Comparison of environmental forcings affecting suspended sediments variability in two macrotidal, highly-turbid estuaries
The relative contribution of environmental forcing frequencies on turbidity variability is, for the first time, quantified at seasonal and multiannual time scales in tidal estuarine systems. With a decade of high-frequency, multi-site turbidity monitoring, the two nearby, macrotidal and highly-turbid Gironde and Loire estuaries (west France) are excellent natural laboratories for this purpose. Singular Spectrum Analyses, combined with Lomb-Scargle periodograms and Wavelet Transforms, were applied to the continuous multiannual turbidity time series. Frequencies of the main environmental factors affecting turbidity were identified: hydrological regime (high versus low river discharges), river flow variability, tidal range, tidal cycles, and turbulence. Their relative influences show similar patterns in both estuaries and depend on the estuarine region (lower or upper estuary) and the time scale (multiannual or seasonal). On the multiannual time scale, the relative contribution of tidal frequencies (tidal cycles and range) to turbidity variability decreases up-estuary from 68% to 47%, while the influence of river flow frequencies increases from 3% to 42%. On the seasonal time scale, the relative influence of forcings frequencies remains almost constant in the lower estuary, dominated by tidal frequencies (60% and 30% for tidal cycles and tidal range, respectively); in the upper reaches, it is variable depending on hydrological regime, even if tidal frequencies are responsible for up 50% of turbidity variance. These quantifications show the potential of combined spectral analyses to compare the behavior of suspended sediment in tidal estuaries throughout the world and to evaluate long-term changes in environmental forcings, especially in a context of global change. The relevance of this approach to compare nearby and overseas systems and to support management strategies is discussed (e.g., selection of effective operation frequencies/regions, prediction of the most affected regions by the implementation of operational management plans).
(Estuarine, Coastal and Shelf Science. vol. 198, n° 0272-7714, pp. 529-541, 01/11/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The sense of hearing in the Pacific oyster, Magallana gigas
There is an increasing concern that anthropogenic noise could have a significant impact on the marine environment, but there is still insufficient data for most invertebrates. What do they perceive? We investigated this question in oysters Magallana gigas (Crassostrea gigas) using pure tone exposures, accelerometer fixed on the oyster shell and hydrophone in the water column. Groups of 16 oysters were exposed to quantifiable waterborne sinusoidal sounds in the range of 10 Hz to 20 kHz at various acoustic energies. The experiment was conducted in running seawater using an experimental flume equipped with suspended loudspeakers. The sensitivity of the oysters was measured by recording their valve movements by high-frequency noninvasive valvometry. The tests were 3 min tone exposures including a 70 sec fade-in period. Three endpoints were analysed: the ratio of responding individuals in the group, the resulting changes of valve opening amplitude and the response latency. At high enough acoustic energy, oysters transiently closed their valves in response to frequencies in the range of 10 to <1000 Hz, with maximum sensitivity from 10 to 200 Hz. The minimum acoustic energy required to elicit a response was 0.02 m∙s-2 at 122 dBrms re 1 μPa for frequencies ranging from 10 to 80 Hz. As a partial valve closure cannot be differentiated from a nociceptive response, it is very likely that oysters detect sounds at lower acoustic energy. The mechanism involved in sound detection and the ecological consequences are discussed.
(PLoS ONE. vol. 12, n° 1932-6203, pp. e0185353, 25/10/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
From the field to the database: a user-oriented approach to promote cyber-curating of scientific continental drilling cores
Managing scientific data is probably one the most challenging issues in modern science. In plaeosciences the question is made even more sensitive with the need of preserving and managing high value fragile geological samples: cores. Large international scientific programs, such as IODP or ICDP led intense effort to solve this problem and proposed detailed high standard work- and dataflows thorough core handling and curating. However many paleoscience results derived from small-scale research programs in which data and sample management is too often managed only locally – when it is… In this paper we present a national effort leads in France to develop an integrated system to curate ice and sediment cores. Under the umbrella of the national excellence equipment program CLIMCOR, we launched a reflexion about core curating and the management of associated fieldwork data. Our aim was then to conserve all data from fieldwork in an integrated cyber-environment which will evolve toward laboratory-acquired data storage in a near future. To do so, our demarche was conducted through an intimate relationship with field operators as well laboratory core curators in order to propose user-oriented solutions. The national core curating initiative proposes a single web portal in which all teams can store their fieldwork data. This portal is used as a national hub to attribute IGSNs. For legacy samples, this requires the establishment of a dedicated core list with associated metadata. However, for forthcoming core data, we developed a mobile application to capture technical and scientific data directly on the field. This application is linked with a unique coring-tools library and is adapted to most coring devices (gravity, drilling, percussion etc.) including multiple sections and holes coring operations. Those field data can be uploaded automatically to the national portal, but also referenced through international standards (IGSN and INSPIRE) and displayed in international portals (currently, NOAA’s IMLGS). In this paper, we present the architecture of the integrated system, future perspectives and the approach we adopted to reach our goals. We will also present our mobile application through didactic examples.
(12/10/2017)
EDYTEM, USMB [Université de Savoie] [Université de Chambéry], CNRS, Fédération OSUG, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, DTI, INSU - CNRS, CNRS, IRSI, IFREMER, ISTerre, IFSTTAR, INSU - CNRS, USMB [Université de Savoie] [Université de Chambéry], CNRS, UGA [2016-2019], IGE, IRD, Grenoble INP, INSU - CNRS, CNRS, UGA [2016-2019], Fédération OSUG, LOCEAN-VALCO, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, INSU - CNRS
Influence de la crue de juin 2016 sur les flux de matières dans le bassin de la Seine
(05/10/2017)
METIS, UPMC, EPHE, PSL, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GIP-Seine-Aval, GEOSCIENCES, PSL, LEESU, ENPC, UPEC UP12
Relationship between the invasive slipper limpet Crepidula fornicata and benthic megafauna structure and diversity, in Arcachon Bay
The slipper limpet Crepidula fornicata ranks among the main invasive species on French coasts and is known to cause ecological impacts on food web structure and nutrient cycling. This study investigated the effect of C. fornicata on different components of benthic megafauna diversity (species composition, α-, β- and γ-diversity). In Arcachon Bay (France), C. fornicata was present in 58% of the 221 sampling stations. Crepidula fornicata was particularly abundant in four of the main benthic megafauna assemblages, suggesting a non-random distribution of its population. The mean number of megafauna species per station (α-diversity) was 11 with C. fornicata vs six without. Conversely, community similarity among stations (β-diversity) was higher when C. fornicata biomass increased. Opposing α- and β-diversity trends in the presence of C. fornicata explained the similarity of the global number of species (γ-diversity) between both situations (with and without C. fornicata). These results highlighted how this exotic engineer species acted on different types of diversity: the presence of C. fornicata increased the number of species per sample (α-diversity) but homogenized the benthic community (decreasing β-diversity) in comparison with stations where C. fornicata was absent. Crepidula fornicata stock in Arcachon Bay was also monitored and compared with 1999. The spread of C. fornicata between 1999 and 2011 has been limited with a 318 t stock which was not statistically different than the previous estimate performed in 1999. However, the mean length of C. fornicata collected in 2011 was significantly smaller, mainly due to a higher proportion of small individuals.
(Journal of the Marine Biological Association of the United Kingdom, n° 0025-3154, pp. 1-12, 04/10/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Impact of urban effluents on summer hypoxia in the highly turbid Gironde Estuary, applying a 3D model coupling hydrodynamics, sediment transport and biogeochemical processes
Estuaries are increasingly degraded due to coastal urban development and are prone to hypoxia problems. The macro-tidal Gironde Estuary is characterized by a highly concentrated turbidity maximum zone (TMZ). Field observations show that hypoxia occurs in summer in the TMZ at low river flow and a few days after the spring tide peak. In situ data highlight lower dissolved oxygen (DO) concentrations around the city of Bordeaux, located in the upper estuary. Interactions between multiple factors limit the understanding of the processes controlling the dynamics of hypoxia. A 3D biogeochemical model was developed, coupled with hydrodynamics and a sediment transport model, to assess the contribution of the TMZ and the impact of urban effluents through wastewater treatment plants (WWTPs) and sewage overflows (SOs) on hypoxia. Our model describes the transport of solutes and suspended material and the biogeochemical mechanisms impacting oxygen: primary production, degradation of all organic matter (i.e. including phytoplankton respiration, degradation of river and urban watershed matter), nitrification, and gas exchange. The composition and the degradation rates of each variable were characterized by in situ measurements and experimental data from the study area. The DO model was validated against observations in Bordeaux City. The simulated DO concentrations show good agreement with field observations and satisfactorily reproduce the seasonal and neap-spring time scale variations around the city of Bordeaux. Simulations show a spatial and temporal correlation between the formation of summer hypoxia and the location of the TMZ, with minimum DO centered in the vicinity of Bordeaux. To understand the contribution of the urban watershed forcing, different simulations with the presence or absence of urban effluents were compared. Our results show that in summer, a reduction of POC from SO would increase the DO minimum in the vicinity of Bordeaux by 3% of saturation. Omitting discharge from SO and WWTPs, DO would improve by 10% of saturation and mitigate hypoxic events.
(Journal of Marine Systems. vol. 174, n° 0924-7963, pp. 89-105, 01/10/2017)
LPTC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LyRE, CSIRO, DYNECO, IFREMER, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, UFF
Tectonism and volcanism forced by glaciation and deglaciation events in southern Iceland
(01/10/2017)
LDO, INSU - CNRS, UBO EPE, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, iSTeP, INSU - CNRS, SU, CNRS, IFRIS, INRA, EHESS, UPEM, M.E.N.E.S.R., CNRS
The southern Norwegian Sea during the last 45 ka: hydrographical reorganizations under changing ice‐sheet dynamics
The last glacial millennial Heinrich and Dansgaard–Oeschger events have been the subject of many studies in recent decades. However, significant uncertainties remain, notably regarding associated oceanic mechanisms. Here we investigate the evolution of hydrographical conditions in the 3–41 ka cal BP interval of core MD99-2285 located in the southern Norwegian Sea. Our results reveal an unusual scheme with: (i) warm Greenland interstadials marked by a relatively cold and homogeneous upper water column seasonally ice-covered and active deep water formation, (ii) cold Greenland and Heinrich stadials marked by a warm, low-salinity and nearly sea ice-free surface layer with iceberg calving, separated by a strong halocline from a colder and saltier subsurface layer, as well as strongly reduced deep convection, and (iii) close to modern Holocene oceanic conditions, but showing significant differences from interstadial conditions. Hence, our work strongly suggests different deep-water convection modes in the Nordic Seas, with, notably, interstadial deep water formation mainly forced by brine release. According to our results, the transition from the glacial mode of deep water formation to the modern open ocean convection mode might have occurred at the end of deglaciation/beginning of the Holocene, when both modes probably occurred.
(Journal of Quaternary Science. vol. 32, n° 0267-8179, pp. 908-922, 18/09/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Phenotypic effects of the nurse Thylacospermum caespitosum on dependent plant species along regional climate stress gradients
Contrasting phenotypes of alpine cushion species have been recurrently described in several mountain ranges along small-scale topography gradients, with tight competitive phenotypes in stressful convex topography and loose facilitative phenotypes in sheltered concave topography. The consistency of phenotypic effects along large-scale climate stress gradients have been proposed as a test of the likely genetic bases of the differences observed at small-scale. Inversely, plastic phenotypic effects are more likely to vanish at some points along climate stress gradients. We tested this hypothesis for two phenotypes of the alpine cushion species Thylacospermum caespitosum at four points along regional gradients of cold and drought stress in northwest China. We measured the traits of the two cushion phenotypes and quantified their associated plant communities and environmental variables along the regional temperature and aridity gradients. Cushion height, convexity and stem density overall showed significant effect of phenotypes. Difference in tightness of cushions between phenotypes was consistent across climate conditions, whereas differences in cushion convexity and height between phenotypes increased with increasing cold stress. Phenotypic effects on species richness and abundance were consistent along both climate gradients but not effects on species composition, while there were no phenotypic effects on environmental variables. Additionally, RII (relative interaction index) curves were linear along the drought gradient but unimodal along the temperature gradient, likely due to the occurrence of contrasting species pools at the different sites. We conclude that the consistency of phenotypic effects of T. caespitosum was high for species richness and abundance and mainly explained by differences in interference mediated by likely heritable differences in cushion tightness. Additionally, our study shows that the shapes of the relationship between plant responses to neighbours and environmental stresses are not necessarily driven by niche-based deterministic factors.
(Oikos. vol. 127, n° 0030-1299, pp. 252-263, 18/09/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Swelling behavior of polymeric membranes to metalworking fluids
In some working places, such as metal manufacturing or automotive services, mechanical hazards commonly occur along with chemical hazards, particularly metalworking fluids (MWFs). The presence of these chemicals could modify the properties of gloves made from polymeric materials and thus reduce their protective properties against chemical contamination (solvent, MWFs) and mechanical risks (puncture and cutting). This work focused on determining the swelling characteristics and the resistance of six polymeric membranes which were exposed to seven industrial MWFs. We found that the swelling tests can be used to classify the potential of coating polymers in descending order of their resistance to MWFs: nitrile, polyurethane>poly(vinyl chloride), neoprene> butyl, latex. The analysis by multiple linear regression showed, for the first time, that the density or the viscosity-gravity constant of the fluid and Hansen’s solubility parameters of the polymers have a significant impact on the swelling of polymer. For the first time, two new multiple regression models have been proposed, to predict the swelling phenomena of polymers under various MWFs with an accuracy of 80%. The effect of temperature on mechanical properties and morphology of material was also examined
(Journal of Applied Polymer Science. vol. 135, n° 0021-8995, pp. 45717, 12/09/2017)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRSST