Monitoring Subsurface Microbial Ecology in a Sulfate-Amended, Gasoline-Contaminated Aquifer   总被引：3，自引：0，他引：3  

Kerry Sublette  Aaron Peacock  David White  Greg Davis  Dora Ogles  David Cook  Ravi Kolhatkar  Dennis Beckmann  Xiaomin Yang 《Ground Water Monitoring & Remediation》2006,26(2):70-78

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Reconstructing the marine Os/Os record and the particulate flux of meteoritic osmium during the late Cretaceous     

Greg Ravizza 《Geochimica et cosmochimica acta》2007,71(5):1355-1369

Paired analyses of Os isotope composition and concentration of bulk sediment and leachable Os in a metalliferous pelagic clay sequence from the North Pacific, ODP Site 886C, are used to reconstruct the marine Os isotope record and the particulate meteoritic Os flux between 65.5 and 78 Ma. Measured ¹⁸⁷Os/¹⁸⁸Os of bulk sediments ranges from approximately 0.64 to 0.32 and those of leach analyses are very similar to bulk analyses. Hydrogenous Os dominates the sedimentary Os inventory throughout most of the studied interval. As a result the measured ¹⁸⁷Os/¹⁸⁸Os of leachable Os approximates that of contemporaneous seawater. The ODP 886C record shows rising ¹⁸⁷Os/¹⁸⁸Os in the deepest portion of the core, with a local maximum of 0.66 close to 74 Ma. The 67-72 Ma portion of the record is characterized by nearly constant ¹⁸⁷Os/¹⁸⁸Os ratios close to 0.6. The structure of the marine Os isotope record from ODP 886C differs markedly from the seawater ⁸⁷Sr/⁸⁶Sr curve, which rises monotonically throughout the time interval studied here. Calculated particulate meteoritic Os fluxes are between 0.5 and 2 pg cm⁻² kyr⁻¹ throughout most of the studied interval. Two discrete intervals of the core (one of which is within Cretaceous Tertiary, boundary KTB interval) are characterized by higher fluxes of meteoritic Os. Excluding these two intervals, the average background flux of particulate meteoritic Os is roughly half of that estimated from analyses of Cenozoic marine sediments. These are the first Os isotope data to provide evidence of resolvable temporal variations in the background flux of particulate meteoritic material to the Earth.  相似文献   

Origin of the Blue Ridge escarpment along the passive margin of Eastern North America   总被引：1，自引：0，他引：1  

James A. Spotila  Greg C. Bank  Peter W. Reiners†  Charles W. Naeser‡  Nancy D. Naeser‡  Bill S. Henika 《Basin Research》2004,16(1):41-63

The Blue Ridge escarpment is a rugged landform situated within the ancient Appalachian orogen. While similar in some respects to the great escarpments along other passive margins, which have evolved by erosion following rifting, its youthful topographic expression has inspired proposals of Cenozoic tectonic rejuvenation in eastern North America. To better understand the post‐orogenic and post‐rift geomorphic evolution of passive margins, we have examined the origin of this landform using low‐temperature thermochronometry and manipulation of topographic indices. Apatite (U–Th)/He and fission‐track analyses along transects across the escarpment reveal a younging trend towards the coast. This pattern is consistent with other great escarpments and fits with an interpretation of having evolved by prolonged erosion, without the requirement of tectonic rejuvenation. Measured ages are also comparable specifically to those measured along other great escarpments that are as much as 100 Myr younger. This suggests that erosional mechanisms that maintain rugged escarpments in the early post‐rift stages may remain active on ancient passive margins for prolonged periods. The precise erosional evolution of the escarpment is less clear, however, and several end‐member models can explain the data. Our preferred model, which fits with all data, involves a significant degree of erosional escarpment retreat in the Cenozoic. Although this suggests that early onset of topographic stability is not required of passive margin evolution, more data are required to better constrain the details of the escarpment's development.  相似文献   

A study of arctic sea ice and sea‐level pressure using POP and neural network methods     

Benyang Tang  Gregory M. Flato  Greg Holloway 《大气与海洋》2013,51(3):507-529

Abstract

We examine Arctic sea‐ice concentration (SIC) and sea‐level pressure (SLP) data using principal oscillation pattern (POP) and neural network methods. The POP method extracts oscillating patterns from multivariate time series, each pattern being characterized by an oscillation period and a decay time. Predictions can be made for patterns whose decay time is comparable with the period. For both the SIC and SLP, however, the decay times are much shorter than the oscillation periods, and therefore the forcast skill is poor. A neural network is a model of the learning behaviour of a living neural system. Presented with training data, a neural network can learn the linear or non‐linear rules embedded in the data. We trained neural networks with sea‐ice and sea‐level pressure data, and estimated the forecast skill using a cross‐validation technique. The neural networks did not exhibit forecast skill significantly better than that of persistence. We contrast the Arctic situation with previous studies in which POP and neural networks were successfully used to forecast El Niño at lead times up to 6 months. Reasons for the lack of skill in both methods are discussed.  相似文献   

Paving the way for a future underwater omni-directional wireless optical communication systems     

Greg Baiden  Yassiah Bissiri  Andrew Masoti 《Ocean Engineering》2009,36(9-10):633-640

To lay down the foundation for an underwater omni-directional optical communication system for tele-operation, we tested a point-to-point optical communication system, using laser-emitting diodes (LEDs). The LEDs used in the test emitted light in the green and blue light spectrum and were tested in a pool and in a tank filled with lake water. The primary objective of these tests was to get profiles of the behaviors of such communication systems with respect to water characteristics such as turbidity levels, prior to building the proposed omni-directional optical communication. The results of the tests indicated that turbidity level, viewing angle and separation distance plays a significant role in the behavior of blue light in water. Furthermore, it was possible to graph the profile of the behavior of light with respect to the parameters of interest. The results of the tests and related research are discussed in this paper.  相似文献   

Changes in timber haul emissions in the context of shifting forest management and infrastructure     

Sean P Healey  Jock A Blackard  Todd A Morgan  Dan Loeffler  Greg Jones  Jon Songster  Jason P Brandt  Gretchen G Moisen  Larry T DeBlander 《Carbon balance and management》2009,4(1):9

Background  

Although significant amounts of carbon may be stored in harvested wood products, the extraction of that carbon from the forest generally entails combustion of fossil fuels. The transport of timber from the forest to primary milling facilities may in particular create emissions that reduce the net sequestration value of product carbon storage. However, attempts to quantify the effects of transport on the net effects of forest management typically use relatively sparse survey data to determine transportation emission factors. We developed an approach for systematically determining transport emissions using: 1) -remotely sensed maps to estimate the spatial distribution of harvests, and 2) - industry data to determine landscape-level harvest volumes as well as the location and processing totals of individual mills. These data support spatial network analysis that can produce estimates of fossil carbon released in timber transport.  相似文献   

The Wide Field Spectrograph (WiFeS): performance and data reduction     

Michael Dopita  Jonghwan Rhee  Catherine Farage  Peter McGregor  Gabe Bloxham  Anthony Green  Bill Roberts  Jon Neilson  Greg Wilson  Peter Young  Peter Firth  Gianni Busarello  Paola Merluzzi 《Astrophysics and Space Science》2010,327(2):245-257

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Periglacial climate at the 2.5 Ma onset of Northern Hemisphere glaciation inferred from the Whippoorwill Formation, northern Missouri, USA     

Charles W. Rovey  Greg Balco 《Quaternary Research》2010,73(1):151-161

The Whippoorwill Formation is a gleyed diamicton that is present locally within bedrock depressions beneath the oldest glacial till in northern Missouri, USA. Stratigraphy, paleomagnetism, and cosmogenic-nuclide burial ages show that it was deposited between the Matuyama-Gauss magnetostratigraphic boundary at 2.58 Ma and the first advance of the Laurentide ice sheet into Missouri at 2.47 ± 0.19 Ma. High cosmogenic-nuclide concentrations also show that the constituents of the Whippoorwill Formation experienced long exposure at a stable landscape surface with erosion rates of 1-2 m/Ma. However, cosmogenic-nuclide concentrations are invariant with depth below the Whippoorwill Formation surface, indicating active mixing of the soil profile shortly before burial by till. The Whippoorwill Formation retains numerous features indicative of cryoturbation. Therefore, we interpret it as a buried Gelisol, a soil formed under periglacial conditions in the presence of permafrost. At the onset of Northern Hemisphere glaciation, climate cooling established permafrost conditions and accelerated erosion by inducing landscape instability. Thus, weathered regolith materials were mobilized and redeposited by gelifluction shortly before the ice sheet overrode the landscape.  相似文献   

Diagenetic model of carbonate rocks of Guri Member of Mishan Formation (Lower to Middle Miocene) SE Zagros basin,Iran     

Akbar Heidari  Luis A. Gonzalez  Asadollah Mahboubi  Reza Moussavi-Harami  Greg A. Ludvigson  Govind J. Chakrapani 《Journal of the Geological Society of India》2014,84(1):87-104

In order to understand the post-depositional history of carbonate rocks of Guri Member (Lower to Middle Miocene), three stratigraphic sections were selected in north Bandar-Abbas in southeast of Iran. Sampling was carried out, analyzed for selective parameters such as oxygen and carbon isotopic compositions (δ¹⁸O and δ¹³C) and interpreted in the present study. We recognized several diagenetic processes including micritization, cementation, neomorphism, compaction, dissolution, silicification, dolomitization, fracturing and vein filling. Some of the diagenetic processes occurred at different conditions, so in order to achieve precise interpretation, samples from different carbonate components such as, micrite, fracture cement, solution pore cement, intergranular cement, and some biotic allochems were analyzed. In this study micrite samples were subdivided into two groups including micro-spary and micrite. They were recognized under Cathodoluminescence microscope. In addition, micrite samples were classified into five groups based on their depositional environments: supratidal, lagoon, coral bar, open sea, and open basin. There were minor changes in stable isotope ratios based on the sedimentary environments, stratigraphy successions, and micro-spary or micrite properties. In this study, similar calcite cements in petrography studies were differentiated by stable isotope data. Those calcite cements have formed in different diagenetic environments such as meteoric and burial cements. Paragenetic sequence of carbonate rocks were interpreted by integration of petrographic and isotopic studies. We have reconstructed diagenetic models of Guri Member into four stages including marine, meteoric, burial, and uplifting.  相似文献   

A Close Look at Satloc's Real-Time WADGPS System     

Michael L. Whitehead  Gary Penno  Walter J. Feller  Ivan C. Messinger  Willy I. Bertiger  Ronald J. Muellerschoen  Byron A. Iljima  Greg Piesinger 《GPS Solutions》1998,2(2):46-63

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