Oxidation of titanomagnetites in mafic and felsic intrusive rocks

We report opaque mineralogical observations and magnetic properties of primary titanomagnetites in Tertiary submarine gabbros from DSDP, Legs 30 and 37 and in a late Archean, continental granitic pluton, the Shelley Lake granite. The titanomagnetites and silicates in all the submarine gabbros have been deuterically oxidized. There is no indication of subsequent low-temperature oxidation, although serpentization of olivines is pervasive in the deeper Leg 37 units. The Leg 30 samples, from a single thick sill, contain abundant coarse (≈100 μm) titanomagnetites with fully developed ilmenite exsolution lamellae. Curie temperatures are 515–550°C; there are no low Curie temperatures that would indicate surviving unoxidized titanomagnetite. The unserpentinized Leg 37 gabbros contain scarce opaques with pure magnetite Curie points that are barely resolvable microscopically; most occur as inclusions in pyroxene. In the Shelley Lake granite, on the other hand, many samples exhibit bimodal blocking-temperature spectra, with blocking temperature peaks at 250–300°C and 550–575°C. The low-blocking-temperature phase is unidentified. No pyrrhotite was seen in thin section. Optically homogeneous grains coexist with fully exsolved neighbours, but the electron microprobe indicates no titanium. The lamellae appear to be haematite, not ilmenite, and the primary composition of the opaques is pure magnetite. The oxidation state of the opaques is very inhomogeneous, even on a fine scale.     

PCB uptake and accumulation by oysters (Crassostrea virginica) exposed via a contaminated algal diet

Reproductively active oysters were fed daily with 0.2 g algal paste containing 0, 0.1, and 1.0 μg polychlorinated biphenyls (PCBs) (1:1:1 mixture of Aroclor 1242, 1254 and 1260) for either 15 or 30 days, and accumulation of PCBs in different organ tissues and eggs assessed. The effects of PCB exposure on lipid content, lipid class and fatty acid composition were also evaluated. PCBs were accumulated by the oysters and transferred to the eggs. PCB accumulation in oysters was dose, time and tissue dependent. Mean PCB contents were 3150, 1970, and 250 ng/g dry wt., respectively, in the visceral mass, gills+mantle and muscle of oysters fed algal paste containing 1.0 μg PCBs for 30 days. The PCBs in the eggs from the same oysters reached 671 ng PCBs/g dry wt. Feeding oysters with PCB-sorbed algal paste for 30 days significantly increased phospholipid and free fatty acid contents in gills+mantle tissues compared to the same tissues in the undosed control.     

A Klovan-type box corer for use with SCUBA

A stainless steel, Klovan-type box corer for use by SCUBA divers in shallow water has been developed. Details for construction of the 0.45 × 0.30 × 0.20-m wedge-shaped corer are provided together with operational details. Excellent undisturbed samples have been collected from gravelly sands, sands, and muds at water depths ranging from 15 m to intertidal. The wet sand cores typically are treated in the field using an epoxy to obtain high-relief sediment peels.     

Towards realistic simulations of lava dome growth using the level set method

The level set method has been implemented in a computational volcanology context. New techniques are presented to solve the advection equation and the reinitialisation equation. These techniques are based upon an algorithm developed in the finite difference context, but are modified to take advantage of the robustness of the finite element method. The resulting algorithm is tested on a well documented Rayleigh–Taylor instability benchmark [19], and on an axisymmetric problem where the analytical solution is known. Finally, the algorithm is applied to a basic study of lava dome growth.     

Mapping of prospectivity and estimation of number of undiscovered prospects for lode gold,southwestern Ashanti Belt,Ghana

In the southwestern part of the Ashanti Belt, the results of fractal and Fry analyses of the spatial pattern of 51 known mines/prospects of (mostly lode) gold deposits and the results of analysis of their spatial associations with faults and fault intersections suggest different predominant structural controls on lode gold mineralisation at local and district scales. Intersections of NNE- and NW-trending faults were likely predominantly involved in local-scale structural controls on lode gold mineralisation, whilst NNE-trending faults were likely predominantly involved in district-scale structural controls on lode gold mineralisation. The results of the spatial analyses facilitate the conceptualisation and selection of spatial evidence layers for lode gold prospectivity mapping in the study area. The applications of the derived map of lode gold prospectivity and a map of radial density of spatially coherent lode gold mines/prospects results in a one-level prediction of 37 undiscovered lode gold prospects. The applications of quantified radial density fractal dimensions of the spatial pattern of spatially coherent lode gold mines/prospects result in an estimate of 40 undiscovered lode gold prospects. The study concludes finally that analysis of the spatial pattern of discovered mineral deposits is the key to a strong link between mineral prospectivity mapping and assessment of undiscovered mineral deposits.     

Influence of groundwater and topography on stream drying in semi-arid headwater streams

Non-perennial streams comprise over half of the global stream network and impact downstream water quality. Although aridity is a primary driver of stream drying globally, surface flow permanence varies spatially and temporally within many headwater streams, suggesting that these complex drying patterns may be driven by topographic and subsurface factors. Indeed, these factors affect shallow groundwater flows in perennial systems, but there has been only limited characterisation of shallow groundwater residence times and groundwater contributions to intermittent streams. Here, we asked how groundwater residence times, shallow groundwater contributions to streamflow, and topography interact to control stream drying in headwater streams. We evaluated this overarching question in eight semi-arid headwater catchments based on surface flow observations during the low-flow period, coupled with tracer-based groundwater residence times. For one headwater catchment, we analysed stream drying during the seasonal flow recession and rewetting period using a sensor network that was interspersed between groundwater monitoring locations, and linked drying patterns to groundwater inputs and topography. We found a poor relationship between groundwater residence times and flowing network extent (R² < 0.24). Although groundwater residence times indicated that old groundwater was present in all headwater streams, surface drying also occurred in each of them, suggesting old, deep flowpaths are insufficient to sustain surface flows. Indeed, the timing of stream drying at any given point typically coincided with a decrease in the contribution from near-surface sources and an increased relative contribution of groundwater to streamflow at that location, whereas the spatial pattern of drying within the stream network typically correlated with locations where groundwater inputs were most seasonally variable. Topographic metrics only explained ~30% of the variability in seasonal flow permanence, and surprisingly, we found no correlation with seasonal drying and down-valley subsurface storage area. Because we found complex spatial patterns, future studies should pair dense spatial observations of subsurface properties, such as hydraulic conductivity and transmissivity, to observations of seasonal flow permanence.     

Does PCB accumulation affect the lipid metabolism of the reproductively active oyster Crassostrea virginica?

Polychlorinated biphenyls (PCBs) pose a severe ecological risk. They are hydrophobic and are efficiently sequestered in lipid-rich tissues. Lipids function as energy reserves and as membrane components, and are essential for growth and reproductive processes in bivalves. Accumulation of PCBs may affect the mobilization of lipid reserves and membrane lipid composition; thus they may also impair reproductive and developmental processes. To test whether there are any changes in lipid metabolism, the lipid class and fatty acid composition in structural and reserve lipids of visceral mass, gills and mantle, and eggs of reproductively active oysters were examined. Oysters were fed daily with 0.2 g algal paste containing 0, 0.1, or 1.0 μg PCBs for 15 and 30 days. PCBs in the oyster tissues and eggs were also quantified. After 30 days of exposure PCBs were highly accumulated, up to 2635 ng/g in the visceral mass, 1880 ng/g in gill+mantle, and 671 ng/g (dry wt. bases). No significant changes were noted in either lipid class composition or fatty acid composition of structural or reserve lipids from PCB-exposed oyster tissues and eggs.     

A statistical model for spatial patterns of Buruli ulcer in the Amansie West district,Ghana

Buruli ulcer (BU), a skin ulceration caused by Mycobacterium ulcerans (MU), is the second most widespread mycobacterium infection in Ghana. Its infection pathway is possibly related to the potable and agricultural water supply. This study aims to identify environmental factors that influence infection in a part of Ghana. It examines the significance of contaminated surface drainage channels and groundwater using conditional autoregressive (CAR) statistical modelling. This type of modelling implies that the spatial pattern of BU incidence in one community depends on the influence of the environment in neighbouring communities. Covariates were included to assess the spatial relationship between environmental risk factors and BU incidence in the study area. The study reveals an association between (a) the mean As content of soil and spatial distribution of BU and (b) the distance to sites of gold mining and spatial distribution of BU. We conclude that both arsenic in the natural environment and gold mining influence BU infection.