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131.
We present, to our knowledge, the first dissolved arsenic (As) data from the pore waters of a closed-basin, saline lake, Pyramid Lake, USA. The As concentrations first decrease across the sediment-water interface to values below lake water concentrations and then rapidly increase to values as high as 5.85mol L–1 at a depth of 15 cm. This maximum value is reached at the top of the sulfate reduction zone. The profile suggests that As is remobilized in the suboxic and anoxic zones of the sediments and is reprecipitated near the sediment-water interface under oxic conditions. 相似文献
132.
Although carbonate-associated sulfate (CAS) is used widely as a proxy for the sulfur isotope composition of ancient seawater, little is known about the effects of diagenesis on retention of primary δ34S signals. Our case study of the Key Largo Limestone, Pleistocene, Florida, is the first systematic assessment of the impact of meteoric diagenesis on CAS properties. Geochemical and petrographic data show that meteoric diagenesis has affected the exposed coralline facies to varying degrees, yielding differences now expressed as sharp reaction fronts between primary and secondary carbonate minerals within individual coral heads. Specifically, analyses across high-resolution transects in the Key Largo Limestone show that concentrations of strontium and sodium decrease across the recrystallization front from original aragonite to meteoric low-magnesium calcite by factors of roughly 5 and 10, respectively. Predictably, δ18O values decrease across these same fronts. The δ13C relationships are more complex, with the most depleted values observed in the latest-formed calcite. Such trends likely reflect carbon isotope buffering capacity that decreased as reaction progressed, as well as protracted development of soil profiles and the associated terrestrial biomass and thus depleted δ13C during sea-level lowstand. Conversely, δ34S values of CAS vary within a narrow ‘buffered’ range from 20.6 to 22.6‰ (compared to 20.8-22.0‰ of coeval Pleistocene seawater) across the same mineralogical transition, despite sulfate concentrations that drop in the diagenetic calcite by an average factor of 12. Collectively, these data point to robust preservation of primary δ34S for carbonates that have experienced intense meteoric diagenesis, which is encouraging news for those using the isotopic composition of CAS as a paleoceanographic proxy. At the same time, the vulnerability of CAS concentrations to diagenetic resetting is clear. 相似文献
133.
W. Berry Lyons Kathleen A. Welch Andrew G. Fountain Gayle L. Dana Bruce H. Vaughn Diane M. McKnight 《水文研究》2003,17(1):115-130
We have analysed a series of surface samples from the alpine glaciers of Taylor Valley, Southern Victoria Land, Antarctica for their geochemical composition. This was done to better establish the role of glaciochemical variation on the chemical composition of meltwater streams emanating from the glaciers. The chemistry of the snow and ice changes with proximity to the ocean and with elevation of the glacier surface. The aeolian transport of dry valley dust, as indicated by both chemical and particulate matter variations, is a major process affecting the overall glacier chemistry and the chemistry of the meltwaters. Streams originating on the western edges of the glaciers are more impacted by the aeolian input as they are in the direct path of the major regional wind direction. Our data strongly suggest that the variation in stream geochemistry in Taylor Valley is a result in part of the differences in chemical composition of glacier melt. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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135.
This research explores the factors that shape the evolving geographic distribution of business headquarters (HQ) activity. We address an understudied influence on HQ geographies: metropolitan HQ changes driven by the process of small, rapidly expanding businesses growing into mature companies. This investigation focuses on the developmental paths followed by fast-growing firms (FGFs) and the geographic distinctions that can be observed in a FGF tracking study of Canada’s metropolitan regions from 1987 to 2005. Our research findings indicate that geography plays an important role in this development, as FGF tracking records throughout Canada’s metropolitan areas diverge sharply. We find that most FGFs that emerged in Vancouver and Toronto continued as ongoing businesses following their rapid growth phase, while a high proportion of FGFs based in Montréal and Calgary did not. These results contribute to a greater understanding of metropolitan economies, business development, and HQ location in Canada 相似文献
136.
Matthew B Sanders Marion Sebire Joachim Sturve Paul Christian Ioanna Katsiadaki Brett P Lyons Dave Sheahan Jason M Weeks Stephen W Feist 《Marine environmental research》2008,66(1):161-163
Effects of nanoparticles on aquatic organisms have been little studied to date and toxicological data are urgently needed for development of regulatory frameworks for these substances. Here, we report the findings of a study exposing sticklebacks to cadmium sulfide (CdS) as bulk material and quantum dots. Fish were exposed for 21 d in a flow through test system to 5, 50 or 500 microg l(-1) CdS nanoparticles (nCdS) coated in thiol terminated methyl polyethylene glycol (MPEG), bulk CdS or MPEG at 500 microg l(-1) (nominal concentrations). With the exception of the highest nCdS exposure, measured concentrations were approximately one order of magnitude below nominal. A single fish from each group (excluding MPEG) was examined using energy dispersive X-ray analysis (EDX) to localise cadmium, however, cadmium could not be detected in whole body sections. Elevated levels of oxidized glutathione were measured in the gills of fish exposed to 50 and 500 microg l(-1) nCdS. Induction of vitellogenin synthesis was not detected in any of the treatment groups. The number of males engaged in nest-building behaviour following exposure to 500 microg l(-1) nCdS was reduced and livers of 4/6 fish in the same treatment displayed hepatocellular nuclear pleomorphism. The results are discussed emphasising the fundamental importance of experimental design and the need to understand the behaviour of nanoparticles in the aqueous phase. 相似文献
137.
To what extent have laterites contributed to the geochemical,surface reflectance and magnetic properties of adjacent tropical soils? Evidence from Niger and Burkina Faso
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A. Hunt F. Oldfield J. Bloemendal J. F. Boyle R. C. Chiverrell R. Lyons Z. Shen E. R. Williams W. Balsam 《地球表面变化过程与地形》2017,42(15):2554-2569
The present study is based on a suite of surface samples from exposures of eroded laterite, considered to be Tertiary in age, and nearby soils in the Sahelian region of SW Niger and Burkina Faso. X‐ray fluorescence, X‐ray diffraction, computer‐controlled scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, diffuse UV–visible reflectance spectroscopy and a suite of magnetic measurements have been used to shed light on the origin of the soils and their possible derivation from the adjacent, eroded laterite outcrops. On the basis of the wide range of data obtained, we conclude that the mineralogy and magnetic properties of the soils preclude direct derivation from the laterites without further weathering and modification. Nor does the evidence support the view that the soils have evolved entirely independently, uninfluenced by input from the laterites. The only conclusion that is consistent with all the lines of evidence is that the erosion of the laterites provided at least a significant part of the material upon which soil formation took place. This must have occurred at a time early enough to permit a long period of subsequent soil development during which the iron oxides, specifically haematite and ferrimagnetic minerals, were significantly modified. From this, we infer that eroded material from discontinuous laterite exposures has contributed significantly to the remotely sensed, distinctive reflectance characteristics of the Sahel surfaces. The magnetic properties of the soils provide evidence for the in situ neo‐formation of fine, secondary, pedogenic magnetite/maghemite grains typical of those found in many soils across the Sahel region and elsewhere in both temperate and tropical environments. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
138.
Paul R. Durkin Stephen M. Hubbard John Holbrook Zennon Weleschuk Paul Nesbit Chris Hugenholtz Tania Lyons Derald G. Smith 《Sedimentology》2020,67(6):2819-2849
Downstream migration of point bars is an important process in meander belts. Inherent to downstream migration is sediment accumulation in concave channel banks, immediately adjacent to and downstream of convex point bars. Despite this, associated concave bank processes are often overlooked, with depositional products sparsely identified in the stratigraphic record. Counter-point-bar deposits are a type of concave-bank deposit that have been positively identified in subsurface three-dimensional seismic datasets, yet outcrop examples are not well-constrained. This study characterizes and establishes recognition criteria of counter-point-bar deposits in outcrop using extensive exposure of Late-Cretaceous meander-belt deposits in eastern Alberta, Canada. Using a combination of traditional field-based sedimentological analyses and three-dimensional outcrop mapping with an Uncrewed Aerial Vehicle and Structure-from-Motion photogrammetry, point bar, counter-point bar, and associated abandoned-channel deposits, as well as adjacent floodplain deposits are identified. Bed-scale characteristics of counter-point-bar deposits include interlaminated and interbedded siltstone and fine-grained sandstone, abundant organic detritus, and evidence of deformation and slumping. At the bend scale, accretion packages bounded by internal erosion surfaces are composed of dipping siltstone and minor sandstone beds that extend from the top to the base of the meander belt. At the belt scale, positive identification relies on concave accretion surface mapping, their orientation relative to the meander-belt edge (i.e. dipping away), and consideration of meander-bend evolution. These results have implications for recognition of counter-point-bar deposits in analogous, less-constrained data sets, which provides a foundation for more complete palaeoenvironmental interpretations. 相似文献
139.
Dab (Limanda limanda) were sampled from a number of polluted and unpolluted areas in British coastal waters. The 32P-postlabelling assay was used to analyse the level of aromatic/hydrophobic DNA adducts in pooled samples of liver tissue. The mean levels of DNA adducts detected from areas known to receive anthropogenic pollutants ranged from 4.0 to 26.8 adducts per 10(8) nucleotides, with all sites containing samples displaying DNA adduct profiles consisting of diagonal radioactive zones. In contrast no DNA adducts were detectable in samples from an unpolluted reference site. The ranking of polluted sites based on DNA adduct levels did not correspond with the ranking of sites based on sediment associated polycyclic aromatic hydrocarbon levels, highlighting the problem of linking the presence of contamination with detectable biological responses. No correlation could be found in this study between EROD activity and the level of DNA adducts. 相似文献
140.