Nouvelles données sur le téphra de Sarliève et le téphra CF7, marqueurs chrono-stratigraphiques de Grande Limagne (Massif central,France)

A trachytic tephra, discovered in the ancient lake of Sarliève, ‘Grande Limagne’, has been dated using the thermoluminescence technique. The obtained age, 16±4 ka ($\text{2}\text{σ}$), is older than that of the trachytic volcanoes of the Cha??ne des Puys, the ashes of which have already been locally recognised in the region. Its analysis confirms its originality. In the course of the comparisons made to search for its spring, it appears that the wide-dispersion tephra CF7, beforehand correlated by hypothesis to the Puy de Clierzou, probably originates from the Kilian crater or the Puy de Vasset. To cite this article: D. Miallier et al., C. R. Geoscience 336 (2004).     

Assessing selected natural and anthropogenic impacts on freshwater lens morphology on small barrier Islands: Dog Island and St. George Island, Florida, USA

Abstract The freshwater lens morphologies of the barrier islands Dog Island and St. George Island on the panhandle coast of Florida (FL), USA, are controlled to varying degrees by both natural and anthropogenic factors. Variable-density groundwater flow models confirm that spatial variability of recharge values can account for the observed lens asymmetry on these islands. The depth to the base of the lens does not vary significantly seasonally. Human development has altered recharge patterns in some areas, locally thinning the freshwater lens. Aqueduct water supply to St. George Island represents 7–25% of natural recharge; higher recharge rates are required to simulate the lens on St. George Island than on Dog Island. On both islands, coastal erosion rates are sufficiently rapid that the freshwater lens may not be in equilibrium with current boundary conditions.

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Resumen Las morfologías de los lentes de agua dulce en las islas de barrera: Islas Dog y St. George, en la costa alargada y estrecha de Florida, EUA, están controladas en diferentes grados por factores antropogénicos y naturales. Los modelos de flujo con densidad variable del agua subterránea, confirman que la variabilidad espacial de los valores de recarga, pueden ser la causa de la asimetría observada en los lentes de estas islas. La profundidad hasta la base de los lentes no varía significativamente con las estaciones climáticas. El desarrollo humano ha alterado las tendencias de recarga en algunas áreas, causando adelgazamiento local de los lentes de agua dulce. El abastecimiento de agua del acueducto en la Isla St. George, representa entre 7% y 25% de la recarga natural; por otro lado se necesitan cantidades mayores de recarga para simular los lentes en la Isla St. George que en la Isla Dog. En ambas islas, las tasas de erosión costera son tan rápidas, que las lentes de agua dulce podrían no estar en equilibrio con las condiciones actuales de frontera.

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Résumé La morphologie des lentilles deau douce des îles de Dog et de St. George, situés dans le district côtier de Florida-Etats Unis est contrôlé dans une mesure variable par des facteurs naturelles et humaines. Les modèles découlement à densité variable des eaux souterraines confirment que la variation spatiale de la recharge peut expliquer les asymétries observées des lentilles des cettes îles. La profondeur des lentilles ne présente pas des variations saisonnières importantes. Les activités humaines ont modifié la recharge dans certaines zones en amincissant localement les lentilles deau douce. Lalimentation en eaux de lîle de St. George représente 7–25% de la recharge naturelle; pour simuler les lentilles de lîle de Dog il a été nécessaire dintroduire des valeurs plus élevées de la recharge par rapport aux ceux utilisés pour lîle de St. George. Pour les deux îles lérosion côtière est assez rapide ainsi que les lentilles de eau douce ne sont pas en équilibre avec les conditions à la frontière.

     

Early Holocene brackish closed basin conditions in Georgian Bay, Ontario, Canada: microfossil (thecamoebian and pollen) evidence

Microfossils have been critical in unravelling the complex postglacial history of Georgian Bay. Thecamoebians (testate amoebae/rhizopods) record paleolimnological conditions, and pollen stratigraphy allows correlation across the basin, where sedimentation has been spatially and temporally discontinuous. Because parts of Georgian Bay have been non-depositional or erosional since the end of the Nipissing transgression (~5,000 (5,800 cal) BP), early Holocene features are exposed on the lakebed. Among these are shoreline features, such as submerged beaches and relict channels, associated with low-level Lake Hough that was driven far below the level of basin overflow. Cores taken throughout Georgian Bay record the existence of closed basin conditions that persisted several centuries around 7,500 (8,300 cal) BP, corresponding to the late Lake Hough lowstand. Evidence for hydrologic closure includes a low-diversity centropyxid-dominated thecamoebian fauna around the boundary between pollen subzones 2a and 2b in the Flowerpot Beach core, Flowerpot and Killarney basins, and in Severn Sound. This low-diversity centropyxid-dominated fauna is interpreted as recording the development of slightly brackish conditions as a result of a hydrologic deficit associated with relatively arid conditions in the Great Lakes basin during the early Holocene pine zone (~8,800–7,200 (9,900–8,050 cal) BP). The rest of the Holocene record in Georgian Bay (where it is preserved) is more diverse and dominated by difflugiid thecamoebians: predominantly Difflugia oblonga prior to human settlement, and Cucurbitella tricuspis since high-density human occupation and agriculture (and resulting eutrophication) began with the Wendat First Nations people around Severn Sound about 750 years ago. The implication that water budget fluctuations leading to discernible variations in lake level and water chemistry occurred in the relatively recent geologic past is significant to studies of global climate change and resource management in the Great Lakes, one of the world’s largest freshwater resources.     

Corrections for Wind-Speed Errors from Sodar and Lidar in Complex Terrain

The quality of lidar and sodar wind estimates is generally judged through comparisons with mast-mounted instruments, and the resulting regressions. Evaluation of the relative merits of lidars versus sodars is complicated by the fact that lidars are generally placed close to a mast whereas sodars are generally placed some distance from a mast so that acoustic reflections off the mast are reduced. This leads to the two technologies, lidar and sodar, not being compared in similar situations. Differences arising from the two geometries can be expected to be larger in complex terrain, where the wind regime can vary significantly spatially. The current work explores these differences in moderately complex terrain. Lidar–mast comparisons are performed with the lidar close to an 80 m mast, and sodar–mast comparisons performed with the sodar 300 m from the mast. Systematic variations in estimated wind speed are found to occur with height, consistent with predictions from a simple flow model. When the lidar was moved to the sodar location, further from the mast, there were significant changes in the estimated wind speeds and a reduction in correlation with the mast-based wind speeds, as expected. However, the correlation between collocated lidar and sodar winds was high. This finding emphasizes that any comparison of two remote sensing instruments needs to be through similar experiments, and that differences in accuracy often reported for the lidar and sodar technologies are likely to be contaminated due to poor comparison configurations. A method was devised to simulate the sodar being collocated with the mast, by using the lidar–sodar measurements and the lidar–mast measurements. It was found that there was then no statistically detectable difference between lidar–mast regressions and sodar–mast regressions for the particular lidar and sodar tested. Both remote sensing instruments were also found to be good estimators of Weibull parameters, as compared with those derived from mast data. The conclusion is that the sodar measured the winds above the sodar with a similar accuracy to the lidar measuring winds above the lidar.     

Climate change, adaptation and economic growth

This paper explores the links between economic growth and the impacts of climate change. Inclusive, pro-poor growth is central to the development of low-income countries. There is also a broad consensus that growth and development are important to reduce vulnerability to climate change. Growth does not automatically reduce vulnerability, only the right kind of growth does. The paper aims to develop a better understanding of what the ??right kind of growth?? may be. We find that many growth policies, such as investment in skills and access to finance, indeed reduce vulnerability to climate change. However, climate change calls for some adjustments in growth policy. In particular, investment in infrastructure and efforts to stimulate entrepreneurship and competitive markets must take more of a risk management perspective and recognise climate risks.     

Tropical precipitation, SSTs and the surface energy budget: a zonally symmetric perspective

The relative importance of sea surface temperatures (SSTs) and the surface energy budget to tropical precipitation is examined by comparing models with zonally symmetric climates, both fixed SST and coupled to a slab mixed layer ocean. Two models are considered with differing surface flux formulations and in each case solutions that are symmetric about the equator are perturbed to create interhemispheric asymmetry. When SSTs are prescribed in the two models with different flux formulations, the magnitude of tropical precipitation response to identical SST anomalies is significantly different, but the differences can be understood in terms of the altered surface fluxes. In contrast, when the net surface energy fluxes are constrained to be identical in mixed layer simulations of the two different models, the response of tropical precipitation to perturbations in the surface energy balance is very similar. Both perspectives predict qualitatively the same precipitation response, but the energy budget better predicts the magnitude of the precipitation response. Thus, we argue that the atmospheric energy budget, controlled in these experiments primarily by the surface energy budget, is more fundamental to the control of tropical precipitation than the SSTs, in these simulations with axisymmetric climates. We touch briefly on a complication in the interpretation of the model results due to the fact that fixed SST and slab-ocean versions of the model can produce different Hadley cell strengths for the same SSTs.     

A revised approach to water footprinting to make transparent the impacts of consumption and production on global freshwater scarcity

Through the interconnectedness of global business, the local consumption of products and services is intervening in the hydrological cycle throughout the world to an unprecedented extent. In order to address the unsustainable use of global freshwater resources, indicators are needed which make the impacts of production systems and consumption patterns transparent. In this paper, a revised water footprint calculation method, incorporating water stress characterisation factors, is presented and demonstrated for two case study products, Dolmio^® pasta sauce and Peanut M&M's^® using primary production data. The method offers a simple, yet meaningful way of making quantitative comparisons between products, production systems and services in terms of their potential to contribute to water scarcity. As such, capacity is created for change through public policy as well as corporate and individual action. This revised method represents an alternative to existing volumetric water footprint calculation methods which combine green and blue water consumption from water scarce and water abundant regions such that they give no clear indication about where the actual potential for harm exists.     

Relating Urban Surface-layer Structure to Upwind Terrain for the Salford Experiment (Salfex)

Profiles of wind and turbulence over an urban area evolve with fetch in response to surface characteristics. Sodar measurements, taken on 22 April 2002 during the Salford Experiment in the UK (Salfex), are here related to upstream terrain. A logarithmic layer up to z = 65m was observed in all half-hour averaged profiles. Above this height the profile showed a different vertical gradient, suggesting a change in surface cover upstream. The drag coefficient varied by a factor of two over only a 20° direction change. Turbulence intensity (σ _x ) for each wind component (x) decreased with height, but the ratio suggested an underestimate of σ _u compared to previous results. Mean urban and suburban cover fraction within the source area for each height decreased sharply between z = 20 and 50m, increasing slightly above. The near-convergence of cover fractions thus occured for source areas of minimum length ≈ 2,200 m. In comparison, the mean length scale of heterogeneity L _P was calculated from surface cover data to be 1,284 m, and the corresponding mean blending height h _b was 175 m. Finally, the mean streamline angle, α, was negative and the magnitude decreased with height. An exponential fit to α for z ≤ 65m gave an e-folding height scale of 159 m. A simple relationship between this height scale and L _P was assumed, giving L _P ≈ 1,080 m, which is in reasonable agreement with the estimate from surface cover type. The results suggest that more emphasis is required on modelling and measuring surface-layer flow over heterogeneous urban canopies.     

Envisioning carbon capture and storage: expanded possibilities due to air capture,leakage insurance,and C-14 monitoring

In order to meet the challenge of climate change while allowing for continued economic development, the world will have to adopt a net zero carbon energy infrastructure. Due to the world’s large stock of low-cost fossil fuels, there is strong motivation to explore the opportunities for capturing the CO₂ that is produced in the combustion of fossil fuels and keeping it out of the atmosphere. Three distinct sets of technologies are needed to allow for climate neutral use of fossil fuels: (1) capture of CO₂ at concentrated sources like electric power plants, future hydrogen production plants and steel and cement plants; (2) capture of CO₂ from the air; and (3) the safe and permanent storage of CO₂ away from the atmosphere. A strong regime of carbon accounting is also necessary to gain the public’s trust in the safety and permanence of CO₂ storage. This paper begins with an extensive overview of carbon capture and storage technologies, and then presents a vision for the potential implementation of carbon capture and storage, drawing upon new ideas such as air capture technology, leakage insurance, and monitoring using a radioactive isotope such as C-14. These innovations, which may provide a partial solution for managing the risks associated with long-term carbon storage, are not well developed in the existing literature and deserve greater study.