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921.
Nuclear activity on land and dumping of waste in the Siberian shelf seas mean that the Kara Sea is most likely to experience inputs of radioactivity. Industrial and other anthropogenic activities in the expansive Ob' and Yenisey watersheds also contribute organochlorines, heavy metals and oil to this region. Contaminant fate is influenced by the distribution of the river discharge and processes associated with ice formation and ocean currents. Although average conditions are important in the transport of pollutants, events such as storms and iceberg gouging may be critical in deciding the ultimate fate of dumped and released contaminants. 相似文献
922.
N. Sultan M. Voisset T. Marsset A.M. Vernant E. Cauquil J.L. Colliat V. Curinier 《Marine Geology》2007,240(1-4):235-255
We present a new method to characterize free gas, gas hydrates and carbonate concretions occurrence which are considered as high-risk factors for sub-sea developments in the Niger delta. This method is based on the combination of 3D seismic data to the geotechnical site characterizations using piezocone CPTU tests (Cone Penetration Test with additional measurement of the pore water pressure). A special processing of the 3D seismic data has enabled the determination of the interval compressional velocity. Using the effective-medium theory, velocity anomalies (negative and positive) within the first 15 m were translated in gas hydrate and free gas distribution. The calibration of the P wave velocity anomalies was done thanks to in-situ geotechnical testing carried out during two oceanographic surveys (2003 and 2004). Comparison between in-situ testing, recovered cores and the prediction of the gas and the gas hydrate distribution based on the compressional wave velocity have shown that 3D seismic data is a valuable tool to identify heterogeneous areas but the use of the piezocone was essential to discriminate between gas hydrate occurrences and carbonate concretions' presence. Furthermore, in-situ compressional wave velocity (Vp) measurements have clearly demonstrated what it was suspected from the 3D seismic data, the co-existence in the study area between gas hydrate and free gas. 相似文献
923.
—A comprehensive analysis is conducted based on observations on topography.tidal current.salinity.suspended sediment and bed load during the years of 1982.1983.1988.1989.1996 and 1997 in theYangtze Estuary.Results show that the deformation of tidal waves is distinct and the sand carrying capaci-ty is large within the mouth bar due to strong tidal currents and large volume of incoming water and sedi-ments.Owing to both temporal and spatial variation of tidal current.deposition and erosion are extremelyactive.In general a change of up to 0.1 m of bottom sediments takes place during a tidal period.The maxi-mum siltation and erosion are around 0.2 m in a spring to neap tides cycle.The riverbed is silted duringflood when there is heavy sediment load.eroded during dry season when sediment load is low.The annualaverage depth of crosion and siltation on the riverbed is around 0.6 m.In particular cases.it may increaseto 1.4 m to 2.4 m at some locations. 相似文献
924.
J. Nicholson I. Broker J. A. Roelvink D. Price J. M. Tanguy L. Moreno 《Coastal Engineering》1997,31(1-4)
Five different coastal area morphodynamic models have been set up to run on the same offshore breakwater layout and an intercomparison carried out on the hydrodynamic and morphodynamic output produced by each scheme. In addition, the predicted morphodynamics was checked against available laboratory and field data.It is concluded that the models are capable of producing realistic estimates for the dominant morphodynamic features associated with offshore breakwaters. Coupling of the wave, current and sediment transport components of each scheme is shown to yield bathymetry which attains a state of equilibrium, unlike models which are based on the initial transport field only. 相似文献
925.
This article presents a comparative study of the breathing resistance and clearing characteristics of several types of commercially available snorkels in an attempt to device quantitative means that enable the divers to select the best snorkel and the designers to see the possible directions and modifications necessary for improving the performance of such important life support devices.Two test stands have therefore been built, the first to measure the breathing resistance and the second to monitor the clearing efficiency and speed of some of the commonly used snorkels.The tested snorkels varied from the simple J-type to the sophisticated wrap-around snorkels with convoluted flexible hoses and flared ends.The results obtained show that large diameter snorkels of the wrap-around design with sweeping barrels and flared ends (as the AMF Swimmaster snorkel number 2S55) offer the least breathing resistance. As for the clearing characteristics snorkels with small diameters and of the simple J-type (as the Spanish Aquasub snorkel: The Canarias) or with large diameters and sweeping barrels (as the Power Tuned snorkel of U.S. divers) possess the best clearing figure of merit. 相似文献
926.
927.
Sand ridges on the inner Atlantic shelf of North America: Morphometric comparisons with Huthnance stability model 总被引:1,自引:0,他引:1
A. G. Figueiredo Jr. D. J. P. Swift Stubblefield T. L. Clarke 《Geo-Marine Letters》1981,1(3-4):187-191
Sand ridge fields on the inner shelf of the Middle Atlantic Bight are generally thought to have formed in response to northeasterly
storm flows as the shoreface underwent erosional retreat with postglacial sea-level rise. However, the hydrodynamic mechanism
is poorly unerstood. Coastal boundary models see the ridges as responses of the seafloor to distortions in the flow induced
by the coastal boundary. Stability models propose that an irregular initial topography will evolve toward an ordered array
of bedforms in response to repeated flow events. The two classes of models are not mutually exclusive, nor are members within
each class mutually exclusive. Results of measurements of ridge spacing on the inner Atlantic shelf of North America agree
with the predictions of stability models. 相似文献
928.
Measurements of 226Ra and 210Pb in barite samples separated from different depths of a piston core from the eastern equatorial Pacific are reported. 226Ra is enriched in the barite as would be expected from the chemistries of Ra and Ba; the ratio centers around 1.5 · 1014 atoms/mole. The results suggest that barite is concentrating Ra at a rate comparable to its decay rate, viz. 5.78 · 10?3 yr?1. The gross 210Pb depletion with respect to 226Ra is indicative of 222Rn loss due to the smallness of the barite crystals. 相似文献
929.
It is suggested that Bouvet Island is the surface manifestation of a mantle plume which has resulted in the creation of a chain of seamounts in the South Atlantic and a general shoaling of the region.The strike of two newly defined large fracture zones borth and south of the Bouvet Island pedestal have been utilized to determine a pole of rotation at 12.5°S, 12.5°W for the Africa-Antarctica motion. A pole at 75°S, 13°E has been calculated for the South America-Antarctica motion. At the triple junction the South America-Africa relative motion is 3.3 cm yr-1 (whole rate) at 075°. The Africa-Antarctica motion is 1.7 cm yr-1 at 065° and the South America-Antarctica motion is 1.6 cm yr-1 at 085. 相似文献
930.
The distribution of the colour index is considered in the region bounded by 8–11°N and 13°30–18°30W based on the results of measurements made on board vessels of the Marine Hydrophysical Institute of the Ukrainian SSR Academy of Sciences (MHI) in 1977–1985. Mean values and statistical characteristics are calculated for the colour index variability over one-degree squares. A map of its multi-yearly average distribution is plotted.Translated by M. M. Trufanov. 相似文献