Degrees of melting in mantle diapirs and the origin of ultrabasic liquids

The temperature and degree of melting in an upwelling diapir in the mantle may be considerably less than that anticipated from an adiabatic cooling curve. Several geological and thermodynamic parameters may be incorporated to produce a more realistic melting model in diapirs. The latent heat of fusion of mantle material is the greatest buffer on degrees of melting. Models are presented which suggest that an uprising diapir intersecting the anhydrous solidus of mantle material at 50 kbars may be only 29% melted on reaching the surface. A diapir initiated at 100 kbars may be 69% melted. These are maximum values. These calculations imply that the generation of komatiitic liquids by diapiric uprise alone demands that the diapir originate at depths in excess of 300 km. Melting of mantle with an irregular geotherm is preferred for the origin of these liquids.     

Comparison of physical and chemical properties of maceral groups separated by density dradient centrifugation

Eight coals have been selected for study of the physical and chemical properties of the maceral group . The density-gradient centrifugation technique was employed to affect maceral group separation. The maximum reflectance method of Ting and Lo was used for estimating the reflectance of very small coal particles. The reflectograms were used to characterize the separated maceral fractions. The density, elemental composition, reflectance, NMR parameters of aromaticity, protonated aromatic carbon content and ƒ_stuggereda^stuggeredH of the maceral groups were compared. Variations in the aromatic structure of the maceral groups are discussed as well as the observation that ƒ_stuggereda and ƒ_stuggereda^stuggeredH change with particle density.     

Sensitivity of direct global warming potentials to key uncertainties

The concept of global warming potential was developed as a relative measure of the potential effects on climate of a greenhouse gas as compared to CO₂. In this paper a series of sensitivity studies examines several uncertainties in determination of Global Warming Potentials (GWPs). For example, the original evaluation of GWPs for the Intergovernmental Panel on Climate Change (IPCC, 1990) did not attempt to account for the possible sinks of carbon dioxide (CO₂) that could balance the carbon cycle and produce atmospheric concentrations of CO₂ that match observations. In this study, a balanced carbon cycle model is applied in calculation of the radiative forcing from CO₂. Use of the balanced model produces up to 21% enhancement of the GWPs for most trace gases compared with the IPCC (1990) values for time horizons up to 100 years, but a decreasing enhancement with longer time horizons. Uncertainty limits of the fertilization feedback parameter contribute a 20% range in GWP values. Another systematic uncertainty in GWPs is the assumption of an equilibrium atmosphere (one in which the concentration of trace gases remains constant) versus a disequilibrium atmosphere (one in which the concentration of trace gases varies with time). The latter gives GWPs that are 19 to 32% greater than the former for a 100 year time horizons, depending upon the carbon dioxide emission scenario chosen. Five scenarios are employed: constant-concentration, constant-emission past 1990 and the three IPCC (1992) emission scenarios. For the analysis of uncertainties in atmospheric lifetime (τ) the GWP changes in direct proportion toτ for short-lived gases, but to a lesser extent for gases withτ greater than the time horizontal for the GWP calculation.     

Failure of rural schemes in South Africa to provide potable water

The impact of water-borne disease in South Africa is significant. An estimated 43,000 deaths per annum, including 20% of deaths in the 1-5 years age group, are directly attributable to diarrhoeal diseases. Drinking water quality provision in many rural areas is substandard. This paper describes the results of sampling drinking water supplies in rural communities in the Western and Eastern Cape, South Africa. The majority of samples collected failed microbial drinking water quality standards. Overall, schemes dependent on groundwater provided a worse quality water at point of use than surface-water-dependant schemes. This is thought to be the result of pump breakdown, deterioration of the storage and reticulation system, and insufficient monitoring and management of the schemes. Importantly, it is shown that the implementation of well-considered, community accepted drinking-water quality management procedures can effectively change an unacceptable water quality to one that satisfies drinking-water specifications.     

Civ plasma flow near active region filaments

Selected Civ V ₀ lines (lines separating adjacent regions of strong blue shift and strong red shift) located near the solar limb and oriented parallel to the radius vector from disk center are shown to be closely aligned with H dark filaments in active regions. The filaments, in turn, are known to lie in the vicinity of magnetic neutral lines. The radial orientation of the V ₀ lines minimizes uncertainties in image registration and their location near the limb ensures that the observed fluid motion has major components paralleling V ₀. It follows that the filaments are located at sites of velocity shear, and, by inference, of magnetic shear. For a case in which a given V ₀ line is observed near both east and west limbs, the gradient of Doppler velocity across the V ₀ line reverses sign from one limb to the other as is expected for horizontal steady flow. Thus, the velocity vectors remain fixed with respect to the filament.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Toxicity of sediments from around a North Sea oil platform: are metals or hydrocarbons responsible for ecological impacts?

Discharges of contaminated drill cuttings have caused appreciable ecological change of the benthos adjacent to many oil and gas platforms in the North Sea. Many platforms have large piles of cuttings lying beneath them and these probably present the greatest potential hazard to the environment during platform decommissioning and removal. There is, however, a lack of consensus on which aspects of drill cuttings are responsible for the adverse ecological effects. This hinders risk assessment of management options. Here we report data on the toxicity of sediments from around the North West Hutton platform to the amphipod Corophium volutator, the polychaete Arenicola marina and the Microtox" acute test system. Sediment was acutely toxic to Corophium out as far as 600 m from the platform. Sediment from 100 m from the platform remained acutely toxic to Corophium when 3% contaminated sediment was mixed with clean sediment. A 10% dilution of this sediment also inhibited Arenicola feeding almost completely. Sediment elutriates did not inhibit Microtox light output, but organics extracted by dichloromethane were very toxic. Fifteen minute EC50 values were as low as 0.25 mg ml(-1) and were strongly correlated with hydrocarbon concentrations. Metal concentrations in whole sediments were correlated with their toxicity to Corophium but the relationship was much weaker when data on dilutions were included. Except at sites immediately adjacent to the platform, metal concentrations were well below ERL values from the literature, so were too low to explain sediment toxicity. Toxicity of sediments to Corophium was closely correlated with their hydrocarbon content, even when tests on dilutions were included in the analysis. We conclude that hydrocarbons are the most significant cause of toxicity in these sediments contaminated with oil based drill cuttings and that polar organics, sulphide. ammonia and other water soluble substances are of much lower significance. Applying OSPAR guidelines to our data on the toxicity of cuttings pile material to Corophium data would give a maximum allowable concentration of 0.03% in clean sediments. The Microtox data indicate that sediments from deeper in the pile would require an even greater dilution than this.     

The Effects of Industrial Pollution on the Development and Succession of Marine Fouling Communities II. Multivariate Analysis of Succession

Abstract. The successional stages of fouling communities from 3 sites located along a pollution gradient within Port Kembla Harbour (Australia) were compared quantitatively with those from Wollongong Harbour, a relatively unpolluted area located close by.
A multivariate classification of the data showed that the development of fouling communities in Port Kembla Harbour was very different from that in Wollongong Harbour, involving different types of species. In addition, the classification identified a secondary pattern in the data which showed that the species composition of the Port Kembla Harbour communities changed with time, independently of any seasonal effects.
A principal coordinate analysis of the data was able to further expand on these findings. It demonstrated that the succession of fouling communities in Port Kembla Harbour involved a process whereby one group of species (ascidians) was gradually replaced through time by a second group of different species (bivalves). In contrast, the communities in Wollongong Harbour were dominated by inhibitory interactions. The succession in this area mainly involved species (particularly bryozoans) which colonised during the initial stages of development and remained in the communities as they continued to develop.
Changes in the succession of fouling communities from Port Kembla Harbour were thought to be due to the loss of pollution sensitive species, such as bryozoans, from the environment. This was not attributed to the acute, toxic effects of the pollutants, but rather to more subtle and indirect effects.