Paleoseismic potential of sublacustrine landslide records in a high-seismicity setting (south-central Alaska)
Sublacustrine landslide stratigraphy is considered useful for quantitative paleoseismology in low-seismicity settings. However, as the recharging of underwater slopes with sediments is one of the factors that governs the recurrence of slope failures, it is not clear if landslide deposits can provide continuous paleoseismic records in settings of frequent strong shaking. To test this, we selected three lakes in south-central Alaska that experienced a strong historical megathrust earthquake (the 1964 Mw9.2 Great Alaska Earthquake) and exhibit high sedimentation rates in their main basins (0.2 cm yr− 1–1.0 cm yr− 1). We present high-resolution reflection seismic data (3.5 kHz) and radionuclide data from sediment cores in order to investigate factors that control the establishment of a reliable landslide record. Seismic stratigraphy analysis reveals the presence of several landslide deposits in the lacustrine sedimentary infill. Most of these landslide deposits can be attributed to specific landslide events, as multiple landslide deposits sourced from different lacustrine slopes occur on a single stratigraphic horizon. We identify numerous events in the lakes: Eklutna Lake proximal basin (14 events), Eklutna Lake distal basin (8 events), Skilak Lake (7 events) and Kenai Lake (7 events). The most recent event in each basin corresponds to the historic 1964 megathrust earthquake. All events are characterized by multiple landslide deposits, which hints at a regional trigger mechanism, such as an earthquake (the synchronicity criterion). This means that the landslide record in each basin represents a record of past seismic events. Based on extrapolation of sedimentation rates derived from radionuclide dating, we roughly estimate a mean recurrence interval in the Eklutna Lake proximal basin, Eklutna Lake distal basin, Skilak Lake and Kenai Lake, at ~ 250 yrs., ~ 450 yrs., ~ 900 yrs. and ~ 450 yrs., respectively. This distinct difference in recording can be explained by variations in preconditioning factors like slope angle, slope recharging (sedimentation rate) and the sediment source area: faster slope recharging and a predominance of delta and alluvial fan failures, increase the sensitivity and lower the intensity threshold for slope instability. Also, the seismotectonic setting of the lakes has to be taken into account. This study demonstrates that sublacustrine landslides in several Alaskan lakes can be used as reliable recorders of strong earthquake shaking, when a multi-lake approach is used, and can enhance the temporal and spatial resolution of the paleoseismic record of south-central Alaska.
(Marine Geology. vol. 384, n° 0025-3227, pp. 103-119, 01/05/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
One-year study of polycyclic aromatic compounds at an urban site in Grenoble (France): Seasonal variations, gas/particle partitioning and cancer risk estimation
21 PAHs, 27 oxy-PAHs and 32 nitro-PAHs were measured every third day over a year in both gaseous (G) and particulate PM10 (P) phases in ambient air of Grenoble (France). Mean total concentrations (G + P) of PAHs and oxy-PAHs were in the same range and about 10 ng m− 3. Nitro-PAHs were 50 to 100 times less concentrated averaging 100 pg m− 3. Polycyclic aromatic compound (PAC) concentrations were 5 to 7 times higher in “cold” period (October to March) than in “warm” period (April to September). Seasonal variations may be explained by higher primary emissions from residential heating, especially biomass burning in “cold” season. Meteorological conditions and influence of the geomorphology around Grenoble, with the formation of thermal inversion layers leading to the stagnation of pollutants, were additional key parameters. Maximum individual PAC concentrations were observed during two PM10 pollution events in December and February–March. Chemical processes and secondary formation of oxy- and nitro-PAH were probably enhanced by the accumulation of the pollutants during these events. PAC gas/particle partitioning depended on compound molecular weight and vapour pressure. Gas/particle partitioning of oxy- and nitro-PAHs were evaluated using a multi-phase poly-parameter linear free energy relationship model. The PAC cancer risk was assessed using toxic equivalency factors available in the literature (19 PAHs, 10 nitro-PAHs and 1 oxy-PAH). Overall, particle-bound PACs contributed about 76% of the cancer risk. While PAHs accounted for most of the total PAC cancer risk, oxy- and nitro-PAHs could account for up to 24%. The risk quantification across substance classes is limited by toxicological data availability.
(Science of the Total Environment. vol. 565, n° 0048-9697, pp. 1071–1083, 01/05/2016)
UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, INERIS, MPIC, LGGE, INSU - CNRS, CNRS, OSUG, Grenoble INP, INSU - CNRS, IRSTEA, USMB [Université de Savoie] [Université de Chambéry], CNRS, UGA [2016-2019], MU / MUNI
Using global sensitivity analysis to evaluate the uncertainties of future shoreline changes under the Bruun rule assumption
Future sandy shoreline changes are often assed by summing the contributions of longshore and cross-shore effects. In such approaches, a contribution of sea-level rise can be incorporated by adding a supplementary term based on the Bruun rule. Here, our objective is to identify where and when the use of the Bruun rule can be (in)validated, in the case of wave-exposed beaches with gentle slopes. We first provide shoreline change scenarios that account for all uncertain hydrosedimentary processes affecting the idealized low- and high-energy coasts described by Stive (2004)[Stive, M. J. F. 2004, How important is global warming for coastal erosion? an editorial comment, Climatic Change, vol. 64, n 12, doi:10.1023/B:CLIM.0000024785.91858. ISSN 0165-0009]. Then, we generate shoreline change scenarios based on probabilistic sea-level rise projections based on IPCC. For scenario RCP 6.0 and 8.5 and in the absence of coastal defenses, the model predicts an observable shift toward generalized beach erosion by the middle of the 21st century. On the contrary, the model predictions are unlikely to differ from the current situation in case of scenario RCP 2.6. To get insight into the relative importance of each source of uncertainties, we quantify each contributions to the variance of the model outcome using a global sensitivity analysis. This analysis shows that by the end of the 21st century, a large part of shoreline change uncertainties are due to the climate change scenario if all anthropogenic greenhousegas emission scenarios are considered equiprobable. To conclude, the analysis shows that under the assumptions above, (in)validating the Bruun rule should be straightforward during the second half of the 21st century and for the RCP 8.5 scenario. Conversely, for RCP 2.6, the noise in shoreline change evolution should continue dominating the signal due to the Bruun effect. This last conclusion can be interpreted as an important potential benefit of climate change mitigation.
(pp. EGU2016-1477, 18/04/2016)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Influence of the mud shrimp Upogebia pusilla (Decapoda: Gebiidea) on solute and porewater exchanges in an intertidal seagrass (Zostera noltei) meadow of Arcachon Bay: An experimental assessment
The aim of the present study was to investigate the influence of the mud shrimp Upogebia pusilla on porewater and solute exchanges in an intertidal Zostera noltei meadow of Arcachon Bay. Laboratory experiments carried out during three seasons showed that U. pusilla strongly enhanced sediment porewater exchange rates (averaging 26, 45 and 71 L m− 2 d− 1 in winter, spring and summer, respectively) in comparison to uninhabited sediments for which these rates were moderate (averaging 9, 9 and 16 L m− 2 d− 1 in winter, spring and summer, respectively). Total Oxygen Uptakes (TOUs) were increased by factors around 2.5 during the three studied seasons whilst oxygen consumption by the shrimp accounted for 64, 28 and 21% of TOU in winter, spring and summer, respectively. U. pusilla also significantly enhanced the uptake of nitrate (up to 13.8-fold in summer) and the release of ammonium (up to 3.0-fold in summer) and silicate (up to 3.8-fold in spring) by the sediment. Overall, our results highlight the key role of U. pusilla in controlling oxygen and nutrient fluxes in Arcachon Bay. Because U. pusilla populations are predominantly found in the sediments of Z. noltei meadows, the full assessment of the functional effects resulting from the decline of this meadow should include the effects associated to the disappearance of U. pusilla as well.
(Journal of Experimental Marine Biology and Ecology. vol. 477, n° 0022-0981, pp. 69-79, 01/04/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
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