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A two-dimensional numerical model is applied to a coastal ocean wherein alongshore elevation and density gradients, normally calculated by a three-dimensional model, are instead supplied by climatologically averaged data for the California Current System between 25 and 40°N. Surface wind stress is also obtained from climatological data. Both surface and bottom boundary layers are resolved in the model calculations; a second moment turbulence closure submodel supplies vertical diffusivities. Near steady state solutions are possible when surface buoyancy flux is imposed at the surface.Model results are as follows: Southward wind stress produces a broad equatorward current with an embedded coastal jet in accordance with previous studies. Positive wind stress curl reduces the jet current and produces a poleward undercurrent which then surfaces as the curl is increased. The jet currents are reduced and poleward flow increases as bottom steepness increases; to a lesser extent, inclusion of the beta effect has a similar effect. The existence of near bottom, poleward or equatorward flow is explained rather simply in terms of the bottom stress resulting from the alongshore balance of surface wind stress and vertically integrated pressure gradient, the latter involving the alongshore surface elevation and density gradient. A further finding is that the upwelling circulation associated with wind stress is confined to the top 200 to 300 m of the ocean along the California coast. 相似文献
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Satellite remote sensing technique can be effectively utilised in mapping and monitoring the river course changes and associated geomorphological features. Ravi river, flowing along the Indo-Pakistan border, has been in the limelight for its repeated flood havoc during monsoon and abrupt encroachment at some places in the Indian territory, where it was not flowing earlier. This river, meandering in zig-zag fashion along the International boundary in Amritsar and Gurdaspur districts of Punjab, poses perennial threats to the nations’s economy due to extensive destruction happening every year. An attempt has been made to map the shift of this river and the associated geomorphological features along its course using the Indian Remote Sensing Satellite data (IRS-IA and IB LISS-IIFCC) of the period 1991–1993 and the Survey of India topographic sheets of the period 1972–1973. The study shows that there has been drastic changes in the course of Ravi during a span of 20 years due to human activities along its course. The river has shifted its course considerably towards India since its topography is against it. River training structures/bundhs, built by the neighbouring country, across and very near to the earlier river course has been the main reason for this drastic shifting. It is estimated that such massive structures could turn the river course towards India by atleast 1 to 5 km in the border districts of Punjab. This shifting of Ravi along international border poses a serious threat to the Nation’s defence system. 相似文献
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This paper extends the evidence that volcanic rocks may contain initial argon, and investigates some of the implications of the results.The incorporation of initial argon with a composition different to that of air at the time of crystallisation may be an important cause of scatter of K-Ar dates in areas such as the British Tertiary igneous province, but in favourable circumstances the correct age may be recovered.An age of about 60 Ma is indicated for the lavas of Northern Ireland. 相似文献
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Christopher J. Mellor Stephen J. Dugdale Grace Garner Alexander M. Milner 《水文科学杂志》2017,62(4):499-514
The impact of climate change on Arctic rivers is expected to be severe. There is therefore a need for greater understanding of Arctic river temperature processes. This study quantifies the spatio-temporal variability of water temperatures in the Kårsa River, Sweden. Water temperature was monitored over two summers within the main proglacial channel and within braids fed by different sources. Longitudinal and lateral temperature patterns were assessed in relation to prevailing hydro-meteorology. Temperature metrics in the main channel increased with distance downstream but were moderated by a large lake, while temperatures in the braids were dependent upon channel source. The high temperature standard deviation and inter-site differences within the braids highlight the importance of braided channels for creating thermal habitat heterogeneity. Temperatures were dependent on hydro-meteorological conditions, with sensitivity to air temperature maximized during cooler, rainy conditions. These results shed new light on Arctic river temperature patterns and their controlling processes. 相似文献
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Concentrations of polycyclic aromatic hydrocarbons were determined in species of commercial fish and lobsters following an oil-spill just off the protected Madagascan coastline. Samples were collected along the coastline within and outside the affected area. Summed PAH concentrations ranged from 1.9 μg kg−1 to 63 μg kg−1 wet weight, but with no higher molecular weight PAHs (>202 Da) being detected. All concentrations of benzo[a]pyrene, benz[a]anthracene and dibenz[a,h]anthracene were <0.1 μg kg−1 wet weight, well within the EU and UK set limits for the protection of human health. Additionally, samples were calculated as the benzo[a]pyrene toxic equivalency quotient (TEQ) and found to be well below the level of concern in relation to health of human consumers. Evaluation of the biota PAH data indicated the origin of PAH was predominantly petrogenic with >80% arising from oil sources. Profile studies indicate a low-level multisource petrogenic contamination probably representing a pre-spill background for the area. 相似文献
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Sensitivity studies with a new generalized coordinate ocean model are performed in order to compare the behavior of bottom boundary layers (BBLs) when terrain-following (sigma or combined sigma and z-level) or z-level vertical grids are used, but most other numerical aspects remain unchanged. The model uses a second-order turbulence closure scheme that provides surface and BBL mixing and results in a quite realistic climatology and deep water masses after 100 year simulations with a coarse resolution (1° × 1°) basin-scale terrain-following grid. However, with the same turbulence scheme but using a z-level grid, the model was unable to produce dense water masses in the deep ocean. The latter is a known problem for coarse resolution z-level models, unless they include highly empirical BBL schemes.A set of dense water overflow experiments with high-resolution grids (10 and 2.5 km) are used to investigate the influence of model parameters such as horizontal diffusivity, vertical mixing, horizontal resolution, and vertical resolution on the simulation of bottom layers for the different coordinate systems. Increasing horizontal diffusivity causes a thinner BBL and a bottom plume that extends further downslope in a sigma grid, but causes a thicker BBL and limited downslope plume extension in a z-level grid. A major difference in the behavior of the BBL in the two grids is due to the larger vertical mixing generated by the turbulence scheme over the step-like topography in the z-level grid, compared to a smaller vertical mixing and a more stably stratified BBL in the sigma grid. Therefore, the dense plume is able to maintain its water mass better and penetrates farther downslope in the sigma grid than in the z-level grid. Increasing horizontal and vertical resolution in the z-level grid converges the results toward those obtained by a much coarser resolution sigma coordinate grid, but some differences remain due to the basic differences in the mixing process in the BBL. 相似文献
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Lugworms are important members of the macrobenthos of sheltered intertidal sediments, and this study assessed the abundance and distribution of Abarenicola affinis in Otago, southern New Zealand. Using a faecal cast:lugworm ratio (1.00:1.09) revealed a patchy distribution across inlets, with an overall mean abundance of 11.1 individuals/m2 (range: 3.8 to 21.3 individuals/m2). Distribution patterns varied among inlets, with lugworms mostly confined to the high intertidal zone, but spread across all intertidal zones in one inlet. The lugworm habitat was characterised by muddy to medium sand (55–233 µm mean grain size) with low organic matter (< 2%) and chlorophyll a (1–12 µg/g dry sediment) contents. Depending on the inlet, lugworm abundance was related to sediment parameters, indicating that their distribution across Otago inlets is habitat dependent. The present findings also indicate that factors other than those measured contribute to A. affinis distribution and abundance patterns in this region. 相似文献
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The isotopic composition and concentration of Pb was measured in suspended particulate matter of the Irish Sea. Aerosol, surficial and pre-industrial sediment was also analysed to provide information on sources terms. Concentrations of Pb in suspended sediments were lower than previously reported which presumably reflects the international effort to reduce Pb inputs to the environment. Lead concentrations were highest in Liverpool Bay and lowest in the western Irish Sea. A significant negative relationship between Pb and salinity suggests that present inputs and the resuspension of relict lead associated with particles in areas significantly affected by freshwater discharges are the predominant sources of Pb to the Irish Sea. The isotopic composition of Pb in the stratified region of the western Irish Sea demonstrates that atmospheric sources are also significant to this region, which is consistent with current knowledge on the hydrography. Pb isotopic ratios show that water entering the Irish Sea through St George's Channel is significantly influenced by anthropogenic inputs prior to additional contamination by direct inputs to the Irish Sea. 相似文献