The geochemistry of the Dunedin Volcano: Strontium isotope chemistry

The isotopic composition of strontium has been determined for samples from the alkaline lavas of the Dunedin Volcano covering the range basalt, basanite, intermediate compositions, phonolite and quartz normative trachyte. The basaltic, intermediate and phonolitic rocks appear to be comagmatic and have similar low initial Sr⁸⁷/Sr⁸⁶ ratios around 0.7030, comparable with those of other alkaline provinces. The quartz normative trachytes have initial ratios significantly higher than those of the other rocks (0.7040) although their age is comparable. Contamination by sea water or crustal material could explain the higher initial ratios of the trachytes but it does not account for important features of their chemistry. It is suggested that the trachytes formed by partial melting involving an alkali feldspar-rich portion of older igneous rocks. Rb-Sr ages obtained are comparable with published K-Ar dates. The Rb-Sr age for the trachytes is 14.± 7 m.y. and the other alkali-enriched rocks give ages ranging within the limits of 14.4 to 12.0 m.y.     

Preserving Ground Water Samples With Hydrochloric Acid Does Not Result in the Formation of Chloroform

Water samples collected for the determination of volatile organic compounds (VOCs) are often preserved with hydrochloric acid (HCl) to inhibit the biotransformation of the analytes of interest until the chemical analyses can he performed. However, it is theoretically possible that residual free chlorine in the HCl can react with dissolved organic carbon (DOC) to form chloroform via the haloform reaction. Analyses of 1501 ground water samples preserved with HCl from the U.S. Geological Survey's National Water-Quality Assessment Program indicate that chloroform was the most commonly detected VOC among 60 VOCs monitored. The DOC concentrations were not significantly larger in samples with detectable chloroform than in those with no delectable chloroform, nor was there any correlation between the concentrations of chloroform and DOC. Furthermore, chloroform was detected more frequently in shallow ground water in urban areas (28.5% of the wells sampled) than in agricultural areas (1.6% of the wells sampled), which indicates that its detection was more related to urban land-use activities than to sample acidification. These data provide strong evidence that acidification with HCl does not lead to the production of significant amounts of chloroform in ground water samples. To verify these results, an acidification study was designed to measure the concentrations of all trihalomethanes (THMs) that can form as a result of HCl preservation in ground water samples and to determine if ascorbic acid (C₆H₈O₆) could inhibit this reaction if it did occur. This study showed that no THMs were formed as a result of HCl acidification, and that ascorbic acid had no discernible effect on the concentrations of THMs measured.     

Phase changes and thermodynamic properties of CaTiO3. Spectroscopic data,vibrational modelling and some insights on the properties of MgSiO3 perovskite

The effect of pressure (up to 21 GPa at room temperature) and temperature (up to 1570 K at room pressure) on the Raman spectrum of CaTiO₃ is presented. No significant changes, which could be attributed to a major structural change, are observed in the spectra up to 22 GPa. The pressure shifts of the Raman modes can be related to a significant compression of the Ti-O bond. Discontinuous changes in the spectra upon heating may be related to phase changes observed by calorimetry and X-ray diffraction. The important temperature shifts of some low-frequency modes can be related to an increase in the Ti-O-Ti angle in agreement with the X-ray data showing a decrease of the structural distortion with increasing temperature. These data are compared to those available for MgSiO₃-perovskite and show that CaTiO₃ is a good structural analogue for MgSiO₃-perovskite. The present spectroscopic data are used to calculate the specific heat and entropy of CaTiO₃. The role of the low frequency modes in the calculations is emphasized. Good agreement is observed between calculated and experimentally determined values in the 0–1300 K temperature range. A similarly defined model is proposed for MgSiO₃-perovskite. It is found that the entropy lies between 57 and 64 J/mol/K at 298 K and between 190 and 200 J/mol/K at 1000 K in agreement with the values inferred from experimental equilibrium data. Finally we briefly discuss the values of the Grüneisen parameters of both perovskites inferred from macroscopic and microscopic data.     

The Role of Ocean Tides on Groundwater-Surface Water Exchange in a Mangrove-Dominated Estuary: Shark River Slough,Florida Coastal Everglades,USA

Low-relief environments like the Florida Coastal Everglades (FCE) have complicated hydrologic systems where surface water and groundwater processes are intimately linked yet hard to separate. Fluid exchange within these low-hydraulic-gradient systems can occur across broad spatial and temporal scales, with variable contributions to material transport and transformation. Identifying and assessing the scales at which these processes operate is essential for accurate evaluations of how these systems contribute to global biogeochemical cycles. The distribution of ²²²Rn and ^223,224,226Ra have complex spatial patterns along the Shark River Slough estuary (SRSE), Everglades, FL. High-resolution time-series measurements of ²²²Rn activity, salinity, and water level were used to quantify processes affecting radon fluxes out of the mangrove forest over a tidal cycle. Based on field data, tidal pumping through an extensive network of crab burrows in the lower FCE provides the best explanation for the high radon and fluid fluxes. Burrows are irrigated during rising tides when radon and other dissolved constituents are released from the mangrove soil. Flushing efficiency of the burrows—defined as the tidal volume divided by the volume of burrows—estimated for the creek drainage area vary seasonally from 25 (wet season) to 100 % (dry season) in this study. The tidal pumping of the mangrove forest soil acts as a significant vector for exchange between the forest and the estuary. Processes that enhance exchange of O₂ and other materials across the sediment-water interface could have a profound impact on the environmental response to larger scale processes such as sea level rise and climate change. Compounding the material budgets of the SRSE are additional inputs from groundwater from the Biscayne Aquifer, which were identified using radium isotopes. Quantification of the deep groundwater component is not obtainable, but isotopic data suggest a more prevalent signal in the dry season. These findings highlight the important role that both tidal- and seasonal-scale forcings play on groundwater movement in low-gradient hydrologic systems.     

Geochemistry and evolution of Iherzolite-bearing phonolitic lavas from Nigeria,Australia, East Germany and New Zealand

The major and trace element chemistry of phonolites containing spinel Iherzolite xenoliths from Bokkos (Nigeria), Phonolite Hill (northeastern Australia) and Heldburg (East Germany) is consistent with an origin by fractional crystallization of basanitic magmas at upper mantle pressures (10–15 kbar). At Bokkos, spatially associated lavas ranging from hawaiitic nepheline mugearite to nepheline benmoreite can be modeled very well by fractional crystallization of kaersutitic amphibole + olivine + Fe-Ti-spinel + apatite, a crystal extract consistent with experimentally-determined near-liquidus phase relationships for mugearitic liquids. Further fractional crystallization of aluminous clinopyroxene + mica + apatite will yield the phonolites. A similar model relating the unusual Iherzolite-bearing mafic nepheline benmoreite from Pigroot (New Zealand) to basanitic lavas of the East Otago province is not supported by major and trace element data. The Pigroot lava is possibly the product of melting of a mantle source region previously enriched in Sr and light rare earth elements, with subsequent minor fractional crystallization of olivine + kaersutite. Dynamic flow crystallization processes operating within conduit systems from mantle pressures are capable of yielding large volumes of evolved phonolitic liquids from primary basanitic liquids, if magma flow rates are appropriate. This mechanism may provide an explanation for the volumetric bias towards salic differentiates in some alkalic provinces.     

Late Pleistocene sedimentology,taphonomy and megafauna extinction on the Darling Downs,southeastern Queensland

The Kings Creek catchment, southeastern Queensland, contains a variety of Pleistocene – Holocene depositional settings. Fluvial depositional accumulation processes in the catchment reflect both high-energy channel and low-energy episodic overbank deposition. The lithofacies and depositional environments of locality QML796 were examined in detail to aid interpretation of taphonomic accumulation patterns of large and small taxa in the deposit. The basal fossiliferous unit was deposited in a meandering channel and passes upward into overbank deposits that include ephemeral interfluve channels and splays. The most striking taphonomic observations on vertebrates at the locality include: (i) low representation of post-cranial elements; (ii) high degree of bone breakage; (iii) variable abrasion with most identifiable bone elements having a low to moderate degree of abrasion; (iv) low rates of bone weathering; (v) a low degree of carnivore bone modification; and (vi) a low degree of articulated or associated specimens. Collectively, these data suggest that the material was transported into the deposit from the surrounding proximal floodplain and that the assemblages reflect substantial hydraulic sorting. However, despite that, sequential faunal horizons show a stepwise decrease in taxonomic diversity that cannot be explained by sampling or taphonomic bias. The decreasing diversity includes loss of some, but not all, megafauna and is consistent with a progressive local loss of megafauna in the catchment over an extended interval of time. Data are consistent with a climate change model for megafauna extinction but not with nearly simultaneous extinction of megafauna as required by the human-induced blitzkrieg extinction hypothesis.     

85-μm fluxes from asteroids: 2 Pallas, 7 Iris, 15 Eunomia,and 45 Eugenia

Broad-bandpass flux measurements with effective wavelengths at 20, 27 and 85 μm are presented for four asteroids—2 Pallas, 7 Iris, 15 Eunomia, and 45 Eugenia. The observations were made during the Far Infrared Sky Survey Experiment (FIRSSE) with a super-fluid helium-cooled telescope flown to exospheric altitudes aboard a sounding rocket. The 20- and 27-μm fluxes are consistent with published 10- and 20-μm photometry. However, the 85-μm fluxes are a factor of 2 to 3 lower than a Planck law extrapolation of the shorter wavelength fluxes. If the thermal radiation from asteroids at these wavelenghts is adequately described by graybody emission, as is expected on the basis of models of asteroid radiation discussed in the literature, then the value of emissivity in the 85-μm bandpass is likely to be substantially lower than the 10- to 20-μm value. The decrease in emissivity between 20 and 85 μm suggested for these asteroids is in qualitative agreement with studies, both observational and theoretical, of emissivity of a lunar-type regolith. Fluxes measured at 20 and/or 27 μm are also reported for an additional 16 asteroids.     

Using Lightning Data to Better Understand and Predict Flash Floods in the Mediterranean

One of the costliest natural hazards around the globe is flash floods, resulting from localized intense convective precipitation over short periods of time. Since intense convective rainfall (especially over the continents) is well correlated with lightning activity in these storms, a European Union FP6 FLASH project was realized from 2006 to 2010, focusing on using lightning observations to better understand and predict convective storms that result in flash floods. As part of the project, 23 case studies of flash floods in the Mediterranean region were examined. For the analysis of these storms, lightning data were used together with rainfall estimates in order to understand the storms?? development and electrification processes. In addition, these case studies were simulated using mesoscale meteorological models to better understand the local and synoptic conditions leading to such intense and damaging storms. As part of this project, tools for short-term predictions (nowcasts) of intense convection across the Mediterranean and Europe, and long-term forecasts (a few days) of the likelihood of intense convection, were developed and employed. The project also focused on educational outreach through a special Web site http://flashproject.org supplying real-time lightning observations, real-time experimental nowcasts, medium-range weather forecasts and educational materials. While flash floods and intense thunderstorms cannot be prevented, long-range regional lightning networks can supply valuable data, in real time, for warning the public, end-users and stakeholders of imminent intense rainfall and possible flash floods.     

Modeling the electric structures of two thunderstorms and their contributions to the global circuit

This study examines the electricity in two thunderstorms, typical for their respective locales (the Great Plains and the New Mexico mountains), by modeling them as a set of steady-state horizontal layers of external currents. The model electric sources, corresponding to the charge separation processes in the thundercloud, are embedded in an exponential conducting atmosphere. The source parameters are determined by fitting the model electric field to measured profiles. The resulting currents to the ionosphere (i.e., the Wilson current) from the two storms are 0.53 A and 0.16 A, while the calculated electrical energies of the storms are 2.3 × 10¹⁰ J and 2.8 × 10⁹ J, respectively. The more vigorous storm is estimated to transfer 16 000 C in the global circuit during 8.5 h of its lifetime, while the weaker mountain storm transferred about 1200 C in its entire 2-h lifetime. Removal of the screening charge layer from above the updraft region in one modeled storm leads to only a small increase in the net Wilson current of less than 3%, while it provides a substantial local disturbance of the electric field. Overall, the model findings indicate that differences in the Wilson currents and electrical energies of the two storms result from differences in their internal dynamical and electrical structures as well as their geographical locations.