Dust transport and palaeoclimate during the Oldest Dryas in Central Europe — implications from varves (Lake Constance)     

Frank Niessen  Guy Lister  Federico Giovanoli 《Climate Dynamics》1992,8(2):71-81

This paper evaluates evidence for seasonal loess deposits in peri-Alpine Lake Constance at the end of the last Glacial (Oldest Dryas chronozone). The usefulness of such lacustrine deposits for palaeoclimatic interpretations is discussed. The sedimentology of laminated couplets comprising yellow and grey silts has been investigated to test the hypothesis that the couplets are varves (i.e. annual rhythmites) comprising alternations of loess and glacial silt and clay. The laminae are mostly less than 1 mm thick and include from bottom to top: (1) a matrix of well-sorted, non-graded fine yellow silt with sand-size intraclasts, (2) coarsening-upward grey silt with a cap of fining-upward silt to clay. The latter is typical for varves in modern proglacial lakes and reflects summer and winter deposits (silt and clay, respectively). We propose that the lack of grading and the matrix supported fabric is indicative of aeolian transport and therefore interpret the yellow laminae as loess deposits. Volcanic glass intraclasts in the loess layers are probably derived from volcanic terrain to the west of the lake, indicating an easterly palaeowind direction. Deposition of loess in the lake occurred regularly at the beginning of each annual cycle, suggesting that the palaeowinds were associated with winter and/or spring conditions. Two transport scenarios are suggested to explain the sand grains scattered in this deep-water lacustrine record. 1. The grains may have been transported as bedload over the annual winter ice-cover of the lake under moderate wind strengths, frozen into the ice, and released for deposition during spring melt. 2. The sand grains were blown directly out onto the lake water by very strong winds during spring. The first scenario is contrary to the general view that loess was transported during summer, and that loess deposits thus reflect summer conditions only. Loess input to the lake shows a transitional decrease after ca. 14.3 kyr BP and cessation at ca. 14 kyr BP, probably as a result of a change of wind behaviour, increased humidity and/or vegetational changes during the Oldest Dryas in central Europe.This paper was presented at Clima Locarno 90, the International Conference on Past and Present Climate Dynamics: Reconstruction of Rates of Change, held in Locarno, Switzerland, September 24 to 28, 1991, supported by a grant from the Swiss Academy of Sciences. It was convened jointly by the Swiss National Climate Program - ProClim, the Swiss Committee for the IGBP, the Swiss COL, the Swiss SCOPE Committee, and the Swiss CCA. Guest editor for the papers published following the conference is Dr. K. Kelts (see also Climate Dynamics 6:3/4, Jan. 1992)  相似文献   

Frequency separation in structure of solar continuum radio bursts     

Hans Rosenberg  Guy Tarnstrom 《Solar physics》1972,24(1):210-214

A plot of frequency separation in fine structure in solar continuum radio bursts against emission frequency indicates that the frequency structure cannot represent local proton plasma frequency modulation. However, the observations are consistent with the interpretation of the frequency structure as harmonics of the local electron cyclotron frequency and lead to reasonable estimates of the ratio between magnetic and kinetic pressures in stable coronal magnetic field configurations producing continuum radio sources.  相似文献   

Precipitation sensitivity to regional SST in a regional climate simulation during the West African monsoon for two dry years     

C. Messager  H. Gallée  O. Brasseur 《Climate Dynamics》2004,22(2-3):249-266

The influence on precipitation of regional sea surface temperature (SST) during a drought period of the West African monsoon is determined, using a regional climate model (RCM). The results from three simulations of two realistic dry years are compared. The first two experiments are initialised and nested respectively in 1983 and 1984 reanalysis data sets. The third experiment is a hybrid simulation of 1983 which is the same as the first experiment except that the SST field is the 1984 SST. Precipitation from the RCM is compared with several precipitation data sets and, as in observations, the RCM reasonably simulates the West African monsoon (seasonal cycle and monsoon sub-period) for the two different years. In particular, the model reproduces stage by stage the motion of the monsoon band well: installation phase, high rain period with abrupt northward shift of the rain band, and the retreat southward phase. Interannual variability and wet or dry tendencies are also represented. The most significant effect of SST is shown by the hybrid simulation, when the regional SST appears as a major factor in the seasonal and interannual monsoon precipitation regime over the African continent (up to 12°N) although this influence is modulated both by the surface conditions (soil and vegetation) and by the reanalysis flow introduced at the lateral boundaries. Dynamically, a warmer SST leads to a decrease in the magnitude of the African Easterly Jet and an increase in northward equivalent water content transport (from equator to 12°N).  相似文献   

Climate change impacts on groundwater resources: modelled deficits in a chalky aquifer,Geer basin,Belgium   总被引：8，自引：4，他引：4  

Serge?BrouyèreEmail author  Guy?Carabin  Alain?Dassargues 《Hydrogeology Journal》2004,12(2):123-134

An integrated hydrological model (MOHISE) was developed in order to study the impact of climate change on the hydrological cycle in representative water basins in Belgium. This model considers most hydrological processes in a physically consistent way, more particularly groundwater flows which are modelled using a spatially distributed, finite-element approach. Thanks to this accurate numerical tool, after detailed calibration and validation, quantitative interpretations can be drawn from the groundwater model results. Considering IPCC climate change scenarios, the integrated approach was applied to evaluate the impact of climate change on the water cycle in the Geer basin in Belgium. The groundwater model is described in detail, and results are discussed in terms of climate change impact on the evolution of groundwater levels and groundwater reserves. From the modelling application on the Geer basin, it appears that, on a pluri-annual basis, most tested scenarios predict a decrease in groundwater levels and reserves in relation to variations in climatic conditions. However, for this aquifer, the tested scenarios show no enhancement of the seasonal changes in groundwater levels.

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Resumen Se ha desarrollado un modelo hidrológico integrado (MOHISE) para estudiar el impacto del cambio climático en el ciclo hidrológico de cuencas representativas en Bélgica. Este modelo considera todos los procesos hidrológicos de forma coherente, especialmente en relación con los flujos de aguas subterráneas, que son modelados por medio de un enfoque de elementos finitos espacialmente distribuidos. Gracias a esta herramienta numérica precisa, y tras una calibración y validación detalladas, se puede obtener interpretaciones cuantitativas de los resultados del modelo del acuífero. Considerando escenarios de cambio climático IPCC, se ha aplicado el enfoque integrado a la evaluación del impacto de dicho cambio climático en el ciclo hidrológico de la cuenca del Geer. Se describe los detalles y resultados del modelo de las aguas subterráneas en términos del impacto del cambio climático en la evolución de las reservas de los acuíferos. Los resultados preliminares indican que es posible esperar déficits de aguas subterráneas en un futuro en Bélgica.

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Résumé Un modèle hydrologique intégré (MOHISE) a été développé afin détudier limpact du changement climatique sur le cycle hydrologique de bassins versants représentatifs de Belgique. Ce modèle prend en compte tous les processus hydrologiques dune manière physiquement consistante, plus particulièrement les écoulements souterrains qui sont modélisés par une approche spatialement distribuée aux éléments finis. Grâce à cet outil numérique précis, après une calibration et une validation détaillées, des interprétations quantitatives peuvent être réalisées à partir des résultats du modèle de nappe. Considérant des scénarios de changements climatiques de lIPCC, lapproche intégrée a été appliquée pour évaluer limpact du changement climatique sur le cycle de leau du bassin du Geer en Belgique. Le modèle de nappe est décrit en détail et les résultats sont discutés en terme dimpact du changement climatique sur lévolution des réserves souterraines. Les premiers résultats indiquent que des déficits deau souterraine peuvent apparaître dans le futur en Belgique.

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Arsenic contamination of groundwater: Mitigation strategies and policies     

Guy?J.?AlaertsEmail author  Nadim?Khouri 《Hydrogeology Journal》2004,12(1):103-114

Contamination of groundwater by arsenic from natural geochemical sources is at present a most serious challenge in the planning of large-scale use of groundwater for drinking and other purposes. Recent improvements in detection limits of analytical instruments are allowing the correlation of health impacts such as cancer with large concentrations of arsenic in groundwater. However, there are at present no known large-scale technological solutions for the millions of people—mostly rural—who are potentially affected in developing countries. An overall framework of combating natural resource degradation is combined with case studies from Chile, Mexico, Bangladesh and elsewhere to arrive at a set of strategic recommendations for the global, national and local dimensions of the arsenic crisis. The main recommendations include: the need for flexibility in the elaboration of any arsenic mitigation strategy, the improvement and large-scale use of low-cost and participatory groundwater quality testing techniques, the need to maintain consistent use of key lessons learned worldwide in water supply and sanitation and to integrate arsenic as just one other factor in providing a sustainable water supply, and the following of distinct but communicable tracks between arsenic-related developments and enhanced, long-term, sustainable water supplies.

Guy J. AlaertsEmail: Phone: +1-202-4588911

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Chemical response of the middle atmosphere to solar variations     

P. De Baets  G. Brasseur  P. C. Simon 《Solar physics》1981,74(2):349-353

The possible variation of the trace species concentration in the middle atmosphere related to long term solar irradiance variability is estimated by means of a one-dimensional numerical model.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.Aspirant au Fonds National de la Recherche Scientifique.  相似文献   

Structuring factors and recent changes in subtidal macrozoobenthic communities of a coastal lagoon, Arcachon Bay (France)     

Hugues Blanchet  Xavier de Montaudouin  Pierre Chardy  Guy Bachelet 《Estuarine, Coastal and Shelf Science》2005,64(4):561-576

Sediment stability in the shallow Venice Lagoon was investigated by means of numerical modelling. Results from a hydrodynamic model allowed for the determination of the wave climate and bottom effective parameters so that simulations with a Lagrangian model for suspended particulate matter could be performed. A spring–neap cycle in summer 1998 was chosen as integration period since data for calibration and verification were collected within the European project F-ECTS between summer 1998 and spring 1999. Deposition on shallow mud flats as well as short term erosion during a strong wind event were reproduced and mass balances for two areas computed. A relation of patterns of SPM in the water and in the sediment was found and can be ascribed to the displacement of material during storm events from shallow areas to the bottom of very small channels. Assuming about 10 to 14 storm events during the year comparable to the Bora event during the integration time, estimates for long-term trends of sediment loss on shallow flats by Day et al. [Day, J.W., Rybczyk, J., Scarton, F., Rismondo, A., Are, D., Cecconi, G., 1999. Soil accretionary dynamics, sea-level rise and the survival of wetlands in Venice Lagoon: a field and modelling approach. Estuarine, Coastal and Shelf Science 49, 607–628] are met by the simulation results. Evidently, long-term sediment evolution of the lagoon is therefore not dominated by the average (residual) processes that occur in the lagoon, but by the few peak events that happen randomly over the year.  相似文献   

Effect of the 11-year cycle of solar activity on characteristics of the total ozone annual variation     

A. N. Gruzdev  G. P. Brasseur 《Izvestiya Atmospheric and Oceanic Physics》2007,43(3):344-356

The goal of the paper is an analysis of changes in the amplitude and phase characteristics of the annual variation (AC) of total ozone (TO) from ground-based and satellite (TOMS) measurements and their interpretation with a two-dimensional photochemical model. According to ground-based TO measurements, two characteristic types of quasi-decadal variations in the phase of the annual harmonic (AH) of total ozone have been noted: variations in phase and antiphase with solar activity (SA). Changes in the TO AH phase opposite to solar activity variation are noted the high latitudes of the North Atlantic region and in the tropical belt, and in-phase changes are observed in the middle and subtropical latitudes of both hemispheres. Variations in the TO AH amplitude (hence, in the TO AV amplitude) and in the annual mean TO usually coincide in phase with the SA cycle. Analysis of satellite data shows that the 0-phase of the AV and the phase of the AH of the zonal mean TO at middle latitudes vary synchronously with the 11-year solar cycle. Model simulations have shown that the stratospheric ozone influx to the middle latitudes increases in the fall and winter period during a period of maximum solar activity. This dynamic mechanism accounts for up to 30% of the winter ozone increase in the ozone maximum layer in the Southern Hemisphere midlatitudes during the solar maximum as compared with the solar minimum. In the northern midlatitudes, the dynamic mechanism makes the main contribution to ozone changes during the latter half of winter under SA variations. The stratospheric ozone inflow change induced by SA variations affects the annual variation of ozone.  相似文献   

Geological interpretation of combined SEABEAM,GLORIA and seismic data from Porto and Vigo Seamounts,Iberian continental margin     

Denis Mougenot  Robert B. Kidd  Alain Mauffret  Hervé Regnauld  R. Guy Rothwell  Jean-René Vanney 《Marine Geophysical Researches》1984,6(4):329-363

Long-range sidescan sonar (GLORIA) data over Porto and Vigo Seamounts collected in 1978 has been re-interpreted in the light of SEABEAM bathymetric surveys conducted in 1982. The application of quantitative bathymetric information enables the interpreter to allow for artefacts inherent in the GLORIA data and to separate topography-related primary backscattering variations on the sonographs from more subtle changes that result from textural, slope and outcrop effects. The distinctions are made easier when slant-range corrected GLORIA data are available.Use of the combined survey data to precisely locate seismic profiling tracks and to identify likely areas of outcrop has allowed refined geological maps of the seamounts to be drawn and regional fault trends detected. The overall outline of the seamounts appears strongly fault-controlled.Porto and Vigo Seamounts are made up of the same geological formations and have had a similar structural history since their uplift as continental fault blocks in the Late Cretaceous to Middle Eocene period. Ravines that dissect the presumably lithified scarps bounding the seamounts may be relict features but still appear to control sediment input to gulley and channel systems in the surrounding topography. Sedimentary ridges associated with the seamounts represent anomalously thick sequences of post-Eocene material and probably result from interaction of downslope sedimentary processes and contour-following boundary currents.Contribution No. 274 from the Groupe d'Etude de la Marge Continentale (ERA 605).  相似文献   

Seasonal variations in dimethylsulfoniopropionate and dimethylsulfide concentrations in relation to the plankton community in the St. Lawrence Estuary   总被引：1，自引：1，他引：1  

Sonia Michaud  Maurice Levasseur  Guy Cantin   《Estuarine, Coastal and Shelf Science》2007,71(3-4):741-750

Weekly variations in total dimethylsulfoniopropionate (DMSPt) and dimethylsulfide (DMS) were investigated in relation to the phytoplankton assemblage from spring to fall 1994 at a coastal fixed station in the St. Lawrence Estuary. DMSPt and DMS concentrations showed a strong seasonality and were tightly coupled in time. Maximum concentrations of DMSPt and DMS were observed in July and August, during a period of warm water and low nutrient concentrations. Seasonal maxima of 365.4 nmol l⁻¹ for DMSPt and 14.2 nmol l⁻¹ for DMS in early August coincided with the presence of many phytoplankton species, such as Alexandrium tamarense, Dinophysis acuminata, Gymnodinium sp., Heterocapsa rotundata, Protoperidinium ovatum, Scrippsiella trochoidea, Chrysochromulina sp. (6 μm), Cryptomonas sp. (6 μm), a group of microflagellates smaller than 5 μm (mf < 5), many tintinnids, and Mesodinium rubrum. The abundance of mf < 5 followed the general trend of DMS concentrations. The temporal occurrence of high P. ovatum abundance and DMSPt concentrations suggests that this heterotrophic dinoflagellate can either synthesize DMSP or acquire it from DMSP-rich prey. The calculated sea-to-air DMS flux reached a maximum of 8.36 μmol ⁻² d⁻¹ on August 1. The estimated annual emission from the St. Lawrence Estuary is 77.2 tons of biogenic sulfur to the atmosphere.  相似文献