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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.

Michalet R.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Le Bagousse-Pinguet Y.,University of South Bohemia | Maalouf J..-P.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Lortie C.J.,York University
Journal of Vegetation Science | Year: 2014

New evidence demonstrates that facilitation plays a crucial role even at the edge of life in Maritime Antarctica. These findings are interpreted as support for the stress-gradient hypothesis (SGH) - a dominant theory in plant community ecology that predicts that the frequency of facilitation directly increases with stress. A recent development to this theory, however, proposed that facilitation often collapses at the extreme end of stress and physical disturbance gradients. In this paper, we clarify the current debate on the importance of plant interactions at the edge of life by illustrating the necessity of separating the two alternatives to the SGH, namely the collapse of facilitation, and the switch from facilitation to competition occurring in water-stressed ecosystems. These two different alternatives to the SGH are currently often amalgamated with each other, which has led to confusion in recent literature. We propose that the collapse of facilitation is generally due to a decrease in the effect of the nurse plant species, whilst the switch from facilitation to competition is driven by environmental conditions and strategy of the response species. A clear separation between those two alternatives is particularly crucial for predicting the role of plant-plant interactions in mediating species responses to global change. © 2013 International Association for Vegetation Science.

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.

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.

Castelle B.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Ruessink B.G.,University Utrecht
Journal of Geophysical Research: Earth Surface | Year: 2011

We use a nonlinear morphodynamic model to demonstrate that time-varying forcing, in particular the time-varying angle of wave incidence, is crucial to the development of rip channels in terms of rip channel morphology, nonlinear behavior, longshore migration, and mean rip spacing. The time-varying angle of incidence leads to different mean rip spacings than the time-integrated time-invariant forcing and to systematically less developed bar and rip morphologies at more alongshore variable scales. This supports the common field observation of irregular and random alongshore rip spacings, and contrasts with the regular spacing predicted by existing time-invariant template, and instability models. Time-varying wave incidence also generally results in the onset of splitting of shoals and an increase in merging of rip channels. In addition, a time-varying angle of incidence with zero mean can drive a significant net alongshore migration of the rip channels. Abrupt changes in wave conditions are responsible for this net longshore migration through cumulative effects of the mismatch between wave conditions and bar and rip morphology orientation. Copyright 2011 by the American Geophysical Union.

Tuduri L.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Tuduri L.,Institute Of Recherche Robert Sauve En Sante Securite Au Travail | Millet M.,CNRS The Institute of Chemistry and Processes for Energy, Environment and Health | Briand O.,French Agency for Food | Montury M.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC)
TrAC - Trends in Analytical Chemistry | Year: 2012

We review the state of the art in atmospheric passive sampling for semi-volatile organic compounds. After a brief section on principles and theory, we focus on calibration approaches using different passive samplers. We report a selected number of applications for some passive samplers and identify some key issues to improve the performance and the accuracy of passive samplers. We then suggest and discuss possible developments. © 2011 Elsevier Ltd.

Polsenaere P.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Abril G.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC)
Geochimica et Cosmochimica Acta | Year: 2012

Degassing of terrestrially-respired CO 2 from streams and small rivers appears to be a significant component in watershed carbon budgets. Here we propose an original approach to quantify CO 2 degassing in small headwater bodies using pCO 2, DIC (or total alkalinity, TA) and δ 13C-DIC data in stream waters that avoids the difficulty of measuring or choosing a gas transfer velocity. Our inversed model applies to acidic, non-buffered (humic-type) waters and relies on two main assumptions, i.e., the stable isotopic composition of DIC in groundwater seeping to surface water (CO 2 from respired soil organic carbon and HCO3- from weathering) and on kinetic fractionation at the water-air interface ( 12CO 2 degases to the atmosphere more rapidly than 13CO 2). We first consider both the soil organic matter isotopic composition and the isotopic fractionation of CO 2 in the soil, to derive the δ 13C-CO 2 in that soil and groundwater. From the HCO3- concentrations in streams, we estimate the relative contribution of silicate and carbonate weathering (the latter being minor in these waters) to the HCO3- and its associated isotopic composition. Model calculations start from the δ 13C-DIC value computed by the aforementioned method and consist of two interlocked iterative procedures. The first procedure simulates the decrease in pCO 2 and the increase in δ 13C-DIC that occur along the stream watercourse during degassing, starting from an assumed initial soil pCO 2 and ending at the in situ pCO 2 or δ 13C-DIC. The second iteration procedure consists of adjusting the initial soil pCO 2 until pCO 2 and δ 13C-DIC simultaneously reach the in situ measured values. After convergence is obtained, the model computes a theoretical concentration of DIC, [DIC] ex., that has been lost as CO 2 to the atmosphere from the headwater to the sampling point in the river. [DIC] ex. can be multiplied by the river discharge to derive the quantity of carbon degassed from the river surface. The model was tested on seasonal field datasets from three small rivers draining sandy podsols in southern France and gave annual areal degassing rates comparable to those reported in other studies, though somewhat larger (upper half range in two rivers, ∼10 times the average in one stream). Part of this discrepancy might have been caused by an intense degassing in the vicinity of groundwater seeps, which was accounted for our integrative method but not by classical methods based on stream water pCO 2 and gas transfer velocity. The sensitivity of the model results on the assumption of the importance of carbonate weathering might also explain part of this high degassing rate. The model reproduced consistent values and seasonal trends of soil pCO 2 (maximal in summer) and gas transfer velocity (maximal at high water flow). We discuss the sensitivity of the model to the different parameters and assumptions and propose some improvements including groundwater sampling, for better constraining the computed degassing rates. © 2012 Elsevier Ltd.

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.

Belles A.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Pardon P.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC) | Budzinski H.,CNRS Laboratory of Oceanic Environments and Paleo-environments (EPOC)
Analytical and Bioanalytical Chemistry | Year: 2014

POCIS (polar organic chemical integrative samplers) are increasingly used for sampling polar compounds. Although very efficient for a wide range of pollutants, the classic configuration of the device has a number of limitations, in particular for the sampling of highly polar analytes and hydrophobic compounds. This study presents a new version of the POCIS passive sampler which uses a highly porous Nylon membrane of 30 μm pore size, enabling the sampling of hydrophobic pollutants and improving the accumulation rate of other pollutants. This newly designed tool and the classic POCIS were both tested during a laboratory experiment to evaluate the accumulation kinetics of a selection of pesticides and pharmaceuticals. The observed results show unexpected accumulation kinetics for the new version of POCIS. To explain the data, the use of an intraparticulate diffusion model was required, which also enabled us to propose another explanation of the burst effect observed with the classic POCIS, primarily related to the potential wetting of the device as the first step in the accumulation of compounds. [Figure not available: see fulltext.] © 2013 Springer-Verlag Berlin Heidelberg.

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