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   

Evaluation of Mediterranean Sea water and heat budgets simulated by an ensemble of high resolution regional climate models   总被引：2，自引：2，他引：0  

E. Sanchez-Gomez  S. Somot  S. A. Josey  C. Dubois  N. Elguindi  M. Déqué 《Climate Dynamics》2011,37(9-10):2067-2086

Air-sea heat and freshwater water fluxes in the Mediterranean Sea play a crucial role in dense water formation. Here, we compare estimates of Mediterranean Sea heat and water budgets from a range of observational datasets and discuss the main differences between them. Taking into account the closure hypothesis at the Gibraltar Strait, we have built several observational estimates of water and heat budgets by combination of their different observational components. We provide then three estimates for water budget and one for heat budget that satisfy the closure hypothesis. We then use these observational estimates to assess the ability of an ensemble of ERA40-driven high resolution (25 km) Regional Climate Models (RCMs) from the FP6-EU ENSEMBLES database, to simulate the various components, and net values, of the water and heat budgets. Most of the RCM Mediterranean basin means are within the range spanned by the observational estimates of the different budget components, though in some cases the RCMs have a tendency to overestimate the latent heat flux (or evaporation) with respect to observations. The RCMs do not show significant improvements of the total water budget estimates comparing to ERA40. Moreover, given the large spread found in observational estimates of precipitation over the sea, it is difficult to draw conclusions on the performance of RCM for the freshwater budget and this underlines the need for better precipitation observations. The original ERA40 value for the basin mean net heat flux is ?15 W/m² which is 10 W/m² less than the value of ?5 W/m² inferred from the transport measurements at Gibraltar Strait. The ensemble of heat budget values estimated from the models show that most of RCMs do not achieve heat budget closure. However, the ensemble mean value for the net heat flux is ?7 ± 21 W/m², which is close to the Gibraltar value, although the spread between the RCMs is large. Since the RCMs are forced by the same boundary conditions (ERA40 and sea surface temperatures) and have the same horizontal resolution and spatial domain, the reason for the large spread must reside in the physical parameterizations. To conclude, improvements are urgently required to physical parameterizations in state-of-the-art regional climate models, to reduce the large spread found in our analysis and to obtain better water and heat budget estimates over the Mediterranean Sea.  相似文献   

The initiation of the southern central Great Barrier Reef: New multiproxy data from Pleistocene distal sediments from the Marion Plateau (NE Australia)     

Nathalie Dubois  Pascal Kindler  Silvia Spezzaferri  Stjepan Coric   《Marine Geology》2008,250(3-4):223-233

Significant synchronous shifts in the chemistry, mineralogy, grain sizes and color of the sediments at 6 m below sea floor (mbsf) at ODP Site 1195 on the Marion Plateau (NE Australia) are interpreted to reflect a major regional paleoceanographic change: the initiation of the southern province of the Great Barrier Reef (GBR). The onset of this massive carbonate production centre nearby resulted primarily in increased deposition of carbonate-rich sediments of neritic origin. Both sedimentation rate and terrigenous input record a coincident decline attributed to inshore trapping of materials behind the reefs. Our best estimate places the development of reef framework in the southern part of the GBR between 560 and 670 kyr B.P., based on an age model combining magnetostratigraphic and biostratigraphic data. The proposed estimation agrees with previous studies reporting an age between 500 and 930 kyr B.P., constraining more tightly their results. However, it does not support research placing the birth of the GBR in Marine Isotope Stage (MIS) 11 ( 400 kyr), nor the theory of a worldwide modern barrier reef development at that time.  相似文献   

Castiglione (Oletta,Corsica): relationships between phenomena of calcification and tectonic fossiliferous fracture dating     

Elisabeth Pereira  François Rouzaud  Michelle Salotti  Jean-Noël Dubois  Jean Ferrandini  Marie-Madeleine Ottaviani-Spella 《Geodinamica Acta》2013,26(6):371-375

Abstract

Six cavities have been discovered in the Oletta massif. The massif, today constitued of Schistes lustrés with several metres of calcareous layers above them, has undergone intense fracturing. The networks of cavities are organised along north-south and subequatorial directions, and form a narrow bayonnet-network. All the elements in the galleries appear to be karstic: stalagmites, stalactites and calcitic deposits along the walls; but no trace of dissolution or excavation was found. Thus, the origin of the galleries is only tectonic, while the calcitic deposits result from the dissolution of the old, thick calcareous layers above, which are no longer present. The thickness and the volume of the calcitic deposits, which is variable depending on the galleries, indicates the chronology of the different tectonic periods which have fractured the massif. Five tectonic and successsive events have been detected. Calcitic datings confirm the timing of successional fracturing, indicating also the variable age of the fossiliferous Middle Pleistocene deposits found in these cavities. © 1999 Éditions scientifiques et médicales Elsevier SAS  相似文献   

Analyse photométrique de l'ombre intérieure pendant les Éclipses de lune     

J. Dubois  F. Link 《Earth, Moon, and Planets》1971,2(3):354-362

Sommaire On explique les sursauts de lumière observés à plusieurs reprises dans l'ombre intérieure par l'effet de la luminescence lunaire. On prend la position vis-à-vis de récents examens au laboratoire des échantillons lunaires en ce qui concerne la luminescence.

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The surge of light observed sometimes in the central parts of the umbra is explained by the lunar luminescence. The position is takenvis-à-vis of recent examinations in the laboratory of lunar samples in the relation with the lunar luminescence.

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Normal faulting of the Daiichi-Kashima Seamount in the Japan Trench revealed by the Kaiko I cruise, Leg 3     

Kazuo Kobayashi  Jean-Paul Cadet  Jean Aubouin  Jacques Boulgue  Jacques Dubois  Roland von Huene  Laurent Jolivet  Toshihiko Kanazawa  Junzo Kasahara  Kin-ichiro Koizumi  Serge Lallemand  Yasuo Nakamura  Guy Pautot  Kiyoshi Suyehiro  Shin Tani  Hidekazu Tokuyama  Toshitsugu Yamazaki 《Earth and Planetary Science Letters》1987,83(1-4)

A detailed topographic and geophysical survey of the Daiichi-Kashima Seamount area in the southern Japan Trench, northwestern Pacific margin, clearly defines a high-angle normal fault which splits the seamount into two halves. A fan-shaped zone was investigated along 2–4 km spaced, 100 km long subparallel tracks using narrow multi-beam (Seabeam) echo-sounder with simultaneous measurements of gravity, magnetic total field and single-channel seismic reflection records. Vertical displacement of the inboard half was clearly mapped and its normal fault origin was supported. The northern and southern extensions of the normal fault beyond the flank of the seamount were delineated. Materials on the landward trench slope are displaced upward and to sideways away from the colliding seamount. Canyons observed in the upper landward slope terminate at the mid-slope terrace which has been uplifted since start of subduction of the seamount. Most of the landward slope except for the landward walls aside the seamount comprises only a landslide topography in a manner similar to the northern Japan Trench wall. This survey was conducted on R/V “Jean Charcot” as a part of the Kaiko I cruise, Leg 3, in July–August 1984 under the auspices of the French-Japanese scientific cooperative program.  相似文献   

An improved fluid superelement for the coupled solid-fluid-surface wave dynamic interaction problem     

J. J. Dubois  A. L. De Rouvray 《地震工程与结构动力学》1978,6(3):235-245

The dynamic solid-fluid-surface wave interaction problem can be solved with known Finite Element solutions. However, these solutions are complicated by the unsymmetric nature of the matrix equation to be solved. This paper shows how the numerical problem can be simplified by symmetrization, without loss of physical generality, using specialized Lagrange co-ordinates for the fluid free surface wave, and by introducing a Lagrange multiplier representing a generalized fluid pressure. With these improvements, solid-fluid-surface wave analysis capabilities can easily be added to most Finite Element structural analysis programs. Numerical examples of the performance of the improved formulation are given for earthquake analysis.  相似文献   

Evolution de l'état sanitaire de la baie d'Auvernier (lac de Neuchâtel) de 1962 à 1973     

J. -P. Dubois  O. Schetty 《Aquatic Sciences - Research Across Boundaries》1977,39(1):1-11

The evolution of the trophic state of a part of the Lake of Neuchâtel was investigated by means of a study of 4 parameters (temperature, dissolved oxygen, total phosphorus and nitrates) in the waters of the Auvernier Bay (fig. 1). Each year is composed of a stratification period (June to November) and a circulation period (December to May) (fig. 2). Notwithstanding the heavy consumption of oxygen in the metalimnion during the stratification period, the waters are sufficiently abundant in dissolved oxygen (fig. 3). As a matter of fact, over the 12-year period studied, no decrease in the oxygen content was observed at any depth (fig. 4). On the other hand, the quantities of nutrients were enriched in nitrates (30%) and phosphorus (230%) (fig. 5–8). The Auvernier Bay may be thought to have evolved from an oligotrophic state in 1963 to an eutrophic state in 1972 if we consider only these latter two criteria.  相似文献   

Economic significance of the „Continental Terminal“ (CT)     

C. A. Kogbe  D. Dubois 《International Journal of Earth Sciences》1980,69(2):429-436

The Continental Terminal was first defined byKillan (1931) for Saharan Continental Sediments of Miocene-Pliocene age. Since the introduction of the terminology, it's usage has become very ill-defined and ferruginised tertiary sediments of marine origin in the coastal basins of West Africa have all been referred to as part of the Continental Terminal.In this paper the term is restricted to Post Eocene and Pre-Quaternary Continental Sediments with well defined upper and lower limits. According to the new definition, the upper and lower boundaries of the Continental Terminal are determined by geodynamic events. Although these tectonic events are not strictly synchronous over the whole of north and west Africa, they are considered to have been caused by related stress patterns of supraregional validity.These Continental deposits have been and are still of immense economic importance in West Africa as well as in other parts of Africa. They provide several aquifers which constitute the main source of water for millions of inhabitants of northwestern Nigeria, northeastern Nigeria as well as in neighbouring Niger Republic. The mudstones are also useful as an abundant supply of building material. The sediments are also widely utilised as fill in engineering construction works and the porosity is an advantage as sub-base material in the extensive road construction projects in the region. The high Kaolin content of the clays could provide valuable raw-material for ceramic and brick manufacturing industries.Finally, the Continental Terminal includes many highly ferruginous levels which can be exploited for Iron Ore. The presence of other minerals like Uranium has also been observed in areas underlain by several hundreds of metres of Continental Terminal Sediments.

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Zusammenfassung Der Terminus »Continental Terminal« wurde vonKillan (1931) für die Sahara-Sedimente des Miozän-Pliozän erstmals definiert. Seit der Einführung dieses Terminus jedoch wurde er häufig mißverstanden. Man dehnte ihn schließlich auf die gesamten eisenhaltigen Sedimente des Westafrikanischen Küstenbeckens aus.In der vorliegenden Arbeit wird der Terminus ausschließlich für die posteozänen und präquarternären Kontinental-Sedimente, die nach oben sowie nach unten sich durch geodynamische Ereignisse abgrenzen lassen, verwendet. Es handelt sich hier um geodynamische Ereignisse, deren Synchronisierung in Nord- und Westafrika zwar umstritten ist, jedoch in ihrer Gesamtheit weiträumig auf verwandte Streßstrukturen zurückzuführen sind.Die angesprochenen kontinentalen Ablagerungen sind von großer ökonomischer Bedeutung. Sie bilden die zahlreichen Wasserträger-Schichten, die Millionen von Menschen im Nordwesten und Nordosten Nigerias, sowie in der benachbarten Niger-Republik mit Wasser versorgen. Ihre Mudstones werden als Bau- und Versatzstoffe in Konstruktionsarbeiten verwendet und wegen ihrer Porosität bilden sie ein geeignetes Material für die Druckverteilungsschichten im Straßenbau. Eine weitere Verwendung dieser Sedimente kann — wegen ihres hohen Kaolingehaltes — in der Keramik- und Ziegelei-Industrie eine große Bedeutung finden.Abschließend muß auf die Wichtigkeit der eisenhaltigen Horizonte dieser Ablagerungen als potentielle Erzlagerstätten hingewiesen werden. Berichte über uranhaltige Horizonte sind ebenfalls von Gebieten, deren Untergrund aus mehreren hundert Metern »Continental Terminal«-Sedimenten besteht, bekannt.

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Résumé Killan (1931) a été le premier à donner la définition de Continental Terminal aux sédiments continentaux du Sahara qui datent du Miocène-Pliocène. Depuis l'introduction de ce terme, on est arrivé à l'employer à tort, et l'on désigne sous le terme »Continental« les sédiments tertiaires ferruginisés d'origine marine dans les bassins littoraux d'Afrique de l'Ouest.Dans cette étude, ce terme est appliqué aux sédiments continentaux du Post-Eocène et du Pré-Quaternaire avec des limites supérieures et inférieures bien précises. D'après la nouvelle définition, les limites supérieures et inférieures du Continental Terminal sont déterminées par des phénomènes géodynamiques. Bien que ces phénomènes tectoniques ne se soient pas produits au même moment dans toute l'Afrique du Nord et l'Afrique de l'Ouest, on estime qu'ils ont été causés par des phénomènes tectoniques similaires sur une échelle régionale.Ces dépôts continentaux ont eu et ont encore une importance économique considerable en Afrique de l'Ouest ainsi que dans d'autres parties d'Afrique. Ils alimentent plusieurs aquifères qui constituent la source d'eau principale pour des millions d'habitants dans le nord-ouest et le nord-est du Nigéria ainsi que dans la République du Niger voisine. Les pélites constituent également une source abondante pour les matériaux de construction. Les sédiments servent aussi largement de support de subsurface dans les travaux de construction industrielle et leur porosité permet de les employer comme matériaux de substratum dans le cadre des vastes projets de construction de routes dans la région. Les argiles riches en kaolin pourraient fournir une matière première précieuse pour la fabrication de la céramique et de la brique.Finalement, le Continental Terminal comprend de nombreux niveaux extrêmement ferrugineux que l'on peut exploiter pour en extraire du minerai de fer. L'on a également observé qu'il existait d'autres minéraux comme l'uranium dans des régions reposant sur des sédiments du Continental Terminal ayant plusieurs centaines de mètres d'épaisseur.

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Continental Terminal 1931 - . , , - . - - ; , , . . , - - , . , — - — . , o . , . , Continental Terminal .

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This paper is a contribution to the IGCP Project 127 on the Concept of the Continental Terminal in Africa.  相似文献   

Aquatic vegetation of Lake Annecy     

J. P. Dubois  G. Blake  P. Gerbeaux  G. Brun 《Aquatic Sciences - Research Across Boundaries》1988,50(1):96-110

Aquatic vegetation (macrophytes) of lake Annecy has been studied in summer 1981 by underwater observation. Cartography of the plants has been achieved and compared with earlier studies. Emergent plants have regressed. Submerged vegetation is dominated by Charophyceae.  相似文献