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
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
Sedimentary records of past earthquakes in Boraboy Lake during the last ca 600 years (North Anatolian Fault, Turkey)
Multiproxy sedimentological analyses along 4.9 m-long sequence of Boraboy Lake, which is located on the central eastern part of the North Anatolian Fault (NAF), reveal the sedimentary traces of past large earthquakes in the region. The lake has a relatively large catchment area (10 km2) compared to its size (0.12 km2), which renders sedimentation sensitive to heavy rain/storm events. Accordingly, the background sedimentation, which is composed of faintly laminated reddish/yellowish brown clayey silt, is frequently interrupted by organic-rich intercalations probably due to heavy rain/storm events transporting terrestrial plant remains from the densely vegetated catchment. In addition to frequent organic-rich intercalations, the background sedimentation is interrupted by four mass-wasting deposits (MWD) of which thickness range is between 15 and 50 cm. High-resolution ITRAX μXRF data confirms higher homogeneity along the MWDs (E1–E4) compared to the background sedimentation. Based on 137Cs and 210Pbxs dating and radiocarbon chronology, three MWDs detected in Boraboy sequence (E2, E3 and E4) temporally correlate with large historical earthquakes along the NAF; the 1943 Tosya (Ms = 7.6) and/or 1942 Niksar-Erbaa (Ms = 7.1), the 1776 Amasya-Merzifon and the 1668 North Anatolian (Ms = 7.9) earthquakes. The youngest MWD in the sequence (E1), which is dated to early 2000s, does not correlate with any strong earthquake in the region. This MWD was probably a single mass-wasting event due to routine overloading and oversteepening on the delta front formed by the main inlet of the lake. In subaqueous paleoseismology, coevality of multi-location mass-wasting events is used as a criterion to assign a seismic triggering mechanism, and to rule out mass-wasting events due to routine overloading/oversteepening of subaqueous slopes. Within this context, Boraboy sequence provides a valuable example to discuss sedimentological imprints of single- vs. multi-source MWDs.
(Palaeogeography, Palaeoclimatology, Palaeoecology. vol. 433, n° 0031-0182, pp. 1-9, 01/01/2015)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Phenolic fingerprint of the seagrass Posidonia oceanica from four locations in the Mediterranean Sea: first evidence for the large predominance of chicoric acid
Abstract The phenolic fingerprint of the leaves of Posidonia oceanica collected from four different Mediterranean Sea regions was determined using a panel of analytical techniques. It was found to be dominated by caffeic tartrates, along with low amounts of coumaric and ferulic tartrates. Chicoric acid (CA) was unambiguously identified as the major phenolic compound, regardless of the sample or collection site. Caftaric acid (CAF) was the second most abundant phenolic, but in much lower average concentrations. These results contrast with most of the previous works, in which CA was not even mentioned. The dramatic influence of extract handling, as well as the importance of choosing the adequate criteria of identity to standards, was demonstrated. These results show the importance of analyzing the crude extract to avoid some of the major pitfalls in determining the phenolic fingerprints. This is the first report to identify and quantify CAF in the Posidoniaceae and to identify CA as the dominant phenolic in Posidonia leaves. The large accumulation of CA in both living (10.12–12.78 mg g-1 dw) and detrital leaves (2.49–12.11 mg g-1 dw) across large geographical scales is noteworthy. The lack of significant concentrations of flavonoids contrasts with other seagrass genera. Importantly, the phenolic signature of P. oceanica shows significant similarities to those of Cymodocea nodosa and Syringodium filiforme, both belonging to the Cymodoceaceae. These results are discussed in terms of metabolic pathways and phylogenetic relationships.
(Botanica Marina. vol. 58, n° 0006-8055, pp. 379-391, 01/01/2015)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Modeling the deposition of turbidite systems with Cellular Automata numerical simulations: A case study in the Brazilian offshore
Turbidite reservoirs frequently consist of massive sandstones with excellent reservoir properties, but showing a heterogeneity which is difficult to characterize with only well and seismic data. The physical and numerical modeling of the depositional processes is then a way to predict the heterogeneity pattern and to assist the geological interpretation. Recently, Cellular Automata (CA) modeling was adapted to simulate turbidite flow deposits. In this study, CA modeling incorporates the main submarine physical processes involved in turbulent flows, such as water entrainment, erosion, deposition and particle fall-out. These processes are developed through CA simulations, in which the cells interact by exchanging energy and flow properties. In this work, the CA modeling was applied in real oilfields of the Campos Basin (offshore Brazil), in a case where the palaeotopography played a major role on trapping of turbidite sand deposits. The sensitivity tests performed on this case study highlighted that the parameters of flow concentration, composition of the substratum and the deposition model greatly impact the simulation results. The simulation results also realistically reproduced sedimentation patterns, such as successive filling of contiguous sub-basins, increasing flow velocities in confined settings, run-up effects with lateral deposition of fines and concentration of coarser sediments in topographic lows. An important characteristic of the studied turbidite reservoirs is the presence of multiple-stacked depositional cycles. For this reason, CA code was adapted to allow the simulation of multiple flow events and, by this way, to reproduce stacked turbidite cycles. The reservoir distribution and the thicknesses of the geological model fit very well with the results of CA simulations for multiple flow events. A blind test performed thanks to the drilling of a new well in the study area also confirmed the forecast capacity of the CA modeling for both sediment distribution and thickness. The results of the simulations are consistent with the geological model of the study area, and predict reservoir distribution in locations away from the wells. These results also point to the potential of such numerical techniques in improving the prediction of the turbidite reservoir extension, especially in the case where palaeotopography controlled the turbidite sedimentation.
(Marine and Petroleum Geology. vol. 59, n° 0264-8172, pp. 166-186, 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
Evaluation de la sensibilité des jeunes stades d'esturgeons européens aux polluants : chapitre V
Les objectifs de cette étude sont (i) d'évaluer la possibilité de créer artificiellement un sédiment dopé agissant de la même manière qu'un sédiment naturel chez l'esturgeon européen (ii) d'évaluer la sensibilité des jeunes stades d'esturgeon européen à différentes concentrations d'un mélange représentatif des polluants organiques et métalliques rencontrés dans l'environnement (iii) et enfin d'évaluer l'effet combiné de l'exposition aux polluants et à une augmentation de la température.
(pp. 59-70, 23/06/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS