Paleomagnetic and geochemical record from cores from the Sea of Marmara, Turkey: Age constraints and implications of sapropelic deposition on early diagenesis
We present results of a multi-proxy analysis of two sediment cores from the Marmara Sea. The cores were ana- lyzed using paleomagnetic and geochemical measurements. Two sapropels are documented in the last 11 kyr and are recorded in several locations across the Marmara Sea. These two sapropels have contrasting magnetic prop- erties. The magnetic record is affected by intense early diagenesis; the most recent upper sapropelic layer has low remanence and susceptibility values. A record of paleomagnetic inclinations could still be isolated above the dia- genesis front and is compared with secular variation models. The lower sapropel is identified in the deep part of the oldest studied core (Klg07) and has distinct magnetic properties characterized by high remanence and sus- ceptibility values. Using the magnetic properties it is possible to constrain bottom water ventilation and recon- nection episodes between the Marmara Sea and the Black Sea following the sea level rise during the last glacial to inter-glacial transition. ; Peer reviewed
(Marine Geology. vol. 360, n° 0025-3227, pp. 40-54, 01/01/2015)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Turbidity in the fluvial Gironde Estuary (southwest France) based on 10-year continuous monitoring: sensitivity to hydrological conditions
Climate change and human activities impact the volume and timing of freshwater input to estuaries. These modifications in fluvial discharges are expected to influence estuarine suspended sediment dynamics, and in particular the turbidity maximum zone (TMZ). Located in southwest France, the Gironde fluvial-estuarine system has an ideal context to address this issue. It is characterized by a very pronounced TMZ, a decrease in mean annual runoff in the last decade, and it is quite unique in having a long-term and high-frequency monitoring of turbidity. The effect of tide and river flow on turbidity in the fluvial estuary is detailed, focusing on dynamics related to changes in hydrological conditions (river floods, periods of low discharge, interannual changes). Turbidity shows hysteresis loops at different timescales: during river floods and over the transitional period between the installation and expulsion of the TMZ. These hysteresis patterns, that reveal the origin of sediment, locally resuspended or transported from the watershed, may be a tool to evaluate the presence of remained mud. Statistics on turbidity data bound the range of river flow that promotes the upstream migration of TMZ in the fluvial stations. Whereas the duration of the low discharge period mainly determines the TMZ persistence, the freshwater volume during high discharge periods explains the TMZ concentration at the following dry period. The evolution of these two hydrological indicators of TMZ persistence and turbidity level since 1960 confirms the effect of discharge decrease on the intensification of the TMZ in tidal rivers; both provide a tool to evaluate future scenarios.
(Hydrology and Earth System Sciences. vol. 19, n° 1027-5606, pp. 2805-2819, 01/01/2015)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Hydrothermal Activity and Paleoenvironments of the Atlantis II Deep
The Atlantis II Deep is a 65 km2 topographic depression located in the axial trough of the Red Sea at 2,000 m depth. The depression traps 17 km3 of hot and dense brines fed by hydrothermal fluids. This chapter reviews numerous data collected during the last 50 years. Chemical and isotopic data suggest that the processes that lead to the formation of the Atlantis II Deep brines are similar to those that produce open ridge black smoker fluids, but the recharging fluid is sea water in the case of sediment-free ridges, whereas it is sea water that has dissolved evaporites in the case of the Atlantis II Deep. The monitoring of temperature indicates that the heat flux was 0.54 × 109 W between 1965 and 1995. After 1995, the heat flux became 10 times lower. The substratum of the Atlantis II Deep consists of MORB-type basalts, which are covered with 0- to 30-m-thick metalliferous sediments. The solid fraction contains biogenic calcareous and/or siliceous components and silico-clastic detrital particles diluted by metalliferous sediment, which consists of metal oxides, sulphides, carbonates, sulphates, and silicates that precipitated from the hydrothermal fluids. The redox interface between the deepest brine layer and sea water is a major place of mineral precipitation. During glacial periods before the Holocene, the redox boundary was located above the brine–sea water boundary, so that hydrothermal metals spread over a large area of the Red Sea bottom.
(pp. 235-249, 01/01/2015)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Process-based modeling of cross-shore sandbar behavior
A coupled wave–current–sediment transport beach profile model is used to simulate cross-shore sandbar evolution on the time scale from days to months comprising both rapid offshore and slow onshore migrations. The discrimination of four modes of sediment transport driven by velocity and acceleration skewness, mean currents and slope effects allows addressing the dominant hydrodynamic processes governing cross-shore sandbar behavior. Acceleration–skewness-induced transport systematically results in a slow onshore sandbar migration together with a slow bar growth. Velocity–skewness-induced transport can drive onshore and offshore bar migrations with substantially larger rates. Mean–current-induced sediment transport systematically drives an offshore bar migration with either bar growth or decay. Slope effects essentially act as a damping term. The water level above the sandbar crest mainly influences the sandbar migration direction, while wave obliquity regulates the magnitude of the migration rates and is crucial to accurately simulate offshore sandbar migration during energetic obliquely incident waves. The inclusion of acceleration skewness is a necessary requirement to accurately reproduce the onshore migration of shallow sandbars. Detailed inter-site comparison of best-fit model parameters shows large differences meaning that free parameters attempt to compensate some mispecifications of the physics in the model. Although this also applies to other existing beach profile models, this suggests that this model needs further improvements including, for instance, the contribution of the injection of breaking wave turbulence onto the bed to sand stirring.
(Coastal Engineering. vol. 95, n° 0378-3839, pp. 35-50, 01/01/2015)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Storm impact on the seasonal shoreline dynamics of a meso- to macrotidal open sandy beach (Biscarrosse, France)
A three-year dataset (2007-2010) of shoreline and sandbar positions derived from video observations of an open sandy beach (Biscarrosse, France) is analyzed, to explore the impact of storms on the seasonal shoreline dynamics. The results indicate that a clear seasonality is observed in the offshore significant wave height and in the occurrence of 'winter storm' events that are defined as periods with significant wave height greater than 4 m lasting at least 12 h. Data indicate that the range of variation of the inner sandbar positions (120 m) is two and a half times larger than the range of variation of the shoreline position. Correlation analyses suggest that the offshore conditions do not conclusively explain the position of the inner bar. Shoreline positions show a clear seasonal pattern, displaying a stable position occurring in February and July, providing evidence of seasonal-recovery although analysis of storm activity indicates that the number and intensity of storms is highly variable over the three years. The Biscarrosse data show that rapid erosion can be observed also under moderate conditions, and that beach recovery after the storm season can be relatively rapid.
(Geomorphology. vol. 228, n° 0169-555X, pp. 448-461, 01/01/2015)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, OASU, UB, INSU - CNRS, ULR, CNRS, INRAE
Cockle infection by Himasthla quissetensis – II. The theoretical effects of climate change
Numerous marine populations experience parasite pressure. This is the case of the cockles Cerastoderma edule which are often highly infected by trematode macroparasites. These parasites display a complex life cycle, with a succession of free-living and parasitic stages. Climate, and in particular temperature, is an important modulator of the transmission dynamics of parasites. Consequently, global change is thought to have implications for the epidemiology of infectious diseases. Using Himasthla quissetensis, a dominant parasite of cockles as 2nd intermediate host in Arcachon Bay (France), we used mathematical models of parasite emergence (cercariae) and parasite infection (metacercariae) in cockles as a function of water temperature, in order to study different scenarios of temperature increases. Globally, with a + 0.5 °C to + 6.0 °C simulation, cumulated emergence of cercariae and accumulation of metacercariae tended to decrease or stagnate, respectively. This is the consequence of a trade-off between sooner (spring) and later (autumn) cercariae emergence/infestation on one hand, and a longer inhibition period of cercariae emergence/infestation during the hottest days in summer. Using sea water temperature in Oualidia (Morocco) where mean annual sea temperature is 3 °C higher than in Arcachon Bay, our model predicted infestation all year long (no seasonality). The model gave a correct estimation of the total number of parasites that was expected in cockles. Conversely, observed infestation in Oualidia followed a seasonal pattern like in Arcachon Bay. These results suggest that, if temperature is a strong driver of parasite transmission, extrapolation in the framework of climate change should be performed with caution.
(Journal of Sea Research (JSR), n° 1385-1101, 01/01/2015)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The toxic dinoflagellate Alexandrium minutum disrupts daily rhythmic activities at gene transcription, physiological and behavioral levels in the oyster Crassostrea gigas
The objective of the present work was to study the effect of the harmful alga Alexandrium minutum on the daily rhythm of the oyster Crassostrea gigas. Many metabolic and physiological functions are rhythmic in living animals. Their cycles are modeled in accordance with environmental cycles such as the day/night cycle, which are fundamental to increase the fitness of an organism in its environment. A disruption of rhythmic activities is known to possibly impact the health of an animal. This study focused in C. gigas, on a gene known to be involved in circadian rhythmicity, cryptochrome gene (CgCry), on putative clock-controlled genes involved in metabolic and physiological functions, on the length cycle of the style, a structure involved in digestion, and on the rhythmicity of valve activity involved in behavior. The results indicate that daily activity is synchronized at the gene level by light:dark cycles in C. gigas. A daily rhythm of valve activity and a difference in crystalline style length between scotophase and photophase were also demonstrated. Additionally, A. minutum exposure was shown to alter cyclic activities: in exposed oysters, gene transcription remained at a constant low level throughout a daily cycle, valve opening duration remained maximal and crystalline style length variation disappeared. The results show that a realistic bloom of A. minutum clearly can disrupt numerous and diverse molecular, physiological and behavioral functions via a loss of rhythmicity.
(Aquatic Toxicology. vol. 158, n° 0166-445X, pp. 41-49, 01/01/2015)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS
Quels micropolluants peut-on éliminer par les procédés extensifs de traitement des eaux usées domestiques ?
Cet article documente l’élimination de 59 micropolluants (16 métaux et 43 micropolluants organiques) par différentes procédés de traitement extensifs, construits en traitement secondaire ou en traitement complémentaire. Les eaux brutes et traitées de 5 stations de traitement des eaux usées des zones rurales ou péri-urbaines ont été étudiées par temps sec à l’aide d’échantillons prélevés avec du matériel spécifique. Des méthodes analytiques validées ont été mises en ½uvre, avec de faibles limites de quantification (i.e. proches du nanogramme par litre) et des incertitudes maîtrisées. En traitement secondaire, la moitié des rendements obtenus sont supérieurs à 70% dès lors qu'un traitement biologique avec nitrification et une élimination des matières en suspension sont appliqués. Les valeurs de rendements obtenues pour les différents procédés extensifs étudiés sont voisines de celles déterminées pour les boues activées aération prolongée. Concernant les traitements complémentaires, les deux procédés extensifs classiques (filtres horizontaux à gravier ou apatite) étudiés, ainsi que le fossé (temps de séjour de 10 min), ont une contribution très faible dans le traitement des micropolluants réfractaires aux traitements secondaires. L’élimination de ces micropolluants nécessite des procédés spécifiques avec des temps de séjour élevés pour mobiliser la photodégradation naturelle, ou avec l’utilisation de matériaux adsorbants. L’argile expansée est efficace à faible niveaux de concentration, tandis que celle de la zéolite clinoptilolite s’avère intéressante lorsque les micropolluants sont présents à fortes concentrations. Malgré leur faible coût d’achat, mais du fait du temps de séjour élevé nécessaire et de la capacité d’adsorption assez faible, le calcul technico-économique reste favorable au charbon actif en grain pour une utilisation de tels matériaux dans des filtres horizontaux. Nos futures recherches visent à étudier les processus impliqués pour l’élimination des micropolluants dans les zones de rejet végétalisées.
(TSM. Techniques Sciences Méthodes – Génie urbain, génie rural, n° 0299-7258, pp. 51-66, 24/04/2026)
UR MALY, IRSTEA, UR REVERSAAL, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Disentangling the heritable and plastic components of the competitive and facilitative effects of an alpine foundation species
1- Differences in effects between phenotypes of foundation species on subordinate species have been reported, but no study has separated their heritable and plastic components. In a subalpine community of the French Pyrenees, we observed two phenotypes of Festuca gautieri: tight cushions in dry convex outcrops with few subordinate species and loose cushions in wet concave slopes with many subordinate species, suggesting differences in effects of the two phenotypes on subordinates. 2- Using two reciprocal transplantation gardens, we studied the responses of the two phenotypes to changes in environmental conditions, thus assessing the contribution of heritability and plasticity to the phenotypic variation. Using a target cross-transplantation experiment, we assessed the plasticity and heritability bases of their contrasting effects. We also quantified the recolonization of resident plants within the reciprocally transplanted cushions. 3- We found that morphological differences between cushions had both heritability and plasticity bases. The two competition experiments showed heritable increase in competitive effects from loose to tight cushions. This was counteracted by plasticity effects, which decreased competition from the benign to the stressful garden. 4- Synthesis. We conclude that heritable effects overcome plasticity effects resulting in higher diversity in the loose phenotype from the benign habitats.
(Journal of Ecology. vol. 103, n° 0022-0477, pp. 1172–1182, 24/04/2026)
BioGeCo, INRA, UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Corticosterone, prolactin and egg neglect behavior in relation to mercury and legacy POPs in a long-lived Antarctic bird
Seabirds often have high loads of contaminants. These contaminants have endocrine disrupting properties but their relationships with some endocrine mechanisms are still poorly investigated in free-living organisms. This is the case for the stress response which shifts energy investment away from reproduction and redirects it towards survival. In birds, this stress response is achieved through a release of corticosterone and is also accompanied by a decrease in circulating prolactin, an anterior pituitary hormone widely involved in regulating parental cares. We measured blood concentrations of some legacy persistent organic pollutants (POPs) and mercury (Hg) and examined their relationships with the corticosterone and prolactin responses of known-age (9-46 years old) incubating snow petrels (Pagodroma nivea) to a standardized capture/handling stress protocol. In this Antarctic seabird, we also investigated whether high contaminant burden correlates with a higher occurrence of egg neglect, a frequently observed behaviour in snow petrels. POPs and Hg were unrelated to age. Stress-induced corticosterone concentrations were positively related to POPs in both sexes, and stress-induced prolactin concentrations were negatively related to Hg in males. Egg-neglect behaviour was not related to POPs burden, but males with higher Hg concentrations were more likely to neglect their egg. This suggests that in birds, relationships between age and contaminants are complex and that even low to moderate concentrations of POPs and Hg are significantly related to hormonal secretion. In this Antarctic species, exposure to legacy POPs and Hg could make individuals more susceptible to environmental stressors such as ongoing disturbances in polar regions.
(Science of the Total Environment. vol. 505, n° 0048-9697, pp. 180 - 188, 24/04/2026)
CEBC, INRA, ULR, CNRS, UC, LIENSs, INSU - CNRS, ULR, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, NINA, NINA