Grasso F.,University Utrecht |
Castelle B.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) |
Ruessink B.G.,University Utrecht
Continental Shelf Research | Year: 2012
Wave breaking is the primary driver of beach erosion, injecting breaking-induced turbulence at the sea surface and diffusing bed boundary layer turbulence at the sea bed. The limited understanding of the vertical turbulence structure under natural breaking waves, and hence sand entrainment, is one of the reasons that coastal-evolution models produce inadequate estimates of storm response. Here we use a recently collected field dataset to analyze turbulence dissipation under breaking waves and bores on the intertidal beach at Truc Vert, France. The vertical structure of the turbulent dissipation rate indicates that wave breaking is the dominant source of turbulence dissipation. The current-induced turbulence represents no more than 50% of the turbulent dissipation rate close to the bed (at 10% of the water column), even when alongshore currents reach 1. m/s. The data further illustrate that the turbulent dissipation rate is almost depth-uniform under breaking waves, whereas it decreases profoundly toward the bed under bores. Moreover, we found that the fraction of wave energy flux decay dissipated below wave-trough level is about 1% under breaking waves and about 10% under bores. These results imply that the turbulent dissipation rate in the surf zone is severely underestimated by coastal-evolution models that do not consider breaking-induced turbulence as a surface boundary condition. Consequently, they will underestimate sand stirring and transport by mean currents during severe storms. © 2012 Elsevier Ltd.
Bolliet T.,French National Center for Scientific Research |
Jorissen F.J.,French National Center for Scientific Research |
Schmidt S.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) |
Howa H.,French National Center for Scientific Research
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2014
At a 650m deep site in the axis of Capbreton Canyon an 18-cm-thick turbidite was deposited in December 1999. During subsequent campaigns, an almost monospecific fauna of the benthic foraminifer Technitella melo, considered as a pioneer species, was found in May 2000. In 2001 this fauna had disappeared and was replaced by an exceptionally rich fauna strongly dominated by the opportunistic species Bolivina subaenariensis. We present sedimentological, radionuclide and foraminiferal data of new cores, sampled in 2005 and 2011, taken with the aim to study the further evolution of the benthic ecosystem. Cores sampled in 2005 show that in the canyon axis a new, ca. 5cm thick, turbidite has been deposited. The live benthic foraminiferal faunas were much poorer than in 2001, but still had a high dominance and low diversity, although less extreme than in 2001. We conclude that in the canyon axis, benthic foraminiferal faunas remain in an early stage of ecosystem colonization. It appears that the very thick 1999 turbidite marks an exceptional event. The uncommonly rich faunas observed in 2001 could be a response to the concentration of organic-rich material in the fine-grained top of this deposit. In 2011, cores were sampled at a slightly different site, on the lower canyon flank. The sedimentary sequence here is marked by the absence of coarse turbidite layers, although some levels show slightly increased grain size, and lower 210Pbxs activities, indicative of an admixture with advected older sediments. Live foraminiferal faunas are much more equilibrated, as shown by their higher diversity, lower dominance, and deeper penetration into the sediment. All these characteristics are indicative of a much more stable ecosystem. Dead faunas are present throughout the core, indicating that the levels with slightly elevated grain size are not typical turbidites resulting from hyperpycnal currents (which are characterized by levels barren of foraminifera) but denote other, more long-term sedimentary processes leading to the advection of older material, such as bottom nepheloid layers, or repetitive fine-grained turbidite deposits due to small-scale slumping. The comparison of live and dead fauna shows that at both sites, the foraminiferal turnover rates are fairly low. At the lower canyon flank site sampled in 2011, the foraminiferal faunas are renewed every 1.5-2years. Such a fairly long foraminiferal lifespan corresponds to earlier estimates, but is surprisingly high for the opportunistic taxa that dominate the faunal assemblages in these unstable and food-enriched submarine canyon settings. © 2013 Elsevier Ltd.
Marlon J.R.,University of Wisconsin - Madison |
Bartlein P.J.,University of Oregon |
Daniau A.-L.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) |
Harrison S.P.,Macquarie University |
And 4 more authors.
Quaternary Science Reviews | Year: 2013
We synthesize existing sedimentary charcoal records to reconstruct Holocene fire history at regional, continental and global scales. The reconstructions are compared with the two potential controls of burning at these broad scales - changes in climate and human activities - to assess their relative importance on trends in biomass burning. Here we consider several hypotheses that have been advanced to explain the Holocene record of fire, including climate, human activities and synergies between the two. Our results suggest that 1) episodes of high fire activity were relatively common in the early Holocene and were consistent with climate changes despite low global temperatures and low levels of biomass burning globally; 2) there is little evidence from the paleofire record to support the Early Anthropocene Hypothesis of human modification of the global carbon cycle; 3) there was a nearly-global increase in fire activity from 3 to 2 ka that is difficult to explain with either climate or humans, but the widespread and synchronous nature of the increase suggests at least a partial climate forcing; and 4) burning during the past century generally decreased but was spatially variable; it declined sharply in many areas, but there were also large increases (e.g., Australia and parts of Europe). Our analysis does not exclude an important role for human activities on global biomass burning during the Holocene, but instead provides evidence for a pervasive influence of climate across multiple spatial and temporal scales. © 2013 Elsevier Ltd.
Kegel J.U.,Marine Biological Association of The United Kingdom |
Del Amo Y.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) |
Medlin L.K.,Marine Biological Association of The United Kingdom
Environmental Science and Pollution Research | Year: 2013
Microalgae worldwide regularly cause harmful effects, considered from the human perspective, in that they cause health problems and economic damage to fisheries and tourism. Cyanobacteria cause similar problems in freshwaters. These episodes encompass a broad range of phenomena collectively referred to as "harmful algal blooms" (HABs). For adequate management of these phenomena, monitoring of microalgae is required. However, effective monitoring is time-consuming because cell morphology as determined by light microscopy may be insufficient to give definitive species and toxin attribution. In the European Union FP7 project MIDTAL (Microarrays for the Detection of Toxic Algae), we achieved rapid species identification using rRNA genes as the target. These regions can be targeted for probe design to recognise species or even strains. We also included antibody reactions to specific toxins produced by these microalgae because, even when cell numbers are low, toxins can be present and can accumulate in the shellfish. Microarrays are the state-of-the-art technology in molecular biology for the processing of bulk samples for detection of target RNA/DNA sequences. After 36 months, we have completed RNA-cell number-signal intensity calibration curves for 18 HAB species and the analysis of monthly field samples from five locations from year 1. Results from one location, Arcachon Bay (France), are reported here and compared favourably with cell counts in most cases. In general, the microarray was more sensitive than the cell counts, and this is likely a reflection in the difference in water volume analysed with the volume filtered for the microarray an order of magnitude greater. © 2013 Springer-Verlag Berlin Heidelberg.
Caupos E.,University of Poitiers |
Mazellier P.,University of Poitiers |
Mazellier P.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) |
Croue J.-P.,University of Poitiers |
Croue J.-P.,King Abdullah University of Science and Technology
Water Research | Year: 2011
In the present work the degradation of estrone (E1) a natural estrogenic hormone has been studied under simulated solar irradiation. The photodegradation of E1 has been investigated in the absence and in the presence of 7.7-8.9 mg L-1 of dissolved organic carbon (DOC), under solar light simulation with irradiance approximating that of the sun. DOC extracts from different origins have been used. Half-lives ranging between 3.9 h and 7.9 h were observed. Results indicated that E1 was photodegraded even in the absence of DOC. The presence of DOC was found to enhance the degradation of E1. Experiments performed with the addition of reactive species scavengers (azide ions and 2-propanol) have shown that these two species play a significant role in the photodegradation. Some experiments have been performed with a DOC previously submitted to solar irradiation. Changes in optical and physico-chemical properties of DOC strongly affect its photoinductive properties, and hence its efficiency on E1 degradation. A part of the study consisted in the investigation of photoproducts structures. Five photoproducts were shown by chromatographic analysis: one arising from direct photolysis and the four others from DOC photoinduced degradation. © 2011 Elsevier Ltd.