The R{\overline{3}} c \to R{\overline{3}} m transition in nitratine, NaNO3, and implications for calcite, CaCO3

The temperature dependences of the crystal structure and superstructure intensities in sodium nitrate, mineral name nitratine, NaNO₃, were studied using Rietveld structure refinements based on synchrotron powder X-ray diffraction. Nitratine transforms from $R{\overline{3}} c\;\hbox{to}\;R{\overline{3}} m$ at T _c = 552(1) K. A NO₃ group occupies, statistically, two positions with equal frequency in the disordered $R{\overline{3}} m$ phase, but with unequal frequency in the partially ordered $R{\overline{3}} c$ phase. One position for the NO₃ group is rotated by 60° or 180° with respect to the other. The occupancy of the two orientations in the $R{\overline{3}} c$ phase is obtained from the occupancy factor, x, for the O1 site and gives rise to the order parameter, S = 2x ? 1, where S is 0 at T _c and 1 at 0 K. The NO₃ groups rotate in a rapid process from about 541 to T _c, where the a axis contracts. Using a modified Bragg–Williams model, a good fit was obtained for the normalized intensities (that is, normalized, NI^1/2) for the (113) and (211) reflections in $R{\overline{3}} c\hbox {\,NaNO}_{3},$ and indicates a second-order transition. Using the same model, a reasonable fit was obtained for the order parameter, S, and also supports a second-order transition.     

Molecular and cultivation-dependent analysis of metal-reducing bacteria implicated in arsenic mobilisation in south-east asian aquifers

The reduction of sorbed As(V) to the potentially more mobile As(III) by As-respiring anaerobic bacteria has been implicated in the mobilisation of the toxic metalloid in aquifer sediments in SE Asia. However, there is currently only a limited amount of information on the identity of the organisms that can respire As(V) in these sediment systems. Here experiments are described that have targeted As(V)-respiring bacteria using cultivation-independent molecular techniques, and also more traditional microbiological approaches that have used growth media highly selective for organisms that can grow using arsenate as the sole electron acceptor supplied for anaerobic growth. The molecular techniques used have initially targeted DNA from microcosms displaying maximal rates of arsenate reduction, both with and without added electron donor. More recent studies from the authors’ laboratory have used stable isotope probing techniques, targeting DNA from the active microbial fraction in microcosms labelled with [¹³C]acetate supplied as an electron donor for arsenate reduction. Phylogenetic analyses using a highly conserved genetic marker (the 16S rRNA gene) have suggested the involvement of Sulfurospirillum and Geobacter species in arsenate-respiration, and this has been supported further by complimentary experiments using more traditional microbiological techniques. Additional research required to clarify the role of these organisms in the mobilisation of As in situ are discussed.     

Sedimentology and sequence stratigraphy of Aquitanian and Burdigalian stratotypes in the Bordeaux area (southwestern France)

The historical stratotypes of the Aquitanian and Burdigalian in the Aquitaine Basin are studied here by using the tools of facies sedimentology and the concept of sequence stratigraphy. This analytical method combines recognition and sequential organization of facies, and several types of stratigraphic markers. This method allows identification of at least six depositional sequences within the Miocene of the Saucats area: the four lower ones belong to the Aquitanian, the fifth one to the whole Burdigalian, while the sixth sequence corresponds to the Serravallian. In addition, this method provides evidence of a period of emersion before each transgression, suggesting potential fluvial erosion. Nevertheless, these phases are of lower amplitude than those observed in the Rhodano-Provençal Basin.

Résumé

Les stratotypes historiques de l’Aquitanien et du Burdigalien, en Aquitaine, sont étudiés ici en termes de sédimentologie de faciès et de stratigraphie séquentielle. Cette méthode d’analyse combine la reconnaissance et l’organisation séquentielle des faciès à plusieurs types de repères stratigraphiques. Elle permet d’identifier au moins six séquences de dépôt dans le Miocène de la région de Saucats : les quatre premières dans l’Aquitanien, la cinquième pour le Burdigalien et la dernière pour le Serravallien. Elle a également permis de mettre en évidence des phases d’émersion anté-transgression, suggérant de possibles érosions fluviatiles, mais d’ampleurs inférieures à celles reconnues dans le Bassin miocène rhodano-provençal.     

Effects of mid‐twenty‐first century climate and land cover change on the hydrology of the Puget Sound basin,Washington

The distributed hydrology–soil–vegetation model (DHSVM) was used to study the potential impacts of projected future land cover and climate change on the hydrology of the Puget Sound basin, Washington, in the mid‐twenty‐first century. A 60‐year climate model output, archived for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), was statistically downscaled and used as input to DHSVM. From the DHSVM output, we extracted multi‐decadal averages of seasonal streamflow, annual maximum flow, snow water equivalent (SWE), and evapotranspiration centred around 2030 and 2050. Future land cover was represented by a 2027 projection, which was extended to 2050, and DHSVM was run (with current climate) for these future land cover projections. In general, the climate change signal alone on sub‐basin streamflow was evidenced primarily through changes in the timing of winter and spring runoff, and slight increases in the annual runoff. Runoff changes in the uplands were attributable both to climate (increased winter precipitation, less snow) and land cover change (mostly reduced vegetation maturity). The most climatically sensitive parts of the uplands were in areas where the current winter precipitation is in the rain–snow transition zone. Changes in land cover were generally more important than climate change in the lowlands, where a substantial change to more urbanized land use and increased runoff was predicted. Both the annual total and seasonal distribution of freshwater flux to Puget Sound are more sensitive to climate change impacts than to land cover change, primarily because most of the runoff originates in the uplands. Both climate and land cover change slightly increase the annual freshwater flux to Puget Sound. Changes in the seasonal distribution of freshwater flux are mostly related to climate change, and consist of double‐digit increases in winter flows and decreases in summer and fall flows. Copyright © 2010 John Wiley & Sons, Ltd.     

Stratigraphic simulations of the shelf of the Gulf of Lions: testing subsidence rates and sea‐level curves during the Pliocene and Quaternary

Determining the relative importance of factors interacting to control stratigraphic organization is a key issue in sedimentology. The Pliocene‐Quaternary chronostratigraphy on the Gulf of Lions platform is still poorly constrained, giving rise to different interpretations of the evolution of its subsidence through time. This paper examines the Pliocene‐Quaternary sedimentary filling of the Gulf of Lion's shelf with Dionisos, a numerical stratigraphic model. Our results show that a constant subsidence rate accurately reproduces the observed geometries, whereas a varying subsidence rate reproduces them only if the acceleration of subsidence is limited. At this time‐scale, a third‐order eustatic curve is also reappraised: a higher resolution curve (built using δ¹⁸O measurements) gives a more realistic restitution of our stratigraphic markers. Finally, the constant subsidence rate and sediment fluxes implied in these modellings are discussed relative to climate and local factors of sedimentation.     

Risk of injury and death from lightning in Northern Malawi

Rates of lightning mortality in communities on the western shore of Lake Malawi are higher than any other reported rate in the world: 419 strike victims per million people per annum and 84 deaths per million per annum. To document the background to this phenomenon, we conducted comprehensive household interviews with surviving victims and witnesses of every case of lightning strike in seven administrative areas around Nkhata Bay, Malawi. We find that the consequential lightning strikes are significantly more common in the rainy season and during the morning. Among those victims struck by lightning, there is an average ratio of approximately one death to four injuries, which is substantially higher than the commonly accepted ratio of 1:10. Children and adults are at equal risk of being struck. If struck, the probability of death is greater when the victim is outside in the open or outside under cover than indoors under a tin or thatched roof, but is unaffected by different kinds of footwear or whether it is raining. Reported explanations for strikes often center on witchcraft or other forms of social conflict. Our findings extend the study of consequential lightning strikes in the developing world and highlight cultural factors associated with this hazard. We end with recommendations for reducing the risk of lightning for rural populations.     

On the geological availability of germanium

Based on a detailed statistical analysis of chemical data published in the scientific literature, estimates were made of the minimum amounts of recoverable Ge contained within sulphidic zinc ores and coals, given current processing technologies. It is expected that at least 119 kt (～7 kt in zinc ores and ～112 kt in coal) of recoverable germanium exist within proven reserves (at present stage of knowledge) at grades in excess of 100 ppm in sphalerite and 200 ppm in coal, while at least 440 kt (～50 kt in zinc ores and ～390 kt in coal) should become recoverable in the future, being associated to coal reserves at 8–200 ppm Ge and zinc resources containing in excess of 100 ppm Ge in sphalerite. Mississippi Valley Type (MVT) deposits are expected to be the most important hosts of germanium-rich sphalerite, while both brown and hard coals are expected to be equally important as hosts of germanium. The approach taken in this publication shows that reliable minimum estimates for the availability of by-product metals lacking suitable reserve/resource data may be attained by using robust statistical methods and geochemical data published in the scientific literature