Evidence for rapid avian-mediated foraminiferal colonization of Lake Winnipegosis, Manitoba, during the Holocene Hypsithermal

A Holocene ecological succession was documented using palynological, foraminiferal, and molluscan faunas sampled from an excavated trench on the margin of Bell River Bay, Lake Winnipegosis, Manitoba. The palynological data record the known gradually isostatically-induced shift from aquatic to terrestrial conditions at the site, and clearly delineates the Holocene Hypsithermal maximal warm interval (commencing here about 5500 years BP). Concurrent with this warming the site became occupied by the extinct salt tolerant gastropod Marstonia gelida and the marine foraminifer Cribroelphidium gunteri by at least 5430 years BP. Water fowl-assisted colonization of non-marine habitats by foraminifera has previously been suggested as a dispersal mechanism for other non-marine foraminiferal occurrences. However, as this relatively warm-water foraminifer (presently found as far north as Cape Cod, MA on the Atlantic USA coast, and Vancouver, BC on the Canadian Pacific coast but also found in Canadian Maritime provinces during the Hypsithermal) did not inhabit the area either prior to or following the Hypsithermal warm interval, this occurrence indicates the efficiency with which foraminifera can utilize non-selective avian transport to colonize new non-marine and marine habitats. It may be that only a few years were required for colonization of the site to occur (2000–3000 km distant from native populations); this suggests that avian transport is a much more important foraminiferal dispersal mechanism than previously realized. The appearance of foraminifera at this site may also constrain models designed to determine the time required for hydraulically injected glacial freshwater to be flushed from normally brine producing aquifers in the region.     

Estimability of astronomical longitude and latitude only from theodolite observations within three-dimensional networks of terrestrial type

Summary From a two-dimensional network adjustment it is well understood that the one orientation unknown of a theodolite frame is estimable, once the orientation datum parameter, e.g., one azimuth, is fixed. In three-dimensional networks the problem of estimability of three orientation unknowns inherent in a theodolite frame is more complex. Here we prove that not only the classical horizontal orientation unknown is estimable (up to the datum degrees of freedom), but also astronomical longitude and astronomical latitude which can be considered as two additional orientation unknowns of the theodolite frame moving with respect to an earth-fixed equatorial frame of reference. Thus the theodolite instrument can be considered—at least theoretically—a gradiometer measuring the variation of the directional parameters of the gravity vector from one point to another. Or up to the datum degrees of freedom astronomical longitude and astronomical latitude can be determined from only theodolite observations between exclusively terrestrial points. M?nicke (1982), has shown that despite the refraction problem the method works sufficiently well in practice.     

Aquatic ecotoxicology

Information about the toxicity of heavy metals and organics to aquatic organisms can be obtained from bioassays. These are classified according to the type of response obtained: quantal or continuous, and according to whether individual organisms originate from a single clone or have a tolerance distribution. Basic features of the probit, logit, and Weibull dose-response models for one toxic substance are considered. It is shown that a version of the logit model is complementary to the Monod equation for the growth rate of microorganisms under substrate limitation. Multiple toxicity models can be of the non-interactive or competitive type. The standard water quality criterion for concentration addition is based on the assumption that the toxicants act on similar biological systems, and that the action tolerances for individuals are fully correlated. Pertinent examples of the application of the models for one or several toxic substances are discussed.     

Dauphiné twinning and texture memory in polycrystalline quartz. Part 1: Experimental deformation of novaculite

Mechanical Dauphiné twinning in quartz has been of long-standing interest, both in single crystals and polycrystalline aggregates. This study investigates texture development in fine-grained quartz rock novaculite with no initial texture using compression experiments conducted in the Paterson gas apparatus to explore the influence of stress and temperature. Texture patterns are measured with time-of-flight neutron diffraction and hard synchrotron X-rays, analyzing diffraction data with the Rietveld method. Similar texture patterns are observed as described previously but the new results establish a profound influence of temperature and document that twinning initiates at stresses less than 50 MPa. Possibilities of using Dauphiné twinning as a paleopiezometer in quartz-bearing rocks are discussed.     

Diffusive fractionation of U-series radionuclides during mantle melting and shallow-level melt-cumulate interaction

U-series radioactive disequilibria in basaltic lavas have been used to infer many important aspects of melt generation and extraction processes in Earth’s mantle and crust, including the porosity of the melting zone, the solid mantle upwelling rate, and the melt transport rate. Most of these inferences have been based on simplified theoretical treatments of the fractionation process, which assume equilibrium partitioning of U-series nuclides among minerals and melt. We have developed a numerical model in which solid-state diffusion controls the exchange of U-series nuclides among multiple minerals and melt. First the initial steady-state distribution of nuclides among the phases, which represents a balance between diffusive fluxes and radioactive production and decay, is calculated. Next, partial melting begins, or a foreign melt is introduced into the system, and nuclides are again redistributed among the phases via diffusion. U-series nuclides can be separated during this stage due to differences in their diffusivity; radium in particular, and possibly protactinium as well, can be strongly fractionated from slower-diffusing thorium and uranium. We show that two distinct processes are not required for the generation of ²²⁶Ra and ²³⁰Th excesses in mid-ocean ridge basalts, as has been argued previously; instead the observed negative correlations of the (²²⁶Ra/²³⁰Th) activity ratio with (²³⁰Th/²³⁸U) and with the extent of trace element enrichment may result from diffusive fractionation of Ra from Th during partial melting of the mantle. Alternatively, the (²²⁶Ra/²³⁰Th) disequilibrium in mid-ocean ridge basalts may result from diffusive fractionation during shallow-level interaction of mantle melts with gabbroic cumulates, and we show that the results of the interaction have a weak dependence on the age of the cumulate if both plagioclase and clinopyroxene are present.     

Depositional Regimes and Areal Continuity of Sedimentation in a Montane Lake Basin, British Columbia, Canada

Spatially variable sedimentation patterns are described for a small montane lake in southwestern British Columbia through the analysis of contemporary (20th century) varve sequences recovered from a high-density sediment coring program. Average, moderate, extreme, and localized depositional regimes, resolved at decadal to intra-annual scales, are differentiated for the Green Lake system from the stratigraphic record based on the volume and areal extent of the associated deposits. Average-regime sedimentation is mediated by the reliable annual freshet for the catchment. Moderate-regime events of the contemporary period (1930–2000) include periods of rapid glacial recession, extreme late-summer and autumn rainstorm-generated floods, and unusual snowmelt conditions. Only exceptional rainstorm events have led to extreme-regime sedimentation in the lake basin. Spatial sedimentation patterns are quantified by empirically derived surface models. Systematic differences are observed between both moderate and extreme sediment delivery events and the defined average-regime model. Substantial differences are observed between average and extreme regimes because of associated changes in sediment bypassing effects, intermediate sub-basin trapping, and sediment focusing mechanisms. Localized deposits coincide with isolated winter rainstorms in the region and anthropogenic disturbances along lake shorelines. Results indicate that the assumption of areal continuity in lacustrine sedimentation is not always appropriate for making comparisons between the identified depositional regimes. Sediment sampling programs that do not capture these spatially fluctuating sedimentation patterns may lead to biased accumulation chronologies and erroneous paleoenvironmental assessments of important hydroclimatic events.     

Contemporary sedimentation rates and depositional structures in a montane lake basin,southern Coast Mountains,British Columbia,Canada

Spatial variability of recent lacustrine sedimentary structures and sedimentation rates are examined for Green Lake, a morphologically complex lake basin of the southern Coast Mountains, British Columbia. A dense, 100 m grid sampling scheme was used for sediment coring within the 2 km² lake basin. Deltaic, massive, weakly laminated, and varved sediment sequences are identified within the sediment record. Spatial patterns among these sedimentary deposits are related to within‐lake sediment transfer processes, morphometric controls, and the extent of post‐depositional mixing by bioturbation. Unconformities, turbidites, and cohesive slump failure deposits, observed within the contemporary varve sequences, could all be correlated with major flooding events in the catchment area and direct anthropogenic disturbances along the shoreline. There is an overall, non‐linear decrease in sedimentation rates with increasing distance from the lake inflows; however, this pattern is disrupted in deep water sites of intervening lake sub‐basins where locally higher accumulation rates are observed. Spatial sedimentation patterns are quantitatively described by an empirically‐derived model. Systematic variations in the model parameters are observed for different lake sub‐regions and are associated with changing sediment transfer dynamics between proximal and distal sub‐basin settings. Copyright © 2006 John Wiley & Sons, Ltd.     

Analytical solutions for flow to a well through a fault

We present explicit analytical solutions to problems of steady groundwater flow to a pumping well in an aquifer divided by an infinite, linear fault. The transmissivity of the aquifer is allowed to jump from one side of the fault to the other to model the juxtaposition of host rocks with different hydrologic properties caused by faulting. The fault itself is represented as a thin anisotropic inhomogeneity; this allows the fault to act as a combined conduit–barrier to groundwater flow, as is commonly described in the literature. We show that the properties of the fault may be represented exactly by two lumped parameters—fault resistance and fault conductance—and that the effects of the fault on flow in the adjacent aquifer is independent of the fault width. We consider the limiting cases of a purely leaky and a purely conductive fault where the fault domain may be replaced exactly by internal boundary conditions, and we investigate the effects of fault properties on the flow behavior in the adjacent aquifers. We demonstrate that inferring fault properties based on field observations of head in the aquifer is inherently difficult, even when the fault may be described by one of the two limiting cases. In particular, the effects of a leaky fault and a conductive fault on heads and discharges in the aquifer opposite the fault from the well, are shown to be identical in some cases.     

Element contents in mountain birch leaves,bark and wood under different anthropogenic and geogenic conditions

Forty samples each of leaves, bark and wood of mountain birch (Betula pubescens EHRH.) were collected along a 120 km long south–north transect running through Norway’s largest city, Oslo. Concentrations of 26 chemical elements (Ag, As, Au, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, La, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Sr, Ti and Zn) as well as loss on ignition for the three sample materials are reported. By far the highest concentrations of most elements appear in the leaves. Prominent exceptions are Au and Pb, both of which are enriched in wood, indicating the importance of root-uptake, and As which is enriched in bark. Bedrock lithology, ore occurrences, soil pH and urban contamination all have a visible influence on the element concentrations in mountain birch leaves, bark and wood. It is often impossible to differentiate between all the factors that can influence element concentrations in the three sample materials. Mountain birch bark shows the strongest anthropogenic impact of the city of Oslo for dust-related elements (Fe, La, Ti) and Sb. Even in mountain birch bark the influence of the city on element concentrations is no longer discernible from the background variation at a distance of less than 20 km from Oslo centre. Compared to terrestrial moss, mountain birch appears to be of little value as a biomonitor for urban contamination.