A model for the origin of the cell-doubling phase transitions in clinopyroxene and body-centred anorthite     

Andrew G. Christy  Ross J. Angel 《Physics and Chemistry of Minerals》1995,22(2):129-135

Comparisons of the structures of the high-pressure and high-temperature phases of both anorthite and clinopyroxene show that they are quite distinct although they share a common space group and site symmetries for all atoms. The low-pressure, low-temperature phases in both systems are formed by zone-boundary transitions from the high-pressure or high-temperature structures, and have structures that are made up of the alternation of portions of the high-pressure and high-temperature structures. This behaviour is analyzed in terms of the order parameter behaviour of the high-symmetry structures, and it is shown that the stability of the low-symmetry phases arises naturally from inhomogeneity in this order parameter.  相似文献   

Iron,manganese and trace metal concentrations in seaweeds from the central west coast of the Gulf of California     

Miguel Angel Huerta-Diaz  Francisco de León-Chavira  María Lucila Lares  Alfredo Chee-Barragán  Arturo Siqueiros-Valencia 《Applied Geochemistry》2007

Concentrations of Co, Cu, Fe, Mn, Ni, Pb and Zn in four macroalgae species (Ulva lactuca, Chondracanthus squarrulosus, Sargassum sinicola and Gracilariopsis lemaneiformis) were obtained for the first time from the central part of the west coast of the Gulf of California. Generally, no differences in metal concentrations were found among the different seaweed species, although spatial differences were apparent. Iron, Mn and Cu exhibited higher concentrations at the stations located in front of Angel de la Guarda Island, probably because of high vertical mixing processes present in the zone. The results were compared with dissolved metal concentrations reported for the Gulf of California (Cd, Mn and Fe) and the North Pacific Ocean. The resulting linear regression of the results vs. North Pacific Ocean concentrations indicated that the levels of Cu, Ni and Zn measured in this study were within its 95% confidence level. Furthermore, this comparison was capable of detecting dissolved Fe and Mn enrichments in Gulf of California waters relative to the North Pacific Ocean concentrations. Calculations of total masses of metals associated with algal biomass on the west coast of the Gulf of California indicated that the lowest masses were represented by Cu (108 ± 25 kg) and Ni (184 ± 52 kg), whereas Pb (1.1 ± 0.6 ton) and Fe (10.9 ± 8.5 ton) were the elements with the highest associated masses.  相似文献   

Marine Protected Areas as a tool for fishery management and ecosystem conservation: an Introduction     

Hoffmann  Erik; Perez-Ruzafa  Angel 《ICES Journal of Marine Science》2009,66(1):1-5

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CoastLearn: Lessons learnt from a web-based capacity building in Integrated Coastal Zone Management (ICZM)     

Allan P. Krelling  Marcus Polette  Angel Casillas DelValls 《Ocean & Coastal Management》2008,51(12):789-796

The capacity building initiatives for the Integrated Coastal Zone Management (ICZM) intend to create, in a worldwide perspective, a capable critical mass. CoastLearn is one of such outstanding efforts. Through the application of questionnaires to students and to the course coordinator, in addition to its website information, positive features and also aspects that can be improved were recognized. This paper aims at establishing some statements and providing recommendations about aspects to be considered by ICZM capacity building efforts. The outstanding recommendations are the development of feedback policy, the creation of online tutors and discussion forums, always considering the attendants' needs.  相似文献   

Ornithogenic weathering of an ultramafic plutonic rock: St. Peter and St. Paul Archipelago,Central Atlantic     

B. J. Smith  J. J. McAlister  S. E. Sichel  J. Angel  J. A. Baptista-Neto 《Environmental Earth Sciences》2012,66(1):183-197

A phosphatic alteration rind is described comprising a leucophosphite crust above a phosphatised substrate of serpentinized peridotite from an exceptionally isolated location experiencing high rainfall conditions. The formation of the rind is intimately linked to the deposition and subsequent leaching of guano associated with the high concentration of seabirds that nest on the islands and its transformation into a ‘weathering rind’. The favoured pathway into the substrate appears to be along a pre-existing microfracture network, via the alteration of its carbonate infill into soluble apatite. This apatite is only retained within the protected environment of the microfracture network. Surrounding the network, there is evidence of the continued inward migration of the leachate into the surrounding peridotite resulting in its gradual phosphatisation in the form of a ‘halo’ around individual fractures. On the exposed rock surface, the consequence of the reaction between the guano leachate and the underlying substrate is its transformation into a ‘weathering rind’ composed principally of leucophosphite. It appears that the widespread formation of a phosphate crust is constrained by continual surface loss in a high energy, salt-rich maritime environment exposed to extensive overwash, wave attack and ultimately erosion.  相似文献   

High-pressure X-ray study of LiCrSi2O6 clinopyroxene and the general compressibility trends for Li-clinopyroxenes     

Benedetta Periotto  Ross J. Angel  Fabrizio Nestola  Tonci Balić-Žunić  Cinzia Fontana  Daria Pasqual  Matteo Alvaro  Günther J. Redhammer 《Physics and Chemistry of Minerals》2013,40(5):387-399

High-pressure single-crystal X-ray diffraction measurements of synthetic LiCrSi₂O₆ clinopyroxene (with space group P2₁/c) were performed in a diamond-anvil cell up to 7.970 GPa. No phase transition has been observed within the pressure range investigated, but the elastic behavior at lower pressures (up to ~2.5 GPa) is affected by an anomalous softening due to the proximity of the phase transition to the HT-C2/c phase at 330 K and at ambient pressure. A third-order Birch–Murnaghan equation of state fitted to the compression data above 2.5 GPa yields a bulk modulus K _T0 = 93(2) GPa and its first derivative K′ = 8.8(6). The structural data measured up to 7.970 GPa confirm that the space group P2₁/c is maintained throughout the whole pressure range investigated. The atomic parameters, obtained from the integrated diffraction intensities, suggest that the Li coordination polyhedron changes its coordination number from 5 to 6 at 6–7 GPa by means of the approach of the bridging O atom, related to the increased kinking of the B tetrahedral chain. Furthermore, at higher pressures, the structural evolution of LiCrSi₂O₆ provides evidence in the variation of kinking angles and bond lengths of a potential phase transition above 8 GPa to the HP-C2/c space group. A comparison of the Li-clinopyroxenes (M1 = Cr, Al, Sc, Ga, Mg + Fe) previously investigated and our sample shows that their elastic behavior and structural mechanisms of compression are analogous.  相似文献   

Genomics in marine monitoring: New opportunities for assessing marine health status     

Sarah J. Bourlat  Angel Borja  Jack Gilbert  Martin I. Taylor  Neil Davies  Stephen B. Weisberg  John F. Griffith  Teresa Lettieri  Dawn Field  John Benzie  Frank Oliver Glöckner  Naiara Rodríguez-Ezpeleta  Daniel P. Faith  Tim P. Bean  Matthias Obst 《Marine pollution bulletin》2013

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An approach to the intercalibration of benthic ecological status assessment in the North Atlantic ecoregion, according to the European Water Framework Directive   总被引：6，自引：0，他引：6  

Borja A  Josefson AB  Miles A  Muxika I  Olsgard F  Phillips G  Rodríguez JG  Rygg B 《Marine pollution bulletin》2007,55(1-6):42-52

The European Water Framework Directive (WFD) establishes a framework for the protection and improvement of transitional and coastal waters; its final objective is to achieve at least 'good water status' for all waters, by 2015. The WFD requires Member States (MSs) to assess the Ecological Status (ES) of water bodies. This assessment will be based upon the status of the biological, hydromorphological and physico-chemical quality elements, by comparing data obtained from monitoring networks to reference (undisturbed) conditions, and then deriving an Ecological Quality Ratio (EQR). One of the biological quality elements to be considered is the benthic invertebrate component and some structural parameters (composition, diversity and disturbance-sensitive taxa) must be included in the ES assessment. Following these criteria, several approaches to benthic invertebrate assessment have been proposed by MSs. The WFD requires that these approaches are intercalibrated. This contribution describes the comparison of the different methodologies proposed by United Kingdom, Spain, Denmark and Norway. Results show a high consistency between the approaches, both with regard to determining the EQR and boundary settings for the ES.  相似文献   

Temporal estimates of genetic diversity in some Mytilus galloprovincialis populations impacted by the Prestige oil-spill     

Lado-Insua Tania  Pérez MontseDiz Angel P.  Presa Pablo 《Continental Shelf Research》2011,31(5):466-475

The sinking of the tanker Prestige in November 2002 off the coast of Galicia resulted in the release of about 60,000 tons of heavy oil. The oil-spill provoked a serious environmental impact in Spanish and French coasts, which biological consequences are still being assessed. In this study we address the temporal dynamics of genetic diversity in some mussel populations impacted by the oil-spill. Changes in genetic diversity can be measured in natural populations provided that serial samples are available from before (year 2000) and after (years 2003, 2005) the oil-spill. Analyses of seven microsatellites indicate a weak but significant increase of genetic variation after the spill. This phenomenon is interpreted herein in terms of a balance between a enhanced genome mutability on microsatellite variation and a low genetic drift due to toxicants and asphyxia although other stochastic phenomena cannot be ruled out. Per locus annotation showed that in spite of the allelic changes observed in the period 2000-2005, the final size of most allelic series remained quite alike to those of year 2000. Present genetic data suggest that the genotoxic impact of the Prestige spill did not compromise the genetic diversity of studied mussel populations, at least regarding the genetic markers analysed.  相似文献   

Temporal and spatial variability in the Guadalquivir estuary: a challenge for real-time telemetry   总被引：1，自引：1，他引：0  

Gabriel Navarro  Francisco Javier Gutiérrez  Manuel Díez-Minguito  Miguel Angel Losada  Javier Ruiz 《Ocean Dynamics》2011,61(6):753-765

Meteorological, hydrological, and hydrodynamic data for 3 years (2008–2010) have been used to document and explain the temporal and spatial variability of the physical–biogeochemical interactions in the Guadalquivir River Estuary. A real-time, remote monitoring network has been deployed along the course of the river between its mouth and Seville to study a broad range of temporal scales (semidiurnal, diurnal, fortnightly, and seasonal). This network consists of eight hydrological monitoring stations capable of measuring temperature, conductivity, dissolved oxygen, turbidity, and chlorophyll fluorescence at four depths. In addition, six stations have been deployed to study hydrodynamics, obtaining 20-cell water column current profiles, and there is a meteorological station at the river mouth providing data for understanding atmospheric interactions. Completing this data-gathering network, there are several moorings (tide gauges, current/wave sensors, and a thermistor chain) deployed in the estuary and river mouth. Various sources of physical forcing, such as wind, tide-associated currents, and river discharge, are responsible for the particular temporal and spatial patterns of turbidity and salinity found in the estuary. These variables force the distribution of biogeochemical variables, such as dissolved oxygen and chlorophyll fluorescence. In particular, episodes of elevated turbidity (when suspended particle matter concentration >3,000 mg/l) have been detected by the network, together with episodes of declining values of salinity and dissolved oxygen. All these patterns are related to river discharge and tidal dynamics (spring/neap and high/low tide).  相似文献