Stability of the subseismic wave equation for the Earth's fluid core     

Susan Friedlander 《地球物理与天体物理流体动力学》2013,107(1-2):151-167

Abstract

The effects of compressibility on the stability of internal oscillations in the Earth's fluid core are examined in the context of the subseismic approximation for the equations of motion describing a rotating, stratified, self-gravitating, compressible fluid in a thick shell. It is shown that in the case of a bounded fluid the results are closely analogous to those derived under the Boussinesq approximation.  相似文献   

Mafic magmas from Mount Baker in the northern Cascade arc,Washington: probes into mantle and crustal processes     

Nicole?E.?MooreEmail author  Susan?M.?DeBari 《Contributions to Mineralogy and Petrology》2012,163(3):521-546

Five mafic lava flows located on the southern flank of Mount Baker are among the most primitive in the volcanic field. A comprehensive dataset of whole rock and mineral chemistry reveals the diversity of these mafic lavas that come from distinct sources and have been variably affected by ascent through the crust. Disequilibrium textures present in all of the lavas indicate that crustal processes have affected the magmas. Despite this evidence, mantle source characteristics have been retained and three primitive endmember lava types are represented. These include (1) modified low-K tholeiitic basalt (LKOT-like), (2) typical calc-alkaline (CA) lavas, and (3) high-Mg basaltic andesite and andesite (HMBA and HMA). The Type 1 endmember, the basalt of Park Butte (49.3–50.3 wt% SiO₂, Mg# 64–65), has major element chemistry similar to LKOT found elsewhere in the Cascades. Park Butte also has the lowest overall abundances of trace elements (with the exception of the HREE), indicating it is either derived from the most depleted mantle source or has undergone the largest degree of partial melting. The Type 2 endmember is represented by the basalts of Lake Shannon (50.7–52.6 wt% SiO₂, Mg# 58–62) and Sulphur Creek (51.2–54.6 wt% SiO₂, Mg# 56–57). These two lavas are comparable to calc-alkaline rocks found in arcs worldwide and have similar trace element patterns; however, they differ from each other in abundances of REE, indicating variation in degree of partial melting or fractionation. The Type 3 endmember is represented by the HMBA of Tarn Plateau (51.8–54.0 wt% SiO₂, Mg# 68–70) and the HMA of Glacier Creek (58.3–58.7 wt% SiO₂, Mg# 63–64). The strongly depleted HREE nature of these Type 3 units and their decreasing Mg# with increasing SiO₂ suggests fractionation from a high-Mg basaltic parent derived from a source with residual garnet. Another basaltic andesite unit, Cathedral Crag (52.2–52.6 wt% SiO₂, Mg# 55–58), is an Mg-poor differentiate of the Type 3 endmember. The calc-alkaline lavas are least enriched in a subduction component (lowest H₂O, Sr/P_N, and Ba/Nb), the LKOT-like lavas are intermediate (moderate Sr/P_N and Ba/Nb), and the HMBA are most enriched (highest H₂O, Sr/P_N and Ba/Nb). The generation of the LKOT-like and calc-alkaline lavas can be successfully modeled by partial melting of a spinel lherzolite with variability in composition of slab flux and/or mantle source depletion. The HMBA lavas can be successfully modeled by partial melting of a garnet lherzolite with slab flux compositionally similar to the other lava types, or less likely by partial melting of a spinel lherzolite with a distinctly different, HREE-depleted slab flux.  相似文献   

The Effects of Integrated Marsh Management (IMM) on Salt Marsh Vegetation,Nekton, and Birds     

Ilia Rochlin  Mary-Jane James-Pirri  Susan C. Adamowicz  Mary E. Dempsey  Thomas Iwanejko  Dominick V. Ninivaggi 《Estuaries and Coasts》2012,35(3):727-742

An integrated marsh management (IMM) project in an urbanized watershed on Long Island, New York, USA, aimed to mitigate salt marsh degradation and to reduce mosquito production by an innovative combination of restoration and open marsh water management methods. The grid ditch network at two treatment marshes was replaced with naturalized tidal channels and ponds. Effects of the hydrologic alterations were monitored utilizing a before–after–control–impact approach. The treatment marshes experienced a number of beneficial outcomes including a fourfold reduction in the invasive Phragmites australis and increased native vegetation cover in the most degraded portions of the marsh, increased abundance and diversity of marsh killifish and estuarine nekton species, higher shorebird and waterfowl densities, and increased avian species diversity. The successful implementation of IMM concept led to improved marsh health and diminished mosquito production. Therefore, this study may serve as a template for similar large-scale integrated salt marsh restoration projects.  相似文献   

Sub-Saharan African urbanisation and global environmental change     

Susan Parnell  Ruwani Walawege 《Global Environmental Change》2011

Scientific evidence for global environmental change in Africa presents a prima facia case for increased human migration and displacement. Closer scrutiny of the evidence on demographic change, however, suggests that migration and displacement are less important variables in explaining the human dimensions of global environmental change on the continent than is commonly projected. Natural population growth in cities is a more important dynamic in the evolving system of human settlement in Africa and this significant shift in where people live, both now and in the future is overlooked by the emphasis on the potential impact of environmentally induced migration. Even without any movement from the countryside, cities represent the fastest growing sector of the sub-Saharan African population. The existing vulnerability of African cities, with their fast growing populations and weak management means any environmental change is likely to have significant consequences for cities. Taking the sub-Saharan African demographic evidence seriously means that the scholarly and policy emphasis currently directed to GEC migration and displacement might be more effectively redirected to questions of the interface between global environmental change and urban areas.  相似文献   

The long term operation of a biologically based treatment system that removes As, S and Zn from industrial (smelter operation) landfill seepage     

Mattes AlLes J. Evans  W. Douglas GouldW.F.A. Duncan  Susan Glasauer 《Applied Geochemistry》2011,26(11):1886-1896

Passive treatment systems have a long history in the remediation of mining impacted water. The functioning of these systems is poorly understood, in particular the microbial processes that underpin metal removal. A biologically based engineered wetland treatment system that has operated in Trail, B.C. to treat seepage from a historic Pb and Zn smelter landfill, was investigated. The system has functioned for more than a decade, an unusually long life span for a passive bioreactor design. The study focuses on the 5a of operation from 2003 until 2007. Arsenic is a major contaminant in the ore that is processed in Trail, which has caused high As concentrations in the seepage. In addition to As, Zn and Cd removal were investigated. During the 5-a period, the system sequestered 2990 kg of As, 7700 kg of Zn and 85 kg of Cd. Nearly 90% of these elements were removed in two biochemical reactors (BCRs) that comprise the first two components of the six cell system, with the remainder removed in plant-based polishing cells. Average input concentrations over the 5-a period were 2.3 and 4.1 mM for As and Zn, respectively and 0.45 μM for Cd. Final output concentrations were reduced to 0.01 mM for As, 0.05 mM for Zn and 0.18 μM for Cd. Sulfur removal averaged 34% of input concentration. Analysis of mineral formation in the system using X-ray diffraction and scanning electron microscopy indicated kottigite (Zn₃(AsO₄)₂⋅8H₂O) and sphalerite (ZnS) as the major mineral phases controlling As and Zn sequestration; Cd appears to be immobilized as CdS. Evidence for orpiment was obtained from X-ray absorption spectroscopy (XANES) studies, and arsenopyrite was not detected. Although microbial activity dominates the removal of Zn, As and Cd from the soluble phase, abiotic removal mechanisms contribute including sorption of As and Zn to biosolids and filtration of metal precipitates by the solid matrix. The removal of toxic elements over the period appeared to be relatively consistent. Seasonal fluctuations, a large spike in input element concentrations over a 2-month period, and removal of the two biochemical reactors during a period of reconstruction appeared to have relatively little impact on the system as a whole.  相似文献   

Solubility and near-equilibrium dissolution rates of quartz in dilute NaCl solutions at 398-473 K under alkaline conditions     

Michael C. Davis  Jörgen Rosenqvist  Susan L. Brantley 《Geochimica et cosmochimica acta》2011,75(2):401-415

The dissolution-precipitation of quartz controls porosity and permeability in many lithologies and may be the best studied mineral-water reaction. However, the rate of quartz-water reaction is relatively well characterized far from equilibrium but relatively unexplored near equilibrium. We present kinetic data for quartz as equilibrium is approached from undersaturation and more limited data on the approach from supersaturated conditions in 0.1 molal NaCl + NaOH + NaSiO(OH)₃ solutions with pH 8.2-9.7 at 398, 423, 448, and 473 K. We employed a potentiometric technique that allows precise determination of solution speciation within 2 kJ mol⁻¹ of equilibrium without the need for to perturb the system through physical sampling and chemical analysis. Slightly higher equilibrium solubilities between 423 and 473 K were found than reported in recent compilations. Apparent activation energies of 29 and 37 kJ mol⁻¹ are inferred for rates of dissolution at two surface sites with different values of connectedness: dissolution at Q¹ or Q² silicon sites, respectively. The dissolution mechanism varies with ΔG such that reactions at both sites control dissolution up until a critical free energy value above which only reactions at Q¹ sites are important. When our near-equilibrium dissolution rates are extrapolated far from equilibrium, they agree within propagated uncertainty at 398 K with a recently published model by Bickmore et al. (2008). However, our extrapolated rates become progressively slower than model predictions with increasing temperature. Furthermore, we see no dependence of the postulated Q¹ reaction rate on pH, and a poorly-constrained pH dependence of the postulated Q² rate. Our slow extrapolated rates are presumably related to the increasing contribution of dissolution at Q³ sites far from equilibrium. The use of the potentiometric technique for rate measurement will yield both rate data and insights into the mechanisms of dissolution over a range of chemical affinity. Such measurements are needed to model the evolution of many natural systems quantitatively.  相似文献   

The formation of metastable aluminosilicates in the Al-Si-H₂O system: Results from solution chemistry and solid-state NMR spectroscopy     

Harris E. Mason  Robert S. Maxwell  Susan A. Carroll 《Geochimica et cosmochimica acta》2011,75(20):6080-6093

We present the results of a series of experiments designed to probe the interactions between Al and the amorphous silica surface as a function of thermodynamic driving forces. The results from ²⁷Al single pulse magic angle spinning (SP/MAS) and ²⁷Al{¹H} rotational echo double resonance (REDOR) allow us to identify the reaction products and constrain their structure. In all cases, despite low Al and Si concentrations we observe the formation of metastable aluminosilicates. Results from low temperature experiments indicate that despite thermodynamic driving forces for the formation of gibbsite we observe the precipitation of separate octahedrally coordinated Al (Al^[6]) and tetrahedrally coordinated Al (Al^[4]) silicate phases. At higher temperatures the Al^[4] silicate phase dominates the speciation. Structural models derived from the NMR data are also proposed, and the results are discussed as they relate to previous work on Al/Si cycling.  相似文献   

The role of granites in volcanic-hosted massive sulphide ore-forming systems: an assessment of magmatic�Chydrothermal contributions     

David L. Huston  Jorge M. R. S. Relvas  J. Bruce Gemmell  Susan Drieberg 《Mineralium Deposita》2011,46(5-6):473-507

Assessment of geological, geochemical and isotopic data indicates that a significant subgroup of volcanic-hosted massive sulphide (VHMS) deposits has a major or dominant magmatic?Chydrothermal source of ore fluids and metals. This group, which is typically characterised by high Cu and Au grades, includes deposits such as those in the Neoarchean Doyon-Bousquet-LaRonde and Cambrian Mount Lyell districts. These deposits are distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents intimately associated with ore zones. In many of these deposits, ??³⁴S_sulphide is low, with a major population below ?3??; ??³⁴S_sulphate differs from coexisting seawater and ??³⁴S_{sulphate?Csulphide}????20?C30??. These characteristics are interpreted as the consequence of disproportionation of magmatic SO₂ as magmatic?Chydrothermal fluids ascended and cooled and as a definitive evidence for a significant magmatic?Chydrothermal contribution. Other characteristics that we consider diagnostic of significant magmatic?Chydrothermal input into VHMS ore fluids include uniformly high (>3 times modern seawater values) salinities or very ¹⁸O-enriched (??¹⁸O?>?5??) ore fluids. We do not consider other criteria [e.g. variable salinity, moderately high ??¹⁸O_fluid (2?C5??), ??³⁴S_sulphide near 0??, metal assemblages or a spatial association with porphyry Cu or other clearly magmatic-hydrothermal deposits] that have been used previously to advocate significant magmatic?Chydrothermal contributions to be diagnostic as they can be produced by non-magmatic processes known to occur in VHMS mineral systems. However, in general, a small magmatic?Chydrothermal contribution cannot be excluded in most VHMS systems considered. Conclusive data that imply minimal magmatic?Chydrothermal contributions are only available in the Paleoarchean Panorama district where coeval seawater-dominated and magmatic?Chydrothermal systems appear to have been physically separated. This district, which is characterised by chloritic and sericitic alteration assemblages and lacks aluminous advanced argillic alteration assemblages, is typical of many VHMS deposits around the world, suggesting that for ??garden variety?? VHMS deposits, a significant magmatic?Chydrothermal contribution is not required. Other than deposits associated with advanced argillic alteration assemblages, the only deposit for which we ascribe a major magmatic?Chydrothermal contribution is the Devonian Neves Corvo deposit. This deposit differs from other deposits in the Iberian Pyrite Belt and around the world in being extremely Sn-rich, with the Sn closely associated with Cu and in having formed from high ¹⁸O-rich fluids (??¹⁸O_fluid ??8.5??). We consider these characteristics, particularly the last, as diagnostic of a significant magmatic hydrothermal contribution. Our analysis indicates that two subgroups of VHMS deposits have a major magmatic?Chydrothermal contribution: Cu/Au-rich deposits with aluminous alteration assemblages and reduced, very Sn-rich deposits in which Sn was introduced in a high-temperature ore assemblage. Comparison with ??normal?? VHMS deposits suggests that these subgroups of VHMS deposits may form in specialised tectonic environments. The Cu/Au-rich deposits appear to form adjacent to magmatic arcs, an environment conducive to the generation of hydrous, oxidised melts by melting metasomatised mantle in the wedge above the subducting slab. This contrasts with the back-arc setting of ??normal?? VHMS deposits in which relatively dry granites (In this contribution, we use the term granite sensu latto) formed by decompression melting drive seawater-dominated hydrothermal circulation. The tectonic setting of highly Sn-rich VHMS deposits such as Neves Corvo is less clear; however, thick continental crust below the ore-hosting basin may be critical, as it is in other Sn deposits.  相似文献   

Recent advances in offshore geotechnics for deep water oil and gas developments   总被引：3，自引：0，他引：3  

Mark F. Randolph  Christophe Gaudin  Susan M. Gourvenec  David J. White  Noel Boylan  Mark J. Cassidy 《Ocean Engineering》2011,38(7):818-834

The paper presents an overview of recent developments in geotechnical analysis and design associated with oil and gas developments in deep water. Typically the seabed in deep water comprises soft, lightly overconsolidated, fine grained sediments, which must support a variety of infrastructure placed on the seabed or anchored to it. A particular challenge is often the mobility of the infrastructure either during installation or during operation, and the consequent disturbance and healing of the seabed soil, leading to changes in seabed topography and strength. Novel aspects of geotechnical engineering for offshore facilities in these conditions are reviewed, including: new equipment and techniques to characterise the seabed; yield function approaches to evaluate the capacity of shallow skirted foundations; novel anchoring systems for moored floating facilities; pipeline and steel catenary riser interaction with the seabed; and submarine slides and their impact on infrastructure. Example results from sophisticated physical and numerical modelling are presented.  相似文献   

Projecting uncertainty onto marine megafauna trajectories     

Alexander A. Robel  M. Susan Lozier  Steven J. Bograd 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(9):915-921

In this study, a method is proposed for estimating the uncertainty of a Lagrangian pathway calculated from an undersampled ocean surface velocity field. The primary motivation and application for this method is the differentiation between active and passive movements for sea turtles whose trajectories are observed with satellite telemetry. Synthetic trajectories are launched within a reconstructed surface velocity field and integrated forward in time to produce likely trajectories of an actual turtle or drifter. Uncertainties in both the initial conditions at launch and the velocity field along the trajectory are used to yield an envelope of possible synthetic trajectories for each actual trajectory. The juxtaposition of the actual trajectory with the resulting cloud of synthetic trajectories provides a means to distinguish between active and passive movements of the turtle. The uncertainty estimates provided by this model may lead to improvements in our understanding of where and when turtles are engaged in specific behaviors (i.e. migration vs. foraging)—for which potential management efforts may vary accordingly.  相似文献