Post-glacial persistence of turbiditic activity within the Rhône deep-sea turbidite system (Gulf of Lions,Western Mediterranean): Linking the outer shelf and the basin sedimentary records     

Bernard Dennielou  Laurent Jallet  Nabil Sultan  Gwenael Jouet  Pierre Giresse  Michel Voisset  Serge Berné 《Marine Geology》2009,257(1-4):65-86

Emplacement of post-glacial turbidites is commonly controlled by rapid changes in sea level or by seismicity. On the continental rise of the Gulf of Lions (Western Mediterranean), an aseismic area, we identified turbiditic beds deposited during the rising stage and highstand of sea level. Swath bathymetry, sediment cores, in situ Cone Penetrating Tests (CPTU), heavy mineral associations and radiocarbon dating determined the source, composition, distribution and age of the turbiditic beds. Turbidites are composed of homogeneous to positively graded silts to medium sand with quartz (up to 90%), shell debris and shelfal benthic faunas. Their distribution on the sea floor is very patchy and controlled by abundant inherited erosional bedforms. Their source is found in relict regressive sands at the outershelf. Their deposition occurred just after the onset of the post-glacial sea level rise and the concomitant sediment starvation of the Rhône deep sea turbiditic system until recently. Whilst canyons are fed with sand by strong seasonal hydro-sedimentary dynamics on the outershelf, the emplacement of post-glacial turbidites is not controlled by sea level changes but probably by the periodic flushing of the canyons. Our study revealed that this low energy aseismic margin undergoes significant transport of sand, down to the base of slope, during the sea-level rise and the Holocene highstand.  相似文献   

Weather regimes over Senegal during the summer monsoon season using self-organizing maps and hierarchical ascendant classification. Part II: interannual time scale     

A. K. Guèye  Serge Janicot  A. Niang  S. Sawadogo  Benjamin Sultan  A. Diongue-Niang  S. Thiria 《Climate Dynamics》2012,39(9-10):2251-2272

The aim of this work is to define over the period 1979–2002 the main synoptic weather regimes relevant for understanding the daily variability of rainfall during the summer monsoon season over Senegal. “Interannual” synoptic weather regimes are defined by removing the influence of the mean 1979–2002 seasonal cycle. This is different from Part I where the seasonal evolution of each year was removed, then removing also the contribution of interannual variability. As in Part I, the self-organizing maps approach, a clustering methodology based on non-linear artificial neural network, is combined with a hierarchical ascendant classification to compute these regimes. Nine weather regimes are identified using the mean sea level pressure and 850?hPa wind field as variables. The composite circulation patterns of all these nine weather regimes are very consistent with the associated anomaly patterns of precipitable water, mid-troposphere vertical velocity and rainfall. They are also consistent with the distribution of rainfall extremes. These regimes have been then gathered into different groups. A first group of four regimes is included in an inner circuit and is characterized by a modulation of the semi-permanent trough located along the western coast of West Africa and an opposite modulation on the east. This circuit is important because it associates the two wettest and highly persistent weather regimes over Senegal with the driest and the most persistent one. One derivation of this circuit is highlighted, including the two driest regimes and the most persistent one, what can provide important dry sequences occurrence. An exit of this circuit is characterised by a filling of the Saharan heat low. An entry into the main circuit includes a southward location of the Saharan heat low followed by its deepening. The last weather regime is isolated from the other ones and it has no significant impact on Senegal. It is present in June and September, and missing in July and August, meaning that this is a weather regime more specific of the intermediate seasons than the summer. It is included in a large-scale pattern covering the northern latitudes of Europe. The correspondence between these “interannual” synoptic weather regimes and the “pure” synoptic regimes defined in Part I has been established. By selecting a high statistical significance level for these correspondences, each of five out of nine “interannual” weather regimes has a close correspondence with one “pure” synoptic weather regime, one out of them have links with two “pure” regimes, and the last three regimes have no significant correspondence in terms of “pure” regimes. However when considering more moderate links, two out of these three regimes show a connection with a “pure” regime, and the last one remains isolated. The ensemble of the weather regimes occurrences can explain a significant part of interannual variability of summer rainfall amount over Senegal, especially linked to the driest and the wettest weather regimes occurrences. It is also shown that Senegal rainfall state is very sensitive to a small displacement or deformation of the weather regime patterns.  相似文献   

Theoretical and numerical studies of the Vishniac instability in supernova remnants     

Cécile Cavet  Hung Chinh Nguyen  Claire Michaut  Emeric Falize  Serge Bouquet  Laurent Di Menza 《Astrophysics and Space Science》2009,322(1-4):91-95

Vishniac instability has been theoretically studied in supernova remnants where it is supposed to explain the fragmentation of the interstellar medium. However its role is not fully demonstrated in these astrophysical objects. Conditions and assumptions required for the instability growth are explained in detail in the present paper. In addition the HYDRO-MUSCL hydrodynamic code has been used to simulate this instability in order to compare the numerical growth rate with the Vishniac analytical solution.  相似文献   

Cliff-top storm deposits on Banneg Island, Brittany, France: Effects of giant waves in the Eastern Atlantic Ocean     

Serge Suanez  Bernard Fichaut  Rudy Magne   《Sedimentary Geology》2009,220(1-2):12-28

This study is based on the morphosedimentary analysis of the cliff-top storm deposits accumulated on the coast of Banneg Island located in the archipelago of Molène (Brittany, France). These CTSDs comprise large, tabular clasts quarried from the upper part of the cliff and the backing scoured platform by giant oceanic storm waves impacting directly the western coast of the island. An analysis of the distribution and the geomorphology of these accumulations were carried out using the DGPS topographic surveys. Most of the clasts are organised into imbricate boulder clusters or ridges deposited between 7.5 and 14.5 masl. 52 accumulations were inventoried from the north to the south of the island, representing a global volume of 1000 m³. The median size of the clasts calculated is equivalent to 0.8 × 0.6 × 0.4 m and a weight of 0.6 t. The largest one measuring 5.3 × 3.9 × 0.5 m (≈ 32 t) is located in the centre of the island (ridge #28). It has been deposited 14 m inland from the edge of the cliff at the elevation of 9 m. Sediment analysis shows that clast sizes become smaller with increasing distance from the shoreline, but there is no relationship between the sorting and the distance inland. A study of the hydrodynamic conditions inducing clast transport was undertaken by an analysis of the wave data from the 1989 to the 1990 winter storms. Models of wave runup indicate that their highest water levels may have reached up to 19 masl, 5 to 10 m higher than the top of the cliff. Submersion by giant storm waves has been more important and frequent in the centre and the south of the island. Wave data over the 1979 to the 2007 period shows that no events as powerful as those of the 1989 to the 1990 winter were recorded during the last 30 years. Yet, it appears that the 1979–1990 decade was characterized by important morphogeneous events while the following period (1990–2007) has experienced a sharp decrease in storm events. These variations could be attributed to the inversion from a negative towards a positive phase in the North Atlantic Oscillation index.  相似文献   

Phase relationship between sea level and abrupt climate change     

Francisco J. Sierro  Nils Andersen  Maria A. Bassetti  Serge Bern  Miquel Canals  Jason H. Curtis  Bernard Dennielou  Jose Abel Flores  Jaime Frigola  Beatriz Gonzalez-Mora  Joan O. Grimalt  David A. Hodell  Gwenael Jouet  Marta Prez-Folgado  Ralph Schneider 《Quaternary Science Reviews》2009,28(25-26):2867-2881

Direct traces of past sea levels are based on the elevation of old coral reefs at times of sea level highstands. However, these measurements are discontinuous and cannot be easily correlated with climate records from ice cores. In this study we show a new approach to recognizing the imprint of sea level changes in continuous sediment records taken from the continental slope at locations that were continuously submerged, even during periods of sea level lowstand. By using a sediment core precisely synchronized with Greenland ice cores, we were able to recognize major floods of the Mediterranean continental shelf over the past 270 kyr. During the last glacial period five flooding events were observed at the onset of the warmest Greenland interstadials. Consistent correspondence between warm climate episodes and eustatic sea level rises shows that these global flooding events were generated by pronounced melting of the Northern Hemisphere ice sheets, due to rapid intensification of Atlantic Meridional Overturning Circulation.The method described in this study opens a new perspective for inter-hemispheric synchronization of marine climate records if applied in other continental margins from the Southern Hemisphere or the equatorial regions.  相似文献   

A method for regional climate change detection using smooth temporal patterns     

Aurélien Ribes  Jean-Marc Azaïs  Serge Planton 《Climate Dynamics》2010,35(2-3):391-406

This paper introduces an original method for climate change detection, called temporal optimal detection method. The method consists in searching for a smooth temporal pattern in the observations. This pattern can be either the response of the climate system to a specific forcing or to a combination of forcings. Many characteristics of this new method are different from those of the classical “optimal fingerprint” method. It allows to infer the spatial distribution of the detected signal, without providing any spatial guess pattern. The spatial properties of the internal climate variability doesn’t need to be estimated either. The estimation of such quantities being very challenging at regional scale, the proposed method is particularly well-suited for such scale. The efficiency of the method is illustrated by applying it on real homogenized datasets of temperatures and precipitation over France. A multimodel detection is performed in both cases, using an ensemble of atmosphere-ocean general circulation models for estimating the temporal patterns. Regarding temperatures, new results are highlighted, especially by showing that a change is detected even after removing the uniform part of the warming. The sensitivity of the method is discussed in this case, relatively to the computation of the temporal patterns and to the choice of the model. The method also allows to detect a climate change signal in precipitation. This change impacts the spatial distribution of the precipitation more than the mean over the domain. The ability of the method to provide an estimate of the spatial distribution of the change following the prescribed temporal patterns is also illustrated.  相似文献   

Holocene salt‐marsh sedimentary infilling and relative sea‐level changes in West Brittany (France) using foraminifera‐based transfer functions          下载免费PDF全文

Pierre Stéphan  Jérôme Goslin  Yvan Pailler  Rose Manceau  Serge Suanez  Brigitte Van Vliet‐Lanoë  Alain Hénaff  Christophe Delacourt 《Boreas: An International Journal of Quaternary Research》2015,44(1):153-177

In order to reconstruct former sea‐levels and to better characterize the history of Holocene salt‐marsh sedimentary infillings in West Brittany (western France), local foraminifera‐based transfer functions were developed using weighted‐average‐partial‐least‐squares (WAPLS) regression, based on a modern data set of 26 and 51 surface samples obtained from salt‐marshes in the bay of Tresseny and the bay of Brest, respectively. Fifty cores were retrieved from Tresseny, Porzguen, Troaon and Arun salt‐marshes, which were litho‐ and biostratigraphically analysed in order to reconstruct palaeoenvironmental changes. A total of 26 AMS ¹⁴C age determinations were performed within the sediment successions. The Holocene evolution of salt‐marsh environments can be subdivided into four stages: (i) a development of brackish to freshwater marshes (from c. 6400 to 4500 cal. a BP); (ii) salt‐marsh formation behind gravel barriers in the bay of Brest (from 4500 to 2900 cal. a BP); (iii) salt‐marsh erosion and rapid changes of infilling dynamics due to the destruction of coastal barriers by storm events (c. 2900?2700 cal. a BP); (iv) renewed salt‐marsh deposition and small environmental changes (from 2700 cal. a BP to present). From the application of transfer functions to fossil assemblages, 14 new sea‐level index points were obtained, indicating a mean relative sea‐level rise of around 0.90±0.12 mm a^?1 since 6300 cal. a BP.  相似文献   

Weather regimes over Senegal during the summer monsoon season using self-organizing maps and hierarchical ascendant classification. Part I: synoptic time scale     

A. K. Gu��ye  Serge Janicot  A. Niang  S. Sawadogo  Benjamin Sultan  A. Diongue-Niang  S. Thiria 《Climate Dynamics》2011,36(1-2):1-18

The aim of this work is to define over the period 1979?C2002 the main synoptic weather regimes relevant for understanding the daily variability of rainfall during the summer monsoon season over Senegal. ??Pure?? synoptic weather regimes are defined by removing the influence of seasonal and interannual time scales, in order to highlight the day by day variability of the atmospheric circulation. The Self-Organizing Maps (SOM) approach, a clustering methodology based on non-linear artificial neural network, is combined with a Hierarchical Ascendant Classification to compute these regimes. Nine weather regimes are identified using the mean sea level pressure and 850?hPa wind field as variables, and gathered into three classes. Two of these weather regimes represent the classical 3?C5-day African easterly waves with a mean wavelength of about 3,000?km. Three others are characterized by a modulation of the semi-permanent trough located along the western coast of West Africa and might be interpreted in terms of the 6?C9-day easterly waves. The last four weather regimes are characterized by a more or less strong north?Csouth dipole of circulation. They can be interpreted as a northward/southward displacement of the Saharan Heat Low for two of them, and a filling/deepening of this depression for the other two. The circulation patterns of all these nine weather regimes are very consistent with the associated anomaly patterns of precipitable water, mid-troposphere vertical velocity, outgoing longwave radiation, and finally rainfall. Rainfall distribution is also highlighted over the southwestern area of Senegal.  相似文献   

Changes in the interannual SST-forced signals on West African rainfall. AGCM intercomparison     

Elsa Mohino  Bel��n Rodr��guez-Fonseca  Teresa Losada  S��bastien Gervois  Serge Janicot  Juergen Bader  Paolo Ruti  Fabrice Chauvin 《Climate Dynamics》2011,37(9-10):1707-1725

Rainfall over West Africa shows strong interannual variability related to changes in Sea Surface Temperature (SST). Nevertheless, this relationship seem to be non-stationary. A particular turning point is the decade of the 1970s, which witnessed a number of changes in the climatic system, including the climate shift of the late 1970s. The first aim of this study is to explore the change in the interannual variability of West African rainfall after this shift. The analysis indicates that the dipolar features of the rainfall variability over this region, related to changes in the Atlantic SST, disappear after this period. Also, the Pacific SST variability has a higher correlation with Guinean rainfall in the recent period. The results suggest that the current relationship between the Atlantic and Pacific El Ni?o phenomena is the principal responsible for these changes. A fundamental goal of climate research is the development of models simulating a realistic current climate. For this reason, the second aim of this work is to test the performance of Atmospheric General Circulation models in simulating rainfall variability over West Africa. The models have been run with observed SSTs for the common period 1957?C1998 as part of an intercomparison exercise. The results show that the models are able to reproduce Guinean interannual variability, which is strongly related to SST variability in the Equatorial Atlantic. Nevertheless, problems in the simulation of the Sahelian interannual variability appear: not all models are able to reproduce the observed negative link between rainfall over the Sahel and El Ni?o-like anomalies in the Pacific, neither the positive correlation between Mediterranean SSTs and Sahelian rainfall.  相似文献   

The semismooth Newton method for multicomponent reactive transport with minerals   总被引：1，自引：0，他引：1  

Serge Kräutle 《Advances in water resources》2011,34(1):137-151

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