Baseline metal concentrations in marine algae from São Miguel (Azores) under different ecological conditions - Urban proximity and shallow water hydrothermal activity     

Francisco M. Wallenstein  Ruben P. Couto  Martin Wilkinson  Armindo S. Rodrigues 《Marine pollution bulletin》2009,58(3):438-443

  相似文献   

Deriving hillslope sediment budgets in wildfire-affected forests using fallout radionuclide tracers   总被引：3，自引：1，他引：2  

W.H. Blake  P.J. Wallbrink  S.N. Wilkinson  G.S. Humphreys  S.H. Doerr  R.A. Shakesby  K.M. Tomkins 《Geomorphology》2009,104(3-4):105-116

Information on post-fire sediment and nutrient redistribution is required to underpin post-fire catchment management decisions. Fallout radionuclide budgets (²¹⁰Pb_xs, ¹³⁷Cs and ⁷Be) were derived to quantify soil redistribution and sediment yield in forested terrain following a moderately severe wildfire in a small (89 ha) water supply catchment in SE Australia. Application of these techniques in burnt terrain requires careful consideration of the partitioning of radionuclides between organic and mineral soil components. Beryllium-7 and ²¹⁰Pb_xs were shown to be closely associated with ash, litter and soil organic matter whereas ¹³⁷Cs was more closely associated with subsurface coarse mineral soil. Comparison of the three tracer budgets indicated that the dominant sediment source areas were ridgetops and steep valley sideslopes, from which burnt surface material was conveyed to the stream network via pre-existing gullies. Erosion was predominantly driven by sheetwash, enhanced by soil water repellency, and modified by bioturbation which both supplies subsurface sediment and provides sinks for erosive overland flow. Footslope and riparian zones were not important sediment source areas. The estimated event-based (wildfire and subsequent rainfall) sediment yield is 58 ± 25 t km^− 2, based on fallout ⁷Be measurements. The upper estimate of total particulate phosphorus yield (0.70 kg ha^− 1) is more than 10 times that at equivalent unburnt sites. This illustrates that, soon after fire, burnt eucalypt forest can produce nutrient loads similar to those of agricultural catchments. The tracer budgets indicate that wildfire is an important control on sediment and phosphorus inputs to the stream network over the decadal timeframe and the pulsed nature of this release is an important concern for water quality management.  相似文献   

Disseminated ‘jigsaw piece’ dolomite in Upper Jurassic shelf sandstones,Central North Sea: an example of cement growth during bioturbation?     

James P. Hendry  Mark Wilkinson  Anthony E. Fallick  & Nigel H. Trewin 《Sedimentology》2000,47(3):631-644

Unusual textural and chemical characteristics of disseminated dolomite in Upper Jurassic shelf sediments of the North Sea have provided the basis for a proposed new interpretation of early diagenetic dolomite authigenesis in highly bioturbated marine sandstones. The dolomite is present throughout the Franklin Sandstone Formation of the Franklin and Elgin Fields as discrete, non‐ferroan, generally unzoned, subhedral to highly anhedral ‘jigsaw piece’ crystals. These are of a similar size to the detrital silicate grains and typically account for ≈5% of the rock volume. The dolomite crystals are never seen to form polycrystalline aggregates or concretions, or ever to envelop the adjacent silicate grains. They are uniformly dispersed throughout the sandstones, irrespective of detrital grain size or clay content. Dolomite authigenesis predated all the other significant diagenetic events visible in thin section. The dolomite is overgrown by late diagenetic ankerite, and bulk samples display stable isotope compositions that lie on a mixing trend between these components. Extrapolation of this trend suggests that the dolomite has near‐marine δ¹⁸O values and low, positive δ¹³C values. The unusual textural and chemical characteristics of this dolomite can all be reconciled if it formed in the near‐surface zone of active bioturbation. Sea water provided a plentiful reservoir of Mg and a pore fluid of regionally consistent δ¹⁸O. Labile bioclastic debris (e.g. aragonite, Mg‐calcite) supplied isotopically positive carbon to the pore fluids during shallow‐burial dissolution. Such dissolution took place in response to the ambient ‘calcite sea’ conditions, but may have been catalysed by organic matter oxidation reactions. Bioturbation not only ensured that the dissolving carbonate was dispersed throughout the sandstones, but also prohibited coalescence of the dolomite crystals and consequent cementation of the grain framework. Continued exchange of Mg²⁺ and Ca²⁺ with the sea‐water reservoir maintained a sufficient Mg/Ca ratio for dolomite (rather than calcite) to form. Irregular crystal shapes resulted from dissolution, of both the dolomite and the enclosed fine calcitic shell debris, before ankerite precipitation during deep‐burial diagenesis.  相似文献   

The mass of the Andromeda galaxy     

N. W. Evans  M. I. Wilkinson 《Monthly notices of the Royal Astronomical Society》2000,316(4):929-942

This paper argues that the Milky Way galaxy is probably the largest member of the Local Group. The evidence comes from estimates of the total mass of the Andromeda galaxy (M31) derived from the three-dimensional positions and radial velocities of its satellite galaxies, as well as the projected positions and radial velocities of its distant globular clusters and planetary nebulae. The available data set comprises 10 satellite galaxies, 17 distant globular clusters and nine halo planetary nebulae with radial velocities. We find that the halo of Andromeda has a mass of together with a scalelength of 90 kpc and a predominantly isotropic velocity distribution. For comparison, our earlier estimate for the Milky Way halo is Although the error bars are admittedly large, this suggests that the total mass of M31 is probably less than that of the Milky Way . We verify the robustness of our results to changes in the modelling assumptions and to errors caused by the small size and incompleteness of the data set.
Our surprising claim can be checked in several ways in the near future. The numbers of satellite galaxies, planetary nebulae and globular clusters with radial velocities can be increased by ground-based spectroscopy, while the proper motions of the companion galaxies and the unresolved cores of the globular clusters can be measured using the astrometric satellites Space Interferometry Mission ( SIM ) and Global Astrometric Interferometer for Astrophysics ( GAIA ). Using 100 globular clusters at projected radii 20 R 50 kpc with both radial velocities and proper motions, it will be possible to estimate the mass within 50 kpc to an accuracy of 20 per cent. Measuring the proper motions of the companion galaxies with SIM and GAIA will reduce the uncertainty in the total mass caused by the small size of the data set to 22 per cent.  相似文献   

An analcime mugearite-megacryst association from north-eastern New South Wales: implications for high-pressure amphibole-dominated fractionation of alkaline magmas     

J. F. G. Wilkinson  H. D. Hensel 《Contributions to Mineralogy and Petrology》1991,109(2):240-251

An analcime-rich mugearite near Spring Mount in north-eastern New South Wales contains dominant kaersutite, lesser anorthoclase and rare Ti-rich mica megacrysts, and also rare Group I peridotite xenoliths and granitoid inclusions. Mineralogical, experimental and Sr and Nd isotopic data are interpreted to indicate that the megacrysts are cognate with their host and that megacryst precipitation occurred at pressures in the vicinity of 1 GPa. Isotopic and other data indicate minimal crystal contamination of the melt. The generation of this evolved lava (100 Mg/(Mg+Fe²⁺), M55; differentiation index DI52–56) by high-pressure amphiboledominated fractionation of a mantle-derived hydrous alkali basaltic parent (M70) is inconsistent with observed megacryst abundances (<3%) and absence of Group II cumulates, and with the magnitude of the crystal extracts (45% crystals) indicated by crystal fractionation models. These data suggest the mugearite is not a high-pressure differentiate of a hypothetical primary parental magma (M70). Alternatively, its composition might approximate that of a primary magma derived from a relatively Fe-rich amphibole lherzolite mantle source.  相似文献   

Reviews     

O. A. Jones  A. F. Wilson  J. F. G. Wilkinson  W. G. H. Maxwell  D. Hill  A. F. Wilson 《Australian Journal of Earth Sciences》2013,60(2):202-203

F. L. Stillwell Anniversary Volume. Australian Institute of Mining and Metallurgy, Melbourne, 302 pages, many plates and figures. 1958.

Our Mineral Resources, by Charles M. Riley; x + 338 pages; 102 figures; John Wiley and Sons, Inc., New York and London. $6.95.

Researches in Geochemistry, edited by P. H. Abelson; John Wiley and Sons Inc., New York, 1959. $11.00.

Basic Geology for Science and Engineering, by Edward C. Dapples; vii + 609 pages; 231 figures. John Wiley and Sons Inc., New York, 1959. $9.50.

Historical Geology, by Carl O. Dunbar; xi + 500 pages; 406 figures. Second Edition, publication date August, 1960; John Wiley and Sons Inc., New York. $7.95.

Time, Life and Man, by R. A. Stirton; xi + 558 pages; 291 figures. John Wiley and Sons Inc., New York, 1958.

Vector Space, by Martin J. Buerger; xiv + 347 pages; numerous line drawings; John Wiley and Sons Inc., New York and London. $12.00.

Geology of the Country Around Polonnaruwa, by Piyadasa W. Vtkanage. 1959. Memoir No. 1, Department of Mineralogy, Geological Survey of Ceylon; ix + 75 pages; 11 figures; 12 plates.  相似文献   

High-resolution Electrical Resistivity Tomography monitoring of a tracer test in a confined aquifer     

P.B. Wilkinson  P.I. Meldrum  O. Kuras  J.E. Chambers  S.J. Holyoake  R.D. Ogilvy 《Journal of Applied Geophysics》2010,70(4):268-276

A permanent geoelectrical subsurface imaging system has been installed at a contaminated land site to monitor changes in groundwater quality after the completion of a remediation programme. Since the resistivities of earth materials are sensitive to the presence of contaminants and their break-down products, 4-dimensional resistivity imaging can act as a surrogate monitoring technology for tracking and visualising changes in contaminant concentrations at much higher spatial and temporal resolution than manual intrusive investigations. The test site, a municipal car park built on a former gasworks, had been polluted by a range of polycyclic aromatic hydrocarbons and dissolved phase contaminants. It was designated statutory contaminated land under Part IIA of the UK Environmental Protection Act due to the risk of polluting an underlying minor aquifer. Resistivity monitoring zones were established on the boundaries of the site by installing vertical electrode arrays in purpose-drilled boreholes. After a year of monitoring data had been collected, a tracer test was performed to investigate groundwater flow velocity and to demonstrate rapid volumetric monitoring of natural attenuation processes. A saline tracer was injected into the confined aquifer, and its motion and evolution were visualised directly in high-resolution tomographic images in near real-time. Breakthrough curves were calculated from independent resistivity measurements, and the estimated seepage velocities from the monitoring images and the breakthrough curves were found to be in good agreement with each other and with estimates based on the piezometric gradient and assumed material parameters.  相似文献   

A survey of polarization in the JVAS/CLASS flat-spectrum radio source surveys – I. The data and catalogue production     

N. Jackson  R. A. Battye  I. W. A. Browne  S. Joshi  T. W. B. Muxlow  P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2007,376(1):371-377

We have used the very large JVAS/CLASS 8.4-GHz surveys of flat-spectrum radio sources to obtain a large, uniformly observed and calibrated, sample of radio source polarizations. These are useful for many investigations of the properties of radio sources and the interstellar medium. We discuss comparisons with polarization measurements from this survey and from other large-scale surveys of polarization in flat-spectrum sources.  相似文献   

Lateglacial ice-cap dynamics in NW Scotland: evidence from the fjords of the Summer Isles region     

Martyn S. Stoker  Tom Bradwell  John A. Howe  Ian P. Wilkinson  Kate McIntyre 《Quaternary Science Reviews》2009,28(27-28):3161-3184

The seaboard of western Scotland is a classic fjord landscape formed by glaciation over at least the last 0.5 Ma. We examine the glacial geology preserved in the fjords (or sea lochs) of the Summer Isles region of NW Scotland using high-resolution seismic data, multibeam swath bathymetry, seabed sediment cores, digital terrain models, aerial photographs, and field investigations. Detailed analyses include seismic facies and lithofacies interpretations; sedimentological and palaeoenvironmental analyses; and radiocarbon dating of selected microfauna. Our results indicate that the Pleistocene sediments of the Summer Isles region, on- and offshore, can be subdivided into several lithostratigraphic formations on the basis of seismic character, geomorphology and sedimentology. These are: subglacial tills; ice-distal and glacimarine facies; ice-proximal and ice-contact facies; moraine assemblages; and Holocene basin fill. The submarine landscape is also notable for its large-scale mass-movement events – the result of glaciodynamic, paraglacial or seismotectonic processes. Radiocarbon dating of marine shells indicate that deglaciation of this part of NW Scotland was ongoing between 14 and 13 ka BP – during the Lateglacial Interstadial (Greenland Interstadial 1) – consistent with cosmogenic surface-exposure ages from previous studies. A sequence of numerous seafloor moraine ridges charts oscillatory retreat of the last ice sheet from a buoyant calving margin in The Minch to a firmly grounded margin amongst the Summer Isles in the early part of Lateglacial Interstadial (GI-1) (pre-14 ka BP). Subsequent, punctuated, frontal retreat of the ice mass occurred in the following ～1000 years, during which time ice-cap outlet glaciers became topographically confined and restricted to the fjords. A late-stage readvance of glaciers into the inner fjords occurred soon after 13 ka BP, which calls into question the accepted limits of ice extent during the Younger Dryas Stadial (Greenland Stadial 1). We examine the wider implications of our chronostratigraphic model, discussing the implications for British Ice Sheet deglaciation, Lateglacial climate change, and the style and rates of fjord sedimentation.  相似文献   

Using isotopes to understand the evolution of water ages in disturbed mixed land-use catchments     

Katya Dimitrova-Petrova  Josie Geris  Mark E. Wilkinson  Allan Lilly  Chris Soulsby 《水文研究》2020,34(4):972-990

Tracer studies have been key to unravelling catchment hydrological processes, yet most insights have been gained in environments with relatively low human impact. We investigated the spatial variability of stream isotopes and water ages to infer dominant flow paths in a ~10-km² nested catchment in a disturbed, predominantly agricultural environment in Scotland. We collected long-term (>5 years) stable isotope data of precipitation, artificial drainage, and four streams with varying soil and land use types in their catchment areas. Using a gamma model, Mean Transit Times (MTTs) were then estimated in order to understand the spatial variability of controls on water ages. Despite contrasting catchment characteristics, we found that MTTs in the streams were generally very similar and short (<1 year). MTTs of water in artificial drains were even shorter, ranging between 1 to 10 months for a typical field drain and <0.5 to 1 month for a country road drain. At the catchment scale, lack of heterogeneity in the response could be explained by the extensive artificial surface and subsurface drainage, “short-circuiting” younger water to the streams during storms. Under such conditions, additional intense disturbance associated with highway construction during the study period had no major effect on the stream isotope dynamics. Supplementary short-term (~14 months) sampling of mobile soil water in dominant soil-land use units also revealed that agricultural practices (ploughing of poorly draining soils and soil compaction due to grazing on freely draining soils) resulted in subtle MTT variations in soil water in the upper profile. Overall, the isotope dynamics and inferred MTTs suggest that the evolution of stream water ages in such a complex human-influenced environment are largely related to near-surface soil processes and the dominant soil management practices. This has direct implications for understanding and managing flood risk and contaminant transport in such environments.  相似文献