The seismic anomaly beneath Iceland extends down to the mantle transition zone and no deeper   总被引：8，自引：0，他引：8  

G. R. Foulger  M. J. Pritchard  B. R. Julian  J. R. Evans  R. M. Allen  G. Nolet  W. J. Morgan  B. H. Bergsson  P. Erlendsson  S. Jakobsdóttir  S. Ragnarsson  R. Stefansson  K. Vogfjörd 《Geophysical Journal International》2000,142(3):F1-F5

A 3-D teleseismic tomography image of the upper mantle beneath Iceland of unprecedented resolution reveals a subvertical low wave speed anomaly that is cylindrical in the upper 250 km but tabular below this. Such a morphological transition is expected towards the bottom of a buoyant upwelling. Our observations thus suggest that magmatism at the Iceland hotspot is fed by flow rising from the mantle transition zone. This result contributes to the ongoing debate about whether the upper and lower mantles convect separately or as one. The image also suggests that material flows outwards from Iceland along the Reykjanes Ridge in the upper 200 km, but is blocked in the upper 150 km beneath the Tjornes Fracture Zone. This provides direct observational support for the theory that fracture zones dam lateral flow along ridges.  相似文献   

Fluorescent molecular hydrogen in the Eagle nebula     

L. E. Allen  M. G. Burton  S. D. Ryder  M. C. B. Ashley  J. W. V. Storey 《Monthly notices of the Royal Astronomical Society》1999,304(1):98-108

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Wide Binaries among High-Velocity and Metal-Poor Stars     

Christine Allen  M.A. Herrera  A. Poveda 《Astrophysics and Space Science》1999,265(1-4):233-234

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Rehabilitation of Saline Wetland, Olympics 2000 Site, Sydney (Australia)—II: Saltmarsh Transplantation Trials and Application     

M. D. Burchett  C. Allen  A. Pulkownik  G. Macfarlane 《Marine pollution bulletin》1999,37(8-12):526-534

The New South Wales Olympic Co-ordination Authority, which is responsible for the redevelopment of the site for the Olympic Games 2000, Sydney, is committed to the rehabilitation of the remnant ecosystems remaining on the site. This paper describes a 3-year saltmarsh transplantation project, and resulting management approaches for the rehabilitation of other saline wetland areas on the site. Two series of cuttings (spring and autumn) were made, including three dominant species and three species rare in Sydney. It was found that all the species could be propagated without difficulty, but field survival and growth were much higher for the spring series than the autumn one. Measurement was also made of the colonisation of mangrove and saltmarsh species that occurred at the site over the course of the trials. New understandings of estuarine wetland colonisation have emerged, and the information has been used to develop methods of transplantation for other parts of the Olympic site, and to define management needs for monitoring success.  相似文献   

A second review of the international status of engineering geology — encompassing hydrogeology, environmental geology and the applied geosciences     

Allen W. Hatheway  George M. Reeves   《Engineering Geology》1999,53(3-4):259-296

Engineering geology, in 1996, worldwide, was experiencing considerable turmoil due to the uncertain nature of national economies and the general situation of inadequate funds to meet the demands of failing of the national infrastructures that serve citizens. Aside from the previously war-damaged cities of Western Europe, new public service systems of transportation and utilities elsewhere often lagged well behind growth.

It will be some time before international aid and civil engineering contracts are initiated for anything other than humanitarian and basic emergency aid work in these areas.

Many countries in the western hemisphere, eastern Europe, the former Soviet Union and developing nations in particular are still in need of basic water and sewage services as well as repair and replacement of old existing systems. Continued partisan warfare in the Balkan states of Albania, Bosnia, Croatia and Serbia forecast the eventual need for redevelopment. Rumblings of broad-scale economic problems in Far-Eastern economies did little to make overseas contract opportunities in these areas very attractive.

Large consulting firms were challenged by an increasing number of individual and small practices who are prepared to operate on 1970's rates and prices for services and government and industry was taking advantage of that situation. More and more individuals were offering services in engineering geology and associated engineering fields and there was a sense of not having enough work to go around. Hence, price competition was again being promoted. Consequently in both Europe and the Americas, the variability of competence was enlarging and a significant amount of so-called ‘professional ’ work was lacking in overall quality. This was especially evident in ‘Environmental’ areas of work.

This begs the question: ‘Is not engineering geology, or any other aspect of applied geosciences, not environmental in nature and essence, fundamentally and in entirety?’

Environmental restoration demands were still being made by governments, but the pressure to complete such work was being relaxed on account of economics. Our clients were asking for more service at lower fees. Clients were still largely unwilling to openly acknowledge that less money spent on competent engineering geologic consultation means that more risk should be accepted by the owner or operator of projects.  相似文献   

Spatial demography of Calanus finmarchicus in the Irminger Sea     

M.R. Heath  J. Rasmussen  J. Allen  A.S. Brierley  A. Bunker  R. Davidson  W.S.C. Gurney  S. Hay  A.G. Hirst  A. Ingvarsdottir  P. Lindeque  D. Montagnes  R. Pollard  R.A. Saunders  G. Smerdon  P. Walsham  L. Webster 《Progress in Oceanography》2008,76(1):39-88

Continuous Plankton Recorder data suggest that the Irminger Sea supports a major proportion of the surface-living population of the copepod Calanus finmarchicus in the northern North Atlantic, but there have been few studies of its population dynamics in the region. In this paper, we document the seasonal changes in the demographic structure of C. finmarchicus in the Irminger Sea from a field programme during 2001/2002, and the associations between its developmental stages and various apparent bio-physical zones. Overwintering stages were found widely at depth (>500 m) across the Irminger Sea, and surviving females were widely distributed in the surface waters the following spring. However, recruitment of the subsequent generation was concentrated around the fringes of the Irminger Sea basin, along the edges of the Irminger and East Greenland Currents, and not in the central basin. In late summer animals were found descending back to overwintering depths in the Central Irminger Sea. The key factors dictating this pattern of recruitment appear to be (a) the general circulation regime, (b) predation on eggs in the spring, possibly by the surviving G0 stock, and (c) mortality of first feeding naupliar stages in the central basin where food concentrations appear to be low throughout the year.We compared the demographic patterns in 2001/2002 with observations from the only previous major survey in 1963 and with data from the Continuous Plankton Recorder (CPR) surveys. In both previous data sets, the basic structure of G0 ascent from the central basin and G1 recruitment around the fringes was a robust feature, suggesting that it is a recurrent phenomenon. The Irminger Sea is a complex mixing zone between polar and Atlantic water masses, and it has also been identified as a site of sporadic deep convection. The physical oceanographic characteristics of the region are therefore potentially sensitive to climate fluctuations. Despite this, the abundance of C. finmarchicus in the region, as measured by the CPR surveys, appears not to have responded to climate factors linked to the North Atlantic Oscillation Index, in contrast with the stocks in eastern Atlantic areas. We speculate that this may because biological factors (production and mortality), rather than transport processes are the key factors affecting the population dynamics in the Irminger Sea.  相似文献   

A Lagrangian biogeochemical study of an eddy in the Northeast Atlantic     

T.D. Jickells  P.S. Liss  S. Turner  J. Read  L.M. Cardenas  F. Carse  M. Hamren-Larssen  M. Steinke  A. Thompson  S.D. Archer  C.S. Law  P.D. Nightingale  C.E. Widdicombe  L.C. Gilpin  G. Savidge  P. Hadziabdic  R. Upstill-Goddard  R. Simó  A. Allen 《Progress in Oceanography》2008,76(3):366-398

We report the results of an experiment in the Northeast Atlantic in which sulphur hexafluoride (SF₆) was released within an eddy and the behaviour of trace gases, nutrients and productivity followed within a Lagrangian framework over a period of 24 days. Measurements were also made in the air above the eddy in order to estimate air-sea exchange rates for some components. The physical, biological and biogeochemical properties of the eddy resemble those of other eddies studied in this area, suggesting that the results we report may be applicable beyond the specific eddy studied. During a period of low wind speed at the start of the experiment, we are able to quantitatively describe and balance the nutrient and carbon budgets for the eddy. We also report concentrations of various trace gases in the region which are similar to those observed in other studies and we estimate exchange rates for several trace gases. We show that the importance of gas exchange over other loss terms varies with time and also varies for the different gases. We show that the various trace gases considered (CO₂, dimethyl sulphide (DMS), N₂O, CH₄, non-methane-hydrocarbons, methyl bromide, methyl iodide and volatile selenium species) are all influenced by physical and biological processes, but the overall distribution and temporal variability of individual gases are different to one another. A storm disrupted the stratification in the eddy during the experiment, resulting in enhanced nutrient supply to surface waters, enhanced gas exchange rates and a change in plankton community, which we quantify, although overall productivity was little changed. Emphasis is placed on the regularity of storms in the temperate ocean and the importance of these stochastic processes in such systems.  相似文献   

Hydrogeology and geochemistry of near-shore submarine groundwater discharge at Flamengo Bay,Ubatuba, Brazil     

June A. Oberdorfer  Matthew Charette  Matthew Allen  Jonathan B. Martin  Jaye E. Cable 《Estuarine, Coastal and Shelf Science》2008

Near-shore discharge of fresh groundwater from the fractured granitic rock at Flamengo Bay, Ubatuba, Brazil, is strongly controlled by the local geology. Freshwater flows primarily through a zone of weathered granite to a distance of 24 m offshore. In the nearshore environment this weathered granite is covered by about 0.5 m of well-sorted, coarse sands containing pore water with sea water salinity, with an abrupt transition to much lower salinity once the weathered granite is penetrated. Further offshore, low-permeability marine sediments contain saline porewater, marking the limit of offshore migration of freshwater. Freshwater flux rates based on tidal signal and hydraulic gradient analysis indicate a fresh submarine groundwater discharge of 0.17–1.6 m³/day per m of shoreline. Dissolved inorganic nitrogen and silicate are elevated in the porewater relative to seawater, and appeared to be a net source of nutrients to the overlying water column. The major ion concentrations suggest that the freshwater within the aquifer has a short residence time. Major element concentrations do not reflect in situ alteration of the granitic rocks, possibly because the alteration occurred prior to development of the current discharge zones, or because of large volumes of water discharge in this high rainfall region.  相似文献   

Bioremediation in Fractured Rock: 1. Modeling to Inform Design,Monitoring, and Expectations          下载免费PDF全文

Claire R. Tiedeman  Allen M. Shapiro  Paul A. Hsieh  Thomas E. Imbrigiotta  Daniel J. Goode  Pierre J. Lacombe  Mary F. DeFlaun  Scott R. Drew  Carole D. Johnson  John H. Williams  Gary P. Curtis 《Ground water》2018,56(2):300-316

Field characterization of a trichloroethene (TCE) source area in fractured mudstones produced a detailed understanding of the geology, contaminant distribution in fractures and the rock matrix, and hydraulic and transport properties. Groundwater flow and chemical transport modeling that synthesized the field characterization information proved critical for designing bioremediation of the source area. The planned bioremediation involved injecting emulsified vegetable oil and bacteria to enhance the naturally occurring biodegradation of TCE. The flow and transport modeling showed that injection will spread amendments widely over a zone of lower‐permeability fractures, with long residence times expected because of small velocities after injection and sorption of emulsified vegetable oil onto solids. Amendments transported out of this zone will be diluted by groundwater flux from other areas, limiting bioremediation effectiveness downgradient. At nearby pumping wells, further dilution is expected to make bioremediation effects undetectable in the pumped water. The results emphasize that in fracture‐dominated flow regimes, the extent of injected amendments cannot be conceptualized using simple homogeneous models of groundwater flow commonly adopted to design injections in unconsolidated porous media (e.g., radial diverging or dipole flow regimes). Instead, it is important to synthesize site characterization information using a groundwater flow model that includes discrete features representing high‐ and low‐permeability fractures. This type of model accounts for the highly heterogeneous hydraulic conductivity and groundwater fluxes in fractured‐rock aquifers, and facilitates designing injection strategies that target specific volumes of the aquifer and maximize the distribution of amendments over these volumes.  相似文献   

Bioremediation in Fractured Rock: 2. Mobilization of Chloroethene Compounds from the Rock Matrix          下载免费PDF全文

Allen M. Shapiro  Claire R. Tiedeman  Thomas E. Imbrigiotta  Daniel J. Goode  Paul A. Hsieh  Pierre J. Lacombe  Mary F. DeFlaun  Scott R. Drew  Gary P. Curtis 《Ground water》2018,56(2):317-336

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