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J.-M. Gherardi L. Labeyrie J.F. McManus R. Francois L.C. Skinner E. Cortijo 《Earth and Planetary Science Letters》2005,240(3-4):710-723
A first study from the subtropical western Atlantic, using 231Pa/230Th ratios as a kinematic proxy for deep water circulation, provided compelling evidence for a strong link between climate and the rate of Meridional Overturning Circulation (MOC) over the last deglaciation. However, these results warrant confirmation from additional locations and water depths because the interpretation of the sedimentary 231Pa/230Th ratio in terms of circulation vigor can be biased by variations in particle flux and composition. We have measured 231Pa/230Th in a core from the Iberian margin, in the Northeastern Atlantic basin, and have compared these new results to the data from the western Atlantic basin. We find that the reduction in the circulation during H1 and YD and the subsequent increases first recognized in the sediment deposited on Bermuda Rise are also evident in the eastern basin, in a totally different sedimentary regime, confirming that sedimentary 231Pa/230Th ratios record basin-wide changes in deep water circulation. However, some differences between the eastern and western records are also recognized, providing preliminary evidence to differentiate between renewal rates in the two North Atlantic basins and between shallower and deeper overturning. Our results suggest the possible existence of two sources of Glacial North Atlantic Intermediate Deep Water (GNAIW), one in the south Labrador Sea and another west of Rockall Plateau. Both sources contributed to the meridional overturning but the two had different sensitivity to meltwater from the Laurentide and the Fennoscandian ice sheets during the deglaciation. These results indicate that additional information on the geometry and strength of the ventilation of the deep Atlantic can be obtained by contrasting the evolution of sediment 231Pa/230Th in different sections of the Atlantic Ocean. 相似文献
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Measurements made on the floors of the temporarily-drained Glenfarg and Glenquey Reservoirs indicate that sediments with wet volumes of 63.94 × 103 m3 and 12.64 × 103 m3 were deposited in 56 and 73 years respectively. These figures represent 2.5 per cent and 1.1 per cent losses of original storage capacity. When corrected for water, organic, and diatom skeleton contents, and reservoir trap efficiency inorganic sediment yields of at least 31.3 tonnes km?2 yr?1 and of 9.0 tonnes km?2 yr?1 are suggested. The difference is probably related to contrasts of land use. 相似文献
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J. McManus 《地球表面变化过程与地形》1979,4(2):141-146
The modification of scree sediments entering a stream is examined by QDa-Md methods. Loss of fine or coarse subpopulations or both in combination from an initially symmetrical grain size distribution is shown to result in the dispersion of the QDa-Md plots throughout an envelope typical of fluvial sediments. Natural plots from the Rivers Earn and Tay provide live examples of the transenvironmental trend patterns demonstrated. 相似文献
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George B. McManus Kevin D. Wyman William T. Peterson Charles F. Wurster 《Estuarine, Coastal and Shelf Science》1983,17(4):421-430
The effects of feeding, egg laying, and fecal pellet production on the elimination of polychlorinated biphenyls (PCBs) from the marine copepod Acartia tonsa were studied in a series of experiments. Copepods were exposed to 14C-labelled Aroclor 1254 and allowed to depurate in clean seawater. Copepods fed during depuration eliminated PCBs more rapidly than unfed copepods whether or not the original PCB exposure medium had contained food. Both eggs and fecal pellets contained PCBs during depuration, with the weight specific concentration of PCB in the eggs (up to 407 ppm, dry weight) exceeding four times that in the females that produced them. Female copepods eliminated PCBs twice as rapidly as males, indicating that egg production is an important route for PCB elimination. 相似文献
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Phil McManus 《The Australian geographer》2012,43(4):411-424
Measuring the sustainability of a city, and ranking the city against other cities, is increasingly seen as a way to achieve urban sustainability. A number of studies have highlighted how Sydney is unsustainable, with two recent ranking exercises appearing to confirm these findings by placing Sydney below many other Australian cities for urban sustainability. These two exercises are situated within international moves towards ranking cities. The article explores the assumptions and criteria used by Mercer in its Eco-City Index and the Australian Conservation Foundation in its Sustainable Cities Index. The conclusion discusses how Sydney could become more sustainable, and identifies why normative urban sustainability rankings should be recognised for their potential while simultaneously being treated with caution. 相似文献