sealants (i.e., TF-15 grease, Loctite 30561, APT 3, and Dow Corning Compound 111), and dopes (i.e., 60% lead-base, ZN 50, and Eco-Sil) were conducted in a similar manner, although the TF-15 grease, APT 3 thread sealant, and dopes were smeared on the inside of the vial instead of deposited at the bottom (Fig. F2C). Each dope/​temperature condition was run in duplicate, whereas the grease and sealant experiments were run in triplicate.

Fiberglass leaching experiments were conducted on small pieces (~4 cm2 surface area) of pipe that were cut using an ultralow-speed diamond wafering blade rock saw (Buehler) with deionized water as a cutting fluid (Fig. F2D, F2E). Pieces were washed in dilute detergent and rinsed thoroughly with deionized water, followed by rinsing in 100% ethanol and air-drying. Pieces were incubated in 14 mL of sterile seawater (as above) in acid-washed 20 mL glass vials with Teflon-lined screw caps (taking care to keep incubation fluids from contacting the lid as much as possible) for 1 month.

In all experimental incubation set ups, “control” samples that did not contain sample material were incubated and sampled in parallel to correct for any changes not due to material leaching. At the end of all incubations, sample fluid was frozen until subsequent dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) analysis. DOC and TDN concentrations were measured in the Joye Geochemistry Analytical Laboratory at the University of Georgia (USA) according to published protocols (Weston and Joye, 2005). Briefly, 10 mL of fluid from the leaching experiments was transferred into acid-washed, combusted autosampler vials. DOC and TDN concentrations were determined on a Shimadzu TOC-V with an ASI-V autosampler and TNM-1 total nitrogen unit. The lower limits of detection were roughly 1 and 0.1 parts per million for DOC and TDN, respectively. Results for the fiberglass and Tuboscope product leaching experiments have been reported previously (Orcutt et al., 2010) and are reproduced here with permission.

Fluorescence tests with pipe dopes and sealants

To evaluate the fluorescence properties of the pipe dopes and sealants used in observatory construction, select samples were mixed with fluorescent dyes commonly used for DNA-based assays (propidium iodide and SYTO 9 nucleic acid dyes, Invitrogen) and evaluated by epifluorescence microscopy. Briefly, either a smear of dope was placed directly on a glass slide and covered with 10 µL of 1:500 diluted dye, or 0.1 g dope was first mixed with 1 mL of double deionized water, sonicated in a bath for 10 min (FS20 sonicator, Fisher Scientific), mixed with 1 mL of 1:500 diluted dye, and then filtered through a 0.2 µm mesh black Nucleopore polycarbonate membrane filter (Whatman) supported by a 0.8 µm mesh AAWP membrane filter (Millipore). Fluorescence was then evaluated using either an Axiostar Plus epifluorescent microscope (Carl Zeiss Microscopy) equipped with filter set 38HE (470 nm centered excitation in a 40 nm window, 525 nm centered emission in a 50 nm window, and 495 nm beam splitter) or a TCS SPE confocal microscope (Leica Microsystems) using a 488 nm solid-state laser for excitation and emission wavelengths of 495–550 nm for SYTO 9 and 555–700 nm for propidium iodide. The compounds tested included dope commonly used on drill collars on the JOIDES Resolution (Bestolife 60% lead-base dope, Loctite 30561, and Dow Corning Compound 111).