In Belgium a long process (1999–2005) led to the designation of several marine protected areas (MPAs). In order to analyse the designation process, the ‘policy arrangement approach’ was used as an analytical tool. Attention was given to four dimensions (actors and coalitions, arguments, rules and resources). Particular attention was paid to the switch from an authoritative to a more deliberated policy style in reaction to conflicts with stakeholders. This switch in policy style contributed to a successful legal designation, but does not guarantee the best protection of marine biodiversity. This case study linked science (setting ecological goals) to policy (analysis of a policy process) and led to some more general conclusions on the designation of MPAs and the role of participation in this process. 相似文献
Dissolution experiments of a tholeiite basalt glass carried out at different pH and T (up to 300°C) using a rotatingdisc apparatus show that, depending on pH and T, dissolution can be controlled by one of the following steps: (1) surface reaction; (2) transport of reactants in solution; and (3) mixed reaction. The activation energies of these different processes were found to be 60, 9 and 15–50 kJ mol−1, respectively. Taking account of these results, it appears likely that surface reactions are not rate limiting for the hydrolysis of most crystalline silicate minerals in hydrothermal and metamorphic processes, and that caution should be exercised when predicting rate of reactions at high temperatures solely on the basis of activation energies measured at low temperatures.
Comparison of experimental and theoretical potentiometric titrations of the basalt glass and its constituent oxides indicates that the adsorption of H+ and OH− ions at the basalt surface is metal cation specific and that the net adsorption can be predicted from the sole knowledge of the acidity constants of the network-forming constituent oxides. We found that in the acidic pH region dissolution is promoted by the adsorption of H+ on al and Fe surface sites while in the basic region, dissolution is promoted by the adsorption of OH− on Si sites. The combination of the two distinct types of surface sites, Al and Fe on the one hand, and Si on the other hand, results in a dissolution rate minimum at a pH-value between the pHzpc of the two groups of oxide components. Linear regressions with a slope n=3.8 are observed both in acid and alkaline solutions in logarithmic plots of the rate of dissolution vs. the surface charge. The value of n, which represents the number of protonation or hydroxylation steps prior to metal detachment, has been found equal to the mean valence of the network-forming metals.
Combining concepts of surface coordination chemistry with transition state theory afforded characterisation of the activated complexes involved in basalt dissolution processes. From the values obtained for the thermodynamic properties of activation for basalt dissolution it is assumed that the activated complexes formed during the H2O-promoted dissolution of the basalt glass are more tightly bonded than those formed during H+- or OH−-promoted dissolution. 相似文献
The Trinity ophiolite consists of small magma chambers inside a large mantle body. Xenoliths of mantle peridotite occur both in gabbroic cumulates along the walls and in the matrices of ultrabasic breccias on the floors of the magma chambers. Field relationships and petrographic data suggest that these fragments of original mantle peridotite were modified by contact with basic magmas by modal metasomatism. Quantitative elemental mass transfers determined from the composition, volume and density variations of reacting minerals demonstrate both closed and open system conditions for the major (Si, Al, Ti, Na, Ca, Fe and Mg) and trace elements (Cr, Ni). In the open system, material gains and losses provide information on the composition of the fluid taking part in the metasomatic reaction.
During a first stage of metasomatism the mantle xenoliths were affected by high-temperature reactions at 600 to 925°C. They resulted from the interaction between solid mantle lherzolites and basic melts. The reactions are:
3. (3)clinopyroxene+spinel I→pargasitic hornblende+spinel II.
Chemical interactions between the upper mantle and oceanic magma chambers occurred as soon as the basic magmas had ascended through the upper mantle. The chemically modified magmas, within oceanic magma chambers, were depleted in Ti, Fe and Na. This could partly explain regional variations of the chemical compositions of primary magmas produced beneath slow-spreading ridges. The breakdown of olivine to orthopyroxene and magnetite participates in the control of the partition of magnetic Fe---Ti oxides between oceanic crust and mantle.
During the second stage, the serpentinization of olivine and the production of talc were superimposed on the products of the first stage. These reactions require large amounts of H2O. The hydrothermal fluid was probably seawater. It circulated in the brecciated area along the walls and floors of the magma chambers located at shallow depths. Such structural discontinuities thus played the role of penetration channels favoring seawater circulation in the oceanic crust.
All the chemical reactions examined suggest a significant open-system element transfer by infiltrating melts or circulating fluids. The results of this study suggest that caution is required in the interpretation of mineralogical and chemical information provided by mantle xenoliths carried to the surface by ascending magmas. 相似文献
The first meteoritic occurrence of CaAl4O7 is described from a Ca-Al-rich inclusion (CAI) in the Leoville carbonaceous chondrite. This CAI consists mainly of gehlenitic melilite, spinel, perovskite, and hibonite. CaAl4O7 is a minor component and occurs within melilite preferentially in portions rich in perovskite.The CAI is enveloped by a succession of three rims (from inside out): (a) hibonite+melilite+spinel+perovskite, (b) diopside, and (c) olivine.On the basis of mineral associations found and from the presence of moderately volatile elements (Fe and Cr) we conclude that the CaAl4O7-bearing CAI from Leoville is of residual nature. CaAl4O7 is apparently stable in the very Mg- and Si-poor environment of this CAI and is probably of igneous origin.The rims are interpreted as products of partial evaporation (rim (a)) and associated re-condensation (rims (b) and (c)). 相似文献
High-resolution clay mineral records combined with oxygen isotopic stratigraphy over the past 450 ka during late Quaternary from Core MD05-2901 off Middle Vietnam in the western South China Sea are re-ported to reconstruct a history of East Asian monsoon evolution. Variations in Illite, chlorite, and kaolinite contents indicate a strong glacial-interglacial cyclicity, while changes in smectite content present a higher frequency cyclicity. The provenance analysis indicates a mixture of individual clay minerals from various sources surrounding the South China Sea. Smectite derived mainly from the Sunda shelf and its major source area of the Indonesian islands. Illite and chlorite originated mainly from the Mekong and Red rivers. Kaolinite was provided mainly by the Pearl River. Spectral analysis of the kaolin-ite/(illite chlorite) ratio displays a strong eccentricity period of 100 ka, implying the ice sheet-forced win-ter monsoon evolution; whereas higher frequency changes in the smectite content show an ice sheet-forced obliquity period of 41 ka, and precession periods of 23 and 19 ka and a semi-precession period of 13 ka as well, implying the tropical-forced summer monsoon evolution. The winter monsoon evolution is generally in coherence with the glacial-interglacial cyclicity, with intensified winter monsoon winds during glacials and weakened winter monsoon winds during interglacials; whereas the summer monsoon evolution provides an almost linear response to the summer insolation of low latitude in the Northern Hemisphere, with strengthened summer monsoon during higher insolation and weakened summer monsoon during lower insolation. The result suggests that the high-latitude ice sheet and low-latitude tropical factor could drive the late Quaternary evolution of East Asian winter and summer monsoons, respectively, implying their diplex and self-contained forcing mechanism. 相似文献
Qualitative modelling of spatial relationships has often been considered as a contextindependent task that aims at a reasoning model in generic form. Despite the primary interest in these models, there is still a sufficiently large scope for context-dependent reasoning in space and time. This paper proposes a qualitative spatial reasoning model, oriented to the modelling and simulation of several cars acting in a multi-lane circuit, which can be considered as an illustrative example of a constrained frame of reference. The modelling objects of interest are individual cars whose cardinal relationships to external cars and actions are modelled. This dynamic system is analysed, and a set of interrelationships is identified at different levels of abstraction, together with inference rules that model the displacement of several cars in a circuit. The potential of this model is illustrated and calibrated using an agent-based prototype. 相似文献
By combining AVHRR data from the NOAA satellites with information from a database of in situ measurements, large-scale maps can be generated of the microphysical parameters most immediately significant for the modelling of global circulation and climate. From the satellite data, the clouds can be classified into cumuliform, stratiform and cirrus classes and then into further sub-classes by cloud top temperature. At the same time a database of in situ measurements made by research aircraft is classified into the same sub-classes and a statistical analysis is used to derive relationships between the sub-classes and the cloud microphysical properties. These two analyses are then linked to give estimates of the microphysical properties of the satellite observed clouds. Examples are given of the application of this technique to derive maps of the probability of occurrence of precipitating clouds and of precipitating water content derived from a case study within the International Cirrus Experiment (ICE) held in 1989 over the North Sea. 相似文献
Vegetation inherited from a Pliocene subtropical climate evolved through obliquity oscillations and global cooling leading to modern conditions. An integrated, highly time-resolved record of pollen and stable isotopes (δ18O and δ13C of Globigerina bulloides) was obtained to understand vegetation responses to Early Pleistocene climate changes. Continental and marine responses are compared in the Central Mediterranean region with a particular consideration of environmental changes during anoxic events.Pollen data illustrate vegetation dynamics as follows: [1] development of mesothermic elements (warm and humid conditions); [2] expansion of mid- and high-altitude elements (cooler but still humid conditions); and [3] strengthening of steppe and herb elements (cooler and dry conditions). These successions correlate with precession. δ18O variations recorded by Globigerina bulloides define two cycles (MIS 43-40) related to obliquity. At northern low- to mid-latitudes, the pollen signal records temperature and wetness changes related to precession even during global climate changes induced by obliquity. This may result in unexpected increasing wetness during glacial periods, which has to be considered specific to the Central and Eastern Mediterranean region. Lastly, an analysis of anoxic events reveals that enhanced runoff is indicated by increasing frequency of the riparian trees Liquidambar and Zelkova. 相似文献