In situ study of short-term variations of redox species chemistry in intertidal permeable sediments of the Arcachon lagoon
(Hydrobiologia. vol. 699, n° 0018-8158, pp. 69-84, 01/12/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS
Early mid-Holocene SST variability and surface-ocean water balance in the southwest Pacific
[1] We present early mid-Holocene records of Sr/Ca,δ18O and δ18Osw from marine archives collected in Vanuatu: two Porites sp. corals (6.7–6.5 ka BP) and a Tridacna maxima giant clam (6.2–6.0 ka BP). Sr/Ca, δ18O, and δ18Osw were used as proxies for sea surface temperature (SST) and sea surface salinity (SSS). The fossil geochemical records were compared to modern Porites sp. and T. maxima records. Reconstructed mean SSTs from the two fossil Porites sp.and from the modern coral are similar, implying that the Western Pacific Warm Pool (WPWP)' southern edge had reached its modern location by 6.7–6.5 ka BP. The post-glacial SST rise in the Southwest Pacific was thus completed by the early mid-Holocene. The two early mid-Holocene corals and the giant clam recorded saltier conditions than modern related to 1) a decoupling between the precipitation regime and the SPCZ due to a northerly position of this climatic feature and 2) an increase of the moisture transport to the extra-tropics, driven by a strengthened or extended Hadley cell. The longest δ18O coral profile displays an El Niño Southern Oscillation (ENSO) signal reduced by 20–30% compared to the period 1928–1992, in concordance with the reduced ENSO variability observed in the Pacific area during the first half of the Holocene. However, the decoupling between the SPCZ and the precipitation regime may have also contributed to the weak ENSO signal recorded in the early mid-Holocene coral δ18O profile.
(Paleoceanography. vol. 27, n° 0883-8305, 01/12/2012)
PALEOPROXUS, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS
Seagrass burial by dredged sediments: Benthic community alteration, secondary production loss, biotic index reaction and recovery possibility
In 2005, dredging activities in Arcachon Bay (France) led in burying 320,000m(2) of Zostera noltii intertidal seagrass. Recovery by macrobenthos and seagrass was monitored. Six months after works, seagrass was absent and macrobenthos drastically different from surrounding vegetated stations. Rapidly and due to sediment dispersal, disposal area was divided into a sandflat with a specific benthic community which maintained its difference until the end of the survey (2010), and a mudflat where associated fauna became similar to those in adjacent seagrass. Macrobenthic community needs 3years to recover while seagrass needs 5years to recover in the station impacted by mud. The secondary production loss due to works was low. In this naturally carbon enriched system, univariate biotic indices did not perform well to detect seagrass destruction and recovery. Multivariate index MISS gave more relevant conclusions and a simplified version was tested with success, at this local scale.
(Marine Pollution Bulletin. vol. 64, n° 0025-326X, pp. 2340-2350, 01/11/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Antarctic temperature changes during the last millennium: evaluation of simulations and reconstructions
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 Temperature changes in Antarctica over the last millennium are investigated using proxy records, a set of simulations driven by natural and anthropogenic forcings and one simulation with data assimilation. Over Antarctica, a long term cooling trend in annual mean is simulated during the period 1000e1850. The main contributor to this cooling trend is the volcanic forcing, astronomical forcing playing a dominant role at seasonal timescale. Since 1850, all the models produce an Antarctic warming in response to the increase in greenhouse gas concentrations. We present a composite of Antarctic temperature, calculated by averaging seven temperature records derived from isotope measurements in ice cores. This simple approach is supported by the coherency displayed between model results at these data grid points and Antarctic mean temperature. The composite shows a weak multi-centennial cooling trend during the pre-industrial period and a warming after 1850 that is broadly consistent with model results. In both data and simulations, large regional variations are superimposed on this common signal, at decadal to centennial timescales. The model results appear spatially more consistent than ice core records. We conclude that more records are needed to resolve the complex spatial distribution of Antarctic temperature variations during the last millennium.
(Quaternary Science Reviews. vol. 55, n° 0277-3791, pp. 75-90, 01/11/2012)
TECLIM, ELI, UCLouvain, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, BAS, NERC, AWI, LAL, UP11, IN2P3, CNRS, UvA, ACE-CRC, UGent
Accounting for Rough Bed Friction Factors of Mud Beds as a Result of Biological Activity in Erosion Experiments
(Journal of Hydraulic Engineering. vol. 138, n° 0733-9429, pp. 979-984, 01/11/2012)
LECOB, OOB, UPMC, CNRS, UPMC, CNRS, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER
Evaluating Southern Ocean sea-ice for the Last Glacial Maximum and pre-industrial climates: PMIP-2 models and data evidence
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 Sea ice is recognized as an important factor controlling climate conditions at high latitudes. It has a major impact in controlling the ocean to atmosphere exchanges (e.g. for CO 2) as well as surface oceanic conditions and deep water formation in the high latitude oceans. Being at the interface of two major components of the climate system, sea ice is useful to evaluate and intercompare different climate models. We here analyze the results of eight coupled climate models (from which seven are from the PMIP-2 database) against available reconstructions for winter and summer sea ice extent around Antarctica. To evaluate the ability of models in representing different climate states, we compare their results for both the pre-industrial and the Last Glacial Maximum (LGM). We find that models generally have identical seasonal ranges for the two climate states analyzed, which is not supported by data inferences. Indeed, data indicate that the LGM seasonality was enhanced compared to the pre-industrial. The shape of the sea ice distribution is also different in models (circular around the Antarctic continent) and in reconstructions (oval-shaped distribution; similar to modern sea ice distribution). We show that models underestimating the sea ice extent for the pre-industrial are also underestimating the Last Glacial Maximum extent. Our results thus point to difficulties for climate models in representing the sea-ice dynamics in the Southern Ocean.
(Quaternary Science Reviews. vol. 56, n° 0277-3791, pp. 99-106, 01/11/2012)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UvA
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