Abrupt millennial variability and interdecadal-interstadial oscillations in a global coupled model: sensitivity to the background climate state     

Olivier Arzel  Matthew H. England  Alain Colin de Verdière  Thierry Huck 《Climate Dynamics》2012,39(1-2):259-275

The origin and bifurcation structure of abrupt millennial-scale climate transitions under steady external solar forcing and in the absence of atmospheric synoptic variability is studied by means of a global coupled model of intermediate complexity. We show that the origin of Dansgaard-Oeschger type oscillations in the model is caused by the weaker northward oceanic heat transport in the Atlantic basin. This is in agreement with previous studies realized with much simpler models, based on highly idealized geometries and simplified physics. The existence of abrupt millennial-scale climate transitions during glacial times can therefore be interpreted as a consequence of the weakening of the negative temperature-advection feedback. This is confirmed through a series of numerical experiments designed to explore the sensitivity of the bifurcation structure of the Atlantic meridional overturning circulation to increased atmospheric CO₂ levels under glacial boundary conditions. Contrasting with the cold, stadial, phases of millennial oscillations, we also show the emergence of strong interdecadal variability in the North Atlantic sector during warm interstadials. The instability driving these interdecadal-interstadial oscillations is shown to be identical to that found in ocean-only models forced by fixed surface buoyancy fluxes, that is, a large-scale baroclinic instability developing in the vicinity of the western boundary current in the North Atlantic. Comparisons with modern observations further suggest a physical mechanism similar to that driving the 30–40?years time scale associated with the Atlantic multidecadal oscillation.  相似文献   

Holocene circum-Mediterranean vegetation changes: Climate forcing and human impact   总被引：2，自引：0，他引：2  

Guy Jalut  Jean Jacques Dedoubat  Michel Fontugne  Thierry Otto 《Quaternary International》2009,200(1-2):4

The Mediterranean climate and its variability depend on global-scale climate patterns. Close correlations appear when comparing Holocene palaeoenvironmental data (lake levels, fluvial activity, Mediterranean surface temperature and salinity, marine sedimentation) with the main stages of the history of the circum-Mediterranean vegetation. They indicate an evolution of the Mediterranean biome controlled by the climate and emphasize the teleconnections between the climate of the Mediterranean area and the global climatic system. In the circum-Mediterranean area, the Holocene can be divided into three periods: a lower humid Holocene (11 500–7000 cal BP) interrupted by dry episodes; a transition phase (7000–5500 cal BP) during which occurred a decrease in insolation as well as the installation of the present atmosphere circulation in the northern hemisphere; and an upper Holocene (5500 cal BP—present) characterized by an aridification process. Throughout the Holocene, humans used and modified more or less strongly the environment but the climatic changes were the determining factors of the evolution of the Mediterranean biome. Societies had to adapt to natural environmental variations, their impact on the environment increasing the ecological consequences of the global changes.  相似文献   

Grain structure of the Earth's inner core     

Lucile Venet  Thierry Duffar  Renaud Deguen 《Comptes Rendus Geoscience》2009,341(7):513-516

The coarsening rate of an initial grain structure is calculated and compared to the inner core growth rate. An estimate of the present size of the grains in the centre of the core varies from 560 m to 12 km, depending on the value taken for the diffusion coefficient of iron in the core. Regardless of the hypotheses chosen, this size is homogeneous inside the inner core.  相似文献   

Neubenennungen lithostratigraphischer Einheiten in der Helvetischen Kreide     

Schweizerisches Komitee für Stratigraphie  Thierry Adatte  Jean-Pierre Berger  Hansruedi Bläsi  Reto Burkhalter  Stephan DallAgnolo  Danielle Decrouez  Hanspeter Funk  Heinz Furrer  Yves Gouffon  Hansruedi Graf  Werner Heckendorn  Wilfried Winkler 《Swiss Journal of Geoscience》2009,102(2):363-364

In September 2007 Föllmi and coauthors requested the approval of four lithostratigraphic terms of the Swiss Committee of Stratigraphy (SCS). These terms were to be used in their publication on the Cretaceous in the Helvetic realm (Föllmi et al. 2007). At its meeting on October 18, 2007, the SCS decided the following: The Tierwis Formation (replacing the Drusberg Formation) was accepted, with the reserve that a section at Tierwis should be published in the near future. For the former “Lower Orbitolina Beds” the term Rawil Member was accepted, but here too a better type section than the one at Rawil Pass should be published. The term Rohrbachstein bed should not be used as a formal unit because it describes only a minor lithologic variation within the Grünten Member. The term Plaine Morte bed for a thin condensed horizon can not be accepted due to the fact that its definition is based mainly on biostratigraphy. Furthermore, the duplication a locality term which is in use for a previously established lithostratigraphic unit should be avoided.  相似文献   

Relationships between hydrosedimentary processes and occurrence of mercury-resistant bacteria (merA) in estuary mudflats (Seine, France)     

Ramond JB  Berthe T  Lafite R  Deloffre J  Ouddane B  Petit F 《Marine pollution bulletin》2008,56(6):1168-1176

The Seine estuary (France) is one of the world's macrotidal systems that is most contaminated with heavy metals. To study the mercury-resistant bacterial community in such an environment, we have developed a molecular tool, based on competitive PCR, enabling the quantification of Gram-negative merA gene abundance. The occurrence of the Gram-negative merA gene in relation with the topology (erosion/deposit periods) and the mercury contamination of three contrasted mudflats was investigated through a multidisciplinary approach and compared with a non-anthropized site (Authie, France). The higher abundance of the Gram-negative merA gene in the Seine estuary mudflats indicates a relationship between the degree of anthropization and the abundance of the merA gene in the mudflat sediments. In the Seine mudflats, the maxima of abundance are always located in fresh sediment deposits. Therefore, the abundance is closely related with the hydrosedimentary processes, which thus seem to be determining factors in the occurrence of the Gram-negative merA gene in the surface sediments of the Seine's mudflat.  相似文献   

Faecal-indicator bacteria and sedimentary processes in estuarine mudflats (Seine, France)     

Berthe T  Touron A  Leloup J  Deloffre J  Petit F 《Marine pollution bulletin》2008,57(1-5):59-67

Over a three-year period, quantification of faecal indicators and the molecular detection of Escherichia coli and Salmonella were monitored in sediments from three contrasting mudflats of the Seine estuary (France). The elevation of the mudflat surface was monitored concurrently using a high-resolution altimeter. During the period of the study, estuarine mudflats were areas of deposition for faecal-indicator bacteria and were mainly controlled by sedimentary processes. In the intertidal freshwater and subtidal mudflats, the highest abundances of faecal-indicator bacteria were counted during a depositional period. Maximum levels were observed in the freshwater mudflats during periods of high flow: thermotolerant coliforms: 3.9 x 10(4) cfu cm(-2), enterococci: 1.2 x 10(4) cfu cm(-2), Clostridium perfringens spores: 9.8 x 10(5) spores cm(-2). Loss of culturability of enteric bacteria in sediment microcosms demonstrated the remediatory capacity of the mudflats, even if they might be a secondary source of bacteria-forming spores to the water column through erosion and resuspension events.  相似文献   

Comments on Muxika et al. "using historical data, expert judgement and multivariate analysis in assessing reference conditions and benthic ecological status, according to the European Water Framework Directive" [Marine Pollution Bulletin 55 (2007) 16-29     

Ruellet T  Dauvin JC 《Marine pollution bulletin》2008,56(6):1234-1235

  相似文献   

Circulation of bubbly magma and gas segregation within tunnels of the potential Yucca Mountain repository     

Thierry Menand  Jeremy C. Phillips  R. Stephen J. Sparks 《Bulletin of Volcanology》2008,70(8):947-960

Following an intersection of rising magma with drifts of the potential Yucca Mountain nuclear waste repository, a pathway is likely to be established to the surface with magma flowing for days to weeks and affecting the performance of engineered structures located along or near the flow path. In particular, convective circulation could occur within magma-filled drifts due to the exsolution and segregation of magmatic gas. We investigate gas segregation in a magma-filled drift intersected by a vertical dyke by means of analogue experiments, focusing on the conditions of sustained magma flow. Degassing is simulated by electrolysis, producing micrometric bubbles in viscous mixtures of water and golden syrup, or by aerating golden syrup, producing polydisperse bubbly mixtures with 40% of gas by volume. The presence of exsolved bubbles induces a buoyancy-driven exchange flow between the dyke and the drift that leads to gas segregation. Bubbles segregate from the magma by rising and accumulating as a foam at the top of the drift, coupled with the accumulation of denser degassed magma at the base of the drift. Steady-state influx of bubbly magma from the dyke into the drift is balanced by outward flux of lighter foam and denser degassed magma. The length and time scales of this gas segregation are controlled by the rise of bubbles in the horizontal drift. Steady-state gas segregation would be accomplished within hours to hundreds of years depending on the viscosity of the degassed magma and the average size of exsolved gas bubbles, and the resulting foam would only be a few cm thick. The exchange flux of bubbly magma between the dyke and the drift that is induced by gas segregation ranges from 1 m³ s⁻¹, for the less viscous magmas, to 10⁻⁸ m³ s⁻¹, for the most viscous degassed magmas, with associated velocities ranging from 10⁻¹ to 10⁻⁹ m s⁻¹ for the same viscosity range. This model of gas segregation also predicts that the relative proportion of erupted degassed magma, that could potentially carry and entrain nuclear waste material towards the surface, would depend on the value of the dyke magma supply rate relative to the value of the gas segregation flux, with violent eruption of gassy as well as degassed magmas at relatively high magma supply rates, and eruption of mainly degassed magma by milder episodic Strombolian explosions at relatively lower supply rates.  相似文献   

A discrete spherical harmonics method for radiative transfer analysis in inhomogeneous polarized planar atmosphere     

Romuald Tapimo  Hervé Thierry Tagne Kamdem  David Yemele 《Astrophysics and Space Science》2018,363(3):52

A discrete spherical harmonics method is developed for the radiative transfer problem in inhomogeneous polarized planar atmosphere illuminated at the top by a collimated sunlight while the bottom reflects the radiation. The method expands both the Stokes vector and the phase matrix in a finite series of generalized spherical functions and the resulting vector radiative transfer equation is expressed in a set of polar directions. Hence, the polarized characteristics of the radiance within the atmosphere at any polar direction and azimuthal angle can be determined without linearization and/or interpolations. The spatial dependent of the problem is solved using the spectral Chebyshev method. The emergent and transmitted radiative intensity and the degree of polarization are predicted for both Rayleigh and Mie scattering. The discrete spherical harmonics method predictions for optical thin atmosphere using 36 streams are found in good agreement with benchmark literature results. The maximum deviation between the proposed method and literature results and for polar directions \(\vert \mu \vert \geq0.1 \) is less than 0.5% and 0.9% for the Rayleigh and Mie scattering, respectively. These deviations for directions close to zero are about 3% and 10% for Rayleigh and Mie scattering, respectively.  相似文献   

Benthic indicators and index approaches in the three main estuaries along the French Atlantic coast (Seine, Loire and Gironde)     

Jean-Claude Dauvin  Guy Bachelet  Anne-Laure Barillé  Hugues Blanchet  Xavier de Montaudouin  Nicolas Lavesque  & Thierry Ruellet 《Marine Ecology》2009,30(2):228-240

The three main estuaries in the French Atlantic coast – the Seine, Loire and Gironde, all with high tidal regimes – are interfaces between the continental and the coastal ecosystems. The Seine and Gironde are highly contaminated, whereas the Loire remains in a more natural state. Both the Seine and Gironde have suffered from harbour construction, and as a result, their biological units are extremely compartmentalized. Benthic species and communities have adapted to tolerate temporal physical and chemical changes ( e.g. salinity, substrata, depth, and levels of fine particles and oxygen) and human activities ( e.g. dredging, shipping traffic, and habitat reduction). Although numerous bio-indicators and indices are used to define the ecological quality status (EcoQS) of coastal waters, very few of them were developed specifically for environments with a mosaic of conditions and salinity levels, including freshwater. The main problem appears to be that all the indices for determining anthropogenic stress examine the abundances of stress-tolerant species, which may also be able to tolerate natural stressors such as those occurring in estuaries. This paper takes a look at the development status of the benthic indicators and index approaches used in the three main estuaries along the French Atlantic coast. In addition, it examines the adaptation of the different benthic indicators to the taxonomic sufficiency principle, and the adaptation of the Benthic Opportunistic Polychaetes Amphipods index (BOPA) and the Benthic Opportunistic Annelida Amphipod index (BO2A) for use in the freshwater zones of transitional waters ( i.e. up to the upper limit of the tidal range). Several perspectives are discussed in light of the diverse disturbances and the heterogeneity of such stressed zones, such as the use of multimetric and scoring approaches.  相似文献