Laboratory simulation of clast abrasion     

J. Lewin  P. A. Brewer 《地球表面变化过程与地形》2002,27(2):145-164

Experimental abrasion of river‐bed materials has been widely undertaken, producing ‘downstream’ fining rates that generally are believed to be much less than those observed in the field. A conclusion commonly adopted has been that sorting processes are more effective than abrasion processes. A comparative evaluation of results from an abrasion tank and a tumbling barrel are presented, which show that abrasion patterns and rates differ according to the equipment used, clast size and shape, the clast charge (barrel) and water velocity and bed material (tank). Abrasion is a composite process, and the effects achieved appear to be dominated by percussion in the tank and grinding in the barrel. Breakage, crushing and sandblasting are not modelled effectively, nor are effects achieved on clasts when they form part of the bed. Comparisons are made with other equipment used, the very limited amount of direct field abrasion monitoring, and with the probable suite of processes that may occur under field conditions. Also reviewed are the problems that arise when laboratory weight‐loss abrasion coefficients are used or converted into ones of size diminution, as usually derived from field observations of down‐channel trends. It is concluded that field abrasion rates generally have been underestimated, as the processes involved are at best only selectively represented by the experimental equipment so far used, and because the results obtained experimentally are capable of misinterpretation when related to field trends. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

River system recovery following the Novaţ-Roşu tailings dam failure, Maramureş County, Romania     

Graham Bird  Paul A. Brewer  Mark G. Macklin  Dan Balteanu  Mihaela Serban  Basarab Driga  Sorin Zaharia 《Applied Geochemistry》2008,23(12):3498-3518

The River Vişeu catchment in Maramureş County, northwestern Romania, has a long history of base and precious metal mining. Between 1994 and 2003 waste from mining activity at Baia Borşa was stored in the Novaţ-Roşu tailings pond in the upper Vişeu catchment. However, in March 2000, the tailings dam failed releasing approximately 100,000 m³ of contaminated water and 20,000 t of mineral-rich solid waste, which was routed downstream through the Rivers Novaţ, Vaser and Vişeu into the River Tisa. Following the accident metal (Cd, Cu, Pb, Zn) concentrations in river water and river channel sediment were assessed in samples collected annually (July 2000, 2001, 2002 and 2003) from 29 sites in the Vişeu catchment, downstream of the tailings pond. Additionally, the speciation of sediment-associated metals was established using a 4-stage sequential extraction procedure (SEP) and Pb isotope analysis (^206/204Pb and ^207/204Pb) was carried out to establish the provenance of contaminated sediments. Metal concentrations in river water were found to comply with EU directive ‘target’ values within four months of the failure. However, the impact of the spill upon river channel sediments was found to be much longer-lasting, with evidence of the delayed downstream remobilization of tailings stored within the narrow Novaţ valley following the dam failure, as well as continued inputs of contaminated sediment to the River Vişeu from the River Tisla, another mining-affected tributary. Comparison with data from other recent tailings dam failures, indicates that river system recovery rates depend upon local geomorphological conditions, hydrological regimes, and the nature and scale of post-spill clean-up operations.  相似文献   

Magnetically enhanced coagulation of very small iron grains   总被引：3，自引：0，他引：3  

Nuth JA rd  Berg O  Faris J  Wasilewski P 《Icarus》1994,107(1):155-163

Laboratory experiments, in which very small (approximately 20 nm) grains are produced in the presence of a magnetic field on the order of 100 Gauss in a low-pressure hydrogen atmosphere, have demonstrated that such smokes can become permanently magnetized. We show that magnetization results in an enormous enhancement in the coagulation efficiency of such materials even in the absence of external magnetic fields. Small iron grains should have been produced in the solar nebula by thermal processing of preexisting interstellar grains. If such processing occurred via high-energy electromagnetic events then the resultant magnetized grains could have triggered the formation of centimeter- to meter-sized protoplanetessimals by acting as "nets" capable of sweeping up nonconductive silicates suspended in the gas. It is possible that the presence of conductive fractal aggregates observed in modern-day protostellar disks could be explained by the enhanced coagulation efficiency of very small magnetized iron particles.  相似文献   

The high-latitude cloud MBM 7. I. H I and CO observations     

Minh YC  Park YS  Kim KT  Irvine WM  Brewer MK  Turner BE 《The Astrophysical journal》1996,467(2):717-727

The high-latitude cloud (HLC) MBM 7 has been observed in the 21 cm H I line and the 12CO(1-0) and 13CO(1-0) lines with similar spatial resolutions. The data reveal a total mass approximately 30 M solar for MBM 7 and a complex morphology. The cloud consists of a cold dense core of 5 M solar surrounded by atomic and molecular gas with about 25 M solar, which is embedded in hotter and more diffuse H I gas. We derive a total column density N(H I + 2H2) of 1 x 10(21) cm-2 toward the center and 1 x 10(20) cm-3 toward the envelope of MBM 7. The CO line indicates the existence of dense cores [n(H2) > or = 2000 cm-3] of size (FWHM) approximately 0.5 pc. The morphology suggests shock compression from the southwest direction, which can form molecular cores along the direction perpendicular to the H I distribution. The H I cloud extends to the northeast, and the velocity gradient appears to be about 2.8 km s-1 pc-1 in this direction, which indicates a systematic outward motion which will disrupt the cloud in approximately 10(6) yr. The observed large line widths of approximately 2 km s-1 for CO suggest that turbulent motions exist in the cloud, and hydrodynamical turbulence may dominate the line broadening. Considering the energy and pressure of MBM 7, the dense cores appear not to be bound by gravity, and the whole cloud including the dense cores seem to be expanding. The distance to HLCs suggest that they belong to the galactic plane, since the scale height of the cloud is < or approximately equal to 100 pc. Compared to the more familiar dense dark clouds, HLCs may differ only in their small mass and low density, with their proximity reducing the filling factor and enhancing the contrast of the core and envelope structure.  相似文献   

Organic pollution of an inland marine cave from Bermuda     

Thomas M Iliffe  Timothy D Jickells  Martin S Brewer 《Marine environmental research》1984,12(3):173-189

Inland marine caves have served as biological refugia and, as such, frequently contain unique assemblages of taxonomically significant relict populations known only from a single cave or cave system. However, the absence of photosynthesis in this totally lightless environment and the presence of a highly stratified water column and long residence times for cave waters, characteristically result in depleted dissolved oxygen levels. Under such circumstances, organic pollution, even at low levels, can produce anoxic conditions and may consequently result in the extinction of entire species of cavernicolous fauna. We here present data on the normal environment of marine caves in Bermuda and cite as an example a cave which has become grossly polluted as a result of indiscriminate dumping.  相似文献   

Raman spectroscopic measurements of synthetic gas hydrates in the ocean   总被引：1，自引：0，他引：1  

K.C. Hester  S.N. White  E.T. Peltzer  P.G. Brewer  E.D. Sloan   《Marine Chemistry》2006,98(2-4):304-314

A Raman spectrometer extensively modified for deep ocean use was used to measure synthetic hydrates formed in an ocean environment. This was the first time hydrates formed in the ocean have been measured in situ using Raman spectroscopy. Gas hydrates were formed in situ in the Monterey Bay by pressurizing a Pyrex cell with various gas mixtures. Raman spectra were obtained for sI methane hydrate and sII methane + ethane hydrate. Gas occlusion resulting from rapid gas growth of methane hydrate was measured immediately after formation. The Raman shift for methane free gas was coincident with that of methane in the small 5¹² hydrate cage. The methane Raman peak widths were used to discriminate between methane in the free gas and hydrate phase. Methane + ethane sII hydrate was formed for 43 days on the seafloor. In this case, gas occlusion was not measured when the gas hydrates were allowed to form over an extended time period. Equivalent Raman spectra were obtained for the in situ and laboratory-formed sII methane + ethane hydrates, under similar p, T, and x conditions. With the Raman spectrometer operating in the ocean, seawater contributes to the Raman spectra obtained. Both the Raman bands for the sulfate ion and water were used to qualitatively determine the distribution of water phases measured (hydrate, seawater) in the Raman spectra.  相似文献   

Preface     

Yoshihisa Shirayama  Kazuhiro Kogure  Peter G. Brewer  Takashi Ohsumi  Joji Ishizaka  Jun Kita  Yuji Watanabe 《Journal of Oceanography》2004,60(4):691-691

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Effects of Direct Ocean CO<Subscript>2</Subscript> Injection on Deep-Sea Meiofauna     

James P. Barry  Kurt R. Buck  Chris F. Lovera  Linda Kuhnz  Patrick J. Whaling  Edward T. Peltzer  Peter Walz  Peter G. Brewer 《Journal of Oceanography》2004,60(4):759-766

Purposeful deep-sea carbon dioxide sequestration by direct injection of liquid CO₂ into the deep waters of the ocean has the potential to mitigate the rapid rise in atmospheric levels of greenhouse gases. One issue of concern for this carbon sequestration option is the impact of changes in seawater chemistry caused by CO₂ injection on deep-sea ecosystems. The effects of deep-sea carbon dioxide injection on infaunal deep-sea organisms were evaluated during a field experiment in 3600 m depth off California, in which liquid CO₂ was released on the seafloor. Exposure to the dissolution plume emanating from the liquid CO₂ resulted in high rates of mortality for flagellates, amoebae, and nematodes inhabiting sediments in close proximity to sites of CO₂ release. Results from this study indicate that large changes in seawater chemistry (i.e. pH reductions of ∼0.5–1.0 pH units) near CO₂ release sites will cause high mortality rates for nearby infaunal deep-sea communities. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A felsic dyke swarm formed under the sea: the Archean Hunter Mine Group,south-central Abitibi Belt,Quebec, Canada     

W Mueller  JA Donaldson 《Bulletin of Volcanology》1992,54(7):602-610

An extensive rhyolitic dyke swarm has intruded subaqueous pyroclastic deposits, iron-formations, hyaloclastite breccias and lava flows of the 2730 Ma Hunter Mine Group (HMG) in the south-central part of the Archean Abitibi belt, Quebec. The dyke swarm has a minimum width of 500 m and can be traced perpendicular to the section for 2.4 km. Based on crosscutting relationships, chilled margins, quartz content and colour, five distinct dyke generations have been established. Each dyke generation has several magmatic pulses as indicated by parallel rows of columnar joints. Absence of brecciation between parallel rows suggests extremely brief intervals between magma pulses. The central parts of most dykes display inverted V-shaped patterns of columnar-joint convergence, inferred to indicate differential cooling during the late stages of dyke propagation. The dykes commonly display delicate spherulites suggesting rapid cooling, solidification temperatures between 400 and 600°C and penecontemporaneous devitrification. Quartz-feldspar aggregates in the groundmass have locally developed microgranophyric textures. Large spherulites near the chilled margins probably formed at temperatures below 400°C. Percolation of abundant water throughout the dyke complex is suggested by ubiquitous prominent chilled dyke margins. Development of a chilled margin 500 m along one dyke suggests that water percolated at least 500 m below the water/rock interface. Because the dykes intruded subaqueous pyroclastic deposits of similar composition, dyke emplacement below the sea floor is inferred. Interstratification of pillowed flows and brecciated pillowed flows containing rhyolite fragments at the top of the 4–5-km-thick sequence indicates that the central felsic complex probably never emerged during its evolutionary history, supporting the contention that the felsic dyke complex was emplaced beneath the Archean sea floor.  相似文献   

The marine chemistry of iodine in anoxic basins   总被引：1，自引：0，他引：1  

George T.F Wong  Peter G Brewer 《Geochimica et cosmochimica acta》1977,41(1):151-159

The distribution of dissolved iodate and iodide has been determined in two anoxic basins, the Black Sea and the Cariaco Trench; and the oxic Venezuela Basin which serves as a comparison for normal oceanic conditions. In normal oceanic waters, iodate is the predominant species; its concentration is lowest at the surface (ca. 0.3 μM) and increases with depth to ca. 0.5 μM. In contrast, the iodide concentration shows maximum values in surface waters and rapidly decreases to <0.01 μM below the euphotic zone. In anoxic basins, the reduced pE reverses this trend. The concentration of iodide increases rapidly in the oxygen-sulfide mixing zone from 0.02 to 0.46 μM, and 0.01 to 0.43 μM, in the Cariaco Trench and the Black Sea, respectively. The iodate concentration, meanwhile, decreases to zero.The total iodine to salinity ratio is lower in the surface waters with a range of 7.3–12.1 nmoles/g suggesting a possible depletion by organisms. In the anoxic basins, a maximum in this ratio is observed just above the oxygen-sulfide boundary (15–17 nmoles/g) and is indicative of particle dissolution in a strong pycnocline. In the anoxic zone of the Cariaco Trench, the ratio is constant at 12.3 nmoles/g, whereas in the Black Sea, it increases with depth from 10.0 to 19.3 nmoles/g, suggesting a possible flux of iodide from the bottom sediments.By considering the distribution of iodate and iodide in oxic and anoxic basins, the lower limit of the pE of the oxic ocean is estimated to be 10.7, given our present analytical capability. Thermodynamic considerations further suggest that the iodide-iodate couple is a poor indicator for the pE of the oceans with a limited usable range of 10.0–10.7.  相似文献