Procedures for Sampling Deep Subsurface Microbial Communities in Unconsolidated Sediments   总被引：2，自引：0，他引：2  

Brent F. Russell  Tommy J. Phelps  William T. Griffin  Kenneth A. Sargent 《Ground Water Monitoring & Remediation》1992,12(1):96-104

A corehole sampling project utilizing a wireline coring system provided sediment samples for microbiological characterization from deep unconsolidated sediments. Sampling tools were developed or modified to minimize contamination during sample acquisition and to facilitate stringent decontamination requirements. Quality assurance procedures, including the use of tracers, were implemented to minimize and quantify contamination from drilling hardware, drilling fluids and sample processing. Tracers included microspheres, potassium bromide, rhodamine dye, and perfluorocarbons, which enabled the detection and measurement of 1mg of drilling fluid per kg of sediment. In addition, sample processing was performed on-site in an anaerobic chamber to prevent exposure of the subsurface materials to atmospheric oxygen concentrations. Sediment samples were then disbursed to investigators at National Laboratories and universities funded through the Department of Energy Subsurface Science Microbiology Program for microbiological characterization. Results of these efforts demonstrated that representative subsurface samples were collected and disbursed.  相似文献   

Understanding mass fluvial erosion along a bank profile: using PEEP technology for quantifying retreat lengths and identifying event timing          下载免费PDF全文

A. N. Thanos Papanicolaou  Christopher G. Wilson  Achilles G. Tsakiris  Tommy E. Sutarto  Fabienne Bertrand  Massimo Rinaldi  Subhasish Dey  Eddy Langendoen 《地球表面变化过程与地形》2017,42(11):1717-1732

This study provides fundamental examination of mass fluvial erosion along a stream bank by identifying event timing, quantifying retreat lengths, and providing ranges of incipient shear stress for hydraulically driven erosion. Mass fluvial erosion is defined here as the detachment of thin soil layers or conglomerates from the bank face under higher hydraulic shear stresses relative to surface fluvial erosion, or the entrainment of individual grains or aggregates under lower hydraulic shear stresses. We explore the relationship between the two regimes in a representative, US Midwestern stream with semi‐cohesive bank soils, namely Clear Creek, IA. Photo‐Electronic Erosion Pins (PEEPs) provide, for the first time, in situ measurements of mass fluvial erosion retreat lengths during a season. The PEEPs were installed at identical locations where surface fluvial erosion measurements exist for identifying the transition point between the two regimes. This transition is postulated to occur when the applied shear stress surpasses a second threshold, namely the critical shear stress for mass fluvial erosion. We hypothesize that the regimes are intricately related and surface fluvial erosion can facilitate mass fluvial erosion. Selective entrainment of unbound/exposed, mostly silt‐sized particles at low shear stresses over sand‐sized sediment can armor the bank surface, limiting the removal of the underlying soil. The armoring here is enhanced by cementation from the presence of optimal levels of sand and clay. Select studies show that fluvial erosion strength can increase several‐fold when appropriate amounts of sand and clay are mixed and cement together. Hence, soil layers or conglomerates are entrained with higher flows. The critical shear stress for mass fluvial erosion was found to be an order of magnitude higher than that of surface fluvial erosion, and proceeded with higher (approximately 2–4 times) erodibility. The results were well represented by a mechanistic detachment model that captures the two regimes. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Physical dynamics and biological implications of Cyclone Noah in the lee of Hawaii during E-Flux I     

Victor S. Kuwahara  Francesco Nencioli  Tommy D. Dickey  Yoshimi M. Rii  Robert R. Bidigare 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1231

Quasi-synoptic observations of the horizontal and vertical structure of a cold-core cyclonic mesoscale eddy feature (Cyclone Noah) were conducted in the lee of Hawai’i from November 4–22, 2004 as part of the E-Flux interdisciplinary collaborative research program. Cyclone Noah appears to have spun up to the southwest of the ‘Alenuihaha Channel (between Maui and Hawai’i) as a result of strong and persistent northeasterly trade winds through the channel. Shipboard hydrographic surveys 2.5 months later suggest that Noah weakened and was in a hypothesized spin-down phase of its life cycle. Although the initial surface expression of Noah was limited in scale to 40 km in diameter and, as evidenced by surface temperatures, 2–3 °C cooler than the surrounding waters, depth profiles revealed a fully developed semi-elliptical shallow feature (200 m), 144 km long and 90 km wide (based on sigma-t=23 kg m⁻³) with tangential speeds of 40–80 cm s⁻¹, and substantial isopycnal doming. Potential vorticity distribution of Noah suggests that radial horizontal flow of the core water was inhibited from the surface to depths of 75 m, with high vorticity confined above the sigma-t=23.5 kg m⁻³ isopycnal surface. Upward displacements of isopycnal surfaces in the eddy's center (50 m) were congruent with enhanced pigment concentrations (0.50 mg m⁻³). Comparisons of the results obtained for E-Flux I (Noah) and E-Flux III (Opal) suggest that translation characteristics of cyclonic Hawaiian lee eddies may be important in establishing the biogeochemical and biological responses of the oligotrophic ocean to cyclonic eddies.  相似文献   

The transient oasis: Nutrient-phytoplankton dynamics and particle export in Hawaiian lee cyclones     

Yoshimi M. Rii  Susan L. Brown  Francesco Nencioli  Victor Kuwahara  Tommy Dickey  David M. Karl  Robert R. Bidigare 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1275

Macronutrients, photosynthetic pigments, and particle export were assessed in two eddies during the E-Flux I and III cruises to investigate linkages between biogeochemical properties and export flux in Hawaiian lee cyclonic eddies. Cyclone Noah (E-Flux I), speculated to be in the ‘decay’ stage, exhibited modest increases in macronutrients and photosynthetic pigments at the eddy center compared to ambient waters. Cyclone Opal (E-Flux III) also exhibited modest increases in macronutrient concentrations, but a 2-fold enhancement in total chlorophyll a (TChl a) concentration within the eddy center. As indicated by fucoxanthin concentrations, the phytoplankton community in the deep chlorophyll maximum (DCM) of Opal was comprised mainly of diatoms. During an 8-day time series in the center of Opal, TChl a concentration and fucoxanthin in the DCM decreased by 50%, which was potentially triggered by silicic acid limitation. Despite the presence of a substantial diatom bloom, Opal did not deliver the expected export of particulate carbon and nitrogen, but rather a large biogenic silica export (4-fold increase relative to export in surrounding waters). Results suggest that controls on the life cycle of a Hawaiian lee cyclone are likely a combination of physical (eddy dynamics), chemical (nutrient limitation), and biological (growth and grazing imbalance) processes. Comparisons between Noah and Opal and previously studied cyclones in the region point to a relationship between the spin-up duration of a cyclone and the resulting biological response. Nonetheless, Hawaiian lee cyclones, which strongly influence the biogeochemistry of areas 100's of km in scale in the subtropical North Pacific Ocean, still remain an enigma.  相似文献   

Submesoscale features and their interaction with fronts and internal tides in a high-resolution coupled atmosphere-ocean-wave model of the Bay of Bengal   总被引：1，自引：1，他引：0  

Tommy G. Jensen  Igor Shulman  Hemantha W. Wijesekera  Stephanie Anderson  Sherwin Ladner 《Ocean Dynamics》2018,68(3):391-410

Large freshwater fluxes into the Bay of Bengal by rainfall and river discharges result in strong salinity fronts in the bay. In this study, a high-resolution coupled atmosphere-ocean-wave model with comprehensive physics is used to model the weather, ocean circulation, and wave field in the Bay of Bengal. Our objective is to explore the submesoscale activity that occurs in a realistic coupled model that resolves mesoscales and allows part of the submesoscale field. Horizontal resolution in the atmosphere varies from 2 to 6 km and is 13 km for surface waves, while the ocean model is submesoscale permitting with resolutions as high as 1.5 km and a vertical resolution of 0.5 m in the upper 10 m. In this paper, three different cases of oceanic submesoscale features are discussed. In the first case, heavy rainfall and intense downdrafts produced by atmospheric convection are found to force submesoscale currents, temperature, and salinity anomalies in the oceanic mixed layer and impact the mesoscale flow. In a second case, strong solitary-like waves are generated by semidiurnal tides in the Andaman Sea and interact with mesoscale flows and fronts and affect submesoscale features generated along fronts. A third source of submesoscale variability is found further north in the Bay of Bengal where river outflows help maintain strong salinity gradients throughout the year. For that case, a comparison with satellite observations of sea surface height anomalies, sea surface temperature, and chlorophyll shows that the model captures the observed mesoscale eddy features of the flow field, but in addition, submesoscale upwelling and downwelling patterns associated with ageostrophic secondary circulations along density fronts are also captured by the model.  相似文献   

Constructing an idealized model of the North Atlantic Ocean using slippery sacks     

Patrick T. Haertel  Luke Van Roekel  Tommy G. Jensen   《Ocean Modelling》2009,27(3-4):143-159

This paper documents the continued development and testing of a new Lagrangian oceanic general circulation model. The slippery sacks ocean model (SSOM), which represents a body of water as a pile of conforming parcels, is improved and is used to simulate circulations in homogeneous oceans and in an idealized model of the North Atlantic Ocean.A method for including horizontal mixing in the SSOM is presented. A given sack’s nearest neighbors are identified in the positive and negative x- and y-directions, and the sack exchanges momentum and/or tracers with these neighbors. This formulation of mixing is straightforward to implement, computationally efficient, and it produces results similar to a standard Eulerian finite-difference representation of diffusion.The model’s ability to reproduce the Stommel and Munk solutions to the classical western boundary current problem is tested. When steps are taken to reduce the potential energy barrier to sacks crossing one another, the model generates circulations that are consistent with linear theory. In moderately non-linear regimes the model produces appropriate departures from linear solutions including a boundary current that continues along the northern boundary for a time.Taking advantage of the new mixing scheme and lessons learned from simulations of homogeneous oceans, the authors construct an idealized model of the North Atlantic Ocean. They compare simulations conducted with the SSOM to similar simulations conducted with the Massachusetts Institute of Technology general circulation model (MITgcm). The SSOM and the MITgcm produce similar wind-forced gyres, thermocline structure, and meridional overturning. The SSOM is also used to explore how circulations change in the limit when tracer diffusion goes to zero.  相似文献   

Value of information analysis in rock engineering: a case study of a tunnel project in Äspö Hard Rock Laboratory     

Miriam S. Zetterlund  Tommy Norberg  Lars O. Ericsson  Jenny Norrman  Lars Rosén 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2015,9(1):9-24

Geoengineering prognoses are often based on data from a limited number of investigations of soil and rock mass. There is generally a desire to reduce the uncertainty in the prognoses while minimising the investigation costs. Value of Information Analysis (VOIA) is a support for decisions regarding investigation strategies and the aim of this paper is to present methodology for VOIA that takes into account four decision alternatives where the input data could be provided by experts. The methodology will be applied in a case study where the value of information related to an investigation borehole will be calculated. The results indicate that the value of information of the borehole is low compared with the realisation costs of the investigation. It was found that models for VOIA in underground construction projects are complex but that the analysis can be simplified with extensive use of expert knowledge and calculations of the value of perfect information as a benchmark for investigation strategies.  相似文献   

The phase curve survey of the irregular saturnian satellites: A possible method of physical classification     

James M. Bauer  Tommy Grav  Michael D. Hicks 《Icarus》2006,184(1):181-197

During its 2005 January opposition, the saturnian system could be viewed at an unusually low phase angle. We surveyed a subset of Saturn's irregular satellites to obtain their true opposition magnitudes, or nearly so, down to phase angle values of 0.01°. Combining our data taken at the Palomar 200-inch and Cerro Tololo Inter-American Observatory's 4-m Blanco telescope with those in the literature, we present the first phase curves for nearly half the irregular satellites originally reported by Gladman et al. [2001. Nature 412, 163-166], including Paaliaq (SXX), Siarnaq (SXXIX), Tarvos (SXXI), Ijiraq (SXXII), Albiorix (SXVI), and additionally Phoebe's narrowest angle brightness measured to date. We find centaur-like steepness in the phase curves or opposition surges in most cases with the notable exception of three, Albiorix and Tarvos, which are suspected to be of similar origin based on dynamical arguments, and Siarnaq.  相似文献   

Photometric survey of the irregular satellites     

Tommy Grav  Matthew J. Holman  Brett J. Gladman 《Icarus》2003,166(1):33-45

We present BVRI colors of 13 jovian and 8 saturnian irregular satellites obtained with the 2.56 m Nordic Optical Telescope on La Palma, the 6.5 m Magellan Baade Telescope on La Campanas, and the 6.5 m MMT on Mt. Hopkins. The observations were performed from December 2001 to March 2002. The colors of the irregular satellites vary from grey to light red. We have arbitrarily divided the known irregular satellites into two classes based on their colors. One, the grey color class, has similar colors to the C-type asteroids, and the other, the light red color class, has colors similar to P/D-type asteroids. We also find at least one object, the jovian irregular J XXIII Kalyke, that has colors similar to the red colored Centaurs/TNOs, although its classification is insecure. We find that there is a correlation between the physical properties and dynamical properties of the irregular satellites. Most of the dynamical clusters have homogeneous colors, which points to single homogeneous progenitors being cratered or fragmented as the source of each individual cluster. The heterogeneously colored clusters are most easily explained by assuming that there are several dynamical clusters in the area, rather than just one, or that the parent body was a differentiated, heterogeneous body. By analyzing simple cratering/fragmentation scenarios, we show that the heterogeneous colored S IX Phoebe cluster, is most likely two different clusters, a grey colored cluster centered on S IX Phoebe and a light red colored cluster centered on S/2000 S 1. To which of these two clusters the remaining saturnian irregulars with inclinations close to 174° belong is not clear from our analysis, but determination of their colors should help constrain this. We also show through analysis of possible fragmentation and dispersion of the six known uranian irregulars that they most likely make up two clusters, one centered on U XVI Caliban and another centered on U XVII Sycorax. We further show that, although the two objects have similar colors, a catastrophic fragmentation event creating one cluster containing both U XVI Caliban and U XVII Sycorax would have involved a progenitor with a diameter of ∼395 km. While such an event is not impossible it seems rather improbable, and we further show that such an event would leave 5-6 fragments with sizes comparable to or larger than U XVI Caliban. The stable region around Uranus has been extensively searched to limiting magnitudes far beyond that of U XVI Caliban. The fact that only U XVI Caliban, the larger U XVII Sycorax and four much smaller objects have been found leaves us with a distribution not compatible with a catastrophic event with such a large progenitor. The most likely solution is therefore two separate events creating two uranian dynamical clusters.  相似文献   

Interactions between the Indonesian Throughflow and circulations in the Indian and Pacific Oceans   总被引：2，自引：0，他引：2  

Julian P. McCreary  Toru Miyama  Tommy Jensen  Bohyun Bang 《Progress in Oceanography》2007,75(1):70-114

Circulations associated with the Indonesian Throughflow (IT), particularly concerning subsurface currents in the Pacific Ocean, are studied using three types of models: a linear, continuously stratified (LCS) model and a nonlinear, -layer model (LOM), both confined to the Indo-Pacific basin; and a global, ocean general circulation model (COCO). Solutions are wind forced, and obtained with both open and closed Indonesian passages. Layers 1-4 of LOM correspond to near-surface, thermocline, subthermocline (thermostad), and upper-intermediate (AAIW) water, respectively, and analogous layers are defined for COCO.The three models share a common dynamics. When the Indonesian passages are abruptly opened, barotropic and baroclinic waves radiate into the interiors of both oceans. The steady-state, barotropic flow field from the difference (open − closed) solution is an anticlockwise circulation around the perimeter of the southern Indian Ocean, with its meridional branches confined to the western boundaries of both oceans. In contrast, steady-state, baroclinic flows extend into the interiors of both basins, a consequence of damping of baroclinic waves by diapycnal processes (internal diffusion, upwelling and subduction, and convective overturning). Deep IT-associated currents are the subsurface parts of these baroclinic flows. In the Pacific, they tend to be directed eastward and poleward, extend throughout the basin, and are closed by upwelling in the eastern ocean and Subpolar Gyre. Smaller-scale aspects of their structure vary significantly among the models, depending on the nature of their diapycnal mixing.At the exit to the Indonesian Seas, the IT is highly surface trapped in all the models, with a prominent, deep core in the LCS model and in LOM. The separation into two cores is due to near-equatorial, eastward-flowing, subsurface currents in the Pacific Ocean, which drain layer 2 and layer 3 waters from the western ocean to supply water for the upwelling regions in the eastern ocean; indeed, depending on the strength and parameterization of vertical diffusion in the Pacific interior, the draining can be strong enough that layer 3 water flows from the Indian to Pacific Ocean. The IT in COCO lacks a significant deep core, likely because the model’s coarse bottom topography has no throughflow passage below 1000 m. Consistent with observations, water in the near-surface (deep) core comes mostly from the northern (southern) hemisphere, a consequence of the wind-driven circulation in the tropical North Pacific being mostly confined to the upper ocean; as a result, it causes the near-surface current along the New Guinea coast to retroflect eastward, but has little impact on the deeper New Guinea undercurrent.In the South Pacific, the IT-associated flow into the basin is spread roughly uniformly throughout all four layers, a consequence of downwelling processes in the Indian Ocean. The inflow first circulates around the Subtropical Gyre, and then bends northward at the Australian coast to flow to the equator within the western boundary currents. To allow for this additional, northward transport, the bifurcation latitude of the South Equatorial Current shifts southward when the Indonesian passages are open. The shift is greater at depth (layers 3 and 4), changing from about 14°S when the passages are closed to 19°S when they are open and, hence, accounting for the northward-flowing Great Barrier Reef Undercurrent in that latitude range.After flowing along the New Guinea coast, most waters in layers 1-3 bend offshore to join the North Equatorial Countercurrent, Equatorial Undercurrent, and southern Tsuchiya Jet, respectively, thereby ensuring that northern hemisphere waters contribute significantly to the IT. In contrast, much of the layer 4 water directly exits the basin via the IT, but some also flows into the subpolar North Pacific. Except for the direct layer 4 outflow, all other IT-associated waters circulate about the North Pacific before they finally enter the Indonesian Seas via the Mindanao Current.  相似文献