Distribution of carbon in a tropical hypersaline estuary,the Casamance (Senegal,West Africa)     

J. Pagès  J. Lemoalle  B. Fritz 《Estuaries and Coasts》1995,18(3):456-468

The Casamance estuary, on the coast of Senegal, is an inverse hypersaline estuary: salinity increases landward, and dry season salinity values are up to 172 psu due to the evaporation of seawater. Dissolved inorganic carbon (DIC) concentrations decreased landward as a negative linear function of salinity. Thermodynamic modelling and the absence of CaCO₃ in the sediments indicate that this loss of DIC was not due to calcite precipitation in the main water body. The innermost, almost landlocked, waters contained high phytoplankton biomass (50–300 μg chl I^?1) and high concentrations of allochthonous dissolved organic carbon. Photosynthetic uptake of DIC and subsequent particulate organic carbon sedimentation is proposed as hypothetical explanation of the relationship between DIC and salinity; localized overheating in shallow waters might also be involved.  相似文献   

Water quality in rivers of western Switzerland: Application of an adaptable index based on benthic invertebrates   总被引：1，自引：0，他引：1  

Claude Lang  Geneviève l'Eplattenier  Olivier Reymond 《Aquatic Sciences - Research Across Boundaries》1989,51(3):224-234

Water quality was estimated from 205 samples of benthic invertebrates collected between 1982 and 1986 in 51 rivers of western Switzerland (canton of Vaud). Each sample consisted of the combined list of taxa resulting from one spring sample pooled with one summer sample. Water quality was indicated by total number of taxa and number of taxa intolerant of pollution: i. e. Heptageniidae, Plecoptera, and Trichoptera with a case. Six classes of values were delimited for each of these two variables by cluster analysis. Values from zero to five were attributed to each class. The index of water quality was computed by adding these two values in each sample. According to this index, good water quality was indicated by 42% of samples. This index can be adapted to other rivers because its components are easily modified.  相似文献   

Constraints on the formation of cyclic units in ultramafic zones of large basaltic chambers     

Geneviève Brandeis 《Contributions to Mineralogy and Petrology》1992,112(2-3):312-328

Petrological models for the formation of cyclic units in ultramafic zones at the base of large mafic layered intrusions are still few and simple. In this study, we develop simple physical constraints, such as the volume balance and density relationships between the various liquids involved. We consider the formation of an entire ultramafic zone, made of N cyclic units due to N successive reinjections. We tackle the following problems. Are all the injections of the same chemical composition? Are the N injections responsible for the formation of the whole magma chamber? Two end-member models are examined. In the first one, the chamber grows with each injection and does not lose any magma (variable volume model, VV). In the second one, the chamber initially forms with a large volume of magma and remains at a constant volume with subsequent reinjections of small volumes balanced by eruptions of equal volume (fixed volume model, FV). Several scenarios for the formation of a cyclic unit are envisioned. Petrological data such as thicknesses of the cumulate layers and their compositions, together with the fractionation density of the cumulate phases, allow the calculation of the density evolution, as a function of the initial density only. Thus, the model yields constraints on the density of the initial liquid, and hence on its chemical composition. The volumes of the injected magmas are calculated as well as the evolution of the densities of the different involved liquids. We apply the calculation to the specific case of the Ultramafic Series of the Stillwater complex. The multiple reinjection models require that the initial liquids densities vary between 2.71 and 2.72 g/cm³, corresponding to MgO-rich liquids for which there is no field evidence, either in dikes or in chilled margins. They also require that the source produces liquids of different chemical composition. Thus, the evolution of the igneous system requires another, larger reservoir where differentiation takes place prior to injection into the shallower one. Contrary to the multiple reinjection models, a closed system model where crystallization proceeds in an isolated bottom layer does not require any specific value of density for the liquids, provided, of course, that it is of basaltic composition. On the negative side, such a model is not supported by any physical processes which would account for the formation of cyclic units.  相似文献   

The dynamic cusp at low altitudes: a case study utilizing Viking,DMSP-F7, and Sondrestrom incoherent scatter radar observations     

J. Watermann  O. de la Beaujardière  D. Lummerzheim  J. Woch  P. T. Newell  T. A. Potemra  F. J. Rich  M. Shapshak 《Annales Geophysicae》1994,12(12):1144-1157

Coincident multi-instrument magnetospheric and ionospheric observations have made it possible to determine the position of the ionospheric footprint of the magnetospheric cusp and to monitor its evolution over time. The data used include charged particle and magnetic field measurements from the Earth-orbiting Viking and DMSP-F7 satellites, electric field measurements from Viking, interplanetary magnetic field and plasma data from IMP-8, and Sondrestrom incoherent scatter radar observations of the ionospheric plasma density, temperature, and convection. Viking detected cusp precipitation poleward of 75.5○ invariant latitude. The ionospheric response to the observed electron precipitation was simulated using an auroral model. It predicts enhanced plasma density and elevated electron temperature in the upper E- and F-regions. Sondrestrom radar observations are in agreement with the predictions. The radar detected a cusp signature on each of five consecutive antenna elevation scans covering 1.2 h local time. The cusp appeared to be about 2○ invariant latitude wide, and its ionospheric footprint shifted equatorward by nearly 2○ during this time, possibly influenced by an overall decrease in the IMF B_z component. The radar plasma drift data and the Viking magnetic and electric field data suggest that the cusp was associated with a continuous, rather than a patchy, merging between the IMF and the geomagnetic field.  相似文献   

A comparison between transilient turbulence theory and the exchange coefficient model approaches     

J. Cuxart  P. Bougeault  P. Lacarrère  J. Noilhan  M. R. Soler 《Boundary-Layer Meteorology》1994,67(3):251-276

The transilient turbulence model of Stull and Driedonks (1987) and the exchange coefficient model of Bougeault and Lacarrère (1989) are intercompared on four convective days of the HAPEX-MOBILHY experiment. We show that the numerical formulations of the models are very close to each other, despite their totally different theoretical backgrounds. Both models describe the mixing effect of the turbulence via matrices having the same general characteristics. The results of the models are also found to be very similar in general, although the transilient approach requires more computations. Some systematic differences are noted and discussed in detail. We argue that similar work should be conducted on non-convective cases before deciding on the superiority of one or the other approach.  相似文献   

La Tramontane et le Mestral de la Côte Catalane     

E. Fontserè 《Theoretical and Applied Climatology》1949,1(2):127-137

Résumé Pendant la moitié froide de l'année, le grand courant atmosphérique qui la plupart des jours se dirige du Golfe de Biscaye vers la Méditerranée est divisé près du sol en deux branches par les Pyrenées et par la dépression intérieure catalane, alors très froide, de sorte que dequis Blanes jusqu'à Vilanova on ne trouve généralement que des vents locaus. L'une de ces branches, après avoir parcouru le midi de la France jusqu'au Roussillon, pénètre en Catalogne en sautant sur les Albères sous la forme de vent du NNW (tramontane); l'autre suit le bassin de l'Èbre et débouche en mer comme un vent du NW (mestral). Ces deux vents deviennent parfois très violents en Ampourdan et au SE de la Serra de Balaguer, où ils constituent alors des cataractes furieuses d'air sec qui se précipitent vers la mer et qui sont dangereuses pour les petits bateaux pêcheurs et pénibles pour l'aviation. Leur violence, leur siccité et les nuages orographiques qu'ils produisent, font ranger ces deux vents parmi les phénomènes côtiers les plus notables.

---

Summary During the cold months, the great atmospheric current which most of the time goes from the Gulf of Biscay to the Mediterranean sea is divided in its lower layers in two branches by the Pyrenees and the central Catalonian depression, which in this season is very cold. Therefore the zone between Blanes and Vilanova is a protected one, with local winds only. One of the current branches runs over the souther parts of France until the Roussillon, and leaping over the frontier mountains of the Alberes enters in Catalonia as a NNW wind (tramontana). The other branch runs over the Ebro depression and reaches the Mediterranean as a NW wind (mestral). Frequently these two winds become furious at the Ampourdan and at the leeward of the Serra de Balaguer, where they fall down to the sea as cataracts of dry air, violent enough to be dangerous for the fishing boats and troublesome for the aircraft. Their violence, their dryness and the orographic clouds that they produce, place these winds amongst the most conspicuous coastal phenomena.

---

Zusammenfassung Während der kalten Jahreshälte wird die große Luftströmung, die an der Mehrzahl der Tage vom Golf von Biskaya gegen das Mittelmeer weht, durch die Pyrenäen und die zu dieser Zeit sehr kalte innerkatalanische Senke in zwei Arme geteilt, während von Blanes bis Vilanova im allgemeinen nur lokale Winde auftreten. Der eine dieser Arme durchströmt Südfrankreich bis ins Roussillon, überschreitet die östlichen Pyrenäenausläufer (Alberes) und dringt als NNW-Wind in Katalonien ein (Tramontana); der andere folgt dem Ebrobecken und mündet als NW-Wind auf das Meer (Mestral). Beide Winde werden manchmal sehr heftig, der erste im Ampurdan (der nordöstlichen Ecke Kataloniens), der zweite südöstlich der Serra de Balaguer (nordöstlich Tortosa), wo sie einen wilden Katarakt trockener Luft bilden, der sich auf das Meer hinabstürzt und für die kleinen Fischerboote gefährlich und für die Aviatik beschwerlich ist. Durch ihre Heftigkeit, ihre Trockenheit und die von ihnen gebildeten Hinderniswolken gehören diese Winde zu den bemerkenswertesten Küstenerscheinungen.

---

---

Avec 7 figures.  相似文献   

The Gulf of Cadiz: an unstable giant contouritic levee   总被引：1，自引：0，他引：1  

T. Mulder  M. Voisset  P. Lecroart  E. Le Drezen  E. Gonthier  V. Hanquiez  J.-C. Faugères  E. Habgood  F. J. Hernandez-Molina  F. Estrada  E. Llave-Barranco  D. Poirier  C. Gorini  Y. Fuchey  A. Voelker  P. Freitas  F. Lobo Sanchez  L. M. Fernandez  N. H. Kenyon  J. Morel 《Geo-Marine Letters》2003,23(1):7-18

Recent multibeam bathymetry and acoustic imagery data provide a new understanding of the sedimentary system located in the Gulf of Cadiz which is under the influence of a strong current, the Mediterranean Outflow Water (MOW). When it comes out from the Strait of Gibraltar, the MOW is either channelled along major or secondary channels, or spills over a sedimentary levee. Frequent earthquakes and the constant current shearing generate widespread sediment deformation and instability of contourite deposits. Secondary channels can form by retrogression following an initial failure. At their mouth, sediment accumulates in the form of small sandy contourite lobes. These observations suggest that the Gulf of Cadiz system shares many similarities with channel–levee complexes formed by turbidity current activity. The main difference is that, in the Gulf of Cadiz, the main process is a strongly flowing saline current which locally interacts with gravity processes.  相似文献   

Identifying drivers for fishing pressure. A multidisciplinary study of trawl and sea snail fisheries in Samsun,Black Sea coast of Turkey     

Ståle Knudsen  Mustafa Zengin  Mahmut Hakan Koçak 《Ocean & Coastal Management》2010,53(5-6):252-269

This study aims to investigate and model driving forces that lead to increased fishing pressure and an altered state of the environment in the coastal areas near Samsun on the Turkish Black Sea coast. We have applied a modified DPSIR model to structure our investigation and analysis and have investigated the drivers that generate fishing pressure in the Samsun fisheries. The overall health of the ecosystem is declining, and there is a consistent trend of deterioration in the condition of the three major species targeted by the trawl fisheries. Although introduced invasive species have brought significant changes to the Black Sea, it is clear that the state of the environment is significantly and negatively affected by the pressure exerted by fisheries. Fishing pressure has to a certain extent been redirected to pelagic trawling as bottom trawling has become less profitable and a rise in catch capacity has levelled off. This reduction is, however, offset by an increase in illegal trawling and dredging by a very rapidly growing sector of multi-purpose small boats, resulting in a considerable increase in the overall accumulated engine power of fishing boats in Samsun during 2000–2005. Fisheries in Samsun, in particular sea snail fisheries, have constituted a frontier of sorts open to the poorer populations of Samsun during the last 20 years, and, thereby, constitute one of the major drivers for fishing pressure. We identify eight drivers of importance for the period 2000–2005. Although the authorities can impact all or most of those drivers, most of them are beyond the scope of conventional ‘fisheries management’.  相似文献   

Combined climatic and geological forcings on the spatio-temporal variability of piezometric levels in the chalk aquifer of Upper Normandy (France) at pluridecennal scale     

Smail Slimani  Nicolas Massei  Johanna Mesquita  Danièle Valdés  Matthieu Fournier  Benoît Laignel  Jean-Paul Dupont 《Hydrogeology Journal》2009,17(8):1823-1832

The temporal variability of water-level fluctuations in the chalk aquifer of Upper Normandy, France is constrained by natural climate fluctuations and is closely linked to the regional geological patterns. The chalk plateaus are covered with 5–50 m thick semi-permeable surficial formations; the thickness of the underlying chalk aquifer varies from 50 to 300 m. The relationship among climate oscillations, piezometric levels, and geologic structure were investigated by correlation, Fourier spectral, and continuous wavelet analyses of selected piezometric time-series data. Analysis focused on two piezometers located on the uplifted side of a major fault and two piezometers on the downthrown side. After generalization to other piezometers in the region, it was deduced that, in the downthrown compartments, a substantial aquifer and surficial formations thickness would imply a strong attenuation of annual variability, while multi-year variability is clearly expressed. Conversely, in the uplifted compartments, a thin layer of surficial formations and small thickness of the chalk authorizes strong variations on the annual mode with respect to the contribution of long-term climatic oscillations (multi-year variability). The results then demonstrated—and proposed a spatial determination of—the differential influence of geological patterns on the filtering of climate-induced oscillations in piezometric variability.  相似文献   

Improvements in Digestion Protocols for Trace Element and Isotope Determinations in Stream and Lake Sediment Reference Materials (JSd-1, JSd-2, JSd-3, JLk-1 and LKSD-1)     

Sidonie Révillon  Danièle Hureau-Mazaudier 《Geostandards and Geoanalytical Research》2009,33(3):397-413

Total dissolution is a critical step in geochemical analysis. Despite the number of published protocols, this issue still draws attention for sediment samples, which are particularly difficult to dissolve due to the common occurrence and high abundance of refractory phases such as zircon. We present tests of different chemical digestion procedures carried out on reference materials (RM) of stream (JSd-1, JSd-2 and JSd-3) and lake (JLk-1 and LKSD-1) sediments from the Geological Survey of Japan (GSJ) and the Canadian Certified Reference Material Programme (CCRPM). We demonstrate that the fusion technique is not appropriate for our studies as not all elements of interest were recovered and blank levels were too high to permit further Sr and Pb isotopic composition measurements. Similarly, conventional HF+HNO₃ dissolution methods were not efficient enough for detrital samples. Our preferred method involved using high pressure Teflon® vessel bombs in association with HClO₄. This protocol ensured a complete dissolution of the powder, as well as a complete recovery of trace elements. Moreover, blank levels were sufficiently low that Sr or Pb isotope compositions could be measured from the same mother solution. We also tested the homogeneity of RM powders by performing tests on various amount of powder.  相似文献