Factors influencing particulate matter geochemistry in the St. Lawrence estuary turbidity maximum     

Charles Gobeil  Bjørn Sundby  Norman Silverberg 《Marine Chemistry》1981,10(2):123-140

635 samples of suspended particulate matter (SPM), collected in the St. Lawrence river and estuary during periods of high and low river flow from a series of individual and anchor stations on a transect traversing the turbidity maximum zone, as well as two sediment box cores, were analyzed for Al, Si, Ca, Mg, Fe and Mn.An abrupt change in elemental composition occurs when traversing the front at the landward edge of the turbidity maximum. As the SPM concentration increases across the front from 20–200 mg l^?1, the Ca/Al and Mg/Al ratios of the SPM increase and the Si/Al, Fe/Al and Mn/Al ratios decrease. The almost 50% decrease of the Mn/Al ratio is not related to changes in salinity. Within the turbidity maximum the tidal-averaged Si/Al, Ca/Al, Mg/Al and Fe/Al ratios of the SPM do not differ significantly from the landward to the seaward end of the turbidity zone, but on one tidal station the ratios of Si, Ca and Fe to Al are significantly lower at high river flow than at low flow. The Mn/Al ratio is insensitive to the extreme variations of either salinity (0.6–30‰) or SPM concentrations (10–480 mg l^?1) within the turbidity zone. A tendency for higher Mn/Al ratios to be associated with near-bottom SPM, observed in the center of the turbidity zone during the low river flow period, is well developed in the lower reaches of the zone.Diagenetic mobilization within the rare fine-grained bottom sediments of the turbidity maximum is responsible for changes in Mn and Fe content of particulate matter, and early settling of coarse-grained components and size sorting within the zone are responsible for other compositional changes. Local sources, desorption and precipitation are apparently of secondary importance. The depletion of both Mn and Fe in the SPM and sediment of the upper estuary implies a net seaward escape of diagenetically mobilized metal.  相似文献   

The magnetic properties of Deep Sea Drilling Project basalts from the Atlantic Ocean     

William Lowrie  Reidar Løvlie  Neil D. Opdyke 《Earth and Planetary Science Letters》1973,17(2):338-349

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Computer studies of the evolution of planetary and satellite systems I. Description of the program: Preliminary tests     

Nils Aall Barricelli  Tormod Clemetsen  Kjell Aashamar  Erik Bølviken 《Earth, Moon, and Planets》1979,21(4):419-437

In this paper we describe a CDC-Cyber 74 program for computer simulation of the evolution of a system consisting of a large number of objects in orbit around a central body or primary. Some preliminary tests done with the program will also be described.  相似文献   

The Effect of Fluid Content on the Mechanical Behaviour of Fractures in Chalk   总被引：7，自引：0，他引：7  

M. Gutierrez  L. E. Øino  K. Høeg 《Rock Mechanics and Rock Engineering》2000,33(2):93-117

Summary ?The paper presents an experimental study on the effects of fluid content on the mechanical behaviour of natural fractures in chalk. The aims of the study are to provide better understanding of the mechanisms of chalk-fluid interaction, in general, and to explain the behaviour of petroleum chalk reservoirs during water injection, in particular. The experiments were carried out on L?gerdorf chalk using the direct shear apparatus. Two types of fluids were used in the tests: 1) water, and 2) synthetic oil. L?gerdorf chalk is a water-wet material which will develop capillary pressures upon contact with water. Initially saturating the chalk with oil will enhance the water wettability by inducing additional capillary forces between water and the non-wetting oil. In addition to the tests on fractured chalk samples, unconfined compression and direct shear tests on intact chalk samples were performed. The results showed significant differences in the strength and deformation characteristics of intact chalk initially saturated with different fluids. Intact water-saturated chalk showed lower deformation modulus (about 50%) and lower peak (also about 50%) and residual shear strength than the oil-saturated chalk. Water injection in initially oil-saturated fractures resulted in significant normal deformation under constant effective normal stress and shear stress relaxation under fixed shear displacement. The water-induced deformation occurred almost instantaneously after only a few cm³ of water had been injected into the fracture, and further injection of water did not increase the water-induced deformation. After water injection, fractures in initially oil-saturated chalk showed significantly lower normal and shear stiffnesses and lower shear strength. The weakening in shear is attributed partly to the reduction in the basic friction angle, φ_b, and this reduction was verified in a series of tilt tests to measure the frictional resistance between smooth edges of core samples of chalk. The reduction in the basic friction angle implies that the interaction of chalk with water is governed not only by capillary forces, as postulated in several previous studies, but also by chemical and/or physio-chemical effects.  相似文献   

Resurgence of Malaria in the Usambara Mountains, Tanzania, An Epidemic of Drug-Resistant Parasites     

Ren Bødker  William Kisinza  Robert Malima  Hamisi Msangeni  Steve Lindsay 《Global Change & Human Health》2000,1(2):134-153

The recent spread of malaria in the Usambara Mountains in Tanzania has been blamed on climatic changes experienced during the 20^th century. Here we suggest that recent changes in the pattern of malaria does not result so much from these changes as from changes in the use and efficacy of antimalarial drugs. The recent resurgence of malaria in this area corresponds with the rapid evolution of parasite strains resistant to chloroquine. The ineffectiveness of anti-malarial drugs may have left the people of the Usambaras at the same high risk of infection as they were before the introduction of modern medicine.  相似文献   

Leisure and community assessments: Emotional place relations among young teenagers in a Norwegian industrial stronghold     

Elisabeth Gulløy 《Norsk geografisk tidsskrift. Norwegian journal of geography》2020,74(1):35-53

ABSTRACT

The purpose of the article is to explore the role of participation in organized leisure activities in young teenagers’ emotional place relations. Data from a survey of students in lower secondary schools were analysed using multivariate linear regression models to address the research questions concerning whether participation in organized leisure activities was associated with more positive community assessments in youths in line with early Nordic welfare theory and the role played by socio-economic hardships and gender in the association. The results showed that for boys there were no indications of a general positive association between participation in organized leisure activities and community assessments, while for girls the association was modest. Students who experienced socio-economic hardships had more negative assessments of community compared with well-off students, even when they participated in organized leisure activities. The author discusses the results according to a welfare theory approach to emotional place relations, supplemented by other theoretical perspectives. From a theoretical perspective, the findings point to social exclusion and inclusion dynamics instead of early Nordic welfare theory approaches to leisure participation. The author concludes that gender, class and school relations are strongly associated with young teenagers’ emotional place relations.  相似文献   

Direct 40Ar/39Ar dating of Late Ordovician and Silurian brittle faulting in the southwestern Norwegian Caledonides          下载免费PDF全文

Thomas Scheiber  Giulio Viola  Camilla Maya Wilkinson  Morgan Ganerød  Øyvind Skår  Deta Gasser 《地学学报》2016,28(5):374-382

Structural data as well as U–Pb zircon and ⁴⁰Ar/³⁹Ar biotite and muscovite ages were collected from the Rolvsnes granodiorite in western Norway. The granodiorite intruded at c. 466 Ma, cooled quickly and escaped later viscous deformation. Brittle top‐to‐the‐NNW thrust faults (Set I) and WNW–ESE striking dextral strike‐slip faults (Set II) formed in a NNW–SSE transpressional regime. ⁴⁰Ar/³⁹Ar dating of synkinematic mica from both sets reveals a c. 450 Ma (Late Ordovician) age of faulting, which constrains early‐Caledonian brittle deformation. Set I and II faults are overprinted by a set of lower‐grade, variably oriented chlorite‐ and epidote‐coated faults (Set III) constraining WNW–ESE shortening. A lamprophyric dyke oriented compatibly with this stress field intruded at c. 435 Ma (Silurian), indicating that Set III formed at the onset of the Scandian Baltica–Laurentia collision. The preservation of Caledonian brittle structures indicates that the Rolvsnes granodiorite occupied a high tectonic level throughout the Caledonian orogeny.  相似文献   

Spatial and temporal variation in particle size and particulate organic matter content in suspended particulate matter from peatland‐dominated catchments in Finland          下载免费PDF全文

Hannu Marttila  Bjørn Kløve 《水文研究》2015,29(6):1069-1079

Properties of suspended particulate matter play a vital role in transport processes, but information from boreal lowland river systems with high organic loads is limited. This study analysed data from 2 years of sampling at 30 locations in Finland (204 samples in total) using suspended particulate matter samplers to determine effective and absolute particle size and organic fractions. Mean d₅₀ value was 22 and 49 µm for absolute and effective particle size, respectively. The organic fraction content ranged from 2.1% to 36% (mean 9.6%), highlighting the importance of particle organic matter for suspended particulate matter flux in the region. The results indicated that the suspended particulate matter particle size distribution and load in the study region is dominated by composite particles. There were considerable spatial and temporal variations in transport of organic fractions, effective particle size and degree of aggregation (range 1.5–93%). Headwaters and, in particular, late summer and spring flood conditions with flow peaks produced the largest composite particles, whereas agriculture‐dominated sites produced smaller but more tightly compacted particles. Organic plant fibres appeared to play a vital role in floc formation in peat‐covered catchments, whereas in agriculture‐dominated catchments, land use‐derived aggregates dominated the composition. This study provides empirical evidence of the importance of effective particle size measurement in understanding the dynamics of suspended particulate matters in boreal lowland river systems. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Reply to Comment on “The Keisarhjelmen detachment records Silurian–Devonian extensional collapse in Northern Svalbard”          下载免费PDF全文

Alvar Braathen  Per Terje Osmundsen  Harmon Maher  Morgan Ganerød 《地学学报》2018,30(4):322-324

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Air–Sea \mathrm{CO}_{2} Gas Transfer Velocity in a Shallow Estuary     

Eva Thorborg Mørk  Lise Lotte Sørensen  Bjarne Jensen  Mikael K. Sejr 《Boundary-Layer Meteorology》2014,151(1):119-138

The air–sea transfer velocity of $\mathrm{CO}_{2}\, (k_{\mathrm{CO}_{2}})$ was investigated in a shallow estuary in March to July 2012, using eddy-covariance measurements of $\mathrm{CO}_{2}$ fluxes and measured air–sea $\mathrm{CO}_{2}$ partial-pressure differences. A data evaluation method that eliminates data by nine rejection criteria in order to heighten parametrization certainty is proposed. We tested the data evaluation method by comparing two datasets: one derived using quality criteria related solely to the eddy-covariance method, and the other derived using quality criteria based on both eddy-covariance and cospectral peak methods. The best parametrization of transfer velocity normalized to a Schmidt number of 600 $(k_{600})$ was determined to be: $k_{600} = 0.3\,{U_{10}}^{2.5}$ where $U_{10}$ is the wind speed in m $\mathrm{s}^{-1}$ at 10 m; $k_{600}$ is based on $\mathrm{CO}_{2}$ fluxes calculated by the eddy-covariance method and including the cospectral peak method criteria. At low wind speeds, the transfer velocity in the shallow water estuary was lower than in other coastal waters, possibly a symptom of low tidal amplitude leading to low intensity water turbulence. High transfer velocities were recorded above wind speeds of 5 m $\mathrm{s}^{-1}$ , believed to be caused by early-breaking waves and the large fetch (6.5 km) of the estuary. These findings indicate that turbulence in both air and water influences the transfer velocity.  相似文献