Calculation of the visible-UV absorption spectra of hydrogen sulfide,bisulfide, polysulfides,and As and Sb sulfides,in aqueous solution

Recently we showed that visible-UV spectra in aqueous solution can be accurately calculated for arsenic (III) bisulfides, such as As(SH)₃, As(SH)₂S^- and their oligomers. The calculated lowest energy transitions for these species were diagnostic of their protonation and oligomerization state. We here extend these studies to As and Sb oxidation state III and v sulfides and to polysulfides S _n ^2- , n = 2–6, the bisulfide anion, SH^-, hydrogen sulfide, H₂S and the sulfanes, S _n H₂, n = 2–5. Many of these calculations are more difficult than those performed for the As(iii) bisulfides, since the As and Sb(v) species are more acidic and therefore exist as highly charged anions in neutral and basic solutions. In general, small and/or highly charged anions are more difficult to describe computationally than larger, monovalent anions or neutral molecules. We have used both Hartree-Fock based (CI Singles and Time-Dependent HF) and density functional based (TD B3LYP) techniques for the calculations of absorption energy and intensity and have used both explicit water molecules and a polarizable continuum to describe the effects of hydration. We correctly reproduce the general trends observed experimentally, with absorption energies increasing from polysulfides to As, Sb sulfides to SH^- to H₂S. As and Sb(v) species, both monomers and dimers, also absorb at characteristically higher energies than do the analogous As and Sb(III)species. There is also a small reduction in absorption energy from monomeric to dimeric species, for both As and Sb III and v. The polysufides, on the other hand, show no simple systematic changes in UV spectra with chain length, n, or with protonation state. Our results indicate that for the As and Sb sulfides, the oxidation state, degree of protonation and degree of oligomerization can all be determined from the visible-UV absorption spectrum. We have also calculated the aqueous phase energetics for the reaction of S₈ with SH^- to produce the polysulfides, S _n H^-, n = 2–6. Our results are in excellent agreement with available experimental data, and support the existence of a S₆ species.     

Tourmaline-rich Rocks Associated with the Submarine Hydrothermal Rosebery Zn-Pb-Cu-Ag-Au Deposit and Granites in Western Tasmania,Australia

Summary The stratiform massive Zn-Pb sulphide Rosebery deposit of western Tasmania is hosted by metamorphosed deformed acid volcanics and sediments of the Cambrian Mt. Read Volcanics. Tourmalinite, a boron-rich siliceous sulphide facies iron formation, overlies and occurs as an exhalite facies equivalent of the massive sulphides. The orebody is partially replaced by post deformation tourmaline-bearing pyrrhotite-pyrite rocks associated with an alteration facies comprising magnetite-pyrite-tourmaline-phlogopite and the host metavolcanics are transgressed by quartz-tourmaline veins and tourmaline-filled joints. Tourmalinite and tourmaline in alteration zones are associated with other base metal deposits in the area. Tourmaline also occurs as fault-fill and in granitic rocks and associated Sn-W mineralization nearby. Tourmaline associated with the Cambrian massive sulphides is schorl > dravite in contrast to schorl in the Devonian granites.It is suggested that boron was an integral part of the ore fluids at Rosebery which precipitated tourmaline in exhalites immediately after and distal to the mineralization event. Tourmaline from the tourmalinite exhalites appears to have derived from submarine hydrothermal precipitation. Joint- and fracture-fill tourmaline could have derived from remobilization from tourmalinites during Devonian tectonism, however, it is more probable that these discordant tourmaline-bearing veins, tourmaline in the post-cleavage Rosebery Fault and tourmaline-bearing pyrrhotite-pyrite replacement of the Rosebery orebody derived from Devonian granite at a shallow depth which has been intersected in drilling. Tourmaline replacement associated with discordant structures is no different in composition from that from tourmalinites associated with the orebody and hence has undergone re-equilibration with the host rocks during multiple events of deformation and metamorphism associated with Devonian tectonism. In contrast, the composition of tourmaline from the Devonian granites is markedly different from that of the Rosebery area.

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Zusammenfassung Die stratiforme, massive Zn-Pb-Sulfidlagerstätte Rosebery in West-Tasmanien sitzt in metamorphen und deformierten sauren Vulkaniten und Sedimenten der Kambrischen Mt. Read Vulkanit-Serie auf. Turmalingesteine treten im Hangenden dieser Serie auf. Sie stellen eine Bor-reiche Eisenformation in silizuiumreicher Sulfidfazies dar und sind als das exhalative Äquivalent der massiven Sulfide anzusehen. Der Erzkörper wird teilweise von postdeformativen Turmalin-fährenden Pyrrhotin-Pyrit-Gesteinen verdrängt, die mit einer Alterationsfazies, bestehend aus Magnetit-Pyrit-Turmalin-Phlogopit, assoziiert sind. Die erzfährenden Metavulkanite werden von Quarz-Turmalin-Gängen und Turmalinadern durchschlagen. Turmalingesteine wie auch Turmalin in Alterationszonen kommen auch mit anderen Buntmetall-Vererzungen des Arbeitsgebietes vor. Turmalin tritt weiters in Störungszonen, in Graniten und in an diese gebundenen Sn-W Mineralisationen auf.Der mit den kambrischen, massiven Vulkaniten assozierte Turmalin ist ein Schörl > Dravit, während in den devonischen Graniten Schörl dominiert. Es ist anzunehmen, daß Bor einen integralen Anteil der Erzlösungen in der Rosebery-Lagerstätte darstellt. Aus diesen ist Turmalin exhalativ, kurz nach der Sulfidmineralisation distal gebildet worden. Es zeigt sich, daß der Turmalin aus submarin hydrothermalen Absätzen herzuleiten ist. Gangturmaline könnten durch Remobilisation der Turmalingesteine während devonischer Deformation entstanden sein. Es scheint jedoch wahrscheinlicher, daß diese diskordanten Gänge, wie auch der Turmalin in der Rosebery-Störung und die Turmalin-führenden Pyrrhotin-Pyrit-Verdrängungen aus dem devonischen Granit stammen. Verdrängter Turmalin, assoziiert mit diskordanten Strukturen, zeigt in seiner Zusammensetzung keinerlei Unterschiede zum Turmalin in Turmalingesteinen aus dem Erzkörper. Im Zuge mehrphasiger, devonischer Deformation und Metamorphose ist es somit zu Reäquilibrierung des Turmalins mit dem Trägergestein gekommen. Die Zusammensetzung des Turmalins in den devonischen Graniten unterscheidet sich deutlich von der des Rosebery-Gebietes.

     

Biostratigraphy,sedimentology and palaeobathymetry of Waulsortian buildups and peri-Waulsortian rocks during the late Tournaisian regression,Dinant area,Belgium

Recent revision of the biostratigraphy allows the recognition of a stratigraphic entity (here termed Freyrian) between the base of the Moliniacian stage and the base of the Viséan and simplifies sedimentological interpretation of late Tournaisian events around Dinant, in Belgium. Petrographic analysis of Freyrian rocks in Waulsortian buildups and peri-Waulsortian facies reveals a pattern of carbonate sedimentation related to the submarine topography developed by the buildups, and to sea-level changes. Graded beds and thin layers of grainstone in the predominantly fine-grained peri-Waulsortian sediments represent influxes derived mainly from nearby buildups during a period of shallowing. Using the sequence of foraminiferan assemblages which colonized the buildups as a stratigraphic scale, the earlier influxes are shown to have occurred only close to the presumed source, whereas later influxes extended further and marked the culmination of the shallowing phase. Deposition during the latter part of the Freyrian appears to have occurred in rather deeper, less disturbed water. The Moliniacian and Viséan boundary stratotypes, both in peri-Waulsortian facies, are critically assessed because almost all the stratigraphically useful foraminiferans occur in the rare grainstones resulting from sediment influxes. Tetrataxis was one of the few foraminiferans to colonize proximal peri-Waulsortian areas and appears to have ranged to a water depth of about 200 m. Downslope diachronism of colonization is interpreted as evidence of a sea-level fall of about 140 m and is used to draw a sea-level curve for this late Tournaisian regression. Using the same depth scale, microbial coating extended to about 300 m and its development appears to have been related to low sedimentation rates rather than photic conditions. © 1997 John Wiley & Sons, Ltd.     

Sediment sources and transport pathways in a rural catchment,Herefordshire, UK

The relative significance of primary and secondary suspended sediment sources has been identified in a small (15 km²) agricultural catchment through the application of a linear unmixing model using mineral magnetic, geochemical and radionuclide signatures of fine sediments. Roads appear to be important as a secondary source of suspended sediment and in the conveyance of topsoils to the river channel. Roads also alter the source signatures of sediment in transport, especially that derived from agricultural topsoils. Modelling suggests that c. 30% of the suspended sediment collected from suspended sediment traps in the River Leadon were derived from, or transported via, roads. Relative contributions from primary sources of c. 43% and c. 27% were estimated from a combined (subsoil and channel bank) subsurface source, and a combined (arable and grassland) topsoil source, respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

Representing and reducing error in natural‐resource classification using model combination

Artificial Intelligence (AI) models such as Artificial Neural Networks (ANNs), Decision Trees and Dempster–Shafer's Theory of Evidence have long claimed to be more error‐tolerant than conventional statistical models, but the way error is propagated through these models is unclear. Two sources of error have been identified in this study: sampling error and attribute error. The results show that these errors propagate differently through the three AI models. The Decision Tree was the most affected by error, the Artificial Neural Network was less affected by error, and the Theory of Evidence model was not affected by the errors at all. The study indicates that AI models have very different modes of handling errors. In this case, the machine‐learning models, including ANNs and Decision Trees, are more sensitive to input errors. Dempster–Shafer's Theory of Evidence has demonstrated better potential in dealing with input errors when multisource data sets are involved. The study suggests a strategy of combining AI models to improve classification accuracy. Several combination approaches have been applied, based on a ‘majority voting system’, a simple average, Dempster–Shafer's Theory of Evidence, and fuzzy‐set theory. These approaches all increased classification accuracy to some extent. Two of them also demonstrated good performance in handling input errors. Second‐stage combination approaches which use statistical evaluation of the initial combinations are able to further improve classification results. One of these second‐stage combination approaches increased the overall classification accuracy on forest types to 54% from the original 46.5% of the Decision Tree model, and its visual appearance is also much closer to the ground data. By combining models, it becomes possible to calculate quantitative confidence measurements for the classification results, which can then serve as a better error representation. Final classification products include not only the predicted hard classes for individual cells, but also estimates of the probability and the confidence measurements of the prediction.     

An example of fingerprint detection of greenhouse climate change

As an example of the technique of fingerprint detection of greenhouse climate change, a multivariate signal or fingerprint of the enhanced greenhouse effect is defined using the zonal mean atmospheric temperature change as a function of height and latitude between equilibrium climate model simulations with control and doubled CO₂ concentrations. This signal is compared with observed atmospheric temperature variations over the period 1963 to 1988 from radiosonde-based global analyses. There is a significant increase of this greenhouse signal in the observational data over this period.These results must be treated with caution. Upper air data are available for a short period only, possibly too short to be able to resolve any real greenhouse climate change. The greenhouse fingerprint used in this study may not be unique to the enhanced greenhouse effect and may be due to other forcing mechanisms. However, it is shown that the patterns of atmospheric temperature change associated with uniform global increases of sea surface temperature, with El NinoSouthern Oscillation events and with decreases of stratospheric ozone concentrations individually are different from the greenhouse fingerprint used here.     

华北北部中生代岩墙群

岩墙群是深源岩浆浅侵位的产物，它可提供有关壳-幔演化的重要信息。通过华北北部大同早中生代碳酸岩-煌斑岩岩墙群、赤峰早中生代闪长玢岩岩墙群、林西中生代辉绿岩岩墙群、京北晚中生代双峰式岩墙群的对比研究，揭示了华北中生代存在的两次底侵作用及其相关的伸展作用。华北早、晚中生代岩墙群与晋北地区元古代岩墙群的初步对比，从一个侧面反映了华北壳幔的演变。     

Spatial characterisation of the Benguela ecosystem for ecosystem-based management

The three countries of the Benguela Current Large Marine Ecosystem (BCLME), namely Angola, Namibia and South Africa, have committed to implementing ecosystem-based management (EBM) including an ecosystem approach to fisheries (EAF) in the region, to put in practice the principles of sustainable development in ocean-related matters. There is also recognition of the need for marine spatial planning (MSP) as a process for informing EBM with regard to the allocation and siting of ocean uses so that ecosystem health is ensured and trade-offs between ecosystem services are appropriately dealt with. Marine spatial planning is both an integrated and an area-based process, and this paper produces a spatial characterisation of the BCLME for achieving a common basis for MSP in the region, focusing on the oceanography, biology and fisheries. Recognising spatial variation in physical driving forces, primary and secondary production, trophic structures and species richness, four different subsystems are characterised: (1) north of the Angola–Benguela Front, (2) from the Angola–Benguela Front to Lüderitz, (3) from Lüderitz to Cape Agulhas, and (4) from Cape Agulhas to Port Alfred on the south-east coast of South Africa. Research and monitoring requirements of relevance for MSP and EBM in the region are identified, focusing on understanding variability and change, including with regard to the boundary areas identified for the system. To this end, 14 cross-shelf monitoring transects are proposed (including seven that are already being monitored) to estimate fluxes of biota, energy and materials within and between the subsystems. The usefulness of models for understanding ecosystem variability and changes is recognised and the need for fine-scale resolution of both sampling and modelling for adequate MSP as input to EBM for the often-conflicting interests of conserving biodiversity, and managing fisheries, recreation, offshore oil and gas exploration and exploitation, offshore mining and shipping routes, is emphasised.