Étude synoptique des précipitations alpines

Summary The position of the very important climatic limit, definited byBenevent, which separates the humid climate of north Alps and the dry climate of south Alps, is first described. The method used for synoptic study of alpine precipitations is then exposed: it consists in plotting for every day on a great scale chart the amounts of rain measured in the alpine rain-jauge stations and in comparing this result with the isohypses charts at the 700, 500 and 300 mb levels.     

Verleihung der Ehrenmitgliedschaft der Geologischen Vereinigung

Ohne Zusammenfassung     

Roman road pollution assessed by elemental and lead isotope geochemistry in East Belgium

The ability of inorganic geochemistry to record environmental change and especially human impact has been evidenced by several studies across Europe, especially in peat, where it is possible to record the impact of agriculture, mining and other industries. However, despite the numerous investigations on the impact of ancient human activities such as ore mining and smelting, little attention has been paid to geochemistry as a tool to solve problems of palaeopollution in the surroundings of archaeological sites. This paper presents geochemical evidence of the impact of a possible early Roman road built in SE Belgian peatland. Increased Zn and Pb concentrations suggest that Pb–Zn ores were transported on the road. Lead isotope analyses suggest that these ores are locally derived, being compatible with those found in the nearby Pb–Zn ore deposits from East Belgium. Present results provide direct evidence that East Belgian Pb–Zn ores were already being mined during Roman times, i.e. earlier than previously suspected (i.e. 14th century) and that Zn appears to be relatively immobile here. On a broader scale, it also demonstrates that such an early road already had an impact on the environment in terms of metal pollution. This paper enlarges on the range of possibilities offered by geochemistry in the field of geoarchaeology.     

Thermal reservoir modeling in petroleum geomechanics

Thermal oil recovery processes involve high pressures and temperatures, leading to large volume changes and induced stresses. These cannot be handled by traditional reservoir simulation because it does not consider coupled geomechanics effects. In this paper we present a fully coupled, thermal half‐space model using a hybrid DDFEM method. A finite element method (FEM) solution is adopted for the reservoir and the surrounding thermally affected zone, and a displacement discontinuity method is used for the surrounding elastic, non‐thermal zone. This approach analyzes stress, pressure, temperature and volume change in the reservoir; it also provides stresses and displacements around the reservoir (including transient ground surface movements) in a natural manner without introducing extra spatial discretization outside the FEM zone. To overcome spurious spatial temperature oscillations in the convection‐dominated thermal advection–diffusion problem, we place the transient problem into an advection–diffusion–reaction problem framework, which is then efficiently addressed by a stabilized finite element approach, the subgrid‐scale/gradient subgrid‐scale method. Copyright © 2008 John Wiley & Sons, Ltd.     

Hydrological field data from a modeller's perspective: Part 1. Diagnostic tests for model structure

Hydrological scientists develop perceptual models of the catchments they study, using field measurements and observations to build an understanding of the dominant processes controlling the hydrological response. However, conceptual and numerical models used to simulate catchment behaviour often fail to take advantage of this knowledge. It is common instead to use a pre‐defined model structure which can only be fitted to the catchment via parameter calibration. In this article, we suggest an alternative approach where different sources of field data are used to build a synthesis of dominant hydrological processes and hence provide recommendations for representing those processes in a time‐stepping simulation model. Using analysis of precipitation, flow and soil moisture data, recommendations are made for a comprehensive set of modelling decisions, including Evapotranspiration (ET) parameterization, vertical drainage threshold and behaviour, depth and water holding capacity of the active soil zone, unsaturated and saturated zone model architecture and deep groundwater flow behaviour. The second article in this two‐part series implements those recommendations and tests the capability of different model sub‐components to represent the observed hydrological processes. Copyright © 2010 John Wiley & Sons, Ltd.     

Cl and Na Fluxes in an Andean Foreland Basin of the Peruvian Amazon: An Anthropogenic Impact Evidence

The dissolved load of the Amazon River is generally considered to be lowly impacted by anthropogenic activities. In this work, based on the chemical and hydrological database of the Environmental Research Observatory—HYBAM (http://www.ore-hybam.org), we explore the importance of the Peruvian Foreland petroleum activity on the dissolved Na and Cl fluxes of the Amazon River. The main result of this study allows us suggesting that oil extraction activity, concentrated in the El Tigre River basin, a small foreland watershed in the Peruvian Amazon, influenced drastically the Na and Cl exportation of the Amazon River during the 2006–2007 period. During these years,  the dissolved exportations of this basin represented almost 20 % of the annual dissolved Cl Amazon flux and almost 12 % of the annual dissolved Na Amazon flux for a mean annual discharge <1 % of the Amazon River discharge. Since the last decades, the anthropogenic activities are increasing over the whole Amazon basin, especially in Andean countries. In this context, our results demonstrate that extractive activity cannot be considered as negligible on the hydro-chemistry of the Amazonian Rivers especially for the weathering budget estimation based on river-dissolved loads. Moreover, Cl and Na can be used to trace the formation waters derived from oil extraction at a large spatial scale. The environmental impacts of contaminants associated with deep water released to the hydrosystem (polycyclic aromatics hydrocarbons, metallic trace elements, etc.) at local and regional scales are still underestimated and should be monitored to map their local and regional influence and to prevent their risks on human health.     

Physical influences on east coast cyclogenesis

Abstract

Three examples of cyclogenesis off the east toast of North America are studied using an 8‐level primitive equations model. The model includes input of sensible and latent heat from the sea surface, both parameterized convective and large‐scale precipitation and release of latent heat, surface frictional drag and orography. The grid size is 190 km. Twenty‐four‐hour prognoses were made for four time periods with similar results: orography and fluxes of sensible and latent heat from the ocean were of little consequence, while the effect of the land‐water roughness contrast was significant.

The lack of appreciable orographic influences is attributable to the fact that the Lows studied crossed the Appalachians south of the highest terrain. The cyclones formed along well‐developed frontal systems where the difference between air or dew‐point temperature and sea temperature in the warm sector was small or negative. Consequently fluxes of both sensible and latent heat near the Low centres during cyclogenesis were small. They were large, as expected, in the cold air flowing out over the water to the rear of the cyclones. However, the Laplacian of the flures did not favour intensification at the Low centres. Moreover, heating in the cold air destroys available potential energy. It is true that the warm sector air probably had an initial vertical temperature and moisture distribution conducive to precipitation and release of latent heat. However, this arose due to fluxes prior to deepening. The dramatic effect of frictiona drag was associated with a decrease in low‐level mass convergence as the Lows moved from rough land to smooth sea.     

Late Glacial and Holocene vegetation history in the southern part of Transylvania (Romania): pollen analysis of two sequences from Avrig

We present here the results of pollen analysis of two sequences of about 8.06 m and 11.90 m length, originating from two adjacent peat bogs in the southern part of Transylvania province, Romania (155 and 122 pollen spectra). The vegetation record, which is supported by 17 ¹⁴C dates, begins in the Late Glacial interstadial when forest recolonisation began with the development of Pinus, without a pioneer Betula phase. Picea began to expand from regional refuges. After a well‐defined Younger Dryas, the Holocene opens with the expansion of Betula, Ulmus and Picea, followed, at about 10 400 cal. yr BP, by Fraxinus, Quercus and Tilia. The Corylus optimum is correlated with the Atlantic chronozone (after 8600 cal. yr BP). The local establishment of Carpinus occurred at about 6500 cal. yr BP, with a maximum at about 5700 cal. yr BP. Fagus pollen is regularly recorded after 8200 cal. yr BP. This taxon became dominant at about 3700 cal. yr BP. The first indications of human activities appear at around 7200 cal. yr BP. Copyright © 2005 John Wiley & Sons, Ltd.