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Using ODP boreholes for studying sub-seafloor hydrogeology: Results from the first decade of CORK observations
Abstract
A system for sealing and instrumenting ODP boreholes was developed 10 years ago to allow interstitial fluids to be sampled, and natural fluid pressures and temperatures to be monitored over long periods of time. The capabilities of these CORK (Circulation Obviation Retrofit Kit) observatories have been expanded recently to allow monitoring and sampling in multiple isolated horizons, and to allow installations to be completed by wireline in previously drilled holes. To date, 16 hydrologic observatory sites have been established in ridge crest, ridge flank, and accretionary prism settings. Observations at these sites have provided precise constraints on the primary driving forces for, and thermal consequences of, sub-seafloor fluid flow caused by tectonic consolidation and thermal buoyancy. Deep in accretionary prisms, high formation pressures have been observed, confirming that plate boundary faults possess little strength. In young ocean crustal settings, surprisingly low lateral temperature and pressure gradients have been documented, implying that the extrusive rocks of the oceanic crust permit efficient fluid, heat, and chemical transport over distances of many kilometres. CORK observations have also revealed pressure variations and associated fluid flow resulting from co-seismic plate deformation, and from tidal, oceanographic, and barometric loading of the seafloor. The characteristics of the formation response to seafloor loading provide constraints on elastic and hydrologic properties, and allow quantitative estimates of crustal strain to be made from tectonic-strain-related pressure transients. Strain events have been observed up to 150 km away from several seismogenic dislocations along transform and seafloor spreading plate boundaries.
... Around 20 years ago, the scientific community started to use borehole observatories, so-called CORKs (Circulation Obviation Retrofit Kits), which are installed inside submarine boreholes, and which allow the re-establishment and monitoring of in situ con- 10 ditions (see summary in Davis and Becker, 2001). The key principle as well as the main objective is to provide a hydraulic seal between the borehole environment and the overlying ocean water body (Fig. 1). ...
... seismic and aseismic slip, fluid flow events, and possible precursory phenomena, over a wide range of timescales and rates (e.g. Davis et al., 2001, (4) temperature anomalies associated with fluid flow episodes (Davis and Villinger, 2006) or as precursors to earthquakes (Johnson et al., 2000); and (5) transient changes in chemical composition or seepage rate (Brown et al., 2005). The phe- 5 nomena have in common that they are episodic in nature, and time series data are the only feasible way of increasing our understanding of them. ...
... Davis et al., 2001, (4) temperature anomalies associated with fluid flow episodes (Davis and Villinger, 2006) or as precursors to earthquakes (Johnson et al., 2000); and (5) transient changes in chemical composition or seepage rate (Brown et al., 2005). The phe- 5 nomena have in common that they are episodic in nature, and time series data are the only feasible way of increasing our understanding of them. Nonetheless, most boreholes are still left uninstrumented, which is a major loss for the scientific community. ...
Seafloor drill rigs are remotely operated systems that provide a cost effective means to recover sedimentary records of the upper
sub-seafloor deposits. Recent increases in their payload included downhole logging tools or autoclave coring systems. We here
report on another milestone in using seafloor rigs: the development and installation of shallow borehole observatories.
Three different systems have been developed for the MARUM-MeBo seafloor drill, which is operated by MARUM, University of Bremen,
Germany. A simple design, the MeBoPLUG, separates the inner borehole from the overlying ocean by using o-ring seals at the conical
threads of the drill pipe. The systems are self-contained and include data loggers, batteries, thermistors and a differential pressure
sensor. A second design, the so-called MeBoCORK, is more sophisticated and also hosts an acoustic modem for data transfer and, if
desired, fluid sampling capability using osmotic pumps. Of these MeBoCORKs, two systems have to be distinguished: the CORK-A (A = autonomous)
can be installed by the MeBo alone and monitors pressure and temperature inside and above the borehole (the latter for
reference). The CORK-B (B = bottom) has a higher payload and can additionally be equipped with geochemical, biological or other
physical components. Owing to its larger size, it is installed by ROV and utilises a hotstab connection in the upper portion of the
drill string. Either design relies on a hotstab connection from beneath which coiled tubing with a conical drop weight is lowered to
couple to the formation. These tubes are fluid-saturated and either serve to transmit pore pressure signals or collect pore water in
the osmo-sampler. The third design, the MeBoPUPPI (Pop-Up Pore Pressure Instrument), is
similar to the MeBoCORK-A and monitors pore pressure and temperature in a self-contained manner. Instead of transferring data upon
command using an acoustic modem, the MeBoPUPPI contains a pop-up telemetry with Iridium link. After a predefined period, the data unit
with satellite link is released, ascends to the sea surface, and remains there for up to two weeks while sending the long-term data
sets to shore.
In summer 2012, two MeBoPLUGs, one MeBoCORK-A and one MeBoCORK-B were installed with MeBo on German RV Sonne in the
Nankai Trough area, Japan. We have successfully downloaded data from the CORKs, attesting that coupling to the formation worked
and pressure records were elevated relative to the seafloor reference. In the near future, we will further deploy the first two
MeBoPUPPIs. Recovery of all monitoring systems by ROV is planned for 2016.
... Around 20 years ago, the scientific community started to use borehole observatories, so-called CORKs (Circulation Obviation Retrofit Kits), which are installed inside submarine boreholes, and which allow the re-establishment and monitoring of in situ con- 10 ditions (see summary in Davis and Becker, 2001). The key principle as well as the main objective is to provide a hydraulic seal between the borehole environment and the overlying ocean water body (Fig. 1). ...
... seismic and aseismic slip, fluid flow events, and possible precursory phenomena, over a wide range of timescales and rates (e.g. Davis et al., 2001, (4) temperature anomalies associated with fluid flow episodes (Davis and Villinger, 2006) or as precursors to earthquakes (Johnson et al., 2000); and (5) transient changes in chemical composition or seepage rate (Brown et al., 2005). The phe- 5 nomena have in common that they are episodic in nature, and time series data are the only feasible way of increasing our understanding of them. ...
... Davis et al., 2001, (4) temperature anomalies associated with fluid flow episodes (Davis and Villinger, 2006) or as precursors to earthquakes (Johnson et al., 2000); and (5) transient changes in chemical composition or seepage rate (Brown et al., 2005). The phe- 5 nomena have in common that they are episodic in nature, and time series data are the only feasible way of increasing our understanding of them. Nonetheless, most boreholes are still left uninstrumented, which is a major loss for the scientific community. ...
Seafloor drill rigs are remotely operated systems that provide a cost effective means to recover sedimentary records of the upper sub-seafloor deposits. Recent increases in their payload included downhole logging tools or autoclave coring systems. We here report on another milestone in using seafloor rigs: the development and installation of shallow borehole observatories.
Three different systems have been developed for the MARUM-MeBo seafloor drill, which is operated by MARUM, University of Bremen, Germany. A simple design, the MeBoPLUG, separates the inner borehole from the overlying ocean by using o-ring seals at the conical threads of the drill pipe. The systems are self-contained and include data loggers, batteries, thermistors and a differential pressure sensor. A second design, the so-called MeBoCORK, is more sophisticated and also hosts an acoustic modem for data transfer and, if desired, fluid sampling capability using osmotic pumps. Of these MeBoCORKs, two systems have to be distinguished: the CORK-A (A = autonomous) can be installed by the MeBo alone and monitors pressure and temperature inside and above the borehole (the latter for reference). The CORK-B (B = bottom) has a higher payload and can additionally be equipped with geochemical, biological or other physical components. Owing to its larger size, it is installed by ROV and utilises a hotstab connection in the upper portion of the drill string. Either design relies on a hotstab connection from beneath which coiled tubing with a conical drop weight is lowered to couple to the formation. These tubes are fluid-saturated and either serve to transmit pore pressure signals or collect pore water in the osmo-sampler. The third design, the MeBoPUPPI (Pop-Up Pore Pressure Instrument), is similar to the MeBoCORK-A and monitors pore pressure and temperature in a self-contained manner. Instead of transferring data upon command using an acoustic modem, the MeBoPUPPI contains a pop-up telemetry with Iridium link. After a predefined period, the data unit with satellite link is released, ascends to the sea surface, and remains there for up to two weeks while sending the long-term data sets to shore.
In summer 2012, two MeBoPLUGs, one MeBoCORK-A and one MeBoCORK-B were installed with MeBo on German RV Sonne in the Nankai Trough area, Japan. We have successfully downloaded data from the CORKs, attesting that coupling to the formation worked and pressure records were elevated relative to the seafloor reference. In the near future, we will further deploy the first two MeBoPUPPIs. Recovery of all monitoring systems by ROV is planned for 2016.
... Around 20 years ago, the scientific community started to use borehole observatories, so-called CORKs, which were installed inside submarine boreholes, and which allowed the re-establishment and monitoring of in situ conditions (see summary in Davis and Becker, 2001). The key principle as well as the main objective is to provide a hydraulic seal between the borehole environment and the overlying body of water body (ocean) (Fig. 1). ...
... seismic and aseismic slip, fluid flow events, and possible precursory phenomena, over a wide range of timescales and rates (e.g. Davis and Becker, 2001;; (4) temperature anomalies associated with fluid flow episodes (Davis and Villinger, 2006) or as precursors to earthquakes (Johnson et al., 2000); and (5) transient changes in the chemical composition or the seepage rate (Brown et al., 2005). The phenomena have in common that they are episodic in nature, and time series data are the only feasible way of increasing our understanding of them. ...
Seafloor drill rigs are remotely operated systems that provide a cost-effective means to recover sedimentary records of the upper sub-seafloor deposits. Recent increases in their payload included downhole logging tools or autoclave coring systems. Here we report on another milestone in using seafloor rigs: the development and installation of shallow borehole observatories.
Three different systems have been developed for the MARUM-MeBo (Meeresboden-Bohrgerät) seafloor drill, which is operated by MARUM, University of Bremen, Germany. A simple design, the MeBoPLUG, separates the inner borehole from the overlying ocean by using o-ring seals at the conical threads of the drill pipe. The systems are self-contained and include data loggers, batteries, thermistors and a differential pressure sensor. A second design, the so-called MeBoCORK (Circulation Obviation Retrofit Kit), is more sophisticated and also hosts an acoustic modem for data transfer and, if desired, fluid sampling capability using osmotic pumps. In these MeBoCORKs, two systems have to be distinguished: the CORK-A (A stands for autonomous) can be installed by the MeBo alone and monitors pressure and temperature inside and above the borehole (the latter for reference); the CORK-B (B stands for bottom) has a higher payload and can additionally be equipped with geochemical, biological or other physical components. Owing to its larger size, it is installed by a remotely operated underwater vehicle (ROV) and utilises a hot-stab connection in the upper portion of the drill string. Either design relies on a hot-stab connection from beneath in which coiled tubing with a conical drop weight is lowered to couple to the formation. These tubes are fluid-saturated and either serve to transmit pore pressure signals or collect porewater in the osmo-sampler. The third design, the MeBoPUPPI (Pop-Up Pore Pressure Instrument), is similar to the MeBoCORK-A and monitors pore pressure and temperature in a self-contained manner. Instead of transferring data on command using an acoustic modem, the MeBoPUPPI contains a pop-up telemetry with iridium link. After a predefined period, the data unit with satellite link is released, ascends to the sea surface, and remains there for up to 2 weeks while sending the long-term data sets to shore.
In summer 2012, two MeBoPLUGs, one MeBoCORK-A and one MeBoCORK-B were installed with MeBo on RV Sonne, Germany, in the Nankai Trough area, Japan. We have successfully downloaded data from the CORKs, attesting that coupling to the formation worked, and pressure records were elevated relative to the seafloor reference. In the near future, we will further deploy the first two MeBoPUPPIs. Recovery of all monitoring systems by a ROV is planned for 2016.
... Most mid-ocean ridge flank and ocean basin basement is buried under thick, impermeable layers of sediment that significantly restrict sampling opportunities. However, Circulation Obviation Retrofit Kit (CORK) observatories (Davis et al., 1992;Edwards et al., 2011) affixed to Ocean Drilling Program (ODP) and Integrated Ocean Drilling Program (IODP) boreholes (Davis and Becker, 2001;Fisher et al., 2005) offer access to perform measurements and experiments in situ or collect crustal fluids. Fluids within the basement rock can be channeled up through the sediment horizon via fluid delivery lines and collected from sampling ports at the seafloor via submersible (Cowen et al., 2003;Huber et al., 2006;Cowen et al., 2012;Edwards et al., 2012;Lin et al., 2012;Nigro et al., 2012;Jungbluth et al., 2013). ...
To expand investigations into the phylogenetic diversity of microorganisms inhabiting the subseafloor biosphere, basalt-hosted crustal fluids were sampled from Circulation Obviation Retrofit Kits (CORKs) affixed to Holes 1025C and 1026B along the Juan de Fuca Ridge (JdFR) flank using a clean fluid pumping system. These boreholes penetrate the crustal aquifer of young ocean crust (1.24 and 3.51 million years old, respectively), but differ with respect to borehole depth and temperature at the sediment-basement interface (147 m and 39°C vs. 295 m and 64°C, respectively). Cloning and sequencing of PCR-amplified small subunit ribosomal RNA genes revealed that fluids retrieved from Hole 1025C were dominated by relatives of the genus Desulfobulbus of the Deltaproteobacteria (56% of clones) and Candidatus Desulforudis of the Firmicutes (17%). Fluids sampled from Hole 1026B also contained plausible deep subseafloor inhabitants amongst the most abundant clone lineages; however, both geochemical analysis and microbial community structure reveal the borehole to be compromised by bottom seawater intrusion. Regardless, this study provides independent support for previous observations seeking to identify phylogenetic groups of microorganisms common to the deep ocean crustal biosphere, and extends previous observations by identifying additional lineages that may be prevalent in this unique environment.
... Despite the presumed pervasiveness of the basalthosted deep subsurface biosphere, a thick layer of sediment that significantly restricts sampling opportunities covers much of the oceanic basement of the mid-ocean ridge flanks and ocean basins. However, seafloor instrumentation platforms known as Circulation Obviation Retrofit Kit (CORK) observatories (Davis et al., 1992;Edwards et al., 2011) affixed to the Ocean Drilling Program (ODP) and Integrated Ocean Drilling Program (IODP) boreholes (Davis and Becker, 2001;Fisher et al., 2005a) provide a rare opportunity to conduct in situ geophysical studies and sample fluids from the sediment-covered basement rock. By channeling fluids through dedicated microbiological and geochemical sampling lines, natural crustal fluids originating from the deep subsurface can be retrieved at the seafloor for subsequent interrogation. ...
Despite its immense size, logistical and methodological constraints have largely limited microbiological investigations of the subseafloor basement biosphere. In this study, a unique sampling system was used to collect fluids from the subseafloor basaltic crust via a Circulation Obviation Retrofit Kit (CORK) observatory at Integrated Ocean Drilling Program borehole 1301A, located at a depth of 2667 m in the Pacific Ocean on the eastern flank of the Juan de Fuca Ridge. Here, a fluid delivery line directly accesses a 3.5 million years old basalt-hosted basement aquifer, overlaid by 262 m of sediment, which serves as a barrier to direct exchange with bottom seawater. At an average of 1.2 × 10(4) cells ml(-1), microorganisms in borehole fluids were nearly an order of magnitude less abundant than in surrounding bottom seawater. Ribosomal RNA genes were characterized from basement fluids, providing the first snapshots of microbial community structure using a high-integrity fluid delivery line. Interestingly, microbial communities retrieved from different CORKs (1026B and 1301A) nearly a decade apart shared major community members, consistent with hydrogeological connectivity. However, over three sampling years, the dominant gene clone lineage changed from relatives of Candidatus Desulforudis audaxviator within the bacterial phylum Firmicutes in 2008 to the Miscellaneous Crenarchaeotic Group in 2009 and a lineage within the JTB35 group of Gammaproteobacteria in 2010, and statistically significant variation in microbial community structure was observed. The enumeration of different phylogenetic groups of cells within borehole 1301A fluids supported our observation that the deep subsurface microbial community was temporally dynamic.The ISME Journal advance online publication, 12 July 2012; doi:10.1038/ismej.2012.73.
... Decollement initiation results from a combination of factors: low intrinsic friction coefficient [16], removal of grain contact cement [17] and pore pressure cycling [18][19][20][21]. Multiple level pore pressure monitoring is going on in two holes equiped with ACORKs (Advanced Circulation Obviation Retrofit Kit) [15,22]. ...
Studying the Japanese Trenches, and particularly the Nankai subduction has been one objective of French-Japanese bilateral cooperation for nearly 20 years, notably within the Kaiko (and SFJ) projects. Work done within this framework has contributed to our understanding of deformation processes in subduction zones. Deep riser drilling of the subduction seismogenic zone is now a major objective for the international scientific community, undertaken within the framework of IODP. The Nankai subduction zone is among the primary targets (NanTroSEIZE Complex Drilling Proposal). We wish to pursue bilateral cooperation as a component of the NanTroSEIZE international project.
... Borehole packer tests in the seafloor have been relatively short in terms of pumping time, have virtually all been restricted to single-hole experiments (testing only the near-borehole region), and have not been particularly effective at delineating the distribution of properties. The development over the last 15 years of pressure-tight, subseafloor observatories ("CORKs") comprises a major advance in marine hydrogeologic studies (Davis and Becker 2002b;Davis et al. 1992a). These systems allow thermal, pressure, and chemical disturbances associated with drilling to dissipate, and provide monitoring and sampling points for subsequent experiments. ...
Marine hydrogeology is a broad-ranging scientific discipline involving the exploration of fluid-rock interactions below the seafloor. Studies have been conducted at seafloor spreading centers, mid-plate locations, and in plate- and continental-margin environments. Although many seafloor locations are remote, there are aspects of marine systems that make them uniquely suited for hydrologic analysis. Newly developed tools and techniques, and the establishment of several multidisciplinary programs for oceanographic exploration, have helped to push marine hydrogeology forward over the last several decades. Most marine hydrogeologic work has focused on measurement or estimation of hydrogeologic properties within the shallow subsurface, but additional work has emphasized measurements of local and global fluxes, fluid source and sink terms, and quantitative links between hydrogeologic, chemical, tectonic, biological, and geophysical processes. In addition to summarizing selected results from a small number of case studies, this paper includes a description of several new experiments and programs that will provide outstanding opportunities to address fundamental hydrogeologic questions within the seafloor during the next 20-30 years.
... The CORK program has been remarkably successful in demonstrating the feasibility of operating and maintaining a long-term seafloor observatory. It has provided important new scientific insight into many aspects of fluid flow within oceanic crust [4][5] [6][7] [8], arguably one of the most important processes involved in the transfer of mass and energy between the ocean and solid earth. A CORK installation (Fig. 5) includes a sensor instrumentation package that typically consists of a data logger, batteries, a thermistor string, one or more pressure gauges at various formational levels, and a reference pressure gauge at the seafloor. ...
Communication underwater is severely limited when compared to communications in air because water is essentially opaque to electromagnetic radiation except in the visible band. Even in the visible band, light penetrates only a few hundred meters in the clearest waters and much less in waters made turbid by suspended sediment or high concentrations of marine life. Consequently, acoustic techniques have been developed for underwater communication systems and now represent a relatively mature and robust technology. Acoustic systems are capable of long range communication, but offer limited data rates and significant latency (due to the speed of sound in water). We are developing an optical communication system that complements and integrates with existing acoustic systems resulting in an underwater communications capability offering high data rates and low latency when within optical range combined with long range and robustness of acoustics when outside of optical range. Amongst a wide array of applications, this combination of capabilities will make it possible to operate self-powered ROVs from support vessels or platforms without requiring a physical connection to the ROV. Such a capability will help simplify operations and potentially reduce costs through the use of less capable surface vessels. New deployment strategies may offer game-changing opportunities within all areas of undersea activities. For example, rapid event response will be enhanced and repair and maintenance of the emerging ocean observatory infrastructure will become more cost effective. Such through-water communications will likewise enable exchange of large data files from fixed sensors using AUVs (or ROVs) as data mules, shuttling real-time video from untethered vehicles for inspection, identification, and other related operations. Interconnectivity for dense arrays of underwater sensors without the need for expensive and difficult to install undersea cables is also possible. An unmanned batter-
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y operated vehicle, dedicated to a subsea node, that can be wirelessly operated though a combination of acoustic and optical communications, will be an important asset for both scientific exploration and commercial applications. We have demonstrated robust multi-point, low power omnidirectional optical communications over ranges of 100 meters at data rates up to 10 mega bits per second using a few tens of Watts of battery power with small, inexpensive transmitters and receivers. During the next few years, we will be exploring applications of this new technology directly in support of ongoing science and engineering programs. High-speed underwater optical communication is an enabling technology that has many potential applications in a range of environments from the deep sea to coastal waters. This development effort will enhance infrastructure for scientific research and commercial use by providing technology to efficiently communicate between surface vessels, underwater vehicles and seafloor infrastructure.
Sampling of sedimentary and crustal formations across rifted continental margins has long been a priority of DSDP, ODP, and other scientific ocean drilling. Recent results of drilling and related geophysical surveys across several margin segments in the North Atlantic have revealed that continents break apart in two fundamentally different ways. Volcanic margins form when rapid mantle upwelling produces a large amount of melt just prior to and during rifting. On non-volcanic margins, slow rates of rifting the continental crust expose regions of serpentinized mantle with little evidence of melting. Sampling, however, has thus far been restricted to regions of thin sediment cover, which has limited our ability to study the full range of rifted margin evolution. The next phase of scientific drilling will have enhanced capabilities that will allow drilling of both shallow- and deep-water basins, including those with thick sediments with hydrocarbon potential, such as the outer Grand Banks and Scotian margins. To make this a reality, it will be essential to combine both industry and academic interests and work to ensure continued Canadian participation.
Investigations of microbial life inside of the deep seafloor and most reviews on the topic have focused on sediments and largely ignore the prospect of a biosphere inside the basaltic crust underlying the global system of ocean basins. This is despite the potential global importance of biogeochemical cycling that may be occurring in situ within the uppermost igneous ocean crust; a location that is predicted to be one of the most habitable subsurface environments due to its porosity, hydrothermal circulation, and expected chemical disequilibria. Sedimentation processes occurring over geologic time scales cause a majority of the global seafloor to be covered by thick and relatively impermeable blankets that prevent access to the underlying basaltic seafloor. As a result, studies of microorganisms inside the basaltic crust have traditionally been restricted to the exposed seafloor or to locations where hydrothermal fluids exiting the seafloor act as “windows” into the subsurface. However, these traditional methods for observing basaltic rock seafloor microorganisms are inadequate because ocean crust is hydrogeologically active until up to ~65 million years old and a majority of flow is likely to occur over long time scales and deep within the sediment-covered basement. Seafloor observatories that penetrate through sediments and into basement rock provide the infrastructure needed to collect samples from one of the planet’s most remote environments. The broad goals of this study were to estimate the concentrations of microbial biomass and explore the microbial diversity in anoxic, deep subseafloor crustal fluids.
Building on the first characterizations of microbial life in the aging ocean basement, discrete fluid samples were collected and analysed here from new borehole observatories that are the first to incorporate dedicated stainless steel or Teflon-coated fluid delivery lines running along the exterior of the reactive iron casing. Biofouling-resistant materials used during the construction of the seafloor observatory fluid delivery lines permit collection of pristine samples that can be used for estimation of the in situ microbial biomass and reveal a range of cellular abundances that are, on average, roughly an order of magnitude lower that those found in bottom seawater. The cellular abundances reported here will help to constrain estimates of biomass inside the global seafloor and elucidate partitioning between the basaltic crustal and marine sediment communities, and furthermore, underscore the difficulties associated with collecting uncontaminated samples from the deep subsurface.
Sampling from a combination of older and newer borehole observatories has revealed novel microbial diversity and community structure from the seafloor that is distinct from overlying sediments and varies with the alteration state of the basement fluids. Microorganisms detected were largely from uncultivated groups, which means one can only speculate about the metabolic lifestyle for these organisms; however, comparisons to distant relatives indicate that a combination of autotrophic and heterotrophic lifestyles and active iron- and sulfur-cycling processes are present in the deep subseafloor. Temporal variation over annual timescales in the types of microorganisms collected from a single borehole observatory was observed and is the first instance of microbial community turnover observed in the deep subseafloor. A distinct bacterial lineage of Firmicutes first retrieved in 1998 during the first study of this kind was detected here again from a neighboring borehole location, which is consistent with the inferred hydrogeologic connectivity of the system and implies that the subseafloor crust likely has some permanent and widespread residents. Phylogenetic groups of microorganisms identified here extend previous observations by identifying additional lineages that may truly exist in the deep subseafloor, and provide a foundation for future studies exploring important topics relating to the community metabolic potential and contribution to active global geochemical cycling.
In 2001, we revisited thickly sedimented 5.9 Ma crust on the southern flank of the Costa Rica Rift for wireline re-entry of two important ocean crustal boreholes, Holes 504B and 896A, more than 8 years after they were last drilled in 1993. Here we report borehole temperatures measured in both holes within casing through the sediment sections and then into open hole in uppermost basement, as well as a video log from the upper basement section of Hole 896A. Since it first penetrated into oceanic basement in 1979, Hole 504B has been known for downhole flow of ocean bottom water into uppermost basement that was initially strong (~100 m/h) but then waned; our temperature data indicate a very slow lingering downflow at 0.4 m/h. The pressure differential driving this slow flow was determined to be 11-12 kPa from pressure data acquired when the hole was sealed by our wireline installation of a long-term hydrological observatory. The combination of the flow rate and the pressure differential constrains an estimate for the average permeability of the upper basement section in Hole 504B of 1-5×10-14 m2, a value similar to but slightly less than past determinations. In Hole 896A, which is located ~1 km away on a sediment-covered basement high, the temperature log indicated uphole flow of formation fluids at an average temperature of 57.8 °C and at a total rate of 12 m/h through casing; it also showed that at least three zones in uppermost basement produce fluids of different temperatures that contribute to this total flow. Although the associated pressure differential could not be measured in Hole 896A, estimates of average permeability of the section with the producing zones can be derived by assuming a differential of ~20 kPa similar to those measured in other ridge-flank sites in basement highs also known to produce formation fluids; estimated permeability values for uppermost basement in Hole 896A are on the order of 1-4×10-13 m2, again consistent with past packer determinations. The video log in Hole 896A provides unprecedented visual images that document the discrete nature of the permeability of the producing zones. It also suggests an abundance of bacterial floc within the hole that may be either flushed from the formation by the producing fluids or blooming within the hole in response to nutrients advected by the producing fluids.
We describe the response of a compressible submarine hydrologic monitoring instrument to formation pressure changes in low-diffusivity rock. The measured pressure depends on the frequency of the pressure signal, the hydraulic diffusivity, and the wellbore storage. The Nankai advanced circulation obviation retrofit kits (ACORKs) (offshore Japan) record tide-induced formation pressure changes with small amplitudes (25°). The pressure measurements occur in thick, homogeneous, compressible, low-permeability sediment, where in situ tidal pressure responses should approximate the seafloor tidal signal. A wellbore storage of 2 × 10−8 m3 Pa−1 can explain many of the observed tidal responses, given the hydraulic diffusivities of the monitored intervals. A reduced permeability around the wellbore of 1000-fold and a wellbore storage of 10−11 m3 Pa−1 can also reconcile the data. Our analysis suggests that ACORK screens in the Lower Shikoku Basin facies have a critical frequency on the order of 5 × 10−8 Hz (equivalent to a period of 250 days); higher-frequency formation pressure signals will be distorted in the pressure record. Within the Lower Shikoku Basin facies the time for this monitoring system to record 90% of an instantaneous pressure change is on the order of 10 d. We suggest that the ACORK instrument compliance contributes to, but does not fully explain, the small tidal amplitudes and large phase shifts recorded at the least permeable monitoring intervals.
This paper provides a review of 1989-2003 designs and operations of the 20 Circulation Obviation Retrofit Kit (CORK) long-term subseafloor hydrogeological observatories installed in 18 holes during the Ocean Drilling Program (ODP). The basic configura- tions of the four models of CORKs developed during the ODP pe- riod are summarized: the original single-seal CORK (14 installa- tions in 12 holes, 1991-2001) and three multilevel models, including the Advanced CORK or ACORK (2 installations, 2001), a wireline instrumented multipacker system or wireline CORK (2 installations, 2001), and the CORK-II (2 installations, 2002). The evolution of the scientific instrumentation installed in ODP CORKs and the history of postinstallation submersible operations are described. This instrumentation was provided by scientists with support of national ODP research funding, which also sup- ported the extensive submersible time devoted to postinstallation data downloads and instrument servicing. Although the purpose of this paper does not include a review of CORK scientific results, we offer some comments on scientific lessons learned during the ODP CORK effort. We describe the funding and engineering sup- port structure that held for the ODP CORK installations and close with some comments on the importance of engineering support for the Integrated Ocean Drilling Program goals involving long- term borehole observatories. We also provide a complete bibliog- raphy of CORK-related literature through 2004 and all of the data sets in digital form collected through 2003 from the six ODP CORK installations installed in either 1991 or 1996 near the Juan de Fuca Ridge, of which all but one are still in service.
The Integrated Ocean Drilling Program (IODP) began officially on October 1, 2003, the result of a decade of planning by the international scientific community. IODP represents the first-ever multiple platform scientific ocean drilling program, building upon successful single platform programs that began in the late 1960s. Dynamically positioned drilling vessels are being supplied by both the U.S. (riserless) and Japan (riser-equipped), while a European consortium is providing additional drilling capabilities as needed to address scientific objectives in shallow waters and in the high Arctic. The program's decadal science plan emphasizes process-based studies of the world's seismogenic zones beneath convergent margins, the sub-seafloor biosphere, gas hydrates, long- and short-term climate changes, the genesis and evolution of Large Igneous Provinces (LIPS), continental break-up and sedimentary basin formation, and a total penetration of the oceanic crust (the 21st Century Mohole). Central management of the program's technology will assure operational efficiencies, while at the same time providing internationally distributed access to facilities both to store and to analyze cores. IODP is also committed to international partnerships, particularly in the installation, operation, maintenance, and monitoring of seafloor and sub-seafloor observatories.
Sampling of sedimentary and crustal formations across rifted continental margins has long been a priority of DSDP, ODP, and other scientific ocean drilling. Recent results of drilling and related geophysical surveys across several margin segments in the North Atlantic have revealed that continents break apart in two fundamentally different ways. Volcanic margins form when rapid mantle upwelling produces a large amount of melt just prior to and during rifting. On non-volcanic margins, slow rates of rifting the continental crust expose regions of serpentinized mantle with little evidence of melting. Sampling, however, has thus far been restricted to regions of thin sediment cover, which has limited our ability to study the full range of rifted margin evolution. The next phase of scientific drilling will have enhanced capabilities that will allow drilling of both shallow- and deep-water basins, including those with thick sediments with hydrocarbon potential, such as the outer Grand Banks and Scotian margins. To make this a reality, it will be essential to combine both industry and academic interests and work to ensure continued Canadian participation.
During the past decade, geologists have come to appreciate the
interconnectedness of hydrologic, tectonic, thermal, and geochemical
processes operating within the Earth's continental crust [Oliver, 1992].
This has led to a new geologically-based conceptual model of hydrology
which is crustal-scale and is centered in plate tectonics theory (Fig.
1). From a geological perspective, the tectonic and thermal processes
which drive plate motion are also responsible, either directly or
indirectly, for inducing fluid motion across and through the continents.
Supporting evidence for this emerging paradigm is based on observations
of pervasive rock-water interactions associated with geologic processes
as diverse as the chemical alteration of crustal rocks [Shelton et al,
1992; Elliott and Aronson, 1993; McManus and Hanor, 1993; Ague, 1991,
1994], devolatilization of minerals during burial and consequent
metamorphism [Cox and Etheridge, 1989], the formation of energy and
mineral deposits [Garven et al, 1993; and Cathles et al, 1993],
remagnitization of ancient sedimentary rocks [McCabe and Elmore, 1989],
the tectonic deformation of sedimentary basins [Oliver 1992, Ge and
Garven, 1992], and the regulation of global climate [Caldeira et al,
1993, Kerrick and Caldeira, 1993, 1994]. This paper summarizes the many
recent lines of theoretical, laboratory, and field evidence from diverse
disciplines within the Earth Sciences supporting this emerging view of
crustal-scale hydrology. Evidence for two types of long-distance fluid
migration are highlighted: vertical pore water movement through
crystalline rocks to depths greater than six km and lateral groundwater
movement through sedimentary basins over hundereds of km. Also
emphasized are the many driving mechanisms on fluid motion which are not
typically considered in water quality and water supply investigations.
Some geologic terms used in this paper, which may be unfamiliar to the
reader, are defined in geologic dictionaries [American Geologic
Institute, 1976].