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The distribution coefficient (λMg) of Mg2+ ions between calcite and solution was found to be 0.012 ± 0.001 (10°C), 0.014 ± 0.001 (15°C), 0.019 ± 0.001 (25°C), 0.024 ± 0.001 (30°C), 0.027 ± 0.001 (35°C) and 0.040 + 0.003 (50°C). This indicates a remarkable dependence on temperature. The effect of the Mg2+/Ca2+ molar ratio in a parent solution on λMg for calcite is small, where the molar ratio lies in the range 0.04-2. However, the λMg value for aragonite tends to decrease with increasing Mg2+/Ca2+ ratio in the parent solution. The largest Mg content of calcite in the Ca(HCO3)2-Mg2+ → calcite system is around 2 mol% in the temperature range 10–50°C. Neither homogeneous nor heterogeneous distribution laws hold for aragonite precipitation, and the temperature effect on the coprecipitation of Mg2+ ions with aragonite is very small. 相似文献
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The wave transmission, reflection and energy dissipation characteristics of ‘’-type breakwaters were studied using physical models. Regular and random waves in a wide range of wave heights and periods and a constant water depth were used. Five different depths of immersion (two emerged, one surface flushing and two submerged conditions) of this breakwater were selected. The coefficient of transmission, Kt, and coefficient of reflection, Kr, were obtained from the measurements, and the coefficient of energy loss, Kl was calculated using the law of balance of energy. It was found that the wave transmission is significantly reduced with increased relative water depth, d/L, whether the vertical barrier of the breakwater is surface piercing or submerged, where ‘d’ is the water depth and ‘L’ is the wave length. The wave reflection decreases and energy loss increases with increased wave steepness, especially when the top tip of the vertical barrier of this breakwater is kept at still water level (SWL). For any incident wave climate (moderate or storm waves), the wave transmission consistently decreases and the reflection increases with increased relative depth of immersion, Δ/d from −0.142 to 0.142. Kt values less than 0.3 can be easily obtained for the case of Δ/d=+0.071 and 0.142, where Δ is the height of exposure (+ve) or depth of immersion (−ve) of the top tip of the vertical barrier. This breakwater is capable of dissipating wave energy to an extent of 50–80%. The overall performance of this breakwater was found to be better in the random wave fields than in the regular waves. A comparison of the hydrodynamic performance of ‘’-type and ‘T’-type shows that ‘T’-type breakwater is better than ‘’-type by about 20–30% under identical conditions. 相似文献
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The deep‐sea floor is increasingly subject to anthropogenic impacts. Consequently, there are increasing efforts to develop appropriate management strategies. Species‐level indicators and assessments are hampered in the deep sea by the high proportion of unknown species routinely encountered. If environmental management is to keep pace with exploitation, alternative approaches including higher taxon surrogacy (taxonomic sufficiency) must be considered. Here we compare genus‐ and species‐level studies of the diversity and ecology of deep‐sea macrobenthos on the West Shetland Slope (NE Atlantic). This is an environmentally complex region that encompasses a biogeographic transition from temperate North Atlantic to Arctic conditions, and so may be particularly challenging for any general relationship between species‐ and genus‐level analyses. We ask two questions: (i) does genus diversity reflect species diversity and (ii) does genus‐level ecology reflect species‐level ecology? We conclude that among the West Shetland Slope macrobenthos: (i) genus‐level α‐ and β‐diversity measures are highly correlated with and good predictors of their species‐level equivalents and (ii) that their ecology is very well described by genus‐level data. We further note that, given the complexity of the West Shetland Slope environment, it may be reasonable to expect these conclusions to hold in other deep‐sea environments. 相似文献
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Rogrio L. Ferreira Filipe R. Ceia Teresa C. Borges Jaime A. Ramos Alan B. Bolten 《Marine Ecology》2021,42(1):e12636
Within the same population, nesting green turtles (Chelonia mydas) might exploit different niches by exhibiting polymorphic foraging strategies and/or inhabiting geographically distinct foraging areas. This is crucial information for the conservation of this species. Here, we used stable carbon and nitrogen isotope ratios (δ13C and δ15N) to test for differences in a population of green turtles nesting on Príncipe Island (1°37′N; 7°24?′E), Central Africa. A total of 60 nesting females were sampled on the two main nesting beaches of the island in December 2012. Minimum curved carapace length (CCL) was recorded, and δ13C and δ15N values were measured in the epidermis of each individual. Overall, CCL varied from 87.0 to 108.0 cm (mean ± SD =100.0 ± 5.1), δ13C values from ?19.4 to ?8.6‰ (?17.3 ± 1.8) and δ15N values from 7.9 to 17.3‰ (13.6 ± 1.5). Despite the large variation in both isotopic ratios, their distributions were unimodal, showing an absence of polymorphic foraging strategies and isotopically distinct foraging areas. However, smaller females (< median, 100.8 cm) occupied a much larger isotopic niche (i.e., four times greater) than larger females. These results suggest that nesting green turtles may forage opportunistically on the resources available in each of their foraging home ranges, with smaller females venturing to more isotopic‐diversified areas and/or exhibiting broader foraging strategies than larger females. In addition, and in accordance with other studies, findings suggest that the foraging grounds used by the Príncipe green turtle nesting females are distributed mainly throughout the Gulf of Guinea. 相似文献
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Combined stomach content and δ13C/δ15N analyses of oilfish,escolar, snake mackerel and lancetfish in the western North Atlantic 
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下载免费PDF全文 Large, mesopelagic teleost fishes have a potentially keystone position in the ecology of the pelagic water column, yet remain relatively unstudied when compared with large, commercially important, epipelagic fishes. Here, the ecological roles of four, large, vertically migrating teleosts were examined. Stomach content analyses were performed on 48 oilfish (Ruvettus pretiosis), 35 escolar (Lepidocybium flavobrunneum), 32 snake mackerel (Gempylus serpens) and seven lancetfish (Alepisaurus spp.) collected from pelagic longline gear in the Western North Atlantic Ocean from 2007 to 2010. Of these specimens, stable carbon and nitrogen isotope analyses were also performed on white dorsal muscle tissue from 33 oilfish, 16 escolar, 27 snake mackerel and seven lancetfish. Based on literature length‐at‐maturity values, all escolar, snake mackerel and lancetfish specimens were mature, while 13 of the 33 oilfish were juveniles. Crustaceans, annelids, salps, cephalopods and teleosts were present in the stomachs and were presumed to be prey items. A Kruskal–Wallis test showed the four species to be isotopically segregated in both δ13C and δ15N. Escolar were the most depleted in δ13C, followed by adult oilfish, juvenile oilfish and lancetfish, with snake mackerel the most enriched. The depletion in δ13C of adult oilfish and escolar may have been attributable to high C/N values, which were strongly correlated with length in oilfish, weakly correlated with length in escolar and moderately correlated with length in snake mackerel and lancetfish. The high C/N was likely due to the high lipid concentration of these fishes. Other factors that may have contributed to the depletion in δ13C may include spawning or a change in carbon source within the ecosystem. Large escolar occupied the highest trophic level (δ15N = 10.20), followed by snake mackerel (δ15N = 9.66), adult oilfish (δ15N = 9.32), lancetfish (δ15N = 9.05) and juvenile oilfish (δ15N = 7.83). A marked change in oilfish δ13C and C/N at 30–35 cm fork length coincided with a presumed length‐at‐maturity. 相似文献
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Brian Meredith 《Marine Policy》1980,4(4):329-330
The International Maritime Satellite Organization (INMARSAT) has come into being as a result of conferences by the Inter-governmental Maritime Consultative Organisation (IMCO). Its administration has been set up in London, and the organization has called for tenders for the satellites and ground stations required, and as an interim measure is arranging to use a share of the facilities of existing satellite systems. Its aim is to improve telecommunications facilities for the world's shipping and thus to reduce risks to life and property at sea, increase the efficiency of ship management, and to provide a satellite service, owned by the participating governments, that has been long in demand. 相似文献
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Gene de Castro 《Marine Policy》1977,1(4):342-343
A summary of the various forms of pollution control discussed at an international Anti-Pollution Course held at the French Merchant Marine School in Marseilles on 13–25 June 1977. 相似文献
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Two diagnostic dynamic models for flow in hyperbolic and elliptic regions of a geophysical fluid are developed and compared. As the main interest here is in local dynamical processes, these models are used to study trajectories near stagnation points in the flow field. The simplest model presumes a balance between the Coriolis and geopotential accelerations. This model is equivalent to the classic approach that characterizes these regimes by the quadratic equation for the eigenvalues of the velocity gradient. However, since that model imposes geostrophic dynamics, the eigenvalues of the velocity gradient can be replaced by the local curvature or Hessian of the geopotential scaled by Coriolis. The general model adds both local and inertial accelerations to the dynamical balance. In contrast to the classic result the consequent frequency equation is a quartic that involves both the Hessian of the geopotential field, the components of the velocity gradient, and Coriolis. Roots of this equation give two distinct time scales, which are interpreted as Lagrangian time scales. Motion of the geopotential field produces a third Eulerian time scale. Critical trajectories are those whose initial positions and velocities are such that they are independent of the Lagrangian time scales. These simple models establish that within hyperbolic and elliptic regions of the geopotential field there may be trajectories whose time scales differ radically from even their nearest neighbors.A characteristic of critical trajectories in the ocean is that they often are found near stagnation points. These may be hard to identify even in model simulations, but a similar quantity, the null in the geopotential gradient, might be easier to obtain. To analyze the relation between the critical trajectories, stagnation points, and gradient null, evolution models for the later two objects are proposed. For a steady geopotential all three coincide. However with a time varying geopotential, they are distinct even though all have the same time scale. The analysis provides a metric for the separation of all three objects. 相似文献
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The continuing public concern with overfishing ignores the underlying problems that face fishery mangers. Attention needs to be given to (1) the transitory nature of the ocean environment, (2) the natural variation in fish stocks, (3) the role of the fishing industry and market forces in fishery management, and (4) the failure to focus on what it is we most need from the oceans, in what form we need it, and at what price. 相似文献
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C. G. Castro T. R. Baumgartner S. Bograd R. Castro F. P. Chavez C. A. Collins R. Durazo J. García G. Gaxiola-Castro T. Hayward A. Huyer R. Lynn A. S. Mascarenhas M. R. D. Robert R. L. Smith P. A. Wheeler F. A. Whitney 《Progress in Oceanography》2002,54(1-4)
Hydrographic data collected along the West Coast of North America between January 1997 and January 1999 have been compiled into a web-based Atlas of the 1997–8 El Niño event. This paper discusses the organization of the Atlas, describes the data that were incorporated into the Atlas and explains how vertical and horizontal distributions for the different properties were constructed. Examples of figures from the Atlas are shown. 相似文献
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A batch sorption technique for the determination of particle–water interactions of hydrophobic organic micropollutants under simulated estuarine conditions is described. Results are presented for the behaviour of 2,2′,5,5′-tetrachlorobiphenyl (2,2′,5,5′-TCB) in river and sea waters, both in the presence and absence of estuarine suspended particles. Adsorption onto particles in sea water was enhanced compared with adsorption in river water owing to salting out of the compound, and possibly of the particulate organic matter, in the presence of high concentrations of dissolved ions. The particle–water distribution coefficient, KD, decreased from about 120×103 to 10×103 ml g−1, and from about 150×103 to 20×103 ml g−1, in river water and sea water, respectively, over a particle concentration range of 10–1000 mg l−1. Incomplete recovery of compound from the reactor walls is partly responsible for a particle concentration effect, while artefacts relating to inadequate sediment and water phase separation were ruled out following further experiments. The particle concentration effect, which is replicated in many field studies of hydrophobic organic micropollutants, including 2,2′,5,5′-TCB, is incorporated into a simple partitioning model and is discussed in the context of the likely estuarine behaviour of such compounds. 相似文献