A Dye Tracer Approach for Quantifying Fluid and Solute Flux Across the Sediment–Water Interface

We propose a dye tracer method to characterize fluid and solute fluxes across the sediment-water interface. Zones of groundwater discharge within the streambed are first identified, and small volume slugs of 0.5 to 1 mL fluorescein dye are released at known subsurface depths. Fluorescein dye allows for visual identification of interface breakthrough locations and times, and dye concentrations at the point of discharge are recorded over time by a fluorometer to generate high resolution breakthrough curves. Groundwater velocities and dispersivities at the demonstration site are estimated by numerically fitting dye breakthroughs to the classical advection-dispersion equation, although the methodology is not limited to a specific transport model. Breakthroughs across the stream-sediment interface at the demonstration site are nonlinear with tracer release depth, and velocity estimates from breakthrough analysis are significantly more reliable than visual dye (time to first dye expression) and Darcy methods which tend to overestimate and underestimate groundwater velocity, respectively. The use of permanent injection points within the streambed and demonstrated reproducibility of dye breakthroughs allow for study of fluid and solute fluxes under seasonally varying hydrologic conditions. The proposed approach also provides a framework for field study of nonconservative, reactive solutes and allows for the determination of characteristic residence times at various depths in the streambed to better understand chemical and nutrient transformations.     

Elemental abundance data for the Manitouwabing iron meteorite

Abstract The Manitouwabing meteorite whose trace constituents have not been previously quantified was analysed for Au, As, Ga, Ge, Ir, Ni, Os, Pd, Pt, Rh and Ru. Our data confirm that it belongs to subgroup IIIA of the IIIAB group and on the basis of the much higher concentrations of As, Ir, Os, Pt, Rh and Ru, it is not paired with Madoc as had previously been proposed.     

Coronal electron density maps for 7 March, 1970, derived from Mgx λ625 spectroheliograms

We have analyzed daily Mgx 625 spectroheliograms acquired by the Harvard College Observatory experiment on OSO-6 for a 28-day period centered on 7 March, 1970, the date of a well-observed total solar eclipse. These data are used to construct maps of the variation across the solar disk of the electron density at the base of the corona. The correspondence of high and low density regions with regions of enhanced and reduced emission in white light and Mgx pictures made during or near the time of the eclipse are described.     

The ultramafic flora of the Santa Elena peninsula,Costa Rica: A biogeochemical reconnaissance

The Santa Elena peninsula in the northwest of Costa Rica protrudes about 30 km westwards into the Pacific Ocean, and measures about 8–16 km in a north–south direction. Several geological studies have been carried out since 1953, showing that much of the peninsula is made up of peridotite, cut by mafic dykes. Only one previous brief examination appears to have been made of the vegetation in relation to the composition of the soils. We present here the results of a survey of some soils and plants of the eastern part of the peridotite massif, in which 73 plant specimens representing 51 identified species were collected and analyzed. The soils sampled all showed extreme ultramafic characteristics: Fe 10–16%, Mg 4–16%, Ca 0.5–1.4%; Ni 3000–7500 mg/kg, Cr 1400–3650 mg/kg, Co 150–325 mg/kg. The plants collected include several from genera such as Arrabidaea, Chamaesyce, Helicteres, Hyptis, Lippia, Oxalis, Polygala, Turnera and Waltheria that are also represented on ultramafics elsewhere in the Americas (e.g. Cuba, Puerto Rico, Brazil). Few of the species appear to be endemic to Costa Rica or to the ultramafics of Santa Elena. None of the specimens collected exhibited hyperaccumulation of nickel, the highest Ni concentration being 275 mg/kg in Buchnera pusilla.     

Design of tabular excavations in foliated rock: an integrated numerical modelling approach

Summary This paper presents a rock mechanics design methodology applicable to steeply dipping orebodies typical of many underground hardrock mines. The first stage in the design process is the characterization of the rock mass using bothin situ and laboratory data. The effects of anisotropy on rock mass behaviour are discussed with reference to laboratory and field observations. The second stage involves the use of a number of selected numerical modelling techniques to investigate ground response in the near-field rock mass surrounding the mining excavations. This study shows that the use of several numerical methods in conjunction, allowing for the advantages of each method to be maximized, provides a more comprehensive analysis of the different facets of stope design. This approach differs from those in the literature which seek to compare the different numerical methods in order to select just one method best suited for a problem. The design methodology employed emphasizes the importance of developing an understanding of ground deformation mechanisms as opposed to predicting absolute behaviour.     

Observations of substorm fine structure

Particle and magnetic field measurements on the CRRES satellite were used, together with geosynchronous satellites and ground-based observations, to investigate the fine structure of a magnetospheric substorm on February 9, 1991. Using the variations in the electron fluxes, the substorm activity was divided into several intensifications lasting about 3–15 minutes each. The two main features of the data were: (1) the intensifications showed internal fine structure in the time scale of about 2 minutes or less. We call these shorter periods activations. Energetic electrons and protons at the closest geosynchronous spacecraft (1990 095) were found to have comparable activation structure. (2) The energetic (> 69 keV) proton injections were delayed with respect to electron injections, and actually coincided in time with the end of the intensifications and partial returns to locally more stretched field line configuration. We propose that the energetic protons could be able to control the dynamics of the system locally be quenching the ongoing intensification and possibly preparing the final large-scale poleward movement of the activity. It was also shown that these protons originated from the same intensification as the preceeding electrons. Therefore, the substorm instability responsible for the intensifications could introduce a negative feedback loop into the system, creating the observed fine structure with the intensification time scales.     

The role of phosphorus in the upper atmosphere of Jupiter

The reaction of elemental phosphorus and H atoms to form PH₃ was observed and should be a major factor in the recycling of PH₃ in the stratosphere of Jupiter. The formation of PH₃ in this manner should predominate at high altitudes where, due to the very low temperatures, reactions that require higher activation energies than these atom reactions cannot occur. At lower altitudes, in the troposphere, the rapid formation of H atoms from the strong absorption of light by NH₃ will contribute to phosphine production also in this same manner. Recent experiments have also shown that elemental phosphorus reacts readily with aqueous ammonia to form PH₃. This reaction may also be important in the recycling of PH₃ in the upper troposphere of Jupiter if water-ammonia clouds, as had been previously thought, exist. Considerations of the coloration of the Great Red Spot have been made based upon the nature of the phosphorus obtained by decomposition of phosphine.     

Geochemistry of tertiary alkaline rocks of the Eastern Trans-Pecos Magmatic Province,Texas

The Trans-Pecos Magmatic Province (TPMP) is an alkalic field that was active between 48-17 Ma. Rocks of two subprovinces in the eastern alkalic belt of the TPMP, the Big Bend region and the Davis Mountains, have been analyzed for major and trace element concentrations in order to determine what magmatic processes operated to influence the compositional evolution of the magmas, and to explore what relationship existed between the silica-oversaturated evolved rocks and the silica-undersaturated mafic rocks. Similar compositional trends exist in both subprovinces, implying that the evolved rocks are genetically related to the mafic rocks, and that the differentiation processes were broadly reproducible spatially and temporally.Four stages of evolution have been identified: Stage I, alkali basalt to trachyte; stage II, trachyte to quartz trachyte; stage III, quartz trachyte to rhyolite/comendite; and stage IV, rhyolite/comendite to high-silica rhyolite/comendite. These stages were identified by discontinuities in trends on variation diagrams; within stages I and II, more than one subtrend exist.Stage I can best be modeled as the result of simple crystal fractionation with minor magma replenishment. Two subtrends within this stage indicate that variations in the processes or their rates may have occurred. Stage II exhibits both closed- and open-system behavior. The open system behavior consists of combined fractionation-assimilation and episodic mixing of stage II and stage I magmas. Stages III and IV evolved under open system processes of combined fractionation-assimilation, with the assimilant having compositional characteristics of a shale-dominated sedimentary assemblage.The four stages and subtrends within the stages occur in both subprovinces. Further, some subtrends comprise rocks that differ in age by as much as 10 m.y. In each subprovince, the stratigraphy indicates a random interlaying of rocks of the different stages, generally erupted from more than one center. That contemporaneous magmas of different stages existed in a given subprovince is indicated by the interfingering of their erupted products. These constraints argue against a single magma production-evolution scheme. Rather, the data suggest that magmas of the different stages were produced more than once during the evolution of the eastern TPMP, and that during any given time, production and evolution of magma of all stages were occurring.     

The dawn and dusk electrojet response to substorm onset

We have investigated the time delay between substorm onset and related reactions in the dawn and dusk ionospheric electrojets, clearly separated from the nightside located substorm current wedge by several hours in MLT. We looked for substorm onsets occurring over Greenland, where the onset was identified by a LANL satellite and DMI magnetometers located on Greenland. With this setup the MARIA magnetometer network was located at dusk, monitoring the eastward electrojet, and the IMAGE chain at dawn, for the westward jet. In the first few minutes following substorm onset, sudden enhancements of the electrojets were identified by looking for rapid changes in magnetograms. These results show that the speed of information transfer between the region of onset and the dawn and dusk ionosphere is very high. A number of events where the reaction seemed to preceed the onset were explained by either unfavorable instrument locations, preventing proper onset timing, or by the inner magnetospheres reaction to the Earthward fast flows from the near-Earth neutral line model. Case studies with ionospheric coherent (SuperDARN) and incoherent (EISCAT) radars have been performed to see whether a convection-induced electric field or enhanced conductivity is the main agent for the reactions in the electrojets. The results indicate an imposed electric field enhancement.