Solutions of the integral equation of diffusion and the random walk model for continuous plumes and instantaneous puffs in the atmospheric boundary layer

The integral equation method is related to the random walk modelling that has proved so effective and popular in recent years. The I.E. method, by using simple probability techniques, avoids the inefficient determination of thousands of trajectories in order to build up concentration profiles. In fact it is so simple and efficient it can be run on a conventional programmable calculator. The method is applied to passive material being released from an elevated source within a neutrally stable surface layer over a uniform surface, and also to an instantaneous release when the effect of wind shear is examined. The latter scenario is also studied using random walk techniques and a comparison of the solutions obtained. Agreement is very good, although downwind spread is shown to be quite sensitive to gridlength size in the I.E. method.     

Beryllium-10 contents of core samples from the St. Severin meteorite

Eleven samples taken from along the 35-cm core AIII of the LL-chondrite St. Severin have ¹⁰Be contents ranging from 20 to 28 dpm/kg and averaging 24.5 ± 0.9 dpm/kg. The ¹⁰Be contents increase with depth in the outermost 8 cm while at depths greater than 8 cm the ¹⁰Be contents change little. Calculations based on cross sections for proton-induced reactions that make ¹⁰Be disagree seriously with the measured values. Relatively large cross sections were constructed for neutron-induced reactions below 1 GeV. They give calculated ¹⁰Be production rates that agree with the measured values to within 10%. Cosmogenic ¹⁰Be in stony meteorites is better described as a medium-energy product than as a high-energy one.     

Public participation in policy making: the state-of-the-art in Canada

This paper critically reviews the current status of public participation in Canada. Postulating that public participation implies an open, democratic form of planning and policy making, the paper examines factors which have influenced the attainment of meaningful public input in practice. Public participation in Canada has evolved greatly in the past 15 years but several key issues remain unresolved: provisions for participation remain, in large part, discretionary; procedures for the funding of intervenors require further development; and the emphasis in many jurisdictions remains upon the operational level involvement of the lay public, with a public hearing as the final arbiter of public opinion. More attention to the formal evaluation of participatory exercises is essential to the resolution of these concerns. In particular, more attention should be given to the context within which participation occurs. Moreover, greater consideration should be given to public involvement at the normative and strategic levels of planning. The paper concludes by briefly exploring the implications for practice that the concept of ‘normative participation’ might have in Canada.     

Paleohydrologic regimes in the southwestern Great Basin, 0–3.2 my ago,compared with other long records of “gobal” climate

The oxygen-isotope record from fossil foraminifera in deep-sea sediments is commonly used as a proxy for global ice volume. The linkage between δ¹⁸O and ice volume, however, is probably nonlinear. We have developed a simple numerical model of the isotopic response of the oceans to ice-volume change. The major features it simulates are (1) the changing mean isotopic composition of snow as a function of ice volume (colder snow temperatures forced by climate change and higher-elevation accumulation areas imply more negative mean δ¹⁸O); (2) the nonequilibrium isotopic composition of ice sheets (the past history of an ice sheet is integrated into its mean isotopic composition, which introduces a lag of isotopic “ice volume,” i.e., the measured δ¹⁸O record, scaled to ice-volume units, behind true ice volume); (3) selective preservation of isotopically more negative (colder, higher-latitude) ice (this geographic effect can selectively amplify or dampen the isotopic response to the ice-volume signal). We illustrate the response of our model to simple hypothetical ice-volume transitions of ice growth and ice decay. Sensitivity tests are illustrated for all model parameters. The results suggest that oxygen-isotope records reproduce the general patterns of ice-volume change fairly accurately. The foraminiferal isotope record, however, may misrepresent the true amplitude of the ice-volume signal and lag true ice volume by 1000 to 3000 yr.     

Zoned minerals in garnet peridotite nodules from the Colorado Plateau: implications for mantle metasomatism and kinetics

Some garnet peridotite nodules from The Thumb, a minette neck on the Colorado Plateau in the southwestern United States, contain zoned minerals. Zoning does not exceed 1.5 wt.% for any oxide, but some relative changes are large: in one garnet TiO₂ and Cr₂O₃ ranges are 0.05–0.65 and 3.5–5.0 wt.%, respectively. In two porphyroclastic nodules, garnet rims are depleted in Mg and enriched in Fe, Ti, and Na compared to cores, and one garnet is irregularly zoned in Ti and Cr. Olivine crystals in these rocks are unzoned, and pyroxene zoning is slight, yet matrix olivine and pyroxene contain more Fe and Ti and less Mg and Cr than inclusions of these phases in garnet. In three coarse nodules, garnet rims are Ti-rich compared to cores, and Ca, Fe, Mg, and Cr zoning patterns are complex. Several nodules appear to have partially equilibrated near 1200° C and 35 kb, and under these conditions cation mobility in pyroxene was greater than in garnet. The zoning partly reflects Fe and Ti metasomatism in the mantle. Calculations indicate that Fe-Mg gradients in garnet could have persisted for only a short time in the mantle, perhaps thousands of years or less, so the metasomatism occurred shortly before eruption. The minette host, a likely source of the Fe and Ti, is rich in light rare earth elements: since the nodules are much poorer in these elements, little or no infiltrated minette was trapped in them. Diffusion is a possible mechanism for nodule metasomatism. Some fertile peridotite nodules from kimberlites may have been affected by similar events. Compositional differences between inclusions in garnet and matrix phases are intriguingly similar to some of the differences between most peridotite inclusions in diamonds and common lherzolite phases.     

An electron microprobe study of some Alberta placer gold

Summary The detailed characteristics of 435 placer gold grains from the North Saskatchewan and Athabasca rivers have been investigated using a combination of optical microscopy, energy dispersive electron microprobe analysis and SEM techniques. Most grains show high-fineness rims surrounding lower-fineness cores (giving an extreme range of 4.3%–46.1% Ag within an individual grain). Characteristics of the rims lend support to the hypothesis that they are the products ofin situ leaching of silver followed by transport which largely destroys a spongy texture produced by the leaching. There is no change in the average Ag content of grains of any given size range with distance downstream, which also indicates that all significant leaching takes place before transportation. However, differences are apparent in the average Ag content with grain size.The clustering about certain values of fineness of the nuclei of grains which is seen in samples from both rivers, suggests that Au was largely derived from specific sources in the mountains (Omineca geanticline) to the west rather than redistributed from Shield localities during glaciation.

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Mikrosonden-Untersuchungen an Seifengold aus Alberta, Kanada

Zusammenfassung 435 Körner aus Goldseifen im North Saskatchewan und im Athabasca-Fluß wurden einer detaillierten Untersuchung mit optischer Mikroskopie, energie-dispersiver Mikrosondenanalytik und Rasterelektronenmikroskopie unterzogen.In den meisten Körnern umgibt ein Rand mit hohem Feinheitsgrad einen Kern mit niedrigem Feinheitsgrad (dies führt zu beträchtlichen Schwankungen des Ag-Gehaltes innerhalb des einzelnen Kornes; im Extremfall 4,3%–46,1% Ag). Die Charakteristik der Ränder gibt Anlaß zu der Hypothese, daß das Silber dieser Ränder in situ herausgelöst worden ist, bevor die Körmer transportiert wurden; die während des Transportes auf die Körner einwirkenden Kräfte haben dann die poröse Textur, die durch das herauslösen des Silbers entstanden waren, weitgehend zerstört. Es findet sich keine Änderung des durchschnittlichen Ag-Gehaltes mit zunehmender Transportweite flußabwärts, solange nur Kömer aus einem Größenintervall betrachtet werden. Dies deutet ebenfalls darauf hin, daß der überwiegende Teil des Silbers vor dem Transport herausgelöst wurde. Man findet jedoch Unterschiede im durchschnittlichen Ag-Gehalt zwischen Körnern verschiedener Größe.Das Auftreten von mehreren bestimmten Werten-Clustern der Feinheitsgrade, die in Proben aus beiden Flüssen zu finden ist, legt nahe, daß Au zum größten Teil aus mehreren, spezifischen Ursprungsgesteinen in den westlich gelegenen Gebirgen (Omineca Geanticline) stammt. Eine glazigene Umverteilung von Gold aus verschiedenen Lokalitäten des Kanadischen Schildes erscheint weniger realistisch.

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With 9 Figures     

Recycling of magmatic clasts during explosive eruptions: estimating the true juvenile content of phreatomagmatic volcanic deposits

The juvenile content of phreatomagmatic deposits contains both first-cycle juvenile clasts derived from magma at the instant of eruption, and recycled juvenile clasts, which were fragmented and first ejected by earlier explosions during the eruption, but fell back or collapsed into the vent. Recycled juvenile clasts are similar to accessory and accidental lithics in that they contribute no heat to further magma: water interaction, but previously no effective criteria have been defined to separate them from first-cycle juvenile clasts. We have investigated componentry parameters (vesicularity, clast morphology and extent of mud-coating) which, in specific circumstances, can distinguish between first-cycle juvenile clasts, involved in only one explosion, and such recycled juvenile clasts. Phreatomagmatic fall deposits commonly show gross grainsize and sorting characteristics identical to deposits of purely dry or magmatic eruptions. However the abundance of non-juvenile clasts in pyroclastic deposits is a sensitive indicator of the involvement of external water. If this component is calculated including recycled juvenile clasts with accidental and accessory clasts the contrast is even more striking. Data from a Holocene maar deposit in Taupo Volcanic Zone, New Zealand, suggest that the first-cycle juvenile component of the deposits is less than one-third of that determined by simple juvenile:lithic:crystal componentry.     

Lacustrine ostracodes as hydrochemical indicators in lakes of the north-central United States

The modern ostracode distribution in lakes of the north-central United States shows how ostracode abundances are related to concentrations of major ions such as calcium, sulfate, and bicarbonate. These relationships are quantified for species living in lakes that range from fresh water (200 S cm^-1) to saline water (17 000 S cm^-1). Lakes located in the Minnesota forests have different ostracode assemblages and different water chemistry than lakes located on the prairie of North Dakota and South Dakota. These differences are attributed to differences in precipitation and rock-water interactions. Multivariate analyses of the ostracode and water chemistry data set indicate that different ostracode species are associated with different water types. For example, Limnocythere sappaensis and Heterocypris glaucus are found in bicarbonate-enriched sulfate-dominated waters, whereas Limnocythere staplini is found in bicarbonate-depleted sulfate-dominated waters. Candona ohioensis and Limnocythere itasca are found in fresh water, and Candona rawsoni is eurytopic and found in both bicarbonate-enriched and bicarbonate-depleted sulfate-dominated waters. Ostracodes can be used to identify changes in both ionic composition (solutes) and ionic concentration.This publication is the second of a series of papers presented at the Conference on Sedimentary and Paleolimnological Records of Saline Lakes. This Conference was held August 13–16, 1991 at the University of Saskatchewan, Saskatoon, Canada. Dr Evans is serving as Guest Editor for this series.