Temperature Measurements in Hole 395A, Leg 78B

Becker, K.; Lanseth, M.G.; Hyndman, R. D.

doi:10.2973/dsdp.proc.78b.105.1984

Cited by 46 publications

(50 citation statements)

References 15 publications

(27 reference statements)

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“…In many cases where permeable parts of young oceanic crust have been penetrated, the formations have been found to be underpressured (Anderson and Zoback, 1982), at least with respect to the hydrostatic conditions that are produced within the holes that are cooled by circulation during drilling. Downhole fluid flow is stimulated, and in those cases where holes have been later reentered, this stimulated flow has been found to be relatively stable and long lived (e.g., Hyndman et al, 1976;Becker et al, 1983Becker et al, , 1984Becker et al, , 1989Gable et al, in press;Morin et al, in press). This causes serious formation contamination problems and severely limits the quality of many downhole measurements and samples, both over short and long periods of time.…”

Section: Holes In Igneous Crustmentioning

confidence: 99%

CORK: A Hydrologic Seal and Downhole Observatory for Deep-Ocean Boreholes

Davis¹,

Becker²,

Pettigrew³

et al. 1992

Proceedings of the Ocean Drilling Program

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101

105

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A new tool has been developed and successfully deployed that provides a means by which cased reentry holes drilled by the Ocean Drilling Program can be hydrologically sealed and instrumented. The seal prevents flow of water into or out of a hole that would otherwise cause severe thermal and chemical disturbance to the formation drilled. The seal is capable of withstanding both positive and negative differential pressures that may be present in hydrothermally or tectonically active environments, and can be removed for later drilling operations. The instrumentation, developed for initial deployments during Ocean Drilling Program Leg 139, was designed to monitor the formation temperatures and pressures for up to 2 years during and following the recovery from drilling disturbances. A recording gauge measures absolute pressure in the borehole below the seal. A sensor string containing 10 thermistors and a fluid-sampling tube hang in the hole below the recording package. The sampling tube extends through the seal to a port, allowing the differential pressure to be measured and fluids to be tapped from deep within the hole. Data recovery and fluid sampling can be done via submersible or remotely operated vehicle.Two units were deployed in the sediment-filled Middle Valley rift of the northern Juan de Fuca Ridge. The first was installed in Hole 857D, which was drilled to a total depth of 936 meters below seafloor, through 470 m of turbidite sediment and into a highly permeable sediment-sill complex that is inferred to be a sediment-sealed hydrothermal "reservoir." The second was deployed in Hole 858G, which was drilled to a total depth of 433 meters below seafloor into a buried volcanic edifice that underlies a hydrothermal vent field. Data were recovered successfully from both holes about three weeks after deployment. Temperatures and pressures recorded in Hole 858G show that formation conditions are severely affected by drilling and by downward fluid flow into the formation through a nearby uncased exploratory hole that was not adequately sealed with cement. The differential pressure across the seal in Hole 858G was initially -0.24 MPa, and at the time of the data recovery was becoming increasingly negative. Temperatures and pressures recorded in Hole 857D appear to be recovering slowly from drilling disturbances. Initially, the differential pressure across the seal in this hole was -1.10 MPa; at the time of the data recovery, the differential had reduced to -0.55 MPa. The instruments will continue to monitor formation pressures and temperatures once per hour for 2 years.

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Section: Holes In Igneous Crustmentioning

confidence: 99%

CORK: A Hydrologic Seal and Downhole Observatory for Deep-Ocean Boreholes

Davis¹,

Becker²,

Pettigrew³

et al. 1992

Proceedings of the Ocean Drilling Program

Self Cite

101

105

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“…1). A total of 2 decades of temperature and flow records revealed vigorous subsurface flow (Becker et al, 1984;Gable et al, 1992), with geothermal surveys indicating that recharge is from the southeastern side of the basin (near 2B and 3D) flowing to the northwest (towards 4A) (Fig. 1).…”

Section: Sediment and Porewater Collectionmentioning

confidence: 99%

Nitrogen cycling in the deep sedimentary biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

et al. 2015

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Abstract. Nitrogen (N) is a key component of fundamental biomolecules. Hence, its cycling and availability are central factors governing the extent of ecosystems across the Earth. In the organic-lean sediment porewaters underlying the oligotrophic ocean, where low levels of microbial activity persist despite limited organic matter delivery from overlying water, the extent and modes of nitrogen transformations have not been widely investigated. Here we use the N and oxygen (O) isotopic composition of porewater nitrate (NO − 3 ) from a site in the oligotrophic North Atlantic (Integrated Ocean Drilling Program -IODP) to determine the extent and magnitude of microbial nitrate production (via nitrification) and consumption (via denitrification). We find that NO − 3 accumulates far above bottom seawater concentrations (∼ 21 µM) throughout the sediment column (up to ∼ 50 µM) down to the oceanic basement as deep as 90 m b.s.f. (below sea floor), reflecting the predominance of aerobic nitrification/remineralization within the deep marine sediments. Large changes in the δ 15 N and δ 18 O of nitrate, however, reveal variable influence of nitrate respiration across the three sites. We use an inverse porewater diffusion-reaction model, constrained by the N and O isotope systematics of nitrification and denitrification and the porewater NO − 3 isotopic composition, to estimate rates of nitrification and denitrification throughout the sediment column. Results indicate variability of reaction rates across and within the three boreholes that are generally consistent with the differential distribution of dissolved oxygen at this site, though not necessarily with the canonical view of how redox thresholds separate nitrate regeneration from dissimilative consumption spatially. That is, we provide stable isotopic evidence for expanded zones of co-occurring nitrification and denitrification. The isotope biogeochemical modeling also yielded estimates for the δ 15 N and δ 18 O of newly produced nitrate (δ 15 N NTR (NTR, referring to nitrification) and δ 18 O NTR ), as well as the isotope effect for denitrification ( 15 ε DNF ) (DNF, referring to denitrification), parameters with high relevance to global ocean models of N cycling. Estimated values of δ 15 N NTR were generally lower than previously reported δ 15 N values for sinking particulate organic nitrogen in this region. We suggest that these values may be, in part, related to sedimentary N 2 fixation and remineralization of the newly fixed organic N. Values of δ 18 O NTR generally ranged between −2.8 and 0.0 ‰, consistent with recent estimates based on lab cultures of nitrifying bacteria. Notably, some δ 18 O NTR values were elevated, suggesting incorporation of 18 O-enriched dissolved oxygen during nitrification, and possibly indicating a tight coupling of NH + 4 and NO − 2 oxidation in this metabolically sluggish environment. Our findings indicate that the production of organic matter by in situ autotrophy (e.g., nitrification, nitrogen fixation) supplies a large fraction of the...

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“…Temperature measurements in Hole 395A, provided by the DARPA downhole seismometer that was emplaced at 609 mbsf, showed a steady increase in temperature, about 1°C during 35 days (Becker et al, 1986). Temperature measurements in Hole 581C, by OSSIV which was emplaced about 378 mbsf, showed also a steady increase in temperature, about 6°C during a 64-day period .…”

Section: Estimation Of Temperature Change and Tiltingmentioning

confidence: 95%

Performance of the Ocean Broadband Downhole Seismometer at Site 794

Kanazawa¹,

Suyehiro²,

Hirata³

et al. 1992

Proceedings of the Ocean Drilling Program

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The ocean broadband downhole seismometer (OBDS) was successfully emplaced in Hole 794D in the Japan Sea during ODP Leg 128, and OBDS data were obtained continuously aboard JOIDES Resolution during a 60-hr period of real-time observation. During the real-time observation, air-gun profiling was done around Hole 794D using nine ocean-bottom seismometers (OBSs). The OBDS successfully observed air-gun signals from the seismic profiles, five local earthquakes, and an earthquake in Burma (m b 5.4).Signal-to-noise ratios of air-gun signals and local earthquakes observed by the OBDS are higher by over 20 dB than those observed by OBS. The epicentral distance of Burma earthquake was 38.99° to the OBDS. The OBDS could record P, S, and some surface waves from this teleseismic event with good signal-to-noise ratio for both the vertical and horizontal components. Broadband seismic noise spectra (5 m-30 Hz) in the ocean region were revealed for the first time by the OBDS observation. The noise level falls between the two levels of noisy and quiet conditions on land above 10 s. The noise level increases toward longer period. Signals from earthquakes larger than m s = 6 at 30° distance would rise above noise at an 100-s period.Following the real-time observation, an OBDS seafloor recorder was installed and operated for 30 days in event detection mode and time window mode. There was no triggered event. Very long-period data of 1-hr sampling showed only gradual variations without abrupt steplike changes. This indicates that the clamping we used for the OBDS sensors in the hole was sufficiently stable for such a long-term broadband observation.The results obtained in this paper strongly suggest that a broadband downhole seismometer performs well and is dispensable for constructing broadband digital seismograph networks on the ocean floor.

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Temperature Measurements in Hole 395A, Leg 78B

Cited by 46 publications

References 15 publications

CORK: A Hydrologic Seal and Downhole Observatory for Deep-Ocean Boreholes

CORK: A Hydrologic Seal and Downhole Observatory for Deep-Ocean Boreholes

Nitrogen cycling in the deep sedimentary biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

Performance of the Ocean Broadband Downhole Seismometer at Site 794

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