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1.
Fishing, selection, and phenotypic evolution   总被引:9,自引:9,他引:10  
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This paper reports the initial results of a study of groundwater and coastal waters of southern Brazil adjacent to a 240 km barrier spit separating the Patos Lagoon, the largest coastal lagoon in South America, from the South Atlantic Ocean. The objective of this research is to assess the chemical alteration of freshwater and freshwater–seawater mixtures advecting through coastal permeable sands, and the influence of the submarine discharge of these fluids (SGD) on the chemistry of coastal waters. Here we focus on dissolved iron in this system and use radium isotopic tracers to quantify SGD and cross-shelf fluxes. Iron concentrations in groundwaters vary between 0.6 and 180 μM. The influence of the submarine discharge of these fluids into the surf zone produces dissolved Fe concentrations as high as several micromolar in coastal surface waters. The offshore gradient of dissolved Fe, coupled with results for Ra isotopes, is used to quantify the SGD flux of dissolved Fe from this coastline. We estimate the SGD flux to be 2 × 106 mol day− 1 and the cross-shelf flux to be 3.2 × 105 mol day− 1. This latter flux is equal to about 10% of the soluble atmospheric Fe flux to the entire South Atlantic Ocean. We speculate on the importance of this previously unrecognized iron input to regional ocean production and on the potential significance of this source to understanding variations in glacial–interglacial ocean production.  相似文献
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The fidelity of numerical simulations of the general circulation of the North Atlantic Ocean in basin- to global-scale models have improved considerably in the last several years. This improvement appears to represent a regime shift in the dynamics of the simulated flow as the horizontal grid spacing decreases to around 10 km. Nevertheless, some significant biases in the simulated circulation and substantial uncertainties about the robustness of these results with respect to parameterization choices remain. A growing collection of simulations obtained with the POP primitive equation model allow us to investigate the convergence properties and sensitivity of high resolution numerical simulations of the North Atlantic, with particular attention given to Gulf Stream separation and the subsequent path of the North Atlantic Current into the Northwest Corner. Increases in resolution and reductions in dissipation both contribute to the improvements in the circulation seen in recent studies. We find that our highest resolution eddy-resolving simulations retain an appreciable sensitivity to the closure scheme. Our most realistic simulations of the Gulf Stream are not obtained at the lowest levels of dissipation, while the simulation of the North Atlantic Current continues to improve as dissipation is reduced to near the numerical stability limit. In consequence, there is a limited range of parameter space where both aspects of the simulated circulation can be brought into agreement with observations. This experience gained with the comparatively affordable regional North Atlantic model is now being used to configure the next generation of ocean climate models.  相似文献
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The fish assemblages of the Ebrié lagoon (Ivory Coast) were sampled by experimental fishing over the entire lagoon using a purse seine net. The sampling was conducted in the two main hydroclimatic seasons for this ecosystem, i.e. in the dry season (March–April) and in the wet season (August–September). The results obtained showed a fish assemblage organized around a consistently occurring group of twenty species. When analysed in terms of ecological categories, the seasonal influence led to a cycle in the assemblages from freshwater to marine around this permanent species pool, with a seasonal renewal of the assemblage. At the scale of the lagoon, there were variations in the composition of the assemblages that clearly distinguished the western part from the eastern one. The limit was situated at the Vridi canal, a wide artificial channel permanently connecting the lagoon to the sea. To the west, the assemblage was characterised by a strong spatial uniformity and low seasonal variability. To the east, the assemblage formed two different entities; one assemblage with pronounced freshwater affinities occurring in a side arm and the other assemblage with great seasonal variability under the alternating influence of seawater in the dry season and freshwater in the wet season. This part of the lagoon functioned somewhat like a typical estuary.  相似文献
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Positioning fisheries in a changing world   总被引:1,自引:1,他引:0  
Marine capture fisheries face major and complex challenges: habitat degradation, poor economic returns, social hardships from depleted stocks, illegal fishing, and climate change, among others. The key factors that prevent the transition to sustainable fisheries are information failures, transition costs, use and non-use conflicts and capacity constraints. Using the experiences of fisheries successes and failures it is argued only through better governance and institutional change that encompasses the public good of the oceans (biodiversity, ecosystem integrity, sustainability) and societal values (existence, aesthetic and amenity) will fisheries be made sustainable.  相似文献
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High resolution acoustic structure of fish   总被引:1,自引:1,他引:0  
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