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CORK-lite: Bringing legacy boreholes back to life

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Scientific Drilling, No. 14, September 2012 39
CORK-Lite: Bringing Legacy Boreholes Back to Life
by C. Geoffrey Wheat, Katrina J. Edwards, Tom Pettigrew, Hans W. Jannasch,
Keir Becker, Earl E. Davis, Heiner Villinger, and Wolfgang Bach
doi:10.2204/iodp.sd.14.05.2012
3URJUHVV5HSRUWV
Introduction
An essential aspect of the forty years of deep-sea scien-
tific drilling has been to maximize the scientific return
during each expedition while preserving samples for future
investigations. This philosophy also extends to borehole
design, providing the community with tens of cased legacy
boreholes that penetrate into the basaltic crust, each ripe for
future investigations of crustal properties and experiments
to determine crustal processes (Edwards et al., 2012a).
During Integrated Ocean Drilling Program (IODP)
Expedition 336 to North Pond on the western flank of the
Mid-Atlantic Ridge at 22qN, Hole U1383B (Fig. 1) was plan-
ned to be a deep hole, but was abandoned when a 14.75 -inch
tri-cone bit catastrophically failed at 89.9 meters below the
seafloor (mbsf ) (Expedition 336 Scientists, 2012). This
resulted in about 36 meters of open hole below casing, sim-
ilar to conditions within tens of legacy boreholes. Because
the overall experiment required a return to the “natural”
hydrologic state in basaltic basement, it was critical to seal
the hole to prevent a hydrologic “short circuit ”. Thus, a plan
emerged at sea to seal Hole U1383B with a simplified
Circulation Obviation Retrofit K it (CORK) termed
“CORK-Lite” that could be deployed by a remotely operated
vehicle (ROV) on a planned dive series five months later.
To prepare for this deployment, a standard ROV platform
that is used with CORKs was modified to be self-guiding in
the re-entry cone and deployed. The next step was to design
a CORK system that could seal the borehole, yet be physi-
cally manageable with an ROV, and be ready for shipping and
deployment within three months. Several key functional
aspects dictated the design of the new COR K-Lite (Table 1).
Design of CORK-Lite
The COR K-Lite has four major compo-
nents: the body with a seal, a removable
cap, a downhole instrument string, and a
borehole pressure monitoring instrument.
The body is a 4.9 -m-long 12 -inch pipe with a
landing seal ring that has a diameter of
19.5 inches that fits within the 32-inch
guide hole in the ROV plat form ( Figs. 2, 3).
The landing seal ring lands on and seals
in the 20-inch casing hanger. The body
has hooks to hang instruments, two valve
bodies that accept hydraulic connectors
closed in the horizontal position (Wheat
et al., 2011), two flanges (lifting wings) for
deployment that also serve to aid in moving
the body during ROV operations, and a
grooved top ring made of stainless steel to
insure a proper seal is achieved with the
cap. A re-movable “boot ” was designed to fit
the bottom of the body to protect it during
deployment and to prevent it from penetra-
ting into the sediment during free fall. In
addition, a lif ting bar assembly was fabrica-
ted that connects the body to a float pack-
age and eases handling by the ROV.
Figure 1. Location of IODP Sites drilled during Exp. 336 (North Pond) and ODP Hole 1074A
(duplicated from Expedition 336 Scientists, 2012). The CORK-Lite was deployed at Site
U1383. Bathymetry was provided by Schmidt-Schierhorn et al. (2012).
395A
U1382
U1384
(NP-1)
U1383
(NP-2)
1074A
-46°12' -46°10' -46°08' -46°06' -46°04' -46°02' -46°00'
-46°12' -46°10' -46°08' -46°06' -46°04' -46°02' -46°00'
22°54'
22°52'
22°50'
22°48'
22°46'
22°44'
22°42'
22°54'
22°52'
22°50'
22°48'
22°46'
22°44'
22°42'
-6000 -5500 -5000 -4500 -4000 -3500 -3000 -2500 -2000
m
km
0510
N
W
40 Scientific Drilling, No. 14, September 2012
3URJUHVV5HSRUWV
The downhole instrument string utilized components
from Exp. 336 (osmotic pumps, coils of small bore sample
tubing, support rods and various connectors) that were de-
signed for deployment within the 3-inch confines of the
Exp. 336 CORKs. With the larger diameter available to the
CORK-Lite, seven osmotic packages were coupled into one
unit (Fig. 5). These packages include standard, dissolved
gas, acid addition, enrichment, BOSS (fluid sampler that is
preser ved with R NA later for microbial-based analysis),
and microbial colonization experiments ( Jannasch et al.,
2004; Wheat et al., 2011; Orcutt et al., 2010). A frame was
designed to hold these packages, protect them during
The cap was designed to fit on the top of the body and seal
it using a rubber gasket ( Fig. 4). In case the borehole forma-
tion is over-pressured, four latching dogs are included.
These dogs are activated by a mechanical lever system that
forces the dogs in place through vertical motion of a floating
nut driven by a power screw with attached handle. A two -way
valve (closed in the horizontal position) is included in the
cap. This valve is necessary to equalize the pressure before
removing the cap if the borehole is under-pressured. A pad
eye is welded under the cap to at tach the downhole instru-
ment string.
Figure 2. The CORK- Lite body is lowered over the side of the R/V Maria S. Merian.
The boot is held in place with a tee handle and secured with a bungie. The lifting bar
assemblely is attached to the body with triple-strand polyproplyene rope and floats
above. Extra Alvin dive weights were attached to the hooks for faster descent.
Table 1. A list of design consideration of CORK-Lite.
t The CORK-Lite has to be installed using an ROV, with weight being balanced by flotation.
t The CORK-Lite body must be self-centering, fit within the 16-inch casing, robust enough to withstand ROV operations, and
extend ~2 m above the ROV platform for ease of ROV manipulations.
t The seal must apply for either an over-pressured or under-pressured system.
t Any negative differential pressure across the top seal cap must be vented prior to eventual removal of downhole instruments.
t Two valves and ports (for redundancy) must attach to and penetrate the body for pressure monitoring within the borehole.
t Any instrument string has to fit within the steel pipe used as the CORK-Lite body.
t For safety, the instrument package must reside within the casing; intakes for fluid sampling must extend into the open borehole
in an attempt to get “clean” borehole fluids free of possible artifacts from the steel casing and cement above.
Figure 3. Schematic of the CORK-Lite body during
free fall to the seafloor.
FLOATS
LIFTING BAR
ASSEMBLY
SAMPLING
VALVE BODY
INSTRUMENT
HANGER HOOK
PLUG BODY
323.8 mm
ø
(12.75 in)
495.3 mm
ø
(19.49 in)
LANDING/SEAL
RING
BOOT RELEASE
T-PULL PIN
BOOT
4.9 m
(192.1 in)
5.8 m
(228.3 in)
Scientific Drilling, No. 14, September 2012 41
deployment and recover y, and guide them into the
CORK-Lite body. These frame components have a
diameter of 10.75 inches, which easily fit through
the 12-inch CORK-Lite body (12-inch I.D.).
Because of borehole inst ability issues within other
CORKs, we placed the instrument package near
the bottom of the casing yet have the sample
intakes extend meters into the open portion of the
borehole. Intakes were protected with Tygon
tubing and attached to a strength member (rope)
and sinker bar. A weak link was positioned just
below the instrument package in case the bore-
hole is unstable and traps the sinker bar. Thus, the
instrument package can be recovered even if the
sinker bar becomes entombed.
The pressure monitoring device was developed
at the Pacific Geoscience Centre (Sidney, BC,
Canada), identical to most systems deployed on
CORK s today, including those deployed on IODP
Exp. 336 and previously on Exp. 327 and 328 (see
technical descriptions in Davis et al., 2010; Fisher
et al., 2011; Edwards et al., 2012b). The instrument
includes batteries, electronics, two absolute pres-
sure gauges (Paroscientific Model 8B-7000; one
to monitor the formation and the other to monitor
the sea floor), a data logger (set to sample pres-
sure and temperature every t wo minutes like
the Exp. 336 CORKs in IODP Holes U1382A and
U1383C), an underwater mateable connector
(Teledyne ODI), and a stainless steel line that con-
nects to an ROV-deployable hydraulic coupler that
fits in the valve package on the CORK-Lite body.
ROV Operations
Operations were conducted with the
U.S.-operated ROV Jason from the German
research vessel R/V Maria S. Merian during expe-
dition MSM 20/5. The ROV platform was inspected
on Jason dive J2-623 (20 April 2012). Before the
next dive the CORK-Lite body was deployed with
~770 lbs of flotation. During the second dive the
CORK-Lite was located, transported to the bore -
hole, and lowered into place. A black stripe was
painted on the body prior to deployment and used
as an indicator that the body was in the proper position. After
the subsequent dive the downhole instrument string was
deployed. The instrument string included (from bottom to
top) descent weights, a sinker bar, a 12-m-long three-strand
polyproplyene rope with a weak link and intakes that
extended 8 m from the instrument package, the instrument
package (seven OsmoSampler packages, and three
self-contained temperature recorders), a 50-m length of
3/8-inch spectra, the top plug, and flotation. T he instrument
string was located and installed, and the valves were closed.
Later in the dive program the pressure logger was attached,
and the data set that was retrieved indicated that the
CORK-Lite was sealed (Fig. 6).
Future Applications
The design, fabrication, and operational effort at Hole
U1383B illustrate the engineering potential to seal and
instrument any of the tens of legacy boreholes that have been
drilled into basement and cased through the sediment,
leaving tens to hundreds of meters (in some cases up to
1500 meters) of open borehole (Edwards et al., 2012a).
Figure 4. A CORK-Lite was successfully deployed and instrumented in IODP Hole
U1383B. The cap (silver material above the gray pipe) is secured to the body utilizing
the handle with a shor t piece of rope that originally was connected to flotation. T he
pressure logger rests on the ROV plat form and is connected to the CORK-Lite body.
Figure 5. The downhole instrument package is fabricated before connecting it to the
intake and ropes that space the package at the proper depth in the borehole. Seven
osmotic packages are arranged in a bundle.
42 Scientific Drilling, No. 14, September 2012
3URJUHVV5HSRUWV
Acknowledgements
We want to thank the engineering and operational staff
involved in IODP Exp. 336, the crew of the R /V Maria S.
Merian, and the team that operates the ROV Jason. Funding
was awarded from the Gordon and Betty Moore Foundation,
the German Science Foundation (DFG), and the National
Science Foundation ( NSF) through the STC Center for Dark
Energy Biosphere Investigations (C-DEBI) (0939564) and
individual research grants to CGW (OCE-0939564 and
1030061), KJE (OCE-1060634) and KB (OCE-0946795 and
1060855 for pressure-logging system). This is C-DEBI con-
tribution number 132.
References
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the basaltic ocean crust: Implications for chemolithoauto -
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Davis , E.E ., Becker, K., Pet tig rew, T., Carson, B., a nd MacDonald, R.,
1992 . CORK: A hydrologic seal and downhole obser vatory
for deep-ocean boreholes. In Davis, E.E., Mottl, M.J.,
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ment of borehole observator ies and exper iments during
IODP Exp. 3 36. Mid-Atla ntic R idge flank at North Pond.
Placing sensors, samplers,
and experiments in legacy
boreholes could address
a range of f undamental
questions about condi-
tions and processes within
igneous oceanic crust. For
example, the basaltic crus-
tal aquifer plays a sub-
stantial role in cooling the
Earth, regulating biogeo-
chemical cycles within the
oceans, and providing dif-
ferences in redox poten-
tials (i.e., bet ween oxidiz-
ing seawater and reducing
basaltic minerals) that
offer great potential for
abiotic and biologically-mediated electron transfer reactions
(Bach and Edwards, 2003; Fisher and Wheat, 2010). With
appropriate instrumentation in selected legacy boreholes,
we will be able to prov ide a better measure of the range of
biogeochemical processes w ithin the basaltic crust and the
global significance of these processes. Legacy boreholes can
serve other communities as well, for example, by providing
access for a range of sensor suites for geological and geo-
physical studies.
Because legacy boreholes are typically cased with
10.75-inch pipe or larger, they can accept a range of sensors
and instruments that typical CORKs cannot accept
(many limit internal instrument diameters to 3.5 inches).
Furthermore, there are a number of instrument suites de-
veloped by Schlumberger Limited that cannot be used in
typical IODP boreholes but could be used in legacy bore-
holes. Although the initial COR K-Lite did not include electri-
cal cables or an umbilical, futu re COR K-Lites could be mod i-
fied to include such connections that penetrate the cap for
seafloor interrogation of downhole sensors. Also, it is con-
ceivable to deploy swellable packers, baffles, and other
means to eliminate or minimize vertical fluid exchange
within the borehole, allowing one to examine specific geo-
logic or hydrologic horizons.
For some applications CORK-Lite provides an inexpen-
sive alternative. It is especially useful for boreholes with sin-
gle horizons, as it allows for the use of less armored and less
expensive umbilicals, and it eliminates the need for an inner
casing string or extensive wellhead structure. Furthermore,
deploying such systems into legacy boreholes is indepen-
dent from the drilling schedule. In some ways the COR K-Lite
is a rejuvenation of the original CORK concept (Davis et al.,
1992), but it is much more versatile. IODP Hole U1383B is
just the start! We envision future CORK-Lites that address a
range of scienti fic questions, utilizing a variet y of instru-
ments, sensors, and experiments.
00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00 03:00
44970
44980
44990
2930/Apr/2012
Pressure [kPa]
CORK 1383B
seaoor
formation
45000
On ROV platform at U1383C
Attached to U1383B
Figure 6. Pressure data from the CORK-Lite at IODP Hole 138 3B. Before the instrument was attached, both
sensors monitored bottom seawater on the ROV platform at Hole U1383C. After attachment, the two readings
are different, signifying that the borehole is sealed and under-pressured relative to bottom seawater.
Scientific Drilling, No. 14, September 2012 43
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Authors
C. Geoffrey Wheat, Global Undersea Research Unit,
University of Ala ska Fairba nks, P.O. Box 475, Mos s Land ing,
CA 95039, U.S.A ., e-mail: wheat@mbari.org
Katrina J. Edwards, Department of Biological Sciences,
Marine Environmental Biology Section, University of
Southern California, L os Angeles, CA 90089, U.S.A., e-mail:
kje@usc.edu
Tom Pettigrew, Pettigrew Engineering, 479 Nine Mile
Road, Milam, TX 75959, U.S.A., e-mail: pettigrew.engineer-
ing@windstream.net
Hans W. Jannasch, Monterey Bay Aquarium Research
Institute, 7700 Sandholdt Road, Moss Landing, CA 95039,
U.S.A., e-mail: jaha@mbari.org
Keir Becker, University of Miami, 4600 Rickenbacker
Causeway, Miami, FL 33149, U.S.A., e -mail: kbecker@
rsmas.miami.edu
Earl E. Davis, Pacif ic Geoscience Centre, Geological
Survey of Canada, 9860 West Saanich Road, Sidney, BC V8L
4B2, Canada, e-mail: edavis@nrcan.gc.ca.
Heiner Villinger and Wolfgang Bach, Department of
Geosciences, University of Bremen, Klagenfurter Strasse,
28359 Bremen, Germany, e-mail: vill@uni-bremen.de,
wbach@uni-bremen.de
... (B) Detail map of Expedition 301/327 field area on eastern flank of Juan de Fuca Ridge (modified from Fisher et al. (2008)). (C) Detail map of Expedition 336 Field area in North Pond (modified from Wheat et al. (2012)). measurements. ...
... A single-level CORK was deployed in Hole U1382A to monitor conditions in the upper 120 m of volcanic crust (Expedition 336 Scientists, 2012c), and three-level CORKs were deployed in Holes 395A (after removal of an old borehole observatory) and U1383C (Expedition 336 Scientists , 2012b,d). Hole U1382B was drilled and cased during Expedition 336, then left open for later instrumentation using a " CORK-lite " system deployed with a remotely operated vehicle (Expedition 336 Scientists, 2012c; Wheat et al., 2012). Data and samples from these systems will inform understanding of hydrogeologic, geochemical, and microbiological conditions in basement below and around North Pond in coming years. ...
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Basement formation pressures and temperatures were recorded from 1997 to 2017 in four sealed‐hole observatories in North Pond, an isolated ∼8 × 15 km sediment pond surrounded by thinly sedimented basement highs in 7–8 Ma crust west of the Mid‐Atlantic Ridge at ∼23°N. Two observatories are located ∼1 km from the southeastern edge of North Pond where sediment thickness is ∼90 m; the other two are ∼1 km from the northeastern edge where sediment thickness is 40–50 m. Sediments are up to 200 m thicker in the more central part of the pond. The borehole observations, along with upper basement temperatures estimated from seafloor heat flux measurements, provide constraints on the nature of low‐temperature ridge‐flank hydrothermal circulation in a setting that may be typical of sparsely sedimented crust formed at slow spreading ridges. Relative to seafloor pressures, basement formation pressures are modestly positive and increase with depth, except for a slight negative differential pressure in the shallowest 30–40 m in one northeastern hole. Although the observatory pairs are ∼6 km apart, the lateral pressure gradient in basement between them is very small. Formation pressure responses to seafloor tidal loading are consistent with high basement permeability that allows for vigorous low‐temperature circulation with low lateral pressure gradients. In contrast, there is significant lateral variability in upper basement temperatures, with highest values of ∼12.5°C beneath the thickly sedimented southwest section, lower values near the edges, and lowest values near the southeast edge. The results are key to assessing past and recent models for the circulation system.
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1Abstract The fate of carbon while passing through the rocky subseafloor of the ocean has direct implications on the global carbon cycle now and over geologic time, as well as the abundance and distribution of subseafloor life. Many organic geochemical studies require larger volumes of fluids than traditional hydrothermal samplers can provide, and also require rigorous steps to be taken to prevent contamination. The Hydrothermal Organic Geochemistry (HOG) sampler is designed to collect large volume (2–9 L) fluid samples with minimal introduction of organic or microbial contamination, and to be powered and deployed in real time from a submersible. Additional design constraints include utilizing materials appropriate for sampling fluids with elevated temperatures, fitting the sampler into the space available on the submersible, and minimizing the time needed to remove samples and prepare the sampler for re-deployment between dives. It utilizes two inlets, one devoted to natural abundance geochemistry and one that can be used for samples pre-dosed with isotopic labels or preservatives. Temperature probes providing real-time data are incorporated into each inlet to facilitate positioning the intake in areas of the hottest fluid flow, thereby minimizing entrainment of ambient bottom seawater while sampling. Fluids are shunted through two main conduits by a large volume pump. Smaller ports stemming off the main conduit connect to positive displacement fluid sample chambers and in situ filters. The outlets of these chambers and filter holders are connected to a 24-port valve, which in turn is connected to a small volume pump. The HOG sampler has successfully collected over 100 high purity fluid samples and 50 in situ filters during two expeditions to deep sea hydrothermal fields.
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Subseafloor oceanic crust is a vast yet poorly sampled habitat for life. Recent studies suggest that microbial composition in crustal habitats is variable in space and time, but biogeographic patterns are difficult to determine due to a paucity of data. To address this, we deployed hundreds of mineral colonization experiments at and below the seafloor for 4‐6 years at North Pond, a borehole observatory network in cool (<10°C) and oxic oceanic crust on the western flank of the Mid‐Atlantic Ridge. The overall community composition of mineral incubations reveals that colonization patterns are site dependent, with no correlation to mineral type. Only a few members of the Thioalkalispiraceae and Thioprofundaceae exhibited a mineral preference pattern, with generally higher abundance on metal sulfides compared to silicates, while taxa of the Gammaproteobacteria and Deltaproteobacteria were common in the colonization experiments. In comparison to datasets from other crustal habitats, broader biogeographic patterns of crustal communities emerge based on crustal habitat type (surface‐attached communities versus fluid communities), redox environment, and possibly crustal age. These comparisons suggest successional biogeography patterning that might be used as an indicator of how recently permeable pathways were established within oceanic crust. This article is protected by copyright. All rights reserved.
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The permeability, connectivity, and reactivity of fluid reservoirs in oceanic crust are poorly constrained, yet these reservoirs are pathways for about a quarter of the Earth's heat loss, and seawater-rock exchange within them impact ocean chemical cycles. We present results from the second ever cross-hole tracer experiment within oceanic crust and the first conducted during a single expedition and in slow-spreading crust west of the Mid-Atlantic Ridge at North Pond. Here we employed boreholes that were drilled by the Integrated Ocean Drilling Program (Sites U1382 and U1383) that were instrumented and sealed. A cesium salt solution and bottom seawater tracer experiment provided a measure of the minimum Darcy fluid velocity (2 to 41 m/day) within the upper volcanic crust, constraining the minimum permeability of 10⁻¹¹ to 10⁻⁹ m². We also document chemical heterogeneities in crustal fluid compositions, rebound from drilling disturbances, and nitrification within the basaltic crust, based on systematic differences in borehole fluid compositions over a 5-year period. These results also show heterogeneous fluid compositions with depth in the borehole, indicating that hydrothermal circulation is not vigorous enough to homogenize the fluid composition in the upper permeable basaltic basement, at least not on the time scale of 5 years. Our work verifies the potential for future manipulative experiments to characterize hydrologic, biogeochemical, and microbial process within the upper basaltic crust.
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The subduction of seamounts and ridge features at convergent plate boundaries plays an important role in the deformation of the overriding plate and influences geochemical cycling and associated biological processes. Active serpentinization of forearc mantle and serpentinite mud volcanism on the Mariana forearc (between the trench and active volcanic arc) provides windows on subduction processes. Here, we present (1) the first observation of an extensive exposure of an undeformed Cretaceous seamount currently being subducted at the Mariana Trench inner slope; (2) vertical deformation of the forearc region related to subduction of Pacific Plate seamounts and thickened crust; (3) recovered Ocean Drilling Program and International Ocean Discovery Program cores of serpentinite mudflows that confirm exhumation of various Pacific Plate lithologies, including subducted reef limestone; (4) petrologic, geochemical and paleontological data from the cores that show that Pacific Plate seamount exhumation covers greater spatial and temporal extents; (5) the inference that microbial communities associated with serpentinite mud volcanism may also be exhumed from the subducted plate seafloor and/or seamounts; and (6) the implications for effects of these processes with regard to evolution of life. This article is part of a discussion meeting issue ‘Serpentine in the Earth system’.
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Seamounts play a fundamental role in facilitating the exchange of fluids, heat, and solutes between the oceanic lithosphere and the overlying ocean. Global heat flow compilations indicate that much of the seafloor loses a significant fraction of lithospheric heat because of fluid flow from the crust, and most of this advective heat loss occurs on ridge flanks, areas far from the thermal influence of magmatic emplacement at seafloor spreading centers. The driving forces available to move fluid between the crust and ocean are modest, and most of the seafloor is blanketed by low-permeability sediment that prevents vertical fluid flow at thermally significant rates. Thus, most of the thermally important fluid exchange between the crust and ocean must occur where volcanic rocks are exposed at the seafloor; little fluid exchange on ridge flanks occurs through seafloor sediments overlying volcanic crustal rocks. Seamounts and other basement outcrops focus ridge-flank hydrothermal exchange between the crust and the ocean. We describe the driving forces responsible for hydrothermal flows on ridge flanks, and the impacts that these systems have on crustal heat loss, fluid composition, and subseafloor microbiology. We show data collected from two ridge-flank areas that illustrate how the extent of fluid exchange, lithospheric heat loss, and chemical reaction and transport depend on the rate of fluid flow, fluid residence time, and temperature in crustal hydrologic systems. Seamounts are ideal places to sample crustal fluids as they exit the crust and enter the ocean, to determine their chemical and microbial characteristics, and to assess the importance of this global hydrogeologic system on the evolution of Earth's lithosphere, ocean, and biosphere.
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Integrated Ocean Drilling Program (IODP) Expedition 336 successfully initiated subseafloor observatory science at a young mid-ocean-ridge flank setting. All of the drilled sites are located in the North Pond region of the Atlantic Ocean (22°45'N, 46°05'W) in 4414-4483 m water depth. This area is known from previous ocean drilling and site survey investigations as a site of particularly vigorous circulation of seawater in permeable 8 Ma basaltic basement underlying a <300 m thick sedimentary pile. Understanding how this seawater circulation affects microbial and geochemical processes in the uppermost basement was the primary science objective of Expedition 336. Basement was cored and wireline-logged in Holes U1382A and U1383C. Upper oceanic crust in Hole U1382A, which is only 50 m west of Deep Sea Drilling Project (DSDP) Hole 395A, recovered 32 m of core between 110 and 210 meters below seafloor (mbsf). Core recovery in basement was 32%, yielding a number of volcanic flow units with distinct geochemical and petrographic characteristics. A unit of sedimentary breccia containing clasts of basalt, gabbroic rocks, and mantle peridotite was found intercalated between two volcanic flow units and was interpreted as a rock slide deposit. From Hole U1383C we recovered 50.3 m of core between 69.5 and 331.5 mbsf (19%). The basalts are aphyric to highly plagioclase-olivine-phyric tholeiites that fall on a liquid line of descent controlled by olivine fractionation. They are fresh to moderately altered, with clay minerals (saponite, nontronite, and celadonite), Fe oxyhydroxide, carbonate, and zeolite as secondary phases replacing glass and olivine to variable extents. In addition to traditional downhole logs, we also used a new logging tool for detecting in situ microbial life in ocean floor boreholes-the Deep Exploration Biosphere Investigative tool (DEBI-t). Sediment thickness was ∼90 m at Sites U1382 and U1384 and varied between 38 and 53 m at Site U1383. The sediments are predominantly nannofossil ooze with layers of coarse foraminiferal sand and occasional pebble-size clasts of basalt, serpentinite, gabbroic rocks, and bivalve debris. The bottommost meters of sections cored with the advanced piston corer feature brown clay. Extended core barrel coring at the sediment/basement interface recovered <1 m of brecciated basalt with micritic limestone. Sediments were intensely sampled for geochemical pore water analyses and microbiological work. In addition, high-resolution measurements of dissolved oxygen concentration were performed on the whole-round sediment cores. Major strides in ridge-flank studies have been made with subseafloor borehole observatories (CORKs) because they facilitate combined hydrological, geochemical, and microbiological studies and controlled experimentation in the subseafloor. During Expedition 336, two fully functional observatories were installed in two newly drilled holes (U1382A and U1383C) and an instrument and sampling string were placed in an existing hole (395A). Although the CORK wellhead in Hole 395A broke off and Hole U1383B was abandoned after a bit failure, these holes and installations are intended for future observatory science targets. The CORK observatory in Hole U1382A has a packer seal in the bottom of the casing and monitors/samples a single zone in uppermost oceanic crust extending from 90 to 210 mbsf. Hole U1383C was equipped with a three-level CORK observatory that spans a zone of thin basalt flows with intercalated limestone (∼70-146 mbsf), a zone of glassy, thin basaltic flows and hyaloclastites (146-200 mbsf), and a lowermost zone (∼200-331.5 mbsf) of more massive pillow flows with occasional hyaloclastites in the upper part.
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Long-term osmotically pumped fluid samplers, or OsmoSamplers, were developed to reliably and autonomously collect continuous small-volume water samples for monitoring aqueous environments in remote locations for up to several years. OsmoSamplers provide sequential milliliter-size samples that, when analyzed, yield high-resolution time-series for a wide range of dissolved components. These instruments fill an important niche that has not been addressed by automated samplers or in situ analyzers. OsmoSamplers can be customized for flow rate and duration for addressing numerous scientific questions. The samplers consist of an osmotic pump that continuously pulls fluid sample into a long small-bore tube. They are thus extremely simple, reliable, and require neither electrical power nor moving parts. Upon recovery, fluid samples are extracted from subsections of the sample tubing, where each subsection integrates a discrete time interval. The time-stamped subsamples are then analyzed for chemical species of interest. Sample smearing due to static and dynamic diffusion and mixing is kept to a minimum by the use of small-bore tubing (0.5 to 1.2 mm inside diameter) and low flow rates (0.1 to 12 mL d -1). Theory and laboratory experiments show that sample smearing is not significantly greater than that calculated from static diffusion alone. OsmoSamplers have been tested in the laboratory and deployed at sea. Results from laboratory tests and field deployments illustrate initial results and potential applications. © 2004, by the American Society of Limnology and Oceanography, Inc.
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Although oceanic crust is the largest contiguous, hydrologically active environment on Earth, very little is empirically known about crustal habitability due to obstacles faced in scientific sampling, especially in basaltic crust. Geologically young, chemically reduced basaltic crust is not in thermodynamic equilibrium with seawater or hydrothermal fluids; exploitation of the inherent thermodynamic disequilibrium may fuel microbial ecosystems in subsurface environments. One avenue to explore the basaltic deep biosphere is through the deployment of microbial observatories at seafloor exposures and inside boreholes drilled into the crust. We report the design and field-testing of flow-through microbial observatories for use in deep biosphere studies conducted in boreholes within oceanic crust. We also evaluate the suitability of borehole construction materials in order to inform the development of the next generation of observatories for microbial studies, with attention towards minimizing in situ leaching of (potentially) growth-inducing substrates (i.e., carbon, nitrogen, iron).
Article
Fluid sampling capabilities associated with borehole observatories (CORKs) are currently the best mechanism to collect fluids from subsurface hydrologic zones for evaluating the composition, evolution and consequence of fluid circulation in oceanic crust. These capabilities have evolved over the past two decades spanning the Ocean Drilling Program and the Integrated Ocean Drilling Program. Fluid sampling capabilities of the original CORK had a single Teflon tube that connected a valve at the seafloor and ended at depth in the formation. Through successes and disappointments coupled with community desires and efforts, significant iterations in CORK design and capabilities have led to a range of crustal fluid sampling systems. These iterations continue today with the development of new borehole capabilities, sensors and samplers. We present major iterations and transitions, highlighting the pros and cons of various designs, materials, and decisions. Although this evolution has taken years because of the infrequency of CORK deployments and sample recovery operations, we as a community are now in the position to provide groundbreaking results to enhance our understanding of subseafloor hydrogeology, crustal evolution, geochemical fluxes, microbial ecology and biogeochemical processes as indicated by the wealth of work to date and the complexity and flexibility of present and future designs.
Article
Microbial processes within the ocean crust are of potential importance in controlling rates of chemical reactions and thereby affecting chemical exchange between the oceans and lithosphere. We here assess the oxidation state of altered ocean crust and estimate the magnitude of microbial biomass production that might be supported by oxidative and nonoxidative alteration. Compilations of Fe2O3, FeO, and S concentrations from DSDP/ODP drill core samples representing upper basaltic ocean crust suggest that Fe³⁺/ΣFe increases from 0.15 ± 0.05 to 0.45 ± 0.15 within the first 10–20 Myr of crustal evolution. Within the same time frame 70 ± 25% of primary sulfides in basalt are oxidized. With an annual production of 4.0 ± 1.8 × 10¹⁵ g of upper (500 ± 200 m) crust and average initial concentrations of 8.0 ± 1.3 wt% Fe and 0.125 ± 0.020 wt% S, we estimate annual oxidation rates of 1.7 ± 1.2 × 10¹² mol Fe and 1.1 ± 0.7 × 10¹¹ mol S. We estimate that 50% of Fe oxidation may be attributed to hydrolysis, producing 4.5 ± 3.0 × 10¹¹ mol H2/yr.
479 Nine Mile Road, Milam, TX 75959, U.S.A., e-mail: pettigrew.engineering@windstreammail: kbecker@ rsmas.miami
  • Katrina J Edwards
Katrina J. Edwards, Department of Biological Sciences, Marine Environmental Biology Section, University of Southern California, Los Angeles, CA 90089, U.S.A., e-mail: kje@usc.edu Tom Pettigrew, Pettigrew Engineering, 479 Nine Mile Road, Milam, TX 75959, U.S.A., e-mail: pettigrew.engineering@windstream.net Hans W. Jannasch, Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, U.S.A., e-mail: jaha@mbari.org Keir Becker, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, U.S.A., e-mail: kbecker@ rsmas.miami.edu Earl E. Davis, Pacific Geoscience Centre, Geological Survey of Canada, 9860 West Saanich Road, Sidney, BC V8L 4B2, Canada, e-mail: edavis@nrcan.gc.ca.
Geophysical site survey results from North Pond (Mid-Atlantic Ridge)
  • F Schmidt-Schierhorn
  • N Kaul
  • S Stephan
  • H Villinger
Schmidt-Schierhorn, F., Kaul, N., Stephan, S., and Villinger, H., 2012. Geophysical site survey results from North Pond (Mid-Atlantic Ridge). Proc. IODP, 336: Washington, DC (Integrated Ocean Drilling Program Management International, Inc.), in press.
  • Oceanography
Oceanography, 23(1):74-87. doi:10.5670/oceanog.2010.63