A new approach to handle wave breaking in fully non-linear Boussinesq models.
In this paper, a new method to handle wave breaking in fully non-linear Boussinesq-type models is presented. The strategy developed to treat wave breaking is based on a reformulation of the set of governing equations (namely Serre Green-Naghdi equations) that allows us to split them into a hyperbolic part in the conservative form and a dispersive part. When a wave is ready to break, we switch locally from Serre Green-Naghdi equations to Non-linear Shallow Water equations by suppressing the dispersive terms in the vicinity of the wave front. Thus, the breaking wave front is handled as a shock by the Non-linear Shallow Water equations, and its energy dissipation is implicitly evaluated from the mathematical shock-wave theory. A simple methodology to characterize the wave fronts at each time step is first described, as well as appropriate criteria for the initiation and termination of breaking. Extensive validations using laboratory data are then presented, demonstrating the efficiency of our simple treatment for wave breaking.
(Coastal Engineering. vol. 67, n° 0378-3839, pp. 54--66, 15/09/2012)
I3M, UM2, UM, CNRS, IMT, UT Capitole, Comue de Toulouse, INSA Toulouse, INSA, Comue de Toulouse, UT2J, Comue de Toulouse, UT3, Comue de Toulouse, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, DMA, ENS-PSL, PSL, CNRS
Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to late Pliocene/early Pleistocene climate cooling
The global late Pliocene/early Pleistocene cooling (~3.0-2.0 million years ago, Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela Upwelling System (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (δ30Si) record covering the MDM in the BUS. Unexpectedly, the variations in δ30Si signal follow biogenic opal content, whereby the highest δ30Si values correspond to the highest biogenic opal content. We interpret the higher δ30Si values during the MDM as a result of a stronger degree of silicate utilization in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Plio/Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0-2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to late Pliocene/early Pleistocene cooling.
(Climate of the Past. vol. 8, n° 1814-9324, pp. 1435-1445, 13/09/2012)
LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, CAU, GEOMAR, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Assessing parasite community structure in cockles Cerastoderma edule at various spatio-temporal scales
Cockles (Cerastoderma edule) are among the most exploited bivalves in Europe. They live in lagoons and estuaries where they undergo many stressors including parasites. Trematodes are the most prevalent macroparasites of cockles and can exert a significant impact on their host populations depending on parasite species and infection intensity. Monitoring these parasite–host systems in order to predict potential host mortalities require a correct knowledge of the spatio-temporal variation of infection. A yearly monitoring of cockles from six stations around Ile aux Oiseaux, Arcachon Bay (France) was conducted between 1998 and 2005. Distance between two stations was ca. 1 km. Nine trematode species were identified. Despite a relative homogeneity of the parasite community structure in cockles, between three and six clusters were identified by Hierarchical Ascendant Classification showing that among-sites heterogeneity of trematode communities in cockles was higher than within-site heterogeneity. At the scale of 8 years, and for 2-year old cockles, these patterns remained stable in four out of six stations. Spatial aggregation disappeared with cockle age, since parasite communities in 3-year cockles did not reflect any particular station(s): with age, cockles eventually accumulated most trematode species and lost the site signature. On the other hand, we demonstrated that the commonly accepted theory stating that older/larger cockles accumulate more trematode larvae was not verified and that there could exist a vulnerable age/size that doesn’t correspond to largest values. This study provided a new insight in the parasite community heterogeneity in their host, and in the significance of samples in relation with space and time.
(Estuarine, Coastal and Shelf Science. vol. 110, n° 0272-7714, pp. 54-60, 10/09/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
An easy-to-use package for ordination of diatom assemblages using Self-Organizing Kohonen Maps
From about fifteen years, diatoms are routinely used for the ecological status assessment of rivers. Nevertheless classically used diatom indexes don't allow a really fine diagnosis of each type of pollution, furthermore they poorly integer temporal or spatial variation in natural conditions. The aim of this work is then to use new biomathematical methods in order to test their relevance towards diagnosis of ecological quality.
(pp. 1, 26/08/2012)
UR REBX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
New constraints on European glacial freshwater releases to the North Atlantic Ocean
During the late Quaternary, both external and internal forcings have driven major climatic shifts from glacial to interglacial conditions. Nonlinear climatic steps characterized the transitions leading to these extrema, with intermediate excursions particularly well expressed in the dynamics of the Northern Hemisphere cryosphere. Here we document the impact of these dynamics on the north-eastern North Atlantic Ocean, focussing on the 35-10 ka interval. Sea-surface salinities have been reconstructed quantitatively based on two independent methods from core MD95-2002, recovered from the northern Bay of Biscay adjacent to the axis of the Manche paleoriver outlet and thus in connection with proximal European ice sheets and glaciers. Quantitative reconstructions deriving from dinocyst and planktonic foraminiferal analyses have been combined within a robust chronology to assess the amplitude and timing of hydrological changes in this region. Our study evidences strong pulsed freshwater discharges which may have impacted the North Atlantic Meridional Overturning Circulation.
(Geophysical Research Letters. vol. 39, n° 0094-8276, pp. L15601, 01/08/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOTOP, EPM, UdeM, UQAT, UQAR, UQAM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LDO, INSU - CNRS, UBO EPE, CNRS, GM, IFREMER
Global characterization of the Holocene Thermal Maximum
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t We analyze the global variations in the timing and magnitude of the Holocene Thermal Maximum (HTM) and their dependence on various forcings in transient simulations covering the last 9000 years (9 ka), performed with a global atmosphere-ocean-vegetation model. In these experiments, we consider the influence of variations in orbital parameters and atmospheric greenhouse gases and the early-Holocene deglaciation of the Laurentide Ice sheet (LIS). Considering the LIS deglaciation, we quantify separately the impacts of the background melt-water fluxes and the changes in topography and surface albedo. In the analysis we focus on the intensity of the maximum temperature deviation relative to the preindustrial level, its timing in the Holocene, and the seasonal expression. In the model, the warmest HTM conditions are found at high latitudes in both hemispheres, reaching 5 C above the preindustrial level, while the smallest HTM signal is seen over tropical oceans (less than 0.5 C). This latitudinal contrast is mostly related to the nature of the orbitally-forced insolation forcing, which is also largest at high latitudes, and further enhanced by the polar amplification. The Holocene timing of the HTM is earliest (before 8 ka BP) in regions not affected by the remnant LIS, particularly NW North America, E Asia, N Africa, N South America, the Middle East, NE Siberia and Australia. Compared to the early Holocene insolation maximum, the HTM was delayed by 2e3 ka over NE North America, and regions directly downwind from the LIS. A similar delay is simulated over the Southern Ocean, while an intermediate lag of about 1 ka is found over most other continents and oceans. The seasonal timing of the HTM over continents generally occurs in the same month as the maximum insolation anomaly, whereas over oceans the HTM is delayed by 2e3 months. Exceptions are the oceans covered by sea ice and North Africa, were additional feedbacks results in a different seasonal timing. The simulated timing and magnitude of the HTM are generally consistent with global proxy evidence, with some notable exceptions in the Mediterranean region, SW North America and eastern Eurasia.
(Quaternary Science Reviews. vol. 48, n° 0277-3791, pp. 7-19, 01/08/2012)
UvA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, TECLIM, ELI, UCLouvain, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
THE END OF A MYTH: ARPYLORUS ANTIQUUS PALEOZOIC DINOFLAGELLATE CYST
Arpylorus antiquus, erected by Calandra in 1964, was isolated from upper Silurian sedimentary rocks from the Mechiguig 1 borehole in southern Tunisia, with other palynomorphs. The folded vesicle and the quadrangular form of the aperture break down into platelike fragments, resembling the tabulation of dinoflagellates. The presence of these elements has been used to interpret A. antiquus as a dinoflagellate cyst. The morphology and affinity of A. antiquus is reinterpreted herein based on investigation of larger sets of samples, including material from the type locality, together with material of Algeria, Saudi Arabia, and Brazil. More complete specimens than those previously described have been observed using gentle laboratory techniques, showing a large development of a fine membrane at the periphery of vesicles. This element was destroyed using classical palynological treatments, implying that the holotype is an incomplete specimen. The membrane at the periphery of vesicles and dorsoventral differentiation of these vesicles suggest that A. antiquus is a part of a more complex biological structure. We suggest a possible relationship with eurypterids, arthropods related to phyllocarids, represented by abundant fragments in the assemblages. Arpylorus antiquus is possibly a structure of storage. The chemical composition of A. antiquus using a Fourier transform infrared FTIR microspectroscopy analysis, reveals a wall composed of biopolymer that is not consistent with dinosporin. We conclude that Arpylorus antiquus is definitively not a dinoflagellate cyst. Although dinoflagellates may have older Paleozoic or even Proterozoic ancestors as the biomarker record may suggest, the dinoflagellate tabulation evolved only in the early Mesozoic.
(Palaios. vol. 27, n° 0883-0351, pp. 414-423, 26/07/2012)
LDO, INSU - CNRS, UBO EPE, CNRS, CR2P, MNHN, UPMC, CNRS, ULiège, KU
Changements globaux, inondations et terres viticoles : une combinaison à risque pour la qualité des eaux de l’estuaire de la Gironde ?
La fréquence et l’intensité des événements extrêmes, associés à l’élévation du niveau de la mer, prendraient une ampleur sans précédent en raison du changement climatique. Le cumul de ces deux phénomènes provoquerait une augmentation des inondations par crues et submersions marines, notamment sur les zones estuariennes aux interfaces complexes entre terre, mer et fleuve. Le Médoc, sur la rive gauche de l’estuaire de la Gironde, occupé historiquement par des terres viticoles, a subi de graves inondations lors d’événements récents (tempêtes Martin en 1999 et Xynthia en 2010). La remise en eau temporaire de ces terres, fortement contaminées en certains métaux, pourrait avoir des impacts géochimiques sur la qualité des sols et des eaux de l’estuaire. Dans une démarche pluridisciplinaire, associant géochimie, géographie et géomatique, nous proposons d’étudier ces impacts à partir d’une double approche. Après avoir caractérisé les événements météorologiques affectant le Médoc, nous avons déterminé des communes viticoles sensibles aux risques d’inondation à partir de base de données publiques : BD Gaspar sur les arrêtés de catastrophes naturels, BD Agreste pour les surfaces en vigne et BD Primnet pour les zones couvertes par des plans de prévention des risques inondation (approche spatio-statistique). Dans ces communes, nous avons collecté des sols qui ont subi des tests de lixiviation en laboratoire ; les sols ont été mis en contact avec l’eau douce ou estuarienne, afin d’identifier les processus de relargages ou piégeages en métaux et simuler ainsi l’impact des inondations (approche expérimentale). Cette étude s’inscrit dans un programme de recherche pluridisciplinaire Adapt’eau (ANR CEP&S 2011) qui vise à étudier les impacts des changements globaux et à expérimenter des options d’adaptation, notamment la dépoldérisation.
(pp. 1, 09/07/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR ADBX, IRSTEA
Stratégie bio-analytique de type EDA pour l’identification de contaminants émergents dans les milieux aquatiques : Etude de cas en aval d’un rejet industriel
(04/07/2012)
INERIS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CNRS
Application de modèles non paramétriques sous R pour l'analyse et le suivi de la qualité de l'eau
Application de modèles non paramétriques sous R pour l'analyse et le suivi de la qualité de l'eau
(02/07/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS