Large-Scale Carbonate Submarine Mass-Wasting along the Northwestern Slope of the Great Bahama Bank (Bahamas): Morphology, Architecture, and Mechanisms
Along the northwestern margin of the Great Bahama Bank (Bahamas), high-resolution multibeam bathymetry maps have revealed large escarpments, 80-100 m in height, and gigantic carbonate Mass Transport Complexes (MTCs), characterized by megablocks, several hundred to several thousand meters in size.The present-day configuration of this mass-wasting deposit is the result of the specific basinal sedimentation of the GBB during the Neogene. Marginal sedimentation was produced by: (i) massive gravity-flow slope apron carbonates, feeding from the eastern prograding platform, including oversized MTCs; and (ii) thick, elongated, and muddier drift contourite flowing from south to north along the toe of slope. Four distinct MTCs (MTC-1 to -4) resulted from repeated slope failures in the Late Pliocene and the Pleistocene. These MTCs all glided along a common privileged décollement surface, dated Late Messinian – Early Pliocene, which coincided with a regional diagenetic key stratigraphic surface. The MTCs collapsed down from the steep mid- to upper-slope apron, partially draped the drift deposits, and flowed basinward over 10-20 km, extending over an area of approximately 400 km2.With the support of good-quality seismic reflection data, a detailed analysis was produced of the stratigraphic architecture of these MTCs, highlighting the high variability of the seismic facies from tabular bounded strata to chaotic patterns. The analysis of the facies demonstrated the internal stratigraphic complexity of the MTCs as well as that of the subsequent filling of the associated headwall scar-related depressions.A depositional reconstitution of the MTCs is proposed from collapse initiation to final deposition, resulting in the present-day irregular seafloor morphology. The model accounts for the influence of the Early Pliocene drift-induced topography on the distribution and internal architecture of the successive MTCs. Most likely due to sedimentation rate increase, the contourite displayed lateral morphological variations, forming flat to mound-shaped features when upslope collapses occurred. Depending on lee-side steepness, it then acted either as secondary décollement ramp or as natural obstacle for mass-wasting deposits.Strips of sharply-bounded chaotic facies preserved within the Pliocene contourite are interpreted as far-reaching fluid escape-related facies (thixotropy), resulting from frontal impact with the contourite at the toe of the MTCs.The MTCs are not unique mass-wasting carbonate deposits, as similar features with comparable dimensions have been reported in the geological record in the Bahamas and in other carbonate basins. However, they clearly illustrate a significant volume of sediment remobilization over short distances in carbonate slope environments.
(Sedimentary Geology. vol. 317, n° 0037-0738, pp. 27-42, 28/10/2014)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Evolution morphologique et processus sédimentaires actuels du plateau continental interne sud-aquitain : étude comparée des zones de la Salie-Biscarosse (Sud des passes d'Arcachon) et la zone de la tête du canyon de Capbreton.
Ce travail présente une analyse de l'évolution morphologique et des processus sédimentaires actuels du plateau continental interne sud-aquitain, (sud-est du Golfe de Gascogne, France),secteur riche en données, mais sur lequel de nombreuses questions restent néanmoins en suspens. Il s'articule autour de deux zones ateliers complémentaires : la zone de « La Salie-Biscarrosse » sur le plateau continental interne sud-aquitain au sud des passes du Bassin d'Arcachon (entre 5 et 50 m de profondeur d’eau), et la tête du canyon de Capbreton et ses abords (entre 5 et 120 m de profondeur d’eau). Deux approches sont utilisées : (1) une approche descriptive et comparative (dans le temps), utilisant des données géo-acoustiques(sondeur multi faisceaux, sonar latéral et sondeur de sédiments), des prélèvements et (2) une approche mettant en oeuvre des modélisations numériques des interactions houles / courants /sédiments. Les résultats obtenus sur le plateau interne aquitain ont permis d'améliorer la connaissance de la morphologie, de la nature et de la géométrie interne des corps sédimentaires, d'étudier leur évolution au cours des 29 dernières années (entre 1984 et 2013)et de proposer des facteurs à l’origine de cette évolution. Le résultat majeur est la mise en évidence de « sorted bebforms » entretenus par la houle; dont la surprenante migration vers le nord-est est à associer à la récente découverte d'intenses épisodes de « poleward current » sur le plateau. Le suivi entre 1998 et 2013 de l’évolution morphologique de la tête du Canyon de Capbreton, située à seulement 250 m du littoral montre une évolution rapide qui fluctue cependant autour d'une position d'équilibre. Par ailleurs l’influence de la dérive littorale sur les transferts de sédiments du plateau vers le canyon a pu être démontrée. En-effet, les arguments morphologiques et sédimentaires, associés à la modélisation numérique, prouvent que la dérive littorale aquitaine alimente épisodiquement (conditions de houle forte) la tête de canyon en sables littoraux.
(23/10/2014)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Effects of standard humic materials on relative bioavailibility of NDL-PCBs in juvenile swine
(05/10/2014)
URAFPA, INRA, UL, LPTC, UB, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Origin and architecture of a Mass Transport Complex on the northwest slope of Little Bahama Bank (Bahamas): Relations between off-bank transport, bottom current sedimentation and submarine landslides
The analysis of the sedimentary dynamics of the carbonate slope of the northwest part of Little Bahama Bank (LBB, Bahamas) reveals a complex interaction between slope destabilisations, off-bank sediment export and longitudinal transport, the latter being driven by the Antilles and the Florida currents, at the northern end of the Florida Strait. Their combined action since the middle Miocene resulted in an extensional growth slope, previously called ‘LBB Drift’ (Mullins et al., 1980). Deposition within this extensional growth slope is dominated by either platform-derived downslope sedimentation or bottom current sedimentation. The latter induces the formation of a plastered drift, showing both upslope and downslope migrations, which do not correspond to the ‘LBB Drift’ as described by Mullins et al. (1980). Interestingly, a large submarine landslide affects the upper part of this plastered drift, and displays a complex and striking geomorphology on the seafloor. A new high-quality multibeam echosounder and seismic dataset allowed a detailed characterisation of the architecture of this Mass Transport Complex (MTC). A 44 km-long circular incision at 275 m and 460 m water depths, with a steep external edge (from 40 to 70 m high), forms the only present day evidence of this ancient MTC. It comprises confined Mass Transport Deposits (MTDs), which are delimited by frontal and lateral edges that developed inside the plastered drift. The top of this plastered drift is marked by a major erosional surface, most likely induced by an increase in oceanic current circulation. Channelised geometries, laterally associated with overspill deposits, developed within the depression induced by the MTC, and are an additional evidence of bottom current activity in this area. In addition, recent pockmarks are visible on the seafloor in front of the circular scarp of the MTC and probably relate to fluid escape, originating from the underlying MTDs' compressional area.
(Sedimentary Geology. vol. 317, n° 0037-0738, pp. 9-26, 01/10/2014)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
21,000 Years of Ethiopian African monsoon variability recorded in sediments of the western Nile deep-sea fan
(Regional Environmental Change. vol. 14, n° 1436-3798, pp. 1685-1696, 01/10/2014)
GEOAZUR 6526, IRD, UPMC, UNS, INSU - CNRS, UniCA, CNRS, GEOPS, UP11, CNRS, ETH Zürich, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOAZUR 7329, INSU - CNRS, UniCA, CNRS, IRD [Occitanie], UniCA, UAG, INSU - CNRS, UM, CNRS, CTAD, ENS-PSL, PSL, EHESS, UPN, CNRS, DREAM, Inria, IRISA-D7, IRISA, UR, INSA Rennes, UBS, ENS Rennes, Inria, CNRS, OOVM, UPMC, INSU - CNRS, CNRS
Analysis of airborne pesticides from different chemical classes adsorbed on Radiello® Tenax® passive tubes by thermal-desorption-GC/MS
An analytical methodology using automatic thermal desorption (ATD) and GC/MS was developed for the determination of 28 pesticides of different chemical classes (dichlobenil, carbofuran, trifluralin, clopyralid, carbaryl, flazasulfuron, mecoprop-P, dicamba, 2,4-MCPA, dichlorprop, 2,4-D, triclopyr, cyprodinil, bromoxynil, fluroxypyr, oxadiazon, myclobutanil, buprofezin, picloram, trinexapac-p-ethyl, ioxynil, diflufenican, tebuconazole, bifenthrin, isoxaben, alphacypermethrin, fenoxaprop and tau-fluvalinate) commonly used in nonagricultural areas in atmospheric samples. This methodology was developed to evaluate the indoor and outdoor atmospheric contamination by nonagricultural pesticides. Pesticides were sampled passive sampling tubes containing Tenax® adsorbent. Since most of these pesticides are polar (clopyralid, mecoprop-P, dicamba, 2,4-MCPA, dichlorprop, 2,4-D, triclopyr, bromoxynil, fluroxypyr, picloram, trinexapac-p-ethyl and ioxynil), a derivatisation step is required. For this purpose, a silylation step using N-(t-butyldimethylsilyl)-N-methyltrifluoroacetamide (MtBSTFA) was added before thermal desorption. This agent was chosen since it delivers very specific ions on electronic impact (m/z = M-57). This method was established with special consideration for optimal thermal desorption conditions (desorption temperature, desorb flow and duration; trap heating duration and flow; outlet split), linear ranges, limits of quantification and detection which varied from 0.005 to 10 ng and from 0.001 to 2.5 ng, respectively, for an uncertainty varied from 8 to 30 %. The method was applied in situ to the analysis of passive tubes exposed during herbicide application to an industrial site in east of France.
(Environmental Science and Pollution Research. vol. 22, n° 0944-1344, pp. 2726-2734, 11/09/2014)
ICPEES, UNISTRA, INC-CNRS, CNRS, MNGE, UNISTRA, Université de Haute-Alsace (UHA), INSERM, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Communities: Are they groups of hidden interactions?
Questions Ecologists are increasingly interested in community-level consequences of biotic interactions. However, community-level studies have not considered that biotic interactions might have contrasting directions within communities, and indirect interactions are rarely quantified although they may influence community-level outcomes. We tested the hypotheses that in species-rich plant communities from intermediate severe environmental conditions: (1) direct facilitation by dominant functional groups is balanced by negative indirect interactions among beneficiary species with no net effect at the community level on diversity and biomass, and (2) both direct and indirect interactions contribute to community composition. Location A species-rich subalpine community of the eastern Tibet Plateau (China). Methods We removed dominant shrubs and graminoids and quantified, at the community and species levels, their direct and indirect effects on 43 forb species. We used multivariate analyses to assess the contribution of direct and indirect effects on community composition. Results There were no community-level effects of either dominant life form on forb diversity and biomass. There were multiple species-level interactions that we grouped into six types based on the direction and intensity of indirect effects. We found significant relationships between species-level interactions and community composition. Conclusions Our study highlights that communities are sets of hidden interactions that contribute to community composition, although no interaction might be detected at the community level because hidden interactions balance each other. Future studies should assess the ecological and functional drivers of these hidden interactions.
(Journal of Vegetation Science. vol. 26, n° 1100-9233, pp. 207-218, 01/09/2014)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
How does the resuspension of the biofilm alter the functioning of the benthos–pelagos coupled food web of a bare mudflat in Marennes-Oléron Bay (NE Atlantic)?
Intertidal mudflats are ecosystems submitted to natural hydrodynamical forcings during each tide. When the off-shore water flows at high tide, a proportion of the biofilm produced at low tide can be resuspended in the water column and interact with the pelagic food web. As a consequence, the resuspension creates a link between the benthos and the pelagos, modifying their properties and the stability of the meta-ecosystem they form together. The aim of this study is to describe the consequences of the microbial biofilm resuspension on the pelagic food web, and to investigate the question of the stability of the benthos–pelagos coupling resulting from the biofilm resuspension. Two food webs were considered, corresponding to different hydrodynamical conditions in sum-mer condition: one allowing the biofilm massive resuspension, and one without resuspension, but with particle sedimentation. The Monte-Carlo Markov Chain Linear Modelling was used to estimate the unknown flows of the food web. The comparison of the Ecological Network Analysis indices for the two food webs allowed defining their respective differences of structure and functioning. The results showed that the massive resuspension of the microbial biofilm stimulates pelagic primary production and microbial food web via a higher bacterivory. The higher activity of the whole system coupled with both a drop in the specialisation of the trophic pathways and a low cycling activity demonstrated that when massive resuspension occurs, the system is disturbed. In con-trast, when sedimentation occurs, the food webs show functioning features pointing out to a higher stability of the whole system.
(Journal of Sea Research (JSR). vol. 92, n° 1385-1101, pp. 144-157, 01/09/2014)
LIENSs, INSU - CNRS, ULR, CNRS, CRESCO, MNHN, IFREMER, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CRESCO, MNHN, IFREMER, LECOB, OOB, UPMC, CNRS, UPMC, CNRS, CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], LMGE, UCA [2017-2020], CNRS, MMS, UM, UN UFR ST, UN, UFR SPB, UN, BioMEA, UNICAEN, NU, CNRS
A new sliced inverse regression method for multivariate response
A semiparametric regression model of a q-dimensional multivariate response y on a p-dimensional covariate x is considered. A new approach is proposed based on sliced inverse regression (SIR) for estimating the effective dimension reduction (EDR) space without requiring a prespecified parametric model. The convergence at rate square root of n of the estimated EDR space is shown. The choice of the dimension of the EDR space is discussed. Moreover, a way to cluster components of y related to the same EDR space is provided. Thus, the proposed multivariate SIR method can be used properly on each cluster instead of blindly applying it on all components of y. The numerical performances of multivariate SIR are illustrated on a simulation study. Applications to a remote sensing dataset and to the Minneapolis elementary schools data are also provided. Although the proposed methodology relies on SIR, it opens the door for new regression approaches with a multivariate response.
(Computational Statistics and Data Analysis. vol. 77, n° 0167-9473, pp. 285-299, 01/09/2014)
IMB, UB, Bordeaux INP, CNRS, CQFD, IMB, UB, Bordeaux INP, CNRS, Inria, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, MISTIS, Inria, LJK, UPMF, UJF, Grenoble INP, CNRS, Grenoble INP, ENSC
Physiological responses of Manila clams Venerupis (=Ruditapes) philippinarum with varying parasite Perkinsus olseni burden to toxic algal Alexandrium ostenfeldii exposure.
Manila clam stock from Arcachon Bay, France, is declining, as is commercial harvest. To understand the role of environmental biotic interactions in this decrease, effects of a toxic dinoflagellate, Alexandrium ostenfeldii, which blooms regularly in Arcachon bay, and the interaction with perkinsosis on clam physiology were investigated. Manila clams from Arcachon Bay, with variable natural levels of perkinsosis, were exposed for seven days to a mix of the nutritious microalga T-Iso and the toxic dinoflagellate A. ostenfeldii, a producer of spirolides, followed by seven days of depuration fed only T-Iso. Following sacrifice and quantification of protozoan parasite Perkinsus olseni burden, clams were divided into two groups according to intensity of the infection ("Light-Moderate" and "Moderate-Heavy"). Hemocyte and plasma responses, digestive enzyme activities, antioxidant enzyme activities in gills, and histopathological responses were analyzed. Reactive oxygen species (ROS) production in hemocytes and catalase (CAT) activity in gills increased with P. olseni intensity of infection in control clams fed T-Iso, but did not vary among A. ostenfeldii-exposed clams. Exposure to A. ostenfeldii caused tissue alterations associated with an inflammatory response and modifications in hemocyte morphology. In the gills, superoxide dismutase (SOD) activity decreased, and an increase in brown cell occurrence was seen, suggesting oxidative stress. Observations of hemocytes and brown cells in tissues during exposure and depuration suggest involvement of both cell types in detoxication processes. Results suggest that exposure to A. ostenfeldii disrupted the pro-/anti-oxidant response of clams to heavy P. olseni intensity. In addition, depressed mitochondrial membrane potential (MMP) in hemocytes of clams exposed to A. ostenfeldii suggests that mitochondrial functions are regulated to maintain homeostasis of digestive enzyme activity and condition index.
(Aquatic Toxicology. vol. 154, n° 0166-445X, pp. 27-38, 01/09/2014)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, IFREMER, INSTM, UFPB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS