Enregistrement de la variabilité hydroclimatique au cours des 6500 dernières années sur le littoral de Cabo Frio (Rio de Janeiro,Brésil)

This study concerns a core collected in Brejo do Espinho's lagoon from Cabo Frio littoral (Brazil) submitted to dry influence of local upwelling controlled by north-east trade winds from the South Atlantic and particularly strengthened during El Niño events. Diatoms study supported by sedimentological and isotopic analyses shows dry phases infrequent before 4000 yr, a highly variable climatic phase between 3600 and 2900 yr and from 2400 yr onward a dryness enhancement. To cite this article: B. Laslandes et al., C. R. Geoscience 338 (2006).     

珠江流域降水干湿时空特征及气候因子影响研究

利用模糊C-均值聚类算法、皮尔逊相关和滑动相关分析等方法,对珠江流域做了气候一致性分析,在此基础上,研究了珠江流域不同分区年降水和干湿季降水变化的时空特征,分析了区域干湿变化与厄尔尼诺-南方涛动(ENSO)、北大西洋涛动(NAO)、印度洋偶极子(IOD)和太平洋10年涛动(PDO)等主要气候因子的遥相关关系,探讨了珠江流域干湿变化的气候成因。在此基础上,进一步研究上述气候指标对不同时间尺度干湿变化影响的平稳性与差异性。除此之外,还研究了气候指标的冷暖期对基于6个月SPI值的珠江流域干湿状态的影响。研究表明:(1)IOD、NAO和ENSO分别是导致珠江流域年降水、湿季降水和干季降水发生变化的主要影响因素,且对当年及下一年降水的影响是相反的。(2)珠江流域不同时间尺度的降水与对其有显著影响的气候指标(年降水与IOD,湿季降水与NAO,干季降水与ENSO),两者之间不同时期的滑动相关往往具有较强的相关性和前后相关一致性。(3)各气候指标对珠江流域不同时间尺度降水的影响在空间分布上不太均匀。(4)不同位相下气候指标对珠江流域干湿状态的影响存在较大差异。总体而言,当处于各气候指标暖期时珠江流域出现湿润期的概率较冷期时更大且在空间分布上更均匀。     

Datation UPb sur zircons des dolérites tholéiitiques pyrénéennes (ophites) à la limite Trias–Jurassique et relations avec les tufs volcaniques dits « infra-liasiques » nord-pyrénéens

The tholeiitic doleritic magmatism (ophites) in the Aspe valley of the Pyrenees has been dated on the Triassic–Jurassic boundary (199±2 Ma) by the UPb method on zircon (SHRIMP). Emplacement of the ophites was probably synchronous with that of the earliest ‘Infraliassic’ Ségalas tuffs. The ophites are thus related to the Central Atlantic Magmatic Province (CAMP) whose emplacement linked with the fracturing of Pangea, preceded the opening of the Atlantic Ocean. To cite this article: P. Rossi et al., C. R. Geoscience 335 (2003).     

Sur la structure,l'âge et l'origine des « brèches de Bosmendiette » (Pyrénées-Atlantiques)

By us considered as Albo-Aptian in age and generated through halokinetic processes, the Bosmendiette breccias have been recently interpreted as Selandian (Palaeocene) globigerine-bearing sediments deposited in sub-marine canyons within a deep trough crossing the Pyrenees, from the Mediterranean Sea to the Atlantic Ocean. These breccias are really azoic in their lower part and contain a scarce microfauna including radolarians and benthic foraminifera at the top of the formation. They are unconformably covered by the Urgo-Aptian limestones and marls and indicate, under opening marine conditions, Lower Cretaceous collapse movements and northward sliding of the Jurassic slumped cover, related to the growth of the Béloscare–Apoura diapir. To cite this article: J. Canérot et al., C. R. Geoscience 336 (2004).     

Amazon River discharge estimated from TOPEX/Poseidon altimetry

This paper presents an application of the TOPEX/Poseidon (T/P) satellite altimetry data to estimate river discharge at three sites along the Amazon River. We discuss the methodology to establish empirical relationships between satellite-derived water levels and daily estimations of river discharges based on rating curves and in situ level measurements at gauging stations. Three sites are chosen: Manacapuru (River Solimões), Jatuarana (nearby the confluence of the Solimões and Rio Negro rivers) and Óbidos (Amazon River). We then reconstruct the satellite-based river discharge over a 10-year time span (1992–2002). Comparison between satellite-derived and river discharge at the gauging stations shows that the T/P data can successfully be used for hydrological studies of large rivers, in providing in particular discharge estimates when in situ data are not available. To cite this article: E.A. Zakharova et al., C. R. Geoscience 338 (2006).     

Differential modulation of eastern oyster (<Emphasis Type="Italic">Crassostrea virginica</Emphasis>) disease parasites by the El-Niño-Southern Oscillation and the North Atlantic Oscillation

The eastern oyster (Crassostrea virginica) is affected by two protozoan parasites, Perkinsus marinus which causes Dermo disease and Haplosporidium nelsoni which causes MSX (Multinucleated Sphere Unknown) disease. Both diseases are largely controlled by water temperature and salinity and thus are potentially sensitive to climate variations resulting from the El Niño-Southern Oscillation (ENSO), which influences climate along the Gulf of Mexico coast, and the North Atlantic Oscillation (NAO), which influences climate along the Atlantic coast of the United States. In this study, a 10-year time series of temperature and salinity and P. marinus infection intensity for a site in Louisiana on the Gulf of Mexico coast and a 52-year time series of air temperature and freshwater inflow and oyster mortality from Delaware Bay on the Atlantic coast of the United States were analyzed to determine patterns in disease and disease-induced mortality in C. virginica populations that resulted from ENSO and NAO climate variations. Wavelet analysis was used to decompose the environmental, disease infection intensity and oyster mortality time series into a time–frequency space to determine the dominant modes of variability and the time variability of the modes. For the Louisiana site, salinity and Dermo disease infection intensity are correlated at a periodicity of 4 years, which corresponds to ENSO. The influence of ENSO on Dermo disease along the Gulf of Mexico is through its effect on salinity, with high salinity, which occurs during the La Niña phase of ENSO at this location, favoring parasite proliferation. For the Delaware Bay site, the primary correlation was between temperature and oyster mortality, with a periodicity of 8 years, which corresponds to the NAO. Warmer temperatures, which occur during the positive phase of the NAO, favor the parasites causing increased oyster mortality. Thus, disease prevalence and intensity in C. virginica populations along the Gulf of Mexico coast is primarily regulated by salinity, whereas temperature regulates the disease process along the United States east coast. These results show that the response of an organism to climate variability in a region is not indicative of the response that will occur over the entire range of a particular species. This has important implications for management of marine resources, especially those that are commercially harvested.     

Enrichissement en uranium authigène dans les sédiments glaciaires de l'océan AustralEnrichments in authigenic uranium in glacial sediments of the Southern Ocean

Four sediment cores from the Polar frontal zone and the Antarctic zone in the Indian sector of the Southern Ocean present an increase of authigenic uranium during glacial periods. We show that this increase in uranium is due to a combination of (i) an increase in the lateral transport of organic matter, (ii) a decrease in the oxygen in deep waters, and (iii) a process of diagenesis. It appears that uranium concentration cannot be used as a proxy of palaeoproductivity in the Southern Ocean, as previously suggested by Kumar et al. in 1995. To cite this article: L. Dezileau et al., C. R. Geoscience 334 (2002) 1039–1046.     

Un nouveau point de départ pour l'histoire de l'Atlantique central

The first oceanic crust in the central Atlantic is usually thought to have a Middle Jurassic age. The new interpretation of the two key parameters, the African homologue of the East Coast Magnetic Anomaly and the situation of the Triassic salt basin of Morocco and Novia Scotia, shows that this age was underestimated by about 20 Ma. In our kinematic reconstruction, the first oceanic crust begins at the Late Sinemurian. This difference in age is crucial for the evolution of those margins and we discuss here its consequences. To cite this article: M. Sahabi et al., C. R. Geoscience 336 (2004).     

Variabilité spatiale du signal palynologique dans le bassin de Paris à la limite Dogger–Malm

The drilling of new cores performed for ANDRA in eastern France allowed us to compare palynological data between central and eastern parts of the Paris Basin. Such a comparison, which was also motivated by the existence of a set of geochemical data in contradiction with the first palynological results, showed a spatial differentiation in palynological record from the Oxfordian. Such a palynological signal could result from overlapping of both local and global signals, the latter being in connection with the contemporaneous opening of proto-Atlantic Ocean. It could also be of major palaeogeographic and palaeoclimatic interest. To cite this article: V. Huault et al., C. R. Geoscience 335 (2003).     

Apport des marqueurs isotopiques et biogéochimiques dans la reconstitution du paléoenvironnement de la grotte du Lazaret (Nice,Alpes-Maritimes) au cours du Pléistocène supérieur (stade isotopique 5)

The isotopic composition of calcite from the stalagmitic floor E of the Lazaret Cave is interpreted as proxy of atmospheric circulation and vegetal cover changes during IOS 5. The ${\delta }^{18}\mathrm{O}$ variations could indicate change in precipitation sources, which could originate from the Mediterranean Sea during warm periods and from the Atlantic Ocean during colder periods. The ${\delta }^{13}\mathrm{C}$ variations could be related to vegetal cover and soil type. Tree cover appears to be dominant according to pollen spectra, and organic molecules trapped into calcite (sterols, terpenoids, humic acids). To cite this article: L. Rousseau et al., C. R. Geoscience 337 (2005).     

Satellite-Derived ERS scatterometer sea-surface wind-stress curl in the southwestern Indian Ocean

Surface marine wind data base from ERS-1 scatterometer has been processed to define the characteristic seasonal distribution of wind-stress curl throughout the southwestern Indian Ocean between January and December 1994. A compact model to obtain satellite-derived wind-stress curl fields on smaller scales than previously available is proposed and evaluated. The results indicate the strong capability of the ERS-1 scatterometer to monitor wind-driven variations in the mesoscale ocean patterns. To cite this article: M. Petit et al., C. R. Geoscience 338 (2006).     

Three monthly coral Sr/Ca records from the Chagos Archipelago covering the period of 1950–1995 A.D.: reproducibility and implications for quantitative reconstructions of sea surface temperature variations

In order to assess the fidelity of coral Sr/Ca for quantitative reconstructions of sea surface temperature variations, we have generated three monthly Sr/Ca time series from Porites corals from the lagoon of Peros Banhos (71°E, 5°S, Chagos Archipelago). We find that all three coral Sr/Ca time series are well correlated with instrumental records of sea surface temperature (SST) and air temperature. However, the intrinsic variance of the single-core Sr/Ca time series differs from core to core, limiting their use for quantitative estimates of past temperature variations. Averaging the single-core data improves the correlation with instrumental temperature (r > 0.7) and allows accurate estimates of interannual temperature variations (~0.35°C or better). All Sr/Ca time series indicate a shift towards warmer temperatures in the mid-1970s, which coincides with the most recent regime shift in the Pacific Ocean. However, the magnitude of the warming inferred from coral Sr/Ca differs from core to core and ranges from 0.26 to 0.75°C. The composite Sr/Ca record from Peros Banhos clearly captures the major climatic signals in the Indo-Pacific Ocean, i.e. the El Niño–southern oscillation and the Pacific decadal oscillation. Moreover, composite Sr/Ca is highly correlated with tropical mean temperatures (r = 0.7), suggesting that coral Sr/Ca time series from the tropical Indian Ocean will contribute to multi-proxy reconstructions of tropical mean temperatures.     

Discovery of the Paleo-Tethys residual peridotites along the Anyemaqen–KunLun suture zone (North Tibet)

The spinel peridotite from the Anyemaqen suture contains ?5% residual clinopyroxene and is characterized by a high abundance of the magmaphile elements Fe, Al and Ti in the primary mineral phases. Our data demonstrate that this rock represents residual mantle material, which has been affected by less than 10% partial melting prior to its emplacement. Its textural features indicate that the rock has been plastically deformed in a non-coaxial regime under lithospheric physical conditions at a relatively cool thermal regime below solidus temperature. We suggest that the peridotites from the Anyemaqen suture represent mantle material, which was either emplaced during incipient rifting on the Palaeozoic passive margin of Asia, or uplifted at slow spreading ridge setting in Paleo-Tethyan Ocean. Further researches are needed to make a definite choice between these two alternatives. To cite this article: E.A. Konstantinovskaia et al., C. R. Geoscience 335 (2003).     

New data on the palaeobiogeography of Loftusia genus (Foraminiferida). An in situ presence of the genus in eastern Greece (Boeotia)

An Upper Maastrichtian horizon rich in Loftusia is for the first time described in situ in Greece in the province of Boeotia. It is found in a continuous undisturbed carbonate sequence of the eastern Greece platform (Subpelagonian zone) of Maastrichtian–Paleocene age followed by flysch sedimentation. Loftusia is found in a facies reflecting an outer shelf environment, associated with debris of rudists, Orbitoides spp., Siderolites calcitrapoides, Omphalocyclus macroporus, Hellenocyclina beotica, Sulcoperculina sp., and echinoderms. Similar fauna, but without Loftusia, is found in the surrounding levels of Late Maastrichtian age as well. This recovery of the genus in the western part of its distribution area, where it is not as abundant as in the eastern part, is considered significant for the palaeobiogeography of the genus in Tethys Ocean during Late Cretaceous. To cite this article: A. Zambetakis-Lekkas, A. Kemeridou, C. R. Geoscience 338 (2006).     

Enhancement of regional variations in salinity and temperature in a coral reef lagoon, New Caledonia

The variability in salinity and temperature in the southwest lagoon of New Caledonia (2100 km²) under non-storm conditions is analysed using a 4-year dataset (1997–2001). Seasonal and interannual variations in salinity are amplified nearshore. Temperature is larger in bays than in the open lagoon during summer, the reverse is true in winter. El Niño Southern Oscillation (ENSO) related nearshore temperature variations parallel those at regional scale, but with seasonal variations amplified. Haline stratification, if any, is enhanced in coastal areas. To cite this article: S. Ouillon et al., C. R. Geoscience 337 (2005).     

Apports de la modélisation sur bathymétries historiques dans la compréhension des évolutions des bancs de sable estuariens

Formation and evolution of estuarine sand ridges are some of the less well known among the different classes of sand banks. Simulation of tides and related sand bedload transport on historical bathymetries brings new insights about the secular evolution of two estuarine sand ridges (the Saint-Georges and the ‘Longe de Boyard’ sand banks, Atlantic coast of France). Two different mechanisms are involved in order to explain the evolutions of these banks, suggesting the category of estuarine sand banks to be less homogenous than it is proposed in the last classifications of sand banks. To cite this article: X. Bertin, É. Chaumillon, C. R. Geoscience 337 (2005).     

Modélisation du transport réactif en milieux poreux non saturés avec une méthode ELLAM en maillage variable

Modelling contaminant transfer with biological/chemical/radioactive processes needs appropriate numerical methods able to reproduce sharp concentration fronts. In this work, we develop a new Eulerian–Lagrangian Localized Adjoint Method (ELLAM) for solving the reactive transport equation with non-constant coefficients. To avoid interpolation (leading to errors), we use a moving grid to define the solution and test functions. The method is used to simulate first the infiltration of solute into a column of unsaturated porous medium and second the multispecies transport. The developed ELLAM gives accurate results without non-physical oscillations or numerical diffusion, even when using large time steps. To cite this article: A. Younes, C. R. Geoscience 336 (2004).     

Comportement de l'oscillateur DORIS/Jason au passage de l'anomalie sud-atlantique

We point out an acceleration of the DORIS clock on-board the Jason satellite during passes over the South Atlantic Anomaly (SAA). When this effect is ignored in the current geodetic positioning of the DORIS stations, derived coordinates show almost linear trends in time, corresponding to anomalous horizontal and vertical velocities of the order of 1 m yr^?1. We propose a simple scientific explanation of this physical phenomenon that is corroborated by direct Jason/TOPEX clock comparisons with respect to the DORIS master beacons in Kourou and Toulouse. To cite this article: P. Willis et al., C. R. Geoscience 336 (2004).     

Variability of the Intertropical Convergence Zone recorded in coral isotopic records from the central Indian Ocean (Chagos Archipelago)

We have analyzed the stable oxygen isotopic composition of two Porites corals from the Chagos Archipelago, which is situated in the geographical center of the Indian Ocean. Coral δ¹⁸O at this site reliably records temporal variations in precipitation associated with the Intertropical Convergence Zone (ITCZ). Precipitation maxima occur in boreal winter, when the ITCZ forms a narrow band across the Indian Ocean. The Chagos then lies within the center of the ITCZ, and rainfall is strongly depleted in δ¹⁸O. A 120-yr coral isotopic record indicates an alternation of wet and dry intervals lasting 15 to 20 yr. The most recent 2 decades are dominated by interannual variability, which is tightly coupled to the El Niño-Southern Oscillation (ENSO). This is unprecedented in the 120 yr of coral record. As the ITCZ is governed by atmospheric dynamics, this provides evidence of a major change in the coupled ENSO-monsoon system.     

古里雅冰芯气候记录对ENSO事件的响应

ENSO现象是一个产生于大尺度海-气相互作用的全球事件, 它是影响全球中低纬度大部分地区气候年际变化的一个重要的因子. 通过高通滤波法、累积异常法以及非参数检验等方法, 对古里雅冰芯中所记录的气候信息与ENSO事件进行相关分析表明, 在厄尔尼诺年, 古里雅冰芯中记录的降水量显著减少, 但对于δ¹⁸O而言, 虽然也在厄尔尼诺年偏低, 但未达到显著性水平.