Chemical dynamics of N-containing ionic species in a boreal forest snowcover during the spring melt period

A study of the changes in the ionic loads of NO, NH, SO and H⁺ in a boreal forest snowpack at Lake Laflamme, Québec was carried out using hydrological and chemical data from field lysimeters. The results showed that depletion of the N-containing species occurs periodically in the snowpack during meltwater discharge. Rain-on-snow events led to in-pack losses of NO and NH at a rate of 130 μeq m^?2 day^?1 and 101·3 μeq m^?2day^?1 respectively. On dry days, however, dry deposition and deposition of organic debris from the canopy resulted in increases of 183·3 μeq m^?2day^?1 for NO and 4·5 μeq m^?2day^?1 for NH in the pack. In contrast, SO₄^2? showed continual in-pack increases due to deposition of 5·0 μeq m^?2day^?1 for wet days and 92·6 μeq m^?2day^?1 for dry days. The depletion of NO and NH is due to microbiological uptake of these nutrients during periods when the free water content of the pack is high. Controlled melts in a laboratory snowmelt simulator containing snow and organic matter from the forest canopy at Lake Laflamme showed losses of NO and NH similar to those observed in the field. As the microbiological uptake proceeds at a rate comparable to that of ionic load increases in the pack by dry deposition, models of the chemical dynamics of snowmelt should take the former into account in any system where organic content of the snowpack is appreciable.     

Are all maps mental maps?

The article focuses on the way in which map content reflects the cartographer's World view and system of values. Different World views are illustrated historically. Examples of topographical, land-use and vegetation maps from different parts of the World indicate the prevalence of Eurocentric perceptions in cartography. Different geological maps of Norden show how the visual image depends on the classification system adopted. All maps are mental maps in that their content is culturally determined and ethnocentric in origin.     

Characteristics of VLF emissions manifested by their cross-spectral phase information

Natural VLF emissions received by a single antenna can be characterised at each point in the emissions' frequency-time domain by a power and a phase. Emissions received at a single point by two antennae with a fixed relative orientation in space can be similarly described by the cross-spectral power and relative phase. It is shown that the cross-spectral phase contains information on the propagation characteristics of the waves which is better utilised in wave analysis than the power. In fact, the phase information allows weak signals to be identified more readily than is possible from a power spectrogram. It also allows the recognition of waves propagating with different wave normal directions. Data from the Geos-1 electric and magnetic antennae, pre-processed by the on-board correlator, are used to study the cross-spectral characteristics of VLF hiss and chorus in the Earth's magnetosphere.     

Correlation of the upper devonian rocks of Australia

A heavy mineral concentrate from the undeformed Mundi Mundi Granite N of Broken Hill yielded very few zircons. U‐Th‐Pb measurements on microgram fractions of those extracted showed no indication of the stock's true 1500–1600 Ma intrusive event but revealed something inherited and of an age probably greater than 2 Ga. These zircons, either survivors of those inherited from the magma source or accidental inclusions from the wall rocks, may either represent sedimentary accumulations in the lower Willyama Supergroup with an older craton source i.e. provenance, or indicate the presence of a pre‐Willyama Supergroup basement. Considerable loss of Pb from the zircons is deduced to have occurred at (1) the time of granite intrusion, (2) in the lower Palaeozoic, and, (3) in the case of ²⁰⁸Pb, probably right up to recent time.     

Diversity and spatial distribution of Opuntia spp. in the Mediterranean Basin

This work offers a methodology based on statistical tools and GIS applications in a study of the adaptability of Opuntia to the environment, applied on the Mediterranean island of Sardinia. Detailed surveys of habitats containing naturalized populations of Opuntia spp. were made in order to select study sites. The topographic, soil and climatic features of these are described. The local biotypes are ascribed mainly to the spineless Opuntia ficus–indica (L.) Mill. and to the spiny Opuntia amyclaea Ten. Although introduced at different times, for different uses, they have adapted to the Sardinian environment and established in the wild. The distributions of the two species differed. The FloraMap^® modelling approach was used to simulate Opuntia distribution as a function of the island's climate and produced individual distribution maps using the accession points for the two species. Our analysis showed that environmental conditions at elevations above 800 m are the main limiting factors for the presence and abundance of Opuntia in Sardinia. Spatial representation developed by GIS software indicated temperatures below 2 °C as the threshold impairing the species naturalized distribution. The statistic results also show that variation in rainfall does not affect Opuntia spatial distribution in Sardinia.     

Formation of silica oncoids around geysers and hot springs at El Tatio, northern Chile

Siliceous oncoids, up to 4 cm in diameter, are common on the laterally extensive sinter aprons that surround the spectacular geysers and hot springs at El Tatio in northern Chile. Many of these complex oncoids developed close to geyser and spring vents that discharge boiling water. Internally the oncoids, which are composed of precipitated amorphous silica, are formed of complex arrays of spicules and concentric laminae as well as detrital volcanic grains. Spicular growth is dominant in most examples. The formation and growth of the spicules and concentric laminae were mediated by a microbial community which included filamentous microbes, mucus, and possibly bacteria. The microbes and mucus were silicified by replacement and encrustation. In some laminae the filamentous microbes lay parallel to the growth surface; in other laminae most filaments forming the thin mats were suberect. Amorphous silica precipitated between the filaments occluded porosity and commonly disguised the microbial fabric. The oncoids grew on the proximal sinter aprons around the geyser vents and hot spring pools. Most growth took place subaerially with the silica delivered to the precipitation sites by splashing water from the geysers and/or periodic shallow flooding of the discharge aprons. Unlike silica oncoids at other geothermal sites, vertical growth of oncoids that formed in some rimstone pools was not limited by water depth.     

A shallow seismic refraction study of the Versailles cryptoexplosion structure,central Kentucky

Abstract— The Versailles cryptoexplosion structure, located in central Kentucky, contains a partially brecciated central uplift and a boundary marked by arcuate faulting. Seismic refraction data were used to divide the structure into distinct units on the basis of velocity. A zone of brecciated material shows a decrease in velocity compared with surrounding rocks. Locally thickened strata are present on the flanks of the central uplift. An increase of the bedrock velocity in the area surrounding the structure suggests localized dolomization of fractured bedrock, and a plug of fractured strata near the base of the brecciation appears to be uplifted. Based on the geometry of deformation seen in known impact structures, and the integration of this study with previous geological and geophysical work in the area, it is suggested that our results support the interpretation of the Versailles structure as an eroded astrobleme (Black, 1964b; Seeger, 1972).