New frontiers in calcium stable isotope geochemistry:Perspectives in present and past vertebrate biology

International audienc

Analyse vibratoire numérique et expérimentale d'un système couplé "voie ferrée - sol"

International audienceResults of railway traffic, concerning with the environmental disturbances (vibrations, noises, various pollutions, ...) are all the more important as the train velocities are higher. For vibrations, the effect of this velocity is directly linked to its relative value against that of waves propagating in the soil (particularly for Rayleigh surface waves). For soft soils (clay, peat, ...), a Rayleigh wave velocity very lower than 100 m/s is quite possible, and in this case, the reach of a super-Rayleigh regime can be envisaged for trains moving at high velocity. This situation includes important displacements in the rail (sometimes higher than 12 mm), not acting on the passengers comfort but troubling for the life duration of structure. This paper describes the numerical approach with a semi-analytical model for the waves propagation in the case of moving loadings. Also, sets of tests were able to be performed on two specific sites (peaty soil) with variable parameters (type and composition of trains, train velocity, traffic weight). The comparison achieved between displacements and velocities, obtained on the one hand through the numerical simulations and on the other hand by means of test measurements, must pass for a relatively satisfactory result, taking into account the numerous uncertainties in the two approaches. This agreement is enough correct to consider that the proposed model allows to obtain accurate informations for the railway behaviour and that of the surrounding soil.Les conséquences de la circulation ferroviaire, en termes de nuisances environnementales (vibrations, bruits, pollutions diverses, ...) sont d'autant plus importantes que les vitesses des trains sont élevées. En ce qui concerne les vibrations, l'effet de cette vitesse est directement lié à son positionnement relatif vis-à-vis de celle des ondes se propageant dans le sol (en particulier, celle des ondes superficielles de Rayleigh). Pour des sols assez mous (argile, tourbe, ...), une vitesse d'onde de Rayleigh bien inférieure à 100 m/s est tout-à-fait possible, et dans ce cas, l'atteinte d'un régime super-Rayleigh est bien envisageable pour des trains circulant à grande vitesse. Cette situation se traduit par des déplacements importants au niveau du rail (supérieurs éventuellement à 12 mm), ne jouant pas sur le confort des passagers mais préoccupant pour la durée de vie de la structure. Cet article présente la mise en œuvre numérique d'un modèle semi-analytique de propagation d'ondes soumis à un ensemble de charges mobiles. Des séries d'essais ont pu également être opérées sur deux sites spécifiques (sol tourbeux) avec des paramètres variables (type et composition des trains, vitesse du train, poids du convoi). La comparaison qui a pu être réalisée entre les déplacements et les vitesses obtenus, d'une part, grâce aux simulations numériques et, d'autre part, par les mesures expérimentales, doit être considérée comme relativement satisfaisante compte tenu des différentes incertitudes présentes dans les deux démarches. Cet accord est suffisamment significatif pour estimer que le modèle qui est proposé permet d'obtenir des informations crédibles sur le comportement de la voie et du sol environnant

Assessing atmospheric and oceanic teleconnections between the eastern and western Mediterranean over the past 8000 years

Holocene climate records from the Mediterranean are marked by pervasive millennial to centennial-scale climate variability. Here, we investigate East-West Mediterranean atmospheric and oceanic teleconnections by computing phase-relationships between oxygen isotope (δ18O) records generated on Soreq (East) and Chorchia (West) spelaeothems, as well as between δ18O and carbon isotope (δ13C) records from planktonic and benthic foraminifera from core PS009PC (East, Levantin Basin), ODP Site 963D (Central, Sicily Strait), and core KESC9-14 (West, Ligurian Basin). These marine sites are all located at intermediate water depths (560–460 m depth). Hence, the benthic foraminiferal δ18O records reflect mainly the intermediate ocean temperature/δ18O of the water mass, and the benthic δ13C is a proxy for the intensity of water flowing at the studied depth called Levantine Intermediate Water (LIW). For both western and eastern cores, the planktonic stable isotopic records reflect the climate-induced activity of the nearby river system. We find broadly in-phase relationships between the spelaeothem δ18O records and between the planktonic δ18O and δ13C records at most multi-centennial and millennial periodicities. This is indicative of closely linked (hydro-) climatic conditions in Southern Europe, the Levant, and North Africa over the last 8000 years. Conversely, at intermediate water depths, we find a distinct out-of-phase relationship between the East/Central and West Mediterranean benthic δ18O and δ13C records at 1000–2000 years periodicities. We interpret this see-saw pattern as indicative of a persistent regional influence of LIW on oceanographic conditions in the intermediate depths of the eastern basin. Conversely, we suggest a strong influence of the modified Atlantic Ocean inflow (MAW) in the intermediate water formation in the Western Mediterranean (‘Winter Intermediate Water’; WIW). This WIW overprints, at least partially, the LIW signal that reaches the western Mediterranean causing the out-of-phase relationship between the east and the west oceanographic signals at intermediate depths

Antarctic climate, Southern Ocean circulation patterns, and deep water formation during the Eocene

We assess early-to-middle Eocene seawater neodymium (Nd) isotope records from seven Southern Ocean deep-sea drill sites to evaluate the role of Southern Ocean circulation in long-term Cenozoic climate change. Our study sites are strategically located on either side of the Tasman Gateway and are positioned at a range of shallow (Nd(t) = −9.3 ± 1.5). IODP Site U1356 off the coast of Adélie Land, a locus of modern-day Antarctic Bottom Water production, is identified as a site of persistent deep water formation from the early Eocene to the Oligocene. East of the Tasman Gateway an additional local source of intermediate/deep water formation is inferred at ODP Site 277 in the SW Pacific Ocean (εNd(t) = −8.7 ± 1.5). Antarctic-proximal shelf sites (ODP Site 1171 and Site U1356) reveal a pronounced erosional event between 49 and 48 Ma, manifested by ~2 εNd unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites. This erosional event coincides with the termination of peak global warmth following the Early Eocene Climatic Optimum and is associated with documented cooling across the study region and increased export of Antarctic deep waters, highlighting the complexity and importance of Southern Ocean circulation in the greenhouse climate of the Eocene

Campanian-Maastrichtian ocean circulation in the tropical Pacific

The Pacific Ocean is the largest water body on Earth, and circulation in the Pacific contributed significantly to climate evolution in the latest Cretaceous, the culmination of a period of long-term cooling. Here, we present new high-resolution late Campanian to Maastrichtian benthic and planktic foraminiferal stable isotope data and a neodymium (Nd) isotope record obtained from sedimentary ferromanganese oxide coatings of Ocean Drilling Program Hole 1210B from the tropical Pacific Ocean (Shatsky Rise). These new records resolve 13 million years in the latest Cretaceous, providing insights into changes in surface and bottom water temperatures and source regions of deep to intermediate waters covering the carbon isotope excursions of the Campanian-Maastrichtian Boundary Event (CMBE) and the Mid-Maastrichtian event (MME). Our new benthic foraminiferal δ18O and Nd isotope records together with published Nd isotope data show markedly parallel trends across the studied interval over a broad range of bathyal to abyssal water depths interpreted to reflect changes in the intensity of deep-ocean circulation in the tropical Pacific. In particular, we observe a three-million-year-long period of cooler conditions in the early Maastrichtian (72.5 to 69.5 Ma) when a concomitant change toward less radiogenic seawater Nd isotope signatures probably marks a period of enhanced admixture and northward flow of deep waters with Southern Ocean provenance. We suggest this change to have been triggered by intensified formation and convection of deep waters in the high southern latitudes, a process that weakened during the MME (69.5 to 68.5 Ma). The early Maastrichtian cold interval is closely related to the negative and positive carbon isotope trends of the CMBE and MME. The millions-of-years long duration of these carbon cycle perturbations suggests a tectonic forcing of climatic cooling, possibly related to changes in ocean basin geometry and bathymetry

A review of the Late Permian – Early Triassic conodont record and its significance for the end-Permian mass extinction

As a marine microfossil with a long-lasting fossil record stretching from the Cambrian to the Triassic, the tiny conodont plays an important role for the study of the end-Permian mass extinction. In the past few decades, numerous studies on Permian-Triassic conodonts have been published. This paper summarizes the progress made on high-resolution conodont biostratigraphy, timing of the mass extinction across the Permian-Triassic Boundary, conodont apparatus and phylogeny, conodont size variation, conodont oxygen isotope as well as other isotopes and chemical elements. Finally, future perspectives are also discussed

Propagation des vibrations dues au trafic routier

La méthode de calcul présentée conduit à la détermination analytique des composantes verticale et horizontale du déplacement d'un point de la surface d'un massif semi-infini, homogène, isotrope, élastique lorsque celui-ci est soumis à l'action d'un chargement uniformément réparti sur une bande schématisant une voie de circulation routière. Les solutions déduites de cette étude tiennent compte des contributions de l'onde superficielle R et des ondes de volume P et S. Les résultats appliqués aux cas de massifs sableux et argileux permettent de justifier des mesures expérimentales relevées in-situ et mettent en lumière d'une part l'insuffisance de la théorie selon laquelle l'influence de l'onde R est toujours prépondérante et d'autre part le domaine de validité pour lequel la contribution des ondes de volume peut être effectivement négligée

Supplement to The influence of changing seawater Ca concentration on Elements/Ca ratios in planktonic foraminifera: a culture experiment - AGU G3

Table S1 and S2 : Data tables (S1 : elemental/Ca data and S2 : ANCOVA results) Table_culture : Resume table of planktic foraminifera G. siphonifera cultur