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21.
Geochemistry of the Rare Earth Elements in Natural Terrestrial Waters:A Review of What Is Currently Knows 总被引:3,自引:0,他引:3
The range of observed chemical compositions of natural terrestrial waters varies greatly especially when compared to the essentially constant global composition of the oceans.The concentrations of the REEs in natural terrestrial waters also exhibit more variation than what was reported in seawater,In terrestrial waters ,pH values span the range from acid up to alkaline,In addition,terrestrial waters can range from very dilute waters through to highly concentrated brines.The REE concentrations and their behavior in natural terrestrial waters reflect these compositional ranges,Chemical weathering of rocks represents the source of the REEs to natural terrestrial waters and ,consequently,the REE signature of rocks can impart their REE signature to associated waters,In addition,Because of the typical low solubilities of the REEs both surface and solution complexation can be important in fractionating REEs in aqueous solution.Both of these processes are important in all natural terrestrial waters,however,their relative importance varies as a function of the overall solution composition,In alkaline waters,for example,Solution complexation of the REEs with carbonate ions appears to control their aqueous distributions whereas in acid waters,the REE signature of the labile fraction of the REEs is readily leached from the rocks.In circumneutral pH waters,both processes appear to be important and their relative significance has not yet been determined. 相似文献
22.
Claude Boutron Kevin Rosman Carlo Barbante Michael Bolshov Freddy Adams Sungmin Hong Christophe Ferrari 《Comptes Rendus Geoscience》2004,336(10):847-867
The investigation of the occurrence of lead in dated snow and ice from Greenland and Antarctica has played a major role in our understanding of the history of the pollution of the atmosphere of our planet by this metal. Such studies have however proved to be very demanding, mainly because of the extreme purity of polar snow and ice. Reliable measurements can be obtained only if ultra-clean and highly sensitive procedures are used, as pioneered by Clair Patterson. The Greenland data show evidence of large-scale pollution of the atmosphere of the Northern Hemisphere for lead as early as two millennia ago during Greco–Roman times, especially because of mining and smelting activities in southern Spain. It peaked at the end of the 1960s, with lead concentrations in snow about 200 times higher than natural values, before declining during recent times because of the fall in the use of leaded gasoline. Lead pollution in Antarctica was already significant at the end of the 19th century as a consequence of whaling activities, the traffic of coal-powered ships crossing the Cape Horn, and mining activities in South America, South Africa and Australia. After declining because of the opening of the Panama Canal, the great economic depression and World War II, it reached a maximum during the 1980s, with lead concentrations 20 times higher than natural values. Other studies focus on past natural variations of lead in ancient ice dated from the last climatic cycles. To cite this article: C. Boutron et al., C. R. Geoscience 336 (2004). 相似文献
23.
Global dust trajectories indicate that signi?cant quantities of aeolian‐transported iron oxides originate in contemporary dryland areas. One potential source is the iron‐rich clay coatings that characterize many sand‐sized particles in desert dune?elds. This paper uses laboratory experiments to determine the rate at which these coatings can be removed from dune sands by aeolian abrasion. The coatings impart a red colour to the grains to which previous researchers have assigned variable geomorphological signi?cance. The quantities of iron removed during a 120 hour abrasion experiment are small (99 mg kg?1) and dif?cult to detect by eye; however, high resolution spectroscopy clearly indicates that ferric oxides are released during abrasion and the re?ectance of the particles alters. One of the products of aeolian abrasion is ?ne particles (<10 µm diameter) with the potential for long distance transport. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
24.
Broadly speaking, there is, at least within geomorphic circles, a general acceptance that rocks with low albedos will warm both faster and to higher temperatures than rocks with high albedos, reflectivity influencing radiative warming. Upon this foundation are built notions of weathering in respect of the resulting thermal differences, both at the grain scale and at the scale of rock masses. Here, a series of paving bricks painted in 20 per cent reflectivity intervals from black through to white were used to monitor albedo‐influenced temperatures at a site in northern Canada in an attempt to test this premise. Temperatures were collected, for five months, for the rock surface and the base of the rock, the blocks being set within a mass of local sediment. Resulting thermal data did indeed show that the dark bricks were warmer than the white but only when their temperatures were equal to or cooler than the air temperature. As brick temperature exceeded that of the air, so the dark and light bricks moved to parity; indeed, the white bricks frequently became warmer than the dark. It is argued that this ‘negating’ of the albedo influence on heating is a result of the necessity of the bricks, both white and black, to convect heat away to the surrounding cooler air; the darker brick, being hotter, initially convects faster than the white as a product of the temperature difference between the two media. Thus, where the bricks become significantly hotter than the air, they lose energy to that air and so their respective temperatures become closer, the albedo influence being superceded by the requirement to equilibrate with the surrounding air. It is argued that this finding will have importance to our understanding of weathering in general and to our perceptions of weathering differences between different lithologies. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
25.
Kevin R. T. Whelan Thomas J. Smith Donald R. Cahoon James C. Lynch Gordon H. Anderson 《Estuaries and Coasts》2005,28(6):833-843
We measured monthly soil surface elevation change and determined its relationship to groundwater changes at a mangrove forest
site along Shark River, Everglades National Park, Florida. We combined the use of an original design, surface elevation table
with new rod-surface elevation tables to separately track changes in the mid zone (0–4 m), the shallow root zone (0–0.35 m),
and the full sediment profile (0–6 m) in response to site hydrology (daily river stage and daily groundwater piezometric pressure).
We calculated expansion and contraction for each of the four constituent soil zones (surface [accretion and erosion; above
0 m], shallow zone [0–0.35 m], middle zone [0.35–4 m], and bottom zone [4–6]) that comprise the entire soil column. Changes
in groundwater pressure correlated strongly, with changes in soil elevation for the entire profile (Adjusted R2 = 0.90); this relationship was not proportional to the depth of the soil profile sampled. The change in thickness of the
bottom soil zone accounted for the majority (R2 = 0.63) of the entire soil profile expansion and contraction. The influence of hydrology on specific soil zones and absolute
elevation change must be considered when evaluating the effect of disturbances, sea level rise, and water management decisions
on coastal wetland systems. 相似文献
26.
Kevin M. Theissen David A. Zinniker Robert B. Dunbar 《Geochimica et cosmochimica acta》2005,69(3):623-636
Our analysis of lipid molecular fossils from a Lake Titicaca (16° S, 69° W) sediment core reveals distinct changes in the ecology of the lake over an ∼25,000-yr period spanning latest Pleistocene to late Holocene time. Previous investigations have shown that over this time period Lake Titicaca was subject to large changes in lake level in response to regional climatic variability. Our results indicate that lake algal populations were greatly affected by the changing physical and chemical conditions in Lake Titicaca. Hydrocarbons are characterized by a combination of odd-numbered, mid- to long-chain (C21-C31) normal alkanes and alkenes. During periods when lake level was higher (latest Pleistocene, early Holocene, and late Holocene), the C21n-alkane, and the C25 and C27 alkenes dominate hydrocarbon distributions and indicate contribution from an algal source, potentially the freshwater alga Botryococcus braunii. The C30 4 α-methyl sterol (dinosterol) increases sharply during the mid-Holocene, suggesting a greatly increased dinoflagellate presence at that time. Long-chain alkenones (LCAs) become significant during the early Holocene and are highly abundant in mid-Holocene samples. There are relatively few published records of LCA detection in lake sediments but their occurrence is geographically widespread (Antarctica, Asia, Europe, North America). Lake Titicaca represents the first South American lake and the first low-latitude lake in which LCAs have been reported. LCA abundance and distribution may be related to the temperature-dependent response of an unidentified algal precursor. Although the LCA unsaturation indices cannot be used to determine absolute Lake Titicaca temperatures, we suspect that the published LCA U37K unsaturation calibrations can be applied to infer relative temperatures for early to mid-Holocene time when LCA concentrations are high. Using these criteria, the U37K unsaturation indices suggest relatively warmer temperatures in the mid-Holocene. In contrast to previous speculation, lipid analysis provides little evidence of a greatly increased presence of aquatic plants during the mid-Holocene. Instead, it appears that a few algal species were dominant in the lake. Based on the dramatic rise in abundances of LCAs and dinosterol during the early to mid-Holocene, we suspect that the algal producers of these compounds rose in response to a combination of physical and chemical changes in the lake. These include temperature, salinity, and alkalinity changes that occurred as lake level dropped sharply during a multi-millennial drought affecting the Central Andean Altiplano. 相似文献
27.
Abutment behavior significantly influences the seismic response of certain bridge structures. Specifically in the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment mobilization and inelastic behavior of the soil material under high shear deformation levels dominate the response of the bridge and its column bents. This paper investigates the sensitivity of bridge seismic response with respect to three different abutment modeling approaches. The abutment modeling approaches are based on three increasing levels of complexity that attempt to capture the critical components and modes of abutment response without the need to generate continuum models of the embankment, approach, and abutment foundations. Six existing reinforced concrete bridge structures, typical of Ordinary Bridges in California, are selected for the analysis. Nonlinear models of the bridges are developed in OpenSees. Three abutment model types of increasing complexity are developed for each bridge, denoted as roller, simplified, and spring abutments. The roller model contains only single-point constraints. The spring model contains discrete representations of backfill, bearing pad, shear key, and back wall behavior. The simplified model is a compromise between the efficient roller model and the comprehensive spring model. Modal, pushover, and nonlinear dynamic time history analyses are conducted for the six bridges using the three abutment models for each bridge. Comparisons of the analysis results show major differences in mode shapes and periods, ultimate base shear strength, as well as peak displacements of the column top obtained due to dynamic excitation. The adequacy of the three abutment models used in the study to realistically represent all major resistance mechanisms and components of the abutments, including an accurate estimation of their mass, stiffness, and nonlinear hysteretic behavior, is evaluated. Recommendations for abutment modeling are made. 相似文献
28.
Stephen Grebby Dickson Cunningham Jonathan Naden Kevin Tansey 《International Journal of Earth Sciences》2012,101(6):1645-1660
Structural maps are traditionally produced by mapping features such as faults, folds, fabrics, fractures and joints in the field. However, large map areas and the spatially limited ground perspective of the field geologist can potentially increase the likelihood that not all structural features will be identified within a given area. The ability to recognise and map both local and regional structural features using high-resolution remote sensing data provides an opportunity to complement field-based mapping to help generate more comprehensive structural maps. Nonetheless, vegetation cover can adversely affect the extraction of structural information from remotely sensed data as it can mask the appearance of subtle spectral and geomorphological features that correspond to geological structures. This study investigates the utility of airborne Light Detection And Ranging (LiDAR) data and airborne multispectral imagery for detailed structural mapping in vegetated ophiolitic rocks and sedimentary cover of a section of the northern Troodos ophiolite, Cyprus. Visual enhancement techniques were applied to a 4-m airborne LiDAR digital terrain model and 4-m airborne multispectral imagery to assist the generation of structural lineament maps. Despite widespread vegetation cover, dykes and faults were recognisable as lineaments in both data sets, and the predominant strike trends of lineaments in all resulting maps were found to be in agreement with field-based structural data. Interestingly, prior to fieldwork, most lineaments were assumed to be faults, but were ground-verified as dykes instead, emphasising the importance of ground-truthing. Dyke and fault trends documented in this study define a pervasive structural fabric in the upper Troodos ophiolite that reflects the original sea-floor spreading history in the Larnaca graben. This structural fabric has not previously been observed in such detail and is likely to be continuous in adjacent regions under sedimentary cover. This information may be useful to future exploration efforts in the region focused on identification of structurally controlled mineral and groundwater resources. Overall, our case study highlights the efficacy of airborne LiDAR data and airborne multispectral imagery for extracting detailed and accurate structural information in hard-rock terrain to help complement field-based mapping. 相似文献
29.
Oxygen and sulfur isotope systematics of sulfate produced by bacterial and abiotic oxidation of pyrite 总被引:4,自引:0,他引:4
Nurgul Balci Wayne C. Shanks III Kevin W. Mandernack 《Geochimica et cosmochimica acta》2007,71(15):3796-3811
To better understand reaction pathways of pyrite oxidation and biogeochemical controls on δ18O and δ34S values of the generated sulfate in acid mine drainage (AMD) and other natural environments, we conducted a series of pyrite oxidation experiments in the laboratory. Our biological and abiotic experiments were conducted under aerobic conditions by using O2 as an oxidizing agent and under anaerobic conditions by using dissolved Fe(III)aq as an oxidant with varying δ18OH2O values in the presence and absence of Acidithiobacillus ferrooxidans. In addition, aerobic biological experiments were designed as short- and long-term experiments where the final pH was controlled at ∼2.7 and 2.2, respectively. Due to the slower kinetics of abiotic sulfide oxidation, the aerobic abiotic experiments were only conducted as long term with a final pH of ∼2.7. The δ34SSO4 values from both the biological and abiotic anaerobic experiments indicated a small but significant sulfur isotope fractionation (∼−0.7‰) in contrast to no significant fractionation observed from any of the aerobic experiments. Relative percentages of the incorporation of water-derived oxygen and dissolved oxygen (O2) to sulfate were estimated, in addition to the oxygen isotope fractionation between sulfate and water, and dissolved oxygen. As expected, during the biological and abiotic anaerobic experiments all of the sulfate oxygen was derived from water. The percentage incorporation of water-derived oxygen into sulfate during the oxidation experiments by O2 varied with longer incubation and lower pH, but not due to the presence or absence of bacteria. These percentages were estimated as 85%, 92% and 87% from the short-term biological, long-term biological and abiotic control experiments, respectively. An oxygen isotope fractionation effect between sulfate and water (ε18OSO4-H2O) of ∼3.5‰ was determined for the anaerobic (biological and abiotic) experiments. This measured value was then used to estimate the oxygen isotope fractionation effects between sulfate and dissolved oxygen in the aerobic experiments which were −10.0‰, −10.8‰, and −9.8‰ for the short-term biological, long-term biological and abiotic control experiments, respectively. Based on the similarity between δ18OSO4 values in the biological and abiotic experiments, it is suggested that δ18OSO4 values cannot be used to distinguish biological and abiotic mechanisms of pyrite oxidation. The results presented here suggest that Fe(III)aq is the primary oxidant for pyrite at pH < 3, even in the presence of dissolved oxygen, and that the main oxygen source of sulfate is water-oxygen under both aerobic and anaerobic conditions. 相似文献
30.
Kalil Traoré David Menier Erwan Gensac Pascal Le Roy Clément Lambert Paul Bessin Kevin Pedoja Anne Duperret Romain Le Gall 《地学前缘(英文版)》2021,12(5):166-181
The morphology and internal structure of the Horaine Bank(Bay of Saint-Brieuc, NW France) are described based on multibeam echosounder and high-resolution seismic datasets coupled with vibro-core data. The Horaine Bank shows large-scale bedforms in the lee of a submerged rocky shoal, which allowed defining it as a Banner Bank.The internal structure of the sandbank reveals four seismic units(U1–U4) on a Cambrian basement(U0). The basal unit U1 is interpreted as reworked lowstand fluvial sediments those infilled micro incised valleys during a rise in sea level. This unit is overlain by paleo-coastal barrier sand-spit(U2) whose development was controlled by swell in the context of a rapid rise in sea level. The successive prograding unit(U3) is interpreted as flooding deposits in continuity with unit U2. The unit U4 is characterized by oblique reflectors oriented in two opposite directions. This last unit, dated post 3500 yr BP, corresponds to migrating dunes superimposed on the bank and observable in the high-resolution bathymetric data. The strong correlation between tidal currents and the apparent clockwise migration of dune crests suggests the presence of a tidal gyre controlling the present-day dynamics of most of the Horaine bank dunes. This study proposes a new model for the construction of banner banks characterized by the gradual transition of a sand spit to a banner bank during marine transgression and ensuing hydrodynamic variability. 相似文献