Uncertainties in Sandy Shorelines Evolution under the Bruun Rule Assumption
In the current practice of sandy shoreline change assessments, the local sedimentary budget is evaluated using the sediment balance equation, that is, by summing the contributions of longshore and cross-shore processes. The contribution of future sea-level rise induced by climate change is usually obtained using the Bruun rule, which assumes that the shoreline retreat is equal to the change of sea-level divided by the slope of the upper shoreface. However, it remains unsure that this approach is appropriate to account for the impacts of future sea-level rise. This is due to the lack of relevant observations to validate the Bruun rule under the expected sea-level rise rates. To address this issue, this article estimates the coastal settings and period of time under which the use of the Bruun rule could be (in)validated, in the case of wave-exposed gently-sloping sandy beaches. Using the sedimentary budgets of Stive (2004) and probabilistic sea-level rise scenarios based on IPCC, we provide shoreline change projections that account for all uncertain hydrosedimentary processes affecting idealized low-and high-energy coasts. Hence, we incorporate uncertainties regarding the impacts of longshore processes, sea-level rise, storms, aeolian, and other cross-shore processes. We evaluate the relative importance of each source of uncertainties in the sediment balance equation using a global sensitivity analysis. For scenario RCP 6.0 and 8.5 and in the absence of coastal defenses, the model predicts a perceivable shift toward generalized beach erosion by the middle of the 21st century. In contrast, the model predictions are unlikely to differ from the current situation in case of scenario RCP 2.6. Finally, the contribution of sea-level rise and climate change scenarios to sandy shoreline change projections uncertainties increases with time during the 21st century. Our results have three primary implications for coastal settings similar to those provided described in Stive (2004) : first, the validation of the Bruun rule will not necessarily be possible under scenario RCP 2.6. Second, even if the Bruun rule is assumed valid, the uncertainties around average values are large. Finally, despite these uncertainties, the Bruun rule predicts rapid shoreline retreat of sandy coasts during the second half of the 21st century, if greenhouse gas concentration in the atmosphere are not drastically reduced (scenarios RCP 4.5, 6.0, and 8.5).
(Frontiers in Marine Science, n° 2296-7745, 01/04/2016)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Depleted uranium induces sex- and tissue-specific methylation patterns in adult zebrafish
(Journal of Environmental Radioactivity. vol. 154, n° 0265-931X, pp. 25-33, 01/04/2016)
IRSN, CIBEST, SYMMES, INC-CNRS, CNRS, UGA [2016-2019], IRIG, DRF (CEA), EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, C3R, IRSN, CNRS
Concentrations and atmospheric exchanges of carbon dioxide (CO2) and methane (CH4) in a tropical eutrophic estuary (Guanabara Bay, RJ, Brazil)
The production, transformation, emission and burial of carbon at the land-ocean interface are globally significant, but rather poorly quantified in tropical regions. The increasing atmospheric concentrations of dioxide carbon (CO2) and methane (CH4) alerts to the importance and necessity of monitoring and quantifying the concentrations and fluxes of these greenhouse gases at coastal zone. The present doctoral thesis was divided into several chapters. Chapter 1 presents a general introduction to the thesis. Chapter 2 corresponds to a general introduction which focuses on the state of art of knowledge of the thesis subject, dealing with the CO2 and CH4 dynamics in estuaries. Chapter 3 describes the system applied for the online and continuous measurements of the aquatic partial pressure of CO2 (pCO2) and compares its estimate between the method of the continuous measurements with indirect estimates based on calculations with total alkalinity and pH in two contrasting Brazilian estuaries. One being the marine dominated and highly anthropogenically disturbed Guanabara Bay (State of Rio de Janeiro, SE-Brazil) and the other, the oligotrophic Sao Francisco River Estuary (State of Alagoas, NE-Brazil), impacted by dams. For Guanabara Bay, the measured and calculated pCO2 values showed an excellent agreement (R2 = 0.95, p < 0.0001). In contrast, the Sao Francisco estuary, showed good agreements between both methods in the estuarine mixing zone but not for it´s freshwater end member samples, which yielded substantial overestimations for the calculated pCO2. The average overestimation was 72%, reaching 737%. These discrepancies were attributed to the interference of organic alkalinity in the calculations particular in acid, poorly buffered freshwaters. Chapters 4 and 5 correspond to the part of this study, addressing the results of the temporal and spatial variations of CO2 and CH4 concentrations and atmospheric exchanges in Guanabara Bay. The study was conducted between April 2013 and April 2014, with continuous on line monitoring along trajectories of pCO2, temperature, salinity, fluorescence and dissolved oxygen. In addition, discrete sampling was performed at fixed stations along the trajectories for CH4, Chlorophyll a and dissolved inorganic nutrients. The annual concentrations of CO2 and CH4 ranged between 22-3715 ppmv and 18-10350 nmol L-1, respectively. Marked undersaturations of pCO2 were prevalent in shallow, confined and stratified waters especially at summertime, whereas oversaturations were restricted to the vicinity of the polluted river mouths and effluent discharge. The CO2 presented diurnal variations related to the processes of photosynthesis and respiration, with higher values at nigh-time period. CH4 was oversaturated in all samples, with higher concentrations primarily in the polluted regions. Methanogenesis seemed to be low in the sampled regions due to the competition with sulphate-reduction, with the major part of the CH4 sustained by allochthonous sources, derived from the sewage network. In contrast to the major part of the world´s estuarine systems, Guanabara Bay was considered a strong sink of CO2 due to concomitant effects of high photosynthetically active radiation intensity (PAR), thermal stratification and net autotrophy (autotrophic metabolism of 52.1 mol C m-2 yr-1). [...]
(15/03/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Sediment failure types, preconditions and triggering factors in the Gulf of Cadiz
A series of morphological structures, such as scars and escarpments related to seafloor instabilities, were observed in the Gulf of Cadiz using multibeam bathymetry and acoustic imagery. According to the geometry of the slide scars, the slope angle, the surrounding seafloor morphology and the mechanical parameters of the sediment, we suggest the likely mechanisms initiating the failures for the different types of observed structures. Most of the small-scale sediment failures (≤2 km2) seem directly related to dome-like structures (where slopes are steep) or are located in the vicinity of such structures (fluid flows). It appears that progressive deformation or fluid flow related to the growing of dome-like structures may have weakened the sediments sufficiently to bring 7°-steep slopes to metastable conditions (with a factor of safety close to 1.0). The other instability types are likely related to high-magnitude (Ms > 6) earthquakes, which are prone to occur in this area (located in the neighbourhood of the 1755 Lisbon earthquake area). Some particular large-scale structures were observed among these seafloor features, for example on the Guadalquivir Bank. On this bank, a series of successive large scars (at least 4 km long), composed of multiple and very regular arcuate segments (1 km in diameter), were observed at different bathymetric levels (every 40 m). These structures might be related to a deep-rooted detachment zone (e.g. successive listric faults) and triggered by high-magnitude earthquakes or by accumulated displacement along a tectonic discontinuity. This would explain such a large-scale deformation, providing a regular escarpment of 40 m high without any sediment flow downslope, thereby suggesting an ongoing (or unfinished) deformation.
(Landslides, n° 1612-510X, 07/03/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Euro-Atlantic teleconnection patterns, weather regimes and inter-annual shoreline variability at a high-energy sandy beach
On coasts dominated by cross-shore sediment-transport, incident wave-energy primarily controls temporal shoreline variability (Splinter et al., 2014). Truc Vert beach (SW France) is a high-energy meso-macrotidal multiple-barred beach where monthly to bimonthly surveys have been performed since May 1998. Surveys with an alongshore coverage larger than 350 m (from May 2005 to May 2014) are used to calibrate an equilibrium shoreline model (Castelle et al., 2014). The calibrated model explains 66% of the observed shoreline variability over the calibration period. Over the entire survey period (1998-2014), the model skilfully reproduces the observed shoreline evolution patterns. Especially, the intra-annual shoreline variability driven by the seasonal wave climate as well as shoreline response to individual storms and storm groups are well reproduced. A significant shoreline inter-annual variability (blue arrows in Figure 1) is also found, which is likely driven by the climate variability over the North Atlantic Ocean.
(06/03/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM, LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, CNRM, INSU - CNRS, CNRS, Comue de Toulouse, WRL, UNSW
Wave Set-up and Run-up Variability on a Complex Barred Beach During Highly Dissipative Storm Conditions
This study assessed the ability of the SWASH model to reproduce wave set-up and run-up on complex realistic 3D morphology during highly dissipative stormy conditions, based on the most energetic field data set reported in the bibliography (ECORS-Truc Vert’08 beach experiment). Several approaches (1D and 2D) and forcing methods (spectral and parametric) were applied. For the three days of high-energy conditions caused by the Johanna storm, wave set-up was accurately reproduced, with simulation performance in 1D and 2D at R² = 0.66, 0.81 respectively for all data considered; RMSE = 0.13 m, 0.08 m; bias = 0.06, -0.02. Run-up in the 1D configuration is significantly overestimated while in 2D, the reproduction of run-up using spectral forcing was very accurate with R² = 0.73; RMSE = 0.19; bias = 0.04, underlining the role of spectral frequency and directional spread to precisely reproduce the surf zone processes during a storm on a complex barred beach. The maximum estimated values for set-up, run-up and spatial variability of run-up are comparable with results from previous studies, even though significantly higher offshore wave conditions. These results support the hypothesis of a run-up saturation signature in dissipative contexts, mainly influenced by extreme offshore wave conditions.
(Journal of Coastal Research. vol. Proceedings of the 14th International Coastal Symposium (Sydney, Australia)., n° 0749-0208, pp. 882-886, 06/03/2016)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A fault detection method for an automatic detection of spawning in oysters
Using measurements of valve activity (i.e. the distance between the two valves) in populations of bivalves under natural environmental condition (16 oysters in the Bay of Arcachon, France, in 2007, 2013 and 2014), an algorithm for an automatic detection of the spawning period of oysters is proposed in this paper. Spawning observations are important in aquaculture and biological studies, and until now, such a detection is done through visual analysis by an expert. The algorithm is based on the fault detection approach and it works through the estimation of velocity of valve movement activity, that can be obtained by calculating the time derivative of the valve distance. A summarized description of the methods used for the derivative estimation is provided, followed by the associated signal processing and decision making algorithm to determine spawning from the velocity signal. A protection from false spawning detection is also considered by analyzing the simultaneity in spawning. Through this study, it is shown that spawning in a population of oysters living in their natural habitat (i.e. in the sea) can be automatically detected without any human expertise saving time and resources. The fault detection method presented in the paper can also be used to detect complex oscillatory behavior which is of interest to control engineering community.
(IEEE Transactions on Control Systems Technology. vol. 24, n° 1063-6536, pp. 1140--1147, 01/03/2016)
NON-A, Inria, CRIStAL, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Role of macrofauna on benthic oxygen consumption in sandy sediments of a high-energy tidal beach
Sandy beaches exposed to tide and waves are characterized by low abundance and diversity of benthic macrofauna, because of high-energy conditions. This is the reason why there are few studies on benthic communities living in such highly dynamic environments. It has been shown recently that tidal sandy beaches may act as biogeochemical reactors. Marine organic matter that is supplied in the sand during each flood tide is efficiently mineralized through aerobic respiration. In order to quantify the role of macrofauna in the whole beach benthic respiration, we studied the macrofauna and the pore water oxygen content of an exposed sandy beach (Truc Vert, SW of France) during four seasons in 2011. The results showed that macrofauna was characterised by a low number of species of specialized organisms such as the crustaceans Eurydice naylori and Gastrosaccus spp. and the polychaetes Ophelia bicornis and Scolelepis squamata. The distribution and abundance of macrofauna were clearly affected by exposure degree and emersion time. The combined monitoring of benthic macrofauna and pore waters chemistry allowed us to estimate (1) the macrofauna oxygen uptake, calculated with a standard allometric relationship using biomass data, and (2) the total benthic oxygen uptake, calculated from the oxygen deficit measured in pore waters. This revealed that benthic macrofauna respiration represented a variable but low (<10%) contribution to the total benthic oxygen consumption This suggests that oxygen was mainly consumed by microbial respiration.
(Continental Shelf Research, n° 0278-4343, 01/03/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Untangling the complex origin of turbidite activity on the Calabrian Arc (Ionian Sea) over the last 60ka
The Ionian Sea, due to the presence of two accretionary prisms, the Calabrian Arc and the Mediterranean Ridge, associated with the subduction of the Nubia plate and the Eurasia plate, is the witness of large and catastrophic turbidite events. These events are associated with high magnitude earthquakes and tsunamis. They lead an important gravity-driven sedimentary deposit in the Ionian basin. In this study, we analysed turbidite deposits in order to establish a calendar of the palaeoseismicity and volcaniclastic events from Etna on the Calabrian Arc. Two gravity cores collected in a slope basin on the Calabrian Arc and in the Ionian abyssal plain record more than two hundred turbidites over the last 60,000 years. These turbidites were dated with a multi-proxy approach: radiometric dating, tephrochronology and sapropels. The origin of the turbidites was studied with a sedimentary approach: grain-size, lithology, thin section, and geochemistry of volcanic glass. The results suggest that three triggers are responsible for the deposits of turbidites. There are siliciclastic turbidites triggered by earthquakes and tsunamis waves, and volcaniclastic turbidites triggered by the Etna volcano eruptions or flank collapses. Co-seismic turbidites present different recurrence times depending on the location of the core. On the Calabrian Arc, recurrence times vary between 450 and 1000 years according to the periods in time. On the abyssal plain, recurrence times are shorter and more regular: around every 240 years.
(Marine Geology. vol. 373, n° 0025-3227, pp. 11-25, 01/03/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, SHOM, LMV, UBP, INSU - CNRS, UJM, CNRS, IUEM, IRD, INSU - CNRS, UBO EPE, CNRS
Sub-chronic exposure to fluoxetine in juvenile oysters (Crassostrea gigas): uptake and biological effects
The bioconcentration potential of fluoxetine (FLX) and its biological effects were investigated in juvenile Pacific oyster exposed for 28 days to environmentally relevant concentrations of FLX (1 ng L−1, 100 ng L−1 and up to 10 μg L−1). FLX bioaccumulated in oyster flesh resulting in 28-day bioconcentration factors greater than 2,000 and 10,000 by referring to wet and dry weights, respectively. Nevertheless, FLX did not induce oyster mortality, delayed gametogenesis, or lead to adverse histopathological alterations. At the two highest concentrations, despite non-optimal trophic conditions, FLX stimulated shell growth but only in a transient manner, suggesting a role of serotonin in the regulation of feeding and metabolism in bivalves. Those high concentrations seemed to drive bell-shaped responses of catalase and glutathione S-transferase activities throughout the exposure period, which may indicate the activation of antioxidant enzyme synthesis and then an enhanced catabolic rate or direct inhibition of those enzymes. However, no clear oxidative stress was detected because no strong differences in thiobarbituric acid-reactive substance (TBARS) content (i.e. lipid peroxidation) were observed between oyster groups, suggesting that cellular defence mechanisms were effective. These results demonstrate the importance of considering additional biomarkers of oxidative stress to obtain a comprehensive overview of the FLX-induced changes in marine bivalves exposed under realistic conditions. Considering the battery of biomarkers used, FLX appears to induce little or no effects on oyster physiology even at a concentration of 10 μg L−1. These results do not confirm the lowest observed effect concentration (LOEC) values reported by some authors in other mollusc species.
(Environmental Science and Pollution Research. vol. 23, n° 0944-1344, pp. 5002-5018, 01/03/2016)
GMPc, UNICAEN, NU, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, LEFE, INEE-CNRS, CNRS, UT3, Comue de Toulouse, CNRS, Toulouse INP, Comue de Toulouse, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LPTC, UB, CNRS