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81.
Nathaniel Bensoussan Jean-Claude Romano Bouazza El-Haikali Michel-Guy Lafont 《Comptes Rendus Geoscience》2004,336(10):909-918
Semi-continuous (1/30 min) records of physicochemical parameters (T,S, DO and pH) have been measured at 1.50 m in Mediterranean coastal waters (Marseilles) from 1998 to 2000, together with meteorological parameters. Physicochemical data were studied in order to synthesise the information at different time scales (inter-annual, season, day, hour), particularly the semi-conservative DO and pH response to hydroclimatic variables. At a daily time scale, important circadian dynamic has been measured under all circumstances with a strong reactivity to irradiance change under the influence of biological activity. This work may contribute to the definition of new tools for coastal waters observation. To cite this article: N. Bensoussan et al., C. R. Geoscience 336 (2004). 相似文献
82.
Jean-Claude Dionne 《Geomorphology》1988,1(4)
Ploughing boulders are defined as large stones moved by drift ice with a ploughing action into the substrate, leaving a linear depression on the back and building a frontal push ridge. They are commonly found on unconsolidated tidal flats and on rock shore platforms along cold-region shorelines in the marine, lacustrine and fluvial environments. It is an erosional process of great significance, particularly for consolidated substrates. A total of 176 ploughing boulders were measured in eighteen localities along the St. Lawrence estuary. The largest boulder weighed 176 tons and was moved 3 m, while a 50 t boulder was moved 40 m. On shore platforms cut in shales, one boulder 49 t, has scoured a depression 19 m long and up to 40 cm deep, and built a frontal ridge 40 cm high. Along the St. Lawrence estuary about 95 of ploughing boulders were moved seaward by ice floes entrained by ebb currents. 相似文献
83.
Jean-Claude Bader Gilles Belaud Jean-Pierre Lamagat Thibaud Ferret Philippe Vauchel 《水文科学杂志》2017,62(3):447-466
In the Senegal River valley and Niger Inner Delta, the annual floods inundate a wide floodplain consisting of a complex network of lakes and channels, where topographic information needed by standard hydraulic models is difficult to obtain. To represent the flood propagation between mainstream and floodplain, we use a model designed for flood propagation in river mainstreams with flat bed and large overflow and without topographic data. Depending on the water level in the riverbed, the model calibrated on the levels observed at two stations gives the level in the floodplains and propagation time between stations. Several cases are tested for various types of hydraulic connections between mainstream and floodplain. The model could correctly reproduce the flood rise and fall in the floodplain, even for a lake connected by a single channel to the riverbed or in the case of a strong attenuation of the flood between very distant stations. 相似文献
84.
Rémi de Matos-Machado Jean-Pierre Toumazet Jean-Claude Bergès Jean-Paul Amat Gilles Arnaud-Fassetta François Bétard Clélia Bilodeau Joseph P. Hupy Stéphanie Jacquemot 《地球表面变化过程与地形》2019,44(7):1430-1448
Acting as efficient earth-movers, soldiers can be viewed as significant geomorphological drivers of landscape change when replaced in the recent debates on Anthropocene Geomorphology. ‘Polemoforms’, generated by military activities, correspond with a set of human-made landforms of various sizes and geometries. They are particularly common on the World War One battlefield of Verdun (France) which ranks among the largest battles of attrition along the Western Front. The artillery bombardments and building of defensive positions in that battle significantly altered the landscape, resulting in thousands of shell craters, dugouts, and gun positions that have altered both the meso and microtopography. This paper proposes an innovative methodology to make an exhaustive inventory of these small-scale conflict-induced landforms (excluding linear features such as trenches) using a digital terrain model (DTM) acquired by airborne LiDAR on the whole battlefield. Morphometric analysis was conducted using Kohonen's self-organizing maps (SOMs) and hierarchical agglomerative clustering (HAC) in order to quantify and classify the high number of war landforms. This combined approach allowed for mapping more than one million landforms which can be classified into eight different shapes including shell craters and various soldier-made landforms (i.e. shelters, gun positions, etc.). Detection quality evaluation using field observations revealed the algorithm successfully classified 93% of shell craters and 74% of anthropologically constructed landforms. Finally, the iconographic database and map series produced will help archaeologists and foresters to better manage the historic site of Verdun, today covered by a large forest of ~10 000 ha. © 2019 John Wiley & Sons, Ltd. 相似文献
85.
Jean-Claude Dauvin Guy Bachelet Anne-Laure Barillé Hugues Blanchet Xavier de Montaudouin Nicolas Lavesque & Thierry Ruellet 《Marine Ecology》2009,30(2):228-240
The three main estuaries in the French Atlantic coast – the Seine, Loire and Gironde, all with high tidal regimes – are interfaces between the continental and the coastal ecosystems. The Seine and Gironde are highly contaminated, whereas the Loire remains in a more natural state. Both the Seine and Gironde have suffered from harbour construction, and as a result, their biological units are extremely compartmentalized. Benthic species and communities have adapted to tolerate temporal physical and chemical changes ( e.g. salinity, substrata, depth, and levels of fine particles and oxygen) and human activities ( e.g. dredging, shipping traffic, and habitat reduction). Although numerous bio-indicators and indices are used to define the ecological quality status (EcoQS) of coastal waters, very few of them were developed specifically for environments with a mosaic of conditions and salinity levels, including freshwater. The main problem appears to be that all the indices for determining anthropogenic stress examine the abundances of stress-tolerant species, which may also be able to tolerate natural stressors such as those occurring in estuaries. This paper takes a look at the development status of the benthic indicators and index approaches used in the three main estuaries along the French Atlantic coast. In addition, it examines the adaptation of the different benthic indicators to the taxonomic sufficiency principle, and the adaptation of the Benthic Opportunistic Polychaetes Amphipods index (BOPA) and the Benthic Opportunistic Annelida Amphipod index (BO2A) for use in the freshwater zones of transitional waters ( i.e. up to the upper limit of the tidal range). Several perspectives are discussed in light of the diverse disturbances and the heterogeneity of such stressed zones, such as the use of multimetric and scoring approaches. 相似文献
86.
Ground temperature changes in eastern Canada: borehole temperature evidence compared with proxy data
Borehole temperature logs have been inverted to infer ground temperature histories (GTH) in eastern and central Canada. Regional ground temperature histories were obtained by simultaneous inversion of several temperature profiles from the same areas. Simultaneous inversion of 21 temperature logs sampled across all of eastern and central Canada yielded an average solution for this region. All but three of the studied sites show signs of warming in the last 150 years. This period of warming, which started after 1800 AD, was found throughout this part of Canada. The warming followed a cooler period corresponding to the little Ice Age. The inferred ground temperature histories exhibit long-term trends similar to those obtained from treering growth indices in nearby regions and stable isotope data in the southern hemisphere. The modern warming appears correlated with the atmospheric concentration of CO2 as measured in ice cores. 相似文献
87.
88.
Adélie Delacour Marie-Christine Gerbe Jean-Claude Thouret Gerhard Wörner Perrine Paquereau-Lebti 《Bulletin of Volcanology》2007,69(6):581-608
Minor centres in the Central Volcanic Zone (CVZ) of the Andes occur in different places and are essential indicators of magmatic
processes leading to formation of composite volcano. The Andahua–Orcopampa and Huambo monogenetic fields are located in a
unique tectonic setting, in and along the margins of a deep valley. This valley, oblique to the NW–SE-trend of the CVZ, is
located between two composite volcanoes (Nevado Coropuna to the east and Nevado Sabancaya to the west). Structural analysis
of these volcanic fields, based on SPOT satellite images, indicates four main groups of faults. These faults may have controlled
magma ascent and the distribution of most centres in this deep valley shaped by en-echelon faulting. Morphometric criteria
and 14C age dating attest to four main periods of activity: Late Pleistocene, Early to Middle Holocene, Late Holocene and Historic.
The two most interesting features of the cones are the wide compositional range of their lavas (52.1 to 68.1 wt.% SiO2) and the unusual occurrence of mafic lavas (olivine-rich basaltic andesites and basaltic andesites). Occurrence of such minor
volcanic centres and mafic magmas in the CVZ may provide clues about the magma source in southern Peru. Such information is
otherwise difficult to obtain because lavas produced by composite volcanoes are affected by shallow processes that strongly
mask source signatures. Major, trace, and rare earth elements, as well as Sr-, Nd-, Pb- and O-isotope data obtained on high-K
calc-alkaline lavas of the Andahua–Orcopampa and Huambo volcanic province characterise their source and their evolution. These
lavas display a range comparable to those of the CVZ composite volcanoes for radiogenic and stable isotopes (87Sr/86Sr: 0.70591–0.70694, 143Nd/144Nd: 0.512317–0.512509, 206Pb/204Pb: 18.30–18.63, 207Pb/204Pb: 15.57–15.60, 208Pb/204Pb: 38.49–38.64, and δ
18O: 7.1–10.0‰ SMOW), attesting to involvement of a crustal component. Sediment is absent from the Peru–Chile trench, and hence
cannot be the source of such enrichment. Partial melts of the lowermost part of the thick Andean continental crust with a
granulitic garnet-bearing residue added to mantle-derived arc magmas in a high-pressure MASH [melting, assimilation, storage
and homogenisation] zone may play a major role in magma genesis. This may also explain the chemical characteristics of the
Andahua–Orcopampa and Huambo magmas. Fractional crystallisation processes are the main governors of magma evolution for the
Andahua–Orcopampa and Huambo volcanic province. An open-system evolution is, however, required to explain some O-isotopes
and some major and trace elements values. Modelling of AFC processes suggests the Charcani gneisses and the local Andahua–Orcopampa
and Huambo basement may be plausible contaminants. 相似文献
89.
90.