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doi:10.2204/iodp.proc.327.109.2011

Introduction

In the past several decades the scientific community has recognized the importance of fluid flow through the oceanic crust and the impact of this flow, coupled with biotic and abiotic reactions, on the physical, chemical, and biological evolution of the crust and the overlying oceans. These revelations stem indirectly from global data sets of heat flow, sediment thickness, basaltic alteration, pore water composition, and seawater-basalt laboratory studies (e.g., Alt, 2004; Edwards et al., 2005; Parsons and Sclater, 1977; Seyfried and Bischoff, 1979; Wheat et al., 2003b; Wheat and Mottl, 2004). However, each of these data sets is limited, and the goal of collecting pristine formation fluids from the basaltic crust and zones of hydrologic interest has been difficult to reach. Until recently, the only means of collecting such fluids was in open boreholes after drilling operations ceased; however, this tactic presented its own difficulties (e.g., Mottl and Gieskes, 1990; Gieskes and Magenheim, 1992; Magenheim et al., 1992, 1995).

The desire to elucidate crustal processes, define oceanic geochemical budgets, and investigate the subsurface biosphere harbored in oceanic crust has led to the development of fluid-sampling and experimental capabilities in subseafloor borehole observatories (“CORKs”) as an alternative to previous attempts (Davis et al., 1992). The basic concept behind a CORK is to drill into the hydrologic zone of interest, case the overlying material, seal the borehole from exchange with seawater, instrument the hydrologic zone, and monitor physical, chemical, and biological changes while the borehole recovers from disturbances induced during the drilling process and for natural variability thereafter.

The initial CORKs were deployed in 1990 during Ocean Drilling Program (ODP) Leg 139 at Sites 857 and 858 in Middle Valley on the Juan de Fuca Ridge (Davis, Mottl, Fisher, et al., 1992), which is a site of active high-temperature (264°C) hydrothermal venting (Butterfield et al., 1994; Cruse and Seewald, 2006). Since this initial deployment, CORKs have been deployed in a sedimented mid-ocean ridge and in the flanks of mid-ocean ridges and convergent margins during seven ODP legs and six Integrated Ocean Drilling Program (IODP) expeditions (Table T1; Fig. F1). Numerous scientific papers have been published based on data from these CORKs. Two papers in particular are of interest to the general scientific community. One is a compilation of first-order scientific results spanning hydrogeological, physical, and geochemical conclusions (Kastner et al., 2006). The other highlights the evolution of CORK design and physical sensors, presents methods of submersible operation, and provides an outlook for future work and funding pathways (Becker and Davis, 2005). This paper is also designed for a general audience but focuses on fluid-sampling capabilities and chemical sensors associated with CORK observatories during the past two decades.

The goal of this paper is to provide a framework for future scientists to design fluid-sampling and sensor schemes that best suit their immediate scientific concerns but that are flexible enough to accommodate unforeseen experiments and new fields of study. First, we present CORK engineering efforts as a continuum of development, generally following advances incorporated with the evolution of CORK sampling systems. We then focus on detailed fluid-sampling efforts, dividing those associated with seafloor-deployed systems from those deployed within the borehole (downhole systems). We present borehole efforts first because they are primarily focused on the central technology of continuous fluid samplers (OsmoSamplers) (Jannasch et al., 2004). In contrast, OsmoSamplers are just one of several different types of samplers and sensors deployed at the seafloor. Lastly, we present engineering works in progress that will advance sampling and analytical capabilities.

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