21 research outputs found
South Atlantic intermediate water advances into the North-east Atlantic with reduced Atlantic meridional overturning circulation during the last glacial period
The Nd isotopic composition (epsilon Nd) of seawater and cold-water coral (CWC) samples from the Gulf of Cadiz and the Alboran Sea, at a depth of 280-827 m were investigated in order to constrain middepth water mass dynamics within the Gulf of Cadiz over the past 40 ka. epsilon Nd of glacial and Holocene CWC from the Alboran Sea and the northern Gulf of Cadiz reveals relatively constant values (-8.6 to -9.0 and -9.5 to -10.4, respectively). Such values are similar to those of the surrounding present-day middepth waters from the Mediterranean Outflow Water (MOW; epsilon Nd approximate to -9.4) and Mediterranean Sea Water (MSW; epsilon Nd approximate to -9.9). In contrast, glacial epsilon Nd values for CWC collected at thermocline depth (550-827 m) in the southern Gulf of Cadiz display a higher average value (-8.90.4) compared to the present-day value (-11.70.3). This implies a higher relative contribution of water masses of Mediterranean (MSW) or South Atlantic origin (East Antarctic Intermediate Water, EAAIW). Our study has produced the first evidence of significant radiogenic epsilon Nd values (approximate to -8) at 19, 23-24, and 27 ka, which are coeval with increasing iceberg discharges and a weakening of Atlantic Meridional Overturning Circulation (AMOC). Since MOW epsilon Nd values remained stable during the last glacial period, it is suggested that these radiogenic epsilon Nd values most likely reflect an enhanced northward propagation of glacial EAAIW into the eastern Atlantic Basin
Developmental trajectories of neuroanatomical alterations associated with the 16p11.2 Copy Number Variations
Effects of eight neuropsychiatric copy number variants on human brain structure
Many copy number variants (CNVs) confer risk for the same range of neurodevelopmental symptoms and psychiatric conditions including autism and schizophrenia. Yet, to date neuroimaging studies have typically been carried out one mutation at a time, showing that CNVs have large effects on brain anatomy. Here, we aimed to characterize and quantify the distinct brain morphometry effects and latent dimensions across 8 neuropsychiatric CNVs. We analyzed T1-weighted MRI data from clinically and non-clinically ascertained CNV carriers (deletion/duplication) at the 1q21.1 (nâ=â39/28), 16p11.2 (nâ=â87/78), 22q11.2 (nâ=â75/30), and 15q11.2 (nâ=â72/76) loci as well as 1296 non-carriers (controls). Case-control contrasts of all examined genomic loci demonstrated effects on brain anatomy, with deletions and duplications showing mirror effects at the global and regional levels. Although CNVs mainly showed distinct brain patterns, principal component analysis (PCA) loaded subsets of CNVs on two latent brain dimensions, which explained 32 and 29% of the variance of the 8 Cohenâs d maps. The cingulate gyrus, insula, supplementary motor cortex, and cerebellum were identified by PCA and multi-view pattern learning as top regions contributing to latent dimension shared across subsets of CNVs. The large proportion of distinct CNV effects on brain morphology may explain the small neuroimaging effect sizes reported in polygenic psychiatric conditions. Nevertheless, latent gene brain morphology dimensions will help subgroup the rapidly expanding landscape of neuropsychiatric variants and dissect the heterogeneity of idiopathic conditions
Impact of the millennial-scale climate changes of the last glacial cycle on erosion and sediment transfers in the south of Alps (SE France)
While dominant processes and time-scales controlling denudation rates are intensively debated, past terrigenous input remains difficult to detect from the marine sedimentary record, especially during the Quaternary because of the strong overprint exerted by the sea-level changes. In this study, we focus on the Var sediment-routing system (SE France) where the absence of a continental shelf off the Var river mouth (Ligurian margin, NW Mediterranean Sea) resulted in the direct connection between the Var River and the deep basin during both highstand and lowstand conditions. Moreover hyperpycnal flow initiated during Var floods are the main sediment transfer processes in the Var turbidite system, making changes in sediment supply within headwater source regions possible to discern in the stratigraphic record of the distal sedimentary basin...Alors que les processus contrĂŽlant lâĂ©rosion et les transferts de sĂ©diment sont intensĂ©ment dĂ©battus, il est toujours difficile dâobtenir des archives sĂ©dimentaires qui permettraient dâaccĂ©der aux flux terrigĂšnes passĂ©s, particuliĂšrement au cours du Quaternaire oĂč les variations du niveau marin ont eu un profond impact sur la sĂ©dimentation marine. Cette Ă©tude se focalise sur le systĂšme sĂ©dimentaire du Var (SE de la France), oĂč lâabsence de plateau continental au niveau de la marge Nord-ligure a permis une alimentation continue en sĂ©diment du systĂšme turbiditique profond par le fleuve Var, sans quâelle ne soit affectĂ©e par les variations du niveau marin. Par ailleurs, les courants hyperpycnaux, dĂ©clenchĂ©s lors des crues du Var hautement concentrĂ©es en sĂ©diments, semblent jouer un rĂŽle majeur dans cette alimentation et ainsi, permettent dâĂ©tablir un lien Ă©troit entre les flux sĂ©dimentaires du fleuve Var et les dĂ©pĂŽts turbiditiques. Cette thĂšse prĂ©sente une reconstitution des transferts terre-mer menĂ©e Ă partir de lâĂ©tude de ces dĂ©pĂŽts turbiditiques, son objectif est dâapporter des Ă©lĂ©ments nouveaux pour mieux cerner la relation climat-Ă©rosion-transfert Ă lâĂ©chelle millĂ©naire. Ce travail repose sur des carottes sĂ©dimentaires prĂ©levĂ©es dans les dĂ©pĂŽts turbiditiques de la Ride SĂ©dimentaire du Var et dont le cadre chronostratigraphique est Ă©tabli avec une rĂ©solution millĂ©naire pour le dernier cycle glaciaire (0 - 75 ka). Il propose une approche inĂ©dite dans des dĂ©pĂŽts turbiditique, alliant (1) une Ă©tude sĂ©dimentologique permettant de reconstituer lâactivitĂ© turbiditique sur la Ride du Var et (2) une Ă©tude gĂ©ochimique incluant le traçage des sources sĂ©dimentaires par lâisotopie du Nd. En complĂ©ment, une simulation des flux sĂ©dimentaires du fleuve Var, a Ă©tĂ© Ă©tablie pour la mĂȘme pĂ©riode Ă partir du modĂšle Hydrotrend (Syvitski et al., 1998). Les rĂ©sultats de cette simulation montrent que les variations de lâactivitĂ© turbiditique enregistrĂ©es sur la Ride du Var sont gouvernĂ©es par des changements de lâactivitĂ© hyperpycnale du fleuve..
Variabilité des transferts sédimentaires vers l'océan prodond à l'échelle du millénaire: le systÚme sédimentaire du Var
A ce jour, trĂšs peu dâĂ©tude ont mis en Ă©vidence lâimpact des changements climatiques sur les transferts sĂ©dimentaires dans les enregistrements sĂ©dimentaires marins. Avec son plateau continental Ă©troit, le systĂšme sĂ©dimentaire du Var est un site idĂ©al pour lâĂ©tude des transferts terre-mer au cours du Quaternaire. MalgrĂ© les variations du niveau marin, son « deep-sea-fan » (ride sĂ©dimentaire du Var) est restĂ© continuellement alimentĂ© par un canyon directement connectĂ© Ă lâembouchure du fleuve. LâactivitĂ© turbiditique rĂ©cente de ce systĂšme, dominĂ©e par les courants hyperpycnaux, est Ă©troitement liĂ©e aux crues du Var. Le cadre chronostratigraphique de 3 carottes, longues de 20 mĂštres, prĂ©levĂ©es dans les dĂ©pĂŽts turbiditiques de la ride sĂ©dimentaire du Var a Ă©tĂ© Ă©tabli Ă haute-rĂ©solution. Cet enregistrement met pour la premiĂšre fois en Ă©vidence que les transferts sĂ©dimentaires ont pu rĂ©pondre aux fluctuations climatiques rapides de la derniĂšre pĂ©riode glaciaire (Cycles de Dansgaard-Oeschger). Au cours du stade isotopique marin 3 (MIS3), lâactivitĂ© turbiditique est maximale pendant les stades climatiques froids et arides (stadials et Heinrich stadials) lorsque le couvert vĂ©gĂ©tal Ă©pars favorise une intense dĂ©charge sĂ©dimentaire du fleuve et, dĂ©croit lorsque les conditions interstadiaires sâinstallent et que le dĂ©veloppement rapide de la vĂ©gĂ©tation stabilise les sols (Figure 1). Au moment de lâHeinrich stadial 1, le retrait des glaciers du bassin versant est marquĂ© par une diminution rapide de la frĂ©quence des turbidites associĂ©e Ă une rĂ©duction des apports de sĂ©diments en provenance des massifs englacĂ©s
Nutrient intake in high performance show-jumping horses in France
The nutrient requirements of athletic horses are closely dependent on workload and need to be defined for each discipline. As only few surveys have focused on show-jumping, the aim of the present work was to describe dietary practices in elite show-jumpers in France and compare them with the NRC 2007 recommendations. Seventeen horses (12 stallions, 3 mares, 2 geldings; age 12±1 y; BW 591±13 kg) were included in the study. Their feeds were analysed and their general health, feeding schedule and meal composition were recorded. All data were expressed as mean ± SEM. Mean digestible energy (DE) intake was 1.4±0.1 times the maintenance requirement but varied considerably (from 1.0 to 1.9) with no effect of gender. Crude protein (CP) intake ranged from 84 to 147 % of the recommendations for exercise horses, with a mean CP:DE ratio of 45±8 g/MCal DE. Mineral intake exceeded the recommendations, except for sodium and chloride. Body condition was satisfactory in all horses indicating that energy intake met the energy requirement for maintenance plus exercise, despite large variations between animals. Mineral intake varied widely, and in most cases, the actual intake made any supplementation, especially of calcium, unnecessary. Our results emphasize 1) the imbalanced diets compared to current recommendations and 2) the similar performances of the horses despite the different diets offered to them. They also show that the variation in workload, within a single athletic discipline, may be wide.vo
Millennial-Scale Response of a Western Mediterranean River to Late Quaternary Climate Changes: A View from the Deep Sea
Although it is widely accepted that erosion and sediment transfer respond to millennial-scale climatic variability, these changes remain difficult to detect in marine sedimentary archives. In the Var sediment-routing system, northwestern Mediterranean Sea, the absence of a continental shelf results in a direct connection between the Var River mouth and the deep basin during both highstand and lowstand conditions. This makes the Var sediment-routing system an ideal target to test whether rivers can transmit climate-driven high-frequency changes in sediment flux to the ocean. On the basis of an unprecedented (centennial-to-millennial-scale) resolution in turbidite sequences, we reconstructed the activity of turbidity current overflows along the deep-sea Var Sedimentary Ridge over the past 75 kyr. The overflow activity is highest (one event every 10-30 yr) during maximum glacial conditions (30 kyr-16 kyr ago [ka]) and rapidly decreases (down to one event every 100-500 yr) during the last glacial-interglacial transition (Termination 1). During marine isotope stage (MIS)4 and MIS3 (75-30 ka), peaks in the overflow activity occurred synchronously with cold and arid Dansgaard-Oeschger stadials, while warmer and wetter interstadial conditions correspond to low overflow activity. We conclude that overflow activity on the Var Sedimentary Ridge mainly reflects changes in the magnitude of hyperpycnal currents flowing in the turbiditic channel-levee system in relation with variations in suspended-sediment concentration during Var River floods. We show that this signal is sensitive to changes in pure sediment flux induced by climatic perturbations occurring inland: (1) the decrease in glacier-derived sediment input after glacier retreat and (2) changes in erosion induced by shifts in the vegetation cover in response to Dansgaard-Oeschger climate swings
Glacial erosion dynamics in a small mountainous watershed (Southern French Alps): A source-to-sink approach
In this study we used major element composition, neodymium isotopes ratios (ΔNdΔNd) and concentration of REE to track and quantify the sediment routing in the Var sedimentary system from source (Southern French Alps) to sink (Ligurian Sea) over the last 50 ka. Our data reveal that changes in sediment sources over that period, associated with concomitant changes in the hyperpycnal (i.e. flood-generated turbidity currents) activity in the Var submarine canyon, were mainly driven by paleoenvironmental conditions in the upper basin and in particular by the presence of glaciers during the last glacial period. Based on this evidence, we determined when and how glacier-derived sediments were produced, then excavated and transferred to the ocean, allowing us to ultimately tune offshore sedimentary records to onshore denudation rates. In contrast to large glaciated systems, we found that sediment export from the Var River to the Mediterranean Sea directly responded to climate-induced perturbations within the basin. Finally, we estimated that sediment fluxes in the Var routing system were 2.5 times higher during the Last Glacial Maximum than today, thus confirming that glacier denudation rates exceed fluvial rates and that such a pattern also governs the interglacialâglacial sediment flux cycle in other small mountainous basin
Reservoir Ages in the Western Tropical North Atlantic from One Coral off Martinique Island (Lesser Antilles)
International audienceSea surface reservoir ages (R) are reported from radiocarbon (14C) measurements of the annual growth bands of coral Siderastrea siderea collected on the Atlantic coast off Martinique Island, in the Lesser Antilles volcanic arc. Mean values of R are similar between 1835 and 1845 during pre-anthropogenic times at 385±30 yr and between 1895 and 1905 at 382±20 yr when there was a huge eruption from the Montagne PelĂ©e volcano in 1902â1903. Limited 14C aging of sea surface (~40 yr) may be due to enhanced volcanic activity. Variability of R is slightly greater during 1835â1845 than during 1895â1905. It is linked to a moderate increase of â14C of 5â°, strengthened by a clear increase of ÎŽ18O of 0.4â°. This is attributed to a decrease of the northward advection of the South Atlantic Waters into the western tropical North Atlantic and Caribbean Sea and relative enhanced westward flux of the tropical North Atlantic surface waters, the southern waters having lower values of 14C and ÎŽ18O than the North Atlantic ones. From 1835 to 1845, the fraction of the South Atlantic Waters transported up to Martinique Island was reduced from 25% to 15%
Fingerprinting Northeast Atlantic water masses using Neodymium isotopes
International audienceDissolved neodymium (Nd) isotopic composition (expressed as ΔNd) has been analysed for 82 seawater samples collected from 13 stations stretching from the Alboran Sea to the Iceland Basin. The distribution of the ΔNd values of water masses was thus investigated for the first time along the western European margin in order to explore whether the water masses flowing in the eastern subpolar and subtropical Atlantic reveal distinct isotopic patterns. The Modified Atlantic Water (MAW) in the Alboran Sea displays ΔNd values (between -9.2±0.2 and -8.9±0.2) that are significantly more radiogenic than those reported in previous studies (-10.8±0.2 to -9.7±0.2), suggesting temporal variations in the Nd isotopic composition of the water that enters the Mediterranean Sea from the Strait of Gibraltar. The ΔNd value of the underlying modified Winter Intermediate Water (WIW) has been established for the first time (-9.8±0.3) and is compatible with a Nd signature acquired from the sinking of MAW in the northwestern Mediterranean Sea. Within the Gulf of Cådiz, southern Mediterranean Sea Water (MSW) (-10.6±0.2) differs slightly from the northern MSW (-9.9±0.4) owing to a significant contribution of modified East Antarctic Intermediate Water (EAAIW) (-10.9±0.2). In the northeast Atlantic, the North Atlantic Current surface water located in the inter-gyre region (north of 46°N) displays ΔNd values of between -14.0±0.3 and -15.1±0.3, reflecting the subpolar gyre signature. Along the western European margin, ΔNd values of surface water decrease toward the north (from -10.4±1.6 to -13.7±1.0) in agreement with the gradual mixing between subtropical and subpolar water. At intermediate depth, ΔNd values decrease from -9.9±0.4 within the Gulf of Cådiz to -12.1±0.3 within the Porcupine Seabight, indicating a strong dilution of the MSW with subpolar water. Within the Rockall Trough and the Iceland Basin, the more negative ΔNd values at mid-depth (< -13.5±0.3) indicate that the MSW has no influence, even during periods of low NAO index. Water masses deeper than 1200 m in the northeast Atlantic are clearly influenced by the less radiogenic Labrador Sea Water (LSW) (-13.2±0.3 and -14.5±0.3) that mixes locally (ΔNd between -10.3±0.2 and -11.3±0.3) in the Iceland basin with the Iceland-Scotland Overflow Water (ISOW)