Les Diatomées de la Tourbière du Cachot (Jura neuchâtelois)     

Dr. Marguerite Wuthrich  Prof. Dr Willy Matthey 《Aquatic Sciences - Research Across Boundaries》1980,42(2):269-284

By means of 18 traps, 124 species (including 4 fossil ones) with a total of 3.5×10⁵ cells/m² have been identified an determined as transported by wind. 119 species have been detected on the feet and bills of waterbirds (Gallinago gallinago). Large migratory insects are capable of transporting diatoms over long distances, whereas small insects partake in the microdistribution. An average of 13.5 diatoms per insect (43 diatom species) were found on 44 insects.  相似文献   

Contrasting patterns of precipitation seasonality during the Holocene in the south‐ and north‐central Mediterranean     

Michel Magny  Odile Peyron  Laura Sadori  Elena Ortu  Giovanni Zanchetta  Boris Vannière  Willy Tinner 《第四纪科学杂志》2012,27(3):290-296

Pollen‐based quantitative estimates of seasonal precipitation from Lake Pergusa and lake‐level data from Lake Preola in Sicily (southern Italy) allow three successive periods to be distinguished within the Holocene: an early Holocene period before ca. 9800 cal a BP with rather dry climate conditions in winter and summer, a mid‐Holocene period between ca. 9800 and 4500 cal a BP with maximum winter and summer wetness, and a late Holocene period after 4500 cal a BP with declining winter and summer wetness. This evolution observed in the south‐central Mediterranean shows strong similarities to that recognized in the eastern Mediterranean. But, it contrasts with that reconstructed in north‐central Italy, where the mid‐Holocene appears to be characterized by a winter (summer) precipitation maximum (minimum), while the late Holocene coincided with a decrease (increase) in winter (summer) precipitation. Maximum precipitation at ca. 10 000–4500 cal a BP may have resulted from (i) increased local convection in response to a Holocene insolation maximum at 10 000 cal a BP and then (ii) the gradual weakening of the Hadley cell activity, which allowed the winter rainy westerlies to reach the Mediterranean area more frequently. After 4500 cal a BP, changes in precipitation seasonality may reflect non‐linear responses to orbitally driven insolation decrease in addition to seasonal and inter‐hemispheric changes of insolation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

A Close Look at Satloc's Real-Time WADGPS System     

Michael L. Whitehead  Gary Penno  Walter J. Feller  Ivan C. Messinger  Willy I. Bertiger  Ronald J. Muellerschoen  Byron A. Iljima  Greg Piesinger 《GPS Solutions》1998,2(2):46-63

  相似文献   

Distribution and Sources of Carbon,Nitrogen and Their Isotopic Compositions in Tropical Estuarine Sediments of Mtoni,Tanzania     

Mihale  Matobola Joel  Tungaraza  Clavery  Baeyens  Willy  Brion  Natacha 《Ocean Science Journal》2021,56(3):241-255

Ocean Science Journal - Elemental (C, N) and isotopic (δ13C, δ15N) signatures were used as proxies to identify seasonal changes in proportions of sedimentary organic matter (OM) in the...  相似文献   

Analysis of decade-long time series of GPS-based polar motion estimates at 15-min temporal resolution     

Aurore E. Sibois  Shailen D. Desai  Willy Bertiger  Bruce J. Haines 《Journal of Geodesy》2017,91(8):965-983

We present results from the generation of 10-year-long continuous time series of the Earth’s polar motion at 15-min temporal resolution using Global Positioning System ground data. From our results, we infer an overall noise level in our high-rate polar motion time series of 60 \(\upmu \hbox {as}\) (RMS). However, a spectral decomposition of our estimates indicates a noise floor of 4 \(\upmu \hbox {as}\) at periods shorter than 2 days, which enables recovery of diurnal and semidiurnal tidally induced polar motion. We deliberately place no constraints on retrograde diurnal polar motion despite its inherent ambiguity with long-period nutation. With this approach, we are able to resolve damped manifestations of the effects of the diurnal ocean tides on retrograde polar motion. As such, our approach is at least capable of discriminating between a historical background nutation model that excludes the effects of the diurnal ocean tides and modern models that include those effects. To assess the quality of our polar motion solution outside of the retrograde diurnal frequency band, we focus on its capability to recover tidally driven and non-tidal variations manifesting at the ultra-rapid (intra-daily) and rapid (characterized by periods ranging from 2 to 20 days) periods. We find that our best estimates of diurnal and semidiurnal tidally induced polar motion result from an approach that adopts, at the observation level, a reasonable background model of these effects. We also demonstrate that our high-rate polar motion estimates yield similar results to daily-resolved polar motion estimates, and therefore do not compromise the ability to resolve polar motion at periods of 2–20 days.  相似文献   

Using Two-Point Set Statistics to Estimate the Diameter Distribution in Boolean Models with Circular Grains     

Xavier Emery  Willy Kracht  álvaro Ega?a  Felipe Garrido 《Mathematical Geosciences》2012,44(7):805-822

This paper deals with the counting and measuring of overlapping circular objects in binary images, a problem that arises in the mineral processing industry when estimating the distribution of bubble diameters in flotation cells in order to predict the geometallurgical performance of the flotation process. By viewing the images as realizations of a stationary planar Boolean model with circular grains and by using two-point set statistics, it is possible to jointly estimate the average number of objects per unit area and their diameter distribution. When applied to real and simulated images, this method is shown to give accurate estimates, to be robust to the presence of noise contaminating the images and of moderate drifts in the number of objects per unit area, and to speed up the processing time with respect to currently used methods. Combined, these properties serve to make the method suitable for an on-line monitoring of the flotation process.  相似文献   

Elemental mercury concentrations and formation rates in the Scheldt estuary and the North Sea     

W. Baeyens  M. Leermakers 《Marine Chemistry》1998,60(3-4)

Concentrations of Hg⁰ in surface waters and atmosphere of the Scheldt estuary and the North Sea are presented and their relationship with biological processes is discussed. Hg⁰ concentrations in the Scheldt estuary range from 0.1 to 0.38 pmol·l⁻¹ in the winter and from 0.24 to 0.65 pmol·l⁻¹ in the summer and show a positive relationship with phytoplankton pigments. In the North Sea Hg⁰ concentrations range from 0.06 to 0.8 pmol·l⁻¹ and are higher in coastal stations. Transfer velocities across the air–sea interface were calculated using a classical shear turbulence model. Volatilization fluxes of Hg⁰ were calculated for the Scheldt estuary and the North Sea. For the Scheldt estuary the fluxes range from 226–284 pmol·m⁻²·d⁻¹ in winter and 500–701 pmol·m⁻²·d⁻¹ in summer and for the North Sea the fluxes range from 59–1110 pmol·m⁻²·d⁻¹ for an average windspeed of 8.1 m·s⁻¹. These fluxes are comparable to the wet and dry depositional fluxes to the North Sea. Hg⁰ formation rates necessary to balance the volatilization fluxes vary from 0.2 to 4% d⁻¹.  相似文献   

Holocene vegetation and fire dynamics in the supra‐mediterranean belt of the Nebrodi Mountains (Sicily,Italy)     

Martina Bisculm  Daniele Colombaroli  Elisa Vescovi  Jacqueline F. N. van Leeuwen  Paul D. Henne  Julian Rothen  Giovanni Procacci  Salvatore Pasta  Tommaso La Mantia  Willy Tinner 《第四纪科学杂志》2012,27(7):687-698

High‐resolution pollen, macrofossil and charcoal data, combined with accelerator mass spectrometry ¹⁴C dating and multivariate analysis, were used to reconstruct Holocene vegetation and fire dynamics at Urio Quattrocchi, a small lake in the supra‐mediterranean belt in the Nebrodi Mountains of Sicily (Italy). The data suggest that after 10 000 cal a BP increasing moisture availability supported closed forests with deciduous (Quercus cerris, Fagus sylvatica and Fraxinus spp.) and evergreen (Quercus ilex) species. Species‐rich closed forest persisted until 6850 cal a BP, when Neolithic activities caused a forest decline and affected plant diversity. Secondary forest with abundant Ilex aquifolium recovered between 6650 and 6000 cal a BP, indicating moist conditions. From 5000 cal a BP, agriculture and pastoralism led to the currently fragmented landscape with sparse deciduous forests (Quercus cerris). The study suggests that evergreen broadleaved species were more important at elevations above 1000 m a.s.l. before ca. 5000 cal a BP than subsequently, which might reflect less human impact or warmer‐than‐today climatic conditions between 10 000 and 5000 cal a BP. Despite land use since Neolithic times, deciduous supra‐mediterranean forests were never completely displaced from the Nebrodi Mountains, because of favourable moist conditions that persisted throughout the Holocene. Reconstructed vegetation dynamics document the absence of any pronounced mid‐ or late‐Holocene ‘aridification’ trend at the site, an issue which is controversially debated in Italy and the Mediterranean region. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Prevention of oil spill from shipping by modelling of dynamic risk   总被引：1，自引：0，他引：1  

Eide MS  Endresen O  Breivik O  Brude OW  Ellingsen IH  Røang K  Hauge J  Brett PO 《Marine pollution bulletin》2007,54(10):1619-1633

This paper presents a new dynamic environmental risk model, with intended use within a new, dynamical approach for risk based ship traffic prioritisation. The philosophy behind this newly developed approach is that shipping risk can be reduced by directing efforts towards ships and areas that have been identified as high priority (high risk), prior to a potential accident. The risk model proposed in this paper separates itself from previous models by drawing on available information on dynamic factors and by focusing on the ship's surroundings. The model estimates the environmental risk of drift grounding accidents for oil tankers in real time and in forecast mode, combining the probability of grounding with oil spill impact on the coastline. Results show that the inherent dynamic risk introduced by an oil tanker sailing along the North Norwegian coast depends, not surprisingly, significantly upon wind and ocean currents, as well as tug position and cargo oil type. Results of this study indicate that the risk model is well suited for real time risk assessment, and effectively separates low risk and high risk situations. The model is well suited as a tool to prioritise oil tankers and coastal segments. This enables dynamic risk based positioning of tugs, using both real-time and projected risk, for effective support in case of a drifting ship situation.  相似文献   

Elemental and organic carbon in atmospheric aerosols at downtown and suburban sites in Prague   总被引：1，自引：0，他引：1  

Jaroslav Schwarz  Xuguang Chi  Willy Maenhaut  Martin Civi&#x;  Jan Hovorka  Ji&#x;í Smolík 《Atmospheric Research》2008,90(2-4):287-ICNAA07

Organic and elemental carbon (OC and EC) content in PM₁₀ was studied at two sites in Prague, which were located in a suburb and in the downtown. Similar overall average levels were found for both species and also for the PM₁₀ mass at the two sites (i.e., 5.5 and 4.8 μg/m³ for OC, 0.74 and 0.80 μg/m³ for EC, and 33 μg/m³ and 37 μg/m³ for the PM₁₀ mass at the suburb and downtown site, respectively), but substantial differences were observed between the two sites in some seasons and/or meteorological situations. Approximately three times higher values were found for OC in winter compared to summer, with a higher winter/summer ratio for the suburban site. The differences for EC were smaller, but still, compared to summer, more than two times higher EC levels were observed during autumn at the suburban site and 1.5 higher EC levels in winter and autumn at the downtown site. The lowest OC to EC ratios at the suburban site were 3.4, while they were around 1.3 for the downtown site. It was found that the origin of the air masses had a major impact on the observed PM₁₀ mass and OC levels, with largest concentrations noted for air masses recirculating over central Europe and arriving from southeastern Europe in winter. Trajectories coming from the west and northwest originating above the Atlantic Ocean and the Artic brought the cleanest air masses to the sites. For EC the largest difference between the two sites was observed for northwesterly winds during the non-heating season when the suburban site was upwind of Prague.  相似文献