A mixed finite-element method for solving the poroelastic Biot equations with electrokinetic coupling     

C. C. Pain  J. H. Saunders  M. H. Worthington  J. M. Singer  W. Stuart-Bruges  G. Mason  A. Goddard 《Geophysical Journal International》2005,160(2):592-608

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Methylmercury production in sediments of Chesapeake Bay and the mid-Atlantic continental margin   总被引：3，自引：0，他引：3  

T.A. Hollweg  C.C. Gilmour  R.P. Mason 《Marine Chemistry》2009,114(3-4):86-101

Methylmercury (MeHg) concentration and production rates were studied in bottom sediments along the mainstem of Chesapeake Bay and on the adjoining continental shelf and slope. Our objectives were to 1) observe spatial and temporal changes in total mercury (HgT) and MeHg concentrations in the mid-Atlantic coastal region, 2) investigate biogeochemical factors that affect MeHg production, and 3) examine the potential of these sediments as sources of MeHg to coastal and open waters. Estuarine, shelf and slope sediments contained on average 0.5 to 1.5% Hg as MeHg (% MeHg), which increased significantly with salinity across our study site, with weak seasonal trends. Methylation rate constants (k_meth), estimated using enriched stable mercury isotope spikes to intact cores, showed a similar, but weaker, salinity trend, but strong seasonality, and was highly correlated with % MeHg. Together, these patterns suggest that some fraction of MeHg is preserved thru seasons, as found by others [Orihel, D.M., Paterson, M.J., Blanchfield, P.J., Bodaly, R.A., Gilmour, C.C., Hintelmann, H., 2008. Temporal changes in the distribution, methylation, and bioaccumulation of newly deposited mercury in an aquatic ecosystem. Environmental Pollution 154, 77] Similar to other ecosystems, methylation was most favored in sediment depth horizons where sulfate was available, but sulfide concentrations were low (between 0.1 and 10 μM). MeHg production was maximal at the sediment surface in the organic sediments of the upper and mid Bay where oxygen penetration was small, but was found at increasingly deeper depths, and across a wider vertical range, as salinity increased, where oxygen penetration was deeper. Vertical trends in MeHg production mirrored the deeper, vertically expanded redox boundary layers in these offshore sediments. The organic content of the sediments had a strong impact on the sediment:water partitioning of Hg, and therefore, on methylation rates. However, the HgT distribution coefficient (K_D) normalized to organic matter varied by more than an order of magnitude across the study area, suggesting an important role of organic matter quality in Hg sequestration. We hypothesize that the lower sulfur content organic matter of shelf and slope sediments has a lower binding capacity for Hg resulting in higher MeHg production, relative to sediments in the estuary. Substantially higher MeHg concentrations in pore water relative to the water column indicate all sites are sources of MeHg to the water column throughout the seasons studied. Calculated diffusional fluxes for MeHg averaged  1 pmol m^− 2 day^− 1. It is likely that the total MeHg flux in sediments of the lower Bay and continental margin are significantly higher than their estimated diffusive fluxes due to enhanced MeHg mobilization by biological and/or physical processes. Our flux estimates across the full salinity gradient of Chesapeake Bay and its adjacent slope and shelf strongly suggest that the flux from coastal sediments is of the same order as other sources and contributes substantially to the coastal MeHg budget.  相似文献   

A wave model for the Great Barrier Reef   总被引：1，自引：0，他引：1  

Thomas A. Hardy  Luciano B. Mason  Jason D. McConochie 《Ocean Engineering》2001,28(1):1869

A new wind wave generation model, WAMGBR, is presented that has been adapted from WAM especially for use in the complex geometry of the Great Barrier Reef. A technique (reef parameterization) has been presented that incorporates sub-grid scale dissipation caused by coral reefs. Three other improvements to WAM have been proposed. An explicit/implicit finite difference scheme has been implemented that allows for more efficient modelling (longer time steps) while maintaining diffusive characteristics that are at least as good as those of WAM. An offset in discrete angles creates more uniform diffusive characteristics. And, a transformed spherical coordinate system allows for more efficient grid sizes and smaller grid dependent refraction. Comparisons between modelling techniques and between model and measured data show that WAMGBR produces very good results in the difficult challenge of modelling both non-cyclonic and tropical cyclone waves in the geographically complex environment of the Great Barrier Reef.  相似文献   

Nonequilibrium Processes in the Solar Corona,Transition Region,Flares, and Solar Wind <Emphasis Type="Italic">(Invited Review)</Emphasis>     

Jaroslav Dudík  Elena Dzifčáková  Nicole Meyer-Vernet  Giulio Del Zanna  Peter R. Young  Alessandra Giunta  Barbara Sylwester  Janusz Sylwester  Mitsuo Oka  Helen E. Mason  Christian Vocks  Lorenzo Matteini  Säm Krucker  David R. Williams  Šimon Mackovjak 《Solar physics》2017,292(8):100

We review the presence and signatures of the non-equilibrium processes, both non-Maxwellian distributions and non-equilibrium ionization, in the solar transition region, corona, solar wind, and flares. Basic properties of the non-Maxwellian distributions are described together with their influence on the heat flux as well as on the rates of individual collisional processes and the resulting optically thin synthetic spectra. Constraints on the presence of high-energy electrons from observations are reviewed, including positive detection of non-Maxwellian distributions in the solar corona, transition region, flares, and wind. Occurrence of non-equilibrium ionization is reviewed as well, especially in connection to hydrodynamic and generalized collisional-radiative modeling. Predicted spectroscopic signatures of non-equilibrium ionization depending on the assumed plasma conditions are summarized. Finally, we discuss the future remote-sensing instrumentation that can be used for the detection of these non-equilibrium phenomena in various spectral ranges.  相似文献   

Resource depletion,peak minerals and the implications for sustainable resource management     

T. Prior  D. Giurco  G. Mudd  L. Mason  J. Behrisch 《Global Environmental Change》2012,22(3):577-587

Today's global society is economically, socially and culturally dependent on minerals and metals. While metals are recyclable, terrestrial mineral deposits are by definition ‘non-renewable’ over human timescales and their stocks are thus finite. This raises the spectre of ‘peak minerals’ – the time at which production from terrestrial ores can no longer rise to meet demand and where a maximum (peak) production occurs. Peak minerals prompts a focus on the way minerals can be sustainably used in the future to ensure the services they provide to global society can be maintained.As peak minerals approaches (and is passed in some cases), understanding and monitoring the dynamics of primary mineral production, recycling and dematerialisation, in the context of national and global discussions about mineral resources demand and the money earned from their sale, will become essential for informing and establishing mechanisms for sustainable mineral governance and use efficiency into the future. Taking a cross-scale approach, this paper explores the economic and productivity impacts of peak minerals, and how changes in the mineral production profile are influenced not only by technological and scarcity factors, but also by environmental and social constraints. Specifically we examine the impacts of peak minerals in Australia, a major global minerals supplier, and the consequences for the Asia-Pacific region, a major destination for Australia's minerals.This research has profound implications for local and regional/global sustainability of mineral and metal use. The focus on services is useful for encouraging discussion of transitions in how such services can be provided in a future more sustainable economy, when mineral availability is constrained. The research also begins to address the question of how we approach the development of strategies to maximise returns from mineral wealth over generations.  相似文献   

Element zoning trends in olivine phenocrysts from a supposed primary high-magnesian andesite: an electron- and ion-microprobe study     

S. C. Kohn  C. M. B. Henderson  R. A. Mason 《Contributions to Mineralogy and Petrology》1989,103(2):242-252

Electron and ion-probe microanalysis have been used to obtain zoning profiles for major and trace elements in olivine phenocrysts from a high-magnesian andesite from Shodo-Shima island, southwest Japan. This rock was previously thought to represent undifferentiated, primary magma. Some crystals have unzoned cores, while others show cores which are reversely zoned with respect to Mg/ (Mg+Fe), Ni, Mn and Cr. In addition, some Ni profiles show a normally zoned hump at the most central portions of the reversely zoned crystals. All crystals show normally zoned rims. The Li concentrations are constant throughout the cores of all crystals studied, but rise sharply, by a factor of up to at least six, in the rims. The Ca and Co concentrations are essentially constant throughout all the crystals. Mechanisms for producing the observed zoning profiles are discussed, and it is concluded that the reverse zoning was produced by the introduction of crystals into a less differentiated magma than that in which they grew. The reversely zoned crystals could therefore represent xenocrysts which were introduced into an undifferentiated magma, or phenocrysts introduced into a more primitive magma by a magma mixing process. The Ni profiles are used to estimate the residence time of these crystals in the more primitive magma. The following trace element partition co-efficients have been estimated for the olivine-groundmass system in this rock: D ^Ni=16; D ^Mn=1.1; D ^Co=4.2; D ^Ca =0.02; D ^Ti=0.005; D ^V=0.05; D ^Sc=0.2; D ^Na=0.0002. Studies of trace element zoning will become increasingly important as the new generation of trace element microprobes become available but a larger database of experimentally determined values for trace element partition coefficients and diffusion coefficients in crystals and magmas, and a better understanding of other disequilibrium processes are required to fully exploit the new data.  相似文献   

The response of lake levels and areas to climatic change   总被引：3，自引：0，他引：3  

I. M. Mason  M. A. J. Guzkowska  C. G. Rapley  F. A. Street-Perrott 《Climatic change》1994,27(2):161-197

The levels and areas of lakes, particularly closed lakes (those without outlet) are known to be sensitive indicators of changes in climate, and so in principle they can play a role in monitoring current and future climatic changes. In this paper we derive solutions to the water balance equation giving the response of the level and area of closed lakes to steps, spikes and sinusoidal variations in aridity, and show that such a lake acts approximately as a simple low pass filter having a characteristic equilibrium response timeτ _e. We also review the similar response of open lakes to changes in runoff. It is shown howτ _e depends on lake geomorphology and climate, and for a number of lakes we calculateτ _e values, ranging from 1.5 to 350 yr for closed lakes, and from 2.9 days to 2 yr for open lakes. We propose methods involving Fourier analysis for inverting closed lake level or area records to obtain plots of a simple aridity index C. It is shown that for all ≈ 200 of the world's large (? 100 km²) closed lakes, satellite remote sensing of lake levels and areas is currently sensitive enough to monitor variations in C (e.g. in average basin precipitation) of order 1% to 10% on the time-scale of years to decades.  相似文献   

Boundary-layer flow over low hills   总被引：1，自引：0，他引：1  

P. A. Taylor  P. J. Mason  E. F. Bradley 《Boundary-Layer Meteorology》1987,39(1-2):107-132

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Accurate and efficient shot-gather dip moveout processing in the log-stretch domain1     

B. Zhou  I.M. Mason  S.A. Greenhalgh 《Geophysical Prospecting》1995,43(7):963-978

An accurate analytical expression for shot-gather dip-moveout (DMO) in the timespace log-stretch domain has until now not been published. We present a simpler, alternative derivation of the exact DMO relationships of Black et al. which correctly take account of the repositioning of the midpoint. A new computationally efficient frequency-wavenumber (F-K) DMO operator for shot profiles is then derived, based on these DMO relationships in the time-space log-stretch domain. The newly derived DMO operator is, unlike most other log-stretch DMO operators) accurate for the full range of reflector dips. Along with other schemes which are performed in the log-stretch domain, it offers considerable time savings over conventional DMO processing. We have compared numerically the impulse response of the new operator with those of a number of other shot-gather DMO operators, and found it to be superior and well match to the theoretical elliptical DMO response.  相似文献   

The radio frequency dielectric properties of the stratified UG1–UG2 geological unit in the Bushveld Complex     

Marc Rütschlin  Johannes H. Cloete  Iain M. Mason  Keith D. Palmer   《Journal of Applied Geophysics》2007,62(4):354-360

A new measurement technique enables the complex dielectric properties of the geological strata comprising the UG1–UG2 (Upper Group 1–Upper Group 2) unit of the Bushveld Complex in South Africa to be determined with unprecedented detail at radio frequencies (RF). Results of non-destructive laboratory measurements of representative diamond drill core samples from the UG1–UG2 unit are presented at 25 MHz. These data establish that the UG1 and UG2 chromitite layers are embedded in rock strata (norite, pyroxenite and anorthosite) which are translucent in the HF spectral band, whereas the chromitite layers themselves exhibit significant velocity contrast, making them good radar reflectors. The data presented here is useful for calibration of the radar system, and for predicting the range and resolution performance of borehole radars operating in both the hanging and footwalls of the economically important platiniferous UG2 reef.  相似文献