We generated a high-resolution SSTMg/Ca record for the surface-dwelling planktonic foraminifera Globigerina bulloides from the core MD99-2346 collected in the Gulf of Lion, and compared it to that obtained using modern analogue techniques applied to fossil foraminiferal assemblages (SSTMAT). The two temperature records display similar patterns during the last 28,000 years but the SSTMg/Ca estimates are several degrees warmer (∼ +4 °C) than SSTMAT. The temperature shift between SSTMg/Ca and SSTMAT remained relatively constant over time. This seems to exclude a bias on the Mg/Ca record associated with salinity or secondary Mg-rich calcite encrustation on the foraminiferal tests during early diagenesis. Therefore, anomalously high Mg/Ca suggests either: (1) the empirical equation for G.bulloides of Elderfield and Ganssen (2000) is incorrect; or (2) there is a specific Mediterranean genotypes of G.bulloides for which a specific Mg/Ca-temperature calibration is needed. 相似文献
The study area is the N’zi watershed, sub-watershed of the Bandama River (Ivory Coast). The N’zi watershed is located between longitudes 3°49′ and 5°22′ West and latitudes 6°00′ and 9°26′ North and covers an area of 35,500 km2. This study aims to identify trends in the rainfall-runoff relationship by using a monthly conceptual model. The methodology has consisted on the one hand in highlighting the existence of interannual climate and hydrological variability by using the method of segmentation of Hubert, and on the other hand, in applying the crossed simulations method by using the GR2M model, over several 7-year sub-periods. The results of the application of the method of segmentation of Hubert have demonstrated the presence of a hydroclimatic variability in the N’zi watershed. The modifications of the climate and physical conditions of the flow resulted in a modification of the hydrological response of the watershed translated by a non-stationarity in the rainfall-runoff relation. 相似文献
A dinosaur tracksite was discovered in Batha on the side of the road from Harissa to Ghosta (Keserwan, Lebanon). About ten trackways are exposed at the top of two beds of Lower Cretaceous limestones over an area of approximately 1000 m2. These footprints were probably made by at least two dinosaur species, Sauropoda and either Theropoda or Ornithopoda. The site, which is the first record from Lebanon, should be protected to allow further scientific investigations. 相似文献
Understanding the physical vulnerability of buildings and infrastructure to natural hazards is an essential step in risk assessment for large cities. We have interpreted high spatial resolution images, conducted field surveys, and utilized numerical simulations, in order to assess vulnerability across Arequipa, south Peru, close to the active El Misti volcano. The emphasis of this study was on flash floods and volcanic or non-volcanic hyperconcentrated flows, which recur on average every 3.5 years across the city. We utilized a geographic information system to embed vulnerability and hazard maps as a step to calculate risk for buildings and bridges along the Río Chili valley and two tributaries. A survey of ~1,000 buildings from 46 city blocks, different in age, construction materials, and land usage, provided architectural and structural characteristics. A similar survey of twenty bridges across the three valleys was based on structural, hydraulic, and strategic parameters. Interpretation of high spatial resolution (HSR) satellite images, which allows for quick identification of approximately 69 % of the structural building types, effectively supplemented field data collection. Mapping vulnerability has led us to pinpoint strategic areas in case of future destructive floods or flows. Calculated vulnerability is high if we examine structural criteria alone. We further consider physical setting with the most vulnerable city blocks located on the lowermost terraces, perpendicular or oblique to the flow path. Statistical analysis conducted on 3,015 city blocks, considering nine criteria identified from HSR images, indicated that building-type heterogeneity and the shape of the city blocks, along with building and street network density, are the most discriminant parameters for assessing vulnerability. 相似文献
A series of undrained monotonic triaxial compression tests were performed on natural, medium-dense (relative density (RD) = 50%) Chlef sand containing 0.5% of non-plastic fines, under different confining pressures of 50 kPa, 100 kPa, and 200 kPa. This article focuses on distinctive states of the monotonic undrained response of sands, namely the critical state, the phase transformation state, the quasi-steady state, and the state of undrained instability (onset of flow liquefaction). Specimens were prepared using dry funnel pluviation and wet deposition to investigate the effect of the initial sand fabric on these states. The present data suggest that the initial fabric of the sand appears to have a significant effect on the undrained behavior in the early stages of shearing, with its influence vanishing at large strains. Wet deposition specimens demonstrate considerably larger undrained instability state strength than their dry funnel pluviation counterparts, and a unique critical state locus is reached by both dry funnel pluviation and wet deposition. 相似文献
The effect of the modifications of the threshold values generally adopted for the five EcoQ (Ecological Quality) classes recognized by the European Water Framework Directive (WFD) for the most used benthic indicators and diversity indicators (AMBI, BENTIX, BOPA, BQI, H', ITI and M-AMBI) were studied to test whether it is possible to obtain the same or similar ecological classifications for transitional waters using these different indicators, and determine whether the current classifications can be improved. The analysis included: (i) the use of indicator equations, (ii) the use of reference indicators, and (iii) the use of indicator distribution laws. These investigations demonstrated that it was impossible to obtain an exact intercalibration of the ecological classifications with the selected indicators. However, some propositions to improve the actual classification were suggested. 相似文献
This paper presents the first results obtained during cruises since 1995 in the southeastern part of the Bay of Seine. New sedimentological data concerning sediment samples, box cores and water column measurements have been obtained recently in the framework of the Research Programme PNEC (French National Coastal Environment Programme). Fine sediments are deposited on form of temporary veneers of fluid-to-soft mud formed during high floods episodes. In the subtidal area (<10 m water depth), mobility of fine sediments is important and temporary mud deposited during high discharge period composes part of the distal estuarine system of the Seine River. To cite this article: S. Garnaud et al., C. R. Geoscience 334 (2002) 323–330.相似文献
The successive courses of the Rio Pastaza in the upper Amazonian Puyo plateau (Ecuador) during the past century have been followed using historical maps, aerial photographs, satellite imagery, topographic and river long profiles, and field studies. The abrupt change in direction of the Rio Pastaza from transverse to longitudinal was a result of two avulsions occurred between 1906 and 1976 at the braided-meandering transition of the former alluvial plain. These avulsions are related to aggradation at the toe of a braided piedmont fan prograding on to a hinterland-dipping topographic slope formed by ongoing tectonic backtilting. The main avulsion proceeded by annexation of a south-dipping depression created in front of the cordillera by backtilting of the plateau. A partial and gradual avulsion having occurred upstream of the former site between 1976 and 2008 is marked by the progressive predominance of a newly formed inner branch. Tectonic backtilting enhanced aggradation upstream of the initial site while it offered the newly avulsed channel a still more favorable way along the cordillera by creating a westward lateral slope. The correlation between ENSO events and the occurrence of the 1976–2008 avulsions strongly suggests that the triggers of the avulsions were the floods caused by the high water and sediment discharges associated with ENSO (La Ni?a) events contrasting with the regular monthly discharge and the lack of actual ‘normal’ floods during the inter-ENSO periods. 相似文献
Experimental observations have shown that the resilient modulus Mr of fine/coarse soil mixture can be significantly affected by the coarse grain content fv, deviator stress σd and suction \(\psi\). In this study, a constitutive model incorporating the soil–water retention curve (SWRC) was proposed to describe the effects of \(\psi\) and \(\sigma_{{\text{d}}}\) on Mr. This model was then extended to the effect of fv. The proposed model implied the resilient modulus at saturation condition (Mr-sat), the resilient modulus at optimum moisture content (OMC) condition (Mr-opt), the suction at OMC (\(\psi_{{{\text{opt}}}}\)) and the parameters related to SWRC. The model was validated using experimental data from five studies reported in the literature. Comparisons with three representative existing models showed that the proposed model was capable to well describe the suction-dependent effect of deviator stress in the full range of suction, while the existing models gave satisfactory simulation results only in the low suction range. Indeed, experimental studies revealed that there was a threshold suction \(\psi_{{{\text{th}}}}\), and with increasing \(\sigma_{{\text{d}}}\), the Mr decreased when \(\psi < \psi_{{{\text{th}}}}\), but increased when \(\psi > \psi_{{{\text{th}}}}\). When \(\psi < \psi_{{{\text{th}}}}\), all models gave good simulations. On the contrary, when \(\psi > \psi_{{{\text{th}}}}\), only the proposed model gave good simulations, in particular when \(\psi_{{{\text{th}}}} > \psi_{{{\text{opt}}}}\). This showed the performance of the proposed model in describing the variation in resilient modulus of unsaturated fine/coarse soil mixtures with changes in coarse grain content, deviator stress and suction.