Dynamics of a wave-dominated tidal inlet and influence on adjacent beaches,Currumbin Creek,Gold Coast,Australia     

Bruno Castelle  Julien Bourget  Nathalie Molnar  Darrell Strauss  Sophie Deschamps  Rodger Tomlinson 《Coastal Engineering》2007

Currumbin Creek on the Australian Gold Coast is a wave-dominated tidal inlet which exhibits a particularly active morphology. The recent history of Currumbin Creek entrance has seen rapid growth of the entrance for access to the ocean by fishermen, as a world class surfing site, and as a recreational area. Before the construction of two groynes in the 70's, Currumbin Creek entrance was highly variable in terms of inlet location and sand bar characteristics due to a cyclical behaviour of spit migration. Nowadays, the entrance is stabilised. However, natural processes continue with the entrance infilling causing flood and navigation issues, resulting in a regular dredging program to maintain an open entrance and for regular beach nourishment plans.  相似文献   

Comparative study of radiation-induced damage in magnesium aluminate spinel by means of IL,CL and RBS/C techniques     

Iwona Jozwik  Jacek Jagielski  Grzegorz Gawlik  Przemyslaw Jozwik  Renata Ratajczak  Gerard Panczer  Nathalie Moncoffre  Anna Wajler  Agata Sidorowicz  Lionel Thomé 《Physics and Chemistry of Minerals》2016,43(6):439-445

A comparative study of damage accumulation in magnesium aluminate spinel (MgAl₂O₄) has been conducted using ionoluminescence (IL), cathodoluminescence (CL) and Rutherford Backscattering Spectrometry/channeling (RBS/C) techniques. MgAl₂O₄ single crystal and polycrystalline samples were irradiated with 320 keV Ar⁺ ions at fluencies ranging from 1 × 10¹² to 2 × 10¹⁶ cm^?2 in order to create various levels of radiation damage. RBS/C measurements provided quantitative data about damage concentration in the samples. These values were then compared to the luminescence measurements. The results obtained by IL and RBS/C methods demonstrate a two-step character of damage buildup process. The CL data analysis points to the three-step damage accumulation mechanism involving the first defect transformation at fluencies of about 10¹³ cm^?2 and second at about 10¹⁵ cm^?2. The rate of changes resulting from the formation of nonluminescent recombination centers is clearly nonlinear and cannot be described in terms of continuous accumulation of point defects. Both, IL and CL techniques, appear as new, complementary tools bringing new possibilities in the damage accumulation studies in single- and polycrystalline materials.  相似文献   

Roman road pollution assessed by elemental and lead isotope geochemistry in East Belgium     

Virginie Renson  Nathalie Fagel  Nadine Mattielli  Serge Nekrassoff  Maurice Streel  Franois De Vleeschouwer 《Applied Geochemistry》2008,23(12):3253-3266

The ability of inorganic geochemistry to record environmental change and especially human impact has been evidenced by several studies across Europe, especially in peat, where it is possible to record the impact of agriculture, mining and other industries. However, despite the numerous investigations on the impact of ancient human activities such as ore mining and smelting, little attention has been paid to geochemistry as a tool to solve problems of palaeopollution in the surroundings of archaeological sites. This paper presents geochemical evidence of the impact of a possible early Roman road built in SE Belgian peatland. Increased Zn and Pb concentrations suggest that Pb–Zn ores were transported on the road. Lead isotope analyses suggest that these ores are locally derived, being compatible with those found in the nearby Pb–Zn ore deposits from East Belgium. Present results provide direct evidence that East Belgian Pb–Zn ores were already being mined during Roman times, i.e. earlier than previously suspected (i.e. 14th century) and that Zn appears to be relatively immobile here. On a broader scale, it also demonstrates that such an early road already had an impact on the environment in terms of metal pollution. This paper enlarges on the range of possibilities offered by geochemistry in the field of geoarchaeology.  相似文献   

P-T-t modelling, fluid circulation, and 39Ar-40Ar and Rb-Sr mica ages in the Aar Massif shear zones (Swiss Alps)     

Nathalie Challandes  Didier Marquer  Igor M. Villa 《Swiss Journal of Geoscience》2008,101(2):269-288

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Temporal variability of contemporary floodplain sedimentation in the Rhine–Meuse delta,The Netherlands     

Nathalie E. M. Asselman  Hans Middelkoop 《地球表面变化过程与地形》1998,23(7):595-609

It is often believed that extreme but infrequent events are most important in the development of landforms. When evaluating the overall effect of large floods on floodplain sedimentation, quantitative measurements of both high- and low-magnitude events should be considered. To analyse the role of flood magnitude on floodplain sedimentation, we measured overbank sedimentation during floods of different magnitude and duration. The measurements were carried out on two embanked floodplain sections along the rivers Rhine and Meuse in The Netherlands, using sediment traps made of artificial grass. The results showed an increase in total sediment accumulation with flood magnitude, mainly caused by enhanced accumulation of sand. At low floodplain sections the increase in sediment deposition was smaller than expected from the strong increase in suspended sediment transport in the river. Spatial variability in sediment accumulation was found to depend both on flood magnitude and duration. Deposition of sand on natural levees mainly takes place during high-magnitude floods, whilst low floods and slowly receding floods are important for the deposition of silt and clay in low-lying areas, at greater distance from the main channel. © 1998 John Wiley & Sons, Ltd.  相似文献   

Development and Intercomparison of Condensed Isoprene Oxidation Mechanisms for Global Atmospheric Modeling     

Ulrich Pöschl  Rolf von Kuhlmann  Nathalie Poisson  Paul J. Crutzen 《Journal of Atmospheric Chemistry》2000,37(1):29-52

A new condensed isoprene oxidation mechanism forglobal atmospheric modeling (MIM) was derived from ahighly detailed master chemical mechanism (MCM). In abox model intercomparison covering a wide range ofboundary layer conditions the MIM was compared withthe MCM and with five other condensed mechanisms, someof which have already been used in global modelingstudies of nonmethane hydrocarbon chemistry. Theresults of MCM and MIM were generally in goodagreement, but the other tested mechanisms exhibitedsubstantial differences relative to the MCM as well asrelative to each other. Different formation yields,reactivities and degradation pathways of organicnitrates formed in the course of isoprene oxidationwere identified as a major reason for the deviations.The relevance of the box model results for chemistrytransport models is discussed, and the need for avalidated reference mechanism and for an improvedrepresentation of isoprene chemistry in global modelsis pointed out.  相似文献   

Dynamics and sources of suspended particulate organic matter in the Marennes-Oléron oyster farming bay: Insights from stable isotopes and microalgae ecology     

Nathalie Malet  Pierre-Guy Sauriau  Mireille Ryckaert  Pascale Malestroit  Gael Guillou 《Estuarine, Coastal and Shelf Science》2008

The aim of this study was to distinguish between sources of the complex variety of Marennes-Oléron Bay suspended particulate organic matter (SPOM) contributing to the tropho-dynamics of the Marennes-Oléron oyster farming bay. Basic biomarkers (Chl a, C/N and POC/Chl a ratios), carbon and nitrogen stable isotopes from SPOM were analyzed and the microalgae community was characterized. The sampling strategy was bimonthly from March 2002 to December 2003; samples were taken from an intertidal mudflat. Four main sources contributed to the SPOM pool: terrigenous input from rivers, neritic phytoplankton, resuspended microphytobenthos and periodic inputs from intertidal Zostera noltii meadows. Seasonal fluctuations were observed in both years of the study period: (1) SPOM collected in the spring of 2002 (δ¹³C = −25‰ to −23‰) was mainly composed of fresh estuarine inputs; (2) SPOM from the summer and fall of 2002 and 2003 was predominantly neritic phytoplankton (δ¹³C = − 22‰ to −19‰); (3) SPOM from the winter of 2002, spring of 2003 and winter of 2003 (δ¹³C = −21 to −23‰) was composed of a mixture of decayed terrigenous river inputs and pelagic phytoplankton, which was predominantly resuspended microphytobenthos. In the summer of 2003—the warmest summer on record in southern France and Europe—SPOM was particularly enriched for ¹³C, with δ¹³C values ranging from −14‰ to −12‰. Pulses in δ¹³C values, indicative of ¹³C-enriched decaying materials, extended into the fall. These were attributed to benthic intertidal inputs, including both resuspended microphytobenthos and Z. noltii detritus. Changes in SPOM sources in Marennes-Oléron Bay may lead to differences in the quality of the trophic environment available for reared oysters.  相似文献   

Change of Support in Spatial Variance-Based Sensitivity Analysis     

Nathalie Saint-Geours  Christian Lavergne  Jean-Stéphane Bailly  Frédéric Grelot 《Mathematical Geosciences》2012,44(8):945-958

Variance-based global sensitivity analysis (GSA) is used to study how the variance of the output of a model can be apportioned to different sources of uncertainty in its inputs. GSA is an essential component of model building as it helps to identify model inputs that account for most of the model output variance. However, this approach is seldom applied to spatial models because it cannot describe how uncertainty propagation interacts with another key issue in spatial modeling: the issue of model upscaling, that is, a change of spatial support of model output. In many environmental models, the end user is interested in the spatial average or the sum of the model output over a given spatial unit (for example, the average porosity of a geological block). Under a change of spatial support, the relative contribution of uncertain model inputs to the variance of aggregated model output may change. We propose a simple formalism to discuss this issue within a GSA framework by defining point and block sensitivity indices. We show that the relative contribution of an uncertain spatially distributed model input increases with its correlation length and decreases with the size of the spatial unit considered for model output aggregation. The results are briefly illustrated by a simple example.  相似文献   

Millennial-scale variations in hydrography and biogeochemistry in the Eastern Equatorial Pacific over the last 100 kyr     

Nathalie Dubois  Markus Kienast  Stephanie Kienast  Claire Normandeau  Stephen E. Calvert  Timothy D. Herbert  Alan Mix 《Quaternary Science Reviews》2011,30(1-2):210-223

In this study, we use records of nitrogen isotope ratios (δ¹⁵N), UK’37 temperature estimates, organic carbon and opal percentages from high-resolution sediment cores located in the eastern equatorial Pacific (EEP) to explore the mechanisms linking millennial-scale changes in low-latitude sea surface temperature, water column denitrification and surface productivity to the timing of northern or southern polar climate during the last 100,000 yr. Our results support a hypothesis that the Southern Hemisphere, and its connection to the low latitudes via shallow subsurface ocean circulation, has a primary influence on the biogeochemistry of the EEP. In addition, our results suggest that, during the last glacial stage, denitrification rates fluctuated on millennial timescales in response to water-column ventilation rather than upstream oxidant demand in intermediate-depth waters.However, due to the poor age constraints available for Marine Isotopic Stage (MIS) 3, the EEP sedimentary data presented here could support two conflicting mechanisms, one driven by enhanced intermediate overturning circulation in the Southern Ocean during Heinrich Events/Antarctic Warm Events, implying that subsurface flow rates control thermocline ventilation, and a second one consistent with more sluggish intermediate circulation during Antarctic Warm Events and giving a central role to the temperature control on oxygen solubility in Southern Ocean surface waters.  相似文献   

Occurrence of the toxic dinoflagellate Ostreopsis cf. ovata in relation with environmental factors in Monaco (NW Mediterranean)     

Cohu S  Thibaut T  Mangialajo L  Labat JP  Passafiume O  Blanfuné A  Simon N  Cottalorda JM  Lemée R 《Marine pollution bulletin》2011,62(12):2681-2691

To study environment characteristics favoring the toxic benthic dinoflagellate Ostreopsis cf. ovata, a survey was conducted in Monaco (NW Mediterranean Sea), in summers 2007 and 2008. Epiphytic and planktonic blooms occurred almost simultaneously and a high variation of abundances at low spatial scales was observed. An early and very marked bloom occurred in 2007, compared to a later and less abundant development in 2008. These distinct patterns in bloom timing corresponded with very different hydroclimatic scenarios in 2007 (hot spring and relatively cold summer) and 2008 (standard year compared to the median year profile estimated with data from 1995 to 2008). No clear impacts of summer seawater temperature, rainfall or nutrient concentrations were evident. Strong wind may favor the dispersal of benthic and planktonic cells. Our study suggests that further investigations are needed to examine the potential role of Ostreopsis nutritional mode (i.e. autotrophy vs. mixotrophy).  相似文献