Differences in fluorescence properties between humic acid and its size fractions separated by preparative HPSEC
We applied three dimensional excitation-emission-matrix (3D-EEM) spectrofluorometry to investigate the fluorescence properties of a humic acid (HA) solution at different pH values and its size-fractions separated by preparative high performance size exclusion chromatography (HPSEC). 3D-EEM fluorescence spectra revealed peak maxima in the bulk HA which were assigned to protein-like, phenol-like and naphthol-like components. Moreover, changes of peak maxima with pH showed that phenol-like and naphthol-like molecular classes were composed of sub-components with different acidities, and, thus, different structures. The 3D-EEM spectra of three size-fractions separated by HPSEC showed similar peak maxima as for the bulk HA, with additional components, such as highly condensed aromatic systems, which had not been visible in the bulk HA. Furthermore, the fluorescence intensity of peak maxima in 3D-EEM spectra of size-fractions appeared invariably greater than that for the bulk HA. This phenomenon as well as the appearance of new maxima in size-fraction spectra is explained by the reduced self-quenching effect in the less complex and conformationally looser size-fractions. In fact, the close mutual proximity of fluorescent humic molecules in the tight supramolecular association of the bulk HA decreased or even inhibited their fluorescence quantum yield. This work shows that, due to self-quenching of humic molecules, fluorescence spectroscopy cannot be used to characterise the molecular complexity of humic matter and, thus, differentiate its environmental origin. \textcopyright 2012 Elsevier B.V.
(Journal of Geochemical Exploration. vol. 129, n° 0375-6742, pp. 23--27, 29/08/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Investigations into the differential reactivity of endogenous and exogenous mercury species in coastal sediments
Stable isotopic tracer methodologies now allow the evaluation of the reactivity of the endogenous (ambient) and exogenous (added) Hg to further predict the potential effect of Hg inputs in ecosystems. The differential reactivity of endogenous and exogenous Hg was compared in superficial sediments collected in a coastal lagoon (Arcachon Bay) and in an estuary (Adour River) from the Bay of Biscay (SW France). All Hg species (gaseous, aqueous, and solid fraction) and ancillary data were measured during time course slurry experiments under variable redox conditions. The average endogenous methylation yield was higher in the estuarine (1. 2 %) than in the lagoonal sediment (0. 5 %), although both methylation and demethylation rates were higher in the lagoonal sediment in relation with a higher sulfate-reducing activity. Demethylation was overall more consistent than methylation in both sediments. The endogenous and exogenous Hg behaviors were always correlated but the exogenous inorganic Hg (IHg) partitioning into water was 2. 0-4. 3 times higher than the endogenous one. Its methylation was just slightly higher (1. 4) in the estuarine sediment while the difference in the lagoonal sediment was much larger (3. 6). The relative endogenous and exogenous methylation yields were not correlated to IHg partitioning, demonstrating that the bioavailable species distributions were different for the two IHg pools. In both sediments, the exogenous IHg partitioning equaled the endogenous one within a week, while its higher methylation lasted for months. Such results provide an original assessment approach to compare coastal sediment response to Hg inputs.
(Environmental Science and Pollution Research. vol. 20, n° 0944-1344, pp. 1292--1301, 29/08/2026)
IPREM, UPPA, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Potential role of giant marine diatoms in sequestration of atmospheric CO2 during the Last Glacial Maximum: δ13C evidence from laminated Ethmodiscus rex mats in tropical West Pacific
Giant marine diatoms, blooming or aggregating within deep chlorophyll maxima under stratified conditions, can generate substantial production and a large export flux of organic carbon from surface waters. However, their role in regulating glacial-interglacial variation in atmospheric pCO 2 remains unclear. Here, we report the organic carbon isotopic compositions of Ethmodiscus rex diatoms (δ 13 C E. rex) and bulk sediments (δ 13 C org) from a sediment core in the eastern Philippine Sea dated to ~19.5-31.0 kyr B.P. and consisting of (from youngest to oldest) (1) laminated E. rex diatom mats (LDM), (2) diatomaceous clay (DC), and (3) pelagic clay (PC). Our results suggest that δ 13 C E. rex provides a better record of palaeoceanographic processes during LDM and DC deposition than δ 13 C org because of reduced differential vital effects in near-monospecific E. rex fractions. We used the isotopic composition of the coarse E. rex fraction (δ 13 C E. rex (>154 μm)) to calculate the CO 2 partial pressure of eastern Philippine Sea surface waters (pCO 2-sw) during the Last Glacial Maximum (LGM). Our pCO 2-sw records suggest that the eastern Philippine Sea switched from being a strong CO 2 source during DC deposition to a weak CO 2 sink during LDM deposition. The role of the eastern Philippine Sea as a CO 2 sink during the LGM was promoted by elevated primary production and, to a lesser extent, intensified water-column stratification. These observations highlight the potential role of giant marine diatoms in the sequestration of atmospheric CO 2 during the LGM and, hence, support changes in biogenic silica fluxes as a potential cause of lower glacial atmospheric CO 2. Our findings are consistent with an eolian source of silica, as proposed by the 'silica hypothesis' and the 'silicon-induced alkalinity pump hypothesis' but not by the 'silicic acid leakage hypothesis.
(Global and Planetary Change. vol. 108, n° 0921-8181, pp. 1-14, 29/08/2026)
IOCAS, CAS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UC
L'adaptation au changement climatique : contraintes et opportunités
Éléments issus de la synthèse sur la biodiversité en Aquitaine, réalisée pour le Conseil Régional d'Aquitaine sur les thématiques Biodiversité et Ressources exploitées.
(pp. 14, 29/08/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR EPBX, IRSTEA, LERAR, COAST, IFREMER, IFREMER, IRSTEA, MNHN
Etude intégrée de l’effet des apports amont et locaux sur le fonctionnement de la Garonne estuarienne (ETIAGE) : Rapport année 3 Avril 2012 - Mars 2013
Le programme ETIAGE a été mis en place avec pour objectif de répondre aux questions suivantes : que représentent les apports des effluents de la Communauté Urbaine de Bordeaux (CUB) par rapport à ceux venant de l’amont en termes de charge organique et de micro-polluants ? Quels rôles sur le devenir des effluents jouent la présence du bouchon vaseux et la stagnation résiduelle des eaux (déplacement net entre mouvement de flot et de jusant) au niveau de l’estuaire fluvial amont en période d’étiage estival ? Réciproquement, à quels moments et jusqu’où s’étend l’impact de ces effluents sur la qualité des eaux de la Garonne estuarienne ? Quelles incidences des effluents sur le comportement des populations biologiques en place ou migratoires dans la Garonne estuarienne ? Quelle tendance évolutive va connaître l’oxygénation des eaux ? Quel sera l’impact sur le comportement des micro-polluants et des populations biologiques ? Quelles recommandations de gestion pourraient être préconisées à partir de la synthèse des pressions exercées sur les eaux de la Garonne estuarienne ? Le programme est divisé en 5 axes, dont les bilans de travail sont présentés axe par axe.
(pp. 53, 29/08/2026)
UR EPBX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Un nouveau modèle couplé vagues-courant 3D : développement et validation
A numerical model coupling the three-dimensional oceanic circulation, thanks to the MARS3D model, and the sea state computed by the WAVEWATCH III model, is developed in order to study the hydrodynamic of the nearshore zone. The main principle of the coupled model based on the coupler PALM and the necessary modifications made for the coupling procedure to both numerical codes are described. First tests in horizontal two-dimension are made and they allowed us to develop a primary version. For three-dimensional flow, we show that the coupled model must solve the quasi-Eulerian velocity. In fact, a coherent analytical form of the wave forcing for the Lagrangian velocity does not exist. This point is illustrated by one example with large errors in comparison with the analytical solution when solving for the Lagrangian mean flow.
(Revue Paralia. vol. 6, n° 1760-8716, pp. 8.1-8.12, 29/08/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER
Orbital forcing on West African monsoon system revealed by KZai 02 pollen record spectral analysis.
(29/08/2026)
SPE, CNRS, PEPS, UCBL, INSU - CNRS, CNRS, LGL-TPE, ENS de Lyon, UCBL, INSU - CNRS, UJM, UJM EPE, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS
Mise au point d’indices diatomiques pour les cours d’eau de la Réunion (IDR), des Antilles (IDA), de Guyane et de Mayotte : Bilan des actions 2008-2012, perspectives et suites à donner
La DCE (JOCE, 20 septembre 2000) a rendu obligatoire l’évaluation de l’état écologique des écosystèmes aquatiques des états-membres de l’Union Européenne. Cette Directive a aussi force d’application dans les DOM Français dans les meilleurs délais. Cependant, les méthodes d’évaluation biologique actuellement utilisées en France métropolitaine ne peuvent s’y appliquer en raison d’un fort décalage biogéographique touchant à la fois la composition des communautés biologiques qui y vivent (nombreuses espèces non présentes en France, voire nouvelles pour la science) et les conditions géo-climatiques particulière qui y exercent leur effet et influent fortement sur la sélection des assemblages. Dans ces conditions, divers programmes se sont successivement initiés dans plusieurs DOM, sous financements locaux (Offices de l’Eau, DEALs locales), nationaux (ONEMA, Ministère de l’Outre-mer…) voire Européens (FEDER), en partie co-financés par les organismes chargés de leur mise en ½uvre concrète (notamment par le consortium ASCONIT-IRSTEA pour le maillon des diatomées benthiques des cours d’eau de la Réunion, de Martinique, de Guadeloupe et de Guyane). Ces programmes visent à terme à la création d’indices diatomiques adaptés aux contextes biogéographiques spécifiques de ces DOM et à la conception de systèmes d’évaluation permettant de diagnostiquer l’état écologique de leurs cours d’eau à partir du compartiment phytobenthique. Ils prennent en charge différentes étapes couvrant : l’identification taxonomique ; le comptage des inventaires ; l’investigation de l’auto-écologie des espèces par couplage entre descripteurs abiotiques de la qualité des eaux et inventaires biologiques prélevés aux mêmes sites et aux mêmes dates ; l’élaboration de nouveaux indices diatomiques adaptés au contexte biogéographique local ; l’édition de guides d’identification taxonomique, de guides-utilisateurs servant de référentiel à l’application de la méthode par les futurs intervenants dans le cadre des marchés publics de surveillance. Certains de ces programmes, initiés depuis quelques années, s’approchent actuellement du stade de l’achèvement (Réunion avec la sortie effective du nouvel Indice Diatomique Réunion ou IDR, Antilles avec le nouvel Indice Diatomique des Antilles ou IDA). Les prochaines années nécessiteront encore un effort substantiel de travail sur les documents d’accompagnement destiné à faciliter leur transfert opérationnel. D’autres programme ont connu un démarrage plus tardif et sont actuellement en milieu de réalisation dans un contexte logistique et biogéographique très particulier (Guyane), voire viennent de passer très récemment en phase de réalisation concrète du programme de terrain (Mayotte). La présente communication de synthèse vise à présenter un état d’avancement actualisé de ces différents chantiers en cours.
(pp. 44, 29/08/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR REBX, IRSTEA
Abattement des micropolluants par les stations d’épuration : zoom sur le projet ARMISTIQ
(pp. 15, 29/08/2026)
UR MALY, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Rip current morphodynamics in a wave basin
Experiments have been performed in a large wave tank in order to study the morphodynamics of rip current systems. Both accretive and erosive shore normal wave conditions were applied, the beach evolving through all the states within the intermediate beach classication, under the so-called down-state (accretive) and up-state (erosive) morphological transitions. Results show that any prescribed change in the wave conditions drastically increases the rate at which the morphology changes. The surfzone morphology tends toward a steady state when running a given wave climate for a long duration. We quantitatively describe a full down-state sequence characterized by the progressive evolution of an alongshore-uniform bar successively into a crescentic planshape, a bar and rip channel morphology, and a terrace. From the analysis of a large dataset of dense Eulerian measurements and bathymetric surveys, we depict several feedback mechanisms associated with wave-driven rip current circulation, wave nonlinearities and the seabed evolution. At rst, a positive feedback mechanism drives a rapid increase in the rate of morphological change, beach three-dimensionality and rip intensity. By the time the sandbar evolves into a bar and rip morphology a negative feedback mechanism, characterized by a decaying beach change rate and an increasing beach alongshore uniformity, overwhelms the former mechanism. An erosive sequence characterized by both an overall ohore bar migration and an increase in beach three-dimensionality is also described.
(pp. 1, 29/08/2026)
UR HHLY, IRSTEA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS