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doi:10.2204/iodp.proc.336.108.2012

Introduction

Subseafloor borehole observatories (CORKs) have been used successfully for several decades to study hydrological and geochemical dynamics in deep oceanic crust (Becker and Davis, 2005; Fisher et al., 2011). Essentially, CORKs are instrumented experimental wells deployed in boreholes created through ocean drilling that consist of a series of pipes extending below the seafloor that house the instruments and sensors, seals at the seafloor and various depths to isolate intervals, and a wellhead protruding above the seafloor. Traditionally, CORKs were constructed from “low alloy” steel pipe. While this is relatively inconsequential for hydrological experiments, the corrosion of steel has potential undesirable effects for microbiological and biogeochemical studies. For example, corrosion of steel pipe leads to leaching of iron and other metals into the environment (Wheat et al., 2004), which changes the biogeochemistry of the crustal environment, potentially masking in situ iron cycling within the basement basalts.

Within the last decade, several CORKs on the Juan de Fuca Ridge flank in the northeastern Pacific Ocean have been instrumented with experiments for studying the microbiology of oceanic crust. These experiments include the use of nonreactive coated tubes for pumping fluids from basement formations as well as the deployment of colonization experiments within the boreholes (Cowen et al., 2012; Fisher et al., 2011, 2005; Orcutt et al., 2011; Smith et al., 2011). During Integrated Ocean Drilling Program (IODP) Expedition 327 to the Juan de Fuca Ridge flank, several new CORKs that were installed featured steel pipe that had been coated with epoxy resins to limit corrosion (Fisher et al., 2011). The decision to use coated steel was based, in part, on a series of experiments conducted to evaluate the leaching characteristics of alternative observatory construction materials (Orcutt et al., 2010). In particular, these experiments evaluated the release of carbon and nitrogen from various epoxy resins, as well as fiberglass pipe and other construction materials. Building on those experiences, during IODP Expedition 336 to the North Pond location on the western flank of the Mid-Atlantic Ridge, all borehole observatory materials placed with the formations of interest were composed of either epoxy-coated steel or fiberglass pipe—the first time that this material has been used in scientific ocean drilling (Expedition 336 Scientists, 2012). Furthermore, new plastic centralizers and strapping bands were also used to reduce the amount of metal materials within the observatory zones.

Here, we summarize all of the available results regarding the release of carbon, nitrogen, and iron from these alternative construction materials. Some of these data have been presented elsewhere (Orcutt et al., 2010) and are reproduced here with permission. We also discuss the fluorescence of various greases and lubricants used during observatory construction, as background fluorescence may obfuscate efforts to evaluate microbial abundances based on fluorescence of cells marked with DNA stains (Orcutt et al., 2011).

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